Green Synthesis of Cr2O3 Nanoparticles by Cassia Fistula, their Electrochemical and Antibacterial Potential

Chromium oxide (Cr2O3) nanoparticles (NPs) find applications in modern science and technology due to their chemical stabilities, high-density corners and magnetic/electrical/catalytic properties. Current studies were performed to produce the (Cr2O3)aq and (Cr2O3)et NPs by treating chromium acetate with the aqueous and ethanolic extracts, respectively of Cassia fistula leaves; the same reaction was also performed in the presence of NaOH to yield the (Cr2O3)aqNa and (Cr2O3)etNa NPs, respectively. The synthesized NPs were characterized by XRD, FTIR, Raman spectroscopy,UV–Vis spectroscopy, SEM, TGA and DSC analysis and examined for their electrochemical properties. Their antibacterial potential was tested by biofilm inhibition and agar well diffusion methods. XRD studies revealed that Cr2O3 NPs possessed hexagonal crystal structures with the crystallite sizes of 14.85 to 23.90 nm; the lowest size (14.85 nm) was possessed by (Cr2O3)et. FTIR and Raman spectroscopies verified the +3-oxidation state of chromium and corresponding Cr-O and Cr=O vibrations. Raman spectroscopy determined A1g vibration modes (540.50–557.07 cm−1) with rhombohedral Cr2O3 structure, high degree of crystallinity and existence of Cr3+ ions in octahedral coordination whereas Eg vibration modes were displayed at 306.04–350.87 cm−1 and 602.47–613.81 cm−1. UV–Visible spectroscopy has shown band gaps in the range of 4.06–4.40 eV. The SEM images demonstrated the spherical morphology with a high degree of agglomeration between fine particles. The synthesized NPs exhibited good thermal stabilities up to 600 °C. The CV curves displayed the oxidation–reduction peaks and reversible behavior whereas GCD curve indicated the possible energy storage applications of NPs. (Cr2O3)aqNa NPs showed the highest specific capacitance (234.35 mAhg−1) at 1 mA current density. The biofilm inhibitions of the investigated NPs were comparable to those of the standard antibacterial drug (ciprofloxacin); the activity of (Cr2O3)etNa was found even better than that of ciprofloxacin. The NPs were more active against Escherichia coli (Gram-negative) as compared to those against Staphylococcus aureus (Gram-positive).