Construction Of Plasmon Bi Metal Based Composites Photocatalyst And The Reaction Mechanism For NO_x Purification

The indoor air quality has surged increasing world wild attention.Even quite low concentrations of NOx can cause damage of lung,heart and liver even increase the risk of cancer,severely affecting human health.In recent years,photocatalysis as a green technology arises a lot attention to purify low-concentration NOx.Thus,in this paper,we are aiming at exploring a kind of non-noble Bi metal based composites photocatalysts with more economic benefits and development prospects.We first constructed a Bi/graphene oxide system?Bi-NPs@GO?to study the mechanism of Bi metal as a direct photocatalyst with surface plasmon resonance effect.GO,as a carrier,will promote photocatalytic activity and chemical stability of catalyst.Next,Bi/amorphous bismuth oxide system?Bi-BiO?was constructed.The photocatalytic activity of amorphous semiconductors was successfully activated by the surface plasmon effect of Bi metal.The function of Bi metal was systematically analyzed.In the end,density functional theory?DFT?calculations were combined to design Bi/Bi₂O₂SiO₃ photocatalyst system?Bi@BiOSi?.Through detailed study of this model catalyst system,a universal photocatalytic reaction mechanism of Bi/bismuth-based semiconductors was established.In all three system studies,the in situ FT-IR analysis method was used to reveal the chemical behavior over catalyst surface during the whole photocatalysis process.The key steps and reaction mechanism of NO photocatalytic oxidation were then proposed.The results are as follow:Bi-NPs@GO photocatalysts:Bi-NPs with uniform size were successfully prepared by using surfactant PVP.The as prepared Bi-NPs was loaded onto GO to get Bi-NPs@GO photocatalysts.The repeated washing procedure with hydrazine hydrate ethanol solution ensures the removal of surface PVP,which guarantee the direct contact between catalyst and contaminants.The as prepared Bi-NPs@GO samples exhibited excellent photocatalytic properties during the NO removal.Through Finite-Difference Time-Domain?FDTD?simulation,it is proved that Bi metal could excite a localized electromagnetic field under the UV light irridiation.Combined with DFT calculation,the hot electrons generating via surface plasmon effect would pass through grapheme carbon layer to the carboxyl group at the edge in GO,thereby promoting the carrier separation greatly.Further,in-situ FT-IR analysis shows that the carboxyl group at the GO edge is the active site for both adsorption and reaction during NO photocatalytic removal.Bi-Bi O photocatalysts:The visible light photocatalytic activity of amorphous bismuth oxide was successfully activated by in-situ partial reduction of Bi metal.The as prepared samples showed enhanced photocatalytic activity in gaseous pollutants NO removal.In this system,the surface plasma effect of Bi metal enhanced the visible light absorption ability remarkably.At the same time,the introduction of Bi metal greatly accelerated the separation of photogenerated electrons and holes,then overcoming the disadvantages of amorphous semiconductor.In-situ reduction of Bi metal introduces a certain amount of oxygen vacancies?OVs?simultaneously,which effectively adjusts the band structure of the catalyst,thereby producing increased photogenerated electron to reacted with surface O₂ to generate·O₂^-.Then,the in situ FT-IR technology was used to monitor the whole adsorption and reaction process of NO photo oxidation.The intermediates and final products during the whole process of photocatalytic oxidation of NO were recorded.Then,the gradual oxidation process of NO pathway was obtained.Bi@BiOSi photocatalysts:we firstly designed Bi@Bi₂O₂SiO₃?Bi@BiOSi?structure by utilizing DFT calculations to get the optimized electronic structure then predicting the mechanism of charge transfer at the interface.Based on DFT insights,Bi@BiOSi composites were fabricated via a facile chemical reduction method and used for the removal of ppb-level NO in a continuous air flow reactor under visible light illumination.NO₂^-and NO₃^-are detected to be the final products.The surface plasmon resonance property of Bi metal enhanced the visible light capture and charge separation efficiencies effectively.Moreover,oxygen vacancies?OVs?are introduced simultaneously with the deposition of Bi metal.OVs generation induced the formation of an intermediate gap and promoted O₂ activation.Consequently,the production of active radicals on Bi@BiOSi was significantly enhanced,leading to much more efficient photocatalytic NO removal under visible light irradiation.Most importantly,the adsorption and photocatalytic oxidation of NO on Bi@BiOSi were investigated by in situ FT-IR,which revealed that the combined effect of Bi metal as well as OVs inhibited the generation of toxic intermediates?N₂O₄?and increased the selectivity of the NO-to-NO₃^–conversion largely.This work not only provides new insights for the design of non-noble metal Bi-based composites photocatalysts but also establishes an analytical model combining in situ FT-IR and DFT theoretical calculations to systematic studies on the photocatalytic oxidation of NO.This paper also provides a theoretical and technological foundation for the practical application of photocatalytic technology.