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. 2024 Oct 17;14(20):1666.
doi: 10.3390/nano14201666.

Mandarin Peels-Derived Carbon Dots: A Multifaceted Fluorescent Probe for Cu(II) Detection in Tap and Drinking Water Samples

Marwa El-Azazy  1 , Alaa AlReyashi  1 , Khalid Al-Saad  1 , Nessreen Al-Hashimi  1 , Mohammad A Al-Ghouti  2 , Mohamed F Shibl  3 , Abdulrahman Alahzm  1 , Ahmed S El-Shafie  1
Affiliations

Mandarin Peels-Derived Carbon Dots: A Multifaceted Fluorescent Probe for Cu(II) Detection in Tap and Drinking Water Samples

Marwa El-Azazy et al. Nanomaterials (Basel). .

Abstract

Carbon dots (CDs) derived from mandarin peel biochar (MBC) at different pyrolysis temperatures (200, 400, 600, and 800 °C) have been synthesized and characterized. This high-value transformation of waste materials into fluorescent nanoprobes for environmental monitoring represents a step forward towards a circular economy. In this itinerary, CDs produced via one-pot hydrothermal synthesis were utilized for the detection of copper (II) ions. The study looked at the spectroscopic features of biochar-derived CDs. The selectivity of CDs obtained from biochar following carbonization at 400 °C (MBC400-CDs towards various heavy metal ions resulted in considerable fluorescence quenching with copper (II) ions, showcasing their potential as selective detectors. Transmission electron microscopic (TEM) analysis validated the MBC-CDs' consistent spherical shape, with a particle size of <3 nm. The Plackett-Burman Design (PBD) was used to study three elements that influence the F0/F ratio, with the best ratio obtained with a pH of 10, for 10 min, and an aqueous reaction medium. Cu (II) was detected over a dynamic range of 4.9-197.5 μM and limit of detection (LOD) of 0.01 μM. Validation testing proved the accuracy and precision for evaluating tap and mountain waters with great selectivity and no interference from coexisting metal ions.

Keywords: Plackett–Burman Design; carbon dots; copper (II) detection; fluorescence sensor; hydrothermal process; mandarin peels biochar.

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Conflict of interest statement

The authors declare no conflicts of interest.

Figures

Scheme 1
Scheme 1
Synthesis of MBC400-CDs from waste mandarin peels.
Figure 1
Figure 1
UV–vis spectra of the as-prepared MBC400, 600, and 800-CDs, including an inset image showing the CDs samples under UV light at 365 nm compared to DIW (far right).
Figure 2
Figure 2
Fluorescence emission spectra of the as-synthesized MBC400-CDs emitted using different excitation wavelengths in the range between 250 and 350 nm.
Figure 3
Figure 3
TEM micrographs of the prepared samples: (a–c) MBC400-CDs, (d–f) MBC600-CDs, and (g–i) MBC800-CDs at different scales between 5 and 50 nm. Micrographs denoted by the letters (j–l) are the PSD of the prepared samples from MBC400, 600, and 800, respectively.
Figure 4
Figure 4
(a) FTIR spectrum of MBC400-CDs and (b) powder XRD pattern of the samples MBC400 (blue line) and MBC400-CDs (red line).
Figure 5
Figure 5
(a) The MBC400-CDs fluorescence intensity (FI) measured in different concentrations of NaCl and (b) MBC400-CDs FI measured versus time.
Figure 6
Figure 6
(a,b) is the selectivity test of the prepared MBC 400-CDs towards different metal ions, (c) a photo showing the MBC400-CDs sample before and after quenching using different heavy metal ions under irradiation using a longer wavelength UV lamp.
Figure 7
Figure 7
(a) Pareto chart of standardized effects, (b) 2D contour plots, and (c) 3D surface plots for pH and CT.
Figure 8
Figure 8
(a) The calibration curve for different concentrations of copper (II), determined using MBC400-CDs. (b) Fluorescence spectra of MBC400-CDs before and after adding different concentrations of copper (II).
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