Simultaneously photocatalytic removal of Cr(VI) and metronidazole by asynchronous cross-linked modified sodium alginate

Abstract

Conventional photocatalysts for environmental applications are mainly transitional metal compounds or precious metal nanoparticles, which suffer from weak pollutant adsorption performance, thus limited their applications for high concentrated wastewaters. In this study, asynchronous cross-linked triethylenetetramine modified sodium alginate (CFTS) was used as photocatalyst for the simultaneously catalytic degradation of Cr(VI) and metronidazole (MNZ). Experimental results suggested that asynchronous cross-linking and triethylenetetramine modification have dramatically enhanced the chemical stability as well as the adsorption and photocatalytic behavior of the material. The grafted amino functional groups and cross-linked Fe3+ ions can promote the rapid separation and transfer of electrons, thus reducing the recombination rate of photo-generated electron-hole pairs. The optimum removal rate of Cr(VI) has reached 99.5 % and MNZ can be completely removed within 20 and 30 min at pH 1.0 under UV light irradiation, respectively. The removal mechanism of Cr(VI) by CFTS is the synergistic effect of electrostatic adsorption and photocatalytic reduction, while photocatalytic oxidation dominated the degradation process of MNZ. Moreover, the removal efficiency can be enhanced in the binary solution of these two pollutants due to the utilization of photo generated electron-hole pairs, which provides new pathways in the treatment of complicated pharmaceutical and domestic sewage wastewaters.