Eco-friendly synthesis of a silver nanohybrid with carbon dots derived from Quebracho Colorado leaves and its application in the colorimetric detection of Al3+

Abstract

The Schinopsis lorentzii tree leaves were utilized for the first time in the production of carbon dots (CDs) with a diameter of 6 nm through hydrothermal carbonization at 200 °C. The heating of AgNO₃ aqueous solutions up to 70 °C in the presence of CDs results in the formation of silver nanohybrids (AgNP@CDs), with a zeta potential of −48 mV, a diameter of 33 nm, and a surface plasmon resonance (SPR) absorption band centered at 440 nm. Among the various cations examined, only the incorporation of Al³⁺ in the AgNP@CDs solution induced a color shift from yellow to brown, leading to the formation of colloidal aggregates with an approximate diameter of 550 nm. The formation of AgNP@CDs nanohybrids and aggregates in the absence and presence of Al³⁺, respectively, was modeled by combining UV–vis absorption spectra with multivariate curve resolution-alternating least squares (MCR-ALS) analysis. For the AgNP@CDs, a sequential nucleation-aggregation mechanism was observed, with a global activation energy of 28 kJ/mol. In the presence of Al³⁺, a four-species sequential mechanism describes the progressive formation of larger aggregates, with dose-response curves that are characteristic of highly cooperative binding equilibriums with an average global binding constant of 7 × 10⁴ M⁻¹. The analytical performance of the AgNP@CDs resulted in a sensitivity of 0.03 μM, a linear range between 10 and 20 μM, and a limit of detection of 3.5 μM. These parameters are consistent with those previously reported for the colorimetric determination of Al³⁺ using AgNPs capped with different molecules.