Converting pine cone into functional nanomaterials: Glutamic acid-assisted synthesis of carbon dots for sensitive monitoring of iron Ions in environmental waters

Abstract

In this work, carbon quantum dots (CQDs) were fabricated through a straightforward, green, one-pot hydrothermal route, employing Pine cone as a renewable carbon precursor and L-glutamic acid as a co-dopant. Comprehensive characterization via STEM, XRD, and FT-IR revealed that the resulting CQDs exhibited a quasi-spherical shape, narrow size dispersion, and a high density of oxygen- and nitrogen-rich surface moieties. Optical evaluations confirmed robust, excitation-dependent photoluminescence with a characteristic band gap of 2.45 eV. These CQDs served as an exceptionally selective fluorescent sensor for Fe3+ detection, operating on the principle of efficient fluorescence quenching. At an optimal pH of 7.0, the probe exhibited a strong linear correlation (R2 = 0.9978) across a range of Fe3⁺ concentrations, with an exceptionally low limit of detection (LOD) of 2.37 × 10–8 mol L−1. Selectivity assays further demonstrated that the sensor effectively distinguished Fe3+ even in the presence of competing metal ions. The practical utility of the proposed method was verified using tap water, lake water, and certified materials (NASS-5 and SM-WW1), yielding high precision with recoveries between 101.2% and 104.4% (RSD < 3.7%). This study highlights biomass-based CQDs as a sustainable and efficient tool for monitoring heavy metals in complex environmental matrices.