Enhancing Chlorine Resistance and Water Permeability during Forward Osmosis Separation Using Superhydrophilic Materials with Conjugated Systems

Abstract

Poor resistance to free chlorine severely impairs the service of conventional polyamide (PA) membrane in water treatment. Here we design a series of superhydrophilic aromatic sulfonate materials (ASMs) comprising successively increasing conjugated systems and ionizable groups (ASM-1, ASM-2, ASM-3) to develop a chlorine-resistant membrane via chemical modification. By altering the membrane physicochemical properties and surface structure, ASMs substantially improve the chlorine resistance and water permeability of membrane. With 0.5 M NaCl as the draw solution, all ASMs enhance membrane water fluxes by more than 60% relative to those of the nascent PA membrane in forward osmosis (FO) processes. After exposed to a 1000 ppm sodium hypochlorite solution for 2–8 h, the modified membranes exhibit smaller variations in FO performance than the PA membrane. Having the largest conjugated system and the most sulfonate groups, ASM-3 enables the membrane to sustain a chlorination strength of up to 8000 ppm·h with an insignificant NaCl loss during the FO process, surpassing other recently developed PA membranes in chlorine resistance. These results manifest that the combination of a large conjugated system and ionizable group is key for imbuing membrane with excellent chlorine resistance and water permeability.

Graphene Quantum Dot-Added Thin-Film Composite Membrane with Advanced Nanofibrous Support for Forward Osmosis

“…Accordingly, the crosslinking network of the PA surface developed on the basis of chemical bonds and the internal hydrogen bonds was damaged, which deteriorated the selectivity of the membrane, resulting in a rise in the SRSF value. Similar results for the water flux and SRSF values were stated by Meng et al [ 79 ] and Song et al [ 58 ]. Thus, it was confirmed that the 0.050-B-GQD/PA TFNC membrane showed a much slower rate of PA layer damage while exposed to free chlorine and therefore possessed good chlorine resistance characteristics.…”

“…Due to its corrosive properties, a chlorine attack can cause significantly worsen membrane performance [ 77 , 78 ]. A chlorine attack is a critical challenge that could damage membrane integrity, reduce a membrane’s lifetime, or/and upsurge maintenance expenses [ 79 , 80 ]. In the current study, a 1000 ppm sodium hypochlorite solution was prepared using sodium hypochlorite (NaOCl) and DI water for the chlorine resistance analysis.…”

ZnO Nanoneedle-Modified PEEK Fiber Felt for Improving Anti-fouling Performance of Oil/Water Separation

“…Their FTIR spectra were collected and are shown in Figure b. In comparison with the original PEEK felt (PEEK-f), all of sulfonated felts had two new absorption peaks located at 960–1010 and 1038 cm –1 , which could be ascribed to vibrations of SO. − The result proved that the pressed felts were successfully sulfonated.…”

How Do Chemical Cleaning Agents Act on Polyamide Nanofiltration Membrane and Fouling Layer?

“…The triazine ring has a stable conjugated bond structure, which can improve the mechanical stability, thermal stability, and acid resistance of the NF membrane, , while sulfonated graphene and graphene oxide have long-term stability in alkaline solutions . Chlorine resistance of the NF membrane may be improved by applying aliphatic diamines as aqueous monomers, and melamine and aromatic sulfonate materials can also be used for preparing chlorine-resistant membranes. − Constructing a sacrifice layer to preferentially react with oxidants mitigates the chlorination and hydrolysis of the PA NF membrane . Also, increasing membrane surface charge and hydrophilicity may reduce the adsorption of cleaning agents and their corresponding actions on the membranes, and improving the physical structure stability of the separation layer also can alleviate the compaction and pore swelling caused by chemical cleaning.…”