Herein, we study the feasibility of using nanocellulose (NC)-based composites with silver and platinum nanoparticles as additive materials to fabricate the support layer of thin film composite (TFC) membranes for water purification applications. In brief, the NC surface was chemically modified and then was decorated with silver and platinum nanoparticles, respectively, by chemical reduction. These metalized nanocellulose composites (MNC) were characterized by several techniques including: FTIR, XPS, TGA, XRD, and XANES to probe their integrity. Thereafter, we fabricated the MNC-TFC membranes and the support layer was modified to improve the membrane properties. The membranes were thoroughly characterized, and the performance was evaluated in forward osmosis (FO) mode with various feed solutions: nanopure water, urea, and wastewater samples. The fabricated membranes exhibited finger-like pore morphologies and varying pore sizes. Interestingly, higher water fluxes and solute rejection was obtained with the MNC-TFC membranes with wastewater samples. The overall approach of this work provides an effort to fabricated membranes with high water flux and enhanced selectivity.

Forward osmosis (FO) has been emerging and gaining attention within the membrane-based processes because it can achieve high water fluxes while minimizing energy consumption, making it a cost-effective approach for wastewater treatment. However, membrane fouling remains an obstacle to this application. To address this concern, we fabricated an electroconductive membrane composed of polysulfone and polyaniline (PAni). These membranes have the potential to oxidize targeted organic compounds and/or electrostatically remove the fouling layer. After optimizing the PAni loading, we performed bench-scale tests using sodium alginate as model foulant. The membranes were fouled resulting in a decrease in FO efficiency of 72%. Fouled membranes were treated with a cathodic potential for 30 min, the fouling and antifouling processes were monitored with scanning electron microscopy (SEM), and contact angle and electrochemical methods were used. The fouled membrane exhibited a clogged surface and high electrical resistance, while the treated membrane recovered the PAni nanofibers morphology, its electrical and hydrophilic properties, and 84% of its FO efficiency. Thus, PAni can improve the overall membrane permeability while incorporating antifouling properties. Moreover, the EIS results of this study shed light on the mechanisms that govern the water separation process before and after fouling in the FO mode.

Forward osmosis (FO) is a passive liquid separation process where a hypertonic solution drives water across a semipermeable membrane. Compared to other membrane-based water purification processes, FO has the potential of producing clean water with minimal energy consumption. To achieve its potential, membranes with enhanced properties, such as high fouling resistance and solute rejection, high hydrophilicity and water permeability, and a wide pH and temperature tolerance, must be developed. In this work, we studied the effect of amine N-oxide zwitterionic polymer additives in the properties and morphology of polysulfone (PSf) based membranes. These additives were synthesized via a three-step reaction in which analogues of trimethylamine oxide (TMAO) were covalently incorporated into PSf. TMAO is a well-known organic osmolyte and its antifouling properties offer an interesting avenue to explore its potential use in water purification applications such as FO. Moreover, we studied three analogues which varied in their alkyl chain length: diethyl, dibutyl, and dihexyl. Our interest in these three alkyl groups was to systematically increase the carbon chain and study their effect in the overall membrane formation and performance. The successful synthesis of the amine N-oxide zwitterionic polymer additives was confirmed by FT-IR, NMR, and XPS. Then, we fabricated the membranes through the nonsolvent induced phase separation (NIPS) process. The morphology of the membranes was evaluated with SEM, while the hydrophilicity was monitored with contact angle measurements. Our results showed that the addition of these TMAO analogues significantly affects the PSf membrane formation and properties. Moreover, the PSf–DEAO membrane with the shortest carbon chain improve the membrane surface hydrophilicity and enhanced the water flux by a 4-fold increase. Altogether, our results suggest that longer alkyl groups could compromise the antifouling properties of the amine oxide.

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Membrane-based technologies, such as forward osmosis (FO), offer the advantage of treating water through a spontaneous process that requires minimal energy input while achieving favorable water permeability and selectivity. However, the FO process still has some challenges that need to be solved or improved to become entirely feasible. The main impediment for this technology is the recovery of the draw solute used to generate the osmotic potential in the process. In this paper, we discuss the use of a switchable polarity solvent, 1-cyclohexylpiperidine (CHP), as a draw solute that responds to external stimuli. Specifically, the miscibility of CHP can be switched by the presence of carbon dioxide (CO 2 ) and is reversible by applying heat. Thus, in this study, the hydrophobic CHP is first converted to the hydrophilic ammonium salt (CHPH + ), and its capability as a draw solution (DS) is thoroughly evaluated against the typical osmotic agent, sodium chloride (NaCl). Our results show that the water permeability across the thin film composite membrane increases by 69% when CHPH + is used as the DS. Also, the water permeability when using different feed solutions: aqueous solutions of (a) urea and (b) NaCl were evaluated. In both cases, the CHPH + generates water fluxes in the range of 65 ± 4 LMH and 69 ± 2 LMH, respectively. We then separate the diluted DS by applying 75 °C to the solution to recover the pure CHP and water. The results of this work provide a proof-of-concept of a CHP wastewater and desalination method via an FO process.

A chabazite-type silicoaluminophosphate (SAPO-34) was grown within the meso-and macropores of activated carbon (AC) via a confined space synthesis and functionalized via the addition of strontium(II) (i.e., Sr 2+ -CSAPO-34) for the selective adsorption of CO 2 in the presence of humidity. The in situ growth of the SAPO phase was corroborated through SEM/ EDAX, XRD, and pore size distribution profiles. About 80% of the meso-and macropores of AC were occupied by the SAPO. Sr 2+ -CSAPO-34 was further characterized via XRD, TGA, ICP-OES, and water contact angle measurements. A physical mixture of Sr 2+ -SAPO-34 and AC was also prepared to contrast against the hierarchical variant. The selectivity and capacity for trace CO 2 removal were evaluated through single-component equilibrium and multicomponent fixed-bed adsorption. Bed tests (v = 200 mL min −1 and C i = 500, 1000, or 2500 ppm) showed that the CO 2 capacity remains in the presence of 90% relative humidity, with no signs of rollup. Specifically, the uptake capacity of the Sr 2+ -CSAPO-34 bed for a CO 2 feed content of 1000 ppm was 0.11 mmol per cm 3 of bed and with a breakthrough point greater than 2000 bed volumes; this is superior compared to other adsorbents for CO 2 capture under humid conditions. The Sr 2+ -CSAPO-34 composite bed was also subjected to various cycles upon vacuum-assisted thermal regeneration, and no decrease in adsorption capacity was observed. The adsorbent hierarchical design approach showed that a synergistic combination of hydrophobicity and enhanced adsorbate−adsorbent interactions at the physisorption level is a promising strategy for removing trace CO 2 under humid conditions.

The design of functionalized selective layers to develop novel membranes is essential to provide potential solutions that meet the continuously growing demand of providing safe water. Herein, we present the interfacial response of an enzymatic thin-film composite (E-TFC) membrane displaying dual functionality and fabricated as a proof-of-concept for both efficient lipopolysaccharide (LPS) separation and ester bond hydrolysis. The enzymatic membrane model was constructed by employing lipase b from Candida antarctica (CALB) covalently coupled via chemically activated bisepoxide groups onto the surface of the di-block copolymer polystyrene-b-poly(4-vinyl pyridine) (PS-b-P4VP) layer. Our results show a complete rejection of size-excluded LPS molecules when using the fabricated E-TFC membrane in a forward osmosis (FO) application. Moreover, the immobilized enzyme was able to retain 97% of its enzymatic activity when using 4-nitrophenyl acetate (pNPA) and up to 74% to liberate free fatty acids from LPS molecules within the feed side of the FO system. This work provides fundamental insights into new emerging functional biomaterials that find applications in hybrid catalytic filtration processes that also selectively remove LPS molecules from water sources.