Synthesis Of Ternary Alumina-based Complex Oxide Photocatalysts And Their Photocatalytic Performance

With the rapidly development of industrialization in the world,the problem of environment pollution becomes more and more serious.Semiconductor photocatalysis is an effective strategy in solving the energy and environment crises because of the generation of photo-induced electrons and holes upon light irradiation over photocatalysts that would facilitate the chemical reactions producing fuels or eliminating pollutants.To realize the economical application in large-scale industry of photocatalysis technique,the development of inexpensive photocatalysts made of earth-abundant elements is a crucial step.Based on aluminum and magnesium are typical earth-abundant elements,so they as a raw material prepara MgAl-LDHs.But it has low transfer efficiency of electron as a photocatalyst.Considering that magnesium aluminum hydrotalcite is layered structure,there is a large amount of oxygen exposure on the surface.Through studying,it is found that the construction of surface oxygen vacancy can effectively shorten the gap width of the material and enhance the absorption of light.In this paper,magnesium aluminum hydrotalcite with surface oxygen vacancy was synthesized by hydrothermal method.The materials were characterized by X-ray diffraction?XRD?,Scanning electron microscopy?SEM?,Transmission electron microscopy?TEM?,UV-vis diffuse reflectance?DRS?,Photoluminescence?PL?,Brunauer-Emmett-Teller?BET?and so on.Degradation of colourless phenol solution was put into effect to evaluate the photocatalytic activity under ultraviolet irradiation.The catalyst shows the higtest photocatalytic activity,which made by Al?NO₃?₃·9H₂O?Mg?NO₃?₂·6H₂O?NaOH and Na₂CO₃.The higtest photocatalytic activity could be attributed to the fact that the surface is rich in oxygen vacancy,which can effectively transfer photogenic electrons and enhance the utilization of light.The single magnesium aluminum hydrotalcite has low utilization of sunlight.In order to promote the utilization of the semiconductor to the light,it is a good choice to build heterogeneity.CoAl-LDHs/MgAl-LDHs heterojunction is synthesized via a simple hydrothermal route,improving the optical response range of MgAl-LDHs.It has obvious light absorption in the ultraviolet-visible area.Because of the defective energy level of MgAl-LDHs,it can effectively transfer the photogenic electrons produced by CoAl-LDHs and improve the separation efficiency of photogenic electron-hole pairs.By photocatalytic degradation of phenol,the photocatalytic activity of heterogeneous junction was higher than that of single substance.MgAl-LDHs is calcined at different temperatures to form MgAl₂O₄.Theoretical calculation indicates that pure MgAl₂O₄ crystal has an energy band gap of 7.505 eV,and that the top of the valence band is mainly formed by hybridization between Mg-p and O-p states,while the bottom of the conduction band mainly originates from the Mg-s/p and O-s/p states.The UV-vis DRS results show that MgAl₂O₄ containing amorphous matter absorbs ultraviolet light with a band gap of 3.90 eV,which arises from the longer Mg-O bond length and presence of defects.This research also confirms that the visible-light photocatalytic activity reported in a previous paper is derived from the nitrogen element doping.The photocatalytic activity of MgAl₂O₄ is evaluated via the decomposition of methylene blue?MB?under UV-vis light illumination.The electron transfer route and the photocatalytic mechanism of MgAl₂O₄ for degrading MB are proposed.The potentials of the energy bands of MgAl₂O₄ are obtained using Mott-Schottky electrochemical measurement.