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

TLDR

A hydrothermal method using citric acid with urea or thiourea produces N and S, N co‑doped graphene quantum dots. The co‑doped GQDs show high quantum yields (78 % and 71 %), excitation‑independent emission, a broad visible absorption band, and, when coupled with TiO₂, degrade rhodamine B at rates 3–10 times faster than N‑doped GQDs or commercial P25.

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.