Photo-switchable imprinted adsorbent towards a selective phenol recovery from wastewater

Here we report the design and synthesis of a novel surface imprinted adsorbent, with an UV-switchable wettability towards an efficient and highly selective phenol recovery from wastewater. The high selectivity of phenol is achieved through surface molecularly imprinted cavities featuring a smart phenol identification function, whilst the UV-switchable wettability is accomplished by the co-loading of nano-sized, photosensitive TiO₂ and hydrophobic 3-(trimethoxysilyl) propyl methacrylate imprinted layer. Through numerous adsorption experiments and extensive characterizations including FESEM, TEM, FT-IR, BET, XRD, XPS, and synchrotron NEXAFS, it is confirmed that upon a prior 0.5 h - long UV irradiation, the imprinted surface of the as-synthesized adsorbent can be switched from hydrophobic to hydrophilic, which in turn results in an equilibrated adsorption capacity of 8.24 mg-phenol/m²-adsorbent that are superior over all the reported values. More intriguingly, with the progress of the adsorption in the dark, the surface of the adsorbent can be gradually reversed to hydrophobic. This in turn enhances the repulsion of particles from the aqueous phase, leading to a quick self-agglomeration and precipitation of the spent adsorbent for an easy recovery. Moreover, 98% of the adsorbed phenol can be recovered via a subsequent washing by methanol, and the regenerated adsorbent is also confirmed to exhibit a nearly stable adsorption capacity upon five cycles.