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

A simple hydrothermal method was conducted to transform chrome shavings (CS) into carbon quantum dots (CS-CQDs) that were then applied as supersensitive chemical sensors for the detection of Cr6+ (1.40 μM limit of detection (LOD)) and Fe3+ (1.67 μM LOD) ions. Meanwhile, most of the chromium in CS deposited in the resulting precipitate, realizing the separation and recovery of chromium. CS-CQDs were further used to prepare an "intelligent fluorescent switchable sensor" (IFSS) hydrogel with high sensitivity for the identification of Cr6+ in tannery wastewater (LOD of 45.59 μmol/L). Interestingly, the quenched IFSS-Cr6+ hydrogel system could be applied to determine ascorbic acid (AA) with a LOD of 21.33 μmol/L, owing to the reduction of Cr6+ into Cr3+ by AA and thus the IFSS's fluorescence regeneration. This ″fluorescent on/off″ effect could be recycled at least four times. IFSS hydrogel also could adsorb Cr6+ ions (13.50 mg/g) and is done so after the reduction by AA. The possible sensing mechanism to Cr6+ was confirmed to be the internal filtration effect and electron transfer. This work not only developed a feasible and clean recycling method of CS but also produced a smart functional material for the determination and separation of Cr6+, achieving "turning trash into treasure".