Structure Optimization Of Bi-based Nanocatalyst And The Photocatalytic Mechanism Study

Due to the advantages of mild reaction conditions and direct conversion of solar energy into chemical energy,semiconductor photocatalysis technology has shown great promising potential in solving energy shortage and environmental pollution problems,and the development of efficient and stable photocatalysts has become one of the research hotspots in recent years.However,the low solar energy utilization rate,low photocatalytic reaction efficiency and unclear photocatalytic reaction mechanism still restrict the practical application of this technology.Therefore,to develop highly efficient and stable semiconductor photocatalytic materials and reveal the key scientific problems in the photocatalytic reaction process,in this work,we have synthesized a series of Bi-based photocatalytic materials,including bismuth tungstate,bismuth molybdate and bismuth oxyhalides,and investigated the photocatalytic prefermonce of NO removal.And we have enhaced the photocatalytic activity by boosting the utilization ratio of solar energy,enhancing separation ratio of carriers and improving the photocatalytic reaction process.Via using ethylene glycol assistanted solvothermal and the calcination process,we have successfully constructed the Bi₂WO₆(BWO)with gradient oxygen vacancies,carbonate doped defective Bi₂WO₆(CO₃-BWO-VO),carbonate doped Bi₂MoO₆(CO₃-BMO)and Bi₂Mo₃O₁₂@Bi₂O₂CO₃ heterojunction(BMO@BOC),and a series of Bi OCl_xBr_1-x(0?x?1)photocatalysts.A variety of characterization techniques were used to investugate the crystal structure,morphology,chemical composition and optical properties.Photocatalytic NO removal efficiency was used to evaluate the photocatalytic activity of Bi-based samples,and exploring the relationship between catalyst structure and light absorption,the carrier separation and migration,and the photocatalytic performance promotion.Meanwhile,the photocatalytic reaction process of NO oxidation was deeply investigated by combining with in situ characterization methods and density functional theory(DFT)calculations.The main research contents of this work are as follows:(1)Defects engineering of Bi₂WO₆ photocatalyst for enhancing photocatalytic performance.We successfully synthesized the Bi₂WO₆(BWO)with gradient concentration of oxygen vacancies and exhibited the excellent photocatalytic NO oxidation activity.And the oxygen vacancy introduced in photocatalyst is a popular method to enhance the photocatalytic performance.The formation of oxygen vacancy defects in BWO is responsible for the tuning band structure and modifying surface chemical state to improve carrier's separation efficiency,enlarge visible light absorption range and facilitate reactant activation,which is unambiguously verified by the UV-vis DRS,XPS,EPR and DFT calculations.Moreover,the role of surface oxygen vacancy defects and reaction mechanism of photocatalytic NO oxidation were discussed in detail by combing the in situ DRIFT and theoretical calculations.This work could be broadly used to the design and synthesize highly efficient photocatalysts and pave a way to understand the reaction mechanism of NO oxidization.On the basis of the above work,we design and favorably fabricate the carbonate intercalated Bi₂WO₆ with oxygen vacancies via employing a mild hydrothermal method with ethylene glycol assist.The prepared catalysts exhibit an excellent photocatalytic NO oxidation activity under visible light irradiation,attributing to the inserted carbonate coupled with oxygen vacancies.Additionally,the promotion mechanism and reaction pathway of photocatalytic NO removal are carefully discussed by experimental detection assisted with density functional theory(DFT)calculation.Our results explicitly reveal that the carbonate coupled with oxygen vacancies can remarkably retard the recombination of electro-hole pairs,and improve the carriers transforming to activity species.The reactants would be easily activated and converted over the carbonate-intercalated defective Bi₂WO₆ surface,such as the H₂O provided electrons to form·OH and O₂ accepted electrons to generate·O₂^-,which are certified by utilizing DFT simulation to calculate adsorption of reactants on the surface.In addition,the in situ DRIFTS spectra was used to dynamic analyze the photocatalytic NO oxidation process and reveal the promotion mechanism.Finally,the synthesis strategy and mechanism analysis would possess guiding significance for improving photocatalytic efficiency and applications.(2)Structure regulation and increasing photocatalytic activity of bismuth molybdate catalyst.We have favorably fabricated the carbonate doped Bi₂MoO₆ via a facile one-pot solvothermal method,which was verified by structure and constituent characterization analysis.In addition,the NO removal efficiency of carbonate-intercalated Bi₂MoO₆ is?34%,far-exceeding that of the pure Bi₂MoO₆,whilst exhibits a good stability and durability,owing to that the dopants could modulate the electron states of the Bi₂MoO₆,thus stimulating charge separation and migration,incenting transformation of reactive oxygen species and facilitating reactants activation,which are synthetically investigated by experimental characterization coupled with DFT calculation.Significantly,the in situ DRIFTS measurement was employed to dynamic monitor the NO oxidation process and clarify the photocatalytic mechanism under visible light irradiation.This work provides an efficient strategy to design photocatalysts with tunable motivating charge conversion and reactants activation towards NO photooxidation.In addition,charge separation and transformation are one of key factors for high-efficiency photocatalysis.As well,the photocatalytic reaction mechanism possesses a guide-line for development of high-efficiency photocatalysts and its commercialization.Herein,we designed and favorably synthesized the BMO@BOC heterojunctions by a facile solvothermal route and following the heat treatment for high-efficiency photocatalytic NO removal activity.More importantly,both continuous stream method and intermittent stream method performed on in situ DRIFTS were applied to intuitively and dynamically investigate the adsorption process and oxidation process of NO removal over the photocatalysts surface.The intermediate products(NO^-,NO₂^-and NO₂)can be explicitly detected in both adsorption process and oxidation process,whilst the final products(NO₃^-)appeared in oxidation process,which can be ascribed to the separation,migration and conversion of photoinduced electron-hole pairs.(3)Regulating the interlayer halogen anions of bismuth oxyhalides for boosting photocatalytic performance.We have favorably synthesized the bismuth oxyhalides(Bi OCl_xBr_1-x,0?X?1)photocatalysts by utilizing the ethylene glycol assisted solvothermal method and the calcination procedure for photocatalytic nitric oxide oxidation.By regulating the halogen proportion in anions layer,the lattice strain has been induced in the structure of bismuth oxyhalides,specifically the tensile strain in c axis.By virtue of in situ DRIFTS and DFT calculation,we found that the optimized surface reaction thermodynamic process should be the main factors response for prominent enhanced photocatalytic activity,rather than the light absorption and charge conversions.The Bi OCl_xBr_1-x-3:1 catalyst possess the lowest thermodynamic energy barrier for photocatalytic nitric oxide oxidation reaction,whilst both associative and dissociative reaction process exist in the initial elementary reaction about oxygen reduction.Finally,we develop a feasible strategy to depress thermodynamic energy barriers via tuning the ratio of halogen in anions layer and bringing the lattice strain,as well build relationship between the adjusted structures and surface reaction process.