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The Chemistry of Silica

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... Materials based on sol-gel processes using silicates are widely used as matrixes for the incorporation of functional molecules of various natures into them (fluorophores, photochromes, proteins, etc.). A large number of works have been devoted to the study of sol-gel processes based on TEOS (Si(OC 2 H 5 ) 4 and TMOS (Si(OCH 3 ) 4 silicates using magnetic resonance and optical spectroscopy methods [1][2][3][4][5][6][7][8][9][10][11][12][13]. TEOS and TMOS molecules are initial (or intermediate) compounds that react with the formation of Si-O-Si bonds. ...
... The total reactions involving TEOS and TMOS, leading to the formation of gels, can be described by Eqs. (1) and (2): ...
... probes during the sol-gel process A significant number of works have been devoted to the study of the effect of pH on the chemical stages of sol-gel processes-the reactions of hydrolysis and polymerization (see reviews in [1,2]). Iler [1] divides the polymerization process into approximately three pH ranges: <2; 2-7; >7. ...
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The molecular dynamics and partition of nitroxide spin probes in the tetrakis(2-hydroxyethyl) orthosilicate (THEOS)/ethylene glycol/water system during its transformation from a liquid solution into a sol and gel structures were studied depending on the processing time and the pH of the medium. In acidic (pH 3.5) and neutral (pH 6.8) media, an increase in the effective rotation correlation time (τeff) of positively charged probes (Cat 7 and Cat 14) in the liquid phase of the sol–gel system and a subsequent decrease in τeff was found, with the growth and a decay times of τeff decreasing with an increase in pH. The values of τeff are due to the “dynamic exchange” of probes between the solution and the surface of colloidal particles formed in the sol–gel process. The decrease in τeff is apparently due to a slowdown in the exchange of probes between the solution and the surface of the particles due to a decrease in the surface during the enlargement of particles, as well as to the formation of a gel. These changes are accompanied by a decrease in the concentration of probes in the solution and the appearance of strongly immobilized EPR signals (SIS), apparently from probes that are bound in the bulk of sol and gel particles and do not exchange with the solution. The sizes of sol particles, determined from the parameters of the SIS shape, increase with the duration of incubation in the range of several nm. Spin probe EPR spectra in tetrakis(2-hydroxyethyl) orthosilicate/ethylene glycol/water system at different processing times.
... Nanooxides such as fumed silica (nanosilica) are important industrial materials used in both unmodified [1][2][3][4][5] and modified functionalized [6][7][8][9][10][11][12][13] states. Various silanes and siloxanes are widely used to modify silica particles [14][15][16][17][18][19][20][21][22]. ...
... Hybrid organic(organometallic)silica materials are an important class of composites of high interest ranging from fundamental developments to advanced applications. In composites, organic (or organometallic) fragments (functional groups) are covalently bound to a matrix [5][6][7][8][33][34][35][36][37][38][39][40][41]. Organophilization of a silica surface can be performed using different kinds of modifying agents, including organosiloxanes as the most attractive and environmentally friendly silylating reagents [5][6][7][8][9][10][11][12]. ...
... In composites, organic (or organometallic) fragments (functional groups) are covalently bound to a matrix [5][6][7][8][33][34][35][36][37][38][39][40][41]. Organophilization of a silica surface can be performed using different kinds of modifying agents, including organosiloxanes as the most attractive and environmentally friendly silylating reagents [5][6][7][8][9][10][11][12]. Linear organosiloxanes are generally not considered to be reactive with inorganic oxide surfaces, and enormous efforts have been made over the last 50 years to develop silicon-containing reagents with reactive functional groups [42]. ...
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The investigation of molecular interactions between a silica surface and organic/inorganic polymers is crucial for deeper understanding of the dominant mechanisms of surface functionalization. In this work, attachment of various depolymerized polydimethylsiloxanes (PDMS) of different chain lengths, affected by dimethyl carbonate (DMC), to silica nanoparticles pretreated at different temperatures has been studied using 29Si, 1H, and 13C solid-state NMR spectroscopy. The results show that grafting of different modifier blends onto a preheated silica surface depends strongly on the specific surface area (SSA) linked to the silica nanoparticle size distributions affecting all textural characteristics. The pretreatment at 400 °C results in a greater degree of the modification of (i) A-150 (SSA = 150 m2/g) by PDMS-10/DMC and PDMS-1000/DMC blends; (ii) A-200 by PDMS-10/DMC and PDMS-100/DMC blends; and (iii) A-300 by PDMS-100/DMC and PDMS-1000/DMC blends. The spectral features observed using solid-state NMR spectroscopy suggest that the main surface products of the reactions of various depolymerized PDMS with pretreated nanosilica particles are the (CH3)3SiO-[(CH3)2SiO-]x fragments. The reactions occur with the siloxane bond breakage by DMC and replacing surface hydroxyls. Changes in the chemical shifts and line widths, as shown by solid-state NMR, provide novel information on the whole structure of functionalized nanosilica particles. This study highlights the major role of solid-state NMR spectroscopy for comprehensive characterization of functionalized solid surfaces.
... This was expected, since the applied thermal range is inferior than the temperatures required for silica phase transitions and also because there are no organic groups to degrade. 47,48 On the other hand, TGA assessed the significant organic content of the silica after the amino functionalization (a-SiO 2 ) and after the coupling reaction with the carbon nanodots (silica−Cdots). The TGA profile of silica−Cdots shows an event between ∼140 and 350°C, which is due to the thermal degradation of amorphous α-CDs. ...
... There are lone pairs from the amide group (the bond between SiO 2 and α-CD), the Si− O− bonds between silica and α-CD, and other −Si−OH and −Si−O−O−Si− groups that may exist, since these defects are commonly observed on SiO 2 surfaces. 47,48 Therefore, the surface groups of the silica−Cdots hybrids selectively detect Na + or Cl − ions present in the controlled pH solutions. The main chemical groups of the hybrids, identified by XPS, are the COOH of the carbon nanodots (α-CDs), the NH− (CO) from the amide group (the bond between SiO 2 and α- At this moment, considering that the pH of the initial aqueous solution is clearly acidic (4.30) and that there are still several groups capable of hydrogen bonding (stabilizing the excited states), we can consider that the hybrids behave as the other acidic carbon nanodots cited. ...
... Since this effect causes the stabilization of the fluorophores, the red-shift is observed. 35,52 The possibly lower number of −COOH groups is not necessarily a problem here: it is known that basic pHs (higher than 10) usually deprotonate colloidal and nanostructured silica's silanol groups, 47,57,58 increasing the hybrids' charges. ...
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ACS Appl. Nano Mater. 2021, 4, 9, 9738–9751. The fabrication of a biodegradable and fluorescent cylindrical waveguide with doped hybrid nanoparticles (silica–carbon nanodots) is reported. The fluorescent hybrids were obtained by coupling amino-functionalized fumed silica nanoparticles with the carboxylic acid surface groups of amorphous carbon nanodots obtained from the thermolysis of citric acid. The hybrid nanoparticles present diameters lower than 10 nm, maximum fluorescence at 465 nm, and excitation-wavelength-dependent behavior. They were occluded into an agarose matrix, providing a low-cost and easily scalable sensor capable of detecting pH variations with maximum sensitivity of 5.61 nm/(pH unit) when excited by a 403 nm UV light-emitting diode (LED).
... Sumber silika yang ada di Indonesia cukup melimpah, baik dalam bentuk mineral pasir kwarsa (quartz), maupun dalam bentuk amorf (amorphous silica). Meskipun pasir kwarsa memiliki kadar silika yang tinggi, yakni lebih dari 98% (Prayogo and Budiman, 2012), akan tetapi produksi silika dari pasir kwarsa tidak cukup ekonomis karena memerlukan proses pada suhu tinggi (Iler, 1979;Kirk-Othmer, 1998). Sedangkan produksi silika yang cukup bernilai ekonomi adalah silika yang bersumber dari limbah biomassa seperti abu sekam padi (rice husk) (Okutani, 2009;Sun and Gong, 2001), abu bagasse, atau yang bersumber dari limbah pertambangan seperti abu batubara dan geothermal sludge karena silika yang terkandung dalam biomassa (tumbuhan), abu batubara dan geothermal sludge umumnya bersifat amorf (amorphous silica). ...
... Penggunaan silika dalam dunia industri dapat dimanfaatkan untuk berbagai keperluan, diantaranya untuk industri pasta gigi, karet, dan industri roti (sebagai bahan anti-cake agent, adsorbent, dan catalyst suppor ) (Iler, 1979;Kirk-Othmer, 1998). Silika juga digunakan sebagai bahan penjerap air karena memiliki sifat higroskopis. ...
... However, pure iron devices are susceptible to clogging [11][12][13][14]. The work of Btatkeu et al., and other authors [15][16][17][18][19][20] have shown the need to unclog the reactive surface, notably by the Fe°/S (Iron/sand) involvement, thanks to the responsiveness of the Si-OH groups present in the silica (SiO 2 ). This mixed efficiency has led to the combination of a porous absorbent/adsorbent and non-expansive material, through a Fe°/S/Pz filter (Iron/Sand/Pozzolan) capable of collecting these CPs [21]. ...
... These results are consistent with the disposal process of Fe°-based filters. Pure, they are prone to rapid clogging [55][56][57]; associated with S [20], Pz [16,21,23,[44][45][51][52], or CN [22,[28][29][53][54], they are improved [11][12][13][14][21][22][23]. The reactivity of the Fe°, and largely that of Fe°-based filters, involves electrochemical reactions of the wet corrosion of iron, and generates adsorbents that collect contaminants responsible for the discoloration. ...
... In materials science, silanols play important roles as intermediates in the sol-gel process to produce organosilicon materials (e.g., silicone oils, rubbers, and resins), inorganic materials (e.g., silicas and zeolites), and organic-inorganic hybrid materials (e.g., silane coupling agents and silsesquioxane derivatives), because the SiOH groups can potentially be converted into siloxane bonds (Si-O-Si) using, e.g., heating, dehydration reactions, or catalytic reactions. Among the silanol species, orthosilicic acid (Si(OH) 4 ) 19,20 , which consists of four hydroxy groups on a silicon atom, is the smallest inorganic silanol and the smallest building block for silicas and silicates, which are the most abundant natural substances in the earth's crust. ...
... Preparation of 2. 2 was prepared according to a literature procedure by the reaction of silica gel and tetramethylammonium hydroxide in water 49 20.0% yield), were also obtained from the further recrystallization. ...
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By precisely constructing molecules and assembling these into well-defined supramolecular structures, novel physical properties and functionalities can be realized, and new areas of the chemical space can be accessed. In both materials science and biology, a deeper understanding of the properties and exploitation of the reversible character of weak bonds and interactions, such as hydrogen bonds and π–π interactions, is anticipated to lead to the development of materials with novel properties and functionalities. We apply the hydrogen-bonded organic frameworks (HOFs) strategy to inorganic materials science using the cubic octamer of orthosilicic acid, [Si8O12][OH]8, as a building block, and find that various types of hydrogen-bonded inorganic frameworks (HIFs). We succeed in parallel π-stacking pure benzene, thiophene, selenophene, p-benzoquinone, thiophene·p-benzoquinone, and benzene·p-benzoquinone polymers infinitely. These polymers interact via their π-systems by taking advantage of the flexible pores of the three-dimensional nano-honeycomb HIFs, which consist of periodic wide and narrow segments. Hydrogen-bonded inorganic frameworks are porous structures that may lead to novel materials with unprecedented properties and functionalities. Here the authors report the solid-state structures of orthosilicic acid-based hydrogen-bonded inorganic frameworks that can encapsulate small unsaturated cyclic molecules such as benzene, which are found stacked in parallel.
... The removal of Fe 2þ ðaqÞ from solution could occur either by precipitation of Fe(II)-secondary minerals, or by oxidation (Fe 2þ ! Fe 3þ þ e À ); in the latter case, we can assume the precipitation kinetics of Fe(III)-secondary minerals are fast compared with their oxidation rate, and are therefore not rate-limiting (Raiswell et al., 2011;Jiang and Tosca, 2019 Amorphous Fe(II)-silicate precipitation: The precipitation of amorphous silica can occur at low temperatures, below its saturation point, in the presence of any surface that contains exposed OHgroups (Iler, 1979). As the dissolution of fayalitic olivine involves protonation of the mineral surface, metal cations released into solution are initially complexed with OHanions. ...
... These metal-hydroxyl complexes can grant their OHgroups to initiate coprecipitation with silica to form an Fe-Mg-rich amorphous silica phase. This process is strongly pH dependent, with precipitation being most favored at circumneutral pH (Iler, 1979). ...
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While indigenous organic matter has been previously reported in the Mars meteorite Nakhla, little is known as to either its form or distribution. A notable feature of Nakhla is the prevalence of secondary phases associated with aqueous alteration. By analogy with the terrestrial environment, our objective was to determine whether Martian secondary minerals could also act to accumulate and preserve such organic matter. Through a multidisciplinary approach, we have characterized the nature of carbonaceous matter and spatially associated phases within the Martian meteorite Nakhla using a wide-ranging suite of analytical instrumentation including optical microscopy, laser Raman spectroscopy, focused ion beam microscopy, secondary ion mass spectrometry, and scanning and transmission electron microscopy. In freshly fractured chips of Nakhla, we found carbonaceous phases intimately associated with secondary aqueous alteration phases, both mineral and amorphous, interpreted to have formed through the low-temperature aqueous dissolution of the host basalt while on Mars. The carbonaceous matter is present both in condensed phases and in a dispersed state spatially associated with secondary alteration phases. In the former, we identified discrete refractory micron to submicron assemblages that appear macromolecular in nature and, in several cases, associated with fluorine and, in one case, significant nitrogen. Textural, chemical, mineralogical and isotopic considerations argue for a non-terrestrial origin of this carbonaceous matter. Additionally, we report the presence of the ferrous hydroxycarbonate mineral chukanovite (Fe2OH2CO3) within some of the secondary mineral aggregates studied. Neither the intimate association of carbonaceous matter with secondary phases nor the identification of chukanovite have been previously reported in any of the Martian meteorites. In this regard, we note such microscale features within alteration phases would most likely be lost in the preparation of conventional polished thin sections and thus explain why they have not been previously reported. In lieu of sample return, the sui generis nature provided by Mars meteorites provide insight to alteration processes on Mars currently denied to robotic exploration and remote sensing. Our results show a variety of habitability-related sample attributes, formed hundreds of millions of years ago near Mars’ surface, have persisted there until very recently and may be more widespread in the surface regolith than previously thought. This may have implications in sample selection criteria for Mars sample return.
... This assumption is experimentally supported by mass spectrometrical analysis ( Figure S4) and ultracentrifugation results ( Figure S5) showing both a trend towards smaller species with increasing pH which is moreover in good agreement with literature. (25)(26)(27) Further on-line mass spectrometrical analysis was performed to shed light on the processes in a sodium silicate solution at pH 13 during titration of calcium ( Figures S6 and S7). Here, it can be qualitatively observed that bigger species are developing with the ongoing addition of calcium until they vanish again towards the nucleation point, which can be attributed to an insufficient ionization so that the oligomers cannot be detected anymore by mass spectrometry. ...
... From the pH variation experiments in combination with analytical ultracentrifugation and mass spectrometry it could be concluded that the pH has a high impact on the species distribution of the starting silicate solution, which is further supported by literature. (25)(26)(27) Oligomerization leading to bigger silicate species occurs for pH values of 11 and 12 whereas it is prevented or at least slowed down for pH 13. From titration experiments at different pH values, different degrees of calcium binding on silicate were observed, leading to the assumption that silicate monomers and smaller aggregates are not able to significantly bind calcium at low concentrations. ...
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Calcium silicate hydrates (C-S-H), the main components of hydrated cement, are known for being responsible of its cohesion. In this respect, they act as "glue" for the other solid components of mortar or concrete and thus strongly influence the mechanical properties of the outcoming material. Given the scarce knowledge about the influence of polymers on the growth and nucleation of C-S-H, this work focuses on the investigation of ongoing processes in the pre- and postnucleation stage of C-S-H precipitation. With the help of titration in combination with ion selective electrodes, effects of additives on the formation of C-S-H can be monitored and quantified resulting in new insights into the C-S-H formation in the presence of additives. Thus, this work can be regarded as a step towards a facilitated design of tailor-made C-S-H, which might result in superior cementitious materials on the long term.
... Composition and phase or dopant distributions in particles of complex nanomaterials may strongly affect the properties and characteristics of whole systems [1][2][3][4][5][6][7][8][9][10][11][12]. First, new active surface sites (e.g., bridging M1OM2, M1O(H)M2 at M1 = Si and M2 = Al, Ti, etc.), absent in individual components, appear in the complex systems. ...
... Third, the mechanical and thermal properties of the materials depend on composition and phase distributions in composites [15][16][17]. Practically all the characteristics and properties of complex nanomaterials could be varied due to changes in their structure, composition, and phase distributions at a nano-scale level [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17]. Therefore, accurate modeling of the nanostructures, appropriate description and evaluation of the interphase interactions in complex nanomaterials are of importance for correct analyses of their practically important characteristics and properties. ...
Article
Development of theoretical tools to analyze electronic structure of complex nanomaterials depending on features of spatial and chemical organizations of different phases is of interest from both practical and theoretical points of view. Therefore, in this work, an approach based on computations of the atomic charge distribution functions (CDF) in parallel to calculations of the distribution functions of the chemical shifts (SDF) of protons is developed to be applied to a set of complex oxide and carbon nanomaterials. Binary nanooxides (alumina/silica, titania/silica), 3d-metal-doped anatase, activated carbon, carbon nanotube, fullerene C60, graphene oxide, and N-doped Kagome graphene are considered here as representatives of different classes of nanomaterials. The analyses of the CDF and SDF as nonlocal characteristics of certain kinds of atoms in complex systems provide a deeper insight into electronic structure features depending on composition of the materials, guest phase-doped host phase at various amounts of dopants, structure of O- and OH-containing surface sites, amounts and organization of adsorbed water, formation of neutral and charged surface functionalities, bonding of solvated ions, etc. The CDF of metal and hydrogen atoms (electron-donors) are more sensitive to the mentioned factors than the CDF of O, N, and C atoms (electron acceptors) in various systems. As a whole, the use of the CDF and SDF in parallel expands the tool possibility in detailed analysis of the structural and interfacial effects in dried and wetted complex nanomaterials.
... Several forms of Si are commonly presented in natural water: monosilicic acid, polysilicic acid (oligomers and polymers with large number of Si atoms), and organo-silicon compounds (Iler 1979;Dietzel 2002;Bocharnikova and Matichenkov 2012). However, plants uptake Si only in the form of monosilicic acid (Ma et al. 2001). ...
... With decreasing monosilicic acid, equilibrium between soluble forms of Si shifts, resulting in acceleration of depolymerization, which is typical for the systems with low concentrations of monosilicic acid, in turn leading to decreasing polysilicic acid (Iler 1979). ...
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In order to increase shrimp production and minimize detrimental environmental impacts of aquaculture, the maintenance and regulation of the growth and composition of phytoplankton communities and nutritional balance are critical. Silicon (Si) is an essential nutrient for diatoms and other types of microorganisms, but the information about the Si impact on their growth is extremely scarce. Monosilicic and polysilicic acids were tested in several shrimp cultivation systems in Jiangsu Province, China. In pond waters, the concentrations of monosilicic and polysilicic acids sharply reduced by 36–95% and 35–75%, accordingly, as compared with those in supply water sources. The microbial cell abundance was strongly dependent on monosilicic acid, while the correlation with polysilicic acid was absent. In laboratory experiments, monosilicic acid added to pond water or probiotic solution at 1 and 2 mM Si had a significant positive effect on cell abundance. Over three days, the concentrations of monosilicic acid decreased by 81 to 91% in pond water and by 11 to 24% in probiotic solution. In probiotic solutions, the degree of polymerization of silicic acid was more intensive than that in shrimp pond waters. The data obtained demonstrates the importance of systematic studies related to the functions of Si in shrimp aquaculture.
... While the dissociation of H 2 O into two surface -OH groups is energetically more favorable at α-Fe 2 O 3 surface as compared to molecular water adsorption [34,35]. The Al 2 O 3 present in red mud is liable to form neutral oxygen vacancies because of presence of low defect formation energy [36] however it also supports water molecule dissociation.The low percentage of SiO 2 in red mud has been reported to exhibit oxygen vacancy associated with emission peaks [37] and SiO 2 reacts with water molecules to form (Si− OH) group [38]. Red mud having composition of multiple metal oxides mixture shows the characteristics of individual metal oxides. ...
Article
Globally a prominent hazardous industrial waste red mud (RM) residue is released in million tons everyday from alumina refinery. One of the best options to utilize red mud is the fabrication of Hydroelectric Cell (HEC) to produce green electricity, has been reported. Hydroelectric Cell is a 21st century phenomenal revolutionary invention to produce green electricity by water splitting at room temperature by oxygen-defects and nanopores deliberately created in metal oxides. HECs have been fabricated to produce green electricity by using mixture of red mud and iron oxide (RMFe). Splitting of water molecule heterolytically takes place on the cation-oxygen vacancy pair (Mδ+-Voδ−) present on the surface of RM and RMFe pellets. It has been observed from the Williamson-Hall, plots and Photoluminescence analysis that RMFe particles exhibit large strain and defects due to inter-ionic diffusivity of different metal cations. More hetero-ionic pairs of Fe³⁺-Voδ-, Ca²⁺-Voδ-and Al³⁺-Voδ- present on the RMFe surface increase the adsorption and chemidissociation of water. The RM and RMFe based HECs have delivered 7 mA and 17 mA peak current and voltage 0.8 V and 1.02 V. Red mud utilization in the fabrication of Hydroelectric Cell is a significant step towards waste management and wealth creation.
... Surface chemistry of amorphous silica is mainly based on the concentration and activity of superficial silanol groups (-SiOH) [8,16,44,45]. These functionalities may exist in a variety of conditions, and they may be either isolated or interacting with each other through hydrogen bonding as a function of thermal treatment. ...
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This work reports for the first time a quantum mechanical study of the interactions of a model benzodiazepine drug, i.e., nitrazepam, with various models of amorphous silica surfaces, differing in structural and interface properties. The interest in these systems is related to the use of mesoporous silica as carrier in drug delivery. The adopted computational procedure has been chosen to investigate whether silica–drug interactions favor the drug degradation mechanism or not, hindering the beneficial pharmaceutical effect. Computed structural, energetics, and vibrational properties represent a relevant comparison for future experiments. Our simulations demonstrate that adsorption of nitrazepam on amorphous silica is a strongly exothermic process in which a partial proton transfer from the surface to the drug is observed, highlighting a possible catalytic role of silica in the degradation reaction of benzodiazepines.
... This type of chemiadsorbate is thus a pro-drug form, from which the active substance is rapidly released after contact with an aqueous dissolution medium such as intestinal fluids [32][33][34]. ...
Thesis
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Drug excepient interaction , molocular level , using sofosticated tecniques DSC, FTIR, X-ray diffraction
... The amount of SiO 2 had a significant effect on the functional composition of EPT communities together with the temperature, amount of CO 2, and spring size. The majority of dissolved SiO 2 is released from geological bedrock and its presence in surface waters is often associated with the occurrence of diatoms (Bacillariophyceae), which assimilate SiO 2 to form shells from this compound (Iler, 1979). Diatoms, as a part of periphytons, represent an important source of food for scrapers; consequently, we can assume that the influence of SiO 2 may be hidden behind this relationship. ...
Article
Karst springs represent valuable and often the most threatened habitats in the riverine landscape. Unlike other stream habitats, they have several specifics that determine their insularity in the river continuum, e.g., high seasonal thermal and chemical stability. The presented study aimed to find out the taxonomical and functional richness of three groups of aquatic insects (Ephemeroptera, Plecoptera and Trichoptera) in the Western Carpathians karst springs, as well as uncover the mechanism of the EPT community assembly. Low within-site species richness was generally found, however, there was high between-site diversity and thus high total diversity of the studied groups of benthic invertebrates as well. Species richness of the EPT community was higher in larger and colder springs: those with lower concentrations of CO2 and Fe, as well as higher concentrations of SO4²⁻. Analysis of functional richness, as well as functional dispersion, did not reveal any clear assembly mechanism in the spring EPT community; however, both analyses indicated a higher proportion of environmental filtering there. Unlike the taxonomic richness, the functional richness of the EPT community was significantly higher in small and medium springs with higher water temperatures, as well as in springs with the presence of deadwood. Between-site dissimilarities in the functional composition of EPT were significantly correlated with environmental differences of springs, which determined variables such as spring size and temperature, as well as the concentration of CO2 and SiO2.
... The most abundant cations in natural water are Na + , K + , Ca 2+ , Mg 2+ ; the ones present in polluting emissions Cs + , Rb 2+ , Sr 2+ , Ba 2+ have been shown to have an enormous impact on the silica-water interface properties. For instance, each of these cations have been shown to promote the accumulation of surface negative charges on the silica surface by cation-anion specific electrostatic interactions [196,197]. The promotion of negative charges at the silica surface induced by ions is of particular interest for our work since it can modulate the water organization at the interface. ...
Thesis
The microscopic comprehension of chemical reactions that occur at the boundary between water and other media represents an essential step in chemical science for the development of high yield chemical reactions. However the experimental difficulty in discerning the specific catalytic effect originating from the specific interfacial water environment makes the role of the interface along the reaction pathways still far to be understood.The main objective of this PhD thesis has been to provide a molecular description of chemical reactions at aqueous interfaces by Density Functional Theory-based Molecular Dynamics simulation techniques (DFT-MD/AIMD) in order to rationalize the catalytic roles of interfaces, especially from the structural point of view.The first part of the manuscript is dedicated to the study of chemical reactions of relevance in prebiotic chemistry, where many routes at aqueous interfaces have been envisaged in the literature in order to rationalize the origin of the first biopolymers on the primordial Earth. In particular the first peptide bond condensation reaction is a highly debated topic. The condensation of amino acids into oligopeptides in absence of enzymes is known to be hindered by both thermodynamic and kinetic reasons in bulk water at ambient conditions. By contrast, Prof. Vaida group has experimentally observed the formation of polypeptides at room temperature in dilute conditions from amino acid esters and CuCl2 salt at the air-water interface, suggesting the surface of oceans as a suitable environment for the birth of life on the prebiotic Earth. However the specific role of the air-water interface during the peptide bond formation and the reasons for which this reaction occurs at the interface and not in bulk water are still unclear.We provide a microscopical insight into the peptide bond formation reaction at the air-water interface by DFT-MD simulations. The characterization of the interfacial water network, coupled with the comparison between energetics and reaction mechanisms observed at the air-water interface versus bulk water allows us to reveal the key factors that promote the polypeptides formation in such heterogeneous conditions. Our data point to novel catalytic roles of the air-water interface which are essential in making the reaction occur. We especially identify why the solvation properties of the reactive species and the presence of Cl- anions at the interface are of utmost importance in catalyzing the peptide bond condensation reaction.In the second part of this PhD, we have focused on the characterization of the structure and reactivity of aqueous amorphous silica interfaces by coupling DFT-MD and SFG (Sum Frequency Generation) spectroscopy. This is especially relevant for the development of new technologies in the field of materials design and heterogeneous catalysis. The main targets of our investigation is the comprehension of the silica surface reactivity in contact with liquid water as a function of pH conditions. We have followed the evolution of the silica surface structure and chemistry in response to the variation in the water pH conditions by coupling experimental SFG spectroscopy (in collaboration with Prof. Wei-Tao Liu, China) with DFT-MD simulations. Our work provides a deep insight into the controversial acid-base behaviour of the silica surface, showing that a molecular picture based only on the balance between silanol SiOH and silanolate SiO- species at the silica surface is not enough to rationalize the trends in the SFG bands as a function of pH. The emergence of a third molecular species, denoted ”Si5”, reveals a more complex acid-base surface chemistry, and strongly modulates the silica surface acidity. Our data provide a new microscopical rationalization of the acid-base bimodal behaviour of the silica surface groups observed experimentally and reveal the Si5 species as an essential key to understand the chemistry at aqueous silica surfaces.
... Некоторыми авторами также упоминалось, что концентрация гидроксила на поверхности выращенного путем окисления моносилана кислородом ТПДК снижается с ростом температуры нагрева подложки [7]. При этом отмечалось, что экспериментально обнаруженное поведение гидроксила на поверхности выращенной ТПДК количественно идентично данным, приведенным для различных порошковых образцов диоксида кремния, полученных разными авторами [8]. ...
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В четвертой части обзора проанализированы данные по температурным зависимостям скоростей роста и плотности тонких пленок диоксида кремния (ТПДК) при атомно-слоевом осаждении с термической и плазменной активацией (ТА-АСО и ПА-АСО) и использованием различных реагентов-предшественников. Выделены характерные температурные диапазоны, в которых наблюдаются принципиальные отличия ростовых характеристик при ПА-АСО и ТА-АСО, а также плотности ТПДК. In the fourth part of the review, data on the temperature dependencies of the growth rates and density of thin silicon dioxide films during atomic layer deposition with thermal and plasma activation (TA-ALD and PA-ALD) with the use of various precursors are analyzed. The characteristic temperature ranges have been identified, in which there are fundamental differences in the growth characteristics for PA-ALD and TA-ALD, as well as the density of SiO2.
... The hydrolysis rates in Table 1 suggest that almost all TEOS molecules hydrolyzed in the reaction system were dissolved in the solution and condensed into silica to be precipitated as a shell on the core or generated as secondary particles. Because the amount of silica dissolved in a mixed solvent of alcohol and water is much lower than the number of TEOS molecules present in the reaction system, 51,52 we calculated the number of secondary particles from a combination of the average size of secondary particles finally obtained (D V,2nd ) and Si concentration in the solution ([Si] soln ). Here, the secondary particles were collected from the supernatant of the reaction mixture after one-time centrifugation (see the Supporting Information for details). ...
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Mesoporous silica shells were formed on nonporous spherical silica cores during the sol–gel reaction to elucidate the mechanism for the generation of secondary particles that disturb the efficient growth of mesoporous shells on the cores. Sodium bromide (NaBr) was used as a typical electrolyte for the sol–gel reaction to increase the ionic strength of the reactant solution, which effectively suppressed the generation of secondary particles during the reaction wherein a uniform mesoporous shell was formed on the spherical core. The number of secondary particles (N2nd) generated at an ethanol/water weight ratio of 0.53 was plotted against the Debye–Hückel parameter κ to quantitatively understand the Debye screening effect on secondary particle generation. Parameter κa, where a is the average radius of the secondary particles finally obtained in the silica coating, expresses the trend in N2nd at different concentrations of ammonia and NaBr. N2nd was much lower than that expected theoretically from the variation of secondary particle sizes at a constant Debye–Hückel parameter. A similar correlation with κa was observed at the high and low ethanol/water weight ratios of 0.63 and 0.53, respectively, with different hydrolysis rate constants. The good correlation between N2nd and κa revealed that controlling the ionic strength of the silica coating is an effective approach to suppress the generation of secondary particles for designing mesoporous shells with thicknesses appropriate for their application as high-performance liquid chromatography column packing materials.
... During sorption of various compounds onto a surface of nanooxides, e.g., nanosilica, polar dispersion media play an important role [1][2][3]. In polar solvents, especially water, it is possible charging of both an adsorbent surface and adsorbed molecules that depends strongly on pH of the solution [3][4][5][6][7][8][9]. ...
Article
The model sizes of solid particles as well as used quantum chemical methods can affect results of calculations with density functional theory (DFT) methods. The aim of this study was to analyze the effects of the silica cluster sizes, a number of bound water molecules, protonation and deprotonation of silanols, addition of Eigen cation alone or solvated, attachment of anions F- and Cl- alone or solvated, and whole solvation effects (with SMD) with the DFT calculations using a functional ωB97X-D with the cc-pVDZ basis set. The calculations of the distribution functions of atom charges (CDF), chemical shifts of the proton resonance (SDF), and integral density of electron states (IDES) show that small clusters with 8 or 22 (SiO4/2) units could give rather inappropriate results in contrast to larger clusters with 44 or 88 units. This is due to the fact that the small silica clusters do not have appropriate capability for delocalization of excess charges that leads to certain distortion of the electron states of the whole system. The IDES are more sensitive with respect to the cluster charging and less sensitive to the solvation effects than the CDF and SDF. As a whole, the use of several types of the distribution functions, such as integral characteristics with the CDF, SDF, and IDES, allows one to obtain a more detailed picture on the interfacial phenomena at silica surface for neutral and charged systems.
... Esse método de síntese é definido como qualquer processo que envolve uma solução ou um sol que passa por uma transição sol-gel. Nessa transição, a solução ou dispersão transforma-se pelo estabelecimento de ligações químicas entre as partículas ou entre as espécies moleculares, levando à formação de uma rede sólida tridimensional (gel) (ILER, 1979). ...
... In the kaolin clay used, silicon dioxide (SiO2) and Al2O3 are main ingredients. However, in nature, SiO2 is very stable [30,31]. Consequently, the effect of SiO2 on the production rate for CaCO3 was not considered in this study. ...
Article
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Recently, microbially induced carbonate precipitation (MICP) has been studied as an alternative for the improvement of sand–clay mixtures. However, the cementing uniformity of MICP-treated sand–clay mixtures cannot be guaranteed. In this present study, enzymatic-induced carbonate precipitation (EICP) was used to deal with it. The ions used in kaolin clay was predicted to affect the production rate for calcium carbonate (CaCO3), which was studied using the calcification test. The solidification test was conducted using two different methods (the premixing method and the diffusion method). The permeability, unconfined compressive strength and the content of CaCO3 of treated samples were obtained to evaluate the solidification effect of the EICP method. Moreover, in EICP treatment, the particle aggregation decreased the liquid limit, but the addition of solution increased it. Therefore, there were contrary effects to the soil consistency. In this study, the two types of liquid limits of treated samples were measured with deionized water and 2M-NaCl brine, respectively. The results show that the Al2O3, NaCl and MgCl2 in the kaolin clay had a slight impact on the production rate for CaCO3, while FeCl3 significantly inhibited it. The EICP method can improve sand–clay mixtures and decrease their permeability. Different from MICP, the EICP method can guarantee the uniformity of treated samples. Moreover, the liquid limit of the sample treated with the premixing method decreased, while that of the sample treated with the diffusion method increased firstly and then decreased with the increasing treatment cycles. Different from the deionized water, the pore-fluid chemistry had a larger effect on the liquid limit with 2M-NaCl brine.
... The silanol groups on the surface of the glass, and traces of metal that could be released by dissolution under the alkaline conditions of the experiment may contribute to the observed reactivity 27,28 . The presence of Si-O-H groups enhanced by the alkaline conditions facilitates the absorption of the organic molecules synthesized in the gas and the liquid water in contact with the glass 29 . ...
Article
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We have designed a set of experiments to test the role of borosilicate reactor on the yielding of the Miller–Urey type of experiment. Two experiments were performed in borosilicate flasks, two in a Teflon flask and the third couple in a Teflon flask with pieces of borosilicate submerged in the water. The experiments were performed in CH4, N2, and NH3 atmosphere either buffered at pH 8.7 with NH4Cl or unbuffered solutions at pH ca. 11, at room temperature. The Gas Chromatography-Mass Spectroscopy results show important differences in the yields, the number of products, and molecular weight. In particular, a dipeptide, multi-carbon dicarboxylic acids, PAHs, and a complete panel of biological nucleobases form more efficiently or exclusively in the borosilicate vessel. Our results offer a better explanation of the famous Miller's experiment showing the efficiency of borosilicate in a triphasic system including water and the reduced Miller–Urey atmosphere.
... Consequently, the presence of caves and other weathering fingerprints in quartz-rich lithologies is currently widely known [166]. Once quartz dissolution occurs, the dissolved silica forms the Si(OH)4 monomer [167], monomolecular orthosilicic acid (H4SiO4), or polycyclic acids, mostly colloidal [168]. The overall reaction of quartz with water is described in Eq. (1). ...
Article
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Sandstones are common rocks mainly composed of a framework of grains dominated by relatively weathering-resistant silicates and aluminosilicates, whereas matrix and cement minerals in general are less resistant to weathering. Sandstone in both natural and anthropogenic environments are exposed to (bio)weathering processes, causing the release of elements from minor constituents (matrix and cement minerals) and major framework minerals and resulting in the presence of an irreversible fingerprint on the mineral/rock surface. As the result of bioweathering some adverse features such as corrosion, cracking and rock fatigue occur which arises a strong concern regarding durability of sandstones in a long-term perspective. This review paper describes analytical methods applied for determining the mineralogical composition of sandstones and their alteration features, defines bioweathering process and factors attributed to it, analyzes susceptibility of sandstone minerals to dissolution, presents experimental simulations dedicated to stability assessment. This review highlights that bioweathering processes may affect durability of construction and building materials. The gaps in the experimental research are indicated and recommendations on how to fill these gaps are provided.
... Even simple fluid and melt inclusions can be irreversibly modified after their entrapment by crystallisation and diffusive re-equilibration with the host mineral and its surroundings [51][52][53][54][55][56]. In the case of colloid systems such modifications can be further complicated by ageing, which on its own can be irreversible [17,57,58]. Nevertheless, several studies report inclusions that were inferred to be hydrosilicate fluids, including SiO 2 -rich colloids, at the time of entrapment. ...
Article
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Experimental studies increasingly often report low-temperature (200–800 °C) and low-pressure (0.05–3 kbar) hydrosilicate fluids with >40 wt.% of SiO2 and >10 wt.% of H2O. Compositionally similar fluids were long suggested to potentially exist in natural systems such as pegmatites and hydrothermal veins. However, they are rarely invoked in recent petrogenetic models, perhaps because of the scarcity of direct evidence for their natural occurrence. Here we review such evidence from previous works and add to this by documenting inclusions of hydrosilicate fluids in quartz and feldspar from Itrongay. The latter comprise opal-A, opal-CT, moganite and quartz inclusions that frequently contain H2O and have negative crystal shapes. They coexist with inclusions of CO2- and H2O-rich fluids and complex polycrystalline inclusions containing chlorides, sulphates, carbonates, arsenates, oxides, hydroxides and silicates, which we interpret as remnants of saline liquids. Collectively, previous studies and our new results indicate that hydrosilicate fluids may be common in the Earth’s crust, although their tendency to transform into quartz upon cooling and exhumation renders them difficult to recognise. These data warrant more comprehensive research into the nature of such hydrosilicate fluids and their distribution across a wide range of pressure and temperature conditions and geological systems.
... It is also known that protein content of EPS enhances the affinity of EPS to negatively charged surfaces (Jenkinson, 1994) and lipid content of EPS enhances the affinity of EPS to solid surfaces . Since sand surface is electronegative (Iler, 1979), it therefore seems that observed amounts of carbohydrate, protein and lipid contents of EPS are likely to contribute to EPS-EPS attachment as well as attachment of EPS to sand particles. In the absence and presence of fluvial activities, total EPS extracted from bacteria-treated sand as well as its components were found to increase with incubation duration (Table 2, Figure 7). ...
Article
Microbe-induced reduction of soil erodibility, since natural, is expected not to disrupt the natural environmental system. Although the role of bacteriogenic EPS in aggregating soil particles is widely recognized the impact of various environmental parameters e.g., groundwater velocity and nutrient availability on bacteriogenic EPS in reducing the erodibility of soil is not very clear. In this study, a species of EPS producing soil bacteria Bacillus megaterium RB-05 isolated from a naturally cemented intertidal silt site was used to investigate the influence of flow velocity and nutrient availability on microbially mediated reduction of erodibility of sand. Durations of nutrient availability and media circulation velocity were observed to influence the bacterial population, amounts, and composition of EPS found within sand specimens. The drained shear strength of loose sand samplers was found to increase due to EPS-related interparticle aggregation. EPS produced under fluvial activities seem to be more capable of aggregating sand grains as well as reducing erodibility of sand. Results of the model sand erosion test further strengthen this conclusion.
... The reactivity of silica is mainly explained by the presence and nature of surface silanols, the siloxane bridges being not very chemically reactive at room temperature [89]. Surface silanols have a pKa of 7.0 ± 0.2 [90,91] and the isoelectric point (IEP) of silica is around pH 2; the pH of the medium will, therefore, modify the protonation state of the hydroxyl groups and the charge of the surface and, therefore, influence its reactivity. In addition, with respect to functional compounds, the reactivity of the surface sites is different according to the type of surface hydroxyl [83,[92][93][94]. ...
Thesis
Notwithstanding the growth of the market of the new lithium-ion batteries, lead-acid batteries still offer advantages that the new ones are not able to equate especially in terms of cost, manufacturing base and the actual market need. In this context, the aim of this work is to enhance the properties of lead-acid batteries PE- separators that predominate 90% of the market of lead-acid batteries separators. These porous membranes consist mainly of precipitated silica, a backbone of ultra-high molecular weight Polyethylene (UHMWPE) and they are processed using a thermally induced phase separation process (TIPS) with naphthenic oil that is subsequently extracted. The resulting porosity is thereafter infiltrated with the electrolyte of the battery. Yet, due to the limited wettability of the pores of the membrane by the polar electrolyte, only a fraction of the available porosity is efficient. This thesis focuses on the enhancement of such wettable porosity by the electrolyte in order to reduce the electrical resistivity of the separator. The wettability of the pores is not only related to the presence of silica but also to the nature of silica surface. Paradoxically, hydrophobic silica favors the blend and the dispersion of aggregates; while hydrophilic silica promotes the wettability of the porosity by the electrolyte. To fulfill these criteria and obtain a material as homogeneous as possible with maximum accessible porosity, a reversible modification of the surface of silica was realized by physical impregnation of surfactants or by chemical modification before the blending and the dispersion in the membrane. Therefore, rheological characterization of the suspensions, contact angle and sorption isotherms and other techniques were used to evaluate the change in the surface properties of the new silica. Then, these tuned silica were dispersed in membranes and the prorosity, the structure, the electrical and mechanical properties were investigated.
... Он основан на гидролизе алкоксидов металлов или металлоидов в присутствии кислот или оснований с последующей конденсацией образующихся гидроксосоединений и сшивкой образующихся кластеров с формированием частиц золя [14,15]. В дальнейшем частицы золя объединяются с образованием трехмерной сетки лиогеля [4,16]. ...
Article
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Аэрогели представляют собой уникальные твердофазные материалы, характеризующиеся крайне высокой открытой пористостью и удельной поверхностью. Благодаря этим особенностям аэрогели широко используются в качестве тепло- и звукоизоляторов, газовых фильтров, сорбентов и др. Кроме того, аэрогели являются перспективными матрицами для создания селективных катализаторов, газовых сенсоров, люминофоров и т.д. Методы и подходы координационной химии открывают принципиально новые возможности для конструирования новых гибридных материалов, характеризующихся сочетанием практически важных физико-химических свойств, присущих аэрогелям и комплексам металлов. Модификация аэрогелей координационными соединениями позволяет получать полифункциональные материалы, обладающие высокой пористостью и удельной поверхностью в сочетании с превосходными каталитическими, фотокаталитическими, магнитными, люминесцентными и другими свойствами. В настоящем обзоре впервые обобщены и проанализированы подходы координационной химии, обеспечивающие химическое связывание координационных соединений с матрицей аэрогеля и позволяющие получать аэрогели с новыми функциональными свойствами. Рассмотрены известные примеры успешной реализации указанных подходов, в том числе предложенные ранее авторами обзора, а также приведены сведения о практическом применении получаемых таким образом материалов.
... Polysilicic acids with a maximum degree of polymerization are classified as polymeric or high-molecular-weight-silica, whereas oligomeric or low-molecular-weight-silica has H 4 SiO 4 chains up to 10 Si atoms in length [43]. Different types of oligomeric and polysilicic acids can be found [48]. Plant absorption and nutrition are affected by monosilicic acid, while soil aggregation is affected by polysilicic acid. ...
Chapter
Silicon (Si) is an important nutrient, particularly under stressful enticements, although its essentiality for higher plants still needs more evidence. This element in bulk- and nano-form has fascinating features, which attracts the workers in agriculture, industry, pharmaceutical, and many other allied sectors. The sources of Si are crucial information for better understanding the nature of this element and cycling in soils and plants, especially for recent applications as nano-fertilizers, nano-pesticides, nano-sensors, and others. Based on these sources and forms, the bioavailability and uptake by plants of different Si forms depend on soil and rhizosphere catheterizations. These sources and forms of Si are also important for better understanding the fate and action of Si in soil and plants. Further, studies are needed about this element, in which many fascinating features about it will be discovered day by day.
... Esse método de síntese é definido como qualquer processo que envolve uma solução ou um sol que passa por uma transição sol-gel. Nessa transição, a solução ou dispersão transforma-se pelo estabelecimento de ligações químicas entre as partículas ou entre as espécies moleculares, levando à formação de uma rede sólida tridimensional (gel) (ILER, 1979). ...
... Condensation reactions of silica, under almost all conditions, form amorphous, spherical particles. However, the size of nucleated clusters (or sols) and their density depends upon the concentration, temperature, pH and the presence of other charge-balancing species 208 . ...
Article
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Standard methods to assess the durability of vitrified radioactive waste were first developed in the 1980’s and, over the last 40 years, have evolved to yield a range of responses depending on experimental conditions and glass composition. Mechanistic understanding of glass dissolution has progressed in parallel, enhancing our interpretation of the data acquired. With the implementation of subsurface disposal for vitrified radioactive waste drawing closer, it is timely to review the available standard methodologies and reflect upon their relative advantages, limitations, and how the data obtained can be interpreted to support the post-closure safety case for radioactive waste disposal.
... Silicon dioxide or silica, is a silicon oxide with the chemical formula SiO2, most common in nature as quartz and in various living things [3], [4]. ...
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Nano-structure SiO 2 was prepared in this work by use Sol-Gel method. Then, studying optical and structural properties of SiO 2 , the absorption spectrum was determined in UV region, while nano-structure and morphology was investigated by XRD and AFM respectively. The particle size measured by use AFM Analysis which about (55.12 nm).super hydrophilic was gotten after 1 hour of UV irradiation for the prepared SiO 2 thin-film.
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Discover a rigorous treatment of aerogels processing and techniques for characterization with this easy-to-use reference. Presents the basics of aerogel synthesis and gelation to open porous nanostructures, and the processing of wet gels like ambient and supercritical drying leading to aerogels. Describes their essential properties with their measurement techniques and theoretical models used to analyse relations to their nanostructure. Linking the fundamentals and with practical applications, this is a useful toolkit for advanced undergraduates, and graduate students doing research in material and polymer science, physical chemistry, and chemical and environmental engineering.
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PREFACE The insertion of new and enhanced materials based on materials belonging to the Nano scale in the day-by-day has growth up in a silent way. In part, a number of works in the nanotechnology stemming of theoretical research using Density Functional Theory (DFT) and sophisticated simulation methods; another part is associated to the protected technologies associated to the military and patented nanomaterial and its process. In this sense, open access to recent aspects on the nanostructures application and properties can be reached in this book. Here, an interesting set of chapters gives opportunity of access texts that reach process and processing of nanostructures, applications of nanotechnology, advanced techniques to theoretical development. A broad set of nanostructures are here covered such as, nanocrystal, superficial nanograins, inner microstructures with nanograins, nanoaggregates, nanoshells, nanotubes, nanoflowers, nanoroad, nanosheets, Also, reveals new investigations areas as nanograinsboundary in ceramics and metals. A great number of software has been used as a tool of development of Science and Technologies for nanotechnology COMSOL Multiphysics 5.2. Phenomena and properties has been investigated by recent or classical techniques of materials characterization as Localized Surface Plasmon Resonance (LSPR), X-ray photoelectron spectroscopy (XPS), Field Emission Gun Scanning Electron Microscopy (FEG-SEM) with Energy Dispersive Spectroscopy (EDS), Raman Scattering Spectroscopy (RSS), X ray diffraction (XRD), 57Fe Mössbauer spectroscopy, UV-vis spectroscopy, dynamic light scattering (DLS), Atomic Force Microscopy (AFM), and Field Emission Gun Scanning Electron Microscopy (FEG-SEM). In this sense, collections of spectra from Mössbauer spectroscopy, UV-vis spectroscopy and Infrared spectroscopy can be found. As a matter of fact, some chapter’s item can be seemed as specific protocols for synthesis, preparations and measurements. I hope you enjoy your reading. Prof. Dr. Marcos Augusto Lima Nobre (Organizer)
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Sialylation plays an important role in tumor-related physiological processes. Therefore, intervention of sialylation has great potential to explore new paths for tumor therapy. In view of the immune modulation of sialic acid (SA) on tumors, this work designs a multifunctional mesoporous silica nanoparticle (MFMSN) to divert intracellular sialylation for tumor suppression. The galactose groups covered on MFMSN act as sialylation substrates to bind intracellular SAs competitively, which inhibits the SA expression on the tumor cell surface. The diverted intracellular sialylation can be visualized on living cells and in vivo by specifically binding the sialylated galactose with a phenylboronic acid labeled ssDNA probe released from the pore of MFMSN to induce DNA strand displacement, which recovers the fluorescence of the dsDNA probe covered on MFMSN surface. The diverting of sialylation efficiently suppresses tumor growth in mice, demonstrating the great potential of the designed strategy for revealing SA-related biological processes and clinical cancer therapy.
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By means of dissipative particle dynamics simulations, we study static and dynamic properties of a concentrated colloidal system. In particular, we look at the effect of particle softness on the transition temperature, and on the ordering and dynamics of the system. It is shown that the transition temperature decreases linearly with increasing softness. Also, we study the spatial ordering of particles through radial distribution function and compare among different systems with varying degree of particle softness at the thermodynamic melting temperature. We further investigate the dynamical behaviors of the colloidal system in the vicinity of transition temperature and study the variation of diffusion constant as a function of both temperature and degree of softness. We find that, with increasing particle softness, the particle relaxation time increases and thus the diffusion constant also decreases.
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The article presents the results on the structure of various types of activated kaolin: ultrasonic treatment, acid activation, exposure to high temperatures. It is found that the high activation promotes the formation of an amorphous structure, which is confirmed by X-ray analysis - presence of an amorphous halo range 2θ = 15-30o, ultrasound and acid treatment does not destroy the structure of the filler that has been previously demonstrated using the method of IR spectroscopy study. It is shown that the combined use of activated kaolin, with their different quantitative ratio to one another contributes to the manifestation of synergy. Increasing the basic lacquer coating characteristics on the dispersion E-21 (coverage, washability, water and moisture absorption, the adhesive strength) occurs at 1,2-1,4, which is apparently due to the presence in the paint filling amount of the amorphous and crystalline structures.
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Recent studies have shown that silicon (Si) dissolution from biochar may be influenced by the pyrolysis temperature. In addition, the enhancement of biochar by treatment with alkali has been proposed to produce a Si source that can be used for environmentally friendly plant disease control. In this study, biochars from rice straw and rice husk pretreated with KOH, CaO and K 2 CO 3 and then pyrolyzed at 350, 450 and 550 °C were prepared to evaluate the effects of pyrolysis temperature on Si release and plant uptake from alkali-enhanced Si-rich biochar. Extractable Si and dissolution Si from the prepared biochars were assessed by different short-term chemical methods and long-term (30-day) release in dilute acid and neutral salt solutions, respectively, along with a rice potting experiment in greenhouse. For both rice straw- and husk-derived alkali-enhanced biochars (RS-10KB and HS-10K2B, respectively), increasing the pyrolysis temperature from 350 to 550 °C generally had the highest extractable Si and increased Si content extracted by 5-day sodium carbonate and ammonium nitrate (5dSCAN) designated for fertilizer Si by 61–142%, whereas non-enhanced biochars had more extractable Si at 350 °C. The alkali-enhanced biochars produced at 550 °C pyrolysis temperature also released 82–172% and 27–79% more Si than that of 350 °C produced biochar in unbuffered weak acid and neutral salt solutions, respectively, over 30 days. In addition, alkali-enhanced biochars, especially that derived from rice husk at 550 °C facilitated 6–21% greater Si uptake by rice and 44–101% higher rice grain yields than lower temperature biochars, non-enhanced biochars, or conventional Si fertilizers (wollastonite and silicate calcium slag). Overall, this study demonstrated that 550 °C is more efficient than lower pyrolysis temperature for preparing alkali-enhanced biochar to improve Si release for plant growth.
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It’s well known that wear can accelerate degeneration of materials in corrosive media. Less attention has been paid to effects of different cathodic reactions on tribocorrosion behaviors. In this study, linear reciprocating sliding wear test of AISI 430 was carried out in distilled water and 0.5 mol/L sulfuric acid media, respectively. The results revealed that oxygen reduction reaction is in favor of oxide films forming on the surface, which increased subsurface hardness of the wear track. However, hydrogen evolution reaction restrained the formation of oxide films and induced hydrogen embrittlement, thus worsened the tribocorrosion properties and increased material removal. Interaction between wear and corrosion contributed most mass loss in the material deterioration, which was related to the reciprocating frequency.
Article
Composite systems with certain cytotoxic (AM1/lectin) and adsorption (AM1/gelatin) activity have been developed on the basis of methyl silica and protein molecules – lectin and gelatin. For both types of composites, mechanisms of water binding to the surface and methods of transferring of hydrophobic materials into the aquatic environment have been investigated. The state of interfacial water in air, organic and acid media was studied. It has been found that the presence of a hydrophobic component in composites stabilizes of surface water in a weakly associated state, when a significant part of water molecules does not form hydrogen bonds. Liquid hydrophobic medium enhances this effect, and the strong acid (trifluoroacetic), added to it, promotes the transition of water to a strongly associated state. It has been shown that the redistribution of water in the interparticle intervals of AM1 with protein molecules immobilized on their surface changes under the influence of mechanical loads. Mechanoactivated samples are characterized by the possibility of water penetration into the spaces between the primary particles of methyl silica. It has been shown that immobilization of lectin on the surface of AM1 is accompanied by an increase in the interfacial energy gS from 4.1 to 5.2 J/g. This is due to an increase in the concentration of strongly bound water. If we analyze the changes in the distributions of radii R of the clusters of adsorbed water, we can state that in the water adsorbed by native lectin molecules, there are two main maxima at R = 1 and 3 nm. In the immobilized state, the maximum at R = 1 nm is present in both types of water (of different order), but the second maximum is observed only for more ordered associates.
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In order to increase shrimp production and minimize detrimental environmental impacts of aquaculture, the maintenance and regulation of the growth and composition of phytoplankton communities and nutritional balance are critical. Silicon (Si) is an essential nutrient for diatoms and other types of microorganisms, but the information about the Si impact on their growth is extremely scarce. Monosilicic and polysilicic acids were tested in several shrimp cultivation systems in Jiangsu Province, China. In pond waters, the concentrations of monosilicic and polysilicic acids were sharply reduced by 36-95% and 35-75%, accordingly, as compared with those in supply water sources. The microbial cell abundance was strongly dependent on monosilicic acid. In laboratory experiments, monosilicic acid added to pond water or probiotic solutions at 1- and 2-mM Si had a significant positive effect on cell abundance. Over three days, the concentrations of monosilicic acid decreased by 81 to 91% in pond water and by 11 to 24% in probiotic solution. In probiotic solutions, the degree of polymerization of silicic acid was more intensive than that in shrimp pond waters. The data obtained demonstrates the importance of systematic studies related to the functions of Si in shrimp aquaculture.
Thesis
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Fly ash is the most commonly used supplementary cementitious material (SCM) in concrete production today. In recent years, however, the quantity of freshly produced fly ash in the United States has declined by nearly 60% and this has caused a fly ash shortage to produce high-quality and durable concrete. To address this challenge, in the first part of this dissertation, alternative sources of fly ash including harvested and high sulfur/alkali fly ash were evaluated and suitable beneficiation strategies were identified to address challenges in their performance. The potential issues with using landfilled fly ash as a concrete pozzolan was summarized based on a literature review. Accordingly, a statistical sampling approach was developed to determine the viability of a given landfill as a pozzolan source and this approach was applied to a Class F fly ash landfill in Pennsylvania. Samples taken from the landfill were tested based on ASTM C618 requirements and statistical analyses were performed to determine the necessary beneficiation strategies to make the material viable for use as concrete pozzolan. Blended mortar and concrete mixtures incorporating the beneficiated fly ash were tested for slump, plastic and hardened air content, compressive strength, and mitigation of alkali-silica reaction (ASR). High sulfur and/or high alkali fly ashes are produced in coal-fuel power plants with semi-dry or dry flue gas desulfurization (FGD) systems that produce fly ash comingled with FGD products. Such fly ashes do not meet the ASTM C618 SO3 content limit (5.0% max.) and may be unable to mitigate the ASR in concrete due to the high alkali content of the fly ash. The chemistry and mineralogy of the sulfur present in these ashes can vary significantly (e.g., CaSO4, CaSO3, Na2SO4) based on the FGD technology used and this in turn affects the performance of these fly ashes in cementitious systems. Thus, the single SO3 content limit prescribed by ASTM C618 is not sufficient to capture the complexity and performance of these fly ashes and this has resulted in elimination of potentially viable SCMs. In this research, the effect of these fly ashes on various concrete performance parameters such as workability (flow and flow retention), pore fluid pH, setting time, strength development, and potential for deleterious expansion were evaluated by considering both real and simulated fly ashes (i.e., by blending of specification-compliant fly ash with different sulfur compounds). While many measured properties of the resulting concretes were acceptable, poor performance was observed in the case of setting time and pore fluid pH with some fly ashes. In such cases, novel beneficiation strategies were devised and implemented to successfully address the problem. The second part of this dissertation addresses the mitigation of ASR in concrete and service life prediction of susceptible structures. A new generation of ASR-inhibiting chemical admixtures were developed for concrete. These admixtures, which are in the form of soluble inorganic and organic salts, are cheaper and more abundant than lithium admixtures, yet provide more consistency in terms of quality, supply, and performance in comparison with SCMs. A methodical approach was developed to identify such admixtures that primarily mitigate ASR by reducing the pH of concrete pore solution. The mechanism of pH reduction was identified and the set of criteria that a potential admixture must meet were developed. The suitable admixtures were screened using ASTM C1293 as a proof-of-concept. Additionally, the performance of these admixtures in concrete and mortar mixtures was extensively evaluated. The properties studied include flow, flow retention, concrete slump, plastic air content, setting time, compressive strength of mortar and concrete, pore fluid pH at 0, 7, 28, 90, and 180 days, formation factor (along with porosity and pore connectivity), and drying shrinkage. The admixtures were found to maintain the reduced pH in the long term and had minimal impact on workability, plastic air content, and strength. These admixtures may increase the pore connectivity of the system without increasing the porosity. Drying shrinkage was also found to be slightly higher when compared to ordinary portland cement (OPC), but within the limits specified by the ASTM standards. A final list of eight promising admixtures were identified. Finally, estimating the service life of structures affected by ASR is essential for effective investment of resources for maintenance, repair, or replacement of crucial infrastructure. Current ASR prediction models either do not consider all the important factors that impact the magnitude and rate of ASR progression or are too complicated to implement in practice. In this study, mini-mortar bar specimens were used to evaluate the development of ASR expansion using five evenly spaced levels of aggregate reactivity (ASTM C1293 1-year expansion value), pore solution pH, temperature, and moisture access. The experiments were designed using the response surface methodology and a quadratic regression model was used to relate the ASR expansion rate to the testing conditions. Further, a service life model was developed for predicting the time to failure (time when expansion reaches 0.04%) based on the concrete mix design and exposure conditions. The predictions of the developed model were in good agreement with the outdoor exposure blocks data available in literature. Overall, this dissertation addresses key challenges in improving the sustainability and durability of concrete. The evaluation and beneficiation protocol developed in this dissertation for the use of landfilled fly ash will hopefully encourage their use and ultimately increase the supply of fly ash available for producing high quality and green concrete. Additionally, the work done on high sulfur and/or high alkali fly ash will encourage more research into these materials and possibly lead to a re-evaluation of the current standard specifications that currently limit their use. The cheap and abundant admixtures developed for mitigation of ASR will provide the industry with a reliable strategy for addressing this durability challenge. Additionally, the service life model developed for ASR susceptible structures addresses the impact of the most important parameters and can be used for effective asset management.
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