Multilayer UF membrane assisted by photocatalytic NZVI@TiO2 nanoparticle for removal and reduction of hexavalent chromium

Abstract

Photocatalytic polyethersulfone (PES) membranes with a high degree of hexavalent chromium (Cr(VI)) removal, hydrophilicity, water permeability and antifouling properties were fabricated via layer by layer assembly (LBL) technology. The novel PES ultrafiltration (UF) membranes were developed with different bilayers of chitosan (CHI)-alginate (ALG) and nano zero-valent iron@TiO2 (NZVI@TiO2) photocatalytic nanoparticles. The morphology, chemical structure and wettability of synthesized nanoparticles and fabricated membranes were characterized by FESEM, AFM, EDX, XRD, FTIR and contact angle analyzer. The PES-UF membrane containing four CHI layers and one layer of NZVI@TiO2 photocatalytic nanoparticles (M5) has shown maximum efficiency for Cr(VI) removal from permeate and retentate streams compared to the other membranes, 100 %, 98.1 % and 95.5 % Cr(VI) removal in permeate and 76.4 %, 46.7 % and 34.4 % Cr(VI) removal in retentate were obtained for 5, 15 and 30 ppm feed concentration, respectively. The modifications of the neat PES led to high hydrophilicity and desirable antifouling properties. The water flux of neat PES, M1, M2, M3, M4 and M5 membrane were obtained 161, 152, 186, 147, 178 and 170 L/m2.h, respectively. According to results, the membranes containing NZVI@TiO2 photocatalytic nanoparticles have shown high water flux. Moreover, M5 membrane has exhibited 68 % flux recovery whereas neat PES membrane has shown 43 %. For 5 ppm feed concentration, the Cr(VI) removal decreased from an about 100 % to 71 ± 2%, 48 ± 2% and 42 ± 1% with increasing pH from 3 to 5, 7 and 10, respectively.