Adsorption capacity of biocarbons from residue of supercritical extraction of raw plants

Abstract

Bioadsorbents prepared by chemical activation (H3PO4) of the residue of supercritical extraction of green tea leaves and marigold flowers were characterized by elemental analysis, Boehm titration, adsorption/desorption isotherm and scanning electron microscopy (SEM). The adsorption performance aimed at the removal of malachite green, nitrogen oxide and hydrogen sulfide was investigated. The impacts of various influential parameters of malachite green adsorption such as: contact time (8 h), initial dye concentration (20–140 mg/L), temperature (25–65 °C) and adsorbent mass (0.015–0.025 g) were investigated. The adsorption kinetic follows pseudo second-order reaction kinetics (R 2 > 0.99). The adsorption process was best described by the Langmuir isotherm and the maximum capacity of the monolayer was from 126.58 mg/g to 333.33 mg/g for the biocarbons obtained. The negative values of Gibbs free energy indicate the spontaneous character of the process. The presence of steam in the stream of the mixture of gases had a positive effect on adsorption of nitrogen oxide and hydrogen sulfide by the bioadsorbents obtained. The most effective adsorbent of malachite green and toxic gas pollutants proved to be the biocarbon obtained from the residues of supercritical extraction of green tea leaves.