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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