Abstract
The low-toxicity treatment of chromium-containing wastewater represents an important way of addressing key environmental problems. In this study, a core-shell structural ZIF-8@TiO2 photocatalyst was synthesized by a simple one-step hydrothermal method. The obtained composite photocatalyst possessed improved photocatalytic activity compared with TiO2. The results indicated that the optimized ZIF-8@TiO2 composite exhibited the highest removal efficiency with 93.1% of Cr(VI) after 120 min under UV-vis irradiation. The removal curves and XPS results indicated that the adsorbed Cr(VI) on the ZIF-8 during the dark process was preferentially reduced. The superior removal efficiency of ZIF-8@TiO2 is attributed to the combination of both high adsorption of ZIF-8, which attracted Cr(VI) on the composite surface, and the high separation efficiency of photo-induced electron-hole pairs. For the mixture of wastewater that contained methyl orange and Cr(VI), 97.1% of MO and 99.7% of Cr(VI) were removed after 5 min and 60 min light irradiation, respectively. The high removal efficiency of multiple pollutants provides promising applications in the field of Cr(VI) contaminated industrial wastewater treatment.
Highlights
Water pollution has become increasingly severe following the development of industry, attracting widespread attention [1]
The morphology of the synthesized ZIF-8 and ZxTy samples with different recombination ratios was observed by SEM imaging
Photocatalytic degradation experiments and XPS results indicated that the reduction reaction initially occurred at the adsorbed Cr(VI) on the surface of ZIF-8, and the reduction rate during the first 5-min was higher than the subsequent process
Summary
Water pollution has become increasingly severe following the development of industry, attracting widespread attention [1]. Chromium is one of the most dangerous pollutants in water, and it mainly exists in electroplating, petrochemical industry, leather processing, metallurgy, and other industrial wastewaters. As the most common existent form of chromium in wastewater, Cr(VI) has high toxicity and is harmful to the ecological environment and humans. Adsorption and photocatalysis [4,5,6] have been used to remove Cr(VI) from wastewater due to their sustainability, high efficiency, and reasonable cost. Metal-organic frameworks (MOFs) have been widely used as adsorbents to remove pollutants from water due to their high surface area, large pore size, tunability, and suitable nanoscale cavities [7]. Many successes have proven that MOFs are effective adsorbents to remove Cr(VI) from wastewater, the existing form of the adsorbed chromium is still a potential hazard to the environment
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