Multi-effect Synergistic Enhancement Of Photocatalytic Activity Of TiO₂ Nanosheets

Photocatalysis technology is a new technology with great potential to solve the goals of"carbon peaking"and"carbon neutralization",and its core is to develop the efficient photocatalyst materials.As an economical and stable semiconductor nanomaterial,TiO₂ is of practical significance to design an efficient photocatalytic system.However,TiO₂ still has problems such as ultra-high carrier recombination efficiency,extremely low utilization of sunlight,limited effect of traditional modification strategies,and single mechanism,which greatly hinders its further development.It has been proved that it is an effective strategy to construct a complex TiO₂ structure with multi-effect synergistic catalysis and high intrinsic activity,and it is also meaningful to study its complex photocatalytic enhancement mechanism in depth.In this paper,a series of photocatalytic systems have been constructed to enhance the photocatalytic activity of TiO₂ nanosheets（NSs）.Furthermore,the different multi-effect strategies（including band gap engineering,cocatalysts,heterojunctions,surface defects,et al）for enhancing catalytic activity and its related synergistic mechanism were explored,which further enriched the related research on the synergistic enhancement of semiconductor photocatalytic activity by multi-effects.The research contents are as follows:（1）Designing surface active site engineering containing oxygen vacancies（OVs）and Pd nanoparticles（NPs）is helpful to construct a multi-effect synergistic catalytic system based on TiO₂.Using Na BH₄ as reducing agent,OVs-TiO₂/Pd photocatalysts were synthesized by solid-phase milling.When the Pd NPs loaded mass ratio was 5wt%with a low content,the OVs-TiO₂/Pd composite catalyst not only exhibited an excellent photocatalytic hydrogen production rate(22.15 mmol·h^-1·g^-1 under a 300 W xenon lamp,which was 124.2 times higher than that of TiO₂),also showed good photocatalytic ability to oxidize antibiotics（such as tetracycline and oxytetracycline）and TMB under visible light.It was proved that the improved photocatalytic activity is that the synergistic effect of OVs and Pd NPs on the surface of TiO₂ NSs can not only serve as highly active reaction sites,but also broaden the visible light response range of TiO₂,thereby ensuring the improvement of the separation efficiency of photogenerated carriers and promoting the generation of active species such as holes（h⁺）,singlet oxygen（¹O₂）,superoxide anion(O₂^-·),and hydroxyl radicals（·OH）,which ultimately promote the photocatalytic oxidation and reduction reactions.（2）Constructing a multi-effect synergistic catalytic interface of TiO₂ NSs with cocatalyst Pd NPs and monolayer Ti₃C₂ NSs is one of the effective ways to develop efficient photocatalysts for hydrogen production.A series of TiO₂/Pd/Ti₃C₂ composite catalysts with different mass ratios were prepared by photoreduction and electrostatic self-assembly.Under the irradiation of 300 W xenon lamp,the photohydrogen production rate of TiO₂/3%Pd/1%Ti₃C₂ reaches 21.60 mmol·h^-1·g^-1,which are 135times,25.4 times and 1.5 times that of TiO₂ NSs,TiO₂/1%Ti₃C₂ and TiO₂/3%Pd,respectively.This study proves that the mechanism of the enhanced photocatalytic activity can be attributed to the close interfacial contact of TiO₂ NSs with highly active Pd NPs and monolayer Ti₃C₂ NSs,which in turn shortens the charge transport distance and facilitates the efficient separation of photogenerated charges.（3）A series of TiO₂/Pd/NC composite nanomaterials with different mass ratios were synthesized by means of photoreduction and secondary hydrothermal methods.The visible light catalytic activity of TiO₂ is effectively enhanced by the synergistic effect of NC and cocatalyst Pd.It has been showed that the TiO₂/1%Pd/5%NC composite nanomaterials exhibited excellent photocatalytic activity for the degradation of TC under 420 nm cut off filter,and the degradation rate reached 73.5%,which was 2.47 times that of TiO₂ NSs,1.36 times that of TiO₂/5%NC,and 1.73times that of TiO₂/1%Pd.The EPR results showed that the mechanism of this reaction,under illumination,NC,Pd NPs and TiO₂ can form a heterojunction to promote the separation of photogenerated electrons and holes;at the same time,the active oxygen species such as ¹O₂,O₂^-·and·OH with strong oxidizing properties were generated during the photoreaction process,which could effectively degrade TC.Furthermore,the presence of NC broadens the utilization efficiency of TiO₂ for sunlight.