Synthesis and characterization of heterostructured carbon nanodots derived from Pinus pinea L. bark for enhanced Fe3+ sensing and antioxidant activity

Abstract

Pinus pinea L. bark residues were utilized for the environmentally friendly synthesis of PP300-3 carbon nanodots (synthesized via pyrolytic treatment at 300 °C for 3 hours). Comprehensive structural characterization employing high-resolution transmission electron microscopy (HR-TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS) revealed a hybrid nanostructure comprising crystalline graphitic domains and amorphous carbon regions. This heterogeneous structure provides excellent photoluminescent properties with a quantum yield of 3.8%. Photoluminescent characteristics were investigated through wavelength-dependent optical studies, revealing optimal photon emission efficiency at 320 nm. Screening experiments with thirty-three metal ions demonstrated that Fe³⁺ exhibited high selectivity. Although five metal ions (Au³⁺, Bi³⁺, Pd²⁺, Pt²⁺) caused some fluorescence quenching, only Fe³⁺ demonstrated a linear dose-dependent response suitable for quantitative analysis. With excellent analytical performance (R² = 0.9926, RSD < 2%, LOD = 35.43 µg L⁻¹), a simple spectrofluorometric protocol for Fe³⁺ determination was developed and validated in real water samples, achieving 99.56% recovery rates. Antioxidant evaluation using FRAP, CUPRAC, and DPPH assays demonstrated significant free-radical scavenging efficiency. Low SC₅₀ concentrations (4.36 ± 0.92 mg mL⁻¹) indicate robust electron-transfer capacity and valuable antioxidant activity. In conclusion, PP300-3 carbon nanodots represent a versatile platform material with simple synthesis, environmentally friendly production, excellent analytical performance, and significant antioxidant activity, making them suitable for environmental monitoring, water quality control, and biomedical research.