Preparation And Performance Of Full Spectrum,Light-Storing Titanium Dioxide And Carbon Nitride Photocatalysts

In recent years,semiconductor photocatalysts for treatment of waste gas,wastewater and degradation of organic pollutants in the field of environmental purification have attracted widespread attentions and extensive research.The photocatalytic technology can convert solar energy into chemical energy or directly degrade and mineralize of organic pollutants,it will not cause secondary pollution.But so far the practical application of photocatalysts are limited for its narrow photoresponse and out of commission the full spectrum.They are mainly used for removal of organic pollutants in wastewater,not to mention NOx gas.There are still exit many disadvantages.For example,the photogenerated e--h+ was likely recombination,nanoparticles were easy to aggregate and could not to use recycling.Photocatalytic properties of semiconductor restricted by its inherent optical specific,it required a appropriate light source matching their energy or even greater than the band gap of the semiconductor,the photoreaction could not occur in the absence of external light.All of these disadvantages were seriously restricted its practical application.In this paper,on the one hand TiO₂ and C₃N₄ were modified to broaden its range of spectral response,and at the same time they were used to degrade the organic pollutants and NOx,the adsorption,adsorption kinetics and thermodynamics were studied also.On the other hand,the modified photocatalysts were composited with up-conversion phosphors to prepare the full spectrum photocatalyst,and it was used to degrade NOx under different light source.Then the light-storing photocatalyst was received by long afterglow phosphors and nano-photocatalyst,and the performance of bacteriostasis and degradation of organicpollutants were studied under no illumination.（1）TiO₂ modification,adsorption and photocatalytic performanceNanocrystalline modified TiO₂ was synthesized by solvothermal method using metal and non-metal as dopant.Crystal phase composition,crystallinity,microstructures,morphologies and optical properties the materials were characterized using XRD,DRS,XPS,SEM and EDX et al.The photocatalytic activity was determined by degradation of methyl orange（MO）reaction and NOx gas.The results show that doping with nonmetal is more advantageous to improve the crystallinity and its adsorption,favorable reaction where N is best.Doping TiO₂ with Cr and Ag can broaden the scope of light absorption,reduce combination of electron-hole pairs,increase the absorption of visible light significantly.It can even absorb the wavelength of 600 nm.The adsorptive property and reaction kinetics of modified TiO₂ was determined using methylene blue（MB）as template molecules.Anatase and rutile N-TiO₂ were synthesized via hydrothermal method.UV-Vis spectra,XRD,SEM et al supplied information of the structure and adsorption thermodynamic properties of N-TiO₂.The results show that the adsorption quantity of nonmetal doping TiO₂ is higher than metal doping.The crystal of semiconductor will affect the adsorption performance,rutile N-TiO₂ displayed higher adsorption capacity than anatase and its adsorption behavior followed Langmuir isotherm model and the pseudo-second-order kinetics,while anatase had much better visible light capacity than rutile.As a result,when they are mixed with proper proportion,the photocatalytic efficiency improve.The process is a spontaneous exothermic adsorption.In addition,the photocatalytic reaction rate is proportional to the concentration of solution reaction under visible light.（2）The preparation of carbon nitride polymerThe g-C₃N₄ particles with large surface area were successfully realized by a fractional thermal polymerization method using different precursors,and the synthesis regulation of g-C₃N₄ are studied.The photocatalytic performance of Ag₃PO₄/g-C₃N₄ complex was studied by degradation NOx.The products composition,characterized,microstructures and optical properties were characterized with XRD,DRS,XPS,SEM and EDX et al.The results show that the precursors strongly influence the polymerization reaction temperature and process,melamine and dicyandiamide as precursors preferred to obtain tri-s–triazine-base g-C₃N₄,while guanidine carbonate preferred to get triazine-base g-C₃N₄.The elementary analysis revealed that 1.9-2.0mass% of hydrogen was contained in the composition and it should be g-C₃N₄H2.Ag₃PO₄/g-C₃N₄ composites showed different band gap and morphology,and also decreased the photo-corrosion and self-corrosion by forming heterojunction.The charge separated efficiently.（3）The preparation and photocatalytic performance of full spectrum photocatalystThe up-conversion phosphors and as synthesized products are composited,and the morphology,crystallinity,property of light absorption and conversion performance are characterized by XRD,DRS,SEM,EDX and PL.The photocatalytic activity of NOx is detected under wavelength irradiation of 980 nm,627nm,530 nm,445nm and 390 nm.The research results show that 477 nm,543nm and 660 nm emission band can be detected to these three kinds of up-conversion phosphors after they were excited by infrared light of 980 nm.The photocatalytic activity of composite can be strongly enhanced when TiO₂ is promoted by the presence of organic up-conversion phosphors.It can absorb ultraviolet,visible and infrared light,achieve the full spectrum response of the solar spectrum.G-up/N,Ag-TiO₂ has the maximum NOx degradation ability of 64% under 10 min irradiation.（4）The preparation and photocatalytic performance of light-storing photocatalystThe long afterglow phosphors were prepared by a combustion method and the light-storing composites of LAP-TiO₂ were synthesized at the same time.The fluorescence feature of the long afterglow phosphors was characterized by Fluorescence spectrum.The degradation performance of methyl orange and bacteriostasis under no light irradiation was detected.The research results show that the light-storing photocatalyst was obtained and it can be used to disinfect and degrade MO under no irradiation.The antibacterial performance suggested that the sample has high activity on antibacterial staphylococcus aureus.The MO degradation of MgSrAl₂O₄:Dy/Ag@AgI-TiO₂-Cr can reach to 82.3% after 180 min.The light-storing property was realized by compositing long afterglow phosphors and photocatalysts,and strengthen the use of ultraviolet light.In this context,the rule of modified TiO₂ and g-C₃N₄ were systematically expounded.The relationship of microstructure,adsorption,optical properties of them with photocatalysis was studied seriously.Through these researches we tried to figure out the ideal photocatalyst,and then composited it with up-conversion phosphors or long afterglow phosphors to get full spectrum and light-storing photocatalyst.This research was a good attempt to expand photocatalyst applications on environmental purification,clarify photocatalytic mechanism and creating new photocatalytic technology.