Preparation Of Micron-level Copper-based Photocatalysts And High-efficiency Reduction Of Cr(Ⅵ)

With the development of society,the pollution posed by heavy metal chromium is becoming more and more serious.Although Cr（III）is not only non-toxic but also one of the trace metal elements required by the human body,the water pollutant Cr（Ⅵ）has great harm to human health.As an efficient and environmentally friendly technology,photocatalysis has great prospects in the application of Cr（Ⅵ）degradation.There are many disadvantages when employing the traditional powder-formed catalysts,so it is necessary to develop all-solid-state catalysts.as candidates.It’s known that the photocatalytic performance are determined by the morphology and crystal structures and the as-prepared catalysts.Therefore,developing photocatalysts with a wide absorption range and more reactive sites under visible light is a hot spot of current research.In recent years,sulfides have attracted widespread attention due to their suitable energy band gap,simple synthesis methods,and sensitivity towards the visible light.However,most of the reported photocatalysts were in powder-form.In view of above concerns,in this work copper mesh was taken as substrates to in-situ grow all-solid-state photocatalysts for the reduction of Cr（Ⅵ）under visible light.Main investigation results and new discovers are summarized below.（1）The prepared CuO/Cu₂S crystallites are micron-scale cubes with a crystal face heterojunction structure of Cu₂S as the core and CuO as the shell.Since CuO and Cu₂S forbidden band widths are both less than 1.9 e V,the prepared CuO/Cu₂S crystallites are easily excited by visible light to generate electron-holes.The presence of in-situ heterojunction not only improves the stability of Cu₂S in the water environment,but also promotes the rapid transfer of photogenerated electrons,improves the separation efficiency of photogenerated pairs,and accelerates the toxic Cr（Ⅵ）to non-toxic Cr（III）Fast conversion.Studies have shown that the reduction product of Cr（Ⅵ）is Cr₂O₃,which is adsorbed and fixed on the surface of CuO/Cu₂S,which realizes the rapid detoxification and separation of toxic and harmful Cr（Ⅵ）in water.The above research results indicate that the all-solid CuO/Cu₂S catalyst has a good potential application prospect in the actual treatment of Cr（Ⅵ）in wastewater.（2）On the basis of the above research work,we found that although CuO/Cu₂S can rapidly photocatalyze the reduction of Cr（Ⅵ）to Cr（III）,there is still a certain degree of further reduction of Cr（III）to Cr（0）for chromium recovery difficult.In order to solve this problem,this research work uses a three-dimensional copper mesh as the substrate and hydrothermally grows an all-solid Cu₂WS₄ microcrystalline photocatalyst with a richer electronic structure.Through XPS analysis,the catalyst can effectively achieve the conversion of Cr（Ⅵ）to Cr（0）,which is attributed to the electron-rich structure of Cu₂WS₄,various chemical composition components and excellent self-stability.In addition,the S bond in the Cu₂WS₄ crystallites combines with the H bond in the HCr O₄^-solution to form a strong H-S bond.Even when the solution p H is low,the photoreduction product of Cr（Ⅵ）can be efficiently fixed on the surface of the material.The Cu₂WS₄/Cu can efficiently convert Cr（Ⅵ）to Cr（III）and Cr（0）,providing a new idea for the photocatalytic treatment of Cr（Ⅵ）in low p H wastewater.