Molecular design of chlorine-resistant polymer for pervaporation desalination

Polyethyleneimine-Based Cryogels Enabling the Selective and Reversible Adsorption of Chlorine

Herein hyperbranched polyethyleneimine (hPEI) cryogels are reported for the selective and reversible adsorption of elemental chlorine. The cryogels are prepared in an aqueous solution by crosslinking with glutaraldehyde at subzero temperatures. The final macroporous composites bearing ammonium chloride groups are obtained after freeze-drying. The cryogels CG1[Cl]-CG3[Cl] adsorb chlorine with capacities of 0.22-0.26 g Cl2/g cryogel as an average over three adsorption-desorption cycles. The adsorption process is based on the reversible and selective halogen bonding of chlorides (Cl-) with chlorine (Cl2) forming the corresponding trichloride ([Cl3]-) species, indicated by Raman spectroscopy. The reversibility of chlorine adsorption is shown by applying heat and vacuum to the loaded cryogel CG1[Cl3] releasing 63% of the adsorbed chlorine within 3 h and 72% within 16 h. The unique ability to selectively adsorb chlorine in the presence of other gases is successfully employed for the selective adsorption of chlorine from a gas mixture, potentially enabling the recycling of chlorine from tail gas streams.

Sulfonated graphene oxide-based pervaporation membranes inspired by a tortuous brick and mortar structure for enhanced resilience against silica scaling and organic fouling

A novel tortuous brick-and-mortar structure utilizing intercalation of polyvinyl alcohol (PVA) on sulfonated graphene oxide (SGO) membranes was specifically tailored for brine treatment by pervaporation to ensure excessive resistance to silica scaling and organic fouling, as well as ultrafast water transport without compromising salt rejection. The synthesized SGO membrane showed a smoother surface morphology, improved zeta potential, and a higher hydration capacity than the graphene oxide (GO) membrane. Further intercalation of PVA through glutaraldehyde (GA) crosslinking, confirmed by Fourier transform infrared spectroscopy and X-ray diffraction analysis, conferred increased cohesiveness, and the SGO-PVA-GA membrane was therefore able to withstand ultrasonication tests without any erosion of the coating layer. According to a pervaporative desalination test, the SGO-PVA-GA membrane exhibited 62 kg m^-2 h^-1 of permeate flux, with an extraordinary salt rejection of 99.99% for a 10 wt% NaCl feed solution at 65 °C. The 72 h organic fouling, silica scaling, and combined fouling and scaling tests proved that the SGO-PVA-GA membrane sustains a stable flux with less scaling and fouling than the GO-PVA-GA membrane, attributable to dense surface negative charges and great hydration capacities caused by sulfonic acid. Thus, the SGO-PVA-GA membrane offers superlative advantages for long-term brine treatment by pervaporation, related to its ability to withstand silica scaling and organic fouling.