Snthesis Of Graphene Based Pd And Pd/Fe₃O₄Nanoparticles Catalysts And Their Applications In Cr（Ⅵ） Pollutant Treatment

Since2004AK Giem and KS Novoselov successfully synthetized free-standing and one-atom-thick graphene by mechanical exfoliation, the scientific community has began a vigorous study of the new carbon material graphene. Only one-atom-thick graphene material has a strictly two-dimensional structure and exhibits surprising properties. Graphene nano-composite materials have great potential applications in the field of catalysis. The large specific surface area, excellent electrical conductivity and superior thermal conductivity of graphene can improve the activity of catalyst significantly. The graphene supported catalysts have many advantages compared with the conventional catalysts. Therefore, many studies are focusing on graphene based catalysts and their applications in various reactions. With the enhancement of environmental protection awareness, the chromium pollution problems of soil and industrial waste water have attracted much attention. In the past two decades, scientists studied a variety of chromium pollution treatment methods, including adsorption, membrane separation, electrochemical, and catalytic reduction etc. The catalytic reduction method is often used to deal with Cr(Ⅵ) because of its simple process and high efficiency. This paper focuses on how to prepare the graphene based catalysts and the catalytic reduction reactions of Cr(Ⅵ) using formic acid as a reducing agent. The main conclusions are as follows:(1) Synthesis of Pd-graphene nanocatalyst and its catlyatic property in reduction of Cr(Ⅵ). The Pd-graphene was prepared by the chemical reduction method with formic acid as a reducing agent, which exhibits excellent activity in the reaction of the degradation hexavalent. The graphene composite catalyst containing7.32×10-7mol Pd has ability to completely degrate5.0×10-4mol Cr(Ⅵ) ion in just8mins at45℃and with pH=3.11. This result is far better as compared to the colloidal PdNPs catalyst. The catalyst performance is affected by the temperature, pH and the size of Pd nanoparticles. The catalytic efficiency is better under the higher temperature, higher acidity, higher specific surface area. The stability and the feasibility of recycling of catalyst can be confirmed by the repetitive experiments.(2) Synthesis of magnetic Pd-graphene nanocatalyst and its catlyatic property in reduction of Cr(Ⅵ). The Pd/Fe3O4-graphene nanocomposite catalyst was prepared by solvothermal method. Results of transmission electron microscope (TEM) show that the magnetic Fe3O4and Pd nanoparticles are uniformly dispersed on grapheme. In addition, the particle morphology of magnetic Fe3O4and Pd nanoparticles approximates to be spherical. The synthesized catalyst also showed excellent activity in the degradation reaction of the hexavalent. The results show that the Cr(VI)(7mL,71.4mM) was competely reduced into Cr(III) using Pd/Fe3O4/graphene catalyst with1.4×10-6mol of Pd in22mins under the reaction conditions of T=45℃and pH=3.98. Compared with the Pd-Fe3O4catalyst, the present magnetic catalyst has higher activity due to the presence of the graphene. The result of the vibrating sample magnetometer (VSM) show that the saturation magnetization of the catalyst is27emu g-1, which indicate the possible complete separation of the catalyst by the applied magnetic field. The catalyst shows good stability in the recycling use.