RESCON 2022

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

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Nutrient analysis of cultivars of cucurbita spp. (pumpkin) grown in the dry zone of Sri Lanka
(Postgraduate Institute of Science (PGIS), University of Peradeniya, Sri Lanka, 2022-10-28) Ruwanthika, K.O.G.H.; Munasinghe, M.L.A.M.S.; Marapana, R.A.U.J.
Different Cucurbita spp. generally recognized as pumpkin, is a commonly grown vegetable in dry and intermediate zones of Sri Lanka. C. maxima and C. moschata are popular cucurbits that include different types of open-pollinated, hybrid and imported varieties. This study aimed to conduct a nutrient analysis of seven pumpkin cultivars collected from Kudaoya in the Monaragala District to identify the differences in the nutrient composition among the selected cultivars. The study area comes under the dry zone low country 1b (DL1b) agro-ecological region. Rajah, Leela, Malbaro, Batana, Bingha, Katana and Meemini were the selected pumpkin cultivars, and out of these, Rajah, Leela and Katana were recognized as C. maxima varieties. In contrast, Bingha, Meemini, Batana and Malbaro were recognized as C. moschata varieties. All the selected cultivars were collected within a range of 5 km from the Kudaoya town and at their fullest harvestable maturity in the Maha season. The collected samples were stored under ambient temperature, and the flesh part of each cultivar was powdered before the nutrient analysis. In the nutrient analysis, the proximate composition, Fe, Mg and K compositions and the anti-oxidant (AO) activity in different pumpkin cultivars were evaluated using standard analytical methods (Protein-Bradford assay, Carbohydrate-Phenol sulphuric method, Lipid content-Bligh and Dyer method, Crude fibre-Weende method, Moisture level- Rapid moisture analyser, Minerals-Atomic absorption spectroscopy method, AO activity-Ferric reducing anti-oxidant power assay). The nutrient compositions among the cultivars were statistically compared through one-way ANOVA. In 100 g of powdered pumpkin flesh, the nutrient composition was reported as protein content in the range of 32.8-32.9 g, carbohydrate 57.8-57.9 g, lipid content 1.04-6.13 g, crude fibre 2.19-10.94 g, moisture level 8.24%-10.95%, Fe content 4.11-7.76 mg, K content 5,055-8,841 mg, Mg content 96.0-337.02 mg and AO activity 145.1-147.1 mg AAE (Ascorbic acid equivalent) in dry-weight basis. The three varieties of C. maxima have recorded significantly higher nutrient levels (p<0.05) than the C. moschata varieties. The overall nutrient composition was significantly higher in the cultivar type ‘Rajah’, an imported hybrid variety, compared to the other cultivars analysed in the study.
TiO ₂ nanoparticles incorporated CMC-MMT nanocomposite for food packaging applications
(Postgraduate Institute of Science (PGIS), University of Peradeniya, Sri Lanka, 2022-10-28) Perera, A.W.N.D.; Wijesooriya, S.N.; Adassooriya, N.M.
The demand for sustainable food packaging material has increased compared to nonbiodegradable packaging because plastic waste is a serious environmental problem. In this study, different composites of citric acid (CA) crosslinked montmorillonite (MMT) reinforced carboxymethyl cellulose (CMC) films with TiO₂ nanoparticles (NPs) (average size < 20 nm) incorporated to act as antimicrobial agents were investigated for applications in food packaging. Films were fabricated using the solvent casting method with 25% (w/w) CA as the crosslinking agent, and 1%, 3%, and 5% TiO₂ NPs were added to the CMC- MMT nanocomposite with glycerol as a plasticizer. The films were characterized by FTIR, TGA, and PXRD and evaluated for water solubility, moisture content, and moisture uptake ability. The addition of CA and TiO₂ NPs lowered the moisture uptake (MU), water solubility (WS), and moisture content (MC) by reducing polymer network interactions. FTIR analysis confirmed the formation of ester crosslinks between CMC and CA. It was found that MC decreased from 34.3% to 33.3% when the concentration of CA increased and reduced to 29.3% with the addition of 5.0% TiO₂ NPs. The WS was reduced from 67.9% to 66.9% when the amount of CA increased from 15.0% to 25.0% and reduced from 66.7% to 65.2% when the amount of TiO₂ NPs increased from 1.0% to 5.0%. Incorporation of 3% TiO₂ NPs into CMC/MMT/CA25% film remarkably reduced the MU by 21.9% at 97.0% RH and 16.1% at 40.0% RH. According to the thermal analysis, the addition of TiO₂ NPs enhanced the thermal stability of CMC films. The PXRD revealed that TiO₂ NPs and MMT modified the original structure of the CMC by increasing the crystallinity of the films. From the overall results, CA crosslinked TiO₂ NPs incorporated CMC-MMT films were found to exhibit the lowest WS, MU, and MC.
Biodegradable polymer-coated urea granules as a slow-release nitrogen source
(Postgraduate Institute of Science (PGIS), University of Peradeniya, Sri Lanka, 2022-10-28) Dilhan, J.A.M.; Rajapakse, R.M.G.; Adassooriya, N.M.
Urea is the most popular nitrogenous fertilizer due to its relatively low cost and high nitrogen composition. However, approximately 30-50% of urea is only utilized by plants resulting in low nutrient use efficiency (NUE). Several environmental issues originate via the loss of urea throughout various processes, such as direct volatilization, accumulation of urea via runoff, and leaching of urea as nitrates. Controlled-release fertilizers (CRFs) are one of the promising methods to increase NUE and minimize environmental impact. During this study, attempts were made to synthesize biodegradable polymers coated urea granules using cellulose acetate (CA) and polyvinyl alcohol (PVA). 4.5% (v/v) CA solution was prepared in acetone at room temperature with constant stirring at 800 rpm, and this solution was coated on urea granules by the solvent casting method. 3% (v/v) PVA solution was prepared by dissolving PVA in distilled water at 80 °C with constant stirring at 1,000 rpm. Then 30% (w/w) by polymer mass citric acid was added as a crosslinker to the PVA solution after it cooled to room temperature. This solution was sprayed on CA-coated urea granules to synthesize CRFs (UCPC30). Finally, CRFs were dried at 105 °C for 2.5 h for cross-linking. The successful polymer coatings were confirmed by Fourier transform infrared spectroscopy, powder X-ray diffraction, and scanning electron microscopy. The release behaviour of the prepared polymer-coated urea was investigated in the soil medium (pH=5.9), and it was observed that 92% of urea was released from the CRFs in a slow and sustained manner for up to 16 days. Meanwhile, 90% of urea was released from commercial grade within 8 days. The porous hydrogel matrix of the PVA regulates the penetration of urea molecules and extends the release time. Therefore, biodegradable polymer-coated urea granules are ideal candidates for slow-release fertilizer.
Antioxidant activity of propolis of the endemic stingless bee, Tetragonula praeterita, from different climatic zones of Sri Lanka
(Postgraduate Institute of Science (PGIS), University of Peradeniya, Sri Lanka, 2022-10-28) Thilakarathna, U.C.M.; Uduwela, D.R.; Welegedara, A.P.; Bandara, B.M.R.; Karunaratne, W.A.I.P.
Tetragonula praeterita (Walker) is the only endemic stingless bee species found in Sri Lanka. Propolis is a sticky lipophilic resinous substance produced by a mixture of bee wax, plant resins, pollen and exudates, including organic and inorganic earth components and salivary secretions of stingless bees. The bioactivity of propolis depends on its chemical composition, which varies with the bee species, food source, ecosystem, climatic zone, season and vegetation. This study aimed to compare the antioxidant activity of propolis samples obtained from Kandy (KAN), Kurunegala (KUR) and Batticaloa (BAT) belonging to wet, intermediate and dry climatic zones of Sri Lanka, respectively. Ethanol extracts prepared by Soxhlet extraction were assessed for antioxidant capacity by 1,1-diphenyl-2-picrylhydrazyl (DPPH) assay, ferric reducing antioxidant power (FRAP) assay, Folin-Ciocalteu method (for assaying total polyphenolic content, TPC) and aluminium chloride colorimetric method (for assaying total flavonoid content, TFC). The IC50 values of DPPH radical scavenging assay were 155.75±8.19 (KAN), 538.89±16.14 (KUR) and 1,191.67±2.92 mg L-1 (BAT) and the corresponding FRAP values were 102.46±0.01, 71.30±0.01 and 60.17±0.01 mmol g-1 dm-3. The TPC values of KAN, KUR and BAT samples were 37.0±3.1, 16.8±1.5 and 14.4±1.1 mg (gallic acid equivalent) g-1, respectively. The antioxidant activities correlated with the TPC values but not with the TFC values, 179.2±31.8 (BAT), 135.2±1.1 (KAN) and 111.3±3.9 (KUR) mg (quercetin equivalent) g-1. Therefore, it can be concluded that the antioxidant capacity of T. praeterita propolis depends on the climatic zones from which the samples are collected and that the TPC contributes to the antioxidant capacity of the bee propolis.
Molybdenum disulfide on reduced graphene oxide hybrids were developed via one pot hydrothermal route as a catalyst for hydrogen evolution reaction
(Postgraduate Institute of Science (PGIS), University of Peradeniya, Sri Lanka, 2022-10-28) Premadasa, P.M.; Panamldeniya, S.A.; Abeykoon, Y.K.; Munasinghe, H.M.M.; Gunawardhana, N.
Green hydrogen production from the cathodic reaction of water splitting (hydrogen evolution reaction) is one of the most significant discoveries in recent years. In this regard, molybdenum disulfide (MoS₂) is used as an alternative catalyst for platinum due to its high availability and lower binding energy, which is close to zero. 1-T MoS₂, 3-R MoS₂, and 2-H MoS₂ are the major phases of MoS₂, and 2-H MoS₂ is the most stable form, but only the edge sites are activated, and the whole basel plane is almost inactive. Therefore, the activity of 2-H MoS₂ is based on the nature of the edges-sites. In this study, MoS₂–graphene oxide (MoS₂–GO) composites were prepared via a one-step hydrothermal method on the three distinct GO materials, which were prepared under different oxidation durations (24, 48, and 72 h) in the modified hummer’s method. The MoS₂ with differently oxidized GO was characterized by SEM, PXRD, and FTIR to disclose the characteristics of the materials. In addition, the electrochemical performance of MoS₂-GO was investigated by using linear sweep voltammetry (LSV). The results showed that MoS₂ layers were successfully grown on the surface of GO, which is prepared at the highest oxidation duration (72 h). It has a higher number of shaped edges with uniform growth. According to the FTIR results of GO and GO- MoS₂, 72 h oxidized GO has more (COOH) carboxylic groups, and the growth of MoS₂ has been initiated through COOH groups. The XRD spectrum of the MoS₂/RGO revealed that the MoS₂ prepared on 72 h oxidized GO nanosheets (MoS₂/RGO-72) had the highest d spacing value due to the inserted GO into the MoS₂ layers. Moreover, MoS₂/RGO-72 was the best catalyst for the hydrogen evolution reaction (HER) because MoS₂/RGO-72 needs the lowest potential value to initiate the HER reaction (overpotential). Finally, the growth of MoS₂ on GO is possible to change by varying the oxidation duration of GO to have MoS₂/RGO material with a greater number of activated sharp edges.
Green synthesis of Zinc oxide nanoparticles from amaranthus viridis and Costus speciosus: process optimization and antimicrobial potential
(Postgraduate Institute of Science (PGIS), University of Peradeniya, Sri Lanka, 2022-10-28) Thrikawala, S.W.; Perera, H.A.I.R.; Thomas, M.P.
Nanomaterials have been emerging as a new generation of antimicrobial agents to mitigate the crisis associated with antimicrobial resistance. Among them, Zinc Oxide Nanoparticles (ZnO NPs) stand out due to their biocompatibility and easy synthesis. The objective of this study was to explore a simple, eco- friendly method to synthesize ZnO NPs using zinc acetate dihydrate as the precursor from aqueous leaf extracts of Amaranthus viridis (Kurathampala) and Costus speciosus (Thebu). Aqueous leaf extracts of both plants were prepared, and optimization of the synthesis in response to yield, characterization and antimicrobial activity determination were conducted. The effects of precursor concentration and reaction temperature and their interactions during the synthesis were determined by response surface methodology employing the central composite design. Within the chosen range, the precursor concentration was identified as a significant variable (p < 0.05) as opposed to the reaction temperature in the synthesis. From the PXRD patterns, ZnO NPs were highly pure, confined to the wurtzite structure with mean crystallite sizes of 20.01 and 15.99 nm for A. viridis and C. speciosus mediated synthesis, respectively, and most effectively calcinated at 450 °C. Investigation of FTIR spectra verified functional groups in charge of stabilizing and capping of ZnO NPs. Roughly spherical particles of average sizes < 60 nm were observed from SEM imaging. In comparison to Sigma-Aldrich ZnO (< 50 nm), ZnO NPs mediated via A. viridis and C. speciosus showed a high antifungal potential against a standard isolate of Candida albicans (ATCC 90028). A minimum inhibitory concentration of 5.12 mg/mL against standard isolates of gram-negative bacteria Pseudomonas aeruginosa (ATCC 27853) and Escherichia coli (ATCC 25922) were obtained for the ZnO NPs synthesized via A. viridis and C. speciosus from the agar dilution method, while the effect on gram-positive bacteria was not notable. Overall, the results elucidated a rapid, cost-effective, environmentally-friendly method for ZnO NP synthesis, which showed antimicrobial potential against fungal and gram-negative bacterial strains.
Montmorillonite nanoclay reinforced carboxymethyl cellulose/hydrophobic TiO2nanocomposite as a biodegradable food packaging material
(Postgraduate Institute of Science (PGIS), University of Peradeniya, Sri Lanka, 2022-10-28) Ihalavithana, C.V.; Jagoda, S.S.S.D.S.; Adassooriya, N.M.
Recent studies have been conducted on biodegradable polymer nanocomposites from a structural and functional perspective and their applications in food packaging due to triggered concerns of looking for materials and processes compatible with the environment. In this regard, due to its hydrophilic nature, titanium dioxide (TiO₂) underwent hydrophobic modification by stearic acid (SA, 3 w/w% of TiO₂) via a physical coating method using ethanol as the solvent to prepare functional carboxymethyl cellulose (CMC) based nanocomposite film appropriate for food packaging. The novel CMC-based ternary nanocomposite film was synthesized by incorporating 5 w/w% of sodium montmorillonite (Na+MMT) and 1 w/w% of modified TiO₂via a drop-casting method. As prepared, the modified TiO₂ and nanocomposite film were characterized by FTIR spectroscopy to demonstrate the interactions and PXRD and TGA analysis to investigate the crystallinity and thermal behaviour of the nanocomposite films, respectively. FTIR results showed that SA was closely and firmly combined with TiO₂particles; therefore, the changes in surface characteristics of TiO₂ promoted the interaction between CMC, MMT, and TiO₂ in nanocomposite film. According to PXRD analysis, the CMC chains were loaded into the silicate layers' gallery to produce an intercalated nanomorphology. TGA analysis highlighted that physically coated SA in TiO₂ microcrystals had improved thermal stability. The performance of the nanocomposite films was demonstrated by moisture content and tensile tests. The results showed that modified TiO₂ decremented moisture content, tensile strength, and elongation at the break by 2.9%, 29.4%, and 27.0%, respectively. It was deduced that the long hydrocarbon chain of SA, which is non-polar, has conferred hydrophobicity to the nanocomposite, promoting the water-resistance and increasing the extensibility of the film.
Mechanochemical synthesis of urea: salicylic acid cocrystal as a sustained released nitrogen source
(Postgraduate Institute of Science (PGIS), University of Peradeniya, Sri Lanka, 2022-10-28) Madanayake, M.S.N.; Madanayake, N.H.; Adassooriya, N.M.
Global agriculture and food and nutrition security are challenged by the premature decomposition of urea in the soil before plant uptake. Crystal engineering is a solution to reduce the nitrogen (N) loss from urea due to its high-water solubility. Thus, cocrystals of urea have recently gained interest as synthetic N fertilizers to reduce solubility barriers and release kinetics of urea. In this study, urea cocrystals with salicylic acid as the coformer was prepared using mechanochemistry via neat grinding and liquid-assisted grinding in both 1:1 and 2:1 stoichiometric ratio and subjected to solid state characterization techniques, including Powder X-ray diffraction (PXRD), Fourier transform Infrared spectroscopy (FTIR), and Thermogravimetric analysis (TGA). The results confirmed the formation of already reported 1:1 cocrystal while suggesting a possible new form of 2:1 urea: salicylic acid (U: SA) cocrystal. Results of the TGA confirmed the anhydrous and guest-free nature of cocrystals. PXRD patterns revealed the presence of a new crystalline phase which is different from a physical mixture of starting compounds. Shifting of peaks in FTIR spectra validated the formation of intermolecular amide–acid interactions in the cocrystal crystal structure. The release study was carried out using the reported 1:1 cocrystal system in soil (pH=5.9), and it took 10 days to elute around 85% of urea compared to commercial urea (8 days) confirming that U: SA cocrystal is a potential candidate for sustained-release nitrogen fertilizer. Reduced urea leaching in soil resulting from mechanochemical cocrystallization of urea with SA can be thereby indicated as a viable strategy towards improving N uptake in an efficient, eco-friendly, and less toxic method.
Zinc-doped hydroxyapatite/chitosan biodegradable polymer composite for bone grafting applications
(Postgraduate Institute of Science (PGIS), University of Peradeniya, Sri Lanka, 2022-10-28) Mohotti, R. T.; Manipura, A.; Jagoda, S.; Adassooriya, N.
The occurrence of bacterial infections during and after bone graft surgeries are rising to the point of concern, despite the use of antibiotics and controlled hygienic practices. Better methods of preventing bacterial infections are needed, and the fabrication of materials with antibacterial properties within the material itself can be of added advantage. Hence, an investigation into the possibility of synthesizing a bone graft material with antibacterial properties was conducted. Suitable materials for the composite were reviewed and selected. These materials had the added advantage of biocompatibility and degradation. Thus, a polymer composite for bone grafting applications was prepared using chitosan, hydroxyapatite, and zinc. Four composites with varying zinc (doped at 0.2, 0.4 and 2% of Zn) and chitosan ratios were synthesized, and scaffolds were prepared by a compression pelletizing process with 10 kN force. The composites were characterized through Fourier Transform Infrared (FTIR), Powdered X-Ray Diffraction (PXRD), and Thermogravimetric analysis (TGA) techniques. The composites were thermally stable till around 300 °C proving suitable use in the specific application. Water absorption, stability in fluids, compressive strength and antibacterial properties of the composites were tested. The compressive strength of the scaffolds obtained ranged from 4-11 MPa, which is satisfactory for cancellous bone applications. The composites displayed effective inhibition against Escherichia coli and Staphylococcus aureus after 18 and 30 h of incubation. Stability in fluids had to be further enhanced, though satisfactory water absorption levels were observed.
Structural and morphological investigation of sodium dodecyl sulfate (sds) - directed linde type-a (lta) zeolite synthesized at varying crystallization temperatures
(Postgraduate Institute of Science (PGIS), University of Peradeniya, Sri Lanka, 2022-10-28) Perera, M.D.R.; Amarasena, R.A.L.R.; Bandara, W.M.A.T.; Weerasooriya, R.; Jayarathna, I.P.L.
Recently, nanocrystalline LTA-type zeolites have attracted much research attention due to their unique and promising functioning in a wide area of applications like catalysis, gas adsorption and separation, and medicinal applications. However, obtaining morphologically controlled LTA nanocrystals is a complicated but necessary task since the morphology of LTA crystals substantially influences the performance of their applications. This study aimed to investigate the structure-directing ability of sodium dodecyl sulfate (SDS), an eco-friendly anionic surfactant for forming nanocrystalline LTA zeolites with controlled morphology at varying crystallization temperatures. Following the microwave crystallization approach, synthesis was carried out at 100, 110, 130, and 150 °C crystallization temperatures with 900 W for 3 h, starting from the gel solution with the molar ratio of 5.5 Na₂O:1.0 Al₂O₃:4.0 SiO₂:190 H₂O: 0.2 SDS. The resulting materials were characterized by powder X-ray diffraction (PXRD) and scanning electron microscopic (SEM) techniques for an in-depth understanding of their structure and morphology. The PXRD results confirmed the successful synthesis of LTA zeolites at all four temperatures. However, with the increase in crystallization temperature, the phase purity tends to decrease due to the formation of hydroxy- sodalite (HS) impure phases at elevated temperatures (130 °C and 150 °C). A remarkable decrease in the crystallinity (80.2%) was observed for the sample crystallized at 130 °C but had the lowest average crystallite size (78 nm). Moreover, SEM monographs revealed the formation of the spheroidal “cotton- ball” structure of HS on surfaces and along with cubic crystals of LTA zeolite and crystal defects confirmed by the deeply truncated edges with rough crystal surfaces predominated at both higher temperatures. Accordingly, the study concludes that the best suitability of 100 °C crystallization temperature for the LTA synthesis is to have a controlled morphology with the highest crystallinity, with the aid of SDS.
Synthesis of graphene oxide quantum dots using local graphite
(Postgraduate Institute of Science (PGIS), University of Peradeniya, Sri Lanka, 2022-10-28) Wedasingha, W.A.L.P.; Bandara, W.M.A.T.; Wijesinghe, M.B.; Jayarathna, I.P.L.; Weerasooriya, S.V.R.; Perera, M.D.R.
Graphene-based quantum dots are zero-dimensional biocompatible nanomaterials that are less than 10 nm in size, and it carries distinctive features such as good thermal conductance, excellent mechanical strength, good chemical stability, and excellent electronic properties. Owing to the versatile nature of graphene- based quantum dots, extensive attention has been gained in many industries to utilize graphene oxide quantum dots (GOQDs). Numerous research efforts have been made so far to develop successful synthesis pathways to obtain GOQDs with desired properties. However, using local graphite as the precursor material, this study reports an environmentally friendly synthesis route for GOQDs. In this particular method, local graphite powder was converted into graphene oxide by improved Hummer’s method and the subsequent conversion of graphene oxide to GOQDs using the one-step hydrothermal synthesis approach. The prepared materials were characterized by Ultraviolet-visible (UV-Vis) spectroscopy and ultraviolet transilluminator. According to the UV-vis spectroscopic analysis of graphene oxide showed peaks around 250 nm which is due to π → π* transitions of the aromatic π electrons. In contrast to that, GOQD showed an extra peak at around 340−360 nm, which ascribes to the n → π* transition of carbonyl bonds or other oxygenated functional groups present on the surface of GOQD. The formation of a quantum dot was confirmed by an ultraviolet transilluminator which gave a light blue colour under the UV light. These GOQDs have potential applications in biomedical imaging, adsorption of heavy metals, and electronic applications.
Design and analysis of a high-speed blowing sanitizing mechanism unit for disinfection chambers
(Postgraduate Institute of Science (PGIS), University of Peradeniya, Sri Lanka, 2022-10-28) Gamage, W.G.K.P.; Dharmathilaka, I.P.
The current study presents a design and analysis of an efficient and innovative mechanism to disinfect in controlling and preventing COVID-19. This mechanism is an alternative to the time-consuming and expensive disinfection process, and it can be focused on specific places on the body. The proposed device uses a high-speed airflow that passes through a venture. The high-pressure sprinkle will spread the sanitizing chemical in the middle of the venture. After spraying the chemical, the device will blow air to dry the chemicals on the skin. The study aims to assess the sparing speed of the sanitizing chamber. These whole simulations and analyses were done using SOLIDWORKS. The diffusion angle, contraction ratio, inlet-outlet pressure difference, and velocity characteristics were crucial parameters when choosing the best shape for the venture. After choosing and designing a better shape for the venture, the analysis part was done. Flow rates of air and water were applied to respective inlet sides and venture inlet. A venture inlet has been installed, and its needle has been attached at the most velocity point of the venture tube. In this study, an input flow velocity of air has been supplied at 100 m s ⁻¹ , and the output side has been set up as environment pressure. The validated computational fluid dynamic model was used to evaluate two scenarios; one is an increase in mass flow rate, and the second thing is to reduce turbulence and develop well flow at the end of the unit. At the end of the study, the well-analyzed mechanism could be invented with high speed and expected objectives. A higher flow rate is thought to increase the atomization quality and spray coverage of alcohol-based sanitizer liquid for sanitizing chamber and walkthrough gates applications.
Graphite powder based layer for activated carbon supercapacitor to enhance connectivity between activated carbon electrode and current collector
(Postgraduate Institute of Science (PGIS), University of Peradeniya, Sri Lanka, 2022-10-28) Medagedara, A.D.T.; Gardiarachchi, H.W.; Kumara, G.R.A.; Bandara, T.M.W.J.; Tennakone, K.
One of the most widely used techniques for making a supercapacitor is the fabrication of electrodes with activated carbon. The interface between the electrode material and the current collector has a significant impact on its performance. In this work, we used the spray pyrolysis method to form a graphite layer on top of the current collector, and on top of it, an activated carbon layer was formed. We discovered that the existence of a layer made of graphite powder between the electrode material and the current collector could significantly improve the performance of the supercapacitor. The rectangular shape of the Cyclic Voltammetry (CV) exhibits ideal supercapacitor behaviour, but the loose contact between the current collector and the electrode material causes the rectangular shape of the CV to be distorted. The behaviour of a supercapacitor made of graphite slightly deviated from the optimum CV, proving the importance of the graphite layer for the connection of the activated carbon electrode. The supercapacitor with the best performance was obtained when the concentration of the binder in the graphite powder was 20% (w/w) and the suspension and heat-treated at 300°C for 20 min; the procedure showed a specific capacitance of 23.51 F g⁻¹ . The cell with the same conditions except the graphite layer had a relatively low specific capacitance value of 19.76 F g⁻¹. Electrochemical Impedance Spectroscopy measurements show that the series resistance of the cell with a graphite layer is 0.720 , and the series resistance of the cell without a graphite layer is 0.774 . These results show the feasibility of employing graphite powder as a layer between an electrode and a current collector, increasing the specific capacitance and acting as an anti-corrosive material at the same time. As a result, it extends the supercapacitor's performance and durability.
Low-cost proton exchange membranes for microbial fuel cells using clay and activated carbon
(Postgraduate Institute of Science (PGIS), University of Peradeniya, Sri Lanka, 2022-10-28) Molagoda, H.M.P.P.; Bandara, T.M.W.J.; Fernando, E.Y.
The proton exchange membrane (PEM) is a significant component that affects the performance of the microbial fuel cell (MFC). Electro-neutrality between the two chambers is very important in MFCs, and it is performed by PEM, which transfers the protons across the membrane. A Nafion membrane is widely used as PEM in MFC for exchanging protons, but it is costly. Therefore, further research on low-cost PEM, which is high in porosity and mechanical strength, is vital. In this study, a PEM was made using natural clay and activated carbon derived from coconut shells (ACCS) and was compared with the results obtained for the Nafion membranes in other studies. In both MFCs, the volume of the anode and cathode chamber was 250 ml, and a phosphate buffer solution (50 mmol dm⁻3) was added to the cathode while wastewater was added to the anode chamber. In this study, lake sediment was used as the source of electrochemically active bacteria in the anode chamber of MFC. Open circuit voltage and short circuit current density of clay and ACCS membrane were observed as 270 mV and 920.0 mA m⁻², respectively. The maximum power density obtained from the MFC using clay and ACCS (43.3 mW m⁻²) was lower than the MFC with Nafion as PEM (202±6 mW m⁻². However, calculations showed that the cost per square meter for PEM developed from clay and ACCS (5,600 LKR) was much lower than the Nafion membrane (4.0 million LKR). Furthermore, a performance comparison of MFCs revealed that the cost per watt for clay and ACCS membrane was 0.13 million LKR, while that of Nafion was about 19.8 million LKR. Hence, low-cost clay and ACCS membranes were found to have the potential to replace Nafion membranes in MFCs for their field-scale applications. Therefore, MFC prepared using clay and ACCS can be used as a low-cost and clean energy source to generate bioelectricity.
Tin and zinc oxide composite dye-sensitized solar cells with an extremely thin liquid film as the redox electron mediator
(Postgraduate Institute of Science (PGIS), University of Peradeniya, Sri Lanka, 2022-10-28) Gardiarachchi, H.W.; Medagedara, A.D.T.; Kumara, G.R.A.; Tennakone, K.
Some major issues that hamper the stability of dye-sensitized solar cells (DSCs) are dye degradation, liquid electrolyte leakage, and evaporation. This can occur because of sealing imperfections and photocatalytic reactions that transpire at the TiO2 surface triggered by the ultraviolet component of solar radiation in the presence of water. To overcome imperfections in sealing, solid-state DSCs can be developed. In these cells, the liquid redox mediator is replaced by a p-type hole conducting material. Compared to their liquid equivalents, solid hole conductors typically have lower electron mobility. Hence, recombination reactions predominate in solid-state DSCs, and the cells exhibit poorer power conversion efficiencies. The photo- degradation of both dye and the electrolyte can be eliminated by adopting less photocatalytically active larger band-gap n-type oxide semiconductors with the conduction band edge positioned competently. SnO₂ (band gap 3.8 eV) fulfils this condition, but DSCs based on SnO₂ working electrodes are inefficient due to the rapid recombination reactions. This can be overcome by applying an ultra-thin layer of higher band gap oxide to cover the crystallite surface of SnO₂. In this work, the usual liquid electrolyte (I⁻ /I3 ⁻ ) was used to fill the pores of the SnO₂/ZnO composite working electrode, sensitized with the N719 dye. Then, the excess electrolyte was wiped off. Finally, these pores were sealed using graphite powder. This treatment annihilates losses due to evaporation and leakage while sustaining high electron mobilities. An optimum energy conversion efficiency of 3.06% was obtained for this DSC with the corresponding cell parameters of open circuit voltage 0.57 V, short circuit current density 8.19 mA cm⁻², and fill factor 0.66 under 1.5 AM illumination. A maximum incident photon to the current conversion efficiency of 39% was attained in the wavelength range from 510 nm to 535 nm.
Synthesis of cyclodextrin-coated magnetite nanoparticles as a potential drug for treating atherosclerosis
(Postgraduate Institute of Science (PGIS), University of Peradeniya, Sri Lanka, 2022-10-28) Tennakoon, T.M.K.I.B.; Kumari, M.R.D.G.; Thomas, M.P.; Seneviratne, V.N.
Cardiovascular diseases derived from atherosclerosis are the most common cause of mortality worldwide. Nevertheless, it has been found that the current drug treatment methods are incapable of regressing atherosclerosis plaques. Some studies have shown that cyclodextrins (CDs) can regress atherosclerosis plaques by dissolving the intracellular and extracellular cholesterol crystals (CCs), which induce an artificial inflammatory response that could destabilize the atherosclerosis plaques. Current work presents a novel synthesis route using the co-precipitation method to synthesize β-cyclodextrin coated magnetite nanoparticles (BCD-MNPs). An inclusion complex (S@BCD-MNPs) was assembled between Simvastatin and BCD-MNPs using the co-evaporation technique to enhance the efficiency of BCD-MNPs performance. Synthesized particles were characterized using powder X-ray diffraction (PXRD), Fourier-transform infrared spectrophotometry (FTIR), scanning electron microscopy (SEM)) and thermogravimetry analysis (TGA). SEM results showed that synthesized BCD-MNPs and S@BCD-MNPs are in the range of (59.51±11.19) nm and (49.41±13.15) nm, respectively. The appearance of characteristic β-CD bands at 1048 cm⁻¹ and 3650-3050 cm⁻¹, corresponds to -OC-O-CO- stretching (α-1,4-glycosidic linkages) and O- H stretching (alcohol groups) in BCD-MNPs FTIR spectra confirmed the successful functionalization of BCD-MNPs. Furthermore, TGA data shows 7.18% (W/W) weight loss, corresponding to the thermal decomposition of β-CD in the temperature range of 180-350 °C for BCD-MNPs. Simvastatin loading and Simvastatin releasing profiles in a cholesterol microenvironment were studied with the help of a UV- Visible Spectrophotometer (UV-Vis). Drug loading efficiency was found to be 65.5%. The trend in UV- vis absorbance for the simvastatin release profile in the cholesterol microenvironment shows that the cholesterol content in the medium decreases and the simvastatin content in the medium increases over time.
Chitosan-coated magnetite nanoparticles loaded with polar extracts of Osbeckia octandra leaf
(Postgraduate Institute of Science (PGIS), University of Peradeniya, Sri Lanka, 2022-10-28) Kumari, M.R.D.G.; Tennakoon, T.M.K.I.B.; Rajapakse, R.M.G.; Thomas, M.P.; Bandara, B.M.R.; Rajapakse, R.P.V.J.
Targeted drug delivery improves drug bioavailability and safety, particularly in cancer chemotherapy. When drug-loaded magnetite nanoparticles (MNPs) are employed, the rate of drug release can be controlled by an external magnetic field. The present study aims to synthesize chitosan-coated magnetite nanoparticles (CMNPs) loaded with leaf extracts of Osbeckia octandra; chitosan, a linear copolymer polysaccharide derived from chitin, confers biocompatibility to magnetic nanoparticles. The plant O. octandra, which is endemic to Sri Lanka, is known for its anticancer, antidiabetic, and hepato-protective properties. The dry leaf powder of O. octandra was extracted sequentially with hexane, dichloromethane, methanol, and water using Soxhlet extraction. The antioxidant capacity of the sequential extracts was determined using 2,2- diphenyl-1-picrylhydrazyl (DPPH) radical scavenging and ferric reducing antioxidant power (FRAP) assays; antioxidants prevent free radical damage associated with cancer development. To evaluate the toxicity of the extracts toward healthy cells, the extracts were subjected to in vitro cell viability studies on Vero 76 cells. The polar extracts (methanol and water) displayed the highest antioxidant capacity comparable to that of ascorbic acid and the highest cell viability (100%) on Vero 76 cells. Accordingly, the methanol and water extracts were treated with CMNPs to obtain the corresponding extract-loaded nanoparticles, MCMNPs and WCMNPs, respectively; MNPs were prepared by the co-precipitation method and CMNPs by surface coating of MNPs with chitosan. The presence of magnetite in each type of magnetic nanoparticles was confirmed by powder X-ray diffractometry and Fourier transforms infrared (FTIR) spectroscopy. Scanning electron microscopy revealed the average particle size of MNPs, CMNPs, MCMNPs, and WMNCPs as 34.19±9.34, 32.67±7.21, 42.89±8.73, and 41.49±8.21 nm, respectively. The incorporation of chitosan into CMNPs was indicated by FTIR, and thermogravimetric analysis (TGA) revealed that 20.4% of the MNP was coated with chitosan. Methanol and water extracts were loaded onto CMNPs with encapsulation efficiencies of 81% and 70%, respectively.
Highly conducting fluorine-doped tin oxide thin films by spray pyrolysis technique for optoelectrical applications
(Postgraduate Institute of Science (PGIS), University of Peradeniya, Sri Lanka, 2022-10-28) Rathnayaka, K.U.R.R.S.; Bandara, T.M.W.J.; Kumara, G.R.A.; Wijayaratne, K.
Transparent conductive oxide (TCO) films are one of the main components of many electrochemical devices, such as dye solar cells (DSCs) and supercapacitors. Fluorine-doped tin oxide (FTO) films are the most widely used TCO substrates due to their inexpensive preparation and higher temperature tolerance. As a rule-of-thumb, FTO films with 80% transmittance and a standard sheet-resistance (Rₛₕ) value of 10 Ω □⁻¹ are usually chosen for solar cell applications. Optical transmittance and electrical sheet resistance trade off each other. Here, the effect of spray time on FTO layer thickness, sheet resistance, transparency, and film morphology was studied. For this purpose, a series of FTO films were prepared on glass substrates by changing the film thickness by varying the spray time. The precursor solution, containing 9.01 g of SnCl₄.5H2O and 2.40 g of NH₄F in 400 cm3 of methanol, was sprayed onto a soda-lime glass substrate at 500 °C. The electrical, optical, structural, and morphological properties of fabricated FTO films were compared with a commercially available FTO glass (CFTO) sample. In addition, a series of DSCs was prepared using fabricated FTO films and CFTO. By using a simple spray pyrolysis technique, it was possible to reduce the sheet resistance of FTO film below 1 Ω □⁻¹ while keeping the resistivity around 3.5 Ω cm. According to the DSCs prepared using these films, better energy conversion efficiencies can be obtained via FTO films with low transparency and low sheet resistance. Their stability and fill factor were significantly better (higher than 70%) than standard commercial FTO films with higher transmittance (T) and average Rₛₕ. The efficiency of the DSC series showed a linear relationship with T² /Rₛₕ. The results indicate the transparency of FTO is not a dominant factor, and translucent FTO films with carefully controlled light scattering properties may be used in fabricating dye solar cells with superior efficiency.
Nanoliposomes of Spondias pinnata stem bark aqueous extract: in vitro antidiabetic activity and releasing profiles
(Postgraduate Institute of Science (PGIS), University of Peradeniya, Sri Lanka, 2022-10-28) Wadasinghe, R.R.; Kalansuriya, P.; Attanayake, A.P.; Bandara, B.M.R.
Nanoliposomes are amongst the most versatile lipid‐based carriers, which can encapsulate a range of compounds with different polarities. Decoctions, prepared from Spondias pinnata (L. f.) Kurz (wal ambarella) stem bark is used in Sri Lankan traditional medicine for the management of diabetes mellitus. Encapsulation of aqueous extract of stem bark (SAE) of S. pinnata in nanoliposomes could enhance its therapeutic potential by increasing bioavailability and providing controlled release. The present study investigates the in vitro anti-hyperglycaemic activity of SAE-encapsulated nanoliposomes (SAE-NLS) using α-amylase inhibitory, α-glucosidase inhibitory, glucose uptake, and glucose adsorption assays along with in vitro release profiles. Dried, powdered stem bark parts of S. pinnata were extracted using distilled water under ultrasonication to prepare SAE. SAE-NLS were synthesized from SAE, [phosphatidylcholine and cholesterol (20:1)] and an aqueous phase [phosphate buffer saline (pH 6.8) with Tween® 80 (0.1% v/v)], using a modified emulsification and ultrasonication methods. The synthesized SAE-NLS were characterized via size, zeta potential and FTIR data, encapsulation efficiency (EE) and loading capacity (LC) determination. The free polyphenol content was determined by the Folin-Ciocalteu method and was used in the estimation of EE. Further, the in vitro antidiabetic activity of SAE-NLS was screened using α- amylase, α-glucosidase inhibitory, glucose uptake and glucose adsorption activity assays. The Z-average particle diameter (389 nm), polydispersity index (0.37), and zeta potential (−27.27 mV) of SAE-NLS indicated moderate polydispersity. The free polyphenol content was determined by the Folin-Ciocalteu method. The highest EE (95.42±0.56%) and LC (0.02±0.00%) were observed when SAE was loaded at 3.0% w/v. The α-amylase inhibitory activity and α-glucosidase inhibitory activity (IC50) of SAE-NLS were 2.29±0.14 and 1.44±0.03 mgmL-1, respectively, while those for SAE were 0.05±0.01 and 0.08±0.00 mg mL-1, respectively. The glucose uptake (16.07±0.14%) at 10 mM glucose concentration and glucose adsorption (0.22±0.06 mmolg-1) of SAE-NLS at 50 mM were significantly higher (p<0.05) than those of reference standard metronidazole (5.81±1.27% and 0.05±0.01, respectively). The release of SAE from SAE-NLS was higher in simulated gastric fluid (60.63±0.27%) than in simulated intestinal fluid (24.11±0.94%) after 10 h. SAE-NLS showed higher α-glucosidase inhibitory and glucose adsorption activities than acarbose, and metronidazole, respectively. The results revealed that SAE-NLS are potential nanocarriers with potent in vitro antidiabetic activity providing controlled release.
Removal of calcium and magnesium ions from sludge generated in electrocoagulation and development of a method to separate aluminium ions
(Postgraduate Institute of Science (PGIS), University of Peradeniya, Sri Lanka, 2022-10-28) Jayasekera, N.K.; Herath, A.C.
A sludge generated during electrocoagulation (EC) consists of harmful ions which could cause deleterious effects on the environment. Instead of simply discarding it, the ions trapped in sludge can be separated and recovered to gain economic value. The present study focused on developing a method to separate Mg²⁺ , Ca²⁺ , and Al³⁺ present in sludge. A sludge consisting of Mg²⁺, Ca²⁺, and Al³⁺ was generated through EC. It was dissolved in HCl, and upon the addition of NaOH, a precipitate of Mg(OH)₂ and Ca(OH)₂ was formed while Al³⁺ got converted into[Al(OH)₄ ] −. After sucrose was added to the precipitate, Mg(OH)₂ remained while Ca(OH)₂ converted into a soluble complex of Ca²⁺. The Ca²⁺ component was separated as CaCO₃ by passing CO₂ to the calcium-sucrate solution. At the end of the procedure, 53% and 68%, respectively, of Mg(OH)₂ and CaCO₃ were separated from the sludge. These high recovery percentages indicate this method is suitable for separating Ca²⁺ and Mg²⁺, and the isolated CaCO₃ and Mg(OH)₂ can be used as industrial raw material. As the recovery percentage of sucrose was 98, it is possible to reuse it in this procedure. Next, a method was developed to remove [Al(OH)₄ ] − in the filtrate. A polyaniline/zirconia composite (PZC) was synthesized and equilibrated with a 100 mg/l [Al(OH)₄] − solution at different pH values. These ions received a removal efficiency of 85% at pH 9. Therefore, this method could be applied to remove Al³⁺ present in the sludge after converting it into[Al(OH)₄ ] −. The recovery percentages of Ca²⁺ and Mg²⁺ indicate that further improving this treatment method by optimizing the conditions would be beneficial in minimizing sludge disposal problems.

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