TAGRA 2025

Carbon and graphene quantum dots (CQDs and GQDs) are highly attractive for a wide range of applications due to their excellent characteristics, including high photoluminescence, tunable bandgap, water solubility, and biocompatibility. These nanomaterials exhibit strong quantum confinement and edge effects, which can be further modulated through surface functionalization with groups such as -OH, -COOH, and -NH₂. Their capacity to participate in electron transfer and radical scavenging reactions makes them particularly useful for developing novel sensing platforms [1-3]. Furthermore, their synthesis from cost-effective precursors like citric acid facilitates scalable production.
Vanadium is extensively used in steel production and other industrial processes, leading to its environmental release, primarily through the combustion of fossil fuels. Among its various oxidation states, V(V) is notably more toxic than its reduced forms, posing significant risks to ecosystems and human health [4]. Vanadium's dual role as both an essential trace element and a potential toxin underscores the need for accurate monitoring.
This work introduces an innovative approach for the colorimetric detection of V(V) using nitrogen-doped CQDs (N-CQDs), synthesized via the thermal treatment of a mixture of citric acid and 3,4-diaminobenzoic acid. The synthesized N-CQDs were characterized using appropriate microscopic and spectroscopic techniques. In the detection mechanism, V(V) oxidizes 3-methyl-2-benzothiazolinone hydrazone in an aqueous solution containing sodium dodecyl sulfate and hydrochloric acid to generate a diazonium cation. This cation then couples with the N-CQDs to form a pink-colored azo dye. A linear calibration curve for V(V) was established in the range of 1.8–240 µM. The method achieved a low detection limit of 0.9 µM and a relative standard deviation of 1.7–5.3%. An interference study confirmed the method's high selectivity. To validate its practical utility, the method was successfully applied to the analysis of various environmental water samples.