A New Class of Adsorptive Photocatalysts for Enhanced Adsorption and Destruction of 4-chlorophenol and perfluorooctanoic acid

Abstract

Four novel Ti-based adsorptive photocatalysts, namely titanate nanosheets (TNS), graphene grafted titania/titanate nanosheets (G/TNS), activated carbon modified titanate nanotubes (TNTs@AC), and iron doped, activated carbon supported anatase nanotubes (Fe/TNTs@AC), were synthesized based on commercial activated carbon and titanium oxide. The composite materials were thoroughly characterized, and tested for enhanced adsorption and photocatalytic degradation of some persistent organic pollutants (POPs) such as 4-chlorophenol (4-CP) and perfluorooctanoic acid (PFOA). The photocatalysts were synthesized through a one-step facial alkaline hydrothermal process followed by proper metal doping and calcination. While titanate (TNS or TNTs) alone acted as an cation exchanger for taking up various metal cations such as Pb2+ and Cd3+, AC-modified TNTs was able to effectively adsorb hydrophobic contaminants such as 4-CP, and upon deposition of iron (hydr)oxide, Fe/TNTs@AC was able to effectively adsorb PFOA. All materials offered excellent photocatalytic activity under UV irradiation/solar light. Taking advantage of the unique properties of these composites, we developed an unique “Concentrate-and-Destroy” strategy for treating trace concentrations of POPs. First, low concentrations of a contaminant is pre-concentrated on photoactive sites on the material surface, then the pre-concentrated contaminant is destroyed upon UV or solar light irradiation. The effective photocatalytic degradation also regenerates the material, allowing for repeated uses of the material without involving expensive chemical regeneration and without generating the process waste residual as is the case for conventional adsorption processes. Overall, the adsorptive photocatalysts and the new “Concentrate-&-Destroy” strategy represent a significant advancement in the treatment of POPs. The new materials hold the promise to treat some of the most challenging contaminants in water in a more cost-effective manner.