Hydrothermal and pyrolytic biochars from waste milk thistle (Silybum marianum) extrudates as precursors for production of effective isoproturon adsorbents

Abstract

Removal of residual pesticides from water reservoirs is constantly important environmental issue, that is why many attempts are concentrated on the production of efficient adsorbents of such chemicals. In present study, activated carbons (ACs) from chars of pyrolytic (500 °C) and hydrothermal (190 °C) treatment of waste milk thistle (MT) extrudes were obtained by KOH (1:3) activation. The obtained MT-ACs have different surface characteristics: pHPZC varied from 10.57 to 3.85 and were predominantly microporous. The SBET changed from 940 to 2970 m2 g−1. For chosen activated carbons, the adsorptive properties towards isoproturon (IPU) were determined. The equilibrium time and equilibrium sorption capacity were measured. Adsorption kinetics of IPU was studied by means of pseudo-first-order, pseudo-second-order, Elovich, Bangham and Weber-Morris models, while the equilibrium models were interpreted by Freundlich and Langmuir models. The adsorption processes were relatively fast. The porosity and surface chemical characteristics influenced the kinetics as well as the mechanism of IPU adsorption, but the adsorption capacity at equilibrium was pore size dependent. The basic surface characteristics and high volume of pores with size bigger than 1.3 nm enhanced the IPU adsorption on MT-based activated carbons. The adsorption of IPU was ruled by its second widest dimension.