Partial Structural Collapse Research Articles

Synthesis of nanoparticles, nanorods, and mesoporous SnO2 as anode materials for lithium-ion batteries

Abstract

Spectroscopic studies of the unfolding of a multimeric protein α‐crystallin

α-Crystallin is a multimeric eye lens protein having molecular chaperone-like function which is crucial for lens transparency. The stability and unfolding-refolding properties of α-crystallin plays important roles for its function. We undertook a multi probe based fluorescence spectroscopic approach to explore the changes in the various levels of organization of this protein at different urea concentration. Steady state fluorescence studies reveal that at 0.6M urea a compact structural intermediate is formed which has a native-like secondary structure with enhanced surface exposure of hydrophobic groups. At 2.8M urea the tertiary interactions are largely collapsed with partial collapse of secondary and quaternary structure. The surface solvation probed by picosecond time resolved fluorescence of acrylodan labeled α-crystallin revealed dry native-like core of α-crystallin at 0.6M urea compared to enhanced water penetration at 2.8M urea and extensive solvation at 6M urea. Activation energy for the subunit exchange decreased by 22 kJ mol(-1) on changing urea concentration from 0 to 0.6M compared with over 75 kJ mol(-1) on changing urea concentration from 0 to 2.8M. Light scattering and analytical ultracentrifugation techniques were used to determine size and oligomerization of the unfolding intermediates. The data indicated swelling but no oligomer breakdown at 0.6M urea. At 2.8M urea the oligomeric size is considerably reduced and a monomer is produced at 6M urea. The data clearly reveals that structural breakdown of α-crystallin does not follow hierarchical sequence as tertiary structure dissolution takes place before complete oligomeric dissociation.

Study of the Relationship between Framework Cation Levels of Y Zeolites and Behavior during Calcination, Steaming, and n-Heptane Cracking Processes

The synthesis process and production of forms of the Y zeolite (i.e., NaY, NH4Y, HY, and USY) have been studied in depth, in order to investigate the thermal stability of the Y structure throughout calcination, steaming, and cracking processes. The results indicate that an increase in the cation content within the Y framework during calcination and/or steaming processes led to an increase in the catalyst stability and a reduction in the rate of any associated dehydroxylation reactions. It was also found that the presence of sodium ions hindered the extraction of Al atoms from the crystal lattice structure during the steaming treatment, which minimized partial and/or entire structural collapse at high temperatures. Finally, enhancements in the distribution of the acid sites, and an increase in the activity and selectivity of the produced USY catalysts during n-C7 cracking reactions, have also been observed.

Analytical Study of Seismic Progressive Collapse in a Steel Moment Frame Building

Progressive collapse is defined as total or remarkable partial collapse of structure following the damage occurred at a small portion of the structure. In most cases, the study is focused on progressive collapse of structures due to explosion, vehicle impact, fire and other man-made hazards; with less attention on progressive collapse mechanism of structure due to earthquake. Although the post earthquake inspections show that structural elements, mostly columns in the corner of the plan, can be severely damaged during earthquake. If neighboring columns are not properly designed to resist and redistribute the additional gravity load that is imposed by the column loss, partial collapse of the structure will occur; which would lead to progressive collapse of the structure. In this regard, progressive collapse potential of a moment resisting steel building is investigated via analytical procedure under earthquake action. In this research, a corner-column of the building was weakened intentionally to navigate the damage toward a certain part of the structure. Then, nonlinear static analysis is carried out on the three dimensional model of the building and the total behavior of the structure is studied. The results indicate that after the failure of the corner-column, the lateral resistance of the frame in which the removed (failed) column was located decreases, and the failure of the other columns occurs. Large plastic deformations and the failure of the other members could cause progressive collapse in the whole structure and the expected ductile behavior of the structure would not be observed.

Analytical Study of Seismic Progressive Collapse in a Steel Moment Frame Building

Progressive collapse is defined as total or remarkable partial collapse of structure following the damage occurred at a small portion of the structure. In most cases, the study is focused on progressive collapse of structures due to explosion, vehicle impact, fire and other man-made hazards; with less attention on progressive collapse mechanism of structure due to earthquake. Although the post earthquake inspections show that structural elements, mostly columns in the corner of the plan, can be severely damaged during earthquake. If neighboring columns are not properly designed to resist and redistribute the additional gravity load that is imposed by the column loss, partial collapse of the structure will occur; which would lead to progressive collapse of the structure. In this regard, progressive collapse potential of a moment resisting steel building is investigated via analytical procedure under earthquake action. In this research, a corner-column of the building was weakened intentionally to navigate the damage toward a certain part of the structure. Then, nonlinear static analysis is carried out on the three dimensional model of the building and the total behavior of the structure is studied. The results indicate that after the failure of the corner-column, the lateral resistance of the frame in which the removed (failed) column was located decreases, and the failure of the other columns occurs. Large plastic deformations and the failure of the other members could cause progressive collapse in the whole structure and the expected ductile behavior of the structure would not be observed.

Characteristics and Catalytic Properties of Mesocellular Foam Silica Supported Pd Nanoparticles in the Liquid-Phase Selective Hydrogenation of Phenylacetylene

An ultra-large pore mesocellular foam silica (MCF) was employed as a support for preparation of supported Pd catalysts for the liquid-phase selective hydrogenation of phenylacetylene. The catalysts were prepared by three different routes: (i) incipient wetness impregnation using Pd(II)acetate solution (Pd/MCF-imp), (ii) impregnation of colloidal Pd nanoparticles obtained by the solvent reduction method (Pd/MCF-col), and (iii) in situ synthesis of MCF in the presence of the Pd colloid (Pd/MCF-ss). The conventional impregnation method resulted in more agglomeration of Pd particles and partial collapse of MCF structure, hence the Pd/MCF-imp exhibited the lowest selectivity towards styrene at total conversion of phenylacetylene. Only the Pd/MCF-ss, in which most of the Pd nanoparticles were encapsulated by the silica matrix, was found to retain high styrene selectivity (>80%) after complete conversion of phenylacetylene. Comparing to the other highly efficient Pd catalysts reported in the literature under similar reaction conditions, it can be emphasized that coverage of Pd surface by the support produces great beneficial effect for enhancing styrene selectivity, regardless of the type of supports used (i.e., TiO2, carbon nanotubes, or mesostructured silica). The direct incorporation of palladium nanoparticles before hydrolysis of the silica precursor during the synthesis of mesocellular foam silica (Pd/MCF-ss) resulted in superior catalytic performance in the selective hydrogenation of phenylacetylene, comparing to those obtained via impregnation of Pd acetate solution (Pd/MCF-imp) and deposition of Pd colloid (Pd/MCF-col). High styrene selectivity (> 80%) was retained after complete conversion of phenylacetylene over the Pd/MCF-ss.

Reversible binding of zinc in Plasmodium falciparum Sir2: Structure and activity of the apoenzyme

Reversible zinc chelation via thiol groups of cysteines leading to modulation of activity in redox regulated proteins forms a basis for switching on–off of various biochemical processes. Silent information regulator 2 (Sir2), a NAD + dependent deacetylase, contains a non-catalytic zinc ion coordinated by thiol groups of cysteines. Using Plasmodium falciparum Sir2 (PfSir2), we have examined the effect of zinc removal on the structure and activity of this enzyme. Our studies show that the enzyme with high affinity for zinc exhibits partial collapse of structure upon removal of the metal ion. Zinc reconstitution of apo PfSir2 led to recovery of both structure and activity highlighting the reversibility of the process.

Investigation of catalytic activity of CrSBA-1 materials obtained by direct method in the dehydrogenation of propane with CO 2

A series of the Cr-containing SBA-1 ( xCrSBA1) cubic mesoporous catalysts with various Cr/Si molar ratios have been prepared by direct method using cetyltriethylammonium bromide, ammonium dichromate, tetraethyl orthosilicate and hydrochloric acid. The obtained materials have been characterized by different physicochemical techniques including ICP, XRD, UV–vis DRS, H 2-TPR and N 2-adsorption. XRD and N 2-adsorption results have revealed that xCrSBA1 materials possess well organized three-dimensional pore structure. However, incorporation of Cr into the SBA-1 framework leads to small perturbation of the structural order. ICP results have shown that the amount of Cr incorporation in SBA-1 can be controlled by adjustment of the molar ratio of (NH 4) 2Cr 2O 7 to Si(C 2H 5O) 4 in the gel. Finally, the catalytic activity of pure SBA-1 and Cr-containing SBA-1 materials were investigated in the dehydrogenation of propane with CO 2. In the case of the most active, 0.04CrSBA1 catalyst, the effect of various reaction parameters such as, reaction temperature, reaction time and feed gas composition on the conversion of propane, yield and selectivity to propene as well as on molar ratio of CO/H 2 has been evaluated. Moreover, stability of the catalyst during the dehydrogenation/regeneration conditions was studied as well. It has been found that during the fourth consecutive cycle the catalyst undergoes two types of deactivation processes – reversible and irreversible. The former is caused mainly by the coke deposition, which can easily overcome by air treatment of the catalyst at 550 °C. The latter one, insignificant, is due to partial collapse of mesoporous structure of the catalysts.

Studies on KIT-6 Supported Cobalt Catalyst for Fischer–Tropsch Synthesis

KIT-6 molecular sieve was used as a support to prepare cobalt catalyst for Fischer–Tropsch synthesis (FTS) using an incipient wetness impregnation method to produce cobalt loadings of 15 and 25 wt%. The catalysts were characterized by BET surface area, X-ray diffraction, scanning transmission election microscopy (STEM), extended X-ray absorption fine spectroscopy and X-ray absorption near edge spectroscopy. The catalytic properties for FTS were evaluated using a 1L CSTR reactor. XRD, pore size distribution, and STEM analysis indicate that the KIT-6 mesostructure remains stable during and after cobalt impregnation and tends to form smaller cobalt particles, probably located inside the mesopores. The mesoporous KIT-6 exhibited a slightly higher cobalt dispersion compared to amorphous SiO2 supported catalyst. With the higher Co loading (25 wt%) on KIT-6, partial structural collapse was observed after the FTS reaction. Compared to an amorphous SiO2 supported cobalt catalyst, KIT-6 supported cobalt catalyst displayed higher methane selectivity at a similar Co loading, likely due to diffusion effects. KIT-6 molecular sieve was used as a support to prepare cobalt catalyst for Fischer–Tropsch synthesis (FTS) using an incipient wetness impregnation method to produce cobalt loadings of 15 and 25 wt%. The catalysts were characterized by BET surface area, X-ray diffraction (XRD), scanning transmission election microscopy (STEM), extended X-ray absorption fine spectroscopy (EXAFS) and X-ray absorption near edge spectroscopy (XANES). The catalytic properties for FTS were evaluated using a 1L CSTR reactor. The mesoporous KIT-6 exhibited a slightly higher cobalt dispersion compared to amorphous SiO2 supported catalyst. With the higher Co loading (25 wt%) on KIT-6, partial structural collapse was observed after the FTS reaction. XRD, pore size distribution, and STEM analysis indicate that the KIT-6 mesostructure remains stable during and after cobalt impregnation and tends to form smaller cobalt particles, probably located inside the mesopores. Compared to an amorphous SiO2 supported cobalt catalyst, KIT-6 supported cobalt catalyst displayed higher methane selectivity at a similar Co loading, likely due to diffusion effects.

Improvement of Mesopore Structure of Resorcinol and Formaldehyde Carbon Cryogels by Acid Solution

Resorcinol and formaldehyde (RF) carbon cryogels are prepared by sol-gel polycondensation by using sodium carbonate (C) as a catalyst with water (W) as solvent, immersed in acid solution, hydrochloric acid (HCl), dried by freeze-drying technique and then carbonized under inert atmosphere, respectively. Compared with their carbon precursors, both Vmes and mesopore size distributions of all carbon cryogels can be developed since the pore shrinkage is the crucial role in the change of pore structure of carbon gels. HCl may promote the strength of small pore structure and increase the pore shrinkage of large pore structure. Consequently, the treatment of HCl does not only enhance the partial collapse of large pore structure, the treatment also increases the strength of small pore structure to inhibit the shrinkage of this structure during carbonization as well.

Attempt to examine the origin of magnetism in water-immersed [formula omitted

Magnetization measurements and focused ion beam-scanning ion microscopy (FIB-SIM) observation have been performed in order to examine the origin of magnetism in water-immersed Rb 2 Ni 3 S 4 , where the intrinsic substance is non-magnetic because of the low spin state of Ni 2 + in a kagomé lattice. Cracks were observed on the surface of water-immersed specimen. A possible ferromagnetism induced by the partial collapse of crystal structure was obtained.

Avalanches at the core‐mantle boundary

The partial collapse of topographic structure at the core‐mantle boundary (CMB) in avalanches, slumps or turbidity flows, would cause sudden temperature changes in both the upper core and the lower mantle. Although such collapses are hypothetical, it is interesting to investigate the potential consequences. Downwelling from such events could disrupt core convection cells and trigger geomagnetic excursions and reversals. Buoyant sediment from the freezing of the inner core is hypothesized to rebuild the avalanched structures. Large avalanches could trigger mantle plumes. Oblique extraterrestrial impacts impart high shear to the CMB, and can trigger one or more simultaneous avalanches, yielding observed coincidences between craters, tektite fields and reversals. A triggered avalanche can explain the coincidence between the formation of the largest known volcanic province (the Ontong‐Java Plateau), the start of the 35 Myr Cretaceous geomagnetic quiet period, and reported coincidences between large flood basalts and extinctions.

Complexity of Intercalation of Hydrazine into Kaolinite—A Controlled Rate Thermal Analysis and DRIFT Spectroscopic Study

Controlled rate thermal analysis (CRTA) allows the separation of adsorbed and intercalated hydrazine. CRTA displays the presence of three different types of hydrogen-bonded hydrazine in the intercalation complex: (a) The first is adsorbed loosely bonded on the kaolinite structure fully expanded by hydrazine–hydrate and liberated between approx 50 and 70°C (b) The second intercalated hydrazine is lost between approx 70 and 85°C. (c) The third type of intercalated-hydrazine molecule is lost in the 85–130°C range. CRTA at 70°C enables the removal of hydrazine–water and results in the partial collapse of the hydrazine-intercalated kaolinite structure to form a hydrazine-intercalated kaolinite. Removal of the adsorbed hydrazine enables the DRIFT spectra of the hydrazine-intercalated complex without any adsorbed hydrazine to be obtained. A band at 3626 cm−1 attributed to the inner surface hydroxyls of kaolinite hydrogen bonded to hydrazine is observed. The intercalation of hydrazine–hydrate into kaolinite is complex and results from the different types of surface interactions of the hydrazine with the kaolinite surfaces.

Adsorption mechanism of cationic surfactants onto acid- and heat-activated sepiolites

Systematic adsorption tests were carried out to determine the uptake of typical quaternary amines, dodecyltrimethylammonium bromide and hexadecyltrimethylammonium bromide and a primary amine, dodecylamine hydrochloride by sepiolite. Bottle adsorption tests conducted with untreated, acid- and heat-activated sepiolites exhibit two distinct regions. The first stage is characterized by low rate and governed through an ion exchange process between ammonium ions and magnesium ions in the octahedral sheet. The second stage is ascribed to a combination of chain–chain interactions through Van der Waals forces and ion exchange process. Despite several-fold increases in surface areas upon activation, surprisingly no improvement in adsorption is observed. The observed differences are explained on the basis of partial collapse of the sepiolite crystal structure, the removal of zeolitic and bound waters and modification of the pore size distribution of sepiolite upon treatments.

Thermal shrinkage of various cation forms of zeolite A

The thermal shrinkage of Li, Na, K, Cs, ammonium, H, and Ca forms of zeolite A has been investigated by dilatometry up to 650°C. The shrinkages of Li, Na, K, Cs and Ca forms are attributed to the dehydration and partial structural collapse which predominates over the normal thermal expansion and cation migration from one site to another in the zeolitic structure. The ammonium form shows a noticeable shrinkage and a possible catalytic action of the acid sites produced in the zeolite A in the combustion of ammonia evolved upon heating. The H form undergoes collapse at temperatures higher than 350–400°C depending on the heating rate.

Characterization of supercritically dried porous silicon

Porous silicon (PS) has been formed by electrochemical etching of p-type silicon. During drying in air the sponge-like structure of the porous layers is exposed to capillary forces which will partially destroy the microstructure of highly PS. One possibility for avoiding the partial structural collapse is by supercritically drying the PS. This technique is already known from the formation of highly porous aerogels and has now been applied to PS. Porosities of 90% can be achieved. These highly porous layers were investigated using photoluminescence, Raman, reflectance and X-ray photoemission spectroscopy. The porosity was determined by gravimetric measurements. The effect of the drying process on the properties of PS was also studied.

Mechanism of Thermal Decomposition of Potassium/Ammonium Salts of the 12-Molybdophosphoric Acid and Effect on the Catalytic Performance in the Isobutyric Acid Oxidehydrogenation

Heteropolycompounds of the composition Kx(NH4)3−xPMo12O40 were prepared by precipitation, through addition of HNO3 to an aqueous solution of the salts. The precipitated compounds were calcined at increasing temperatures to evaluate the thermal behavior, and were characterized by means of X-ray diffraction, FTIR spectroscopy, surface area measurements, ionic chromatography, EPR spectroscopy, and reactivity in the oxidative dehydrogenation of isobutyric acid to methacrylic acid. A monophasic system was obtained by calcination at 640 K, with patterns characteristic of the Keggin-type cubic secondary structure. The cationic composition was found to be very close to that expected for the complete salification of the Keggin anion. The structural decomposition began at temperatures close to 693 K for the ammonium and ammonium/potassium compounds, with formation of an intermediate heteropolycompound characterized by crystallographic parameters and cationic composition different from the original one and more stable than the latter. The potassium salt remained instead structurally intact up to 753 K. The data were interpreted with the assumption that the decomposition of the heteropolycompound might occur in a stepwise way, with an initial structural collapse of a part of the compound and displacement of some molybdenum ions (originally located in peripheral position in the Keggin anion) in the cationic position of the not yet decomposed compound. The highest amount of this intermediate molybdenum-salified heteropolycompound apparently formed during decomposition of the (NH4)3PMo12O40 compound. The calcination temperature remarkably affected the catalytic behavior in the oxidative dehydrogenation of isobutyric acid to methacrylic acid. The partial structural collapse occurring by calcination at 693 K led to a decrease in the activity for the potassium/ammonium mixed salts. On the contrary, the ammonium salt increased its activity. It was assumed that this phenomenon could be due to the formation of the intermediate molybdenum-salified heteropolycompound.

Pore development during carbonization of coals

Changes in pore properties during carbonization at a constant heating rate and no external pressure were followed for bituminous and subbituminous coals by porosimetry, sorption and density measurements. Observations were supplemented by scanning electron microscopy and rate of volatilization measurements. All coals exhibited similar devolatilization behaviour and pore structure development, showing maximum micro and macropore volumes around 600 °C, and a partial collapse of pore structure after 800 °C. The micropore structure did not collepse in the case of non-caking coal. Pore volume maxima occur at least 100 °C above the temperature of the devolatilization rate maxima. Some interpretation is provided.