Utility of cauliflower waste/garlic biomass admixture for green synthesis of multi-doped CQDs as a fluorescent optosensor for Fe3+ in different matrices

Abstract

A simple method for the synthesis of multi-doped carbon quantum dots (CQDs) has been developed via a fast, affordable, and green pathway from natural, nontoxic, and inexpensive substrates as garlic and cauliflower leaves and stalk as a plant by-product by the aid of microwave. The synthesized fluorescent CQDs have excellent quantum yield of 42 % at λ_ex/λ_em of 330/411 nm with superb stability. The CQDs were fully described using energy-dispersive X-ray, X-ray diffraction, transmission electron microscopy, Fourier transform infrared spectroscopy, Zeta potential, UV–visible spectroscopy, and fluorescence spectroscopy which demonstrate that CQDs are doped with multiple elements including sulfur, nitrogen, phosphorus, potassium, sodium, and calcium. It has been noted that Fe³⁺ specifically quenches the CQDs’ fluorescence, unlike other heavy metals. Based on this phenomenon, the produced CQDs revealed outstanding results as a fluorescent optosensor for iron determination over the concentration range of 10.0–400.0 μM with a limit of detection of 3.29 μM. The proposed method is effective for determining Fe³⁺ in pharmaceutical dosage form with mean % recovery of 98.73 ± 0.75 %. Additionally, the synthesized CQDs also showed a significant promising potential in environmental applications for detection of Fe³⁺ in tap, irrigation, and river water with mean % recovery of 99.45 ± 1.71, 100.57 ± 1.32, and 101.49 ± 2.44 %, respectively. Several greenness measures and software approved the greenness of the designed optosensor. This approach proved that green synthesis could furnish CQDs from natural low-cost substrates with distinct outstanding characteristics that are suited for certain uses without consuming hazard materials unlike traditional methods.