Efficient adsorption of aromatic compounds on KOH-modified biochar: Mechanistic insights into competitive adsorption

Lignocellulosic biomass can be converted into sustainable biofuels or valuable chemical precursors via microbial fermentation, but pretreatment produces inhibitors that hinder subsequent fermentation. Among these inhibitors, aromatic compounds are particularly abundant and highly toxic to microbial cells. Biochar is commonly used to remove inhibitors from prehydrolysate. However, previous studies have mainly focused on single-component adsorption, and both the competitive adsorption of multiple aromatic inhibitors and the use of KOH-modified biochar for their targeted removal from prehydrolysates remain insufficiently explored. This study aimed to elucidate the competitive adsorption mechanisms of seven aromatic inhibitors in model aqueous solutions using KOH-modified corn stover biochar (K-CSB), based on adsorption kinetics, isotherm models, biochar characterization, density functional theory (DFT) calculations, and correlation analysis of molecular properties. The results showed that KOH modification increased surface carbonyl groups by 54.35%. In the multi-component system, the overall removal rate of aromatic compounds by K-CSB (63.98%) was significantly higher than that of CSB (11.53%). The adsorption kinetics of the compounds were better described by the Pseudo-Second Order and Elovich models. The order of adsorbed amounts was: furfural = 4-hydroxybenzaldehyde > vanillin > syringaldehyde > hydroxymethylfurfural > 4-hydroxybenzoic acid > vanillic acid. DFT calculations indicated that the adsorption behavior was jointly governed by molecular structure, adsorption configuration, and interfacial electronic interactions. The results suggested that non-covalent interactions contributed to the adsorption process, without significant large-scale electron transfer. A total removal efficiency of 88.53% for aromatic compounds in dilute acid prehydrolysate was achieved by K-CSB, demonstrating its potential for selective detoxification of lignocellulosic prehydrolysates. These findings provide mechanistic insights into the competitive adsorption of aromatic compounds and offer a theoretical basis for the rational design of biochar to improve detoxification efficiency and facilitate downstream bioconversion in lignocellulosic biorefineries.