Controllable Preparation Of Perovskite Metal Oxide-based Photocatalyst And Their Performance And Mechanism

With the rapid development of the global economy,energy exhaustion and environmental pollution have become the key problems demanding prompt solution.It is urgent to establish an efficient,cheap,green and environmentally sustainable social system.Solar photocatalytic water splitting technology combines the advantages of solar energy and hydrogen energy,realizing the efficient conversion of solar energy into hydrogen energy with water as raw material,and building a real environment-friendly system.In the photocatalytic system,the photocatalyst is the core of the whole reaction and plays a decisive role in hydrogen production efficiency.Therefore,it is particularly important to explore an efficient,cheap and green photocatalyst.Among many photocatalytic materials,perovskite oxides have attracted wide attention due to their unique crystal structure,excellent photochemical properties and cheap availability.However,the photocatalytic activity of single perovskite oxides is limited due to the low photo-induced carrier separation efficiency and less exposure of effective active sites under photoexcitation.Therefore,this thesis focuses on the work of perovskite oxide-based composite photocatalyst:Controllable preparation of perovskite metal oxide heterojunction with different morphologies to improve the separation and migration efficiency of photogenerated carriers;A quantum dot regulated perovskite metal oxide composite photocatalyst was constructed to increase the exposure of effective active sites and improve the absorption and utilization of light;Defect-rich modified perovskite metal oxide composites optimize overall water splitting reaction configuration;The physical and chemical properties,photoelectrical properties,photocatalytic performance and mechanism of perovskite metal oxide composites were studied in depth through the above three regulation strategies.The main research contents of this thesis are shown as follows:1.Controllable preparation of perovskite metal oxide heterojunction with different morphologies and study on their photocatalytic properties and mechanisms（1）The Z-scheme Mo S₂/CaTiO₃ heterostructure is constructed by the morphology-controlled strategy,in which the Mo S₂ nanospheres tightly anchor on the surface of macroporous multishelled hollow CaTiO₃ cubes.The Z-scheme Mo S₂/CaTiO₃ heterostructure displays dramatically enhanced photocatalytic performance for generating hydrogen(622.14μmol·g^-1·h^-1)and degrading tetracycline（TC,70.6%,1h）in water compared to single Mo S₂ and CaTiO₃.The main reasons for enhancing photocatalytic performance are the Z-scheme electron transport mechanism and the strong interaction between the Mo S₂ nanosphere and the multishelled hollow CaTiO₃ cube.Furthermore,the photo-electrochemical analysis indicates that the Z-scheme Mo S₂/CaTiO₃ heterostructure has more efficient charge-carrier separation,a faster charge transfer and a longer photoproduced charge lifetime,as well as the greatly enhanced photocatalytic activities.（2）The novel multi-shelled hollow cube Bi₁₂O₁₇Cl₂/CaTiO₃ heterostructure has been successfully synthesized by a facile template-free method for photocatalytic hydrogen production and degradation pollutants in water under the visible light.The investigations of microstructure,physicochemical property and photoelectrical behaviors indicate that the multi-shelled hollow cube architecture and synergetic effect of 2D-3D structural coupling are dominant reasons to enhance phototcatalytic performance,which can significantly improve the absorption and utilization of visible light,multiply abundant active radical generation and boost the separation and migration efficiency of photoproduced electron-hole pairs.Under visible light irradiation,the photocatalytic hydrogen production rate of Bi₁₂O₁₇Cl₂/CaTiO₃-3%can reach783.61μmol·g^-1·h^-1,which is six times than that of pure CaTiO₃(131.01μmol·g^-1·h^-1).Notably,Bi₁₂O₁₇Cl₂/CaTiO₃-3%photocatalytic degradation of TC reached 90.7%in 30 min,which is much higher than the TC degradation capacity of CaTiO₃（8.2%,30 min）.Moreover,the probable photocatalytic reaction mechanisms,the feasible migration behaviors of photo-produced charges,the influence factors of enhancing photocatalytic activities are proposed in depth.2.Controllable preparation of active sites regulated perovskite-type metal oxide composites and study on their photocatalytic properties and mechanismThe Ni₂P quantum dots（QDs）are decorated in the multi-shelled CaTiO₃ cube for creating the abundance of inter-shelled channel active sites by hydrothermal method and high temperature calcination method,which greatly improve the photocatalytic performances for generating H₂relative to pure CaTiO₃ and Ni₂P.Moreover,the Z-scheme mechanism and the quantum effect of the Ni₂P in multi-shelled CaTiO₃ cube play a crucial role for enhancing photocatalytic performance.Furthermore,the photoelectric researches demonstrate that the Ni₂P/CaTiO₃heterostructure possesses more abundant active sites,smaller interface transmission resistance and faster photo-generated charge transfer efficiency.Therefore,the photocatalytic hydrogen production efficiency of Ni₂P/CaTiO₃-1%is 1260.21μmol·g^-1·h^-1,which is 4.90 times and 65.03times that of single-phase CaTiO₃(257.38μmol·g^-1·h^-1)and Ni₂P(19.38μmol·g^-1·h^-1),respectively.3.Preparation of defect-rich modified perovskite metal oxide composites and study on their photocatalytic properties and mechanisms for overall water splitting（1）The O-vacancy rich Ni Co-LDH atomic layers（denoted Vo-LDH）featuring an exposed（001）facet grow vertically on perovskite oxide cubes（e.g.,Al-CaTiO₃ and Al-Sr Ti O₃）have been prepared by hydrothermal methods combined with rapid nucleation,which can provide multi-accessible OER-sensitive active sites to boost the overall water splitting performance.As a result,the overall water splitting production rate on the Al-CaTiO₃/Vo-LDH（44%）catalyst(H₂:1.01mmol·g^-1·h^-1 and O₂:0.46 mmol·g^-1·h^-1)is 2.37 times higher than that of the pristine Al-CaTiO₃catalyst.Meanwhile,the overall water-splitting production rate on the Al-Sr Ti O₃/Vo-LDH（44%）catalyst(H₂:0.90 mmol·g^-1·h^-1 and O₂:0.37 mmol·g^-1·h^-1)is 2.08 times that of the pristine Al-Sr Ti O₃ catalyst.In-situ diffuse reflection infrared Fourier transform spectroscopy（DRIFTS）reveals that the O-vacancy rich Ni Co-LDH atomic layers can serve as the OER-sensitive active sites and varies with the O-vacancy concentration.The kinetic analysis further confirms that the O-vacancy induced water decomposition(1612 cm^-1)is the most dominant OER configuration on Ni Co-LDH atomic layers.Furthermore,density functional theory（DFT）indicates that O-vacancies on Ni Co-LDH atomic layers lower the energy barriers of OER steps.（2）The Al-CaTiO₃ photocatalyst with rectangular grooves was prepared by hydrogen-argon mixture reduction method.Under white light irradiation,the optimal Al-CaTiO₃-1h exhibited excellent overall water splitting performance(H₂:678.8μmol·g^-1·h^-1),which is 1.87 times that of the unoptimized Al-CaTiO₃(H₂:363.7μmol·g^-1·h^-1).The reasons for the formation of the groove were explored through the XRD,EPR and HRTEM.Furthermore,the reasons for improvement of the overall water splitting were analyzed by transient photocurrent,electrochemical impedance,solid ultraviolet diffuse reflection spectra and transient fluorescent life.