Janis Kleperis

Gas-sensitive gap formation by laser ablation in In2O3 layer: application as humidity sensor

Abstract A new method of preparing a gas-sensitive device by laser ablation of a thin gap in a thin conducting In2O3 layer has been discovered. In the bottom of the gap no products from In2O3 are found, thereby indicating that the reorganized surface of the glass substrate is responsible for the humidity sensitivity. Impedance spectra of the gap processed by a laser beam are measured in the humidity range RH25–100% at temperatures T0–45°C, where a linear dependence of the logarithm of resistivity on the values of humidity is estimated.

Nature of fundamental absorption edge of WO3

The fundamental absorption edge of amorphous, polycrystalline and crystalline tungsten trioxide (WO3) thin films obtained by different techniques (thermal evaporation, rf plasma sputtering, chemical gas transport) was investigated. Special attention was paid to correct measurements of absorption values of all WO3 thin films taking into account the scattered light, interference effects and reflection losses. The indirect edge at 2.70 eV was determined for crystalline WO3, but for crystal WO3:Ti the direct edge in the same place (2.72 eV) was found. For polycrystalline WO3 thin film first edge transition located at 2.76 eV had a quadratic dependence similar to the amorphous film at a higher photon energy (3.26 eV). Localized states are involved in these transitions with quadratic dependence. The gap energy shift from crystalline to amorphous WO3 is explained by changes in the first coordination sphere of octahedral WO3 cluster. Higher direct allowed transition at 4.1 eV is estimated both for amorphous and polycrystalline thin WO3 films.

Water Electrolysis with Inductive Voltage Pulses

The main idea of Hydrogen Economy is to create a bridge between the energy resources, energy producers and consumers. If hydrogen is produced from renewable energy sources (wind, solar, hydro, biomass, etc.), and used for energy production in the catalytic combustion process, then the energy life cycle does not pollute nature longer. With transition to Hydrogen Economy the Society will live accordingly to the sustainable development model, defined in the 1987 (Our Common Future, 1987).

Influence of the initial acidification step on biogas production and composition

Laboratory‐scale experiments were carried out to evaluate the effect of initial acidification of feedstock consisting of different components on biogas production and composition. Feedstock containing different agricultural wastes, biomass, and microorganisms was collected from five full‐scale biogas plants. Two continuously stirred tank reactors were used. The fermentation temperature was 37 °C. The pH value was adjusted to 6.0 in the first reactor at the beginning of the experiment, and an initial pH value of 7.0 was implemented after 48 H. The second reactor was used as a control reactor with a constant pH of 7.0. The experiment lasted a total of 7 days. In the reactors, the gas phase was dominated by CH4, CO2, and N2. The results showed that acidification increased biogas and carbon dioxide production in five cases, increased methane production and reduced nitrogen production in four cases, and reduced methane content in biogas in four of five cases. Only feedstock composed of 74% of different manures and 26% of plant material reduced the production of methane and increased the production of nitrogen after acidification. Other feedstock contained 47% to 96% plant material. An initial pH value of 6 could be recommended for mesophilic single‐phase methanogenesis with a prevalence of plant material.

Catalyst activation of silica nano-based pore structure material for hydrogen storage

Silica based composite material with palladium synthesized by extractive-pyrolytic method is used for hydrogen absorption-desorption experiments. The results obtained of the study on dynamic sorption experiments showed that Pyrex glass based composite sample reaches high hydrogen concentration in the material quite fast. Thought silica gel based composite material rapidly reaches 1/2 of hydrogen load but afterwards the amount of hydrogenation increases slowly. The overall amount of absorbed hydrogen for Pyrex glass based material exceeds the amount of absorbed hydrogen by silica gel based material approximately 5.6 times.

Air Quality in Riga and Its Improvement Options

Air Quality in Riga and Its Improvement Options Air quality in the city of Riga is evaluated from direct monitoring results and from accounting registered air pollutants in the city. It is concluded that from all air polluting substances listed in the European Commission directives, only nitrogen dioxide NO2 and particulate matter PM10 exceed the limits. In assessing the projected measures to improve air quality in Riga, it can be concluded that the implementation of cleaner fuels and improvements in energy efficiency of household and industrial sectors will decrease particle pollution, but measures in the transport sector will also contribute to reducing air pollution from nitrogen oxides. Gaisa Kvalitāte Rīgā un Tās Uzlabošanas Risinājumi Latvijas Republika ir saņēmusi Eiropas Komisijas formālo paziņojumu pārkāpuma procedūras lietā Nr. 2008/2195 (2010.g. 28. janvāris), kurā norādīts, ka Latvijas Republikas iesniegtie ziņojumi par gaisa kvalitātes novērtējumu 2007. un 2008.gadā liecina, ka Rīgas aglomerācijā ir pārsniegti Padomes 1999.gada 22.aprīļa Direktīvā 1999/30/EK un Eiropas Parlamenta un Padomes 2008.gada 21.maija Direktīvā 2008/50/EK par gaisa kvalitāti un tīrāku gaisu Eiropai daļiņām PM10 noteiktie robežlielumi cilvēka veselības aizsardzībai - gada robežlielums (40 μg/m3) un diennakts robežlielums (50 μg/m3, ko kalendāra gada laikā nedrīkst pārsniegt vairāk kā 35 reizes). Tāpēc svarīgi ir izvērtēt gan PM10 rašanās avotus, gan to relatīvo īpatsvaru kopējā piesārņojuma radīšanā. Rakstā izvērtētas Rīgā registrētās smalko daļiņu PM10 koncentrācijas un analizētas dienas, kad veidojušies normatīvu pārsniegumi, cenšoties identificēt lokālo piesārņotāju, atmosfēras apstākļu un arī piesārņojuma pārneses ietekmes. Gaisa kvalitātes novērtējumam izmantoti dati, kas iegūti tiešo mērījumu ceļā pilsētas teritorijā izvietotajās monitoringa stacijās (Rīgas domei piederošajās gaisa monitoringa stacijās Kr. Valdemāra ielā 18 un Brīvības ielā 73), kā arī Latvijas Universitātes Ķīmijas fakultātes veiktais smalko daļiņu monitorings Kr. Valdemāra ielā 48. PM10 gada vidējo koncentrāciju izvērtējums Rīgā visās monitoringa stacijās, kas kontrolē PM10 piesārņojumu liecina, ka tikai stacijās, kas atrodas ielās ar intensīvu transporta satiksmi (Brīvības iela, Kr, Valdemāra iela) vērojami šī robežlieluma pārsniegumi, kas gan pēdējos piecos gados uzrāda tendenci samazināties vidēji par 2% gadā. Divus pēdējos gadus Brīvības ielā PM10 gada vidējā koncentrācija pat nepārsniedz robežlielumu, savukārt Kr. Valdemāra ielā 2009.g. tā bija zem normatīva, bet 2010.g. drusku pārsniedza to. Līdzīgi smalko daļiņu PM10 diennakts vidējā koncentrācijas pārsniedz 50 μg/m3. vairāk kā 35 kalendāra dienas gadā tikai gaisa monitoringa stacijas, kas Rīgā atrodas intensīvas transporta satiksmes zonā (uz tipiskām kanjona ielām ar intensīvu transporta satiksmi Kr. Valdemāra ielā 18 un Brīvības ielā 73). Gaisa monitoringa stacijas Kr. Valdemāra ielā dati rāda, ka PM10 diennakts koncentrāciju pārsniegumiem ir tendence samazināties - vidēji par 9 % gadā, un, ja saglabāsies esošā tendence, tad 2015. gadā pārsniegumu vairs nebūs. Tādēļ, plānojot rīcības PM10 piesārņojuma mazināšanai Rīgā, galvenā uzmanība pievērsta transporta intensitātes samazināšanai pilsētas centra kanjona tipa ielās. Viens no galvenajiem pasākumiem būs transporta plūsmu optimizēšana un transporta izplūdes gāzu samazināšana, jo tieši intensīva automašīnu noslodze uz ielām paaugstina piesārņojumu ar smalkajām daļiņām, slāpekļa oksīdiem, tvana gāzi un ogļūdeņražiem. Plānots pilnībā novirzīt smago transportlīdzekļu plūsmu no centra magistrālēm, pabeidzot Austrumu magistrāli un izbūvējot Ziemeļu šķērsojumu. Ielu tīrīšana un ielu mazgāšana ir būtiska, sevišķi smilšu un putekļu savākšana no visām vietām, kur tika kaisītas smiltis ziemā, turklāt pavasara un vasaras sausajās un karstajās dienās ielas var laistīt speciālu šķīdumu, kas saista smalkās daļiņas pie ielas seguma. Uzsvars tiek likts arī uz nulles emisiju autotransporta (elektriskie un ūdeņraža auto) atbalsta pasākumiem pilsētas satiksmē un centra autostāvvietās. Качество воздуха в Риге и решения по его улучшению Латвийская Республика получила официальное сообщение Европейской комиссии по процедуре нарушения в деле №. 2008/2195 (28 января 2010 года), где говорится, что предоставленные Латвийской Республикой данные по мониторингу качества воздуха за 2007 и 2008 год позволяют сделать вывод, что в Риге и ее окрестностях превышены нормы для частиц РМю, указанных в директивах 1999/30/ЕК от 22 апреля 1999 года Совета Европы и 2008/50/ЕК от 21 мая 2008 года Европейского Парламента и Совета. Поэтому важно оценить влияние и вклад в общее загрязнения частицами РМю различных источников. В статье проанализированы данные по концентрации частиц РМю и особое внимание уделено дням, когда концентрация превышала нормы, пытаясь выявить источник загрязнения, природные условия и влияние переноса частиц. Для этого использовались данные 2 станций мониторинга (на улицах Бривибас и Кр.Валдемара), принадлежащих Рижской думе, и мониторинг частиц, проводимый на Химическом факультете Латвийского университета (так же на улице Кр.Валдемара). Результаты измерений указывают, что превышение норм концентрации частиц происходило на улицах с интенсивным движением, но даже там за последние годы наблюдается снижение концентраций в среднем на 2% в год. По результатам мониторинга на улице Бривибас последние два года концентрация не превышала критического значения, на улице Кр.Валдемара в 2009 г. норма не была превышена, а в 2010 г. немного превышена. Превышение критического значения среднесуточной концентрации в 50 мкг/м3 более чем 35 дней в году наблюдалось так же на улицах каньонного типа с интенсивным движением. Однако этот показатель так же снижается, в среднем на 9%; при сохранении такой тенденции к 2015 году превышений нормы не будет. Таким образом, планируя меры по снижению загрязнения частицами РМю необходимо уделить наибольшее внимание улицам каньонного типа с интенсивным движением транспорта. Одним из наиболее эффективных мероприятий является оптимизирование транспортного потока и снижение выбросов, т.к. именно автомобильное движение является причиной загрязнения воздуха как мелкими частицами, так и оксидами азота, угарным газом и углеводородами. Планируется перевести тяжелый транспорт на окружные дороги в обход центра, закончив строительство Восточной магистрали и построив Северную развязку. Также важна уборка улиц, особенно после обработки их зимой, и их полив в сухие дни весной и летом специальным составом, позволяющим привязать мелкие частицы к покрытию дорог. Также необходимо проводить мероприятия, стимулирующие переход на автотранспорт с нулевой эмиссией (электрический и водородный).

Composite Nanomaterials for Hydrogen Technologies

Analyzing today’s situation and tracing tendencies, it is clear that the primary energy consumption is increasing but reserves are running out very rapidly. Meanwhile, global utilization of fossils is causing environmental problems throughout the world. As a consequence, investigations of alternative energy strategies have recently become important, particularly for future world stability. The most important property of alternative energy sources is their environmental compatibility. One such new energy carrier currently being investigated is hydrogen. Many hold the hopes that it could maintain mankind’s growing need for energy. However, the hydrogen alternative has both positive and negative aspects. The main advantage of hydrogen as a fuel is sustainable development. It is a non-toxic energy carrier and holds a higher energy content: 9.5 kg of hydrogen is equivalent to that of 25 kg of gasoline (Midilli, 2005). Hydrogen can be produced in many ways, however the most environmentally friendly and the less fossils consuming are processes driven directly by sunlight – photocatalysis and photo-biological methods. Studies demonstrate that solid materials can be utilized to solve the storage problem by reversible absorption and desorption of large amounts of hydrogen (Schlapbach & Zuttel, 2001). Although several metal hydrides and composite materials are capable of meeting this target, the high desorption temperatures, slow absorption/desorption rates and small cycling capacity limit the widespread application of current metal hydrides. Nanostructuring of materials and enhancement of surface absorption capability are two main factors to increase the amount of sorbed hydrogen. One way to combine the effectiveness of hydrogen absorption in metal hydrides and the desirable weight/volume proportion is to make composite material from alloy forming hydride and appropriate support material. In this chapter a short description of water photocatalysis and photosynthetic hydrogen production and work of our laboratory on these subjects are given. There are described various composite materials for solid hydrogen storage and compared their characteristics. The chapter is concluded with the main results of our work on hydrogen storage in the modified AB

Kinetic Behavior of LiFePO4/C Thin Film Cathode Material for Lithium-Ion Batteries

Kinetic Behavior of LiFePO4/C Thin Film Cathode Material for Lithium-Ion Batteries LiFePO4 was prepared in a solid state synthesis with various levels of carbon content. LiFePO4/C thin films were obtained via magnetron sputtering. The surface morphology and structure was examined. Electrochemical properties of LiFePO4/C were studied, by using cyclic voltammetry, chronopotentiometry and electrochemical impedance spectroscopy. Thin films acquired show a potential use as a cathode in lithium ion batteries, displaying charge capacity up to 34 mAh g-1.

Structure and Photocatalytic Properties of TiO2-WO3 Composites Prepared by Electrophoretic Deposition

In this work TiO2-WO3 composite films containing different oxide concentrations were prepared by electrophoretic deposition on steel substrates. Composite coating structures were analyzed by X -ray diffraction, Raman spectra and scanning electron microscopy. The results showed an even distribution of WO3 particles in the entire composite layer. Light absorption measurements were used for photocatalytic properties evaluation. It was found that the removal ratio of methylene blue depends on the (TiO2):(WO3) concentration ratio. The most effective photodegradation was determined for the sample that was electrophoretically deposited from the suspension with the molar content ratio n(TiO2):n(WO3) 2:1.

Electrophoretic Nanocrystalline Graphene Film Electrode for Lithium Ion Battery

Graphene sheets were fabricated by electrophoretic deposition method from water suspension of graphene oxide followed by thermal reduction. The formation of nanocrystalline graphene sheets has been confirmed by scanning electron microscopy, X-ray diffraction and Raman spectroscopy. The electrochemical performance of graphene sheets as anode material for lithium ion batteries was evaluated by cycling voltammetry, galvanostatic charge-discharge cycling, and electrochemical impedance spectroscopy. Fabricated graphene sheets exhibited high discharge capacity of about 1120 mAhg−1 and demonstrated good reversibility of lithium intercalation and deintercalation in graphene sheet film with capacity retention over 85 % after 50 cycles. Results show that nanocrystalline graphene sheets prepared by EPD demonstrated a high potential for application as anode material in lithium ion batteries.