Effect Of Hydrothermal Reaction Time Research Articles

Hydrothermal Synthesis of Hierarchical Hollow Li(Ni0.8Co0.15Al0.05)O2 Microspheres for Lithium Ion Batteries

Li(Ni0.8Co0.15Al0.05)O2 (NCA) cathode material for lithium ion batteries is synthesized by calcining Ni–Co–Al hydroxide or carbonate hydroxide hydrate precursor, which is obtained by hydrothermal method, and the NCA cathode material is hierarchical hollow microspheres with the diameter in the range of 3–5 µm and composed of nanoflakes and/or nanowires. The effect of hydrothermal reaction time on the morphologies and the crystalline quality of the NCA cathode material is investigated on the basis of scanning electron microscopy, X‐ray diffraction, and tunneling electron microscopy. The NCA cathode material shows smooth and monotonous charge/discharge characteristics, delivers a reversible capacity as 144.4 mAh/g and retains 90.4% after 50 cycles at a current density of 0.1 C between 2.5 and 4.3 V.

Fabrication of TiO2 hollow microspheres assembly from nanosheets (TiO2-HMSs-NSs) with enhanced photoelectric conversion efficiency in DSSCs and photocatalytic activity

Fabrication of TiO2 hollow microspheres (TiO2-HMSs) with complex structure is of great importance but remains a great challenge. In this paper, hierarchical TiO2 hollow microspheres assembly from nanosheets (TiO2-HMSs-NSs) were prepared by hydrothermal treatment of TiO2-HMSs precursor in NaOH solution and followed by acid wash and calcination. The effect of hydrothermal reaction time on the structure and photoelectric conversion performances of TiO2-HMSs-NSs film solar cells was systematically studied. It was found that both the BET surface area and photocatalytic activity of TiO2-HMSs-NSs, in photocatalytic degradation of Brilliant Red X-3B dye, are positively related to the hydrothermal reaction time (from 0 to 3h). The BET specific area of TiO2-HMSs-NSs steady increase from 21m2g−1 of TiO2-HMSs precursor (H0) to 184m2g−1 (H3), improved by a factor of 8.76, while the photocatalytic activity of H3 increased 7.50 times when compared with that of H0 sample. The highest photoelectric conversion efficiency (5.97%) of TiO2-HMSs-NSs film solar cell was obtained for H2 sample, exceeding that of TiO2-HMSs precursor (H0) based film solar cell (3.75%) with the same film thickness by a factor of 1.6. The improved photoelectric conversion efficiency of TiO2-HMSs-NSs based solar cell was attributed to the unique hierarchical hollow structure, which results in a good contact between TiO2 and FTO glass, enlarged pore volume, enhanced adsorption to sensitizer and improved light scattering ability.

Facile Hydrothermal Synthesis of Molybdenum Disulfide (MoS2) as Advanced Electrodes for Super Capacitors Applications

ABSTRACTA facile hydrothermal method was used to synthesize molybdenum disulfide (MoS2) microspheres. The effect of hydrothermal reaction time on morphology and electrochemical properties of MoS2 microspheres was evaluated. X-ray diffraction showed presence of crystalline MoS2 structure, where content of crystalline phase was observed to increase with hydrothermal reaction time. Electrochemical properties of MoS2 were evaluated using cyclic voltammetry (CV) and galvanostatic charge-discharge in 3M KOH solution. Specific capacitance of nanostructured MoS2 was observed to be between 68 F/g and 346 F/g at different scan rates along with excellent cyclic stability. High power density (∼1200 W/kg) and energy density (∼5 Wh/kg) was observed for MoS2 sample synthesized for 24 hours of hydrothermal reaction time. Overall optimal electrocapactive performance was observed for sample prepared for 24 hours of reaction time. It is demonstrated that the obtained MoS2 microspheres with three-dimensional architecture has excellent electrochemical performances as electrode materials for supercapacitor applications.

A simple hydrothermal synthesis of flower-like ZnO microspheres and their improved photocatalytic activity

Flower-like ZnO microspheres with high uniformity have been successfully fabricated by a simple hydrothermal method without surfactants. The effect of hydrothermal reaction time on the morphologies of the resulting products is investigated. The structural properties were systematically investigated by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The formation process of flower-like ZnO microspheres is discussed. Finally, flower-like ZnO microspheres show significantly improved photocatalytic activity for the degradation of Methylene blue (MB) as compared to commercial ZnO.

Hydrothermal synthesis of boehmite on alumina membranes for superhydrophobic surfaces

Boehmite (γ-AlOOH) coatings with nanoflakes and flower-like structures have been successfully synthesised on alumina membrane surfaces by hydrothermal reaction. The effects of hydrothermal reaction time and temperature on the morphologies of the layers were investigated. During the hydrothermal reaction, γ-AlOOH nanoflakes grew randomly on the Al2O3 particles, which changed the surface morphology of the alumina membrane and promoted its roughness. X-ray powder diffraction and field emission scanning electron microscope were used to characterise the structure and morphology of the membranes. Contact angle measurements were used to analyse the wetting property of the alumina membrane surface. Alumina membranes coated with boehmite layers possessed the wetting property from superhydrophilic to superhydrophobic after chemical vapour deposition of 1H,1H,2H,2H-perfluorooctyltriethoxysilane.

Effect of hydrothermal reaction time and alkaline conditions on the electrochemical properties of reduced graphene oxide

Reduced graphene oxide sheets (rGO) were prepared by hydrothermal treatment of aqueous dispersions of graphite oxide (GtO) applied for short (4h) and prolonged reaction times (19–24h). The effect of process duration as well as the alkaline conditions (pH ∼10) by addition of K2CO3 on the quality characteristics of the produced rGO materials was investigated. Both reduction and exfoliation occurred during this process as it was evidenced by FTIR and XRD data. SEM, TEM and HRTEM microscopy displayed highly exfoliated rGO materials. XPS verified that the re-establishment of the conjugated graphene network is more extensive for prolonged times of hydrothermal processing in accordance to Raman spectroscopy measurements. The sample produced under alkaline conditions bore fewer defects and almost 5 times higher BET surface area (∼181m2/g) than the sample with no pH adjustment (∼34m2/g) for the same hydrothermal reaction time (19h), attributed to the developed microporosity. The specific capacitance of this material estimated by electrochemical impedance using three-electrode cell and KCl aqueous solution as an electrolyte was ∼400–500F/g. When EDLC capacitors were fabricated from rGO materials the electrochemical testing in organic electrolyte i.e. TEABF4 in PC, revealed that the shortest hydrothermal reaction time (4h) was more efficient resulting in capacitance around 60F/g.

Effect of hydrothermal reaction time and calcination temperature on properties of Au@CeO2 core–shell catalyst for CO oxidation at low temperature

Au@CeO2 core–shell nanostructure catalysts were synthesized by hydrothermal reaction method. The effect of hydrothermal reaction time and calcination temperature on the textural and morphological characteristics of the catalyst was investigated by TEM, SEM, XRD, XPS, ICP, UV–Vis, and N2 adsorption–desorption techniques. The results proved that gold core and CeO2 shell formed simultaneously at the beginning of the reaction. By extending the hydrothermal reaction time, both the grain size of Au core and CeO2 shell increased. The crystallization degree of CeO2 and the interaction between Au and CeO2 were also enhanced. The 90 % CO conversion temperature (T90 %) of Au@CeO2 declined from 187 to 142 °C with the hydrothermal reaction time extended from 6 to 20 h. After 70-h reaction, the catalytic activity was still maintained without any loss. The effect of the calcination temperature on the catalytic performance was also investigated and it turned out that high calcination temperature has a positive influence on the catalytic activity. The likely active sites are the interface between Au core and CeO2 shell. Gold content, metal–support interaction (MSI), and oxygen vacancy are all related to the activity. The excellent performance of 20 h-600 °C-Au@CeO2 in catalytic activity and stability results from the joint effects of these triple factors.

The Effect of Hydrothermal Reaction Time on Formation of AuNPs by Sacrificial Templated Growth Hydrothermal Approach

This work describes the formation of gold nanoparticles (AuNPs) by using the sacrificial template growth hydrothermal method. AuNPs was grown on Aluminum/ polymethylsilsesquioxanes (PMSSQ) /Silicon substrates. Sputtered Al was used as a sacrificial template. The effect of hydrothermal reaction time on AuNPs properties was investigated for 1, 2, 3 and 4 hours. Properties of AuNPs were studied by using Field-Emission Scanning Electron Microscope (FESEM), X-ray Diffraction (XRD) and Semiconductor Characterization System (SCS). This approach allows the formation of AuNPs directly on the substrates. XRD analysis proved that Al template was removed during hydrothermal reaction. This approach allows the formation of AuNPs directly on the substrates. The number of AuNPs increased with increasing hydrothermal reaction time. However, longer than 1 hour reaction time, AuNPs tend to grow in clusters that could be due to unintended aggregation and agglomeration caused by self-association of the AuNPs. I-V characteristics showed hysteresis properties that indicated charge storage capability of AuNPs embedded in PMSSQ. AuNPs grown in 1 hour hydrothermal reaction produced the best memory properties due to well distribution of isolated AuNPs as observed in SEM image with the lowest abrupt current of 2.4 V.

Branch density-controlled synthesis of hierarchical TiO2 nanobelt and tunable three-step electron transfer for enhanced photocatalytic property.

The successful adjustment of phase composition and morphology of hierarchical TiO2 nanobelts, which feature homoepitaxial nanobranches, has been developed via the hydrothermal method and chemical bath deposition technique. Effects of hydrothermal reaction time, titanium butoxide treatment in chemical bath deposition, and calcination temperature are systematically investigated. For the first time, three-step ultrafast electron transfers between the band edges of the engaged phases are realized through the enhanced photocatalytic activity results. Growth mechanism related to branch density control on nanobelt surface under such soft chemical process is discussed in detail on the basis of classical nucleation theory. The current work might provide new insights into the fabrication of one-dimensional homoepitaxial branched TiO2 nanostructures as high performance photocatalysts and facilitate their application in environmental cleanup.

A maskless synthesis of TiO2-nanofiber-based hierarchical structures for solid-state dye-sensitized solar cells with improved performance

TiO2 hierarchical nanostructures with secondary growth have been successfully synthesized on electrospun nanofibers via surfactant-free hydrothermal route. The effect of hydrothermal reaction time on the secondary nanostructures has been studied. The synthesized nanostructures comprise electrospun nanofibers which are polycrystalline with anatase phase and have single crystalline, rutile TiO2 nanorod-like structures growing on them. These secondary nanostructures have a preferential growth direction [110]. UV–vis spectroscopy measurements point to better dye loading capability and incident photon to current conversion efficiency spectra show enhanced light harvesting of the synthesized hierarchical structures. Concomitantly, the dye molecules act as spacers between the conduction band electrons of TiO2 and holes in the hole transporting medium, i.e., spiro-OMeTAD and thus enhance open circuit voltage. The charge transport and recombination effects are characterized by electrochemical impedance spectroscopy measurements. As a result of improved light harvesting, dye loading, and reduced recombination losses, the hierarchical nanofibers yield 2.14% electrochemical conversion efficiency which is 50% higher than the efficiency obtained by plain nanofibers.

Monodisperse WO3 hierarchical spheres synthesized via a microwave assisted hydrothermal method: time dependent morphologies and gas sensing characterization

Monodisperse WO3 hierarchical spheres were successfully synthesized via a microwave assisted hydrothermal method and a subsequent annealing process. The synthesis was performed using peroxopolytungstic acid as a precursor in the presence of sodium sulfate. The effects of hydrothermal reaction time on the microstructure were also investigated and discussed. It is found that the reaction time influences the morphologies in terms of particle sizes and dispersities. A gas sensor based on the as-prepared WO3 was fabricated and tested. The results revealed that the sensor showed relatively good selectivity and repeatability to acetone vapour. When the acetone concentration was in the range of 100 to 1000 ppm, the relationship between the response and the acetone concentration exhibited a good linearity.

Effect of hydrothermal reaction time on morphology and photocatalytic activity of H2Ti3O7 nanotubes obtained via a rapid synthesis route

The traditional hydrothermal method for synthesis of H2Ti3O7 nanotubes was modified, and the total hydrothermal reaction time of forming a matured network of H2Ti3O7 nanotubes was successfully decreased by 50%. The effect of hydrothermal reaction time on morphology and photocatalytic activity of H2Ti3O7 nanotubes was investigated and discussed. Various morphologies can be observed in the as-prepared samples with different hydrothermal reaction times. The photocatalytic activity of the as-prepared samples was evaluated for degradation of methyl orange (MO) under simulated solar irradiation. It was found that the sample treated in the hydrothermal condition for 36h with a matured network of H2Ti3O7 nanotubes showed excellent photocatalytic activity. The photocatalytic activity results were discussed in detail. The stronger absorption in the ultraviolet (UV) range, the increasing crystallization of H2Ti3O7 phase, and larger surface area and pore volume contributed to the enhancement of photocatalytic activity of the as-prepared samples.

Template-free hydrothermal synthesis of SrSO 4:Sm 3+ microrods and its electron trapping luminescence properties

A hydrothermal process without using any surfactants or templates has been employed to prepare SrSO 4 microrods with different crystallographic morphologies. The pH value of the reaction solution is determined to be the key factor in the formation of rod-like morphology. It is found that the length-to-diameter ratio ( L/ D) of the rod-like SrSO 4 crystals increases from 1 to 4 when the pH value increases from 3 to 12. Besides, the effects of hydrothermal reaction time and temperature have been investigated to illustrate the morphological evolution process of SrSO 4 crystals, and it is also discussed that the microcrystals formation mechanism of the evolution process.

Hydrothermal Synthesis and Characteristics of Porous Mullite Honeycomb Coated with Silicalite Film.

The formation and some properties of sintered kaolin honeycomb monolith with thick silicalite film, prepared by a hydrothermal reaction, were investigated. To enhance the adhesion strength of the silicalite film onto the honeycomb surface and the mechanical strength of the honeycomb body, the Malaysian kaolin was sintered at 1500°C and then treated in 1M NaOH solution at 180°C to form a partially porous mullite layer on the honeycomb. Silicalite film was hydrothermally prepared on porous honeycomb from colloidal silica, NaOH, tetrapropylammonium bromide and H2O at 180°C. The effect of hydrothermal reaction time on the formation of the silicalite film onto the porous honeycomb surface and Teflon vessel was studied. Due to the formation of a porous mullite layer of 150 to 160μm in thickness on the honeycomb surface by leaching silica in the honeycomb, the adhesion strength of silicalite film on the honeycomb was improved, and a sintered kaolin honeycomb monolith with high strength which was coated with a silicalite film of 100 to 150μm in thickness at 180°C for 25 to 30h could be prepared by hydrothermal reaction.