Oxygen-deficient Bi₂MO₆?M=Mo,W? Materials:Design,Fabrication And Photocatalytic Properties

With the rapid development of the world economy,the energy shortage and environmental pollution are increasingly severe,which not only restricts the sustainable development of society,but also brings serious hidden troubles of food safety.As a typical advanced oxidation technology,semiconductor photocatalysis has been widely utilized in exploiting renewable energy and removing environmental pollutants,by virtue of its greenness and sustainability.Unfortunately,the low quantum efficiencies of photocatalysts significantly constrain its practical application.Among the various modification strategies,defect engineering,especially the introduction of oxygen vacancies?OVs?,has caught great attentions recently,since OVs can not only reform the photoelectric properties of oxide semiconductors,but serves as active sites for the enhanced adsorption and activation of substrate molecules.In this case,photocatalysts with OVs have become the research hotspots in the field of photocatalysis.Nevertheless,most researches mainly focus on the enhancement of photocatalytic activities,while three key issues remain to be discussed.First,the methods of introducing OVs are relatively deficient and poorly adjustable.Second,the single OVs introduction reveals limited improvement in photocatalytic performance,which requires to be combined with other modification methods.Third,serving as the active sites,the impacts of OVs on the activation and conversion of substrate molecules remain to be figured out.Bi₂MO₆?M=Mo,W?,the typical Aurivillius oxides,are provoking tremendous interest by virtue of their unique layered structures,appropriate band potentials and adjustable band structures.What's more,Bi₂MO₆ possess exceptional characteristic of facile OVs generation under O₂-deficient thermal conditions because of the low energy of surface Bi-O bonds.Hence,Bi₂MO₆?M=Mo,W?might be the ideal platform for carrying out the related researches.In view of the above backgrounds,this dissertation dedicates to integrate the advantages of OVs introduction and other modifications?construction of heterojunctions,deposition of noble metal,etc.?to enhance the performances of oxygen-deficient Bi₂MO₆,on the one hand,and,on the other,focuses on the the impacts of OVs on the conversion of substrate molecules;thereby providing theoretical and experimental basis for the design and fabrication of efficient photocatalysts with OVs.The detail research contents and conclusions are summarized as follows:1. Taking Bi₂Mo O₆as the research model,we successfully constructed oxygen-deficient Bi₂Mo O₆ with concentration-adjustable OVs,and checked the impacts of OVs on the photocatalytic performances.In detail,?001?facets exposed Bi₂Mo O₆ with concentration-adjustable OVs?BMO-OVs?was synthesized via a facial solvothermal approach.Under visible-light irradiation,BMO-OVs demonstrated superior activities in ciprofloxacin degradation and CO₂ photoconversion.Notably,the CO and CH₄ formation rates achieved 0.27 and 2.01?mol/g/h over BMO-OVs,corresponding to the highest CH₄selectivity of 96.7%,which is significantly superior to defect-free Bi₂Mo O₆?BMO?.DFT calculations and characterizations demonstrated that well-designed OVs can not only enhance the photoelectric properties of Bi₂Mo O₆,but also act as the natural active site for the CO₂adsorption in a possible special bidentate carbonate mode,which thermodynamically supports the further generation of target CH₄.2. Aiming to solve the problems of lack of active sites and low carrier separation efficiency of pristine Bi₂Mo O₆,we integrated the advantages of OVs and heterojunctions by constructing the regularly shaped bismuth molybdate heterojunction with OVs.Specifically,a mixed solvothermal system of oleylamine and water was designed,and utilized to fabricate 0D/1D Bi_3.64Mo_0.36O_6.55/Bi₂Mo O₆ heterojunction for the first time.According to the verified crystal growth mechanism of Bi_xMo_yO_z,we successfully constructed oxygen-deficient Bi_3.64Mo_0.36O_6.55/Bi₂Mo O₆heterojunction?BMO-12-H?by hydrogenation.Under visible-light irradiation,BMO-12-H revealed fascinating acivity in the photocatalytic removal of environmental pollutants?NO and ciprofloxacin?,which attributes to the synergistic effects of OVs and heterojunctions according to the DFT calculations and characterizations.In detail,the former afford sufficient active sites,and the latter ensures the efficient separation and transport of carriers.3. Taking Bi₂WO₆as the research model,we developed a mild and controllable strategy for constructing atomically-thin 2D materials with OVs,and figured out the impacts of OVs and atomically-thin strucure on the photocatalytic performances.In detail,we successfully fabricated oxygen-deficient Bi₂WO₆ atomic layers via a facile solvothermal strategy with the assistance of chloridion.Theoretical calculations and speciation determination implied chloridion would be electrostatically adsorbed onto the surface of[Bi₂O₂]²⁺layers and played an indispensable role in the controllable synthesis of Bi₂WO₆:suppressing the stacking of the Bi₂WO₆ layers and facilitating the formation of oxygen vacancies simultaneously.As anticipated,this oxygen-deficient ultrathin Bi₂WO₆displayed intriguing photocatalytic performances in visible-light-powered ciprofloxacin degradation and deep oxidation?98%?of NO to NO₃^-.Baesd on the DFT calculations and systematic characterizations,the origins of fantastic performances in NO oxidation was figured out.In detail,the ultrahigh activity originates from the improved photoelectric properties,while the intriguing selectivity could be ascribed to the strengthened·O₂^-generation ability,which thermodynamically faciliates the oxidation of NO to NO₃^-.4. Aiming to solve the problems of lack of active sites and poor light harvesting of pristine Bi₂WO₆,we integrated the advantages of OVs and Au-NPs by constructing the oxygen-deficient Bi₂WO₆ with loaded Au-NPs?Au-BWO-OVs?.Specifically,a chloridion-assisted ethylene glycol post-treatment strategy was proposed according to the effects of chloridion on the OVs formation over Bi₂WO₆,and utilized to introduce OVs and Au-NPs onto Bi₂WO₆ at the same time.Under visible-light irradiation,the as-prepared Au-BWO-OVs revealed fascinating photocatalytic performances in ciprofloxacin degradation and selective oxidation?>99%?of benzyl alcohol to benzaldehyde,which attributes to the synergistic effects of OVs and Au-NPs on the basis of DFT calculations and systematic characterizations.In detail,the ultrahigh activity derives mainly from the improved photoelectric properties,while the intriguing selectivity originates from the appropriate band positions and enhanced O₂ activation ability.