Pèter Nèmeth

Pèter Nèmeth
Institute for Geological and Geochemical Research

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102
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Publications

Publications (102)
Article
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Research on new reaction routes and precursors to prepare catalysts for CO2 hydrogenation has enormous importance. Here, we report on the preparation of the permanganate salt of the urea-coordinated iron(III), [hexakis(urea-O)iron(III)]permanganate ([Fe(urea-O)6](MnO4)3) via an affordable synthesis route and preliminarily demonstrate the catalytic...
Article
Full-text available
Studies of dense carbon materials formed by bolide impacts or produced by laboratory compression provide key information on the high-pressure behavior of carbon and for identifying and designing unique structures for technological applications. However, a major obstacle to studying and designing these materials is an incomplete understanding of the...
Article
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Biogenic amorphous calcium carbonate (ACC) is typically metastable and can rapidly transform through aging, dehydration, and/or heating to crystalline calcium carbonate. Gaining insight into its structure and properties is typically hampered by its tendency to crystallize over short time periods once isolated from the host organism, and also by the...
Article
Full-text available
Diamond-SiC composites are attractive for improving the catastrophic fracture behaviour of SiC. However, fundamental knowledge is missing about the structure of this system and the mechanism of diamond graphitization. We used spark plasma sintering to study the diamond-Si-SiC system between 1600 and 2000?C in the function of nanocrystalline (ND) an...
Article
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We have developed a simple method to prepare nano-(ZrC 0.93 , ZrO 2- polymorphs)@carbon composites with graphite/amorphous carbon content and adjustable Zr/C ratio based on using a multistep tube furnace and plasma-assisted heat treatment of zirconium-loaded sulfonated styrene–divinylbenzene (STY-DVB) copolymers. Pre-pyrolysis of zirconium-loaded s...
Article
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Shock waves resulting from asteroidal and laboratory impacts convert sp ² -bonded graphitic material to sp ³ -bonded diamond. Depending on the shock pressure and temperature conditions, complex nanostructures can form that are neither graphite nor diamond but belong to the diaphite material group, which are characterized by structurally intergrown...
Article
The aim of the study was to reveal and compare the microbiota of different carbonate speleothems from two different epigenic karst regions (Baradla and Csodabogyós caves) in Hungary. Stalagmites, stalactites, soda straws, moonmilks, cave wall surfaces and dripping waters were sampled and plated on subsurface-environment imitating culture media cont...
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Ikaite is a calcium carbonate hexahydrate that forms at temperatures close to the freezing point of water, thus its occurrence is associated with cryogenic conditions. This mineral is metastable and quickly transforms to calcite at temperatures above 5 °C. Pseudomorphs of calcite after ikaite are known as glendonite. The nanostructure of 25,000-43,...
Preprint
Full-text available
Biogenic amorphous calcium carbonate (ACC) is typically metastable and can rapidly transform through aging, dehydration, and/or heating to crystalline calcium carbonate. Gaining insight into its structure and properties is typically hampered by its tendency to crystallize over short time periods once isolated from the host organism, and also by the...
Article
Full-text available
Nanodiamonds (ND) with 1-5 nm dimensions found in meteorites or produced by chemical vapour deposition (CVD) and detonation synthesis are typically described in terms of an sp³-bonded carbon network. However, ultra-high-resolution transmission electron microscopy (uHRTEM) combined with density functional theory (DFT) modelling leads to a different...
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During phase transitions the ordering of cations and/or anions along specific crystallographic directions can take place. As a result, extra reflections may occur in diffraction patterns, which can indicate cell doubling and the reduction of the crystallographic symmetry. However, similar features may also arise from twinning. Here the nanostructur...
Article
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The 1:1 type double salt of AgNO 3 and NH 4 NO 3 (NH 4 NO 3 ·AgNO 3 , compound 1 ) was prepared and its Raman spectrum was evaluated. IR and far‐IR spectra of compound 1 and its deuterated analog (ND 4 NO 3 ·AgNO 3 , compound 1‐D ) were also studied. We identified two types of nitrate ions, one had a relatively strong, whereas the other is only wea...
Preprint
Full-text available
Two monoclinic polymorphs of [Ag(NH3)2]MnO4 containing a unique coordination mode of permanganate ions were prepared, and the high-temperature polymorph was used as a precursor to synthesize pure AgMnO2. The hydrogen bonds between the permanganate ions and the hydrogen atoms of ammonia were detected by IR spectroscopy and single-crystal X-ray diffr...
Article
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The influence of the semiconductor microstructure on the photocatalytic behavior of Pt-PtO x /TiO2 catalysts was studied by comparing the methanol-reforming performance of systems based on commercial P25 or TiO2 from sol-gel synthesis calcined at different temperatures. The Pt co-catalyst was deposited by incipient wetness and formed either by calc...
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A statement in the article by Németh [ IUCrJ , (2020), 7 , 368–369] is corrected.
Article
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Speleothems (dominated by cave-hosted carbonate deposits) are valuable archives of paleoclimate conditions. As such, they are potential targets of clumped isotope analyses that may yield quantified data about past temperature variations. Clumped isotope analyses of stalagmites, however, seldom provide useful temperature values due to various isotop...
Article
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Copper manganese oxides (CMO) with CuMn2O4 composition are well-known catalysts, which are widely used for the oxidative removal of dangerous chemicals, e.g., enhancing the CO to CO2 conversion. Their catalytic activity is the highest, close to those of the pre-crystalline and amorphous states. Here we show an easy way to prepare a stable CMO mater...
Article
2005-ben Somogy megyében autóút építését megelőző nagyfelületű ásatáson, Balatonlelle határában két késő rézkori csontvázas sír került elő. Mindkét sírban az elhunyton kívül további koponyák maradványait is megtalálták. A 415. sírba temetett 8–9 éves gyermek csuklóján csaknem tiszta rézből készült pántkarperec, a nyakán szerves anyagból kialakított...
Article
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Prednisolone loaded mesoporous silica nanocomposites with different amounts of maghemite core were prepared to design a drug delivery system suitable for drug administration in magnetic field. Textural investigations evidenced that 80–150 nm sized spherical particles with 3–3.5 nm pore size are formed by the applied synthesis method, varying with t...
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Meteoritic diamonds and synthesized diamond-related materials contain a wide variety of complex nanostructures. This Comment highlights and classifies this structural complexity by a systematic hierarchical approach, and discusses the perspectives on nanostructure and properties engineering of diamond-related materials.
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Amorphous calcium carbonate (ACC) is a precursor of crystalline calcium carbonates that plays a key role in biomineralization and polymorph evolution. Here, we show that several bacterial strains isolated from a Hungarian cave produce ACC and their extracellular polymeric substance (EPS) shields ACC from crystallization. The findings demonstrate th...
Article
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Quasicrystals (QCs) are unique materials, whose crystallographic identity has been controversial for many years. Using recent advances in shock synthesis, Hu et al. [(2020), IUCrJ, 7, 434–444] reproduce for the first time the formation conditions of the icosahedral Al62Cu31Fe7 QC (i-phase II) found in the Khatyrka meteorite. The authors demonstrate...
Article
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The search for new nanostructural topologies composed of elemental carbon is driven by technological opportunities as well as the need to understand the structure and evolution of carbon materials formed by planetary shock impact events and in laboratory syntheses. We describe two new families of diamond-graphene (diaphite) phases constructed from...
Article
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Shock caused by impacts can convert carbonaceous material to diamond. During this transition, new materials can form that depend on the structure of the starting carbonaceous materials and the shock conditions. Here we report the discovery of cage-like nanostructured carbonaceous materials, including carbon nano-onions and bucky-diamonds, formed th...
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Compounds containing redox active permanganate anions and complexed silver cations with reducing pyridine ligands are used not only as selective and mild oxidants in organic chemistry but as precursors for nanocatalyst synthesis in low-temperature solid-phase quasi-intramolecular redox reactions. Here we show a novel compound (4Agpy2MnO4·Agpy4MnO4)...
Article
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Diamond is a material of immense technological importance and an ancient signifier for wealth and societal status. In geology, diamond forms as part of the deep carbon cycle and typically displays a highly ordered cubic crystal structure. Impact diamonds, however, often exhibit structural disorder in the form of complex combinations of cubic and he...
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We reported on the synthesis of nanosized hydroxyapatite particles by wet chemical precipitation method and the consolidation of the nanoparticles by spark plasma sintering. We studied the effect of the synthesis temperature on the particle size and phase composition of the obtained HAp. During synthesis beyond HAp, another phase supposedly nonstoi...
Article
The effect of catalyst restructuring on the polydopamine-supported Pd catalyzed transfer hydrogenation of ethyl 4-nitrobenzoate and the catalytic hydrogenation of (E)-2-methyl-2-butenoic acid is reported. Transmission electron microscopy investigation of different catalyst pre-treatment and reaction conditions revealed high catalytic activity in bo...
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Despite its thermodynamical metastability at near-surface conditions, aragonite is widespread in marine and terrestrial sediments. It abundantly forms in living organisms, and its abiotic formation is favored in waters of a Mg 2+ /Ca 2+ ratio > 1.5. Here, we provide crystallographic evidence of a nanocrystalline CaCO 3 polymorph, which precipitates...
Article
Silicon nitride (Si3N4) ceramics have superior mechanical properties allowing their broad application in many technical fields. In this work, Si3N4-based composites with 1–5 wt% multilayer graphene (MLG) content were fabricated by spark plasma sintering at different temperatures and holding time in order to improve the fracture resistance of the Si...
Article
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Fe Mössbauer spectroscopy, XRD, and TEM were used to investigate the effect of mandelic- and salicylic acid coatings on the iron oxide nanoparticles. These two carboxylic acids have similar molecules size and stoichiometry, but different structure and acidity. Significant differences were observed between the Mössbauer spectra of samples coated wit...
Article
The application of an easily prepared and highly active polydopamine-supported Pd nanoparticles catalyst in Suzuki cross-couplings and tandem Suzuki cross-coupling/catalytic transfer hydrogenation sequences under green reaction conditions is described. In Suzuki cross-couplings between aryl bromides and arylboronic acids Pd concentrations down to p...
Article
Ultrashort laser pulses provide an excellent dry and clean patterning technique in nanoscience for preparing quantum dots and quantum wires as well as depositing nanocrystalline grains of technologically important semiconductors. Here, we experimentally demonstrate the formation of silicon carbide (SiC) nanocrystals with wide size distribution (70–...
Article
New composite materials based on clay minerals had been prepared by reductive calcination. These materials exhibit very strong infrared (IR) emission at quite low temperatures. The structural properties and emission capabilities of the new materials have been studied by various theoretical and experimental methods. In addition, a brief overview of...
Article
Two new occurrences of porous, S-bearing, amorphous silica are described within metal-sulfide nodules (MSN) and as interchondrule patches in EH3 chondrites SAH 97072 and ALH 84170. This porous amorphous material, which was first reported from sulfide-bearing chondrules, consists of sinewy SiO2-rich areas containing S with minor Na or Ca as well as...
Article
In this work PtOx/β-Ga2O3 is prepared and characterized in order to test its properties in the photoinduced methanol reforming reaction using UV-visible irradiation. XRD, TEM and XPS techniques are used to characterize the fresh and recovered Pt-containing and Pt −free samples. Our results prove that in the presence of Pt the Ga2O3 is converted int...
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Water-bearing minerals provide fundamental knowledge regarding the water budget of the mantle and are geophysically significant through their influence on the rheological and seismic properties of Earth's interior. Here we investigate the CaO–SiO2–H2O system at 17 GPa and 1773 K, corresponding to mantle transition-zone condition, report new high-pr...
Article
Silicon carbide (SiC) ceramics have superior properties in terms of wear, corrosion, oxidation, thermal shock resistance and high temperature mechanical behavior, as well. However, they can be sintered with difficulties and have poor fracture toughness, which hinder their widespread industrial applications. In this work, SiC-based ceramics mixed wi...
Article
The application of Pd-polydopamine and magnetic Fe3O4@Pd-polydopamine catalysts in catalytic transfer hydrogenation reactions and Heck-arylation is reported. The reduction of a wide range of aromatic nitro-compounds bearing both electron donating and withdrawing substituents to the corresponding anilines could be efficiently performed, while the re...
Article
Ti(1−x)MoxO2–C carbon composite supported platinum electocatalysts with systematically varied Ti/Mo ratio were prepared by a multistep sol–gel-based synthesis method. The effect of the composition of the support material on the electrochemical behavior of the 20 wt% Pt electrocatalysts was investigated and the samples were also characterized by XRD...
Article
Effects of modification of PtOx-TiO2 photocatalysts by tin were elucidated by exploring relationships between the structural properties of variously prepared tin-loaded catalysts and their catalytic activity in methanol photocatalytic reforming. Tin free and amorphous tin-oxide decorated TiO2 samples were prepared by sol-gel method from titanium-is...
Article
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Speleothem deposits are among the most valuable continental formations in paleoclimate research, as they can be dated using absolute dating methods, and they also provide valuable climate proxies. However, alteration processes such as post-depositional mineralogical transformations can significantly influence the paleoclimatic application of their...
Article
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Tunneling nanotubes (TNTs) are long intercellular connecting structures providing a special transport route between two neighboring cells. To date TNTs have been reported in different cell types including immune cells such as T-, NK, dendritic cells, or macrophages. Here we report that mature, but not immature, B cells spontaneously form extensive...
Article
In this work, in addition to the conventional thermal process, two non-conventional ways, the plasma and ion beam activations are described for preparing gold nanoparticles from microcrystalline AuCN precursor. The phase formation at plasma and ion beam treatments was compared with that at thermal treatments and the products and transformations wer...
Article
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One of the most important micronutrients for plants is iron. We have prepared iron(III) oxyhydroxide and magnetite nanoparticles with the aim to use them as possible nutrition source for plants. The iron(III)-oxide/oxyhydroxide nanoparticles prepared under our experimental conditions as colloidal suspensions proved to be 6-line ferrihydrite nanopar...
Article
Silicaatzirconiaatpoly(malic acid) nanocarriers of 110 nm mean diameter were designed, synthesized and characterized for the targeted delivery of diagnostic and therapeutic 99mTc to folate-overexpressing tumors. An important achievement was that a multifunctional l-(-)-malic-acid-based copolymer was formed in situ at the surface of the inorganic co...
Article
Products of microwave-assisted urea-induced co-precipitation of Ga(NO3)3 and Zn(NO3)2 or Ga2O3 and ZnO were nitridated in order to obtain Ga-Zn-based photocatalysts. Irrespectively to the starting material, wurtzite-like Ga-Zn-oxynitride phases formed. The preparation was completed by deposition of a Pt co-catalyst, which was activated by either re...
Article
SBA-16 and MCM-41 silica materials were synthesized and modified by post-synthesis method with different amounts of Zn (2 and 4 wt.%). Quercetin, a flavonol compound, was loaded by incipient wetness impregnation method on the pure silica and Zn-modified mesoporous MCM-41 and SBA-16 supports. The parent and drug loaded formulations were characterize...