Epoxidation of Cyclohexene over Crystalline and Amorphous Titanosilicate Catalysts

A microporous titanosilicate (TS-1) catalyst was synthesised from an amorphous titanosilicate precursor, and both the amorphous precursor and TS-1 were characterised by Ti K-edge X-ray absorption spectroscopy which revealed that Ti (IV) ions are in tetrahedral coordination in the calcined state. Each of these solids is catalytically active for the conversion of cyclohexene to cyclohexene oxide in the presence of H₂O₂. Use of urea–H₂O₂ adduct as oxidant increased the activity and selectivity for the formation of the epoxide with TS-1 as catalyst. However, a significant loss in catalytic activity is seen for the amorphous precursor.     

Efficient catalytic epoxidation of olefins with hierarchical mesoporous TS-1 using TBHP as an oxidant

A series of hierarchical mesoporous TS-1 zeolites with MFI structure were successfully synthesized via hydrothermal route using amphiphilic organosilanes as pore directing templates. These materials were characterized by nitrogen sorption (for surface area, pore volume and pore size distribution), FTIR, SEM and UV–Visible spectroscopy. These materials are efficient catalysts for liquid phase epoxidation of olefins using TBHP as the oxidant. All these TS-1 samples oxidized cyclohexene selectively into epoxide. For the TS-1 sample with 4.4 % Ti complete conversion of cyclohexene into epoxide was observed.     

Alkene epoxidation with mesoporous materials assembled from TS-1 seeds – Is there a hierarchical pore system?

Hexagonal mesoporous solids were synthesized from solutions containing TS-1 seeds. The products were characterized by XRD, nitrogen and argon physisorption, TEM, TG/DTA of template decomposition (also after extraction of the mesopore template), UV–Vis and IR spectroscopy, and XANES at the TiK edge. Their catalytic activities were assessed for cyclohexene epoxidation in hydrophilic and hydrophobic environment (CH₃OH/water, with H₂O₂ oxidant, and decane, with tert-butyl hydro-peroxide oxidant, respectively) and for n-hexene epoxidation in hydrophilic environment. The mesopore system was clearly documented by XRD, physisorption measurements, and TEM, whereas evidence for micropores by physisorption proved elusive. However, the micropore template was detected in the solids by TG/DTA even after extraction of the mesopore template, and among the Ti sites, which were confirmed to be tetrahedrally coordinated by UV–Vis and XANES, a clear majority was able to coordinate two water molecules. It was concluded that the pore walls had been built up from nanoparticulate TS-1 precursors resulting in walls of ca. 1.5 nm thickness, which resemble rather the exterior layers of a TS-1 crystallite than its (hydrophobic) interior. In cyclohexene epoxidation, the micro-mesophases were by 1–2 orders of magnitude more active than TS-1 and outperformed also Ti-MCM-41, at similar selectivity in hydrophobic medium. With 1-hexene in hydrophilic medium, however, the micro-mesophases failed completely whereas TS-1 exhibited high activity.     

Preparation and electrochemical characterization of MnOOH nanowire–graphene oxide

MnOOH nanowire–graphene oxide composites are prepared by hydrothermal reaction in distilled water or 5% ammonia aqueous solution at 130 °C with MnO₂–graphene oxide composites which are synthesized by a redox reaction between KMnO₄ and graphene oxide. Powder X-ray diffraction (XRD) analyses and energy dispersive X-ray analyses (EDAX) show MnO₂ is deoxidized to MnOOH on graphene oxide through hydrothermal reaction without any extra reductants. The electrochemical capacitance of MnOOH nanowire–graphene oxide composites prepared in 5% ammonia aqueous solution is 76 F g⁻¹ at current density of 0.1 A g⁻¹. Moreover, electrochemical impedance spectroscopy (EIS) suggests the electrochemical resistance of MnOOH nanowire–graphene oxide composites is reduced when hydrothermal reaction is conducted in ammonia aqueous solution. The relationship between the electrochemical capacitance and the structure of MnOOH nanowire–graphene oxide composites is characterized by cyclic voltammetry (CV) and field emission scanning electron microscopy (FESEM). The results indicate the electrochemical performance of MnOOH nanowire–graphene oxide composites strongly depends on their morphology.     

Enhanced NO2 detection using hierarchical porous ZnO nanoflowers modified with graphene

Because of their potential applications in gas sensing and catalysis, reduced graphene oxide (RGO) and ZnO have been the focus of much recent attention. However, few reported materials have been produced via the combination of hierarchical ZnO structures with RGO to achieve high sensing performances. In this paper, a hydrothermal method was used to synthesize hierarchical porous ZnO nanoflowers, which were then combined with graphene to enhance their sensing performances. The rapid detection of 1 ppm NO₂ was achieved at 174 °C. The morphologies and structures of these materials were characterized using scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and Raman spectroscopy. Photoluminescence measurements and X-ray photoelectron spectroscopy were also used to investigate the mechanism of gas sensing by these materials.     

Uncalcined TS-2 immobilized Au nanoparticles as a bifunctional catalyst to boost direct propylene epoxidation with H2 and O2

Developing stable yet efficient Au–Ti bifunctional catalysts is important but challenging for direct propylene epoxidation with H₂ and O₂. This work describes a novel strategy of employing uncalcined titanium silicalite-2 (TS-2-B) to immobilize Au nanoparticles as a bifunctional catalyst for the reaction. Under no promoter effects, the Au/TS-2-B catalyst compared to the referenced Au/TS-1-B catalyst delivers outstanding catalytic performance, that is, exceptionally high stability over 100 hr, propylene oxide (PO) formation rate of 118 g_PO·hr⁻¹·kg_cat⁻¹, PO selectivity of 90% and hydrogen efficiency of 35%. The plausible relationship of catalyst structure and performance is established by using multiple techniques, such as UV–vis, high-angle annular dark-field scanning transmission electron microscopy, thermogravimetric analysis, and X-ray photoelectron spectroscopy. A unique synergy of Au–Ti⁴⁺–Ti³⁺ triple sites is proposed for our developed Au/TS-2-B catalyst with the higher stable PO formation rate and hydrogen efficiency. The insights reported here could shed new light on the rational design of highly stable and efficient Au–Ti bifunctional catalysts for the reaction.     

Synthesis and catalytic properties of TS-1 with mesoporous/microporous hierarchical structures obtained in the presence of amphiphilic organosilanes

Titanosilicates TS-1 with mesoporous/microporous hierarchical structures have been synthesized in the presence of an organosilane surfactant. Highly porous crystals, with regular pores of ca. 2.5–3.5 nm diameter, are obtained under hydrothermal conditions similar to those used for the preparation of conventional catalysts. The organosilane has a great influence on the textural properties of TS-1, but does not significantly affect the amount and coordination of Ti species in the framework. Mesoporous TS-1 have been used as catalysts in various oxidation reactions with an aqueous H₂O₂ and their activity has been compared with those of a conventional TS-1 and a mesoporous amorphous TiMCM-41. Data show that mesoporous TS-1 does not possess the expected properties for hierarchical catalysts, i.e. the properties of the conventional catalysts with advantages of mesoporous solids. In particular, the gain in diffusion due to intracrystalline mesopores is totally inhibited by the increase of the hydrophilic character of the zeolite, resulting from very high silanol group populations on the external surface.     

Effects of graphene oxide sheets-zirconia spheres nanohybrids on mechanical,thermal and tribological performances of epoxy composites

In this work, graphene oxide sheets-zirconia spheres (ZrO₂-rGO) nanohybrids were fabricated by Schiff base or Michael addition reaction. Their structure was characterized by FT-IR spectroscopy, UV–vis absorption spectra, Raman spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy and atomic force microscope in detail. The reaction process of PDA-capping on rGO and APTES treatment on ZrO₂ nanoparticles were verified and it was proved that the ZrO₂ nanoparticles were successfully adhered onto the wrinkled surface of the graphene oxide. As a new multifunctional nanofillers, the ZrO₂-rGO nanohybrids were introduced into epoxy matrix and the mechanical, thermal properties and tribological performances of the fabricated composites were also detailedly investigated. Compared with the neat EP composites, the tensile strength and elongation at break of 0.1?wt% ZrO₂-rGO/EP are improved by 33% and 40%, respectively. Besides, the propagation of decomposition reactions in the composites could be impeded by anchoring ZrO₂ nanoparticles on the lamellar skeleton of graphene oxide. Furthermore, the lubricating effect and strong interfacial interaction contributed by the ZrO₂-rGO nanohybrids result in efficient load transfer from the matrix to the hybrids, which enables the ZrO₂-rGO/EP composites to have a fairly high wear resistance performance. This novel and effective approach using ZrO₂-rGO nanohybrids as multifunctional nanofillers could be beneficial to promote the development of high performance composites.     

Preparation of titanium silicalite-1 catalytic films and application as catalytic membrane reactors

Titanium silicalite-1 (TS-1) films were prepared on porous α-Al₂O₃ tubes using nanosized silicalite-1 (Sil-1) particles as seeds by hydrothermal treatment and a TS-1 catalytic membrane reactors (CMR) was reasonably designed and evaluated by phenol hydroxylation with hydrogen peroxide as oxidant. Some factors on influencing TS-1 film formation and catalytic properties were investigated and the TS-1 films were characterized by scanning electron microscope (SEM), transmission electron micrograph (TEM), X-ray diffractometer (XRD), FTIR, UV–vis and X-ray fluorescence (XRF). It was indicated that TS-1 films prepared from Sil-1 and TS-1 seeds were comparable in structure, morphology and reaction behavior. The crystallization time and times of TS-1 film had a strong effect on its morphology, thickness and orientation. However, the film thickness could be easily controlled by crystallization time and times. The Ti/Si ratio in synthesis solution intensely influenced the content of the titanium atoms incorporated as framework Ti that was correlated well with the activity. The maximum Ti (IV) incorporated corresponds to a Ti/Si ratio of approximately 0.02–0.03. A constant conversion for phenol hydroxylation was obtained with the film thickness of over 7.5 μm. It is demonstrated that most of the reaction occurred in a shallow layer near the film due to the mass transfer effects in the TS-1 films.     

Facile preparation of Bi-doped ZnO/β-Bi2O3/Carbon xerogel composites towards visible-light photocatalytic applications: Effect of calcination temperature and bismuth content

This work aimed to study the development and properties of Bi-doped ZnO/β-Bi₂O₃/Carbon xerogel composites towards visible light photocatalysis applications. The materials were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, dispersive energy spectroscopy, infrared spectroscopy, nitrogen adsorption isotherms, Raman spectroscopy, diffuse reflectance spectroscopy and X-ray photoelectron spectroscopy. The photocatalytic activity of the developed composites was evaluated through the photodegradation of the 4-chlorophenol molecule and by chronoamperometry tests. The results obtained show that the calcination temperature poses a major influence in the final structure of the materials developed. The calcination temperature of 600 °C resulted in the formation of the β-Bi₂O₃ and Bi⁰ phases, consequently enhancing the photocatalytic activity of the composites due to the increased charge mobility provided by the heterojunctions between zinc oxide, carbon xerogel, bismuth oxide and metallic bismuth. The composite with intermediate bismuth composition (XC/ZnO–Bi₂O₃ 5%) displayed the best photocatalytic response among the materials tested, which was confirmed by its increased photocurrent generation capability. The photocatalytic mechanism is highly dependent in the generation of hydroxyl radicals and the composite presents good reusability properties.     

Pore size-controlled synthesis of 3D hierarchical porous carbon materials for lithium-ion batteries

3D hierarchical porous carbons (3DCs) with different pore size distributions are prepared by using Ni(OH)₂ as template. The morphology, crystalline features, pore structure and surface composition of the hierarchical porous carbons are characterized using various analytic techniques including scanning electron microscopy, transmission electron microscopy, N₂ physical adsorption, powder X-ray diffraction and X-ray photoelectron spectroscopy. It is found that the pore size distributions of the 3DCs play an important role in the lithium-storage capacity when they are used as anode materials for rechargeable lithium-ion batteries. The typical sample 3DC-20 has a specific reversible capacity of 630 mAh g^??1 in the first cycle and and 363 mAh g^??1 after 50 cycles. The high capacity of 3DC-20 can be attributed to the existence of the largest amount of micropores with 0.6–0.9 nm pore width, which increase the lithium storage capacity; in addition, the existence of mesoporous and macroporous effectively shortens the distance for charge diffusion, the turbostratic graphite structure low resistance for electron conduction.     

Synthesis of TS-1 by microwave heating of template-impregnated SiO2–TiO2 xerogels

TS-1 was prepared by microwave heating of a SiO₂–TiO₂ xerogel dry-impregnated with the template, TPAOH. A highly crystalline product was obtained within 30 min after microwave irradiation with yields over 90%. These are significant advantages over the TS-1 obtained by conventional oven heating using alkoxide precursors in liquid phase, which requires 1–2 day crystallization time with low product yields. Characterization of the TS-1 obtained was carried out using XRD, SEM, FT-IR, and UV-vis spectroscopy, and catalytic activity was examined for 1-hexene epoxidation using H₂O₂ as oxidant. These studies revealed that the material obtained by microwave heating of the mixed oxide gel shows essentially identical physicochemical properties to those prepared by conventional means.     

High interfacial thermal resistance induced low thermal conductivity in porous SiC-SiO2 composites with hierarchical porosity

The incorporation of a thermally insulating secondary phase can significantly increase the interfacial thermal resistance attributed to its low intrinsic thermal conductivity and the creation of multiple phonon scattering interfaces between adjacent SiC particles. The newly developed porous SiC-33 wt% SiO₂ composites with SiO₂ as a thermally insulating secondary phase exhibited a very low thermal conductivity (0.047 Wm⁻¹ K⁻¹, 72.4 % porous), which is an order of magnitude lower than the previously reported lowest thermal conductivity (0.14 Wm⁻¹ K⁻¹, 76.3 % porous) for powder processed porous SiC ceramics and is even lower than the thermal conductivity (0.060 Wm⁻¹ K⁻¹, 87.9% porous) of SiO₂ aerogel. The porous SiC-(16–73 wt%) SiO₂ composites processed from nano β-SiC and a 40 wt% carbon template exhibited a hierarchical (meso-/macro-porous) pore structure that transformed to a trimodal (micro-/meso-/macro-porous) porous structure when polysiloxane was added and sintering was performed at 600–1000 °C in air.     

Electrochemically exfoliated graphene oxide/iron oxide composite foams for lithium storage,produced by simultaneous graphene reduction and Fe(OH)3 condensation

We describe the production of graphene-based composites for energy storage, obtained by a combination of electrochemical and solution processing techniques. Electrochemically exfoliated graphene oxide sheets (EGO) are produced using an original setup that allows fast expansion of graphite flakes and efficient exfoliation of expanded graphite via an electrochemical route. The sheets are deposited on a sacrificial nickel foam together with an iron hydroxide colloidal precursor. Calcination treatment simultaneously renders the EGO foam conductive and transforms Fe(OH)₃ into hematite (α-Fe₂O₃), yielding a nanoporous Fe₂O₃ layer on the surface of the mesoporous EGO foam, creating an ideal structure for lithium storage. The obtained graphene/metal oxide hybrid is a continuous, electrically conductive three-dimensional (3D) composite featuring a hierarchical meso–nano porous structure. A systematic study of these composites, varying the Fe₂O₃:EGO ratio, is then performed to maximize their performance as nanostructured electrodes in standard coin cell batteries.     

Synthesis of nitrogen-doped graphene-based binary composite aerogels for ultralightweight and broadband electromagnetic absorption

The development of ultralightweight and broadband electromagnetic wave (EMW) absorbing materials remains a big challenge. In this work, porous magnesium ferrite microspheres decorated nitrogen-doped reduced graphene oxide (NRGO/MgFe₂O₄) composite aerogels were prepared by a two-step route of solvothermal synthesis and hydrothermal self-assembly. Results of microscopic morphology characterization showed that NRGO/MgFe₂O₄ composite aerogels had a unique hierarchical porous structure. Moreover, the influence of additive amounts of graphene oxide on the electromagnetic parameters and EMW absorption properties of NRGO/MgFe₂O₄ composite aerogels was explored. Remarkably, the attained binary composite aerogel with the content of NRGO of 70.21 wt% exhibited the best EMW absorption performance. The minimum reflection loss reached up to −55.7 dB, and the corresponding effective absorption bandwidth was as large as 5.36 GHz at a thin matching thickness of 1.98 mm. Furthermore, when the matching thickness was slightly increased to 2.29 mm, the widest effective absorption bandwidth was enlarged to 7.1 GHz, covering the entire Ku-band. The magnetodielectric synergy and unique hierarchical porous structure in NRGO/MgFe₂O₄ composite aerogels not only improved the impedance matching, but also greatly enhanced the EMW absorption capacity. It was believed that the results of this work could be helpful for the preparation of graphene-based magnetic composites as broadband and efficient EMW absorbers.     

Porous indium oxide thin films deposited by electrostatic spray deposition technique

This paper presents the preparation process of porous indium oxide (In₂O₃) films using a novel deposition technique, i.e., electrostatic spray deposition (ESD). The films were deposited on platinum-coated alumina substrates using as precursor solution indium chloride in ethanol and acetic acid. The films were characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM) and Raman spectroscopy. The nanocrystalline structure of the films was evidenced by TEM and also by XRD studies. The Raman spectroscopy and XRD measurements revealed the cubic phase of In₂O₃ films. Considering the obtained results, we conclude that the ESD technique is an efficient, cheap and successful method for the preparation of porous indium oxide films.     

Preparation,microstructure and electrical property of GdSmZr2O7-(Li0.52Na0.48)2CO3 composite electrolyte via carbonate infiltration

Porous GdSmZr₂O₇ (GSZ) with different porosities has been prepared by the solid state reaction, and GSZ-carbonates composites have been prepared by infiltrating (Li_0·52Na_0.48)₂CO₃ (LNC) molten carbonates. Phase structure, microstructure and electrical property have been analyzed by X-ray diffractometer (XRD), scanning electron microscope (SEM) and electrochemical impedance spectroscopy (EIS). SEM results show that the voids in porous GSZ are uniformly distributed. The relative density of GSZ-LNC composites obtained by molten salt infiltration is above 93%. The electrical conductivity of the GSZ-LNC composites obtained by molten salt infiltration reaches the highest value of 0.50 S cm⁻¹ at 600 °C, which is much higher than that of GSZ-LNC composites prepared by traditional mechanical mixing method. This excellent electrical property strongly indicates that the GSZ-LNC composite obtained by molten salt infiltration is a promising ionic conductor.     

Graphite oxide/polypyrrole composite electrodes for achieving high energy density supercapacitors

Fabrication and characterization of high energy density supercapacitor based on graphite oxide/polypyrrole (GO/PPy) composites is reported. Improvement in charge storage has been obtained by exfoliation of graphite oxide sheets via intercalation of polypyrrole. The formation of composite has been shown by the analysis of X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, and Fourier transfer of infrared spectroscopy data. Scanning electron and transmission electron microscopy clearly show sheet-like layered structure of graphite oxide surrounded by polypyrrole. Supercapacitors fabricated using this composite system result in a reduced equivalent series resistance value ~1.85 Ω. Such low value can be attributed to the intercalation of conducting polypyrrole into the graphite sheets. A specific capacitance of ~181 F g^?1 in 1 M Na₂SO₄ aqueous electrolyte with a corresponding specific energy density of ~56.5 Wh kg^?1 could be achieved. These values make GO-based materials suitable for their use as electrodes in high performance supercapacitors.     

A general strategy for the synthesis of reduced graphene oxide-based composites

Well-exfoliated graphene oxide sheets were initially fabricated through a modified pressurized oxidation method with powdered flake graphite as raw material. A variety of inorganic-reduced graphene oxide composites have been then successfully synthesized through a general solvothermal strategy with the graphene oxide sheets as supports, ethanol as solvent, and metal salts as precursors. After the solvothermal reactions, Ni(OH)₂ nanoparticles, Fe₂O₃ nanorods, W₁₈O₄₉ nanowires, ZnO nanoparticles, and Ag nanoparticles were in situ grown on the surfaces of the graphene oxide sheets, accompanied by effective reduction of graphene oxide to reduced graphene oxide. The as-prepared products have been systematically characterized by electron microscopy, X-ray diffraction, X-ray photoelectron spectrometry, and Raman spectroscopy. The present work opens up a versatile route for preparing the reduced graphene oxide-based composites.     

Fabrication and centeracterization of ordered CuIn(1?x)GaxSe2 nanopore films via template-based electrodeposition

Ordered CuIn_(1−x)Ga_xSe₂ (CIGS) nanopore films were prepared by one-step electrodeposition based on porous anodized aluminum oxide templates. The as-grown film shows a highly ordered morphology that reproduces the surface pattern of the substrate. Raman spectroscopy and X-ray diffraction pattern show that CIGS nanopore films had ideal chalcopyrite crystallization. Energy dispersive spectroscopy reveals the Cu-Se phases firstly formed in initial stage of growth. Then, indium and gallium were incorporated in the nanopore films in succession. Cu-Se phase is most likely to act as a growth promoter in the growth progress of CIGS nanopore films. Due to the high surface area and porous structure, this kind of CIGS films could have potential application in light-trapping CIGS solar cells and photoelectrochemical water splitting.