Study On The Treatment And Mechanism Of Chromium-containing Wastewater By Chitosan Modified With Fe And Mo

As one of the"five poisons"of heavy metals,Cr mainly comes from electroplating,metallurgy,leather,printing and dyeing industries.Compared with Cr（III）,Cr（Ⅵ）is more toxic and will enter the human body by the food chain through bioconcentration.Cr（Ⅵ）often coexists with various dyes in printing and dyeing wastewater.The presence of these dyes usually hinders the removal of Cr（Ⅵ）.Therefore,the development of methods that can remove Cr（Ⅵ）and simultaneously remove Cr（Ⅵ）and dyes is of great significance to water pollution control.Because of its unique structure and abundant functional groups,as well as low cost and environmental friendliness,chitosan has received extensive attention in the removal of water pollution.Therefore,in this study,chitosan modified by different methods was applied in the adsorption and degradation of Cr（Ⅵ）-containing wastewater,its adsorption and reduction mechanism was determined by SEM,TEM,FTIR and XPS and other characterization methods,the degradation mechanism of activating H₂O₂ to remove Cr（Ⅵ）and dye coexisting wastewater was speculated.The main research contents are as follows:（1）Combined the modification of chitosan by H₂O₂ with the coordination of Fe³⁺through the Fenton reaction,the adsorption material with dual modification effects was obtained simply and efficiently,which effectively improved the adsorption ability for Cr（Ⅵ）and reduced it to Cr（III）in the p H range of 3-10.The adsorption of Cr（Ⅵ）by the Fenton modified chitosan conformed to the Freundlich model,and the maximum adsorption capacity exceeded 120 mg/g.（2）Mo-1/2Fe-CS composite was synthesized by hydrothermal method,which doped MoS₂ with chitosan,and added a certain proportion of Fe³⁺.The composite material was in good agreement with the Langmuir adsorption model,and the maximum adsorption capacity at 298 K was 179.53 mg/g.The adsorbed Cr（Ⅵ）was coordinated with N/O and reduced by MoS₂ to Cr（III）.XAFS technology had determined that the doped Fe³⁺was anchored to the N/O of chitosan with a coordination number of about 6.By reducing the number of negative charges and increasing the zeta potential on the surface of the material,Fe³⁺increased the electrostatic effect and accelerated the adsorption rate of Cr（Ⅵ）.（3）Cr（Ⅵ）and dye AR73 were simultaneous removed through a Fenton-like reaction with Mo-1/2Fe-chitosan used as a catalyst.It was speculated that Mo⁶⁺/Mo⁴⁺was used as a co-catalyst to degrade AR73 through the bimetallic catalysis of Fe³⁺/Fe²⁺and Cr⁶⁺/Cr⁵⁺,which also promoted the adsorption and reduction of Cr（Ⅵ）.Its removal effect was not affected by p H,and the addition of Cr（Ⅵ）had a promoting effect on the degradation of AR73,and Mo-1/2Fe-chitosan also had a good degradation effect on other dyes.