Norfloxacin and Bisphenol-A Removal Using Temperature-Switchable Graphene Oxide.

Graphene oxide (GO) is a competitive candidate used for adsorption of emerging organic contaminants (EOCs) from water. To overcome GO's spontaneous aggregation tendency in adsorption and to ease contaminant desorption from the adsorbent for adsorbent regeneration, a modified GO (P-GO), with temperature-switchable hydrophilicity/hydrophobicity, obtained by grafting temperature-responsive poly(N-n-propylacrylamide) was proposed. Two model EOCs, norfloxacin (NOR) and bisphenol A (BPA), with distinct hydrophilicity/hydrophobicity were employed. P-GO showed significant temperature-responsive adsorption behaviors: P-GO was more hydrophilic at a lower temperature and was beneficial for the adsorption of hydrophilic NOR; whereas it turned more hydrophobic at a higher temperature and was preferred for the adsorption of hydrophobic BPA. Compared with GO, P-GO under corresponding optimal conditions had comparable large adsorption amounts for NOR due to an "adsorption sites replacement" strategy, and notably enhanced adsorption for BPA because of strengthened hydrophobic association. Main interfacial binding interactions were π-π electron donor-acceptor effect and H-bonding for NOR adsorption, and hydrophobic association and H-bonding for BPA uptake. Based on the temperature-responsive adsorption behaviors and studied interfacial interactions, regeneration of the adsorbent at designed temperatures using water (without additional chemicals) as eluent is realized. This achievement is important for reducing risks of secondary environmental pollution during regeneration and easing further recovery of organic contaminants if needed.