Electrospray fabrication of anti-fouling nanocellulose desalination membrane with high flux
Graphical abstract
Introduction
Cellulose-based membranes are a growing and competitive area of research and development at the forefront of water purification, to replace the commonly used synthetic polymers. However, the non-dissolution of native cellulose in many solvents is a long-standing challenge for the membrane community [1]. The way around this is to use cellulose derivatives such as cellulose acetate (CA), including cellulose diacetate (CDA) and cellulose triacetate (CTA), which have been used intensively to manufacture porous ultrafiltration (UF), nanofiltration (NF), and desalination membranes. CA is favoured for its excellent mechanical strength, chemical resistance and film-forming property, but is often ill-posed to possess low water flux due to the dense active layer and low porosity [2]. This type of membrane is typically prepared by casting before undergoing a phase inversion and annealing process, where the conditions in the multi-step fabrication process have critical implications for the microstructure and chemistry of the membranes. The concentration of polymer casting solutions, the choice of solvent and non-solvent, and the annealing temperature are examples of crucial considerations in making a high-performance membrane [3], [4]. For instance, the pure water permeability of the membrane is adversely affected by increasing the annealing temperature since there would be a narrowing of the membrane pore size and crystallinity [5]. Most publications have used two main techniques to deal with the low water flux, either by blending CA with other polymers or by forming nanocomposites with the inclusion of nanofillers. The blended polymers containing polar functional groups have much higher hydrophilicity than CA to improve the membrane permeation performance [6], [7], [8]. A low water contact angle of 46° and increased pure water permeability of 370 L m−2 h−1 bar−1 were observed by Pandey and his co-workers (2020) by grafting 7% w/w aminopropylated polysilesquiozane (APS) converted from (3-aminopropyl)triethoxysilane (APTES) in a sol–gel process following quaternization with methyl iodide. On the other hand, many other researchers have investigated on adding hydrophilic and porous carbon-based nanomaterials into the CA casting solution to prepare nanocomposites membrane [9], [10], [11].
Another serious impediment to the widespread usage of CA-based desalination membranes is that they suffer from high organic and biological fouling propensity, which can drastically impede water flux [12], [13]. In a pressure-driven filtration process, fouling is influenced by the surface chemistry of the membrane, the nature of the feed solution, the process operating conditions, and the filter module configuration. Deposition and accumulation of microorganisms, proteins and organic matter of high molecular mass are identified as the most common fouling phenomena on membrane surfaces. Typically, fouling begins with pore constriction when there is a partial blockage of the membrane pores, restricting water flow. This is followed by further deposition of the foulants before a cake formation on the membrane surfaces [14]. Extensive evidence supports the concept of concentration polarization (CP) at the active layer side of the membrane surface where the solutes are concentrated near the membrane surface on the feed side, referred to as the external CP, and initiate the reversible gel formation on the surface [15], [16]. A retrospective analysis by Fu et al. (2008) showed that the incidence of fouling with humic acid was more frequent with rougher and hydrophobic membranes [17]. Furthermore, the high porosity of the CA membrane allows for diffusion and adsorption/ deposition of foulants on the pore structures, making flux recovery difficult during backwashing [18]. Apart from humic acid, many studies have consistently used sodium alginate as model foulants due to their close association with an algal bloom in recent years. Therefore, the objective of mitigating fouling behaviour has been pursued by different domains and restated in the present work. This research aims to demonstrate a possible method to reduce the effect of CP by introducing hydration layer and turbulence using the hydrophilic nanofillers in the pores and on the surface of the CA membrane, as illustrated in Fig. 1.
A systematic review of prospective observational studies found that modification strategies of membranes lead to successful antifouling properties, mainly through hydrophilic polymer blending and mixed matrix membranes [19], [20]. Surface wettability and oleophobicity, induced by blending hydrophilic polymers such as polydopamine, were found to be key indicators of desirable antifouling performance against proteins and organic matter [21], [22]. It was previously revealed by Ounifi et al. (2021) that 97.7% water flux recovery was achieved in CA membrane blended with 15% w/w poly(acrylic) acid, which created a repulsive force against humic acid [23]. On the other hand, mixed matrix membranes were integrated with inorganic nanofillers that include titania, alumina, MXene, and zeolites [24], [25], [26], [27]. Vatanpour and his co-workers (2021) successfully observed 95% flux recovery with 0.25 wt% zinc oxide@graphitic carbon nitride compared to 74% from the bare CA membrane [28]. In addition, the incorporation of inorganic nanofillers results in macro voids on the active layer to facilitate a higher water permeance rate. This brings us to the question of whether a crystalline and hydrophilic nanostructure can assist in the enhancement of antifouling properties. Dopamine-modified cellulose nanocrystals (PDA@CNC) were integrated into the CA blend at 4 wt% to form a hydration layer on the nanocomposite membrane surface to inhibit protein adsorption by 32% [29]. However, CNC derivatives tend to agglomerate during membrane preparation in an organic solvent, in which CA is soluble while exhibiting high dispersibility in an aqueous solution due to the abundance of hydroxyl functional groups. Hence, it is postulated that CNC should be better integrated as a water-based coating on prepared CA membrane surfaces to avoid agglomeration between the nanoparticles.
Nanocelluloses are promising sustainable biomaterials for use in water treatment membrane applications and have been highlighted in several published articles for their advantages in imparting antifouling, self-cleaning and highly adsorbing characteristics [30], [31], [32], [33]. Clear, strong, and well-documented evidence supports that the hierarchical membrane structure upon nanocellulose coating not only has increased water permeance but also excellent antifouling capability [34], [35]. This can also be attributed to lowered variation in height of the membrane surface and the presence of negatively charged carboxylate or sulfate functional groups to repel biofouling and proteins [36], [37]. Here we report a neglected aspect in previous studies that majorly use CNF as coating materials instead of CNC. Still, the latter is believed to offer a greater advantage with mechanical integrity during high hydraulic pressure operation. Additionally, very little work has been undertaken to validate nanocellulose coating on CA-based desalination membranes. Spray coating techniques are commonly adopted when producing nanocellulose thin film because it is a rapid process with high controllability over its parameters [35], [38]. Conversely, the thermal spray coating process may not result in well-aligned CNC crystals and can hamper the efficiency in effecting a smooth and superhydrophilic surface, necessitating investigation of the novel electrospray technique to externally charge the nanoparticles and promote self-alignment during coating.
The present work aims to facilely prepare CNC/CA nanocomposite asymmetric desalination membranes by nonsolvent-induced phase separation (NIPS) and optimized electrospray-mediated coating while ensuring that the CNC coating has high adhesion with the CA substrate membrane. Different advanced analytical techniques were performed to investigate the improvement in desalination performance, water permeability and antifouling properties against both organic and bio-foulants (static adsorption) after coating with different concentrations of CNC. The relationship between the number of electrospray scans and coating layer thickness was examined and validated. Finally, the overall water/salt permselectivity and water permeability coefficient of the CNC-coated CA membrane prepared in this work were compared to the CA desalination membranes described in the literature with the latest upper bound relationship.
Section snippets
Materials
Freeze-dried sulfonated cellulose nanocrystals (CNC), of width 5–20 nm and length 100–250 nm, were purchased from Cellulose Lab (Fredericton, NB, Canada). Microdyn Nadir® UP150 UF flat sheet membrane (average pore size = 150 kDa) was supplied by MANN + HUMMEL Water & Fluid Solutions GmbH (Wiesbaden, Germany). Cellulose triacetate (CTA, 43% acetyl content) was supplied by Aik Moh Paints & Chemicals Pte. Ltd. (Singapore). Methanol (HPLC, 100%), absolute ethanol (ACS, ≥99.8%), sodium sulfate
Characteristics of CNC-coated cellulose acetate membranes
Here, we present a detailed evaluation of the results assessing the prepared CNC-coated CA desalination membranes. The layer-by-layer coating of PAHCl cationic polyelectrolyte and negatively charged CNC was successfully demonstrated taking advantage of their electrostatic interaction to ensure the strong adhesion onto the CA substrate membrane. The negative charge along the CNC backbone is attributed primarily to the presence of carboxylate and sulfate ester groups from its sulfuric acid
Conclusion
In conclusion, a high-performance CA/CTA asymmetric desalination membrane with CNC coating was sequentially prepared by both phase inversion and 3D-electrospray techniques to endow high controllability over coating thickness and surface morphology that conventional fabrication methods cannot achieve. Overall, the prepared CA membrane coated with 0.05% w/v CNC possessed excellent salt ion rejection of up to 94.0%, 99.2%, 92.3%, and 93.8% for Na+, Mg2+, Cl−, and SO42−, respectively.
Owing to the
CRediT authorship contribution statement
E.E. Liang Ying: Formal analysis, Investigation, Methodology, Data curation, Writing – original draft. T.A.N. Regina Pei Woon: Investigation, Methodology. C.H.I.A. Sean Yi Rong: Investigation, Methodology. L.I. Sam Fong Yau: Conceptualization, Formal analysis, Investigation, Methodology, Writing – review & editing.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgement
The research was financially supported by a grant (R-143-000-B24-592) co-funded by the Singapore National Additive Manufacturing – Innovation Cluster (NAMIC) and MIPS Innovations Pte. Ltd.. The authors acknowledge the support from PUB, Singapore’s National Water Agency, with facility support from NUS Chemical, Molecular and Materials Analysis Centre (CMMAC). The first author would like to acknowledge the Singapore Ministry of Education (MOE) for providing a scholarship for his Ph.D. research
References (72)
- et al.
Recent advances in cellulose and chitosan based membranes for water purification: A concise review
Carbohydr Polym
(2016) - et al.
Cellulose acetate in fabrication of polymeric membranes: A review
Chemosphere
(2022) - et al.
Method for the preparation of cellulose acetate flat sheet composite membranes for forward osmosis—Desalination using MgSO4 draw solution
Desalination
(2011) - et al.
Properties of cellulose acetate nanofiltration membranes. Application to brackish water desalination
Desalination
(2004) - et al.
Investigation of polyvinylchloride and cellulose acetate blend membranes for desalination
J. Mol. Struct.
(2017) - et al.
Self-sterilized composite membranes of cellulose acetate/polyethylene glycol for water desalination
Carbohydr. Polym.
(2016) - et al.
Development of graphene oxide-cellulose acetate nanocomposite reverse osmosis membrane for seawater desalination
Compos. B Eng.
(2019) - et al.
Lipase immobilization on glutaraldehyde activated graphene oxide/chitosan/cellulose acetate electrospun nanofibrous membranes and its application on the synthesis of benzyl acetate
Colloids Surf. B Biointerfaces
(2022) - et al.
Fouling and transport of organic matter in cellulose triacetate forward-osmosis membrane for wastewater reuse and seawater desalination
Chem. Eng. J.
(2020) - et al.
Organic fouling of thin-film composite polyamide and cellulose triacetate forward osmosis membranes by oppositely charged macromolecules
Water Res.
(2013)
Characterization and theoretical analysis of protein fouling of cellulose acetate membrane during constant flux dead-end microfiltration
J. Membr. Sci.
Fouling, performance and cost analysis of membrane-based water desalination technologies: A critical review
J Environ Manage
Effect of surface morphology on membrane fouling by humic acid with the use of cellulose acetate butyrate hollow fiber membranes
J. Membr. Sci.
Membrane fouling properties of hollow fiber membranes prepared from cellulose acetate derivatives
J. Membr. Sci.
Development of antifouling thin-film-composite membranes for seawater desalination
J. Membr. Sci.
Preparation of antifouling cellulose acetate membranes with good hydrophilic and oleophobic surface properties
Mater. Lett.
Mitigating the fouling of mixed-matrix cellulose acetate membranes for oil–water separation through modification with polydopamine particles
Chem. Eng. Res. Des.
A fouling-resistant mixed-matrix nanofiltration membrane based on covalently cross-linked Ti3C2TX (MXene)/cellulose acetate
J. Membr. Sci.
Synthesis, characterization and desalination study of polyvinyl chloride-co-vinyl acetate/cellulose acetate membranes integrated with surface modified zeolites
Microporous Mesoporous Mater.
Enhancing the permeability and antifouling properties of cellulose acetate ultrafiltration membrane by incorporation of ZnO@graphitic carbon nitride nanocomposite
Carbohydr Polym
Improvement of filtration and antifouling performance of cellulose acetate membrane reinforced by dopamine modified cellulose nanocrystals
J. Membr. Sci.
Charged ultrafiltration membranes based on TEMPO-oxidized cellulose nanofibrils/poly(vinyl alcohol) antifouling coating
RSC Adv.
A microgel-structured cellulose nanofibril coating with robust antifouling performance for highly efficient oil/water and immiscible organic solvent separation
Colloids Surf. A Physicochem. Eng. Asp.
Biofouling-resistant nanocellulose layer in hierarchical polymeric membranes: Synthesis, characterization and performance
J. Membr. Sci.
In-situ incorporating zwitterionic nanocellulose into polyamide nanofiltration membrane towards excellent perm-selectivity and antifouling performances
Desalination
Waterborne nanocellulose coatings for improving the antifouling and antibacterial properties of polyethersulfone membranes
J. Membr. Sci.
Antifouling nanocellulose membranes: How subtle adjustment of surface charge lead to self-cleaning property
J. Membr. Sci.
Suppressed crystallization and enhanced gas permeability in thin films of cellulose acetate blends
Polymer
Permeability and selectivity of reverse osmosis membranes: Correlation to swelling revisited
Water Res.
Li-ion conduction on nanofiller incorporated PVdF-co-HFP based composite polymer blend electrolytes for flexible battery applications
Solid State Ion.
Effects of plasticizer and nanofiller on the dielectric dispersion and relaxation behaviour of polymer blend based solid polymer electrolytes
Curr. Appl Phys.
Effects of ceramic filler in poly(vinyl chloride)/poly(ethyl methacrylate) based polymer blend electrolytes
Chin. Chem. Lett.
Finger-like voids induced by viscous fingering during phase inversion of alumina/PES/NMP suspensions
J. Membr. Sci.
Effect of TiO2 nanoparticles on the surface morphology and performance of microporous PES membrane
Appl. Surf. Sci.
Engineering surface roughness of nanocellulose film via spraying to produce smooth substrates
Colloids Surf A Physicochem Eng Asp
Characterizing surface porosity of porous membranes via contact angle measurements
J. Membr. Sci. Lett.
Cited by (2)
Cyclodextrin-modified layered double hydroxide thin-film nanocomposite desalination membrane for boron removal
2023, Chemical Engineering Journal