1. Membranes: Requirements, Types, Classification, and Separation Mechanisms

1.2. Types and Classification

Membranes can be classified based on driving forces, membrane structure, membrane materials, membrane material preparation method, and membrane materials’ structure . The main driving forces are pressure gradients, concentration gradients, or electrical potential differences such as in lithium battery separation membranes. Based on membrane structure, membranes can be classified as symmetric/asymmetric. Asymmetric membranes have a finger-like pore structure with the size of pores gradually changing from one side to the other and symmetric membranes often have a sponge-like pore structure with relatively monodisperse pores. According to the chemical nature of membrane materials, they can be divided into organic (polymeric), inorganic (ceramic, metallic, glass, zeolite, and carbon), and composites if made from different materials in the same kind or hybrid made from both organic and inorganic materials. The most common types of organic membranes are cellulose, polyamides, polysulfones, polyethylene, and polycarbonate [1]. Asymmetric polymeric composite membranes comprise a top layer of nonporous selective barrier, a porous sublayer from a different material that provides mechanical support, and sometimes a backing bottom layer. A hybrid membrane may be made from an inorganic particle-reinforced polymeric material. There are several membrane material preparation methods such as phase inversion, sol-gel, extrusion, stretching, and interfacial polymerization. According to membrane configuration, form, or arrangement, they are classified as flat sheet, hollow fiber, spiral wound, and plate & frame membranes [9]. The chosen configuration (spiral wound, tubular hollow fibers, or others) significantly impacts factors like packing density, pressure handling, and cleaning requirements.

Figure 1. Classification of membranes.

Figure 1. Classification of membranes.

According to IUPAC, a mesopore is defined as a pore with a diameter of 2-50 nm and is intermediate between micropores (≤2nm) typical of zeolites, and macropores (≥50nm) typical of porous glass. Historically, different fields have their traditional size classification and naming. The size range for each category of membranes is notional and not strictly defined or consistent in various literature. The size classification in this paper is based on the recognized definition of nanotechnology as the manipulation of matter with at least one dimension sized from 1 to 100 nanometers, qualified as nanoporous, and less than 1 nm at molecular levels is qualified as nonporous or dense, above 100 nm – 10 µm as microporous, and > 10 µm as macroporous. summarizes size ranges and terms used in this review.

Table 1. Particle size range and terminology.

Table 1. Particle size range and terminology.

Size Range	Terminology
Nanoscale 1-100 nm	nanoparticles, nanomaterial, electrospun nanofibers, nanofibrils, nanocrystals, nanoporous, nanopores, nanofiltration (1-2 nm), ultrafiltration (2-100 nm)
Microscale 100 nm - 10 µm	microfibrils, microcrystals, microfibers, electrospun microfibers, fibrils, crystallites, microporous, micropores
Macroscale >10 µm	fibers, electrospun fibers, crystals, microporous, macropores

Based on membrane material’s structure and selectivity, membranes can be classified into different types:

Nonporous, dense, or semi-permeable membranes do not have permanent pores and rely solely on fluctuating free volume spaces between molecules and depend on the solution-diffusion mechanism for gas and vapor permeation. Reverse osmosis (RO) and gas separation membranes (the selective layer) are predominantly made from nonporous polymeric materials. RO membranes are designed to be highly selective towards water while rejecting most dissolved salts and other solutes. Gas separation membranes, however, can be tailored to selectively permeate specific gases based on their size, solubility, and other properties.

Nanoporous membranes are a specific type of membrane characterized by the presence of pores in the nanometer range (1-100 nanometers). These pores play a crucial role in enabling various filtration separation processes.

Nanofiltration membranes with pores less than 1-2 nm typical of zeolites where Knudsen and surface diffusion occur can retain ion hydrates and organic molecules for water purification or larger gas molecules for gas separation [1,10,11].

Ultrafiltration membranes with pores ranging from 2 to 100 nm can separate larger molecules like proteins and viruses.

Microporous or microfiltration membranes contain microscopic pores ranging from 100 nm to 10 μm that allow the passage of molecules while excluding bacteria and fine particulates.

Macroporous membranes or conventional filters contain pores larger than 10 μm, removing yeast cells, coarse particulates, and sand.

1.4. Factors Affecting Permeation (Permeance and Selectivity)

Membrane gas and vapor separation are used in various applications including the production of nitrogen and oxygen-enriched gases, hydrogen recovery from refinery streams, and CO₂ separation from natural gas. It is a process that utilizes nonporous membranes such as polyamide and cellulose acetate, or nanofiltration membranes from ceramic materials to separate different gases and vapors based on their molecular size, shape, solubility, and diffusivity properties. The size of a gas and vapor molecule can be estimated by its kinetic diameter (Error! Reference source not found.), which is close to the molecular sieving dimension and is a sensitive measure of the ability to move in pores. Diffusion increases with decreasing molecule size [16].

Table 2. Kinetic diameters and critical temperatures of common gases.

Table 2. Kinetic diameters and critical temperatures of common gases.

	H₂O	H₂	CO₂	O₂	H₂S	N₂	CO	CH₄	C₂H₆
Kinetic diameter (nm)*	0.265	0.289	0.33	0.346	0.36	0.364	0.376	0.38	0.43
Critical temperature (K)**	647.1	33.2	304.2	154.6	373.5	126.2	133.2	190.6	305.3

*[17], **[18].

Nanofiltration membranes of ceramic, zeolite, and carbon primarily utilize size exclusion as the separation mechanism, particularly effective for separating gases and vapors with significant size differences. On the other hand, polymer membranes are modeled as a dense or nonporous material with fluctuating free volume spaces between macromolecules where gases are first dissolved onto the membrane and then diffuse through it at different rates, the so-called solution-diffusion mechanism. Both reverse osmosis and gas separation polymeric membranes rely on the solution-diffusion mechanism for separation.

The volume of a polymer comprises the volume occupied by polymer chains and the free volume between them in the form of “holes”. These spaces are dynamic and constantly fluctuate in size and shape due to the thermal motion of the polymer chains and are crucial for the movement of small molecules, ions, or segments of the polymer chains themself [19]. Except for the effects of molecular sizes, critical temperature is a measure of the ease of condensation for gaseous molecules and the solubility increases with it. The membrane material's affinity for a permeant also plays a role in affecting solution and diffusion. The affinity must not be too strong such that its mobility is reduced. In general, higher solubility in a polymer is obtained for gases with greater critical temperatures and stronger interaction, while weaker interaction and smaller size of the permeating gas increase diffusion [16]. The gas permeability of a nonporous polymer is not controlled either by the gas diffusivity or the gas solubility in the polymer, but the overall result of diffusivity multiplying solubility [20].

Gaseous substances can be classified as light gases based on molecular sizes or condensable gases such as those with critical temperatures larger than 300 K as well as vapors such as water and volatile hydrocarbons. Condensable gases and vapors typically have high solubility in membranes enabling them preferentially to permeate over the less soluble components including H₂. Water vapor and CO₂ have smaller kinetic parameters and higher critical temperatures, typically leading to larger permeation than other gaseous substances. Additionally, CO₂ is a weak Lewis acid having larger quadrupole moments than other gas molecules, it preferentially adsorbs onto surfaces with Lewis base components because of acid-base interactions. However, strongly adsorbing vapors can clog up the membrane pores. Vapors in a gas mixture affect gas permeation; selectivity typically decreases with increasing the pressure drop across the membrane; the water and other vapors in the membranes may have a plasticizing effect [9]. In summary, pore sizes and pore wall surface functionalities need to be designed for maximal effective and efficient separation.

2. Cellulose Membranes

2.3. Potential of Cellulose as a Material for Membranes

In pursuit of sustainable membrane material development with a focus on high hydrophilicity, ideal porosity, and desirable mechanical strength, cellulose has become a central focus of interest among membrane researchers [22]. This intensified interest stems from a multitude of key advantages, including its intrinsic hydrophilic nature, high crystallinity, insolubility in various solvents, non-toxicity, and ease of processing, all of which are underpinned by the robust hydrogen bonding within cellulose [23]. A particularly notable facet of cellulose-based materials lies in the abundant functional groups, such as hydroxyl and carboxylate groups, present in nanocellulose. These functional groups serve as exceptional adsorption sites, effectively removing numerous organic and inorganic contaminants. Moreover, cellulose contributes to the development of mechanically robust membranes characterized by excellent porosity. In the realm of water filter membranes, cellulose serves versatile roles, functioning as a filler to enhance mechanical strength and reduce pore size distribution, as a barrier layer for selective filtration, as a self-standing membrane for efficient nanoscale filtration, or as a support layer to bolster structural stability and overall membrane performance [24].

This distinctive amalgamation of properties underscores cellulose as an exceptionally promising and environmentally friendly material for advancing membrane technology, particularly in the pursuit of sustainable solutions for water purification. An illustrative example of this research direction is the work of Li et al., who developed a composite membrane (LBL-NF-CS/BCM), comprising a selective film of alternate CMC and chitosan (CS) layers through layer-by-layer spray coating (LBL) on a porous sublayer of bamboo cellulose/CS as the support [25]. The cellulose-based composite membrane had an average pore size of 2.2 nm and could be considered a nanofiltration membrane. Under optimized conditions with a transmembrane pressure difference of 0.3 MPa, the membrane had a flux of 12 L m^-2 h^-1 and a substantial NaCl rejection rate of 36 %.

Figure 2. Schematic diagram of cellulose membrane technology from a cellulose source to a filtration application including creating a nanofiltration film on a porous regenerated cellulose-based support (LBL-NF-CS/BCM), adapted with permission from reference [26].

Figure 2. Schematic diagram of cellulose membrane technology from a cellulose source to a filtration application including creating a nanofiltration film on a porous regenerated cellulose-based support (LBL-NF-CS/BCM), adapted with permission from reference [26].

3. Preparation and Structure of Cellulosic Membranes through Dissolution

3.1. Phase Inversion

Cellulosic membranes via the solution of cellulose and cellulose derivatives are prepared predominantly by phase inversion like most other polymeric membrane fabrication. Phase inversion is a process to de-mix a homogeneous polymer solution into a solid phase of the polymer and a liquid phase of the solvent. There are various ways to induce this phase separation like cooling, changing pH, adding a non-solvent, or supersaturation. Most commonly, a non-solvent is introduced to exchange or partially exchange the solvent, causing polymer macromolecule precipitation to form a networked structure. The typical process of making phase inversion membranes is as follows:

Solution preparation: A polymer is dissolved in a suitable solvent to form a homogeneous solution.

Casting: The polymer solution is cast onto a support layer, such as a glass plate or a moving belt.

Controlled evaporation: the cast film is exposed under programmed temperatures and humidities. If a non-solvent is already added to the solution, the evaporation of the solvent due to high volatility causes an enriched non-solvent and polymer content, leading to partial phase separation.

Immersion: The cast film is immersed in a non-solvent bath, which induces the formation of a solid membrane by inducing solvent exchange and phase separation of the solvent and polymer.

Washing: The membrane is washed to remove any residual solvent and non-solvent.

Drying: The membrane is dried to remove any remaining water or solvent.

Figure 3. Schematic illustration of making phase inversion membranes (a) lab preparation adapted from [27] and (b) Continuous web production adapted from [28].

Figure 3. Schematic illustration of making phase inversion membranes (a) lab preparation adapted from [27] and (b) Continuous web production adapted from [28].

3.2. Structure of Phase Inversion Membranes

When the cast film is added to the anti-solvent bath, the polymer precipitates, and pores can form within the membrane structure. Factors such as the type of polymer, solvent and non-solvent, polymer concentration, the additives in and temperature of the casting solution and non-solvent bath can influence the phase separation process and final membrane morphology as well as its separation properties such as permeability, diffusivity, and selectivity [29]. The degree of miscibility between the solvent and non-solvent significantly affects the phase separation process and membrane morphology. For a miscible solvent system, faster exchange between the phases can lead to an asymmetric structure comprising a denser skin layer with smaller pores on top and a more porous sublayer with finger-like pores underneath (a & b). The skin layer is responsible for permeability and selectivity, while the sublayer provides mechanical strength and support. These membranes generally have lower permeability due to the denser skin and larger maximum pores. When the cast film is added to the anti-solvent bath, the solvent in the cast film rushing towards the non-solvent side drags the polymer along with and meets the non-solvent moving reversely at the interface, leading to the formation of two distinct phases: A dense polymer-rich phase that forms the skin layer of the membrane and a lean phase rich in non-solvent due to the removal of the solvent and some polymer that forms the sublayer. Pores initiate in the frontier of the non-solvent and grow into finger-like pores in the lean phase due to polymer coalescence induced by the arriving non-solvent. When the solvent and non-solvent are immiscible, limited miscibility restricts the interaction between the two phases, resulting in a slower exchange rate. This slower exchange leads to a “spongier” morphology with smaller, interconnected pores closer to the membrane surface (c & d). These pores offer higher permeability but pore selectivity.

Figure 4. The cross-section of phase inversion membranes of cellulose acetate (CA): asymmetric structure of dense skin/finger-like pores (a & b) and homogeneous sponge-like structure (c & d). The microstructure was tuned by the ratio of the non-solvent glycerol to CA with acetone/dimethylacetamide as the solvent [29].

Figure 4. The cross-section of phase inversion membranes of cellulose acetate (CA): asymmetric structure of dense skin/finger-like pores (a & b) and homogeneous sponge-like structure (c & d). The microstructure was tuned by the ratio of the non-solvent glycerol to CA with acetone/dimethylacetamide as the solvent [29].

3.3. Factors Affecting Structure and Properties of Phase Inversion Membranes

It's important to note that miscibility is just one factor affecting membrane morphology. Other factors like polymer concentration, coagulation bath temperature, additives, washing liquids, and drying methods also play a role. shows the effect of washing and drying methods on regenerated cellulose membrane structure prepared by phase inversion [30]. Supercritical CO₂ drying generated an open cellulose fibrous network with pores for both water and ethanol-washed and swollen samples, which was deemed as the structure in the wet state before drying since the capillary forces exerted on the cellulose network by the evaporating liquid can nearly be eliminated by supercritical drying. Ambient pressure drying seems to collapse water-washed samples to form a dense structure without visible pores at the designated resolution but might contain smaller pores (b′), but it generated a porous structure for ethanol-washed samples (d′). Solution casting without non-solvent coagulation and drying without constraints, especially in solvents with high surface tension such as water, can create a very dense structure.

In summary, combining an understanding of miscibility with these other variables allows for optimizing the phase inversion process for specific needs. Pore size indicates the largest pore diameter and can be related to the membrane’s ability to filter out particles of a certain size. Cellulose membranes can be tuned with a range of pore sizes from hundreds of micrometers, a few nanometers, to hundreds of Daltons nominal molecular weight cutoff for microfiltration, ultrafiltration, and nanofiltration [31].

Figure 5. The effect of washing and drying methods on regenerated cellulose membrane structure. Solvent: lithium chloride/dimethylacetamide, non-solvent: aqueous ethanol, 96 vol %, washing liquid: Milli-Q water or 96% ethanol, and drying method: supercritical point drying (CPD) or ambient pressure drying (APD) [30].

Figure 5. The effect of washing and drying methods on regenerated cellulose membrane structure. Solvent: lithium chloride/dimethylacetamide, non-solvent: aqueous ethanol, 96 vol %, washing liquid: Milli-Q water or 96% ethanol, and drying method: supercritical point drying (CPD) or ambient pressure drying (APD) [30].

To fabricate membranes with the phase inversion method, the polymer must be soluble in a solvent mixture. Phase inversion is often used to fabricate membranes of regenerated cellulose, cellulose acetates, and cellulose nitrates. There are two types of hydroxyl groups in cellulose: ring hydroxyl groups and the C-6 exocyclic hydroxyl. Different reactions occur depending on reagents and reaction conditions, leading to different degrees of substitution and distribution of derivative groups such as acetyl along the cellulose chain. Dissolving cellulose is difficult and needs special solvents. Derivation such as acetylation and nitration makes cellulose derivatives dissolution easier. The combination of phase separation and mass transfer affects the membrane structure. Their porosity and morphology can be tuned for specific application requirements. They are widely used in various applications, including water purification, filtration, and separation processes.

Figure 6. The chemical structure of cellulose (-H), cellulose acetate (-COCH₃), or cellulose nitrate (-NO₂), carboxymethyl cellulose (-CH₂COOH), or ethyl cellulose (-CH₂CH₃). The red text C-6 marks the exocyclic carbon in one of the rings, adapted from [32].

Figure 6. The chemical structure of cellulose (-H), cellulose acetate (-COCH₃), or cellulose nitrate (-NO₂), carboxymethyl cellulose (-CH₂COOH), or ethyl cellulose (-CH₂CH₃). The red text C-6 marks the exocyclic carbon in one of the rings, adapted from [32].

3.5. Cellulose Acetate Membranes

Cellulose acetates are produced by reacting cellulose with acetic anhydride, replacing some of the hydroxyl (OH) groups with acetyl (-CH₃CO) groups. In what is commonly known as cellulose acetate, no less than 92% of the hydroxyl groups are acetylated. In cellulose triacetate (CTA), only ~1% of the hydroxyl groups remain free, and of these about 80% are C-6 hydroxyls [32]. Cellulose acetate can be made to be slightly hydrophilic to highly hydrophobic depending on the presence of remaining hydroxyl (OH) groups from the original cellulose [35]. As the degree of acetylation increases, the overall hydrophobicity of the cellulose acetate also increases. While a moderate level of acetylation can promote crystallinity when combined with controlled heat treatment, it's crucial to consider the interplay of various factors to achieve the desired outcome for specific applications. Cellulose acetates are known for their effective film-forming properties, toughness, and smoothness, which makes them suitable for membrane fabrication [36,37]. Hydrophilic cellulose acetate membranes have very low protein binding capacity and so are excellent for protein recovery and osmotically driven membrane processes, but they have limited chemical resistance. A higher degree of substitution yields superior salt rejection but lower flux values due to increasing hydrophobicity [38]. Cellulose acetate membranes are less prone to absorptive fouling than more hydrophobic membranes [32].

Cellulose acetate can be dissolved in organic solvents to form membranes via the phase-inversion process (Wang et al., 2016). Wang et al report a fabrication method using a mixture of acetone and dimethylacetamide as the solvent, and glycerol and water as the non-solvents. Through adjusting the ratios of the agents and processing conditions to change the rate of phase separation, the microstructure was tuned from an asymmetric structure of dense skin/porous underlayer (a & b) to a material network with relatively homogeneous pores (c & d). The maximum pore size and porosity were tuned ranging from 0.61 to 2.33 μm and 85 to 95 percent, respectively, and the water permeance ranged from 182 to 24,472 L^-2 h^-1 bar^-1, falling in the category of microfiltration. The salient influencing factors were the ratios of acetone/dimethylacetamide and glycerol/cellulose acetate, where glycerol was found to perform the dual function of pore-forming and plasticizing [29]. Glycerol has a high boiling point and interacts with cellulose through hydrogen bonding, making it difficult to completely displace with water or drying, leading to residual glycerol in the polymer that can be beneficial for maintaining flexibility and processability of cellulose acetate but negatively impacts mechanical properties and thermal stability.

Cellulose acetate membranes can be structured for ultrafiltration, nanofiltration, reverse osmosis, and forward osmosis [40,41] in the fields of water purification, protein purification, heavy metal removal, dye wastewater treatment, blood hemodialysis, and oil-water separation [42,43,44,45,46]. Asymmetric cellulose acetate membranes developed in 1959 were the first viable reverse osmosis membranes [9] and dominated the application until the commercialization of thin-film composite membranes was invented in 1972. The first commercially available membrane for osmotically driven processes, developed by Hydration Technologies, Inc. (HTI), consisted of a thin woven polyester mesh embedded within a cellulose triacetate (CTA) substrate (a) [47], exhibited a lower water permeability of 0.36 L m⁻² h⁻¹ atm⁻¹ and a salt rejection of 94 percent [48]. A thin film composite membrane (b), including a top ultrathin polyamide selective barrier layer, a microporous polysulfone support layer, and a bottom PET nonwoven backing layer, demonstrated a significantly higher value of 1.16 L m⁻² h⁻¹ atm⁻¹ and a slightly higher salt rejection of 97% [48]. The HTI membrane design eliminated the need for a thick backing layer but resulted in a denser membrane far thicker than the selective barrier layer of the thin-film composite membrane, while the latter offered superior water permeability, potentially leading to higher water production rates but still maintaining comparable salt rejection. Instead of polysulfone, cellulose acetate can also be used as the support layer for the polyamide active layer, increasing the number of possible material choices in thin film composite membranes [49].

Figure 7. SEM micrographs display the cross-section of (a) a commercial HTI-CTA membrane comprising a polyester mesh embedded in cellulose triacetate (CTA) substrate and (b) a thin film composite membrane including a top ultrathin polyamide selective barrier layer, a microporous polysulfone support layer, and a bottom PET nonwoven backing layer [48].

Figure 7. SEM micrographs display the cross-section of (a) a commercial HTI-CTA membrane comprising a polyester mesh embedded in cellulose triacetate (CTA) substrate and (b) a thin film composite membrane including a top ultrathin polyamide selective barrier layer, a microporous polysulfone support layer, and a bottom PET nonwoven backing layer [48].

However, because of the presence of β-dehydrated glucose, cellulose acetate is susceptible to bacterial attacks, leading to significant damage to the membrane surface and compactness [50]. Cellulose acetate membranes are susceptible to hydrolysis in both alkaline and acidic environments, limiting their operational pH range, typically between pH 4 and 6 [51]. These drawbacks along with high fragility have recently prompted a shift toward alternative membrane materials.

To address this challenge, NH₂-functionalized-cellulose acetate and silica composite nanofibrous membranes, have been developed to enhance antibacterial properties which exhibit remarkable adsorption capacity for Cr⁶⁺ ions (19.46 mg g^-1) compared to pure cellulose acetate (1.28 mg g^-1) or cellulose acetate/silica composite (3.03 mg g^-1) [52]. Furthermore, cellulose acetate-based membranes have also been employed for the removal of pharmaceutical and personal care products. For instance, Emam and colleagues established a highly porous photoactive cellulose acetate@Ti-MIL-MOF film, exhibiting both adsorption and photodegradation capacity for paracetamol in the presence of visible light [53]. The overall paracetamol removal significantly increased from 72.6 mg g^-1 for pure Ti-MIL-MOF film and 82.7 for cellulose acetate film to 519.1 mg/g for porous CA@Ti-MIL-NH₂ film.

3.8. Water Vapor Separation Applications

Cellulosic materials generally absorb moisture and are plasticized by it. Their free volume decreases initially and then increases again with increasing humidity depending on the degree of hydroxyl substitution; their gas and vapor permeability coefficients also follow a similar pattern to the free volume [58,59]. shows cellulosic membranes preferentially permeate water vapor. They have higher moisture solubility but lower diffusivity than those of high-free-volume polymers such as silicone rubbers. Cellulosic membranes have the potential to be utilized to dehydrate exhaust air to recover water and heat for energy recovery ventilation. There are three typical ways to dry air streams. A refrigerated dryer consuming electricity dehydrates air by cooling it down to condense the water while desiccant dryers dehydrate air by adsorbing water on a solid granular absorbent that needs to be regenerated regularly. In contrast, membrane dehydration provides a wide range of drying capacities depending on membrane separation properties. Cellulosic membranes have higher selectivity coefficients but lower permeability than polydimethylsiloxane (PDMS) membranes. PDMS has high permeability coefficients, owing to its large free volume, and reasonable selectivity for condensable gases, and has been studied in detail because of the vast utility of PDMS for the removal or harvest of water from air [60,61]. Silicone rubber is extremely permeable and has adequate vapor/inert gas selectivity for most applications; composite membranes of silicone rubber are used in almost all of the installed vapor separation systems [15]. Compared with other high-performance polymers, cellulose acetate membranes are reasonably performative [9].

Figure 8. Comparison of water vapor permeability and water vapor/N₂ selectivity for various polymers at 30 °C [62]. CA: cellulose acetate.

Figure 8. Comparison of water vapor permeability and water vapor/N₂ selectivity for various polymers at 30 °C [62]. CA: cellulose acetate.

3.9. Carbon Dioxide Capture Applications

Error! Reference source not found. shows regenerated cellulose is a good barrier to gases and poorly selective to different gases in the dry state and gradually loses its barrier and is increasingly permeable to nitrogen with increasing moisture content. It also can be seen that the structure of regenerated cellulose was prepared to be more porous to increase gas permeability and selectivity, especially in a wet state [63]. Cellulose acetate, initially developed for membrane reverse osmosis, is the most widely used and tested material for CO₂ removal [15]. Cellulose acetate contains polar functional groups such as carbonyl (C=O) and residual -OH groups, which strongly interact with CO₂ molecules, affecting absorption and enhancing CO₂ permeance. They are used to fabricate large-scale CO₂ separating membranes [57]. It is noted that cellulose nitrate membranes have relatively lower nitrogen permeability and higher selectivity coefficients toward nitrogen.

Nonporous ethyl cellulose membranes have been used to separate CO₂ owing to polar ether oxygen atoms that interact with quadrupolar CO₂ molecules resulting in high solubility [55]. Because of this interaction, it has slightly lower diffusivity in ethyl cellulose than O₂ even though CO₂ has a smaller kinetic diameter than O₂. Solubility is a key factor that enables CO₂ to preferentially permeate over less soluble gases_. However, the affinity of membrane materials for CO₂ must not be too high such that its mobility is reduced, otherwise the CO₂ flux will suffer. In general, ethyl cellulose has a larger permeability to CO₂ than to other light gases, which tends to increase with increasing ethyl content in the polymer, probably due to an increase in the polymer free volume [20]. Compared with cellulose acetate, ethyl cellulose has a higher gas permeability and a lower CO₂/ N₂ selectivity because of its larger free volume and higher chain mobility.

Table 3. Gas permeability and selectivity of cellulosic membranes at 25 °C and relevant humidity (RH) [64].

Table 3. Gas permeability and selectivity of cellulosic membranes at 25 °C and relevant humidity (RH) [64].

Cellulosic material		Permeability (Barrer)					Selectivity Coefficient
		H₂O	CO₂	H₂	O₂	N₂	H₂O/N₂	CO₂/N₂	H₂/N₂	O₂/N₂
Regenerated cellulose	0%RH		0.005	0.006	0.002	0.003		1.5	2.0	0.7
	43%RH		0.013	0.016	0.007	0.007		1.9	2.4	1.1
	76%RH		0.072	0.033	0.009	0.007		9.6	4.4	1.2
	100%RH	25,198	0.256	0.080	0.012	0.018	1,369,565	13.9	4.3	0.6
	Dry*		127.7	9.14	6.28	2.58		49.5	3.5	2.4
	Wet*		1957.4	134.7	93.42	37.13		52.7	3.6	2.5
Cellulose acetate**		7,333	23.07	3.506	0.780	0.280	26,191	82.4	12.5	2.8
Cellulose nitrate		6,293	2.120	2.000	1.947	0.116	54,253	18.3	17.2	16.8
Ethylcellulose		8,933	113.1	87.06	14.67	4.426	2,018	25.5	19.7	3.3
Polydimethylsiloxane		43,000	4651.6	939.9	926.6	470.6	91.4	9.9	2.0	2.0

*[63]; ** plasticized.

4. Nonwoven Membranes from Cellulose Particles

4.1. Types of Cellulose Particles

Cellulose exists mostly in plant cell walls such as wood, cotton, flax, and bamboo, and it is also produced by different types of bacteria and animals. Predominant wood cells are tracheid in softwood, vessels, and fibers in hardwood (Error! Reference source not found.). Plant cells contain a cell wall and lumen with a length of up to 7 mm and 10-70 μm in diameter. Pulping is a process of separating plant cells into individual fibers. After bleaching, fibers mostly contain cellulose and are thus also called cellulose fibers, which also refer to spun filaments of cellulose derivatives and regenerated cellulose depending on the context it is used. Cellulose is macromolecules of glucose monomers, organized into hierarchical structures of elemental fibrils consisting of alternate amorphous and crystalline regions, microfibrils of aggregated elemental fibrils, mainly existing in the S1, S2, and S3 layers of a cell wall. Technically, cell walls can be breakdown and various-sized components can be separated and harvested. Three representative sizes are cellulose fibrils (> 100 nm in diameter, > 200 μm in length) (f), cellulose nanofibrils (CNFs) (5-100 nm in diameter, 0.5-200 μm in length) (g), and cellulose nanocrystals (CNCs) (5-70 nm in diameter, < 500 nm in length) (h)[65]. Both CNFs and CNCs are also called nanocellulose.

Figure 9. The size and morphology of major wood cells [66]. (a) Softwood tracheid, (b) hardwood vessels, (c) hardwood fibers, (d) cell wall structure (S₁–S₃) of two neighboring wood cells. Fiber development by refining: (e) isolated wood cells also known as cellulose fibers at zero fibrillation refining time showing complete absence of fibrils, i.e. 0% degree of fibrillation [67], (f) part of a broken fiber with attached smaller fibrils, or fibrillar fines, (g) networked nanofibrils [68], and (h) cellulose nanocrystals by acid hydrolysis of cellulose fibers [69].

Figure 9. The size and morphology of major wood cells [66]. (a) Softwood tracheid, (b) hardwood vessels, (c) hardwood fibers, (d) cell wall structure (S₁–S₃) of two neighboring wood cells. Fiber development by refining: (e) isolated wood cells also known as cellulose fibers at zero fibrillation refining time showing complete absence of fibrils, i.e. 0% degree of fibrillation [67], (f) part of a broken fiber with attached smaller fibrils, or fibrillar fines, (g) networked nanofibrils [68], and (h) cellulose nanocrystals by acid hydrolysis of cellulose fibers [69].

4.2. Impact of Particle Morphology on Pore Size and Porosity of Membrane Materials

Figure 10. The relationship between fiber diameter and pore size in non-woven membranes with the same porosity produced from a range of diameter sizes: (a) 0.1 μm Diameter fibers, (b) 1.0 μm Diameter fibers, and (c) 2.0 μm diameter fibers [70]. Pore sizes are tuned by constituent fiber diameters and the thickness of the membrane.

Figure 10. The relationship between fiber diameter and pore size in non-woven membranes with the same porosity produced from a range of diameter sizes: (a) 0.1 μm Diameter fibers, (b) 1.0 μm Diameter fibers, and (c) 2.0 μm diameter fibers [70]. Pore sizes are tuned by constituent fiber diameters and the thickness of the membrane.

There are three types of pores in membranes made from fibers: inter-particle pores, fiber lumens, and pores inside cell wall material. The latter two pore systems are decided by the nature of fibers. The porosity and separation properties are mainly decided by inter-particle pores, which are simply referred to as pores. A nonwoven membrane of fibers can be modeled as a stack of many thin sheets with the same pore size. Within a sheet, the diameter of fibers, fibrils, and crystals decides pore size and distribution, but adding one layer on a stack of sheets will reduce the pore size by half. So, the thicker the membrane, the smaller its pore size. illustrates three digital twin replica geometry of air filters of varied diameter sizes of cellulose particles. When the porosity is maintained, the effective mean pore size decreases with decreasing fiber diameter. Generally, the mean pore size is directly proportional to the fiber diameter in nonwoven fiber membranes. At the same thickness of membranes, air filtration efficiency and airflow resistance decrease exponentially with fiber diameter but selectivity increases [70]. Generally, smaller diameter fibers lead to a higher number of pores and smaller average pore size.

Fiber lengths should have less effect on pore sizes than fiber cross-sectional dimensions. Longer fibers generally possess more kinks and orient themselves into a less compact form during formation and drying than short fibers, resulting in a larger pore size. Thick and stiff fibers can resist larger capillary action during drying resulting in less fiber collapse and consolidation. Generally, fibers with a higher degree of polymerization are stronger. For example, cellulose fibrils with a degree of polymerization of 410 exhibited a membrane porosity of 20%, while fibrils with 1100 showed a porosity of 28% [71].

4.3. Structure of Membrane Materials Made from Cellulose Particles

shows the morphology of membrane materials made from various cellulose particles. Cellulose fibers originate from wood cells which vary in size from species to species. Pore sizes of cellulose fiber paper were found to be 1-5 µm for the base layer and 50-500 nm for the coating pores [72]. The coating of a glassy paper has an average pore size of about 180 nm, and an estimated porosity and permeability at 34 percent and 0.09 mDarcy, respectively [73]. A base paper was estimated to have a pore size from 3 to 3.5 µm and 50-130 nm for the coating and a porosity of 32 to 44 percent for the base paper and 20 to 36 percent for the coating, respectively [74]. Hence, cellulose fiber paper can be considered microfiltration membranes, and its pigmented coatings fall into upper ultrafiltration and lower microfiltration.

Electrospinning is a versatile technique that can generate a wide range of fiber diameters depending on process parameters and solution properties. Cellulose and its derivatives can be dissolved into solvents. The solutions can be spun into fibers with average diameters from 50 to 900 nm [70], which can form membranes of randomly distributed fibers (e & f). The term nanofiber is usually used to designate those with diameters from 1-100 nm while the term microfiber refers to those with diameters ranging from about 100 nm to 10 µm. Adjusting electrospinning parameters (e.g., flow rate, applied voltage, coagulation conditions) and formulations of cellulose solutions, the surface chemistry and morphology along with other physiochemical characteristics such as tensile strength of fibers, swelling property, porosity, permeance, and adsorption can be finely tuned for specific pore size and distribution either as the support layer or selective layer. These materials are mostly evaluated in labs without wide commercialization.

Figure 11. SEM morphology of membranes made from cellulose fibers (a) [75], fibrils (b) and nanofibrils (c) [76], nanocrystals (d) [65], electrospun nanofibers of cellulose acetate (e) [77] and regenerated cellulose (f) [78].

Figure 11. SEM morphology of membranes made from cellulose fibers (a) [75], fibrils (b) and nanofibrils (c) [76], nanocrystals (d) [65], electrospun nanofibers of cellulose acetate (e) [77] and regenerated cellulose (f) [78].

Decreasing fiber diameter and increasing fiber thickness can finely tune the pore size and topology of pore networks, and hence affect selectivity and permeance. CNFs with diameters in the range of 3-6 nm can produce a thin membrane barrier layer of 100 nm with a mean pore size on the order of 20 nm [79]. The obtained nanofibers have a uniform diameter of 7.5 ± 2.5 nm, thickness down to 23 nm and pore sizes ranging from 2.5 to 12 nm, and a ferritin molecules rejection rate of 94% [80]. At 20 g m^-² (around 20 μm), A CNC membrane has an average pore size of 2.4 nm, and a tetramethylpiperidine-1-oxyl (TEMPO)-oxidized CNF membrane having 19 nm with water permeance both at ~4 L m^-2 h^-1 MPa^-1 [81]. CNCs are the smallest particles in size and form the thick dense structure of membranes (d) with pores of free volume less than 1 nm in diameter [82], which can be used to regulate gases and moisture in air. These pore sizes correspond to the ultrafiltration range. The size of pores varies from micrometers to sub-nanometers for other membranes made from cellulose particles between cellulose fibers and CNCs.

4.5. Cellulose Particles-Based Membrane Structure Design

Cellulose nanoparticles including CNCs and CNFs, having a size of 2-10 nm and fiber length up to a few microns, are suitable for the construction of membranes with defined mean pore sizes for pressure-driven ultrafiltration and microfiltration in several ways: 1) self-standing membranes, 2) the top selective layer supported by more porous substrates as shown in 3) as a substrate layer providing a smooth surface for interfacial polymerization of a thin dense polymer on it, 4) as a matrix reinforced by a polymer fiber scaffold, and 5) as a reinforced scaffold for a polymer matrix.

Conventionally, membranes are typically asymmetrical layered structures consisting of a thin selective layer on the top side, a finely porous support sublayer in the middle, and a coarsely nonwoven backing layer at the bottom. This construction provides structural strength to resist pressure and a smoother surface to support a selective layer that is thick enough to be selective but not so thick that it causes low permeation rates. The thin selective layer decreases the requirement of the driving force or pressure gradient and increases permeance, thus, the membrane may possess a higher permeation flux and can be operated at a lower pressure. Accordingly, cellulose particle-based membranes can be constructed with a thin layer of nanoscale CNCs or CNFs as the selective layer, cellulose microfibrils or electrospun cellulose nanofibers as the support interlayer, and cellulose fibers as the backing layer as, but such a completely cellulose-based membrane has not been reported while various composite three-layered structures have been studied.

Figure 12. (a) Schematic membrane structure with hierarchical fiber diameters from microns to nanometers forming three-layered pores: the top thin ultrafiltration layer of nanoparticles, the middle microporous support layer of microfibers, and the bottom backing layer of fibers [84], and (b) a thin-film nanofibrous composite membrane with the top thin ultrafiltration layer (the maximum pore size of 55 nm at the thickness of 100 – 200 nm) of TEMPO-oxidized CNFs coated on the support layer of electrospun polyacrylonitrile microfibers [79]. The inset of the overlapping blue and red nets illustrates that the pore size decreases with increasing thickness.

Figure 12. (a) Schematic membrane structure with hierarchical fiber diameters from microns to nanometers forming three-layered pores: the top thin ultrafiltration layer of nanoparticles, the middle microporous support layer of microfibers, and the bottom backing layer of fibers [84], and (b) a thin-film nanofibrous composite membrane with the top thin ultrafiltration layer (the maximum pore size of 55 nm at the thickness of 100 – 200 nm) of TEMPO-oxidized CNFs coated on the support layer of electrospun polyacrylonitrile microfibers [79]. The inset of the overlapping blue and red nets illustrates that the pore size decreases with increasing thickness.

Using cellulose nanomaterials for barrier layer fabrication in the design of new filtration membranes was reviewed as shown in [84]. When TEMPO-oxidized CNFs were used as the barrier layer in an asymmetric three-layered nonwoven fibrous structure containing fibers of different diameters, the membranes exhibited a two- to ten-fold increase in permeation flux over commercial membranes for ultrafiltration of oil and water emulsions [87]. The thin-film nanoporous composite membrane had a pure water permeance several times higher than that of commercial polyacrylonitrile membranes because cellulose is more hydrophilic than polyacrylonitrile and a nominal molecular weight cutoff of 2000 kDa at a rejection rate of larger than 90%, which corresponds a maximum pore size of 54.6 nm [79]. Serving as the interlayer between the coarse substrate support and thin selective layer, a nanocellulose layer can provide a smooth surface on which a thin dense selective polymer layer can be formed via interfacial polymerization to fabricate nonporous membranes for reverse osmosis [5,88] as shown in, or a thin layer of graphene oxide is coated for dye removal [89]. The nanocellulose interlayer helps direct the water permeation due to its hydrophilic feature.

Figure 13. Schematic diagram of the formation of a triple-layered composite membrane with CNC as the interlayer [5].

Figure 13. Schematic diagram of the formation of a triple-layered composite membrane with CNC as the interlayer [5].

Based on the design as shown in a with a polymer network as the support, the two-layered nonwoven composite membranes, a layer of TEMPO-oxidized CNFs or CNCs (5-8 nm in diameter) being infused into an electrospun polyacrylonitrile fibrous sheet (150 nm in fiber diameter) backed by a poly(ethylene terephthalate) nonwoven substrate (20 μm in diameter), exhibited a high water permeance and a high ability to remove bacteria (by size exclusion) and viruses (by adsorption) simultaneously [87,90]. It has been demonstrated that nanocellulose (CNFs and CNCs) can be embedded in a polymer matrix (e.g., cross-linked polyamide formed by interfacial polymerization) forming an interconnected fibrous scaffold, which acts as a directed water channel, leading to an increase in permeance without loss of selectivity [91]. CNCs-reinforced chitosan membranes, having a thickness of 250 μm with pores of 13-17 nm, had a rejection rate of up to 99 percent for positively charged dyes [92].

4.7. CNC Membranes

CNCs hold significant value in water membranes owing to their unique attributes, such as shorter length, heightened charge density, large surface area, good thermal stability, and impressive strength [25,107]. Notably, CNCs offer the capability to produce membranes with smaller and precisely controlled pore sizes, thanks to their inherent needle-like structure [108]. This feature proves especially advantageous when dealing with applications necessitating the filtration of minute particles or molecules. Additionally, CNCs typically exhibit a greater surface charge density due to their compact size and expanded surface area, enhancing the adsorption of charged particles and molecules from water [109]. Furthermore, they can be chemically modified easily to tailor their porosity and other properties [110]. Moreover, due to their hydrophilic nature and diminutive size, CNC-based membranes contribute to a reduction in fouling by preventing the accumulation of particles and contaminants on the membrane surface [111,112,113,114]. Furthermore, CNCs are renowned for their outstanding mechanical properties, encompassing high tensile strength [111].

CNCs serve as crucial components in the construction of water filtration membranes, notably as functional layers. For example, CNCs were employed as functional layers in layered cellulose nanocomposite membranes [115]. This synthesized membrane had pore structures in the microfiltration range (5.0-6.1 μm), resulting in remarkably high water permeability (900-4000 L h^-1 m^-2) at pressures below 1.5 bars. These membranes exhibited a tensile strength of 16 MPa in dry conditions and 0.2 MPa when wet. When they were used to treat model industry effluent containing metal ions (Ag⁺ and Cu²⁺/Fe³⁺/Fe²⁺), CNC-based membranes demonstrated effective removal rates. The efficiency of removal varied depending on the functional groups of the CNCs that were employed, with phosphorylated CNC membranes exhibiting the highest removal rates.

CNCs are also used to develop composite membranes with different organic polymers (such as PES, PVDF, PSF, etc.) [116,117]. For instance, in a study by Zheng et al., high-performance ultrafiltration membranes were fabricated by blending multi-branched nanocellulose (multi CNC) within a polyethersulfone (PES) matrix using non-solvent induced phase separation (NIPS) technology as shown in [117]. This composite ultrafiltration membrane exhibited high hydrophilicity, a thicker skin layer, and a lower negative charge due to the presence of carboxyl (-COOH) groups in multi-CNC. Consequently, this membrane showed a significantly higher water flux (962 L m^-2 h^-1) and excellent Bovine serum albumin (BSA) rejection (96.4%) compared to the original PES membrane. In another study, CNC-PVDF membranes were developed for wastewater treatment which significantly increased permeability (up to 206.9 L m^-2 h^-1) due to improved porosity, surface roughness, and hydrophilicity as compared to PVDF (9.8 L m^-2 h^-1) [116]. In a study conducted by Bai et al., a CNC/polyamide TFC was developed onto a PES membrane using interfacial polymerization [109]. When only 0.2 wt.% of CNC was added to the polyamide thin film, the pure water permeability under 0.25 MPa increased by 60%, while the rejection of NaCl rose from 16.19% to 22.7%. Even with an increased CNC content, the rejection of SO₄^2- divalent salts remained consistently high at over 98%. Similarly, Asempour et al. developed a TFC reverse osmosis membrane by incorporating CNC into the polyamide active layer. This CNC/polyamide nanocomposite membrane proved effective in recovering water from synthetic brackish water. Importantly, the study revealed that the permeability of the membrane doubled to 63 L m^-2 h^-1 with no significant impact on salt rejection, which remained at 97.8%, even when a small amount (0.1 w/v%) of CNC was incorporated [118].

CNCs combined with other biomaterials to create sustainable membranes have also been investigated. For example, CNC/chitosan composite membranes were prepared through freeze drying, compaction, and crosslinking using glutaraldehyde vapors. These membranes exhibited enhanced mechanical properties, a suitable pore diameter for ultrafiltration, and high efficiency in adsorbing positively-charged dyes, namely Victoria blue (98 %), Methyl violet (90 %), and Rhodamine 6 G (78 %) [92].

In oil/water separation, CNCs-based hybrid membranes were developed with resistance to swelling. These hydrophilic membranes featured highly interconnected channels, ensuring non-swell ability, and maintaining mechanical and structural integrity. For instance, Wang et al. developed CNC/H-PAN/PEI/SiO₂ hybrid membranes which showed high separation efficiencies, exceeding 94% for various emulsions, even after 20 filtration cycles. In this process, CNCs played a key role in improving the development of highly interconnected channels for improving hydrophilicity and efficient non-swell ability[119].

Figure 14. Diagrammatic illustration of muti-CNC/PES-based membranes adapted with permission from reference [117].

Figure 14. Diagrammatic illustration of muti-CNC/PES-based membranes adapted with permission from reference [117].

5. Summary

References

1. Tanskyi, O. Zeolite Membrane Water Vapor Separation for Building Air-Conditioning and Ventilation Systems. 2015.
2. Werber, J.R.; Osuji, C.O.; Elimelech, M. Materials for Next-Generation Desalination and Water Purification Membranes. Nature Reviews Materials 2016, 1, 16018. [Google Scholar] [CrossRef]
3. Le, N.L.; Nunes, S.P. Materials and Membrane Technologies for Water and Energy Sustainability. Sustainable Materials and Technologies 2016, 7, 1–28. [Google Scholar] [CrossRef]
4. Lee, A.; Elam, J.W.; Darling, S.B. Membrane Materials for Water Purification: Design, Development, and Application. Environmental Science: Water Research & Technology 2016, 2, 17–42. [Google Scholar] [CrossRef]
5. Tan, H.-F.; Ooi, B.S.; Leo, C.P. Future Perspectives of Nanocellulose-Based Membrane for Water Treatment. Journal of Water Process Engineering 2020, 37, 101502. [Google Scholar] [CrossRef]
6. Bowen, W.R.; Cassey, B.; Jones, P.; Oatley, D.L. Modelling the Performance of Membrane Nanofiltration—Application to an Industrially Relevant Separation. Journal of Membrane Science 2004, 242, 211–220. [Google Scholar] [CrossRef]
7. Galiano, F.; Briceño, K.; Marino, T.; Molino, A.; Christensen, K.V.; Figoli, A. Advances in Biopolymer-Based Membrane Preparation and Applications. Journal of Membrane Science 2018, 564, 562–586. [Google Scholar] [CrossRef]
8. Mansoori, S.; Davarnejad, R.; Matsuura, T.; Ismail, A.F. Membranes Based on Non-Synthetic (Natural) Polymers for Wastewater Treatment. Polymer Testing 2020, 84, 106381. [Google Scholar] [CrossRef]
9. Schell, W.; Wensley, C.; Chen, M.; Venugopal, K.; Miller, B.; Stuart, J. Recent Advances in Cellulosic Membranes for Gas Separation and Pervaporation. Gas Separation & Purification 1989, 3, 162–169. [Google Scholar]
10. Hung, D.C.; Nguyen, N.C. Membrane Processes and Their Potential Applications for Fresh Water Provision in Vietnam. Vietnam Journal of Chemistry 2017, 55, 533–533. [Google Scholar]
11. Yang, Z.; Zhou, Y.; Feng, Z.; Rui, X.; Zhang, T.; Zhang, Z. A Review on Reverse Osmosis and Nanofiltration Membranes for Water Purification. Polymers 2019, 11, 1252. [Google Scholar] [CrossRef]
12. Yu, Y.; Chen, H.; Liu, Y.; Craig, V.S.; Lai, Z. Selective Separation of Oil and Water with Mesh Membranes by Capillarity. Advances in colloid and interface science 2016, 235, 46–55. [Google Scholar] [CrossRef]
13. Ding, M.; Kantzas, A. Capillary Number Correlations for Gas-Liquid Systems. Journal of Canadian Petroleum Technology 2007, 46. [Google Scholar] [CrossRef]
14. Siddiqui, M.A.Q.; Salvemini, F.; Ramandi, H.L.; Fitzgerald, P.; Roshan, H. Configurational Diffusion Transport of Water and Oil in Dual Continuum Shales. Scientific Reports 2021, 11, 2152. [Google Scholar] [CrossRef]
15. Bernardo, P.; Drioli, E.; Golemme, G. Membrane Gas Separation: A Review/State of the Art. Ind. Eng. Chem. Res. 2009, 48, 4638–4663. [Google Scholar] [CrossRef]
16. Shieh, J.; Chung, T.S. Gas Permeability, Diffusivity, and Solubility of Poly (4-vinylpyridine) Film. Journal of Polymer Science Part B: Polymer Physics 1999, 37, 2851–2861. [Google Scholar] [CrossRef]
17. Wikipedia Kinetic Diameter Available online: https://en.wikipedia.org/wiki/Kinetic_diameter.
18. Wikipedia Critical Point (Thermodynamics) Available online: https://en.wikipedia.org/wiki/Critical_point_(thermodynamics).
19. Li, H.; Zhang, X.; Chu, H.; Qi, G.; Ding, H.; Gao, X.; Meng, J. Molecular Simulation on Permeation Behavior of CH4/CO2/H2S Mixture Gas in PVDF at Service Conditions. Polymers 2022, 14, 545. [Google Scholar] [CrossRef]
20. Houde, A.; Stern, S. Solubility and Diffusivity of Light Gases in Ethyl Cellulose at Elevated Pressures Effects of Ethoxy Content. Journal of membrane science 1997, 127, 171–183. [Google Scholar] [CrossRef]
21. Gul, B.Y.; Pekgenc, E.; Vatanpour, V.; Koyuncu, I. A Review of Cellulose-Based Derivatives Polymers in Fabrication of Gas Separation Membranes: Recent Developments and Challenges. Carbohydrate Polymers 2023, 121296. [Google Scholar]
22. Visanko, M.; Liimatainen, H.; Sirviö, J.A.; Hormi, O. A Cross-Linked 2,3-Dicarboxylic Acid Cellulose Nanofibril Network: A Nanoporous Thin-Film Layer with Tailored Pore Size for Composite Membranes. Separation and Purification Technology 2015, 154, 44–50. [Google Scholar] [CrossRef]
23. Norizan, M.N.; Shazleen, S.S.; Alias, A.H.; Sabaruddin, F.A.; Asyraf, M.R.M.; Zainudin, E.S.; Abdullah, N.; Samsudin, M.S.; Kamarudin, S.H.; Norrrahim, M.N.F. Nanocellulose-Based Nanocomposites for Sustainable Applications: A Review. Nanomaterials 2022, 12, 3483. [Google Scholar] [CrossRef]
24. Abdelhamid, H.N.; Mathew, A.P. Cellulose-Based Materials for Water Remediation: Adsorption, Catalysis, and Antifouling. Frontiers in Chemical Engineering 2021, 3. [Google Scholar] [CrossRef]
25. Li, S.; Gao, Y.; Bai, H.; Zhang, L.; Qu, P.; Bai, L. Preparation and Characteristics of Polysulfone Dialysis Composite Membranes Modified with Nanocrystalline Cellulose. BioResources 2011, 6, 1670–1680. [Google Scholar] [CrossRef]
26. Li, S.; Wang, D.; Xiao, H.; Zhang, H.; Cao, S.; Chen, L.; Ni, Y.; Huang, L. Ultra-Low Pressure Cellulose-Based Nanofiltration Membrane Fabricated on Layer-by-Layer Assembly for Efficient Sodium Chloride Removal. Carbohydrate polymers 2021, 255, 117352. [Google Scholar] [CrossRef] [PubMed]
27. Shaari, N.Z.K.; Abd Rahman, N.; Sulaiman, N.A.; Tajuddin, R.M. Thin Film Composite Membranes: Mechanical and Antifouling Properties.; EDP Sciences, 2017; Vol. 103, p. 06005.
28. Synder Filtration Definition Of Phase Inversion Membrane Available online: https://synderfiltration.com/learning-center/articles/introduction-to-membranes/phase-inversion-membranes-immersion-precipitation/.
29. Wang, J.; Song, H.; Ren, L.; Talukder, M.E.; Chen, S.; Shao, J. Study on the Preparation of Cellulose Acetate Separation Membrane and New Adjusting Method of Pore Size. Membranes 2021, 12, 9. [Google Scholar] [CrossRef] [PubMed]
30. Li, H.; Kruteva, M.; Mystek, K.; Dulle, M.; Ji, W.; Pettersson, T.; Wågberg, L. Macro-and Microstructural Evolution during Drying of Regenerated Cellulose Beads. ACS nano 2020, 14, 6774–6784. [Google Scholar] [CrossRef] [PubMed]
31. Tekin, F.S.; Çulfaz-Emecen, P.Z. Controlling Cellulose Membrane Performance via Solvent Choice during Precursor Membrane Formation. ACS Appl. Polym. Mater. 2023, 5, 2185–2194. [Google Scholar] [CrossRef]
32. Alsvik, I.L.; Hägg, M.-B. Pressure Retarded Osmosis and Forward Osmosis Membranes: Materials and Methods. Polymers 2013, 5, 303–327. [Google Scholar] [CrossRef]
33. Wang, S.; Lu, A.; Zhang, L. Recent Advances in Regenerated Cellulose Materials. Progress in Polymer Science 2016, 53, 169–206. [Google Scholar] [CrossRef]
34. Song, Z.; Chen, R.; Luo, S.; Yu, W.; Yuan, J.; Lin, F.; Wang, M.; Cao, X.; Liao, Y.; Huang, B. Regenerated Cellulose Membranes for Efficient Separation of Organic Mixtures. Separation and Purification Technology 2024, 328, 125118. [Google Scholar] [CrossRef]
35. Zhou, X.; Lin, X.; White, K.L.; Lin, S.; Wu, H.; Cao, S.; Huang, L.; Chen, L. Effect of the Degree of Substitution on the Hydrophobicity of Acetylated Cellulose for Production of Liquid Marbles. Cellulose 2016, 23, 811–821. [Google Scholar] [CrossRef]
36. Araújo, D.; Castro, M.C.R.; Figueiredo, A.; Vilarinho, M.; Machado, A. Green Synthesis of Cellulose Acetate from Corncob: Physicochemical Properties and Assessment of Environmental Impacts. Journal of Cleaner Production 2020, 260, 120865. [Google Scholar] [CrossRef]
37. Peng, B.; Yao, Z.; Wang, X.; Crombeen, M.; Sweeney, D.G.; Tam, K.C. Cellulose-Based Materials in Wastewater Treatment of Petroleum Industry. Green Energy & Environment 2020, 5, 37–49. [Google Scholar] [CrossRef]
38. Shenvi, S.S.; Isloor, A.M.; Ismail, A.F. A Review on RO Membrane Technology: Developments and Challenges. Desalination 2015, 368, 10–26. [Google Scholar] [CrossRef]
39. Wang, Z.; Wang, D.; Zhang, S.; Hu, L.; Jin, J. Interfacial Design of Mixed Matrix Membranes for Improved Gas Separation Performance. Advanced Materials 2016, 28, 3399–3405. [Google Scholar] [CrossRef]
40. Li, F.; Fei, P.; Cheng, B.; Meng, J.; Liao, L. Synthesis, Characterization and Excellent Antibacterial Property of Cellulose Acetate Reverse Osmosis Membrane via a Two-Step Reaction. Carbohydrate Polymers 2019, 216, 312–321. [Google Scholar] [CrossRef]
41. Zou, F.; Yao, F.; Liu, L.; Cai, M. Recyclable Heterogeneous Palladium-Catalyzed Carbon–Carbon Coupling Polycondensations toward Highly Purified Conjugated Polymers. Journal of Polymer Research 2019, 27, 1. [Google Scholar] [CrossRef]
42. De Guzman, M.R.; Andra, C.K.A.; Ang, M.B.M.Y.; Dizon, G.V.C.; Caparanga, A.R.; Huang, S.-H.; Lee, K.-R. Increased Performance and Antifouling of Mixed-Matrix Membranes of Cellulose Acetate with Hydrophilic Nanoparticles of Polydopamine-Sulfobetaine Methacrylate for Oil-Water Separation. Journal of Membrane Science 2021, 620, 118881. [Google Scholar] [CrossRef]
43. Kanagaraj, P.; Nagendran, A.; Rana, D.; Matsuura, T. Separation of Macromolecular Proteins and Removal of Humic Acid by Cellulose Acetate Modified UF Membranes. International Journal of Biological Macromolecules 2016, 89, 81–88. [Google Scholar] [CrossRef]
44. Kumar, M.; Isloor, A.M.; Todeti, S.R.; Ibrahim, G.P.S.; Inamuddin; Ismail, A.F.; Asiri, A.M. Improved Separation of Dyes and Proteins Using Membranes Made of Polyphenylsulfone/Cellulose Acetate or Acetate Phthalate. Environmental Chemistry Letters 2020, 18, 881–887. [Google Scholar] [CrossRef]
45. Kumar, M.; RaoT, S.; Isloor, A.M.; Ibrahim, G.P.S.; Inamuddin; Ismail, N.; Ismail, A.F.; Asiri, A.M. Use of Cellulose Acetate/Polyphenylsulfone Derivatives to Fabricate Ultrafiltration Hollow Fiber Membranes for the Removal of Arsenic from Drinking Water. International Journal of Biological Macromolecules 2019, 129, 715–727. [Google Scholar] [CrossRef]
46. Lu, W.; Duan, C.; Zhang, Y.; Gao, K.; Dai, L.; Shen, M.; Wang, W.; Wang, J.; Ni, Y. Cellulose-Based Electrospun Nanofiber Membrane with Core-Sheath Structure and Robust Photocatalytic Activity for Simultaneous and Efficient Oil Emulsions Separation, Dye Degradation and Cr(VI) Reduction. Carbohydrate Polymers 2021, 258, 117676. [Google Scholar] [CrossRef] [PubMed]
47. Herron, J. Asymmetric Forward Osmosis Membranes. 2008.
48. Yip, N.Y.; Tiraferri, A.; Phillip, W.A.; Schiffman, J.D.; Elimelech, M. High Performance Thin-Film Composite Forward Osmosis Membrane. Environmental science & technology 2010, 44, 3812–3818. [Google Scholar]
49. Alsvik, I.L.; Hägg, M.-B. Preparation of Thin Film Composite Membranes with Polyamide Film on Hydrophilic Supports. Journal of membrane science 2013, 428, 225–231. [Google Scholar] [CrossRef]
50. Islam, M.D.; Uddin, F.J.; Rashid, T.U.; Shahruzzaman, M. Cellulose Acetate-Based Membrane for Wastewater Treatment—A State-of-the-Art Review. Materials Advances 2023, 4, 4054–4102. [Google Scholar] [CrossRef]
51. Vos, K.D.; Burris Jr., F.O.; Riley, R.L. Kinetic Study of the Hydrolysis of Cellulose Acetate in the pH Range of 2–10. Journal of Applied Polymer Science 1966, 10, 825–832. [Google Scholar] [CrossRef]
52. Taha, A.A.; Wu, Y.; Wang, H.; Li, F. Preparation and Application of Functionalized Cellulose Acetate/Silica Composite Nanofibrous Membrane via Electrospinning for Cr(VI) Ion Removal from Aqueous Solution. Journal of Environmental Management 2012, 112, 10–16. [Google Scholar] [CrossRef] [PubMed]
53. Emam, H.E.; El-Shahat, M.; Abdelhameed, R.M. Observable Removal of Pharmaceutical Residues by Highly Porous Photoactive Cellulose acetate@MIL-MOF Film. Journal of Hazardous Materials 2021, 414, 125509. [Google Scholar] [CrossRef] [PubMed]
54. Sun, H.; Liu, S.; Ge, B.; Xing, L.; Chen, H. Cellulose Nitrate Membrane Formation via Phase Separation Induced by Penetration of Nonsolvent from Vapor Phase. Journal of membrane science 2007, 295, 2–10. [Google Scholar] [CrossRef]
55. Li, X.-G.; Kresse, I.; Xu, Z.-K.; Springer, J. Effect of Temperature and Pressure on Gas Transport in Ethyl Cellulose Membrane. Polymer 2001, 42, 6801–6810. [Google Scholar] [CrossRef]
56. Li, L.; Baig, M.I.; de Vos, W.M.; Lindhoud, S. Preparation of Sodium Carboxymethyl Cellulose–Chitosan Complex Membranes through Sustainable Aqueous Phase Separation. ACS Appl. Polym. Mater. 2023, 5, 1810–1818. [Google Scholar] [CrossRef]
57. Vatanpour, V.; Pasaoglu, M.E.; Barzegar, H.; Teber, O.O.; Kaya, R.; Bastug, M.; Khataee, A.; Koyuncu, I. Cellulose Acetate in Fabrication of Polymeric Membranes: A Review. Chemosphere 2022, 295, 133914. [Google Scholar] [CrossRef] [PubMed]
58. Chen, G.Q.; Kanehashi, S.; Doherty, C.M.; Hill, A.J.; Kentish, S.E. Water Vapor Permeation through Cellulose Acetate Membranes and Its Impact upon Membrane Separation Performance for Natural Gas Purification. Journal of Membrane Science 2015, 487, 249–255. [Google Scholar] [CrossRef]
59. Wang, J.; Gardner, D.J.; Stark, N.M.; Bousfield, D.W.; Tajvidi, M.; Cai, Z. Moisture and Oxygen Barrier Properties of Cellulose Nanomaterial-Based Films. ACS Sustainable Chemistry & Engineering 2017, 6, 49–70. [Google Scholar]
60. Alikhani, N.; Bousfield, D.W.; Wang, J.; Li, L.; Tajvidi, M. Numerical Simulation of the Water Vapor Separation of a Moisture-Selective Hollow-Fiber Membrane for the Application in Wood Drying Processes. Membranes 2021, 11, 593. [Google Scholar] [CrossRef] [PubMed]
61. Alikhani, N.; Li, L.; Wang, J.; Dewar, D.; Tajvidi, M. Exploration of Membrane-Based Dehumidification System to Improve the Energy Efficiency of Kiln Drying Processes: Part I Factors That Affect Moisture Removal Efficiency. Wood and Fiber Science 2020, 52, 313–325. [Google Scholar] [CrossRef]
62. Metz, S.J.; Van de Ven, W.; Potreck, J.; Mulder, M.; Wessling, M. Transport of Water Vapor and Inert Gas Mixtures through Highly Selective and Highly Permeable Polymer Membranes. Journal of Membrane Science 2005, 251, 29–41. [Google Scholar] [CrossRef]
63. Wu, J.; Yuan, Q. Gas Permeability of a Novel Cellulose Membrane. Journal of membrane science 2002, 204, 185–194. [Google Scholar] [CrossRef]
64. Pauly, S. Permeability and Diffusion Data. In The Wiley Database of Polymer Properties; Wiley Online Library, 2003; pp. 543–568.
65. Kaushik, M.; Fraschini, C.; Chauve, G.; Putaux, J.-L.; Moores, A. Transmission Electron Microscopy for the Characterization of Cellulose Nanocrystals. The transmission electron microscope-theory and applications 2015, 130–163. [Google Scholar]
66. Patten, A.M.; Vassão, D.G.; Wolcott, M.P.; Davin, L.B.; Lewis, N.G. 3.27 - Trees: A Remarkable Biochemical Bounty. In Comprehensive Natural Products II; Liu, H.-W. (Ben), Mander, L., Eds.; Elsevier: Oxford, 2010; pp. 1173–1296. ISBN 978-0-08-045382-8. [Google Scholar]
67. Anderson, G.D. A Photographic Study of the Effects of Beating on Fiber Structure. 1956.
68. Tayeb, A.H.; Tajvidi, M.; Bousfield, D. Paper Based Oil Barrier Packaging Using Lignin-Containing Cellulose Nanofibrils. Molecules 2020, 25, 1344. [Google Scholar] [CrossRef]
69. Anžlovar, A.; Krajnc, A.; Žagar, E. Silane Modified Cellulose Nanocrystals and Nanocomposites with LLDPE Prepared by Melt Processing. Cellulose 2020, 27, 5785–5800. [Google Scholar] [CrossRef]
70. Beckman, I.P.; Berry, G.; Cho, H.; Riveros, G. Alternative High-Performance Fibers for Nonwoven HEPA Filter Media. Aerosol Science and Engineering 2023, 7, 36–58. [Google Scholar] [CrossRef]
71. Henriksson, M.; Berglund, L.A.; Isaksson, P.; Lindstrom, T.; Nishino, T. Cellulose Nanopaper Structures of High Toughness. Biomacromolecules 2008, 9, 1579–1585. [Google Scholar] [CrossRef] [PubMed]
72. Matilainen, K.; Hämäläinen, T.; Savolainen, A.; Sipiläinen-Malm, T.; Peltonen, J.; Erho, T.; Smolander, M. Performance and Penetration of Laccase and ABTS Inks on Various Printing Substrates. Colloids and Surfaces B: Biointerfaces 2012, 90, 119–128. [Google Scholar] [CrossRef] [PubMed]
73. Aslannejad, H.; Hassanizadeh, S.; Raoof, A.; de Winter, D.; Tomozeiu, N.; Van Genuchten, M.T. Characterizing the Hydraulic Properties of Paper Coating Layer Using FIB-SEM Tomography and 3D Pore-Scale Modeling. Chemical Engineering Science 2017, 160, 275–280. [Google Scholar] [CrossRef]
74. Rioux, R.W. The Rate of Fluid Absorption in Porous Media. 2003.
75. Motamedian, H.R.; Halilovic, A.E.; Kulachenko, A. Mechanisms of Strength and Stiffness Improvement of Paper after PFI Refining with a Focus on the Effect of Fines. Cellulose 2019, 26, 4099–4124. [Google Scholar] [CrossRef]
76. Toivonen, M.S.; Onelli, O.D.; Jacucci, G.; Lovikka, V.; Rojas, O.J.; Ikkala, O.; Vignolini, S. Anomalous-Diffusion-Assisted Brightness in White Cellulose Nanofibril Membranes. Advanced Materials 2018, 30, 1704050. [Google Scholar] [CrossRef]
77. Rosu, C.; Maximean, D.M.; Kundu, S.; Almeida, P.L.; Danila, O. Perspectives on the Electrically Induced Properties of Electrospun Cellulose/Liquid Crystal Devices. Journal of Electrostatics 2011, 69, 623–630. [Google Scholar] [CrossRef]
78. Quan, S.-L.; Kang, S.-G.; Chin, I.-J. Characterization of Cellulose Fibers Electrospun Using Ionic Liquid. Cellulose 2010, 17, 223–230. [Google Scholar] [CrossRef]
79. Ma, H.; Burger, C.; Hsiao, B.S.; Chu, B. Ultrafine Polysaccharide Nanofibrous Membranes for Water Purification. Biomacromolecules 2011, 12, 970–976. [Google Scholar] [CrossRef]
80. Zhang, Q.G.; Deng, C.; Soyekwo, F.; Liu, Q.L.; Zhu, A.M. Sub-10 Nm Wide Cellulose Nanofibers for Ultrathin Nanoporous Membranes with High Organic Permeation. Advanced Functional Materials 2016, 26, 792–800. [Google Scholar] [CrossRef]
81. Mautner, A.; Lee, K.-Y.; Tammelin, T.; Mathew, A.P.; Nedoma, A.J.; Li, K.; Bismarck, A. Cellulose Nanopapers as Tight Aqueous Ultra-Filtration Membranes. Reactive and Functional Polymers 2015, 86, 209–214. [Google Scholar] [CrossRef]
82. Nuruddin, M.; Chowdhury, R.A.; Lopez-Perez, N.; Montes, F.J.; Youngblood, J.P.; Howarter, J.A. Influence of Free Volume Determined by Positron Annihilation Lifetime Spectroscopy (PALS) on Gas Permeability of Cellulose Nanocrystal Films. ACS applied materials & interfaces 2020, 12, 24380–24389. [Google Scholar]
83. Wohlert, M.; Benselfelt, T.; Wågberg, L.; Furó, I.; Berglund, L.A.; Wohlert, J. Cellulose and the Role of Hydrogen Bonds: Not in Charge of Everything. Cellulose 2022, 1–23. [Google Scholar] [CrossRef]
84. Sharma, P.R.; Sharma, S.K.; Lindström, T.; Hsiao, B.S. Nanocellulose-enabled Membranes for Water Purification: Perspectives. Advanced Sustainable Systems 2020, 4, 1900114. [Google Scholar] [CrossRef]
85. Sehaqui, H.; Michen, B.; Marty, E.; Schaufelberger, L.; Zimmermann, T. Functional Cellulose Nanofiber Filters with Enhanced Flux for the Removal of Humic Acid by Adsorption. ACS Sustainable Chemistry & Engineering 2016, 4, 4582–4590. [Google Scholar]
86. Lalia, B.S.; Guillen, E.; Arafat, H.A.; Hashaikeh, R. Nanocrystalline Cellulose Reinforced PVDF-HFP Membranes for Membrane Distillation Application. Desalination 2014, 332, 134–141. [Google Scholar] [CrossRef]
87. Ma, H.; Burger, C.; Hsiao, B.S.; Chu, B. Ultra-Fine Cellulose Nanofibers: New Nano-Scale Materials for Water Purification. Journal of Materials Chemistry 2011, 21, 7507–7510. [Google Scholar] [CrossRef]
88. Soyekwo, F.; Zhang, Q.; Gao, R.; Qu, Y.; Lin, C.; Huang, X.; Zhu, A.; Liu, Q. Cellulose Nanofiber Intermediary to Fabricate Highly-Permeable Ultrathin Nanofiltration Membranes for Fast Water Purification. Journal of Membrane Science 2017, 524, 174–185. [Google Scholar] [CrossRef]
89. Liu, P.; Zhu, C.; Mathew, A.P. Mechanically Robust High Flux Graphene Oxide-Nanocellulose Membranes for Dye Removal from Water. Journal of hazardous materials 2019, 371, 484–493. [Google Scholar] [CrossRef]
90. Ma, H.; Burger, C.; Hsiao, B.S.; Chu, B. Nanofibrous Microfiltration Membrane Based on Cellulose Nanowhiskers. Biomacromolecules 2012, 13, 180–186. [Google Scholar] [CrossRef]
91. Ma, H.; Burger, C.; Hsiao, B.S.; Chu, B. Highly Permeable Polymer Membranes Containing Directed Channels for Water Purification. 2012.
92. Karim, Z.; Mathew, A.P.; Grahn, M.; Mouzon, J.; Oksman, K. Nanoporous Membranes with Cellulose Nanocrystals as Functional Entity in Chitosan: Removal of Dyes from Water. Carbohydrate Polymers 2014, 112, 668–676. [Google Scholar] [CrossRef] [PubMed]
93. Ku, B.-J.; Kim, D.H.; Yasin, A.S.; Mnoyan, A.; Kim, M.-J.; Kim, Y.J.; Ra, H.; Lee, K. Solar-Driven Desalination Using Salt-Rejecting Plasmonic Cellulose Nanofiber Membrane. Journal of Colloid and Interface Science 2023, 634, 543–552. [Google Scholar] [CrossRef]
94. Yin, Z.; Li, M.; Chen, Z.; Chen, X.; Liu, K.; Zhou, D.; Xue, M.; Ou, J.; Xie, Y.; Lei, S.; et al. A Superhydrophobic Pulp/Cellulose Nanofiber (CNF) Membrane via Coating ZnO Suspensions for Multifunctional Applications. Industrial Crops and Products 2022, 187, 115526. [Google Scholar] [CrossRef]
95. Ma, H.; Yoon, K.; Rong, L.; Mao, Y.; Mo, Z.; Fang, D.; Hollander, Z.; Gaiteri, J.; Hsiao, B.S.; Chu, B. High-Flux Thin-Film Nanofibrous Composite Ultrafiltration Membranes Containing Cellulose Barrier Layer. Journal of Materials Chemistry 2010, 20, 4692–4704. [Google Scholar] [CrossRef]
96. Bettotti, P.; Scarpa, M. Nanocellulose and Its Interface: On the Road to the Design of Emerging Materials. Advanced Materials Interfaces 2022, 9, 2101593. [Google Scholar] [CrossRef]
97. Uetani, K.; Izakura, S.; Kasuga, T.; Koga, H.; Nogi, M. Self-Alignment Sequence of Colloidal Cellulose Nanofibers Induced by Evaporation from Aqueous Suspensions. Colloids and Interfaces 2018, 2, 71. [Google Scholar] [CrossRef]
98. Ma, H.; Burger, C.; Hsiao, B.S.; Chu, B. Fabrication and Characterization of Cellulose Nanofiber Based Thin-Film Nanofibrous Composite Membranes. Journal of Membrane Science 2014, 454, 272–282. [Google Scholar] [CrossRef]
99. Liu, S.; Low, Z.-X.; Xie, Z.; Wang, H. TEMPO-Oxidized Cellulose Nanofibers: A Renewable Nanomaterial for Environmental and Energy Applications. Advanced Materials Technologies 2021, 6, 2001180. [Google Scholar] [CrossRef]
100. Norrrahim, M.N.F.; Mohd Kasim, N.A.; Knight, V.F.; Ong, K.K.; Mohd Noor, S.A.; Abdul Halim, N.; Ahmad Shah, N.A.; Jamal, S.H.; Janudin, N.; Misenan, M.S.M.; et al. Emerging Developments Regarding Nanocellulose-Based Membrane Filtration Material against Microbes. Polymers 2021, 13, 3249. [Google Scholar] [CrossRef]
101. Sharma, P.R.; Sharma, S.K.; Hsiao, B.S. Chapter 5 - Nanocellulose in Membrane Technology for Water Purification. In Separation Science and Technology; Ahuja, S., Ed.; Academic Press, 2022; Vol. 15, pp. 69–85 ISBN 1877-1718.
102. Zhu, C.; Liu, P.; Mathew, A.P. Self-Assembled TEMPO Cellulose Nanofibers: Graphene Oxide-Based Biohybrids for Water Purification. ACS Applied Materials & Interfaces 2017, 9, 21048–21058. [Google Scholar] [CrossRef]
103. Rabiee, N.; Sharma, R.; Foorginezhad, S.; Jouyandeh, M.; Asadnia, M.; Rabiee, M.; Akhavan, O.; Lima, E.C.; Formela, K.; Ashrafizadeh, M.; et al. Green and Sustainable Membranes: A Review. Environmental Research 2023, 231, 116133. [Google Scholar] [CrossRef] [PubMed]
104. Visanko, M.; Liimatainen, H.; Sirviö, J.A.; Haapala, A.; Sliz, R.; Niinimäki, J.; Hormi, O. Porous Thin Film Barrier Layers from 2,3-Dicarboxylic Acid Cellulose Nanofibrils for Membrane Structures. Carbohydrate Polymers 2014, 102, 584–589. [Google Scholar] [CrossRef] [PubMed]
105. Ma, H.; Hsiao, B.S.; Chu, B. Thin-Film Nanofibrous Composite Membranes Containing Cellulose or Chitin Barrier Layers Fabricated by Ionic Liquids. Polymer 2011, 52, 2594–2599. [Google Scholar] [CrossRef]
106. Yin, Z.; Cheng, Y.; Deng, Y.; Li, Z.; Liu, K.; Li, M.; Chen, X.; Xue, M.; Ou, J.; Lei, S.; et al. Functional and Versatile Colorful Superhydrophobic Nanocellulose-Based Membrane with High Durability, High-Efficiency Oil/Water Separation and Oil Spill Cleanup. Surface and Coatings Technology 2022, 445, 128714. [Google Scholar] [CrossRef]
107. Bai, H.; Wang, X.; Zhou, Y.; Zhang, L. Preparation and Characterization of Poly(Vinylidene Fluoride) Composite Membranes Blended with Nano-Crystalline Cellulose. Progress in Natural Science: Materials International 2012, 22, 250–257. [Google Scholar] [CrossRef]
108. Norfarhana, A.S.; Ilyas, R.A.; Ngadi, N. A Review of Nanocellulose Adsorptive Membrane as Multifunctional Wastewater Treatment. Carbohydrate Polymers 2022, 291, 119563. [Google Scholar] [CrossRef] [PubMed]
109. Bai, L.; Liu, Y.; Bossa, N.; Ding, A.; Ren, N.; Li, G.; Liang, H.; Wiesner, M.R. Incorporation of Cellulose Nanocrystals (CNCs) into the Polyamide Layer of Thin-Film Composite (TFC) Nanofiltration Membranes for Enhanced Separation Performance and Antifouling Properties. Environmental Science & Technology 2018, 52, 11178–11187. [Google Scholar] [CrossRef]
110. Shojaeiarani, J.; Bajwa, D.S.; Chanda, S. Cellulose Nanocrystal Based Composites: A Review. Composites Part C: Open Access 2021, 5, 100164. [Google Scholar] [CrossRef]
111. Bai, L.; Ding, A.; Li, G.; Liang, H. Application of Cellulose Nanocrystals in Water Treatment Membranes: A Review. Chemosphere 2022, 308, 136426. [Google Scholar] [CrossRef] [PubMed]
112. Bai, L.; Wu, H.; Ding, J.; Ding, A.; Zhang, X.; Ren, N.; Li, G.; Liang, H. Cellulose Nanocrystal-Blended Polyethersulfone Membranes for Enhanced Removal of Natural Organic Matter and Alleviation of Membrane Fouling. Chemical Engineering Journal 2020, 382, 122919. [Google Scholar] [CrossRef]
113. Solhi, L.; Guccini, V.; Heise, K.; Solala, I.; Niinivaara, E.; Xu, W.; Mihhels, K.; Kröger, M.; Meng, Z.; Wohlert, J.; et al. Understanding Nanocellulose–Water Interactions: Turning a Detriment into an Asset. Chemical Reviews 2023, 123, 1925–2015. [Google Scholar] [CrossRef]
114. Wu, Z.; Ji, X.; He, Q.; Gu, H.; Zhang, W.; Deng, Z. Nanocelluloses Fine-Tuned Polyvinylidene Fluoride (PVDF) Membrane for Enhanced Separation and Antifouling. Carbohydrate Polymers 2024, 323, 121383. [Google Scholar] [CrossRef] [PubMed]
115. Karim, Z.; Mathew, A.P.; Kokol, V.; Wei, J.; Grahn, M. High-Flux Affinity Membranes Based on Cellulose Nanocomposites for Removal of Heavy Metal Ions from Industrial Effluents. RSC Advances 2016, 6, 20644–20653. [Google Scholar] [CrossRef]
116. Lv, J.; Zhang, G.; Zhang, H.; Zhao, C.; Yang, F. Improvement of Antifouling Performances for Modified PVDF Ultrafiltration Membrane with Hydrophilic Cellulose Nanocrystal. Applied Surface Science 2018, 440, 1091–1100. [Google Scholar] [CrossRef]
117. Zheng, S.; Yang, S.; Ouyang, Z.; Zhang, Y. Robust and Highly Hydrophilic Ultrafiltration Membrane with Multi-Branched Cellulose Nanocrystals for Permeability-Selectivity Anti-Trade-off Property. Applied Surface Science 2023, 614, 156157. [Google Scholar] [CrossRef]
118. Asempour, F.; Emadzadeh, D.; Matsuura, T.; Kruczek, B. Synthesis and Characterization of Novel Cellulose Nanocrystals-Based Thin Film Nanocomposite Membranes for Reverse Osmosis Applications. Desalination 2018, 439, 179–187. [Google Scholar] [CrossRef]
119. Wang, D.; Mhatre, S.; Chen, J.; Shi, X.; Yang, H.; Cheng, W.; Yue, Y.; Han, G.; Rojas, O.J. Composites Based on Electrospun Fibers Modified with Cellulose Nanocrystals and SiO2 for Selective Oil/Water Separation. Carbohydrate Polymers 2023, 299, 120119. [Google Scholar] [CrossRef] [PubMed]
120. Gao, M.; Li, J.; Bao, Z.; Hu, M.; Nian, R.; Feng, D.; An, D.; Li, X.; Xian, M.; Zhang, H. A Natural in Situ Fabrication Method of Functional Bacterial Cellulose Using a Microorganism. Nature Communications 2019, 10, 437. [Google Scholar] [CrossRef]
121. Saud, A.; Saleem, H.; Zaidi, S.J. Progress and Prospects of Nanocellulose-Based Membranes for Desalination and Water Treatment. Membranes 2022, 12, 462. [Google Scholar] [CrossRef] [PubMed]
122. Ullah, H.; Wahid, F.; Santos, H.A.; Khan, T. Advances in Biomedical and Pharmaceutical Applications of Functional Bacterial Cellulose-Based Nanocomposites. Carbohydrate Polymers 2016, 150, 330–352. [Google Scholar] [CrossRef]
123. Wijeyaratne, W.D.N. Potential Differences of Plant Nanocellulose and Bacterial Nanocellulose in Water Purification. In Nanocellulose and Its Composites for Water Treatment Applications; CRC Press, 2021; pp. 91–105.
124. Tahir, D.; Karim, M.R.A.; Hu, H.; Naseem, S.; Rehan, M.; Ahmad, M.; Zhang, M. Sources, Chemical Functionalization, and Commercial Applications of Nanocellulose and Nanocellulose-Based Composites: A Review. Polymers 2022, 14, 4468. [Google Scholar] [CrossRef] [PubMed]
125. Xu, T.; Jiang, Q.; Ghim, D.; Liu, K.-K.; Sun, H.; Derami, H.G.; Wang, Z.; Tadepalli, S.; Jun, Y.-S.; Zhang, Q.; et al. Catalytically Active Bacterial Nanocellulose-Based Ultrafiltration Membrane. Small 2018, 14, 1704006. [Google Scholar] [CrossRef] [PubMed]
126. Yang, L.; Chen, C.; Hu, Y.; Wei, F.; Cui, J.; Zhao, Y.; Xu, X.; Chen, X.; Sun, D. Three-Dimensional Bacterial Cellulose/Polydopamine/TiO2 Nanocomposite Membrane with Enhanced Adsorption and Photocatalytic Degradation for Dyes under Ultraviolet-Visible Irradiation. Journal of Colloid and Interface Science 2020, 562, 21–28. [Google Scholar] [CrossRef] [PubMed]
127. Ferreira-Neto, E.P.; Ullah, S.; da Silva, T.C.A.; Domeneguetti, R.R.; Perissinotto, A.P.; de Vicente, F.S.; Rodrigues-Filho, U.P.; Ribeiro, S.J.L. Bacterial Nanocellulose/MoS2 Hybrid Aerogels as Bifunctional Adsorbent/Photocatalyst Membranes for in-Flow Water Decontamination. ACS Applied Materials & Interfaces 2020, 12, 41627–41643. [Google Scholar] [CrossRef]
128. Gholami Derami, H.; Jiang, Q.; Ghim, D.; Cao, S.; Chandar, Y.J.; Morrissey, J.J.; Jun, Y.-S.; Singamaneni, S. A Robust and Scalable Polydopamine/Bacterial Nanocellulose Hybrid Membrane for Efficient Wastewater Treatment. ACS Applied Nano Materials 2019, 2, 1092–1101. [Google Scholar] [CrossRef]
129. Jiang, Q.; Ghim, D.; Cao, S.; Tadepalli, S.; Liu, K.-K.; Kwon, H.; Luan, J.; Min, Y.; Jun, Y.-S.; Singamaneni, S. Photothermally Active Reduced Graphene Oxide/Bacterial Nanocellulose Composites as Biofouling-Resistant Ultrafiltration Membranes. Environmental Science & Technology 2019, 53, 412–421. [Google Scholar] [CrossRef]
130. Das, R.; Lindström, T.; Sharma, P.R.; Chi, K.; Hsiao, B.S. Nanocellulose for Sustainable Water Purification. Chemical Reviews 2022, 122, 8936–9031. [Google Scholar] [CrossRef]
131. Liang, Y.; Ma, H.; Taha, A.A.; Hsiao, B.S. High-Flux Anti-Fouling Nanofibrous Composite Ultrafiltration Membranes Containing Negatively Charged Water Channels. Journal of Membrane Science 2020, 612, 118382. [Google Scholar] [CrossRef]
132. Hadi, P.; Yang, M.; Ma, H.; Huang, X.; Walker, H.; Hsiao, B.S. Biofouling-Resistant Nanocellulose Layer in Hierarchical Polymeric Membranes: Synthesis, Characterization and Performance. Journal of Membrane Science 2019, 579, 162–171. [Google Scholar] [CrossRef]
133. Aguilar-Sanchez, A.; Jalvo, B.; Mautner, A.; Rissanen, V.; Kontturi, K.S.; Abdelhamid, H.N.; Tammelin, T.; Mathew, A.P. Charged Ultrafiltration Membranes Based on TEMPO-Oxidized Cellulose Nanofibrils/Poly(Vinyl Alcohol) Antifouling Coating. RSC Advances 2021, 11, 6859–6868. [Google Scholar] [CrossRef]
134. Benítez, A.J.; Walther, A. Cellulose Nanofibril Nanopapers and Bioinspired Nanocomposites: A Review to Understand the Mechanical Property Space. Journal of Materials Chemistry A 2017, 5, 16003–16024. [Google Scholar] [CrossRef]
135. Lindström, T. Aspects on Nanofibrillated Cellulose (NFC) Processing, Rheology and NFC-Film Properties. Current Opinion in Colloid & Interface Science 2017, 29, 68–75. [Google Scholar]
136. Sharma, P.R.; Sharma, S.K.; Lindström, T.; Hsiao, B.S. Water Purification: Nanocellulose-Enabled Membranes for Water Purification: Perspectives (Adv. Sustainable Syst. 5/2020). Advanced Sustainable Systems 2020, 4, 2070009. [Google Scholar] [CrossRef]
137. Yang, W.; Bian, H.; Jiao, L.; Wu, W.; Deng, Y.; Dai, H. High Wet-Strength, Thermally Stable and Transparent TEMPO-Oxidized Cellulose Nanofibril Film via Cross-Linking with Poly-Amide Epichlorohydrin Resin. RSC advances 2017, 7, 31567–31573. [Google Scholar] [CrossRef]
138. Mautner, A.; Lucenius, J.; Österberg, M.; Bismarck, A. Multi-Layer Nanopaper Based Composites. Cellulose 2017, 24, 1759–1773. [Google Scholar] [CrossRef]
139. Toivonen, M.S.; Kurki-Suonio, S.; Schacher, F.H.; Hietala, S.; Rojas, O.J.; Ikkala, O. Water-Resistant, Transparent Hybrid Nanopaper by Physical Cross-Linking with Chitosan. Biomacromolecules 2015, 16, 1062–1071. [Google Scholar] [CrossRef] [PubMed]
140. Zhang, H.; Shi, L.; Feng, X. Use of Chitosan to Reinforce Transparent Conductive Cellulose Nanopaper. Journal of Materials Chemistry C 2018, 6, 242–248. [Google Scholar] [CrossRef]
141. Pahimanolis, N.; Salminen, A.; Penttilä, P.A.; Korhonen, J.T.; Johansson, L.-S.; Ruokolainen, J.; Serimaa, R.; Seppälä, J. Nanofibrillated Cellulose/Carboxymethyl Cellulose Composite with Improved Wet Strength. Cellulose 2013, 20, 1459–1468. [Google Scholar] [CrossRef]
142. Visanko, M.; Liimatainen, H.; Sirvio, J.A.; Heiskanen, J.P.; Niinimäki, J.; Hormi, O. Amphiphilic Cellulose Nanocrystals from Acid-Free Oxidative Treatment: Physicochemical Characteristics and Use as an Oil–Water Stabilizer. Biomacromolecules 2014, 15, 2769–2775. [Google Scholar] [CrossRef]
143. Fernandes Diniz, J.; Gil, M.; Castro, J. Hornification—Its Origin and Interpretation in Wood Pulps. Wood Science and Technology 2004, 37, 489–494. [Google Scholar] [CrossRef]
144. Idström, A.; Brelid, H.; Nydén, M.; Nordstierna, L. CP/MAS 13C NMR Study of Pulp Hornification Using Nanocrystalline Cellulose as a Model System. Carbohydrate polymers 2013, 92, 881–884. [Google Scholar] [CrossRef] [PubMed]
145. Österberg, M.; Vartiainen, J.; Lucenius, J.; Hippi, U.; Seppälä, J.; Serimaa, R.; Laine, J. A Fast Method to Produce Strong NFC Films as a Platform for Barrier and Functional Materials. ACS Applied Materials & Interfaces 2013, 5, 4640–4647. [Google Scholar] [CrossRef] [PubMed]
146. Smyth, M.; Fournier, C.; Driemeier, C.; Picart, C.; Foster, E.J.; Bras, J. Tunable Structural and Mechanical Properties of Cellulose Nanofiber Substrates in Aqueous Conditions for Stem Cell Culture. Biomacromolecules 2017, 18, 2034–2044. [Google Scholar] [CrossRef] [PubMed]