Construction Of Transition Metal Oxide Z-scheme Heterojunction For Study In Photocatalytic And Photoeletrocatalytic Production Of Value-added Chemicals

The production of chemical value-added products by photocatalytic and photoelectrocatalytic technology is a green,efficient and low-cost method to convert renewable solar energy into chemical energy.At present,one of the core issues in the development of photocatalytic and photoelectrocatalytic methods is the design of photocatalytic and photoelectrocatalytic materials.Therefore,the ingenious design of semiconductor heterojunction can not only broaden the absorption of visible light and near-infrared light by catalysts,promote the separation of photogenerated carriers,extend the life of photogenerated electrons,and improve the high efficiency and high stability of photocatalysis and photoelectrocatalysis.The adjustment of catalyst microstructure can make it have abundant active sites and fast electron transport channels,so as to achieve high catalytic activity.Hence,several yolk-shell and hollow double-shell Z-type heterojunction catalysts with excellent visible light response were designed and successfully prepared,and used in photocatalytic and photoelectrocatalytic synthesis of chemical value-added products.At the same time,the mechanism of its catalytic reaction is systematically explored.A Z-type heterojunction nanoreactor（YS-Cu Co₂S₄@Cu₂O-NR）photocatalyst with octahedral structure Cu₂O as yolk core and tubular structure Cu Co₂S₄ as yolk shell was designed and synthesized successfully.The Z-type heterojunction nanoreactor catalyst system showed excellent multifunctional catalytic activity.It was applied to photocatalytic production of H₂O₂ with a yield of 12 m M g^-1,and selective oxidation of benzyl alcohol to high value-added benzaldehyde.The conversion rate of benzyl alcohol was 80%,and the selectivity of benzaldehyde synthesis was 99%.YS-Cu Co₂S₄@Cu₂O-NR is also used as a photofenton catalyst in situ synthesis of H₂O₂combined with the photofenton-like reaction at the catalyst interface to rapidly remove a variety of organic pollutants,with degradation efficiency up to 90%.The results show that the high catalytic activity is attributed to the formation of Z-type heterointerface electron transfer channels and the stronger redox capacity.The activity,selectivity and stability of photoelectrocatalytic oxygen reduction and benzyl alcohol oxidation can be significantly improved by the nanoconfinement effect of the construction of yolk-shell structure.The putaminal void can promote the multi-directional reflection of light in the shell and enhance the absorption performance of light.The smaller shell thickness shorens the transfer distance of charge and enhances the transfer efficiency of charge.The specific surface area of both the inner and outer surfaces increased and the redox activity of the surface was enhanced.The regulation design of variable valence Cu²⁺/Cu⁺catalyst components could be beneficial to enhance the formation of H₂O₂ and the activity of Fenton-like reaction.The experimental results show that the YS-Cu Co₂S₄@Cu₂O-NR catalyst still shows excellent stability after four cycles of photocatalysis,which is attributed to the external shell structure can inhibit the photocorrosion of yolk Cu₂O and increase the cyclic stability of the catalyst.The photocatalytic synthesis path of H₂O₂,benzaldehyde and various organic matter degradation mechanism were revealed through free radical capture experiment,ESR,XPS analysis,photoelectrochemical test and high performance liquid chromatography-mass spectrometry analysis,which providing theoretical basis for photocatalytic efficient production of chemical value-added products.A porous hollow double-shell structure Fe₂O₃@Ov-Ni Fe₂O₄（PDS-Fe₂O₃@Ov-Ni Fe₂O₄-HR）Z-type heterojunction nanorods array integrated photocathode with oxygen vacancy and chemical bond interface was in-situ grown on a Ti network by using an in situ self-assembly template strategy.The maximum production rate of H₂O₂ was 6.3 m M h^-1 with PDS-Fe₂O₃@Ov-Ni Fe₂O₄-HR-Ti using for photocathode catalytic oxygen reduction.The high H₂O₂ production rate is attributed to the rapid carrier transfer and stronger redox activity at the Z-type heterogeneous interface.The abundant oxygen vacancy in Ov-Ni Fe₂O₄ enhances the carrier concentration,and the construction of chemical bond interface provides a fast transport path for the high concentration carriers.The hollow double shell structure can realize multiple scattering and reflection of light in the space of double-shell and enhance the light absorption performance.Providing a large specific surface area enhances surface redox activity and interfacial charge separation efficiency.PDS-Fe₂O₃@Ov-Ni Fe₂O₄-HR-Ti||Fe₂O₃-Ti photoelectrochemical cell of the yield of H₂O₂ is 4.07 m M h^-1 under the bias of 0.5 V,the yield of H₂O₂ is 9.8μmol min^-1 cm^-2 on two electrodes without bias.The charge transfer mechanism of catalyst,the catalytic production path of H₂O₂ and the mechanism of photoelectrochemical cell were revealed by the trapping experiment,ESR,XPS analysis and photochemical test.The high value-added chemicals Na Zn PO₄ can be synthesized in the phosphate buffer electrolyte of PDS-Fe₂O₃@Ov-Ni Fe₂O₄-HR-Ti||Zn batteries,and two Zn-H₂O₂ battery can also provide sufficient power to light emitting diode（LED）.PDS-Fe₂O₃@Ov-Ni Fe₂O₄-HR-Ti||Zn has 12 m W cm^-2 in KOH electrolyte of high power density.The results show that the preparation of integrated electrode is beneficial to improve the conductivity of electrode.Ni²⁺/Ni³⁺,Fe²⁺/Fe³⁺of catalyst are beneficial to enhance the efficiency of Zn-H₂O₂ cells.By introducing oxygen vacancy and hollow double shell structure to improve the charge separation efficiency,this study provides a new path for the design of high efficiency photoelectrodes for the non-biased photoelectric production of H₂O₂,and a new idea for the construction of photoelectric energy-related devices.A porous hollow double-shell Mo₂N-Co₃O₄-Fe₂O₃ nanocubes Z-scheme heterostructures with enriched oxygen vacancies by controlling thermal annealing of ZIF-67@Mo-Co Fe Prussian blue analogue（PBA）is purposely devised.Polyvinylidene fluoride（PVDF）modified HPDS Mo₂N-Co₃O₄-Fe₂O₃ NCs was loaded on Ni foam to construct a photocathode with porous skeleton structure of gas-liquid-solid three-phase interface（HPDS Mo₂N-Co₃O₄-Fe₂O₃ NCs/PVDF）.The H₂O₂ generation rate of HPDS Mo₂N-Co₃O₄-Fe₂O₃ NCs/PVDF hydrophobic photocathode is 7.9 m M h^-1,much higher than the H₂O₂ generation rate of HPDS Mo₂N-Co₃O₄-Fe₂O₃ NCs hydrophilic electrode is3.2 m M h^-1.It is attributed to the synergistic effect of hollow double shell nanostructure and hydrophobic modification,which can maintain a high O₂ concentration around the electrode,promote the rapid mass transfer of O₂,and accelerate the reaction of O₂ with the active site on the electrode surface.In addition,Mo₂N as a co-catalyst for H₂O₂production has unique local surface plasmon resonance（LSPR）effect,high electrical conductivity and photothermal effect,showing great potential in promoting H₂O₂production.HPDS Mo₂N-Co₃O₄@Fe₂O₃ NCs/PVDF photocathode and Co₃O₄ NCs photoanode constitute a photochemical cell,the total yield of H₂O₂ in the anode and cathode chamber is 3.8 m M h^-1 at voltage of-0.6V.The charge transfer mechanism of the photocatalyst and the path of photocatalytic synthesis of H₂O₂ were revealed by free radical capture experiment,ESR,XPS analysis and photochemical test.HPDS Mo₂N-Co₃O₄@Fe₂O₃NCs/PVDF||Co₃O₄ photoelectrochemical cell of NCs under 1.2 V bias,cathode catalytic production of H₂O₂,anode catalyst PET upgrade to reshape for high value-added chemicals（terephthalic acid and potassium diformate）,the production of H₂O₂ is 3.5 m M h^-1,The Faraday efficiency of PET upgrade remodeling is up to 80%.The study showed that the production of H₂O₂ was increased by 3 times when the PET remolding reaction was used as anodic oxidation reaction to promote the cathode reduction reaction.The introduction of a porous hollow double-shell structure and a three-phase interface to improve the light absorption performance and gas mass transfer efficiency,this study provides a new idea for the construction of efficient PEC for the production of H₂O₂ hollow structure photocathode catalyst provides an innovative method for PET upgrading and reshaping and energy-saving H₂O₂ production.It also provides a feasible strategy for the reasonable design of photoelectric chemical cells.