The role of carboxylated cellulose nanocrystals placement in the performance of thin-film composite (TFC) membrane

Highly Permeable Nanofibrous Composite Nanofiltration Membranes by Controllable Interfacial Copolymerization

An ultrathin nanofibrous composite nanofiltration (NF) membrane was developed through controlled interfacial copolymerization where an electrospun sulfonated poly(ether sulfone) (SPES) nanofibrous membrane serves as the substrate and 2,5-diaminobenzenesulfonic acid (2,5-DABSA) and piperazine (PIP) serve as aqueous phase monomers. The integration of the electrostatic interaction and hydrogen bonding between SPES nanofibers and PIP/2,5-DABSA triggered the controlled diffusion rate of monomers into the organic phase, resulting in the fabrication of an ultrathin polyamide barrier layer (∼56 nm). Additionally, a polyamide structure was created through the ternary interfacial copolymerization of PIP/2,5-DABSA and trimesoyl chloride (TMC), which offers high permeability to the composite NF membrane. Meanwhile, the -SO3H groups on 2,5-DABSA issued highly negative charges to the polyamide barrier layer, leading to a significant improvement in the rejection ratio against SO42- and fouling resistance against bovine serum albumin. The impact of 2,5-DABSA monomer on the cross-linking degree and pore size distribution of the polyamide barrier layer was investigated by optimizing the proportion of PIP and 2,5-DABSA monomers in the interfacial polymerization (IP) process. The ion selectivity and robustness of the composite NF membrane was determined and compared with conventional and commercial NF membranes comprehensively. Molecular dynamics simulations were conducted to demonstrate the mechanism of the controlled diffusion of monomers; the cross-linking degree and fractional free volume of the polyamide barrier layer were also evaluated. The NF-M(1:1) composite membrane exhibited a significant enhancement in the permeation flux as 137.4 L/m2·h at 0.5 MPa, which was 4 times higher than that of conventional NF membranes, while maintaining excellent divalent salt rejection against Na2SO4 at 99.4%, compared with 98.0% of the conventional NF membrane, effectively breaking through the trade-off effect in the long-term filtration performance.

Networked cellulose-integrated highly permeable TFC polyamide membranes with tailored nanofiltration performance

Thin-film composite (TFC) membranes typically consist of a thin active polyamide layer atop a highly porous support layer, offering both enhanced permeability and excellent salt rejection. In this study, we propose the incorporation of networked cellulose (NC) into the aqueous layer leading to changes in the morphology, hydrophilicity, and surface charge, thereby significantly boosting membrane permeance and resistance to chlorine attack. The relatively unexplored NC, distinguished by its interconnected cellulosic fibrous structures, is introduced into the selective layer, resulting in a customized nanofiltration performance that varies depending on the concentration of NC. The fabricated TFC membranes, incorporating NC at a concentration of 0.01 % in the aqueous phase, exhibit a permeance of 19.1 ± 1.8 LMH bar-1 combined with excellent rejection (>90 %) for divalent salts, a remarkable improvement over pristine TFC membranes which offered 7.2 ± 0.5 LMH bar-1. Conversely, higher loading of NC (0.02 %) during fabrication results in highly permeable membranes up to 38.7 ±%3.1 LMH bar-1 maintaining exceptional dye rejection properties. Furthermore, our findings indicate enhanced resistance to chlorine attack, highlighting the versatility of NC incorporation in the selective layer. This study underscores the scope of NC as a cost-effective and environmentally benign additive for enhancing the performance of polyamide TFC nanofiltration membranes in water treatment and desalination applications.

Synthesis of Carboxylate-Dialdehyde Cellulose to Use as a Component in Composite Thin Films for an Antibacterial Material in Wound Dressing

Wound infections can lead to life-threatening infection and death. Antibacterial materials from biopolymers in the form of films are a promising strategy for wound dressings. Carboxylate-dialdehyde cellulose (CDAC) is a proper candidate for use as an antibacterial material due to its biocompatibility, nontoxicity, and antibacterial property. Additionally, CDAC can be synthesized from cellulose through environmentally friendly and nontoxic methods. Thus, this study aims to synthesize CDAC from microcrystalline cellulose (MCC) PH102 and use it in composite films for an antibacterial application. The CDAC was synthesized using Fe2+/H2O2, followed by NaIO4 oxidation. The obtained CDAC was characterized in terms of carboxylate and aldehyde content as well as FTIR and XRD spectra. The CDAC was mixed with HPMC in different ratios to prepare films. To determine the optimal formulation for clindamycin HCl loading, the films were evaluated for morphology, mechanical properties, and swelling ratio. Finally, the films containing clindamycin HCl were evaluated for drug loading content, in vitro drug release, and antibacterial activity. This study found that CDAC contained 2.1 ± 0.2 carboxylate and 4.15 ± 0.2 mmol/g of aldehyde content. The FTIR spectra confirmed the successful synthesis. X-ray diffractograms indicated that CDAC was less crystalline than MCC. The film, consisting of CDAC and HPMC E50 in the ratio of 2:1 (D2H1), was identified as the most suitable for clindamycin HCl loading due to its superior appearance, mechanical strength, and swelling properties compared to other formulations. D2H1 exhibited a high drug loading capacity (91.49 ± 5.48%) and demonstrated faster drug release than the film composed only of HPMC because of the higher swelling ratio and lower mechanical strength. This formulation was effective against Staphylococcus aureus (MSSA), S. aureus (MRSA), and Pseudomonas aeruginosa. Furthermore, the D2H1 film containing clindamycin HCl showed a larger inhibition zone against these bacteria, likely due to a synergistic effect. This study found that CDAC has the potential to be applied as an antibacterial material for wound dressing.

A review on the potential of cellulose nanomaterials for the development of thin film composite polyamide membranes for water treatment

Membrane-based separation technologies have drawn significant interest because of their compactness, low energy consumption, and ability to be easily integrated with existing processes. There has been significant interest in the utilization of natural materials derived from sustainable and renewable resources for membrane fabrication. Cellulose is one of the promising polymers which has been extensively studied in membrane fabrication and modification due to its abundant availability, non-toxicity and biodegradability. While there have been several reviews in recent years separately on TFC membranes and cellulose-based materials for different applications, reviews exclusively focusing on cellulosic nanomaterials-based TFC membranes are still lacking. This review provides an overview of the types of cellulose nanomaterials exploited for the development and modification of TFC membranes, particularly those used for desalination and wastewater treatment. We have presented a brief description of cellulose-based nanomaterials followed by a detailed discussion of different studies addressing each cellulose nanomaterial separately. In addition, we have summarized the performance of different studies in the literature, paying particular attention to the enhancement achieved by the incorporation of cellulose nanomaterial in the membrane.

Fabrication of Loose Nanofiltration Membrane by Crosslinking TEMPO-Oxidized Cellulose Nanofibers for Effective Dye/Salt Separation

Dye/salt separation has gained increasing attention in recent years, prompting the quest to find cost-effective and environmentally friendly raw materials for synthesizing high performance nanofiltration (NF) membrane for effective dye/salt separation. Herein, a high-performance loose-structured NF membrane was fabricated via a simple vacuum filtration method using a green nanomaterial, 2,2,6,6-tetramethylpiperidine-1-oxide radical (TEMPO)-oxidized cellulose nanofiber (TOCNF), by sequentially filtrating larger-sized and finer-sized TOCNFs on a microporous substrate, followed by crosslinking with trimesoyl chloride. The resulting TCM membrane possessed a separating layer composed entirely of pure TOCNF, eliminating the need for other polymer or nanomaterial additives. TCM membranes exhibit high performance and effective dye/salt selectivity. Scanning Electron Microscope (SEM) analysis shows that the TCM membrane with the Fine-TOCNF layer has a tight layered structure. Further characterizations via Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) confirmed the presence of functional groups and chemical bonds of the crosslinked membrane. Notably, the optimized TCM-5 membrane exhibits a rejection rate of over 99% for various dyes (Congo red and orange yellow) and 14.2% for NaCl, showcasing a potential candidate for efficient dye wastewater treatment.

Evaluating Post-Treatment Effects on Electrospun Nanofiber as a Support for Polyamide Thin-Film Formation

Poly(acrylonitrile-co-methyl acrylate) (PAN-co-MA) electrospun nanofiber (ENF) was used as the support for the formation of polyamide (PA) thin films. The ENF support layer was post-treated with heat-pressed treatment followed by NaOH hydrolysis to modify its support characteristics. The influence of heat-pressed conditions and NaOH hydrolysis on the support morphology and porosity, thin-film formation, surface chemistry, and membrane performances were investigated. This study revealed that applying heat-pressing followed by hydrolysis significantly enhances the physicochemical properties of the support material and aids in forming a uniform polyamide (PA) thin selective layer. Heat-pressing effectively densifies the support surface and reduces pore size, which is crucial for the even formation of the PA-selective layer. Additionally, the hydrolysis of the support increases its hydrophilicity and decreases pore size, leading to higher sodium chloride (NaCl) rejection rates and improved water permeance. When compared with membranes that underwent only heat-pressing, those treated with both heat-pressing and hydrolysis exhibited superior separation performance, with NaCl rejection rates rising from 83% to 98% while maintaining water permeance. Moreover, water permeance was further increased by 29% through n-hexane-rinsing post-interfacial polymerization. Thus, this simple yet effective combination of heat-pressing and hydrolysis presents a promising approach for developing high-performance thin-film nanocomposite (TFNC) membranes.

Thin-Film Nanocomposite (TFN) Membranes for Water Treatment Applications: Characterization and Performance

Thin-film nanocomposite (TFN) membranes have been widely investigated for water treatment applications due to their promising performance in terms of flux, salt rejection, and their antifouling properties. This review article provides an overview of the TFN membrane characterization and performance. It presents different characterization techniques that have been used to analyze these membranes and the nanofillers within them. The techniques comprise structural and elemental analysis, surface and morphology analysis, compositional analysis, and mechanical properties. Additionally, the fundamentals of membrane preparation are also presented, together with a classification of nanofillers that have been used so far. The potential of TFN membranes to address water scarcity and pollution challenges is significant. This review also lists examples of effective TFN membrane applications for water treatment. These include enhanced flux, enhanced salt rejection, antifouling, chlorine resistance, antimicrobial properties, thermal stability, and dye removal. The article concludes with a synopsis of the current status of TFN membranes and future perspectives.

Progress and Prospects of Nanocellulose-Based Membranes for Desalination and Water Treatment

Membrane-based desalination has proved to be the best solution for solving the water shortage issues globally. Membranes are extremely beneficial in the effective recovery of clean water from contaminated water sources, however, the durability as well as the separation efficiency of the membranes are restricted by the type of membrane materials/additives used in the preparation processes. Nanocellulose is one of the most promising green materials for nanocomposite preparation due to its biodegradability, renewability, abundance, easy modification, and exceptional mechanical properties. This nanocellulose has been used in membrane development for desalination application in the recent past. The study discusses the application of membranes based on different nanocellulose forms such as cellulose nanocrystals, cellulose nanofibrils, and bacterial nanocellulose for water desalination applications such as nanofiltration, reverse osmosis, pervaporation, forward osmosis, and membrane distillation. From the analysis of studies, it was confirmed that the nanocellulose-based membranes are effective in the desalination application. The chemical modification of nanocellulose can definitely improve the surface affinity as well as the reactivity of membranes for the efficient separation of specific contaminants/ions.

On the Control Strategy to Improve the Salt Rejection of a Thin-Film Composite Reverse Osmosis Membrane

Since the specific energy consumption (SEC) required for reverse osmosis (RO) desalination has been steeply reduced over the past few decades, there is an increasing demand for high-selectivity membranes. However, it is still hard to find research papers empirically dealing with increasing the salt rejection of RO membranes and addressing the SEC change possibly occurring while increasing salt rejection. Herein, we examined the feasibility of the process and material approaches to increase the salt rejection of RO membranes from the perspective of the SEC and weighed up a better approach to increase salt rejection between the two approaches. A process approach was confirmed to have some inherent limitations in terms of the trade-off between water permeability and salt rejection. Furthermore, a process approach is inappropriate to alter the intrinsic salt permeability of RO membranes, such that it should be far from a fundamental improvement in the selectivity of RO membranes. Thus, we could conclude that a material approach is necessary to make a fundamental improvement in the selectivity of RO membranes. This paper also provides discussion on the specific demands for RO membranes featuring superior mechanical properties and excellent water/salt permselectivity to minimize membrane compaction while maximizing the selectivity.

Preparation and Surface Functionalization of Carboxylated Cellulose Nanocrystals

In recent years, cellulose nanocrystals (CNCs) have emerged as a leading biomass-based nanomaterial owing to their unique functional properties and sustainable resourcing. Sulfated cellulose nanocrystals (sCNCs), produced by sulfuric acid-assisted hydrolysis of cellulose, is currently the predominant form of this class of nanomaterial; its utilization leads the way in terms of CNC commercialization activities and industrial applications. The functional properties, including high crystallinity, colloidal stability, and uniform nanoscale dimensions, can also be attained through carboxylated cellulose nanocrystals (cCNCs). Herein, we review recent progress in methods and feedstock materials for producing cCNCs, describe their functional properties, and discuss the initial successes in their applications. Comparisons are made to sCNCs to highlight some of the inherent advantages that cCNCs may possess in similar applications.