scholarly journals Nanocomposites SnO2/SiO2:SiO2 Impact on the Active Centers and Conductivity Mechanism

Materials ◽  
2019 ◽  
Vol 12 (21) ◽  
pp. 3618 ◽  
Author(s):  
Dayana Gulevich ◽  
Marina Rumyantseva ◽  
Artem Marikutsa ◽  
Tatyana Shatalova ◽  
Elizaveta Konstantinova ◽  
...  
Keyword(s):  
Active Sites ◽  
Nitrogen Adsorption ◽  
Hydroxyl Groups ◽  
Pure Sno2 ◽  
Active Centers ◽  
Paramagnetic Resonance ◽  
Surface Hydroxyl ◽  
Chemisorbed Oxygen ◽  
Temperature Dependences ◽  
Sio2 Nanocomposites

This paper is focused on the effect of the stabilizing component SiO2 on the type and concentration of active sites in SnO2/SiO2 nanocomposites compared with nanocrystalline SnO2. Previously, we found that SnO2/SiO2 nanocomposites show better sensor characteristics in CO detection (lower detection limit, higher sensor response, and shorter response time) compared to pure SnO2 in humid air conditions. Nanocomposites SnO2/SiO2 synthesized using the hydrothermal method were characterized by low temperature nitrogen adsorption, XRD, energy dispersive X-ray spectroscopy (EDX), thermo-programmed reduction with hydrogen (TPR-H2), IR-, and electron-paramagnetic resonance (EPR)-spectroscopy methods. The electrophysical properties of SnO2 and SnO2/SiO2 nanocomposites were studied depending on the oxygen partial pressure in the temperature range of 200–400 °C. The introduction of SiO2 results in an increase in the concentration of paramagnetic centers Sn3+ and the amount of surface hydroxyl groups and chemisorbed oxygen and leads to a decrease in the negative charge on chemisorbed oxygen species. The temperature dependences of the conductivity of SnO2 and SnO2/SiO2 nanocomposites are linearized in Mott coordinates, which may indicate the contribution of the hopping mechanism with a variable hopping distance over local states.

scholarly journals Analysis of water state adsorbed by cellulose fibers

2019 ◽  
Vol 58 (5) ◽  
pp. 24-31
Author(s):  
Daria S. Masas ◽  
◽  
Maria S. Ivanova ◽  
Gocha Sh. Gogelashvili ◽  
Alexander S. Maslennikov ◽  
...  
Keyword(s):  
Adsorbed Water ◽  
Lattice Relaxation ◽  
Spin Lattice Relaxation ◽  
Water Molecules ◽  
Hydroxyl Groups ◽  
Active Centers ◽  
Surface Hydroxyl ◽  
Spin Lattice ◽  
Donor Acceptor ◽  
Elementary Fibrils

Modernized model of microfibril cellulose layered structure is proposed. This model considers presence of slit-shaped micropores in space between elementary fibrils and cellulose microfibrils. It’s discussed the nature of donor-acceptor hydrogen bonds formation: intra-, intermolecular, and interlayer bonds inherent in each glucopyranous cellulose link. It’s described the mechanism of water molecules specific adsorption interactions in a monolayer with active centers located on the hydrophilic surfaces of elementary fibrils. Dipole-dipole energy transition into energy of hydrogen bond is discussed during adsorption process between active centers of cellulose and water adsorptive molecules. Analysis of water molecules dipole-dipole interactions with surface hydroxyl groups of cellulose showed that at distance of 2.5-3 Å energy of this interaction transforms into energy of hydrogen bond. It is discussed the formation mechanism of water molecules donor-acceptor bonds with cellulose surface hydroxyl groups. Thermodynamic parameters characterizing adsorbate state the in these layers are determined by proton magnetic relaxation and sorption measurements. It’s established the possibility of determining adsorption net heat in bilayer considering Arrhenius nature of adsorbate thermal molecular motions correlation times. Increase in entropy of adsorbed water during adsorption process is revealed basis on Vant Hoff equation and certain adsorption equilibrium constant. The calculation established that distance between nearest active centers of cellulose is 6.5 Å. This leads to disunity of adsorbed water molecules and allows application of Langmuir and BET adsorption theory. Analysis of spin-lattice relaxation times dependence on cellulose moisture content made it possible to establish the cause of its crystallite wedging from adsorbed water molecules at adsorption initial stages. Decline of the spin-lattice relaxation unambiguously indicates the process of cellulose dispersion into its structural elements. It was established that during adsorption a part of the internal regions of crystallites passes to their surface with participation of cellulose hydroxyl groups. During desorption reverse process is observed.

scholarly journals THERMODINAMIC PARAMETERS ON THE SORPTION OF PHOSPHATE IONS BY MONTMORILLONITE

2016 ◽  
Vol 4 (1) ◽  
Author(s):  
Ikhsan Jaslin ◽  
Wijayanti Endang ◽  
Sunarto Sunarto
Keyword(s):  
Active Sites ◽  
Surface Complexation ◽  
Outer Sphere ◽  
Hydroxyl Groups ◽  
Process Data ◽  
Surface Complexes ◽  
Surface Complexation Model ◽  
Surface Hydroxyl ◽  
Phosphate Ions ◽  
Sorbate Concentration

The sorption of phosphate by montmorillonite at 10, 30, and 50 oC were investigated aiming to mainly determine thermodynamic parameters for the formation of surface complexes in the adsorption of phosphate ions by montmorillonite. Data were collected by adsorption edge experiments investigating the effect of pH, adsorption isotherms enabling the effect of sorbate concentration, and acid-base titration calculating protons released or taken up by adsorption process. Data analysis was carried out using surface complexation model to fit the data collected in this study using the parameters obtained from previous study, as well as to calculate the values of ΔH and ΔS. Previous study reported that phosphate ions formed two outer-sphere surface complexes with active sites of montmorillonite through hydrogen bonding. In the first complex,  [(XH)0– H2L─]─, the phosphate was held to permanent-charge X─ sites on the tetrahedral siloxane faces, and the second complex, [[(SO─)(SOH)]– – [H2L]─] 2─ was formed through the interaction between the phosphate and variable charge surface hydroxyl groups at the edges of montmorillonite crystals and on the octahedral alumina faces. The values of ΔH for the first and second reactions are 39.756 and 3.765x10-7 kJ mol‒1 respectively. Since both reactions have positive enthalpy values, it can be concluded that the reactions are endothermic. Large energy for the first reaction is needed by X─  sites (permanent negatively charge sites of montmorillonite) to be partially desolvated, on which K+ or other surface cations are replaced by H+ ions in the surface protonated process, and are then ready to interact phosphate ions in the solution. Small values of ΔH for the second reactions indicates that hydrogen bonds formed by phosphate and SOH sites in the second reaction are easily broken out, and the phosphate can easily desorbed from the surface. The values of ΔS for the first and second reactions are 122.523 and 2.393 x10-2  J K‒1 mol‒1, which are greater than -10 kJ mol‒1 and indicates that the surface reactions occurs through dissociative mechanisms.Keywords:   montmorillonite, adsorption edge, extended constant capacitance, surface complexation model, enthalpy, reaction mechanisms

scholarly journals Spectroscopic Signature and Structure of Active Centers in Ziegler-Natta Polymerization Catalysts revealed by Electron Paramagnetic Resonance

2020 ◽  
Author(s):  
Anton Ashuiev ◽  
mathieu humber ◽  
sebastien norsic ◽  
jean blahut ◽  
david gajan ◽  
...  
Keyword(s):  
Active Sites ◽  
Atomic Scale ◽  
Paramagnetic Species ◽  
Polymerization Catalysts ◽  
Active Centers ◽  
Paramagnetic Resonance ◽  
Joint Application ◽  
Spectroscopic Signatures ◽  
Electron Paramagnetic ◽  
Ziegler Natta Catalysts

Despite decades of extensive studies, the atomic-scale structure of active sites in heterogeneous Ziegler-Natta (ZN) catalysts remains elusive and a matter of debate. Here, the structure of polymerization ZN catalysts is elucidated from magnetic resonance experiments carried out on samples reacted with increasing amounts of BCl<sub>3</sub> so as to enhance the concentration of active sites and observe clear spectroscopic signatures. Notably, we show that EPR and NMR spectroscopy of the activated ZN catalysts enables to observe paramagnetic species whose amount increases in conjunction with the catalytic activity. The joint application of 2D HYSCORE experiments and DFT calculations reveals the presence of bimetallic alkyl-Ti(III),Al complexes that are assigned to the catalytic centers of MgCl<sub>2</sub>-supported Ziegler-Natta catalysts

scholarly journals Reaction ability of alternative mineral dispersed materials as a tool for developing efficient road composites

2019 ◽  
Vol 81 (1) ◽  
pp. 282-288
Author(s):  
M. A. Vysotskaya ◽  
S. Yu. Shehovtsova ◽  
D. A. Kuznetsov
Keyword(s):  
Active Sites ◽  
Materials Science ◽  
Construction Materials ◽  
Raw Material ◽  
Hydroxyl Groups ◽  
High Porosity ◽  
Active Centers ◽  
Pore Architecture ◽  
Wide Range

The avalanche-like growth of traffic intensity and freight traffic, the tightening of requirements for the quality of road clothes, the shortage of conditioned mineral raw materials in many regions of the Russian Federation prompt the construction materials science sector to search for new, promising methods for improving the quality of products. Road construction, one of the most material-intensive areas, is focused on maximizing the use of local, often non-conditioning materials, so composites made on their basis do not meet modern operational requirements. In this paper, a number of porous fine dispersed fillers have been investigated that could perform, on the one hand, the functions of a mineral powder, and on the other hand, serve as the carrier of a certain substance that regulates the properties of a road composite. The identification of the mechanism of interaction of mineral powders with bitumen was carried out by studying surface, physical-mechanical and chemical properties, as well as microstructural features and reactivity. It was found that the high porosity characteristic of fillers from perlite and zeolite is due to the highly developed pore architecture with the diameter of the entrance windows in a wide range. The study of the chemistry of the surface of a solid was carried out by evaluating the surface on which there are active centers due to the presence of hydroxyl groups and impurity centers. By the results of the experiment, it was found that an increase in the content of active sites on the surface of a mineral filler is directly proportional to its porosity. As a result of the conducted studies it was established that zeolites are the most promising raw material for organomineral composites. They have a developed specific surface, unique pore architecture, high structuring and adsorption capacity.

scholarly journals Zr(OH)4/GO Nanocomposite for the Degradation of Nerve Agent Soman (GD) in High-Humidity Environments

Materials ◽  
2020 ◽  
Vol 13 (13) ◽  
pp. 2954 ◽  
Author(s):  
Seongon Jang ◽  
Dongwon Ka ◽  
Hyunsook Jung ◽  
Min-Kun Kim ◽  
Heesoo Jung ◽  
...  
Keyword(s):  
Active Sites ◽  
Adsorbed Water ◽  
Interaction Force ◽  
Nerve Agents ◽  
Nerve Agent ◽  
Zirconium Hydroxide ◽  
Hydroxyl Groups ◽  
High Humidity ◽  
Surface Hydroxyl ◽  
Diffuse Reflectance Infrared

Zirconium hydroxide, Zr(OH)4 is known to be highly effective for the degradation of chemical nerve agents. Due to the strong interaction force between Zr(OH)4 and the adsorbed water, however, Zr(OH)4 rapidly loses its activity for nerve agents under high-humidity environments, limiting real-world applications. Here, we report a nanocomposite material of Zr(OH)4 and graphene oxide (GO) which showed enhanced stability in humid environments. Zr(OH)4/GO nanocomposite was prepared via a dropwise method, resulting in a well-dispersed and embedded GO in Zr(OH)4 nanocomposite. The nitrogen (N2) isotherm analysis showed that the pore structure of Zr(OH)4/GO nanocomposite is heterogeneous, and its meso-porosity increased from 0.050 to 0.251 cm3/g, compared with pristine Zr(OH)4 prepared. Notably, the composite material showed a better performance for nerve agent soman (GD) degradation hydrolysis under high-humidity air conditions (80% relative humidity) and even in aqueous solution. The soman (GD) degradation by the nanocomposite follows the catalytic reaction with a first-order half-life of 60 min. Water adsorption isotherm analysis and diffuse reflectance infrared Fourier transform (DRIFT) spectra provide direct evidence that the interaction between Zr(OH)4 and the adsorbed water is reduced in Zr(OH)4/GO nanocomposite, indicating that the active sites of Zr(OH)4 for the soman (GD) degradation, such as surface hydroxyl groups are almost available even in high-humidity environments.

HYPERBRANCHED ALIPHATIC POLYESTER MODIFIED ACTIVATED CARBON PARTICLES WITH HOMOGENIZED SURFACE GROUPS

2007 ◽  
Vol 14 (06) ◽  
pp. 1025-1032 ◽  
Author(s):  
PENG LIU ◽  
LIUXUE ZHANG
Keyword(s):  
Activated Carbon ◽  
Photoelectron Spectroscopy ◽  
Active Sites ◽  
Hydroxyl Groups ◽  
Surface Groups ◽  
Aliphatic Polyester ◽  
One Pot ◽  
Surface Hydroxyl ◽  
Carbon Particles ◽  
Activated Carbon Particles

The hyperbranched aliphatic polyester grafted activated carbon (HAPE-AC), was successfully prepared by the simple "one-pot" method. The surface functional groups of commercial activated carbon particles were homogenized to hydroxyl groups by being oxidized with nitric acid and then reduced with lithium tetrahydroaluminate ( LiAlH 4) at first. Secondly, the surface hydroxyl groups were used as the active sites for the solution polycondensation of the AB2 monomer, 2, 2-bis(hydroxymethyl)propionic acid (bis-MPA), with the catalysis of p-toluenesulfonic acid (p-TSA). The homogenization of the surface groups of the activated carbon particles and the graft polymerization of the hyperbranched aliphatic polyester were investigated by X-ray photoelectron spectroscopy (XPS) technique. The products were also characterized with Fourier transform infrared (FT-IR) and scanning electron microscope (SEM). The competitive adsorption properties of the products toward the heavy metal ions ( Cu (II), Hg (II), Zn (II), and Cd (II)) also proved the translations of the surface groups.

scholarly journals Spectroscopic Signature and Structure of Active Centers in Ziegler-Natta Polymerization Catalysts revealed by Electron Paramagnetic Resonance

2020 ◽  
Author(s):  
Anton Ashuiev ◽  
mathieu humber ◽  
david gajan ◽  
sebastien norsic ◽  
jean blahut ◽  
...  
Keyword(s):  
Active Sites ◽  
Atomic Scale ◽  
Paramagnetic Species ◽  
Polymerization Catalysts ◽  
Active Centers ◽  
Paramagnetic Resonance ◽  
Joint Application ◽  
Spectroscopic Signatures ◽  
Electron Paramagnetic ◽  
Ziegler Natta Catalysts

Despite decades of extensive studies, the atomic-scale structure of active sites in heterogeneous Ziegler-Natta (ZN) catalysts remains elusive and a matter of debate. Here, the structure of polymerization ZN catalysts is elucidated from magnetic resonance experiments carried out on samples reacted with increasing amounts of BCl<sub>3</sub> so as to enhance the concentration of active sites and observe clear spectroscopic signatures. Notably, we show that EPR and NMR spectroscopy of the activated ZN catalysts enables to observe paramagnetic species whose amount increases in conjunction with the catalytic activity. The joint application of 2D HYSCORE experiments and DFT calculations reveals the presence of bimetallic alkyl-Ti(III),Al complexes that are assigned to the catalytic centers of MgCl<sub>2</sub>-supported Ziegler-Natta catalysts

scholarly journals Spectroscopic Signature and Structure of Active Centers in Ziegler-Natta Polymerization Catalysts revealed by Electron Paramagnetic Resonance

2020 ◽  
Author(s):  
Anton Ashuiev ◽  
mathieu humber ◽  
david gajan ◽  
sebastien norsic ◽  
jean blahut ◽  
...  
Keyword(s):  
Active Sites ◽  
Atomic Scale ◽  
Paramagnetic Species ◽  
Polymerization Catalysts ◽  
Active Centers ◽  
Paramagnetic Resonance ◽  
Joint Application ◽  
Spectroscopic Signatures ◽  
Electron Paramagnetic ◽  
Ziegler Natta Catalysts

Despite decades of extensive studies, the atomic-scale structure of active sites in heterogeneous Ziegler-Natta (ZN) catalysts remains elusive and a matter of debate. Here, the structure of polymerization ZN catalysts is elucidated from magnetic resonance experiments carried out on samples reacted with increasing amounts of BCl<sub>3</sub> so as to enhance the concentration of active sites and observe clear spectroscopic signatures. Notably, we show that EPR and NMR spectroscopy of the activated ZN catalysts enables to observe paramagnetic species whose amount increases in conjunction with the catalytic activity. The joint application of 2D HYSCORE experiments and DFT calculations reveals the presence of bimetallic alkyl-Ti(III),Al complexes that are assigned to the catalytic centers of MgCl<sub>2</sub>-supported Ziegler-Natta catalysts

scholarly journals Effect of Humidity on Light-Activated NO and NO2 Gas Sensing by Hybrid Materials

Nanomaterials ◽  
2020 ◽  
Vol 10 (5) ◽  
pp. 915 ◽  
Author(s):  
Abulkosim Nasriddinov ◽  
Marina Rumyantseva ◽  
Elizaveta Konstantinova ◽  
Artem Marikutsa ◽  
Sergey Tokarev ◽  
...  
Keyword(s):  
Relative Humidity ◽  
Hybrid Materials ◽  
Active Sites ◽  
Gas Sensing ◽  
Paramagnetic Resonance ◽  
Factors Affecting ◽  
Chemisorbed Oxygen ◽  
Sensor Properties ◽  
Diffuse Reflectance Infrared ◽  
Electron Paramagnetic

Air humidity is one of the main factors affecting the characteristics of semiconductor gas sensors, especially at low measurement temperatures. In this work we analyzed the influence of relative humidity on sensor properties of the hybrid materials based on the nanocrystalline SnO2 and In2O3 and Ru (II) heterocyclic complex and verified the possibility of using such materials for NO (0.25–4.0 ppm) and NO2 (0.05–1.0 ppm) detection in high humidity conditions (relative humidity (RH) = 20%, 40%, 65%, 90%) at room temperature during periodic blue (λmax = 470 nm) illumination. To reveal the reasons for the different influence of humidity on the sensors’ sensitivity when detecting NO and NO2, electron paramagnetic resonance (EPR) spectroscopy and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) investigations were undertaken. It was established that the substitution of adsorbed oxygen by water molecules causes the decrease in sensor response to NO in humid air. The influence of humidity on the interaction of sensitive materials with NO2 is determined by the following factors: the increase in charge carrier’s concentration, the decrease in the number of active sites capable of interacting with gases, and possible substitution of chemisorbed oxygen with NO2− groups.

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