Browsing by Author "Wijayasinghe, H.W.M.A.C."

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    Antibacterial Activity of Silver Deposited Vein Graphite against Waterborne Pathogenic Escherichia coil
    (Uva Wellassa University of Sri Lanka, 2018) Kumar, K.K.A.D.; Amaraweera, T.H.N.G.; Premetilake, M.M.S.N.; Wijayasinghe, H.W.M.A.C.
    The microbial contamination of drinking water is a major health problem in the world which requires an effective treatment. Silver ion (Ag+2) is used as nonspecific antibacterial factor and it acts against a very broad spectrum of bacterial species. In this study, antibacterial efficiency of Ag deposited vein graphite were studied using Escherichia coli strain. Ag was deposited on the graphite surface by reduction of Ag+2 in silver nitrate solution using reducing agent. Scanning electron microphotographs of the Ag deposited graphite reveal that the deposited silver particles are highly agglomerated or spongy voids. Although the size of silver particle agglomerates are relatively coarse, the average size of individual silver nanoparticle is around 75 nm. Antibacterial efficacy of the synthesized sample was investigated using waterborne pathogenic E. coli strain. The antibacterial test was done using prepared composite samples and samples of E. coli, using shake flask method. A commercial antibiotic (Ofloxin-200 mg) was used as the positive control. The samples were drawn periodically (1, 1.5, 2, 2.5 and 3 hours) from the flask and tested against E. coli by plate count method using standard procedures. There was a significant E. coli removal efficiency by the synthesized Ag Graphite composite compared to purified graphite and positive control (One-way ANOVA, p-value=0.00). Therefore, this study suggests that Ag- vein graphite composite could be used as an effective material in water purification, especially in removing of E. coli.
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    Antibacterial Activity of Silver Deposited Vein Graphite Against Waterborne Pathogenic Escherichia coli Synthesized by Chemical Reduction Method
    (Uva Wellassa University of Sri Lanka, 2019) Kumari, T.D.D.; Swarnamali, V.M.R.; Amaraweera, T.H.N.G.; Premathilake, M.M.S.N.; Wijayasinghe, H.W.M.A.C.; Balasooriya, N.W.B.
    Graphite is one of the common materials using for the fabrication of composite materials. Graphite oxide, graphene oxide and many other materials are used as effective antibacterial substances, but most of them are expensive and need highly toxic chemicals for the synthesis. Nowadays, silver is considered as a most effective antibacterial material. Therefore, this study was focused on synthesizing cost effective less hazardous antibacterial material using silver and graphite. Graphite sample was purified by acid leaching, followed by modifying the surface with Conc. HNO3. The silver graphite composite material was synthesized using AgNO3 as precursor and tri-sodium citrate as reducing agent. X-ray diffractometry and Scanning electron microscopy investigations of the synthesized silver graphite composite revealed that the pure crystalline nano silver particles were deposited on the graphite surface. Antibacterial efficacy of the synthesized material was investigated using waterborne pathogenic Escherichia coli. The antibacterial test was carried out against E. coli using prepared composite samples according to the shake flask test. A commercial antibiotic (Ofloxin-200 mg) was used as the positive control. The samples were drawn at times 0, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 5 and 6 hours by counting the number of surviving bacterial colonies on Eosin Methylene Blue (EMB) Agar, using plate count method according to standard procedures. After 24 hours, the results showed that surviving bacterial colonies contained in counted petri plates of all the synthesized composites with different Ag: Graphite ratios were reduced, with the time in an efficiency of over 98%. Therefore, this study suggests that Ag-vein graphite composite synthesized via chemical reduction method can be effectively used as an antibacterial agent against E. coli.
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    Characterization of Electrical Properties of Sri Lankan Graphite
    (Uva Wellassa University of Sri Lanka, 2010) Geethika, A.K.K.; Wijayasinghe, H.W.M.A.C.; Attanayake, A.N.B.; Udagedara, T.
    Sri Lankan graphite is famous for its high quality which makes it suitable for various technological applications. However investigations on electrical properties of different varieties of Sri Lankan graphite have been very limited. The main objective of this project is to investigate different structural varieties of Sri Lankan vein graphite and characterize their electrical properties with particular attention on examining its applicability in rechargeable battery industry. Graphite is an extensively used carbonaceous material in industries. There are two main types of graphite, synthetic and natural. Various types of vein graphite samples were collected from Bogala and Kahatagaha/Kolongaha mines. The powdered graphite specimens were subjected to phase, purity, morphology, particle size and chemical analyses. Electrical conductivity of dense graphite pellets were measured by the d.c. four probe method in the temperature range between 25 °C to 100 °C. XRD phase analysis indicates the existences of appropriate phases of these graphite specimens. Further, the electrical characterization reveals the possessing of significant electrical conductivity hence indicating the high potentiality of Sri Lankan graphite for rechargeable battery applications. Key words: Electrical properties, Graphite, Conductivity
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    Development of Lithium Ion Rechargeable Batteries by Using Sri Lankan Graphite and Locally Synthesized Low-Cost Materials
    (Uva Wellassa University of Sri Lanka, 2011) Dewappriya, M.P.; Wijayasinghe, H.W.M.A.C.
    Note: See the PDF Version Lithium-ion battery (LIB) is a family of rechargeable battery types in which the lithium ions move from the negative electrode to the positive electrode through the electrolyte. LIBs are currently one of the most popular types of battery for portable electronics with one of the best energy-to-weight ratios, no memory effect and a slow loss of charge when not in use. However, the present generation of LIBs has many limitations, such as high internal resistance, expensiveness, temperature effect, aging effect, short circuiting, and environment effect and overheating. The present inferior electrode materials are the main reason for these drawbacks and hence the main obstacle to achieve reliable and cheaper lithium-ion batteries (Pushpaka et al., 2008). This abstract presents a study of developing Li (Ni1i3Co1j3Mn1n) 02 based cathode electrodes and NiO-LiFe02-LiCo02 based anode electrodes with the Sri Lankan graphite as electrical conductivity enhancer. These novel electrode materials were synthesized by using Glycine-nitrate and Pechini methods, which are low cost techniques but can result in powders with high purity, homogeneity and particle morphology that are highly desired for LIB electrodes (Wijayasinghe et al., 2006). On the other hand, the expensive synthetic carbon materials are now being used as electrical conductivity enhancer of LIB electrodes, currently. In a recent research work on Sri Lankan graphite at the Uva Wellassa University with the collaboration of Institute of Fundamental Studies our group indicated of having sufficient electrical conductivity in Sri Lankan graphite to be used as conductivity enhancer (Geethika et al., 2010). Sri Lanka has been well known for processing high purity graphite, which is mainly being exported as cheap raw materials. Introducing this cheaper material for the high-tech energy conversion devices will definitely reduce the cost of these devices while also adding value to our mineral resources. By considering these factors, Sri Lankan Bogala graphite was investigated in this study as a conductivity enhancer in LIB electrodes.
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    Development of Sri Lankan Vein Graphite for Lithium-Ion Rechargeable Battery Anodes by Chemical Oxidation
    (Uva Wellassa University of Sri Lanka, 2012) Bandara, S.M.J.G; Wijayasinghe, H.W.M.A.C.; Attanayake, A.N.B.
    Graphite has been used as an anode material in state-of-the art Li-ion batteries due to high capacity (337 mAh/g) and low potential (0.1 — 0.3 V vs. Li+/LI) of its lithium intercalation compound (Li,C6, X=1) (Kurzweil and Brandt, et al., 2009). Reversible intercalation and deintercalation of Li+ ions with graphite are attributed to successful formation of a stable and protecting solid electrolyte interface (SE1) on the graphite surface, which is known to complete in initially few cycles. Previous studies have shown that formation of the SE1 is greatly affected by electrolyte composition, morphology and surface chemistry of graphite (Fu et al., 2006). For this reason, only a limited number of graphite has been found to be suitable for the anode of Li-ion batteries. To use natural graphite that is inexpensive and abundant, many researchers have currently focused on the surface modification of natural graphite (Fu et al., 2006). The graphite surface can be modified by mild oxidation in air and using solution of strong oxidant (Balasooriya, et al., 2006,2007). Mild oxidation induce acidic group on the graphite surface, which act as surface film to produce SEI resulting high reversible capacity. However, in gas-solid inter-phase oxidation reaction, control of the homogeneity of the product is difficult to maintain. Consequently, a liquid-solid interface oxidation reaction has been introduced as the use of chemical oxidant. Nitric acid is well known as a strong oxidant and its standard potential is > I .5V (Wu et al., 2003). Sri Lanka is well known for high quality vein graphite, containing 95-99% of pure carbon (Herath, 1995). They were categorized into four structural types, namely, coarse flakes of radial (CFR) graphite, coarse striated-flaky (CSF) graphite, needle-platy (NPG) graphite and shiny-slippery-fibrous (SSF) graphite, based on the structural and physical characteristics (Touzain, et al., 2010). Recent investigation pointed out that vein graphite from Bogala mine have sufficient electrical conductivity to be used as potential candidate for Lithium ion rechargeable batteries (Geethika, et al., 2010) and chemical oxidation in (NH4)2 5208 increase the reversible capacity (Balasooriya, et al., 2006,2007). The present study aims to chemical oxidation of natural vein graphite in nitric acid in order to upgrade the quality of vein graphite as anode material for lithium ion rechargeable batteries.
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    Erosive Wear Resistance of Sri Lankan Rocks Used for Flooring
    (Uva Wellassa University of Srilanka, 2011) Ruwanpura, U.D.M.N.; Wijayasinghe, H.W.M.A.C.; Attanayake, A.N.B.
    NOTE: see the PDF version Varieties of floor tiles are amongst many of the specialties in ancient Sri Lankan architectural wonders. Even today floor tiles in Sri Lanka claim a high regard in world export market being one of the biggest equity grosser in commodities. Stone floors are admired for their splendid appearance as well as for higher durability. Natural stones such as slate, granite, gneisses and marble are commonly used for interior designs and flooring. Stone floor tiles being materials which are always in physical contact with moving objects are prone to wear, although at a comparatively slower rate. Therefore, the durability of tiles should also be of concern in addition to their aesthetic appearance. However, wear resistance of stone floor tiles has not been attracted adequate attention in material testing. Hence, it is essential to ascertain tribological properties, including resistant to wear, when selecting the most suitable flooring material. This research aims at investigating and documenting the wear resistance of commonly used Sri Lankan rocks in flooring.
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    Investigation on Structural Modification of Sri Lankan Vein Graphite for Ion Intercalation
    (Uva Wellassa University of Sri Lanka, 2015) Amiyangoda, A.G.T.R.; Rathnayake, R.M.N.M.; Karunarathne, R.I.C.N.; Wijayasinghe, H.W.M.A.C.
    Rechargeable batteries have become the main energy source for the portable electronic devices. Synthetic graphite have been used as anode electrode material in rechargeable batteries. Presently these rechargeable batteries are expensive mainly due to high cost of materials, such as synthetic graphite and metal oxides, used in their electrodes. It is suggested that the cost of these batteries can be reduce by introducing cheaper natural graphite for their anode electrode. Sri Lankan natural vein graphite can be classified into four distinct structural verities. They are Shiny-Slippery- Fibrous Graphite (SSF), Needle-Platy Graphite (NPG), Coarse Striated-Flaky Graphite (CSF) and Coarse Flakes of Radial Graphite (CFR). Development of Sri Lankan natural vein graphite to the anode of Li-ion rechargeable batteries, through purification and surface modification have been investigated recently. Furthermore, natural graphite has to be structurally modified by expanding interlayer distance to facilitate the intercalation of larger Na ions for the application in rechargeable Sodium Ion Batteries (SIB) (Wei, 2011). The present study investigated the possibility of expanding the interlayer distance of Sri Lankan natural vein graphite for accommodating Na-ion intercalation by converting into Graphite Oxide (GO). Materials and methods Purified samples from all four structural varieties of Sri Lankan vein graphite, were used in this study. Raw graphite samples were oxidized to Graphite Oxide (GO) by using improved hummers method (Madusanka Y.N., Amareweera T.H.N.G.,Wijayasinghe H.W.M.A.C., 2013). In this method 96% H2SO4 (Sigma-Aldrich) and 85% H3PO4 (Sigma-Aldrich) were added to purified vein graphite. Then KMnO4 (Belgolabo) was added little by little to the mixture with in two hours and stirred. Sample was allowed to cool until room temperature. Solution was poured into 30% H 2O2 in an ice bath and the sample was vacuum filtered using Fisher brand filter papers using distilled water. The d.c. electrical conductivity of raw graphite and prepared GO samples were measured using the standard four probe method. Fourier Transform Infrared (FTIR) spectra of raw graphite and GO samples were employed to study the structural modification. Further the X-ray diffractometry was used to confirm the formation of GO.For the Na-ion intercalation study, the modified graphite oxide was tape casted by the doctor blade method to fabricate electrodes. GO was the active material, carbon black was selected as the conductive additive and the binder was polyvinylidene fluoride (PVDF). All the materials were weighed using a chemical balance and placed in a small beaker. Then excessive amount of acetone and dimethylformamide (1:1 ratio) were added to the beaker, covered with an aluminum foil and stirred for 12 hours. Mixture was poured on to a copper foil pasted on a glass to form a very thin layer. It was allowed to dry. The electrodes were fabricated by cutting the copper foil to required shape. A half-cell was assembled using the fabricated GO anode with a gel electrolyte and sodium metal as the reference electrode. Assembling and testing of the cell was conducted inside a N2 filled glove box. Discharging current of the half-cell under 0.5 kΩ load over time was measured and it was recorded using a computer interfaced program.
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    Li2CO3-coated Sri Lankan Vein Graphite Electrode for Rechargeable Lithium- ion Battery
    (Uva Wellassa University of Sri Lanka, 2013) Manthirathna, M.A.N.C.; Wijayasinghe, H.W.M.A.C.; Amaraweera, T.H.N.G.
    High quality vein graphite, containing 95-99% of pure carbon in Sri Lanka has been identified as promising candidate as anode material in lithium ion rechargeable battery. Purification and mild oxidation have been widely used to enhance the property of the vein graphite as anode material (Balasooriya et al., 2007; Amaraweera et al., 2013). However, alkali carbonates coating which are identified as cost effective and nontoxic approach for the surface modification have not been investigated for vein graphite in Sri Lanka (Komaba et al., 2008; Zhang et al., 2003). Therefore, present work is aimed to develop low cost anode material based on Li2CO3 coating of purified vein graphite. Methodology Purified vein graphite powder less than 53µm (<53 µm) was used for this study (Amaraweera et al., 2013). Graphite powder were added into an agate motor and milled for about 2 hours by adding aqueous Li2CO3to ensurethat the graphite was completely witted. Then the surrey was dried in vacuum at 100 C. The modification of the graphite mixture was characterized by FTIR Spectroscopy D.C conductivity of graphite powder and sheet conductivity of graphite electrode was measured by four-probe and VanderPauw, methods respectively.
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    Low Cost Electrode Materials for the Molten Carbonate Fuel Cell
    (Uva Wellassa University of Sri Lanka, 2010) Karunanayaka, W.M.M.D.; Wijayasinghe, H.W.M.A.C.
    The most common method of storing energy in an electrochemical cell is in the form of chemical energy. A fuel cell is an electrochemical energy conversion device, which converts chemical energy directly into electrical energy. Molten Carbonate Fuel Cells (MCFC) have attracted wide attention due to promising characteristics for large-scale electric power generation. This work is based on synthesis and electrically characterization of low cost electrode materials for the Molten Carbonate Fuel Cell (MCFC). At present, the dissolution of the state-of-the-art lithiated nickel oxide cathode material is a most crucial lifetime limiting factor and the major obstacle for the commercialization of MCFC. A solid solution consisting of LiCoO2 and NiO is expected to posses some of the desirable properties of these two materials. LiCoO2 and NiO in the solid solution are expected to lower its resistivity and LiCoO2 is expected the decrease the dissolution of lithiated nickel oxide cathode. In this study, powder compositions in the NiO-LiCoO2 binary system were prepaired by the glycine nitrate method. The electrical conductivity of these materials was determined by performing d.c. conductivity measurements on sintered pellets by the four-probe method. The conductivity measurements were performed in a cyclic manner on heating and cooling in air, in the temperature range, 25 - 750 °C. The pressing study shows that there is an optimum pressure to obtain the sintered pellet at the highest density. In this study the optimum pressing pressure for NiO system is determined as 150 MPa. The electrical conductivity study shows the ability of obtaining NiO-LiCoO2 binary materials with appropriate electrical conductivity obove 1 S/cm for the MCFC cathode. Futher, the significantly high room temperature conductivity of these materials indicates the potentiality of them for electrodes in room temperature applications such in re-chargeable Li - ion batteries. Key words: fuel cells, Molton carbonate fuel cell, Electrode materials, Cathodes, binary oxides
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    Low Cost Electrode Materials for The Rechargeable Li-Ion Batteries
    (Uva Wellassa University of Sri Lanka, 2010) Sivabalasatkunam, K.; Wijayasinghe, H.W.M.A.C.
    Lithium-ion rechargeable battery is a rapid developing technology to provide stationary storage solutions to enable the effective use of renewable energy sources. The technology is already in use for low power applications such as consumer electronics and power tools. However, for the popularization of this technology as a cheaper portable power source need the development of low cost and performance enhanced materials. Among various materials proposed for the cathode in Li-ion battery (LIB), LiCo02 has most widely been used. However, the high cost of this material is a main obstacle for reaching it to the common mass as a cheaper and reliable potable power source. This work was based on synthesis and electrical characterization of Li(Ni113Mni13CoR113)-xiCux)02 (x = 0.00, 0.11, 0.22, 0.33) materials synthesized by Pechini method. The Pechini method is a low cost technique which results in powders with high purity, homogeneity and particle morphology that are greatly preferred for Li-ion battery cathodes. Subsequently powders were calcined and characterized with X-ray diffractometry. The four probe d.c electrical characterizations were performed on the pellets sintered at 1000 °C for 4 h in static air. The electrical conductivity at 25 °C is about 1x10-4 S/cm and 1.5x10-3 S/cm at 150 °C for Li(Niii3Mnii3C01/3)02. For the Li(Ni113Mn113Co1{i3)-xiCux)02 (x =, 0.11, 0.22, 0.33) materials, electrical conductivity is in the range of 16 to 49 S/cm. The materials show an increase of the conductivity with the temperature and hence a possible semiconducting behaviour. As a whole, this study shows the ability of preparing low cost Cu doped Li(Niii3Mn113C0(013)-xiCux)02 (x = 0.11, 0.22 and 0.33) by Pechini method, having excellent electrical properties suitable for LIB electrodes. Key words: Rechargeable batteries, Li-ion battery, Electrode materials, Cathodes, ternary oxides
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    Purification of Vein Graphite by Alkali Roasting for Anode Material in Lithium Ion Batteries
    (Uva Wellassa University of Sri Lanka, 2013) Wewegedara, W.G.C.N.; Amaraweera, T.H.N.G.; Wijayasinghe, H.W.M.A.C.
    Unique vein graphite deposits with highly crystallized and high purity graphite are present in the mineralization zone of the central highlands of Sri Lanka This graphite has been identified as a potential candidate for the lithium ion rechargeable batteries (Balasooriyaet al., 2007). Recent attention has been made towards the purification of vein graphite in order to prevent the anode ageing and decomposition of the electrolyte in lithium ion batteries (Amaraweera et al., 2013). Alkali roasting for purification of graphite has found to be a very effective method to remove sulfide and silicate impurities at low temperatures (Lu et al., 2002). Therefore, this study focused on studying the effectiveness of alkali roasting for the purification of vein graphite in Sri Lanka Methodology Graphite powder (<53 µm) from Needle Platy Graphite (NPG) and Shiny Slippery Fibrous (SSF) morphological types from Bogala and Kahatagaha mines were used for this study. The graphite was treated in aqueous solutions containing 5, 10, 15, 20, 25, 30 and 35 vol. % NaOH (Solid: liquid, 1:2) separately and roasted at 250 C under air for one hour. Then, the roasted sample was acid leached in 10 vol. % H2SO4. After that, the solid was filtered, washed to neutral and vacuum dried at 100 C for 15 hours. Minimum concentrations of NaOH for the purity enhancement were identified for each graphite type. Roasting treatments were repeated at 150 C, 200 C, and 300 C, using the data obtained previously to identify the effect of roasting temperature on purity enhancement. Carbon percentages of the treated graphite samples and untreated graphite samples were determined by heat treating at 950 C for 3 hours in Muffle Furnace, according to ASTM – C 561 and weighing the residues. Pellets of treated and untreated graphite powder (D =12 mm and L = 5 mm) prepared by cold uniaxial pressing at 100 Mpa were used to measure D.C conductivity by four-probe method at room temperature.
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    A Real Time viscometer for Industrial Applications
    (Uva Wellassa University of Sri Lanka, 2010) Dayarathna, P.S.D.; Wasala, K.W.M.M.P.; Wijayasinghe, H.W.M.A.C.
    Viscosity measurements are significantly important in various fields in industry and research. These viscometers are specified as either portable or stable manner. Most of the Stable viscometers can be used only in laboratory environment and are difficult to use in robust industrial environments. Majority of portable rotational viscometers are calibrated viscometers which are using standard Newtonian fluids and accurate laboratory procedure for the calibration process. However, the available viscometers are much expensive. The objective of this project was to design and fabricate an inexpensive, real time viscometer that could be used in industrial as well as in laboratory environment. Mainly a simple DC motor is used to design this viscometer. Torque constant of DC motor and acquired current was measured. Repulsion torque resulted by spindle rotation is measured. As a result, an absolute value of the viscosity is calculated and displayed. Since the viscosity is calculated using the repulsion torque, viscosity of the non-Newtonian fluids also can be measured by designing a suitable spindle. Series of spindles were designed to increase the sensitivity. Some of the spindles were designed to measure the absolute viscosity even in the portable conditions. This device can be operated by unskilled persons due to the user-friendly interface of the control panel. All the readings and results can be taken as a computer output through RS 232 port. Further, software can be developed to give out a graphical output. This constructed viscometer gives readings with considerable accuracy compared to the standard temperature-viscosity tables. It is a valuable instrument with many industrial applications. Key words: Viscosity, Viscometer, Newtonian fluids, RS 232 port
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    Synthesis of Graphite Oxide from Kahatagaha Vein Graphite using a Localized Improved Hummers Method
    (Uva Wellassa University of Sri Lanka, 2013) Madusanka, Y.V.; Amaraweera, T.H.N.G.; Wijayasinghe, H.W.M.A.C.
    In modern world, materials, - regardless of their make, whether natural or synthetic – play a huge role. From all these materials, Graphite is taking a wide consideration of scientists as they are naturally occurring, cheap material with very interesting physical, chemical and mechanical properties. Within the range of applications of Graphite, Graphite Oxide (GO) and Graphene are more important as they are having many applications and very good potential in Nano scale materials and Nano Technology. GO has attracted much interest recently as a possible route for the large scale production and manipulation of Graphene, a material with extraordinary electrical properties. Sri Lanka has two major natural vein graphite deposits in Kahatagaha- Kolongaha and Bogala. Of the two Kahatagaha vein graphite has the highest purity that can be upgraded up to 99.97% Carbon by HCl leaching (Amaraweera et al, 2013). No researches and experiments have been conducted on Kahatagaha vein graphite which has been upgraded up to 99.97% Carbon in nano scale. The potential for value addition to Kahatagaha graphite has not yet been adequately explored. This study aims at synthesizing GO using a localized version of the Improved Hummers Method and characterization of GO to confirm the oxidation. Methodology Graphite sample, KNPG (Kahatagaha Needle-Platy Graphite) was first crushed using a hammer to obtain +10 mm chips and then the sample was milled in a disc mill for 15 minutes. The milled sample was sieved using a sieve shaker and <53 microns portion was taken for further treatments. 675 ml of 5% HCl was added to 50 g of graphite in 1000 ml beaker and it was vigorously stirred for 1.5 hours at 60 C. The solution was vacuum filtered and washed with distilled water (500 ml) and the same procedure was repeated once. Finally purified graphite was washed until the pH become neutral. KNPG achieved purity level of 99.97% Carbon. 9: 1 mixture of conc. H2SO4 (96% 360 ml) and conc. H3PO4 (85% 40 ml) were added to a mixture of 3 g of purified KNPG and 18 g of KMnO4. The mixture was stirred for 6 hours at 50 C. Then the solution was poured on to ice (200 ml) with 30% H 2O2 3 ml and then vacuum filtered through Fisherbrand filter paper. The brown product left on the filter paper was collected and washed with water (200 ml x 3) and left in a vacuum drier at 105 C for 2 hours. The hard black solid taken out from the vacuum drier was crushed using an agate mortar and pestle to obtain finer particles of 6.86 g of GO. A pellet for electrical conductivity measurements was made using 1g of GO and FTIR Spectrum for GO was taken. A tape was casted using GO for sheet resistance measurements and XRD spectrum was obtained for characterization of GO.
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    Synthesis of Silver - Graphite Composite via Ultrasonication Associated Chemical Reduction and Study of its Antibacterial Properties
    (Uva Wellassa University of Sri Lanka, 2020) Gamlath, J.G.V.I.; Swarnamali, V.M. R.; Amaraweera, T.H.N.G.; Premathilake, M.M.S.N.; Wijayasinghe, H.W.M.A.C.; Balasooriya, N. W. B.
    Graphene oxide is widely used to produce an antibacterial silver composite, but mostly required toxic chemicals for production and they are comparatively expensive. The present study was focused on synthesizing cost-effective less hazardous antibacterial composite using vein graphite and silver. Silver graphite composites can be made using various methodologies and those methods can affect the antibacterial property. Therefore, in this study, silver graphite composite was synthesized by ultrasonication associated chemical reduction method. Sri Lankan vein graphite was purified by the patented acid leaching method, then surface modified with patented mild chemical oxidation method. The silver-graphite composite was synthesized from an AgNO3 silver precursor with a concentration of 0.00025 M, 0.001 M, 0.002 M by using tri-sodium citrate as a reducing agent. X-ray Diffractometry analysis indicated that composite only consists of silver nanoparticles and carbon in pure crystalline form. The composite was characterized by Scanning Electron Microscopy. Nano-scale silver particles were seen deposited on the surface of graphite. Antibacterial efficiency of the synthesized composites was analysed using Escherichia coli and the test was carried out using the shake flask method. For positive and negative controls, modified graphite and commercial antibiotic ofloxacin were used respectively. The samples were drawn out with a one-hour time interval from 0 to 6 hours and the number of surviving colonies on Eosin Methylene Blue agar was counted after 24 hours of incubation. The removal of the Colony Forming Unit for all samples gave efficiency over 99 %. The Kruskal-Wallis test suggests that colony removal depends on the time and concentration of AgNO3 used in the synthesized composite. Therefore, this study suggested that silver-graphite composite synthesized via ultrasonication associated chemical reduction can be used for E. coli as an effective antibacterial agent. Keywords: Graphite, Silver nanoparticles, Ultrasonication, Chemical reduction, Trisodium citrate