Adsorptive removal of pharmaceutical and personal care products by carbon nanotubes: Insights into the adsorbent pore size and adsorbate size

Understanding the molecular factors that govern the adsorption of pharmaceutical and personal care products (PPCPs) on carbon nanotubes (CNTs) is essential for designing highly efficient porous adsorbents. We hypothesize that adsorbent pore and adsorbate size matching is the dominant factor controlling the adsorption process. Therefore, this study examined the effects of the molecular size of PPCPs and pore size of CNTs on the adsorption performance using the combination of experiments and molecular dynamics simulations. The results show that the adsorption capacity of unit specific surface area increased with increasing both the molecular size of PPCPs and the pore size of CNTs. In the coexisting system, adsorption capacity declined with decreasing molecular size, showing negative correlation (R²=0.842). This indicates that small PPCPs are more vulnerable to competitive inhibition, whereas larger molecules exhibit stronger resistance to competition and maintain more stable adsorption capacities in complex media. Molecular dynamics simulation revealed that the interaction between CNTs and PPCPs was mainly dominated by van der Waals forces, with larger-sized molecules showing higher binding energy and being more likely to occupy adsorption sites on CNTs. These findings not only reveal the internal relationship between the pore size of sorbents and their adsorption capacity, but also provide an important theoretical basis and practical guidance for optimizing PPCPs removal strategies.