Construction And Characterization Of Multinary Spinels-Structured Materials And Their Photo-induced Catalytic Properties

The world is currently facing severe challenges of environmental pollution and energy crisis,photoelectrochemical conversion and photo-induced green catalysis technology can effectively convert solar energy into electrical energy and chemical energy respectively,which has broad application prospects in the environment and energy fields based on their efficient pollutant removal and energy recycling with no secondary pollution and environmental friendly advantages.However,the defects of low quantum efficiency,narrow light absorption range,and low visible light utilization rate of semiconductor photoelectrochemistry and photocatalysis technology hinders the technological practical applications.From a technology future development point of view,to further improve the harvesting of solar-light energy and conversion efficiency as well as deeply understanding the detail mechanisms of photo-electricity conversion and catalytic transformation or elimination process tend to be the important scientific issues and research hot spots in this field.With the aim of addressing the above key scientific issues,this study has developed a series of novelty multinary spine 1-structured based photo-electric functional materials.By referring to the crystal structure,electronic structure and micro-structure perspective,various spinels photo-electric functional materials with different structures have been rational molecularly designed,and the joint technology derived tandem systems including photoelectrocatalysis,photocatalysis and Fenton-like coupling systems have also been shaped in terms of facilitating the efficiency of photo-induced interfacial charge transfer and catalytic process.With the support of a variety of modern physical-chemical characterization methods and theoretical calculations,the structural features,surface physicochemical characteristics,photo-induced spatial separation and interfacial migration as well as redox process mechanism,catalytic performance and the synergetic effect of coupling system have been accordingly investigated and interpreted.The intrinsic correlation between the structural features,photoelectrochemical and photocatalytic performance of spinel-structured functional materials were systematically revealed.The specific research outcomes are summarized as follows:(1)Highly oriented and vertically-aligned stoichiometric copper and zinc based ferrites i.e.,Cu₀.5Zn₀.5Fe₂O₄ quantum dots anchored onto titania nanotube array electrodes composites(Cu₀.5Zn₀.5Fe₂O₄QDs/TiO₂ NAEs)with n-n heterojunctions have been successfully fabricated and prepared via electrochemical anodization and molecular surface chemical modification strategies.It has been deduced that the photo-electrochemical conversion efficiency of Cu₀.5Zn₀.5Fe₂O₄QDs/TiO₂ NAEs nanocomposites is approximately 4 times higher than that of TiO₂ NAEs alone,which is primarily due to the promoted spatial separation and interfacial migration of the photo-induced charges in terms of the crystal structure of spinel,the surface-interface structure properties and the n-n heterojunctions which finally enabling the effective harvesting and conversion of solar energy.Cu₀.5Zn₀.5Fe₂O₄QDs/TiO₂ NAEs nanocomposites possess obvious ultrafast charge transfer process within 10^-6?10^-7 s,and the lifetime of photo-generated charges could be relaxed to 72.23 ?s.The specific features of the dedicate spinel crystal structure,n-n nano-heterojunction electronic structure and the interfacial microstructure of the nanocomposites play an vital role in promoting the spatial separations of photo-generated charges and surface interface transportations.Under the optimum reaction conditions,Cu₀.5Zn₀.5Fe₂O₄QDs/TiO₂ NAEs nanocomposites showed excellent capability towards photoelectrocatalytic(PEC)degradation of antibiotics sulfamethoxazole and methylene blue.Various in-situ spectroscopy characterization methods including in-situ electron paramagnetic resonance(EPR),transient absorption spectroscopy(TAS)and other spectroscopic studies quantitatively demonstrated that more ·O2-species as derived from molecular uptaking played a predominant role in the PEC oxidations of SMX and MB species.Moreover,HPLC-MS-MS investigations in combination with the research outcomes of the catalytic reactions have been jointly used to gain further insight into the degradation mechanism of MB species.Overall,it has been demonstrated that Cu₀.5Zn₀.5Fe₂O₄QDs/TiO₂ NAEs nanocomposites exhibited outstanding performance in terms of both photoelectrochemical conversion and photoelectrocatalytic reactions,which is primarily due to the specific structure features of the dedicate spinel crystal structure,the interfacial microstructure and the electronic structure of the n-n heterojunction which could accordingly promote the spatial separation and interfacial migration of the photo-induced charge carriers,thereby favoring the effective harvesting and conversion of light especially visible light energy.(2)Based on the multi-technology coupling technology and element doping perspective,Cu_xZn_1-xFe₂O₄(0?x?1)hierarchical yolk-shell hollow nano-microspheres(HYSHNMs)have been accordingly prepared via solvothermal process followed by successfully construction of combined Cu_xZn_1-xFe₂O₄(0?x?1)/PMS/Vis(ZCF/PMS/Vis)photocatalytic Fenton-like tandem systems.Specifically,as evidenced from various spectroscopic characterizations,the physicochemical characteristics of Cu_xZn_1-xFe₂O₄(0?x?1)HYSHNMs were systematically investigated in terms of the correlations between the structure and the derived properties followed by revealing the synergetic mechanism of the photo-induced PMS activation and photocatalysis mutual coupling system.Interestingly,Cu_xZn_1-xFe₂O₄(0?x?1)HYSHNMs spinel-structured material has rich electronic structure characteristics.In the Cu₀.5Zn₀.5Fe₂O₄ structure,it could be seen that the VBM primarily consisted of hybrid orbitals of Zn 2p,Fe 3d,Cu 3d,and O 2p,and Fe 3d mainly contributed to the deeper CBM.Under visible light excitations,the photo-excited electrons in the valence band of Cu₀.5Zn₀.5Fe₂O₄ structure could migrate form the Zn 2p,Fe 3d,Cu 3d and O 2p orbitals to the Fe 3d orbitals in the conduction band,forming more electro-hole Pairs and charge density.Compared with Cu_xZn_1-xFe₂O₄(x=1.0 and x=0.0),Cu_xZn_1-xFe₂O₄(x=0.5)HYSHNMs has a wider visible light response range,the average lifetime of photogenerated carriers is up to 14.5 ?s,and owned better surface-interface charge separation and migration behaviours,more surface oxygen vacancies,higher solar energy utilization and conversions as well as effective PMS activation and marvelous photocatalytic performance.It has been noticed that the catalytic removal rate of the antibiotic enrofloxacin(ENR)over Cu_xZn_1-xFe₂O₄(x=0.5)HYSHNMs with magnetic recycle capability reached 90.5%,which is 3.6 times and 2.5 times higher that single photocatalytic system and PMS catalytic activation system,respectively.The coupling system could efficiently activate molecular oxygen and generate ROS active free radicals followed by favoring the tailoring of the photo-induced electron-hole generations,spatial separations and interfacial transfer process.Hence,the site occupation metal ions in the Cu_xZn_1-xFe₂O₄ spinel structure and the photo-generated charges carriers could activate molecular oxygen and permonosulphate synergistically followed by generation ROS active species including ·OH active species and SO4·-sulfate radicals respectively,and the photo-generated charges derived from photocatalytic process could also favor PMS activation to produce SO4·-species.Both of the sulfate radicals SO4·-and ·OH hydroxyl radicals could jointly serve as the active species for the highly efficient catalytic oxidation of ENR pollutants.(3)A serials of Copper Zinc Ferrites multinary spinel hierarchical hollow nano-microspheres with different internal structures,e.g.,solid nano-microspheres,yolk-shell hollow nano-microspheres and double shelled hollow nano-microspheres have been successfully developed by a facile solvothermal wet chemical strategy followed by exploration their properties of photocatalytic oxidations and reductions towards future carbon capture and environmental rehabilitation.Various on-line physical characterizations have been employed to probe and identify their physicochemical characteristics,and specifically,the affects of sub sequential thermal annealing treatments on the formation hierarchical intrinsic structure have been accordingly investigated followed by revealing the correlations between the interfacial structure and catalytic performance.The research outcomes indicated that whilst the heating rate approaches 20?min^-1,double-shell hollow nano-microsphere(DSHMs)structure would be preferably formed,which would incur pretty higher catalytic behaviour over copper zinc ferrite multiple spinel-structured materials with the dedicate DSHMs,and it has been found that copper zinc ferrite nanocomposites DSHMs has higher catalytic activity with a dedicate 8.8 and 38 ?mol for H2 and CO formations.For the degradation of SMX species,the multinary spinel nano-microsphere structure materials with various internal structures exhibit different catalytic performance,and the catalytic efficiency of antibiotics degradation is 80.4%(double-shell hollow sphere structure),66.7%(solid sphere structure)and 73%(yolk shell nanosphere structure),respectively.For multinary spinel semiconductors with different intrinsic structures,it has been demonstrated that there are strong interactions between Fe and O atoms,Cu and O atoms,Zn and O atoms within the electronic structures of spinels,which could inevitably promote the interfacial electron transfers.The average lifetime of the carriers is 16.61 ?s for DSHMs,while the average lifetime of the carriers for YSMs and SMs is only 11.97 and 0.28 ?s,respectively.Hence,Cu-Zn-Fe multiple spinels DSHMs posses excellent characteristics towards ultrafast photo-induced spatial charge separations and interfacial transfers,and the sebsequential photo-generated charge carrers could activate the pre-adsorbed molecular oxygen followed by forming ROS species including superoxide radical ·O2-.Obviously,it is shown that the physicochemical characteristics and catalytic behaviors of the multinary spinels could be tuned by tailoring the crystal structure,interfacial microstructure and electronic structures.(4)By tuning the occupation element of A-sites within AB2O4 spinels structures,bunch of Co-based spinel A_1-?Co_?(A_?Co_2-?)O₄(A=Zn,Ni,and Cu)nanocomposites with diverse hierarchical nano-microspheres were rational designed and synthesized using a facile self-templated solvothermal strategy,and the intrinsic influence of A-site occupation element on the structural features of crystal-and micro-structure,the optical and physicochemical characteristics as well as the catalytic behaviours has been systematically investigated with the support of various on-line or off-line physical means in combination of DFT calculations.The alternative formation of diverse microstructures was found to be in connection with the A-site element replacements of the Co-based spinels,the NiCo₂O₄ spinels tend to form solid microspheres(SMs)with higher capability towards photo-generated charge electrons,and ZnCo₂O₄ spinels prefer to form core-shell hollow microspheres(CSHoMs)with better surface adsorption performance for CO₂ greenhouse gas molecular,whereas CuCo₂O₄ spinels tend to form double-shell hollow microspheres(DSHoMs)with higher SBET and more oxygen vacancy content.It has been shown that there are strong interactions between site-occupied metal ions and oxygen atoms for the Co-based spinels A_1-?Co_?(A_?Co_2-?)O₄(A=Zn,Ni,Cu)nanocomposites with excellent capability in terms of visible light harvesting and catalytic redox reactions,and we found that efficient photocatalytic reduction of CO₂ to CO and CH4 over CuCo₂O₄ DSHoMs.NiCo₂O₄ SMs and ZnCo₂O₄ CSHoMs spinels could be accomplished under mild conditions.Specifically,CuCo₂O₄ DSHoMs and NiCo₂O₄ SMs exhibit preferential selectivity towards CO and CH4 evolution,respectively.Compared with NiCo₂O₄ SMs and ZnCo₂O₄ CSHoMs,CuCo₂O₄ DSHoMs produces more CO(26.54 ?mol h-1),whereas the amount of CH4 generated over NiCo₂O₄ SMs is approximately 1.7 times as that of CuCo₂O₄ DSHoM.The reproducibility test of the catalytic reaction shows that the cobalt-based spinel catalytic materials exhibits excellent catalytic activity and stability.Combined with the dynamic catalytic reaction spectroscopic characterization outcomes,the initial mechanism of photocatalytic reduction of CO₂ species over Co-based spinels A1-xCox(AxCo2-x)O4(A=Zn,Ni,Cu)nanocomposites have been accordingly proposed and discussed by referring to the more details spinels structure,the catalytic reaction informations as well as semiconductor photocatalytic principles.