重金属Cr(Ⅵ)新型光催化还原方法研究

Creative Study on Photocatalytic Reduction of Heavy Metal Cr(Ⅵ)

铬在废水中常以Cr(Ⅲ)与Cr(Ⅵ)存在,而当Cr(Ⅵ)的浓度达到一定程度时,会对生物造成强致畸、致癌、致突变的作用,本研究旨在通过光催化新技术还原Cr(Ⅵ)。采用三聚氰胺为实验原料,高温灼烧的方法获得氮化碳(g-C_(3)N_(4)),通过对比紫外(UV)/HCOOH、UV/g-C_(3)N_(4)、UV/g-C_(3)N_(4)/HCOOH三种反应体系对Cr(Ⅵ)的还原效率,探究g-C_(3)N_(4)在光催化还原过程中的作用。首先采用X射线衍射实验(XRD)、扫描电子显微镜(SEM)对合成的g-C_(3)N_(4)的表面性质进行研究;然后探究四种影响因素对实验结果的影响,包括pH、HCOONa投加量、污染物Cr(Ⅵ)浓度、水中常见阴离子(HCO_(3)^(-)、SO_(4)^(2-)、NO_(3)^(-)、Cl^(-));接着通过甲基紫精淬灭实验探究g-C_(3)N_(4)还原Cr(Ⅵ)的反应机理。结果表明:在pH=3,g-C_(3)N_(4)浓度6.5 mmol/L,HCOONa浓度10 mmol/L,Cr(Ⅵ)浓度5 mg/L的条件下,UV/g-C_(3)N_(4)/HCOOH体系在20 min之内对Cr(Ⅵ)的还原率能达到100%;水体中的Cl^(-)、SO_(4)^(2-)、HCO_(3)^(-)、NO_(3)^(-)这4种主要的阴离子对g-C_(3)N_(4)还原Cr(Ⅵ)的能力产生不同程度的抑制,抑制效果由大到小依次是:HCO_(3)^(-)、SO_(4)^(2-)、NO_(3)^(-)、Cl^(-)。最终采用甲基紫精淬灭实验对Cr(Ⅵ)的还原机理进行探究,结果发现对还原Cr(Ⅵ)起主要作用的是光生电子,二氧化碳自由基(CO_(2)^(·-))起辅助作用。

Cr(Ⅲ)and Cr(Ⅵ)often exist in wastewater,and when the concentration of Cr(Ⅵ)reaches a certain level,it will cause strong teratogenic,carcinogenic and mutagenic effects on organisms.This study aims to reduce Cr(Ⅵ)through a new photocatalytic technology.Using melamine as the experimental raw material,carbon nitride(g-C_(3)N_(4))was obtained by burning at high temperature.Through batch experiments,the reduction efficiency of three reaction systems of ultraviolet(UV)/HCOOH,UV/g-C_(3)N_(4) and UV/g-C_(3)N_(4)/HCOOH for leached Cr(Ⅵ)was compared to explore the role of g-C_(3)N_(4) in the process of photocatalytic reduction.First,the surface properties of the synthesized g-C_(3)N_(4) were studied by X-ray diffraction(XRD)and scanning electron microscopy(SEM).Then explore the influence of four main factors on the experimental results,including pH value,HCOONa dosage,Cr(Ⅵ)concentration of pollutants,common anions in water(HCO_(3)^(-)、SO_(4)^(2-)、NO_(3)^(-)、Cl^(-));Then,the mechanism of reduction of Cr(Ⅵ)by g-C_(3)N_(4) was investigated by means of methyl violet quenching experiment.The results showed that under the conditions of pH 3,g-C_(3)N_(4) concentration 6.5 mmol/L,HCOONa concentration 10 mmol/L,Cr(Ⅵ)concentration 5 mg/L,UV/g-C_(3)N_(4)/HCOOH system can reduce Cr(Ⅵ)to 100%within 20 min.The four main anions in the water,Cl^(-),SO_(4)^(2-),HCO_(3)^(-),and NO_(3)^(-),inhibit the ability of gC_(3)N_(4) to reduce Cr(Ⅵ)to different degrees,and the inhibition effect is in descending order:HCO_(3)^(-),SO_(4)^(2-),NO_(3)^(-),Cl^(-);However,cations have little influence on the reduction of Cr(Ⅵ).Finally,methylene violet quenching experiment was used to explore the reduction mechanism of Cr(Ⅵ),and the results showed that photogenerated electrons played a major role in the reduction of Cr(Ⅵ),while the effect of carbon dioxide free radical(CO_(2)^(·-))was not obvious.