RESCON 2022

Permanent URI for this collectionhttps://ir.lib.pdn.ac.lk/handle/20.500.14444/5952

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Photovoltaic performance of dye-sensitized solar cells fabricated with cellulose acetate nanofiber-based gel electrolyte
(Postgraduate Institute of Science (PGIS), University of Peradeniya, Sri Lanka, 2022-10-28) Hettiarachchi, M.S.H.; Dissanayake, M.A.K.L.; Senadeera, G.K.R.; Jaseetharan, T.; Umair, K.
Polymer nanofibers have emerged as scientifically intriguing novel materials where that can perform extraordinarily well with their unique chemical and physical properties. Electrospinning has become one of the simple and versatile methods to produce nanofibers, and electrospun polymer nanofibers can be applied in dye-sensitized solar cells (DSSCs). In contrast to conventional liquid electrolytes, which inherently lack long-term stability and suffer from electrolyte evaporation and liquid leakage, electrospun polymer nanofiber membrane-based quasi-solid-state gel electrolytes have offered a promising alternative. The quasi-solid-state gel electrolyte, made by trapping an electrolyte solution within a three-dimensional polymer nanofiber matrix, exhibits almost liquid-like ionic conductivities while offering better mechanical strength by a non-flowing electrolyte medium. In the present study, cellulose acetate (CA) nanofiber gel electrolyte-based DSSCs were fabricated. Their photovoltaic performance was investigated as a comparative study with conventional liquid and gel electrolyte-based DSSCs. Scanning electron microscopic images showed a porous membrane containing ultra-thin polymer nanofibers with an average diameter of 180 nm. In order to prepare quasi solid-state gel electrolyte, the CA nanofiber membrane was soaked with the liquid electrolyte prepared by dissolving iodine (I2), tetrapropylammonium iodide (Pr4NI), potassium iodide (KI) in ethylene carbonate (EC) and propylene carbonate (PC) co-solvent system. The photovoltaic parameters of DSSCs with nanofiber gel electrolyte show an efficiency of 6.06%, a short circuit current density (Jsc) of 13.9 mA cm⁻² under the simulated sunlight of 100 mW cm⁻² (1.5 AM). This efficiency value lies in between those of conventional liquid and gel electrolyte-based DSSCs exhibiting efficiencies of 6.53% and 5.50%, respectively. This study suggests that CA electrospun nanofiber gel electrolyte-based DSSC offers a possible alternative to obtain higher efficiencies than those of conventional gel electrolyte-based DSSCs while providing sufficient stability compared to the liquid electrolyte-based solar cells.
Experimental and theoretical investigation on photocatalytic hydrogen production from water/methanol solutions by cuprous oxide and cupric oxide composite catalyst
(Postgraduate Institute of Science (PGIS), University of Peradeniya, Sri Lanka, 2022-10-28) Perera, J.S.; Dissanayake, D. P.
Water can be split into hydrogen and oxygen by using semiconductor metal oxide photocatalysts and solar energy. This is a clean and inexhaustible energy source, as both water and sunlight are plentiful. The goal of the present investigation was to generate hydrogen by photo-splitting water using a cuprous oxide-based nano photocatalyst. Using the hydrothermal methodology, a series of Cu₂O/CuO photocatalysts were produced by altering the processing conditions. The efficiency of the photocatalytic activity of the synthesized catalyst was studied using methanol/water (40/60%) mixtures. It was observed that the photocatalytic activity initially increased with increasing Cu₂O content in the catalyst and then decreased. According to XRD characterization of the catalysts, it was observed that the catalyst with the Cu₂O/CuO molar ratio of 68/32 has the highest photocatalytic activity (i.e., the most efficient gas evolution under illumination). A theoretical study was carried out to understand the role of Cu2O in the photocatalytic process. The catalyst surfaces were modelled using the Quantum Espresso Suit of software and the graphical user interface of the same “BURAI”. Density functional theory calculations were conducted using Perdew-Burke-Ernzerhof exchange-correlation (PBE) ultra-soft pseudopotentials. The efficiency of adsorption of the molecules of interest, i.e., H₂O, CH₃OH, H₂ and CO₂, on Cu₂O (111) and CuO (111) surfaces was investigated by calculating the adsorption energies. The theoretical investigation revealed that hydrogen adsorption on Cu₂O (111) is ~49 times stronger than that on CuO (111). Also, the Cu₂O (111) surface is more hydrophilic than CuO (111). Formation of CuO (111) on Cu₂O (111) surface may impart the desired properties by minimizing the adsorption of H₂ and thereby minimizing its dissociation. This would have improved the photocatalytic activity of the Cu₂O (111)/CuO (111) composite surface.
Micro-pattern transfer using epoxy-resin compound as an alternative to poly-dimethylsiloxane
(Postgraduate Institute of Science (PGIS), University of Peradeniya, Sri Lanka, 2022-10-28) Senarathna, W.D.G.M.; Jayawardhana, S.
Lithographic techniques provide tools with which micro-nano patterns can be transferred from one surface to another. This is highly beneficial in fields such as the development of superhydrophobic surfaces, semiconductors, and microfluidic devices. Soft lithography is an increasingly popular sub-technique that enables the replication of microstructures to and from flexible membranes, materials, and surfaces. Nevertheless, polymer double casting is a cumbersome procedure requiring additional treatment for anti- adhesion of the moulds and replicates. Here, we present an alternative material using commercially available epoxy resin for soft lithographic nano/micro-scale patterning. The negative mould was created by mixing the silicon and catalyst materials at a ratio of 100:2 by weight and allowed to dry. The epoxy resin was then mixed with the hardener at a ratio of 3:1 by weight and poured into the negative mould. The hardened epoxy resin was later peeled off to obtain the replication. The process was demonstrated using three natural plant species as master templates. They were taro (Colocasia esculenta), lotus (Nelumbo nucifera) and canna (Canna coccinea). The nano/microstructures of natural leaves and their replicates were characterized using scanning electron microscopy and contact angle measurements. It is crucial to notice that the non-wetting properties of the replicates were significantly lower than their original counterparts. Nonetheless, a comparison of the surface images revealed that the micro pattern of the original sample had been successfully transferred to the replicate. The replication approach presented here represents a simple and economical alternative method for the micro-replication of natural surface structures.
Single-stage vertically aligned carbon nanotubes (vacnts) synthesis by pyrolysis of ferrocene and acetylene
(Postgraduate Institute of Science (PGIS), University of Peradeniya, Sri Lanka, 2022-10-28) Wijerathne, G.D.G.D.P.; Sewwandi, B.V.N.; Kumarasinghe, A.R.
Carbon nanotubes (CNTs) have drawn much interest in material science due to their unique structure and extraordinary properties. Among different morphologies of CNTs, vertically aligned carbon nanotubes (VACNTs) are a fascinating class of nanomaterials that are highly dense and well-oriented along their longitudinal axis. For the fabrication of CNT macrostructures with morphologies ranging from network to aligned structures, the floating catalyst chemical vapour deposition (FC-CVD) technique is more successful and favourable than the conventional CVD methods. This study represents an effective method for synthesizing VACNTs using a novel single-stage FC-CVD process with high CNT yield, low cost, and facile fabrication. FC-CVD process was carried out by pyrolysis of ferrocene and acetylene at the temperature of 850 0C under a stream of Nitrogen (flow rate of 200 sccm) and Hydrogen (flow rate of 50 sccm). This single-stage FC-CVD approach has a substantial potential to produce VACNTs on a large scale compared to the traditional multi-stage assisted FC-CVD process. The as-grown CNTs were collected separately from the Si/SiO2 wafer, silicon wafer, and the inner walls of the quartz furnace. The morphology and structure of the as-grown CNTs were investigated by SEM, Raman, and XRD. The formation of dense VACNT arrays was observed on the inner walls of the quartz furnace and silicon wafer under optimized conditions where 0.4 g of ferrocene and an acetylene flow rate of 100 sccm were used for a growth period of 30 minutes. CNT bundles with an average diameter of 70 nm and 90 nm with vertical heights of 170 μm and 9 μm were found on the quartz and silicon wafer surfaces, respectively. Steric effects and Van der Waals repulsive interactions led to the arrangement of dense vertical alignment. More randomly-oriented CNTs with varying diameter distribution were also observed on the Si/SiO2 substrate. It revealed the dependency of the surface properties on the formation of CNTs with a distinct morphology. XRD and Raman studies showed that as-grown VACNTs are well-graphitized and indicated that the graphite structure resembles MWCNTs.
Investigation of size-tunable non-catalytic carbon spheres by varying growth parameters in chemical vapor deposition
(Postgraduate Institute of Science (PGIS), University of Peradeniya, Sri Lanka, 2022-10-28) De Silva, T.G.T.K.; Sewwandi, B.V.N.; Kumarasinghe, A.R.
Carbon is a unique, life-forming element that can create various structures. These structures obtained from carbon have gained popularity in the scientific field due to their remarkable properties. Among them, the carbon sphere (CS) is a synthetically formed carbon structure that has attracted recent attention due to its applications in energy-storing devices, adsorption, and nanocomposites. In this study, NCS (Non-catalytic Carbon Spheres) in size range of 0.2-1.4 μm were produced via Chemical Vapor Deposition (CVD) through pyrolysis of acetylene in a nitrogen atmosphere. The effect of collector material in CVD, reaction time (30 – 90 min), deposition temperature (800 – 1100 °C), and precursor mass flow rate (at the constant ratio of C2H2/N2) on the morphology (diameter) of the NCS produced using CVD was investigated. The characterization of the as-synthesized NCS was done through Scanning Electron Microscopy (SEM), Raman Spectroscopy, X-ray Diffraction (XRD), and Fourier Transform Infrared Spectroscopy (FTIR). SEM results showed that the size of the NCS particles depends on the reaction time and temperature but not on the mass flow rates of the precursor gasses at a constant ratio. The collector material in CVD showed a substantial effect on the size of the spheres, possibly due to the surface roughness of the substrates and the differences in the nucleation rates. The NCS with the lowest dimensions (~364 nm) of uniform sphericity were collected from the thermal blocks of the CVD. The XRD and Raman spectroscopy results of the NCS grown on the thermal block showed the characteristic graphitic peaks of the carbon structures, which confirmed the existence of graphitized hexagonal carbon networks. FTIR analysis of the NCS indicated that their surface consists of hydroxyl, carbonyl, and carboxylic functional groups. The presence of these groups in NCS would be an advantage when using them for their potential applications.
Investigation of palmyrah (Borassus flabellifer l.) nutshell derived activated carbon for removal of nitrates from groundwater
(Postgraduate Institute of Science (PGIS), University of Peradeniya, Sri Lanka, 2022-10-28) Mayurika, M.; Prabagar, J.
Nitrate is one of the most worldwide contaminants due to its tendency to leach from soil to water, polluting drinking water resources, especially groundwater. The effect of nitrate on human health is described as primary toxicity, causing methemoglobinemia (blue baby syndrome), tumours and gastrointestinal cancers. The WHO has set the maximum contaminant level of 50 mgL⁻¹ nitrates in drinking water. Therefore, this research was conducted to remove nitrate ions from groundwater using citric acid-activated carbon developed from palmyrah nutshells. The advantage of using this activated carbon made from palmyrah nutshell is that it can act as an absorbent like coconut shell and is available as waste material in South Asian countries. The palmyrah nutshells were cleaned, dried in the sun, and carbonized in a muffle furnace at 500 °C for 2 h. The chemical activation of carbon of the carbonized product was performed using citric acid with the impregnation ratio of carbon: citric acid at 1:2 at 30 °C for 24 h. The resulting slurry was washed with deionized water to neutral pH, dried at 110 °C for 8 h, and the activated carbon was obtained. This activated carbon was characterized for different physical and chemical parameters using standard Association of Official Analytical Chemists methods. Moisture, ash, fixed carbon, pH and bulk density were determined, and the values obtained were 4.0%, 3.5%, 75.2%, 6.83 and 0.64 g cm⁻³, respectively. The nitrate removal efficiency was estimated at different pH values of 2, 4, 6, 8 and 10 by varying adsorbent dosages of 2, 4, 6, 8 and 10 gL⁻¹ at the equilibrium contact time of 1, 2, 3, 4 and 5 h based on the concentration of adsorbed nitrate ion by palmyrah nutshell activated carbon. The results revealed that the maximum nitrate adsorption of 82.8% was found to be at the pH of 6 with the adsorbent dosage of 6 gL⁻¹ and with a contact time of 3 h. At the pH of 6, the maximum amount of nitrate ions was adsorbed by the electrostatic interaction between the positive charge of the adsorbent and nitrate anion. In the pH range from 4 to 10, the maximum percentage of nitrate removal was achieved, while this percentage slightly decreased at pH 2. Nitrate removal showed an increasing trend from pH 2 to 6, and it decreased afterwards. This may be due to the presence of positive adsorption sites that favours nitrate adsorption and then OH− ions that compete for the same adsorption sites. The results revealed that the activated carbon effectively reduced the nitrate content in groundwater below the permissible limits; hence, the activated carbon derived from palmyrah nutshells can be successfully applied in water treatment technologies to control the nitrate content.
Fabrication of precipitated calcium carbonate (PCC) based superhydrophobic gloves from Sri Lankan dolomite
(Postgraduate Institute of Science (PGIS), University of Peradeniya, Sri Lanka, 2022-10-28) Dilhani, K.G.S.S.; Karunaratne, D.G.G.P.; Manipura, A.
Manufacturing bioinspired superhydrophobic covering on natural rubber gloves surface from Sri Lankan dolomite as a value-added process to local dolomite. In this study, we introduce a simple and effective method to synthesize superhydrophobic coating on glove surfaces using superhydrophobic precipitated calcium carbonate nanoparticles (nPCC) using dolomite as the raw material. Sodium stearates were used as a binder, while fatty acid was used to improve the superhydrophobicity. nPCC suspension was made with ethyl acetate, and it was applied on the glove surfaces via spray coating and dip coating methods. The products were subjected to scanning electron microscopy (SEM) to identify the morphology of nPCC and coating. SEM images confirm the presence of nano coating on PCC (1-100 nm) and on the glove surface (200 nm). Fourier Transform Infrared Spectroscopy (FTIR) was used to identify functional groups on surface coating, which confirmed the presence of stearates, ethyl acetate and fatty acid on the glove surfaces, while water contact angles were measured using a drop shape analyzer. In spray coating methods, obtained contact angles on glove surfaces were 142° for stearic modified and 144.5 ° for stearic\fatty acid- modified coating. It was 154.7° for dip coating methods. According to the results, stearates and fatty acids improve superhydrophobicity, while ethyl acetate gives a uniform nanoparticle suspension. Among the coating methods compared, spray coating gave a uniform coating on the glove surface.
9.4% Efficiency of a quasi-solid-state dye-sensitized solar cell under low light irradiance
(Postgraduate Institute of Science (PGIS), University of Peradeniya, Sri Lanka, 2022-10-28) Gunathilake, S.M.S.; Bandara, T.M.W.J.; Pemasiri, B.M.K.
To convert highly abundant solar energy to electricity, low-cost dye-sensitized solar cells (DSCs) have attracted researchers' attention. Solar cells do not receive constant irradiance throughout the day when used in real outdoor applications. The efficiency of Si solar cells decreases with decreasing irradiance. However, very few studies have focused on studying the performance of DSCs as a function of light intensity. The present research is focused on improving gel polymer electrolyte-based DSCs and studying their performances under variable irradiance. The cells were fabricated with photoelectrodes having six spin- coated TiO2 layers photo-sensitized by N719 dye. The counter electrode was a piece of Pt-coated glass, and the gel polymer electrolyte contained binary salts tetrahexylammonium iodide and lithium iodide. Performance enhancers, 4-tert-butyl pyridine and 1-methyl-3-propylimidazolium iodide, were added to maximize the efficiency of the cell. In addition, the cell's performance was enhanced by the infusion of graphene into the fourth layer. The fabricated DSC was irradiated using Peccell PEC-LO1 solar simulator, and the irradiation level varied from 1,000 W m⁻² to 67 W m⁻², changing the distance from the solar simulator to the cell. To the best of our knowledge, this is the first study of the light intensity dependence of efficiency in graphene-incorporated DSCs. The fabricated quasi-solid-state DSC performed at an overall maximum efficiency of 6.8%, an open-circuit voltage of 770 mA, a short circuit current density of 13.4 mA cm⁻² , and a 66.3% fill factor under 1,000 W m⁻² irradiation. The efficiency and fill factor of the DSC increased gradually with the decreasing solar irradiance. The DSC achieved maximum efficiency and fill factor of 9.4 and 83.3%, respectively, at 67 W m⁻² of input solar irradiance. The present study concludes that the efficiency and fill factor of graphene-added DSC increase with the decrease of solar irradiance. Lower efficiencies at higher irradiance relate to the transport limitation of the redox mediator in such cells.
NMDA and trpv1 receptors: potential therapeutic targets of paspanguwa herbal formula
(Postgraduate Institute of Science (PGIS), University of Peradeniya, Sri Lanka, 2022-10-28) Gunaratne, J.C.; Uduwela, D.R.; Ranatunga, R.J.K.U.
Despite the broad use of cough (antitussive and expectorant) medicine, there is little evidence for its clinical use. Dextromethorphan is a widely used antitussive that is considered effective by the U.S. Food and Drug Administration. N-methyl D-aspartate (NMDA) receptors are the therapeutic target of dextromethorphan. The transient receptor potential vanilloid 1 (TRPV1) receptor stimulates the cough reflex and has recently been identified as a potential drug target for treating cough. We hypothesize that the mechanism of the anti- cough effects of paspanguwa, an ayurvedic herbal drink, is due to inhibiting NMDA and TRPV1 receptors.This study aimed to identify natural products in the formula that bind favourably to the active sites of the receptors. Twenty-three natural products from paspanguwa were examined. The cryo-EM structures of NMDA receptor (PDB 7eu7) and TRPV1 receptor (PDB 3J5P) were used as receptor coordinates. AutoDock Vina was used for molecular docking at four active sites: glycine-binding site, glutamate- binding site and the ion-channel of NMDA, and the active site of TRPV1 receptor. Diosgenin, solasodine and tomatidenol showed the highest binding affinity to both the glutamate-binding site and glycine-binding site; the affinity well above that of references indicates the possibility of these natural products acting as NMDA antagonists and non-competitive antagonists. Diosgenin, tomatidenol, and oleanolic acid showed the highest affinity to the NMDA channel; an affinity higher than that of references indicates the ability to act as better channel blockers. At the active site of TRPV1, solasodine, diosgenin, and tomatidenol showed binding affinity on par with the references, indicating that they might act as TRPV1 antagonists. Findings from the study show that natural products from paspanguwa bind to active sites of NMDA and TRPV1 receptors. The reported anti-cough properties of the formula may, at least in part, be due to inhibiting NMDA and TRPV1 receptors.
Commiphora wightii gum extract mediated synthesis of silver nanoparticles and their bactericidal efficacy
(Postgraduate Institute of Science (PGIS), University of Peradeniya, Sri Lanka, 2022-10-28) Wickramarathne, C.; Rajapakse, S.; Seneviratne, V.N.
Nanobiotechnology is an important division in nanotechnology that involves various biological entities for nano-synthesis. Silver nanoparticles (AgNPs) received tremendous attention owing to their versatile and promising properties and their wide range of applications. Moreover, nano-synthesis using plants is a promising approach among other biological sources because of the presence of the high amount of phytochemicals and the feasible procedures required in nano-synthesis. However, AgNP synthesis by incorporating Commiphora wightii (guggul) plant gum is not attempted previously. C. wightii, belonging to the family Burseraceae, is used in ayurvedic medicine due to its anticancer, antimicrobial and anti- inflammatory properties. The objective of this study was to green synthesize AgNPs using the gummy extract of C. wightii in a feasible, cost-effective and environmentally-friendly manner and evaluate their bactericidal efficacy. AgNPs were fabricated by the addition of C. wightii extract to AgNO3 while stirring and heating. Bactericidal efficacy was determined against Escherichia coli and Staphylococcus aureus using the standard Kirby-Bauer Disk diffusion method. A rapid colour transformation was observed from light brown to deep brown indicating AgNP formation, and it was confirmed by a characteristic band at 427 nm. X-Ray Diffraction patterns revealed the crystalline nature and the Face Centred Cubic structure of AgNPs. Moreover, Transmission Electron Microscopic analysis highlighted well-dispersed spherical AgNPs around 5-20 nm. Fourier Transform Infra-Red spectra revealed the presence and involvement of functional groups of steroids, flavonoids, terpenoids, carbohydrates etc. C. wightii gummy extract alone and AgNPs synthesized using gummy extract showed antibacterial potential against both E. coli and S. aureus. The diameters of zones of inhibition were 12.56±0.35 nm and 10.27±0.25 nm for E. coli and S. aureus, respectively. Therefore, this method was an effective, single-step green synthetic approach for the synthesis of stabilized AgNPs and bactericidal efficacy for both bacterial gram classes proposes their applicability in biomedical utilities. Moreover, further modifications of this green procedure must be carried out before any industrial-scale production and applications.
Milk protein composition in different lactation stages of dairy cattle grazing on saltmarsh pastures in Mannar, Sri Lanka
(Postgraduate Institute of Science (PGIS), University of Peradeniya, Sri Lanka, 2022-10-28) Kumari, G.M.M.; Navaratne, A.N.; Ranawana, K.B
Cow milk is a nutrient-rich dairy product which has high demand worldwide. Improving local dairy production is essential to overcome malnutrition in the Sri Lankan population hit by the current food crisis. Cow milk is a vital source of high-quality proteins consisting of all nine essential amino acids required for humans. Considering the solubility factor, milk proteins belong to two main fractions that are casein (approximately 80% of total protein content) and whey protein (about 20% of total protein content). The composition of raw cow milk depends upon the stage of lactation, the feeding source, the cow's health and genetic factors. The study aimed to investigate the differences in total milk protein composition of cow milk within the lactation curve of cattle grazing on two types of pastures in Sri Lanka. The samples were collected during early, mid and late lactation stages from two cattle groups grazing on saltmarsh pastures in Mannar and dry pastures in Medawachchiya. The milk samples were tested for total protein composition (%w/w) by the ultrasonic Lactoscan MCC milk analyzer. Considering the results, the total milk protein composition of saltmarsh pasture feeding cattle was significantly higher (p<0.05) during the mid (3.48%) and late (3.54%) lactation stages than the dry pasture-feeding cattle. During the early lactation stage, the mean total protein composition (n=30, 3.38 %) of saltmarsh pasture feeding cattle was high compared to the mean total protein composition (n=25, 3.28%) of dry pasture feeding cattle, though statistically not significant (p>0.05). Since the milk protein yield is relatively proportional to the energy content of the diet in dairy cattle, this indicates that the saltmarsh pasture-based diet gives high energy to cattle. This study concludes that the protein composition of raw cow milk depends on the feeding pasture and the stage of the lactation period of dairy cattle.
Preparation of sulfonated polystyrene blended polystyrene film and its water absorption property under different pH environments
(Postgraduate Institute of Science (PGIS), University of Peradeniya, Sri Lanka, 2022-10-28) Kapilraj, N.; Koneswaran, M.
Polystyrene (PS) is one of the most widely used plastics. The hydrophobic nature of the PS film restricts its application in several fields. In this work, PS films were prepared with different formulations and their water absorption properties in acidic, alkaline, and neutral environments were studied. The sulfonated polystyrene (S-PS) was prepared by homogeneous sulfonation using acetyl sulfate as a sulfonating agent. S-PS was characterized using FTIR. The degree of sulfonation was 10 based on the calculation using NaOH titration. The films were made by independently mixing S-PS at mass ratios of 0, 5 and 10% with PS. The films were prepared by solvent–casting method. The mass percentage of the polymer in the solvent (ethyl acetate 80% + chloroform 20%) was 20, and the same method was adopted to prepare the films with a plasticizer (diethyl phthalate). The viscosity of the polymer solution was measured with Brookfield digital viscometer. The addition of S-PS and plasticizer change the viscosity. The average thickness of the films was 0.33 mm. A water droplet on the film's surface was captured using a digital camera with a macro lens. The contact angle was measured using the image-processing program Image j. The contact angle for the pure polystyrene film was increased by the addition of a plasticizer. However, the contact angle decreased with the addition of a plasticizer for the film blended with a higher percentage of sulfonated polystyrene. The water absorption test was performed according to ASTM D570. From each film, 30  25 mm² specimens were cut, and samples were dried in an oven for 24 h at 50 °C. It was promptly weighed after cooling in a desiccator. The samples were then submerged individually in distilled water (pH 7), acidic water (pH 2), and basic water (pH 12), and the water absorption characteristics of the films were determined by weighing the specimens every two days. The overall analysis shows that the mass of S-PS in the film and the addition of plasticizer have an impact on the water absorption capacity of the film. The plasticizer increases the hydrophobic nature of the pure polystyrene film. However, the addition of plasticizer increased the hydrophilic nature of the film blended with S-PS. The film blended with S-PS at a higher ratio exhibits higher water absorption capacity in acidic and neutral environments than in the alkaline environment.
Ferromagnetic thin films with fcc structure as described by fourth order perturbed heisenberg hamiltonian with seven magnetic parameters
(Postgraduate Institute of Science (PGIS), University of Peradeniya, Sri Lanka, 2022-10-28) Farhan, M.S.M.; Samarasekara, P.
Magnetic properties of fcc structured ferromagnetic ultra-thin films with two spin layers were described using fourth-order perturbed Heisenberg Hamiltonian with all seven magnetic energy parameters. Spin exchange interaction, magnetic dipole interaction, second-order and fourth-order magnetic anisotropy constants, in-plane and out-plane, applied magnetic fields, demagnetization factor and stress-induced anisotropy were considered in the model. 3D plots of total magnetic energy versus angle and stress-induced anisotropy were plotted for different values of fourth-order magnetic anisotropy constants. All other magnetic energy parameters were fixed at constant values. All the peaks are closely packed in the graphs plotted using the fourth-order perturbed Heisenberg Hamiltonian compared to peaks in the graphs plotted using the second and third-order perturbed Heisenberg Hamiltonian. The maximum energy varies from 10⁵¹ to 10⁴⁹ as the fourth-order magnetic anisotropy constants in the bottom (D1⁽⁴⁾) and top (D2 ⁽⁴⁾ ) spin layers are changed from D1 ⁽⁴⁾ω = 5 and D2⁽⁴⁾ω = 10 to D1 ⁽⁴⁾ ω = 10 and D2 ⁽⁴⁾ ω = 5, respectively. The order of magnetic energy changes when the values of fourth-order anisotropy constants of two spin layers are interchanged. The magnetic energy was higher when the value of the fourth-order anisotropy constant in the bottom spin layer was higher than that of the top spin layer. In addition, the graphs of energy versus angle were plotted to find the magnetic easy and hard directions. The angle between the magnetic easy and hard direction was not 90 degrees in all the cases. The orientation of the magnetic easy axis is important in the applications of magnetic recording media.
Exploration of cosmeceutical potential of leaf extracts of guava (Psidium guajava l.)
(Postgraduate Institute of Science (PGIS), University of Peradeniya, Sri Lanka, 2022-10-28) Dewage, D.D.D.H.; Karunaratne, S.H.S.; Rajapakse, C.S.K.
Sunscreen formulations are widely used to prevent and minimize harmful UV-induced photodamage. Nowadays, sunscreen development using natural ingredients revolutionises the cosmetic industry as they are healthier and safer than synthetic chemicals. Therefore, this study was focused on the evaluation of the cosmeceutical potential of leaf extracts of Psidium guajava L. (collected from Padukka, Sri Lanka) by determining their photoprotective properties and antimicrobial activities. Chemical constituents of guava leaves were cold extracted to ethanol, ethyl acetate and distilled water separately. The in-vitro sun protection factor (SPF) of each extract was determined using a spectrophotometric method and the Mansur equation. As many natural antioxidants and antimicrobial agents are phenolic, and flavonoid compounds, the total phenolic content (TPC) and total flavonoid content (TFC) of each extract were determined by Folin-Ciocalteau method and AlCl3 colorimetric method, respectively. Antimicrobial activity was determined by Agar well diffusion method against the bacterial strains of Staphylococcus aureus (ATCC 25923), Pseudomonas aeruginosa (ATCC 9027), Escherichia coli (ATCC 25922) and a fungal strain of Candida albicans (ATCC 10231), the potential pathogens in cosmetics. The treatments were triplicated (n=3). All extracts exhibited UV B absorption. Among them, the ethyl acetate extract showed an SPF value of 43.77±0.16 at 2.0 mg/mL while the SPF of the reference sunscreen was 39.18±0.56 (sunscreens with SPF>30 provide high protection against sunburn). The highest TPC was found to be in ethyl acetate extract (544.06±4.81 mg of gallic acid equivalent/g of dry weight), while the highest TFC was observed in ethanol extract (13.84±0.89 mg of quercetin equivalent/g of dry weight). According to the results, all extracts showed antibacterial activity against tested bacterial strains, while only the ethanol extract showed antifungal activity. This study revealed that guava leaves could be considered a promising natural source for the cosmeceutical industry as it is rich in chemical constituents with photoprotective properties and antimicrobial activities.
Density, distribution and population dynamics of rufous woodpecker (Micropternus brachyurus jerdonii) over three decades in Sri Lanka
(Postgraduate Institute of Science (PGIS), University of Peradeniya, Sri Lanka, 2022-10-28) Gunasekara, V.R.; Seneviratne, S.S.
The Rufous Woodpecker (Micropternus brachyurus jerdonii) is arguably the rarest woodpecker and probably one of the rarest birds in Sri Lanka. Its population seems to be declining in the recent past. Its density, distribution, and population status were evaluated using various techniques. Variable line transects with a fixed 20 m distance for either side were taken in locations where Rufous Woodpecker had been reported over the past 30 years. The information from the Global Biodiversity Information Facility (www.GBIF.org), eBIRD (www.ebird.org), and Ceylon Bird Club notes (CBCN: www.ceylonbirdclub.org) were used to determine the extent of occurrence (EOO) and area of occupancy (AOO). The EOO and AOO are 42,609.84 km² and 180 km², respectively. The total population size of the species calculated using the line transect data from 2020 to 2022 in Sri Lanka was estimated to be about 32,744 individuals. Kernel density estimation in QGIS was used to produce a heatmap to understand its density and distribution from the past to the present using GBIF (n=139). The equation (H opt = (2/3n)(1/4)×σ) was adopted to calculate the kernels using the mean centre and standard distance. This occurrence data resulted in 48,733.26 km² of EOO. The area of occupancy evaluated over the past three decades (1990-2020) represents over 15 generations of the species to determine whether there has been any shrinking of its range during this period. Our analysis showed that the range of the species had not changed during the past three decades. Further, it suggests that the Rufous Woodpecker has a patchy distribution with fluctuating population size.
Comparative in vitro antidiabetic activity of two amides from black pepper seeds (Piper nigrum l.) against postprandial glucose regulatory enzymes
(Postgraduate Institute of Science (PGIS), University of Peradeniya, Sri Lanka, 2022-10) Sampath, S. N. T. I.; Jayasinghe, J. M. S.; Attanayake, A. P.; Karunaratne, V.
Postprandial high blood sugar could be a risk factor for diabetes mellitus, and this condition is one of the critical points in diabetic treatments. Medication of postprandial hyperglycemia could be attained by mainly inhibiting key regulatory enzymes such as α-amylase and α-glucosidase, which are involved in carbohydrate digestion. Herbal plants are an excellent source to treat this disease and improve the ease of health. Piper nigrum L. (black pepper) is a well-known herbal plant belonging to the Family Piperaceae, and it contains a higher number of bioactive compounds. The present study reports the anti-postprandial hyperglycemic activity of an amide (pipnoohine) isolated from the hexane extract of P. nigrum seeds and compares it with that of isolated piperine (an antidiabetic compound from P. nigrum plant) and commercially available acarbose (a standard antidiabetic drug). The piperine and pipnoohine have been previously isolated from the genus Piper (P. nigrum, Piper longum, Piper chaba). However, the comparison of in vitro anti-postprandial hyperglycemic activity of these two compounds is untapped up to date. The two compounds were isolated from hexane extract of P. nigrum seeds using chromatographic techniques (vacuum liquid chromatography and flash column chromatography), and they were identified as piperine and pipnoohine, using ¹H and ¹³C NMR, liquid chromatography-mass spectrometry (LC-MS), UV, IR spectroscopy and melting point data. The in vitro anti-postprandial hyperglycemic activity of the isolated compounds was determined in terms of the 50% inhibitory potential of α-amylase and α- glucosidase enzymes. Both piperine and pipnoohine inhibited 50% of α-amylase enzyme activity at 37.04±0.94 and 62.22±2.06 mg l⁻¹ concentrations, respectively. In the α-glucosidase assay, the piperine and pipnoohine inhibited 50% of the enzyme activity at 51.12±0.09 and 82.42±2.25 mg l-1 concentrations, respectively. The pipnoohine showed no significant difference between the above activities with the piperine (p>0.05). The acarbose inhibited 50% of the α-amylase and α-glucosidase enzymes at concentrations of 5.72±0.33 and 17.72±0.48 mg l⁻¹, and the activities, however, showed significant differences with the inhibition activities of piperine and pipnoohine (p<0.05). This is the first report of α- amylase and α-glucosidase inhibitory activities of pipnoohine and the comparison of in vitro anti- postprandial hyperglycemic activity of piperine and pipnoohine. Results concluded that pipnoohine exerted considerable α-amylase as well as α-glucosidase inhibitory activities that indicate that it also can be considered a drug lead for the treatment of diabetes mellitus.
Shell morphometry and radulae analysis of freshwater gastropod genus paludomus
(Postgraduate Institute of Science (PGIS), University of Peradeniya, Sri Lanka, 2022-10-28) Liyanagedara, P.H.; Wathuliyadde, N.; Kumburegama, S.
Paludomus is the most common genus represented among freshwater gastropods in Sri Lanka. Of the 12 recorded Paludomus species, 10 are endemic to the country. Shell morphology is the major taxonomic feature that has been used for their identification. However, the identification of Paludomus species using shell features is ambiguous due to shell plasticity and homoplasy. One characteristic that can be reliably used in the systematic identification of gastropods is the radula, unique molluscs feeding structure. Five species of Paludomus were identified (Paludomus chilinoides, P. bicinctus, P. decussatus, P. neritoides, P. sulcatus) using shell morphology from 47 sampling sites spanning the Kandy, Matale and Nuwara Eliya districts. Different shell morphometries, i.e. Shell Height (SH), Shell Width (SW), Aperture Height (AH) and Aperture Width (AW), were measured using a digital Vernier calliper, and shell indices were calculated. A Principal Component Analysis (PCA) was conducted to check whether the species/morphotypes can be distinguished using shell morphometry. Furthermore, the median, lateral and marginal teeth of the dissected radulae were examined using Scanning Electron Microscopy for species characterization. According to the PCA, several of the Paludomus species clustered together (P. chilinoides and P. sulcatus together and P. bicinctus and P. decussatus), indicating that shell morphometry is not a reliable characteristic for species separation and identification. However, especially the pattern and shape of the cusps of the median teeth in the radulae varied and was unique to each of the species. Hence, the radulae teeth pattern can be used as a reliable character for identifying closely related Paludomus species.
Effect of bisphenol a on growth-related outcomes and survival of early life stages of polypedates cruciger
(Postgraduate Institute of Science (PGIS), University of Peradeniya, Sri Lanka, 2022-10-28) Rajapaksha, R.M.H.N.; Dissanayaka, P.; Rajapaksha, R.P.G.K.
Bisphenol A is a widely used chemical in the plastic industry worldwide. Urban water sources are frequently polluted by bisphenol A leaching from plastic waste and industrial effluents, hence threatening aquatic species. Bisphenol A is an endocrine disruptor that perturbs natural hormone signalling pathways affecting living organisms' growth, development, and physiology. This study assessed the impact of long- term exposure to Bisphenol A on the early life stages of Polypedates cruciger (Common hourglass tree frog). Twenty tadpoles of Gosner stage 26 – 27 were assigned to triplicate tanks treated with environmentally relevant concentrations of bisphenol A (1, 10, 100 μg/l) and treatment control (1% v/v ethanol) for 80 days. The total body length, tail length, and body weight of tadpoles were observed weekly. The survival rate, tail length ratio and increments in body weight and length were calculated at the end of the treatment. The total body length of tadpoles increased with increasing concentrations of bisphenol A. Total body lengths of tadpoles in all bisphenol A treatments were significantly higher than those in control (p<0.05). The mean tail length ratio gradually increased with increasing concentrations of bisphenol A. Tail length ratio of those in control and 1 μg/l bisphenol A was significantly lower than those exposed to higher exposures (p<0.05). Body weight increment was not significantly different between treatment and controls (p>0.05). About 90% of all tadpoles survived in treatments and control, with no significant differences in survival between treatments and control (p>0.05). Accordingly, it can be concluded that environmentally relevant concentrations of bisphenol A do not affect survival but has significant negative impacts on growth-related parameters in Polypedates cruciger.
Application of purified and modified - pyrolytic carbon char in rubber compounding
(Postgraduate Institute of Science (PGIS), University of Peradeniya, Sri Lanka, 2022-10-28) De Zoysa, D.M.D.A.; Sudusinghe, Y.C.Y.; Hewage, J.S.; Ranaweera, A.S.
The waste tire pyrolysis process has attracted considerable interest as a sustainable solution to manage the accumulation of waste tires worldwide. The process produces three main fractions: gas, liquid and solid. The gaseous and liquid fractions are useful in industry as fuels; however, the solid fraction rich in carbon black has no use in Sri Lanka due to the presence of many impurities. The present study describes an efficient and economical route to purify contaminated pyrolytic char to manufacture value-added products. The pyrolytic carbon char was first passed through a 200 μm mesh to separate small particles, followed by size reduction by ball milling. These particles were demineralized stepwise using dilute HCl acid and NaOH at 60 °C for 1.0 h. Treated and untreated samples were characterized by carbon, hydrogen and nitrogen analysis, X-Ray Diffraction analysis and iodine adsorption experiments. The purified carbon black samples were used as reinforcing fillers for preparing rubber compounds according to the American Chemical Society 1 (ACS 1) formula. The physicomechanical properties of rubber compounds of purified carbon black prepared were consistent with compounds prepared with commercial carbon black, N660 and N330. CHN analysis shows that crude pyrolytic char (C-PT) contains 69% carbon, which can be improved up to 90% after washing with 2 M HCl twice and 2 M NaOH once. The iodine number of the sample was improved after demineralization (C-PT 180 mg/g and demineralized sample have 215 mg/g and 188 mg/g, 240 mg/g N660 and N330). There is no significant difference between the abrasion, tensile, tear, and compression properties of controls and ball-milled-treated samples. The average of all compound hardness is similar to the controls. The efficiency and value of the purification protocol in the current study were confirmed by test results and showed high potential application in the industry.
Antibacterial activity of different plant extracts and their combinations with turmeric extract against staphylococcus aureus strains
(Postgraduate Institute of Science (PGIS), University of Peradeniya, Sri Lanka, 2022-10-28) Silva, M.C.G.; Uduwela, D.R.; Jayasinghe, J.M.S.; Gunathilake, W.S.S.; Liyanapathirana, L.V.C.; Ekanayake, E.W.M.A.; Dissanayake, U.P.R.U.; Wickramasinghe, A.
Drug resistance in bacteria has become a major concern in pharmaceutical research. Natural products have high structural diversity and potent antibacterial activity (AA). Hence, they can be a good source for antibacterial drug development. This study aimed to investigate the AA of Coffea arabica (Coffee- CF) leaves, Murraya koenigii leaves (Curry leaves- CL), Tabernaemontana dichotoma (Poison nut- PN) leaves and Curcuma longa (Turmeric-TR) rhizomes and their combinations. The crude extracts were prepared using dried, powdered plant parts where the leaves were extracted into water-acetone (v/v 1:1), and TR rhizomes were extracted into methanol-acetone (v/v 1:1) using a bottle shaker. The individual extracts and the nine combinations of three plant extracts with TR extract in 1:3, 1:1 and 3:1 ratios were assessed for AA by broth microdilution assay against five Staphylococcus aureus bacterial strains as they are involved in wound infections. Among the four individual extracts, TR showed the lowest Minimum Inhibitory Concentration (MIC) of 98 mg/l, for all five bacterial strains and the lowest Minimum Bactericidal Concentration (MBC) values ranging from 195 - 390 mg/l resulting in the highest AA. CL, CF and PN showed MICs ranging from 780 - 1,560 mg/l, 1560 - 3,125 mg/l and 780 - 6,250 mg/l, respectively and MBCs ranging from 1,560 - 6,250 mg/l, 6,250 - 12,500 mg/l and 1,560 - 12,500 mg/l, respectively. From the nine combinations, CL/TR with 3:1 ratio showed the highest AA (MIC- 48 mg/l, MBC- 98 mg/l). However, in CF/TR and PN/TR, 1:3 ratio showed the majority of low MIC and MBC values against the five bacterial strains. An enhanced AA for the three leaf extracts was observed when combined with TR extract. Amongst the four individual extracts and the nine combinations, CL/TR 3:1 combination exhibited the highest antibacterial properties. Though TR shows the highest AA among individual extracts, it increased the overall AA when present in the mixture of CL/TR in 3:1 ratio. The results revealed that using these plant extracts in combination with TR enhances the AA more than using them as individual plant extracts.

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