Photocatalytic Degradation Of 2,4-dinitrophenylhydrazine By Modified Titanium Dioxide

Nowadays,nitroaromatic compounds are widely used in military,medicine,and pesticide fields.However,during their production and use process,a large number of wastewaters containing such substances will be discharged into the nature,causing serious harm to the animal and human system.2,4-dinitrophenylhydrazine is a carcinogenic and highly stable pollutant.Therefore,the effective degradation of nitroaromatic compounds is particularly important.Photocatalytic degradation method is considered to be a clean,economical and efficient pollutant degradation technology.In this paper,TiO₂ based photocatalyst was modified by metal loading,element doping and heterojunction construction.The obtained composites have superior photocatalytic activity and great potential in practical application.Ag/Cu/TiO₂ composite was successfully synthesized by a one-step solvothermal process combined with chemical reduction method.The composite has a strong response in the wavelength range of 400-600 nm under LSPR of Ag nanoparticles.The degradation experiments show the degradation rate of 2,4-dinitrophenylhydrazine（2,4-DNPH）can reach85.9%within 70 min under simulated solar light irradiation when the loading of Ag and Cu were 2 wt%and 1 wt%,respectively.Non-linear least squares fitting indicates that the degradation process follows pseudo-first-order kinetic model,and the apparent activation energy is 19.97±2.07 k J mol^-1.In addition,the photocatalytic degradation also followed Michaelis-Menten kinetics,with v_maxand K_M of 0.6986±0.0096 mg L^-1 min^-1 and2.3980±0.2917 mg L^-1,respectively.Using urea as N source,a novel N-TiO_2-X/g-C₃N₄（NTCN）composite was designed and constructed successfully by a facile hydrothermal-calcination method,which has excellent visible light absorption,charge separation and transfer capability.The co-doping N and Ti³⁺/Ov were achieved to reduce the band gap of TiO₂,and the g-C₃N₄ nanosheets can be tightly wrapped on the surface of N-TiO_2-X,which can act as a“highway”for electron transfer.When the content of g-C₃N₄ in composite is 30 wt%(NTCN_0.3)with calcination temperature of 350℃,the photocatalytic degradation rate of 2,4-DNPH can reach 93.2%after 70 min irradiation,much higher photocatalytic degradation rates than monomers and other composites.Furthermore,the degradation process was verified to be pseudo-first-order kinetic model,and the apparent activation energy is 17.23±2.47 k J mol^-1.The characterization results of Ag/Cu/TiO₂ and NTCN_0.3 show that the electron transfer mechanism of the two TiO₂-based composites conforms to the hot electron transfer mechanism and the S-scheme electron transfer mechanism,respectively.In addition,possible degradation pathway was proposed based on the liquid chromatography-mass spectrometry（LC-MS）analysis and theory calculation.