Preparation And Characterization Of Transition Metal (Cu, Fe, Mo) Oxide And GC₃N₄-based Composite Materials, As Well As The Performance Of Water Vapor Shift And Photocatalytic Reactions

Transition metals（Cu,Fe,Mo）oxides and g-C₃N₄-based composites are particularly important industrial catalysts and they are widely used in CO oxidation,water gas shift reaction,solar cells and photocatalysis.Our work focuses on the preparation of CuO/?-Fe₂O₃,MoO₃-g-C₃N₄ and MoO₃@α-Fe₂O₃ catalysts.The morphology,phase composition and surface phase are well characterized by XRD,HR-TEM and XPS.Water gas shift reaction（LT-WGS）and photocatalytic degradation of pollutants in water were selected as probe to study the effect of phase composition on the reaction activity.Firstly,CuO/?-Fe₂O₃ catalyst was prepared by co-precipitation with Cu（NO₃）₂?3H₂O and Fe（NO₃）₃?9H₂O as precursors.XRD,HR-TEM,STEM and H₂-TPR studies were used to track the structural evolution,reducibility and surface phase of CuO/?-Fe₂O₃ sample.Integrated analyses of bulk and surface,the catalyst was composed of?-Fe₂O₃ and CuO nanoparticles.In a temperature range of 100-150 ^oC,CuO could be reduced to metallic Cu⁰ and?-Fe₂O₃ was reduced to Fe₃O₄ at 150-200 ^oC.And Fe₃O₄ will be reduced to Fe⁰ at higher temperature.Cu⁰/Fe₃O₄ could be obtained by controllable reduction of CuO/?-Fe₂O₃ composite.At a temperature range of 180-250 ^oC,the activation barrier of Cu/Fe₃O₄ catalyst was lower than Cu/Al₂O₃ sample by 10-15 kJ/mol,suggesting Fe₃O₄ took part in LT-WGS.AP-XPS results confired that the active phases contained Cu⁰ and Fe₃O₄ nanoparticles during LT-WGS.Secondly,high performance MoO₃-g-C₃N₄ composites photocatalysts were prepared by impregnation-calcination method with g-C₃N₄ and（NH₄）₆Mo₇O₂₄?4H₂O as precursors.The phase compositions and valence states of MoO₃-g-C₃N₄ catalysts were characterized by XRD,FT-IR and HR-TEM.The results of nitrogen sorption isotherm showed that obtained MoO₃-g-C₃N₄samples exhibited excellent high photocatalytic activity for photocatalytic reaction due to the increased surface area and pore volume of the catalysts.The DRS spectrum and valence band XPS analysis showed the band gap and valence band position of g-C₃N₄ and MoO₃.It was found that the photocatalytic activity for methyl orange（MO）degradation of obtained MoO₃-g-C₃N₄composites were much higher than that of pure g-C₃N₄ and MoO₃ and the content of MoO₃obviously affected the photoactivity.1.60 wt%MoO₃-g-C₃N₄ sample showed the best activity（the kinetic constant k was 34 times higher than that of pure g-C₃N₄）,and the catalytic activity decreased when the content was further increased.Consistent with Z-type photoelectron transport mechanism,^·O^2-and h⁺were the main active substances in photocatalytic reaction which were confirmed by selective deposition of noble metal Pt and hole-radical group capture experiments.That is to say,the hybrid structure of g-C₃N₄ and MoO₃ would inhibit the recombination rate of photogenerated electron-hole pairs and prolonged lifetime of charge carriers.Finally,the MoO₃@α-Fe₂O₃ core-shell nanostructures were prepared by template method.The structure and morphology of the catalysts were characterized by HR-TEM.It was found that the core-shell structures were homogeneous and theα-Fe₂O₃ was uniformly deposited on surface of MoO₃ nanorod,consistent with the results of electron microscope mapping.The MoO₃@α-Fe₂O₃ core-shell nanostructures with different Mo/Fe mole ratios could be successfully obtained when fixing the Mo/Fe ratio.It was found that the photocatalytic activity of MoO₃@α-Fe₂O₃ composites in degradation of rhodamine B（RhB）were much higher than that of pure Fe₂O₃,which means that the addition of MoO₃ promoted the photocatalytic reaction and the catalytic activity increased with the content of MoO₃.