Rational design of microporous biochar based on ion exchange using carboxyl as an anchor for high-efficiency capture of gaseous p-xylene

Abstract

Capturing p-xylene from waste gas is a top priority, as it is classified as a Group I carcinogen, which can cause great harm to the human living environment. In this study, a facile synthetic route was designed to prepare microporous biochar (CABCs) through esterification and ion exchange and successively introduce carboxyl and alkali metal ions on the surface of biochar precursor before carbonation. The CABCs showed excellent performance in capturing p-xylene. The optimal preparation conditions were citric acid concentration of 0.6 mol L−1, KOH concentration of 2 mol L−1, carbonization temperature of 800 °C, and time of 60 min. The pore size of CABCs was 1.48 nm, which was 2.60-fold larger than n-CABCs derived from biochar precursor without citric acid modification. The presence of moisture had a negative effect on capturing p-xylene. In addition, the adsorption of p-xylene onto CABCs was described well using pseudo-second-order kinetic and Langmuir isothermal models, and the maximum monolayer adsorption capacity was 110.74 mg g−1 at 313 K. Furthermore, the adsorption properties of p-xylene onto CABCs were demonstrated by theoretical calculations based on density functional theory and molecular dynamics simulation to guide the optimization of pore size. Moreover, p-xylene adsorption was endothermic and spontaneous in nature, and the adsorption mechanism primarily included micropore filling and π–π interaction.