Preparation Of C₃N₄/TiO₂ Nanocomposites And Study On Photocatalytic Degradation To Orange ? Dye Wastewater

With the development of society and economy,the problem of environmental pollution has increasingly become the primary factor constraining the sustainable development of the economy.More and more attention from people has been paied on this issue.A large amount of organic-rich wastewater produced by petrochemical,pharmaceutical,printing and dyeing industries has the characteristics of complex composition,high chroma,and not easy biodegradation,which lead to uneffective degradation efficiency with some traditional water treatment technologies.Semiconductor photocatalytic technology is a green technology which combines light energy with photocatalyst and degrades most of the refractory organics into CO₂,H₂O and some non-toxic and harmless micromolecule substances.As a kind of semiconductor photocatalyst,TiO₂ has been paid attention by many researchers due to its characteristics of cheapness,availability,non-toxicity and good photocatalytic activity.However,a wider bandgap leads to a lack of a good visible light response and a low utilization of light energy.Meanwhile,the defect of easy recombination of photoelectrons and holes also restricts its application in the field of photocatalysis to some extent.g-C₃N₄ is an emerging non-metal semiconductor material with a narrow bandgap and better absorption of visible light.Due to the small specific surface area and the recombination easily of photoelectron-holes,its photocatalytic activity needs to be further improved.Based on the above,g-C₃N₄/TiO₂ nanocomposites was prepared in this study using the method of ultrasonic treatment,one-step calcination.The preparation,characterization,photocatalytic properties and photocatalytic mechanism of the composites were also studied.The specific research results are as follows:1.g-C₃N₄/TiO₂ nanocomposites were synthesized successfully by using ultrasonic treatment and one-step calcination method with commercial TiO₂ and melamine as raw materials.Characterization and analysis by XRD,FT-IR,EDX and XPS confirmed the synthesis of g-C₃N₄/TiO₂ nanocomposites successfully.The SEM and TEM observations showed that the agglomeration effect of TiO₂ particles was inhibited and evenly dispersed well on the surface of g-C₃N₄.The band gap of the composite is significantly reduced,and the absorption sideband undergoes a red shift compared with TiO₂.2.The photocatalytic activity of g-C₃N₄/TiO₂ nanocomposites was evaluated using Orange??AO7?solution as the target contaminant.When the raw material ratio of TiO₂ to melamine is 1:4,the composite prepared by calcination at 450?for 4 h has the highest photocatalytic activity.The dosage of catalyst can affect its photocatalytic efficiency.In acidic condition and at lower concentration,the degradation of the AO7 solution by the catalyst is much better than that of in the alkaline condition and at higher concentration.3.After using five times,the g-C₃N₄/TiO₂ nanocomposite still maintained good photochemical stability,indicating that it can be used repeatedly.4.Through the UV-vis and COD changes over time and active free radical capture experiments,it was demonstrated that during the photocatalytic degradation of AO7,the chromophoric groups of AO7 dye molecules are gradually decomposed and mineralized into CO₂ and H₂O under the action of active free radicals such as·O₂^-,·OH and h⁺.