Study On Multifunctional Properties Of Graphene Oxide In The Construction Of Perovskite Composite Photocatalyst

The depletion of traditional energy has become the focus of attention and the main contradiction in the world.It is an ideal way to solve the energy crisis to find,develop and utilize clean and efficient new renewable energy.As an efficient energy carrier,hydrogen possesses the advantages of clean,high energy density,convenient transportation and so on.Therefore,it is an ideal way to convert solar energy into hydrogen energy in order to effectively solve the shortage of energy.Photocatalytic water splitting to hydrogen is one of the most direct and convenient hydrogen energy conversion methods.However,for the photocatalysis system of single phase,the activity of photocatalytic hydrogen evolution is still low.Therefore,the design and construction of high performance photocatalytic system is of great significance to improve the photocatalytic activity and the possibility of practical application.The main idea of this paper is to construct different perovskite-graphene catalytic systems by using graphene with high conductivity as carrier.The interaction between perovskite and graphene and the mechanism of multifunctional properties of graphene oxide in the formation and catalysis of composites were studied.The specific contents of the study are as follows:(1)An indirect Z-schematic heterojunction system of TiO2 and LaFeO3(LFO)with a solid state electron mediator(RGO)is proposed and applied for photocatalytic hydrogen(H2)evolution.Through a facile 2-step synthesis strategy including adsorption of LFO on GO sheets and growth of TiO2 between the LFO-GO frameworks,a Ti-O-C bonds strongly linked sandwich-like TiO2/RGO/LFO composite is obtained.The structure,morphology,optical properties and catalytic mechanism of the Z-scheme heterojunction are thoroughly investigated.The obtained visible light responded TiO2/RGO/LFO composite displays significantly elevated photocatalytic performance for water splitting with excellent stability,and its H2 production rate(0.893 mmol h-1 g-1)is approximately 3.2,14.4 and 11.4 times superior to the direct Z-scheme TiO2/LFO composite,pure TiO2 and LFO,respectively.The sandwich-like structure with strong interaction between three components and short diffusion distance for impactful separation of e--h+ pairs bring about a vast improvement in H2 evolution performance of TiO2/RGO/LFO composite.In addition,Ti-O-C bonds could also enhance electronic conductivity and structure stability as a bridge of photogenerated carriers.Based on the investigation results,possible mechanisms for synthesis and photocatalytic charge transfer pattern for TiO2/RGO/LFO are developed(2)Compared with randomly distributed on the graphene surface,fully wrapped encapsulated structure of photocatalysts in graphene sheets processes much more excellent photocatalytic activity and stability attribute to the strong interaction between them.However,the preparation of this architecture usually needs to modify the material surface using some toxic organic reagents and the fabrication process is relatively complex.Therefore,it is of great significance to develop a green and simple preparation method for graphene encapsulated structure.This paper selected a LaNiO3 photocatalyst riched in oxygen vacancies,utilizing the anchoring effect of oxygen vacancies and chemical bonding reactions between LaNiO3 and graphene sheets to form a graphene encapsulated LaNiO3 nanocomposite via a simple photocatalytic reduction process.This encapsulation structure with open meso-macroporous framework can be served as a nanoreactor which provides an engineered confined nanospace for chemical reactions and improves the catalytic activity and stability.The maximum H2 production rate was 3.22 mmol h-1 g-1 which is 12 times higher than that of pure LaNiO3 with excellent long-term stability for 36 h.The morphology formation and photocatalytic mechanism were investigated in details.The combined effect of chemical bonding reaction(O=C-O and Ni-C)and the anchoring effect of oxygen vacancies to carboxyl groups are critical for the formation of graphene encapsulated structure.At the same time,the formed Ni-C bonds between LaNiO3 and graphene acted as a bridge to promote the electronic transmission rate which greatly improved photocatalytic activity and stability.(3)We designed a one-step lattice-confined etching perovskite nanoparticles and self-sacrificing graphene oxide(GO)induced self-assembly strategy to synthesize novel 3D nest-like LaCO3OH and flower-like Ni(OH)2@graphene(RGO)hierarchical composite as a high performance photocatalyst and electrode material.The lattice-confined effect regulates the concentration and distribution of nickel ions migrating from perovskite to GO,and thus constructs a homogeneous Ni(OH)2@RGO nanostructure.La(OH)3 formed by residual lattice frames react with CO32-from self-sacrificing of GO self-assembly to form nest-like LaCO3OH,which is embedded in the Ni(OH)2@RGO nanosheets.Benefit from the extremely rapid transfer of electron on the homogeneous Ni(OH)2@RGO nanosheets and high light-harvesting capacity of 3D nest and flower-like composite of LaCO3OH-Ni(OH)2@RGO,the properties of photocatalysis and supercapacitor are greatly enhanced.This composite synthesized from GO mediated etching solid phase perovskite surface ion migration under lattice-confined action provides a new insight for the fabrication and function design of 3D semiconductor-RGO materials.(4)Based on the previous studies,we found that the oxygen vacancy on the perovskite surface and the oxygen-containing functional groups on the graphene oxide surface are the key to the formation of special morphology and structure in the process of the interaction between perovskite and graphene.On this basis,a simple solvothermal method was developed to prepare oxygen vacancy riched LaNiO2.5 and graphene composites.The material has a single nanoparticles’ porous hollow nanocage structure,which effectively increases the specific surface area of the material to provide more active sites and enhances the light capture ability of the material.At the same time,the increase of oxygen vacancy content effectively promotes the separation of photogenerated electrons from holes and expands the absorption range of visible light,thus further enhancing the photocatalytic activity of the catalyst under visible light.