Fabrication Of Highly Efficient Heterojunction Composite Photocatalysts And Their Visible-light-driven Photocatalytic Properties

With the development of global industrialization,the problems of energy shortage and environmental pollution present an ascending trend.Recently,photocatalysis using solar energy has been considered as an efficient technology to solve both energy shortage and global environmental pollution.Thus,it has been usefully applied for the photocatalytic degradation of organic pollutants,solar water-splitting for hydrogen production and photoreduction of CO₂ to produce hydrocarbon fuels.However,there are several factors for the low efficiency of photocatalysis,such as wide bandgap,which could only adsorb 5%of entire solar energy and a high recombination rate of photogenerated charge carriers,which hinder their practical applications.As a result,the quantum yield of single semiconductors,such as TiO₂,Ag₃PO₄,BiOCl,and Bi₂WO₆,is very low.For this reason,instead of using a single semiconductor,combining two or more semiconductors with appropriate band positions to improve the photocatalytic performance is an established idea because they can lead to enhanced charge separation or interfacial charge-transfer efficiency and enhance solar light absorption in the visible region.Therfore,the ideas of this dissertation are the fabrication of the highly active photocatalysts with controllable surface-interterfac to achieve the enhanced photocatalytic performance.The main contents are as follows:1.It takes advantage of the potential difference between the reductive P25 TiO₂ with oxygen vacancies（P25-OV）and silver nitrate precursors,Ag nanoparticles are uniformly deposited on the defective P25-OV surface in the absence of any reducing agents or stabilizing ligands.The heterojunction structures of P25-OV/Ag/Ag₃PO₄ composite was prepared by a coprecipitation method.The obviously enhanced photocatalytic activity of P25-OV/Ag/Ag₃PO₄ for the degradation of rhodamine B can be ascribed to the light absorption and the separation efficiency of photogenerated electrons and holes.2.One-dimensional Ti³⁺ self-doped Ag/TiO_2-x heterojunctions are fabricated through a hydrolysis reaction.The photocatalytic performances demonstrated that the as-prepared Ag/TiO_2-x nanocomposites exhibited higher photocatalytic activity than pure TiO_2-x.The photocatalysis mechanism was investigated and discussed.The established heterojunction between the interfaces of TiO_2-x nanoparticles and Ag nanowires as well as introduced Ti³⁺ led to the rapid electron transfer rate and improved photoinduced electron-hole pair’s separation efficiency,resulting in the improved photocatalytic performance of the Ti³⁺ self-doped Ag/TiO_2-x heterojunctions.3.Blue Ti³⁺ self-doped TiO₂ nanoparticles with mixed phases of anatase and rutile have been synthesized via a facile solvothermal method.The phase evolution of the blue TiO₂ varying from anatase to rutile has been studied by simply controlling the initial volume ratios of TiCl3 to titanium isopropoxide in the reaction solutions.The blue TiO₂ has a distinct improvement of visible light harvesting and remarkable enhancement in photocatalytic activity,which could be ascribed to the presence of Ti³⁺centers and the synergetic effect between the two phases.In addition,the as-prepared blue TiO₂ shows an excellent stability during the photocatalytic reactions.A photocatalytic mechanism of the self-doped blue TiO₂ was proposed at last.4.A novel nanocomposite,Bi nanorods and Bi₂WO₆ nanosheets supported on reduced graphene oxide（Bi/Bi₂WO₆/rGO）,was synthesized via a facile one-pot solvothermal method.In the reaction process,Bi₂WO₆ nanosheets and Bi nanorods were grown in situ on the rGO sheets,which were simultaneously achieved by the reduction of GO.Such a synthetic strategy can form effective close interfacial contacts and strong interactions among Bi₂WO₆,Bi and rGO,leading to efficient separation and transfer of photogenerated electron-hole pairs.As a result,the ternary plasmonic photocatalyst exhibits a much higher photocatalytic activity than pure Bi₂WO₆ and the binary composites in the photocatalytic degradation of rhodamine B and p-chlorophenol under visible light irradiation,which could be ascribed to the synergic effects of the improved electon-hole pair separation efficiency,enhanced visible-light harvesting and the good adsorptive capacity toward dye molecules.5.The fabrication of semiconductor with proper band alignment and reactive exposing facets is very attractive for environmental and energy applications.Herein,we develop a BiOCl/（BiO）₂CO₃ heterostructure via an etching and re-growth method.In this approach,the precursor of guanidine hydrochloride not only acts as the sources of chloride and carbonate ions to form BiOCl/（BiO）₂CO₃ heterojunction but also acts as the crystal growth inhibitor to tune the growth of BiOCl nanosheets.The morphologies of the final samples can be tuned by simply changing the ethanol/water volume ratio in the initial reaction system.The composites with intimate interfacial contacts between BiOCl and（BiO）₂CO₃ exhibited superior photocatalytic activity towards the degradation of rhodamine B under visible light irradiation,which can be ascribed to the synergistic effect of suitable BiOCl/（BiO）₂CO₃ heterojunction interface and the exposed high-energy facets.