Engineering of a kaolin/SLS-functionalized biochar@β-cyclodextrin composite for adsorption of o-nitrophenol; optimization, mechanistic study, and Box–Behnken design

Abstract

In this investigation, a good adsorbent was created by combining kaolin, β-cyclodextrin, and sodium lauryl sulfate-functionalized biochar, resulting in a new Kaol/SLS-BC/β-CD composite. Assorted analyses were used to characterize the chemical/physical properties of the Kaol/SLS-BC/β-CD. The adsorption capability of the Kaol/SLS-BC/β-CD was evaluated, using an experimental adsorption batch study of o-nitrophenol (o-NP). The experimental batch experiments showed that o-NP removal of 100% was achieved at room temperature after 180 minutes with pH = 3, Kaol/SLS-BC/β-CD dose = 10 mg, and o-NP concentration = 50 mg L⁻¹. Kinetic and isotherm analyses of the experimental data implied that the Freundlich isotherm model and the pseudo-second-order kinetic model were obeyed for the o-NP adsorption reaction. Surprisingly, the maximal adsorption capacity of Kaol/SLS-BC/β-CD towards o-NP, calculated from Langmuir analysis, was 588.24 mg g⁻¹. The optimization of o-NP adsorption onto Kaol/SLS-BC/β-CD was investigated using response surface methodology (RSM) based on a Box–Behnken design (BBD) with three independent variables: initial o-NP concentration, adsorbent dosage, and contact time. The quadratic response surface model was validated through analysis of variance (ANOVA). The reduced quadratic model demonstrated good agreement between the predicted and experimental results. Thus, the validated model can be reliably applied to predict the optimal conditions for o-NP adsorption onto Kaol/SLS-BC/β-CD. The mechanistic study of the o-NP adsorption onto Kaol/SLS-BC/β-CD clarified that the process may occur via Lewis acid–base, pore-filling, coordination bond, hydrogen bond, and pi–pi interactions. Notably, the cycling test indicated that the Kaol/SLS-BC/β-CD could be reused for six adsorption cycles of o-NP with promising efficacy.