RESCON 2022

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

Browse

Now showing 1 - 20 of 198

Ammonia gas detection using doped Zinc oxide thin films
(Postgraduate Institute of Science (PGIS), University of Peradeniya, Sri Lanka, 2022-10-28) Ranasinghe, R.A.U.D.; Bandaranayake, P.W.S.K.
Ammonia is a toxic gas which is harmful to human health and the environment. It is mainly emitted from agricultural fertilizer and in manufacturing plastics, dyes and fabrics. The exposure limit of ammonia to the human being is 25 mg l⁻¹ for 8 h or 35 mg l⁻¹ for 10 minutes. Therefore, accurate monitoring of ammonia gas in the environment is critical. The present study investigates doped zinc oxide thin films for constructing low-cost, quick-response and high-sensitivity ammonia gas sensors. Pure zinc oxide (ZnO), Al-doped and Fe-doped ZnO thin films were synthesized on glass or alumina slides via a simple and costeffective sol-gel method using zinc acetate, 2-methoxyethanol and monoethanolamine. The elemental composition, structure and surface morphology of crystals were characterized by X-ray fluorescence (XRF), X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. In addition, the effects of various doping materials on optical properties were investigated by UV-Visible spectroscopy. The bandgap energy (Eg) for pure ZnO thin films was 3.40 eV, and the lowest bandgap energy of 3.38 eV was observed for Al-doped thin films. The sensor responses for Al-doped ZnO thin film are 83% and 49% for 500 mg l⁻¹ NH3 at operating temperatures of 200 ⁰C and at room temperature, respectively. The response time and recovery time at 200 ⁰C were 11 and 7 min, respectively. The gas sensing analysis showed that increased NH₃ concentration and doping material improved the gas sensing response.
Fabrication of reduced graphene Oxide-based paper using L-ascorbic acid
(Postgraduate Institute of Science (PGIS), University of Peradeniya, Sri Lanka, 2022-10-28) Samarakkody, H.H.; Dahanayake, D.W.P.; Liyange, J.P.; Bandara, L.R.A.K.
Reduced graphene oxide (rGO) is a material with potentially interesting properties which leads to many applications. Paper-based rGO is effective in applications like bioelectrical electrodes, water purification and sensors. Fabrication of paper-based rGO begins with oxidizing graphite to graphene oxide (GO) and reducing paper-based GO using chemical or thermal reduction. In chemical reduction, hydrazine hydrate (H₆N₂O), sodium borohydride (NaBH₄), and hydroiodic acid (HI) are used, as they are strong reducing agents. However, their toxic nature has doubted the possibility of using paper-based rGO for bioelectric signal acquisition and water purification. Therefore, there is a necessity to fabricate paper-based rGO using green and non-toxic methods. This study presents a novel method of fabricating cellulose membrane (CM) filter paper-based rGO using L-ascorbic acid, a non-toxic reducing agent. The precursor, GO, was synthesized by the modified Hummer's method using Sri Lankan graphite. The vacuum filtration technique was used to deposit GO on the CM filter paper, and the CM filter paper-based GO reduced at 70 ºC using L-ascorbic acid. Fourier-transform infrared spectroscopy (FTIR) and Raman spectroscopy confirmed the deposition of GO and the reduction state of paper-based GO. Oxygen functional groups seen in the FTIR spectrum of CM filter paper-based GO confirmed the hydrophilic nature, which helps the proper bonding between GO and CM filter paper. Raman analysis revealed a significant increase in ID/IG ratio from 0.886 to 1.186 and I2D/IG ratio from 0.030 to 0.076 after reducing CM filter paper-based GO with the concentration of 500 mg l⁻¹ at 70 ºC. This increase showed the reduction ability of L-ascorbic acid and the restoration of carbon-carbon bonds under sp² hybridization. Also, the I2D/ IG ratio increased as the GO concentration increased from 62.5 mg l⁻¹ to 500 mg l⁻¹, indicating that the optimized CM filter paper-based rGO may have high electrical properties.
Adsorption of Trp-cage mini protein on a graphene surface: a molecular simulation approach
(Postgraduate Institute of Science (PGIS), University of Peradeniya, Sri Lanka, 2022-10-28) Jayaweera, A.P; Weerasinghe, S.
Examination of protein adsorption to solid surfaces with molecular dynamic simulations will yield many different aspects of innovations in the field of biochemistry. In contrast to computational simulations, laboratory experiments for protein adsorption on solid surfaces are rather expensive and time-consuming. Therefore, a computational approach is preferred, and protein adsorption to solid surfaces remains a challenge to chemists due to its highly complex behaviour. This research was primarily focused on trpcage mini protein (PDB ID: 1L2Y) adsorption on a graphene solid surface. Molecular dynamic simulations were conducted using GROMACS software, and the Kirkwood-Buff derived force field (KBFF20) was incorporated. Four simulations were conducted: the original protein near the solid surface, the protein rotated by 180° around a horizontal axis, and the protein adsorption on the solid surface having +0.1e or - 0.1e partial charge on each atom in the graphene layer. Adsorption was explained by the change of distance between the centre-of-masses (COMs) of protein and the graphene surface along the vertical axis. The diffusion coefficient was used to indicate the rate of adsorption of the protein. The first and second simulations concluded that the protein was stable near the COM distances of 0.732 nm and 0.760 nm starting from 1 nm away from the graphene surface. The calculated average one-dimensional diffusion coefficients along the vertical axis were 1.914 (±0.008) × 10⁻⁴ nm² ns⁻¹ and 1.248 (±0.009) × 10⁻⁴ nm² ns⁻¹ for simulations one and two, respectively. For other simulations, overall adsorptions of the protein were not indicated. The study concludes that protein adsorption depends on the number of hydrophobic and hydrophilic residues exposed to the solid surface, and the more hydrophobic residues it has, the higher tendency for the protein to adsorb onto the non-polarized surface.
Closed space sublimated cds thin films for Cds/CdTe solar cells: effect of Cds layer thickness
(Postgraduate Institute of Science (PGIS), University of Peradeniya, Sri Lanka, 2022-10-28) Bandara, K.M.N.S.; Lakmal, A.A.I.; Seneviratne, V.A.; Dissanayake, M.A.K.L.; Dassanayake, B.S.
The target of photovoltaic systems has always been to reduce costs while increasing efficiency. Cadmium telluride (CdTe) has a narrow bandgap of 1.45 eV and is utilized as the absorber material in CdS/CdTe thin film solar cells, while cadmium sulfide (CdS), which has a wider bandgap of 2.42 eV, is used as the window material. There are numerous ways to deposit a CdS window layer, and among them, the close-spaced sublimation (CSS) technique is one of the most effective methods. The work reported here mainly focused on optimizing the thickness of CSS synthesized CdS window layer. To reach the desired thickness range, the deposition time duration was changed from 100 to 180 s. Temperatures for the source and substrate were set at 660 and 560°C, respectively. Around 2-3 Torr of an inert atmosphere was maintained using Ar gas. UV-visible spectroscopy was used for the optical characterization, and a PEC L01 solar simulator was used to study the electrical characteristics. The thickness of the CdS layer was measured using an X-ray fluorescence spectrometer. The highest average efficiency of 7.0% was obtained for the small area dot cells of 0.2 cm² , with an open-circuit voltage (VOC) of 692 mV, a short circuit current (JSC) of 20.2 mA/cm² , and a fill factor (FF) of 50.3% under the AM 1.5 illumination for the deposited CdS layer thickness of 310 nm.
Solute descriptors for cinnamyl acetate by gas chromatography and liquid-liquid partition systems
(Postgraduate Institute of Science (PGIS), University of Peradeniya, Sri Lanka, 2022-10-28) Hewage, K.P.; Ariyasena, J.A.T.C.
Cinnamyl acetate is a naturally occurring compound in Cinnamon leaf oil. It is widely used in the flavour and fragrance industry because of its sweet balsamic and floral odour. Hence, the quantification of its properties, such as toxicity, is important as it is used in cosmetics which are in direct contact with the consumer. The conventional methods of determining these properties are costly and need a significant amount of human and technical resources. However, the use of the Abraham solvation parameter model, which is based on the quantitative structure-property relationships, has become popular in estimating solute properties and the environmental distribution with significantly lower cost by using fewer resources. This model is expressed as 𝑙𝑜𝑔 𝑙𝑜𝑔 𝑆𝑃 = 𝑐 + 𝑒𝐸 + 𝑠𝑆 + 𝑎𝐴 + 𝑏𝐵 + 𝑣𝑉 for transfers between two condensed phases. Here, SP is a Free energy-related solute property, simple letters are system constants, and capital letters are Solute descriptors. V: McGowan’s Characteristic Volume, E: excess molar refraction, S: dipolarity/polarizability, A and B: hydrogen-bond acidity and basicity. The determination of solute descriptors for cinnamyl acetate was carried out using the gas chromatographic technique with poly (dimethyldiphenylsiloxane) and poly (cyanopropylphenyldimethylsiloxane) stationary phases and organic biphasic partition systems. The stationary phases were calibrated, and isothermal retention factor values were determined at 20 °C intervals from 80 °C to 260 °C. Cinnamyl acetate was equilibrated in 19 organic biphasic systems, and the partition coefficients were determined. The descriptor values were then determined using the Solver algorithm in MS excel® such that the standard deviation would be minimum. The determined descriptor values for cinnamyl acetate are, E= 0.983 S=1.203 A= 0.000, L=5.980, B= 0.648 and V= 1.453, respectively, with a standard deviation of 0.077. The determined descriptor values can be used to estimate the distribution of cinnamyl acetate in environmental and industrial partition compartments.
Antimicrobial and antioxidant activities of stingless bee (Tetragonula praeterita and T. iridipennis) propolis from Ratnapura district, Sri lanka
(Postgraduate Institute of Science (PGIS), University of Peradeniya, Sri Lanka, 2022-10-28) Pathirana, W.P.C.O.; Welegedara, A.P.; Nanayakkara, B.S.; Karunaratne, W.A.I.P.
Propolis is a biologically active, resinous substance produced by stingless bees by mixing their saliva and wax excretions with substances collected from botanical sources. Accordingly, the bioactivity of propolis depends on many factors, including geographical region, vegetation, and bee species. According to literature, ethanolic extract of Tetragonula iridipennis (TI) stingless bee propolis collected from Kandy, Sri Lanka, shows a remarkable in vitro antioxidant activity against 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical and antibacterial activity against Gram-positive bacteria [Minimum Inhibitory Concentration (MIC) values of 16 - 32 mg L⁻¹ ]. The bioactivities of propolis collected from other districts of Sri Lanka have not been reported. Therefore, the current study aimed to investigate the antimicrobial and antioxidant activities of Tetragonula praeterita (TP) and TI stingless bee propolis sourced from Ratnapura, Sri Lanka. The ethanol extracts of propolis were obtained using the Soxhlet method. The antioxidant and antimicrobial activities of extracts were determined using the DPPH radical scavenging assay and agar dilution method by determining the MIC, respectively. The TI extract showed a higher antioxidant activity (IC₅₀=253.707±6.075 mg L⁻¹ ) compared to the TP extract (IC₅₀=737.493 ± 8.451 mg L⁻¹ ) while that of Lascorbic acid was IC₅₀ = 8.140 ± 0.093 mg L⁻¹ . Antimicrobial activity was tested against three Gramnegative (Escherichia coli, Klebsiella pneumoniae and Pseudomonas aeruginosa), two Gram-positive (Staphylococcus aureus and Methicillin-Resistant Staphylococcus aureus-MRSA) bacterial strains and the fungus, Candida albicans within the concentration range of 16 to 1,280 mg L⁻¹ . TI extract showed remarkable antimicrobial activity, with MICs of 16 mg L⁻¹ . In contrast, the MICs of TP extracts were ≥ 320 mg L⁻¹ . Our results, compared with the previous findings, emphasize the dependence of the propolis bioactivity on the bee species and vegetation from which the bees source their food and hive-construction material.
Efficient dye-sensitized solar cell containing binary salt electrolyte and irradiance level dependance of their performance
(Postgraduate Institute of Science (PGIS), University of Peradeniya, Sri Lanka, 2022-10-28) Wickramasinghe, H.M.N.; Wijayaratne, K.B.; Bandara, T.M.W.J.
Liquid electrolytes (LEs) are being used as electrolytes in Dye-Sensitized Solar Cells (DSSCs) due to their superior conductive properties and versatility. The electrical contact between electrolytes and porous electrodes can be easily achieved using LEs since LEs readily diffuse into pores and voids of electrodes. Therefore, in general, LE-based DSSCs deliver higher efficiencies. However, the adverse effects of liquid electrolytes, such as electrolyte leakage, volatility, and flammability, should be mitigated to prepare chemically and physically statable DSSCs. In this study, the performances of new LE-based DSSCs have been investigated. DSSCs exhibit enhanced charge transport properties, leading to higher efficiency for photoelectrochemical energy conversion applications. The effect of the frequency dependence of the real and imaginary components of the AC conductivity on the dielectric polarization of the electrolyte was investigated to comprehend the capacitive effect of the cell. The novel liquid electrolyte investigated in this study comprised ethylene carbonate (EC), propylene carbonate (PC), 1-butyl-3-methylimidazolium iodide (BMII), 4-tert-butyl pyridine (4TBP), tetrahexylammonium iodide (Hex4NI), and lithium iodide (LiI). The combination of iodide salts establishes a binary system of small and large cations instead of a conventional single-salt electrolyte. The ambient temperature conductivity of the electrolyte was 11.43 mS cm⁻¹ , which is high enough to prepare efficient DSSCs. This electrolyte, previously optimized TiO₂ multi-layer photoelectrodes, and standard Pt counter electrodes were used in assembling DSSCs. When observed under definitive 1,000 W m⁻² simulated solar irradiation, the highest conversion efficiency was 8.37%. The corresponding short circuit current density (Jsc) was 16.61 mA cm⁻² , the open-circuit voltage (Voc) was 720 mV, and the fill factor (FF) was 69.99%. However, when the light intensity was reduced to 397 W m2 , a significantly high efficiency of 10.57% was observed. Further, it was observed that the heavy ions as a binary salt system improve the performance of the studied liquid electrolyte without compromising the short-term stability.
Activated carbon synthesized from jack wood for supercapacitors
(Postgraduate Institute of Science (PGIS), University of Peradeniya, Sri Lanka, 2022-10-28) Alahakoon, A.M.B.S.; Wickramasinghe, H.M.N.; Bandara, T.M.W.J.
Supercapacitors (SCs), a novel energy storage system, have attracted significant attention because of their higher power density and longer cycling stability compared to those of secondary batteries. In addition, their energy density is higher than that of traditional capacitors. As an electrode material, activated carbon has many advantages, such as high surface area and porous structure, high chemical and thermal stability, and comparably high electric conductivity. In this study, electrochemical double-layer capacitors (EDLC) are prepared using the activated carbon (AC) derived from Jack wood (Artocarpus heterophyllus). Porous carbon material with a high surface area was prepared by carbonization of the Jack-wood. Subsequently, activation was accomplished by NaOH treatment and heating to 800 ⁰C for 1 h. The AC-based electrodes were prepared on fluorine-doped tin oxide (FTO) substrate in order to build SCs. In this work, biomass- based AC was prepared as electrode material, while aqueous H2SO4(1 M) was used as the electrolyte. The electrochemical properties of AC-based SCs were investigated using cyclic voltammetry and galvanostatic charge-discharge measurements. CV confirmed that charge storage takes place electrostatically without occurring any redox reactions. In addition, SCs exhibited a relatively high specific capacity of 147.19 F g⁻¹ at 2 mV s⁻¹ scan rate along with the aqueous 1 M H2SO4 electrolyte. Further, the supercapacitor demonstrated a power density of 68. 47 W kg⁻¹ and an energy density of 8.02 Wh kg⁻¹ at the charge- discharge current density of 0.5 mA cm⁻². SCs showed ∼94.98% of initial capacitance retention after 1,000 cycles implying excellent cycling stability and rate capability according to cyclic voltammetry. Recurrent charge/discharge curves confirmed specific capacitance retention of 92.58% at 3 mA cm⁻² after 100 cycles.
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.

Browse

Recent Submissions