Wettability UV-switchable TiO₂-based surface molecularly imprinted adsorbent for selective phenol removal and its...

Aiming at the selective adsorption removal and efficient separation of pollutant phenol from wastewater, a photo-responsive surface molecularly imprinted adsorbent with smart ultraviolet (UV)-switchable wettability has been designed and synthesized. The selective adsorption of phenol is achieved by constructing phenol-imprinted cavities with o-phenylenediamine (o-PD) as the functional monomer, while the reversible switching of surface wettability is realized through the synergistic effect of the photo-induced hydrophilic hollow titanium dioxide (H-TiO₂) matrix and the cross-linked hydrophobic trimethylolpropane trimethacrylate imprinted polymer layer. The surface wettability of the constructed adsorbent o-PD/SMIP@H-TiO₂ can be changed from hydrophobic (water contact angle of 113°) to hydrophilic (water contact angle of 21°) after 30 min of UV irradiation, which is beneficial to the dispersion of the adsorbent and mass transfer of adsorbate. As the phenol adsorption takes place in the dark and reaches equilibrium (24.4 mg/g), the surface of o-PD/SMIP@H-TiO₂ gradually reverts to hydrophobicity, which facilitate the separation and regeneration of adsorbent, and the adsorption capacity in the 5th reuse maintains 94 %. Furthermore, 97 % of the adsorbed phenol can be recovered from the saturated o-PD/SMIP@H-TiO₂ adsorbent. Meanwhile, the adsorbent demonstrates distinct specific recognition and selective adsorption performance towards phenol when multiple phenolic pollutants are present in the solution. The selectivity is attributed to the formation of hydrogen bonds between the nitrogen atoms on the directionally-arranged o-PD monomers within the imprinted cavities and the hydrogen atoms of phenol molecules. This photo-responsive imprinted adsorbent material is expected to exert a substantial influence on the wastewater purification industry.