Visible Light Photocatalytic Degradation Of Macromolecular Organic Pollutants In Water By N-TiO₂/GO Nano Materials

Humic acid and MC-LR are common organic pollutants in natural water.Humic acid is a typical precursor substance in the chlorinated disinfectant water treatment process,and Microcystin-LR can produce and release from cyanobacteria cells in the outbreak of algal bloom.Two kinds of organic pollutants seriously threaten the safety of drinking water.So it is of great significance to explore efficient and convenient removal methods for removing refractory organic matter to ensure the safety of drinking water.In this study,N-TiO₂/GO photocatalytic materials were prepared by hydrothermal method with urea as the nitrogen source,butyl titanate as the precursor and graphene as the carrier.Characterization techniques such as SEM,XRD,Raman,FT-IR,TGA,BET,UV-Vis DRS were used to analyze the surface morphology,crystal phase structure,functional groups and chemical bonds of the materials.In addition,N-TiO₂/GO was used to catalyze the degradation of humic acid in visible light,and factors affecting the degradation effect were analyzed to select the best photocatalytic materials.Furthermore,the effect,kinetics,reaction mechanism and degradation pathway of Microcystin-LR by N-TiO₂/GO in visible light were investigated.The results showed that the particle size of the modified N-TiO₂/GO photocatalytic material decreased,the specific surface area increased,and the layered void effectively eliminated agglomeration.XRD and Raman spectra showed that the crystalline form of the material was dominated by anatase,and N element successfully entered the TiO₂lattice.FT-IR characterization proved that Ti-O-C bond was formed between TiO₂ and graphene,and the spectral response range increased significantly.When the hydrothermal temperature was 180℃,the content of N was 6wt%,and the loading capacity of graphene was 5wt%,then the photocatalytic activity was optimal.When the dosage was 1g/L,the catalytic degradation rate and mineralization rate of humic acid at the initial concentration of 10mg/L reached 86.6%and 80.4%respectively after 180min,and the reaction rate constant was 0.0099min^-1.N-TiO₂/GO is stable and the degradation rate and mineralization rate can still reach 72.6%and 58.5%after five cycles.According to the above experiments,the optimal performance of 6%N-TiO₂/5%GO was selected for the catalytic degradation of Microcystin-LR.When the dosage was 1g/L and the initial concentration of Microcystin-LR was 1mg/L,the degradation rate reached 89.8%and the reaction rate constant was 0.0126min^-1 after 90min of visible light catalytic degradation.The free radical capture experiment showed that the largest contribution of free radical was·OH,accounting for 95.0%,while h⁺only accounted for 3.9%.Degradation pathway analysis showed that the Adda chain was the primary target of·OH,and toxicity of the solution was positively correlated with residual Microcystin-LR concentration.