The Investigation Of Structure Regulation Of Bi-based Photocatalytic Materials And Reaction Mechanism Of Photocatalytic NO Removal

At present,the complicated air pollution and haze weather of urban environment in China are still serious and nitrogen oxide?NO?is the key to trigger them.The NO is a crucial precursor for the formation of PM_2.5 due to its unique properties of low concentration and high reactivity in the atmosphere.The photocatalysis technology is considered as one of the most promising green environmental technologies to control NO pollutant in the air,which can utilize sunlight at room temperature and normal pressure and react at mild condition.Bi-based photocatalysts exhibit good performance in NO removal due to the unique electronic structure.The?BiO?₂CO₃ with the advantages of low-cost and facile tuning is a hot material among various Bi-basesd photocatalytic materials.However,the wide band gap leads to low visible light utilization and low photocatalytic activity.Also,the reaction mechanism of photocatalytic NO removal has not been fully revealed.This greatly limited the photocatalytic applications of Bi based materials.The work proposed the non-metal doping,heterojunction design and defects construction to achieve the structural regulation of?BiO?₂CO₃ and increase the visible light responsive spectra.The combination of in-situ DRIFTS and simulation calculation were utilized to reveal the adsorption pattern and reaction mechanism of NO on the Bi-based photocatalyst surface at the molecular level,which prividede the theoretical basis for the enhancement of photocatalytic activity.On the basis on these results,the structural regulation and the enhancement of photocatalytic activity on Bi₂MoO₆ have been achieved.In response to these scientific issues,this paper systematically carried out the following researches.The N-doped?BiO?₂CO₃ hierarchical microspheres were synthesized by template-free hydrothermal treatment.The dynamic observation of time-dependent evolution of crystal structure,chemical composition and morphology revealed the growth mechanism of this novel structure.The growth of hierarchical microspheres undergoes several major processes including amorphous intermediates,Ostwald ripening,reaction-dissolution-recrystallization and layer splitting.The N atom in NH₄⁺is in-situ doped into the?BiO?₂CO₃ lattice during the formation of?BiO?₂CO₃ in the hydrothermal reaction,substituting the oxygen atom of the?BiO?₂ layer to form N-doped?BiO?₂CO₃.The combined experimental and theoretical methods uncover the microscopic mechanism of N doping to improve the visible-light photocatalytic activity of?BiO?₂CO₃.The doped nitrogen can improve the absorption of visible light of?BiO?₂CO₃ by reducing the band gap.The doped nitrogen could effectively promote the convergence of electrons from the surface BOC to nitrogen atom,boosting the separation and transformation of photogenerated charges.Moreover,the doped nitrogen optimizes the local electronic structure,improves the activation efficiency of catalysts on reactants?H₂O,O₂ and NO molecules?and promotes the generation of oxidative active radicals.The novel N-doped?BiO?₂CO₃ hierarchical microspheres as a photocatalyst exhibit excellent purification performance for the oxidation and removal of low concentration NO under the visible-light irradiation,and the purification efficiency is up to 41.5%.The present work could provide new understanding in the growth mechanism of 3D hierarchical structure.In comparison with N element,the F element has a higher electronegativity,which could enable more loclzied electrons.The F-doped?BiO?₂CO₃ hierarchical microsphere photocatalyst was prepared by one-step hydrothermal method.The micro-structure and electronic structure of F-doped?BiO?₂CO₃ were studied by combined experimental and theoretical method.The results showed that the doped fluorine could reduce the band gap of?BiO?₂CO₃,promote the visible light absorption and enhance the separation of photogenerated charges.The doped fluorine substitutes the oxygen atom of the?BiO?₂⁺layer,which changes the charge distribution of the catalyst surface and improves the activation of the reactants and the generation of oxidative active species.The NO removal efficiency of the optimized catalyst increases from 16.4%to 48.1%.The in-situ DRIFTS was used to investigate the adsorption and visible-light photocatalytic reaction processes of NO on the catalyst surface.The mechanism of NO conversion at the molecular level was proposed.The doped fluorine changes the reaction pathway of photocatalytic NO oxidation on?BiO?₂CO₃.Compared with?BiO?₂CO₃,the F-doped?BiO?₂CO₃ induced the generation of an intermediate NO⁺during photocatalytic reaction,which changed the reaction pathway of photocatalytic NO oxidation and improved NO removal efficiency.This study combines simulation calculation and in-situ DRIFTS to study the electronic structure of photocatalyst and the reaction mechanism of photocatalytic NO oxidation,providing a new method for investigate the gas-solid phase photocatalytic reaction system.To overcome the disadvantage of photosensitive BiOI,oxygen vacancies,Bi particles and Bi₂O₂CO₃ were co-induced into BiOI via a facile in situ assembly method at room temperature to form the Bi/BiOI/?BiO?₂CO₃ ternary heterojunctions.In the synthesized ternary Bi/BiOI/?BiO?₂CO₃,the oxygen vacancies,the dual heterojunctions?i.e.Bi/BiOI and BiOI/?BiO?₂CO₃?and the surface plasmon resonance effect of Bi particles all contributed to an extended light absotption,efficient electron-hole separation and increase in charge carrier concentration,thus boosting the overall visible light photocatalysis efficiency.The as-prepared catalysts were applied in removal of ppb-level NO in air in a continuous air flow under visible light illumination.The result indicated that the Bi/BiOI/?BiO?₂CO₃ exhibited a highly enhanced NO removal ratio of50.7%,much higher than that of the pristine BiOI?1.2%?.Density functional theory calculations and experimental results revealed that Bi/BiOI/?BiO?₂CO₃ composites can observably promote the production of reactive oxygen species for the photocatalytic NO oxidation.This work could provide a new strategy to modify narrow-band semiconductors and explore other bismuth-containing heterostructured visible-light-driven photocatalysts.In order to clarify the function mechchanism of oxygen vacancy in photocatalysis,we developed a facile method to introduce artificial oxygen vacancy into Bi₂MoO₆ with stable structure.The experimental and theoretical methods were combined to explore the effects of oxygen vacancy on the electronic structure,photocatalytic activity and the reaction mechanism toward NO removal.The results showed that the addition of NaBH₄ during catalyst preparation induced the formation of oxygen vacancy in Bi₂MoO₆,which played a significant role in extending the visible light absorption of Bi₂MoO₆.The visible light photocatalytic activity of Bi₂MoO₆ with oxygen vacancy was obviously enhanced with a NO removal ratio of 43.5%,in contrast to that of 25.0%with the pristine Bi₂MoO₆.This can be attributed to the oxygen vacancy that creates a defect energy level in the band gap of Bi₂MoO₆,thus facilitating the charge separation and transfer processes.Hence,more reactive radicals were generated and participated in the photocatalytic NO oxidation reaction.The in situ FT-IR was used to dynamically monitor the photocatalytic NO oxidation process.The reaction intermediates have been observed and the adsorption-reaction mechanism was proposed.It was found that the reaction mechanism was unchanged by introducing the oxygen vacancy in Bi₂MoO₆.This work could provide theoretical and technological basis for the structural regulation of Bi-based photocatalytic materials and the revealing of reaction mechanism of the visible light photocatalytic NO removal.