Photocatalytic, electrochemical, antibacterial and antioxidant behaviour of carbon-sulphur Co-doped zirconium (IV) oxide nanocomposite

In this work, carbon-sulphur co-doped ZrO₂ nanocomposites were synthesised using the aqueous leaves extract of Plumeria acuminate, zirconia salt precursor, polyvinylpyrrolidone and sodium hydrosulphide. The structural, elemental and morphological properties of the synthesized nanomaterials were examined by different analytical techniques UV-visible spectrophotometer, HRSEM-EDS, HRTEM-SAED, XRD and BET. HRSEM analysis of C-S-ZrO₂ revealed the presence of spherical and irregular hexagonal shapes. The XRD pattern demonstrated formation of crystalline tetragonal and a mixture of tetragonal and orthorhombic phases for ZrO₂ and C-S-ZrO₂ composite with an average size of 20.03 nm and 12.40 nm respectively. The band gap values of 5.2 eV and 3.4 eV were obtained for ZrO₂ and C-S-ZrO₂ respectively. The adsorptive and photocatalytic properties of ZrO₂ based nanomaterials for the removal of azo dye in local dyeing wastewater were investigated. The electrochemical activities of the nanomaterials were assessed using cyclic voltammetry, while Agar well diffusion, DPPH and ABTS methods were followed for the determination of antibacterial and antioxidant activities of ZrO₂ and C-S-ZrO₂. The maximum COD, BOD, TOC, SO₄^2-, CO₃^2, Cl⁻ and NO₃⁻removal efficiencies of 77.3%, 87.6%, 97.7% 63.9%, 84.4%, 70.3% and 83.3 % at 120 min were obtained using C-S-ZrO₂ composite due to its higher surface area (80.165 m²/g) and lower band gap (3.4 eV) compared with ZrO₂ (10.682 m²/g). Carbon-sulphur co-doped ZrO₂ composite exhibited moderate antioxidant activity and increased peak current than other ZrO₂ based nanomaterials due to its highest surface area than ZrO₂ alone. The order of antibacterial activity of the nanomaterials against the Salmonella typhi, Pseudomonas aeruginosa, Escherichia coli is ZrO₂-C-S (15.40±1.11 mm, 25.10±1.80 mm, 20.03±2.50 mm) > C-ZrO₂ (9.45±2.65 mm, 11.18±0.33 mm, 15.45±3.25 mm) > S-ZrO₂ (7.52±1.55 mm, 12.45±0.11 mm, nil) >ZrO₂ (6.33±0.90 mm, 4.25±0.52 mm, nil). The experimental data best described by pseudo-first-order, followed by parabolic-diffusion and modified Freundlich models. The results showed that the synthesized C-S-ZrO₂ nanocomposite is highly efficient with excellent regenerative potential even after five cycles.