Nb2O5-graphene heterojunction composite with ultrahigh photocatalytic activity for solar light driven photodegradation of ciprofloxacin

Abstract

Poor visible light absorption capacity and intrinsic conductivity restrict many applications of Nb2O5 in photocatalysis. The paper describes one solution for synthesizing Nb2O5-graphene photocatalyst with functional graphene quantum dot (GQD). Firstly, Nb(V) was coordinated with GQD to form water-soluble complex. Then, it was bound to graphene sheet via π-π stacking, reduced with ascorbic acid to produce graphene oxide gel and annealed in N2 at 900 °C. The resultant Nb2O5 nanocrystals offer ultrasmall size of 8.8 ± 0.6 nm and good crystallinity. The introduction of GQD realizes the construction of heterojunction. This narrows bandgap energy of Nb2O5 and optimizes the band structure. The narrowed bandgap energy leads to an enhanced visible light absorption, and more negative conduction band potential and more positive valence band potential promote production of superoxide (•O2–) and hydroxyl radicals (•OH). Combination of graphene with GQD improves adsorption of ciprofloxacin, separation of generated electrons and holes and light absorption capacity. G-Nb2O5-900 exhibits an excellent photocatalytic performance for solar light driven photodegradation of ciprofloxacin. The photodegradation efficiency is more than 3.58 times under ultraviolet light radiation and 12.4 times under visible light radiation over pristine Nb2O5. G-Nb2O5-900 shows a broad application prospect in antibiotic treatment in environmental water.