Evaluating malachite green removal from aqueous solution by hydroxyl enhanced hydrochar and biomass

This work intends to evaluate the feasibility of improving the adsorption performance of biomass by both hydrothermal carbonization (HTC) pretreatment and single-step NaOH and ethanol modification. Peanut shell (PS) and pine (PE) are utilized as parent materials to produce efficient adsorbents, and malachite green (MG) is regarded as contaminants to evaluate the adsorption capacity of prepared materials. Adsorption test was performed under various operating conditions, including pH, interfering ions and contact time. The adsorbents were characterized by N 2 adsorption–desorption, SEM, FT-IR spectra and elemental analysis to explore the potential adsorption mechanism. Results show that single-step NaOH and ethanol modification is an effective chemical modification to improve the adsorption performance of adsorbents by increasing the surface hydroxyl functional groups. The adsorption performance of adsorbents prepared by HTC following with chemical modification is best; the q e of modified hydrochar from PS and PE (MPS-HC and MPE-HC) reach as high as 570.34 mg/g and 562.2 mg/g, respectively. According to adsorption isothermal and kinetics analysis, the adsorption process mainly occurs on the surface of adsorbents, and MG removal is dominant by chemical adsorption resulting from the increase of surface hydroxyl functional groups by chemical modification. HTC pretreatment could enhance the п–п bond interaction, thus further promoting MG removal by MPS-HC and MPE-HC because it increases the aromaticity of hydrochar evidenced by the H/C ratio decrease. This work indicates that the combination of HTC pretreatment and chemical modification is a feasible way to improve the adsorption performance of biomass.