Fabrication And Photocatalytic Properties Of Titanium-Based Hybrid Materials Modified By Two-Dimensional Porphyrin Metal-Organic Frameworks

In order to solve the increasingly serious shortage of fossil energy and environmental pollution,the urgent need in renewable energies that can replace traditional fossil energy has aroused wide attention of researchers.In the presence of sufficient and sustainable solar energy and photocatalyst,producing hydrogen with high energy density from water reduction has been an efficient green way to solve energy shortage and avoid environmental pollution.In it,the design and assembly of highly active photocatalysts are the key to realize efficient conversion of light energy.TiO₂ microspheres（TMS）and Ti₃C₂ MXene are stable,hydrophilic and easy to be adjusted semiconductors.In this thesis,with TMS and Ti₃C₂ MXene as substrates,a series of novel and efficient organic/inorganic nanohybrid photocatalysts were constructed by combining with porphyrin metal-organic frameworks（MOFs）through various methods.The assembly mechanism,photocatalytic hydrogen production activity and electron transfer mechanism of the obtained nanocomposites were systematically studied.The main contents are as follows:1.It is significant to fabricate cheap and active compounds used in energy conversion.Herein,a new nano-micro composite was facilely fabricated by constructing two-dimensional Cu carboxyphenyl porphyrin metal-organic framework（CTMOF）on TiO₂ microspheres（TMS）.It showed that the light absorption and the transfer of photogenerated charges in TMS could be greatly improved by the introduction of CTMOF.Importantly,the obtained nano-micro composite（TMS/CTMOF）displayed excellent performance in photocatalytic hydrogen production.Under the same condition,its photocatalytic hydrogen evolution(86.11 mmol g^-1,6 h irradiation)was 14.5 times and 21.2 times of pure TMS and CTMOF,respectively,indicating the synergetic effect of TMS and CTMOF.Moreover,after 5 cycles（Every cycle was6 h）,the photocatalytic stability of the nano-micro composite was still greatly higher than those of the pure TMS and CTMOF.Furthermore,photocatalytic mechanism was clarified in order to demonstrate the improved activity in the nano-micro composite.This research will provide new ideas for constructing greatly active composite systems for photocatalytic H₂ evolution.2.Highly efficient nanohybrids used in photocatalytic H₂ production from water reduction have attracted many attentions in energy conversion and storage of clean energy.Herein,a new dimension-matched nanohybrid was prepared by fabricating two-dimensional copper carboxyphenyl porphyrin metal-organic frameworks（Cu-PMOF）on two-dimensional Ti₃C₂MXene/TiO₂ nanosheets（TCs）.The visible light response and the separation of photoinduced charges in TCs can be efficiently enhanced after the coupling of Cu-PMOF.Furthermore,the prepared nanohybrid showed high activity in photocatalytic H₂evolution.Without adding any other co-catalysts,the H₂ production over the TCs/Cu-PMOF with optimum content of Cu-PMOF was 29 times of pure TCs,suggesting the synergetic effect of TCs and Cu-PMOF in the nanocomposite.Moreover,the electron transfer mechanism was explored so as to explain the enhanced activity in the nanohybrid.This study will offer a feasible strategy for fabricating effective nanocomposites used in photocatalysis.3.By riveting Cu²⁺onto Ti₃C₂@TiO₂（TT）,Cu-TCPP MOF was grown in situ on the surface of TT-Cu²⁺using Cu²⁺as the growth site,and thus the increased visible light absorption as well as charge transfer in TT can be obtained.By means of electron microscopes and XPS,it was demonstrated that there existed a close interface connection between TT and CuTMOF in the TT/CuTMOF composite,and the CuTMOF was uniformly distributed on the surface of TT.The results of fluorescence spectra indicated that the close interfacial connection was conducive to the separation of photogenerated electron-hole pairs.Through the photocatalytic hydrogen production activity test,it was found that the photocatalytic performance of the TT in-situ grown by CuTMOF was much better than that introduced with TCPP molecules on TT or the mechanical mixture of TT and CuTMOF.In addition,with methanol as sacrificial agent,the TT/CuTMOF showed higher photocatalytic hydrogen production activity and cycle stability,and the TT/CuTMOF nanocomposite followed the type-Ⅱmechanism in the photocatalytic hydrogen production reaction.In this thesis,a variety of highly active organic/inorganic nanocomposite photocatalytic systems had been constructed by coupling titanium-based semiconductors with two-dimensional porphyrin MOFs,it will provide new ideas and experimental basis for the assembly,hydrogen production performance and photogenerated electron transfer mechanism of other nanocomposites used for solar energy conversion and utilization.