Phosphoric acid assisted synthesis of fluorescent carbon dots from waste biomass for detection of Cr(VI) in aqueous media

A green and facile method for the synthesis of carbon dots (CDs) have been developed using lignocellulosic biomass (banana stem) and phosphoric acid to construct fluorescent sensor for Cr(VI) detection. The effects of phosphoric acid and temperature on the fluorescence behavior of carbon dots have been explored elaborately. The optical and structural properties of the CDs were determined by different characterization techniques. The prepared CDs display excellent fluorescence properties with intense bright blue emission spectra around 447 nm at an excitation wavelength of 350 nm. The CDs possessing the highest quantum yield (15.1%) have an immense sensing potential to detect Cr(VI) in linear detection range (10–30 μM) with detection limit of 2.4 μM. Furthermore, the CDs have been applied to quantitatively detect Cr(VI) in real water samples. Theoretical studies based on DFT and TDDFT calculations suggested the detection pathway of Cr(VI) occurs via photoinduced electron transfer (PET) which furthur supports the experimental studies.