Coupling of self-supporting geopolymer membrane with intercepted Cr(III) for dye wastewater treatment by hybrid photocatalysis and membrane separation

Abstract In this study, hazardous Cr(III) trapped by a geopolymer membrane was crystallized in situ and coupled with the membrane to afford dye wastewater treatment by hybrid photocatalysis and membrane separation for the first time. The X-ray powder diffraction, field emission scanning electron microscopy, and X-ray photoelectron spectroscopy results confirmed that Cr(III) was highly dispersed on the membrane surface as nano Cr2O3 particles. The photoluminescence peak decreased with increasing Cr2O3 along with an increase in the photocatalytic degradation efficiency for basic green under static conditions (0 MPa downstream pressure). The photocatalytic performances under different downstream pressures confirmed that the degradation efficiency increased with increasing downstream pressure (below atmospheric pressure): 100 min was required for 100% degradation of basic green under static conditions, whereas only 50 min was required at 0.09 MPa owing to suitable membrane-induced concentration of the dyes. Density functional theory calculations indicated that the geopolymer membrane matrix was weakly nucleophilic, allowing it to effectively reject basic green, while the Cr2O3 was strongly nucleophilic, enabling it to adsorb basic green effectively for further photocatalytic degradation. The membrane reported here would be a brand-new choice for the wastewater treatment with inorganic membranes.