Humidity-dependent benzene adsorption in indoor environments: The critical transition between competition and cooperation

Benzene, a prevalent indoor air pollutant, poses significant health risks. While carbonaceous materials are widely used for benzene removal, their performance under humid conditions remains controversial, with reports showing both detrimental and beneficial effects of moisture. The underlying mechanisms governing these seemingly contradictory observations remain poorly understood, impeding the rational design of adsorbents that can maintain consistent performance across varying humidity levels. To address this knowledge gap, we combined molecular simulations with experimental measurements to investigate water-benzene interactions in carbon nanopores. Our investigation reveals that the transition between cooperative and competitive adsorption behaviors is regulated by the interplay of relative humidity, benzene concentration, and the pore width of adsorbent. In the environmentally relevant low concentration of benzene (∼1 ppm), water molecules form clusters that serve as additional adsorption sites, enhancing benzene capture until a humidity threshold is reached. Beyond this threshold, water condensation dominates the pore space, leading to competitive displacement of benzene. Pore width also plays a crucial role, with small pores (particularly ultra-micropores) facilitating benzene to resist water uptake. Moreover, our work reveals that water clusters forming in pores affect adsorption kinetics at lower humidity levels than those impacting overall capacity. These insights enable strategic optimization of pore structure and surface chemistry for enhanced VOC capture under varying moisture conditions.