Browsing by Author "De Silva, D. S. M."

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Abundance and microplastic characterization found in the mud crab Scylla serrata inhabiting Negombo Lagoon, Sri Lanka
(Faculty of Science, University of Kelaniya Sri Lanka, 2023) Dias, B. C. G.; Amarathunga, A. A. D.; De Silva, D. S. M.; Sivyer, D. B.; Maddumage, M. D. S. R.
Microplastics (MPs) are tiny plastic particles less than 5 mm in size. The danger imposed by MPs continues to rise in the world due to an increase in anthropological pollutants in the environment. The tremendous socioeconomic value and biodiversity of the lagoon have been threatened by a significant accumulation of plastics, particularly MPs. MPs have many negative impacts on the fauna. Herein, the high adsorption capability of MPs increases the toxicity of contaminants as well as oxidative stress that may lead to damaging cell membranes of fauna. Here, we report the investigation on the abundance of MPs in the digestive tract and gills of the mud crab species Scylla serrata, which is a prominent edible food source of humans. We collected fifty two (N = 52) individuals of mud crabs from three crab trapping sites in the Negombo Lagoon, Sri Lanka during November 2022 to March 2023. The gills and digestive tract of the crabs were extracted and digested in KOH, and subsequently the putative MPs were separated and imaged using a stereomicroscope (VWR VisiScope 360) for characterization. In the analysis, a total of 455 MP particles were detected in the crabs, out of which, 187 (41.10%) were in the gills and 268 (58.90%) were in the digestive tracts. The average MP abundance in the gills was 0.70 ± 0.52 items per gram, while that in the digestive tracts was 0.71 ± 0.52 items per gram. The most abundant shapes of MP particles were fibers in the gills (54.01%) and in the digestive tracts (85.07%) followed by fragments and films. Further, the prevailing colours of the MPs were blue, transparent, red, black, and purple. Herein, the digestive tract had the highest concentration of MPs in blue (47.38%), whereas the majority of the MPs found in the gills were transparent (51.8%). The range of MP sizes in the crabs was also determined. The most frequent size range in the gills and digestive tracts were 0.002-0.25 mm (39.5%), and 1.0-5.0 mm (48.8%) respectively. Despite the fact that the current study offered details on the presence of MPs in the gills and digestive tract of the mud crab species Scylla serrata inhabits in the Negombo Lagoon, it also serves as a benchmark for the quick detection of MPs in mud crabs in the lagoons of Sri Lanka.
An alternative sulfur precursor for chemical bath deposition of CdS thin film
(Gajanayake, G. K. U. P., De Silva, D. S. M and Atapattu, H. Y. R. (2019). An alternative sulfur precursor for chemical bath deposition of CdS thin film. 4th International Research Symposium on Pure and Applied Sciences, Faculty of Science, University of Kelaniya, Sri Lanka. p98, 2019) Gajanayake, G. K. U. P.; De Silva, D. S. M.; Atapattu, H. Y. R.
Solar energy is the most appropriate electrification method for a tropical county like Sri Lanka. At present, Sri Lanka generates more than 72% of its electricity needs at a high cost by burning coal and diesel. To overcome the major obstacle of high initial cost in installation of solar power plants, many research groups worldwide at present are focusing towards manufacture of low cost and highly efficient photovoltaic cells based on cadmium sulfide and cadmium telluride (CdS/CdTe) semiconductors. Among the range of methods available for fabrication of CdS window layer, the chemical bath deposition (CBD) is an ideal method due to its simplicity and low cost. In this study, CdS layers were deposited on the FTO glass substrate by CBD method, using an alternative sulfur precursor; ammonium thiosulfate ((NH4)2S2O3) against the well-established but costly precursor thiourea (CS(NH2)2). The CBD bath was prepared with 0.25 mol/L cadmium acetate (Cd(CH3COO)2), 1.00 mol/L ammonium acetate (NH4COOCH3), concentrated NH4OH (pH adjuster), and 0.50 mol/L (NH4)2S2O3. The best growth condition for CdS was identified by varying the parameters; Cd:S ratio, pH, deposition temperature, and deposition time while preserving a constant stirring speed. Uniform CdS layers rich in Cd, were observed in an alkaline electrolyte with Cd:S ratio of 2:5 at a temperature of 95 °C in 90 minutes. The spectrophotometric studies revealed the energy band gap of the material as 2.41 eV which is the typical value for CdS. Further, the X-ray diffractions observed at angles of 26°, 28°, 36°, and 53° representing the planes of (002), (101), (102), and (201) verified the cubic structure, while the scanning electron microscopic studies confirmed the uniform surface morphology of the material with average grains sized of 105 nm. However, the presence of pin-holes observed in the cross-sectional view implied the need of further optimization of parameters to obtain materials comparable to thiourea based chemical bath deposited CdS layers.
Assessment of litter and microplastic pollution in the water and sediment of Hirikatuoya stream, within the Walawe River basin, Sri Lanka
(Faculty of Science, University of Kelaniya Sri Lanka, 2023) Lahiru, A. A. S.; Amarathunga, A. A. D.; Malavipathirana, S.; De Silva, D. S. M.; Sivyer, D. B.
Rapid urbanization and mismanagement have led to a surge in plastic pollution in crucial aquatic ecosystems globally therefore accumulation of debris in aquatic ecosystems is rapidly increasing and they are becoming ultimate sinks for the contaminants. This results in a long-term and widespread threat causing a great challenge for remediation. Poor disposal practices and littering behavior of communities have resulted in considerable quantities of litter in river banks and streams affecting their aesthetic appeal and living beings. This study was conducted to understand the status of litter and microplastic contamination at selected locations in Hirikatuoya stream, a remote stream outside the urban environment in the Rathnapura district, Sri Lanka. The percentage of plastic in litter and the percentages of microplastic particles (based on colour and morphotypes) in water and sediments were estimated, and the corresponding polymer types were also identified. Three samples of water were collected from each of the nine locations along the stream from September to October 2022. In the sampling process, the samples were filtered through a 150 μm mesh. Sediment samples were collected from the shoreline of the stream at each location using a stainless-steel scoop covering 30 cm2 of surface area and 2-3 cm depth. Lowdensity particles in the samples were separated by density separation and organic matter in the sample was removed by digestion. Whatman GF/C glass microfiber filter papers of a pore size of 1.2 μm were used for sample filtration. Microscopic imaging was done using a staining method. The ATR-FTIR analysis was performed to identify the polymer type of plastic particle in water samples. The most frequently observed colour for microplastic particles in water and sediments were white (26.87%) and colourless (40.20%), respectively. Based on morphotype, fragments were more abundant in both water (49.62%) and in sediments (59.79%) compared to other morphotypes. The highest microplastic abundance in water (69±22, 60±29, 61±26 items 100 m- 3) and highest abundance of microplastics in sediment (15±5.92 items/kg (top), 7±3.28 items/kg (bottom)) were observed in more human and tourist activity locations. According to the ATRFTIR analysis, polypropylene was the most abundant polymer type in plastic litter (25%). In water polypropylene was the most dominant microplastics (38.10%), followed by low-density polyethylene (14.29%) and polyethylene terephthalate (9.52%). Polypropylene was the dominant microplastics in sediments (32.2%), followed by thermoplastic vulcanizates (22.5%), highdensity polyethylene (19.3%). Accordingly, it can be concluded that the Hirikatuoya stream, which is in a remote area, is contaminated with microplastics. There are potential environmental and health risks to the aquatic biota in the stream and the neighboring communities. Further investigations are required to understand the effect on aquatic animals.
Biofiltration of wastewater by mangrove ecosystem
(Faculty of Science, University of Kelaniya Sri Lanka, 2024) Sovis, W. S. N.; De Silva, D. S. M.; Chathurani, S. H. U.
The mangrove ecosystem consists of salt-tolerant trees and shrubs that thrive in coastal intertidal zones. Mangroves are particularly important as natural biofilters, their dense root systems trap sediments and pollutants, while associated microorganisms break down organic matter, significantly improving water quality. This research aimed at determining the changes in water quality parameters after filtration through the mangrove ecosystem. The water samples were collected mainly in two sites as triplicates at the NARA regional center in Kadolkele, Negombo, Sri Lanka. Samples collected before filtration through the mangrove ecosystem were indicated as BMF samples, and the samples collected after filtration through the mangrove ecosystem were indicated as AFM samples. Samples were collected from August 2023 to January 2024. The data of different parameters were statistically analyzed using paired t-test in the Minitab 17 version. Ammonium ion levels were examined using the phenate method. The BMF samples (88.9 ± 20.5 ppm) indicated a significantly higher average value of ammonium ion than the AMF samples (62.7 ± 19.6 ppm) (p < 0.05). Phosphate levels were examined using the stannous chloride method. The BMF samples contained significantly higher phosphates (115.6 ± 12.8 ppm) than the AFM samples (75.8 ± 14.8 ppm) (p < 0.05). Nitrate levels were examined using the UV spectrometric screening method. The BMF samples showed a significantly higher average value of nitrate content (28.5 ± 6.2 ppm) than AMF samples (17.4 ± 6.1 ppm) (p < 0.05). There was no significant difference recorded between pH values of AMF and BMF samples (p > 0.05). The multiparameter analyzer was employed in measuring conductivity, resistivity, and total dissolved solid (TDS) levels. The BMF samples indicated higher resistivity and TDS levels than BMF samples, while the conductivity levels of AFM samples were higher than BMF samples. Average total suspended solid (TSS) levels were significantly higher in AMF samples (302.0 ± 12.3 mg/L3) than in BMF samples (272.1 ± 11.1 mg/L3) (p < 0.05). Heavy metal analysis was conducted by the atomic absorption spectrophotometer (AAS). Cu, Cr, Zn, Fe and Mn were the most prevalent heavy metals. Cd was not at detectable levels in both sampling sites. The average Cu level in the AMF samples (0.182 ± 0.035 ppm) was higher than BMF samples (0.172 ± 0.053 ppm), p = 0.551. Average Cr content was higher in BMF samples (0.105 ± 0.057 ppm) than in AMF samples (0.064 ± 0.019 ppm), p = 0.184. The average value of Zn in BMF samples (0.156 ± 0.066 ppm) indicated a higher value than AMF samples (0.106 ± 0.034 ppm), p = 0.138. But none of these were statistically significant. The average Fe content in BMF samples (0.331 ± 0.053 ppm) was significantly higher than that of AMF samples (0.131 ± 0.042 ppm), (p < 0.05). The average Mn level in BMF samples (0.020 ± 0.009 ppm) was significantly higher than AMF samples (0.004 ± 0.001 ppm) (p < 0.05). The average BOD level in AMF samples (4.0 ± 0.4 mg/L) was significantly higher than in BMF samples (3.0 ± 0.5 mg/L), (p < 0.05). The COD of BMF samples (185.3 ± 29.5 mg/L) indicated a significantly higher average value than AMF (150.5 ± 13.9 mg/L) samples (p < 0.05). The statistical analysis revealed a significant difference between AMF and BMF samples for ammonium ion, phosphate, nitrate, TSS, heavy metals (Fe, Mn), BOD, and COD, indicating the mangrove filtration's effectiveness in reducing these pollutants. However, there was no significant difference in pH levels and heavy metal concentrations of Cu, Cr, and Zn, suggesting that these parameters were not notably affected by the filtration process.
Characterization of airborne microplastics in different indoor environments in University of Kelaniya, Sri Lanka-A preliminary study
(Faculty of Science, University of Kelaniya Sri Lanka, 2024) Saumya, R. L. K.; Deeyamulla, M. P.; De Silva, D. S. M.; Athukorala, A.; Bakir, A.; McGoran, A. R.
Airborne microplastic (MP) contamination in indoor environments is an increasing concern due to potential health risks from inhalation. This study examined the distribution, polymer composition, and morphology of airborne MPs in five indoor settings at the University of Kelaniya, Sri Lanka. Passive sampling was conducted over 14 days in one office, two laboratories, and two lecture halls. A diverse array of MP forms and colors were identified using stereomicroscopy and advanced micro imaging. Further analyses were carried out using laser direct infrared spectrometer (LDIR) to identify the constituent polymer types of MPs. Fibers dominated the fallout samples in the office (100%), lecture hall 2 (60%), laboratory 1(56.25%), lecture hall1 (25%), whereas no fibers were found in the sample taken from laboratory 2. However, fragments were identified only in the sample collected from laboratory 2. Films were present at all locations except the office, but their number was relatively lower compared to fibers. The deposition rates of fibers were 3.7 × 102 fibers/m2/day in the laboratory 1, 0.82× 102 fibers/m2/day in the lecture hall 1, 1.23 × 102 fibers/m2/day in the lecture hall 2, and 1.64 × 102 fibers/m2/day in the office. The deposition rates of films in laboratory 1 and the lecture hall 2 were close to each other, corresponding to 1.64 × 102 films/m2/day. Among the selected indoor environments examined in this study, laboratory 1 exhibited the highest deposition rate of MPs on both fibers and films. The increased accumulation is likely due to the proximity of an active construction site, which could facilitate the transport of MPs into the laboratory. Furthermore, the laboratory's heavy use by approximately 60 students daily may have contributed to higher MPs levels. Conversely, laboratory 2 displayed the lowest deposition rate of MPs. This difference can be linked to several factors, including its relatively lower student occupancy, the shorter durations students spend within the laboratory environment and the air-conditioned nature. In all selected indoor environment settings, the prevalent color among MPs is transparent. Laboratory 1 exhibits a relatively balanced representation of transparent (35.29%), green (35.29%) and red (17.69%) MPs, while laboratory 2 predominantly comprises blue (50%) MPs. Lecture hall 1 shows a significant presence of blue MPs (50%), while lecture hall 2 primarily consists of transparent MPs (60%). The office environment exclusively contains transparent MPs. Laboratory 1 and laboratory 2 predominantly have MPs in the 100–250 μm range, while lecture hall 1 and lecture hall 2 show more varied sizes with larger particles being more prevalent, and the office environment mainly contains particles in the 250–500 μm. LDIR spectroscopy was revealed that the MPs were composed of polyamide (17%), polyethylene (10%), polyurethane (7%), polyester (6%), polypropylene (4%), and acrylonitrile butadiene styrene (2%). This study highlights the prevalence of MPs in various indoor environments, emphasizing the importance of evaluating health risks associated with long term exposure.
Development and application of rice-straw biochar for removal of selected heavy metals (Pb, Cd and Cr) in contaminated paddy soil.
(International Research Symposium on Pure and Applied Sciences, 2017 Faculty of Science, University of Kelaniya, Sri Lanka., 2017) Irosha, K. P. C.; De Silva, D. S. M.
Biochar which is derived from carbon rich biomass such as wood, manure and leaves, is increasingly recognized as multifunctional material for various applications like contaminant management in soil and water, soil amendment in agriculture etc. In this study, rice-straw derived biochar was produced at a temperature of 400 ºC in the presence of concentrated H3PO4. The resulted biochar was subjected to oxidation by different agents including KOH, HNO3 and H2O2 to enhance its adsorption properties. The pore size distribution of modified, non-modified and commercial biochar types was studied using scanning electron microscope (SEM) technique and functional group analysis was carried out using the Fourier transform infrared spectroscopic (FTIR) technique. The FTIR spectroscopic analysis revealed significant increase in concentrations (based on peak area with constant amount of samples) of the functional groups such as carboxylic, alcoholic hydroxyl, phenolic hydroxyl and carbonyl groups available on the surface of the KOH treated sample. The SEM analysis revealed about 40% increment in pore diameter of the rice straw biochar that was modified with KOH. The paddy soil sample analyzed was amended with known amounts of heavy metal (Pb, Cd, and Cr) containing salts prior to analysis. To study the heavy metal adsorption capacity of modified, non-modified rice straw biochar and commercial biochar types, biochar (5 g x 7) which were packed and sealed in cellulose bags (5 x 5 cm2) were introduced to the soil samples (3 kg in a side sealed rain-gutter). All the experiments were performed in triplicate. The amounts of heavy metals in amended soil, after treating with biochar, and adsorbed by biochar were measured using Atomic absorption spectroscopic (AAS) technique. The AAS study revealed that all modified rice straw biochar types adsorbed heavy metal ions more efficiently than its non-modified counterpart. Further, this analysis revealed that H2O2 treated biochar is more likely to adsorb Pb and Cd, while the KOH treated biochar is more suitable for Cd and Cr adsorption.
Development of energy briquettes using Schleichera oleosa (Ceylon oak) wood, Oryza sativa (rice husk, rice straws and rice brain) and Saccharum officinarum (bagasse)
(Faculty of Science, University of Kelaniya Sri Lanka, 2023) Dulanjana, K. D. A.; Udawatta, M. M.; Prasad, P. D. A.; Bodaragama, T. P.; De Silva, D. S. M.
Fossil fuels and firewood are the primary household energy sources in Sri Lanka. However, due to the economic crisis and the increasing inflation, fossil fuels are no longer a preferable choice. The use of firewood also has limitations, such as household air pollution due to the accumulation of smoke and toxic compounds causing immediate health issues. One of the solutions to this problem is the use of charcoal energy briquettes. Charcoal energy briquettes are compressed blocks made from pyrolyzed biomass residues. Burning these briquettes as an energy source, minimizes household air pollution and is energy efficient and cost-effective. Sri Lanka, a tropical agricultural country with significant vegetation growth, has great potential for developing carbonized charcoal briquettes from biomass energy sources such as ceyloan oak, rice husk, rice straws, bagasse and rice brain. In this study, Schleichera oleosa wood (Ceylon Oak) was used as the main component of the briquettes, as it was known to have a high calorific value. Ceylon Oak is used in furniture manufacturing, producing a large amount of sawdust waste, and this sawdust could be efficiently utilized to produce briquettes. Further, rice husk, rice straws, and bagasse with high ash content were used as additives to increase the burning time of the briquettes. Rice brain was used as the binding agent. During the study, the mixing ratios of the raw materials, pressure, and moisture content were varied to enhance the efficiency of the briquettes. Biomasses were pyrolyzed (300 °C, 1 h) to produce biochar. Different biochar mixtures (particle size < 2 mm) were compressed under different pressures (10 kPa - 60 kPa) using a newly innovated compressing machine to produce briquettes (OD: 4.15 cm, Height: 3.34 ±0.48 cm). They were dried in an oven (50 ℃) by varying the drying time (48 h, 72 h, 86 h, and 110 h) to change the moisture content. For each briquette produced, proximate analyses were carried out by measuring moisture (2% - 75%), volatile matter (20% - 36%), ash (10% - 30%), and fixed carbon content (38% - 70%). Calorific values were estimated based on the proximate analyses. The calorific values measured were in the range of 19,340 kJ kg-1 – 27,983 kJ kg-1 . Cooking efficiencies calculated were in the range of 2.5 kJ kg-1 - 27 kJ kg-1 exhibiting the potential of using these briquettes as a household energy source. According to this study, Schleichera oleosa and rice brain mixture 3:1 (w/w) ratio, showed the highest heating value and the highest cooking efficiency. The addition of rice husk, rice straw, and bagasse reduced the cooking efficiency of the briquettes. This study can be further extended to optimize other parameters of the briquettes (size, moisture content, compressed pressure and mixing ratios) to further enhance the cooking efficiency and burning time.
Electrochemical conversion of graphite to graphene oxide and electrophoretic deposition of graphene oxide
(Faculty of Science, University of Kelaniya Sri Lanka, 2022) Rifka, A. R. F.; De Silva, D. S. M.
Graphene and graphene oxide (GO) have gained huge importance in multiple fields, including chemistry and physics due to the desirable and incomparable properties which they possess. Practical applications of graphene and graphene related materials (GRM) such as graphene and GO is a progressive topic in the research world. Various methods are available for the synthesis of graphene and GO. Conventional chemical methods have the drawbacks of the evolution of toxic gases, which are highly expensive and environmentally unfriendly. Current approaches targeted on increasing the yield of GO synthesis with minimal environmental effects using vein graphite obtained from Bogalapathala, Sri Lanka. The electrochemical methods are much more favoured since they are scalable, high yielding, cost effective and less time consuming. In this work, an electrochemical synthesis method was followed in the production of GO by oxidizing graphite and subsequently, its electrophoretic deposition was carried out on various substrates. During the first part of the research, electrochemical exfoliation of graphite to GO was carried out using (NH4)2SO4 solution as the electrolyte. Initially, a cylindrical graphite pellet was made using graphite powder and was covered with a cellulose bag. Electrolysis was carried out by using the prepared graphite pellet as the anode and carbon electrode as the cathode. Various experimental conditions were tested to find out the optimum conditions which give rise to an efficient electrolysis with a maximum production yield of GO. Concentration of (NH4)2SO4 was varied from 0.5 M to 1.0 M, electrochemical exfoliation time was varied from 1 to 8 hours, applied voltage was varied as 5 V, 10 V and 15 V, the temperature was varied from 30 ℃ to 50 ℃ and mechanical stirring speed was varied from 100 rpm to 300 rpm. The second part of the research is based on the electrophoretic deposition of GO. This was carried out by using Pt as one terminal and glass-FTO or the stainless steel substrate as the counter terminal. The process was carried out using a mixture of N,N- DMF and MgCl2.6H2O as the dispersion medium. The GO coatings were annealed at 350 ℃ under N2 atmosphere as the post electrophoretic deposition treatments. The experiments resulted in a maximum yield of 59.25% of GO. The UV-Visible, the FTIR spectra and XRD diffractograms obtained confirmed the formation of GO. The two main factors which cause the exfoliation of graphite are; intercalation of ions between the adjacent layers of graphite and the expansion of graphite induced by the evolution of gases at the electrodes. This research revealed that the GO can be effectively synthesized using a (NH4)2SO4 electrolyte (1 M) under an applied voltage of 15 V, at a temperature of 50 ℃ with mechanical stirring (300 rpm) for 8 hours. Moreover, a uniform coating of GO was deposited on the glass-FTO and stainless steel substrates in both organic and inorganic suspension media of N,N- DMF and MgCl2.6H2O, respectively. This communication brings a viable method of synthesizing GO from vein graphite, using an environmentally benign and less costly method, into the spotlight.
Electrodeposited metal sulfide thin films for gas sensing applications
(4th International Research Symposium on Pure and Applied Sciences, Faculty of Science, University of Kelaniya, Sri Lanka, 2019) Namawardana, D. G. K. K.; Wickramathilaka, P. A. K. Y.; Atapattu, H. Y. R.; De Silva, D. S. M.
Quantitative measurements of gases are based on a variety of physical or chemical principles. Among them semiconductor gas sensors are best candidates for the development of commercial gas sensors due to their higher specificity and sensitivity. They are mainly based on metal oxide and metal sulfide materials. Due to certain drawbacks of metal oxides, metal sulfides are extensively investigated as novel gas sensing materials. In this study ZnS and CdS were investigated for their gas sensing ability. Both types of thin films were fabricated by electrodeposition using a three electrode electrolytic system consisted of a fluorine doped tin oxide glass substrate (1×3 cm2) as working electrode and a high purity carbon as counter electrode. An aqueous electrolyte containing CdCl2 (0.10 mol/L) and Na2S2O3 (0.01 mol/L) precursors were used for the electrodeposition of CdS material and aqueous electrolyte containing ZnCl2 (0.10 - 0.05 mol/L) and Na2S2O3 (0.01 - 0.05 mol/L) precursors were used for electrodeposition of ZnS material. The CdS depositions were carried out in the cathodic deposition potential (CDP) range of 0.65 to 0.70 V vs. saturated calomel electrode and pH range of 1.5 to 2.0 at a temperature of 55 °C for 30 minutes. The ZnS depositions were carried out in the CDP range of 0.70 to 1.10 V vs. Ag/AgCl reference electrode and pH range of 4.0 to 3.5 at a temperature of 30 °C for 90 minutes. Both types of thin films were characterized for their crystalline structure, surface morphology, and elemental composition by using the techniques of X-ray diffraction spectroscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy respectively and were exposed to various gases namely; NO2, H2S, and LPG. CdS thin films grown at CDP of 0.67 V and pH of 1.5 and ZnS thin films grown at CDP of 1.05 V and pH of 3.7 were found to have notable gas sensing properties. CdS has shown highest resistance variation of 1.2 Ω towards H2S with respect to the initial resistance of 36.0 Ω and ZnS has shown highest resistance variation of 2 Ω with respect to the initial resistance of 26.2 Ω when exposed to NO2 gas at 30 oC. Both CdS and ZnS thin films showed resistance variation of 1.1 Ω and 0.6 Ω towards LPG respectively at 30 oC.
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.
Evaluating heavy metal accumulation in Scylla serrata (mud crabs) inhabiting the Negombo lagoon, Sri Lanka
(Faculty of Science, University of Kelaniya Sri Lanka, 2024) Dias, B. C. G.; De Silva, D. S. M.; Amarathunga, A. A. D.; Bakir, A.; McGoran, A. R.; Sivyer, D. B.; Reeve, C.
A multitude of anthropogenic and industrial uses lead to the extensive dispersion of heavy metals in aquatic environments. The protracted presence and poisonous nature of heavy metals inflict negative impacts including organ malfunction and the inactivation of enzymes in aquatic organisms. The bottomdwelling mud crabs are frequently used as bioindicators for evaluating such heavy metal contamination in lagoons and estuaries. Therefore, the main emphasis of this study was on the amounts of heavy metals found in the meat of the Scylla serrata mud crab that lives in Negombo Lagoon, Sri Lanka. Due to their great sensitivity, mud crabs, bottom dwelling crustaceans that live in the bottom zones of lagoons, are frequently utilized as indicators for evaluating heavy metal contamination. Mud crab samples (n = 42) were randomly collected from the Negombo Lagoon from March to May 2023. Three replicates, 1 g each, of the flesh from each crab sample, were treated to acid digestion (conc. HNO3 and H2O2) and analysed separately using an atomic absorption spectrophotometer (AAS). Cu, Fe, Mn, and Zn were found to be the most common heavy metals in crab flesh based on the metal analysis. The amounts of Cd and Cr were not detectable. Zn (0.70 ± 0.24 mg/L) was the most prevalent heavy metal in the meat, followed by Mn (0.08 ± 0.07 mg/L), Cu (0.15 ± 0.12 mg/L), and Fe (0.46 ± 0.30 mg/L). The study's findings support the notion that the mud crabs living in the Negombo Lagoon have heavy metals in their meat. A recent study offers strong proof that heavy metals are present in mud crabs, a popular edible shellfish in Sri Lanka. The Negombo Lagoon's whole food chain may be affected by this contamination.
The influence of substrates on the device performance of the TCO/CBD-CdS/ EDCdTe and TCO/CBD-CdS/CSS-CdTe solar cells
(Faculty of Science, University of Kelaniya Sri Lanka, 2023) Gajanayake, G. K. U. P.; Bandara, K. M. N. S.; De Silva, D. S. M.; Atapattu, H. Y. R.
The development of cost-effective efficient photovoltaic cells is crucial for generating electricity with the most abundant solar energy to eliminate the energy crisis globally. At present, there is a growing interest in CdS/CdTe solar cells due to minimal material cost and easy and cost-effective methods of thin film deposition. The aim of this work is to investigate the influence of different transparent conducting oxide (TCO) substrates in superstrate configuration (glass/ITO:5 Ω/sq, glass/FTO:13 Ω/sq, and glass/FTO:7 Ω/sq) on the device performance of CdS/CdTe solar cells. Herein, chemical bath deposited CdS (CBD-CdS) layers were grown using 0.0333 mol/L Cd(CH3COO)2, 0.0667 mol/L CS(NH2)2, concentrated NH4OH and 1.0 mol/L NH4(CH3COO) at 90 ℃ for 55 min. Subsequently, the CdTe layers were deposited using electrodeposition (ED) and close spaced sublimation (CSS) techniques as required. For electrodeposition of CdTe layers, CdSO4 (1.0 mol/L) and TeO2 (1.0 mmol/L) precursors were used at pH of 2.3 and 65 ℃ and deposition was run for 3 hrs. The CSS-CdTe layers were developed by maintaining the substrate and source temperature at 580 °C and 640 °C, respectively, and the deposition proceeded for 25 min. at 7.9 Torr. The glass/TCO/CBD-CdS/ED-CdTe samples were treated with CdCl2, and glass/TCO/CBD-CdS/CSS-CdTe were undergone NP etching as suitable post-deposition treatments. The device fabrication was completed with the back contact formation (Cu/Au). The devices; glass/TCO/CBD-CdS/ED-CdTe/Cu/Au and glass/TCO/CBD-CdS/CSS-CdTe/Cu/Au prepared with FTO:13 Ω/sq delivered the highest efficiency of 5.7% (JSC = 19.2 mA/cm2, VOC = 0.672 V, FF = 44%) and 8.6% (JSC = 30.3 mA/cm2, VOC = 0.606 V, FF = 47%), respectively while the cells prepared with glass/ITO:5 Ω/sq delivered the lowest efficiency. Hence, the glass/FTO:13 Ω/sq substrate was recognized as the most appropriate substrate for the fabrication of CBDCdS/ ED-CdTe and CBD-CdS/CSS-CdTe solar cells. The resultant optical transmittance (over 80%, above 500 nm) and surface roughness (RMS roughness of bare FTO:13 Ω/sq was 12.49 nm, and FTO:13 Ω/sq/CBD-CdS was 10.15 nm) of CBD-CdS further confirmed the suitability aptness of the glass/FTO:13 Ω/sq substrate in CdS/CdTe based solar cell fabrication.
Introducing Spin‑coated ZnO Anti‑reflection Coating for CdS/CdTe Solar Cells
(The Minerals, Metals & Materials Society, 2024) Wijesingha, J. R.; Gajanayake, G. K. U. P.; Wickramasinghe, W. A. V. U.; Damayanthi, R. M. T.; De Silva, G. I. P.; De Silva, D. S. M.
Second-generation solar cells, commonly known as thin-film solar cells, have emerged as promising alternatives to traditional silicon-based first-generation photovoltaic cells. The superstrate configuration is the most widely used structure for constructing thin-film solar cells. Nevertheless, light reflection from the front cover glass surface significantly contributes to energy losses in thin-film solar cells. In this study, a ZnO anti-reflection (AR) coating was introduced using the spin coating technique on a glass/FTO/CdS/CdTe/Cu/Au substrate to improve the power conversion efficiency of the solar cell by reducing front-surface reflectance. The ZnO layer deposited at 3000 rpm in 15 s showed the minimum reflectance and higher transmittance over a wavelength range of 500–900 nm. Further, the thickness of the film under optimal conditions was 63.32 nm, which is compatible with the ideal theoretical AR coating thickness of 65 nm. Comparing the device performance of the CdS/CdTe solar cell with and without AR coating, all tested devices showed an average short-circuit current density improvement of 6.8% and overall enhancement in power conversion efficiency of 9.3%.
Intrusion of Cd, As, Cr, Pb & Hg into selected rice varieties (Oryza sativa L.) in relation to their status in two different agricultural management systems.
(International Research Symposium on Pure and Applied Sciences, 2017 Faculty of Science, University of Kelaniya, Sri Lanka., 2017) Navarathna, N. M .C. M.; Pathiratne, K. A. S.; De Silva, D. S. M.
Five traditional varieties (TRV) and five newly improved hybrid varieties of paddy (NIRV) were cultivated under both conventional and organic farming conditions during Yala and Maha seasons at selected areas in Anuradhapura district where chronic kidney disease was prevalent and Kurunegala districts where chronic kidney disease was not known to exist at the time of the study. The area used for cultivation under each organic and conventional farming condition in each district was approximately 11 m x 11 m and was well separated from each other. The contents of each of the selected toxic elements; Cd, As, Cr, Hg, and Pb in the soil, irrigation water, conventional and organic fertilizers and pesticides used for cultivation together with the relevant physicochemical parameters for soil were estimated before the beginning of the cultivation while the required physicochemical parameters and contents of the elements in irrigation water were estimated regularly during the cultivation. After the maturity periods at each cultivation, paddy were harvested and the contents of the elements in rice grains, straws and roots were determined. All samples for determination of the elements were processed and microwave acid digested according to US EPA 3052 method and analyzed using atomic absorption spectrometer. (Hitachi ZA3000 Zeeman Polarized). Analytical methods were validated using either standard reference materials or recovery tests. The study revealed that, the contents of any of the selected elements in any of the rice varieties grown did not exceed the safe limits of 200 μg kg-1 for Cd, 200 μg kg-1 for As, 300 μg kg-1 for Pb, 2000 μg kg-1 for Cr and 20 μg kg-1 for Hg recommended by the World Health Organization (WHO) and Food and Agricultural Organization (FAO) for milled rice. Hg, As and Pb were not detected in any of the rice varieties grown. The highest content of Cr detected was one tenth of the allowable WHO limit of 2000 μg kg-1. The contents of cadmium were in the range below the detection limit of 159 μg kg-1. Arsenic was below the detection limits in agrochemicals, soils and irrigation waters. Pb and Cr were present in fertilizers below the SLSI limits of 10 mg kg-1 and 250 mg kg-1, respectively. Slightly elevated levels of cadmium (1.80 mg kg-1 to 3.44 mg kg-1) were detected in Muriate of Potash (MOP) and Triple Super Phosphate (TSP) respectively. The green fertilizers contained Cd in the range from 0.44 mg kg-1 to 1.67 mg kg-1 . Irrigation water did contain Cd below the detection limits of 0.2 ± 0.0 μg L-1, while Cr contents were in the range of 13.8 ± 1.9 μg L-1 to 157.9 ± 22.7 μg L-1. The Cd contents in paddy soils were in the range 0.41 ± 0.02 mg kg-1 to 0.75 ± 0.03 mg kg-1 and while the Cr contents were in the range 1.33 ± 0.15 mg kg-1 to 1.63 ± 0.09 mg kg-1. Cd was detected in rice straws along with roots in the range, 12.2 ± 2.6 μg kg-1 to 1582 ± 74.3 μg kg-1.
Microplastic contamination in selected commercial fish species in Negombo Lagoon, Sri Lanka
(Faculty of Science, University of Kelaniya Sri Lanka, 2023) Athukorala, A.; Amarathunga, A. A. D.; De Silva, D. S. M.; Bakir, A.; McGoran, A.; Sivyer, D. B.; De Silva, C. L. C. L.; Narangoda, S. R. C.
Microplastics (MPs) act as physical anthropogenic pollutants and their ability to act as contaminant vectors in biological matrices has become a serious ecosystem and human health concern. The present study, for the first time, has screened and detected MPs in the gastrointestinal tract and gill of a select group of commonly consumed fish species from Negombo lagoon, Sri Lanka. Negombo lagoon is one of the most productive ecosystems in Sri Lanka. A total of 60 fish samples were investigated for the microplastic presence, abundance, and morphological types within the guts and gills of commercial fish consisting of seven (7) species: Siganus javus (SJ:n=5), Leiognathus splendens (LS: n=8), Leiognathus blochii (LB: n=5), Mugil cephalus (MC: n=19 ), Strongylura leiura (SL: n=10), Stolephorus indicus (SI: n=10), and Caranx heberi (CH: n=3) with different feeding habits and habitats. Samples were collected between July–December 2022. Fish gut content was screened for the presence of MPs using the alkaline digestion and density gradient separation technique (NaCl hypersaline solution) and examined using a stereomicroscope and micro-Fourier transform infrared spectrometer (m-FTIR). Microplastics, ranging from 0.05 to 4.80 mm, were found in the investigated fish species. Remarkably, this study revealed that 51.67% and 32.00 % of the fish samples contained microplastic in their guts and gills respectively. A total number of 67 MP particles (size < 5 mm) were found in the excised fish guts of the seven species. The most common morphology of microplastics discovered in fish guts was fragments, which accounted for 87.5% of all MPs present. The MP content in guts differed between species. Of that Mugil cephalus recorded the greatest amount of MP ingestion, with an average MP count of 2.68±0.23 items per individual in fish gut corresponding to an average abundance of 0.22±0.26 particles/g and 0.84 ±0.46 items per individual in gills corresponding to an average abundance of 0.41±0.68 particles/g. The majority of ingested particles were fragments (40.3%), followed by fibers (34.33%), films (19.40%), microbeads (4.48%), filament (2.29%), and no pellets were observed. In terms of colour, the most abundant were blue (58.20%), followed by green (13.43%), transparent particles (8.96%), yellow (7.46%), red (5.97%), black (2.98%), white, brown, pink (1.49%) were found in low number. The majority of MPs presented were identified by m-FTIR as particles of polypropylene and polyethylene (HDPE), rayon. The results are evident in the growing threat of MPs on biological matrices and ingested MPs in edible fish species present in the Negombo lagoon.
Microplastic contamination in shrimps from the Negombo Lagoon- Sri Lanka
(Faculty of Science, University of Kelaniya Sri Lanka, 2023) Lawan, P. L. M. J. H.; De Silva, D. S. M.; Amarathunga, A. A. D.; McGoran, A.; Bakir, A.; Sivyer, D. B.
Microplastics (MPs) are minute pieces of plastic debris that are smaller than 5 millimeters in size. They are created through the fragmentation or degradation of more oversized plastic items such as bottles, bags, and packaging materials. Additionally, MPs can also be intentionally manufactured for certain products like microbeads in personal care products. Microplastic pollution has turned into a severe global issue affecting freshwater systems, coastal regions, and oceans. These non-biodegradable materials have a detrimental impact on marine species and ecosystems, causing disruption to their feeding, breathing, and reproduction. The intention of this study was to identify and categorize the MPs present in shrimps from the Negombo lagoon, Sri Lanka, based on the type, shape, size, and color and to characterize the polymer composition of the identified MPs. Fresh samples of two species of shrimps, Penaeus monodon (n=25) and Penaeus indicus (n=95) were collected from the ten locations where the known habitats of shrimps in the Negombo lagoon and MPs were isolated by gastrointestinal tracts and gills by alkali digestion followed by vacuum filtration. Stereomicroscopy coupled with advanced microimaging and analyzing software was used for characterizing the isolated MPs. From those samples, 415 MPs were identified and characterized. The results showed that the average number of MPs per individual was higher in P. monodon (4.72 ± 2.72) compared to P. indicus (3.13 ± 2.04). The average number of MPs per gram of gut tissue was also higher in P. monodon (8.29 ± 4.63) compared to P. indicus (5.52 ± 3.78). Identified MPs were categorized into five size groups, 1000 μm. The majority of MPs identified were under the category of >1000 μm, and six color categories were observed, with blue being the most prevalent. The study identified two main types of MPs; fibers and fragments, and the predominant form of MPs was fiber (93.0%), with the remaining being fragments. The polymer composition of most of the MPs included polystyrene, polyamide, polyester, polypropylene, and rayons, as identified by µ-FTIR and ATR-FTIR studies.
Microplastics in selected offshore pelagic fish in Indian Ocean
(Faculty of Science, University of Kelaniya Sri Lanka, 2023) Jayarathna, N. K. D. M. P.; Walpita, C. N.; Amarathunga, A. A. D.; De Silva, D. S. M.; Sivyer, D. B.
Microplastics (MPs) pollution in marine environment is an emerging threat to marine biota. Marine pelagic fish species such as tuna and tuna-like species caught during offshore fisheries in open seas, are known to be more commercially important and could be contaminated by MPs. As such, MPs could pose a risk to fish by themselves and to human health due to consumption of contaminated seafood. The present study was planned to investigate the MPs contamination of commercially important three pelagic fish species (Thunnus albacares, Katsuwonus pelamis, and Elagatis bipinnulata) caught from offshore fisheries using multiday boats from several locations of the Indian Ocean to fill the knowledge gap on MPs contamination of pelagic fish, especially in the Indian Ocean. Fish samples were collected from Beruwala, Galle, Panadura and Negombo fishery harbors in Sri Lanka, and the gastrointestinal tract (GIT) and gills were examined for possible MP contamination. A total of 40 samples belonging to three fish species were used for the study. The abundance and morphology (i.e. color, shape) of the MPs were assessed, and the polymer type of the MPs was investigated by using ATR-FTIR. Descriptive analysis was done by using IBM SPSS statistical version 26 and MS excel was used to calculate the percentages of MPs by color, shape and polymer type. There was a contamination of MPs in all three fish species. Nevertheless, 12.5% of E. bipinnulata and 21.7% of K. pelamis did not show MPs in analyzed tissues. T. albacares was found to have the greatest number of MPs (15±6 items individual-1). The morphology of the MPs found from the GIT and gills of all the three fish species were fibers (51%), followed by fragments (37%) and films (12%). In GIT, the most prominent color was blue in all the fish species. Moreover, the polymer types found belonged to three categories viz, thermoplastic elastomers (TPE), phenol formaldehyde resin (PF), and polyethylene copolymer (PE-Copolymer). Among them, the most prominent type of polymer was PF. PE-copolymer was found only in T. albacares. Therefore, continuous monitoring of marine environment and implementing stringent regulations are recommended to minimize plastic pollution in the Indian Ocean to protect both the marine ecosystem and humans.
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.
Pyrolysis of plastic waste into liquid fuel
(Faculty of Science, University of Kelaniya Sri Lanka, 2023) Uthpalani, P. G. I.; De Silva, D. S. M.; Weerasinghe, V. P. A.; Premachandra, J. K.
The accumulation of plastic waste in the environment has emerged as a significant global concern. The versatile properties of plastics, such as low weight, low cost and durability which led to their widespread use as substituents for traditional materials like wood, metals, ceramics, and glasses. However, the improper handling and disposal of plastic waste have imposed negative consequences for the environment. The non-biodegradable nature of plastics makes them persist in the environment for extended periods, causing pollution and posing threats to ecosystems. Pyrolysis of plastic waste has been studied extensively in recent years as an effective solution, by exposing the plastic waste to high temperatures in an oxygen-free environment to decompose it into fuel oil, char, and gases. In this study, the waste of four types of plastics samples, low-density polyethylene (LDPE), high-density polyethylene (HDPE), polypropylene (PP), and a mixture of these three types of plastics, were subjected to pyrolysis. Lab-scale, low-cost pyrolysis system was used to obtain liquid oils and herein, the non-condensed vapor was trapped into an organic solvent. Thermal pyrolysis or non-catalyzed pyrolysis resulted in a liquid yield of 65.64 ± 5.42 – 79.57 ± 1.66 wt.% at a temperature range of 340 – 360 ℃. Considering catalytic activity, high temperature stability, local availability, and abundance, four types of naturally available minerals were selected as potential catalysts for the pyrolysis of waste plastics. The mineral which resulted in the highest liquid yield was identified as the best-performing catalyst and used for further analysis. The catalyzed process resulted in an increased liquid yield of 71.79 ± 0.99 - 80.29 ± 1.76 wt.% at the temperature range of 290 – 320 ℃. The calorific value of the resulting oil in thermal and catalyzed pyrolysis processes were 10,850 -10,961 Kcal/kg and 10,556 - 11,473 Kcal/kg respectively. This reveals that the mineral selected is an ideal catalyst for pyrolysis of plastics and further indicates the quality enhancement of the fuel produced in catalyzed pyrolysis. Further, the fuel quality indicators; calorific values, density, kinematic viscosity, ash content, and water content of the resulting liquid oils under both catalyzed and uncatalyzed/thermal pyrolysis processes were significantly compatible with commercial grade diesel and kerosene fuel oils.
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.