Construction Of All-Solid-State Z-Scheme Catalysis Systems And Its Investigation On Energy And Environmental Purification

The gradual energy exhaustion and environment deterioration have seriously affected the long-term stable development of human society.However,solar energy is a new renewable and clean energy that we can use.Therefore,it is a challenge for us to find suitable catalytic materials and make efficient use of solar energy to quickly solve the problem of environmental pollution and energy shortage.Silver and bismuth based semiconductor materials play important roles in photocatalytic water splitting,photocatalytic degradation of volatile organic pollutants and catalytic hydrogenation reduction.In this thesis,Ag₂Ta₄O₁₁ and Bi₂MoO₆ were used as the base material to develop the catalyst with excellent catalytic performance and good stability.And through a series of modification methods,such as,precious metal loading,semiconductor compound,synthesis methods improvement and band structure regulation,semiconductor composite heterojunction materials which can be used for efficient and stable solar water splitting and environmental purification is designed and constructed.The research content is as follows:?1?The Z-scheme catalytic system Bi₂MoO₆/Ru/g-C₃N₄ was prepared by gentle hydrothermal method,which could high-efficiently oxidize water into O₂.The optimal oxygen production efficiency reached highly to 328.34?mol?g^-1?h^-1 under visible light irradiation.Moreover,the catalyst presented excellent stability and the catalytic activity remained at 91.4%after seven recycling tests.The metal Ru in the Z-type catalytic system provides a powerful bridge for the effective transfer of interface electrons,thus changing the migration mode of photogenerated electrons and forming a fast electron migration route:Bi₂MoO₆?Ru?g-C₃N₄?NaIO₃.Since a large number of electrons are transferred,the holes with high oxidation ability are continuously enriched in the valence band of Bi₂MoO₆,thereby effectively promoting the progress of the multi-electron participating water oxidation half reaction.This not only facilitates the effective separation of photogenerated carriers,but also maintains the higher redox capacity of the composites.Therefore,in the Bi₂MoO₆/Ru/g-C₃N₄composite photocatalytic system,Ru,as an electronic transport intermediate,plays a crucial role in synergistically improving the utilization rate of sunlight,enhancing photoelectric conversion capacity,and promoting the photohydrolysis water oxidation capacity.?2?A wide spectral response heterojunction photocatalyst Ag₂Ta₄O₁₁/Ag/g-C₃N₄was successfully constructed by in situ assembling progress.The catalyst has largely improved the separation efficiency of carriers and broadened the response range of sunlight,and so make the activity of photohydrolysis of water for hydrogen production is more active.The optimal H₂ production reached up to 100.47?mol?g^-1?h^-1 under visible light??>420 nm?and 253.03?mol?g^-1?h^-1 under simulated solar light.After five cycles,the catalytic activity remained 98%and the original structure remained almost unchanged.The Ag particles produced by in situ reduction from Ag₂Ta₄O₁₁ play an important role as surface plasmon resonance electron excitation center and photogenic electron transport bridge.The electrons migrate in a z-scheme way,which not only improves the separation efficiency of photogenic carriers,but also maintains the original high redox activity of the catalyst.The research offers a new idea for constructing Z-scheme photocatalysts under wide-spectrum light irradiation.?3?A novel tri-phase catalyst Ag₂Ta₄O₁₁/Ag@CeO₂ with core-shell structure was successfully assembled via an in-situ catalytic reduction process toward p-nitrophenol?4-NP?reduction.After the circular reduction reaction,the Ag nanoparticles were produced from Ag₂Ta₄O₁₁ and homogeneously deposited on the surface of Ag₂Ta₄O₁₁,which were wrapped by octahedron-shaped CeO₂.Therefore,the three-phase core-shell structure Ag₂Ta₄O₁₁/Ag@CeO₂ catalyst can reduce p-nitrophenol into p-aminophenol more efficiently and specifically.Moreover,the stability was more outstanding,which was evaluated by 15 rounds cyclic experiments.This is attributed to the importance of the core-shell structure of Ag₂Ta₄O₁₁/Ag@CeO₂ catalyst,in which the effective connection between interfaces promotes the rapid and effective transfer of electrons,and the use of CeO₂ shell to fix Ag nanoparticles between the interfaces of CeO₂ and Ag₂Ta₄O₁₁ prevents Ag nanoparticles from falling off and agglomerating,thus improving the catalytic performance and cycling stability of the catalyst.?4?Similarly,the advantages of in situ reduction method were adopted.In the process of reduction of p-nitrophenol,Bi nanoparticles were successfully reduced from Bi₂MoO₆ and uniformly distributed on the surface of the leaves of Bi₂MoO₆flower-like spheres and coated by Cu₂O simultaneously,forming a Cu₂O/Bi/Bi₂MoO₆catalytic system.The multiphase samples achieved highly effective catalytic activity(10053.6 min^-1?g^-1)for the conversion of the high toxic 4-NP to less toxic aminobenzene,compared to the original Cu₂O and Bi₂MoO₆ nanoparticles.Moreover,the excellent reusable stability was confirmed by executing the successive recycling experiments.It was supposed the Bi³⁺/Bi⁰ pairs were the key active species which realizes the rapid redox conversion between Bi³⁺/Bi⁰ and Cu⁺/Cu²⁺at the Cu₂O/Bi/Bi₂MoO₆ interface with the assistance of Cu₂O.As a result,the active site Bi³⁺/Bi⁰ constantly produces and maintains a certain balance,so as to maintain the fresh active species and contribute to the catalytic reduction reaction of p-nitrophenol.Therefore,the design of the catalytic material provides a new idea for the construction of efficient and stable catalysts.?5?By assembling Ag₂Ta₄O₁₁,Ag-Ag⁺shuttle as electron mediator,and the cationvacancy-richAg₈(Nb_0.5Ta_0.5)₂₆O₆₉,AfullsolidZ-scheme Ag₂Ta₄O₁₁/?Ag-Ag⁺?/Ag₈(Nb_0.5Ta_0.5)₂₆O₆₉ heterojunction was prepared,which is used to degrade gaseous HCHO under indoor temperature,humidity,and sunlight irradiation.The activity estimation presented that this sample could converse HCHO of 200 ppm into CO₂ and H₂O completely.Its long-term utility was confirmed with an unchanged activity after six recycling tests under sunlight illumination.Meanwhile,enviornmental factor's estimation confirmed its superior CO₂ selectivity and humidity resistance.The excellent properties are assigned to the formation of a large number of cationic holes and Ag defects in the catalytic system,which produced by the in situ reduction of Ag-Ag⁺redox shuttle and the doping of Nb.This helps to make full use of solar energy,rapidly separate photogenic electrons and holes,and prevent Ag nanoparticles from falling off and aggregating,thus improving their photocatalytic activity.Consequently,the sample is expected to be used in practical applications to effectively degrade indoor HCHO.?6?Bi₂MoO₆/Bi/g-C₃N₄,a ternary catalyst,was masterly constructed by an in situ catalytic reduction reaction.The in-situ reduced Bi nanoparticles were distributed on the surface of Bi₂MoO₆ petal nanosheets and the surface of g-C₃N₄ and their interface as an electron transport medium.It could degrade efficiently and stably gaseous HCHO with high concentrations?400-1600 ppm?in a simulated indoor environment under visible light.After six cycles,the catalytic activity remained unchanged,and the sample had superior CO₂ selectivity?99.79%?and excellent humidity resistance.As a solid-state electron transfer medium,Bi nanoparticles not only improve the utilization of visible light,but also rapidly transfer interface electrons,which enables space separation of photogenerated electrons and holes,thus greatly improves carriers separation efficiency and maintains the original strong oxidation.In addition,theoretical simulation calculation proves that g-C₃N₄ has excellent adsorption of formaldehyde and drainage,which is also helpful to improve the photocatalytic activity and enhance its moisture resistance.This work is expected to be popularized in the practical applications of high concentration HCHO removal.