| Solar power has become a significant part of renewable energy resource while fossil fuel decreased.The solar power is mainly conversed by the plant photosynthesis process in nature.This process may take months or even millions of years to take part in the normal production and living.Since Fujishima report his research in Nature titled"Electrochemical photolysis of water at a semiconductor electrode" at 1970s,"photocatalysis" was first proposed by him and H2O was splitting into H2 and O2 by TiO2 photoelectrode.Hopefully photocatalytic technology will accelerate or partially skip the conversion process from solar to chemical energy.It has been applied in many fields like decomposition of water into hydrogen,degration of organic pollutants to purify the environment,photocatalytic synthesis of organic compounds to be used for industry.The essential key to apply the photocatalytic technology for solving problems of environment and energy is development of photocatalytic system with excellent performance.In this thesis,we start with design of several photocatalytic systems for organic compounds synthesis.The catalytic activity was optimized by varying the component,loading noble metal,construction the composite that aims to develop high-performance photocatalysts responded by visible light irradiation.This thesis makes further exploration about the catalytic performance,reaction mechanism and future applications.The research contents are as follows:(1)Short ordered NaxTaOy·nH2O catalyst that exhibited exceptional and highly efficient visible light photocatalytic reactivity toward aerobic oxidation was designed and prepared.SRWAXS and TEM results indicated that the as-synthesized catalyst showed short-ordered feature with well-controlled short-range ordering limits and defect chemistry.Short ordered structure of NaxTaOy·nH2O predicted large amounts of defective centers and high surface areas that may play critical roles in visible light harvesting and photocatalytic aerobic oxidation.This work may provide a novel strategy for the development of short ordered catalytic systems with well controlled defective chemistry that exhibit highly efficient photocatalytic properties.(2)Sn2Ta2O7@SnO2 composite was prepared via a hydrothermal approach.The formation process of the unique hollow structure and p-n heterostructure was investigated by XRD,TEM and SEM technology in detail.The visible light response is concluded to be the consequence of the impurity band formed by Sn2+ doped in Sn02 and Sn4+ in Sn2Ta2O7 via in-situ redox by analyzing the XPS and mossbauer spectrum.The existence of coupled Sn2+ and Sn4+ ions in p-n heterostructure is responsible for the absence of defeats and the regenerated catalytic activities.The findings reported here may provide an approach to fabricate the new types of photocatalysts with a synergetic promotion for visible-light-absorption as well as sustained photocatalytic activities by coupling different wide-band semiconductors.(3)Bi@ZnFe2O4 composite was ingeniously fabricated by homogeneously coating ZnFe2O4 nanoparticles onto the surface of metallic Bi spheres.The optimized Bi@ZnFe2O4 composite presented an exceptional high catalytic activity by thermal driving with a complete reduction of 4-NP ratio up to 98%within 25 min,far superior to bare ZnFe2O4 and metallic Bi.Importantly,the results exhibited a drastically accelerated visible light catalytic activity,finishing the same reduction within only 5 mins.Moreover,no significant activity loss was observed after reuse over 10 cycles,which demonstrates an excellent stability and reusability of current Bi@ZnFe2O4 catalyst.A probable mechanism is proposed based on the strong interfacial redox due to the close contact between ZnFe2O4 and Bi that the produced massive Bi3+ ions avail the maximum activities.Meanwhile,the Schottky barrier between ZnFe2O4 and Bi favors the efficient separation of the electron/hole pairs,promoting the positive photo-thermal synergetic effect.The shell design provides a great convenience for recycling and reusing the samples through the magnetically separation technology.This work also delivers the feasibility of utilizing economical Bi element as an alternative to noble metals to advance cost-effective,recyclable,and environment-friendly hydrogenation of the various nitroaromatics.(4)Artificial photocatalytic reduction of C02 into valuable fuels with high activity,selectivity and stability under renewable sunlight provides a package solution to handle the depletion of fossil fuels and increasing environmental issues.In response,we rationally established an all earth abundant photocatalytic system,where ZnFe2O4 acted as a visible light harvester and the post-transition metal Bi nanospheres served reactive sites and held the position of electron reservoir that triggered efficient and selective conversion of CO2 to CO with high stability.Benefiting from the combination of ZnFe2O4 and Bi,transient IR measurement indicated that rapid migration of photogenerated electrons was achieved from the conduction band of ZnFe2O4 to Bi.As a consequence,the efficiency of spatial charge separation was greatly improved with IPCE value of 34.6%(?400 nm),being larger than several spinel ferrite based heterojunctions.With well-defined chemical composition,surface structure,the CO evolution yield over Bi@ZnFe2O4 materials was optimized to be 40.2?mol·g-1·h-1 under visible light irradiation(??420 nm).Emphasis is focused on identifying the underlying mechanism by detecting the chemical variation of the catalysts.A novel conception of the photocatalytic reaction mechanism was proposed that Bi3+/Bi0 redox shuttle played dual roles in determining the photocatalytic activity and selectivity.(5)The metal-semiconductor type Schottky heterojunction in Pd/g-C3N4 system can continuously transfer photogenerated electrons to Pd nanoparticles and generate holes with oxidizability in g-C3N4 under visible light irradiation.The electrons and holes played different roles during the photocatalytic Suzuki coupling process.The electrons in Pd nanoparticles can cut off the X-C bonds(X=I,Br,Cl),and the holes can break the B-C bonds,respectively,which result in the activation of two kinds of reactants.The Pd/g-C3N4 in the coupling of iodobenezene and phenylboronic acid showed a high turnover frequency of 117 h-1 and a selectivity of nearly 99%under visible-light irradiation.It provides a green photocatalytic route for synthesizing biaryl compounds and an effectivity strategy for designing novel photocatalysts in a wide range of organic transformations driven by visible light.(6)The CsTaW06/Au photocatalyst was first synthesized by a photo-deposition technique,then coupled with g-C3N4 to the novel CsTaWO6/Au/g-C3N4.The CsTaW06/Au/g-C3N4 can enhance the light absorption efficiency and electron-hole pair separation efficiency,resulting in enhanced photocatalytic activity for photocatalytic generation of hydrogen.The Au particles between CsTaWO6 and g-C3N4 act as an important role in facilitating the transfer of interfacial electron in the composite.This study demonstrates a possible way for the fabrication of highly efficient ternary photocatalysts and facilitates their practical applications in hydrogen generation. |
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