Preparation and Photocatalytic Activity of an Inorganic–Organic Hybrid Photocatalyst Ag<Subscript>2</Subscript>WO<Subscript>4</Subscript>/g-C<Subscript>3</Subscript>N<Subscript>4</Subscript>

Ag₂WO₄/g-C₃N₄ composites with different Ag₂WO₄ concentration and calcination temperature were synthesized via a mixing and heating approach. Various techniques were used to investigate the characters of the as-prepared samples, such as thermogravimetric analysis, X-ray diffraction, Fourier transform infrared spectroscopy, UV–Vis diffuse reflectance spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy and photoluminescence spectroscopy. The degradation of rhodamine B (20 ppm) under visible light was performed to investigate the photocatalytic activity of Ag₂WO₄/g-C₃N₄ composites. Results indicate that the Ag₂WO₄/g-C₃N₄ is actually Ag/Ag₂WO₄/g-C₃N₄ ternary system. 7.5 wt% Ag₂WO₄/g-C₃N₄ prepared at 300 °C presented the best photocatalytic performance in rhodamine B degradation. The degradation rate reaches 0.0679 min^?1, which is 3.25 times higher than the value of pure g-C₃N₄. The enhanced activity is attributed to the synergetic effect of Ag₂WO₄, g-C₃N₄ and metal Ag. Additionally, cycling experiments also proved that the Ag₂WO₄/g-C₃N₄ photocatalyst has good stability.     

Preparation of a Novel Nano-scale Lead (II) Zig-Zag Metal–Organic Coordination Polymer with Ultrasonic Assistance: Synthesis,Crystal Structure,Thermal Properties,and NBO Analysis of [Pb(μ-2-pinh)N<Subscript>3</Subscript> H<Subscript>2</Subscript>O]<Subscript>n</Subscript>

A novel nano-cauliflower-shaped lead(II) metal–organic coordination polymer, [Pb(μ-2-pinh)N₃ H₂O]_n (1), was synthesized using an ultrasonic method. The nanostructure was characterized by scanning electron microscopy (SEM), X-ray powder diffraction, IR spectroscopy, elemental analysis, and thermal analysis. The compound was structurally characterized by single-crystal X-ray diffraction. The coordination compound takes the form of a zig-zag one-dimensional polymer in solid state. The coordination number of the lead(II) ions is six (PbN₄O₂) with three nitrogen atoms and one oxygen atom from two linker organic ligands, as well as one oxygen from coordinated water and one nitrogen atom from terminal coordinated azide anion. It has a stereo-chemically active lone electron pair, and the coordination sphere is hemidirected. The zig-zag 1D chains interact with neighbouring chains through weak interactions, creating a 3D supramolecular metal–organic framework. Lead oxide nanoparticles were obtained by thermolysis of the new nano coordination compound at 180 °C with oleic acid as a surfactant. The morphology and size were further studied using SEM. Natural bond orbital analyses demonstrate the electronic properties of the lead centre and other atoms.     

Preparation of Si<Subscript>3</Subscript>N<Subscript>4</Subscript>–ZrO<Subscript>2</Subscript> ceramic composites by self-propagating high-temperature synthesis

Results are provided for a study of Si₃N₄–ZrO₂ composite ceramic material preparation by self-propagating high-temperature synthesis from ferrosilicon and zirconium concentrate. It is noted that as a result of high-temperature dissociation of ZrSiO₄ silicon dioxide is nitrided with formation of silicon oxynitride and it is condensed in surface layers of a specimen in the form of filamentary crystals.     

Oscillatory Behaviour during C<Subscript>2</Subscript>–C<Subscript>4</Subscript> Hydrocarbon Oxidation over Palladium Catalysts

Abstract  

Oscillatory behaviour during ethane, propane and butane oxidation over a palladium foil had been studied using on-line mass-spectrometry and a catalyst temperature monitoring. The striking similarity of oscillations properties in all these reactions had been observed. In reactant mixtures with the constant carbon atoms content no significant differences in the parameter space, oscillation shape, or period of temperature oscillations in all three reactions studied had been detected. It was shown that the temperature range of the oscillation phenomena on Pd coincides not only for C₂–C₄ hydrocarbon oxidation, but also for methane oxidation. However, by contrast to the oscillations during methane oxidation, the sustained oscillations with the large amplitude during C₂–C₄ hydrocarbon oxidation could be obtained only for the diluted reactant mixtures. It was demonstrated that the oscillatory phenomena during all light hydrocarbons oxidation reactions have the common origin and are related to oxidation–reduction processes of a Pd catalyst.     

Structural heterogeneity of SiO<Subscript>2</Subscript>–Na<Subscript>2</Subscript>O–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> glass

It is shown that the phase heterogeneity of SiO₂–Na₂O–Al₂O₃ glass has a liquation and crystallization nature, the balance between which is determined by the conditions of their synthesis. An increase in the aluminum oxide content decreases the number of liquation and crystallization sites, and also the linear sizes of the crystalline formations without eliminating the phase separation due to the liquation. The area of metastable immiscibility in the SiO₂–Na₂O–Al₂O₃ system, which is determined by scanning electron microscopy, is probably wider than the area detected by the optical methods.     

Mechanical,Structural and Thermal Properties of Transparent Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>–Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–ZnO–TeO<Subscript>2</Subscript> Glass System

Oxide based optical glass materials has important potential material in many applications from fiber optic to sensor due to the high transparency and amourphous structures. The objective of this study is to synthesize the novel optical glass materials based on the bismuth and aluminum contents to be able to determine the physical, chemical and mechanical properties by considering the systematic experimental steps. In this study, Bi₂O₃–Al₂O₃ based tellurite optical glasses have been prepared by using conventional melt quenching method as a function of the both Bi₂O₃ and Al₂O₃ compositions. There is a strong interactions between the glass former and modifier ions that might effect on the structure and mechanical properties. During the experimental steps, thermal, structural and mechanical properties of the prepared glass materials have been determined considering the DTA/DSC, FT-IR spectroscopy, SEM and Vicker’s hardness techniques, respectively. Thermal parameters, like glass transition, T_g, onset, T_x, crystallization, T_p, and melting, T_m, temperatures were obtained by using DTA scan.     

Preparation and Characterization of SiO<Subscript>2</Subscript>/SiO<Subscript>2</Subscript> Core–Shell Microspheres as RP-HPLC Stationary Phase

Novel SiO₂/SiO₂ core–shell monodisperse silica spheres for high-performance liquid chromatography packing materials are prepared by the layer-by-layer self-assembly technique. The core–shell silica spheres consist of micrometer-sized porous silica spheres as the core and a thin mesoporous silica shell formed from multilayer nanometer-sized silica particles. In addition, a reversed-phase packing by bonding octadecyltrichlorosilane on SiO₂/SiO₂ particles through alkyl-modified method is prepared and characterized. The results show that the carbon content of the new reversed-phase stationary phase increases by approximately 45% compared with the uncoated octadecyl-bonded SiO₂ stationary phase. Eight kinds of tested aromatic compounds are well-separated on the packing and the peaks are symmetrical, which demonstrates that the packing acts as an excellent reversed-phase chromatographic stationary phase.     

3-Hydroxybenzoic acid as AISI 316L stainless steel corrosion inhibitor in a H<Subscript>2</Subscript>SO<Subscript>4</Subscript>–HF–H<Subscript>2</Subscript>O<Subscript>2</Subscript> pickling solution

3-Hydroxybenzoic acid (3-HBA) was studied for possible use as a AISI 316L stainless steel (SS) corrosion inhibitor in an environmental-friendly aqueous pickling solution of 75 g l^–1 sulphuric acid (H₂SO₄), 25 g l^–1 hydrofluoric acid (HF) and 30 g l^–1 hydrogen peroxide (H₂O₂). 3-HBA was tested in concentrations from 5 × 10^–5 to 5 × 10^–1 M at 298 and 313 K temperature. Inhibition efficiency increased with the 3-HBA concentration. The inhibitor mechanism is discussed in terms of the properties of the isotherm equations of Frumkin, Hill-de Boer and Kastening–Holleck mainly. The shape, the trend of the slopes along the curve and the existence of inflection points, were analysed as the characteristics that differentiate one adsorption equation from another. The best fit was obtained using the Frumkin isotherm model. The projected molecular area of 3-HBA was calculated as a structural parameter to elucidate its optimal inhibition mechanism.     

Physicomechanical properties of refractory Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–Si<Subscript>3</Subscript>N<Subscript>4</Subscript>–C materials with ACPC

A study has been made on the effects of the amount of silicon nitride and graphite on the physicomechanical properties of Al₂O₃–Si₃N₄–C composites for lining purposes. Adding 2.5–5.0 wt.% silicon nitride and 0.5 wt.% reactive alumina improves the properties, raises their apparent density, and increases the mechanical strength, while reducing the open porosity. Optimized compositions have been determined for refractory materials of Al₂O₃–Si₃N₄–C composition, and it has been found that to attain the higher values of physicomechanical properties the amount of graphite should constitute 5–10 wt.%.     

Preparation and Improved Photocatalytic Activity of WO<Subscript>3</Subscript>·0.33H<Subscript>2</Subscript>O Nanonetworks

Abstract  

Multi-structural tungsten oxide (WO₃·0.33H₂O) samples were prepared using a hydrothermal method in the presence of different salts Na₂SO₄ and CaCl₂ respectively. The experimental results showed that pH value of the reaction solution greatly affects crystal morphology of the final products. To explore the photocatalysis originated from nanonetwork hierarchical structure, the photodegradation of methylene blue was carried out under simulated sunlight irradiation. The photocatalytic activity of the WO₃·0.33H₂O nanonetworks was compared with that of the nanoplates, and the former showed a higher photocatalytic activity owing to its novel hierarchical structure. Our investigation demonstrates that nanonetwork hierarchical structure can promote sunlight absorption due to higher specific surface area.     

Structural and thermal degradation studies on thin films of the nanocomposite system PVP–Ce(SO<Subscript>4</Subscript>)<Subscript>2</Subscript>·4H<Subscript>2</Subscript>O

Newly prepared and well-characterized nanocomposite thin films of polyvinylpyrrolidone (PVP) containing 2, 5, 10, and 15 wt% cerium (IV) sulfate have been subjected to structural and thermal stability investigations using the transmission electron microscopy (TEM), atomic force microscope (AFM), X-ray diffraction (XRD), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). The nanostructural nature of the investigated films was confirmed from the estimated average size of the particles. Better crystallinity was achieved with the addition of 15 wt% cerium disulfate to PVP. The thermograms of DSC and its derivative for the investigated composites indicated the development of a new endothermic peak of decomposition nature, and the values of peak position and associated enthalpy were found to be composition dependent, indicating a decrease in thermal stability of PVP with the increase of dopant concentration. Thermograms of TGA and its derivative revealed that the weight loss in the composite samples is composition dependent, and two main steps of degradation were clearly evident, the first assigned mainly to dehydration processes at relatively lower temperature range (30–200 °C) and the second at higher temperatures up to 400 °C attributed to decomposition processes. Thermodynamic parameters, such as activation energy, entropy, enthalpy, and Gibbs free energy, were also determined on the basis of thermogravimetric data.     

Operando X-ray Absorption Spectroscopy Study of Pt/γ-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> During the Total Oxidation of C<Subscript>3</Subscript>H<Subscript>6</Subscript>

Operando X-ray absorption fine structure (XAFS) investigations were performed on Pt/γ-Al₂O₃ during the total oxidation of C₃H₆ in reducing and oxidizing atmospheres. Study of the Pt valance state and catalytic conversion behavior as a function of temperature revealed that both the creation of metallic Pt sites and the activation of adsorbed species on Pt are important for the functioning of the catalytic reaction at low temperature.     

An Efficient and Eco-friendly MoO<Subscript>3</Subscript>–SiO<Subscript>2</Subscript> Solid Acid Catalyst for Electrophilic Aromatic Nitration with N<Subscript>2</Subscript>O<Subscript>5</Subscript>

Abstract  

Electrophilic aromatic nitration using N₂O₅ as a green nitrating agent catalyzed by MoO₃–SiO₂ under mild conditions has been described. A series of MoO₃–SiO₂ catalysts with varying MoO₃ loadings (5–20 mol%) were prepared by sol–gel technique and characterized using FTIR, XRD, SEM, BET and NH₃–TPD to study its surface properties. MoO₃–SiO₂ shows good catalytic activity and reusability for the nitration of alkyl and halogen aromatics giving high conversions, but less efficiency for the deactivated aromatics. Reactions conducted under non-acidic conditions using N₂O₅ makes the process safe and environmentally friendly.