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Abstract: We used wet-chemistry techniques to prepare colloidal tungsten (W) nanoparticles (NPs). The synthesis of W NPs was conducted using the so called hot-matrix method in 1-octadecene [1]. The sizes of obtained W NPs are in the order of 2 - 5 nm. These W NPs are coated with hydrophobic molecules which allow their dispersion in organic solvents like choloroform (CHCl3). It was found that the colloidal stability of the dispersions is exceptionally high exceeding several years. The stability of W NPs which prevents coagulation allows the preparation of thin films with uniform thicknesses by spin-coating, inkjet-printing and spray coating. We have prepared tungsten carbide (W2C, WC) thin films. The preparation of W2C and WC was achieved by spin-coating of pre-synthesized W NPs on graphite substrate and following heat treatment under Ar atmosphere at 1000 and 1450°C. The obtained W2C and WC films were used both in electrochemical water splitting studies. We also made a composite W2C-Pt films where we used only 5 at.% of Pt. The W2C-Pt composite has shown similar performance as pure Pt-C for hydrogen (H2) evolution. In conclusion, we have developed a procedure for the synthesis of W NPs which can be applied for the preparation of tungsten carbides films and their use for electrochemical water splitting.
Keywords: water splitting, nanoparticles, hot-matrix
Published in RUNG: 09.10.2017; Views: 5986; Downloads: 0
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Keywords: TiO2, water treatment, surface modification
Published in RUNG: 23.08.2017; Views: 4538; Downloads: 0
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Abstract: Water security and quality are a global issue of concern, which have recently become alarming due to the growth of the human population, industrialisation and expanded agricultural activities. Biologically active compounds, such as pharmaceuticals and personal care products can have major adverse effects on aquatic organisms, and are therefore one of the biggest threats in water quality. Another major concern is the spread of waterborne pathogens, including multidrug resistant (MDR) bacteria, which can cause serious illnesses in humans. In order to maintain water abundance and quality, it is necessary that adequate wastewater treatment and analytical techniques allowing for sensitive and fast-response detection of water hazards are in place. Conventional (waste)water treatment technologies often fail to adequately remove all of the water hazards detailed above. Moreover, conventional analytical techniques currently used in water quality control are, although highly selective and sensitive, time-extensive, with throughput of merely 2 to 3 samples per hour, excluding the time for sample preparation. With respect to these drawbacks, research was proposed to explore new approaches for degradation of recalcitrant compounds, inactivation of microorganisms, and fast screening methods, which are listed in the second chapter of this dissertation as research objectives. In the third chapter, an extensive theoretical background on the hazards found in aquatic environment, namely pharmaceuticals and waterborne pathogens, is given. Pharmaceuticals enter the environment through several routes (disposal of unused medication via the toilet, pharmaceuticals passing through the human body unchanged/slightly transformed, animal excretions of pharmaceutically active compounds, insufficient wastewater treatment, etc.); therefore, traces of pharmaceuticals have repeatedly been reported in surface waters, groundwater, wastewater effluents, and even drinking water. Iodinated contrast agents (ICAs), as the compounds of interest in this project are further described. ICAs are eliminated from the human body practically unchanged; therefore a large proportion of them end up in municipal and hospital wastewater, where they can be present in concentrations of up to 2.4 g/L. Their ecotoxicity, degradation attempts, as well as detection monitoring in the environment are reviewed within the chapter. Additionally, waterborne pathogens, which account for 2.2 million deaths per year, are reviewed in this chapter, with emphasis on multidrug-resistant (MDR) bacteria. Although MDR infections are mostly prevalent in hospital environments, the presence of MDR bacteria in the environment is not a rarity. A high percentage of bacterial isolates in waters have been shown to be of an MDR phenotype. The theoretical background in analytical methods in water quality monitoring is also given in this chapter. Vanguard and rearguard techniques are explained, the first offering simple, cheap, and rapid sample screening, but sacrificing sensitivity and selectivity, whereas the second providing the highest quality information, excellent sensitivity and selectivity, but in expense of complicated and timely sample handling and high-cost instruments. By combining the two techniques the benefits of both can be exploited in a single system. The basic principles of thermal lens spectrometry (TLS) and its miniaturised version - the thermal lens microscopy (TLM) as fast screening methods providing high sensitivity are further explained, and their practical applications are reviewed. Furthermore, composite materials have recently been finding applications in water treatment technologies, as filter materials, adsorptives for pollutants, catalysts for degradation reactions, and disinfectants. The applications of three main types of composites: synthetic composites, biocomposites, and nanocomposites, are also reviewed within this chapter. The core of this dissertation is presented in the fourth and the fifth chapter, which examine two separate approaches for water treatment, as well as analytical methods for fast screening purposes. The fourth chapter is investigating options for degradation of iodinated X-ray agents (ICAs), namely diatrizoate, through biodegradation with extracellular enzymes of white rot fungus Dichomitus squalens, and chemical oxidation with manganese(III) acetate. Enzymatic degradation with laccase (Lac) and manganese peroxidase (MnP) at low enzymatic activities was unsuccessful, whereas at approximately 3-times higher activities the enzymes were capable of 60 % degradation in 12 days. Chemical oxidation of diatrizoate with manganese(III) acetate resulted in 85 % degradation in 12 days. Moreover, the suitability of microfluidic flow injection analysis coupled with thermal lens microscopy (μFIA-TLM) as a fast screening method for diatrizoate degradation was examined. The degradation was monitored through the release of iodide from the diatrizoate molecule. μFIA-TLM proved to be a preferable method over UV-Vis spectrophotometry, due to its higher sensitivity, sample throughput, and simple sample handling. Limit of detection (LOD) for μFIA-TLM method was estimated to be 0.14 µM in a 100 µm channel, which is 9 times lower than LOD obtained in UV-Vis measurements. In addition to μFIA-TLM and UV-VIS, high-pressure liquid chromatography (HPLC) was used to monitor the remaining parent compound in the reaction mix. In the fifth chapter, the second water treatment approach is described. This includes synthesis of biocomposite materials from cellulose (CEL) and keratin (KER), with metal (Ag0, AgCl, Au0) nanoparticles (NPs). Materials were characterised for presence, species, and size of NPs with X-ray diffraction (XRD) and with scanning electron microscopy (SEM). Nanoparticles were confirmed to be of expected species, with sizes as follows: 6.3 ± 0.5 nm for Au NPs, 12 ± 2 nm for Ag NPs, and 22 ± 1 nm for AgCl NPs. In order to evaluate antibacterial properties of the materials, contact tests with gram-negative (Escherichia coli and Pseudomonas aeruginosa) and gram-positive bacteria (Staphylococcus aureus, Methicillin-resistant S. aureus (MRSA), and Vancomycin-resistant Enterococcus faecalis (VRE)) were conducted. Direct-contact assay over 24 hours showed a dose and species-dependent antibacterial activity of [CEL:KER + Ag NPs] materials. The highest potency against the selected bacteria (up to 6-log of reduction) was observed for the material with 500 mg of Ag NPs. AgCl NPs appeared to be less potent than Ag NPs, whereas Au NPs exhibited antibacterial activity only against MRSA and VRE. In addition, antiviral properties of materials were investigated on selected bacteriophages (MS2, phiX174, and fr). However, biocomposite materials with 500 mg of Ag NPs and AgCl NPs, as well as, 240 mg of Au NPs did not exhibit any activity against selected bacteriophages. Biocompatibility with human fibroblasts was evaluated through a direct contact assay for 3 and 7 days of exposure. High concentrations of metal NPs turned out to be cytotoxic for human fibroblasts, whereas the amount of 69 mg of Ag NPs in [CEL:KER] was low enough not to affect the viability of the fibroblasts after 3 days of exposure. Composites with Ag NPs and AgCl NPs were also tested for leachability of NPs out of the materials. Both types of NPs were leaching out in two different forms, as silver ions, and as colloidal silver. Leaching of ionic silver from both materials stabilised after 3 days, whereas colloidal silver was still leaching out on the 7th day. The overall percentage of the total silver (ionic + colloidal) leached was only 0.04 % of silver incorporated in the material. In summary, this dissertation investigates alternative approaches for water treatment technologies, which could potentially serve as unit improvements of existing technologies, or as on-point pre-treatment technologies to facilitate further conventional water treatment techniques. It also demonstrates the suitability of μFIA-TLM for fast screening measurements in aquatic samples, offering high sample throughput, simple handling of the samples and superior sensitivity over the UV-Vis spectrophotometry.
Keywords: Antibacterial biocomposites, nanomaterials, water treatment technologies, multidrug-resistant bacteria, iodinated contrast agents, thermal lens microscopy, flow-injection analysis, microfluidics
Published in RUNG: 26.04.2017; Views: 6272; Downloads: 208
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Abstract: The hospital water system can be a causative agent for acquiring hospital-acquired infection. Many microorganisms can be detected in potable water and one of this is Legionella spp. These bacteria live also in nature, but are usually present in low numbers. When entering into the buildings and their water supply, Legionella finds ideal conditions to multiply, especially if this systems are extensive and old. To control the conditions in the levels that cannot harm humans, many procedures – physical and chemical – have been established. All of them have advantages as well as limitations. According to these facts, in University Clinic of Respiratory and Allergic Diseases Golnik we tried to reestablish the protocols that would keep us on the safe side and be environmentally and health friendly as well. We have been trying to use the protocol without added chemicals – just with maintaining proper temperatures, heat disinfection and flushing for many years now. With this study we wanted to extend our knowledge of our hospital water system, so we intensified the sampling and introduced extended measures. We found out that the presence of Legionella in water system is connected to moderate temperatures and it is present more frequently in high risk zones (inappropriate temperatures, dead legs, water stagnation). With constant measures, the Legionella can be controlled but not eradicated. To contain it on a safe level, the group of experts must work together and introduce procedures that will provide safe environment for the patients and employees.
Keywords: Legionella spp., hospital water system, prevention, temperature, flushing.
Published in RUNG: 30.09.2016; Views: 6146; Downloads: 276
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Abstract: The karst ecosystem shows heterogeneity and variability of geology, hydrology, morphology and ecology in space and time. Chemical composition of water in karst plays a crucial role not only in dissolution of karst rocks and deposition but also in ecological processes. The heterogeneous nature of karst aquifers leads to difficulties in predicting groundwater flow and contaminant transport direction and travel times. For its position at the top of karst, epikarst represents the interface between surface and underground. Epikarst ecology, biodiversity and fauna have rarely been systematically studied. The typical absence of enterable passages makes necessary an indirect approach. In this research, epikarst biodiversity in relation to environmental conditions was studied in seven Alpine and Pre-Alpine caves, located at different altitudes, in Slovenia and in Italy: Snežna jama na planini Arto (1556 m a.s.l.), Jama pod Babjim zobom (860 m a.s.l.), Zadlaška jama (300 m a.s.l.) and Pološka jama (500 m a.s.l.), in Slovenian Alps and Pre-alps, and Grotta A del Ponte di Veja (600 m a.s.l.), Covolo della Croce (875 m a.s.l.) and Grotta di Roverè Mille (1005 m a.s.l.) in Lessinian Massif. In these caves, percolating water was monthly monitored for fauna in the period of one year. Temperature, discharge, conductivity and pH were measured at the same time, and water samples for the laboratory analyses of total hardness, concentrations of various ions (calcium, chlorine, nitrate, sulphate and phosphate) and dissolved organic carbon were taken. 66 aquatic and terrestrial, mostly hypogean, species were found. Aquatic fauna was dominant in all caves, with the exception of Covolo della Croce. Caves located at higher elevations harbour less diverse communities. No animals were found when discharge was very low and in correspondence of moonmilk formations. The most abundant and diverse group was Copepoda, with thirteen different species and 776 individuals at different maturity stadia, totally representing 61% of the community (between two and three copepod species per cave in Slovenia and between one and six per cave in Italy). The 62% of copepod species were stygobionts. Some copepod species (e.g. Speocyclops infernus) have wide ecological tolerance to environmental variables, other have more restricted tolerances (e.g. Lessinocamptus insoletus). With regard of copepods, there was a good agreement between the number of observed species and the total number of predicted species, confirming that the sampling method was appropriate and sampling complete. Correlations between the copepod community structure and measured parameters, obtained with Pearson correlation coefficient and principal component analysis (PCA) show different patterns. Presence of copepods was positively correlated with conductivity and dissolved organic carbon in Grotta di Roverè Mille, and with carbonate and nitrate in Pološka jama. In other caves not so high correlations were found between copepod species and measured parameters and between pairs of species. Investigations of the Alpine and Pre-alpine epikarst fauna can help to understand better the ecology of the epikarst fauna and its roles within the large range of different shallow subterranean habitats.
Keywords: Epikarst, Alpine and Pre-Alpine caves, percolating water, speleobiology, fauna.
Published in RUNG: 31.08.2016; Views: 5364; Downloads: 284
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