Fast preparation of ordered crystalline mesoporous titania with high thermal stability and photo oxidation performance

Ordered mesoporous titania with crystalline anatase walls has been synthesized through fast evaporation-induced self-assembly method in a non-aqueous solution that only needs a 30 h synthetic period. The ordered mesostructure and crystalline anatase frameworks are characterized by the low-angle and wide-angle X-ray diffraction (XRD) and transmission electron microscopy (TEM). The ordered titania mesostructure is thermally stable to 733 K, and the corresponding N₂ adsorption–desorption analysis exhibits that it has a surface area of 246 m²/g and a narrow pore distribution centered at 3.7 nm. Crystalline mesoporous titania exhibits the higher catalytic performance in photooxiding α-methylstyrene to acetophenone.     

Synthesis and characterization of soluble polyamides from bis-[(4′-aminobenzyl)-4-benzamide] ether and various diacids

New aromatic diamine containing preformed amide, ether, and methylene; bis-[(4′-aminobenzyl)-4-benzamide] ether (BABE), was synthesized and characterized by FT-IR, NMR, and mass spectrometry. Aromatic–aliphatic polyamides were prepared from BABE with aliphatic/aromatic diacids via Yamazaki’s polymerization. The polyamides were characterized by FT-IR, ¹H NMR, inherent viscosity [η_inh], solubility tests, differential scanning calorimetry [DSC], thermogravimetric analysis [TGA], and X-ray diffraction [XRD]. Polyamides had inherent viscosities 0.35–0.84 dL/g, soluble in aprotic polar solvents like N-methyl-2-pyrrolidone, N, N-dimethyl acetamide and dimethyl sulphoxide containing LiCl due to an amorphous to partially crystalline morphology; as XRD patterns indicated. DSC analysis of polyamides showed glass transition temperatures 166–268 °C. Polyamides showed high thermal stability as they did not degrade below 300 °C, had 10% weight loss temperature higher than 375 °C, and the char yields at 900 °C were 22–55%; indicating potential applications as engineering materials.     

Pseudo-capacitance properties of porous metal oxide nanoplatelets derived from hydrotalcite-like compounds

Nanoplatelets of metal oxides with interesting porous structure were obtained by thermal treatment of Ni/Al hydrotalcite. Structural and surface properties of the porous oxides were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM and HRTEM), and N₂ adsorption–desorption. The electrochemical performance of the electrodes was investigated by cyclic voltammetry, electrochemical impedance spectroscopy and constant current charge–discharge measurements. Ni/Al hydrotalcite calcined at 450 °C (NA-450) displayed a maximum specific capacitance (419.0 F g⁻¹) due to the porous structure with the highest specific surface area (142.3 m² g⁻¹) and small pore size (4.4 nm). The present study shows the potential of NiO nanoplatelets composite material for electrochemical pseudo-capacitors.     

The influence of preparation method on the physicochemical properties of titania–silica aerogels: Part two

Titania–silica aerogels with different titania content were prepared. Four preparation methods differing mainly in approach to precursors hydrolysis were applied, while only three of them allowed total hydrolysis of silica precursor before titania precursor was added. The preparation of mixed products of titania and silica hydrolysis precursors containing gels was followed by high temperature supercritical drying (HTSCD) and thermal treatment at 500 °C. Obtained mixed oxides in form of aerogels were characterized by BET surface areas up to 1000 m²/g, mesopore volumes up to 1.6 cm³/g and bulk densities as low as 0.04 g/cm³. Even 18 h lasting aging did not allow to produce narrow diameter range mesoporous materials, their broad pore diameter distributions resulted in average pore sizes varying from 10 to nearly 30 nm. XRD measurements proved the presence of anatase crystalline form of titania, while silica was present in amorphous form. SEM studies indicated presence of isolated titania particles on titania–silica surface while joint hydrolysis method was applied. Titania–silica aerogels obtained by the simultaneous hydrolysis of precursors and the impregnation method showed high photocatalytic activity in degradation of salicylic acid in water. Activities of these mesoporous photocatalysts were higher than commercial P25 Degussa TiO₂. Comparison of activity of pure TiO₂ (P25 Degussa) and aerogels indicates higher utilization of titania present in mesoporous mixed oxides.     

Synthesis and characterization of 5?V LiCoxNiyMn2?x?yO4 (x?=?y?=?0.25) cathode materials for use in rechargeable lithium batteries

Double doped spinel LiCo _x Ni _y Mn_2−x−y O₄ (x = y = 0.25) have been synthesised via sol–gel method using different chelating agents viz., acetic acid, maleic acid and oxalic acid to obtain 5 V positive electrode material for use in lithium rechargeable batteries. The sol–gel route endows lower processing temperature, lesser synthesis time, high purity, better homogeneity, good control of particle size and surface morphology. Physical characterizations of the synthesized powder were carried out using thermo-gravimetric and differential thermal analysis (TG/DTA), X-ray diffraction (XRD), scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). The electrochemical behaviour of the calcined samples has been carried out by galvanostatic charge/discharge cycling studies in the voltage range 3–5 V. The XRD patterns reveal crystalline single-phase spinel product. SEM photographs indicate micron sized particles with good agglomeration. The charge–discharge studies show LiCo_0.25Ni_0.25Mn_1.5O₄ synthesized using oxalic acid to be as a promising cathode material as compared to other two chelating agents and delivers average discharge capacity of 110 mA h g⁻¹ with low capacity fade of 0.2 mA h g⁻¹ per cycle over the investigated 15 cycles.     

The Influence of the Temperature on the Optical Absorption Properties and Morphologies of WO<Subscript>3</Subscript> Nanorods Synthesized by the Hydrothermal Method

Crystalline WO₃ nanorods of less than 100 nm in diameter have been successfully synthesized at 240 °C for 48 h at pH 1.5 by the hydrothermal method with sodium tungstate as a tungsten source and potassium sulphate as a subsidiary salt. The morphologies and structures of WO₃ rods were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM) and selected-area electron diffraction (SAED). SEM analysis confirms that the slenderness ratio of the WO₃ rods is enlarged with the increase of the reaction temperature at pH 1.5. SAED analysis shows that the synthesized WO₃ nanorods are crystalline. Ultraviolet–visible (UV-VIS) absorption spectroscopy shows that absorbent power of UV light for WO₃ nanorods enhances with an increase of the slenderness ratio.     

Manganese oxide nanocomposites with improved surface area prepared by one-pot surfactant route for electro catalytic and biosensor applications

Braunite phase manganese oxide is naturally available in manganese–silicate rocks with minor amount of silicate content. New synthetic route is attempted to prepare the manganese oxide nanoparticle and silica incorporated manganese oxide nanocomposite in the present study. XRD patterns reveal the braunite phase formation for as synthesized manganese oxide nanocomposite and silica incorporated MnO₂ nanocomposite materials. Improved BET surface area values are achieved by one step surfactant assisted method (i.e., 82 and 151 m²/g) compared to conventional route prepared manganese oxide nanomaterial. Flaky pastry type morphology was observed for as synthesized Si–MnO₂ nanocomposites. Cyclic voltammetry studies predict the electrocatalytic activity of manganese oxide nanoparticle and Si–MnO₂ nanocomposite in presence of electroactive redox couple. Si–MnO₂ nanocomposite modified glassy carbon (GC) electrode shows the effective electroactive response in presence of Fe²⁺/Fe³⁺ redox couple at 0.69 V with current density of 0.343 × 10⁻⁵ A/cm² compared to manganese oxide nanoparticle modified GC electrode. The biosensor responses for ascorbic acid have been tested in the present study and manganese oxide nanoparticle modified GC electrode shows effective response at low concentration of (1 × 10⁻⁵ M) ascorbic acid in phosphate buffer solution. Manganese oxide nanoparticle modified electrode shows the better response with current density value of 0.115 × 10⁻⁵ A/cm² compared to Si–MnO₂ nanocomposite.     

Preparation of Zinc(II) Oxide Nanoparticles from a New Nano-Size Coordination Polymer Constructed from a Polypyridyl Amidic Ligand; Spectroscopic, Photoluminescence and Thermal Analysis Studies

A new zinc(II) coordination polymer, {[Zn(bpcdp)₂(DMF)₄](ClO₄)₂·(H₂O)₂}_n (1) bpcdp = 2,6-bis(4-pyridinecarboxamide)pyridine has been synthesized and characterized by IR, ¹HNMR and ¹³CNMR spectroscopy. The single crystal X-ray data of compound 1 shows the zinc(II) atom has been considered as octahedral with ZnN₂O₄ coordination sphere. Two nitrogen atoms of bpcdp ligand and four oxygen atoms of DMF molecules have occupied coordination sphere around zinc(II) atoms. The prepared zinc(II) coordination polymer grows in three-dimensional network by hydrogen bonding and π–π stacking interaction. The nanostructure of compound 1 were obtained by sonochemical process and studied by scanning electron microscopy (SEM), X-ray powder diffraction (XRD), IR and NMR spectroscopy. Thermal stabilities of single crystalline and nano-size samples of compound 1 were studied by thermal gravimetric (TG) and differential thermal analyses (DTA). The ZnO nanoparticles were obtained by direct calcination of compound 1 at 400 °C and by thermolysis in oleic acid at 200 °C. The obtained zinc(II) oxide nanoparticles were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM).     

Sulfated and Persulfated TiO2/MCM-41 Prepared by Grafting Method and their Acid-catalytic Activities for Cyclization of Pseudoionone

Solid acid catalysts of SO₄²⁻/TiO₂/MCM-41 and S₂O₈²⁻/TiO₂/MCM-41 were prepared via grafting method and sulfate/persulfate promotion. The catalysts exhibited desirable activity and better selectivity for cyclization reaction of pseudoionone compared to traditional SO₄²⁻/TiO₂. A combination of XRD, N₂ adsorption–desorption and FTIR spectroscopy indicated that the catalysts possess well-ordered mesostructure, and the grafted TiO₂ are in highly dispersed amorphous form rather than crystalline phase. For S₂O₈²⁻/TiO₂/MCM-41 higher S content and more Br?nsted acid sites can be achieved by persulfation, which is favorable for the protons participated cyclization reaction. The similar Si–O–Ti–O–S=O structure of all acid sites on pore surface of the catalysts is attributed to the improvement of selectivity in comparison with SO₄²⁻/TiO₂.     

Novel MgO–SnO<Subscript>2</Subscript> Solid Superbase as a High-Efficiency Catalyst for One-Pot Solvent-Free Synthesis of Polyfunctionalized 4<Emphasis Type="Italic">H</Emphasis>-pyran Derivatives

Abstract  

We report for the first time the hydrothermal synthesis of MgO–SnO₂ solid superbase using P123 as template. The basicity of the materials was determined by two approaches of Hammett indicators method and temperature-programmed desorption using CO₂ as adsorbate (CO₂-TPD). It was found that Mg/Sn molar ratio has an effect on MgO–SnO₂ basicity, and superbasicity was observed only at Mg/Sn molar ratio of 1. With variation of Mg/Sn molar ratio, superbase strength (H _-) was in the 26.5–33.0 range, showing superbasic value up to 0.939 mmol/g. The structure and texture of the as-prepared materials were studied by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), and N₂ physio-adsorption methods. We detected particles of spherical morphology having diameter of ca. 150 nm. N₂ adsorption–desorption results suggested that the materials are of mesoporous structure, having specific surface area of 115.2 m²/g and average pore diameter of 6 nm. The superbase was found to exhibit excellent catalytic activity towards the one-pot synthesis of polyfunctionalized 4H-pyrans through the condensation of aldehydes, malononitrile, and an active methylene compound. Its excellent catalytic efficiency is related to its superbasicity of the MgO–SnO₂. The results provide a new route for the design and preparation of composite oxide superbases. Furthermore, the solid superbases will facilitate a strategy for high-efficiency synthesis of polyfunctionalized 4H-pyrans.     

Development of a simple aqueous solution based chemical method for synthesis of mesoporous γ-alumina powders with disordered pore structure

A technically simple chemical method for the synthesis of mesoporous γ-alumina has been reported. Mesoporous γ-aluminas with different pore structure and surface area were synthesized by using aluminium nitrate as a source of aluminum. Supramolecular liquid crystalline phase of acid soap template synthesized via reaction of different carboxylic acids (stearic acid, oliec acid and lactic acid) with excess of triethanolamine (TEA) acts as a structure directing agent and water was used as solvent. Precursors were calcined at 550 °C in air for 2 h to obtain mesoporous alumina powders. Synthesized γ-alumina powders were characterized by using thermogravimetric analysis, X-ray diffraction, high resolution transmission electron microscope and N₂ adsorption–desorption surface area and pore size analyzer. Pore size and ordering of pores were influenced by the chain length of carboxylic acids. Surface area of synthesized alumina powders varied from 214 to 376 m²/g and average pore diameter from 3.3 to 6.5 nm depending upon the chain length of the carboxylic acid.     

Nonstoichiometric Titanium Oxides via Pulsed Laser Ablation in Water

Titanium oxide compounds TiO_, Ti₂O₃, and TiO₂ with a considerable extent of nonstoichiometry were fabricated by pulsed laser ablation in water and characterized by X-ray/electron diffraction, X-ray photoelectron spectroscopy and electron energy loss spectroscopy. The titanium oxides were found to occur as nanoparticle aggregates with a predominant 3+ charge and amorphous microtubes when fabricated under an average power density of ca. 1 × 10⁸ W/cm² and 10¹¹ W/cm², respectively followed by dwelling in water. The crystalline colloidal particles have a relatively high content of Ti²⁺ and hence a lower minimum band gap of 3.4 eV in comparison with 5.2 eV for the amorphous state. The protonation on both crystalline and amorphous phase caused defects, mainly titanium rather than oxygen vacancies and charge and/or volume-compensating defects. The hydrophilic nature and presumably varied extent of undercoordination at the free surface of the amorphous lamellae accounts for their rolling as tubes at water/air and water/glass interfaces. The nonstoichiometric titania thus fabricated have potential optoelectronic and catalytic applications in UV–visible range and shed light on the Ti charge and phase behavior of titania-water binary in natural shock occurrence.     

An Innovative Synthesis of Calcium Zeolite Type A Catalysts from Eggshells via the Sol–Gel Process

Calcium zeolite type A (CaNaAlSi₂O₇), called soda melilite, with a molar ratio of CaO:Al₂O₃:Na₂O:SiO₂ of 1:1:2:8 and calcined at 300 °C for 1 h was successfully synthesized by a sol–gel process using eggshell as the starting material. The CaNaAlSi₂O₇ catalysts had N₂ adsorption–desorption isotherms and good electrical properties. The specific surface area, pore volume, and average pore diameter were 55.15 m²/g, 0.51, and 37.19 nm, respectively. The dielectric constant, electrical conductivity, and loss tangent are 46.5785, 5.2360 × 10⁻³ (Ω m)⁻¹, and 2.75, respectively as measured at room temperature and at 1000 kHz (1 MHz). The transmission electron microscopy (TEM) images showed a moderately good dispersion of uniform particles with an average diameter of about 0.5 nm. X-ray diffraction patterns (XRD), Fourier transform infrared spectra, and simultaneous thermal analysis data (STA) were obtained to confirm the synthesis products.     

Novel amorphous precursor densification to transparent Nd:Y2O3 Ceramics

A novel approach of neodymium ion doped yttrium oxide (Nd:Y₂O₃) amorphous precursor compaction and sintering is being reported for the first time. Precursor of 2 at.% Nd³⁺ doped Y₂O₃ was synthesized by gelation of sol of yttrium and neodymium nitrates with l-alanine at 80 °C for 16 h followed by gel combustion in microwave. A part of microwave precursor was heat treated at 700 °C for 5 h to give the partially crystalline Nd:Y₂O₃ amorphous precursor. Thermogravimetric analysis (TGA) of partially crystalline amorphous precursor of Nd:Y₂O₃ gave 8.5% total weight loss indicating removal of maximum organics. X-Ray diffraction (XRD) showed broad peaks indicating incomplete crystallization of cubic Nd:Y₂O₃. Morphology was found to be close to spherical with particles in size range 17–19 nm by TEM. Another part of microwave precursor on calcination at 1000 °C for 3 h led to formation of fully crystalline Nd:Y₂O₃ with particles in size range of 35–85 nm. Both partially crystalline amorphous precursor and fully crystalline Nd:Y₂O₃ were compacted at 400 MPa by cold isostatic press and sintered at 1750 °C for 10 h under vacuum (10^?5 mbar). The partially crystalline Nd:Y₂O₃ amorphous precursor densified to 99% with 65% transmission at 2500 nm (0.5 mm thickness) compared to 96% densification with 34% transmission for fully crystalline Nd:Y₂O₃ without any sintering aids. Retention of cubic phase purity of Y₂O₃ was observed in both the ceramic pellets post sintering by XRD. Good grain fusion with grain growth to ≤2 μm was observed by scanning electron microscope (SEM) for partially crystalline Nd:Y₂O₃ amorphous precursor. Thus partially crystalline Nd:Y₂O₃ amorphous precursor nanopowders, with homogeneous close to spherical fine particles and high reactivity due to ionic mobility of amorphous phase, led to better densification.     

(100) facets of γ-Al2O3: The Active Surfaces for Alcohol Dehydration Reactions

Abstract  

Temperature programmed desorption (TPD) of ethanol, as well as ethanol and methanol dehydration reactions were studied on γ-Al₂O₃ in order to identify the active catalytic sites for alcohol dehydration reactions. Two high temperature (>473 K) desorption features were observed following ethanol adsorption. Samples calcined at T ≤ 473 K displayed a desorption feature in the 523–533 K temperature range, while those calcined at T ≥ 673 K showed a single desorption feature at 498 K. These two high temperature desorption features correspond to the exclusive formation of ethylene on the Lewis (498 K) and Br?nsted acidic (~525 K) sites. The amount of ethylene formed under conditions where the competition between water and ethanol for adsorption sites is minimized is identical over the two surfaces. Furthermore, a nearly 1-to-1 correlation between the number of under-coordinated Al³⁺ ions on the (100) facets of γ-Al₂O₃ and the number of ethylene molecules formed in the ethanol TPD experiments on samples calcined at T ≥ 673 K was found. Titration of the penta-coordinate Al³⁺ sites on the (100) facets of γ-Al₂O₃ by BaO completely eliminated the methanol dehydration reaction activity. These results demonstrate that in alcohol dehydration reactions on γ-Al₂O₃, the (100) facets are the active catalytic surfaces. The observed activities can be linked to the same Al³⁺ ions on both hydrated and dehydrated surfaces: penta-coordinate Al³⁺ ions (Lewis acid sites), and their corresponding –OH groups (Br?nsted acid sites), depending on the calcination temperature.     

An organic/inorganic hybrid mesoporous silica membrane: preparation and characterization

An organic/inorganic hybrid mesoporous silica membrane composed of mesoporous silica materials inside the channels of polycarbonate filtration membrane (PC) was synthesized by using aspiration-induced infiltration method, and the surfactant in as-prepared membrane was removed by employing template-extraction method. The obtained materials were characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD),transmission electron microscopy (TEM) and N₂ adsorption–desorption measurement. The SEM images and EDS elemental analyses show that as-synthesized materials in PC are one-dimensional silica rods estimated as 200 nm in diameter and 9 μm in length. Moreover, the results of XRD, TEM and N₂ adsorption–desorption analysis clearly demonstrate that such silica rods are mesoporous materials with two-dimensional hexagonal mesostructure and the average mesopore diameter is about 3.0 nm. In addition, the porosity of organic/inorganic hybrid mesoporous silica membrane was further examined by molecule permeation. It is found that small molecule, such as rhodamine B, can transport across the membrane, but relatively large molecule, such as horse radish peroxidase, can not transport across the membrane, indicating that it is size-selectivity of such a membrane for molecule permeation, which has the potential application in the molecule filters to separate bio-macromolecule from small molecule.     

Hydrothermal synthesis of amorphous MoS2 nanofiber bundles via acidification of ammonium heptamolybdate tetrahydrate

MoS₂ nanofiber bundles have been prepared by hydrothermal method using ammonium molybdate with sulfur source in acidic medium and maintained at 180 °C for several hours. The obtained black crystalline products are characterized by powder X-ray diffraction (PXRD), Fourier transform infrared spectrometer (FTIR), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The PXRD pattern of the sample can be readily indexed as hexagonal 2H-MoS₂. FTIR spectrum of the MoS₂ shows the band at 480 cm⁻¹ corresponds to the γ_as(Mo-S). SEM/TEM images of the samples exhibit that the MoS₂ nanofiber exist in bundles of 120–300 nm in diameter and 20–25 μm in length. The effects of temperature, duration and other experimental parameters on the morphology of the products are investigated.     

Changes in Surface Property and Catalysis of Mesoporous Nb<Subscript>2</Subscript>O<Subscript>5</Subscript> from Amorphous to Crystalline Pore Walls

Abstract  

The amorphous inorganic phase of an ordered amorphous mesoporous Nb₂O₅ with two dimensional hexagonal (2D-hex) structure was crystallized with maintaining the original well arranged porous structure. The difference in surface property between amorphous and crystalline Nb₂O₅ with similar ordered mesoporous structure was compared. It was found from water adsorption–desorption isotherms and observation by infrared (IR) spectroscopy that the amorphous sample was hydrophilic and that the surface OH groups were acidic. On the other hand, the OH groups on crystalline mesoporous Nb₂O₅ were non-acidic and inside the pores was less hydrophilic. The surface property was also compared by a catalytic reaction, oxidation of cyclohexe by an aqueous solution of H₂O₂. The high (95%) selectivity for 1,2-epoxycyclohexane was obtained at 40 °C for 2 h in methanol solvent over crystalline mesoporous Nb₂O₅ at 12% conversion, while amorphous mesoporous Nb₂O₅ showed high (68%) selectivity for 1,2-cyclohexanediol in acetonitrile solvent at 60 °C for 2 h at 22% conversion. The differences in selectivity and the optimal solvent between amorphous and crystalline samples were interpreted in terms of the acidic feature of surface OH groups and hydrophilicity. While similar selectivity was observed over non-porous crystalline Nb₂O₅, much higher conversion over crystalline mesoporous Nb₂O₅ was attained at the same surface area. Thus, an advantage of mesoporous structure is attributed to the higher contact time of molecules inside the pores to the catalyst surface than those outside the particles.     

Glycothermal Synthesis and Catalytic Properties of Nanosized Zn1?xCoxAl2O4 (x?=?0, 0.5, 1.0) Spinels in Phenol Methylation

Abstract  

Zn_1−x Co _x Al₂O₄ (x = 0, 0.5, 1.0) spinels were synthesised under microwave-assisted solvothermal conditions using 1,4-butanediol as reaction medium. The results of XRD and HRTEM have indicated nanocrystallinity of prepared materials (average crystallite size in the range 6–16 nm), and N₂ adsorption–desorption measurements have revealed high feature of their surface area and mesoporous nature. Acid–base properties of prepared materials were determined using TPD-NH₃ method and cyclohexanol test. All studied spinels that underwent examination were active in phenol methylation but Co-substituted zinc aluminate (Zn_0.5Co_0.5Al₂O₄) was found to be the most efficient in the selective formation of ortho-methylated products. It could be ascribed to its dominant basic character and the presence of weak and strong acid centres, and the highest surface area as well.     

Catalytic activities and properties of mesoporous sulfated Al2O3–ZrO2

Mesoporous sulfated Al₂O₃–ZrO₂ (MSAZ) catalysts with large surface areas and pore volumes after calcination at high temperature (650 °C) and with higher Al₂O₃ content than 20wt% were successfully prepared from a template of block copolymer (P84). The MSAZ catalysts were characterized by X-ray diffraction (XRD), N₂ adsorption, transmission electron microscopy (TEM), ²⁷Al magic-angle spinning nuclear magnetic resonance (MAS NMR), thermogravimetric analysis (TG–DTG), temperature-programmed desorption of ammonia (NH₃-TPD) and infrared spectra (IR) of adsorbed pyridine. It is shown that the resulting mesostructured sulfated Al₂O₃–ZrO₂ samples have a well-developed textural mesoporosity. The number of acid sites present on MSAZ catalysts is higher than that on conventional sulfated zirconia, and the former catalysts are more active than the latter one for various acid-catalyzed reactions.