Study On The Photoelectrocatalytic Performance Of Anodes With RuO₂?IrO₂?Doped TiO₂?SnO₂?Oxide

Photocatalytic technology is one of the most widely studied technology applying in organic wastewater treatment.However,due to the limitations of the photocatalytic material?such as low utilization of sunlight,photocatalytic compound fast,etc.?,which limits its wide range of applications.The ion doping of semiconductor photocatalytic materials is an important method to improve photocatalytic activity.Doping a certain electrocatalytic activity of the metal oxide in semiconductor material theoretically can not only improve the photocatalytic activity of the electrode,but also make the electrode has a certain electrocatalytic activity.However,up to now,photocatalytic materials and electrocatalytic materials are two kinds of separated materials,seldom reported research simultaneous consideration of photocatalytic activity and electrocatalytic activity.In view of problems from the development of semiconductor photocatalytic technology,the electrocatalytic activity of RuO₂?IrO₂?and the photocatalytic activity of TiO₂?SnO₂?oxides were used to prepare the composite anodes and its photoclectrocatalytic performance were studied.At the same time,the photoelectrocatalytic performances of semiconductor materials doped with precious metallic elements were studied by using the first principle calculation and experiment.The aim was to expand the optical response of semiconductor photocatalytic materials and improve the optical current density by analyzing the effect of doping elements and their composition on the band structure.The mechanism of the doped semiconductor was clarified.The results were as follows:?1?The calculation results show that semiconductor materials of SnO₂ and TiO₂ have a wide bandgap.Their conduction band and valence band both move down after doping Ru⁴⁺ or Ir⁴⁺.Because of the a orbitals from the precious metal ion,the formation of impurity energy in the forbidden band reduced the band gap,which was favor to separate the electronic and hole and extend the spectral response range.When the doping amount was 6.25%,the impurity level formed in the band gap region,the electrons occupied part of the forbidden band and the density of the state moved to low energy.However,when the doping content exceeded certain limit?e.g.,25%doped?,the forbidden band of the semiconductor would disappeared and formed a metal or quasi-metal conductor.At this time,the transfer rate of electrons increased,but the recombination rate of electrons and holes increased with the increasing of oxygen deficiency,which led to the decrease of photogenerated carriers and the weakening of photocatalysis.?2?The Ru⁴⁺ or Ir⁴⁺ doped Ti/Sn0₂?or Ti/TiO₂?four kinds of electrodes were prepared by thermal decomposition at 500?.XRS,EIS,DRS and LSV tests show that,when the metal ions?Ru or Ir?were doped,the charge resistance Rct of the electrode decreased and the conductivity increased due to the presence of metal ions.Secondly,the band gap of the semiconductor reduced,which was consistent with the calculated results,the photocatalytic flux increased and the spectral response range increased.In addition,the metal ions had a certain inhibitory effect on a part of phase?such as anatase?,which led to the formation of multi-phase coexistence or solid solution,so doped 6.25%of the metal ions could effectively improved the electrode photocurrent and promoted photoelectrocatalysis effectiveness.However,as the doping amount of metal ions increased,the band gap of the semiconductors decreased and the redox ability of the photogenerated electrons and holes decreased when the dopant was excessive.Moreover,the dopant metal atoms that couldn't enter the crystal would accumulate on the crystal surface and become the composite center of the electron and hole,weakening the photocatalytic ability.The results of UV and TOC showed that the synergistic effect of photocatalysis and electrocatalysis was the best when the 6.25%metal ions were doped.?3?When doped with the same metal ions,the comparison of photocatalytic materials SnO₂ and Ti0₂?such as Chapter 3 and Chapter 4?showed that the photocatalytic effect of semiconductor Ti0₂ was better than that of SnO₂,which mainly due to the following reasons:First,after the doping of metal ions,the growth of anatase TiO₂ was inhibited and the formation of rutile phase and anatase phase coexistenced,which has been proved conducive to the progress of photocatalysis;Second,the band gap of TiO₂ smaller than SnO₂,so its light response range was larger than SnO₂.When doped with different metal ions,the metal ions have different effects on the photocatalytic effect?e.g.Chapter 4 and Chapter 5?.Both Ru and Ir had multiple oxidation valence states,and both were good conductive materials and electrocatalytic materials.But in the process of catalytic degradation,Ir had an f-electron orbit,which could react with the degradation products accumulated on the surface of the catalytic material,increasing the catalytic rate.Therefore,under the same conditions,doping Ir had better photocatalytic effect than Ru.In this paper,the four types of electrodes are the best catalytic degradation effect when the doping amount of electrocatalytic components?RuO₂,Ir0₂?was 6.25%.Among the four kinds of electrodes,the Ti/IrxTi_1-xO₂ electrodes had the best photocatalytic effect,and the Ti/RuxSn_1-xO₂ electrodes had the worst.