Hydrothermal Preparation Of Cu₂O/ZnO Photocatalysts

ZnO,as a new multi-functional non-polar material,has promising prospects in industrial production and life today.Due to its unique physical and chemical properties and non-toxic advantages,ZnO is widely used in industrial wastewater treatment,environmental purification,chemical sterilization and other areas.Since ZnO can only absorb high-energy ultraviolet light,how to modify it to possess physical properties other than intrinsic ZnO is one of the current research hotspots.In this paper,ZnO/Cu_xO composite photocatalyst was prepared by hydrothermal method,and the effect of different copper species on the catalytic effect of ZnO in this sample was studied.A series of changes in the structure and performance of ZnO after the introduction of copper ions were discussed from the aspects of electronic structure and optical properties by a combination of calculation simulation and experiment.The main contents include the following two parts:1.ZnO composite powders containing different copper species were prepared with different addition amounts of NaBH4.Morphological analysis revealed that when the concentration of the reducing agent was low,the prepared ZnO was flaky and the(CuO,Cu₂O)morphology was irregular and lumpy.With the increase of reducing agent concentration,ZnO(Cu₂O)was formed,and the morphology of thin ZnO shortened in the radial direction became near-spherical morphology,and cluster phenomenon appeared.The reducing agent dose continued to increase and the product was ZnO(Cu₂O).The particles were obviously dispersed and the crystallinity was better.After increasing the amount of reducing agent,the product became ZnO(Cu₂O,Cu),and the ZnO particles increased significantly.When the ratio of the reducing agent to the copper salt reaches 2:1,the product is only ZnO(Cu).The ZnO particles grow larger,and the larger the particles,the worse the photocatalytic performance.After the degradation test,the catalytic ability of each sample are shown below:ZnO<ZnO(Cu)<ZnO(CuO,Cu₂O)<ZnO(Cu₂O).It is concluded that ZnO(Cu₂O)has the best catalytic effect.2.The fixed ratio of reducing agent to copper salt is 1:2(mole),and the ratio of copper and zinc salts is adjusted under the condition that the product(ZnO/Cu₂O)is unchanged,and the change of catalyst performance is discussed from the morphology perspective.When Cu:Zn in the raw material is 1:20,no copper particles are observed,and at this time,ZnO is formed into a flower shape by overlapping multiple sheets.When Cu:Zn is 1:5,flower-like ZnO is embedded on the bulk copper particles.When the ratio is 1:3,the flower-like ZnO is broken and the petals are tiled on the copper particles.The photocatalytic activity was directly affected by the change of morphology.As the proportion continues to increase,the morphology of ZnO becomes fine particles,the particle size of Cu₂O becomes smaller,and the specific surface area becomes larger.The results showed that the photocatalytic degradation ability was the strongest when the copper-zinc ratio was5:8,and the catalytic degradation rate reached 98.62%.The experimental results show that when the copper and zinc are relatively large,bidirectional doping occurs in the composite powder.It is found through calculation that ZnO-doped copper ions will shift the conduction band down,impurity levels appear in the band gap,and the light absorption range is widened.In addition,after the doping,the covalent bond component becomes smaller,the ionic bond component increases,the system becomes unstable,the ability of the oxygen atomic nucleus to bind electrons is weakened,and the electron holes are easily separated.Cu₂O-doped zinc ions have a smaller forbidden band width,and their ability to recombine electrons and holes decreases.The calculation results show that bidirectional doping is beneficial to photocatalysis.