Efficient Reduction of Cr(VI) with Carbon Quantum Dots

Abstract

Hexavalent chromium (Cr(VI)) pollution is a global problem, and the reduction of highly toxic Cr(VI) to less toxic Cr(III) is considered to be an effective method to address Cr(VI) pollution. In this study, low-toxicity carbon quantum dots (CQDs) were used to reduce Cr(VI) in wastewater. The results show that CQDs can directly reduce Cr(VI) at pH 2 and can achieve a reduction efficiency of 94% within 120 min. It is observed that under pH higher than 2, CQDs can activate peroxymonosulfate (PMS) to produce reactive oxygen species (ROS) for the reduction of Cr(VI) and the reduction efficiency can reach 99% within 120 min even under neutral conditions. The investigation of the mechanism shows that the hydroxyl groups on the surface of CQDs can be directly oxidized by Cr(VI) because of the higher redox potential of Cr(VI) at pH 2. As the pH increases, the carbonyl groups on the surface of CQDs can activate PMS to generate ROS, O 2 •– , and 1 O 2 , which result in Cr(VI) being reduced. To facilitate the practical application of CQDs, the treatment of Cr(VI) in real water samples by CQDs was simulated and the method reduced Cr(VI) from an initial concentration of 5 mg/L to only 8 μg/L in 150 min, which is below the California water quality standard of 10 μg/L. The study provides a new method for the removal of Cr(VI) from wastewater and a theoretical basis for practical application.

Orange Pomace-Derived Fluorescent Carbon Quantum Dots: Detection of Dual Analytes in the Nanomolar Range

“…Cr 2 O 7 2– and CrO 4 2– are in equilibrium in the solution, and as the solution becomes acidic, the reaction equilibrium moves toward left (eq ), and as shown in eq , Cr 2 O 7 2– is instantaneously converted to HCrO 4 – as the primary constituent. The CQD surface contains profuse number of functional groups like hydroxyl, carboxyl, amide, and carbonyl, some of which have reduced capabilities. As a result, Cr 6+ directly reduced to Cr 3+ in the presence of CQDs . The effect of pH on the performance of the sensors for the selective detection of Cr 6+ was also studied.…”

Cleaner, High-Efficiency, and High-Value Conversion of Chrome-Containing Leather Solid Waste into Carbon Quantum Dots as Renewable Bimetallic Ions Detection Sensors

“…In addition, the XPS energy spectra of IFSS and IFSS-Cr 6+ systems (Figure b) were also recorded and compared to further study the interaction mechanism between Cr 6+ and CS-CQDs. By comparing the high-resolution XPS spectra of C 1s (Figure c), N 1s (Figure d), and O 1s (Figure e), obvious change could be observed in the binding energy assigned to the C–N and CO peaks in the IFSS-Cr 6+ system, indicating that nitrogen-containing and oxygen-containing functional groups in IFSS may interact with Cr 6+ ions . Notably, the IFSS system had no detectable peaks assigned to the chromium ion (Figure b), while the peaks corresponding to both Cr 6+ and Cr 3+ ions were observed in the IFSS-Cr 6+ system (Figure f).…”

“…By comparing the high-resolution XPS spectra of C 1s (Figure 8c), N 1s (Figure 8d), and O 1s (Figure 8e), obvious change could be observed in the binding energy assigned to the C−N and C�O peaks in the IFSS-Cr 6+ system, indicating that nitrogen-containing and oxygen-containing functional groups in IFSS may interact with Cr 6+ ions. 72 Notably, the IFSS system had no detectable peaks assigned to the chromium ion (Figure 8b), while the peaks corresponding to both Cr 6+ and Cr 3+ ions were observed in the IFSS-Cr 6+ system (Figure 8f). The appearance of Cr 3+ could be attributed to the partial reduction of Cr 6+ ions in the IFSS-Cr 6+ system to Cr 3+ ions due to certain reducing property of CS-CQDs.…”

Advances in the ratiometric combination of quantum dots for their use in sensing applications

“…1 Due to their small size, high surface-to-volume ratios, and quantum confinement effect, they are widely used in various applications. From the application of energy storage 2 to pollution remediation, 3 from biomedical 4 to aerospace 5 applications, they have proved themselves useful. Due to the quantum confinement effects, these materials possess photoluminescence properties.…”