A Brief Overview on Synthesis and Size Dependent Photocatalytic Behaviour of Luminescent Semiconductor Quantum Dots

Supersaturation was found to play a pivotal role during nanoparticle-synthesis and its subtle variation helped to achieve two prime objectives: a) high photoluminescence quantum efficiency (PLQE) and b) narrow size distribution, thereby obviating the need for post-preparative treatments. The as-prepared CdS and CdTe QDs were found to have size distribution as low as 4% at higher supersaturation. Focussing of size distribution was also demonstrated in dendrimer-mediated synthesis of CdTe QDs by controlling the temperature. For a four-fold increase in supersaturation, PLQE of cysteine-capped CdTe QDs (4.3 nm) rose by 5 times to a remarkably high value of 54%. The focusing of size distribution with increasing supersaturation was found to work well even in the absence of any stabilizer. This study provides a simplified route for producing highly monodisperse, photoluminescent and surface-functionalized nanoparticles. Thiophenol capped CdS QD has been used as a model system to demonstrate the size dependence of photocatalysis of nitroaromatics. The catalytic efficiency of CdS quantum particles was quintupled with decrease in particle size from 5.8 nm to 3.8 nm. An empirical equation has been derived to correlate the catalytic efficiency of the nanoparticles with the twin factors operating in the quantum confinement regime: (i) change in surface to volume ratio and (ii) shift in conduction band edge. In addition, quenching of photoluminescence of thiophenol capped CdS QDs by nitromatics can be used for developing a protocol for a sensor. The Stern-Volmer constant of dinitrobenzene was about 15-fold higher than nitrobenzene, which indicates that introduction of nitro groups in the benzene ring increases the quenching efficiency.