Highly concentrated amino-modified biochars using a plasma: Evolution of surface composition and porosity for heavy metal capture

Abstract

Highly concentrated amino group-modified biochars derived from twelve biomass residuals are achieved using a two-step radio-frequency Ar/NH3 plasma. The dependence of amino number, N bonding states, surface defects on the pretreatment time of Ar plasma, post-treatment power, duration and gas ratio are well established. For bamboo-biochar, the amino number and N content reach the maximum (8.04 × 1016/mg of biochar, 8.84 at.%) at 8.0% NH3 in NH3/Ar, presenting a highly consistent variation tendency with the emission intensity of NH radical. Notably, micropores can be created in matrix by the processing of plasma in moderate conditions, i.e., a given pretreatment time (e.g., 12.5 min), specific gas ratios of post-treatment (≥50% of NH3) at high RF power (e.g., 240 W) and proper duration (≤15.0 min). The uptake capacities of Pb(II) (123.1 mg g−1), Cu(II) (98.5 mg g−1) and Cd(II) (61.2 mg g−1) on aminated biochars are 5.42, 5.38 and 7.56 times higher than those on raw biochars. This study shows attractive prospects for the fundamental research in powder modification as well as potentials in environmental management.