Microwave-assisted synthesis of biomass-derived N-doped carbon dots for metal ion sensing

Biomass-derived carbon dots (CDs) have gained significant research interest for environmental monitoring applications thanks to their cost-effectiveness and sustainability. Using eco-friendly biowastes as precursors for CDs production offers an alternative to expensive and unsustainable inorganic and chemically synthesized CDs. This study presents the findings regarding the successful synthesis of biomass-based nitrogen-doped carbon dots (N-CDs) via a rapid, cost-effective, and environmentally friendly microwave-assisted method. Carboxymethyl cellulose (CMC) and glycine were used as carbon precursors and nitrogen dopants for the first time. The N-CDs exhibited a moderately high quantum yield of 31.6 ± 1.5% with an optimal fluorescence excitation wavelength of 400 nm. FTIR, CHNS, and SEM–EDX analyses characterized the N-CDs' surface functional groups and elemental composition. The optical stability of the N-CDs was validated across varying pH levels and NaCl concentrations. The N-CDs displayed notable selectivity and sensitivity for Fe3⁺, Cu2⁺, and Hg2⁺ ions. The primary quenching mechanisms involve electrostatic interactions, π–π interactions, inner filter effects, and energy transfer. Stern–Volmer analysis revealed strong linear quenching for Fe3⁺, Cu2⁺, and Hg2⁺ ions within the 0–10 µM range concentrations, with detection limits (LOD) of 6.0 µM, 1.41 µM and 1.36 µM for Fe3⁺, Cu2⁺, and Hg2⁺, respectively. The fluorescence quenching for Fe3⁺ ions enhanced sensitivity at higher concentrations, while selectivity decreased at lower concentrations. These findings highlight the potential of these N-CDs as a cost-effective and sustainable tool for environmental monitoring, offering a promising approach to addressing critical water contamination issues.