Pauling-type adsorption of O2 induced reactive oxide species in photocatalytic oxidation by TiOx sensitized Pb-hyperaccumulated biochar

A novel TiOx-loaded Pb-hyperaccumulated biochar (Pb@BC-TiOx) was obtained from the hyperaccumulator Iris siberian L. Compared with other metal@BC-TiO2 (Ce, Co, Ni, Fe), Pb@BC-TiOx showed a stronger potential for pollutant degradation under ultraviolet (UV) irradiation, achieving 97.9 % of 2,4-dichlorophenol (2,4-DCP) removal within 240 min. Quenching experiments exhibited the selective enhancement of superoxide radicals (& sdot;O2-) and singlet oxygen (1O2) in the Pb@BC-TiOx/UV system (5.6 and 7.9 times than Pb@BC/UV system, respectively). The characterization revealed TiOx and PbO2 in the Pb@BC-TiOx, and the photogenerated electrons (e-) and holes (h+) flowed between them. In TiOx, TiO1.04 was formed due to the reductive effects of CO and/or Pb0. Moreover, the heterojunction schemes of TiO1.04 and TiO2 also exhibited a superior photogenerated e- transfer capability. Density functional theory calculations showed that TiO1.04 on the surface of Pb@BC-TiOx induced Pauling-type adsorption of O2, which reduced the overall activation energy barrier (-1.76 eV), facilitated the maintenance of O-O bonds and the accumulation of & sdot;OOH, and futher promoted the generation of & sdot;O2-/1O2 instead of H2O under UV irradiation. The Pb@BC-TiOx/UV system exhibited superior reusability and applicability, which was beneficial to practical wastewater treatments. This study provided a novel idea for the preparation of catalysts using metal-hyperaccumulated biomass produced after phytoremediation.