Template-free syntheses of CdS microspheres composed of ultrasmall nanocrystals and their photocatalytic study

Abstract

Template-free CdS microspheres composed of nanocrystals have been successfully synthesized by a one-pot solvothermal method using 4,4′-dipyridyldisulfide (DPDS = (C5H4N) 2S2)) as a temperature controlled in situ source of S 2- ions without (S1-S3) and with the use of capping agent (S4). The powder X-ray diffraction measurements of all four (S1-S4) samples revealed the cubic structure of the CdS microspheres and SEM analyses showed almost spherical morphology of the CdS microspheres with a broad size range of 0.5 to 2 μm. TEM analyses of the samples S3 and S4 revealed that the CdS microspheres are composed of assembled CdS nanocrystals of ultrasmall (2-5 nm) size. Optical investigation of the samples (S1-S4) showed blue-shift in the UV-vis absorption maxima compared to that of bulk CdS due to quantum confinement effects. Photocatalytic investigation of the uncapped (S3) and mercaptoethanol (MCE)-capped (S4) CdS microspheres for degradation of methyl orange (MO) revealed that the rate of photocatalytic activity of S3 is much higher than that of S4 under both UV and natural sunlight irradiation. The relatively lower activity of S4 has been attributed to the presence of MCE capping agents which acts as a barrier for the interaction of MO molecules with the CdS nanocrystals. The proposed mechanism for the formation of CdS microspheres and their photocatalytic activity has also been presented.