International Research Symposium on Pure and Applied Sciences (IRSPAS)
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Item Electrodeposited metal sulfide thin films for gas sensing applications(4th International Research Symposium on Pure and Applied Sciences, Faculty of Science, University of Kelaniya, Sri Lanka, 2019) Namawardana, D. G. K. K.; Wickramathilaka, P. A. K. Y.; Atapattu, H. Y. R.; De Silva, D. S. M.Quantitative measurements of gases are based on a variety of physical or chemical principles. Among them semiconductor gas sensors are best candidates for the development of commercial gas sensors due to their higher specificity and sensitivity. They are mainly based on metal oxide and metal sulfide materials. Due to certain drawbacks of metal oxides, metal sulfides are extensively investigated as novel gas sensing materials. In this study ZnS and CdS were investigated for their gas sensing ability. Both types of thin films were fabricated by electrodeposition using a three electrode electrolytic system consisted of a fluorine doped tin oxide glass substrate (1×3 cm2) as working electrode and a high purity carbon as counter electrode. An aqueous electrolyte containing CdCl2 (0.10 mol/L) and Na2S2O3 (0.01 mol/L) precursors were used for the electrodeposition of CdS material and aqueous electrolyte containing ZnCl2 (0.10 - 0.05 mol/L) and Na2S2O3 (0.01 - 0.05 mol/L) precursors were used for electrodeposition of ZnS material. The CdS depositions were carried out in the cathodic deposition potential (CDP) range of 0.65 to 0.70 V vs. saturated calomel electrode and pH range of 1.5 to 2.0 at a temperature of 55 °C for 30 minutes. The ZnS depositions were carried out in the CDP range of 0.70 to 1.10 V vs. Ag/AgCl reference electrode and pH range of 4.0 to 3.5 at a temperature of 30 °C for 90 minutes. Both types of thin films were characterized for their crystalline structure, surface morphology, and elemental composition by using the techniques of X-ray diffraction spectroscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy respectively and were exposed to various gases namely; NO2, H2S, and LPG. CdS thin films grown at CDP of 0.67 V and pH of 1.5 and ZnS thin films grown at CDP of 1.05 V and pH of 3.7 were found to have notable gas sensing properties. CdS has shown highest resistance variation of 1.2 Ω towards H2S with respect to the initial resistance of 36.0 Ω and ZnS has shown highest resistance variation of 2 Ω with respect to the initial resistance of 26.2 Ω when exposed to NO2 gas at 30 oC. Both CdS and ZnS thin films showed resistance variation of 1.1 Ω and 0.6 Ω towards LPG respectively at 30 oC.Item An alternative sulfur precursor for chemical bath deposition of CdS thin film(Gajanayake, G. K. U. P., De Silva, D. S. M and Atapattu, H. Y. R. (2019). An alternative sulfur precursor for chemical bath deposition of CdS thin film. 4th International Research Symposium on Pure and Applied Sciences, Faculty of Science, University of Kelaniya, Sri Lanka. p98, 2019) Gajanayake, G. K. U. P.; De Silva, D. S. M.; Atapattu, H. Y. R.Solar energy is the most appropriate electrification method for a tropical county like Sri Lanka. At present, Sri Lanka generates more than 72% of its electricity needs at a high cost by burning coal and diesel. To overcome the major obstacle of high initial cost in installation of solar power plants, many research groups worldwide at present are focusing towards manufacture of low cost and highly efficient photovoltaic cells based on cadmium sulfide and cadmium telluride (CdS/CdTe) semiconductors. Among the range of methods available for fabrication of CdS window layer, the chemical bath deposition (CBD) is an ideal method due to its simplicity and low cost. In this study, CdS layers were deposited on the FTO glass substrate by CBD method, using an alternative sulfur precursor; ammonium thiosulfate ((NH4)2S2O3) against the well-established but costly precursor thiourea (CS(NH2)2). The CBD bath was prepared with 0.25 mol/L cadmium acetate (Cd(CH3COO)2), 1.00 mol/L ammonium acetate (NH4COOCH3), concentrated NH4OH (pH adjuster), and 0.50 mol/L (NH4)2S2O3. The best growth condition for CdS was identified by varying the parameters; Cd:S ratio, pH, deposition temperature, and deposition time while preserving a constant stirring speed. Uniform CdS layers rich in Cd, were observed in an alkaline electrolyte with Cd:S ratio of 2:5 at a temperature of 95 °C in 90 minutes. The spectrophotometric studies revealed the energy band gap of the material as 2.41 eV which is the typical value for CdS. Further, the X-ray diffractions observed at angles of 26°, 28°, 36°, and 53° representing the planes of (002), (101), (102), and (201) verified the cubic structure, while the scanning electron microscopic studies confirmed the uniform surface morphology of the material with average grains sized of 105 nm. However, the presence of pin-holes observed in the cross-sectional view implied the need of further optimization of parameters to obtain materials comparable to thiourea based chemical bath deposited CdS layers.Item Development and application of rice-straw biochar for removal of selected heavy metals (Pb, Cd and Cr) in contaminated paddy soil.(International Research Symposium on Pure and Applied Sciences, 2017 Faculty of Science, University of Kelaniya, Sri Lanka., 2017) Irosha, K. P. C.; De Silva, D. S. M.Biochar which is derived from carbon rich biomass such as wood, manure and leaves, is increasingly recognized as multifunctional material for various applications like contaminant management in soil and water, soil amendment in agriculture etc. In this study, rice-straw derived biochar was produced at a temperature of 400 ºC in the presence of concentrated H3PO4. The resulted biochar was subjected to oxidation by different agents including KOH, HNO3 and H2O2 to enhance its adsorption properties. The pore size distribution of modified, non-modified and commercial biochar types was studied using scanning electron microscope (SEM) technique and functional group analysis was carried out using the Fourier transform infrared spectroscopic (FTIR) technique. The FTIR spectroscopic analysis revealed significant increase in concentrations (based on peak area with constant amount of samples) of the functional groups such as carboxylic, alcoholic hydroxyl, phenolic hydroxyl and carbonyl groups available on the surface of the KOH treated sample. The SEM analysis revealed about 40% increment in pore diameter of the rice straw biochar that was modified with KOH. The paddy soil sample analyzed was amended with known amounts of heavy metal (Pb, Cd, and Cr) containing salts prior to analysis. To study the heavy metal adsorption capacity of modified, non-modified rice straw biochar and commercial biochar types, biochar (5 g x 7) which were packed and sealed in cellulose bags (5 x 5 cm2) were introduced to the soil samples (3 kg in a side sealed rain-gutter). All the experiments were performed in triplicate. The amounts of heavy metals in amended soil, after treating with biochar, and adsorbed by biochar were measured using Atomic absorption spectroscopic (AAS) technique. The AAS study revealed that all modified rice straw biochar types adsorbed heavy metal ions more efficiently than its non-modified counterpart. Further, this analysis revealed that H2O2 treated biochar is more likely to adsorb Pb and Cd, while the KOH treated biochar is more suitable for Cd and Cr adsorption.Item Intrusion of Cd, As, Cr, Pb & Hg into selected rice varieties (Oryza sativa L.) in relation to their status in two different agricultural management systems.(International Research Symposium on Pure and Applied Sciences, 2017 Faculty of Science, University of Kelaniya, Sri Lanka., 2017) Navarathna, N. M .C. M.; Pathiratne, K. A. S.; De Silva, D. S. M.Five traditional varieties (TRV) and five newly improved hybrid varieties of paddy (NIRV) were cultivated under both conventional and organic farming conditions during Yala and Maha seasons at selected areas in Anuradhapura district where chronic kidney disease was prevalent and Kurunegala districts where chronic kidney disease was not known to exist at the time of the study. The area used for cultivation under each organic and conventional farming condition in each district was approximately 11 m x 11 m and was well separated from each other. The contents of each of the selected toxic elements; Cd, As, Cr, Hg, and Pb in the soil, irrigation water, conventional and organic fertilizers and pesticides used for cultivation together with the relevant physicochemical parameters for soil were estimated before the beginning of the cultivation while the required physicochemical parameters and contents of the elements in irrigation water were estimated regularly during the cultivation. After the maturity periods at each cultivation, paddy were harvested and the contents of the elements in rice grains, straws and roots were determined. All samples for determination of the elements were processed and microwave acid digested according to US EPA 3052 method and analyzed using atomic absorption spectrometer. (Hitachi ZA3000 Zeeman Polarized). Analytical methods were validated using either standard reference materials or recovery tests. The study revealed that, the contents of any of the selected elements in any of the rice varieties grown did not exceed the safe limits of 200 μg kg-1 for Cd, 200 μg kg-1 for As, 300 μg kg-1 for Pb, 2000 μg kg-1 for Cr and 20 μg kg-1 for Hg recommended by the World Health Organization (WHO) and Food and Agricultural Organization (FAO) for milled rice. Hg, As and Pb were not detected in any of the rice varieties grown. The highest content of Cr detected was one tenth of the allowable WHO limit of 2000 μg kg-1. The contents of cadmium were in the range below the detection limit of 159 μg kg-1. Arsenic was below the detection limits in agrochemicals, soils and irrigation waters. Pb and Cr were present in fertilizers below the SLSI limits of 10 mg kg-1 and 250 mg kg-1, respectively. Slightly elevated levels of cadmium (1.80 mg kg-1 to 3.44 mg kg-1) were detected in Muriate of Potash (MOP) and Triple Super Phosphate (TSP) respectively. The green fertilizers contained Cd in the range from 0.44 mg kg-1 to 1.67 mg kg-1 . Irrigation water did contain Cd below the detection limits of 0.2 ± 0.0 μg L-1, while Cr contents were in the range of 13.8 ± 1.9 μg L-1 to 157.9 ± 22.7 μg L-1. The Cd contents in paddy soils were in the range 0.41 ± 0.02 mg kg-1 to 0.75 ± 0.03 mg kg-1 and while the Cr contents were in the range 1.33 ± 0.15 mg kg-1 to 1.63 ± 0.09 mg kg-1. Cd was detected in rice straws along with roots in the range, 12.2 ± 2.6 μg kg-1 to 1582 ± 74.3 μg kg-1.