Visible light induced efficient activation of persulfate by a carbon quantum dots(CQDs)modifiedγ-Fe_(2)O_(3) catalyst

In this study,a carbon quantum dots modified maghemite catalyst(CQDs@γ-Fe_(2)O_(3))has been synthesized by a one-step solvothermal method for efficient persulfate(PDS)activation under visible light irradiation.Transmission electron microscopy(TEM),scanning electron microscopy(SEM)and UV-vis diffuse reflectance spectroscopy(UV-vis DRS)characterization indicated that the formation of heterojunction structure between CQDs and y-Fe_(2)O_(3) effectively reduced the catalyst band gap(Eg),favoring the separation rate of electrons and holes,leading to remarkable efficient sulfamethoxazole(SMX)degradation as compared to the dark-CQDs@γ-Fe_(2)O_(3)/PDS and vis-γ-Fe_(2)O_(3)/PDS systems.The evolution of dissolved irons also demonstrated that CQDs could accelerate the in-situ reduction of surface-bounded Fe^(3+).Electron paramagnetic resonance(EPR)and radical scavenging experiments demonstrated that both*OH and SO_(4)·were generated in the reaction system,while*OH was relatively more dominant than SO_(4)·for SMX degradation.Finally,the reaction mechanism in the vis-CQDs@y-Fe_(2)O_(3)/PDS system was proposed involving an effective and accelerated heterogeneous-homogeneous iron cycle.CQDs would enrich the photo-generated electrons from y-Fe_(2)O_(3),causing efficient interfacial generation of surfacebond Fe^(2+)and reduction of adsorbed Fe3+.This visible light induced iron cycle would eventually lead to effective activation of PDS as well as the efficient degradation of SMX.

Ag–AgBr/TiO_2/RGO nanocomposite:Synthesis,characterization,photocatalytic activity and aggregation evaluation

Ag-AgBr/TiO2 supported on reduced graphene oxide （Ag-AgBr/TiO2/RGO） with different mass ratios of grapheme oxide （GO） to TiO2 were synthesized via a facile solvothermal-photo reduction method. Compared to the single-, two- and three-component nanocomposites, the four-component nanocomposite, Ag-AgBr/TiO2/RGO-1 with mass ratio of GO to TiO2 at 1%, exhibited a much higher photocatalytic activity for the degradation of penicillin G （PG） under white light-emitting diode （LED-W） irradiation. The PG degradation efficiency increased with the increase of mass ratio of GO to TiO2 from 0.2% to 1%, then it decreased with the increase of mass ratio of GO to TiO2 from 1% to 5%. The zeta potentials of RGO-nanocornposites became more negative with the presence of humic acid （HA） due to the negatively charged HA adsorption, resulting in the shift of points of zero charge to lower values of pH. The aggregations of nanocomposites were more significant due to the bridging effect of HA. Furthermore, the aggregated particle sizes were larger for ROO-nanocomposites compared to other nanoparticles, due to the bindings of the carboxylic and phenolic functional groups in HA with the oxygen-containing functional groups in the RGO-nanocomposites. The microfiltration （MF） membrane was effective for the nanocomposites separation. In the continuous flow through submerged membrane photoreactor （sMPR） system, backwashing operation could efficiently reduce membrane fouling and recover TiO2, and thus indirectly facilitate the PG removal.