Graphitic Carbon Nitride Loaded Nickel-iron Hydrotalcite Activated Persulfate Treatment Of Dye Wastewater

At present,the dye industry is an important supporting industry for Chinese national economy,mainly used in paints,medicine,textiles,cosmetics and other fields.However,in the process of production and use of dyes,the environmental pollution problems caused by direct discharge without treatment or failure to meet emission standards are urgently needed.Three kinds of activators of graphitic carbon nitride（g-C₃N₄）,layered nickel-iron hydrotalcite（NiFe-LDH）and graphitic carbon nitride-supported layered nickel-iron hydrotalcite（g-C₃N₄@NiFe-LDH）were prepared.Using the advanced oxidation technology of persulfate and simulating dye wastewater with cationic dye methylene blue（MB）,the effects of different factors on the degradation of dyes during the experiment were studied,and the active species and degradation mechanism of the reaction were analyzed through the free radical quenching experiments and UV-Visible Spectroscopy.The main research contents and results show that:（1）Preparation and characterization of g-C₃N₄ by polycondensation,and sodium persulfate（PS）was activated with methylene blue（MB）as a target contaminant.The effects of g-C₃N₄ dosage,sodium persulfate concentration,initial p H and temperature on the degradation of methylene blue in g-C₃N₄/PS system were investigated.When n（PS）:n（MB）=20:1 and g-C₃N₄ dosage is 1.0 g/L,the degradation rate of MB at 120 min is up to 93.2%.（2）Preparation and characterization of NiFe-LDH by simultaneous precipitation method,which activated PS to degrade MB.The effects of different factors on the degradation of MB in NiFe-LDH/PS system were investigated.When the dosage of NiFe-LDH is 1.0 g/L and n（PS）:n（MB）=20:1,the degradation rate of MB at 120 min is up to 86.2%.（3）The g-C₃N₄@NiFe-LDH was prepared and activated as an activator.The effects of different factors on the degradation of MB in g-C₃N₄@NiFe-LDH/PS system were investigated.Kinetic experiments show that the dosage of g-C₃N₄@NiFe-LDH activates PS degradation MB follows first order reaction kinetics model.The main influence order of the reaction was g-C₃N₄@NiFe-LDH dosage>PS concentration>initial p H.SEM,TEM image and XRD,the characteristic peaks of g-C₃N₄ and NiFe-LDH appearing in XPS indicate that NiFe-LDH has been loaded onto the g-C₃N₄ layer.G-C₃N₄@NiFe-LDH can effectively activate PS to produce×SO4^-,×OH,O2^-and h+.These active radicals degrade MB.When g-C₃N₄@NiFe-LDH dosage is 1.0 g/L,n（PS）:n（MB）=20:1,60 min can completely degrade MB,far exceeding g-C₃N₄ and NiFe-LDH alone effect.The UV-Visible Spectroscopy indicates that the benzene ring and naphthalene ring of MB are broken during the reaction,and the dimethylamino conjugated system is destroyed,thereby decolorizing the dye.