Chemistry
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Item Pervasive Microplastic Ingestion by Commercial Fish Species from a Natural Lagoon Environment(Water, 2024) Athukorala, A.; Amarathunga, A. A. D.; De Silva, D. S. M.; Bakir, A.; McGoran, A. R.; Sivyer, D. B.; Dias, B. C. G.; Kanishka, W. S.; Reeve, C.Microplastics have emerged as a significant global environmental concern in the recent decade. The aim of this study was to elucidate microplastic contamination of commercial fish species in a natural lagoon environment. Microplastic contamination was examined in the gastrointestinal tracts and gills of 157 commercial fish from 18 species with varying feeding habits in a vital and sensitive lagoon ecosystem, which connects to the Indian ocean. Microplastics were extracted using digestion, followed by stereomicroscopic inspection using Nile Red stain, and identified via μ-FTIR analysis. Over half of studied fishes ingested microplastics (54.14%). Filaments (50%) and blue items (43%) were the most commonly ingested. Of all the fish species, Eubleekeria splendens had the highest average concentration of microplastics in GIT (1.41 ± 2.52 items/g w.w. tissues), although no statistically significant difference in amount of ingested microplastics (items/g w.w. tissues) was observed among species. The highest concentrations of inhaled microplastics were recorded in Sillago vincenti (1.38 ± 1.30 items/g w.w. tissues). The majority of the extracted microplastics (33%) belonged in the size class 500–1500 μm with rayon, polyethylene terephthalate, and polypropylene as the primary polymers. This study found no correlation between microplastic ingestion and fish species and feeding habits, but a positive correlation with fish size was observed. These findings reveal widespread microplastic contamination in edible fish, posing potential risks to commercially important species due to increasing pollution in lagoon ecosystems.Item Pyrolysis of waste polypropylene to fuel oil(Chemistry in Sri Lanka, 2022) Uthpalani, P. G. I.; Premachandra, J. K.; Weerasinghe, V. P. A.; De Silva, D. S. M.Plastic waste accumulation in the environment has increased rapidly. This is mainly due to their versatile properties, which allow them to be used as substitutes for wood, metals, ceramics, and glass. They have diverse applications, as they are light-weight, durable, cost-effective, and stable products. However, the world is experiencing the adverse effects of plastic debris in the environment due to plastic waste mismanagement. Pyrolysis of plastic has been identified as an effective method of plastic waste management by converting the waste into fuel oil, char, and gases. The pyrolysis of waste polypropylene (PP) using a low-cost, simple lab-scale apparatus in the presence and absence of catalysts is discussed here. In the current research, the efficiency of the catalyst, Zeolite Socony Mobil-5 (ZSM- 5), in pyrolysis process was investigated. The generated volatile products were condensed into resultant liquid oil. Active carbon filters and organic solvents were used to trap the non-condensed gas fraction to prevent possible atmospheric pollution. The non-catalyzed pyrolysis of PP resulted a high liquid yield of 79.57 ± 1.66 wt. % with a low gaseous yield (14.64 ± 0.84 wt. %) at 330 °C while the ZSM-5 catalyzed process reduced the liquid yield to 56.88 ± 2.29 wt. % and increased the gaseous yield (38.13 ± 1.88 wt. %) at 280 °C. Then resultant liquids were fractionated based on the boiling points of several petroleum fractions (naphtha, kerosene, and diesel) and each fraction was analyzed by GC-MS to identify the constituent compounds. Accordingly, the non- catalyzed pyrolysis produced 3,3,5-trimethyl-heptane (C10H22), 4-methyl-2-undecene (C12H24), 1-dodecene (C12H24), and 2-methyl-1-hexadecanol (C17H36O) while the catalyzed pyrolysis with the ZSM-5 resulted 1-ethyl- 2-methyl-benzene (C9H12), 3,3,5-trimethyl-heptane (C10H22), (Cyclopentylmethyl)-cyclohexane (C12H22), and n-Nonylcyclohexane (C15H30) as the major constituents.Item ZnS Assisted ZN Doping in CdZnS Electrodeposition(Journal of Science 2019, Department of Chemistry, University of Kelaniya, Sri Lanka, 2019) Sarathchandra, K. A. D. M. S.; De Silva, D. S. M.; Pathiratne, K. A. S.Many reports have been published elsewhere on making thin films of cadmium zinc sulphide (CdZnS) using different techniques. This article summarizes a method developed to form CdZnS by incorporating electrodeposited Cd and S atoms simultaneously to the chemically formed ZnS material in the electrolytic bath at the conducting surface of fluorine doped tin oxide (FTO) coated glass substrate. Moreover, the mechanism of formation of CdZnS is proposed as a solid state reaction between electrodeposited Cd and S atoms on the glass/FTO substrate with adsorbed ZnS particles from the electrolytic bath. The precursors used for Cd, S and ZnS in the electrolyte were aqueous solutions of CdCl2, ZnCl2 and Na2S2O3. Two different methods were tested to form ZnS within the electrolyte bath where one forming ZnS in the bath at the beginning of electrodeposition of Cd and S and in the other one, ZnS is formed before the electrodeposition of Cd and S. The results of the band gap measurements show an undulation which is closer to the band gap energy of CdS indicating probable codeposition of one or more materials such as CdS, (2.42 eV), ZnS (3.7 eV), CdO (2.2 eV), and ZnO (3.2 eV) along with CdZnS. The Tauc plot resulted by the material produced in method 1 has shown an undulation at the onset of Tauc plot which is near the band gap energy of CdS indicating the codeposition of CdS with CdZnS, but the Tauc plot of CdZnS electrodeposited from method 2 has shown clear separation in band gaps from 2.44 – 2.52 eV, when the annealing temperature, the Zn2+ ion concentration in bath and the electrodeposition pH were varied. These thin films were also characterized by photoelectrochemical (PEC) cell analysis, x-ray diffraction (XRD), energy dispersive x-ray analysis (EDXA) and scanning electron microscopy (SEM) techniques.Item Electrodeposition and characterization of as-deposited and annealed CdTe thin films.(Ceylon Journal of Science, 45(2), 53–59. DOI: http://doi.org/10.4038/cjs.v45i2.7388, 2016) Kumarasinghe, K. D. M. S. P. K.; De Silva, D. S. M.; Pathiratne, K. A. S.; Salim, H. I.; Abdul-Manaf, N. A.; Dharmadasa, I. M.Thin films of CdTe semiconductor materials were grown on fluorine doped tin oxide (FTO) conducting glass substrates using the technique of electrodeposition. CdSO4 at high concentrations and CdCl2, TeO2 at low concentrations were used as precursor salts for electrodeposition. The range of deposition potentials was estimated using cyclic voltammetric measurements. The electrical, optical, structural and morphological characteristics of as-deposited and annealed CdTe thin films were characterized using photo-electrochemical (PEC) cell studies, UV-Vis spectrophotometry, X-ray diffraction (XRD) and scanning electron microscopy (SEM). These particular samples were converted from n-type into p-type after heat treatment. UV-Vis spectrometric measurements for CdTe layers indicated that, the energy band gaps of 1.45±0.02 eV for both as-deposited and annealed samples which exhibited the required optical property for fabricating CdS/CdTe solar cells. Little increase in (220) and (311) peaks of XRD spectra were observed for annealed layers compared to the as-deposited material. However, annealing exhibited a small reduction of cubic phase preferential orientation (111). The optical transmission for both as-deposited and annealed CdTe samples were about 60% for wavelengths longer than about 850 nm.Item Selenium content in meals consumed for lunch by Sri Lankans and the effect of cooking on selenium content.(Ceylon Journal of Science, 46(4), 21–25. DOI: http://doi.org/10.4038/cjs.v46i4.7465, 2017) Kiridena, K. M. S. D.; De Silva, D. S. M.; Wimalasena, S.The selenium (Se) content in meals consumed by Sri Lankans for lunch, composed of fixed and random menus, was determined using Hydride Generation Atomic Absorption Spectrometer. The samples were obtained from five districts in Sri Lanka. The Se content (μg/kg) in meals of fixed and random menus was in the range of 48-70 and 53-60 respectively. These values are comparable to the daily requirement of Se (55 μg/kg) prescribed by the World Health Organization and Food and Agriculture Organization of the United Nations. There is no significant difference in Se content in meals consumed by people in the districts of Kandy, Gampaha, Kurunegala, Rathnapura, and Colombo, as well as among individual households in each district. The effects of different cooking methods on the Se content indicate that the level of Se (μg/kg) in fried chicken (30.45 - 52.49) is less than that in a chicken curry (61.38 - 84.25). The percentage loss of Se during cooking for chicken, dahl (Lens culinaris) and Gotukola (Centella asiatica) were 89.6%, 84.1%, and 79.9% respectively. The present study revealed that Se content in Sri Lankan menus provides the required Se for people. However, the different methods of cooking indicate that there is a loss of Se during cooking.