One-pot, template-free syntheses of spherical ZnS nanocrystals using a new S2− source and their photocatalytic study

Abstract

A facile, one-pot synthesis of template-free ZnS microspheres composed of nanocrystals (NCs) has been successfully carried out using the solvothermal method with 4,4′-dibenzyldisulfide (DBDS = (C₇H₇)₂S₂)) as a new temperature controlled in situ source of S²⁻ ions without (S1–S3) and with the use of a capping agent (S4). The powder X-ray diffraction measurements of all the four (S1–S4) samples revealed the cubic or zinc blende (ZB) structure of the ZnS microspheres. FESEM analyses showed an almost spherical morphology of the ZnS microspheres which are composed of smaller NCs. TEM analyses of samples S3 and S4 confirmed the ZnS microspheres with assembled NCs. Optical measurements of the samples (S1–S4) showed a blue-shift in the UV-vis absorption maxima compared to that of bulk ZnS due to the quantum confinement effect. Photoluminescence measurements show intense blue emission of the samples. Photocatalytic investigation of the uncapped (S3) and mercaptoethanol (MCE)-capped (S4) ZnS microspheres for degradation of methyl orange (MO) revealed higher photocatalytic activity of S3 over S4 under UV light irradiation. The lower catalytic activity of S4 has been attributed to the presence of MCE capping agents which act as barriers for the interaction of MO molecules with the ZnS NCs. The proposed mechanism for the formation of ZnS microspheres and their photocatalytic activity has also been presented.