Occurrence of Pseudotetragonal Mullite

29Si MAS NMR and FTIR study of inorganic–organic hybrid gels

Submicrometer spherical particles of mullite powder were synthesized by ultrasonic spray pyrolysis of emulsion and solutions, using tetra-ethyl-orthosilicate (TEOS) or silicic-acid and Al(NO3)3 · 9H2O as initial compounds. Crystallization of mullite phase was determined by differential thermal (DT), thermogravimetric (TG), infrared (IR), and x-ray analyses. The synthesis of mullite from TEOS emulsion occurs by crystallization of γ–Al2O3 (or Al, Si-spinel) from the amorphous phase and its subsequent reaction with amorphous SiO2, as well as by crystallization of pseudotetragonal mullite below 1000 °C and its subsequent phase transformation into orthorhombic mullite. In the powders produced from silicic acid solutions, synthesis of mullite occurs only by crystallization of γ–Al2O3 between 900 and 1000 °C and its further reaction with amorphous SiO2 between 1100 and 1200 °C. Particle formation mechanism depended directly on the initial emulsion or solution preparation, i.e., on the phase separation in the emulsion and on the silicic-acid crosslinking conditions.

A continuous gas‐phase process under atmospheric pressure for tailoring Pd/SiO2 catalyst particles is described and characterized. Emphasis is placed on controlling the size and number density of Pd nanodots on the surface of the carrier particle. In the first step, sub‐micrometer‐sized SiO2 support particles are generated continuously in a flow reactor by chemical vapor synthesis (CVS) from tetraethyl(ortho)silicate (TEOS). A process‐integrated method is described to vary the surface concentration of hydroxyl groups on the SiO2 between about 1 and 6 OH groups per nm2, by adjusting the synthesis conditions. In a second step, Pd nanodots are deposited onto the SiO2 by metal–organic (MO)CVD of Cp(allyl)Pd [(η3‐allyl)(η5‐cyclopentadienyl)palladium]. The median diameter of the Pd nanodots was varied between about 1.3 and 3 nm (σg ∼1.2) by adjusting the precursor concentration in the gas phase. It is shown that the number density of the Pd islands varied in proportion to the density of hydroxyl groups on the SiO2 in the range 0‐12 Pd islands per 100 nm2 of carrier particle surface.

Disordered fluorite-related solid solutions ${(A{\mathrm{F}}_{2})}_{1\ensuremath{-}x\ensuremath{-}y}$ ${({\mathrm{Ln}}^{\ensuremath{'}}{\mathrm{F}}_{3})}_{x}$ ${({\mathrm{Ln}}^{\ensuremath{''}}{\mathrm{F}}_{3})}_{y}$, where $A=\mathrm{Ca}$, Sr, Ba; ${\mathrm{Ln}}^{\ensuremath{'}}=\mathrm{Er}$, Tm, Yb; ${\mathrm{Ln}}^{\ensuremath{''}}=\mathrm{Lu}$, Y; and $x⪡y=0.001--0.4$, were studied by both optical detection and conventional electron paramagnetic resonance (EPR) techniques. The EPR spectra of paramagnetic rare-earth ions ${\mathrm{Er}}^{3+}$, ${\mathrm{Tm}}^{3+}$, and ${\mathrm{Yb}}^{3+}$ in clusters of diamagnetic ${\mathrm{Y}}^{3+}$ and ${\mathrm{Lu}}^{3+}$ ions were recorded. It appears that the crystalline electric field at the sites of Ln ions in the clusters is of ``nearly'' tetragonal symmetry and provides for high values of factors ${g}_{\ensuremath{\Vert}}$, approaching the theoretical limits, and small values of factors ${g}_{\ensuremath{\perp}}\ensuremath{\sim}0$ in the ground states of the paramagnetic Ln ions. It was assumed that all the clusters of Ln ions in the solid solutions appear to be similar in structure to the hexameric clusters, which are the basic structural units of the homologous series of fluorite-related superstructures ${(A{\mathrm{F}}_{2})}_{1\ensuremath{-}y}{(\mathrm{Ln}{\mathrm{F}}_{3})}_{y}$ with compositions $y=5∕m$, where $m$ is an integer in the range of 13--19. The structure of ``symmetric'' hexameric clusters in $\mathrm{Ca}{\mathrm{F}}_{2}$, $\mathrm{Sr}{\mathrm{F}}_{2}$, and $\mathrm{Ba}{\mathrm{F}}_{2}$ hosts was established by computer simulation. The crystalline electric field and the spectroscopic ground-state parameters for ${\mathrm{Er}}^{3+}$, ${\mathrm{Tm}}^{3+}$, and ${\mathrm{Yb}}^{3+}$ ions in the hexameric clusters were calculated and found to be in agreement with the experimental data, being totally different from those known for the ``isolated'' simple cubic and tetragonal centers in the fluorite crystals.

This paper reports the molecular imprinting at the walls of highly uniform silica nanotubes for the recognition of 2,4,6-trinitrotoluene (TNT). It has been demonstrated that TNT templates were efficiently imprinted into the matrix of silica through the strong acid-base pairing interaction between TNT and 3-aminopropyltriethoxysilane (APTS). TNT-imprinted silica nanotubes were synthesized by the gelation reaction between APTS and tetraethylorthosilicate (TEOS), selectively occurring at the porous walls of APTS-modified alumina membranes. The removal of the original TNT templates leaves the imprinted cavities with covalently anchored amine groups at the cavity walls. A high density of recognition sites with molecular selectivity to the TNT analyte was created at the wall of silica nanotubes. Furthermore, most of these recognition sites are situated at the inside and outside surfaces of tubular walls and in the proximity of the two surfaces due to the ultrathin wall thickness of only 15 nm, providing a better site accessibility and lower mass-transfer resistance. Therefore, greater capacity and faster kinetics of uptaking target species were achieved. The silica nanotube reported herein is an ideal form of material for imprinting various organic or biological molecules toward applications in chemical/biological sensors and bioassay.

Photoactive hybrids with the functionalized Schiff-base derivatives covalently bonded inorganic silica network: Sol–gel synthesis, characterization and photoluminescence

The molecular assembly formed by the inclusion complex of cholesterol in β-cyclodextrin (β-CD:chol) was used as a template for the molecular imprinting of a sol–gel polymer (MIP/β-CD:chol), produced with tetraethoxysilane (TEOS) as precursor. The MIP/β-CD:chol and pure silica matrix (PSM) were tested for the efficiency of cholesterol removal from solutions at different cholesterol concentrations (1–10 mg/mL). The adsorption tests were run at 25°C using 1% (w/v) solid/liquid suspensions during 24 h. The MIP/β-CD:chol data on cholesterol adsorption was fitted by the Langmuir isotherm model, giving a maximum adsorption capacity of 76.5 mg cholesterol/g-adsorbent. The PSM data did conform to the Langmuir model. The maximum cholesterol adsorption achieved with the PSM was higher, 251 mg/g, probably due to multilayer adsorption. The hydrophobic silica matrix, imprinted with the inclusion complex of β-CD and a target molecule, has the potential of being used as an adsorbent for other organic molecules.

The reaction of 3-(4-pyridyl)benzoate (34pbz) under solvothermal and solvent evaporation conditions produced several two-dimensional (2D) square lattice metal–organic frameworks compounds, {[Zn(34pbz)2]·DMF}n (1), {[Zn(34pbz)2]·DMF}n (2), and {[Zn(34pbz)2]·2DMF·CH3OH·1/2H2O}n (3). Although the frameworks of 1, 2, and 3 have identical elemental composition, these networks differ in the binding mode of the carboxylate moiety to the metal center. In compound 1 the carboxylate moiety assumes a monodentate binding mode, while in 2 and 3 it assumes a chelating binding mode. Compounds 1 and 3 crystallize in space group P21/c with different unit cell parameters, while compound 2 crystallizes in the tetragonal crystal system. In all three crystal structures, networks are formed by connecting mononuclear Zn(II) units with 34pbz linkers forming a square grid network. The solvent accessible void volumes in 1 (21%) and 2 (18%) are comparable, while compound 3 has a void volume of 42%, which is extremely large for a 2D...

Silane surface treatments have been developed as an alternative for toxic and carcinogenic chromate-based treatments for years. It is consistently observed that ultra-thin films offer excellent corrosion protection as well as paint adhesion to metals. The silane performance is comparable to, or in some cases better than, that of chromate layers. Based on the tetra-ethylorthosilicate(TEOS) and methlyl trieethoxysilane(MTES), inorganic sol was synthesized and formed hybrid networks with <TEX>$SiO_</TEX><TEX>2$</TEX> nano particle and polypropylene glycol(PPG) on Zn alloyed steel surface. According to SST results, addition of 10nm and 50nm <TEX>$SiO_2$</TEX> nanoparticle in synthesized solution improved anti-corrosion property by its shear stress relaxation effect during curing process. Also, SST results were shown that anti-corrosive property was affected by the amounts of organic compounds.

Na 1.7Ti 6O 11: A new mixed-valence nonstoichiometric sodium titanate with a tunnel structure

Dry depositions contribute to regulate the lifetime of the aerosol in the atmosphere and at the same time they are responsible for the surface flux of nutrients, reactive compounds and pollutants. In polar areas, in particular, atmospheric depositions represent an important source of uncertainty in assessing the lifetime of particulate matter and short-living climate forcers (including black carbon, cloud condensation nuclei and ice nuclei). Dry depositions are deemed to affect snow composition (in terms of reactive compounds, light-absorbing species and persistent pollutants), although its relative importance with respect to wet depositions remains undetermined. There is a paucity of observational data of size-segregated particle fluxes in polar areas, which remains a challenge for the development of reliable parameterizations, given the peculiarities of the turbulence in the polar boundary layer as it is affected by the low solar angles, the presence of a snowpack, the strong surface radiative cooling. The Alaskan Layered Pollution and Chemical Analysis (ALPACA) experiment is the first, comprehensive air quality study at a urban Arctic location. In the frame of ALPACA, atmospheric transport and vertical distribution of anthropogenic aerosols were investigated by a suite of experimental and modelling approaches. At the same time, the characteristic of the atmospheric boundary layer and surface fluxes of energy and particles have been investigated, while the composition of surface snow was determined on a daily basis. ALPACA was conducted in Fairbanks (AK, US) in Jan &amp;#8211; Feb 2022 and comprehensive boundary layer observations were carried out at the sub-urban &amp;#8220;Farm&amp;#8221; location, over a large, flat terrain with little local pollution sources. In the dark Arctic winter, minimum temperatures dropped as low as -35 &amp;#176;C during the first part of the campaign. As a result of the surface cooling, the temperature gradient reached 10 &amp;#176;C in the first 10 meters above the ground. However, surface-based inversions were systematically perturbed by changes in the surface radiative budget caused by the intermittent presence of clouds and by surface winds promoted the thermal gradients between the Fairbanks plain and the surrounding elevated terrains. Whenever the surface inversions shrank and sufficient amount of aerosol was present in the lower levels, a clear surface particle surface flux was observed by means of an eddy-covariance technique. Such fluxes were intensified during the first part of the campaign when anthropogenic pollution developed in the lower atmospheric layers. In the same period, inorganic and organic compounds in surface snow progressively accumulated in absence of precipitations. The assessment of size-segregated particle fluxes and the analysis of particulate matter composition enabled to quantitatively assess atmospheric dry depositions. Their contribution to the evolution of snow chemistry was species-dependent, but in general dry depositions were found to be a significant sources of pollutants in snow during ALPACA. The effect of meteorology, vertical aerosol distribution and aerosol mixing state on the fluxes on the snowpack are discussed.

The release of heavy metals in stabilised MSW by oxidation

In the selection and design of appropriate types of photoreactor system configuration in terms of total irradiated surface area of catalyst per unit volume in photocatalysis reaction, reaction kinetics and light distribution within the reactor are the most important factors. Though several photoreactor system configurations have been reported so far, most of them were complex, focused on degradation of hazardous organic compounds and their application has been very limited for pathogenic microorganism inactivation applications. In the present work, however, photocatalytic bacterial inactivation is studied by immobilized N-doped TiO2 using a novel simplified multistage fixed-bed photoreactor. The photoreactor has been developed from N-doped TiO2 nanoparticles immobilized on glass beads using tetraethoxysilicate (TEOS) as a binder with low-temperature synthesis route. The reactor was irradiated under visible light-emitting diodes (vis-LEDs) with the incident photon flux of 5.23 ± 0.35 × 1016 photons/s. Furthermore, for solar experiment global and UV irradiances were 71.2 and 4.6 mWcm−2, respectively. The photocatalytic inactivation efficiency was investigated on different types of Gram-negative and Gram-positive bacteria in water. From the photocatalytic inactivation efficiencies, the proposed photoreactor demonstrated more than 3 log unit reduction in bacterial removal on both under vis-LEDs and sunlight irradiation. Fast inactivation efficiency for all selected bacterial strain was also observed under sunlight irradiation when compared to under vis-LED irradiation. It has been understood that the rate of photocatalytic inactivation on Gram-negative bacteria was found to be higher than the Gram-positive bacteria on both experiments.

Sol–gel derived organic–inorganic composites recognizing molecular asymmetry

The search for new materials with improved properties for advanced applications is, nowadays, one of the most relevant and booming fields for scientists due to the environmental and technological needs of our society. Within this demand, hybrid siliceous materials, made out of organic and inorganic species (ORMOSILs), have emerged as an alternative with endless chemical and textural possibilities by incorporating in their structure the properties of inorganic compounds (i.e., mechanical, thermal, and structural stability) in synergy with those of organic compounds (functionality and flexibility), and thus, bestowing the material with unique properties, which allow access to multiple applications. In this work, synthesis using the sol-gel method of a series of new hybrid materials prepared by the co-condensation of tetraethoxysilane (TEOS) and 4-chlorophenyltriethoxysilane (ClPhTEOS) in different molar ratios is described. The aim of the study is not only the preparation of new materials but also their characterization by means of different techniques (FT-IR, 29Si NMR, X-ray Diffraction, and N2/CO2 adsorption, among others) to obtain information on their chemical behavior and porous structure. Understanding how the chemical and textural properties of these materials are modulated with respect to the molar percentage of organic precursor will help to envisage their possible applications: From the most conventional such as catalysis, adsorption, or separation, to the most advanced in nanotechnology such as microelectronics, photoluminescence, non-linear optics, or sensorics.