Preparation And Photocatalytic Properties Of Chalcogenides/TiO₂ Nanotube Arrays Composites

In recent years,scientists have become increasingly focused on the research of reuse of wastewater and efficient conversion of renewable energy sources due to the increasing difficulties of water scarcity and energy depletion.Solar energy,as a renewable energy source with easy access,almost unlimited reserves and low acquisition cost,is a suitable choice for achieving efficient water treatment and energy conversion.The goal of photocatalytic technology is to realize the effective energy conversion and application of solar energy,which is an ideal technology to further solve the two major problems of water and energy based on the inexhaustible solar energy.TiO₂ Nanotube Arrays（TNAs）have unique advantages as photocatalysts:high chemical stability;large active surface;excellent adsorption performance;and resistance to photocorrosion,etc.However,it also has the problems of absorbing light wavelengths concentrated in the UV region and low quantum yields.The band gap of sulfur group semiconductors is generally narrow and the absorption range of sunlight is large and the absorption efficiency is high.Therefore,the research topic is on the modification of TiO₂ nanotube by sulfur group semiconductors and the study of its related photocatalytic properties.The specific research of the paper is as follows:1.Regular shaped and ordered TiO₂ nanotube arrays were prepared by two-step anodic oxidation method,which were uniformly grown on Ti sheet substrates,conversion of Te⁴⁺to Te²⁺and reduction of Ag⁺by ascorbic acid as reducing agent,Cd Cl₂,Na₂Te O₃,and Ag NO₃ as precursors and CTAB（cetyltrimethylammonium bromide）as surfactant to control the morphology,the TiO₂ nanotube arrays co-modified by Cd Te and Ag were prepared,and a Z-Scheme heterogeneous structure was formed between Cd Te and TiO₂,and Ag acted as the complex center of electrons and holes,The SPR effect of Ag further enhanced the transfer rate of photogenerated carriers,and after 2 h of visible light irradiation,MB（methylene blue）degradation efficiency was achieved at 100%,Cr（VI）reduction effect at 95.95%,and the average hydrogen production rate was 52.99μmol·h^-1·cm^-2.2.Cd S is a photocatalytic chalcogenide extremely sensitive to sunlight,an ideal choice for modified TiO₂ nanotube arrays,Sn S₂ addition retards the photocorrosion rate of Cd S,thus realizing the cyclic stability of photocatalysis.The flower-like structure increases the light absorption area of the material and improves the utilization of sunlight.The most exciting photocatalytic effect is seen in Nanotube Arrays of Cd S/Sn S₂/TiO₂ NTs,with MB（2 h）and Rh B（Rhodamine B）（3 h）degradation reaching 100%and 85.93%respectively,the degradation of MB remaining at 100%after four cycles.The average hydrogen production rate reached 97.14μmol·h^-1·cm^-2,A proposed Z-II Scheme heterojunction photocatalytic carrier migration mechanism was suggested,as the mean hydrogen production rate was 97.14μmol·h^-1·cm^-2.3.The double narrow band gap chalcogenides Cd Se,Mo Se₂were selected as the materials for the modified TiO₂ NTs,the Cd Se/Mo Se₂/TiO₂ NTs were prepared by a simple solvothermal method,Se⁴⁺precursor solution was prepared by reducing selenium powder with hydrazine hydrate.Na₂Mo O₄,Cd Cl₂ were used as the precursor solution,and electrochemical impedance spectroscopy（EIS）showed that Cd Se/Mo Se₂/TiO₂ NTs had the smallest charge transfer resistance value,indicating that this ternary catalyst had the highest transfer rate of photogenerated carriers,the MB removal efficiency reached100%after 2 h photocatalytic treatment,in addition,after 3 h photocatalytic degradation,the Rh B,Cr（VI）degradation efficiency reached 90.11%and 85.47%,respectively,revealing the considerable photocatalytic energy conversion of Cd Se/Mo Se₂/TiO₂ NTs,and the average hydrogen production rate reached 172.63μmol·h^-1·cm^-2,possible photocatalytic mechanism of double Z-Scheme heterojunction was proposed,which indicates the direction for the practical application of TiO₂ NTs.