Naked eye colorimetric detection of fluoride through TiO₂ NPs/CQDs based detector

Fluoride (F^-) occurs naturally in a soil, air and water as commonly found element in earth crusts. Almost 200 million populations worldwide and approximately 60 million in India are facing F^- contamination problem. Therefore, development of low-cost and highly sensitive colorimetric detector for F^- ions using carbon quantum dots (CQDs) and metal salts is required. For this, CQDs were synthesized using flower waste from temples by green method and further characterized. CQDs-TiO₂ complex solution color changes from green to black on addition of F^- ions due to exchange of F^- ions with hydroxyl ions of the solution. Absorption spectrum of CQDs-TiO₂ complex solution depicts change in spectral graph on adding F^- ions with the appearance of new band at approx. 550 nm. The color spectral as a function of F^- ions concentration gave a linear response in the range of 2-8 ppm (R² = 0.9808). The color change can be observed at 2 ppm after incubation of 5 min by naked eye. Developed colorimetric detector shows high selectivity with other ions (Cl^-, Br^-, I^- and H₂PO₄^-). The F^- ion detection was done in different water samples collected from districts of Haryana using developed detector. The developed colorimetric detector allows wide range of F^- sensing for water sample even at every low concentration i.e 2 ppm.