Tailoring the adsorption potential and selectivity of microporous carbon through a two-step chemical-thermal modification approach: insights into the prolonged breakthrough adsorption of volatile organic compounds in air

Abstract

A better knowledge of prolonged breakthroughs is vital for developing durable adsorbents. This knowledge helps us assess their capacity for ongoing pollutant removal and lasting efficiency in real-world situations. To enhance the VOC adsorption capacity of activated carbon (AC, denoted as 'A' in subsequent adsorbent names), this study introduces a two-step chemical–thermal modification: (i) functionalization with amine/sulfur (F) or amino/silane (L) groups and (ii) a subsequent nitrogen thermal treatment (T) at 250 °C for 2 h. The adsorption capabilities of the resulting adsorbents, named AFT and ALT, are evaluated for the simultaneous adsorption of formaldehyde (FA) and benzene (both at 10 Pa). The two-step chemical-thermal treatment promotes surface interactions, leading to enhanced diffusivity of gaseous aldehyde/aromatic VOCs onto AFT and ALT beds. AFT exhibits superior adsorption capacities for both FA and benzene in a binary phase (at the maximum feeding volume of 136 L), reaching 10.9 and 44.7 mg g−1, respectively. These values surpass those of pristine AC by factors of 4.58 and 1.07, respectively. Notably, AFT shows a significantly higher (616 times) adsorption affinity for benzene than for FA, while its selectivity coefficient for FA over benzene (αF/B= 0.05) is lower than that of ALT (αF/B= 0.263). Kinetic studies indicate that FA adsorption on AFT is governed primarily by surface interactions and pore diffusion, while benzene adsorption is controlled by physical surface/pore diffusion. Density functional theory calculations further confirm that thermal treatment promotes carbon flake splitting, which increases surface area and enhances VOC binding interactions. This study provides strategic guidelines for optimizing the adsorption performance of common AC products through multi-step treatment approaches.