An Efficient Continuous Hydrothermal Flow Synthesis of Carbon Quantum Dots from a Targeted Biomass Precursor for On-Off Metal Ions Nano-Sensing

Glucose, a readily available biomass precursor is used for the production of carbon quantum dots (CQDs) via a fast, efficient, and environmentally benign continuous hydrothermal flow synthesis (CHFS) process using supercritical water, an approach that can readily be scaled-up for industrialization, producing materials with enhanced properties. The water soluble CQDs exhibit an average particle size of 2.3 ± 0.5 nm, with optimum emission intensity at 446 nm on excitation at 360 nm. The as-synthesized CQDs with no extra modification show promising sensitivity and good selectivity for the highly toxic, carcinogenic, and mutagenic chromium (VI) ion (limit of detection of 1.83 ppm) and for the essential bioactive transition metal, iron (II) ion (limit of detection of 6.09 ppm). The life-cycle assessment confirms that in comparison to conventional batch synthetic method, continuous hydrothermal flow synthesis process is significantly a more efficient and greener route for the synthesis of carbon quantum dots from the glucose biomass precursor.