Bamboo-derived hydrophobic porous graphitized carbon for adsorption of volatile organic compounds

Abstract

Biomass-derived activated carbons (BACs) are often used as green adsorbents for the removal of VOCs, however, their abundant surface functional groups severely reduced their adsorption selectivity under humid conditions. In this study, hydrophobic bamboo-derived porous graphitized carbons (BPGCs) were prepared using a combined catalytic graphitization method. The optimal micro-mesoporous BPGC had a large specific surface area of 2181 m2/g and a low surface O/C ratio of 0.038. Under dry conditions, its adsorption capacities for toluene, cyclohexane and ethanol were 6.7, 3.8 and 2.4 mmol/g, respectively. At 80 % relative humidity, its adsorption capacities for toluene and cyclohexane remained 82 % and 66 %, while the uptake of ethanol even increased by 33 %. In the two-component adsorption test, BPGC showed a high selectivity for toluene adsorption over ethanol, with 198 times more toluene than ethanol. The adsorption mechanism at the microscopic molecular level was revealed by DFT calculation. The abundant π electrons and high polarizability of BPGC allow for strong π-π interactions and dispersion forces with non-polar organics, while the abundant oxygen-containing groups on BAC have strong adsorption force on water. The absorption of ethanol by capillary condensed water in mesopores of BPGC may contribute to its increased uptake under humid conditions. BPGC allowed for faster adsorption kinetics than activated carbon. More than 90 % of the adsorbed toluene was desorbed from BPGC at 90 °C. Owing to abundant renewable raw materials, excellent hydrophobicity and desirable textural properties, BPGCs may be promising adsorbents.