Facile synthesis of surface-functionalized fluorescent carbon quantum dots for the selective detection of ferric ions

Abstract

Biomass-derived carbon quantum dots are gaining a lot of attention from contemporary researchers because of their sustainable approach in a plethora of applications. In the current study, a highly functionalized and florescent carbon-quantum-dot based ferric ion sensor was prepared from a plant extract of Phlomis bracteosa (PB-CQDs) by a one-step hydrothermal method without using any oxidizing or passivating agent. The synthesized quantum dots were characterized by several spectroscopic and analytical techniques like Fourier transform infra-red (FTIR), X-ray diffraction (XRD), dynamic light scattering (DLS), electron microscopy, X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. FTIR studies demonstrated excellent surface functionality and hydrophilicity with numerous hydroxyl, carboxyl and ammine functional groups. The PB-CQDs were seen to be spherical with diameters in the 2–10 nm range, as depicted by DLS measurements. Moreover, these functional carbon dots exhibited good optical properties with vivid blue photoluminescence and a quantum yield of 57.0%. The fluorescence properties were seen to be dependent on several factors like pH, temperature and excitation wavelength. The fluorescent lifetime (τ) of the carbon dots was investigated by time-resolved fluorescence and the fluorescent decay at two different emissions (390 nm and 405 nm) was calculated to be 2.14 ± 0.0043 and 2.76 ± 0.0032 nanoseconds, respectively. Furthermore, the prepared carbon dots demonstrated selective fluorescence quenching behavior towards ferric ions with good sensitivity and a low detection limit of 0.041 ppm. In addition, the sensor array showed good selectivity towards ferric ions (Fe³⁺) and the least interference with several interfering agents. It is pertinent to mention that a biomass-derived sensor can serve as a potential sensing array for the selective detection of ferric ions from a contaminated environment.