Adsorption of pharmaceuticals and personal care products over metal-organic frameworks functionalized with hydroxyl groups: Quantitative analyses of H-bonding in adsorption

The removal of pharmaceuticals and personal care products (PPCPs) from water is important for ensuring a clean aquatic environment. In this work, the adsorptive removal of five PPCPs such as p-chloro-m-xylenol, bisphenol-A, triclosan, ketoprofen, and naproxen was carried out using metal-organic framework (MOF, here MIL-101) with or without modifications, i.e., introduction of hydroxyl groups. Quantitative investigations were conducted in order to understand the major mechanisms for adsorption. H-bonding is suggested as the principal mechanism for the adsorption of PPCPs over MOFs, where the PPCPs and MOFs can be H-acceptors and H-donors, respectively. This conclusion is drawn based on the fact that the quantity of adsorbed PPCPs increased monotonously with (i) increase in the number of H-acceptors (O in PPCPs) and (ii) increase in the number of –OH groups in the MOFs. The effect of solution pH on the amount of adsorbed triclosan also supports the suggested mechanism. Additionally, MIL-101-(OH)₃ appears to be a useful adsorbent for PPCPs, especially for p-chloro-m-xylenol and ketoprofen.