Inner-filter Effect Induced Fluorescence Quenching of Carbon Dots for Cr(VI) Detection with High Sensitivity

Carbon dots (CDs) were used to develop a sensitive sensing technique for detecting Cr(VI). CDs were made using a hydrothermal technique from citric acid and glutamic acid. These prepared CDs emitted blue fluorescence under excitation of 350 nm (λ_em = 420 nm), and the fluorescence quantum yield was 48.41%. Transmission electron microscope was used to examine the morphology of the CDs, which had an average size of 2.21 ± 0.39 nm. The elementary composition and bonding structure of the CDs were conducted by XPS and FT-IR spectrum. Cr(VI) quenched the fluorescence of CDs through a static quenching effect and an inner filter effect, allowing Cr(VI) to be detected quantitatively. This approach was used to detect Cr(VI) in two samples of water, with the findings demonstrating that it is reliable and accurate. The fluorescence intensity change was linearly related to the concentration of Cr(VI) in the range from 0.5 to 400 μM, with the detection limit being 0.10 μM. This approach has the virtues of wide detection range, low cost and fast response. The strategy has a great application prospect for detecting Cr(VI) in practical samples.