Browsing by Author "Pathiratne, K.A.S."

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A kinetic study on slow natural degradation of polycyclic aromatic hydrocarbons in Bolgoda Lake waters and a technique for rapid destruction of them in the aquatic environment
(Proceedings of the Annual Research Symposium 2005-Faculty of Graduate Studies, University of Kelaniya, 2005) Pathiratne, K.A.S.; de Silva, O.C.P.
Polycyclic aromatic hydrocarbons (PAHs) are unique environmental contaminants that exhibit strong toxic, carcinogenic and mutagenic properties. They are generated through incomplete combustion of organic matter such as fossil fuels (petrol, diesel, and natural gasses, etc.), wood and many other organic compounds used in variety of industrial and domestic processes. Once formed, they are adsorbed on to particulate matter and deposited on ground and in water bodies through continuous atmospheric fallouts. During rainy seasons, PAHs deposited on ground surfaces are washed into water bodies through surface runoff. A recent study revealed that water and sediment in Bolgoda lake to contain PAHs above safe levels. Further, the levels observed during dry seasons were found to increase after heavy rains, followed by gradual degradation during dry periods. As a part of the present investigation, the kinetics of degradations of four selected PAHs; naphthalene, phenanthrene, pyrene and chrysene (2, 3, 4 and 5 member ring compounds) found in Bolgoda lake were carried out. Four different environmental matrices given below (a) to (d): (a) Bolgoda lake water exposed continuously to incandescent radiation of a 60 W tungsten lamp at room temperature. (b) Bolgoda lake water kept in dark at room temperature. (c) Deionized water with pH and electrical conductivity (EC) adjusted to those of Bolgoda lake water, exposed continuously to incandescent radiation of 60 W tungsten lamp at room temperature (d). Deionized water with pH and EC adjusted to those of Bolgoda lake water, kept in dark at room temperature. These four different media could represent unique environmental components found in Bolgoda lake that could be responsible for degradations of PAHS in the Bolgoda lake. The results indicate that pseudo first order rate constants corresponding to degradations of all four PAHs in the four different media at room temperature decrease in the order a > b > c > d. Also, in all four media the order of the pseudo first order rate constants for degradations of the four PAHs found to vary as chrysene > naphthalene > pyrene > phenanthrene. As the other part of the investigation, the suitability of a modified Fenton based oxidation process to enhance the rate of degradation of PAHs in aquatic environment was investigated. The effect of initial concentration of H2 O2 & Fe2+ ions, pH of the solution and the presence of triton X-100, a surfactant which could bring non polar PAHs and polar Fenton reagents in close proximity to facilitate degradation reaction were examined for 3,4 and 5 member ring compounds: phenanthrene, pyrene and benzo(a)pyrene found in local aquatic environments. Pseudo first order rate constants for degradations of all three PAHs found to increase with increasing initial H2 O2 concentrations and initial Fe2+ concentration in aqueous media. High degradation rates were observed for concentration ratios, [H2 O2 ]:[Fe2+] in the range of ~50 to ~100. Decrease of pH of solutions, also increased the rates of degradation of all three PAHs. Presence of Triton X-100 at low levels, (1% v/v in the solution) found to increase the degradation rates of all three PAHs. Under all conditions studied, the pseudo first order rate constants for degradation of Benzo(a)pyrene were found to be the largest among the three PAHs .
A low cost electro-deposition procedure for growth of n- type cds semiconductor material used in fabrication of cds/cdte thin film solar cells
(Book of Abstracts, Annual Research Symposium 2014, 2014) Chaturangi, R.A.; Kumarasinghe, K.D.M.S.P.K.; Pathiratne, K.A.S.; de Silva, D.S.M.
CdS/CdTe thin film solar cells have exceeded the efficiencies of nearly 20% and 16% in laboratory and industrial scale devices respectively. Owing to the large band gap of 2.42 eV of CdS semiconductor, it is used as the window material in these devices. A low cost electro-deposition experimental procedure which utilizes electro-purified analytical grade chemicals and a method which does not produce wastes need to be discarded into the environment is described here. CdS thin films with thickness <100 nm was potentiostasticaly electro-deposited utilizing EG & G Princeton Applied Research Model 366 A bipotentiostat on fluorine doped tin oxide(FTO) conducting glasses which function as working electrodes in three electrode cells comprising of silver/silver chloride reference electrodes and graphite counter electrodes. Prior to use, conducting glasses were mechanically cleaned in a dust free environment. Electro-purified CdCl2 and Na2S2O3 were used as the Cd and S sources for depositing thin films of CdS on FTO glasses. Ranges of working electrode potentials, relative proportions of the two salts and the pH in the electroplating baths which could yield CdS thin films that showed satisfactory photovoltaic activities were estimated. Bath temperature and deposition time were kept at previously established values of 470C and 1 hour for all depositions. Also all CdS thin films were annealed at 400 0C for 10 minutes in air prior to estimation of their photovoltaic properties. It was found that, deposition potentials in the range of -1300 to �1500 mV with respect to silver/silver chloride electrode, concentration ratios of [Cd]/[S] = 10:1 to 15:1 having [Cd] concentrations in the range of 10 to 15 mmol dm-3 in solution and pH in the range of (1.2�1.4) in the plating bath could produce CdS thin films with optical band gaps lying in the range of (2.3 � 0.1) eV. X-ray diffraction studies showed that all CdS deposits were to consist of cubic lattice structure. Current- Voltage measurements indicated that, the thin films grown were of n-type in electrical conductivity. Photo-electrochemical cell experiments produced open circuit voltages and short circuit current densities in the ranges of -150 to -250 mV and 3.75 to 20 ?A cm-2 respectively indicating the level of photovoltaic activity that the deposits of CdS could demonstrate. Studies are in progress for further improvements of the electro-deposition procedure.
Accumulation of heavy metals in a food fish, Mystus gulio inhabiting Bolgoda Lake, Sri Lanka
(University of Kelaniya, 2007) Senarathne, P.; Pathiratne, K.A.S.
Analysis of elemental profiles in selected industrial effluents reaching Kelani River using inductively coupled plasma spectrometry
(Sri Lanka Association for the Advancement of Science, 2013) Pathiratne, K.A.S.; Pathiratne, A.; Hemachandra, C.K.; de Silva, N.
Assessment of Bile Fluorescence Patterns in a Tropical Fish, Nile tilapia (Oreochromisniloticus) exposed to Naphthalene, Phenanthrene, Pyrene and Chrysene using Fixed Wavelength Fluorescence and Synchronous Fluorescence Spectrometry
(Bulletin of Environmental Contamination and Toxicology, 2010) Pathiratne, A.; Hemachandra, C.K.; Pathiratne, K.A.S.
Bile fluorescence patterns in Nile tilapia, a potential fish for biomonitoring tropical water pollution were assessed following exposure to selected polycyclic aromatic hydrocarbons (PAHs): naphthalene, phenanthrene, pyrene and chrysene. Non-normalized fixed wavelength fluorescence signals in the fish exposed to these PAHs reflected dose and/or time response relationships of their metabolism. Normalizing signals to biliverdin introduced deviations to these response patterns. The optimal wavelength pairs (excitation/emission) for synchronous fluorescence scanning measurements of bile metabolites of naphthalene, phenanthrene, pyrene and chrysene were identified as 284/326, 252/357, 340/382 and 273/382 respectively. This study supports the use of bile fluorescence in Nile tilapia by fixed wavelength fluorescence and synchronous fluorescence spectrometry with non-normalized data as a simple method for screening bioavailability of these PAHs.
Assessment of biological effects of pollutants in a hyper eutrophic tropical water body, lake Beira, Sri Lanka using multiple biomarker responses of resident fish, Nile tilapia
(Ecotoxicology, 2010) Pathiratne, A.; Pathiratne, K.A.S.; de Seram, P.K.C.
Biomarkers measured at the molecular and cellular level in fish have been proposed as sensitive ?early warning? tools for biological effect measurements in environmental quality assessments. Lake Beira is a hypertrophic urban water body with a complex mixture of pollutants including polycyclic aromatic hydrocarbons (PAHs) and Microcystins. In this study, a suite of biomarker responses viz. biliary fluorescent aromatic compounds (FACs), hepatic ethoxyresorufin O-deethylase (EROD) and glutathione S-transferase (GST), brain and muscle cholinesterases (ChE), serum sorbitol dehydrogenase (SDH), and liver histology of Oreochromis niloticus, the dominant fish inhabiting this tropical Lake were evaluated to assess the pollution exposure and biological effects. Some fish sampled in the dry periods demonstrated prominent structural abnormalities in the liver and concomitant increase in serum SDH and reduction in hepatic GST activities in comparison to the control fish and the fish sampled in the rainy periods. The resident fish with apparently normal liver demonstrated induction of hepatic EROD and GST activities and increase in biliary FACs irrespective of the sampling period indicating bioavailability of PAHs. Muscle ChE activities of the resident fish were depressed significantly indicating exposure to anticholinesterase substances. The results revealed that fish populations residing in this Lake is under threat due to the pollution stress. Hepatic abnormalities in the fish may be mainly associated with the pollution stress due to recurrent exposure to PAHs and toxigenic Microcystis blooms in the Lake.
Assessment of the levels of three selected heavy metals in black tiger shrimp, Penaeus monodon cultured in the North western province of Sri Lanka
(Sri Lanka Association for Fisheries and Aquatic Resources, 2002) Senadheera, S.P.S.D.; Pathiratne, K.A.S.
Assessment of toxic heavy metal levels in black tiger shrimp, Peneaus monodon cultured in the north western province of Sri Lanka
(Sri Lanka Association for Fisheries and Aquatic Resources, 2005) Senadheera, S.P.S.D.; Pathiratne, K.A.S.
Biliary fluorescence aromatic compounds in Nile tilapia (Oreochromis niloticus) as biomarkers of exposure to polycyclic aromatic hydrocarbons
(Sri Lanka Association for Fisheries and Aquatic Resources, 2007) Pathiratne, A.; Hemachandra, C.K.; Pathiratne, K.A.S.
Bioaccumulation potential of three toxic heavy metals in shrimp, Penaeus monodon from different fractions of the culture environment
(Sri Lanka Association for Fisheries and Aquatic Resources, 2003) Senadheera, S.P.S.D.; Pathiratne, K.A.S.
A comparison of performance between chemical bath deposited and electrochemical bath deposited CdS thin films in CdS/CdTe thin film solar cells
(The U.S. Workshop on the Physics and Chemistry of II-VI materials, 2013) Pathiratne, K.A.S.; de Silva, D.S.M.; Kumarasinghe, K.D.M.S.P.K.; Dasanayake, B.S.; Colegrove, E.; Xin Zheng, R.D.; Sivananthan, S.
Corrosion stability of an aluminium alloy used in making of some cooking pans in Sri Lanka
(Sri Lanka Association for the Advancement of Science, 2008) Nadeesha, M.A.Y.L.; Pathiratne, K.A.S.
In addition to aluminium, aluminium alloys commonly used for making of some cooking pans in Sri Lanka contain of Si, Fe, Cu, Mn, Mg, Cr, Zn and Ti as minor elements. In the present work, the stability of one such alloy against corrosion, at ambient temperature in several aqueous media in the pH range of 5.0 to 6.5 that closely resembles the physicochemical status of liquid foods cooked using these vessels were investigated. The electrochemical techniques; immersion test, open circuit potential measurements and potentiodynamic polarization techniques were used to determine the corrosion parameters and the rate of corrosion of the alloy in the selected experimental conditions. The results of the immersion tests indicated that, the rates of corrosion of the alloy in several aqueous media; tap water from municipal water supply, citric acid and acetic acid dissolved in tap water and pH adjusted to 5.0 did not exceed 0.7 mm yr-1.The open circuit potentials corresponding to the alloy in all above solutions increased positively with time indicating the formation of passive oxide films on the alloys resulting a decrease in the rate of corrosion with time. Potentiodynamic polarization studies showed that in the above aqueous media the corrosion potentials fall in the ranges of (-362 to -739 mV) vs. the silver/silver chloride electrode and corrosion currents fall in the range of (~10.00 to ~24.24) μA cm-2. The immersion test results indicated that, the alloy can undergo corrosion with rates in the range of about 1.4 to about 2.1 mm yr-1 in solutions of tap water, gallic acid and tartaric acid containing sodium chloride [2%(w/v) NaCl].The highest rates of corrosion of about 2.1 mm yr-1 for the alloy were observed in tartaric acid solution containing 2 %( w/v) NaCl. The open circuit potentials for these solutions increased negatively with time indicating adsorption of negatively charged chloride ions on the surface of the alloys resulting in an increase in the rate of corrosion with time. The corrosion potentials and corrosion current found from the potentiodynamic studies for the alloy containing 2%(w/v) sodium chloride solution of municipal tap water, gallic acid and tartaric acid at pH 5.0 were in the ranges of about -693 to about -760 mV vs. Ag/AgCl electrode and ~ 59.26 to ~79.43 μA cm-2 respectively. The results indicated that the alloy can undergo corrosion significantly if it is used in aqueous media containing gallic acid or tartaric acid at pH 5 or 2 %( w/v) NaCl in tap water, gallic or tartaric acid solutions at pH 5 containing 2 %( w/v) NaCl in the ranges studied.
Development of three simple voltammetric techniques for detection of theophylline
(Sri Lanka Association for the Advancement of Science, 2008) Maduwanthi, S.A.N.; Pathiratne, K.A.S.; Wijayabandara, J.
The potential of employing the three voltammetric techniques; linear sweep voltammetry (LSV), differential pulse voltammetry (DPV) and square wave voltammetry (SWV) using pyrolytic graphite working electrode for detection of theophylline (TP), a common drug used for treatment of respiratory diseases was investigated. Phosphate buffer at the concentration of 2.0 x 10-2 mol dm-3 and at the pH of 6.6 were found to be the best electrolytic medium for all three voltammetric techniques. TP was found to undergo an irreversible oxidation reaction producing concentration dependent reproducible anodic peak currents at the peak potentials of +0.995 V, +0.772 V and +0.785 V with respect to Ag(s) / AgCl(s) / Cl-(aq) reference electrode (+0.197 V vs. NHE) for the three techniques, LSV, DPV and SWV, respectively. The optimum scanning rate of working electrode potential for LSV was 100 mV s-1. The optimum scanning rates of working electrode potential and pulse height for DPV were 25 mV s-1 and 140 mV, respectively. The optimum pulse height and frequency for SWV were 110 mV and 50 Hz, respectively. Under optimum conditions, there were good linear relationships between anodic peak current and TP concentration for the three techniques. The linear concentration ranges for LSV, DPV and SWV were from 3.0 x 10 -4 mol dm-3 to 1.3 x 10-3 mol dm-3, 7.0 x 10-5 mol dm-3 to 8.0 x 10-4 mol dm-3 and 5.0 x 10-5 mol dm-3 to 1.1 x 10-3 mol dm-3, respectively. The limit of detection observed with LSV, DPV and SWV were 2.5 x 10-4 mol dm-3, 6.0 x 10 -5 mol dm-3 and 4.0 x 10-5 mol dm-3, respectively. The results obtained during an analysis of a commercial TP drug, theophylline sustained release uncoated tablets with the three techniques, LSV, DPV and SWV were found to exhibit percentage deviations of 4.8 %, 3.1 % and 2.7 %, respectively from the value given on the tablet. All three techniques have potentials for detecting TP in the therapeutic range of 10 to 20 mg dm-3.
Effect of application of three phosphate fertilizer sources on long term availability of different phosphorus fractions in lateritic soils in the intermediate zone of sri lanka
(Proceedings of the Annual Research Symposium 2005-Faculty of Graduate Studies, University of Kelaniya, 2005) Duminda, D.M.S.; Pathiratne, K.A.S.; Somasiri, L.L.W.
The application of three different phosphorous (P) fertilizer sources, viz., Eppawela rock phosphate (ERP), Imported rock phosphate (IRP) and Triple super phosphate (TSP) on the long term availability of several different P fractions in Lateritic soils in the intermediate zone of Sri Lanka was investigated. Each P fertilizer was treated at three different levels: 25, 50 and 100 g / palm/ 6 months in triplicate over a period of 11 years to all 6 coconut trees grown in each of the 30 experimental plots. Three experimental plots with 6 coconut trees in each with no fertilizer application were used as controls. After 11 years of fertilizer applications, soils were sampled 90 cm away from the base of coconut palm at 2 depths; (0-25) cm and (25-50) cm from randomly selected three plants from each of the plot. Soils of each treatment, sampled in triplicate, for each of the two depths were composited separately. Different P fractions, viz., saloid bound P ( Sa-P), aluminum bound P (Al-P), iron bound P (Fe-P), occluded P (Occ-P) and calcium bound P (Ca-P) were determined in each composited soil. The results showed that, in the soil depth of (0-25) cm, the ability of different fertilizers in producing plant available P; Sa-P and Al-P vary in the order of TSP>> IRP>ERP. Further, it was found that, the availability of Sa-P and Al-P in the TSP treated soil increased with increasing level of TSP application to the soil. The concentration of different P fractions in the TSP treated were in the order of Sa-P>Al-P>Occ-P>Fe-P>Ca-P. The increasing level of IRP and ERP applications did not increase the Sa-P and Al-P concentrations in the soil. The trend of the availability of different P fractions in the soil depth of (25-50 cm) was the same for all three of fertilizer sources at all three levels applications. However, the concentrations of soil P fractions found in this depth was smaller than the amounts found in the (0-25) cm depth.
THE EFFECT OF CONCENTRATION AND PH OF CdC12 SOLUTION USED IN CdC12 TREATMENT ON THE PROPERTIES OF CdS THIN FILMS
(Solar Asia 2018 Int. Conf. National Institute of Fundamental Studies, Kandy, Sri Lanka., 2018) Atapattu, I I.Y.R.; De Silva, D.S.M.; Pathiratne, K.A.S.; Dharmadasa, I.M.
Among the post deposition treatments available for development of CdS/CdTe solar cells, CdCl2 treatment has been identified as one of the key processing steps that can be effectively used for improving power conversion efficiency of the CdS/CdTe solar cell. This method was identified in late 1970s and currently is used for the CdS layers as well. The present study focuses on the effect of the concentration and pH of the CdCl2 solution used for the CdCl2 treatment on the quality of CdS layers based on their electrical, optical and morphological properties. In this study, CdS layers were potentiostatically electrodeposited on glass/FTO substrates at cathodic deposition potential of 660 mV verses a saturated calomel electrode at pH of 1.80 for 30 minutes in electrolytic baths containing 0.10 mol/L CdCl2 and 0.01 mol/L Na2S2O3. The temperature and the stirring rate of electrolytic baths were maintained constant at 55 °C and 60 rpm respectively. After the depositions, the samples were rinsed in de-ionized water and dried under a high purity N2 gas flow and conveyed for the CdCl2 treatment. Nine sets of samples with two replicates in each were treated separately with aqueous CdCl2 solutions having concentrations of 1.0, 0.5 and 0.1 mol/L and for each concentration three different pH values; as-prepared (5.60, 6.30 and 7.10 respectively), 2.00 and 6.50 were used. To perform the treatment, CdCl2 solutions were sprayed for 1 minute on the CdS layer until the layers were fully covered by the solution, allowed to dry and the samples were transferred for the process of annealing at 400 °C for 15 minutes in air. Subsequently, samples were rinsed in de-ionized water and dried under a high purity N2 gas flow. The electrical, optical and morphological properties of the CdS layers were then studied using photo-electrochemical cell measurements, UV-Vis absorption spectroscopy and scanning electron microscopy respectively. As results revealed, the CdCl2 solution with the concentration of 1.0 mol/L and the pH of 2.00 is suitable for achieving good material properties in the CdS layers.
Effect of stirring rate of the electrolyte on properties of electrodeposted CdS layers
(International photovoltaic solar energy conference-Solar Asia, Pune, India, 2015) Atapattu, H.Y.R.; de Silva, D.S.M.; Pathiratne, K.A.S.; Dharmadasa, I.M.
Effect of stirring rate of the electrolyte on properties of electrodeposted CdS layers
(Springer US, 2016) Atapattu, H.Y.R.; de Silva, D.S.M.; Pathiratne, K.A.S.; Dharmadasa, I.M.
CdS is the most matching window material available for the CdTe absorber layer of CdS/CdTe solar cells and electrodeposition is a promising technique adaptable for fabrication of thin films of CdS owing to its simplicity, low cost, scalability and manufacturability. The quality of electrodeposited thin film semiconductor layers depends significantly on the electrodeposition potential, concentrations of precursor salts, pH, temperature and the rate of stirring of the electrolyte. In this study, the attention was focused on the effect of “stirring rate of electrolyte” since it has not been studied in detail in the past, despite of its strong relation to the rate of mass transport towards the working electrode where the thin film semiconductors are electrodeposited. This study was carried out via electrodepositing of CdS thin layers on fluorine doped tin oxide conducting glass working electrodes at different rates of stirring of the electrolyte while keeping the rest of the electrodeposition parameters unchanged at a previously identified set of values. The morphological, electrical and optical properties of the CdS layers grown at different stirring rates were used to determine the effect of stirring rate on the quality of CdS layers. The study revealed that, a stirring rate in the range of 60–125 rpm which produced orderly flows in the electrolyte around the working electrode (1 × 3 cm2) placed at the center of a 100 ml electrolytic bath with a distance of 2 cm apart between the graphite counter electrode and the conducting glass electrode could produce good quality CdS layers when electrodeposition was carried out at a cathodic deposition potential of 660 mV with respect to the saturated calomel electrode. The concentrations of CdCl2 and Na2S2O3 in the bath used were 0.10 and 0.01 M respectively. The temperature and pH of it were 60 °C and 1.80 respectively.
Effect of Thermal Annealing on Electrodeposited CdS and CdS/CdTe Heterojunction
(Faculty of Graduate Studies, University of Kelaniya, Sri Lanka, 2016) Atapattu, H.Y.R.; de Silva, D.S.M.; Pathiratne, K.A.S.
At present CdS/CdTe based solar cells have a significant commercial impression due to its lowcost, scalability, manufacturability and simplicity. Nevertheless, it is essential to elevate the optoelectronic qualities of CdS and CdTe materials and the interface properties of CdS/CdTe heterojunction and ultimately the efficiency of the solar cells. In this regard thermal annealing is one of the key steps to be considered in order to enhance the material and heterojunction properties. Hence, in this study, the effect of thermal annealing on electrodeposited CdS and CdS/CdTe heterojunction was investigated. CdS and CdTe semiconductor layers were potentiostatically electrodeposited on bare fluorine doped tin oxide (FTO) glass substrates and FTO/CdS respectively using the typical three electrode electrolytic cell. For both layers, saturated calomel electrode and high purity (99%) graphite rod were used as reference and counter electrodes respectively. 0.10 mol/L CdCl2 and 0.01 mol/L Na2S2O3 were used as Cd and S precursors respectively to produce CdS thin films while 1.35 mol/L CdSO4 and 1.0 mmol/L TeO2 were used as Cd and Te precursors respectively for CdTe. CdS layers were grown at cathodic deposition potential of 660 mV at pH 1.6 and temperature of 55 °C. Afterwards, one set of electrodeposited CdS samples was conveyed for fabrication of CdS/CdTe heterojunction. CdTe layers were grown on CdS layers at cathodic deposition potential of 650 mV at pH 2.3 and temperature of 65 °C. Subsequently, thermal annealing was carried out for both CdS and CdS/CdTe at three different temperatures; 390, 400 and 410 °C, for each annealing three different time periods; 10, 15, 20 min were considered. After the process of annealing all the samples were inspected for their optical, electrical and morphological properties using the techniques of optical absorption spectroscopy, photoelectrochemical cell and scanning electron microscopy respectively. According to the results, the optimum annealing conditions which yielded good optoelectronic qualities for CdS and CdS/CdTe were found to be 400 °C, 15 min and 390 °C, 15 min respectively.
Effects of waterborne cadmium on biomarker enzymes and metalothioneins in Nile tilapia, Oreochromis niloticus
(Journal of National Science Foundation of Sri Lanka, 2008) Chandrasekera, L.W.H.U.; Pathiratne, A.; Pathiratne, K.A.S.
Cadmium is widely used in modern industry and ranks among the most toxic metals in the aquatic ecosystems. In the present study, activities of several biomarker enzymes viz. ethoxyresorufin O-deethylase (EROD), glutathione S-transferase (GST) and cholinesterase (ChE) were determined in Nile tilapia (Oreochromis niloticus) at different waterborne Cd22+ exposure levels (0, 0.001, 0.005, 0.01, 0.1, and 1 mg/L for 28 days) to evaluate the potential influence of environmental cadmium on these enzymes. In addition, hepatic metallothionein (MT) levels in these fish at different waterborne Cd2+ exposure levels were also studied to evaluate their response to waterborne cadmium exposure. The results revealed that hepatic MT levels in the fish exposed to Cd2+ increased 2-26 fold depending on the exposure level and duration. Hence hepatic MT in Nile tilapia is a sensitive biomarker to indicate cadmium pollution in the natural environments. Continuous exposure of fish to ? 0.01 mg/L of Cd2+ had no significant effect on hepatic EROD, hepatic GST and brain and muscle ChE activities whereas exposure to ? 0.1 mg/L Cd2+ evoked time dependent significant depression of hepatic EROD (41-55%) activity. Brain and muscle ChE activities of the fish exposed to 1 mg/L Cd2+ were depressed to 24-32% and 33-35% respectively. Results revealed that high concentrations of Cd2+ in the natural environments could inhibit the basal activities of the hepatic EROD and brain and muscle ChE in Nile tilapia affecting the normal functioning of these biomarker enzymes and influencing the biomarker response to targeted organic pollutants in the environment.
Electro-deposition of Cadmium Zinc Sulphide at High Cadmium Ion Concentration, Low Zinc Ion Concentration, High Temperature and Low pH
(Faculty of Graduate Studies, University of Kelaniya, 2015) Sarathchandra, K.A.D.M.S.; De Silva, D.S.M.; Pathiratne, K.A.S.
Thin films are nanoscale materials which are widely used for solar cells and other optoelectronic devices. Cd(1-x)ZnxS (cadmium zinc sulphide) is formed by incorporating zinc ions to CdS (cadmium sulphide). Cd(1-x)ZnxS is a n-type semiconductor material which has a wider band gap than that of n-type CdS. Therefore, Cd(1-x)ZnxS can be used as a window material when application required low absorption of light and n-type semiconductor properties. Cd(1-x)ZnxS has been electro-deposited by varying cadmium ion concentration, zinc ion concentration, pH, deposition temperature and deposition time. Results reported here were based on the depositions conditions; 0.1 mol dm-3 cadmium ion concentration, 0.01 mol dm-3 zinc concentration, 2.45 - 2.50 pH and 50 °C deposition temperature. Electro-deposition experiments were carried out by Gamry ―series G 300‖ potentiostat while, working electrode was fluorine doped tin oxide/glass substrate, reference electrode was Ag/AgCl electrode and counter electrode was a semi-spherical graphite rod. The deposition voltage was identified from the cyclic voltammograms and shapes of the deposition current vs time plots. Electrodeposition reported in here was carried out at under-deposition voltages. The best values for electro-deposition parameters; voltage, pH, temperature and time were identified by observing their influence on the band gap values of the thin films deposited and the open circuit voltages of photo-electrochemical cell consisting of 0.1 mol dm-3 sodium thiosulphate electrolyte and the thin film semiconductor. A band gap range of 2.5 eV – 2.6 eV was obtained for Cd(1-x)ZnxS layer which is higher than the band gap of CdS. The open circuit voltage varied from -48 mV to -190 mV during optimization of voltage, pH, temperature and time. An X-ray diffraction spectrum has shown that Cd(1-x)ZnxS layer has a single hexagonal crystal phase. The crystal parameter, a = 4.1264 Å and it was lower than the standard CdS (a = 4.1364 Å). The results indicate that Cd(1-x)ZnxS thin films can be produced under the given conditions as a window layer for thin film solar cells in order to harvest more light and hence to improve the efficiency.