Preparation Of Cu₂O-based Composite Material And Its Catalytic Reduction Of P-nitrophenol

Para-nitrophenol is one of the most widely used organic compounds in industrial and agricultural production.It is widely used as intermediates or raw materials for pesticides,pigments,dyes,wood preservatives,etc.It not only benefits human beings,but also brings pollution to the environment.Especially in water with high solubility and stability,it is difficult to degrade.Therefore,it is very important to treat p-nitrophenol in industrial and agricultural wastewater efficiently and green.So far,the liquid phase hydrogenation reduction method is considered to be one of the most appropriate methods using noble metal nanoparticles as catalyst and Na BH₄as hydrogen source.It can not only deal with the pollution caused by p-nitrophenol,but also obtain the drug intermediate p-aminophenol with added value,and the operation process is simple and gentle.However,the use of precious metal nanoparticles has been limited due to their high cost and limited content.The researchers hope to find alternatives to the highly active precious metal catalyst.Among them,Cu₂O has become an ideal substitute for noble metal catalysts because of its simple preparation,low price,rich copper reserves and good catalytic hydrogenation reduction effect on p-nitrophenol.However,its catalytic activity is weaker than that of precious metals.When the size of Cu₂O is reduced and the surface area is increased,its activity can be improved.But it is easy to agglomerate and be oxidized into Cu O by air,so its stability is poor.Based on the above problems,hydrothermal method and calcination method were adopted in this paper.ZnWO₄,Co₃O₄and vulcanized Co₃O₄were selected as active carriers.Four catalysts,ZnWO₄/Cu₂O,Co₃O₄/Cu₂O,Co₃O₄@Cu₂O and S/Co₃O₄@Cu₂O,were prepared for the catalytic hydrogenation reduction of p-nitrophenol,and their catalytic activity and mechanism were studied.The main research contents are as follows:（1）ZnWO₄nanorods of about 50nm were prepared by simple hydrothermal method,and ZnWO₄/Cu₂O-X composite catalysts with different proportions were prepared by chemical precipitation method.The morphology and structure of the catalysts were characterized by SEM,TEM,XRD,HRTEM and XPS.The rod-like ZnWO₄was closely attached to the surface of Cu₂O.Using Na BH₄as hydrogen source and Na BH₄as catalyst,the catalytic activity and cyclic stability of the prepared composite for the hydrogenation reduction of 4-NP were investigated.The experimental results show that the unique electron configuration of d10 and d0 of ZnWO₄makes it capable of rapidly transferring electrons to p-nitrophenol ions adsorbed on the surface of the catalyst when it is combined with Cu₂O.And-NO₂is catalytically reduced to-NH₂.As 4-NP is electrically neutral,it is easy to desorb from the surface of the catalyst to give up the active site and continue the reaction.Therefore,the synthesized ZnWO₄/Cu₂O-5 has good activity and stability in the experiment.（2）Two kinds of 3D flower-like Co₃O₄-1 and Co₃O₄-2 materials with slightly different morphology were prepared by one-step hydrothermal method and hydrothermal calcination method.The ratio of raw material mass was adjusted.Then the composite catalysts Co₃O₄/Cu₂O and Co₃O₄@Cu₂O were prepared by simple chemical precipitation method.The composite catalyst was characterized by XRD,SEM,HRTEM and H2-TPR.The catalytic activity and cyclic stability of p-nitrophenol were studied by hydrogenation reduction experiments.The results showed that the catalytic activity of Co₃O₄@Cu₂O-0.02 was high and its apparent rate constant was 21.77×10^-3S^-1,but its cycling stability was poor.The catalytic activity of Co₃O₄/Cu₂O-0.02 was slightly lower than that of Co₃O₄@Cu₂O-0.02,and it became an ideal catalyst because of its good cycling stability.The improvement of catalytic activity of Co₃O₄/Cu₂O-0.02and Co₃O₄@Cu₂O-0.02 is mainly attributed to the polyvalent electronic structure of Co₃O₄and the existence of oxygen vacancy,which is conducive to the transfer of electrons and the adsorption of 4-NP.（3）Co₃O₄-2 was further vulcanized,and S/Co₃O₄@Cu₂O composite catalysts with different qualities were prepared by chemical precipitation method.The composite catalysts were characterized by XRD,SEM,HRTEM and H₂-TPR.From the morphology,it could be seen that the morphology and size of Cu₂O were changed by vulcanization.Through the characterization of H₂-TPR,the interaction between each component is enhanced after curing.The possible reasons are that the contact between S/Co₃O₄and Cu₂O becomes closer with the decrease of Cu₂O particle size,and that the curing treatment increases the active sites and improves the stability.The results showed that its active factor was about 2.5 times that of Co₃O₄@Cu₂O.