Highly luminescent S, N co-doped graphene quantum dots with broad visible absorption bands for visible light photocatalysts

Abstract

A facile hydrothermal synthesis route to N and S, N co-doped graphene quantum dots (GQDs) was developed by using citric acid as the C source and urea or thiourea as N and S sources. Both N and S, N doped GQDs showed high quantum yield (78% and 71%), excitation independent under excitation of 340–400 nm and single exponential decay under UV excitation. A broad absorption band in the visible region appeared in S, N co-doped GQDs due to doping with sulfur, which alters the surface state of GQDs. However, S, N co-doped GQDs show different color emission under excitation of 420–520 nm due to their absorption in the visible region. The excellent photocatalytic performance of the S, N co-doped GQD/TiO₂ composites was demonstrated by degradation of rhodamine B under visible light. The apparent rate of S, N:GQD/TiO₂ is 3 and 10 times higher than that of N:GQD/TiO₂ and P25 TiO₂ under visible light irradiation, respectively.