Hydrothermal Treatment Time Research Articles

Instant synthesis of mesoporous monolithic materials with controllable geometry, dimension and stability: a review

The development of the nanoscale structures and their integration into components, systems, and natural architectures (such as monoliths), and large-scale devices, is one of the most promising areas in the emerging field of nanotechnology. We believe that it is time to write a review that focused on the rapid synthesis and the functional properties of HOM mesoporous monoliths. Thus, we here introduce comprehensive and up-to-date reports on the instant synthesis (within minutes) of a range of mesoporous silica monoliths (HOM-type, High-Order-Monolith) by means of a direct-templating method of lyotropic and microemulsion liquid crystalline phases. A number of nonionic n-alkyl-oligo(ethylene oxide), namely, Brij-type (CxEOy), and Triton- and Tween-type and cationic alkyl trimethylammonium bromide or chloride (CnTMA-B or -C, where n = 12, 14, 16 and 18) surfactants were used as soft templates. A variety of 1D, 2D and 3D mesostructure geometries were successfully fabricated by using this simple, fast and yet reproducible design strategy. This is the first and detailed review of using rapid synthesis to fabricate disordered and ordered silica/surfactant mesophases with supermicro- and meso-pore engineering systems. In this review, we also addressed the prominent factors affected the formation of the large-scale ordered and worm-like structures (HOM): (1) the phase composition of domains, (2) the extent of solubilization of hydrocarbons, and (3) the nature of surfactant molecules (corona/core features). Significantly, due to large morphological particle sizes, these HOM monolithic structures exhibited considerable structural stability against longer hydrothermal treatment times. Such retention is crucial in industrial applications.

Analysis of growth parameters for hydrothermal synthesis of ZnO nanoparticles through a statistical experimental design method

Nanocrystalline ZnO particles were synthesized from an aqueous solution composed of zinc acetate dihydrate (Zn(CH3COO)2·2H2O) and urea (H2NCONH2). A precipitating precursor, basic zinc carbonate (Zn5(CO3)2(OH)6), was first formed by hydrothermally treating the solution at 120 °C for 2–4 h. Nanocrystalline ZnO particles were then obtained by calcining the precursors at 350–650 °C for 0.5–2 h. The synthesis products were characterized using thermogravimetry–differential scanning calorimetry–mass spectrometry, X-ray diffraction, scanning electron microscopy, transmission electron microscopy and photoluminescence techniques. Based on the experimental results, a possible reaction mechanism for the ZnO formation was proposed. The effects of experimental parameters (namely, the hydrothermal treatment time, the calcination time, and the calcination temperature) on the characteristics of the resulting ZnO products (i.e., the crystalline size and the photoluminescence properties) were analyzed by the Taguchi method to attain the optimum synthesis conditions. By using the appropriate parameters derived from this method, we verified that the optimized synthesis provided a yield of ~70% and that the resulting ZnO particles possessed the characteristics of a ~25 nm crystalline size and a satisfactory photoluminescence property.

Thermal and hydrothermal stability of ZrMCM-41 mesoporous molecular sieves obtained by microwave irradiation

ZrMCM-41 mesoporous molecular sieves were synthesized by using the zirconium sulfate as zirconium source and using cetyltrimethyl ammonium bromide as a template under microwave irradiation condition. The samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), inductive coupled plasma (ICP) technique, Fourier transform infrared spectroscopy (FT-IR) and N2 physical adsorption, respectively. The effect of the different initial ZrO2: SiO2 molar ratio, the different thermal treatment temperature and hydrothermal treatment time on textural property was investigated. The results show that the obtained products possess a typical mesoporous structure of MCM-41 and have specific surface areas in the range of 598·1∼971·4 m2/g and average pore sizes in the range of ca. 2·46∼3·43 nm. On the other hand, the BET specific surface area and pore volume of the synthesized ZrMCM-41 mesoporous molecular sieve decrease with the increased amount of zirconium incorporated in the starting material, the rise of thermal treatment temperature and the prolonging of hydrothermal treatment time, the mesoporous ordering deteriorates. The mesoporous structure of the ZrMCM-41 mesoporous molecular sieve still retains after calcination at 750°C for 3 h or hydrothermal treatment at 100°C for 6 days, however, the mesoporous ordering is poor.

Neck Size of Ordered Cage-Type Mesoporous Silica FDU-12 and Origin of Gradual Desorption

To evaluate the neck size of ordered cage-type mesoporous silica FDU-12 and also to elucidate the origin of the gradual desorption always observed for the ordered silicas with cage-like pores of large necks, we measured successive adsorption of water at 283 K and nitrogen or argon at 77 K on five kinds of FDU-12 samples. For all the materials examined here, the amount of nitrogen or argon condensed inside the large cavities decreased rapidly over a relatively small range of water filling with an increase in water filling. Eventually, it reached a small value at water filling, well before the onset of pore condensation of water inside the large cavities. This clearly indicates that most of the cavities are isolated from bulk nitrogen or argon gas with water frozen in the necks. With the assumption that the necks in cage-like pores are cylindrical in shape, we assessed the pore size distribution of the necks available for desorption from the equilibrium relative pressure of water, in which the amount of nitrogen or argon condensed in the large cavities drops considerably. The neck size in the materials is increased with an increase of the hydrothermal treatment temperature and time. For a sample hydrothermally treated at 373 K for 7 days, the hysteresis loop of argon at 77 K gradually closed above the corresponding lower limit of the adsorption hysteresis, as is often observed in cage-like pores of large necks. However, the wide distribution of the capillary evaporation pressure did not correspond directly to the pore size distribution of the necks in the material.

Thermally stable mesoporous zirconia prepared via post-synthesis hydrothermal restructuring

The zirconia-based mesoporous materials with thermal stability up to 700 °C were prepared by post-synthesis hydrothermal restructuring treatment. The structural parameters of the resultant hydrothermally restructured materials change dramatically in comparison with the as-synthesized mesoporous zirconia, and the mesoporous structure order and stability are improved due to the pore wall thickening. The mesoporous zirconia without hydrothermal restructuring shows a disordered and wormhole-like pore structure, but the hydrothermal restructuring treatment can increase its thermal stability and retain its ordered mesopore arrangement up to 600 °C. The optimal temperature and time of post-synthesis hydrothermal treatment are 130 °C and 10 h, respectively. The obtained materials can be expected to act as a catalyst for the various organic reactions or a support for the activators.

Factorial design to optimize microwave-assisted synthesis of FDU-1 silica with a new triblock copolymer

The synthesis of FDU-1 silica with large cage-like mesopores prepared with a new triblock copolymer Vorasurf 504® (EO) 38(BO) 46(EO) 38 was developed. The hydrothermal treatment temperature, the dissolution of the copolymer in ethanol, the HCl concentration, the solution stirring time and the hydrothermal treatment time in a microwave oven were evaluated with factorial design procedures. The dissolution in ethanol is important to produce a material with better porous morphology. Increases in the hydrothermal temperature (100 °C) and HCl concentration (2 M) improved structural, textural and chemical properties of the cubic ordered mesoporous silica. Also, longer times induced better physical and chemical property characteristics.

Low Temperature Synthesis of (Ca, Ce)3Sc2Si3O12 Phosphor by Hydrothermal Gelation Method Using Novel Water Soluble Silicon Compound

Low temperature synthesis of a (Ca, Ce)3Sc2Si3O12 (CSS) phosphor with a garnet structure has been achieved by a hydrothermal gelation (HTG) method using a water soluble silicon compound. The CSS phase was obtained by calcining a hydrothermally driven gelations matter at 1073 K in the HTG method while synthesis of CSS by a solid state reaction required the calcinations at higher temperature than 1673 K. The low temperature synthesis of CSS stands on the homogeneity of the metallic components in a gel obtained from a homogeneous aqueous solution of starting materials by hydrothermal treatment at 473 K. It was revealed from investigation of the hydrothermal conditions that the homogeneity of the gels was independent of the concentration of components and the time of hydrothermal treatment but dependent on temperature because the temperature affected the rate of the gel formation.

Fabrication, formation mechanism and optical properties of novel single-crystal Er3+ doped NaYbF4 micro-tubes

A novel Er3+ doped NaYbF4 hexagonal-prismatic micro-tubular structure with single crystalline nature was synthesized by a facile hydrothermal method. The typical morphologies and structure were investigated by transmission electron microscopy (TEM) and scanning electron microscopy (SEM) which revealed that the as-prepared samples presented a tubular structure with open ends and uniform size. Based on TEM analysis of the samples prepared at different hydrothermal treatment times, the formation mechanism of the NaYbF4 hexagonal-prismatic micro-tube was concluded to be that the nano-sized clusters nucleated first and then self-assembly aggregated into thin sheets and finally rolled into NaYbF4 hexagonal-prismatic micro-tubes. Intense red upconversion luminescence was observed by the naked eye under 980 nm excitation, which indicated that the novel NaYbF4 micro-tubular structure is a potential host material for photoluminescence. Due to the unique luminescence, these NaYbF4 hexagonal-prismatic micro-tubes may be promising for further fundamental research and find applications in color displays and solid-state lasers.

Surface properties and epoxidation catalytic activity of Ti-SBA15 prepared by direct synthesis

The influence of hydrothermal treatment time on the physicochemical properties and the catalytic activity in cyclohexene epoxidation of titanium-substituted SBA15 silicas prepared by direct one-step synthesis was systematically studied using a combination of N2 physisorption at −196 °C, X-ray diffraction, X-ray photoelectron spectroscopy, diffuse reflectance UV–Vis, and elemental analysis. The other synthesis parameters were chosen to illustrate the different chemical environments of the titanium species formed before, during, and after the precipitation of anatase TiO2. At the beginning of hydrothermal treatment, results showed that the titanium species are homogeneously dispersed in the silica framework. When anatase TiO2 clusters precipitate, they do so mainly on the external surface of the mesoporous material. At higher hydrothermal treatment times, the material showed a decreased catalytic activity even if essentially no variation in their specific surface area was then observed. This lower activity was shown to be due to a partial coverage of active tetrahedral Ti species by extraframework higher coordination TiO2 deposit.

Glycine-assisted hydrothermal synthesis of peculiar porous α-Fe 2O 3 nanospheres with excellent gas-sensing properties

In this work, peculiar porous α-Fe 2O 3 nanospheres were fabricated by a glycine-assisted hydrothermal method. They have large mesopores (ca. 10 nm) in the core and small mesopores (<4 nm) in the shell. To our best knowledge, there have been so far no reports on the synthesis of such peculiar porous α-Fe 2O 3 nanospheres. X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy and transmission electron microscopy were employed to characterize the obtained Fe 2O 3 nanospheres. Effects of preparation conditions, such as reactants, reaction temperature and reaction duration, were investigated on the morphology and structure of Fe 2O 3 nanospheres. It was shown that the morphology and structure could be readily controlled by the time and temperature of hydrothermal treatment. The formation mechanism was proposed based on experimental results, which shows that glycine molecules play an important role in the formation of the morphology and porous structure of α-Fe 2O 3. The α-Fe 2O 3 porous nanospheres were used as gas sensing layer, and exhibited excellent gas-sensing properties to ethanol in terms of response and selectivity. The sensors showed good reproducibility and stability as well as short response (9 s) and recovery time (43 s) even at an ethanol concentration as low as 50 ppm. The gas-sensing properties of porous α-Fe 2O 3 nanospheres are also significantly better than those of previously reported Fe 2O 3 nanoparticles (ca. 30 nm). The sensitivity of the former is over four times higher than that of the latter at varied ethanol concentrations. The gas-sensing mechanism was discussed in details. Both fast response and steady signal make these peculiar nanostructures a promising candidate for ethanol detection.

Nanohydroxyapatite coating on a titanium–niobium alloy by a hydrothermal process

A novel one-step hydrothermal coating process was used to produce nanohydroxyapatite (nano-HA) coating on a titanium–niobium (TiNb) alloy substrate in a newly designed solution containing calcium and phosphate ions. The morphology of the coating was studied using scanning electron microscopy. The phase identification of the coating was carried out using X-ray diffraction, attenuated total reflectance Fourier transform infrared spectroscopy and transmission electron microscopy. The reaction between the surface of TiNb alloy and the solution during the hydrothermal process was studied by X-ray photoelectron spectroscopy. Results show that the coating formed on the surface of TiNb alloy was composed of nano-HA particles. During the hydrothermal process, TiO 2 and Nb 2O 5 formed on the TiNb alloy surface and hydrated to Ti(OH) 4 and Nb(OH) 5, respectively. Calcium phosphate nucleated and grew into a layer of nano-HA particles on the surface of TiNb alloy under the hydrothermal conditions. The crystallinity of the nano-HA coating was improved with the increase in hydrothermal treatment temperature and time duration. Nano-HA coating with good crystallinity was produced on the TiNb alloy via the hydrothermal process at a temperature of 200 °C for 12 h.

Microstructure, bioactivity and osteoblast behavior of monoclinic zirconia coating with nanostructured surface

A monoclinic zirconia coating with a nanostructural surface was prepared on the Ti-6Al-4V substrate by an atmospheric plasma-spraying technique, and its microstructure and composition, as well as mechanical and biological properties, were investigated to explore potential application as a bioactive coating on bone implants. X-ray diffraction, transmission electron microscopy, scanning electron microscopy and Raman spectroscopy revealed that the zirconia coating was composed of monoclinic zirconia which was stable at low temperature, and its surface consists of nano-size grains 30-50 nm in size. The bond strength between the coating and the Ti-6Al-4V substrate was 48.4 + or - 6.1 MPa, which is higher than that of plasma-sprayed HA coatings. Hydrothermal experiments indicated that the coating was stable in a water environment and the phase composition and Vickers hardness were independent of the hydrothermal treatment time. Bone-like apatite is observed to precipitate on the surface of the coating after soaking in simulated body fluid for 6 days, indicating excellent bioactivity in vitro. The nanostructured surface composed of monoclinic zirconia is believed to be crucial to its bioactivity. Morphological observation and the cell proliferation test demonstrated that osteoblast-like MG63 cells could attach to, adhere to and proliferate well on the surface of the monoclinic zirconia coating, suggesting possible applications in hard tissue replacements.

Optimisation of hydrothermal treatment for dehulling pigeon pea

This study was carried out to investigate the effect of hydrothermal treatment and drying time at a constant drying temperature of 50 °C on the dehulling behavior of pigeon pea seed. Response surface methodology (RSM) based on a two-factor, five-level, central composite design was employed to study the effect of the independent variables and optimize processing conditions. A second-order polynomial model described dehulling quality in terms of: (1) dehulled seeds, (2) undehulled seeds, (3) broken seeds, (4) powder loss and (5) dehulling efficiency. The process parameters showed significant effects on dehulled seeds and dehulling efficiency. The optimized processing conditions for maximum dehulled seeds, dehulling efficiency and minimum powder loss were a hydrothermal treatment time of 10.2 min and a drying time of 2.9 h.

Synthesis of large-pore SBA-15 silica from tetramethyl orthosilicate using triisopropylbenzene as micelle expander

The low temperature synthesis of large-pore SBA-15 silicas with two-dimensional (2-D) hexagonal structure was elaborated using tetramethyl orthosilicate (TMOS) as a silica source, Pluronic P123 (EO 20PO 70EO 20) triblock copolymer as a template, and 1,3,5-triisopropylbenzene as a micelle expander. The adjustment of the initial synthesis temperature, the hydrothermal treatment time and the amount of the swelling agent allowed us to obtain well-ordered SBA-15 (with three or more peaks on small-angle X-ray scattering patterns) with (1 0 0) interplanar spacings tunable in the range from 15 to 22 nm and with pore diameters up to 21 nm. These materials exhibited narrow pore size distributions and large pore volumes (above 1 cm 3 g −1).

Superhydrophobic Titania Membranes of Different Adhesive Forces Fabricated by Electrospinning

Large area superhydrophobic titania membranes with high adhesive forces were fabricated by electrospinning, followed by calcination and surface modification with 1H, 1H, 2H, 2H-perfluorooctyltriethoxysilane (POTS). Varied surface structures were realized by controlling precursor aging time (taging) and electrospinning time (telectrospinning) and by combination of electrospinning and hydrothermal treatment. A close relationship was observed between the contact angle and pore size of membrane. Water droplets on the surface appear spherical, which adsorb firmly onto the substrate even when the substrate is turned upside down. We investigated the dependence of the maximum adhesive force on pore size, which further revealed the relationship of the maximum adhesive force with the ratio of the pore size/fiber diameter. We found that taging and hydrothermal treatment time (thydrothermal) significantly affects the fiber substructure, which in turn largely influences the surface properties of the membrane, especial...

Studies on mesoporous niobosilicates synthesized using F127 triblock copolymer

A detailed characterization of cage-like mesoporous SBA-16 niobosilicate with tailored features of the structure is reported. The materials were synthesized in a EO106PO70EO106(F127)-water system under acidic conditions and the pore diameters were tuned by varying the hydrothermal treatment temperature and time. The effects of the synthesis parameters on the structural/textural properties of the cubic Im3m niobosilicates have been investigated systematically. We show that the total pore volume, pore diameter, and micro-/mesopores ratio can be controlled very efficiently by changing the synthesis parameters.

Hydrothermal synthesis of well-dispersed YVO 4:Eu 3+ microspheres and their photoluminescence properties

Spherical-shaped Eu-doped yttrium orthovanadate (YVO 4:Eu 3+) powders were fabricated via disodium ethylenediamine tetraacetate (Na 2EDTA)-assisted hydrothermal technique. The as-synthesized YVO 4:Eu 3+ microspheres were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and photoluminescence spectroscopy (PL). The experimental results showed that the morphology and size of the microspheres had a strong dependence on the concentration of Na 2EDTA and the reaction time of hydrothermal treatment. Spherical YVO 4:Eu 3+ crystals with the diameter of 1.0–3.0 μm were obtained in the presence of 0.025 M Na 2EDTA at 180 °C for 24 h. The photoluminescence measurement revealed that YVO 4:Eu 3+ powders with well-spherical shape have better red luminescence properties among all the samples.

Physicochemical Study of Nanocapsular Layered Double Hydroxides Evolution

A sol−gel method for the synthesis of MgAl layered double hydroxides is presented. The sols thus obtained were submitted to several hydrothermal treatments, in presence or absence of water, in order to examine the thermal evolution of specific physicochemical properties, such as morphology, crystal size, basicity, and textural properties. The morphological evolution was followed by transmission electron microscopy (TEM) and scanning electron microscopy techniques. TEM analyses revealed unique nanocapsular morphology; the nanocapsules grow with increasing hydrothermal treatment time and aggregate in the presence of water. X-ray diffraction confirms the expected increase in crystal size. The nitrogen adsorption−desorption surface analysis (Brunauer−Emmett−Teller) of the calcined solids indicates that surface areas range from 251 to 289 m2 g−1. Furthermore, CO2 thermoprogrammed desorption and Fourier-transform infrared analyses using CDCl3 as a probe molecule indicate that basic strength is inversely proportional to crystal size.

A Study on the Relationship Between Low-Temperature Reducibility and Catalytic Performance of Single-Crystalline La0.6Sr0.4MnO3+δ Microcubes for Toluene Combustion

Single-crystalline La0.6Sr0.4MnO3+δ microcubes of cubic perovskite phase were prepared hydrothermally. The adopted temperature and time of hydrothermal treatment and the amount of KOH used had great effects on the low-temperature reducibility of La0.6Sr0.4MnO3+δ . The initial H2 consumption rate of La0.6Sr0.4MnO3+δ played a vital role in determining its catalytic activity for toluene combustion. It is concluded that the perovskite-type oxide catalyst with a higher initial H2 consumption rate displayed a higher catalytic activity for the addressed reaction.

Effect of the thermal and hydrothermal treatment on textural properties of Zr-MCM-41 mesoporous molecular sieve

Zr-containing mesoporous molecular sieves were synthesized by hydrothermal method using cetyltrimethyl ammonium bromide as a template and sodium silicate and zirconium sulfate as raw materials. The structure and morphology of the synthesized samples were characterized via various physicochemical methods, including X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared (FT-IR) spectroscopy, solid state nuclear magnetic resonance ( 29Si MAS-NMR) techniques, thermal gravimetric–differential scanning calorimeter (TG–DSC) and N 2 physical adsorption, respectively. The effect of the different initial ZrO 2:SiO 2 molar ratio, the different thermal treatment temperature and the different hydrothermal treatment time on textural property was investigated. The experimental results reveal that the as synthesized samples possess a typical mesoporous structure of MCM-41. On the other hand, the specific surface area and pore volume of the synthesized Zr-MCM-41 mesoporous molecular sieve decrease with the increase of the amount of zirconium incorporated in the starting material, the rise of thermal treatment temperature and the prolonging of hydrothermal treatment time, the mesoporous ordering becomes poor. Also, when the molar ratio of ZrO 2:SiO 2 in the starting material is 0.1, the mesoporous structure of the Zr-MCM-41 mesoporous molecular sieve still retains after calcination at 750 °C for 3 h or hydrothermal treatment at 100 °C for 6 d, and have specific surface areas of 423.9 and 563.9 m 2/g, respectively.