Multi-Element Co-Regulation Of The Photogenerated Charge Behavior At The Surface Interface Of TiO₂ Nanoparticles

Titanium dioxide is used for the degradation of numerous organic pollutants or photocatalytic conversion for the synthesis of other energetic substances,but the low quantum efficiency and difficulty in utilizing visible light limit its practical applications.In order to improve the performance of titanium dioxide photocatalytic synthesis of hydrogen peroxide,the graphitization reaction of organic molecules containing C,N,O,S and other heteroatoms or other metal elements on the surface of nano-Ti O₂was systematically studied,which regulated the surface structure of the catalyst,significantly enhanced the generation,transport and separation capacity of the catalyst for photogenerated charges,broadened the spectral response range,improved the photocatalytic conversion efficiency,and provided a convenient way for the development of low-cost and efficient synthesis of H₂O₂photocatalysts.Using organic small molecules（6-amino-5-cyano-4-（4-hydroxyphenyl）-2-methy l-3-carboxylic acid ethyl ester-1,4-dihydropyridine）that can enter the Ti O₂nanopores,graphite-like structures co-doped with C,N and O were obtained by gradient calcination,and their visible photocatalytic performance was explored in depth.The results showed that the hybrid species enhanced the separation and transport of photogenerated charges and reduced the photocatalytic decomposition of H₂O₂,and the visible light performance of the catalyst was significantly improved,and the H₂O₂yield reached 3.12 mmol/（h·g）under light irradiation above 420 nm,and an energy conversion efficiency of up to 1.17%was obtained.Due to the diversity of such organic molecules,this method provides researchers with many opportunities to further optimize the hybridized species on the titanium dioxide surface and is therefore of great importance for photocatalyst development.To investigate the effect of S elements on the performance of composite photocatalysts,nanotitanium dioxide photocatalysts co-modified with bismuth vanadate and thiourea were designed and prepared.The structures and properties of the catalysts obtained by hydrothermal and high-temperature calcination methods were compared.The results showed that bismuth vanadate occupied part of the Ti active site,thiourea successfully carried out graphite-like reaction on the surface of titanium dioxide P25 to generate carbon nitride structure,and the modified catalyst（abbreviated as BV-Ti-SN）achieved H₂O₂yield of 6.75 mmol/（h·g）under light irradiation above 300 nm and apparent quantum efficiency of 32.3%at 365±5 nm;Under the visible light above 420 nm,3.17 mmol/（h·g）of H₂O₂could be obtained with an apparent quantum efficiency of 7.41%at 435±10 nm,and the solar energy conversion efficiency under visible light was as high as 1.85%,showing excellent photocatalytic energy conversion performance.To explore the effects of other metal elements,different metal ions were successfully introduced on the surface of the modified catalyst BV-Ti-SN by impregnating Cu Cl₂,Ni Cl₂,Co Cl₂and Ag NO₃solutions,respectively,which reduced the forbidden band width of BV-Ti-SN catalyst,further broadened the visible light absorption range and increased the specific surface area.The performance study shows that the Cu-ion-loaded BV-Ti-SN has remarkable performance under visible light,and the H₂O₂production rate can reach 4.62 mmol/（h·g）,the solar energy conversion efficiency reaches 2.1%,and the decomposition rate of hydrogen peroxide under visible light is slowed down,the structure is more stable,and the relative productivity of hydrogen peroxide can still reach 85.36%after repeated use for 7times.Compared with BV-Ti-SN,the Cu ion modification obtained higher apparent quantum efficiency,reaching 48.5%and 9.41%at 365±5 nm and 435±10 nm,respectively.The success of multi-element modulation of the apparent interfacial structure of titanium dioxide provides ideas for the development of high-performance and low-cost composite catalysts.The above study shows that the introduction of multiple elements of C,N,O,and S by graphite-like transformation of organic molecules containing multiple heteroatoms on the surface of nanophotocatalysts,as well as the further introduction of metal ions,can effectively modulate the surface structure of catalysts,which herein significantly affect the charge behavior at the surface interface,promoting the generation,transport,and separation of photogenerated charges,improving the activity and selectivity of oxygen reduction reaction,enhancing the photocatalytic conversion efficiency.This provides a convenient way to develop low-cost and efficient synthetic hydrogen peroxide photocatalysts.