Quantum dots of SnS and SnS2 modified with Rhodamine B - sonochemical synthesis, improved sono- and photocatalytic activity, and kinetic modeling.

The aim of this study was to sonochemically synthesize SnS and SnS2 quantum dots modified in situ with organic dye. For this purpose Rhodamine B, a dye from the xanthene group, is used. The resulting nanomaterials were characterized with the following techniques: X-ray powder diffraction, XPS, Raman and EDX spectroscopic techniques to confirm the production of desired compounds. HR-TEM observations prove the formation of quantum dots while the Tauc method was used to study the optical energy bandgap of both modified and unmodified nanomaterials. Raman studies showed not only that nanometric samples of SnS and SnS2 were obtained, but the recorded fluorescence from Rhodamine B indicates the presence of its molecules on the surface of these nanoparticles. The modification with Rhodamine B preserved the morphology and phase composition of tin sulphides but caused the occurrence of additional electron transitions as revealed by Tauc analysis. The contact angle measurements showed increase and decrease of contact angle due to modification with dye, for SnS2 and SnS respectively. The photo- and sonocatalytic activities of both modified and unmodified quantum dots are studied and compared, including kinetic analyses, investigations of influence of degree of functionalization and catalyst's amount, and determination of reactive intermediates (scavenging experiments). The modification of SnS with Rhodamine B improved it's sono- and photocatalytic activity. The investigation of the best catalyst after 5 cycles of sonocatalytic process showed it's oxidation to SnO2. Scavenging experiments revealed that the main reactive intermediate in the case of SnS with optimized amount of dye was radical anion •O2-. Finally, the n-th order kinetic model provided the most accurate description of photocatalytic processes.