Construction Of High Specific Surface Area Defect Boron Nitride Nanosheets For Adsorption Antibiotics In Water

As a broad-spectrum series of antibiotics,tetracycline is widely used because of its low price and bactericidal effect.However,the excessive use of tetracycline has bad effect on the body’s resistance.In addition,tetracycline is difficult to be absorbed by the human,and is often discharged into the environment by the form of the original drug,and enters the water through soil penetration and so on,causing water pollution.At present,the methods for removing tetracycline from water include photocatalysis,membrane separation,etc.Among them,the adsorption method has the advantages of green,economy and high efficiency.In this paper,a series of thin layer boron nitride nanosheets（BNNSs）adsorbents with high adsorption performance and strong regeneration ability were synthesized based on the regulation of pores or defects on boron nitride surface.A series of thin BNNSs with different specific surface area and surface defect properties were prepared by changing the solvent or introducing defects.The adsorption properties for these BNNSs were systematically studied by using tetracycline（TC）as adsorption target.The adsorption mechanism and the cycle ability were investigated.1.Two-dimensional porous thin layer BNNSs with different specific surface area and pore size distribution were prepared by modulating solvent.The structure was characterized by N₂ adsorption-desorption,FT-IR,XRD,UV-vis DRS,SEM,TEM,AFM and XPS.It was indicated that the solvent has an effect on the BN pore size.Among them,porous BN-M with methanol as solvent own the largest specific surface area（840 m²/g）,BN-P chose n-propanol as solvent has the largest pore size and pore volume.The adsorption experiments showed that the larger specific surface area of BN-P is beneficial to expose more active sites and the larger pore size and pore volume which will promote the diffusion of TC into the interior,thus the adsorption capacity for TC was highest.The equilibrium can achieve in 6 hours and the adsorption capacity was 386 mg/g.Also,the adsorption mechanism was discussed.2.KOH in-situ etching assisted in the synthesis of two-dimensional porous BNNSs（Nv-BNNSs）with nitrogen defects.The introduction of defects in the molecular structure of nanomaterials can change the electron distribution on the surface of the material mean to improve the adsorption performance.The structure and composition were characterized.It is suggested that the introduction of KOH destroys the structure of BNNSs and changes the electronic state of BNNSs.Some N atoms in the structure are etched and N-defect vacancies are formed.The results of static adsorption experiments showed that Nv-BNNSs-0.1 with nitrogen deficiency had the best adsorption ability,and it entered equilibrium after 3 hours of adsorption.The final equilibrium adsorption capacity was 410 mg/g.3.ZnCl₂ in-situ etching assisted in the synthesis of two-dimensional porous BNNSs（Bv-BNNSs）containing boron defects.Due to the electronegativity difference between Zn and B,the B atom in BNNSs is first replaced by Zn,and then Zn volatilizes at 1000 ^oC under high temperature could leave vacancies to form B defects.The characterization shown that the electronic states of the BNNSs were changed.The atomic ratio of boron to nitrogen is reduced,boron defect vacancies are formed,and the specific surface area of Bv-BNNSs is significantly increased（1186.2 m²/g）.The structure contains both mesopores and number of micropores.The adsorption experiments showed that the adsorption ability of Bv-BNNSs was significantly improved.The adsorption reached equilibrium stage after 2 h,and the adsorption equilibrium achieved at 6 hours.The final adsorption capacity of Bv-BNNSs was 433mg/g.In addition,the dyes Rhodamine B and Methylene Blue also have good adsorption properties.The cycle performance of Bv-BNNSs was excellent,and the TC removal rate decreased by only 10%after 6 cycles.