Construction Of Co Or Cu Active Sites On TiO₂ Surface And Study On The Photocatalytic Performance Of NO Reduction To NH₃

Nitric oxide（NO）is one of the main air pollutants,and its massive emissions into the atmosphere will cause serious environmental problems and endanger people’s health.A series of photocatalytic redox reactions are driven by sunlight as an energy source.It has the advantages of green and mild,and is currently a research hotspot in the field of catalysis.Photocatalysts can convert the adsorbed NO molecules into ammonia（NH₃）through the proton-coupled electron transfer（PECT）process.As an important economic compound,NH₃is widely used in industry and agriculture.Therefore,it is of far-reaching significance and broad development prospects to convert harmful NO into NH₃with high economic value through photocatalysis.Titanium dioxide（TiO₂）semiconductor photocatalyst has the advantages of easy preparation,good stability,non-toxic and environmental protection.Among them,crystal plane co-exposed anatase TiO₂with high catalytic activity has been widely used in the fields of environment and energy,and is regarded as an ideal substrate material.At present,photocatalytic NO reduction to NH₃has the problem of poor catalytic activity and selectivity due to the lack of efficient reactive sites.Related studies have shown that transition metals can effectively adsorb and activate NO,which is expected to become an efficient active site for NO reduction to NH₃.In view of this,based on TiO₂semiconductor photocatalyst,this paper uses different methods to construct transition metal Co and Cu as reaction active sites on TiO₂catalyst to prepare efficient semiconductor materials for photocatalytic NO reduction to NH₃,and further explores the reaction mechanism of different catalytic active sites for NO reduction to NH₃.The specific research contents of this paper are as follows:1.Firstly,oxygen vacancies（OVs）were introduced by Na BH₄reduction method,and then Co single atom（SA）was synthesized by photoreduction method to prepare Co SA-loaded OVs-rich TiO₂catalyst（TiO₂-OVs-Co）.The asymmetric diatomic sites formed by Co SA and adjacent OVs are constructed.The morphology and structure of the materials and the fine structure of the diatomic sites were investigated by spectroscopy,spectroscopy and imaging techniques.The photocatalytic NO reduction performance test showed that the TiO₂-OVs-Co material exhibited stable and efficient NH₃production activity in the methanol aqueous solution system,and the amount of NH₃produced by photocatalytic NO reduction was 206.9μmol·g^-1within 4 hours.In addition,ruthenium dioxide（RuO₂）was loaded on TiO₂-OVs-Co by photo-deposition as an oxidizing cocatalyst to prepare TiO₂-OVs-Co-RuO₂catalyst to enhance the catalytic ability in pure water reaction system.A series of characterization and experimental results show that the asymmetric diatomic active sites have a unique adsorption model for NO and play a crucial role in the charge transfer process between the photocatalyst and NO,thereby efficiently reducing photocatalytic NO to NH₃.2.Through a simple in-situ photoreduction method,highly dispersed Cu sites were constructed by anchoring transition metal Cu with photogenerated oxygen defects on the crystal plane co-exposed TiO₂catalyst（TiO₂-Cu）.The morphology,structure and elemental composition of the catalyst were investigated by XRD,SEM,HRTEM,Raman and XPS.The photocatalytic NO reduction performance test shows that the TiO₂-Cu material prepared when the Cu introduction amount is 0.2 wt%and the Cu photoreduction time is 7 min exhibits the best NO reduction performance.In the aqueous solution system containing methanol,the amount of photocatalytic NO reduction to NH₃can reach 404.8μmol·g^-1within 4 hours,and the material has good catalytic stability.A series of in-situ experiments show that on the one hand,the dynamic valence state change of Cu sites makes TiO₂-Cu materials have excellent carrier separation and migration ability;on the other hand,the bimetallic sites formed by photogenerated Cu⁺and Ti³⁺can enhance the adsorption and activation ability of NO,so that the materials have excellent NO reduction to NH₃activity.