Photocatalytic Properties Of Ag-Pd Modified MnO₂/TiO₂ Photoelectrodes

The direct use of solar energy via TiO₂ photocatalysis is considered as one of the most promising environmental treatment technologies in the 21st century.It not only proposes a solution to energy crisis but also satisfies the urgent necessity to pollution prevention.When comparing TiO₂ photoelectrodes it is found that TiO₂ nanotubes（NTs）possess high surface area,good light absorption properties and the abilities of pollutants degradation in solar cells.Thus,the field of photodegradation of pollutants in water has received great attention.However,TiO₂ has a low efficiency at utilizing visible light,which is a large portion of solar light energy（45%）.Thus,based on the highly ordered TiO₂ NTs,the MnO_x modification was investigated,and both morphology of the photoelectrodes surface and their photocatalytic performance were systematically examined in order to determine the treatment of TiO₂ NTs photocatalytic and the techniques it could provide a practical basis for the application of the degradation of organic pollutants in wastewater.In order to resolve the problem of recovery and reuse of powdered catalysts,this research propose TiO₂ NTs on a Ti foil substrate as a suitable solution.The fabricated the electrochemical anodization for preparing TiO₂ in situ on the surface of Ti foils,and investigated the effect of four different types of electrolyte solutions on the prepared TiO₂ NTs properties,which are represented by ammonium sulfate,sodium sulfate,sodium fluoride and ethylene glycol.The TiO₂ NTs properties and surface morphology were characterized using SEM,XRD and UV-vis/DRS.the Rhodamine B was used for evaluating the performance of photocatalytic abilities.The results revealed that the TiO₂NTs made by（CH₂OH）₂ electrolyte solution demonstrated the best performance with the Rhodamine B degradation rate of 85%compared with that of 80%,75%and 55%via the Na₂SO₄,（NH₄）₂SO₄ and NaF electrolyte solutions,respectively.In order the overcome the disadvantage of low visible light utilization of TiO₂ NTs,MnO₂/TiO₂ NTs photoelectrodes were successfully prepared via anodization and electrochemical deposition.The surface morphology of the fabricated Pd-MnO₂/TiO₂NTs was characterized using SEM,XRD and UV-vis/DRS.The results show that Pd and MnO₂ particles were successfully loaded onto the electrode surface.Pd-MnO₂codoping modification has significantly improved the visible light absorption of TiO₂,promote the transport of the photo-generated carriers and improve the photocatalytic activity.The photodegradation rate of Rhodamine B using Pd-MnO₂/TiO₂ NTs is 1.73times greater than that of Pd/TiO₂ NTs while it is 0.67 times greater than that of MnO₂/TiO₂ NTs.In order to improve the photocatalytic properties of TiO₂ NTs photoelectrode furthermore,MnO₂ and Ag were deposited on the surface of TiO₂ NTs photoelectrode via electrodeposition in a three-electrode cell.After crystallization,Ag₂Mn₈O₁₆ NCs was successfully formed on TiO₂ NTs photoelectrode.The surface morphology,crystal composition and light absorption properties of the fabricated Ag₂Mn₈O₁₆ NCs/TiO₂ NTs photoelectrode were characterized via SEM,XRD,and XPS.While photocatalytic properties evaluation was demonstrated via the photodegradation performance of Rhodamine B.The results show that Ag and Mn₈O₁₆（α-MnO₂）nanocrystals are successfully loaded onto the surface of TiO₂ NTs photoelectrode.The co-modification of Ag and Mn₈O₁₆ nanocrystals enhances the absorption of visible light and promotes the transfer of photo-generated carriers.The prepared Ag₂Mn₈O₁₆6 NCs/TiO₂ NTs photoelectrode possess excellent light absorption ratio and photocatalytic performance.The degradation rates of Rhodamine B were 0.71 times and 4.74 times greater than that of Ag/TiO₂ NTs and MnO₂/TiO₂ NTs,respectively.In order to employ Ag₂Mn₈O₁₆ NCs/TiO₂ NTs in an applicable system,a wastewater treatment reactor with a capacity of 500 mL was designed.The reactor employs five photoelectrodes simultaneously.The degradation efficiency of Rhodamine B after 2 h of operation time can reach 96%,while the photocatalytic activity rate constant was 0.0311 min^-1.Therefore,the photoreactor proposed in this study shows remarkable photocatalytic degradation of the large volume of organic pollutants,which provides a significant theoretical support for the practical use of TiO₂ nanotechnology applications.