Browsing by Author "Rathnayake, R. M. A. S."

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Catalytic activity of green synthesized Co3O4 and CuO nanoparticles in photoreduction of rhodamine B dye and transesterification of sunflower oil
(Faculty of Science, University of Kelaniya Sri Lanka, 2024) Perera, M. D. H.; Abeysinghe, A. A. S. K.; Rathnayake, R. M. A. S.
Recent advances in the field of nanotechnology have gained significant attention in developing ecofriendly methods for synthesizing nanoparticles (NPs), particularly metal oxide NPs. Present study explored the green synthesis of Co3O4 and CuO NPs using the extracts of Centella asiatica (gotukola) stems and Persea americana (avocado) seeds, respectively. This project was specifically aiming to minimize environmental impact while leveraging the natural properties of waste materials for effective NP production. UV-visible spectrometry, Fourier Transform Infrared (FTIR) spectrometry, X-ray Diffraction (XRD), and Scanning electron microscopy (SEM) analysis confirmed the successful NP formation and their characteristics. As regards photocatalytic properties, both Co3O4 and CuO NPs demonstrated significant effectiveness on degrading Rhodamine B (RhB) dye under direct solar irradiation. The optimized reaction conditions of each NP on dye degradation were studied by considering the maximum photodegradation obtained under tested conditions. With regards to Co3O4 NPs, pH of 8 with a 5mg catalytic load and a 5 ppm RhB dye concentration was considered as optimum conditions while achieving a 62% photodegradation efficiency which is 19% higher than the control. CuO NPs showed a maximum percentage photodegradation efficiency of approximately 55% under optimized conditions of 10 mg of catalytic load, pH of 8, and 5 ppm RhB concentration, which is 12% greater than that of the control. For both types of NPs, degradation performance was evaluated using fluorometry over a period of 240 minutes at 40-minute intervals. Furthermore, these NPs were studied as potential catalysts in the transesterification of sunflower oil to biodiesel. Optimization involved by varying oil-to-methanol ratio and the catalytic dose. The yield of biodiesel improved with an oil-tomethanol ratio of 1:3, showing a distinct layer separation. Further, experiments identified 15 mg of CuO NPs and 25 mg of Co3O4NPs as optimal catalytic loads, suggesting CuO NPs have comparatively higher efficiency in biodiesel production under relatively mild reaction conditions. During the transesterification process, two distinct layers were separated, and the bottom layer was identified as glycerol and the lighter top layer was confirmed to be biodiesel through an ignition test. Under the above-mentioned optimized conditions, CuO NPs showed better performance with a yield of ~67% (w/w%), compared to that of Co3O4 NPs which yielded ~59% (w/w%) of biodiesel. In conclusion, this study emphasizes NPs’ catalytic capabilities in both photocatalytic degradation of RhB and biodiesel production applications showcasing the significance of integrating natural resources and green chemistry principles in advancing nanotechnology for environmental remediation and renewable energy applications.
Investigating the Photocatalytic Dye Degradation and Antibacterial Abilities of Manihot esculenta Peel-based Mn3O4 Nanoparticles
(Faculty of Science, University of Kelaniya Sri Lanka, 2024) Madubhashinie, M. A. D. A. I.; Rathnayake, R. M. A. S.
With increasing population in the modern world, removing domestic and industrial waste has become a global challenge. Therefore, studies have been focused on adding values to these waste materials by utilizing them for various applications. The green synthesis of nanoparticles (NPs) through waste products recently emerged as an eco-friendly and low-cost method for waste management and recycling waste products. This specific study focused on synthesizing Mn3O4 NPs using cassava (Manihot esculenta) peel, which is a common household waste in Sri Lanka. Further, this study focused on studying the ability of that NPs on photocatalytic dye degradation of Methylene Blue (MB), a common textile dye, and the antibacterial activity against Gram-positive Staphylococcus aureus and Gramnegative Escherichia coli bacteria. Mn3O4 NPs were successfully synthesized under optimized reactions conditions of plant-to-metal ratio (1:8), metal salt concentration (0.1 moldm-3) and pH (10) with an incubation time of 48 hours. Then the formed NPs were characterized by using UV-Visible spectroscopy, Fourier Transfer Infrared spectroscopy (FTIR) and X- ray diffraction (XRD) analysis. The UV- Vis spectra of Mn3O4 NPs characteristic peak at ~ 267 nm clearly indicating the formation of NPs. The FTIR spectrum showed a sharp peak at 587.86 cm-1 indicating a Mn—O stretching vibration. This suggested that the formed product is the desired NPs. The crystallinity of Mn3O4 NPs was identified using XRD analysis and they are found to be in body-centered cubic crystal structure. According to the Debey-Scherrer equation the average crystallite size of these NPs was found to be 36.69 nm. The presence of both Mn2+ and Mn3+ in the final product suggested an air oxidation process of Mn2+ ions under applied conditions. The NPs were further investigated for their ability on photocatalytic dye degradation of MB under optimized parameters of catalytic load (10 mg), dye concentration (5 ppm), and pH (10). The percentage degradation was calculated by taking absorbance (λmax = 663 nm) of the reaction mixture for 240 minutes at 30-minute intervals. Under optimized conditions, these Mn3O4 NPs showed 78.8% photodegradation indicating their suitability as photocatalysts under ambient conditions. The antibacterial activity of the synthesized NPs was tested against Staphylococcus aureus and Escherichia coli by well diffusion method using Muller-Hinton medium. The experiments were carried out by using different NP concentrations (50 ppm to 150000 ppm), plant extract, positive control (Gentamicin) and negative control (deionized water). During the investigation, inhibition zones were not observed even with high NPs concentrations. Overall, these cassava-peel based Mn3O4 NPs were found to be potential photocatalysts for the removal of certain textile dyes from wastewater, but they are not effective against S. aureus and E. coli. Therefore, these NPs have the ability to be used as tools to remediate certain environmental impacts caused by certain organic pollutants under ambient conditions.