Assembly,Interface Modification And Performance Of Oxide-based Nanocomposites

Due to fast development of social economy,the demand for energy is getting higher and higher.While fossil energy is facing exhaustion,and environmental problems are also becoming increasingly prominent.Therefore,it is imperative to develop green energy by a sustainable path.Hydrogen energy is considered as an ideal alternative to fossil energy due to its high energy density and environmental protection.Although the demand for hydrogen energy in some fields can be partially solved by some traditional technologies of hydrogen production,the above problems are still present because of the close dependence on fossil energy.The photocatalytic hydrogen production by water splitting using solar energy is a truly environmentally friendly and sustainable way for hydrogen production,which has been a research hotspot.Graphene oxide（GO）is an important two-dimensional photoelectric material.However,its performance has been limited due to the shortcoming of easy recombination of photo-generated charges.Titanium dioxide（TiO₂）is a classic semiconductor photocatalyst due to its advantages of non-toxic,cheap and chemical stability.However,only UV light can be absorbed and photoproduced charges are easily recombined.Based on the above problems,firstly GO were modified by an environmentally friendly gas-solid phase method.Additionally,a series of special nanocomposites were prepared by introducing porphyrin with high visible light absorption and low-cost transition metals into TiO₂ microspheres.The assembly,photocatalytic hydrogen evolution activity,and photogenerated charge transfer mechanisms of the nanocomposites were further studied.The main contents are as follows:A composite of special metal chromium oxide modified GO was prepared by in-situ riveting of metal chromium ions in wet GO matrix through electrostatic interaction,and then the Cr³⁺was synergistically oxidized by GO and oxygen in the air.Then the composite was treated by CO₂,and the electrochemical properties were studied.The result showed that chromium ions can be easily bound to GO surface by electrostatic interaction and in-situ oxidized to special metal oxide Cr₂O₅.The results showed that the functional groups on the surface and at the edges of the GO can be greatly affected by treated with CO₂ gas and thus a great impact on the crystal structure of Cr₂O₅ was achieved.Subsequently,the transfer of photogenerated electrons from the edge to the inside of the GO can be effectively facilitated.In the end,the reduced interfacial resistance,increased charge separation and photocurrent response were obtained.To obtain efficient photocatalysts by coupling architectures,developing novel materials and elucidating the charge transport mechanism at the semiconductor interface are vital.Herein,a special nanocomposite（TiO₂ microsphere/Cu NPs/THPP）for photocatalytic hydrogen production was facilely fabricated with copper nanoparticles（Cu NPs）as the interfacial linker of the TiO₂ microspheres and meso-tetra（4-hydroxyphenyl）porphyrin（THPP）.The assembly mode of the nanocomposite was studied in detail.It was found that the Cu NPs implanted at the interface of the TiO₂ microspheres and THPP can dramatically strengthen the interaction between the TiO₂ microspheres and THPP,and improve the separation and transfer of photo-produced charges.Therefore,the nanocomposite displayed excellent performance for photocatalytic hydrogen production.Moreover,by recycling hydrogen production,it is demonstrated that the nanocomposite was a highly efficient and long-term stable photocatalyst.By investigating the energy band location and the charge transfer,the photocatalytic mechanism over the special nanocomposite was explored and proposed to explain the better activity of the TiO₂ microsphere/Cu NPs/THPP photocatalytic system.With Co as the bridge agent of THPP and TiO₂,TiO₂ microsphere/Co/THPP nano composite was assembled.By means of scanning electron microscope and UV-visible spectrum,it was found that the stacking of THPP in the TiO₂ microsphere can be greatly reduced by the introduction of Co.Thus,the self-aggregation of THPP was effectively suppressed,and the light absorption was greatly improved.By X-ray powder diffraction（XRD）analysis,it was demonstrated that the crystal structure of TiO₂ microsphere was not affected by the introduction of THPP and a small amount of Co.Moreover,through electrochemical test and photocatalytic measurement of hydrogen evolution,it was shown that the photocurrent response and photocatalytic hydrogen evolution activity of the TiO₂ microsphere/THPP nano composite were greatly improved by the interfacial linkage of Co.Furthermore,the mechanism of electronic transfer in the nano composite was further studied by X-ray photoelectron（XPS）analysis,and a type II charge transfer mechanism was proposed.In this paper,the photochemical property of graphene oxide was improved by the introduction of special metal chromium oxides in a simple and environmentally friendly way.Besides,the assemblies of TiO₂ microsphere/metal/porphyrin were prepared rapidly by using transition metal copper and cobalt as the interface linkers of hydroxyporphyrin and TiO₂microsphere.Assembly,photocatalytic hydrogen production,and charge transfer mechanism were studied in detail.The above work will provide new ideas for the preparations of some special photocatalytic systems composed of oxides with excellent performance.