Electrospinning Preparation And Photocatalytic Properties Of Titanium Based Heterojunction Composite Nanofibers

In recent years,water pollution has become one of the social problems concerned by governments and people.Especially with the rapid development of textile printing and dyeing industry,printing and dyeing wastewater has become one of the main sources of water pollution because of its large amount of water,high concentration of dye organic matter and difficulty in purification and treatment.The treatment methods of printing and dyeing wastewater include physical adsorption,electrolysis,oxidation,coagulation and biological process.Among them,photocatalytic oxidation has attracted more and more attention due to its advantages of low cost,fast and high efficiency.The core of photocatalytic oxidation method is how to design and prepare low cost,high activity and high solar light utilization photocatalyst,which has become the research direction of many researchers in the field of photocatalysis.Titanium based semiconductor materials,such as rutile titanium dioxide?TiO₂?,strontium titanate?SrTiO₃?and calcium titanate?CaTiO₃?,have become one of the important members of photocatalyst family due to their advantages of friendly environment,stable physical and chemical properties and low price.However,titanium based nano-semiconductor materials?rutile TiO₂,SrTiO₃ and CaTiO₃?,as wide-band gap semiconductors,only respond well to ultraviolet light,which greatly limits the utilization of solar light.In addition,How to further improve the photocatalytic activity and photostability of titanium-based photocatalysts while expanding their photoabsorption range has also become one of the most urgent problems to be solved in the development of a new type of visible light-responsive titanium photocatalyst with high efficiency and good light stability.In order to further expand the range of photoabsorption and improve the photocatalytic activity of titanium-based photocatalysts,the optimum conditions for the preparation of titanium-based nanofibers by electrospinning were determined in this paper.a novel SrTiO₃ modified rutile TiO₂nano-photocatalysts with heterojunction were prepared by one-step electrospinning method in this paper.Furthermore,the influence of heterojunction on the catalytic activity of the composite photocatalyst was discussed.Then the narrow band gap Ag₃PO₄ semiconductor is matched with the wide band gap SrTiO₃ semiconductor to form a composite photocatalyst with heterojunction.The effects of Ag₃PO₄ sensitized SrTiO₃ on the photoabsorption range and photocatalytic activity of SrTiO₃ were also discussed.In addition,MoS₂ nanosheets were grown on CaTiO₃ nanofibers,and the effect of MoS₂ nanosheets as co-catalyst on their photocatalytic activity were also discussed.The main contents and results of the study are as follows:1.The effect of the catalyst on the crystal structure and fiber morphology of the prepared titanium-based nano-photocatalysts were investigated through optimizating preparation conditions of electrospinning by the applying voltage,the receiving distance,the heat treatment temperature and the heating rate of the heat treatment process.The results show that one-dimensional rutile TiO₂nanofibers,SrTiO₃ nanofibers and CaTiO₃ nanofibers can be successfully prepared at 700°C heat treatment temperature.2.The one-step electrospinning technique was used to prepare one-dimensional SrTiO₃ modified rutile TiO₂ composite nanofiber photocatalyst with heterojunction and its photocatalytic properties were studied.The results show that compared with single-phase TiO₂ nanofibers,one-dimensional SrTiO₃/TiO₂?ST-3?heterojunction nanofibers have the best degradation rate to methyl orange under UV irradiation.Its degradation rate is about twice as high as that of single-phase rutile TiO₂.3.The one-dimensional Ag₃PO₄ sensitized SrTiO₃ nanofiber photocatalysts with heterojunction was successfully prepared by combining electrostatic spinning and in-situ deposition.It is found that the introduction of Ag₃PO₄ can not only further expand the optical absorption range of SrTiO₃ to visible region,but also make a good match with SrTiO₃ to form heterojunction.The heterojunction can effectively inhibit photogenerated electron-hole recombination and improve its response to visible light.Compared with SrTiO₃ nanofibers,Ag₃PO₄/SrTiO₃?3AS?composite nanofibers have more excellent photocatalytic degradation activity for methylene blue?MB?under visible light irradiation,and the degradation activity is about 10 times as high as that of single-phase SrTiO₃ nanofibers.4.By designing a combination of electrospinning technology and hydrothermal technology,the composite photocatalysts of MoS₂ nanosheets were successfully grown on CaTiO₃ nanofibers,and their photocatalytic properties were also studied.Compared with single-phase CaTiO₃ photocatalysts,MoS₂/CaTiO₃?MC-3?heterojunction composite nanofiber photocatalyst has higher catalytic activity for Rhodamine B?RhB?degradation under xenon lamp irradiation.This is due to the fact that,MoS₂ acts as a co-catalyst to rapidly transfer photogenerated electrons through the heterojunction formed between MoS₂ and CaTiO₃,which hinders the recombination of photogenerated electrons and holes and thus improves its photocatalytic activity.In addition,due to the large surface area of MoS₂ nanosheets,the area involved in the reaction will also increase,and increasing the reaction area,which has a very important effect on the improvement of photocatalytic activity.5.The photocatalytic cycling experiments were carried out to evaluate the photostability of titanium based heterojunction nanofibers.The titanium-based heterojunction composite photocatalysts designed in this paper have very good photostability,and the photocatalytic activity decreases by less than 10%after several cycles of catalytic reaction.This is very promising for the future application in the treatment of actual dye wastewater.