RESCON 2023

Permanent URI for this collectionhttps://ir.lib.pdn.ac.lk/handle/20.500.14444/5953

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Preparation and characterization of coconut shell activated carbon black for electrophotography toner application
(Postgraduate Institute of Science (PGIS), University of Peradeniya, Sri Lanka, 2023-11-03) Samanmali, V.G.C.; Wijewardhana, G.D.M.H.; Mantilaka, M.M.M.G.P.G.; Madugalla, T.B.N.S.; Wijesinhe, W.P.S.L.
Coconut shells (CS) are one of the main domestic wastes that are abundantly used as a precursor to producing activated carbon black (ACB) for various purposes. This study investigated a low- temperature chemical activation method (LTCA) using NaOH to prepare ACB from CS to apply as the black colourant in toner production. Initially, the cleaned CSs were subjected to a pyrolysis process at 550 °C for 4 hrs, and the resulting coconut charcoal was activated using NaOH at 120 °C. The porosity of the resulting ACB was investigated at different charcoal and NaOH solution volume ratios. The chemical characteristics, surface morphology, surface area and crystallinity of the ACB, and mineralogy of initial coconut ash were examined using Fourier-transform infrared (FT-IR) spectroscope and scanning electron microscopy (SEM) and powder X-ray diffraction (PXRD) analyses. The current study found that the weight percentage of ash in a CS is 0.6% and consists of SiO₂, MgO, CaCO₃, MnO, TiO₂, CaO, Al₂O₃, Fe₂O₃, P₂O₅, and fixed carbon. The PXRD shows the increase of graphitic nature with increasing NaOH volume. The FT-IR proves that ACB consists of carbonyl groups, carboxylic groups, aromatic C=C bonds and aromatic C-H out-of-plane deform bonds as the main functional groups, indicating the formation of aromatic compounds. The SEM images indicate that increasing NaOH volume causes irregular-shaped micropores with large diameters compared to the low NaOH volume exhibiting spherical micropores. Therefore, it concludes that LTCA with less NaOH volume causes the slow removal of C as CO₃ ²⁻ from the ACB and increases the surface area. In the future, these ACBs will be used to produce toners to identify the eligibility as the colourant for electrophotography toners.
Investigating the sound absorption characteristics of coconut shell-based structures
(Postgraduate Institute of Science (PGIS), University of Peradeniya, Sri Lanka, 2023-11-03) Senarath, N.D.D.D.; Jayalath, J.A.C.P.; Mendis, D.R.A.
This study investigates the sound absorption characteristics of structures developed using two filler materials: coconut shell powder and charcoal powder, with natural liquid rubber as the binder. Selected filler material and the binder are readily available in Sri Lanka. The sound absorption coefficient, defined as the ratio of absorbed energy to incident energy indicating the amount of sound being absorbed by a material, was experimentally studied using the impedance tube method in the frequency range of 1000-3500 Hz. Samples were prepared by varying the volume ratio of the binder and the filler. The sound absorption property of the prepared samples was tested by using the impedance tube for different frequencies within the range. The structures were further improved by increasing their thickness and changing the surface roughness by introducing holes with different depths to improve sound absorption. The coconut shell powder structure of 50% volume ratio with 1.5 cm thickness and hole depth of 1.1 cm showed a sound absorption coefficient in the range of 0.80-0.83 for 2500 Hz and the range of 0.85-0.93 for 3000 Hz. This implies that the coconut shell powder structure absorbs over 80% of the incident sound energy with a 2500 Hz or 3000 Hz frequency. Further, the charcoal powder structure of 66% volume ratio with 1.5 cm thickness and hole depth of 1.1 cm exhibited sound absorption of over 60% beyond 2000 Hz within the tested frequency range. Both structures are versatile, cost-effective, and eco-friendly sound absorption structures for various acoustic applications for high frequencies due to their flexibility, ease of preparation, and thin profile.
Evaluation of the potential of canarium zeylanicum seed oil for biodiesel production
(Postgraduate Institute of Science (PGIS), University of Peradeniya, Sri Lanka, 2023-11-03) Keshiya, P.A.W.; Ganehenege, M.Y.U.
Canarium zeylanicum, Sri Lankan Kekuna is an endemic plant in Sri Lanka with a high amount (around 51.80%) of oil in its seed kernel. The gas chromatography (GC) results showed that C. zeylanicum had a promising free fatty acid profile, suggesting that producing biodiesel with C. zeylanicum as feedstock was feasible. The acid value and the saponification value of the oil were found to be 1.0 ± 0.1 (mg KOH ⁄ g) and 178 ± 1 (mg KOH ⁄ g), respectively. As the acid value was ~1.0, C. zeylanicum oil can be directly converted to biodiesel by transesterification without performing any pre-treatments. Therefore, transesterification of C. zeylanicum oil with methanol using potassium hydroxide as the catalyst was performed to produce methyl esters, which can be used as biodiesel. The optimum conditions for the transesterification were investigated by varying the parameters: methanol: oil molar ratio (3:1 – 9:1), catalyst concentration (0.50 – 1.5%), and temperature (303 – 343 K). Periodic acid titrations were carried out to evaluate the free glycerol content. The methyl ester concentration was assessed by mass balancing. The optimal triglyceride conversion (94%) was achieved at room temperature in the presence of 1% potassium hydroxide as the catalyst when the methanol: oil ratio was kept at 6:1. Biodiesel properties including flash point, fire point, calorific value, density, cloud point, pour point and kinematic viscosity at 40 o C of C. zeylanicum biodiesel were characterized according to the ASTM standards, and the results obtained were 60.0 ⁰C, 75.0 ⁰C, 40.56 MJ kg⁻¹, 0.8370 g cm- ³, 10.0 ⁰C, 6.3 ⁰C, and 7.2 mm s⁻¹, respectively. As both the flash point and the fire point are lower than the minimum standard value, and the viscosity is slightly higher than the standard range of 1.9-6.0 mm s-1, C. zeylanicum methyl esters exhibit unpromising biodiesel properties. However, blending with diesel could be employed to improve the properties of the final biodiesel blend.
Low-cost counter electrode prepared using activated carbon derived from rice husk for dye-sensitized solar cells
(Postgraduate Institute of Science (PGIS), University of Peradeniya, Sri Lanka, 2023-11-03) Weerasinghe, M.I.U.; Kumarage, P.M.L.; Amarathunga,I.G.K.D.; Bandara, T.W.M.J.; Kumara, G.R.A.
Dye-sensitized solar cells (DSSCs) have emerged as promising alternatives for efficient and cost-effective solar energy conversion devices. However, the high cost and limited availability of platinum (Pt), traditionally used as a counter electrode (CE) material, has motivated the search for sustainable and low-cost alternatives. This study explored the potential of using activated carbon synthesized from rice husk to prepare low-cost CE for DSSCs. Rice husk is an abundant agricultural waste product, and the present study reveals that the active carbon synthesized from rice husk can be used to prepare DSSC counter electrodes. At first, dried rice husk was carbonized and then activated by heating to 900 °C for 20 minutes and quenching several times. The spray pyrolysis method was used to prepare activated carbon CEs using polyvinylpyrrolidone binder and isopropanol solvent. A series of experiments showed that CEs prepared using activated carbon derived from rice husk are suitable for fabricating low-cost and highly efficient Pt-free DSSCs. With the usual N719 dye and liquid electrolyte (I⁻/I³⁻ ), the DSSC utilizing this biomass-derived active carbon CE achieved an energy conversion efficiency of 5.62%, while that for Pt-based CE is 7.73%. The average open circuit voltage (Voc) and short circuit current density (Jsc) of the active carbon-based cell are 0.68 V, 15.90 mA cm⁻² relative to the Pt-based cell.
Comparison of x-ray attenuation in the energy range of 50-80 keV in aluminium and zircon mineral encased in epoxy matrix
(Postgraduate Institute of Science (PGIS), University of Peradeniya, Sri Lanka, 2023-11-03) Sivakumar, V.; Weerasekara, A.D.K.M.; Jayalath, C.P.; Jayasinghe, A.; Bandara, T.M.W.J.; Wijayaratne,K.; Gnanarathne, D.M.T.; Nanayakkara, D.K.K.
X-rays are ionising radiation that can penetrate and be absorbed in varying degrees by different materials. They are used in a range of applications, including radiography. However, exposure to X-rays can have harmful effects. Hence, the appropriate use of radiation shielding is essential to prevent unnecessary exposure to radiation for radiation workers, patients, and the general public. Lead and lead-based compounds are commonly used as shielding materials. Given the hazards associated with lead-based compounds, there is a growing interest in developing leadfree shielding materials that can offer comparable shielding properties. The project aimed to synthesize a lead-free and cost-effective shielding material that could attenuate X-rays in the energy range of 50-80 keV using locally available minerals. Samples with various thicknesses were prepared using 80 wt% zircon sand with 150 µm particle size and by using epoxy as the matrix. These prepared samples were exposed to X-rays with energies ranging from 50 keV to 80 keV in 10 keV increments, with a standard aluminium step wedge as the reference. Images were obtained using a Fujifilm computed radiography system. Subsequently, grayscale values of the exposed regions of the images were processed by a software tool developed using Python programming language. The grayscale values of the prepared samples at various thicknesses were compared with those of aluminium at various thicknesses for each energy value. For the energy range mentioned above, the prepared composite samples with thicknesses varying from 1 mm to 4 mm exhibited an attenuation comparable to those of aluminium with 9 mm to 33 mm thicknesses. This study presents an opportunity to develop radiation shielding materials containing locally abundant natural minerals, such as zircon, for radiation protection in medical diagnostic procedures.
Determination of phenolic content and antioxidant potential of a nutrient supplement developed using selected local grain varieties in Sri Lanka
(Postgraduate Institute of Science (PGIS), University of Peradeniya, Sri Lanka, 2023-11-03) Perera, T.P.S.S.; Godakumbura, P.I.; Prashantha, M.A.B.; Navaratne, S.B.
Antioxidant properties of food products are significantly important due to their potential health benefits. This study investigates the antioxidant properties of an extruded composite flour mixture made of selected local grain varieties in Sri Lanka. The mixture was prepared by combining kalu heenati rice (Oryza sativa), black gram (Vigna mungo), green gram (Vigna radiata), meneri (Panicum miliaceum), black sesame (Sesamum indicum), black seeds (Nigella sativa) and cinnamon in statistically designed ratios to create a balanced nutritional profile. Several antioxidant assays were employed in triplicate to evaluate the antioxidant activity of the composite flour mixture, including total phenolic content (TPC), and radical scavenging activity using 2,2-diphenyl-1-picrylhydrazyl (DPPH), 2,2'-azino-bis (3-ethylbenzothiazoline-6- sulphonic acid) (ABTS) radicals and ferric reducing antioxidant power assay (FRAP). The results indicated that the TPC of the flour formulation was 0.45 ± 0.1 mg gallic acid equivalent /g dry weight. DPPH, ABTS, and FRAP assays revealed that the grain extract had antioxidant activities of 0.67 ± 0.3, 0.92 ± 0.1, and 0.72 ± 0.1 in mg trolox equivalent per gram dry weight (mg, TEAC/g dw) respectively. These values were significantly higher than that of a leading extruded composite flour mixture in the market (p < 0.05). The TPC of the market sample was 0.19 ± 0.2 mg gallic acid equivalent /g dw. DPPH, ABTS, and FRAP assays of this sample exhibited antioxidant activities of 0.50 ± 0.1, 0.74 ± 0.3, 0.59 ± 0.1 TEAC/g dw, respectively. These findings highlight the potential health benefits of the flour mixture as part of a balanced diet to enhance antioxidant defence. In conclusion, the presence of phenolic compounds, along with effective radical scavenging activity, contribute to the overall antioxidant potential of the composite flour mixture. Further investigations into the specific bioactive compounds of the flour mixture would provide valuable insights into the development of functional food products with enhanced antioxidant properties.
Evaluation of insect-repellent activity of Piper longum (l.)based nano-emulsions for the control of Sitophilus oryzae (l.)(Coleoptera: Curculionidae)
(Postgraduate Institute of Science (PGIS), University of Peradeniya, Sri Lanka, 2023-11-03) Sandeepani, G.D.V.A.; Perera, A.G.W.U.; Chinthaka, S.D.M.
The rice weevils (Sitophilus oryzae) cause significant damage to grains and their milled products during storage, and the control of these insects relies on the use of synthetic insecticides. Due to the deleterious impact caused by these chemicals on biological systems, plant-derived essential oils (EOs) have been used as effective bio-insecticides for managing stored grain insects, providing a safer alternative. Therefore, this study aimed to develop nanoemulsions based on Piper longum EO to improve EO’s efficacy and evaluate its repellent activity against Sitophilus oryzae. GC/MS analysis was conducted for P. longum EO, and two combinations, 1:2 and 1:2.5 (EO: Tween 80) of 6% EO concentration, were prepared. Physiochemical characterization of both combinations of P. longum nano-emulsions was conducted. Myristicine (61.42%), and caryophyllene (7.98%) were the major constituents of P. longum EO. Particle sizes of the nano-emulsions were 10.22 nm and 12.10 nm, polydispersity index (PDI) was reported as 0.438 and 0.292, and zeta potentials were -1.7 mV and -0.80 mV, respectively, for these two combinations. Median repellent concentrations (RC₅₀) for the formulated P. longum nano-emulsions of 1:2 and 1:2.5 combinations against S. oryzae were 0.019 μL cm⁻² and 0.014 μL cm⁻² respectively, whereas RC₅₀ recorded for P. longum EO was 0.123 μL cm⁻² within 24 hrs. Accordingly, the formulated nano-emulsions were superior over P. longum EO. Thus, it can be concluded that the prepared nano-sized P. longum EO can be effectively used as an eco-friendly alternative to harmful chemical insecticides to control insect pest infestations in stored grain food commodities successfully.
Development of humidity sensing composite material using SnO2 doped phenol formaldehyde (pf) derived conductive charcoal
(Postgraduate Institute of Science (PGIS), University of Peradeniya, Sri Lanka, 2023-11-03) Heshan,G.D.K.; Madhuwantha,M.D.; Rajapakse, R.M.G.; Wijesinghe, W.P.S.L.
Humidity sensors play a vital role in various industries and medical applications, necessitating the development of cost-effective sensing materials to meet the increasing demand. This study focuses on creating a low-cost sensor material derived from waste polymer materials and compares its sensing characteristics, including resistance, hysteresis, recovery and response times, and stability concerning relative humidity. By subjecting phenol formaldehyde (PF) to thermal modification at 700 °C, conductive carbon was produced. Subsequently, SnO₂ was doped via hydrothermal treatment at 140 °C. The resulting SnO₂-doped pyrolyzed carbon composite was deposited onto gold-coated resistive-type electrodes to fabricate the sensor. The composite material underwent characterization using techniques such as scanning electron microscopy (SEM), powder X-ray diffraction spectroscopy (PXRD), thermal gravimetric analysis (TGA), and Raman spectroscopy. Further, the performance of the humidity sensor was investigated. The resistance response demonstrated values of 54188.30 and 27876.50 Ω as relative humidity (RH) increased from 33% to 95%. The recovery time and response were determined to be approximately 11 s and 40 s, respectively. The humidity sensitivity of the SnO₂ charcoal composite was found to be 227.55 Ω per percentage RH, attributed to the enlarged specific surface area resulting from its unique nanostructure. These are just a few examples of applications where high-sensitivity humidity sensors are valuable. The sensitivity of the sensor directly affects its ability to detect small changes in humidity levels, making it a key factor in achieving accurate and reliable measurements in these critical domains. These findings indicate that the SnO2 charcoal composite holds promise as an ideal material system for producing high-performance and cost-effective humidity sensors.
Characterization of seed oils of four garcinia species to assess potential applications in cosmetics and dietary supplements
(Postgraduate Institute of Science (PGIS), University of Peradeniya, Sri Lanka, 2023-11-03) Thathsara, K.A.H.; Chinthaka, S.D.M.
Sri Lanka has a wide variety of oil-bearing seeds that often end up in waste without proper utilization. On the other hand, plant seed oils have emerged as a promising avenue for application in cosmetics and dietary supplements. However, most of the plant seed oils found in Sri Lanka are not characterized by their chemical compositions. This study aims to characterize seed oils of Garcinia zeylanica, Garcinia xanthochymus, Garcinia morella, and Garcinia mangostana by determining fatty acids (FA) composition, constituents in the unsaponifiable matter, and other physical properties. The oil was extracted into hexane using Soxhlet extraction. Ash content of seeds, acid value (AV), iodine value (IV), and smoke point of oils were also determined. Prepared fatty acid methyl esters (FAME) and constituents in unsaponifiable matter were identified and quantified using GC-MS. TGA was performed to assess the thermal behaviour of seed oils. The findings indicated that G. mangostana and G. zeylanica produced higher oil yields of 53.02% and 48.15%, respectively, compared to the other two. The smoke point varies from 202.1 ± 7.1 °C to 229.6 ± 1.5 °C. The AVs range from 4.43 ± 0.56 to 27.35 ± 0.06 mg KOH g⁻¹, while the IVs ranged from 6.62 ± 1.32 to 13.15 ± 0.05 g I₂ per 100 g. The ash content varied from 1.12 ± 0.10% to 4.43 ± 0.10%. The yield of unsaponifiable matter of these oils ranged from 0.33 ± 0.01% to 3.30 ± 0.01%. The major FAs in all the oils were long-chain FAs such as Oleic, Stearic, and Palmitic acids. Garcinia xanthochymus contained the highest amount of Lanosterol, while G. zeylanica contained the highest amounts of Campesterol and γ-Sitosterol. Garcinia morella contained the highest amount of Stigmasterol and Squalene. In conclusion, the findings suggest that all four oils exhibit a high potential for use in both dietary supplements and in the cosmetic industry.
Multi-target inhibitory activity of Salicornia brachiata and Suaeda maritima seed on α-amylase, tyrosinase and lipase
(Postgraduate Institute of Science (PGIS), University of Peradeniya, Sri Lanka, 2023-11-03) Herath, H.M.N.P.; Perera,D.; Jayasinghe, L.; Attanayake,R.N.; Paranagama, P.A.
Diabetes mellitus is a complex metabolic disorder that involves enzymes like α-amylase, tyrosinase, and lipase. Since currently used antidiabetic drugs have undesirable contraindications, plant metabolites, particularly seed-based metabolites, has gained special attention in scientific research as a promising source of enzyme inhibitors. With previous reports of promising activities of Salicornia brachiata and Suaeda maritima, this study aimed to explore the enzyme inhibition potential of extracts derived from the seeds of these two halophytic plant species. The seeds were sequentially extracted using hexane, dichloromethane (DCM), and methanol by cold maceration and tested for in-vitro inhibitory activity against αamylase, tyrosinase, and lipase. The extracts of S. brachiata and S. maritima seeds effectively inhibited α-amylase activity by 52-83% and 18-73%, respectively, at 0.2 mg mL⁻¹. The hexane fraction of S. brachiata showed 83.50 ± 1.09% (at 0.2 mg mL⁻¹) inhibition activity that was not significantly different from the inhibition activity of acarbose, the positive control (at 0.2 mg mL⁻¹ 84.23 ± 0.88%; p=0.05). It is reported that inhibiting this enzyme slows carbohydrate digestion, lowering postprandial glucose levels. DCM fraction of S. brachiata and S. maritima seeds showed tyrosinase inhibitory activity of 57.90 ± 0.84% and 17.80 ± 0.94%, respectively, at 0.2 mg mL⁻¹, whereas Kojic acid, the positive control had an inhibitory activity of 86.00 ± 0.43% (at 0.2 mg mL⁻¹). Since tyrosinase inhibitors are directly involved with melanin biosynthesis, the findings are useful in managing hyperpigmentation caused by oxidative stress in diabetic patients. Moderate inhibition of lipase was observed in the hexane and methanol extracts of S. brachiata seeds (33-38%, at 0.4 mg mL⁻¹), while the DCM fraction showed activity of 54.39 ± 3.40% at 0.4 mg mL⁻¹, comparable to orlistat (60.83 ± 0.22%, at 0.4 mg mL⁻¹ ), the positive control. The three extracts from S. maritima seeds exhibited 36-43% (at 0.4 mg mL⁻¹) inhibition towards lipase, which is important for managing fasting glucose and insulin levels and reducing the risk of obesity-related type 2 diabetes. The obtained results prompt a preliminary conclusion towards the potential use of S. brachiata and S. maritima seeds as multitarget enzyme inhibitors for the modulation of metabolic diseases such as diabetes and associated complications.
Model validation of cu(Ⅱ)- kaolinite systems by in-situ measurement of free metal ion activities
(Postgraduate Institute of Science (PGIS), University of Peradeniya, Sri Lanka, 2023-11-03) Mudannayake, N.; Heenkenda, K.; Weerasooriya, R.
Surface complexation modelling methods are extensively used to quantify the chemical speciation at the mineral-water interface. However, the input parameters are often not uniquely defined. In 1-pK modelling of metal ions adsorption, the basic Stern layer model (1-pK SLM) calculations require six parameters, viz., specific surface area, site density, inner and outer layer capacitance, and intrinsic acidity/binding constants. The number of input parameters by introducing free Cu²⁺ ions as an observation to determine its binding constants was reduced by 1-pK SLM. The copper selective electrode (Cu-ISE) was calibrated using ethylenediamine/Cu²⁺ metal ions buffer to extend the Nernstian Cu²⁺ detection limit to 10-15 M. Spectral data also suggests bidentate complexation of Cu²⁺ with =AlOH⁻⁰‧⁵ and ion exchange complexes between Cu²⁺ and ≡Si-OH sites as follows, ={AlOH}₂Cu⁺ pK = -2.8, (≡SiO₂)Cu⁰ pK= - 8.4 and (--X)₂Cu pK = -2.02. The ISE measurements of free Cu²⁺ seem to interfere with the presence of CuOH⁺, particularly when the solution is pH > 7.0. When the analytical data are corrected for CuOH⁺ interference, the measured {Cu²⁺} of the Cu-kaolinite system is predicted well with 1-pK SLM modelled data. Using this method, the number of input parameters reduced to five while simulating Cu²⁺ - kaolinite interface processes reasonably well is considered a novel method concerning the experiment results. Quantifying chemical speciation at mineral-water interfaces could be done using consistent parameters with reference to the above experiment.
Removal of magnesium ions by functionalized carbon nanotube
(Postgraduate Institute of Science (PGIS), University of Peradeniya, Sri Lanka, 2023-11-03) Kirushnah, A.B.; Sivanayani, S.
Functionalized carbon nanotubes (CNTs) have been extensively studied for various applications, including environmental remediation. One such application is the removal of magnesium ions (Mg2+) from water. The physicochemical characteristics of carbon nanotubes make them suitable for ion adsorption. The functionalization of carbon nanotubes involves modifying their surface properties by attaching different functional groups or molecules to enhance their performance. Magnesium can be removed from water through various treatment processes. In specific industrial applications, such as manufacturing or chemical processes, magnesium in water becomes necessary to ensure the quality and functionality of the products or processes. Carbon nanotubes were synthesized from camphor by chemical vapour deposition at 700 °C.. Carbon nanotubes were characterized and confirmed with SEM, PXRD, Raman spectroscopy, and UV-Vis spectroscopy. Carbon nanotubes thus synthesized were functionalized with carboxylic and hydroxyl groups by using KMnO₄ solution, characterized and confirmed by using FT-IR analysis. The magnesium removal efficiency of functionalized carbon nanotube was examined with different concentrations of magnesium solution such as 1000, 800, 600, 400, and 200 mg L⁻¹ showed removal efficiency 28.3%, 33.4%, 35.5%, 45%, and 57.5%, respectively. Further, it showed increased efficiency with the increased amount of functionalized carbon nanotubes.
Determination of brine shrimp lethality of different solvent extracts of soft stems of different banana (Musa sp.) cultivars
(Postgraduate Institute of Science (PGIS), University of Peradeniya, Sri Lanka, 2023-11-03) Liyadipitiya, L.R.M.K.N.; Marikkar, J.M.N.; Jayasinghe, U.L.B.
Banana stems are a waste product once the fruit bunches are harvested, and they have also lost their significance among the current generation due to the lack of awareness of their values. In this study, the soft stems of the Ambulkesel, Seenikesel, Suvandel, and Alukesel cultivars of the Musa sp. (banana plant) were investigated for their brine shrimp lethality effect against Artemia salina nauplii. Powdered soft stems of four cultivars were sequentially extracted with dichloromethane (DCM), ethyl acetate (EtOAc), and methanol (MeOH). The crude extracts were tested for brine shrimp lethality (BSL) using A. salina nauplii of the second instar. This work used seawater and 1% dimethyl sulphoxide (DMSO) as the negative control and potassium dichromate (K₂Cr₂O₇) as the positive control. The soft stems of four banana cultivars showed moderate toxicity (LD₅₀ ˂ 2000 mg L⁻¹) toward A. salina, according to the results of the BSLA, while the overall lethality percentage was discovered to be dose-dependent of the crude extract within the chosen range of 62.5–2000 mg L⁻¹. The toxicity properties of DCM, EtOAc, and MeOH extracts of these soft stems showed LD50 values ranging from 891.1-1071.4 mg L⁻¹, 1246.8-1428 mg L⁻¹, and 696.5-822.2 mg L⁻¹, respectively. The DCM crude extracts of banana soft stems of the Ambulkesel, Seenikesel, and Alukesel cultivars and the MeOH extracts of all four cultivars showed toxic activity against the second nauplii of A. salina in accordance with literature, that classified crude extracts and pure substances into toxic (LD₅₀ value 1000 mg L⁻¹) and non-toxic (LD₅₀ > 1000 mg L⁻¹). The BSL assay showed that the most active fraction is the methanol fraction of the Seenikesel cultivar, with an LD₅₀ value of 696.5 mg L⁻¹ . Compared to potassium dichromate, DCM and MeOH extracts of four cultivars displayed moderate toxicity against A. salina. No lethality percentage was detected in the negative control. The LD₅₀ values of soft stems of banana plant extracts to brine shrimps indicate the presence of potent components, which will be explored further.
Assessment of cytotoxicity of selected edible leafy plants of Sri Lanka
(Postgraduate Institute of Science (PGIS), University of Peradeniya, Sri Lanka, 2023-11-03) Ulpathakumbura, B.S.K.; Marikkar, J.M.N.; Jayasinghe, U.L.B.
This study was carried out to assess the cytotoxicity of extracts of leafy plants, namely Premna procumbens Moon (Le-kola pala: LE), Memecylon umbellatum (Kora kaha: KK), Polyscias scutellaria Fosberg (Koppa: KO), Stevia rebaudiana Bertoni (Stevia: ST) and Atlantia ceylanica (Yaki naran: YK) using brine shrimp (Artemia salina) lethality bioassay. According to traditional knowledge, these plants may be believed to have medicinal properties. However, scientific evidence is scarce on their biological properties. Therefore, these plants were selected to assess their cytotoxic property. Plant leaves were sequentially extracted with hexane, ethyl acetate (EtOAc), and methanol (MeOH) as solvents. Brine shrimp eggs were hatched and the active nauplii were used in the bioassay. The cytotoxicity of plant extracts was reported as lethal concentration (LC₅₀). A concentration series (62.5-2000 mg L⁻¹) of crude extracts was prepared by dissolving the crude plant extracts in artificial seawater. Ten active nauplii were added to each 1 mL of extract in 24 well semi microplate and kept at room temperature for 24 h under illumination. The lethal concentration (LC₅₀) was determined by counting surviving nauplii after 24 h. Among hexane extracts, the strongest cytotoxicity was observed for YK (LC50 = 190.98 ± 4.92 mg L⁻¹), while KO and ST showed moderate cytotoxicity with LC₅₀of 500.00 ± 0.00 mg L⁻¹ and 1724.70 ± 80.65 mg L⁻¹, respectively. No cytotoxicity was observed for hexane extract of LE and KK. Among EtOAc extracts, the strongest cytotoxicity was displayed by YK (LC₅₀ = 234.18 ± 13.79 mg L-1), while lower cytotoxicity potential was observed for KO and ST. EtOAc extracts of LE and KK did not show any cytotoxicity. All MeOH extracts showed moderate to weak cytotoxicity. Among them, the strongest activity was observed for KO (LC₅₀ =486.16 ± 30.23 mg L⁻¹). When compared with all plant extracts, the positive control (K₂Cr₂O₇) showed significantly (p < 0.05) higher cytotoxic activity (LC₅₀ = 14.62 ± 0.87 mg L⁻¹). This study concludes that YK and KO have higher cytotoxicity when compared to other leafy plants. Therefore, YK and KO maybe sources of anti-cancer compounds and can have the potential to be used to develop drugs against cancers.
A nano gravimetric approach to study the photocatalytic activity of nano titania thin films
(Postgraduate Institute of Science (PGIS), University of Peradeniya, Sri Lanka, 2023-11-03) Manuda, K.R.J.; Fernando, N.L.; Nissanka, B.; Tillekaratne, A.; Jayasundara, D.R.
Self-cleaning photocatalytic nanocoatings have garnered considerable attention due to recent global public health crises, such as the COVID-19 pandemic. Nevertheless, most of the evaluations validating the efficacy of such coatings have focused on solid-liquid interfaces. There is a scarcity of real-time, in situ information that sheds light on the photocatalytic degradation occurring on titania thin films at the solid-air interface. In this particular investigation, a titania nanocoating was fabricated on a gold surface of a quartz crystal microbalance (QCM) sensor using a spin coating technique. To serve as a representative organic molecule, methyl orange (MO), a potent environmental pollutant, was added to these nanocoatings. Subsequently, the sensor was subjected to ultraviolet (UV) light irradiation while continuously monitoring the mass changes at the solid-air interface in real-time. Results indicated that when the mass of the dye was lower than approximately 3% of the mass of the catalyst, MO could be photocatalytically degraded in approximately six hours of continuous UV irradiation. Conversely, higher MO loadings only exhibited partial degradation. The morphology and elemental compositions of the QCMs were characterized before and after irradiation using Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Spectroscopy (EDX), and X-ray Photoelectron Spectroscopy (XPS). This study offers ample comprehension and profound insight into the molecular-level phenomena taking place during photocatalytic degradation at the solid-air interface, thereby enabling successful modelling and evaluation of the effectiveness of self-cleaning photocatalytic coatings.
Titanium / titanium dioxide schottky junction and highly photoactive antimony sulphide photoanode for solar water splitting
(Postgraduate Institute of Science (PGIS), University of Peradeniya, Sri Lanka, 2023-11-03) Wijerathna, C.N.; Bandara,J.
Artificial photosynthesis has emerged as a promising solution for producing sustainable chemical fuels, including hydrogen, to address the energy and environmental challenges associated with non-renewable energy sources like fossil fuels. Among the various approaches, photoelectrochemical water splitting, mainly based on metal oxide semiconducting materials, has garnered significant attention. These materials offer suitable band gaps, flat band potentials, low electrical resistance, and excellent corrosion resistance in aqueous solutions, making them ideal for achieving efficient solar conversion efficiency. One such material of interest is Ti/TiO₂ nanotube arrays (TNTA) Schottky junction, which is synthesized through electrochemical anodization. This has captured considerable scientific interest due to their simplicity in synthesis, high electron mobility, and controllable dimensional parameters. By employing a facile electrochemical synthesis strategy on a porous Ti metal sheet, the TNTA Schottky junction is synthesized. To enhance its performance further, the concept of an n/n heterostructure is introduced by coating the TNTA photoanode with an n-type stibnite (Sb₂S3) layer. Sb₂S₃ is selected for its suitable band gap position and high visible light response. In this study, it was demonstrated that incorporating a thin layer of Sb₂S₃ significantly enhances the photoelectrochemical response of the TNTA Schottky junction. The highest photoelectrochemical response of 2.81 mA cm⁻² was achieved for the TNTA/Sb₂S₃ photoanode under AM 1.5 G illumination at 0.8 V vs. RHE in a 0.5 mol dm⁻³ Na₂SO₃ aqueous solution. Notably, this response is more than ten times greater than that observed for the bare TNTA photoanode. The improved performance has been attributed to several factors, including a lower recombination rate of photogenerated charge carriers, broadened spectral response, and enhanced charge transfer/transport occurring at the solid/liquid interfaces facilitated by the morphology of TiO₂ and incorporation of Sb₂S3.
Development of an electric vehicle for the differently abled with solar assist
(Postgraduate Institute of Science (PGIS), University of Peradeniya, Sri Lanka, 2023-11-03) Mohamed, E.S.; Kaviraj, K.; Niroshan,T. S.
A wheelchair is a necessary assistive device for differently abled people to improve their independence, mobility, and quality of life. Manual wheelchairs suffer a huge mechanical efficiency loss with the risk of discomfort and damage to the upper limbs and spine. The best way to overcome the imperfection in mechanical working is to find an alternative using electricity with mobility impartments. A survey-based study suggests that the differently abled suffer in handling the joysticks, thus, reluctance towards such power sources. Indeed, this work is concerned with improving the travelling distance using a solar assist system while introducing a smartphone-based controlling mechanism with the modified version of the joystick application. A research gap has been identified regarding portability while powering them two modes. The difficulties in handling the joystick are also clearly addressed using Bluetooth data transmission. The project aims at achieving a maximum velocity of 12 km/h with solar assist and smartphone control. In construction, a manual wheelchair with an adjustable backrest has been chosen, and a solar panel has been mounted as a roof while incorporating a 24 V motor. The mathematical calculations revealed that the system requires 355 W of motor power and 25 Nm torque while producing 133 rpm. The developed unit has been tested for power usage: battery power alone and dual-powered mechanisms. The maximum speed achievable at the given condition was reported as 8 km/h. The system could cover 24 km using the battery power source and 27 km using both the battery and solar assist. The unit achieved an improved range with the dual-source power supply, thus covering nearly 3 km of additional range compared to a system powered by battery only. This confirms that the power from solar increased the travelling distance while making portable and easily dismantlable solar panel frames. The major limitation noted is the time of charging. It is suggested to investigate improving the charging potentials. Overall, the present study provides an effective method of expanding motorized wheelchair travelling distance. The research suggests the importance of maintenance due to the chain transmission system. Moreover, it opens the area for more investigation in terms of minimizing the weight of the system.
Impact of habitat type and floral resource availability on ground-nesting bee establishment in an agro-natural landscape
(Postgraduate Institute of Science (PGIS), University of Peradeniya, Sri Lanka, 2023-11-03) Ekanayake, E.M.D.; Karunaratne, W.A.I.P.; Jayasuriya, K.M.G.G.; Hemachandra, K.S.; Karunarathna4, A.K.
In agroecosystems, ground-nesting bees are crucial for efficient pollination. Ground-nesting bees are susceptible to habitat degradation and resource loss. Habitat destruction has a negative impact on the bee pollination. The effect of changes in habitat and resource availability on ground- nesting bee species composition remains poorly understood. The present study investigates how changing habitat and floral resources affect the species composition of ground-nesting bees. The research was conducted at Meewathura Farm in Peradeniya, where three distinct habitats were established: peripheral weedy, crop, and ornamental habitats. The ground nests of bees and their species, along with floral resources (number of open flowers), were recorded weekly during three developmental stages of the crop in two consecutive years (2021-2023) during the Yala and Maha seasons. Six ground-nesting bee species: Lasioglossum serenum, Leuconomia sp., Lipotriches exagens, L. edirisinghei, L. pulchriventris, and Patellapis kaluterae, (F: Halictidae) were identified. Ground-nesting bee species composition significantly differed among habitats (p = 0.0001). Results revealed that ground-nesting bees were more likely to nest within crop habitats (328 nests) than in peripheral weedy and ornamental habitats (269 and 244 nests, respectively). A weak but significant positive correlation existed between ground nests and their species richness with open flower abundance (R² = 0.230, R² = 0.197, respectively). Significant variations in ground nests and ground-nesting bee species richness were observed across seasons and years (p = 0.0001). Ground-nesting bee species composition varied with floral resources, habitats, seasons, and years, but these factors interacted negatively. A high proportion of bare grounds in crop habitats serve as dwellings for ground-nesting bee establishments. This study highlights the importance of habitat types and resource availability to promote the coexistence and composition of ground-nesting bees, thus maintaining their vital role as pollinators in agroecosystems.
Pantala flavescens (wandering glider) and Ceriagrion coromandelianum (yellow waxtail) as predators of preimaginal stages of aedes aegypti (diptera: culicidae) in fresh and brackish water habitats from Jaffna,Northern Sri Lanka.
(Postgraduate Institute of Science (PGIS), University of Peradeniya, Sri Lanka, 2023-11-03) Arthiyan, S.; Tharsan, A.; Eswaramohan, T.; Surendran, S.N.
The present study aimed to report the efficiency and the potential use of natural predators as biological control agents to control the preimaginal stages of primary dengue vector Aedes aegypti in the Jaffna peninsula as preliminary research. Nymphal stages of dragonfly Pantala flavescens and damselfly Ceriagrion coromandelianum were collected from local ponds. They were acclimatized to the freshwater (0 ppt /g L⁻¹) and brackish water (10 g L⁻¹) to conduct the experiments against the standard laboratory colonies (0 g L⁻¹ and 10 g L⁻¹) of mosquito Ae. aegypti. The experiment was conducted in triplicates and repeated thrice with different individual predators. Hundred, third instar larva of Ae. aegypti were introduced, and the predatory activity was recorded every 24 hours up to 72 hours. The prey density was maintained by replenishing the same number of larvae. The predatory rate (PR), predatory impact (PI), and clearing rate (CR) were calculated for both predators for both salinities. The results indicated that both predators show promising efficacy in controlling the mosquito larvae, where the clearing rate of the P. flavescens was significantly high (p < 0.05) over C. coromandelianum in both freshwater (p = 0.0003), and brackish water (p = 0.0003) experiments, and the predatory impact and the predatory activity were also exhibited considerably high in the dragonfly P. flavescens both in the freshwater and brackish water environments. The damselfly C. coromandelianum shows an increasing trend in its clearing rate of prey over time, with slight variations based on salinity. The preliminary results of the study suggest that these natural predators could be introduced as a green solution to control the preimaginal stages of mosquito species in both freshwater and brackish water habitats, and this could potentially aid in reducing the prevalence of dengue and other mosquito-borne diseases in coastal areas like Jaffna Peninsula.
Risk factors of Dengue hemorrhagic fever among adult dengue patients in the Western Province of Sri Lanka: a case-control study
(Postgraduate Institute of Science (PGIS), University of Peradeniya, Sri Lanka, 2023-11-03) Jayasinghe, C.D.; Deerasinghe, D.S.A.F.; Tissera, K. H.; Wijewikrema, A.
Dengue infection has spread rapidly within countries and across regions in the past few decades, resulting in an increased frequency of epidemics. Infection with any of the dengue virus (DENV) serotypes may result in a broad spectrum of clinical symptoms ranging from a mild flu-like syndrome, dengue fever (DF), to the most severe forms of the disease, dengue hemorrhagic fever (DHF), with coagulopathy and permeability. The signs and symptoms of DHF usually arise late in the disease course when the fever has subsided, making it difficult to predict. Hence, identifying risk factors that accurately predict progress to DHF would significantly contribute to implementing proper intervention and treatment strategies for those at greater risk. This case- control study included 136 adult DHF patients (18 years and above) as cases and 136 DF patients (18 years and above) as controls from four leading hospitals of the Western Province in 2022 to identify the independent risk factors of DHF among adult dengue patients. Participants were recruited for the study by applying consecutive sampling techniques, and independent risk factors under the categories of socio-demographic, clinical and serological were assessed using a questionnaire survey with informed consent. Chi-square and binary logistic regression were performed to identify potential risk factors. Though 20 factors were significant in the bivariate analysis, when the logistic regression was performed to adjust the confounding effect, only six independent predictors showed significant associations with the DHF patients compared to DF patients: Demographic factors such as belonging to other ethnic groups (Tamils, Muslims, Burghers) compared to Sinhalese (aOR = 0.143, 95% CI: 0.043 – 0.470), clinical manifestations; such as abdominal pain (aOR = 3.172, 95% CI: 1.381– 7.285), altered consciousness/ confused state (aOR=8.395, 95% CI: 1.527 - 46.161), systolic blood pressure on admission (aOR=1.014, 95% CI: 1.002-1.027), right hypochondrial tenderness (aOR= 10.839, 95%CI: 3.063 - 38.347), and laboratory characteristics; serum creatinine on admission (aOR= 1.028, 95%CI: 1.018 - 1.038) were identified as significant risk factors of progression of DHF of adult patients (p<0.05). Collectively, the results of this study strengthen the understanding of the risk factors of DHF adult patients of the Western Province in Sri Lanka that could be identified from the patient's clinical parameters and by results of low-cost routine laboratory investigations.

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