Continuous photocatalytic removal of chromium (VI) with structurally stable and porous Ag/Ag3PO4/reduced graphene oxide microspheres

Although silver phosphate (Ag3PO4) exhibits high quantum efficiency and intriguing photocatalytic ability, its poor light stability limits its wide application. Herein, structurally stable and porous Ag/Ag3PO4/reduced graphene oxide microspheres are fabricated with electrostatic spraying, freezing, lyophilizing and crosslinking and used for the first time to remove toxic Cr(VI) ions with high efficiency and durability. Polydopamine serves as both moderate reductant and effective linker for Ag/Ag3PO4 components to distribute well on reduced graphene oxide (rGO) sheets with controlled Ag/Ag3PO4 ratios, endowing the porous microspheres with fast transfer of electrons and enhanced structural stability. Both the heterogeneous junctions of Ag/Ag3PO4 and the conducive rGO sheets accelerate the electron transfer from Ag3PO4 to Ag and rGO, decrease the recombination of electrons and holes and enhance the light stability of Ag3PO4. In addition, both the photogenerated electrons of Ag3PO4 and the pi electrons on rGO sheets reduce Cr(VI). The resulting porous microspheres deliver an excellent visible light photocatalytic efficiency of 0.62 mg min(-1) g(-1) (quantum yield of 2.37%) for reduction of Cr(VI) under the light intensity of 800 mW cm(-2), and a high removal efficiency of more than 90% of Cr(VI) over 30 h under a continuous photocatalytic removal system. These outstanding performances make the structurally stable and porous microspheres promising for continuous removal of Cr(VI) ions.