Preparation Of TiO₂ Nanobelt/Reduced Oxide Graphene/Pg-C₃N₄ Ternary Composite Photocatalytic Heterojunction For EE2 Removal

In recent years,the environmental hazards of environmental endocrine disruptors in water have received widespread attention in society.Among them,the steroid estrogen 17?-ethinyl estradiol?EE2?has the highest estrogenic activity,however it is also the main active ingredient of oral contraceptives.It has been detected in the effluent of wastewater treatment plants and various water environments.Therefore,the effective removal of EE2 is of great significance.Semiconductor photocatalytic technology is a new promising green water treatment technology that can oxidize organic pollutants into non-toxic H₂O,CO₂ and inorganic substances.In this work,firstly,a layer of reduced graphene oxide?RGO?was prepared by hydrothermal method on the surface of titanium dioxide nanobelts by using high-activity titanium dioxide nanobelts?TiO₂?which have been synthesized by the research group,and then combined with self-made porous carbon nitride.A TiO₂nanobelt/RGO/Pg-C₃N₄ ternary photocatalytic heterojunction was assembled.In order to optimize the amount of RGO and Pg-C₃N₄,and to compare with the ternary materials,TiO₂ nanobelts/RGO and TiO₂/Pg-C₃N₄ were prepared,and their photocatalytic properties were evaluated by photocatalytic degradation of EE2.Meanwhile,the estrogenic activities of the sample during the degradation process were detected to evaluate the environmental risk of using the prepared photocatalysts to remove the target pollutant.The physicochemical properties of the composites were characterized by SEM,TEM,XRD,PL,UV-vis DRS,BET and XPS.The relationship between material structure and properties was studied.The details are as follows:1.The TiO₂ nanobelts/RGO composite photocatalysts were prepared by hydrothermal method.The structure was characterized by various technologies.The preparation conditions were optimized depending on the removal rate of EE2 on them.The photocatalytic experiment results showed that when the initial concentration of EE2 was 3 mg/L and the irradiation of 20 W UV lamp for 120 min,the removal rate of EE2 on TiO₂/1%RGO?86.68%?was 1.20 times than that on TiO₂?73.05%?.The degradation rate constants of EE2 on TiO₂/1%RGO(0.01292 min^-1)was 1.53 times than that on TiO₂(0.00846 min^-1).After the introduction of RGO into TiO₂ nanobelts,the photocatalytic activity of the composite is significantly improved.Active species capture experiments showed that h⁺,O₂^·-and·OH were the main active species in the EE2 degradation process on the TiO₂ nanobelt/RGO composite.The reduced graphene oxide,which has superior conductivity and a large specific surface area,can effectively suppress the photo-generated electron-hole recombination and provide more active site to target EE2.2.TiO₂/Pg-C₃N₄ composites are prepared using prepared porous Pg-C₃N₄nanosheets and TiO₂ nanobelts by grinding and secondary calcination.The structure was characterized by various technologies.The calcination temperature,time and the mass ratios of TiO₂ to Pg-C₃N₄ were optimized.The photocatalytic experiment results showed that when the initial concentration of EE2 was 6 mg/L and the visible light illumination for 120 min,the removal rate of EE2 on TiO₂/Pg-C₃N₄?100.00%?was4.41 times and 1.37 times than those on TiO₂?22.68%?and Pg-C₃N₄?72.97%?.The degradation rate constants of EE2 on TiO₂/Pg-C₃N₄(0.02645 min^-1)was 17.87 times and 3.44 times than those on pure TiO₂(0.00148 min^-1)and Pg-C₃N₄(0.0077 min^-1).Active species capture experiments showed that h⁺and·OH were the main active species in the EE2 degradation process on TiO₂/Pg-C₃N₄.3.TiO₂ nanobelts/RGO/Pg-C₃N₄ ternary composites were prepared using TiO₂nanobelts/RGO composites and Pg-C₃N₄ as raw materials via grinding and secondary calcination method.The structure was characterized by various technologies.The mass ratios of Pg-C₃N₄ to RGO,calcination temperature and calcination time were optimized.The photocatalytic experiment results showed that when the initial concentration of EE2 was 6 mg/L and visible light illumination for 120 min,the removal rate of EE2 on TiO₂/0.01RGO/8Pg-C₃N₄?100.00%?was 3.47 times,1.37 times and 1.11 times than those on TiO₂?28.79%%?,Pg-C₃N₄?72.97%?and TiO₂/8Pg-C₃N₄?91.26%?.The degradation rate constants of EE2 on TiO₂/0.01RGO/8Pg-C₃N₄(0.02332 min^-1)was times,22.21 times,17.80 times and 4.73 times than those on TiO₂(0.00105 min^-1),Pg-C₃N₄(0.00131 min^-1)and TiO₂/8Pg-C₃N₄?0.00493?respectively.Active species capture experiments showed that the main active species in the EE2 degradation process on TiO₂ nanobelt/RGO/Pg-C₃N₄ was·OH.Compared with single component and binary composite materials,the photocatalytic efficiency of ternary composites is significantly improved.