Efficient hydrothermal synthesis of carbon dots from argan cake and their applications

Abstract

Argan cake-based fluorescent carbon dots (CDs-CA) were successfully synthesized by a simple, environmentally friendly, one-step hydrothermal method at 180 °C for 12 h, using argan waste as a biobased precursor. The CDs obtained show intense blue fluorescence under 365 nm UV light. Several structural characterization techniques, including EDX, FTIR, electrokinetic titration, and NMR spectroscopy, were employed to study their chemical structures and identify the functional groups. The thermal properties of the CDs-CA were evaluated by TGA. TEM analysis confirmed their nanometric size, with an average size of 4.64 nm. Furthermore, the UV–vis spectroscopy and photoluminescence (PL) analysis were used to investigate the optical properties. These later showed an excitation-dependent PL behavior. Additionally, the fluorescence lifetime exhibits two decay time constants (τ₁ = 4.56 ns and τ₂ = 9.94 ns), and the average value (τ_avg = 11.40 ns) suggests that surface functional groups primarily govern the emission. The synthesized CDs-CA were incorporated into PVA to form nanocomposite films (PVA@CDs-CA), which exhibited excellent mechanical properties at 2 wt% of CDs-CA. The CDs-CA were successfully applied in three areas. Firstly, as inks that are invisible to normal light but fluoresce under UV light, demonstrating their high potential for anti-counterfeiting applications, particularly in sensitive documents such as passports and banknotes. Then, as high-performance UV-blocking PVA nanocomposite films with a sun protection factor exceeding 50, while maintaining over 82 % visible transmittance. Finally, as a downshifting layer on silicon solar cells, it improves energy conversion efficiency from 11.45 % to 12.21 %.