Preparation Of Photocatalysts With Novel Morphologies And Advanced Properties By Template Method

Energy shortage and environmental pollution become increasingly prominent with the rapid development of economy and society,which seriously affect the survival and development of human beings.Solar energy,as a clean and renewable energy,is the most suitable alternative to traditional energy sources.semiconductor-based photocatalysis can use solar energy to generate hydrogen from water splitting,degrade pollutant,and reduce CO₂,which has broad application prospects for solving environmental pollution and the energy crisis.However,the traditional photocatalysts?TiO₂,ZnO?suffer from the insufficient solar light absorption and the low separation rate of photogenerated carriers,which limit the further application.Therefore,it is a hot spot in the photocatalytic field to design the novel photocatalysts with high efficiency by controlling and optimizing the microstructure of traditional photocatalysts.Herein,in the view of the visible light utilization and photogenerated electron-hole pairs separation efficiency,a series of novel photocatalysts were successfully fabricated by using template method.And the photocatalytic activity of as-fabricated photocatalysts was tested by the photocatalytic hydrogen evolution reaction and the degradation of pollution under visible light irradiation.The influence of template type and content on the structure and photocatalytic performance of photocatalysts was studied in detail,respectively.The as-fabricated photocatalysts were characterized in detail by XRD,XPS,SEM,TEM,FT-IR,UV-Vis DRS,N₂adsorption-desorption isotherms,and PL analysis.Moreover,the photocatalytic activity is evaluated by the photocatalytic hydrogen evolution and the degradation of pollution under visible light irradiation.Furthermore,the structure-activity relationship and the photocatalytic mechanisms were studied and discussed in detail.The main results are summarized as follows:?1?Synthesis and photocatalytic properties of ZnO photocatalysts with novel morphologyThe highly dispersive ZnO materials were synthesized by the hydrothermal method using ionic liquid 1-methyl-3-[3'-?trimethoxysilyl?propyl]imidazolium chloride as the template.The effect of ionic liquid concentration and calcined atmosphere on the morphology and photocatalytic activity is studied.The photocatalytic activity is evaluated by the degradation of MB,MO,RhB under visible light irradiation.The results showed that the as-fabricated ZnO materials consisted of individual microrods with self-assembled bowknot-like architecture whose size was about 1?m.Based on the self-assembly of ionic liquid,the possible formation mechanism of the as-prepared ZnO materials is tentatively elucidated.In addition,the ZnO-2.6N sample exhibited the higher photocatalytic activity for the MB photodegradation than the MO or RhB photodegradation.What's more,it was found that the ZnO materials calcined under air atmosphere represented the better photocatalytic activities than that of samples calcined under nitrogen atmosphere for the degradation of methylene blue?MB?under UV irradiation.And the special structure,surface area,adsorption capability of dye,the separation rate of photogenerated electron–hole pairs and band gap had effects on the photocatalytic activity of ZnO photocatalysts.From the trapping experiment,it is found that O₂^·-was the main active species for the photocatalytic degradation of MB.?2?Synthesis of BiOCl materials with enhanced photocatalytic activityThe poly?allylamine hydrochloride?and Bi?NO₃?₃ were used as Cl source,template and Bi source to fabricate BiOCl materials assisted solvothermal method.The influence of polyelectrolyte concentrations on the formation and morphology of BiOCl was systematically investigated.Moreover,the photocatalytic activity of the as-fabricated BiOCl materials was evaluated by the degradation of rhodamine B?RhB?under visible light irradiation.The results showed that the polyelectrolyte,which acted as reactant,template or structure-directing agent,played a critical role to the structure of as-fabricated BiOCl materials during the reactive process.BiOCl microspheres could be obtained when the polyelectrolyte content was low.With the increase of polyelectrolyte content,the plate-like BiOCl materials were synthesized.Through the various characterizations,the relationship between the structure of the BiOCl materials and the photocatalyic activity was studied in details.It is found that BiOCl microspheres exhibited the enhanced adsorption capacity and catalytic activity among the as-fabricated materials,which is caused by the high surface area of microspheres.And the presence of O-vacancies can also improve the light harvesting ability in the visible light range,reduce the interfacial charge recombination rate and enhance the photocatalytic activity.?3?Synthesis of Br-modified g-C3N4 semiconductors for photoredox water splittingThe bromine doped graphitic carbon nitride?CN-Br_X?with highly porous structure by using ionic liquid?1-butyl-3-vinylimidazolium bromide?as the Br source and soft-template was synthesized for the first time.The photocatalytic activity of as-prepared CN-Br_X was evoluated in hydrogen evolution under visible light irradiation.A systematic study was carried out on the optimization in the doping amount.The result found that the as-fabricated CN-Br_X photocatalysts possessed a uniform porous network with thin walls due to the release of volatile domains and decomposition of ionic liquids.And the sample CN-Br_0.02 showed an outstanding H₂evolution rate under visible light irradiation(120?mol h^-1),which is about 3.6 times higher than pure CN.This phenomenon indicates the the large surface area?127 m²/g?and the highly porous structure benefit the exposure of active sites.Meanwhile,the absorption intensity increased which was primarily owing to the multiple reflections of incident light within the porous structure.Moreover,the bromine modification and highly porous structure can narrow the band gap,enhance the separation rate of photogenerated electron-hole pairs,improve the optical and conductive properties of CN,thus contribute to an outstanding H₂ evolution rate under visible light irradiation.?4?Synthesis of hollow mesoporous g-C3N4 spheres for photoredox water splittingA facial,one-step soft templating method to synthesize the hollow mesoporous g-C₃N₄ spheres with high surface area and high porosity was developed,which taking advantage of both supramolecular assembly of cyanuric acid and melamine through hydrogen bonds and the structure-directing character of ionic liquid.And the photocatalytic activity of as-prepared carbon nitride was evoluated in hydrogen evolution under visible light irradiation.The influence of solvent and ionic liquid content on the texture and photocatalytic activity is studied in detail,respectively.It is found that a plenty of mesopores can be found from the structure of as-prepared hollow g-C₃N₄ spheres,which is caused by the release of volatile domains and decomposition of ionic liquids.Besides,as-prepared g-C₃N₄ spheres exhibit improved light absorption in visible ranges,faster separation rate of photogenerated electron-hole pairs than the bulk carbon nitride.In addition,the as-prepared hollow mesoporous carbon nitride spheres exhibit almost 30 times higher than traditional carbon nitride which calcined by melamine for the photocatalytic hydrogen evolution reaction under visible light irradiation,which may be owing to the fact that the high surface area is beneficial for improving light absorption in visible ranges,and finally enhancing the H₂ evolution rate.?5?Synthesis of high-surface-area carbon nitride with tunable texture for enhanced photocatalytic activityMesoporous carbon nitride nanosheets,using ionic liquid and supramolecular precursor cyanuric acid-melamine complex as the template and precursor,were successfully fabricated.The photocatalytic activity is assessed by the photocatalytic hydrogen evolution and the degradation of RhB under visible light irradiation.The morphology and texture of carbon nitride was controlled by changing the ionic liquid concentration and the ionic liquid type.The results found that the supramolecular assembly behavior of precusors,the structure-directing effect of ionic liquid as well as the interaction between precursor and template played a vital role for the final texture of carbon nitride.A disordered hollow carbon nitride box morphology with some pores in the wall could be fabricated under lower IL-1 concentration.While,the morphology changed into a layered structure with the increase of ionic liquid content.The disordered nanosheets and hollow tube with large pores in the wall could be fabricated by using IL-2 and IL-3,respectively.Additionally,as-prepared mesoporous carbon nitride exhibited the excellent light harvesting properties and fast separation rate of photogenerated carrier.Moreover,a higher photocatalytic hydrogen evolution rate(120.3?mol h^-1)under visible light irradiation could be obtained for as-prepared mesoporous carbon nitride CN-0.1 owing to the special structure and the presence of multiple mesopores,which was approximately 25.6 times as high as that of bulk carbon nitride calcined by melamine(4.7?mol h^-1).Furthermore,photocatalytic degradation rate was enhanced by using CN-0.1 compared with CN synthesized without ionic liquid.