Synthesis And Photocatalytic Properties Of Biomorphic Photocatalysts With Hierarchical Structures

Shortage of energy and environmental pollution are two problems which constrain the current socio-economic development.Exploitation of new,pollution-free,renewable clean energy has become a major issue in relation to human survival and sustainable development.Development of efficient,low-cost technology to transfer of solar energy into hydrogen is the longing for the goal.Among the many ways,using of solar photocatalytic decomposition of water,with photocatalysts,is one of the most ideal and most promising means.As we all know,the material with same composition and different structure often show a very different catalytic properties.Therefore,the coupling effect between material hierarchical structure and performance is an important research content in the field.The key scientific issues include:?1?Design and develop a simple and common method from the perspective of structural-functional integration to prepare multi-layered,multi-dimensional,multi-component coupling effect of the new classification of porous semiconductor photocatalytic materials.?2?Explore and study the coupling effect between hierarchical structural and componential factors on photocatalytic activity.The fine grading structure of natural organisms building to meet the needs of the environment provide a broad space for designing new classification of porous semiconductor photocatalysts.Butterfly is a perfect example.The butterfly wings with the macroscopic,microscopic to nano-scale graded porous structure formatting in the long evolution can significantly improve the light capture rate.The fine scales with"quasi-honeycomb"structure on the black wings of Papilionae Butterfly can maximize the absorption of visible light,the average absorption rate of 96%or more.Eggshell,a waste of life,is another example;the structure from the outer surface of the shell to the inside is the epidermis,CaCO₃ shell and egg film.The egg membrane has a three-dimensional cross-pipe interworking network hierarchical structure,which acts like a light trap.The light enters this structure to repeatedly absorb the absorption on its inner surface,thereby having a lower reflectivity than the conventional structure and a higher light absorption.To solve the limitations in the present photocatalysis research area,the dissertation focus on the current trends in this field.Inspiration in the nature of biological fine grading structure and optical function characteristics,we have synthesized several kinds of novel morph-genetic semiconductor photocatalysts,and systematically studied their photocatalytic activities.The mains contents and results are as follows:First,using the butterfly wings which have a high light absorption performance as a template,after surface chemical treatment,and the binary metal oxide WO₃ with UV-photocatalytic activity,which is synthesized by sol-gel method,is compounded into the hierarchical pore structure.Controlling the calcination temperature,the butterfly wing morphology graded porous WO₃ is successfully synthesized.The oxygen efficiency of photodegradation water is 2 times higher than that of the original WO₃ powder material,and it has obvious visible light trapping characteristics and photocatalytic performance.At the same time,the feasibility of this method as a catalyst for the preparation of graded porous artificial butterfly wings is demonstrated,and this method also provides the basis and theoretical guidance for the preparation of graded porous ternary oxide.Second,inspiration in grading structure and high light absorption characteristics of butterfly wings,the synthesis of graded porous ternary oxide BiVO₄ was proposed via graded porous structure of the Paris Tsui Fung butterfly wings as a template.As genetic butterfly wing of the macro,micro to nanometer scale hierarchical structure,controlling the sintering temperature to retain the carbon matrix derived from the natural polymer achieve a typical ternary oxide BiVO₄ carbon element self-doping,which can effectively respond to visible light.Carbon doping and graded tectonic coupling make the artificial butterfly with excellent visible light capture rate,and the photodegradation of water efficiency?160?mol/h?is 6.3 times of ordinary BiVO₄powder material.This technology provides a new way for the simple and efficient preparation of catalyst with excellent photoelectric conversion efficiency,and the in situ self-doping preparation provides a new idea for the traditional element doping.Third,based on fine and ordered porous structure of butterfly fin and its unique optical properties,the heterojunction of porous WO₃/BiVO₄ was synthesized by the secondary sol-gel method and the calcination technique using Paris Tsui Tsui butterfly as a biological template.The composition of this photocatalytic material,which with higher visible light capture ability,is pure.The graded porous WO₃/BiVO₄ has excellent photodegradation of water and the measurable photolytic hydrogen production.The heterojunction can change the valence band structure of WO₃ or BiVO₄,so that it can efficiently conduct photogenerated electrons and holes and realize the possibility of hydrogen production.The three-dimensional graded porous structure can improve the photosensitivity of the photocatalyst in the visible region,and further improve the separation efficiency and charge mobility of the electron-hole pair.It is of great practical significance to study the preparation of special structures and the in-depth study of structure-function integrated photocatalysts.Fourth,inspired by the egg film disordered 3D network hierarchical structure,the concept and synthesis method of"semiconductor-based graphene composite photocatalytic graded porous materials"is proposed.Graphene was introduced into the graded porous TiO₂ 3D network structure,and the graphene composite photocatalytic material based on the semiconductor catalyst was realized by using the electronic film-like morphology as the template and the ultrasonic technique.The effect of graded porous TiO₂/GR composite photocatalyst on the hydrogen production efficiency of photolytic water was explored and studied.In this hierarchical structure,the composite form of semiconducting and graphene is changed from the traditional"point-to-surface contact"to"face-to-surface contact"to maximize the action of graphene transfer and transfer of photogenerated electrons,thus greatly reducing the recombination rate of electron-hole pairs.This study provides a new idea for the design of semiconductor/graphene composite photocatalytic materials,which realizes the integration of structure and function.It provides a reference model for further design and optimization of materials with three-dimensional network hierarchical structure and optical function.