Uncapped SnO2 quantum dots for selective adsorption, separation and photocatalytic degradation of a mixture of dyes

Abstract

Adsorption and photocatalysis processes are considered to have high significance for the remediation of toxic dyes in aquatic media. Herein, we report the remarkable performance of uncapped SnO₂ quantum dots (QDs) synthesized by varying the drying process. Structure property correlations of the QDs were evaluated by XRD, HRTEM, Raman, PL, FTIR, TGA, BET, and zeta potential techniques. A tailored synthesis process delivered zeta potential values up to −50 mV for QDs dried at a temperature of <60 °C. These QDs were highly selective for the adsorption of methylene blue (MB), and showed 91% adsorption in one minute. The optimum adsorbent concentration of the SnO₂ QDs and the pH values for MB removal were found to be 0.3 mg ml⁻¹ and ∼8, respectively. The Raman and FTIR studies revealed the mechanism of adsorption of MB on QDs which occurred through the alkylated nitrogen group of MB with the surface hydroxyl group of the SnO₂ QDs. The selective adsorption of MB was demonstrated by using a mixture of cationic MB and anionic methyl orange (MO). The un-adsorbed MO was then completely degraded in less than 15 min by irradiating it with ultraviolet light. Furthermore, the reason for the exclusive adsorption property of these QDs compared to the SnO₂ QDs synthesized at a relatively high temperature of 100 °C is also discussed. Thus, the induction of an excellent adsorption property as well as the remarkable photocatalytic degradation ability of the uncapped SnO₂ QDs was demonstrated for two carcinogenic pollutant dyes and this will facilitate its use as a novel property in nanomaterials.