Seznam abstraktů 2017: SEKCE B - PRŮMYSLOVÉ A ENVIROMENTÁLNÍ APLIKACE NANOMATERIÁLŮ
Datum: 18.10.2017
An important part of fundamental research in catalysis is based on theoretical and modelling foundations which are closely connected with studies of single-crystalline model catalyst surfaces. These so-called model catalysts are often prepared in the form of epitaxial thin films, and characterized using advanced material characterization techniques. This concept is providing the fundamental understanding and the knowledge base needed to tailor the design of new heterogeneous catalysts with improved catalytic properties. The present contribution is devoted to development of a model catalyst system of CeO2 on a Cu(111) substrate.
Single-atom catalysts maximize the utilization of supported precious metals by exposing every single metal atom to reactants. To avoid sintering and deactivation at realistic reaction conditions, single metal atoms are stabilized by specific adsorption sites on catalyst substrates. We show by combining photoelectron spectroscopy, scanning tunneling microscopy and density functional theory calculations that Pt single atoms on ceria are stabilized by the most ubiquitous defects on solid surfaces-monoatomic step edges. Pt segregation at steps leads to stable dispersions of single Pt2+ ions in planar PtO4 moieties incorporating excess O atoms and contributing to oxygen storage capacity of ceria [1,2]. We experimentally control the step density on our samples, to maximize the coverage of monodispersed Pt2+ and demonstrate that step engineering and step decoration represent effective strategies for understanding and design of new single-atom catalysts.
We have demonstrated the promising properties of the Pt-CeO2 thin films as electrocatalysts in proton exchange membrane fuel-cell technology, specifically their superior noble metal efficiency. The high performance was shown for the anode catalyst with 2 g Pt/cm2 which contained Pt2+ ions only. The catalyst with so small Pt loading can be considered as “almost Pt free” [3].
REFERENCES: [1] Dvorak, F; Camellone, MF; Tovt, A; Tran, N-D; Negreiros, FR; Vorokhta, M; Skala, T; Matolinova, I; Myslivecek, J; Matolin, V; Fabris, S, „Creating single-atom Pt-ceria catalysts by surface step decoration“, Nat. Commun., 7 (Feb): Art. No. 10801, 2016.; [2] Bruix, A; Lykhach, Y; Matolinova, I; Neitzel, A; Skala, T; Tsud, N; Vorokhta, M; Stetsovych, V; Sevcikova, K; Myslivecek, J; Fiala, R; Vaclavu, M; Prince, KC; Bruyere, S; Potin, V; Illas, F; Matolin, V; Libuda, J; Neyman, KM, „Maximum Noble-Metal Efficiency in Catalytic Materials: Atomically Dispersed Surface Platinum“, Angew. Chem.-Int. Edit., 53: 10525–10530, 2014; [3] Fiala, R; Figueroba, A; Bruix, A; Vaclavu, M; Rednyk, A; Khalakhan, I; Vorokhta, M; Lavkova, J; Illas, F; Potin, V; Matolinova, I; Neyman, KM; Matolin, V, “High efficiency of Pt2+- CeO2 novel thin film catalyst as anode for proton exchange membrane fuel cells”, Appl. Catal. B-Environ., 197: 262–270, 2016.
Lithium-ion batteries represent the most used battery type even though there are still some challenges defined by limitations in lifetime and capacity, deep discharging, sensibility to high/low temperatures, etc. In general, LiCoO2 is commonly used as the positive electrode. But its high cost and toxicity represent disadvantages and alternatives needs to be found. Binary transition metal oxides (BTMOs) are promising substitutes for Co oxides due to their widened potential window, superior conductivity and good stability. The Mn-Zn-O ternary system can exploit synergistic impacts on final electrochemical and magnetic properties. ZnMn2O4 is a low cost, environmental friendly, low toxic material consisting of abundant elements and is thus a promising candidate for substitution of Co oxides.
In this work, a facile method for targeted modification of oxidic surfaces is presented. A Mn thickness gradient film superimposed on a homogenous Zn layer was successfully prepared using the thermal co-evaporation technique. Heat treatment of the sandwich structure was carried out in order to obtain oxides. Studies of morphology, composition, topography and surface potential of the metallic as well as of the oxide film have been performed. All results show a strongly thickness dependent correlation of the Mn film. Via SEM imaging, a critical thickness for the overlying Mn layer has been determined where the morphology of the Zn substrate layer is dominating. After annealing, two main structures of the resulting oxides can be identified: Nano-needles and nano-walls whose formation is a function of the supply of the superimposed Mn. Based on these findings, oxide growth mechanisms are proposed.
The use of plasmonic nanostructures in solar energy conversion has recently attracted great attention. Recent demonstrations have been mainly limited to nanostructures made of gold, silver and aluminum. While they show excellent optical properties for plasmonic applications, major issues are related to their high cost, poor chemical (Ag) and thermal stability (Au, Ag) and low melting point.
On the contrary, transition metal nitrides such as titanium nitride (TiN) and zirconium nitride (ZrN) exhibit optical properties similar to Au and can be utilized as plasmonic materials in the visible and near-infrared regions. Combining refractory material properties with plasmonic properties, transition metal nitrides offer a unique solution to material-related problems in applications where high temperature durability and/or chemical stability are needed.
Here, we will present our recent results on superior photocurrent generation for solar water splitting by using TiN nanoparticles (NPs) on TiO2 nanowires (NWs) as compared to using gold. Through a combined experimental and theoretical approach, we will show that the superior performance of TiN is due to the broadband hot electron generation and improved electrical junction at the metal-semiconductor interface.
Finally, our recent results on large-scale fabrication of refractory plasmonic nanostructures will be discussed. We will also show that plasmonic TiN can be obtained after nitridation of TiO2 nanoparticles, tilted TiN NWs deposited through glancing angle deposition, lithographically-patterned TiO2, and more complex TiO2 nanostructures highlighting the potential of this approach, not only for solar energy applications, but also for lasing and flat nanophotonics.
Our results show that plasmonic TiN enable enhanced performance for solar energy conversion holding promise for its implementation in stable and cost-effective devices.
Perovskite-type structures with mixed oxygen-ionic and electronic conductivity, high activity and stability are used as catalysts for high temperature processes such as synthesis gas production and ethylene and propylene subsequent synthesis. The nanostructured perovskite-type oxides GdFe1-xMnxO3 (x = 0, 0.01, 0.05, 0.5 and 1) were synthesized by ceramic and sol-gel technologies and were studied as catalysts for dry reforming of methane and the CO hydrogenation. The complex of physico-chemical investigation methods showed that samples obtained by sol-gel technology are in nanocrystalline state and these have a porous structure, and oxides prepared by ceramic technology are in sub-microcrystalline state. The sol-gel method makes it possible to obtain samples with higher catalytic performances in comparison with ceramic systems. Doping the B-site of gadolinium ferrites with manganese, and also surface modification with Mn leads to an increase in olefin selectivity over the entire temperature range. The highest stability, catalytic activity, and unsaturated hydrocarbons (ethylene and propylene) selectivity in the carbon oxides hydrogenation were observed over GdFeO3, GdFe0.95Mn0.05O3, 5 %wt Mn/GdFeO3 samples. It was established that the phase composition of all ferrites remains unchanged after catalytic reactions. Partial decomposition of catalysts and significant changes in the samples morphology didn’t occur. Carbon is present on the used catalysts surface, but since the catalysts activity didn't change in repeated experiments for a long time, it is suggested that this carbon is mostly active. And formation of inactive carbon for samples obtained by sol-gel method is minimal.
Perovskite and dye-sensitized solar cells, in which the photo-electrochemical system typically relies upon a mesoporous TiO2 layer, have emerged as promising low-cost photovoltaic technology in recent years and constitute the most notable application field for semiconducting photoanodes, which are often used in electro-assisted photocatalytic treatment of water, hydrogen production by water splitting and various sensing systems. Fine mesoporous TiO2 films are usually cured at high temperatures by means of a slow convection heating procedure (at least 30 min above 350 °C) in order reliably to remove all organic components present in the coating formulation. The high sintering temperature, however, precludes the use of such a procedure for thermally sensitive substrates and results in performance deterioration in transparent conducting oxide substrates.
We prepared hybrid mesoporous titania/silica electron-generating and transporting layers using wet coating with a dispersion consisting of prefabricated titania nanoparticles and a methyl-silica binder. Titania/methyl-silica wet layers were deposited by inkjet printing on ITO/PET flexible foils and further mineralized by low-temperature (70 °C) atmospheric-pressure air plasma using diffuse coplanar surface barrier discharge (DCSBD) to form a titania/silica hybrid nanocomposite coating.
The plasma mineralization process provides production performance superior to the previously-considered processes (thermal sintering and UV curing), taking only a fraction of the time required for them at far lower temperatures. The coating can be applied on flexible polymer which makes the application suitable for roll-to-roll fabrication units. The reported method could constitute a major step forward in the large-scale manufacture of flexible solar cells, among many other applications.
The self-organized TiO2 nanotube layers have attracted considerable scientific and technological interest over the past 10 years motivated for their possible range of applications including photo-catalysis, solar cells, hydrogen generation and biomedical uses [1]. The synthesis of 1D TiO2 nanotube structure is carried out by a conventional electrochemical anodization of valve Ti metal sheet. The main drawback of TiO2 is its applicability in the UV light (wavelengths < 390 nm). In order to enhance the efficiency, TiO2 has been doped by N [2] or C [3] to shift its absorption into the visible light.
Except of doping, one of the major issues to extend the functional range of nanotubes is to coat homogeneously tube interiors by a secondary material. It has been shown that additional ultrathin surface coating of TiO2 by secondary materials such as Al2O3 [4], ZnO [5] or MgO [6] annihilates electron traps at the TiO2 surface and thus increases the photogenerated concentration of charge carriers. Recently, it has been demonstrated that just a single cycle of Al2O3 [7] or ZnO [5] deposited by atomic layer deposition (ALD) efficiently improve charge transport properties of the heterostructure while gradual passivation appears with increasing ZnO thickness due to stronger band-bending [5].
The presentation will focus in detail on the coating of the nanotube arrays by secondary materials using ALD. The deposited materials influence strongly photo-electrochemical properties of nanotube films. Experimental details and some very recent photocatalytic [8], solar cell [9] and sensing [10] results will be presented and discussed.
References:
[1] J. M. Macak et al., Curr. Opin. Solid State Mater. Sci. 1-2 (2007) 3.
[2] C. Burda et al., Nano Lett. 3 (2003) 1049.
[3] S. Sakthivel et al., Angew. Chem., Int. Ed. 42 (2003) 4908.
[4] R. Zazpe et al., Langmuir, in press, DOI: 10.1021/acs.langmuir.6b03119.
[5] A. Ghobadi et al., Scientific Reports 6 (2016) 30587
[6] H. Park, et al., Journal of Electroceramics 23 (2009) 146.
[7] J-Y. Kim et al., Nanotechnology 25 (2014) 504003.
[8] H. Sopha et al., Applied Materials Today, submitted.
[9] M. Krbal, Nanoscale, accepted, DOI: 10.1039/C7NR02841E
[10] S. Ng et al., Scientific Reports, submitted.
Nanoscale zerovalent iron (nZVI) particles represent one of the most extensively studied type of nanomaterial used for environmental restoration. Various types of nZVI particles and nZVI-bearing nanocomposites have been designed for reductive and combined technologies of groundwater treatment. Generally, the reactivity and overall applicability of nZVI particles is competitive with conventional remediation technologies. However, the main drawback of the nZVI particles could be their low selectivity and also limited migration/applicability in some particular cases (i.e., in sediments with low permeability etc.). Therefore, material properties (surface modifications, chemical modifications) and various types of combinations (e.g., combination of nZVI with other materials leading to formation of new nanocomposites, or combination with external factors like electric/magnetic field, microbial activity etc.) have been recently invented with the aim to enhance nZVI applicability. In this presentation, the most promising ways leading to improved nZVI reactivity (and overall performance in groundwater treatment processes) will be summarized and demonstrated on laboratory-scale experiments, as well as on results from filed-scale pilot tests.
The main aim of this study was to assess the ability of iron oxides nanoparticles (NPs) to enhance the microbial activity, in order to degrade BTEX compounds more effectively. The ferric iron mineral acts as an electron acceptor for microbial respiration [Fe3+-reduction coupled to oxidation of the BTEX compounds] and can overcome limitations in electron acceptor availability. In addition migration characteristics and remedial efficiency of iron oxides nanoparticles were evaluated using advanced procedures for monitoring both total iron and vertical stratification of BTEX.
Stabilised slurry of nano-Goethite has been developed at the Helmholtz Centre Munich. One of the contamination plumes at the Spolchemie was chosen as a case study site. Enhanced in situ bioremediation has been identified as a suitable remedial technology to treat BTEX compounds based on laboratory tests. This was proved in detail by molecular biology analysis.
The presented contribution will summarize the results from the iron oxide NPs application.The tracer test results confirmed that the Nano-Goethite suspension was injectable into the aquifer; contact between contaminated groundwater and NPs was proved.
BTEX removal was inferred from a decrease in BTEX concentrations between the wells in the inflow and outflow areas and the trends were confirmed by long term monitoring. The use of Nano-Goethite as an electron acceptor for biodegradation was confirmed by a clear increase of dissolved Fe2+ ions and dissolved carbonate in the groundwater. Microbiological analyses confirmed that the microbial community in the water phase did not react significantly to the ferric iron injection.
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CS CLEAN SOLUTIONS is serving the nanomaterials world by treating exhaust gas streams of ALD and CVD processes used for the production of e.g. carbon nanotubes, nanodiamonds, 2-D materials like molybdenum disulfide and diselenide.
It is well-known that a type of used fumed silica nanoparticles plays a dominant role in wettability of the corresponding nanofibrous mats. Fumed silica nanoparticles with different surface modifications, sizes and the specific surface areas were incorporated into polyvinyl butyral (PVB) fibrous membrane prepared by electrospinning process. The wetting properties of PVB fibres containing fumed silica was investigated by the water contact angle measurement and compared with PVB films. The circular and flat cross-section of fibres with various diameters was produced from PVB dissolved in methanol and ethanol, respectively. The results of water contact angle measurements show that the solvent of the polymer could affect the polymer wettability significantly. In addition, the surface modification of fumed silica plays important role in wetting properties. Combination of the type of fumed silica nanoparticles and the type of solvent influence the polymer particle interaction resulting in nanofibres with various silica surface covering.
The access to clean water is nowadays a big issue worldwide and the pressure on water supplies is increasing. In addition to the natural factors affecting the world water cycle system, people, through their technological development, institutional and financial conditions are contributing to ever increasing demands to fresh water. This requires a new efficient low-cost form of sewage treatment with lower energy and chemicals consumption. This approach can guarantee that the environment will be less negatively impacted and there should be sustainable development for the whole of humanity. The most suitable way to solve this problem, from the point of view of our research team, is to enhance the current membrane filtration processes by modifying the fibrous polymeric substrate, which would allow the preparation and subsequent production of nanofibrous filter membranes with new properties. The main idea is to prepare structures with increased resistance to the development of microbial biofilms through incorporation of suitable functional groups directly into the polymeric backbone of the basic copolymer and preparation of nanofibrous structures by electrospinning of the prepared matrix. The presentation will be divided to explanation of our approach to modification of polyurethane fibers by quaternary ammonium salts, to formation of nanofibrous membranes by electrospinning and finally to results from monitoring of dynamics of Escherichia coli (CCM 3954) and Pseudomonas aeruginosa (CCM 3955) biofilm development.
The present study reports an Eco-friendly method for the fabrication of electrospun fibres based on natural tree gum polymers (Gum Arabic, karaya and Kondagogu) using electrospinning. Further, the fabricated electospun fibres have been used as a template for in- situ reduction of ferric chloride to zerovalent iron nanoparticle (ZVI) using sodium borohydride under nitrogen atmosphere. The fabricated electrospun fibres carrying ZVI nanoparticles (EF/ZVI) were characterized by various techniques such as XRD, FT-IR, SEM-EDX, TEM, and HR-TEM, UV-visible spectroscopy, BET and particle size analysis. Various process such as Heat treatment, methane plasma and gamma irradiation techniques was performed to enhance the physicochemical properties of the electrospun fibres. Furthermore, the efficiency of treated EF/ZVI was evaluated with regard to their ability to capture nanoparticles (Ag, Au, Pt and Pd) from contaminated water.
The short carbon fibers reinforced cementitious matrix composites were prepared. The mechanical properties of the materials were investigated.Recycled Short carbon fiber has recently gained popularity in concrete reinforcing applications due to its excellent mechanical properties. The aim of this research is to evaluate the flexural strength, compression strength and tensile strength in enhancing the mechanical behavior of concrete. Concrete specimens were cast with five different formulations of the same fiber. Interfacial properties were also investigated by scanning electron microscopy. A total of 156 specimens with short carbon fiber volume fraction ranging from 0.0% to 0.5% were tested.