Preparation And Characterization Of G-C₃N₄/CuS Composites And Its Photocatalytic Removal Of Methyl Orange And Cr???

In recent years,emissions of organic dyes and heavy metal wastewater have led to severe water pollution and aggravated the water scarcity crisis.The organic dyes have been widely applied to textile,printing and dyeing,electroplating,papermaking,food processing and so on.The wastewater has characteristics of high chromaticity,high chemical oxygen demand(COD),toxic and poor biochemical characteristics.Chromium(Cr)and its compounds have been widely used in electroplating,printing,pharmacy,metallurgy,paper making,leather and other industries.Cr(III)and Cr(VI)are the two main states of chromium in aqueous systems,different from that of Cr(III),the Cr(VI)has highly toxicity,good solubility,easy carcinogenic and mutagenic characteristics.In view of the current severe organic dye and Cr(VI)pollution status and its potential ecological toxicity,there is an urgent need to develop wastewater treatment technology.In many of the technology,photocatalytic technology has the advantages of simple operation,environmental protection,high efficiency and so on.In this study the advantages of graphite carbon nitride(g-C3N4)and CuS were combined.A "one-pot" hydrothermal route was used to fabricate CuS modified graphitic carbon nitride(g-C3N4/CuS)composite photocatalyst.SEM,TEM,XRD,FTIR,XPS,BET,DRS and PL were used to characterize the samples.Organic anionic dye(methyl orange)and heavy metal(hexavalent chromium)were used as the target pollutionsto evaluate the photodegradation performance of catalysts.The results showed that the fine CuS particles are uniformly loaded on the nano-g-C3N4 films with small size and good crystallinity.At the same time,the introduction of CuS enhances the absorption range of visible light and reduces the photogenerated the recombination of electrons and holes pairs.Whenmethyl orangeandCr(VI)was used as targetpollutions,the effect of photodegradation time,initial pH and low concentration of humic acid(HA)on the photodegradation activity of g-C3N4/CuS were systematically studied.The results showed that the photocatalytic activity of g-C3N4-20/CuS was higher than that of single g-C3N4 and CuS,and the photocatalytic rateof MO was more than 90%and basically get a balance in the light 2h,the photocatalytic rateof Cr(?)was more than 70%in the light 3h.The degradation rate of MO and Cr(?)have a strong dependence on the pH value.When the pH value is acidic,the photodegradation effect of g-C3N4-20/CuS is the best,indicating that the acidic condition favors the adsorption of contaminants on the material surface.Meanwhile the contaminants will be degraded by the oxidation of the free radicals generated by the light.When the HA concentration in the solution is low,the removal rate of MO decreases with the increase of HA value,which indicates that there are competition between the negative HA and MO on the surface of g-C3N4-20/CuS effect and HA quenched photogenerated carriers.But the removal rate of Cr(?)did not change in a certain concentration range of HA,indicating that HA also played a role in the reduction of Cr(?).The free radical scavenging experiments showed thatg-C3N4-20/CuS forms Z-type heterojunction,and the superoxide and hole played a leading role in the degradation process.Finally,the regeneration of g-C3N4-20/CuS was investigated by cyclic experiment.Therefore,the composite not only accelerates the separation of photogenerated electrons from holes and has strong redox ability,which can effectively degrade organic dyes and Cr(?)in wastewater.