Assessment of the correlation between optical properties and CQD preparation approaches

Abstract

Various production procedures, for carbon quantum dots (CQDs), are still being extensively researched to understand the nature of CQD luminescence. This study compares and examines the impact of chemical as well as green methods on the structural and optical properties of CQDs. We present a straightforward, cost-effective bottom-up method for producing fluorescent CQDs from lemon peels (L-CQDs), orange juice (O-CQDs), and citric acid (C-CQDs) without having to deal with time-consuming or ineffective post-processing processes. The proposed green synthesis has no toxic by-products, and the residual resources utilized promote the large-scale production of CQDs. X-ray diffraction, high-resolution transmission electron microscopy, FTIR, Raman, DLS, and UV–Vis spectroscopy are utilized to investigate the structure and optical characteristics of the prepared CQDs. The as-prepared CQDS possess small particle sizes of 5.6 nm, 6.2 nm, and 1.1 nm for L-CQDs, O-CQDs, and C-CQDs samples, respectively. FTIR results reveal the coexistence of carboxylic and hydroxyl groups on the surface of the CQDs, as also supported by zeta-potential values. Maximal fluorescence intensity was reached at excitation wavelengths of 365, 250, and 280 nm with an emission color of blue, indigo, and light blue for L-CQDs, O-CQDs, and C-CQDs, respectively. The presented approaches show a high quantum yield of 88% for O-CQDs, 49% for L-CQDs, and 37% for C-CQDs. Due to their minuscule particle size, perfect water solubility, high stability, and tunable luminescence properties, the prepared CQDs are preferred for potential applications in multicolor imaging, metal ion sensing, and wastewater technologies.