Construction Of Z-scheme Catalytic System And Its Catalytic Performance For The Remocal Of Antibiotics From Polluted Water

The use of antibiotics in the treatment of human and animal infections has increased dramatically due to climate change,population growth and rapid economic development.Tetracycline（TC）is currently one of the most widely used and heavily used types of antibiotics and is widely used in human treatment,animal treatment and agricultural production.It has been reported that approximately 210,000 tons of TC have been discharged into water bodies with wastewater each year.In addition,the Chinese Academy of Sciences has found that TC is present in large quantities in various water bodies,such as groundwater,surface water and drinking water,which poses a serious threat to the environment and human health,thus making the removal of tetracycline from the water environment an urgent issue.However,traditional wastewater treatment technologies are not effective in removing TC from wastewater due to their stable chemical structure and resistance to biodegradation,and there is an urgent need for more effective methods to eliminate environmental pollutants.Compared to other treatment methods,photocatalytic oxidation technology is of great interest to researchers because of its mild reaction conditions,strong oxidation capacity,complete degradation of organic pollutants and the absence of secondary pollution.In recent years,graphite-phase carbon nitride（g-C₃N₄）and BiVO₄ have attracted much attention in the field of photocatalysis due to their ability to respond in visible light,the simplicity of their preparation methods,the low cost of raw materials and their controllable electronic properties.However,the wide band gap of g-C₃N₄ can only absorb visible light at wavelengths only below 460 nm,and there are disadvantages such as easy compounding of photogenerated electron-hole pairs,which limits its photocatalytic efficiency.The high compounding rate and low reduction capacity of BiVO₄ photogenerated electron-hole pairs become the resistance to further enhance the photocatalytic performance of BiVO₄.The material therefore needs to be modified to enhance its visible light photocatalytic activity.In this paper,we designed and prepared Z-scheme photocatalysts g-C₃N₄/BiVO₄ and g-C₃N₄/NGBO/BiVO₄ by constructing Z-scheme heterojunctions to enhance their photocatalytic performance.A series of properties of the Z-scheme photocatalysts were investigated and analyzed by characterization methods,and the Z-scheme photocatalysts were used for TC removal,and the removal effect of the prepared materials on TC was evaluated by TC removal rate.The following conclusions are drawn from this paper.（1）Preparation of Z-scheme catalyst g-C₃N₄/BiVO₄ and its performance in photocatalytic degradation of tetracycline.The Z-scheme photocatalyst g-C₃N₄/BiVO₄ was prepared by calcination and hydrothermal methods.Under visible light irradiation,20 mg of photocatalyst was added to 50 m L of 10 mg/L TC solution to study the photocatalytic degradation performance of the photocatalyst on TC.g-C₃N₄/BiVO₄ showed 3.41 and 6.61 times higher removal rates of tetracycline than BiVO₄ and g-C₃N₄,respectively.Through experimental studies,humic acid（HA）and H₂PO₄^-significantly inhibit their performance in photocatalytic degradation of TC,while the effects of Cl^-and NO₃^-are negligible.The HCO₃^-promotes the production of·OH,which can enhance the photocatalytic performance of g-C₃N₄/BiVO₄.The mechanistic analysis revealed that superoxide radicals（·O₂^-）and holes（h⁺）are the active species that play a major role in the photocatalytic degradation of TC.（2）Preparation of Z-scheme catalyst g-C₃N₄/NGBO/BiVO₄ and its photocatalytic degradation performance of tetracycline.Graphene-like（GBO）was prepared from orange peel powder as a raw material,its electron transfer rate was enhanced by nitrogen doping optimization of GBO（NGBO）,and NGBO was used as a solid-state electron mediator to construct Z-scheme ternary photocatalysts at the g-C₃N₄/BiVO₄ interface by calcination and hydrothermal methods.The prepared photocatalysts had a large number of mesoporous structures with specific surface areas of 7.525,16.522 and17.423 m²/g for g-C₃N₄/BiVO₄（CN/BV）、g-C₃N₄/GBO/BiVO₄（CN/GBO/BV）and g-C₃N₄/NGBO/BiVO₄（CN/NGBO/BV）respectively.The photocatalytic degradation of TC by CN/NGBO/BV was the strongest after 90 min of visible light irradiation.Through electrochemical measurements such as I-t curves,EIS and LSV,the mechanism of enhanced photocatalysis was analyzed because NGBO broadens the visible light absorption range and NGBO as an electron mediator significantly promotes the directional migration of electrons at the interface of g-C₃N₄ and BiVO₄,accelerating the transfer of photogenerated carriers and inhibiting the complexation of electron-hole pairs.The results of radical trapping experiments and ESR tests indicate that h⁺and·O₂^-are the main active species in the photocatalytic degradation of TC.（3）Performance study on the degradation of tetracycline by Z-scheme catalyst photo-Fenton like reactionBy adding the oxidant H₂O₂ on top of photocatalysis,a Z-scheme catalyst/photo Fenton-like catalytic composite system is constructed,coupling Fenton-like catalytic degradation technology and photocatalysis technology.The 10 mg catalyst and 5 m M H₂O₂ were added to50 ml of 10 mg/L tetracycline solution.The photocatalytic degradation of TC by Z-scheme catalyst was studied experimentally.After 90 min of illumination,the photocatalytic degradation of TC by CN/NGBO/BV composite was the strongest.The enhanced catalytic capacity of the degraded TC is explained by the fact that light and H₂O₂ promote the production of more·OH and·O₂^-in the catalytically degraded TC system,while experimental results indicate a synergy between photocatalytic and Fenton-like catalytic techniques.