One step ultrasonic synthesis of N,S-co doped carbaon dots and their visible-light sensitive photocatalytic ability

In recent years, considerable attention has been paid to the synthesis and application of carbon quantum dots (CDs), due to their outstanding tunable multi-color photoluminescence (PL) properties, high chemical stability, low toxicity, biocompatibility, and easy functionalization[1]. The unique PL property of CQDs called by upconversion has been found, which could transfer low energy photon to high energy photon over CQDs by sequential absorbing two or multiple longer wavelength photons[2]. Herein, we report the green synthesis of N,S-CDs via a facile ultrasonic method, which exhibits improved photocatalytic activity for organic dyes (methylene blue) under visible-light irradiation. Carbon nanoparticles were synthesized from the mixture of glucose and thiourea. Glucose served as the carbon source, and the thiourea provided nitrogen and sulfur. Co-doped carbon dots were characterized by X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and Fourier transform infrared (FTIR) spectroscopy techniques. We systematically investigated photophysical properties of CQDs prepared by ultrasonication method, in particular upconversion process under low photons irradiation. It was demonstrated that compared to CDs, the as-prepared NCDs show prominent photocatalytic property for the degradation of methylene blue (MB) under visible light. The degradation efficiency of MB by N,S - CDs was 4 times higher than that of pure CDs under visible light.