Synthesis of triethylenetetramine modified sodium alginate/CuS nanocrystal composite for enhanced Cr(VI) removal: Performance and mechanism

Photocatalysis has been widely used for the removal of hexavalent chromium from wastewater as an efficient and environmental friendly method. However, conventional photocatalysts generally exhibit poor adsorption prop-erties toward Cr(VI), resulting in unsatisfactory performance in high concentrated wastewaters. In this study, we synthesized a novel composite material with high Cr(VI) adsorption ability by blending prepared CuS nano-crystals into triethylenetetramine modified sodium alginate for the enhanced photocatalytic removal of Cr(VI). Effect of CuS dosage, pH value, light source and intensity were discussed for the optimum Cr(VI) removal conditions. The synthesized composite has shown good adsorption performance toward Cr(VI) and the overall removal rate reached 98.99 % within 50 min under UV light irradiation with citric acid as hole scavenger. Adsorption isotherm, thermodynamics, and kinetics with corresponding model fitting were discussed, which suggested that the monolayer and chemical adsorption dominated the adsorption process. Characterization re-sults indicated that amino and hydroxyl groups contributed electrons in the photocatalysis reaction for the reduction of Cr(VI) to Cr(III). CuS nanocrystals can enhance the surface charge and light absorbance ability of the composite, and the Cr(VI) removal was governed by electrostatic interaction and photo-induced redox reaction.

Automated summary

In this study, a novel composite material was synthesized by blending CuS nano-crystals into triethylenetetramine modified sodium alginate, showing high adsorption ability for Cr(VI) and enhanced photocatalytic removal. The effects of CuS dosage, pH value, light source, and intensity on Cr(VI) removal were investigated. The synthesized composite achieved a removal rate of 98.99% within 50 minutes under UV light irradiation with citric acid as a hole scavenger. The adsorption isotherm, thermodynamics, and kinetics were discussed, indicating that monolayer and chemical adsorption were dominant mechanisms. Amino and hydroxyl groups contributed electrons in the photocatalysis reaction for the reduction of Cr(VI) to Cr(III). CuS nanocrystals enhanced the surface charge and light absorbance ability of the composite, governing the electrostatic interaction and photo-induced redox reaction in Cr(VI) removal.