The viability of mildly oxidized microporous carbons for adsorptive removal of gaseous aromatic hydrocarbons in humid air

Abstract

The adsorption efficacy of commercial activated carbon (AC) toward volatile organic compounds (VOCs) is generally impeded by the presence of moisture under real environmental conditions. To address this limitation, surface modification strategies such as oxidative treatments are employed to enhance the hydrophilicity of AC. In this study, coconut shell–based AC (CSAC) is subjected to mild hydrogen peroxide (H₂O₂) oxidation at 100 and 125 °C, producing samples labeled as CSAC100 and CSAC125, respectively. The oxidized CSAC samples are tested against gaseous benzene (10 ppm) in dry and humid conditions using raw CSAC as reference. Under dry conditions, CSAC100 and CSAC125 exhibit enhanced adsorption capacities (Q_100%) of 124.1 and 128.7 mg g⁻¹, respectively relative to CSAC (108.1 mg g⁻¹). At 25% RH, they record the optimal uptake performance in terms of Q_100% (135.4/136.9 mg g⁻¹) and partition coefficients (PC_100%: 1.73/1.75 mol kg⁻¹ Pa⁻¹). The intraparticle diffusion model confirms that the diffusions of benzene across the oxidized CSACs proceed more favorably at 25% RH than in dry air, supporting their active adsorption of water vapor. Furthermore, the enhanced benzene uptake (e.g., Q_100% (mg g⁻¹)) of the oxidized AC samples is evident such as CSAC100 (78.3) and CSAC125 (96.6) relative to untreated CSAC (60.8) at 50% RH. The high adsorption performance of the oxidized CSACs, regardless of the moisture level, can be explained by the presence of additional mesopores with strong hydrophilicity. Overall, this study should provide the practical guidelines to tailor the sorbent properties required for the upscaled production of advanced adsorption systems to operate efficiently in the presence of moisture.