Harnessing Arachis hypogaea shells waste into carbon quantum dots for potential surface plasmon resonance detection of 2-nitrophenol

Peanut (Arachis hypogaea) shells have sparked significant interest as a precursor for CQDs synthesis. However, challenges such as elevated temperatures, additivechemicals usage, and high precursor concentrations remain to be addressed. Hence, highly fluorescent CQDs were synthesized from peanut shells with various concentrations (0.1, 0.2, 0.3, 0.4 and 0.5 g/cm3) via hydrothermal method. Afterwards, the synthesized CQDs were characterized using UV–Visible spectroscopy (UV–Vis), photoluminescence spectroscopy (PL), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), and zeta potential to study their optical, structural and morphology properties. The UV–Vis analysis showed an increment in absorbance from 3.53 to 4.00 and corresponding reduction in optical band gap (3.954 eV to 3.831 eV) as peanut shells concentration increased. PL results revealed intense blue fluorescence under the excitation of UV-light (365 nm), with the emission wavelength shiftingto the right as concentration increased. The 0.1 g/cm3of peanut shells produced the shortest wavelength (448 nm), indicating optimal concentration for synthesized CQDs. This optimal concentration was supported by TEM, FTIR, and zeta potential analyses. In TEM analysis, CQDs were uniformly distributed with an average particle size, 6.63 nm. Besides, FTIR spectra confirmed the presence of O—H, C—O, C⚌O, C—H and C⚌C groups. Zeta potential showed that PS-CQDs had high colloidal stability, with a value of −8.5 mV. Lastly, the potential plasmonic sensing of 2-nitrophenol (2-NP) was analysed using surface plasmon resonance (SPR). The immobilization of PS-CQDs on a gold (Au) thin film was fabricated to observe the sensing performance. The PS-CQDs/Au thin film-based SPR sensor showed promising potential for 2-NP detection, with a sensitivity of 0.0094° M−1and a detection limit of 0.01 pM.

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