Fabrication And Application Of Co₃O₄@M（M=Pt,Ag） Heterojunction Nanomaterials

Co₃O₄ is a transition metal oxide with the typical spinel type structure,the cations of Co²⁺and Co³⁺ are tetrahedral coordination and octahedral coordination in the crystal sturcture,respectively.Co₃O₄ is a typical p-type semiconductor nanomaterials and has a narrow band gap of about 2.07 e V,which responds to visible light.The electron conversion between Co（Ⅱ）and Co（Ⅲ）in the structure of Co₃O₄ and the intrinsic redox nature of the Co₃O₄ support,and it can be used as a catalyst and a catalyst carrier.When the noble metal particles were loaded on the surface of Co₃O₄ support,it is easy to agglomerate and disperse unevenly,which leads to the size of noble metal particles and weakens the interaction between noble metal particles and Co₃O₄ support,thus affecting the catalytic activity and cycling stability of the catalyst.Therefore,in order to solve this problem,the newly prepared Co₃O₄ is usually modified to improves the catalytic activity and cycling stability and widen its application range.In this thesis,Co₃O₄@metal heterojunctions were synthesized by surface oxidation-reduction（SOR）method and impregnation reduction（IR）method,respectively.The catalytic oxidation reaction of formaldehyde at room temperature and photocatalytic degradation of tetracycline（TC）and malachite green（MG）were studied separately.The main content of this paper is as follows:1.The nanorods and nanospheres of Co₃O₄ were synthesized by hydrothermal calcination method and solvothermal method separately,and then the heterojunctions of Co₃O₄@Pt were fabricated by using SOR and IR method,respectively.The as-prepared NRs and NSs of Co₃O₄@Pt were applied to catalytic oxidation reaction of formaldehyde at room temperature.The result shows that the morphology of Co₃O₄ and the quantitative loading of Pt were the key factors of the removal of formaldehyde.The Pt loading 0.8%（in weight ratio）of Co₃O₄@Pt synthesized by SOR（loading is theoretical value）showed the best catalytic performance,which can clear formaldehyde completely in 50 minutes.2.Co₃O₄@Ag nanorods were synthesized by SOR and IR method separately by using Co₃O₄ nanorods synthesized by hydrothermal calcination method act as precursor.Under the irradiation conditions of 350W Xenon lamp and 250W Ultraviolet lamp,TC and MG were photocatalytic degradation by as-prepared Co₃O₄@Ag NRs.The results show that the affecting factors on photocatalytic degradation efficiency were as follows:initial concentration of pollutants,the dosage of the catalyst,the loading amount of Ag,the pH value,H₂O₂.The photocatalysis active species of Co₃O₄@Ag were detected by free radical capture experiment.The main active substances for photocatalytic degradation of TC and MG were superoxide radicals（·O₂^-）,holes（h⁺）and hydroxyl radicals（·OH）,respectively.Experiment indicates that Co₃O₄@Ag（Ag%=3 wt%）synthesized by SOR（loading is theoretical value）has the best catalytic performance,and the catalytic effect radiated by ultraviolet lamp is better than that of radiated by xenon lamp.Under the conditions of ultraviolet light irradiation,the degradation rate of TC achieved 67%after 90 min,the degradation rate of MG reached 100% after 120 min.In summary,Co₃O₄@metal heterojunctions prepared by SOR method exhibits excellent catalytic activity and cycling stability during the process of formaldehyde catalytic oxidation and photocatalytic degradation at room temperature.Co₃O₄@Pt and Co₃O₄@Ag heterojunctions prepared by SOR maybe a candidate of promising catalysis applying to formaldehyde catalytic oxidation and photocatalytic degradation.