Exciton separation in CdS supraparticles upon conjugation with graphene sheets

Abstract

Photophysical properties and exciton dynamics of CdS supraparticles (400 nm) composed of quantum dots of CdS (3–5 nm) have been investigated when they are conjugated with the graphene sheet. Favorable electron transfer from photoexcited CdS to graphene was confirmed from the quenching of CdS emission and ultrafast transient absorption spectroscopy. Ultrafast electron transfer (<150 fs) was found to take place from photoexcited CdS to the graphene matrix. The charge separation process was monitored after following the bleach recovery kinetics at the excitonic position of the supraparticle CdS. Ultrafast transient absorption spectroscopic studies showed enhanced stability of exciton and efficient charge separation in the CdS supraparticle–graphene composite as compared to pure CdS supraparticles. These charge delocalizations and ultrafast electron transfers in the CdS supraparticle–graphene composite have been reflected in the photocatalytic dye degradation. The dye degradation rate was observed to be much faster (0.15 min^–1) in the CdS supraparticle–graphene composite system compared to that of the pure CdS supraparticle (0.03 min^–1).