Carbon quantum dots: synthesis and applications as turn-off fluorescence sensors for detection of Co2+ ions in water and eco-friendly catalysts for treatment of wastewater

Abstract

Carbon quantum dots (CQDs) are a new generation of QDs that have unique and interesting optical and structural properties. Fluorescence methods are useful, simple, and rapid for the detection of heavy metal ions in water, which has attracted great attention. In this research, a simple and rapid fluorescence method for the detection of cobalt (Co2+) ions in water is introduced. CQDs were synthesized by using pistachio as a precursor for the first time by a hydrothermal method. The QDs were characterized by structural analyses including x-ray diffraction, tunneling and scanning microscopies, energy-dispersive x-ray spectroscopy, infrared spectroscopy, BET surface area measurements, zeta potential measurements, and Raman spectroscopy. The Raman spectroscopy results showed a 3.54 value for the G/D ratio and this result confirmed that synthesized CQDs possess a graphitic crystalline structure. Zeta potential measurements confirmed the presence of a negative surface charge, resulting in high stability. These CQDs had blue photoemission with a broad PL peak between 300 to 600 nm. TEM images showed that CQDs are spherical with diameters of ∼7 nm. Their photocatalytic activities were studied with different dyes under both sun and UV light. Methylene blue had better degradation by the CQDs than methylene orange and Rhodamine B. The scavenger results indicate that radicals play a key role in the photocatalytic degradation of methylene blue under UV irradiation.