Preparation And Photocatalytic Properties Of Metal Oxide/Ag₃PO₄ Heterojunction Composites

Photocatalysis technology is an environment-friendly redox technology driven by solar energy,which is widely used in energy conversion,pollution control and other fields.Seeking efficient and stable photocatalysts has always been the core task of photocatalytic technology.However,for traditional photocatalysts,a single semiconductor is difficult to meet both high efficiency and stability.Therefore,how to optimize the photocatalytic performance of traditional photocatalysts has become the key to practical applicatioan.On the basis of a large number of research work,morphology control,element doping,metal deposition,semiconductor composite and other methods have been proved to be feasible for the modification of photocatalysts.Ag₃PO₄ is a photocatalytic material that produces light response in the visible region and has excellent performance in photocatalytic water splitting and degradation of organic pollutants.However,Ag₃PO₄ also has obvious disadvantages in practical application,such as photogenerated electrons reducing part of Ag⁺ions leading to photocorrosion,higher photogenerated carrier recombination rate in vivo and Ag source cost.In view of the above problems,three metal oxide nanomaterials were prepared as substrate materials and compounded with Ag₃PO₄ nanoparticles to construct heterojunctions,aiming to promote the separation of photogenerated carriers,improve the photocatalytic performance and photostability of the materials,and reduce the use of Ag sources at the same time.The specific research contents and results are as follows:（1）Flower-like Nb₂O₅ nanostructures were prepared by hydrothermal method,and Ag₃PO₄ nanoparticles were deposited in situ on the surface of Nb₂O₅ nanoflowers to prepare Nb₂O₅/Ag₃PO₄ composites.The results of SEM,TEM and EDS show that Nb₂O₅nanoflowers are beneficial to the deposition of Ag₃PO₄ nanoparticles.The size of Ag₃PO₄is 5～10 nm and the distribution is uniform.The results of XPS showed that a weak Ag peak appeared in the composite sample,indicating that a trace amount of Ag⁺was reduced during the preparation process.The dark reaction experiments with methylene blue revealed that Nb₂O₅ with Lewis acid sites enriched on the surface improved the adsorption of methylene blue molecules on the composites.The photocatalytic degradation performance of Nb₂O₅/Ag₃PO₄ with different composite ratios on methylene blue was studied.The experimental results show that the photocatalytic degradation performance of Nb₂O₅/Ag₃PO₄ is 34.2 times that of Nb₂O₅ and 1.6 times that of Ag₃PO₄ when the composite ratio is 1∶1.The results of light absorption,active group capture experiments and photoelectric properties show that Nb₂O₅/Ag₃PO₄ is a Type-II heterojunction,which promotes the separation and transport of photogenerated carriers.（2）Theα-Fe OOH microspheres were prepared by hydrothermal method,and then theα-Fe OOH microspheres were dispersed in ethanol solution and PO₄^3-and Ag⁺precursor solutions were added sequentially to prepareα-Fe OOH/Ag₃PO₄ composites.The results of SEM,TEM and EDS tests indicate that Ag₃PO₄ particles are evenly distributed on the surface ofα-Fe OOH microspheres,with the size of 3～8 nm.The absorption edge of the composite was expanded to visible-light region and induced improved photoelectric response.The photocatalytic performance was evaluated by photocatalytic degradation of methylene blue solution.The results show thatα-Fe OOH/Ag₃PO₄ exhibits a better photocatalytic performance,which is 75 times that ofα-Fe OOH and 1.8 times that of Ag₃PO₄.According to the experimental results of light absorption,capture experiments and ptoelectronic properties measurement,it is concluded thatα-Fe OOH/Ag₃PO₄ is a Type-II heterojunction,which can promote the photogenerated charge carrier separation and transfer,and hence result in high photocatalytic activity and stability.（3）CuO/Ag₃PO₄ composites were prepared by in-situ deposition of Ag₃PO₄ particles on the surface of CuO nanosheets prepared by hydrothermal method in ethanol solution.The results of SEM,TEM,EDS,XRD and XPS tests show that Ag₃PO₄ nanoparticles with the size of 5～20 nm are uniformly attached to the surface of CuO,and there is a small amount of elemental Ag on the surface of Ag₃PO₄ nanoparticles.The UV-vis DRS results show that the composite material can absorb longer wavelengths of light compared to Ag₃PO₄.When the CuO/Ag₃PO₄ composite ratio is 4∶1,the composite material exhibits the best performance in the degradation of methylene blue experiment,which is1.3 times of Ag₃PO₄ and 164 times of CuO.The results of light absorption,capture experiments and photoelectric properties indicate that the CuO/Ag₃PO₄ heterojunction is a Type-II structure,and the heterojunction effectively inhibits the recombination of photogenerated carriers,showing good photoelectric performance and stability.