Water pollution is a serious concern for developing and undeveloped countries. Photocatalytic degradation of organic pollutants is an effective degradation method to restrain the green ecosystem. This research article presents a green, low-cost, and benevolent eco-friendly biosynthesis of cobalt oxide (Co₃O₄) nanoparticles using Curcuma longa plant extract. The UV and visible region absorbance of Co₃O₄ nanoparticles estimated the Co²⁺ and Co³⁺ transitions on the lattice oxygen, and their bandgap of 2.2 eV was confirmed from the UV-DRS spectroscopy. The cubic structure and spherical shape of Co₃O₄ nanoparticles were estimated by using XRD and TEM characterizations. Plant molecules aggregation and their agglomerations on the nanoparticles were established from FTIR and EDX spectroscopy. Multiple cobalt valences on the oxygen surfaces and their reaction, bonding, and binding energies were analyzed from XPS measurements. The biogenic Co₃O₄ nanoparticles were executed against gram-positive (Staphylococcus aureus—S. aureus) and gram-negative (Escherichia coli—E. coli) bacteria. A gram-positive bacterial strain exhibited great resistivity on Co₃O₄ nanoparticles. Degradation of organic dye pollutants on the Co₃O₄ nanoparticles was performed against methylene blue (MB) dye under the conditions of visible light irradiation. Dye degradation efficiency pseudo-first-order kinetics on the pseudo-first-order kinetics denotes the rate of degradation over the MB dye. This research work achieved enhanced degradation potency against toxic organic dye and their radicals are excited from visible light irradiations. Absorption light and charged particle recombinations are reformed and provoked by the plant extract bio-molecules. In this process, there is no inferior yield development, and electrons are robustly stimulated. Furthermore, the biosynthesized Co₃O₄ nanoparticles determined the potency of bacterial susceptibility and catalytic efficacy over the industrial dye pollutants.

The green synthesis of metal oxide nanoparticles is an efficient, simple, and chemical-free method of producing nanoparticles. The present work reports the synthesis of Murraya koenigii-mediated ZrO₂ nanoparticles (ZrO₂ NPs) and their applications as a photocatalyst and antibacterial agent. Capping and stabilization of metal oxide nanoparticles were achieved by using Murraya koenigii leaf extract. The optical, structural, and morphological valance of the ZrO₂ NPs were characterized using UV-DRS, FTIR, XRD, and FESEM with EDX, TEM, and XPS. An XRD analysis determined that ZrO₂ NPs have a monoclinic structure and a crystallite size of 24 nm. TEM and FESEM morphological images confirm the spherical nature of ZrO₂ NPs, and their distributions on surfaces show lower agglomerations. ZrO₂ NPs showed high optical absorbance in the UV region and a wide bandgap indicating surface oxygen vacancies and charge carriers. The presence of Zr and O elements and their O=Zr=O bonds was categorized using EDX and FTIR spectroscopy. The plant molecules’ interface, bonding, binding energy, and their existence on the surface of ZrO2 NPs were established from XPS analysis. The photocatalytic degradation of methylene blue using ZrO₂ NPs was examined under visible light irradiation. The 94% degradation of toxic MB dye was achieved within 20 min. The antibacterial inhibition of ZrO₂ NPs was tested against S. aureus and E. coli pathogens. Applications of bio-synthesized ZrO₂ NPs including organic substance removal, pathogenic inhibitor development, catalysis, optical, and biomedical development were explored.

Activated carbon doping TiO₂ nanoparticles were synthesised by zapota leaf extract using the co-precipitation method. The bio-constituents of plant compounds were used in the reactions of stabilization and reductions. The carbon loading on the TiO₂ nanoparticles was characterised by XRD, FTIR, UV-DRS, SEM with EDX, and TEM analysis. The loading of activated carbon onto the TiO₂ nanoparticles decreased the crystallite size and optical bandgap, and their doping improved the surface structure of AC/TiO₂ nanoparticles. Mesoporous/microporous instability was remodified from the activated carbon, which was visualised using SEM and TEM analysis, respectively. The photocatalytic dye degradation of Rh-B dye was degraded in TiO₂ and AC/TiO₂ nanoparticles under visible light irradiation. The degradation efficiencies of TiO₂ and AC/TiO₂ nanoparticles were 73% and 91%, respectively. The bacterial abilities of TiO₂ and AC/TiO₂ nanoparticles were examined by E. coli and S. aureus. The water reclamation efficiency and bactericidal effect of TiO₂ and AC/TiO₂ nanoparticles were examined via catalytic dye degradation and bacterial efficiency of activated carbon-doped titanium dioxide nanoparticles.

Biogenic CoFe₂O₄ nanoparticles were prepared by co-precipitation and Hibiscus rosa sinensis plant leaf was used as a bio-reductant of the nanoparticle productions. The biosynthesized CoFe₂O₄ nanoparticles were characterized by XRD, FTIR, UV, VSM, and SEM via EDX analysis. The cubic phase of biosynthesized CoFe₂O₄ nanoparticles and their crystallite size was determined by XRD. The Co-Fe-O bonding and cation displacement was confirmed by FTIR spectroscopy. The presence of spherically-shaped biosynthesized CoFe₂O₄ nanoparticles and their material were confirmed by SEM and TEM via EDX. The super-paramagnetic behaviour of the biosynthesized CoFe₂O₄ nanoparticles and magnetic pulse was established by VSM analysis. Organic and bacterial pollutants were eradicated using the biosynthesized CoFe₂O₄ nanoparticles. The spinel ferrite biosynthesized CoFe₂O₄ nanoparticles generate radical and superoxide ions, which degrade toxic organic and bacterial pollutants in the environment.

Visible light-driven photocatalyst BiFeO₃ (BFO) nanoparticles were synthesised by the auto-combustion method. The honey was used to fuel the auto combustion method to synthesise the BFO nanoparticles. The structural, optical and morphological activities of the bismuth loaded BFO nanoparticles were characterised by X-ray diffraction (XRD), FTIR, UV, photoluminescence (PL) and SEM analysis, respectively. The bismuth content modifies the lattice parameters of XRD and reduces the bandgap energy. The observed crystallite size varies from 19 to 27 nm and the bandgap region is 2.07 to 2.21 eV. The photo-charge carriers increased upon the BFO nanoparticles and their emission at 587 nm in the visible region of the PL spectrum. The 2% bismuth loaded BFO nanoparticles showed better morphology than 0% and 5% bismuth loaded BFO nanoparticles. The oxidation state of BFO nanoparticles and their binding energies were characterised by X-ray Photoelectron Spectroscopy (XPS) analysis. The methylene blue dye (MB) degradation against 2% BFO nanoparticles showed enhanced catalytic activity (81%) than the remaining samples of BFO nanoparticles. The bacterial activity of BFO nanoparticles was assessed against Gram-positive and Gram-negative bacteria, including S. aureus and E. coli. 2% Excess bismuth BFO nanoparticles exhibit better antibacterial activity. Comparatively, 2% Excess bismuth BFO nanoparticles derived an outstanding crystallinity, charge separation, and reduced bandgap activities. Based on these findings, BFO nanoparticles may be applicable in drug delivery and water remediation applications.

Ecosystems worldwide face a serious and life-threatening water crisis due to water contamination. Nanotechnology offers a promising solution to this issue by providing methods for removing pollutants from aquatic sources. In this study, we utilized a green and simple approach to biosynthesize NiSe NPs using Hibiscus rosa-sinensis extract as the bio-source. The plant extract acts as a reducing, stabilizing, and capping agent in the synthesis process. A simple hydrothermal method was employed to blend the NiSe NPs photocatalysts. UV-Visible DRS spectroscopy was utilized to confirm the reduction in and stabilization of Ni²⁺ and Se²⁻ ions. The resulting NiSe NPs have a bandgap of 1.74 eV, which facilitates electron and hole production on their surfaces. To characterize the functional groups on the NiSe NPs and their surface interactions with bio-compounds, FTIR spectroscopy was utilized. XRD analysis revealed the crystallite size of the NiSe NPs to be 24 nm, while FE-SEM and TEM imaging showed their spherical shape and material distribution. EDX spectroscopy confirmed the integrity of the NiSe NPs’ material. XPS analysis provided information on the chemical composition, nickel and selenium valency, and their interface. The efficacy of the NiSe NPs as a blended photocatalyst in photodegrading Methylene Blue (MB) dye was tested under visible light, resulting in 92% degradation. Furthermore, the NiSe NPs exhibited bactericidal activity against Escherichia coli and Staphylococcus aureus bacteria due to their advanced oxidation and reduction in charge particles, which increased the degradation efficiency and suppressed cell proliferation. Based on the obtained findings, the NiSe NPs show promise as a powerful agent for water remediation and microbial resistance.