Preparation And Hydrogen Production Performance Research Of TiO₂ Photocatalyst Based On MOF

With the rapid development of the social economy,the continuous consumption of fossil energy?coal,oil,natural gas,etc.?has brought a series of problems.The two most prominent problems are energy shortage and environmental pollution.However,life of human is closely related to energy and the environment,so the pursuits of renewable energy and green environment are something what people have been insisting on.Solar energy is inexhaustible,clean and pollution-free,but it cannot be stored.It is a good idea to convert solar energy into storable,recycled,and clean hydrogen.In addition,the earth is rich in water resources,and can provide cheap raw materials for photocatalytic hydrogen production.In summary,solar photocatalytic hydrogen production is an effective way to solve the energy crisis and ecological environment to achieve sustainable development.TiO₂ is a high performance semiconductor photocatalytic material with many advantages,such as high catalytic efficiency,stable chemical properties,strong oxidizing ability,non-toxic and harmlessness,low cost and no secondary pollution.It has been widely studied and applied in the fields of photocatalytic hydrogen production,control of environmental pollution and sterilization.However,due to the wide band gap of TiO₂,the light absorption is limited to the ultraviolet region,which makes the solar energy utilization rate lower.Furthermore,the photogenerated charge carriers are easily recombined,which reduces the quantum yield,decreases the photocatalytic efficiency,and limits its wide range application.Effective methods for improving the TiO₂ efficiency are to form a heterojunction betweenTiO₂ and other semiconductors,or to add a cocatalyst in TiO₂.Metal-Organic Frameworks?MOFs?are a class of porous framework materials composed of metal ions or metal ion clusters and organic complexes in different ways.MOFs have the advantages of high porosity,large specific surface area,regular pore structure,and adjustable pore size.Moreover,MOF-templated nanoporous materials,such as porous nanocarbons,carbides,sulfides,phosphides and other porous dispersions have received extensive attention.As inheriting the advantages of MOFs,such as large specific surface area,and they help to form high quality nanoporous materials.In this way,not only the number of the active sites could be increased,but also the transfer of carriers can be promoted.Combining TiO₂ with MOF-templated nanoporous materials is expected to improve the photocatalytic hydrogen production efficiency of TiO₂.After many systematic research,we have obtained some meaningful results:1.Preparation and hydrogen production performance of TiO₂-Ti₃C₂-CoS_x heterojunction.Using ZIF-67 as a template,highly conductive material such as Ti₃C₂ as charge transport bridge,TiO₂-Ti₃C₂-CoS_x heterostructure with constrained nanocrystals was prepared by solvothermal method.When m?Ti₃C₂?/m?TiO₂?was 0.5:100 and n?CoS_x?/n?TiO₂?was 1:100,the photocatalytic hydrogen production performance of the heterojunction was the best.After characterization of the morphology,light absorption and separation efficiency of photogenerated carriers,it was found that TiO₂ formed a three-dimensional porous structure after adding Ti₃C₂ and CoS_x which had good dispersibility and solved the agglomeration problem;the light absorption range of TiO₂ was expanded.In the visible range,the light utilization efficiency was improved;the separation efficiency of photogenerated electrons and holes in photocatalysis was promoted,and the transport of charge carriers was effectively enhanced.Therefore,the photocatalytic hydrogen production performance of TiO₂ was improved.2.Preparation and hydrogen production performance of TiO₂@NiCoS-PC heterojunction.Firstly,the TiO₂ nanoparticles were coated with bimetallic ZIF?NiCo-ZIF?,then the TiO₂@NiCoS-PC heterojunction was prepared by the chemical vapor deposition method.By adjusting the parameters,the optimal hydrogen production effect of TiO₂@Ni_0.5Co_0.5S-PC was 62.5 times that of pure TiO₂,and twice that of commercial P25,which improved the hydrogen production efficiency of TiO₂.The characterization results displayed that the addition of porous Ni_0.5Co_0.5S-PC solved the agglomeration problem of TiO₂ nanoparticles;Ni_0.5Co_0.5S had considerable photocatalytic activity,which could form a heterostructure with TiO₂ and promote the separation of carriers;Ni_0.5Co_0.5S-PC had good HER activity,which could be used as a cocatalyst to improve the efficiency of charge carrier utilization.3.Preparation and hydrogen production performance of TiO₂-Co_3-xCu_xO₄ photocatalyst.Firstly,TiO₂ nanosheets were dispersed by CoCu-ZIF,and then TiO₂-Co_3-xCu_xO₄photocatalyst was prepared by solid phase method.After hydrogen production test,it was found that when the molar ratio of Co and Cu was 7:3,the sample possessed the best hydrogen production effect.The addition of Co₃O₄ and Co_3-xCu_xO₄ had produced many good influences,such as?i?the photoresponsive region of TiO₂ was extended to the visible region,the result was consistent with the conclusion that the TiO₂-Co_3-xCu_xO₄ photocatalyst had a hydrogen production effect in visible light;?ii?the TiO₂ nanosheets were fixed on the frame to solve the agglomeration problem of TiO₂;?iii?the addition of Co_3-xCu_xO₄ improved the separation and utilization efficiency of photogenerated electrons and holes in the catalyst.In summary,this thesis provided theoretical guidance for the preparation of high performance nanoporous TiO₂-based photocatalysts.