Abstract:

Hexavalent chromium compounds are widely used in the chemical industry and are difficult to degrade naturally. Using composite nanomaterials as photocatalysts to treat hexavalent chromium Cr（Ⅵ） shows high photocatalytic activity. g-C₃N₄/ZnIn₂S₄ and g-C₃N₄/CaIn₂S₄ nano heterojunction materials were prepared by hydrothermal method， and characterized by X-ray diffraction （XRD）， scanning electron microscopy （SEM）， physical adsorption analyzer （BET）， UV-visible near-infrared spectroscopy （UV-Vis-NIR）， X-ray photoelectron spectroscopy （XPS） and electron spin resonance （EPR）. The reduction capacity of g-C₃N₄/ZnIn₂S₄ and g-C₃N₄/CaIn₂S₄ materials on Cr（Ⅵ） was tested in both non illuminated and visible light environments， and 1，4-benzoquinone （PBQ， 1 mmol）， disodium ethylenediaminetetraacetic acid （EDTA-2 Na， 1 mmol） and tert-butanol （TBA， 0.5 mL） were used as scavengers for superoxide radicals（·O{}_{\mathrm{2}}^{-}）， holes（h⁺） and hydroxyl radicals （·OH）. The active species of the photocatalytic reaction were determined based on the changes in the degradation concentration of Cr（Ⅵ） after capturing different radicals. The experimental results show that the g-C₃N₄/ZnIn₂S₄（1∶1） composite material and the g-C₃N₄/CaIn₂S₄（1∶1） composite material have the most significant catalytic effects on the reduction ability of Cr（Ⅵ）， with degradation efficiencies reaching 95.5% and 60% respectively. Comparing the reduction ability of Cr（Ⅵ） by g-C₃N₄/ZnIn₂S₄ composite materials with different mass ratios （0.5∶1， 1∶1 and 2∶1）， it was found that a 1∶1 g-C₃N₄/ZnIn₂S₄ composite material had the best catalytic effect，followed by 0.5∶1 and 2∶1， the degradation efficiency was 27% and 16%， respectively； Superoxide radicals （·O{}_{\mathrm{2}}^{-}）， photogenerated holes （h⁺） and hydroxyl radicals （·OH） all participate in the reaction， and the influence of free radicals is in the order of h⁺＞·O{}_{\mathrm{2}}^{-}＞·OH.

Key words: g-C₃N₄/ZnIn₂S₄, g-C₃N₄/CaIn₂S₄, Photocatalytic, Hexavalent chromium