Bio-inspired synthesis of sea urchin–like hierarchical BaO nanostructures using <i>Ocimum sanctum</i> for enhanced UV-driven photocatalytic dye degradation and electrochemical sensing

A facile green synthesis route using Ocimum sanctum (Tulsi) leaf extract was used to synthesise BaO nanoparticles. The prepared BaO exhibited a hierarchical sea urchin-like nanostructure (NS) and was characterised using various analytical and spectroscopic techniques. XRD data indicated that the nanostructure exhibits a tetragonal phase with an assessed average crystallite size of 107 nm. SEM study unveils needle-like cluster morphology, indicating highly crystalline growth of the nanomaterials. TEM analysis further confirmed the 3D hierarchical sea urchin-like architecture, consisting of a central core from which sharp one-dimensional (1D) nanoneedles radiate outward. UV – Vis spectroscopy showed that the bandgap energy of the nanophase BaO was 3.97 eV, lower than that of bulk BaO (4.4 eV). The synthesised BaO NS were evaluated for the photocatalytic degradation of Fast Blue (FB) and Fast Orange (FO) dyes under UV irradiation. The degradation process was monitored at the characteristic absorption maxima of 617 nm (FB) and 496 nm (FO), achieving maximum degradation efficiencies of 77.52% and 73.75%, respectively, which demonstrates enhanced photocatalytic activity. Furthermore, the BaO NS were investigated for electrochemical sensing of lead and lithium ions, exhibiting a positive shift in peak potential with increasing analyte concentration. Electrochemical impedance spectroscopy analysis using Nyquist plots established a charge transfer resistance (Rct) of precisely 3 Ω.