Enhanced photocatalytic hydrogen evolution using green carbon quantum dots modified 1-D CdS nanowires under visible light irradiation

Photoluminescent carbon quantum dots (CQD) have drawn intense attention due to its excellent optical properties, strong confinement effect, and good electrical conductivity. However, sustainable synthesis of CQD from green carbon sources and its application in water splitting has not been well explored. Herein, we synthesized CQD from orange peels and embedded them onto one-dimensional (1-D) cadmium sulfide (CdS) nanowires (average diameter 30 nm and length 2-4 mu m) via a facile chemical adsorption method. The synthesized photocatalysts were thoroughly characterized using various spectroscopic, microscopic, diffraction, and photoelectrochemical techniques. The photocatalysts were tested for water-splitting reaction under visible light. The effect of mass fraction of CQD in CdS on water splitting performance has been investigated both in the presence and absence of sacrificial reagents. The reusability of the photocatalyst has also been tested. The optimal catalyst, 0.4CQD/CdS, exhibited the highest H-2 production rate of 309 mmol g(-1)h(-1) (apparent quantum yield of 32.6%) which is 1.5 times higher than that with bare CdS. The excellent photocatalytic performance of CQD/CdS was due to the existence of sulfur vacancies and the formation of cadmium oxide with effective charge transfer and separation. The higher photostability of CQD/CdS compared to that of CdS in three consecutive cycles can be attributed to suppression of photocorrosion of CdS in the presence of CQD.