Revisiting the Role of Water Molecules in Formaldehyde Adsorption on Activated Carbons with Different Pore Sizes: Insights from Experiments and Multiscale Simulations

The pore size of activated carbon significantly influences its formaldehyde adsorption capacity. Although water vapor is known to significantly affect this process, its role in carbons with different pore sizes remains unclear. This study employs a combined experimental and multiscale simulation approach to investigate the influence of water molecules on formaldehyde adsorption by activated carbons with varying pore sizes. Experimental results show that the modified activated carbon with an increased ultramicropore content exhibits superior formaldehyde adsorption performance, while elevated relative humidity leads to a noticeable decline in adsorption capacity. Multiscale simulations reveal that water clusters tend to accumulate and block ultramicropores, and mesopores lack sufficient confinement effects, both of which greatly reduce formaldehyde uptake. In contrast, the electrostatic interaction between water molecules and formaldehyde can moderately facilitate adsorption. The large micropore structure effectively alleviates water competitive adsorption, provides abundant adsorption sites through the confinement effect, and optimizes molecular mass transfer via wide channels. Combined with the electrostatic synergistic effect of water molecules, it maintains excellent formaldehyde adsorption capacity and humidity resistance. This study clarifies the structure–activity relationship between the pore structure of porous carbon and formaldehyde adsorption performance, providing theoretical support and design guidance for the development of high-efficiency carbon-based formaldehyde adsorbents applied in humid conditions.