Preparation of Heterojunction Composite Nano-photocatalyst Based on Titanium Dioxide and Construction of Artificial Leaves

Author:Wu Ke Liang

Supervisor:liu zhi yong


Degree Year:2019





Environmental problems and energy crisis have always been two hot issues of modern science and technology society.Reasonable exploration and utilization of solar energy is considered as effective ways to solve them.Artificial photosynthesis can imitate the leaves of green plants and realize their biological functions.It can also transform solar energy into chemical energy under artificial control and store it in fuels.At the same time,it is clean,green environmental protection and no pollution,which has attracted wide attention.For the realization of artificial photosynthesis,the problem of choosing suitable photocatalyst is the first one.Compared with other metal semiconductor photocatalysts,titanium dioxide has unique energy band.TiO2 is widely used as a photocatalyst due to its position of absorption band edges,strong chemical stability,excellent light conversion efficiency,corrosion resistance,abundance,low toxicity,cost-effectiveness and high catalytic activity.However TiO2nanoparticles offer fast and direct photoelectron transmission and accelerate the charge separation process.At the same time the wide bandgap limits the absorption,in the ultraviolet range,and the photon conversion efficiency.Moreover,it usually has a band gap of about 3.2 eV and can absorb only a small fraction of the short-wave ultraviolet radiation in the sunlight.In view of these shortcomings,a series of different composite catalysts were designed by different modification methods to study the semi-reaction in artificial photosynthesis,and then for the total hydrolysis of water research.Finally,the reactor"artificial leaves"were prepared.The research contents of this paper are as follows:(1)Preparation and photocatalytic properties of cellulose based aerogels loaded PPy-TiO2/WO3 photocatalyst:In order to explore the photocatalytic degradation of this half reaction,cellulose aerogel was used as the substrate of the bionic blade to load TiO2/WO3,and prepared the composite aerogel catalyst beads.After catalytic degradation of the organic dye RHB cycle for five times,no catalyst was released,avoiding the two pollution of the catalyst powder to the water body,while the degradation rate decreased slightly.Because WO3 increased the absorption band edge of titanium dioxide,polypyrrole PYy increased the absorbance and accelerated the separation of electron holes,the catalytic degradation rate was greatly improved,and the degradation rate was 91%after 2 h.(2)Preparation of titanium TiO2/ZnO from celery template for photocatalytic reduction of CO2 as hydrocarbon fuel:Nanostructured heterojunction photocatalysts have broad application prospects in photocatalytic reduction of CO2.Herein,simple sol-gel and hydrolysis process were used to design the nano structure TiO2/ZnO heterojunction with biological template celery stalk to realize the half reaction of photocatalytic reduction of CO2 by artificial photosynthesis.A well-connected heterojunction was obtained on the stomata and folds of celery stems,and the nanoparticles were well distributed.The specific surface area was increased by 55.5m2/g.The crystal structure,morphology and surface composition of nanostructured photocatalysts were studied by means of electron microscopy,X-ray photoelectron spectroscopy and X-ray diffraction.It was found that nanostructured photocatalysts consisted of anatase TiO2 and wurtzite ZnO nanoparticles.Compared with pure titanium dioxide,the photocatalytic rate of carbon dioxide reduction to CH4 in nanocomposites increased by five times,from 0.55 to 2.56μmol·h–1·g–1 The mechanism of reduction was explained preliminarily.(3)Preparation of hollow CdS@TiO2/Ni2P microspheres by SiO2 template method and research for photocatalytic properties:In the process of realizing the half-reaction of photocatalytic hydrogen production,it is very important to construct a reasonable catalyst interface.A noble metal-free photocatalytic system for space separation of oxidation and reduction surfaces was designed.The hollow core-shell structure CdS@TiO2/Ni2P was prepared by sacrificial template method.The addition of CdS and Ni2P enlarged the light absorption range of the composite catalyst to 720nm.At the same time,the cyclic stability of CdS was improved by titanium dioxide.Electrons generated during the photoreaction could migrate to Ni2P outside the shell of TiO2,and holes could migrate to the inside of the core layer of CdS,which improved the separation efficiency.This design also exposes more surfaces,thus increasing hydrogen production.After 2.5 hours,hydrogen production was 14.80mmol/g under 420 nm visible light and 34.78 mmol/g under xenon lamp with AM1.5G filter.(4)Design of Z-scheme printable artificial leaf device based on CdS@TiO2/Pt/ITO/WO3@Co3O4 and study on Water splitting:Photolysis of aquatic oxygen is a four-electron process.At the same time,the Superpotential of oxygen on the surface of materials is much higher than that of hydrogen.Oxygen atoms need higher activation energy.WO3 and Co3O4 were used as oxygen-producing composite catalysts to realize oxygen evolution reaction.Then,using CdS@TiO2/Pt as catalyst for hydrogen evolution reaction(HEP),WO3/Co3O4 as catalyst for oxygen evolution reaction(OEP),nano-ITO particles as solid electronic shuttle medium,a Z-type composite photocatalyst CdS@TiO2/Pt/ITO/WO3/Co3O4 for water overall and its catalytic effect was studied.The possible reaction mechanism was proposed.Then terpineol,2-butoxyethanol and acrylic resin were used as composite ink to add catalyst powder to realize the printability of the catalyst.Finally,it was printed on the FTO glass substrate to make the leaf,and the artificial leaf device was prepared,and the catalytic effect was explored.