Hibiscus derived nitrogen doped carbon nanochains for visual pH sensing and catalytic methyl orange degradation

Abstract The rapid expansion of synthetic azo dye pollution requires the development of multifunctional nanomaterials capable of simultaneous real-time monitoring and active chemical remediation. Herein, we report the one-pot, microwave-assisted hydrothermal synthesis of nitrogen-doped carbon nano-chains (N-CNCs) using Hibiscus sabdariffa botanical waste as a sustainable precursor. Transmission electron microscopy (TEM) confirmed the fabrication of an interconnected, one-dimensional (1D) beads-on-a-string morphology composed of monodisperse beads (2.08–2.96 nm). Selected area electron diffraction (SAED) verified a short-range turbostratic amorphous carbon framework. The synthesized N-CNCs function as a high-performance dual-mode environmental platform, serving as a high-contrast naked-eye pH sensor and an ultra-rapid catalyst for methyl orange (MO) degradation. Catalytic trials demonstrated a clean, systematic elimination of the chromophore within seconds (< 1 s) at environmental extremes, reaching degradation efficiencies of 79.30% (pH 3) and 74.67% (pH 12). Computational insights from Density Functional Theory (DFT) and Density of States (DOS) analysis decoded the underlying quantum logic, revealing a dramatic collapse of the frontier molecular orbital energy gap (E g ) from 8.5416 eV in native N-CNCs to an ultra-reactive 0.8816 eV within the hybrid matrix. DOS spectra confirmed intense orbital crowding near the Fermi level, which drives instantaneous, non-radiative intramolecular electron transfer for irreversible azo-bond cleavage. This metal-free, circular-economy platform successfully bridges real-time optical tracking with high-capacity chemical remediation, offering a highly competitive blueprint for advanced wastewater treatment.