In recent years, the green chemistry based-approach for the synthesis of nanoparticles has shown tremendous promise as an alternative to the costly and environmentally unfriendly chemically synthesized nanoparticles. In this study, copper oxide nanoparticles (CuO NPs) were synthesized through a green approach using the water extract of papaya (Carica papaya L.) peel biowaste as reducing as well as stabilizing agents, and copper (II) nitrate trihydrate salt as a precursor. The structural properties, crystallinity, purity, morphology, and the chemical composition of as-synthesized CuO NPs were analyzed using different analytical methods. The analytical results revealed that the synthesized CuO was observed as spherical-like in particles with measured sizes ranging from 85–140 nm and has monoclinic crystalline phase with good purity. The Fourier transform infrared (FTIR) spectroscopic results confirmed the formation of the Cu-O bond through the involvement of the potential functional groups of biomolecules in papaya peel extract. Regarding photocatalytic activity, the green-synthesized CuO NPs were employed as a photocatalyst for the degradation of palm oil mill effluent (POME) beneath the ultraviolet (UV) light and results showed 66% degradation of the POME was achieved after 3 h exposure to UV irradiation. The phytotoxicity experiment using mung bean (Vigna radiata L.) seed also showed a reduction of toxicity after photodegradation.

Synthesis of copper oxide (CuO) nanostructures via biological approach has gained attention to reduce the harmful effects of chemical synthesis. The CuO nanostructures were synthesized through a green approach using the Garcinia mangostana L. leaf extract and copper (II) nitrate trihydrate as a precursor at varying calcination temperatures (200–600 °C). The effect of calcination temperatures on the structural, morphological and optical properties of CuO nanostructures was studied. The red shifting of the green-synthesized CuO nanoparticles’ absorption peak was observed in UV-visible spectrum, and the optical energy bandgap was found to decrease from 3.41 eV to 3.19 eV as the calcination temperatures increased. The PL analysis shown that synthesized CuO NPs calcinated at 500 °C has the maximum charge carriers separation. A peak located at 504–536 cm⁻¹ was shown in FTIR spectrum that indicated the presence of a copper-oxygen vibration band and become sharper and more intense when increasing the calcination temperature. The XRD studies revealed that the CuO nanoparticles’ crystalline size was found to increase from 12.78 nm to 28.17 nm, and dislocation density decreased from 61.26 × 10¹⁴ cm⁻¹ to 12.60 × 10¹⁴ cm⁻¹, while micro strain decreased from 3.40 × 10⁻⁴ to 1.26 × 10^–4. From the XPS measurement, only CuO single phase without impurities was detected for the green-mediated NPs calcinated at 500 °C. The morphologies of CuO nanostructures were examined using FESEM and became more spherical in shape at elevated calcination temperature. More or less spherical nanostructure of green-mediated CuO calcinated at 500 °C were also observed using TEM. The purity of the green-synthesized CuO nanoparticles was evaluated by EDX analysis, and results showed that increasing calcination temperature increases the purity of CuO nanoparticles.

Landfill leachate, a complex wastewater generated from municipal solid waste (MSW) landfills, presents significant environmental challenges due to its high organic content and toxic pollutants. This study proposes a sustainable solution by employing the green synthesis of copper oxide nanoparticles (CuO NPs) using durian (Durio zibethinus) husk extract, which serves as a natural reducing and stabilizing agent. This approach transforms agricultural waste into a valuable resource for environmental remediation. The synthesis was carried out under mild conditions, avoiding harmful chemicals and reducing energy consumption. The CuO NPs were characterized by scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM), X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX), Fourier-transform infrared spectroscopy (FTIR), and UV-Vis spectroscopy to examine their morphology, crystallinity, purity, and optical properties. SEM and HR-TEM analyses revealed mainly spherical nanoparticles with an average size of 35–50 nm and minimal aggregation. XRD analysis confirmed the presence of a highly crystalline monoclinic phase of CuO, while the EDX spectrum showed distinct peaks corresponding to copper (72%) and oxygen (28%) by weight, confirming the high purity of the material. Preliminary tests demonstrated the photocatalytic efficiency of the CuO NPs, achieving up to a 79% reduction in chemical oxygen demand (COD) in landfill leachate. These findings underscore the potential of green-synthesized CuO NPs for environmental applications, offering an innovative, sustainable method for wastewater treatment and supporting the advancement of solid waste management practices.

This paper reports the antifungal properties of zinc oxide nanoparticles (ZnO NPs) on Candida albicans ATCC 1023 through the study of growth inhibitory effects of ZnO NPs on C. albicans and the effect of the nanoparticles on the surface of C. albicans. The growth inhibitory effects of ZnO NPs (5, 10, 20, 40, 80, and 160 µg/mL) on C. albicans at 24 h were determined through the reduction in suspension turbidity and colony count. Fourier transform infrared (FTIR) analysis was carried out to establish the functional groups associated with the interaction of ZnO NPs on the yeast cell wall, while scanning electron microscopy (SEM) with energy dispersive X-ray (SEM-EDX) analysis was utilised to determine the surface accumulation of ZnO NPs on the yeast cells and the consequential morphological alterations on C. albicans. The results exhibited a significant (p < 0.05) growth inhibition for all tested concentrations except for 5 µg/mL of ZnO NPs at 24 h as compared to negative control. FTIR analysis revealed the possible involvement of alcohol, amide A, methyl, alkynes, amide I and II, and phosphate groups from the cell wall of C. albicans in the surface interaction with ZnO NPs. Finally, SEM-EDX revealed a considerable accumulation of ZnO NPs on the yeast cells and consequential morphological alterations on C. albicans, including the damage of hyphae, pitting of the cell wall, invagination, and rupture of the cell membrane. The current study demonstrated that ZnO NPs possess antifungal properties against C. albicans in a dose-dependent manner, and the surface interaction of ZnO NPs on fungal cells caused alterations in cell membrane integrity that might have resulted in cell death.

The treatment of palm oil mill effluent (POME) poses a significant challenge for Malaysia’s palm oil industry, necessitating compliance with the Department of Environment (DOE) regulations prior to discharge. This study introduces an eco-friendly synthesis method utilizing mangosteen (Garcinia mangostana L.)-leaf aqueous extract to fabricate copper oxide (CuO), zinc oxide (ZnO) nanoparticles (NPs), and their nanocomposite (CuO-ZnO NCs). The physicochemical properties of these nanomaterials were characterized using various analytical tools and their effectiveness in reducing the chemical oxygen demand (COD) of palm oil mill effluent (POME) was assessed under the illumination of two types of light sources: monochromatic blue- and polychromatic white-light emitting diodes (LEDs). CuO-ZnO NCs demonstrated superior performance, with the lowest energy bandgap (1.61 eV), and achieved a COD removal efficiency of 63.27% ± 0.010 under blue LED illumination, surpassing the DOE’s discharge limit of 100 mg/L. This study offers a cost-effective and environmentally friendly method for synthesizing heterojunction materials, which show great potential as photocatalysts in reducing POME COD to permissible levels for discharge.