Hydrothermal Duration Research Articles

Synthesis of bismuth nickelate nanorods and electrochemical detection of tartaric acid using nanorods modified electrode

Single crystalline bismuth nickelate nanorods with cubic Bi12NiO19 phase and flat tips have been successfully synthesized by a facile hydrothermal route without any additives. Electron microscopy observations show that the length and diameter of the bismuth nickelate nanorods are 1–3 μm μm and 30–100 nm, respectively. The formation, length and diameter of the nanorods depend on the hydrothermal temperature and duration time. The formation of the bismuth nickelate nanorods are explained according to the nucleation and crystalline growth process. The bismuth nickelate nanorods are applied as the glassy carbon electrode (GCE) materials for the detection of tartaric acid in KCl solution. The roles of scan rate, electrolyte species and tartaric acid concentration on the electrochemical responses of tartaric acid have been investigated. The obtained linear concentration calibration plot shows a low detection limit of 0.52 μm, wide linear range of 0.001–2 mM and correlation coefficient of 0.996. The bismuth nickelate nanorods modified GCE shows good reproducibility and stability.

Effect of hydrothermal condition on the formation of multi-component oxides of Ni-based metallic glass under high temperature water near the critical point

The specific feature of multi-component oxides synthesized by hydrothermal process under high temperature (633 K) and highly pressurized water (18.9 MPa) near critical point. Effects of hydrothermal processing duration times 24 hours and 72 hours, respectively, on the oxide formation of the Ni59Zr20Ti16Si2Sn3 metallic glass synthesized by powder metallurgy process were characterized by X-ray diffractometer, differential scanning calorimeter along with the particle size, morphology and crystalline phase of the oxides. The crystallization of the needle-shape NiTiO3, ZrTiO4 and ZrSnO4 ternary oxide phases observed on the surface of metallic glass at below glass transition temperature and the morphology of oxide phases changed to plate-shape around 2 μm in diameter by the increase processing time. This hydrothermal processing in subcritical water provides accelerated dense metal oxide crystals due to the reaction medium being at higher pressure than conventional oxidation processing.

Effects of Hydrothermal Duration on Synthesized Zeolite Rice Husk Particles

Zeolite particles were synthesized through in-situ extraction of silica from rice husk ash without seeding method in the absence of organic template by a static hydrothermal condition at various duration for 8, 12, and 24h. The effect amorphous silica content on hydrothermal duration of synthesis products was evaluated with X-ray diffraction (XRD), and field emission microscopy (FESEM). The present of zeolite Y without seeding method via XRD analysis show a mixture of zeolite A, Y and P. The transformation of amorphous rice husk particle was increased gradually with the increased of hydrothermal reaction. The FESEM images showed agglomerated cubic-shaped morphology of the powders with increase in crystallization reaction. .

Photocatalytic H2 production by ethanol photodehydrogenation: Effect of anatase/brookite nanocomposites composition

In view of the sustainable H2 production, development of more efficient catalysts for photocatalytic reforming of oxygenated compounds is required. In this study, we report the preparation of TiO2 nanocomposite with anatase/brookite composition prepared by hydrothermal treatments of Na-titanate precursor. The anatase/brookite ratio can be modulated changing the synthetic parameters, i.e. precursor/water mass-to volume ratio and hydrothermal treatment duration. The obtained materials present well crystallized particles with polyhedral morphology. The anatase/brookite ratio in the nanocomposite affects the mean size of Pt nanoparticles grown by photodeposition and the photocatalytic activity in H2 production by photodehydrogenation of ethanol, with multiphasic materials presenting smaller Pt nanoparticles and higher H2 production. The present anatase/brookite nanocomposites show higher H2 production normalized to the surface area with respect a reference TiO2 prepared by conventional sol–gel synthesis, suggesting that the present materials might expose a higher fraction of highly reactive facets instead of the most thermodynamically stable.

The Influence of Hydrothermal Duration on Structures and Optical Properties of ZnO Nanoparticles

ZnO nanoparticles were synthesized by hydrothermal method using ethylene glycol as a stabilizer and as well as a template. This study was aimed to examine the influence of hydrothermal duration (3, 6, and 12 hours) on the structures and optical properties of ZnO nanoparticles. X-ray diffraction results show that all peaks appear in the diffraction pattern indicate the hexagonal wurtzite structure of ZnO. The lattice parameters found just slightly varied with addition of hydrothermal duration. It is found that the particles size decreases whereas the average crystals size increase with hydrothermal duration. The average crystal size found increase with addition of hydrothermal duration. On the other hand, the particle grains were spread evenly distributed with decreasing size with hydrothermal duration increase, as indicated in the SEM images. Optical properties were investigated based on the optical transmission of the ZnO films. It is known that the films strongly absorb the visible region, whereas the absorption edge in the UV region. Bandgap energy of the films found increase with hydrothermal duration, that were 3.18 eV, 3.21 eV and 3.24 eV for 3 hours, 6 hours and 12 hours, respectively.

Morphology-dependent photocatalytic activity of octahedral anatase particles prepared by ultrasonication-hydrothermal reaction of titanates.

Octahedral anatase particles (OAPs) were prepared by an ultrasonication (US)-hydrothermal (HT) reaction of partially proton-exchanged potassium titanate nanowires (TNWs). The structural/physical properties of OAP-containing samples, including specific surface area, crystallinity, crystallite size, particle aspect ratio, composition and total OAP content, were analyzed. Photocatalytic activities of samples were measured under irradiation (>290 nm) for oxidative decomposition of acetic acid (CO2 system) and dehydrogenation of methanol (H2 system) under aerobic and deaerated conditions, respectively. Total density of electron traps (ETs) was measured by double-beam photoacoustic spectroscopy (DB-PAS). Mobility and lifetime of charge carriers (electrons) were investigated by the time-resolved microwave conductivity (TRMC) method. The effects of synthesis parameters, i.e., HT duration, HT temperature and US duration, on properties and photocatalytic activities of final products were examined in detail. The sample prepared with 1 h US duration and 6 h HT duration at 433 K using 267 mg of TNWs in 80 mL of Milli-Q water exhibited the highest photocatalytic activity. It was found that change in HT duration or HT temperature while keeping the other conditions the same resulted in changes in all properties and photocatalytic activity. On the other hand, duration of US treatment, before HT reaction, influenced the morphology of both the reagent (by TNWs breaking) and final products (change in total OAP content); samples prepared with various US durations exhibited almost the same structural/physical properties evaluated in this study but were different in morphology and photocatalytic activity. This enabled clarification of the correlation between morphology and photocatalytic activity, i.e., the higher the total OAP content was, the higher was the level of photocatalytic activity, especially in the CO2 system. Although the decay after maximum TRMC signal intensity (Imax) was almost constant for all samples used in this study, photocatalytic activities were roughly proportional to Imax, which tended to be proportional to total OAP content. Assuming that Imax corresponds to the product of density of electrons in mobile shallow ETs and their mobility, the results suggest that OAP particles have beneficial shallow ETs in higher density and thereby the OAP content governs the photocatalytic activities. Thus, morphology-dependent photocatalytic activity of OAP-containing particles was reasonably interpreted by density of ETs presumably located on the exposed {101} facets.

Environmental Stability and Residual Stresses in Zirconia Femoral Head for Total Hip Arthroplasty: In Vitro Aging versus Retrieval Studies.

The objective of this study was to compare the low temperature degradation (LTD) behavior of femoral heads made of 3Y-TZP as observed on retrievals with that induced in vitro upon prolonged exposures to a hydrothermal environment. The time-dependent evolution of tetragonal-to-monoclinic transformation and the related residual stresses were nondestructively monitored by Raman microspectroscopy. An increasing intensification of tensile and compressive stresses was detected with increasing hydrothermal aging duration in tetragonal and monoclinic phases, respectively. The dependence of monoclinic fraction upon exposure time was rationalized through the Mehl-Avrami-Johnson (MAJ) formalism in order to interpret the LTD process according to a two-step mechanism of formation and growth of monoclinic nuclei. In vitro results were compared to in vivo monoclinic contents in the same type of 3Y-TZP head retrievals after implantation periods of 1.6–16.6 y, also including literature data previously reported by other authors. One-hour exposure under the selected aging condition is estimated to correspond to in vivo exposures of 4 and 2 years according to ISO and ASTM criteria, respectively. A critical review of these two criteria according to the present analyses revealed that the ASTM simulation predicts more closely the in vivo results as compared to the ISO one.

The effect of gyrolite structure properties on Zn2+ ion adsorption

The effect of gyrolite structure properties on Zn2+ ion adsorption in an alkaline solution was determined. Gyrolite was synthesized for 32, 48, 72, 120, and 168 h at 200°C from a stoichiometric composition (molar ratio of C/S = 0.66) of the initial CaO and SiO2·nH2O mixtures. It was established that gyrolite does not regroup into related compounds, when the hydrothermal synthesis duration was varied from 32 to 168 h, although its structure changed as the duration of the synthesis was prolonged. Also, the adsorption capacity of gyrolite for Zn2+ ions depends on the structural properties of the adsorbent. By prolonging the duration of synthesis from 32 to 168 h, the adsorption capacity of gyrolite decreased from 99% (29.92 mg Zn2+/g) to 93% (27.91 mg Zn2+/g). It was found that the adsorption reactions are not reversible processes, and follow by a pseudo-second-order model. X-ray diffraction analysis showed that the crystal structure of gyrolite remained stable after the adsorption processes.

In vitro cytocompatibility, ageing and wear behavior of ceria stabilized zirconia bioceramic

Nano sized ceria stabilized zirconia (CSZ) powders were synthesized by co-precipitation method and then sintered conventionally to near full density. Ageing stability of developed materials was predicted through in vitro hydrothermal treatment in the presence of simulated body fluid (SBF). Fretting wear test at different loads was carried out using balls on flat geometry at different intervals of hydrothermal treatment to observe the effects of surface ageing on wear properties. Wear volume, specific wear rate and wear depth were estimated through 3D profile scan of the worn out surface by a surface profiler and it was found that the developed material became more wear resistant with the increase in hydrothermal treatment duration. XRD analysis and hardness study suggest that formation of orthorhombic zirconia during hydrothermal treatment improves the surface hardness (from 946±86HV20 to 964±39HV20 after 100h of hydrothermal treatment) which in turn enhances wear resistance. In vitro cytocompatibility of the developed materials was inferred through the formation of hydroxyapatite-like layer on the surface of the material when soaked in SBF at 37.5°C. Cytocompatibility was further ensured by studding attachment of multilayered human osteoblast cells (MG63) on the surface during cell culture.

Titanate nanotubes produced from microwave-assisted hydrothermal synthesis: Photocatalytic and structural properties

Titanate nanotubes were successfully synthesized using the microwave-assisted hydrothermal method from commercial TiO2-anatase powder. Several samples were obtained at varying temperatures and time. Powder samples containing titanate nanotube (Na2Ti6O13) single phase were obtained at 130°C for 4h and 150°C for 2h, demonstrating the kinetics dependence of reaction temperature. Through XRD analysis and electron diffraction pattern, the nanotube structures were found to be composed of a short range ordering, thus giving rise to a broad XRD peak profile. The higher time and temperature (150°C for 4h) led to the formation of more organized structures. The nanotubes UV–vis spectra showed a band gap of 3.90eV and a shoulder on the curve which led to another band gap value 3.25eV. The photoluminescence spectrum emission peak presented a significant decrease, indicating the reduction of surface or structural defects of titanate nanotubes due to longer hydrothermal treatment duration. All structural, electronics and morphologics transformation led to an improvement on photocatalytic activities for nanotubes, especially the sample obtained at 150°C for 1h that rate of decolorization is 0.01879min−1, 2.25 times faster than TiO2-anatase (starting phase).

Hydrothermal Synthesis and Characterization of Hexagonal Mg(OH)<sub>2</sub> Flame Retardant with Bischofite and NH<sub>3</sub>

Regular hexagonal plates of magnesium hydroxide with high slurry concentration were prepared by hydrothermal reaction without any organic additive or catalyst using bischofite and ammonia as raw materials. The effects of hydrothermal temperature, stirring speed, hydrothermal duration, and dilution multiple on the preparation of Mg(OH)2 flame retardant were investigated. Scanning electron microscopy, X-ray diffraction, and laser particle analysis were performed to characterize the product morphologies, structures, and size distributions. Results indicated that the growth direction of Mg(OH)2 crystal changed, and the regular hexagonal plates of Mg(OH)2 with uniform particle size and high dispersion characteristic formed after hydrothermal modification treatment. A mass fraction of 15.50% Mg(OH)2 of magnesium hydroxide slurry was obtained by high-concentration (4.30mol/L) magnesium chloride and ammonia as the raw materials.

Development of Technological Parameters for the Hydrotermal Processing of Sprouted Wheat Grain Powder

The present work is devoted to the development of technological parameters for the hydrothermal processing of powdered sprouted wheat and justification of use of the powder produced as a food additive. Introduction of sprouts into the diet stimulates metabolism and hematopoiesis, boosts immunity, compensates for vitamin and mineral deficiency, normalizes the acid-alkaline balance, promotes the elimination of toxins from the body, stimulates digestion, and slows the aging process. The use of sprouted wheat grains in public catering is very limited due to the short shelf-life of this product. Storage of dried grains provides a solution for this problem; however, it necessitates the development of a technology for the use of dried sprouted wheat grain. The present study was a part of research on the powder produced from sprouted wheat and centered on the process of hydrothermal treatment of dry sprouted wheat powder. Conventional methods were used in the present work for the analysis of physical and chemical parameters. A range of factors, including the protein content of the powder, the degree of mechanical damage of the starch granules, and the pH value of the solution, affects the water absorption capacity of the powder produced from sprouted wheat. Treatment time, temperature, and mash ratio at pH 4.5 and pH 7.0 were varied in experiments performed to determine the optimum operating parameters of the hydrothermal processing. As a result of the study, an energy-efficient technology has been developed for the hydrothermal processing of powdered sprouted wheat grains. The following process parameters were selected: an optimum swelling temperature of 45°C, hydrothermal treatment duration of 60 min at pH 4.5, and an optimum mash ratio of 1:1.25.

High-efficiency dye-sensitized solar cells based on ultra-long single crystalline titanium dioxide nanowires

High-efficiency dye-sensitized solar cells (DSCs) based on 3D networks of ultra-long single crystalline TiO2 nanowires are fabricated. By hydrothermal reaction of Ti foils in alkali aqueous solution, following ion exchange and high temperature sintering processes, the ultra-long single crystalline TiO2 nanowires can be prepared. Due to long enough of the TiO2 nanowires, they not only form 1D arrays perpendicular to Ti foils, but also extend to form 3D network structure on the top-side of the arrays. By optimizing the hydrothermal duration at 24 h, the formed TiO2 nanowire membrane based front-side illuminated photoanode shows enhanced dye-loading and light scattering abilities and excellent charge transport properties. So the DSC with this photoanode can attain to the highest power conversion efficiency about 8.05%.

In situ hydrothermal deposition as an efficient catalyst supporting method towards low-temperature graphitization of amorphous carbon

In view of the fact that the catalytic activity of supported catalyst is greatly influenced by its impregnation method, an in situ hydrothermal deposition method was explored and applied to load iron catalyst onto the amorphous carbon matrix, which derived from a soft-templating method with sucrose as precursor, to prepare nanoporous graphitic carbon at low temperature. Compared to traditional impregnation method, this hydrothermal loading method could realize the phase transformation from amorphous carbon to graphitic carbon at a temperature as low as 650°C. Systematical studies on the hydrothermal deposition and catalytic graphitization were made by X-ray diffraction and Raman spectrum, indicating that hydrothermal impregnation temperature and duration are the two crucial factors to the catalytic performance of loaded iron oxide. The obtained graphitic carbon by this approach possesses a nanoporous structure with surface area up to 329m2/g, pore volume of 0.39cm3/g and achieves a capacitance per unit surface area of 39.5μF/cm2, much higher than that of the carbon derived from traditional impregnation method (24.6μF/cm2).

Growth Mechanism, Modified Morphology and Optical Properties of Coral-like BaTiO3 Architecture through CTAB Assisted Synthesis

Three-dimensional hierarchical structure coral-like BaTiO3 nanoparticles have been self-assembled by a facile one step hydrothermal method. Cetyltrimethyl ammonium bromide (CTAB), Ba(OH)2·8H2O and tetrabutyl titanate have been used as precursors. The prepared BaTiO3 exhibits cubic perovskite phase at room temperature, and the coral-like architecture is a micro-nano hiberarchy consisted of dendrimer-like structure and trunk-like structure. By adjusting the hydrothermal duration and the precursor substances, a surfactant induced mechanism is proposed to understand the self-assembly process. UV-vis measurement demonstrates that the as-prepared BaTiO3 nanoparticles exhibit dozens of times overwhelming absorptive character compared to the ordinary nanospheres at ultraviolet band, which is benefited from the coral-like porous framework. Moreover, halogen anions( F−, Cl−, Br−, and I−) have been chosen to adjust the coral-like BaTiO3 physical properties. Results show the halogen doping produces distinct modulation effect on the grain size, UV-vis absorbance and photoluminescence properties of the materials. The coral-like BaTiO3 nanoparticle and its halogen modified ramifications offer significant opportunities to develop nano-laser devices, photon detectors, photocatalyst based on BaTiO3 perovskite materials.

Effects of hydrothermal conditions on the morphology and phase composition of synthesized TiO2 nanostructures

We investigate the effects of synthetic parameters on the morphologies during hydrothermal process and the crystal structural transitions from intermediate titanate to final TiO2 products by transmission electron microscopy (TEM) and X-ray diffraction (XRD). It reveals that hydrothermal duration, temperature and reactant amount play important roles in controlling the morphologies and crystal structures of titanate products. Anatase nanotubes, anatase nanorafts, TiO2–B nanoribbons, and anatse/TiO2–B nanoribbons were synthesized by modifying these synthetic parameters. We found that the crystal structures of intermediate titanate products influence on the transitions from titanate to TiO2. Our results show that anatase and TiO2–B derive from the orthorhombic and monoclinic titanate, respectively. We suggest that the crystallographic relationships between the intermediate products (hydrogen titanate) and the final TiO2 products play important roles in heat treatment.

Hydrothermal Synthesis of Vertically Aligned Cesium-Doped ZnO Nanorods for Solar Cell Applications

Single crystalline cesium-doped ZnO nanorods with homogeneous size and shape were hydrothermally grown on Cs–ZnO nucleated glass substrate. The effect of hydrothermal growth duration on the characteristics of Cs-doped ZnO nanorods was examined. The samples were analyzed by X-ray diffraction (XRD), energy dispersive X-ray analysis, scanning electron microscopy, and electrical conductivity, optical transmission and photoluminescence (PL) measurements. XRD analysis showed that Cs-doped ZnO nanorods are wurtzite single crystals and are grown preferentially along the c-axis. Elemental analysis confirmed the presence of 1 at.% of Cs, according to the composition of growth solution. Electrical conductivity of typical samples showed higher values for the 1 at.%-doped sample, which confirmed incorporation of the Cs dopant. The samples were optically transparent and showed two UV and visible PL peaks from which the former peak experienced a red shift and a pronounced increase in intensity with increasing growth time. The fabricated Cs-doped ZnO nanorods are suitable candidates for applications as excitonic solar cells due to their ease of fabrication, morphology control and optical properties.

Phyllosilicates synthesis: a way of accessing edges contributions in NMR and FTIR spectroscopies. Example of synthetic talc

A series of new-generation synthetic talcs were prepared by varying the hydrothermal synthesis duration from a few hours up to 2 months. Crystallinity and particle size analysis of the synthetic products were evaluated by photon correlation spectroscopy, transmission electron microscopy, differential thermal analysis and unoriented X-ray diffraction, and then analyzed by various spectroscopic methods such as Fourier transformed infrared spectroscopy and solid-state 1H and 29Si magic angle spinning nuclear magnetic resonance. The new process for preparing synthetic talcs allows to obtain single-phased particles which after few hours grow heterogeneously and simultaneously in both the c* direction and the (ab) plan. Fine particles, observed for whatever the synthesis duration, lead to the presence of numerous sheet edges surfaces due to particle size which represents the main difference with natural talc. Spectroscopy data show the influence of the fine particles on signals and highlight that synthetic talc characterization is a potential tool for better understanding crystal chemistry of natural talc.

Growth of nanostructured nickel sulfide films on Ni foam as high-performance cathodes for lithium ion batteries

We report a facile and reproducible synthesis of nanostructured Ni3S2 films by a hydrothermal route with Ni foam as the precursor reactant and substrate. The synthetic mechanism was examined by investigating the dependence of the films' crystal morphologies on the hydrothermal duration, and uniform nanostructured Ni3S2 films with a porous carpet-like morphology were synthesized on the substrates. The architectures were used as cathodes for lithium ion batteries (LIBs), and their electrochemical performances were evaluated as a function of the film thickness. The first discharge and charge capacities were 596 and 466 mA h g(-1) for the electrode with an optimal film thickness and a higher reversible capacity of 421 mA h g(-1) was obtained after 60 cycles at a current density of 50 mA g(-1). The simplicity of the synthetic methodology and the better electrochemical performance make the synthesized Ni3S2 films a promising cathode material for next-generation LIBs.

Crystallization of hydroxyapatite during hydrothermal treatment on amorphous calcium phosphate layer coated by PEO technique

Surface modification of titanium implants is recently considered by several researchers. In this study, PEO was performed over commercially Ti-6Al-4V alloy pellets in an aqueous electrolyte containing calcium acetate (C.A.) and calcium glycerphosphate (Ca–GP) with a Ca/P molar ratio of 6.8, and applying current density of 0.212A/cm2, frequency of 100Hz and duty ratio of 60% for 4min. In the next step, hydrothermal treatments were carried out for various durations and at different temperatures inside an autoclave chamber containing a NaOH solution with pH of 11.5. XRD and SEM results confirmed formation of needle-shaped HAp after all hydrothermal conditions. Maximum intensity of HAp peaks was observed for the hydrothermally treated sample at 190°C for 15h. Moreover, crystallinity degree of HAp was increased by increasing hydrothermal duration and temperature. According to the SEM line scan analysis of cross section of the PEO coated sample after hydrothermal treatment at 190°C for 15h, it seems that Ca+2 and [PO4]−3 ions from internal layer of amorphous coating diffuse to the coating surface and dissolve into the solution during hydrothermal treatment, and finally precipitate on the outer layer of coating as needle-shaped HAp.