Enhanced adsorption of phenol using EDTA-4Na- and KOH-modified almond shell biochar

Abstract To enhance the performance of biochar made from almond shells for adsorption of phenol pollutants in water, we prepared an almond shell-based biochar and modified it through combined pyrolysis with KOH and EDTA-4Na at 750 °C, yielding almond shell-based modified activated carbon (A-BC); the mass ratio of biochar, EDTA-4Na, and KOH was 1:1:3. A-BC was characterized by using Scanning Electron Microscopy, Fourier Transform Infrared Spectroscopy, the Brunauer–Emmett–Teller method, and X-ray Diffraction. The adsorption conditions of A-BC for phenol were optimized through single-factor experiments, and the adsorption mechanism was explored through kinetics and thermodynamics assays. The results show that A-BC exhibits a honeycomb-like structure with a specific surface area of 1050 m 2 g −1 and a micropore ratio of 86%. A-BC is rich in functional groups (-OH, -CH 2 , N–C, C-H, N–H) closely related to phenol adsorption. The adsorption of phenol by A-BC is a spontaneous exothermic process involving both physical adsorption and chemical adsorption (including hydrogen bonding and π-π interactions). The pseudo-second-order kinetic model adequately describes the adsorption process, which consists of liquid film diffusion, surface adsorption, and intraparticle diffusion stages. At 25 °C, with an A-BC dosage of 1.0 g L −1 , initial phenol concentration of 400 mg L −1 , and contact time of 60 min, A-BC exhibited significant adsorption capacities of 161 and 149 mg g −1 for simulated water and phenol-containing wastewater from coal chemical industries, respectively. A-BC demonstrated good reuse performance and strong adsorption capacity for phenol, indicating its potential application in treating phenol-containing wastewater from coal chemical industries.