Fabrication And Photocatalytic Hydrogen Evolution Performance Of Conjugated Polymer/Modified Titanium Dioxide Composites

Titanium dioxide?TiO₂?materials have great potential in photocatalytic hydrogen production due to their good stability,low cost and earth-abundant reserves.With a wide band gap,the light absorption of the TiO₂ is limited,resulting in low efficiency of photocatalytic hydrogen production.Conjugated Polymers?CPs?themselves have the low photocatalytic efficiency,but they have adjustable band gaps,which can be designed to match other semiconductor's energy levels.In order to overcome the limitation of the photocatalytic performance of a single material,i.e.,the conjugated polymer or the TiO₂,a composite material of the above two are developed,which has the wider light absorption performance and the improved carrier separation efficiency.However,currently the apparent quantum efficiency?AQY?of the CP&TiO₂ composite material is low,and its hydrogen production efficiency needs to be improved.Therefore,in this thesis,the modified TiO₂ material with visible light response is prepared by using external modification strategies such as noble metal deposition?Au,etc.?,surface disordered treatment?co-ball grinding with TiH₂?,the polymer/modified TiO₂ composites photocatalyst are obtained by the in-situ polymerization,and hydrogen production mechanisms of composites are studied.Moreover,the morphology and crystal surface of the TiO₂ unit in the composites are also regulated in order to improve the photocatalytic hydrogen production activity of the material.The specific research content of this paper is as follows:1.Using the conjugated polymer substrate?modified poly?benzothiadiazole?B-BT-1,4-E denoted as BE,the same as below?as the photosensitizer,the Au nanoparticles as the surface plasmon resonance?SPR?source,the TiO₂ nanoparticles as the electron collection and hydrogen generation medium,the pizza-shaped BE-Au-TiO₂ ternary composite was designed.The hydrogen production rate of the visible light-driven BE-Au-TiO₂ ternary composite was about 1.9 times and about 68times of that of BE-TiO₂ and Au-TiO₂,respectively,and its AQY at 420 nm reached7.8%.The above composite material combines the sensitization mechanism of the BE-TiO₂ composite material with the SPR enhancement mechanism of the Au-TiO₂composite material to overcome the shortcomings of electronic separation and transfer of a single mechanism,and significantly improve the internal electron transfer efficiency.2.The defect TiO₂ was prepared by introducing some active Ti³⁺/O_v sites and surface amorphization structures into the anatase TiO₂ nanoparticles by ball milling with the TiH₂.Then,an organic/inorganic composite material?BE-Defect TiO₂?containing a conjugated polymer?BE?and defect TiO₂ was prepared,and its photocatalytic hydrogen production performance without any noble metal promoter was investigated.Compared with the BE-TiO₂ catalyst,the hydrogen production activity of BE-Defect TiO₂ under visible light??>420 nm?is increased by about 30%.Combined with structural characterization,hydrogen production rate comparison and electron transfer behavior analysis,it was found that the active stites play the key role in promoting the photoactivity by reducing the band gap of the TiO₂ and they also act as electron traps and reaction sites for generating hydrogen to accelerate the transfer of photoelectrons from the BE to the TiO₂.3.?001??101?crystal facet co-exposed TiO₂ material[TiO₂?Facet?]was prepared,then BE-TiO₂?Facet?composite was made by in-situ polymerization,and its photocatalytic hydrogen production performance was investigated.The morphology,physical and chemical properties of the materials were characterized by a series of techniques,such as FT-IR,Raman,DRS,TEM and BET.The optimized composite material can produce 283.3?mol·h^-1 at?>420 nm illumination,and the AQY at?=450 nm was 4.14%.The co-exposed?101?and?001?crystal faces of TiO₂?Facet?form a crystal face heterojunction in TiO₂?Facet?particles.The TiO₂?Facet?has a well-matched band structure with BE,so photogenerated carriers can be effectively separated and transferred,and a improved photocatalytic activity is achieved.