Study On The Catalytic Reduction Of Cr（Ⅵ） And Visible Light Degradation Of Orange Ⅱ By Supported Nano-precious Metal Materials

Orange Ⅱ and Cr（Ⅵ）are widely used in industrial production,because both have very strong carcinogenic and good solubility in water,their emissions will not only cause great pollution to the ecological environment,but also seriously threaten people’s health.Therefore,the treatment of orange Ⅱ and Cr（Ⅵ）in water bodies has become a hot topic in the field of environmental protection.In view of the disadvantages of the traditional treatment methods,the excellent composite materials with simple and controllable process,high efficiency and stability and no secondary pollution were researched and prepared to simulate the degradation of orange Ⅱ and the reduction of Cr（Ⅵ）in industrial.Firstly,a series of Pt/N-Bi₂Mo O₆ photocatalyst with excellent adsorption performance and photocatalytic activity were synthesized by two-step hydrothermal method and Na BH₄ reduction method.The experimental results showed that the degradation efficiency of 0.5%Pt/N-Bi₂Mo O₆ composite photocatalyst was 90.13%,which was 4 times and 1.8 times of pure Bi₂Mo O₆ and N-Bi₂Mo O₆,respectively.Such remarkable photodegradation efficiency is mainly attributed to the joint introduction of Pt and N,which reduces the band gap of the bulk Bi₂Mo O₆.Meanwhile,the surface plasmonic resonance（SPR）effect triggered by Pt nanoparticles makes the optical absorption range of the catalyst significantly expanded and the separation efficiency of electron-hole pairs significantly improved.In addition,the effects of initial p H of solution,the initial concentration of catalyst,the light source and the loading amount of Pt on degradation efficiency of Orange Ⅱ were also investigated.At the same time,according to the fitting of different adsorption isotherm models,it is found that the adsorption process of the system can be described by Freundlich model,and 1/n=0.536,indicating that the concentration has little effect on the adsorption capacity.Finally,through free radical capture experiments,it can be determined that the superoxide anion radical(·O^2-)and photo-generated holes（h⁺）are the main active substances in the photodegradation process of Orange Ⅱ.Cycling experiments show that the catalyst has long-lasting catalytic performance and excellent stability.In addition,this paper also prepared Pd-supported nitrogen-doped carbon material to be used in the reduction of Cr（Ⅵ）in simulated wastewater.In the experiment,urea and chitosan were used as precursors,and a series of Pd/CN materials were synthesized by high-temperature carbonization method and Na BH₄ reduction method.Experiments show that the 8.6%Pd/CN_0.32 material is irregular sheet structure microscopically and has larger specific surface area(613.3 m~2g^-1)and pore volume(0.366 cm~3g^-1)compared with the material without precious metals loading.Meanwhile,the composite has excellent reduction ability for Cr（Ⅵ）,Cr（Ⅵ）（2 m M）was completely reduced after 6min,and the TOF value was 2.2378 min^-1.Experiment also explored the effects of Pd loading,catalyst of carbon and nitrogen ratio and carbonization temperature on the reduction performance of Cr（Ⅵ）.The results show that pyridine N in the catalyst is beneficial to regulate the interaction between Pd NPs and CN materials.Within a certain range,the greater the molar ratio of pyridine N/Pd,the better the catalytic activity of the Pd/CN material,and the higher the reduction efficiency of Cr（Ⅵ）.In addition,the reaction mechanism of the reduction of Cr（Ⅵ）by Pd/CN materials was studied,that is,Pd nanoparticles catalyzed the decomposition of formic acid（HCOOH）to produce H₂,which resulted in reduced Cr（Ⅵ）to Cr（Ⅲ）.