The Enhanced Photocatalytic Reduction Of CO₂ Over TiO₂ By Layered Double Metal Oxides

Carbon dioxide is widely considered to be the main greenhouse gas,leading to a sharp deterioration of the global environment.With the continuous increase in the consumption of fossil energy,the rapid increase of carbon dioxide emissions,and the energy problems caused by the reduction of fossil resources have attracted more and more attention.Solar energy is a rich renewable energy source.Using photocatalytic technology to reduce CO₂ into high-valued fuels,is one of the effective ways to solve environmental and energy problems at the same time.In this paper,using TiO₂ as the main semiconductor,the photocatalytic reduction of CO₂ was carried out.The main contents are follows as below.1.The enhanced activity of CO₂ reduction based on MgAl-LDO/TiO₂:Using titanium isopropoxide and HCl as raw materials,rod-like rutile phase TiO₂ was synthesized by a modified hydrothermal method.MgAl-LDO modified TiO₂?MgAl-LDO/TiO₂?was prepared by in-situ deposition method.X-ray diffraction?XRD?,Scanning Electron Microscope?SEM?and Transmission electron microscope?TEM?analysis showed that the 5-8 nm thickness of MgAl-LDO was evenly distributed on the surface of TiO₂.The yield of CO and CH₄ of Pt/MgAl-LDO/TiO₂ was 2 and 11 times that of Pt/TiO₂,respectively.In situ FT-IR spectroscopy showed that the carbon dioxide chemically adsorbed on the surface of MgAl-LDO/TiO₂ was mainly in the form of monodentate carbonate,and the binding force between the catalyst and the the carbon dioxide was moderate,which was not only favorable for the adsorption and activation of CO₂,but also avoided Mg-O carbonation poisoning.Photoluminescence?PL?spectra show that MgAl-LDO allows the transfer of photogenerated electrons from TiO₂ to Pt,while also inhibiting the occurrence of reversed behavior,thereby enhancing the separation of photogenerated electron-hole pairs.The use of different co-catalysts and the co-catalyst loading with both co-catalysts increases product selectivity.The study shows that the use of MgAl-LDO modified TiO₂ improves the photocatalytic reduction CO₂ activity of TiO₂.2.The enhanced activity of CO₂ reduction based on TiO₂/MgAl-LDO:A one-step hydrothermal method was used to add TiO₂ on the surface of hexagonal MgAl-LDO.X-ray diffraction?XRD?,Scanning Electron Microscope?SEM?,and SEM-Mapping indicate that MgAl-LDO has a regular morphology and TiO₂ uniformly covers the surface.Because the relatively strong surface basicity and large specific surface area of MgAl-LDO provide more CO₂ adsorption activation sites,the CO₂ adsorption capacity increases significantly.The photoelectrons generated on highly uniformly dispersed TiO₂ are trapped by the co-catalyst at the contact interface and are consumed in the reduction reaction in time,which greatly increases the reactive sites,thereby increasing the active of CO₂ reduction to generate CH₄.3.The enhanced activity of CO₂ reduction based on TiO₂/CaMgAl-LDO photocatalyst enhanced the activity of CO₂ reduction:Based on the preparation of TiO₂ supported on MgAl-LDO,Ca ions were introduced into MgAl-LDO by doping method.The structure of the composites was studied by SEM,XRD and SEM-Mapping.The results showed that different proportions of CaMgAl-LDO were successfully synthesized.The results show that when Ca with a larger ion radius replaces part of Mg ions with different proportions,the CO₂ adsorption capacity is further increased on the basis of MgAl-LDO,and the photocatalytic activity of CO₂ reduction is enhaced.