ICAPS 2020
Permanent URI for this collectionhttp://repository.kln.ac.lk/handle/123456789/21780
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Item Electrodeposition and characterization of ZnO thin films for gas sensing(Faculty of Science, University of Kelaniya, Sri Lanka, 2020) Rathnaweera, U.M.C.; De Silva, D.S.M.; Atapattu, H.Y.R.The gas sensor is a sensing device that measures target gas molecules in a given atmosphere specially in the monitoring of environmental contaminants in air, water, and soil. Sensors based on semiconducting metal oxides are being widely used for gas or vapour sensing owing to their properties such as non-toxicity, biocompatibility, compact device structure, high sensitivity and stability and ease of syntheses. The most popular semiconducting metal oxides-based gas sensing materials are ZnO, SnO2, WO3 and TiO2. Among them, ZnO is attracted more due to its other properties such as chemical and photochemical stability and high-electron mobility. Hence, ZnO is one of the most propitious materials in developing sensors in electronic and optical technologies. In this study, characterization and fabrication of ZnO for gas sensing applications using a simple and cost-effective electrodeposition method is discussed. Aqueous electrolytic solutions of Zn (NO3)2 and ZnSO4 were used as the Zn precursors to find the best suited precursor to electrodeposit ZnO. The deposition was performed under a three-electrode electrochemical cell consisted of FTO coated glass (1×3 cm2 , 7 Ω/m2 ), graphite rod (99.995%) and a saturated Ag/AgCl electrode as the working, counter, and reference electrodes respectively. The gas sensing ability of the ZnO films, developed under different deposition parameters (cathodic deposition potential, pH of the electrolyte, precursor concentration), was studied. By obtaining the workable cathodic deposition potentials (CDP) by cyclic voltammetry, the k best suited bath pH and the temperature to develop uniform ZnO thin films were found to be 3.5 - 4.5 and 55 ℃ respectively. Subsequently, the heat treated (425 ℃ for 1 hour) samples were characterized with UV/Vis spectroscopy, X-ray diffraction, scanning electron microscopy and energy dispersive X-ray techniques to investigate the bandgap energy, crystal structure, surface morphology and the material’s composition respectively. The band gap energy of the material grown was fallen within 3.00 – 3.30 eV, while the crystals were found to be preferably grown along the [101] or [002] planes possessing hexagonal wurtzite structure in samples grown using two Zn precursors. SEM micrographs evidenced compact morphology with coral/rod-shaped appearance. According to the EDX analysis, Zn:O atomic ratio was revealed to be 1:1. The gas sensing ability of deposited films was examined against NO2 and H2S gases that causes due to electronic interactions between the crystallographic plane and the subjected gas molecules. The samples grown in 0.10 mol/L ZnSO4 at CDP 1.00 V in pH 4.50 at 55 ℃ was found to have an average sensitivity of 5% and 11% while the samples grown in 0.10 mol /L Zn (NO3)2 at CDP 1.10 V in pH 3.70 at 55 ℃ were found to have an average sensitivity of 2% and 5% after exposing to NO2 and H2S gases respectively for 5 minutes at 30 ℃.Item Catalytically induced pyrolysis of LDPE to liquid fuel(Faculty of Science, University of Kelaniya, Sri Lanka, 2020) Wickramaarachchi, W.A.A.S.; Premachandra, B.A.J.K.; De Silva, D.S.M.Plastics are used in a wide range of applications because of their durability, lightweight, easy fabrication, and desired chemical and physical properties. Usually, plastic products are discarded after use to the environment as solid waste. Therefore, the low degradability of plastics and the high demand for plastic products have created a serious environmental issue. Recycling is one of the methods used in plastic waste management. As a recycling method, energy recycling or producing fuel oil from plastic waste has gained a promising interest. In this study, it was expected to convert selected used plastics to fuel oils through a pyrolysis process using a catalyst. A laboratory-scale pyrolysis system was developed and a low-cost conversation process for plastics to fuel oil was investigated in an environmentally friendly manner. Initially, virgin low-density polyethylene (LDPE) was used in this conversion as the control sample. Then waste wrapping materials made of LDPE were subjected to pyrolysis. A two-neck round bottom flask was used as the reactor while the heat was supplied by a LP gas burner. To control overheating and possible heat losses, the reactor was dipped in a soil bath during heating. A constant heating rate and a constant inert gas flow rate to the reactor were maintained throughout the experiment. The gases evolved by the pyrolysis were condensed. The distillate was collected while the uncondensed fraction was trapped first in a non-polar organic solvent and further in a basic aqueous solution to prevent possible hazardous emissions. A locally abundant mineral was tested as a possible catalyst for the pyrolysis to improve the quality of the resulting products. It was observed that the purity of the resulting fuel oil had been improved with the use of the catalyst. The resultant liquid fraction was conveyed for factional distillation and the fractions were characterized with GC-MS and FTIR techniques. According to the GC-MS analysis, the major constituents in the fraction obtained from virgin LDPE through uncatalyzed pyrolysis were decane, undecane and 1-tetradecene. The major constituents obtained through the catalytic pyrolysis of virgin LDPE were cyclopropane, 1- decene, undecane and pentadecane. The pyrolysis of waste LDPE resulted in cyclopentane, decane, undecane and 1-pentadecene as fractional distillates. The mineral tested as the catalyst has given significant improvement in the purity of the oil fractions produced. The combustion characteristics and viscosities of the resultant oils are to be determined and those will be compared with the commercially available fuel oils. The study will be extended for other plastic waste types including mixed waste.Item Electrochemical conversion of graphite to graphene oxide: A preliminary study(Faculty of Science, University of Kelaniya, Sri Lanka, 2020) Gunarathna, M.D.; De Silva, D.S.M.Graphene-based materials are two-dimensional atomic crystals composed of sp2 hybridized carbon atoms. The family includes graphene, graphene oxide (GO), reduced graphene oxide, and graphene quantum dots. Graphene is an allotrope of carbon with hexagonal lattice and it has gained immense attention in many industries due to its exceptional applications in electronics, water purification, adsorption studies, etc. Many recent studies proposed different routes of GO synthesis. This study reports an electrochemical conversion of locally available raw graphite obtained from Bogalapathala to GO. Electrochemical conversion of graphite to graphene has great potential in the production of graphene oxide and it has gained the attention of the scientific community due to its easiness and environmentally friendly practices. The significance of the electrochemical conversion process is the minimal chemicals requirement compared to other methods developed. The local graphite powder was compressed into pellets using a pellet maker designed by the researcher with a cavity to accommodate the Pt electrode. The graphite pellet was tightly wrapped with a permeable cellulose membrane to avoid loosening of the pellet during electrochemical process. The electrochemical cell consisted of a Pt rod as the working electrode and a carbon rod is as the counter electrode. These electrodes were immersed in an (NH4)2SO4 solution and a constant potential of 10 V was applied for 2 hours. The resulted product was dissolved in deionized water and centrifuged to collect the supernatant. The supernatant was heated at 90 °C under atmospheric pressure on a hot plate to evaporate the water and the residue was characterized using FTIR, UV visible spectrophotometry, and X-ray diffraction techniques. The UV and FTIR absorption spectra and the X-ray diffraction patterns confirmed the partial transformation of graphite to GO while the maximum yield of GO obtained after the evaporation was 1% (based on the mass of graphite powder used) and further investigations need to be performed to increase the yield.Item Activation of wood biochar and red brick using natural coconut vinegar(Faculty of Science, University of Kelaniya, Sri Lanka, 2020) Malka, U.K.M.; De Silva, R.C.L.; De Silva, D.S.M.; Chandrajith, R.Number of studies have been carried out to determine the efficiency of strong oxidizers in activating natural raw materials used in low cost water purification processes. However, rural communities find it difficult to acquire most of such chemicals. Therefore, this study was aimed to determine the ability of natural coconut vinegar, which is a common domestic acidic solution, in activating abundantly available potential water purifying materials to reduce calcium (Ca2+) ions from water, further reducing the water hardness. In this study mature barks of Glyricidia (Glyricidia sepium), Gadumba (Trema orientalis) and Ipil Ipil (Leucaena leucocephala) were collected and air dried. These were carbonized (400-450 °C) in a closed vessel (2 hours) to produce biochar. Both biochar and brick particles in the range of 2.0-5.6 mm were selected for the analysis. For the activation these samples were soaked in natural coconut vinegar (biochar/brick: vinegar, 1:2 V/V) for 24 hours and completely dried in an oven (120 °C) for 3 hours. Laboratory scale glass columns (2 cm in diameter) were used to calculate Ca2+ adsorption and retaining capacities. Filtrates were analyzed for Ca2+ using flame photometer. Ca2+ adsorption and retaining capacities of each material were calculated per unit bulk volume of the material. Each test was duplicated, and the average was recorded. Untreated red brick and biochar of Glyricidia, Gadumba, Ipil Ipil showed Ca2+ adsorption capacities of 0.44, 0.30, 0.31, 0.27 mg cm3 and retaining capacities of 0.19, 0.01, 0.02, 0.02 mg cm-3 respectively. Activated red brick and biochar of Glyricidia, Gadumba and Ipil Ipil showed Ca2+ adsorption capacities of 0.76, 0.58, 0.68 and 0.63 mg cm-3 and retaining capacities of 0.25, 0.20, 0.23 and 0.15 mg cm-3 respectively. Increase in Ca2+ adsorption and retaining capacities were observed in all the materials tested after activation with vinegar. Further studies are continued to use the vinegar activated natural materials in a low-cost domestic drinking water purification process.Item Voltage and wire standards for domestic DC distribution systems(Faculty of Science, University of Kelaniya, Sri Lanka, 2020) Ariyarathne, Y.S.S.,; Jayatissa, N.W.K.; De Silva, D.S.M.Home micro-grid concepts have gained interest in the modern world due to the increased distributed generations with renewable energy sources. The present "DC-AC-DC" route from distributed generations to DC loads via inverters may not be rational from the viewpoint of system simplicity and energy efficiency. Considering the increasing prevalence of DC home appliances, establishing reasonable DC distribution standards for domestic buildings is significant. In this study, the Wattage of household electric appliances and the time duration they are being used were collected. The monthly power consumption of each appliance category was calculated. According to the results, the average monthly electricity demand of a Sri Lankan family is 111 kWh. Only eight equipment categories consume nearly 90% of domestic power. Those are refrigerators (22%), lights (16%), fans (16%), rice cookers (14%), TV (8%), irons (7%), washing machines (4%) and water pumps (3%). When considering the average maximum power demand, the most commonly available appliances have less than 1 kW maximum power demand. By considering the power requirements, to minimize the loss, and keep the system's safety at the maximum level, the midpoint grounding system with main wires at +60 VDC and -60 VDC is proposed. Using this topology, 120 V line to line potential difference can be archived with keeping the ground to line voltage within safety extra-low voltage limit as proposed by the European telecom standards. Following the IEE wiring standards, three commonly available wire sizes (2.5 𝑚𝑚2 , 4 𝑚𝑚2 , 6 𝑚𝑚2 ) were selected to analyze the suitability for the system's sub circuits. Voltage drop, power loss, short circuit current, and insulation resistance were considered to select the maximum allowable current for each wire size in a sub-circuit. Since the wire length for a sub-circuit of a domestic distribution system is usually less than 10 m, the voltage drops and the power losses are too small and negligible. The insulation resistance of each wire was tested against high voltages. All the wires show infinite resistance (more than 1 𝑇Ω) up to 2500 V. The most critical factor in wire selection is the short circuit current. According to the results, for a high power sub-circuit that require power up to 2400 W, wire size of 6 𝑚𝑚2 can be used with 20 A circuit breaker. For sub circuits with power requirement less than 1800 W, 4 𝑚𝑚2 wires can be used with a 15 A circuit breaker. And for low power sub-circuits, 2.5 𝑚𝑚2 wire can be used with 10 A circuit breaker to supply power up to 1200 W. Further studies must be carried out to determine the power/voltage losses and increase the whole distribution system's efficiency under these conditions.Item Influence of ZnS buffer layer on CdS/CdTe based solar cells(Faculty of Science, University of Kelaniya, Sri Lanka, 2020) Madhuwanthi, H.M.L.U.,; Mahanama, G.D.K.; De Silva, D.S.M.Among thin film materials, cadmium sulfide (CdS) is the best suited window material as a heterojunction partner in cadmium telluride (CdTe) based solar cells due to its wide and direct band gap. In order to enhance the solar cell efficiency, a buffer layer such as zinc sulfide (ZnS) having a relatively wider band gap can be introduced into the conventional CdS/CdTe heterojunction solar cell by reducing the thickness of CdS thin layer. ZnS/CdS is an alternative to the conventional CdS window layer since it admits and transmits the maximum amount of photons to the junction to increase the short circuit current density (Jsc) and the efficiency of the solar cell. The electrodeposition of ZnS on fluorine doped SnO2 glass (FTO) has been previously reported and this work focuses on the electrodeposition of intrinsic CdS layers on both FTO substrate and FTO/ZnS substrate, using a three electrode cell. The electrolyte used was consisted of 0.01 mol/L Na2S2O3 and 0.1 mol/L CdCl2 at pH of 1.7 at 55 °C and the deposition potential was varied between -0.68 to -0.72 V. The samples prepared were annealed at 400 °C for 15 minutes. Both thin film structures, FTO/CdS and FTO/ZnS/CdS were analyzed by the UV-Visible spectrophotometry and photoelectrochemical (PEC) cell performance to investigate the optical absorbance and its electrical properties. The optical absorption of the samples was fallen within 2.30-2.46 eV that agree with the typical band gap energy of CdS. Among the two structures, FTO/ZnS/CdS shows lower optical absorbance in 300-900 nm region, which has been recognized as a characteristic feature for a window layer in a solar cell. For the PEC cells, made with FTO/CdS, the Jsc and Jsc×Voc values were between (18.0-1.60) ×10-6 A cm-2 and (5.94-0.38) ×10-6 AVcm-2 respectively, while for the cells made with FTO/ZnS/CdS, these values were (14.8-2.50) ×10-6 A cm-2 and (6.66-0.90) ×10-6 AVcm-2 . Although the Jsc of the FTO/ZnS/CdS based cell was relatively low, the product of Jsc×Voc was high due to its high Voc. The ZnS buffer layer facilitated the electrodeposition of well adhered, compact and pinhole free CdS window layer compared to the deposition of CdS on bare FTO. Hence, the implanting of a ZnS buffer layer on CdS/CdTe based solar cell can enhance the optoelectronic properties of the final solar cell device.Item Effect of thermal annealing of CBD-CdS on the electrical properties of CBD-CdS/ED-CdTe solar cell(Faculty of Science, University of Kelaniya, Sri Lanka, 2020) Gajanayake, G.K.U.P.; De Silva, D.S.M.; Atapattu, H.Y.R.; Thivakarasarma, T.Chemical bath deposition, Electrodeposition, Thermal annealing, CdS/CdTe solar cell Thermal annealing is one of the key steps to enhance the optoelectronic properties of the CdS/CdTe solar cells. In this study, the effects of annealing temperature and annealing time of chemical bath deposited (CBD) CdS on the electrical properties of CBD-CdS/electrodeposited (ED) CdTe solar cells were investigated. CBD-CdS layers were prepared using pre-optimized deposition conditions (90 ℃, 55 min) on fluorine doped tin oxide (FTO) glass substrates utilizing a bath consisted of 0.033 mol/L Cd(CH3COO)2, 0.667 mol/L CS(NH2)2 as cadmium and sulfur precursors, respectively and therein, 1 mol/L CH3CO2NH4 and 0.735 mol/L NH4OH were used for pH adjustment. Thereafter, a set of CBD-CdS samples prepared was annealed at different temperatures (350, 375 and 400 ℃) by varying the annealing time (10, 20, 30, and 40 min). Consequently, CdTe thin films were electrodeposited on annealed CBD-CdS substrates using an ED-bath consisted of 1.0 mol/L CdSO4 and 1.0 mmol/L TeO2 at pH of 2.3, temperature of 65 ℃, and potential of -650 mV against a saturated calomel electrode. The prepared glass/FTO/CBDCdS/ED-CdTe samples were air annealed (400 ℃, 20 min) and Cu/Au back contacts were deposited using thermal evaporation technique. The electrical properties of the CBD-CdS samples were investigated by photo-electrochemical cell (PEC) study at the CBD-CdS/electrolyte junction. As per the PEC analysis, CBD-CdS sample annealed at 375 ℃, 30 min has shown the highest short circuit current density (Jsc) of 21.5 μA/cm2 , while the sample annealed at 400 ℃, 10 min shown the highest open circuit voltage (Voc) of 499 mV. The electrical properties of the CBD-CdS/ED-CdTe/Cu/Au devices were investigated under AM 1.5 light source and therein, CBD-CdS sample annealed at 375 ℃, 30 min scored the highest Jsc (14.12 mA/cm2 ) and the one annealed at 400 ℃, 10 min displayed the highest Voc (616 mV). Also, the device annealed at 375 ℃, 30 min showed the lowest series resistance (205 Ω) while the one annealed at 400 ℃, 10 min demonstrated the highest shunt resistance (1401 Ω). Accordingly, the 375 ℃, 30 min and 400 ℃, 10 min were found to be the effective conditions for annealing CBD-CdS that can result in materials with better electrical properties for CBDCdS/ED-CdTe/Cu/Au device fabrication.