Engineering microporous activated carbon for efficient toluene removal under humid conditions

This study presents the development of a poorly hydrophilic activated carbon (AC) with a high surface area, capable of adsorbing large amounts of toluene. ACs were produced from a wood-derived biochar (C), a renewable bio-based carbon precursor, by activation with potassium hydroxide (KOH), contributing to the valorization of sustainable carbon materials for air purification applications. The influence of different KOH-C mixing methods, namely pestle and mortar mixing (PM), mechanosynthesis (MS) and impregnation (IMP), was systematically evaluated. While IMP increased mesopore volume, it resulted in lower carbon yield and surface area. In contrast, PM and MS effectively enhanced microporosity and surface area with increasing KOH to char (KOH/C) weight ratio while maintaining good yield. The optimal material, AC4PM, exhibited the highest surface area, 2530 m2 g⁻1, and the lowest water affinity due to its low surface oxygen concentration, particularly in carboxylic groups. As a result, AC4PM showed the highest toluene uptake under dry conditions (945 mg g⁻1 at 25 °C) and maintained high adsorption capacities under humid conditions (860, 530 and 300 mg g⁻1 at 5%, 30% and 50% RH, respectively). Notably, AC4PM outperformed the ACs reported in the literature and available on the market under comparable dry conditions, as well as a commercial VOC adsorbent, R-Pure® 20, in both dry and humid environments.