Jiefeng Pan

Recovery of chemically degraded polyethyleneimine by a re-modification method: prolonging the lifetime of cation exchange membranes

Selectivity for monovalent cations is an important property of cation exchange membranes (CEMs). The cation exchange membranes of the CSO modified with polyethyleneimine type have a higher selectivity for monovalent cations than the multivalent cations. Unfortunately, the loss of selectivity for these kinds of CSO seems to be unavoidable due to fouling and degradation of polyethyleneimine groups. In this situation, a “re-modification” technique was developed for recovery of fouled CSO, activating the fouled CSO by methanol and a sulfuric acid solution with ultrasonic vibration, followed by a layered surfacial electro-deposition method to prolong the lifetime of cation exchange membranes. A series of electrodialysis experiments for Na+/Ca2+ separation was performed for evaluating and comparing the monovalent cation selectivity of the samples. The restoration of the surface and cross section morphology after “re-modification” was demonstrated by attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). As a result of the re-modification method the membranes with chemically degraded polyethyleneimine were again made functional. The ion exchange groups of the CSO modified with polyethyleneimine were successfully recovered, giving the membrane a high permselectivity again.

Mimicking the cell membrane: bio-inspired simultaneous functions with monovalent anion selectivity and antifouling properties of anion exchange membrane

A new bio-inspired method was applied in this study to simultaneously improve the monovalent anion selectivity and antifouling properties of anion exchange membranes (AEMs). Three-layer architecture was developed by deposition of polydopamine (PDA) and electro-deposition of N-O-sulfonic acid benzyl chitosan (NSBC). The innermost and outermost layers were PDA with different deposition time. The middle layer was prepared by NSBC. Fourier transform infrared spectroscopy and scanning electron microscopy confirmed that PDA and NSBC were successfully modified on the surfaces of AEMs. The contact angle of the membranes indicated an improved hydrophilicity of the modified membranes. A series of electrodialysis experiments in which Cl−/SO42− separation was studied, demonstrating the monovalent anion selectivity of the samples. The Cl−/SO42− permselectivity of the modified membranes can reach up to 2.20, higher than that of the commercial membrane (only 0.78) during 90 minutes in electrodialysis (ED). The increase value of the resistance of the membranes was also measured to evaluate the antifouling properties. Sodium dodecyl benzene sulfonate (SDBS) was used as the fouling material in the ED process and the membrane area resistance of modified membrane increase value of was only 0.08 Ωcm2 30 minutes later.

Preparation and characterization of the tolerance to acid/alkaline and anti-oil-fouling of regenerated cellulose membranes for oil–water separation

Novel regenerated cellulose (RC) membranes were fabricated using an immersion precipitation phase inversion method from five non-derivative solvents (NaOH/urea/H2O, NaOH/thiourea/H2O, LiOH/urea/H2O, NaOH/urea/thiourea/H2O and LiOH/urea/thiourea/H2O) for oil–water separation. The prepared RC membranes exhibited a similar asymmetric and reticulated pore structure, with a pore diameter ranging from 12.77 to 17.09 nm, which is similar to typical ultrafiltration membranes. The biggest pore diameter was obtained using a NaOH/urea/H2O solvent and the best mechanical properties were obtained using a LiOH/urea/H2O solvent, which indicated that by using different mixed solvents, different pore sizes and mechanical properties can be obtained for fabricated cellulose membranes. Measurements of the flux and the rejection using edible oil/water in this study showed that our prepared membranes possessed excellent oil retention ratios of up to 98%; meanwhile the water flux recovery ratios were around 90% through simple water flushing. Besides, after immersion in strong acid/alkaline solution for a week, the pure water flux (J), dimensions and weight showed no obvious change, and there was no change in filtration performance at room temperature with a pH from 1 to 14, indicating the advantage of high tolerance to acid/alkaline.

A novel nanofiltration membrane inspired by an asymmetric porous membrane for selective fractionation of monovalent anions in electrodialysis

The present study describes the synthesis of new nanofiltration membranes inspired by asymmetric porous membranes used as monovalent anion selective membranes for electro-membrane separation. The membrane surface was firstly modified, by deposition of a mussel-inspired “bio-glue” polydopamine (PDA) layer, and subsequently a compact polyamide layer was polymerized on the surface of the membranes active layer. The chemical constitution and structure of these modified porous membranes were explored by Fourier transform infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM). The surface roughness and hydrophilicity of the membranes were explored by atomic force microscopy (AFM) and water contact angle measurements, respectively. In addition, the electrochemical properties of the surface of the modified membranes were analyzed in terms of membrane surface resistance and zeta potential values. As for the performance of these modified porous membranes, this was investigated by measuring the permselectivity of a Cl−/SO42− system. The obtained results show that the new membranes exhibit an enhanced monovalent anion permselectivity, which is in agreement with the improved membrane surface properties. Furthermore, membranes modified by the addition of a PDA layer and a dense polyamide active layer lead to a significant improvement in selectivity , compared with a conventional interfacial polymerization modified membrane . The excellent performance can be ascribed to the synergistic effect of the compact PDA layer and negatively charged interfacial polymerization layer, dependent on the sieving and electrostatic repulsion, respectively. Thus, this process is promising for the further development of porous monovalent selective anion exchange membranes.