Search

Ammonia borane (AB), with a 19.6-wt% H2 content, is a promising hydrogen storage material for polymer electrolyte membrane fuel cells (PEMFC). However, traditional thermal decomposition of boric acid generates ammonia, which is detrimental to fuel cells. This study explores the use of silicic acid (SA) as a catalyst for AB, yielding 12.0 wt% of H2 at approximately 100 °C, making it suitable for fuel-cell operation. Notably, when the AB mass ratio is increased to 90 wt%, the reaction temperature increases slightly, yet it produces up to 12.3 wt% of H2. Fourier transform infrared (FT-IR) and X-ray photoelectron spectroscopy (XPS) analyses confirm that SA contains more silanol groups than SiO₂. Pyridine infrared analysis reveals that SA has a higher distribution of Lewis acid sites, which play a vital role in the dehydrogenation of AB. In addition, when in-situ mass spectrometry analysis is performed, ammonia is not detected, indicating that no filtration is required for fuel-cell applications. In conclusion, this study demonstrates that SA enhances the dehydrogenation of AB at low temperatures, achieving a high H2 yield without ammonia production. This makes SA a promising catalyst for efficient and safe H2 storage in fuel cells, with potential applications in mobile and aerial vehicles. [ABSTRACT FROM AUTHOR]

The effect of treating SBA-15 with a piranha solution at room temperature was studied for purposes of stabilizing a WO3 film deposited by Atomic Layer Deposition (ALD). For unmodified SBA-15, the film was found to migrate out of the SBA-15 pore structure between 573 and 773 K; however, WO3 remained within the pores in piranha-treated samples at 773 K, as demonstrated by X-Ray Diffraction and Transmission Electron Microscopy. Although N2 adsorption isotherms showed that the pore structure of SBA-15 was unaffected by the piranha treatment, the silanol content increased, as shown by water adsorption isotherms and Diffuse Reflectance Infrared Spectra of the silanol region. Temperature-programmed desorption results for 2-propanol also suggested that the silanols were more reactive in the piranha-treated samples. The results demonstrate the importance of surface modification of SBA-15 for the preparation of supported-oxide catalysts. [ABSTRACT FROM AUTHOR]

Aqueous zinc ion batteries (AZIBs) have garnered significant attention due to their advantages, including high safety, a straightforward manufacturing process, abundant resource availability, and high theoretical capacity. Nevertheless, the industrial application of AZIBs is impeded by the undesirable growth of dendrites and side reactions on the Zn anode. In this study, [3‐(trimethoxysilyl) propyl] urea (3TMS) is utilized as an electrolyte additive to develop a solid/electrolyte interphase (SEI) film on the surface of Zn anode. The in situ formed SEI layer not only prevents side reactions form the direct contact of Zn anode with water but also induces preferential Zn deposition along the (002) crystal plane, suppressing dendrite growth. These synergistic functions enable the Zn anode with ultralong cycle life of over 6000 h at the current density of 1 mA cm−2 with the areal capacity of 1 mAh cm−2, as well as high coulombic efficiency of 99.34% after 750 cycles. Moreover, the Zn//V2O5 full cells with 3TMS additive display a high specific capacity of 114.4 mAh g−1 at a current density of 0.5 A g−1 after 1000 cycles. This work provides a simple yet feasible approach to develop stable Zn anode toward high‐performance AZIBs. [ABSTRACT FROM AUTHOR]

The Lewis acidic framework Ti sites in Ti-Beta and Si-Beta catalysts were compared by FT-IR and NMR characterization methods before they were applied to the conversion of four butenes. The results showed that Si-Beta has fewer Lewis acid sites and abundant weak Brønsted acidic silanol nests, which play an important role in conversions between n-butene, cis-2-butene, and trans-2-butene. The conversions for these butenes over Si-Beta were always higher than those over a series of Ti-Beta catalysts with gradient-varied Lewis acidic framework Ti sites and silanols. This is because isobutene can only oligomerize, which requires stronger acidity, so its conversion over Si-Beta was lower than those over Ti-Beta zeolites. For a series of Ti-Beta catalysts with different abundances of Lewis acidic Ti sites, the more Lewis acid sites it had, the higher the conversions for the four butenes. [ABSTRACT FROM AUTHOR]

The development of efficient Si–O bond formation reaction with 100% atom-economy, excellent functional group tolerance, and broad scope under mild conditions is highly desired due to the prevalence of silanol, silyl ether, and their derivatives in synthetic chemistry and materials science. Here, we have realized the Pd-catalyzed Si–O formation reaction via a Si–C activation approach with 100% atom-economy by employing silacyclobutanes (SCBs) and various hydroxy-containing substrates, including water, alcohols, phenols, and silanols. This protocol features a broad substrate scope, remarkable functional compatibility and mild conditions, providing a series of silanols, silyl ethers in high efficiency. Notably, this protocol could also be used for selective protection of hydroxy functionalities, and for the access of a class of novel polymers containing Si–O main chain. Preliminary mechanistic studies unveiled that this reaction underwent a Pd-catalyzed concerted ring-opening mechanism. [ABSTRACT FROM AUTHOR]

The construction of silicon‐stereogenic silanols via Pd‐catalyzed intermolecular C−H alkenylation with the assistance of a commercially available L‐pyroglutamic acid has been realized for the first time. Employing oxime ether as the directing group, silicon‐stereogenic silanol derivatives could be readily prepared with excellent enantioselectivities, featuring a broad substrate scope and good functional group tolerance. Moreover, parallel kinetic resolution with unsymmetric substrates further highlighted the generality of this protocol. Mechanistic studies indicate that L‐pyroglutamic acid could stabilize the Pd catalyst and provide excellent chiral induction. Preliminary computational studies unveil the origin of the enantioselectivity in the C−H bond activation step. [ABSTRACT FROM AUTHOR]

Infrared spectroscopy (IR) is an important tool to investigate the structure of silicalite-1, but the reported spectra vary considerably depending on instrument configuration, sample preparation methods, and pretreatment conditions. This inconsistency makes the investigation of the structure-property correlations difficult. Herein, we investigate the effects of different optical modes (attenuated total reflectance, transmission, diffuse reflectance), different detectors (Mercury Cadmium Telluride and Deuterated Triglycine Sulfate, MCT and DTGS), different sample preparation methods (powder, silicalite-1/KBr wafer, pure silicalite-1 wafer), and different pretreatment temperatures (RT–400 °C) on the spectral shapes of the skeletal and hydroxyl region IR spectra of silicalite-1. Then the appropriate measurement conditions to obtain reproducible and intrinsic spectra were determined. For the skeletal region IR spectra of silicalite-1, the suitable conditions are the transmission mode with a DTGS detector and 1:500 silicalite-1/KBr wafers. For the hydroxyl region IR spectra, an in-situ transmission cell with pure sample wafers and pretreatment at 400 °C is appropriate. Under these suitable measurement conditions, spectral changes can reflect changes in silicalite-1 structure to facilitate the elucidation of the structure-property correlations of silicalite-1 by IR spectroscopy. [ABSTRACT FROM AUTHOR]

Compared to ubiquitous functional groups such as alcohols, carboxylic acids, amines, and amides, which serve as central "actors" in most organic reactions, sulfamates, phosphoramidates, and di‐tert‐butyl silanols have historically been viewed as "extras". Largely considered functional group curiosities rather than launch‐points of vital reactivity, the chemistry of these moieties is under‐developed. Our research program has uncovered new facets of reactivity of each of these functional groups, and we are optimistic that the chemistry of these fascinating molecules can be developed into truly general transformations, useful for chemists across multiple disciplines. In the ensuing sections, I will describe our efforts to develop new reactions with these "unusual" functional groups, namely sulfamates, phosphoramidates, and di‐tert‐butyl silanols. [ABSTRACT FROM AUTHOR]

A low palladium‐loading heterogeneous catalyst has been developed for the hydrolysis of hydrosilanes to silanols and alkoxysilanes under mild and neutral reaction conditions with broad substrate scope. After five recycling runs, this low palladium‐loading catalyst keeps good activity for this transformation. [ABSTRACT FROM AUTHOR]

As a crucial class of functional molecules in organosilicon chemistry, silanols are found valuable applications in the fields of modern science and will be a potentially powerful framework for biologically active compounds or functional materials. It has witnessed an increasing demand for non‐natural organosilanols, as well as the progress in the synthesis of these structural features. From the classic preparative methods to the catalytic selective oxidation of hydrosilanes, electrochemical hydrolysis of hydrosilanes, and then the construction of the most challenging silicon‐stereogenic silanols. This review summarized the progress in the catalyzed synthesis of silanols via hydroxylation of hydrosilanes in the last decade, with a particular emphasis on the latest elegant developments in the desymmetrization strategy for the enantioselective synthesis of silicon‐stereogenic silanols from dihydrosilanes. [ABSTRACT FROM AUTHOR]

The carbon‐to‐silicon switch in formation of bioactive sila‐heterocycles with a silicon‐stereogenic center has garnered significant interest in drug discovery. However, metal‐catalyzed synthesis of such scaffolds is still in its infancy. Herein, a rhodium‐catalyzed enantioselective formal [4+1] cyclization of benzyl alcohols and benzaldimines has been realized by enantioselective difunctionalization of a secondary silane reagent, affording chiral‐at‐silicon cyclic silyl ethers and sila‐isoindolines, respectively. Mechanistic studies reveal a dual role of the rhodium‐hydride catalyst. The coupling system proceeds via rhodium‐catalyzed enantio‐determining dehydrogenative OH silylation of the benzyl alcohol or hydrosilylation of the imine to give an enantioenriched silyl ether or silazane intermediate, respectively. The same rhodium catalyst also enables subsequent intramolecular cyclative C−H silylation directed by the pendent Si‐H group. Experimental and DFT studies have been conducted to explore the mechanism of the OH bond silylation of benzyl alcohol, where the Si‐O reductive elimination from a Rh(III) hydride intermediate has been established as the enantiodetermining step. [ABSTRACT FROM AUTHOR]

Cage-type silicate with a double six-ring (D6R) structure is successfully functionalized with dimethylsilyl and dimethylsilanol groups. The dimethylsilanol-functionalized cages are assembled to form a 1D structure through intermolecular hydrogen bonding of the silanol groups between the cages. These results will contribute to the development of a building-block approach for the creation of ordered siloxane-based nanomaterials. [ABSTRACT FROM AUTHOR]

High concentration of H2S in acidic natural gas will lead to poisoning of catalysts for hydrogen production by methane steam reforming, thus limiting the further use of natural gas. Reforming CH4 by H2S can be considered as an alternative route to hydrogen production from methane. This process not only achieves the removal of H2S but also obtains chemical raw material CS2 and clean energy H2. By impregnating the Mo source on SiO2 treated with hydrogen peroxide and then using the catalyst in the CH4/H2S reforming reaction, we surprisingly found that the conversion rate of CH4 and H2S increased from 28 and 32% to 34% and 43%, respectively, after hydrogen peroxide treatment. The H2 production rate and the yield of CS2 increased from 20 mmolH2/(gMo*min) and 52% to 30 mmolH2/(gMo*min) and 65%, respectively. Combining with characterization methods such as X-ray diffraction (XRD), hydrogen temperature programmed reduction (H2-TPR), 1H-based solid-state nuclear magnetic resonance (1H MAS NMR), X-ray photoelectron spectroscopy (XPS), Raman spectra (RS), and transmission electron microscopy (TEM), we found that the hydroxyl concentration of the support increased after hydrogen peroxide treatment, which led to the strengthening of the force between the metal and the support, which was easy to form low-level and small-size MoS2, exposing more active sites, and further improving the catalytic activity. This method provides a new idea for hydrogen production by CH4/H2S reforming and the development of high-performance MoS2-based catalysts. [ABSTRACT FROM AUTHOR]

Herein, a four-coordinated organoboron compound, aminoquinoline diarylboron (AQDAB), is utilized as the photocatalyst in the oxidation of silane to silanol. This strategy effectively oxidizes Si–H bonds, affording Si–O bonds. Generally, the corresponding silanols can be obtained in moderate to good yields at room temperature under oxygen atmospheres, representing a green protocol to complement the existing preparation methods for silanols. [ABSTRACT FROM AUTHOR]

The specific features of the siloxane bond unify the compounds based on it into a class with its own chemistry and unique combinations of chemical and physical properties. An illustration of their chemical peculiarity is the behavior of 1,3-bis(2-aminoethylaminomethyl)tetramethyldisiloxane (AEAMDS) in the reaction with carbonyl compounds and metal salts, by which we obtain the metal complexes of the corresponding Schiff bases formed in situ. Depending on the reaction conditions, the fragmentation of this compound takes place at the siloxane bond, but, in most cases, it is in the organic moieties in the β position with respect to the silicon atom. The main compounds that were formed based on the moieties resulting from the splitting of this diamine were isolated and characterized from a structural point of view. Depending on the presence or not of the metal salt in the reaction mixture, these are metal complexes with organic ligands (either dangling or not dangling silanol tails), or organic compounds. Through theoretical calculations, electrons that appear in the structure of the siloxane bond in different contexts and that lead to such fragmentations have been assessed. [ABSTRACT FROM AUTHOR]

Occupational exposure to quartz dust is associated with fatal diseases. Quartz dusts generated by mechanical fracturing are characterized by a broad range of micrometric to nanometric particles. The contribution of this nanometric fraction to the overall toxicity of quartz is still largely unexplored, primarily because of the strong electrostatic adhesion forces that prevent isolation of the nanofraction. Furthermore, fractured silica dust exhibits special surface features, namely nearly free silanols (NFS), which impart a membranolytic activity to quartz. Nanoquartz can be synthetized via bottom-up methods, but the surface chemistry of such crystals strongly differs from that of nanoparticles resulting from fracturing. Here, we report a top-down milling procedure to obtain a nanometric quartz that shares the key surface properties relevant to toxicity with fractured quartz. The ball milling was optimized by coupling the dry and wet milling steps, using water as a dispersing agent, and varying the milling times and rotational speeds. Nanoquartz with a strong tendency to form submicrometric agglomerates was obtained. The deagglomeration with surfactants or simulated body fluids was negligible. Partial lattice amorphization and a bimodal crystallite domain size were observed. A moderate membranolytic activity, which correlated with the number of NFS, signaled coherence with the previous toxicological data. A membranolytic nanoquartz for toxicological investigations was obtained. [ABSTRACT FROM AUTHOR]

The Beckmann rearrangement (BR) of cyclohexanone oxime (CHO) to produce caprolactam (CPL) has been studied over various titanosilicates. TS-1 showed superior catalytic performance, compared to Ti-MWW, Ti-Beta and Ti-MOR. Based on the close relationship between Ti content and CHO conversion, and the Na+-exchange experiments, the silanol groups, adjacent to the "open" Ti sites, were proved to be the active centers for the BR reaction of CHO to produce CPL, in addition to those generated by defects including terminal silanols, hydrogen-bonded silanols and silanol nests. Moreover, monolithic TS-1 (M-TS-1) microspheres showed higher catalytic activity than the conventional TS-1. The diffusion properties of M-TS-1 were further enhanced via the chemical modifications to achieve longer lifetime for the Beckmann rearrangement under optimized reaction conditions. [Display omitted] • TS-1 was superior to other titanosilicates, including Ti-MWW, Ti-MOR and Ti-Beta in the Beckmann rearrangement reaction. • The catalytic performance of TS-1 was highly related to Ti content. • The silanol groups adjacent to the "open" Ti sites were one kind of the active centers. [ABSTRACT FROM AUTHOR]

• Bulky silanol (Ph 3 CO)(i PrO) 2 Si(OH) was prepared as an alternative to (tBuO)3SiOH. • It was converted into three metalosilicates with lithium, aluminum and gallium. • All compounds were characterized by single-crystal X-ray diffraction. • Their electronic structure was studied using Hirshfeld atom refinement and QTAIM. • Ring-opening polymerization was used to compare the steric bulk of the silanols. The molecular silanol (Ph 3 CO)(i PrO) 2 Si(OH) was designed to evaluate the degree of steric bulk the trityl moiety imposes on the Si–OH group. The reactivity of the silanol was evaluated by the formation of three metallosilicates with lithium, aluminum, and gallium, and their molecular structures and the degree of association were determined. Hirshfeld atom refinement or DFT calculation, and QTAIM analysis of the electron density in all compounds were used to analyze the bonding situation in the metallosilicate moieties and determine the strength of the intermolecular hydrogen bonds formed by the silanol. Finally, ring-opening polymerization of ε-caprolactone was used as another criterion for the evaluation of the steric bulk imposed by the trityl group. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • Metal hydrogen atom transfer and radical-polar crossover combined in this study. • Allylic silanol starting materials prepared by one-step condensation. • These silanols were cyclized catalytically at low temperatures to give silacycles. • DFT calculations elucidated the reason for the selectivity of these silacycles. In this study, we have developed an efficient method for silacycle synthesis using metal hydride hydrogen atom transfer (MHAT) and radical-polar crossover (RPC) mechanism. Allylic silanols were synthesized via one-step condensation and then cyclized under mild conditions using N -fluoropyridinium tetrafluoroborate (Me 3 NFPY·BF 4) as the oxidant under cobalt catalysis. This approach yielded five-, six-, and seven-membered silacycles with high selectivity, with the six-membered rings being the favored products. Density functional theory (DFT) calculations provided valuable insights into the reaction mechanisms and highlighted the role of ring strain in determining product selectivity. This study demonstrated the effectiveness of combining MHAT/RPC methodologies with silicon tethering, thus offering a robust platform for expanding the use of silicon-based strategies in synthetic chemistry. [ABSTRACT FROM AUTHOR]

The article presents an in‐depth study of the applicability of cooperative [M]‐/Organo‐catalytic systems in aerobic Si−H‐functionalization. A thorough kinetic study allowed us to identify two "complementary" catalytic systems based on earth‐abundant [M]‐catalysts and inexpensive commercially available organic catalysts. The first system, Co(OAc)2/N‐hydroxysuccinimide, made it possible to oxidize a Si−H‐group to a Si−OH‐group in a wide range of monomers, including previously unknown ones, that dramatically differ in their reactivity. However, this system failed in the case of oligomeric and polymeric substrates. This problem was solved by application of the Cu(OAc)2/N‐hydroxyphthalimide system. A wide potential for gram‐scale (50–100 g) preparation of Si−OH‐containing products with molecular architectures of different complexity was revealed using the established "substrate‐reactivity‐catalytic system" relationship. In particular, previously unknown types of dumbbell‐shaped and graft polymers were synthesized using alkoxysilanols. [ABSTRACT FROM AUTHOR]

The present work reports the changes for the mesoporous materials SBA-15 and KIT-6 associated with the structural, textural, and chemical properties when they are subjected to thermo-alkaline treatment. Despite the fact that the silica supports have not a strong affinity for CO2 adsorption, the adsorption enthalpy profiles (ΔHads) reported that the substrates subjected to the thermo-alkaline treatment (S15H and K6H) have a greater energetic affinity towards CO2 capture if compared to the precursory solids (S15 and K6). The ΔHads is − 26.7 kJ mol−1 at 0.15 mmol g−1 by supported S15H and K6H while the ΔHads is − 20. 7 kJ mol−1 and − 18.7 kJ mol−1 by K6 and S15, respectively, at the same CO2 coverage. Furthermore, the CO2 adsorption performances by the hydrolytic condensation between silica supports and the N´- (3-trimethoxysilylpropyl)diethylenetriamine (NAEPTES) or 3-aminopropiltriethoxysilane (APTES) are presented and it can be seen that the best performer for CO2 adsorption is reported for the S15HN since it is able to absorb 0.93 mmol at 0.15 atm at 318 K. Thereby, the outcomes show that the effects of porous curvature and the magnitude of the amine species are parameters to be considered, as well as the thermo-alkaline treatment, in order to improve the subsequent surface reactions on silica supports. The materials were characterized by XRD, TEM, and N2 adsorption at 77 K, NIR, and pyridine thermodesorption using Fourier Transform Infrared Spectroscopy (FTIR-Py), NMR for 29Si and 13C, DSC, and CO2 adsorption. [ABSTRACT FROM AUTHOR]

A convenient procedure for the chemoselective reduction of tertiary amides at room temperature in the presence of air and moisture using 1,3-diphenyldisiloxane (DPDS) is developed. The reaction conditions tolerate a significant number of functional groups including esters, nitriles, secondary amides, carbamates, sulfoxides, sulfones, sulfonyl fluorides, halogens, aryl-nitro groups, and arylamines. The conditions reported are the mildest to date and utilize EtOAc, a preferred solvent given its excellent safety profile and lower environmental impact. The ease of setup and broad chemoselectivity make this method attractive for organic synthesis, and the results further demonstrate the utility of DPDS as a selective reducing agent. [ABSTRACT FROM AUTHOR]

The synthesis of MCM-48 containing surfactants (CTAB and Triton X-100), ZnO, and CaO aimed to find a potential heterogeneous catalyst in the esterification of Calophyllum inophyllum oil to biodiesel. This research is important in the production of biodiesel from vegetable oils with more than 2% free fatty acids (FFA), such as Calophyllum inophyllum oil using heterogeneous catalysts. Synthesis of heterogeneous catalysts, MCM-48 and ZnO-MCM-48-CaO (ZMC), using the hydrothermal method at various calcination temperatures was conducted to find the optimum calcination temperature for the reaction. The activity of the catalyst in the reaction was determined using acid-base titration methods and GC-MS. The MCM-48 catalyst calcined at 650 °C (MCM-48/650) had a catalytic activity of 35.74% and was selective for converting linoleic acid in Calophyllum inophyllum oil to biodiesel. In addition, this catalyst was also capable of cracking the compounds contained in Calophyllum inophyllum oil into suitable hydrocarbons for biodiesel. In the esterification of vegetable oils, four heterogeneous catalysts (MCM-48/550, ZMC/550, ZMC/650, and ZMC/750) had the potential to replace conventional catalysts (H2SO4), particularly in the generation of biodiesel from Calophyllum inophyllum oil.

Single pulse, solid-state 29Si nuclear magnetic resonance (NMR) spectroscopy offers an additional method of characterisation of opal-A and opal-CT through spin-lattice (T1) relaxometry. Opal T1 relaxation is characterised by stretched exponential (Weibull) function represented by scale (speed of relaxation) and shape (form of the curve) parameters. Relaxation is at least an order of magnitude faster than for silica glass and quartz, with Q3 (silanol) usually faster than Q4 (fully substituted silicates). 95% relaxation (Q4) is achieved for some Australian seam opals after 50 s though other samples of opal-AG may take 4000 s, while some figures for opal-AN are over 10,000 s. Enhancement is probably mostly due to the presence of water/silanol though the presence of paramagnetic metal ions and molecular motion may also contribute. Shape factors for opal-AG (0.5) and opal-AN (0.7) are significantly different, consistent with varying water and silanol environments, possibly reflecting differences in formation conditions. Opal-CT samples show a trend of shape factors from 0.45 to 0.75 correlated to relaxation rate. Peak position, scale and shape parameter, and Q3 to Q4 ratios offer further differentiating feature to separate opal-AG and opal-AN from other forms of opaline silica. T1 relaxation measurement may have a role for provenance verification. In addition, definitively determined Q3/Q4 ratios are in the range 0.1 to 0.4 for opal-AG but considerably lower for opal-AN and opal-CT. [ABSTRACT FROM AUTHOR]

The Brønsted acidity of the perfluorinated trialkoxysilanol {(F3C)3CO}3SiOH is more than 13 orders of magnitude higher than that of orthosilicic acid, Si(OH)4, and even more for most previously known silanols. It is easily deprotonated by simple amines and pyridines to give the conjugate silanolates [OSi{OC(CF3)3}3]−, which possess extremely short Si−O bonds, comparable to those of silanones. [ABSTRACT FROM AUTHOR]

The reaction of sodium salts of perfluorinated tertiary alcohols R3COH with SiCl4 provided the di‐substituted dichlorosilanes (R3CO)2SiCl2 (1 a, R=CF3; 1 b, R=C6F5), the hydrolysis of which produced the corresponding silanediols (R3CO)2Si(OH)2 (2 a, R=CF3; 2 b, R=C6F5). Unlike most other dialkoxysilanediols known in the literature, 2 a and 2 b are stable towards self‐condensation at ambient conditions. In a similar way, the related disiloxanes [(R3CO)2SiCl]2O (3 a, R=CF3) and [(R3CO)2Si(OH)]2O (4 a, R=CF3) were prepared. [ABSTRACT FROM AUTHOR]

[Display omitted] • Amphiphilic surface property was obtained with introducing higher content of amino groups. • Plenty of surface silanol were simultaneously generated. • Mild drying condition is beneficial for the reserve of the silanol. • Large adsorption capacity of 2048 mg g−1 was obtained for the aqueous organic dyes. Surface-silanol-rich hybrid nano silica was synthesized with a reverse-phase microemulsion method. Exposure ratio of the surface silicon atom reached 81.4 % with the mildest drying method of air-drying at room temperature, which enabled a large amount of amino (5.8 mmol g−1) and silanol (8.0 mmol g−1) to be simultaneously generated on the surface. Abundant surface groups enabled the present material to efficiently remove various anionic dyes from the wastewater with a maximum adsorption capacity of 2048 mg g−1. The reported result supplied good reference for the designing of the adsorbent through modulating the surface groups' composition and amount. [ABSTRACT FROM AUTHOR]

The sterically hindered silicon compound 2-methyl-1,1,2,3,3-pentaphenyl-2-silapropane, C33H30Si (I), was prepared via the reaction of two equivalents of diphenylmethyllithium (benzhydryllithium) and dichloromethylphenylsilane. This bisbenzhydryl-substituted silicon compound was then reacted with trifluoromethanesulfonic acid, followed by hydrolysis with water to give the silanol 2-methyl-1,1,3,3-tetraphenyl-2-silapropan-2-ol, C27H26OSi (II). Key geometric features for I are the Si—C bond lengths that range from 1.867 (2) to 1.914 (2) Å and a τ4 descriptor for fourfold coordination around the Si atom of 0.97 (indicating a nearly perfect tetrahedron). Key geometric features for compound II include Si—C bond lengths that range from 1.835 (4) to 1.905 (3) Å, a Si—O bond length of 1.665 (3) Å, and a τ4 descriptor for fourfold coordination around the Si atom of 0.96. In compound II, there is an intramolecular C—H...O hydrogen bond present. In the crystal of I, molecules are linked by two pairs of C—H...π interactions, forming dimers that are linked into ribbons propagating along the b-axis direction. In the crystal of II, molecules are linked by C—H...π and O—H...π interactions that result in the formation of ribbons that run along the a-axis direction.

Abstract Background Silica continues to represent an intriguing topic of fundamental and applied research across various scientific fields, from geology to physics, chemistry, cell biology, and particle toxicology. The pathogenic activity of silica is variable, depending on the physico-chemical features of the particles. In the last 50 years, crystallinity and capacity to generate free radicals have been recognized as relevant features for silica toxicity. The ‘surface’ also plays an important role in silica toxicity, but this term has often been used in a very general way, without defining which properties of the surface are actually driving toxicity. How the chemical features (e.g., silanols and siloxanes) and configuration of the silica surface can trigger toxic responses remains incompletely understood. Main body Recent developments in surface chemistry, cell biology and toxicology provide new avenues to improve our understanding of the molecular mechanisms of the adverse responses to silica particles. New physico-chemical methods can finely characterize and quantify silanols at the surface of silica particles. Advanced computational modelling and atomic force microscopy offer unique opportunities to explore the intimate interactions between silica surface and membrane models or cells. In recent years, interdisciplinary research, using these tools, has built increasing evidence that surface silanols are critical determinants of the interaction between silica particles and biomolecules, membranes, cell systems, or animal models. It also has become clear that silanol configuration, and eventually biological responses, can be affected by impurities within the crystal structure, or coatings covering the particle surface. The discovery of new molecular targets of crystalline as well as amorphous silica particles in the immune system and in epithelial lung cells represents new possible toxicity pathways. Cellular recognition systems that detect specific features of the surface of silica particles have been identified. Conclusions Interdisciplinary research bridging surface chemistry to toxicology is progressively solving the puzzling issue of the variable toxicity of silica. Further interdisciplinary research is ongoing to elucidate the intimate mechanisms of silica pathogenicity, to possibly mitigate or reduce surface reactivity.

While alkyl‐substituted siloxanes are widely known, virtually nothing is known about perfluoroalkyl siloxanes and their congener species, the silanols and silanolates. We recently reported on the tris(pentafluoroethyl)silanide ion, [Si(C2F5)3]−, which features Lewis amphoteric character deriving from the pentafluoroethyl substituents and their strong electron‐withdrawing properties. Transferring this knowledge, we investigated the Lewis amphoteric behavior of the tris(pentafluoroethyl)silanolate, [Si(C2F5)3O]−. In order to examine such Lewis amphoteric behavior, we first developed a strategy for the synthesis of the corresponding silanol Si(C2F5)3OH, which readily condenses at room temperature to the hexakis(pentafluoroethyl)disiloxane, (C2F5)3SiOSi(C2F5)3. Deprotonation of Si(C2F5)3OH employing a sterically demanding phosphazene base allows the characterization of the first example of a dimeric triorganosilanolate: the dianionic hexakis(pentafluoroethyl)disilanolate, [{Si(C2F5)3O}2]2−, implies Lewis amphoteric character of the monomeric [Si(C2F5)3O]− anion. [ABSTRACT FROM AUTHOR]

While alkyl‐substituted siloxanes are widely known, virtually nothing is known about perfluoroalkyl siloxanes and their congener species, the silanols and silanolates. We recently reported on the tris(pentafluoroethyl)silanide ion, [Si(C2F5)3]−, which features Lewis amphoteric character deriving from the pentafluoroethyl substituents and their strong electron‐withdrawing properties. Transferring this knowledge, we investigated the Lewis amphoteric behavior of the tris(pentafluoroethyl)silanolate, [Si(C2F5)3O]−. In order to examine such Lewis amphoteric behavior, we first developed a strategy for the synthesis of the corresponding silanol Si(C2F5)3OH, which readily condenses at room temperature to the hexakis(pentafluoroethyl)disiloxane, (C2F5)3SiOSi(C2F5)3. Deprotonation of Si(C2F5)3OH employing a sterically demanding phosphazene base allows the characterization of the first example of a dimeric triorganosilanolate: the dianionic hexakis(pentafluoroethyl)disilanolate, [{Si(C2F5)3O}2]2−, implies Lewis amphoteric character of the monomeric [Si(C2F5)3O]− anion. [ABSTRACT FROM AUTHOR]

Inhalation of silica particles can induce inflammatory lung reactions that lead to silicosis and/or lung cancer when the particles are biopersistent. This toxic activity of silica dusts is extremely variable depending on their source and preparation methods. The exact molecular moiety that explains and predicts this variable toxicity of silica remains elusive. Here, we have identified a unique subfamily of silanols as the major determinant of silica particle toxicity. This population of "nearly free silanols" (NFS) appears on the surface of quartz particles upon fracture and can be modulated by thermal treatments. Density functional theory calculations indicates that NFS locate at an intersilanol distance of 4.00 to 6.00 Å and form weak mutual interactions. Thus, NFS could act as an energetically favorable moiety at the surface of silica for establishing interactions with cell membrane components to initiate toxicity. With ad hoc prepared model quartz particles enriched or depleted in NFS, we demonstrate that NFS drive toxicity, including membranolysis, in vitro proinflammatory activity, and lung inflammation. The toxic activity of NFS is confirmed with pyrogenic and vitreous amorphous silica particles, and industrial quartz samples with noncontrolled surfaces. Our results identify the missing key molecular moieties of the silica surface that initiate interactions with cell membranes, leading to pathological outcomes. NFS may explain other important interfacial processes involving silica particles. [ABSTRACT FROM AUTHOR]

Silanes and universal adhesives are alternatives for chemical adhesion to ceramics. These materials may share some components, so it is worth studying their performance and synergy. The objective of this study was to compare the association of a universal adhesive with two types of silane on lithium disilicate. Lithium disilicate sheets were made by lost-wax method and divided into 5 groups: silane, silane with phosphate monomers (MDP), universal adhesive, silane + universal adhesive and silane with MDP + universal adhesive. The ceramic was previously etched with hydrofluoric acid in all groups. Ten composite resin cylinders of 0.75mm diameter were attached for each group, the samples were stored 90 days in distilled water at 37ºC. A micro-shear test was performed by pulling with a wire loop. The highest values of the study were obtained by the groups where silanes were used prior to the universal adhesive. Within the limitations of this study, it was concluded that the application of a silane followed by a universal adhesive is essential. Silane with MDP appears to be less efficient compared to a silane without this monomer in promoting chemical adhesion to lithium disilicate (LDS). [ABSTRACT FROM AUTHOR]

Thermal drying of silanes is used for allows the evaporation of vehicles and accelerates condensation on the ceramic surface. The objective of this study was to determine the effect of a thermal drying treatment of two types of silane on the bond strength between a lithium disilicate and a resin cement. Sheets were obtained from a lithium disilicate CAD-CAM block. All ceramic sheets were conditioned with 10% hydrofluoric acid and divided in four groups: The RXR and MNR groups, corresponding to a prehydrolyzed silane and a prehydrolyzed silane with 10-MDP respectively, dried at room temperature. Thermal drying was applied to the RXH and MNH groups, for the same silanes. The hot air was constantly fired for 15 seconds until it reached 100ºC. Tubes of medical grade silicone were positioned on the ceramic surface and filled with dual resin cement, and them polymerized with light LED. A test micro-shear bond strength was used to determinate bond strength. The highest value of bond strength was obtained by the MNH group and the lowest value was obtained by the SXR group. Within the limitations of the present study, it can be concluded that the thermal drying treatment applied to both silanes demonstrates a positive influence on the adhesion values between a lithium disilicate-based ceramic and a dual resin cement. [ABSTRACT FROM AUTHOR]

Auf der inneren Porenoberfläche des calcinierten Zeoliths SSZ‐70 wurden Nester mit drei Silanolgruppen gefunden. 2D‐1H‐Doppel‐/Tripelquanten‐Einquanten‐Korrelations‐NMR‐Experimente erlauben eine eindeutige Identifikation dieser Silanoltriadenester. In der hydrothermal synthetisierten Probe zeigen sie auch eine enge Nachbarschaft zu den Strukturdirigenten (structure directing agents, SDAs), den N,N′‐Diisobutylimidazolium‐Kationen, wobei die Defekte zum Ladungsausgleich hier negativ geladen sind (Silanoldyade und eine geladene SiO−‐Siloxygruppe). Infolge der energetisch ungünstigen Ringspannung findet keine Kondensation der Silanolgruppen zu Dreiringen während der Calcination und Entfernung des SDA statt. Dahingegen sind Tetradenester, die durch Extraktion von Bor aus B‐SSZ‐70 an unterschiedlichen Stellen eigentlich entstehen müssten, nicht stabil, und Silanolkondensation findet statt. Untersuchungen mittels Infrarotspektroskopie von adsorbiertem Pyridin zeigen eine erhöhte Acidität der Silanoltriaden, was wichtige Auswirkungen in der Katalyse nahelegt. [ABSTRACT FROM AUTHOR]

Structural, chemical, morphological, and hydrophilic surface characteristics of SBA-15 silica synthesized by hydrothermal method in an autoclave and in a microwave-heated reactor were analyzed in this work. The influence of time and temperature on these characteristics was investigated. Materials were characterized by textural analysis (BET), FTIR, TGA, XRD, goniometer contact angle, SEM, and TEM. It was possible to obtain SBA-15 silicas assisted by microwave heating irradiation with short-time synthesis (0.5–8 h) compared with the hydrothermal classic method (24 h). Materials presented surface area between 650 and 850 m2 g−1. Through the XRD and TEM results, it was observed that mesostructured materials with two-dimensional, long-range, and hexagonal ordered channels are characteristic of SBA-15. This study showed that heating by microwave irradiation during silica synthesis generates materials with a greater amount of silanol groups. It is possible to control the surface properties of SBA-15 during the microwave-assisted synthesis through temperature tuning. Higher temperature provided SBA-15 with higher hydrophilicity. Highlights: SBA-15 synthesis by MW reduces significant reaction time. SBA-15 synthesized in MW at 80 °C showed 805 m2 g−1 of specific surface area. Heating by MW in the silica synthesis generates materials with higher hydrophilicity. [ABSTRACT FROM AUTHOR]

Copyright of Silicone Material is the property of Silicone Material Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

• Peak tailing of sulfinic acids and carboxylic acids investigated in acidic MP RPLC. • The neutral protonated form of the acids was found responsible for peak tailing. • No correlation between tailing and hydrophobic subtraction model column parameters. • Vicinal silanol pair is a likely cause based on acid wash and DFT calculations. Silanophilic interactions are a primary contributor to peak tailing of acidic pharmaceutical compounds, thus a thorough understanding is especially important for reversed-phase liquid chromatography (RPLC) method development. Herein, a sulfinic acid compound that exhibited severe peak tailing in RPLC with acidic mobile phases was carefully studied. Results indicated that the neutral protonated form of the sulfinic acid is involved in the strong interaction that leads to peak tailing, but that tailing can be mitigated with a blocking effect achieved through use of acetic acid modifier in the mobile phase. Peak tailing was also observed with other structurally-similar sulfinic acids and carboxylic acids but was, in general, less severe with the latter. The Hydrophobic Subtraction Model (HSM) was applied to six commercial C18 columns that exhibited different tailing behaviors for the sulfinic acid compound in attempts to identify key sites of interaction within the stationary phase. A combination of heated acid column wash experiments and density functional theory (DFT) calculations indicate that the differential interactions of the acids with vicinal silanol pairs in the stationary phase play a major role in peak tailing. [ABSTRACT FROM AUTHOR]

The catalytic activity, kinetics, and quantification of H‐bonding ability of incompletely condensed polyhedral oligomeric silsesquioxane (POSS) silanols are reported. POSS‐triols, a homogeneous model for vicinal silica surface sites, exhibit enhanced H‐bonding compared with other silanols and alcohols as quantified using a 31P NMR probe. Evaluation of a Friedel–Crafts addition reaction shows that phenyl‐POSS‐triol is active as an H‐bond donor catalyst whereas other POSS silanols studied are not. An in‐depth kinetic study (using RPKA and VTNA) highlights the concentration‐dependent H‐bonding behavior of POSS‐triols, which is attributed to intermolecular association forming an off‐cycle dimeric species. Binding constants provide additional support for reduced H‐bond ability at higher concentrations, which is attributed to competitive association. POSS‐triol self‐association disrupts H‐bond donor abilities relevant for catalysis by reducing the concentration of active monomeric catalyst. [ABSTRACT FROM AUTHOR]

Ca-α-SiAlON powder was prepared by carbothermal reduction nitridation process at nitrogen atmosphere without using high pressure and long holding time. The precursor was prepared by a novel colloidal sol-gel process consisting of silica, alumina, calcium oxide and carbon. The obtained powders were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). The XRD and SEM analysis results revealed that by heating at 1200 °C for 2 h, spherical particles consisting of amorphous calcium aluminosilicate liquid phase were formed. With increasing temperature to 1360 °C and held for 2 h, the spherical particles with the dominant phase of O–SiAlON were observed. Finally, as the temperature climbed to 1500 °C and held for 2 h, spherical particles disappeared and Ca-α-SiAlON was formed. The XRD analysis of the products showed that with increasing temperature from 1360 °C to 1500 °C, O–SiAlON, β-SiAlON and Ca-α-SiAlON were formed, respectively, and colloidal sol-gel method, due to the high homogeneity of the reactants, had a significant role in increasing the purity of Ca-α-SiAlON. [ABSTRACT FROM AUTHOR]

The sterically hindered silicon compound 2-methyl-1,1,2,3,3-penta­phenyl-2-sila­propane, C33H30Si (I), was prepared via the reaction of two equivalents of di­phenyl­methyl­lithium (benzhydryllithium) and di­chloro­methyl­phenyl­silane. This bis­benzhydryl-substituted silicon compound was then reacted with tri­fluoro­methane­sulfonic acid, followed by hydrolysis with water to give the silanol 2-methyl-1,1,3,3-tetra­phenyl-2-silapropan-2-ol, C27H26OSi (II). Key geometric features for I are the Si—C bond lengths that range from 1.867 (2) to 1.914 (2) Å and a τ4 descriptor for fourfold coordination around the Si atom of 0.97 (indicating a nearly perfect tetra­hedron). Key geometric features for compound II include Si—C bond lengths that range from 1.835 (4) to 1.905 (3) Å, a Si—O bond length of 1.665 (3) Å, and a τ4 descriptor for fourfold coordination around the Si atom of 0.96. In compound II, there is an intra­molecular C—H···O hydrogen bond present. In the crystal of I, mol­ecules are linked by two pairs of C—H···π inter­actions, forming dimers that are linked into ribbons propagating along the b-axis direction. In the crystal of II, mol­ecules are linked by C—H···π and O—H···π inter­actions that result in the formation of ribbons that run along the a-axis direction. [ABSTRACT FROM AUTHOR]

The surface reactivity of waste glass powder (WGP) and sugarcane bagasse ash (SCBA) was evaluated in the partial replacement of cement using simple experimental procedures. As a blend, WGP and SCBA showed an excellent dosage at 5 wt % of each, and the availability and reactivity of silanol groups seem to have been the most important aspect in allowing the growth of calcium silicate hydrate (CSH) onto the quartz surface. XRD and SEM analyses have indicated that WGP and SCBA did not dissolve in the reaction and may have worked as a platform for the conversion of Ca(OH) 2 into CSH. In addition, amorphous WGP was converted into quartz phase during hydration step. Unlike SCBA, whose surface is formed by "pure" silanol groups, WGP may possess one unit of CaO 6 for each three groups of SiO 4 in its structure and this may have enhanced the ability of the WGP surface to convert Ca(OH) 2 into CSH. BET and BJH sorption methods showed that SCBA presented higher specific area and pore volume. However, XRF analysis showed that WGP possesses an important participation of calcium, which may have contributed for the enhancement of its acid-base features. Separately, both waste materials were able to replace at least 10 wt % of cement without compromising its compressive strength. In general, the results indicated the potential of those waste to be used in cement replacement and increase the raw material options in the cement production process. Image 10 • WGP presented high content of CaO, caused enhancement in its surface reactivity. • It was possible to replace up to 20 wt % of cement by WGP and SCBA. • Amorphous WGP was fully converted into crystalline quartz during the reaction. • The residual organic matter helped to promote higher specific area in SCBA. • The blend WGP/SCBA yielded high content of Ca(OH) 2 , preventing early shrinkage. [ABSTRACT FROM AUTHOR]