Fluorescent carbon quantum dots as a novel solution and paper strip-based dual sensor for the selective detection of Cr(VI) ions

Abstract

Herein, we report the development of a simple green methodology to fabricate N-doped carbon quantum dots (N-CQDs) with a high luminescence using R. graveolens leaves following the hydrothermal method. Optical, chemical, morphological, and electrochemical properties were thoroughly investigated employing a variety of analytical techniques. The fabricated N-CQDs have a spherical shape, with an average diameter of 4.5 nm. Excitation dependent emission behaviour, 18% QY and green fluorescence were all observed in the N-CQDs. They are particularly resistant to various impacts such as ionic strength, pH, continuous visible light irradiation, and storage time. Since Cr(VI) ions are highly carcinogenic and mutagenic, there is an urgent demand for sensitive, selective, and efficient sensors for monitoring and measuring the amount of Cr(VI) ion in water in the environment. Hence, we developed the prepared N-CQDs as a label-free fluorescence and electrochemical probe for detecting Cr(VI) ions selectively and sensitively in aqueous solutions. Relying on static quenching together with the inner filter effect, N-CQDs performed exceptionally well as fluorescence sensors for Cr(VI) ions. The N-CQDs exhibit a limit of detection of 300 and 5 nM in the photoluminescence and differential pulse voltammetry analysis, respectively. The detection of Cr(VI) ions in real water samples using the developed sensor through both methods presented high precision without any interference. In addition, we also developed paper sensing strips for field application by depositing N-CQD on filter paper, which has been satisfactorily evaluated for sensing Cr(VI) in solid-state and solution mediums.