Si Linkages Research Articles

Stability and Surface Functionalization of Plasmonic Group 4 Transition Metal Nitrides

Plasmonic transition metal nitrides (TMNs) have emerged as a low‐cost and thermally and chemically robust alternatives to noble metals. While their superior thermal properties have been established, their chemical properties on the nanoscale haven’t been as well studied. Herein, the oxidative stability over time under ambient conditions and colloidal stability as function of pH was explored for plasmonic TiN, ZrN and HfN nanoparticles. It was discovered that the TMN nanoparticles made via solid‐state method had a narrow pH stability range between 2 – 3. Under highly acidic conditions, the particles underwent dissolution and at pH ≥ 4, they aggregate and precipitate from the solution. Additionally, TiN nanoparticles had poor oxidative stability and oxidized to TiO2 after ~40 days. 3‐Aminopropyltriethoxysilane (APTES) and dimethylsilane coated TMNs were synthesized to yield water and organic solvent dispersible particles, respectively. These functionalized colloidal suspensions showed enhanced oxidative stability over 60 days and the APTES coating widened the pH stability window of TMNs to include physiological pH. This study shows that surface functionalization using M–O–Si linkages (where M = Ti, Zr, or Hf) can greatly enhance the stability, dispersibility and therefore applicability of plasmonic TMN nanoparticles.

Effect of structural disorder induced by external irradiation with heavy ions on the alteration of a four oxide borosilicate glass

The irradiation of glass by heavy ions induces structural damage, generally leading to a decrease in its chemical durability whose amplitude strongly depends on the glass chemical composition. Here, we investigate the effects of irradiation by 7 MeV Au ions (simulating the main ballistic effects induced by self-irradiation in nuclear glass) on the behavior of a 4-oxide borosilicate glass in both the initial and residual dissolution regimes. The comparison between irradiated and non-irradiated glasses provides insights into the predominant atomic mechanisms governing glass alteration processes. The most pronounced effect is observed on interdiffusion in acidic conditions, with the rate increased by more than an order of magnitude for the irradiated glass. We show that both the interdiffusion regime and the residual regime are controlled by the hydrolysis of the B—O—Si linkages, whereas under initial dissolution rate regime in basic conditions the rate-limiting step becomes the hydrolysis of Si—O—Si linkages. Overall, the observations suggest structural disorder due to external irradiation by Au ions primarily affects the kinetics of glass alteration without changing the fundamental nature of the limiting reactions.

Advancing silicon-based Li-ion batteries: enhanced stability and performance through carbon-coated Si and rGO linkage

Advancing silicon-based Li-ion batteries: enhanced stability and performance through carbon-coated Si and rGO linkage

Deciphering the structural origins of high sulfur solubility in vanadium-containing borosilicate glasses

The addition of V2O5 has been long known to increase the sulfur (as SO42-) solubility in borosilicate glasses. However, the mechanism governing this effect is still unknown. Although several studies have been published in the past two decades attempting to decipher the structural origins of increasing sulfur solubility as a function of V2O5 in borosilicate glasses, most of these studies remain inconclusive. The work presented in this paper attempts to answer the question, “Why does V2O5 increase sulfur solubility in borosilicate glasses?” Accordingly, a series of melt-quenched glasses in the system [30 Na2O – 5 Al2O3 – 15 B2O3 –50 SiO2](100-x) – xV2O5, where x varies between 0 – 9 mol.%, have been characterized for their short-to-intermediate range structure and the redox chemistry of vanadium using 11B, 27Al, 51V MAS NMR, Raman, and XPS spectroscopy. The impact of V2O5 on sulfur solubility in glasses has been followed by ICP-OES. The addition of ≤ 5 mol.% V2O5 results in a linear increase in sulfur solubility in the investigated glass system. Based on the results, we hypothesize that adding vanadium to the glasses increases their network connectivity, but reduces the network rigidity by replacing stronger Si–O–Si linkages with weaker Si–O–V linkages and forming (VO3)n-single chains. These modifications to the glass structure increase the flexibility of the network, thus making it possible to accommodate SO42− in their voids/open spaces.

New waterborne polyurethane/silica hybrid dispersions based on natural rubber and prepared by sol-gel process: Effects of amino alkoxy-silane and nano-silica contents on dispersion stability and films properties

A bio-polyol based issued from natural rubber was successfully synthesized for the preparation of waterborne polyurethane (WPU) and hybrid waterborne polyurethane (HWPU). The WPU was prepared by prepolymer process from hydroxyl telechelic natural rubber (HTNR), using dimethylolpropionic acid (DMPA) and hexamethylene diisocyanate (HDI). A series of new HWPUs was successfully synthesized by the sol-gel process, using 3-aminopropyltriethoxysilane (APTES) as a coupling agent. Effects of the amount of APTES (0.8–1.3%wt) on properties of the HWPU were investigated. The WPU and HWPU with APTES content ranging from 0.8 to 1.0%wt showed well-dispersed particles with a long shelf life exceeding 3 months. The particle size increased with APTES content. In addition, the HWPUs showed increasing zeta potential with APTES content. The morphology and shape of particles were observed from Transmission Electron Microscopy (TEM) imaging. The chemical structures in WPU and the series of HWPUs were confirmed by FT-IR. The tensile strength of HWPU was improved on incorporating Si–O–Si linkages into the WPU backbone through a sol-gel process. Moreover, effects of the amount of nano-silica (0–15%wt) on properties of the HWPU/silica were investigated. TEM images demonstrated miscibility and specific interactions between HWPU and the dispersed nano-silica particles. The morphology of HWPU/silica films was characterized by Scanning electron Microscopy (SEM), and the elemental analysis of surfaces was carried out by Energy Dispersive X-ray Spectroscopy (EDX). Additionally, nano-silica content enabled the hydrophobicity of HWPU/silica films, leading to water repellence and good water resistance. Moreover, the mechanical and thermal properties were significantly improved on increasing nano-silica content. The investigation demonstrated that using HTNR polyol in the formulation of a new HWPU dispersion is an environmentally friendly alternative, in which performance of the film is improved on adding nano-silica via a sol-gel process. The novel films have potential for coating applications.

A Cyclic Phosphonium Ion with an Asymmetrically Substituted Selenide‐Stabilized Silicon Center: Synthesis, Structure, and Substituent Effects

AbstractA new heterocyclic four‐membered CPSeSi cation was synthesized in its racemic form by B(C6F5)3‐mediated ring‐closing reaction starting from the hydrosilane precursor. The cation has an asymmetrically substituted silicon center, which is stabilized by a selenium–silicon bond. The phosphonium hydroborate and its precursor were characterized by single‐crystal X‐ray diffraction analysis and NMR spectroscopy. 77Se, 31P, and 29Si NMR spectroscopic parameters proved to be sensitive probes for determining small electronic changes around the silylium‐type center. Density functional theory (DFT) calculations of the ring‐opening energy of the selenium‐based cation gave insight into the stability of the Se–Si bond and revealed a stronger intramolecular stabilization of the silicon atom compared to a coordinating phosphane sulfide function. For the first time, the influence of a C6F5 group at the silicon atom of these type of cations was also investigated, showing a slightly increased stabilization of the Se–Si linkage in the cyclic selenium‐based cation.

The Addition of TiO2 Ratios in SiO2–TiO2 Nanocomposite by Sonochemical Process for the Enhancement in Self-cleaning Property

This research aims to study self-cleaning property for removing atmosphere pollutants on the substrate surface. Thus, the modification of nanocomposite material for self-cleaning property is an important challenge to solving the organic pollutants on various surfaces. Nanocomposite material in this work is focused on SiO2-TiO2 based metal oxide materials that synthesized by sonochemical process with the precursors of tetraethyl orthosilicate (TEOS) and titanium isopropoxide (TTIP). The crucial parameter of different amount of titanium ratios in SiO2 matrix is related to the improvement on structural and self-cleaning properties. The ratios of Si:Ti precursor were varied at 1:0.1, 1:0.5, 1:1 and 0:1 (pure TiO2). The structural phase of SiO2-TiO2 nanocomposite powder was detected by X-ray diffraction technique (XRD). Chemical bonding structure in SiO2-TiO2 nanocomposite was analysed by Fourier transform infrared spectrophotometer (FTIR). Surface morphology of SiO2-TiO2 nanocomposite was monitored by field emission scanning electron microscope (FE-SEM). SiO2-TiO2 nanocomposites synthesized by sonochemical process were in form of composite powder with the spherical SiO2 particles and decorated TiO2 on its surface. After that, the products of SiO2-TiO2 nanocomposite with different TiO2 ratios were mixed with TES 40 WN solution and deposited on glass slides substrate by spray coating to study its hydrophilic property by contact angle method. The contact angle of SiO2-TiO2 nanocomposite film was reduced with the increase of Ti ratio in SiO2 matrix resulting to the development of hydrophilic surface on substrate. The influence of TiO2 in SiO2 matrix on self-cleaning and property would be improved by hydroxyl groups on the composite surface corresponding to Ti–O–Si linkages. For self-cleaning property, Si:Ti ratio at 1:1 in SiO2-TiO2 nanocomposite showed the optimized condition with decreasing contact angle at 28.97 degree in 60 min after UVA irradiation.

Cation field‐strength effects on ion irradiation‐induced mechanical property changes of borosilicate glass structures

AbstractWe examine the impact of the glass network‐modifier cation field strength (CFS) on ion irradiation‐induced mechanical property changes in borosilicate (BS) glasses for the ternary M2O–B2O3–SiO2 systems with M = {Na, K, Rb} and the quaternary [0.5M(2)O–0.5Na2O]–B2O3–SiO2 systems with M = {Li, Na, K, Rb Mg, Ca, Sr, Ba}. 11B nuclear magnetic resonance (NMR) experiments on the as‐prepared BS glasses yielded the fractional population of four‐coordinated B species (B[4]) out of all {B[3], B[4]} groups in the glass network, along with the fraction of B[4]–O–Si linkages out of all B[4]–O–Si/B bonds. Both parameters correlated linearly with the (average) CFS of the M+ and/or {M(2)+, Na+} cations. Both the nanoindentation‐derived hardness and Young's modulus values of the glasses reduced upon their irradiation by Si2+ ions, with the property deterioration decreasing linearly with increasing Mz+ CFS, that is, for higher Mz+⋅⋅⋅O interaction strength. The irradiation damage of the glass network also increased linearly with the fraction of B[4]–O–Si linkages, which are the second weakest in the structure after the Mz+⋅⋅⋅O bonds. Our results underscore the advantages of employing BS glasses with high‐CFS cations for enhancing the radiation resistance for nuclear waste storage.

Ethanol dehydrogenation to acetaldehyde over a Cuδ+-based Cu-MFI catalyst

Copper catalysts have been extensively investigated for the dehydrogenation of ethanol to acetaldehyde. However, identifying the essential active sites for this reaction is difficult because of the complex coordination structure and variable valences of the Cu species during the reaction. The stability of the Cu catalysts in the reaction also needs to be substantially improved. In this study, Cu-MFI, a well-defined Cu-based Lewis acid catalyst, was prepared using a post-acid treatment method for ethanol dehydrogenation. Different from the widely reported Cu+ and Cu0 species accounting for the activity of Cu catalysts, conditional experiments and in situ characterizations revealed that the highly dispersed Cuδ+ (1 <δ < 2) species on the MFI support are the essential active sites for ethanol dehydrogenation. Due to the strong interaction between Cu and silica via the Cu–O–Si linkage, the Cuδ+ species were very stable in the reaction and played the role of a Lewis acid catalyst in promoting ethanol activation and dehydrogenation. Over the optimal catalyst 5%Cu-MFI-deCu, 95% selectivity of acetaldehyde and approximately 87% ethanol conversion were obtained at 250 °C and a weight hourly space velocity of 0.64 h−1 in 120 h time on stream.

Robert C. West (1928–2022): A Giant in Organosilicon Chemistry, Cosmopolitan, Mountain Climber and Pilot

Robert C. West (1928–2022): A Giant in Organosilicon Chemistry, Cosmopolitan, Mountain Climber and Pilot

Biomolecule-inspired synthesis of framework zinc in MFI zeolite for propane dehydrogenation

The development of environment-friendly, stable, and efficient catalysts to substitute Pt and Cr-based catalysts for propane dehydrogenation (PDH) is of great importance but challenging to make. Herein, we use zinc gluconate (Zn(C6H12O7)2), an organometallic biomolecule, to embed Zn atoms into pure silica MFI zeolite framework (Zn-MFI) for PDH reaction. Due to the protection by the glucosyl groups in Zn(C6H12O7)2, Zn atoms can be well embedded into the MFI zeolite framework. Multi-scale characterizations (e.g., Cs-corrected HAADF-STEM, FTIR, UV–vis, and NMR spectroscopy) and DFT calculations demonstrate the formation of uniform tetrahedrally coordinated Zn sites in the MFI zeolite framework with two Zn–O–Si and two Zn⋯OH–Si linkages ({(≡SiO)2Zn(HO–Si≡)2}). The Zn-MFI zeolites are used for PDH, exhibiting excellent catalytic performance. Pyridine-FTIR, C3H6-FTIR, C3H6-TPD/MS, and contrast experiments reveal the unique Zn active sites in Zn-MFI zeolites can promote the C–H bond cleavage and weaken the propylene adsorption, thus guaranteeing high activity and selectivity for PDH. The excellent catalytic performance of Zn-MFI zeolites indicates their promising utilization in industry.

Effects of N2 and O2 plasma treatments of quartz surfaces exposed to H2 plasmas

This paper presents a study of methods for reducing the erosion of SiO2 in a high-power density (10–40 W/cm3), purely inductive H2/Ar plasma, using a toroidal transformer-coupled plasma source operated at 0.5 Torr. Quartz samples were exposed to plasma densities of 1–3 × 1013 cm−3 and H atom temperatures of 4000–8000 K [electron densities and H translational temperatures were measured by Stark and Doppler broadening of H Balmer-β (Hβ) emission at 486.1 nm]. Laser interferometry was employed to monitor time-resolved temperatures of the quartz substrate. Etching rates were measured by stylus profilometry, and roughness was quantified by atomic force microscopy (AFM). For 5 min discontinuous H2/Ar plasma exposure (0.5 Torr, 16 W/cm3, 1 min plasma-on, 9 min plasma-off per cycle with five cycles), the etching rate during the plasma-on time was 224 nm/min. This was much higher than the 16 nm/min rate observed for a continuous 1 h H2/Ar plasma exposure. This trend was ascribed to the higher substrate temperatures reached with continuous plasma operation and a negative dependence of the etching rate on temperature, described by an activation energy of roughly −5 kcal/mol. When exposure to 1 min H2/Ar plasmas was alternated with 1 min O2/Ar plasma treatments and 12 min plasma-off periods, the etching rate was reduced to near-zero and the extent of surface roughness was reduced by at least fivefold. N2/Ar plasma treatments were less effective in reducing the etching rate (to 57 nm/min), while the roughness to the surface caused by exposure to the H2/Ar 1 min plasmas was nearly eliminated. A mechanism for the erosion process is proposed, involving the penetration of H atoms below the surface where they insert into Si–O–Si linkages to form SiH and SiOH groups. This opening of the SiO2 network allows easier penetration of H, further bond breakage, and crack propagation that eventually leads to the shedding of small silica particles. Periodic exposure to O atoms hydroxalizes these subsurface regions and subsequently reforms Si–O–Si linkages, accompanied by the formation of H2O that presumably diffuses to the surface and desorbs.

Cobalt Silylenes as Platforms for Catalytic Nitrene‐Group Transfer by Metal–Ligand Cooperation.

A cobalt silylene (Co=Si) linkage enables a distinct metal/ligand cooperative activation of an organic azide, where nitrene transfer occurs to and from the Co⋅⋅⋅Si linkage without ligand dissociation from the 18-electron cobalt center. This process utilizes the orthogonal binding affinities of the silicon and cobalt sites to avoid CO poisoning that would otherwise inhibit reactivity, leading to significantly improved catalytic isocyanate generation compared with related systems. The dual-site approach demonstrates the potential of metal/main-group bonds to access new and efficient catalytic pathways.

Cobalt Silylenes as Platforms for Catalytic Nitrene‐Group Transfer by Metal–Ligand Cooperation.

A powerful approach to cooperative group-transfer catalysis is demonstrated using the Co=Si bond of a cobalt silylene to provide two distinct sites for substrate activation. The orthogonal selectivity of the Co and Si centers enables efficient nitrene-group transfer to carbon monoxide by avoiding poisoning that would result from substrates competing for a single reactive site.

Homogeneous sub-nanophase network tailoring of dual organosilica membrane for enhancing CO2 gas separation

Dual organosilica membranes were synthesized to investigate the effects of differing molar ratios of bis (triethoxysilyl) ethane (BTESE)/glycidyl Polyhedral oligomeric silsesquioxane (glycidyl POSS) on the membrane performance. The reaction mechanism behind CO2 capture using the organosilica membranes under ambient conditions was also investigated. A facile in-situ framework synthesis approach was introduced for the copolymerization reaction of dual organosilica. BTESE has a smaller molecular size than that of glycidyl POSS, and the Si–C–C–Si linkage is the main structure contributing to its high CO2 affinity. Additionally, the dimensional and mechanical stability were maintained at high doping levels owing to the inclusion of glycidyl POSS. Consequently, the free volume of the resulting hybrid networks increased owing to the cage structure and high cross-link density, which was attributed to the coexistence of epoxy ring-opening polymerization and condensation polymerization. The characterization and permeation tests revealed that the 1B0.5P gel with the best copolymerization effect exhibits a high CO2 permeance of 5.74 × 10−8 mol m−2 s−1 Pa−1 at 25 °C and ideal selectivity values of 11.61, 37.55 and 63.67 for CO2/H2, CO2/CH4 and CO2/N2, respectively. Moreover, a new analytical technique was proposed to investigate the surface microstructure of organosilica membranes for the first time using optical microscopy.

Effect of V2O5 on structural and elastic properties of alkali silicate SiO2–Na2O–NaF glasses

A series of V2O5–doped alkali silicate SiO2–Na2O–NaF glasses were prepared by the melt quenching technique. Amorphousness of the samples was characterized using powder X-Ray diffraction (XRD) analysis; and the structural role of V2O5, Na2O and NaF in the silicate network was explored using Fourier Transform Infrared (FTIR) spectroscopy. Elastic properties, determined by using ultrasonic technique, were correlated with the compositional and structural parameters as well as the excess molar volume. The substitution of SiO2 by Na2O and NaF in the base SiO2–Na2O–NaF glass resulted in the breaking of Si–O–Si linkages and creation of NBOs, whereas the addition of V2O5 resulted in formation of VO5 structural units and weak V–O–V and Si–O–V linkages. Makishima-Mackenzie's theory is valid for pure SiO2 and V2O5–free glasses. The discrepancy between theoretical and observed elastic moduli and micro-hardness of V2O5–doped glasses was discussed in details.

Experimental evidences and theoretical calculations on phenanthrene degradation in a solar-light-driven photocatalysis system using silica aerogel supported TiO2 nanoparticles: Insights into reactive sites and energy evolution

Quantitative identification on reactive sites of target organic molecule during photocatalysis can help to get deep insight into the pollutant degradation pathway and energy evolution process. In this study, a new class of silica aerogel supported TiO2 (TiO2/SiO2) photocatalysts were fabricated via a two-step approach, and applied for adsorption and photocatalytic degradation of phenanthrene. Anatase crystalline structure was formed upon calcination at 400 and 600 °C, while mixed crystal interphases of anatase and rutile were generated at 800 °C (anatase:rutile = 0.67:0.33). The higher calcination temperature resulted in better crystallinity of TiO2, higher photocatalytic activity, and reduced adsorption affinity toward phenanthrene. TiO2/SiO2-800 (TiO2/SiO2 calcined at 800 °C) showed minimal phenanthrene uptake (~5.2%) but the strongest photocatalytic activity, and it was able to completely degrade phenanthrene within 3 h. The SiO2 aerogel component in the composite enabled the pre-concentration of phenanthrene on the photoactive sites, while the nanoscale mixed-phases of anatase and rutile of TiO2/SiO2-800 act as an efficient transfer medium for photo-induced charge carriers. Moreover, the formed Ti–O–Si linkage in TiO2/SiO2-800 induced formation of Ti3+ under solar light irradiation, promoting photoexcited electron trap and separation of electron-hole pairs. Based on the degraded phenanthrene intermediates/products, theoretical calculations according to the density functional theory (DFT) reveal that the atoms of phenanthrene with high electrophilic Fukui index (f-) are the most reactive sites towards the radicals. Potential energy surface profile for phenanthrene degradation further reveals the intermediates energy evaluation via radicals attack.

Effect of silylating agents on the superhydrophobic and self-cleaning properties of siloxane/polydimethylsiloxane nanocomposite coatings on cellulosic fabric filters for oil-water separation.

A new facile approach for preparing two nonfluorinated hybrid organic–inorganic siloxane/polydimethylsiloxane nanocomposite coatings for cotton fabrics is presented using two distinct silylating agents. The first coated fabric was prepared predominantly via trimethylsilyl modification using hexamethyldisilazane (HMDS) while higher amounts of trimethoxy(octadecyl)silane (TMOS) further enhanced the superhydrophobicity of the second coating matrix. Unlike HMDS with substituted silyl (Me3Si) groups, TMOS consists of hydrolysable trimethoxy silyl ((MeO)3Si) chemical groups that allowed for the formation of nanosilica with Si–O–Si linkages needed to foster stable coatings. After characterization and testing, these coated fabrics demonstrated varying responses to harsh solvents and thermal conditions. Both sets of coated fabrics exhibited unique capacities for self-cleaning and oil–water separation as superhydrophobic filters due to (a) their low surface energy silylated hybrid polysiloxane chemical groups, (b) their highly reduced surface wettability and (c) nanopatterned surface morphologies. In this study, coated superhydrophobic cotton fabrics revealed a higher static aqueous contact angle of more than 150° and sliding hysteresis angle of less than 5°. Coated fabrics with 30 mg TMOS/10 mg HMDS (CMF3) and 30 mg HMDS/10 mg TMOS (CTF3) exhibited optimal superhydrophobicity. Both fabrics also retained percentage separation efficiencies over 90% for both chloroform–water and toluene–water mixtures. However, CTF3 displayed with a recorded separation efficiency less than 90° after five filtration cycles.

Density Functional Theory Calculations of the Adsorption of Cytosine on Si(100)

We have performed density functional theory (DFT) calculations to investigate the adsorption structures of cytosine on Si(100). Multiple adsorption configurations that could result from Lewis acid–base reactions or cycloadditions were optimized, and the structural and energetic parameters of the obtained adsorption structures were compared. Row‐bridged bidentate configurations with SiOCNCNSi linkages to two silicon atoms in adjacent dimer rows were found to be more stable than other configurations. The SiN bond was formed by NH dissociative adsorption, while the SiO bond was dative. In the monodentate structures, the CH or NH dissociative adsorption structures were more energetically favorable than the datively bonded ones. Cycloaddition through the π‐electrons of the CN or CC bonds of the cytosine ring resulted in relatively unstable adsorption products.

Synthesis and characterization of composite SiO2–Al2O3–Fe2O3 core–shell microspheres

The aim of this study was the synthesis and structural characterization of SiO2–Al2O3 microspheres with SiO2 core and (100 − x)Al2O3·xFe2O3 (x = 0, 5, and 10 mol%) shell. Smooth spherical silica particles of uniform size around 1 μm have been synthesized as core material based on the Stober method. In order to enhance the specific surface area, the silica particles were coated with a thin nanostructurated shell, about 15 nm, of aluminum and iron oxides (100 − x)Al2O3·xFe2O3 (x = 0, 5, and 10 mol%). The embedding of iron oxide in the covering shell was related to potential applications of these composite biomaterials for contrast enhancement in magnetic resonance imaging (MRI) and at the same time for local treatments of cancer by hyperthermia. The XRD results point out the amorphous structure of the obtained core–shell particles. The TEM images evidence continuous shell coating of silica spherical microparticles and the XPS analysis of the surfaces prove the occurrence of iron oxide on the outermost layer of the microspheres. Both FTIR and XPS results evidence the formation of Al–O–Si linkage proving that Al2O3 and SiO2 are chemically bonded in the investigated core–shell microspheres.