Preparation Of Carbon Nitride With Controllable Morphologies And Their Application In Composite Pollution System

Environmental pollution and energy crisis have severely constrained the pace of constructing China into ecological civilization.As a solar energy conversion platform,semiconductor photocatalyst has great application prospects in solving energy and environmental crisis.Among the vast number of semiconductor family members,TiO₂and g-C₃N₄ are widely studied as representatives of inorganic and organic conjugated semiconductors,respectively.Both of these semiconductors have the advantages of low price,stable physical and chemical properties,safety and non-toxicity.However,they also have their own disadvantages,such as narrow spectral response and weak reducing power of TiO₂;small specific surface area and low quantum efficiency of g-C₃N₄.So,a series of strategies are being used to increase the spectral response range and quantum efficiency of TiO₂ and g-C₃N₄.Such as,morphology control,elemental?ion?doping,surface C hybridization,noble metal deposition,heterostructure construction,etc.Heavy metals and organic pollutants in electroplating,papermaking and leather wastes pose a serious threat to human safety and ecological stability.Photocatalytic redox technology has been widely applied to the research of removing these two types of pollutants.The research and mechanisms of photocatalytic oxidation of organic pollutants and photocatalytic oxidation or reduction of heavy metal ions have achieved certain results.However,the composition of wastewater in the natural is complex,so the application of photocatalysis to treat actual wastewater is still difficult.Therefore,it is of great significance to explore the photocatalysts'application and mechanism in multi-pollutant systems.In this paper,photocatalytic activity of TiO₂ and g-C₃N₄ will be improved by morphology control,semiconductor coupling,surface C hybridization and metal ion doping.Then,the prepared catalyst was applied to multi-contaminant system.Then photocatalytic mechanism was explored.The main research contents are as follows:1.The highly active porous g-C₃N₄?pg-C₃N₄?was prepared by treating the precursor melamine with hydrochloric acid?HCl?and ethylene glycol?EG?.The as prepared pg-C₃N₄ was applied to the composite pollutant system of 4-chlorophenol?4-CP?/hexavalent chromium[Cr???],and the synergistic photocatalytic effect under acidic and neutral conditions were explored,respectively.Compared to the photocatalytic oxidation of single-component 4-CP and the photocatalytic reduction of single-component Cr???,the degradation rates of 4-CP and Cr???in the composite system were greatly improved.This means that a new redox reaction between 4-CP and Cr???was unlocked by electron transfer of pg-C₃N₄.2.Atomic level hybrid g-C₃N₄ nanosheets/TiO₂ hollow spheres?g-C₃N₄NSs/TiO₂ HMSs?were prepared by one-step synthesis strategy through the direct mixing of precursor tetrabutyl titanate and melamine.Hydrothermal carbon microspheres?HCSs?act as both dispersant and structure-directing agent for the simultaneous construction of graphitic carbon nitride nanosheets and titanium dioxide hollow microspheres.The prepared g-C₃N₄ NSs/TiO₂ HMSs increase the specific surface area,reduce the mass transfer resistance,and facilitate the migration of photogenerated carriers.As prepared g-C₃N₄ NSs/TiO₂ HMSs were applied to the complex contaminant system of 4-fluorophenol?4-FP?/Cr???and trivalent arsenic[As???]/Cr???,respectively.Compared to single-component system,the efficiencies of photocatalytic oxidation of 4-FP,the photocatalytic reduction of Cr???and the photocatalytic oxidation of As???in the complex pollutant system have all been improved,which shows a significant synergistic photocatalytic effect between contaminants in the composite system.This result shows that on the basis of the original photocatalytic reaction,a new redox reactions between 4-FP and Cr???or As???and Cr???are promoted by the good electron transfer ability of g-C₃N₄NSs/TiO₂ HMSs.3.High-specific-area porous carbon microspheres?PCMSs?was prepared from camellia oleiferashells with theprocessofhydrothermal carbonization,high-temperature annealing,and high-temperature alkali etching.The PCMSs were used as doping agent and structure-directing agent to prepared PCMSs/C₃N₄ NSs by500 ? calcination under argon and air atmosphere,successively.The prepared PCMSs/C₃N₄ NSs were used to deposit Cr???by photocatalytic reducing Cr???,then the highly active Cr_?/PCMSs/C₃N₄ NSs were obtained by curing at 200 ?.The synergistic photocatalytic effects in the 4-FP/Cr???multi-component composite pollution systems were studied by using as-prepared Cr_?/PCMSs/C₃N₄ NSs under different pH conditions.Because of the low electron cloud density of oxygen in the Cr₂O₇^2-,the efficiencies of 4-FP degradation and Cr???reduction were simultaneously improved in the 4-FP/Cr???multi-component synergistic photocatalytic systems relative to the single-component photocatalytic systems under acidic conditions.The total catalytic activity has also been greatly improved in neutral conditions.This result shows that whether acidic or neutral conditions,the redox reaction between 4-FP and Cr???can be promoted by the electron transfer of Cr_?/PCMSs/C₃N₄ NSs.