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

- Adsorptive removal of five PPCPs was done with MOFs having ample -OH groups.
- The adsorption can be explained quantitatively with hydrogen bonding.
- The five PPCPs and MOFs can be H-acceptors and H-donors, respectively.
- Adsorption can be increased with increasing -OH of MOF or O of PPCPs.
- MIL-101-(OH)3 was highly effective in adsorption and reusable by solvent washing.

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.

115