<i>Bauhinia variegata</i> mediated Co ₃ O ₄ and Co ₃ O ₄ @CNT nanomaterials: Electrochemical and antibacterial studies

A green route was established for the synthesis of cobalt oxide, i.e., Co 3 O 4(aq) and Co 3 O 4(et) nanoparticles (NPs) by treating cobalt(II) nitrate hexahydrate with aqueous and ethanolic extracts, respectively, of Bauhinia variegate leaves. The synthesized NPs were sonicated with carbon nanotubes (CNTs) in different (97:3, 94:6, and 91:9) ratios to produce Co 3 O 4(aq) @CNT 1 , Co 3 O 4(aq) @CNT 2 , Co 3 O 4(aq) @CNT 3 , Co 3 O 4(et) @CNT 1 , Co 3 O 4(et) @CNT 2 , and Co 3 O 4(et) @CNT 3 nanocomposites (NCs). The structural, morphological, and thermal studies of the nanomaterials (NMs) were performed by X-ray diffraction (XRD), Fourier-transform infrared (FTIR), UV-Visible, scanning electron microscopy (SEM), thermogravimetric analysis (TGA), and DSC analyses. The average crystalline sizes of Co 3 O 4(aq) (22.54 nm) and Co 3 O 4(et) (20.48 nm) were decreased to 13.73-16.82 nm and 16.08-19.47 nm, respectively, in their respective CNT decorated NC counterparts. The NMs derived from aqueous and ethanolic extracts of B. variegate leaves have shown band gaps in the ranges of 4.74-5.15 and 5.1-5.36 eV, respectively. SEM analysis revealed irregular, spherical, and porous morphologies, except for Co 3 O 4(et) , which was highly agglomerated. CNTs were well-dispersed within the Co 3 O 4 matrix, forming smooth surfaces and enhancing electrical conductivity. The average particle sizes ranged from 22.81 to 54.65 nm. The electrochemical potential of the synthesized NMs was tested by cyclic voltammetry (CV) and galvanostatic charge-discharge (GCD). All the NMs have shown oxidation and reduction peaks, elaborating their reversible charging and discharging behavior and their possible applications for battery. Co 3 O 4et) @CNT 3 exhibited the highest specific capacitance value of 989.25 F g⁻ 1 , showcasing its exceptional potential as a supercapacitor (SC) material. All the synthesized NMs except Co 3 O 4(aq) have shown significant antibacterial potential (ZOI = 9-13mm) as compared to tetracycline (ZOI = 21mm) against Bacillus subtilis (Gram-positive) by disc diffusion method.