Acidic Synthesis Conditions Research Articles

Effect of synthesis media pH and gel separation technique on properties of copper incorporated SBA-15 catalyst

Cu-SBA-15 catalysts were synthesized hydrothermally under acidic and slightly higher acidic conditions via solid separation by either gel filtration or evaporation. XRD (X-ray diffraction) patterns and HRTEM (high resolution transmission electron microscopy) images showed that metal loading caused little changes in the ordered structure of SBA-15. Characteristic structural SBA-15's bonds and acid sites were observed in FTIR (Fourier transform infrared) spectrums and synthesis under high pH was created changes in the ranges of silica and silanol groups. Copper incorporation created enhancements more in Lewis acid sites. Metal loading under severe acidic synthesis conditions resulted in improvements in the ordered structure in addition to increases in wall thickness while rise in its concentration caused little structural deterioration. Synthesis with slightly higher acidic conditions although gave a little higher d100 diffraction, caused little broadening of peak. Positive effects in copper incorporation success by separation through evaporation were supported by XRD, HRTEM images, SEM/MAP (scanning electron microscopy/mapping) and ICP-OES (inductively coupled plasma optical emission spectroscopy) analyses results; however its accumulation on pore walls did more worsening of textural properties. Formation of CuO, Cu2O and Cu3Si species after evaporation separation was observed with XRD, XPS (X-ray photoelectron spectroscopy) and UV–Vis DR (UV–visible diffuse reflectance) analyses.

Unique characteristics of MnOx-incorporated mesoporous silicate, Mn-FDU-5, prepared via evaporation induced self assembly

Mn containing 3D mesostructured FDU-5 (Ia3d) silicates with varying Si/Mn ratios were synthesized for the first time via evaporation induced self assembly (EISA) technique under acidic conditions at room temperature, employing Pl23 triblock copolymer as a structure directing agent. This method facilitates complete incorporation of higher amounts of Mn in the framework and extraframework locations of FDU-5 even under highly acidic synthesis conditions. The Mn-FDU-5 samples possessed surface areas of 300–500 m2/g, pore volumes of 0.42–0.55 cm3/g and narrow pore size distributions of 4.1–4.9 nm. Homogeneous dispersion of Mn species and aggregated Mn oxide clusters were evidenced from FIB-SEM micrographs. Complementary analytical techniques such as diffuse reflectance UV–Vis, FTIR, TPR and EPR analyses provide insights into the nature of the different types of Mn species (Mn2+, Mn3+ and Mn3O4 nanoparticles) that co-exist in FDU-5. The Mn-FDU-5 material is shown to be active for the epoxidation of trans-stilbene (TS, ~60 % conversion) to trans-stilbene epoxide (~64 % selectivity) with TBHP as oxidant. Although the activity of Mn-FDU-5 (~45 % TS conversion) is similar to those observed with MCM-41 and MCM-48 supports containing similar amounts of Mn (1 wt%), higher epoxide selectivity (~64 %) was observed with Mn-FDU-5. The mixed oxidation states of Mn (Mn2+, Mn3+) along with the extraframework Mn3O4 are found to be beneficial in catalyzing TS epoxidation.

Mn-incorporated SBA-1 cubic mesoporous silicates: Synthesis and characterization

Direct one pot synthesis of manganese containing ordered mesoporous silicate with Pm3n cubic symmetry with a maximum manganese loading of approximately 4.8 wt% was achieved under acidic synthesis conditions. XRD, N2 sorption, TEM and SEM studies confirmed well-ordered cubic mesoporous structure typically of SBA-1 type materials. Diffuse Reflectance UV–Vis, FTIR and EPR studies concluded the framework incorporation of Mn3+ ions as well as extra-framework Mn2+ ions at higher Mn loadings. Further, MnSBA-1 was also shown to be active for oxidation of ethylbenzene with TBHP as oxidant.

Thermal-Responsive Behavior of a Cell Compatible Chitosan/Pectin Hydrogel.

Biopolymer hydrogels are important materials for wound healing and cell culture applications. While current synthetic polymer hydrogels have excellent biocompatibility and are nontoxic, they typically function as a passive matrix that does not supply any additional bioactivity. Chitosan (CS) and pectin (Pec) are natural polymers with active properties that are desirable for wound healing. Unfortunately, the synthesis of CS/Pec materials have previously been limited by harsh acidic synthesis conditions, which further restricted their use in biomedical applications. In this study, a zero-acid hydrogel has been synthesized from a mixture of chitosan and pectin at biologically compatible conditions. For the first time, we demonstrated that salt could be used to suppress long-range electrostatic interactions to generate a thermoreversible biopolymer hydrogel that has temperature-sensitive gelation. Both the hydrogel and the solution phases are highly elastic, with a power law index of close to -1. When dried hydrogels were placed into phosphate buffered saline solution, they rapidly rehydrated and swelled to incorporate 2.7× their weight. As a proof of concept, we removed the salt from our CS/Pec hydrogels, thus, creating thick and easy to cast polyelectrolyte complex hydrogels, which proved to be compatible with human marrow-derived stem cells. We suggest that our development of an acid-free CS/Pec hydrogel system that has excellent exudate uptake, holds potential for wound healing bandages.

Synthesis and structural characterization of a new chiral porous hybrid organic–inorganic material based on γ-zirconium phosphates and l-(+)-phosphoserine

Abstract In the present work, a chiral layered derivative of γ-zirconium phosphate (γ-ZrP) containing l -(+)-phosphoserine (γ-ZrP-PS*) covalently attached to inorganic layers has been prepared by means of topotactic exchange reaction. This organic–inorganic derivative is characterized by X-ray diffractometry, Solid 13 C–NMR and FT-IR spectrophotometries and thermal analyses. A maximum level of topotactic replacement of 20% is achieved. Under both the acidic environment of the interlayer region of γ-ZrP and the acidic synthesis conditions, the hydrolysis of the ester bond of PS* is expected to take place to some extent. For this reason, it was impossible to exceed the recent percentage, which in turn reflects the relative moderate stability of the above mentioned bond under these conditions. In order to be more certain with regard to an expected further hydrolysis for this bond after separation, a sample of γ-ZrP-PS* was stored in a desiccator over a saturated solution of BaCl 2 (90% relative humidity) for three months, and then the sample re-analyzed once again. Surprisingly, the results show that the sample still keeps almost the same level of exchange (i.e., 20%). Second, it is revealed that the sample almost gives the same spectroscopic and thermal behavior. This could be attributed to the less acidic character of the partially exchanged inorganic layers of the sample in comparison with that of the precursor γ-ZrP. Therefore, the PS* molecules persist and stay there into the interlayer gallery without further hydrolysis.

Relationship between Synthesis Conditions and Photocatalytic Activity of Nanocrystalline TiO2

The degradation efficiency of methylene blue by TiO2 nanoparticles, which were synthesized under different synthesis conditions (i.e., molar ratio of water and titanium tetraisopropoxide (TTIP), pH, and calcination temperature) in a sol‐gel process, was systematically investigated. The results showed that increasing the molar ratio of water and TTIP led to the enhanced photocatalytic activity of TiO2 nanoparticles, which were likely attributed to the increased specific surface area of TiO2 nanoparticles synthesized with high molar ratio. The results were supported by the relative increase in the size of interaggregated pores of the aggregated TiO2 nanoparticles. The best photocatalytic activity of TiO2 nanoparticles was observed at acidic synthesis conditions; however, the results were not consistent with physical properties for the crystallinity and the crystallite size of TiO2 nanoparticles but rather explained by the presence of abundant hydroxyl groups and water molecules existing on the surface of TiO2 under acidic synthesis environments. Furthermore, methylene blue degradation experiments revealed that the photocatalytic activity of TiO2 nanoparticles was maximized at the calcination temperature of 700°C. The trend was likely due to the combined effect of the anatase crystallinity which showed the highest value at 700°C and the crystallite size/specific surface area which did not excessively increase up to 700°C.

One-Pot Synthesis and CO2 Adsorption Properties of Ordered Mesoporous SBA-15 Materials Functionalized with APTMS

Amino-functionalized SBA-15 materials were synthesized by cocondensation of tetraethoxysilane (TEOS) with organosilane aminopropyltrimethoxysilane (APTMS) in a wide range of molar ratios of APTMS to TEOS in the presence of triblock copolymer P123 under acidic synthesis conditions. The effects of F– periodically added into the synthesis solution and of the APTMS concentration in the initial synthesis solution on the textural properties of the functionalized SBA-15 were investigated in detail. The addition of APTMS into the initial synthesis solution can adversely affect the SBA-15 mesostructure, whereas the ordered mesostructure of the amino-functionalized SBA-15 materials can be reserved by the introduction of F– into the synthesis solution. The results from the adsorption of CO2 on the synthesized materials show that the mesoporous SBA-15 functionalized with a high concentration of APTMS in the initial synthesis solution in the presence of F– could be a potential adsorbent for CO2 capture and separation.

Review on the key controls of designer copolymer-silica mesophase monoliths (HOM-type) with large particle morphology, ordered geometry and uniform pore dimension

This review introduces the extensive key factors of the design of mesostructured monoliths with two- and three-dimensional (2D and 3D) geometries and large particle morphologies. Simple strategy in terms of fabrication time (within 10 min) and composition phase domains was achieved by using an instant direct-templating method of lyotropic and microemulsion phases of a variety of triblock copolymer (EOm-POn-EOm) surfactants, as we recently reported in [33] and [34]. The synthetic strategy provides realistic control over a wide range of mesophase geometries, yet maintains the long-range structural ordering, and thus improved the simplicity, significant periodicity, and high uniformity of the resultant silica monoliths. Cubic mesophases, in particular, exhibit a wide variety of mesostructured geometries when the block copolymers were used as a structure-directing agent under acidic synthesis conditions. For example, triblock copolymer (P123, EO20PO70EO20) was used to fabricate 2D hexagonal (P6mm). Our synthesis protocol revealed that ordered 3D cubic (Fd3m), (Im3m), and (Ia3d) silica monoliths were also fabricated in large domain sizes by templating P123 copolymers. In general, key factors such as the degree of solubilization of the hydrocarbons (co-solvent), the copolymer concentrations used in the phase domains, and the copolymer molecular nature, such as EO/PO ratio, significantly affect the formation of mesostructured phases and their extended long-range ordering in the final replicas of the silica monolith frameworks. The remarkable structural findings of 2D and 3D frameworks, transparent monoliths, and micropores combined with large cage- and cylindrical-like mesopores might show their desirability in many applications.

In-Situ SAXS Studies on the Formation of Silicate/Surfactant Mesophases with Solubilized Benzene under Acidic Conditions

The formation of mesoscopically ordered silica/surfactant composites under acidic synthesis conditions is studied by time-resolved in-situ small-angle X-ray scattering (SAXS) using synchrotron radiation. Benzene is used a an additive which acts as a weak swelling agent although most of the benzene molecules are found to reside near the surfactant/silicate interface region rather than in the micelle cores. With increasing relative amounts of benzene, the curvature of the micellar aggregates decreases, which finally leads to a transition from (hexagonally) rodlike to lamellar; a mechanism for this change in curvature is suggested.

Synthesis and Characterization of Mesostructured Titania-Based Materials through Evaporation-Induced Self-Assembly

Mesostructured TiO2−hexadecyltrimethylammonium bromide hybrid powders, displaying a bidimensional hexagonal pattern (p6m), have been synthesized by an evaporation-induced self-assembly (EISA) method, in ethanol/HCl/H2O media. Thermal treatment of these “titaniatropic” hybrid phases leads to phosphorus-free, high surface area (280−370 m2 g-1) mesoporous titania, with 20−25 A pores. The role of the synthesis parameters (surfactant and acid concentrations and temperature) is thoroughly discussed to understand their influence on the hybrid mesostructures. It is suggested that hydrophilic Ti-oxo nanometric building blocks formed in the acidic synthesis conditions self-assembly upon solvent evaporation to produce organized structures.

Influence of the Sol−Gel Acidic Synthesis Conditions on the Porous Texture and Acidity of SiO2−Al2O3 Catalysts with a Low Al Proportion

The relationship between the porous texture, the coordination number of Al atoms, the type of surface acidity, and the sol−gel acidic synthesis conditions at two pH values (pH ≈ 2 and pH ≈ 0), was studied in SiO2−Al2O3 aerogels made with a molar Si to Al ratio rSi/Al = 100. The influences of chelation of the Al precursor and of the rate of addition of this Al precursor to the Si precursor sol were also investigated and found to have minor effects. Infrared absorbance after pyridine adsorption, 27Al nuclear magnetic resonance (NMR), and nitrogen adsorption isotherms by the Brunauer, Emmett, and Teller (BET) method showed that the structure of the gel network considerably changed depending on the pH, with most Al atoms having a coordination number of IV at pH ≈ 2 while they had a coordination number of VI at pH ≈ 0. This result was also found to correlate very well with an enhancement of Bronsted acidity at pH ≈ 2 by comparison with Lewis acidity, and also of the specific surface area.

Preparation of Highly Ordered Mesoporous Thin Film with Alkyltrimethylammonium(CnTMA+)

ABSTRACTWe synthesized the highly ordered mesoporous thin films with alkyltrimethyl-ammonium (CnTMA+). The arrangement of mesopores was depend on the Si/surfactant ratio. The hexagonal(P6mm) arrangement was observed, when Surfactant/Si ratio was 1/10. Increasing the Surfactant/Si ratio to 1.6/10, the cubic (Pm3n) arrangements were observed. A steel vessel for the measurement of the nitrogen adsorption isotherms of thin film on the substrate was designed. It was found that mesopore arrangements in the film is more regular than that in the powder samples prepared by the same acidic synthesis conditions.