Fluorescent Sensing of Fe³⁺ in Acidic Environment by Carbon Dots Derived From Empty Fruit Bunch Biochar: Central Composite Design Optimization

A rapid, eco-friendly, and selective monitoring of Fe(III) in real media utilizing carbon dots (CDs) as a luminescence detector has been reported. CDs were fabricated by a hydrothermal route from empty fruit bunch biochar. The as-synthesized CDs were analyzed using various analytical tools. The results reveal that CDs have spherical shapes with a narrow particle size distribution and are enriched with multiple active sites, which impart excellent hydrophilicity and photostability. The CDs displayed bright blue emission under UV light with emission/excitation maxima at 452/350 nm, respectively, and a QY of 7.54%. The CDs exhibited high resistance to photobleaching and high salt conditions and pose a long lifetime of up to 6 months with no agglomeration. The detection variables, including pH, temperature, and CDs concentration, were optimized via response surface methodology. The statistical data verified the precision of the quadratic model for predicting the sensing performance of the nanoprobe. Under optimal environments, a linear range from 0 to 50 μM and a detection limit of 0.17 μM was obtained. The turn-off process includes the strong coordination between Fe(III) and electron-donating oxygen species on the edge of CDs. The rapid luminescence recognition using acid-free materials renders CDs a promising option for water treatment.