Liquid Sorption and Nanoparticle Intercalation in Layer-Structured Materials

Abstract

Alkylammonium intercalated graphite oxides (R-GO), palladium intercalated alumina-pillared montmorillonites (Pd/Al₂O₃-PILC) and titania-pillared montmorillonites (TiO₂-PILC) have been prepared and the intercalation materials have been characterized by BET surface area analysis, UV/VIS spectroscopy, ICP-AES, DTG-DTA, XRD and TEM measurements. R-GO particles were prepared by oxidation of natural graphite followed by organophilization with cationic surfactants. For TiO₂-PILC and Pd/Al₂O₃-PILC the synthesis included the interlamellar adsorption of precursor species (polyaluminium-hydroxide, Pd-acetate and tetraethyl orthotitanate) from dilute solutions and subsequent chemical reactions at the montmorillonite/solution interface.     

Synthesis and characterization of mesoporous,tungsten-containing molecular sieve composites

Mesoporous, tungsten-containing molecular sieve (W-SBA-15) composites were successfully synthesized via one-step hydrothermal processing using tetraethyl orthosilicate (TEOS) as the silica precursor, sodium tungstate as the tungsten precursor, and pluronic P123 triblock polymer (EO₂₀PO₇₀EO₂₀, M_av = 5800) as a structure-directing reagent. The influence of various synthesis factors, such as TEOS/sodium tungstate (Si/W) molar ratios, stirring solution temperatures, TEOS pre-hydrolysis time, and crystallization temperatures, on the structure of the W-SBA-15 composite were investigated. The prepared materials were characterized by using X-ray diffraction (XRD), infrared spectroscopy (IR), diffuse reflectance ultraviolet–visible spectroscopy (DR UV–vis), scanning electron microscopy (SEM), and nitrogen adsorption–desorption measurements. The results showed that all the W-SBA-15 composite materials retained the mesopore structure of SBA-15 and the tungsten oxide species successfully substituted silica in the framework.     

Crystallization properties of zeolite A synthesized from coal fly ash using a fusion/hydrothermal method

Abstract

Zeolitic materials were synthesized from coal fly ash (CFA) using the fusion/hydrothermal method. The effect of NaOH/CFA ratio and particle size on the morphological structure of the zeolitic material crystals prepared was investigated by analyzing crystals morphology and crystallinity. The chemical composition, morphology, and crystallinity of the synthesized materials were characterized by SEM, XRD, and XRF. It was possible to synthesize chamfered-edged cubic crystals at NaOH/CFA ratio of 0.9. The particle size of the zeolite crystals tended to decrease with increasing the alkali content of NaOH/CFA from 0.9 to 1.8. The morphological structure of the crystalline particles was similar to that of zeolite A synthesized from the CFA. This study has shown that the fusion/hydrothermal method is a very effective technique for synthesizing the zeolitic materials from the CFA and provides a potential application for obtaining commercial products.     

Synthesis,structural and optical properties of well dispersed anatase TiO2 nanoparticles by non‐hydrothermal method

The formation of nanocrystalline TiO₂ particles has been investigated via a surfactant‐free synthetic non‐hydrothermal method. Titanium isopropoxide and toluene were used as the starting materials. At a low temperature of 250 °C for 6 h, the reaction mixture turned in to a white precipitate (TiO₂) as a result of the thermal decomposition of metal alkoxide. The obtained product was found to crystallize purely in the anatase phase with well defined morphology. The powder XRD study confirms that the average size of the particle is close to ∼15 nm. The TEM analysis indicates the sizes of the primary and secondary particles in the range between 8‐10 nm and 15‐20 nm respectively. The quantum size confinement of the crystallites is evident from the blue shift of the absorption edge in the UV‐Visible absorption spectrum. The luminescence property of the TiO₂ nanoparticles studied by the emission spectrum confirms the presence of defect levels caused by the oxygen vacancies. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthesis of anisotropic gold nanoparticles using xylitol as a dual functional reductant and stabilizer

The morphology of gold nanoparticles was controlled with hydrogentetrachloroaurate (HAuCl₄) and xylitol through a hydrothermal process using xylitol as reducing agent and controlled reagent. The molar ratio of xylitol relative to HAuCl₄, reaction time and temperature played important roles in determining the geometric shape and size of the product. These nanoplates were single crystals with planar width of 80‐500 nm. The formation of nanobelts and two‐dimensional single‐crystal nanosheets is explained by the preferential adsorption of xylitol molecules from the solution onto the {111} planes of Au nuclei. These nanosheets could be used, for example, in gas sensors, in the fabrication of nanodevices and substrate materials, in property studies, and also for inducing hypothermia in tumors. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Capsule‐like α‐Fe2O3 nanoparticles: Synthesis,characterization, and growth mechanism

Uniform capsule‐like α‐Fe₂O₃ particles were synthesized via a simple hydrothermal method, employing FeCl₃ and CH₃COONa as the precursors and sodium dodecyl sulfate (SDS) as soft template. X‐ray powder diffraction (XRD), field emission scanning electron microscopy (FE‐SEM), transmission electron microscopy (TEM), and high‐resolution transmission electron microscopy were used to characterize the structure of synthesized products. Some factors influencing the formation of capsule‐like α‐Fe₂O₃ particles were systematically investigated, including different kinds of surfactants, the concentration of SDS, and reaction times. The investigation on the evolution formation reveals that SDS was critical to control the morphology of final products, and a possible five‐step growth mechanism was presented by tracking the structures of the products at different reaction stages.     

Hydrothermal synthesis of organic hybrid BaTiO3 nanoparticles using a supercritical continuous flow reaction system

Barium titanate (BaTiO₃: BT) nanoparticles were synthesized by the hydrothermal method in the presence of dispersants using a continuous supercritical flow reaction system. The reactants of TiO₂ sol/Ba(NO₃)₂ mixed solution and KOH solution were used as starting materials and that was heated quickly up to 400 °C under the pressure of 30 MPa for 8 ms as reaction time. The dispersant solution such as polyacrylic acid (PAA) and polyoxyethylene(20) sorbitan monooleate (Tween 80) was injected in the cooling process after the reaction. The crystal phase of the obtained particles was identified as perovskite cubic BaTiO₃ by X-ray diffractometry (XRD) and Raman spectroscopy. Raman spectra and thermogravimetric data revealed that PAA and Tween 80 fabricated hybrid BT nanoparicles. Primarily particle size of the BaTiO₃ nanoparticle was determined by means of BET surface area, as small as less than 10 nm irrespective of dispersants. In contrast, dispersed particle size in solution measured by dynamic light scattering (DLS) technique decreased from 282 nm to less than 100 nm depending on the dispersant. Aggregation of BaTiO₃ nanoparticles might be depressed in the presence of dispersants, especially PAA is the most effective among the dispersants examined.     

Effects of progressive changes in organoalkoxysilane structure on the gelation and pore structure of templated and non-templated sol–gel materials

We study how progressive changes in silane structure affect the synthesis and properties of organosilicas. Tetraethoxysilane (TEOS), tetramethoxysilane (TMOS), methyltrimethoxysilane (MTMS), bis(trimethoxysilyl)ethane (BTMSE), bis(trimethoxysilyl)hexane (BTMSH), and bis(trimethoxysilylpropyl)amine (BTMSPA) are used as precursors in non-templated base and acid-catalyzed sol–gel processes, and in templated processes with cetyltrimethylammonium bromide (CTAB) and polyoxyethylene 10 lauryl ether (C₁₂E₁₀). The gel time of materials made without templates is mainly controlled by the structure of the silane rather than its reactivity. For instance, a dangling methyl group (MTMS) inhibits gelation, while a short bridging chain (BTMSE) promotes gelation. In basic conditions, mesoporous materials are obtained with TEOS and TMOS, while microporous materials are obtained with organically modified silanes without added amine. Dipropylamine, originally added as a catalyst, in fact templates mesopores in BTMSH-derived organosilica. In acidic conditions without pore templates, all products are microporous. In the presence of CTAB, mesopore templating occurs with TEOS, TMOS, BTMSE, and BTMSPA. With C₁₂E₁₀, mesopore templating occurs with TEOS, TMOS, and BTMSE. Surprisingly, the BTMSE-based material has the most uniform mesopores of all samples in the C₁₂E₁₀ series. Mesopore templating fails when a dangling organic limits the formation of stable pore walls (MTMS) or a large hydrophobic chain disrupts the formation surfactant micelles (BTMSH).     

Synthesis of SrMnO3 powders with different morphologies by hydrothermal method

By using two different reagents as the starting materials, SrMnO₃ crystallines with two different morphologies rhombus‐like and rod‐like, have been directly synthesized by hydrothermal conditions. The effects of the hydrothermal parameters on the quality of the SrMnO₃ samples were given for the fist time. And a preparative mechanism for the formation of different morphologies using different reagents during the hydrothermal reaction has been discussed. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Self-assembly of highly crystalline spherical BiVO4 in aqueous solutions

Spherical bismuth vanadate particles are self-assembled from aqueous Bi(NO₃)₃ and NH₄VO₃ solutions by adjusting pH and tuning the amount of surfactant sodium dodecyl sulfate (SDS) via facile hydrothermal method. The BiVO₄ samples were characterized by X-ray diffraction (XRD) and the peaks suited well with the pure phase monoclinic scheelite BiVO₄. Field emission scanning electron microscopy (SEM) showed the average size of the spherical particles was 5 μm and the assembling stages in the hydrothermal synthesis process were recorded. Transmission electron microscopy (TEM) and selected area electron diffraction (SAED) revealed the nanoparticles were single crystal. FT-IR spectroscopy test results demonstrated there was no SDS left in the samples. The mechanism of the self-assembling has also been proposed.     

Microstructure and phase transformation of Ti3AC2 (A = Al,Si) in hydrofluoric acid solution

In this paper, Ti₃AC₂ (A = Al, Si) were prepared by pressureless argon shielding synthesis technique. The microstructure and phase transformation of as‐prepared Ti₃AC₂ (A = Al, Si) in hydrothermal hydrofluoric acid (HF) solution were investigated systematically. Results showed that the obtained Ti₃AlC₂ and Ti₃SiC₂ were closely aligned layered structure. In hydrothermal HF solution, Al or Si element was preferentially etched from the layered structure, inducing obvious transformation of microstructure and phase composition. For Ti₃AlC₂, Al atoms diffused out of the structure and reacted with HF to form AlF₃•H₂O, which induced the rearrangement of the Ti and C atoms, and finally resulted in the formation of TiC_x cubic phase. With the hydrothermal temperature and reaction time increasing, the TiC_x phase gradually disappeared and the grain size of AlF₃•H₂O gradually increased. When Ti₃SiC₂ was immersed in hydrothermal HF solution, the main products were TiC and SiC. Interestingly, with the hydrothermal treatment temperature and reaction time increasing, TiC gradually disappeared, while SiC nearly kept unchanged. This can be explained that SiC was covalently bonded carbide, while TiC was metallically bonded, having relatively weak bond energy and consequently being unstable in hydrothermal HF solution.     

Design and synthesis of small molecules with difluoroquinoxaline units for OSCs

Abstract

We designed and synthesized three novel small molecule donors (SM1, SM2 and SM3) that consist of thiophene as the electron-donating end group and 6,?7-?difluoroquinoxaline moiety as a novel electron-withdrawing core group. The organic low band gap molecules with 6,?7-?difluoroquinoxaline and thiophene units were synthesized using Stille coupling to generate SM1, SM2 and SM3. The absorption of SM2 and SM3 in solution was red shifted due to increased conjugation length of added thiophene units. In case of SM2 and SM3, introduction of hexyl chain in terminal thiophene units improve solubility in organic solvent. The maximum absorption peaks of SM1, SM2 and SM3 in solid thin films were at 482, 505 and 518?nm, respectively. SM3 was red shifted as compare to SM2 due to increased π-π stacking of electron donor materials.     

Synthesis and Crystal Structures of Two Complexes with Carboxylic Derivatives of Nitrogen-containing Heterocycle Ligands

Abstract  

Two new complexes [Zn(pcn)₂(H₂O)₂] (1) and [Cd(inic)₂(H₂O)₄] (2) (pcn = 2-pyrazinecarboxylate, inic = isonicotinic acid) were synthesized by the hydrothermal reaction and characterized by single crystal X-ray diffraction, elemental analysis, IR spectrum and UV spectrum. In complex 1, the Zn(II) central ion is six-coordinated by two oxygen atoms and two nitrogen atoms from pcn ligands and two oxygen atoms from two coordinated water molecules. In complex 2, the Cd(II) central ion is six-coordinated by two nitrogen atoms from isonicotinate ligands and four oxygen atoms from the coordinated water molecules. Both complexes are mononuclear but hydrogen bonds enrich the structural construction. The visible spectra of the complexes between 200 and 300 nm are assigned to intraligand (IL) π–π* transitions of the pyridyl or pyrazine ligands.     

Dichloro-{bis(Pyrazol-1-yl)}Palladium(II) Complexes: Structures of a DMSO Solvated Dichloro-{bis(3,5-Dimethylpyrazol-1-yl)Acetic Acid}Palladium(II) and Dichloro-{bis(3,5-Ditertbutylpyrazol-1-yl)Methane}Palladium(II)

Abstract  Two new palladium(II) complexes, dichloro-{bis(3,5-dimethylpyrazol-1-yl)acetic acid}palladium(II)PdCl₂(3,5-Me₂bpza)], (1) (3,5-Me₂bpza = 3,5-dimethylpyrazol-1-yl)acetic acid) and dichloro-{bis(3,5-ditertbutylpyrazol-1-yl)acetic acid}palladium(II), [PdCl₂(3,5-^tBu₂bpza)], (2a) [3,5- ^t Bu₂bpza = 3,5-ditertiarybutylpyrazol-1-yl)acetic acid] complexes, were synthesized from the reactions of pyrazol-1-yl ligands with palladium salts. Attempts to crystallize 2a led to a hydrolyzed product, dichloro-{3,5-ditertbutylpyrazol-1-yl}palladium(II) (2b), in which the acetic acid moiety in the ligand backbone of 1 is lost. Both complexes 1 and 2b have been characterized by single-crystal X-ray crystallography. Both complexes crystallized in triclinic system (P − 1 space group). The cell parameters are: complex 1 (a = 8.7960(14) Å, b = 16.238(2) Å, c = 16.430(2) Å, α = 78.038(10)°, β = 77.817(11)°, γ = 89.970(10)°) and complex 2b (a = 10.1492(2) Å, b = 12.4001(2) Å, c = 13.108(3) Å, α = 103.0690(10)°, β = 97.4120(10)°, γ = 107.2450(10)°). The asymmetric unit of 1 contains two crystallographic independent monomeric units of 1 and three molecules of DMSO solvent, whilst that of 2b has got one monomeric unit with one molecule of chloroform solvent. Index Abstract  Two palladium complexes, dichloro-{bis(3,5-dimethylpyrazol-1-yl)acetic acid}palladium(II), PdCl₂(3,5-Me₂bpza)], (1) (3,5-Me₂bpza = 3,5-dimethylpyrazol-1-yl)acetic acid) and dichloro-{bis(3,5-ditertbutylpyrazol-1-yl)acetic acid}palladium(II), [PdCl₂(3,5- ^t Bu₂bpza)], (3,5- ^t Bu₂bpza = 3,5-ditertiarybutylpyrazol-1-yl)acetic acid) complexes, were synthesized from the reactions of pyrazol-1-yl ligands with palladium salts. Attempt to obtain crystals of tertiarybutylpyrazolyl analogue led to hydrolysis, the crystal structure of the hydrolysis product was established by single crystal X-ray crystallography.      

Facile morphology‐controlled hydrothermal synthesis of flower‐like self‐organized ZnO architectures

Flower‐like self‐organized crystalline ZnO architectures were obtained through a facile and controlled hydrothermal process. As‐synthesized products were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), high‐resolution transmission electron microscopy (HRTEM), X‐ray diffraction (XRD), electron diffraction and UV‐Vis spectroscopy. XRD and electron diffraction results confirmed the obtained materials are pure wurtzite ZnO. The effects of different ratios of starting materials and solvent on the morphologies of ZnO hydrothermal products were also evaluated by SEM observations. It is suggested that the use of water, rather than ethanol as the solvent, as well as employing a precursor of Zn(Ac)₂ and 2NaOH (v/v) in hydrothermal reactions are responsible for the generation of specific flower‐like self‐assembled ZnO structures. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthesis and characterization of electrical features of bismuth manganite and bismuth ferrite: effects of doping in cationic and anionic sublattice: Materials for applications

The electrical, magnetic, and structural features of bismuth manganite (BM), e.g., BiMnO₃, and bismuth ferrite (BF), e.g., BiFeO₃, are reviewed. Induced multiferroicity and enhanced magnetoelectric coupling are required for various modern device applications. BM and BF were synthesized using standard high-temperature sintering and processes such as sol–gel, hydrothermal, or wet chemical methods combined with annealing. The size and morphology of the nanoscale particles were controlled, although they were usually inhomogeneous. BF exhibits structurally stable antiferromagnetic (AFM) and ferroelectric (FE) phases in wide temperature ranges. Ferromagnetic (FM) order was induced in a thick shell around the AFM core of the nanoscale BF particles, which was attributed to a size effect related to surface strains and disorder. BM exhibited both structurally stable and unstable phases. The BiMnO₃, Bi₁₂MnO₂₀, and BiMn₂O₅ structures are nonferroelectric. The perovskite BiMnO₃ form was synthesized under high hydrostatic pressure. FM order occurs in BM at low temperatures. Bi(MnFe)O₃ solid solution samples exhibited competition between AFM and FM ordering. Doping can decrease the content of unavoidable secondary phases. Doping in the Bi ion sublattice can stabilize the crystal lattice owing to local strains caused by the difference in ionic radius between Bi and the dopant. Doping in the Fe and Mn sublattices affects the electrical features. The main achievement of substitution with tetra- and pentavalent ions is compensation of the oxygen vacancies. In turn, leakage current suppression enables switching of FE domains and polarization of the samples. A significant enhancement of magnetoelectric coupling was observed in composites formed from BF and other FE materials. The leakage currents can be diminished when an insulator polymer matrix blocks percolation. The potential applicability is related to enhanced magnetoelectric coupling. The constructed devices meet the size effect limitations for FE and FM ordering. Resistive switching suggests possible use in nonvolatile memories and gaseous sensors. The sensors can be used for hydrophones and for photovoltaic and photoluminescence applications, and they can be constructed from multiphase materials. Bulk multiferroic solid solutions, composites, and nanoheterostructures have already been tested for use in sensors, transducers, and read/write devices for technical purposes.     

Hierarchical strontium carbonate submicron spheres self‐assembled under hydrothermal conditions

Uniform hierarchical strontium carbonate (SrCO₃) submicron spheres bearing detectable cavities on the surfaces and porous structures within the body were efficiently obtained, by a facile hydrothermal treatment (190 °C, 12 h) of the room temperature precipitate derived from Na₂CO₃ and SrCl₂ solution. MgCl₂ and ethylene diamine tetraacetic acid (EDTA) disodium salt were used as the additives. The as‐obtained submicron spheres were self‐assembled by crystalline SrCO₃nanoparticles under hydrothermal conditions. The present hydrothermally synthesized hierarchical SrCO₃ submicron spheres would enlarge the potentials of SrCO₃ micro‐/nanostructures in the hierarchical architectures and porous materials family for further applications in the fields of catalysis, composites, adsorbents, and devices, etc. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthesis and characterization of visible light responsive N-TiO2 mixed crystal by a modified hydrothermal process

N doped TiO₂ with anatase and rutile mixed crystal were prepared by using tetrabutyl titanate as the precursor via a modified hydrothermal process and calcination at 320 °C. The microstructure and morphology of samples were characterized by XRD, UV-vis-DRS, FTIR and XPS. The results showed that N-TiO₂ particles were crystallized to anatase and rutile mixed crystal structure; they were presented narrow particle size distribution, and the average particle size was ca. 13.5 nm calculated from XRD results. It was found that the N-doped TiO₂ particles showed strong visible-light absorption and high photocatalytic activity for the mineralization of Rhodamine B under irradiation by visible light (400-500 nm). The high visible-light photocatalytic activity of the obtained N-doped TiO₂ might result from the synergetic effect of nitrogen doping and the mixed lattice structure of N-TiO₂. Possible mechanism of N-TiO₂ mixed crystal formed under hydrothermal conditions was discussed.     

Thermal and chemical methods for producing zinc silicate (willemite): A review

Thermal and chemical methods for producing zinc silicate, Zn₂SiO₄ phosphor on industrial and laboratory scales are reviewed. Zinc silicate has a promising future in advanced materials as a highly versatile luminescent material due to the wide range of multi-colors that can be obtained from various guest ions. Candidates for future industrial methods of producing zinc silicate are critically reviewed from the point of view of phase formation and compared with the conventional solid-state reaction. Conventional methods require calcination at temperatures higher than 1000 °C and long reaction times to form Zn₂SiO₄ phase and these processes limit particle shape and size. Sol–gel methods are performed in a solvent at ambient pressure, while hydrothermal and solvothermal methods tend use high temperatures and high pressures, and especially supercritical water methods tend use conditions higher than 400 °C and 25 MPa. Hydrothermal and sol–gel literature shows that crystallization of Zn₂SiO₄ requires at least temperatures of around 100 °C. Of all the growth methods, supercritical water is able to bring about phase formation in the shortest reaction time. Vapor methods are performed with a gas phase as the reaction medium. Vapor and sol–gel methods require post-calcination for crystallization and have the advantage of providing characteristic particles such as uniform shapes, spherical particles, or nano-sized particles by varying the experimental conditions; they may be combined with the other crystallization routes in the future.     

A study of the growth process of Co3O4 microcrystals synthesized via a hydrothermal method

Pure Co₃O₄ microcrystals were prepared by a hydrothermal method from Co(NO₃)₂·6H₂O and urea solution, and the effect of thermal treatment time on the growth of Co₃O₄ microcrystals was studied by X‐ray diffraction (XRD), scanning electron microscopy (SEM), Raman and UV‐Vis absorption spectra. The results show that with the thermal treatment time increases from 2 h to 12 h, the shape of as‐prepared Co₃O₄ microcrystals changes from the hedgehog sphere‐like to the as‐cubic one that were stacked by lots of lamella, and finally cubes, and then longer time treatment will only lead to the size growth and agglomeration of particles. In conclusion, the cubic Co₃O₄ microcrystals of uniform size (∼6 μm) are synthesized via a 12‐h thermal treatment. Moreover, the synthesis mechanism has been studied.