Modification Of Graphite Carbon Nitride And Photocatalytic Degradation Of Rhodamine B

Solar energy is a new and sustainable energy source.Converting solar energy into chemical energy for storage has always been the focus and difficulty of research.However,the use of solar energy is concentrated in the ultraviolet region,which greatly limits the utilization of the light source.More recently,graphitic carbon nitride?g-C₃N₄?has been widely used in many photocatalytic application,such as hydrogen production by water-splitting,removal of organic pollutants,photocatalytic nitrogen fixation and synthesis of organic target compounds because of their appropriate bandgap?2.71eV?,two-dimensional layered physical structure,special electronic structure,excellent chemical stability and green pollution free.However,its low specific surface area,fast recombination of the photogenerated the electron-hole pairs and low light energy utilization limit the practical application of g-C₃N₄ in heterogeneous photocatalytic reactions.The effective separation of photogenerated the electron-holes and the efficient transfer of charges are the key to improving photocatalytic activity.Therefore,regulate the energy band structure of g-C₃N₄,reduce the recombination probability of photogenerated electron-holes,increase the absorption efficiency of the light source,and promote the surface migration of photogenerated carriers have become the focus of research.In this paper,g-C₃N₄ was modified by the following aspects,and the activity of the catalytic was tested in the photocatalytic degradation of rhodamine B.The modification schemes were as followed:Preparation of high specific surface area of g-C₃N₄ and photocatalytic degradation of rhodamine B.g-C₃N₄ has a low specific surface area?less than 10m²/g?,and the large mass transfer resistance,so that the photo-generated carriers are recombined when they do not migrate to the surface of the catalyst,which greatly increases the recombination probability of photogenerated the electron-hole pairs,reduced photocatalytic activity.Therefore,using SBA-15 as template,a series of high surface area porous g-C₃N₄ were successfully fabricated by pretreat melamine using hydrochloric acid.The photocatalytic activity of samples was tested by the degradation of rhodamine B?RhB?.The results indicated that the increase of specific surface area can effectively reduce the mass transfer resistance of the catalyst surface,promote the rapid migration of photogenerated carriers on the catalyst surface,reduce the recombination probability of photogenerated electron holes,and increase the utilization rate of the light source.The best catalytic degradation of rhodamine B?RhB?was 13 times as high as g-C₃N₄.Preparation of high specific surface area g-C₃N₄ doped by phosphotungstic acid and its photocatalytic properties.g-C₃N₄ is a dense two-dimensional layered structure with few surface active sites,and photogenerated electron-holes are easy to recombine.Phosphotungstic acid has strong oxidizing,acidity and unique pseudo-liquid phase,which has the disadvantage of being easily soluble in small molecular solvents such as water.High-specific surface area g-C₃N₄ doped by phosphotungstic acid can effectively increase the active site on the surface of the carrier,reduce the recombination probability of photo-electron-holes,and increase the selectivity and oxidation of HPW.The results indicated that the doping of HPW significantly reduces the probability of band gap energy and photogenerated electron-hole recombination,and the absorption wavelength was red-shifted,which improves the utilization of light energy.When the HPW doping amount is 1.5%,the degradation rate of Rhodamine B reaches96.10%under two hours of irradiation,and the rate constant is 0.0394 min^-1,which is 7 times than pure g-C₃N₄.The main active species in the reaction system is superoxide radicals O^2-,and the main reactive species after HPW doping have not changed.Preparation and characterization of iron doped graphitic carbon nitride modified by phosphotungstic acid and its photocatalytic properties.The lower quantum efficiency of g-C₃N₄,low light source utilization,and the presence of grain boundary effects severely limit the migration of photogenerated carriers.For this reason,the doping of iron?Fe?and the surface modification of HPW are used to regulate the energy band structure of the catalyst,increase the absorption efficiency of the light source,and promote the rapid migration of photogenerated carriers.A series of HPW/x%Fe-C₃N₄ photocatalytics were prepared by impregnation method with Melamine,Fe?NO₃?₃·9H₂O,phosphotungstic acid?HPW?as raw materials.The structure of HPW/x%Fe-C₃N₄ was characterized by FT-IR,XRD,UV-Vis,PL,SEM.The results showed that the doping of Fe and HPW changed the band structure of the catalysts and reduced the recombination probability of photogenerated electrons and holes.Besides,the doping of Fe ions inhibited the growth of the g-C₃N₄ crystals.When x=1.5,the activity of photocatalyst was further improved because the co-catalysis between g-C₃N₄ and phosphotungstate.The activities of the HPW/x%Fe-C₃N₄ catalysts were tested in the photocatalytic degradation of rhodamine B under xenon lamp.The rate constant was 7 times as high as that of pure g-C₃N₄ under optimized conditions when x=1.5 and degradation rate of rhodamine B reached 96.10%in 120 min with the rate constant of0.0394min^-1Keggin type Fe mono-substituted heteropolyacid salt doping on g-C₃N₄to tunable band gap and effect on catalytic performance.The band gap of g-C₃N₄ is 2.7eV,and the wider band gap makes the light response range narrower and the light source utilization rate is lower.By doping,hybridization between the electron orbital of the dopant and the molecular orbital of g-C₃N₄ can be achieved,and the position between the conduction band and the valence band can be adjusted,thereby changing the electronic structure and optical properties of g-C₃N₄.Fe substituted heteropoly acid potassium with Keggin type(PW₁₁Fe)was synthesized by extraction method with ether and loaded on g-C₃N₄ to composite catalysts with different amounts.The structure of catalysts was characterized by Fourier transform infrared?FTIR?spectroscopy,X-ray diffraction?XRD?,X-ray photoelectron spectroscopy?XPS?,ultraviolet-visible?UV-Vis?spectroscopy,electrochemical impedance?EIS?spectroscopy and photoluminescence?PL?spectrum.The results indicated that doping of PW₁₁Fe effectively tunable the band gap of g-C₃N₄,position of the valence band?VB?between 1.60 and2.19eV and conduction band?CB?between-1.11 and-0.37eV.In addition,it effectively reduced the recombination probability of the photogenerated electrons and holes and broadens the response range of light.Among them,when the doping amount was 15%?0.15CN?,the best result was obtained.The catalytic activity and stability of the catalysts were tested in the photocatalytic degradation of RhB under xenon lamp with 420nm filter.The results indicated that the doping of PW₁₁Fe could significantly improve the adsorption performance and reactivity of g-C₃N₄.0.15CN showed the best reactivity,and the degradation rate reached 100%after 90min illumination.The reaction rate constant of 0.15CN was 0.04266min^-1,which was 21.9times than pure g-C₃N₄.The catalytic activity was almost unchanged after four times used.