Preparation, characterization, and application of modified magnetic biochar for the removal of benzotriazole: process optimization, isotherm and kinetic studies, and adsorbent regeneration

Abstract

The adsorption of benzotriazole (BTA) by chemically modified magnetic biochar (MMBC) as a cheap and abundant biosorbent was investigated and optimized using response surface methodology (RSM). Initially, the MMBC composite was synthesized and characterized by scanning electron microscopy (SEM) energy dispersive X-ray spectroscopy (EDX), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, and Brunauer–Emmett–Teller (BET) techniques. The characterization results confirmed the existence of Fe3O4 in the composite structure, which had uniformly dispersed over biochar (BC) with porous texture. Moreover, the presence of Zn and Cl elements in EDX analysis indicated that the magnetic biochar (MBC) had been modified successfully. The effects of chemical modification methods on the adsorption capacity of magnetic biochar were investigated. Maximum BTA removal efficiency was demonstrated by MMBC, modifying using ZnCl2 (>99%). Optimization was carried out based on reaction time, BTA concentration and the concentration of adsorbent. Optimum experimental conditions for the removal of BTA from aqueous solutions were found to be 35 min of reaction time, 0.55 g/L of adsorbent, and 50 mg/L of initial BTA concentration. At these optimal conditions, the predicted BTA adsorption efficiency was 92.6%. The adsorption process followed the Avrami fractional-order reaction kinetic and the Langmuir adsorption isotherm with the maximum adsorption capacity of 563.1 mg/g. The values of thermodynamic parameters demonstrated that the adsorption of BTA on ZnCl2-MBC is endothermic and spontaneous. Under optimum usage of MMBC, the adsorptive removal efficiency of BTA non-significantly decreased from 99.2 to 93.9% after the 5th cycle. Thus, MMBC can be recommended as an environmentally friendly and cost-effective adsorbent to remove micropollutants from water. HIGHLIGHTS Among all chemical modification methods, ZnCl2 showed the maximum adsorptive removal of BTA (>99%).; At optimum experimental conditions for the removal of BTA, adsorption efficiency was calculated 92.6%.; The adsorption process followed the Avrami fractional-order reaction kinetic and the Langmuir adsorption isotherm with the maximum adsorption capacity of 563.1 mg/g.;

Keywords

• benzotriazole
• central composite design
• modified magnetic biochar
• response surface methodology
• reusability