Transformation of Indium Nanoparticles to β-Indium Sulfide: Digestive Ripening and Visible Light-Induced Photocatalytic Properties

We report the transformation of polydispersed dodecanethiol stabilized indium nanoparticles, obtained from bulk indium shot by evaporation/condensation solvated metal atom dispersion (SMAD) technique, into highly monodispersed partially alkyl thiolate-capped beta-indiumsulfide (In2S3) by a postpreparative digestive ripening in high boiling point t-butyltoluene (190 degrees C) solvent. Upon digestive ripening, the as-prepared polydispersed black indium nanopartides showed a characteristic color transition from black to cream, pale yellow, yellow, and finally to brown, indicating the transformation of the indium metal nanoparticles into intermediates composed of indium thiolates, sulfides, and polysulfides, and finally into the product In2S3 nanoparticles whose surfaces are partially capped with thiolates. The transformed product (In2S3) was characterized with UV-vis, XRD, EDX, SEM, XPS, and TEM. From XRD and TEM measurements, the average size of the transformed In2S3 nanoparticles is 5 nm. The optical absorbance of the as-prepared sample showed absorption peaks around 538 and 613 nm; upon digestive ripening these two peaks disappeared and stabilized at 375 nm, providing evidence of strong quantum confinement of excitons. The visible light-induced photocatalytic activity test with the In2S3 nanoparticles showed that 95% of Rhodamine B (RhB) dye degraded after 100 min of irradiation with visible light.