Effective Hydrothermal Method Research Articles

In situ grown Co3O4 on hydrogen storage alloys for enhanced electrochemical performance

Co3O4 is an effective additive to enhance the electrochemical performance of hydrogen storage alloys. However, the low utilization efficiency has become a big challenge for direct adding Co3O4 powders into the alloys with mechanical mixing. Here, we report the in situ growth of Co3O4 on the alloy surface by using a facile and effective hydrothermal method. Compared with bare hydrogen storage alloys, the fabricated composite shows larger maximum discharge capacity, 326.37 vs. 302.62 mAh g−1, and enhanced high rate dischargeability with larger discharge capacity at a current density of 3000 mA g−1, 59.01 vs. 40.88 mAh g−1. These are contributed by the unique hybrid architecture of the composite: (1) the in situ grown Co3O4 nanosheets improve the catalytic activity and utilization efficiency of Co3O4 on the electrochemical reaction kinetics; and (2) the low-dimensional Co3O4 coatings seamlessly integrated with hydrogen storage alloys decrease the internal resistance and polarization of the hybrid electrode. Such a simple and novel method can also be extended to other energy storage devices.

Tunable morphology with selective faceted growth of visible light active TiO2 thin films by facile hydrothermal method: structural, optical and photocatalytic properties

Selective faceted growth of highly ordered TiO2 (002) nanorods were coated over fluorine doped tin oxide (FTO) substrate prepared by facile and cost effective hydrothermal method for different reaction temperatures (100, 120, 140 and 160 °C). The rutile phase TiO2 and highly preferential oriented along (002) plane were confirmed from the XRD pattern. The TiO2 thin film, prepared with different reaction temperature consisting of anisotropic structures was analysed by SEM and the elemental composition of the films was identified using EDAX. The optical band gap of the TiO2 thin films was found to be 3.5–3.1 eV using UV–visible spectroscopy. The presence of rutile TiO2 phase was confirmed from raman analysis. As a result of photoluminescence studies, improvement of charge separation with low recombination rate was observed in TiO2 thin films. The anionic (Congo Red, Direct Red) and cationic (Rhodamine B and Malachite Green) dye decolorisation of the TiO2 thin films was investigated under visible light from photocatalytic activity.

Facile synthesis of low dimensional CuO nanostructures and their gas sensing applications

A simple and cost effective hydrothermal method has been employed to synthesis morphology controlled pure and Cr doped (4 and 8 at. %) CuO nanostructures. Crystalline purity and structure of the nanostructures were validated by X‐ray diffraction and Retvield analyses. Field emission scanning electron microscopy revealed the evolution of rod‐like, sheet‐like and boat‐like morphologies for pure, 4 and 8 at. % Cr doped CuO nanostructures respectively. The optical band gap estimated using the K‐M function plot from diffused reflectance spectroscopy showed a shift in band gap from 1.68 to 1.90 eV with respect to Cr concentration. The synthesized CuO nanostructures were investigated for the efficient room temperature gas sensing of ammonia, ethanol and methanol vapours under different concentrations (100‐600 ppm). The 8 at. % Cr doped CuO nano‐boats showed enhanced gas sensitivity than other CuO nanostructures owing to their typical morphology, larger surface area and related properties.

Hydrothermal Synthesis and Luminescence Properties of Monodisperse Spherical CaF<sub>2</sub> and CaF<sub>2</sub>:Ln<sup>3+</sup> (Ln = Eu, Tb, Ce/Tb) Microcrystals

Spherical CaF2 and CaF2:Ln3+ (Ln = Eu, Tb, Ce/Tb) with tunable particle size (about 2.5 µm) have been synthesized by one-step facile and effective hydrothermal method. The spherical structure was highly uniform and well-dispersed. It was found that reaction time, pH value, and reaction temperature have important effects on the controlled synthesis of spherical CaF2. The samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM), photo-luminescence (PL) and luminescence decay curve. Under UV excitation, the CaF2:Eu3+ showed the red emission (5D0→7FJ = 0, 1, 2, 3) and the CaF2:Tb3+ presented the green emission (5D4→7FJ = 6, 5, 4, 3), respectively. Furthermore, Ce3+/Tb3+ co-doped CaF2 showed efficient energy transfer from Ce3+ to Tb3+, which presented strong green photo-luminescence of Tb3+. Due to excellent luminescent properties, the obtained samples can be used in many fields, such as light display systems, optoelectronic devices and biological imaging.

Preferentially grown nanostructured iron disulfide (FeS2) for removal of industrial pollutants

Preferentially grown nanostructured iron disulfide pyrite (111) was successfully synthesized using a low cost effective hydrothermal method, then employed as a photocatalyst for degradation of methylene blue and the textile dye Synazol Yellow K-HL.

Constructing Highly Oriented Configuration by Few-Layer MoS2: Toward High-Performance Lithium-Ion Batteries and Hydrogen Evolution Reactions.

Constructing three-dimensional (3D) architecture with oriented configurations by two-dimensional nanobuilding blocks is highly challenging but desirable for practical applications. The well-oriented open structure can facilitate storage and efficient transport of ion, electron, and mass for high-performance energy technologies. Using MoS2 as an example, we present a facile and effective hydrothermal method to synthesize 3D radially oriented MoS2 nanospheres. The nanosheets in the MoS2 nanospheres are found to have less than five layers with an expanded (002) plane, which facilitates storage and efficient transport of ion, electron, and mass. When evaluated as anode materials for rechargeable Li-ion batteries, the MoS2 nanospheres show an outstanding performance; namely, a specific capacity as large as 1009.2 mA h g(-1) is delivered at 500 mA g(-1) even after 500 deep charge/discharge cycles. Apart from promising the lithium-ion battery anode, this 3D radially oriented MoS2 nanospheres also show high activity and stability for the hydrogen evolution reaction.

Preparation and photocatalytic activity of graphene-modified Ag2S composite

This paper presents a novel visible-light photocatalyst, graphene-modified Ag2S (GR/Ag2S), prepared by a facile and effective hydrothermal method with AgNO3, thioacetamide and graphene oxide (GO) as the precursor. The catalytic activities of the GR/Ag2S hybrids with different GR content (2%, 4%, 6%) were evaluated by photocatalytic decolourisation of rhodamine B (RhB) solution under visible-light irradiation. The improved photocatalytic activity of GR/Ag2S composites compared with pure Ag2S is observed and attributed to the enhanced absorption of organic dyes and increased separation efficiency of photogenerated electron−hole pairs. The 4% GR/Ag2S sample exhibits the best photocatalytic activity than the others.

Simple synthesis of highly catalytic carbon-free MnCo2O4@Ni as an oxygen electrode for rechargeable Li-O2 batteries with long-term stability.

An effective integrated design with a free standing and carbon-free architecture of spinel MnCo2O4 oxide prepared using facile and cost effective hydrothermal method as the oxygen electrode for the Li–O2 battery, is introduced to avoid the parasitic reactions of carbon and binder with discharge products and reaction intermediates, respectively. The highly porous structure of the electrode allows the electrolyte and oxygen to diffuse effectively into the catalytically active sites and hence improve the cell performance. The amorphous Li2O2 will then precipitate and decompose on the surface of free-standing catalyst nanorods. Electrochemical examination demonstrates that the free-standing electrode without carbon support gives the highest specific capacity and the minimum capacity fading among the rechargeable Li–O2 batteries tested. The Li-O2 cell has demonstrated a cyclability of 119 cycles while maintaining a moderate specific capacity of 1000 mAh g−1. Furthermore, the synergistic effect of the fast kinetics of electron transport provided by the free-standing structure and the high electro-catalytic activity of the spinel oxide enables excellent performance of the oxygen electrode for Li-O2 cells.

Stability study of ultra-low Pt thin film on TiO2–C core–shell structure and TiO2 encapsulated in carbon nanospheres as cathode catalyst in PEMFC

As catalyst supports play an important role in the performance, cost, and the stability of fuel cells, we focus on synthesis of novel nanocomposites via different designs to overcome durability and cost of electrocatalyst layer. In this paper, the researchers wished to report a simple and cost effective hydrothermal method for synthesizing titania encapsulated carbon, and carbon–titania core–shell structure. This comparison was conducted in an effort to find better structure of metal oxide–carbon, as a promising replacement for carbon in PEMFC catalyst supports. Different chemical reagents were applied in order to increase the surface area, and control the porosity of supports. All produced supports at each step were extensively analyzed and discussed. Carbon structure and morphology of nanospheres were studied through Raman characterization and scanning electron microscopy. Titania structure studied through X-ray diffraction indicated two phases including the main anatase phase and the minor rutile phase. Low amounts of platinum (0.05mg/cm2) were deposited on prepared supports via constant condition in comparison to the 0.2–0.3mg/cm2 platinum for standard membrane electrode assembly. The performances of PEMFC, consisting different prepared support-platinum as cathode, were compared depending on the measured polarization curves. TiO2–Pt showed the lowest power density around 167mW/cm2 while the maximum power densities belonged to core–shell structure with 10wt% titania around 410mW/cm2 which was comparable with Vulcan–Pt. Notably, titania encapsulated carbon with the same amount of titania gave the same performance as core–shell structure. However, the accelerated potential cycling test indicated that the carbon–titania core shell structure showed higher stability in comparison to titania encapsulated in carbon. This result was discussed through X-ray photoelectron spectroscopy.

The enhanced electrocaloric effect in P(VDF-TrFE) copolymer with barium strontium titanate nano-fillers synthesized via an effective hydrothermal method

An effective hydrothermal method is developed to synthesize barium strontium titanate nanoparticles with a mean size below 30 nm, which are used for the fabrication of nanocomposite films consisting of P(VDF-TrFE) and ceramic nanoparticles.

Graphene nanosheets loaded with Pt nanoparticles with enhanced electrochemical performance for sodium–oxygen batteries

Graphene nanosheets loaded with highly dispersed platinum nanoparticles (Pt@GNSs) are prepared by a simple and effective hydrothermal method.

In situ preparation of flower-like α-Ni(OH)2 and NiO from nickel formate with excellent capacitive properties as electrode materials for supercapacitors

Flower-like precursor with coexisting nickel formate and α-Ni(OH)2 was synthesized via a template-free and cost effective hydrothermal method. It is found for the first time that the decomposition behavior of nickel formate in the presence of α-Ni(OH)2 is completely different from that of pure nickel formate. At a heating temperature of 210 °C, α-Ni(OH)2, which is originally inside the precursor, serving as crystal nucleus could induce nickel formate to transform into α-Ni(OH)2 instead of previously reported highly active metallic Ni. After elevating the heating temperature to 250 °C, single-phase NiO, which well inherited the flower-like morphology of the precursor, was obtained. Electrochemical properties of the precursor, α-Ni(OH)2 and NiO were investigated systematically to provide deep insight into their differences in supercapacitor applications. The precursor shows a relatively high specific capacitance of 923 F g−1 at 1 A g−1 but a poor capacitance retention of ∼50% after 600 cycles. Both the flower-like α-Ni(OH)2 and NiO electrodes exhibit excellent long cycling lives with capacitance retention of 89% and 86% after 1000 cycles, respectively. More importantly, the specific capacitance of α-Ni(OH)2 electrode, which is as large as 810.4 F g−1 at 1 A g−1, is very outstanding.

1D structure of Y2O3:Eu nanorods: controllable synthesis, growth mechanisms and luminescence properties.

Y2O3O:Eu nanorods were successfully synthesized by a facile and effective hydrothermal method in the presence of P123 (EO106PO70EO106) as the surfactant followed by a subsequent heat treatment process. The scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images indicate that the as-prepared samples consist of nanorods with diameters ranging from 80 nm to 100 nm and grow along the (100) direction. The growth mechanism of the as-obtained Y2O3:Eu nanorods was proposed on the basis of pH-dependent experiments. It is found that the pH is a crucial factor in determining the phase, morphology and luminescence properties of Y2O3:Eu nanorods. The luminescent spectra of Y2O3:Eu nanorods show the strong characteristic dominant emission of the Eu3+ ions at 613 nm.

Cu2ZnSnS4 alloys synthesized from Cu2SnS3@ZnS nanoparticles via a facile hydrothermal approach

A facile and low-cost approach was developed to prepare high quality quaternary Cu2ZnSnS4(CZTS) alloys through the thermal treating of the core–shell Cu2SnS3@ZnS nanoparticles. The synthesis process of the core–shell structure involves a simple two-step hydrothermal route that starts from the well-dispersed ternary Cu2SnS3 core with the introduction of poly(vinylpyrrolidone) (PVP) in the reaction solution, and ended by the coated binary ZnS shell upon the adsorption of citrate groups onto the preformed cores. X-ray diffraction, Raman spectrum and UV–vis absorption spectrum confirmed the single-phase formation and the proper bandgap of 1.51eV for the CZTS alloys. This effective hydrothermal method can be readily applied for industrial production.

Synthesis of MoSe2/Reduced graphene oxide composites with improved tribological properties for oil‐based additives

In this work, we developed a facile and effective hydrothermal method synthesis of MoSe2 nanoflowers on reduced graphene oxide (RGO) sheets. The as‐prepared MoSe2/reduced graphene oxide (MoSe2/RGO) composites are characterized by X‐ray diffractometer (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results indicated that MoSe2 nanoflowers were successfully deposited on RGO nanosheets to form a well interconnected hybrid structure. The tribological properties of MoSe2/RGO composites as lubricating oil additive were investigated by a UMT‐2 ball‐on‐plate friction and wear tester. By the addition of MoSe2/RGO composites in paraffin oil, the antiwear ability was improved and the friction coefficient was decreased. The based oil with MoSe2/RGO composites showed better tribological properties than the oil with MoSe2 and pure oil. The good friction and wear properties of MoSe2/RGO composites as additives were attributed to the formation of a thin physical tribofilm on the substrate.

A Facile Synthetic Approach to Reduced Graphene Oxide–Fe3O4 Composite as High Performance Anode for Lithium-ion Batteries

Reduced graphene oxide–Fe3O4 (rGO–Fe3O4) composite has been prepared via a facile and effective hydrothermal method by synthesizing Fe3O4 nanospheres on the planes of reduced graphene oxide (rGO). Characterizations suggest the successful attachment of Fe3O4 nanospheres to rGO sheets. The rGO–Fe3O4 composite (66.7 wt% of Fe3O4 in the composite) exhibits a stable capacity of 668 mAh g−1 without noticeable fading for up to 200 cycles in the voltage range of 0.001–3.0 V, and the superior performance of rGO–Fe3O4 is clearly established by comparison of the results with those from bare Fe3O4 nanospheres (capacity declined to 117 mAh g−1 only at the 200th cycle). The excellent electrochemical performance of rGO–Fe3O4 composite can be attributed to the fact that the uniform dispersion of the Fe3O4 nanospheres growing on the rGO sheets avoids aggregation during Li uptake-release cycling, which is desired for cycle stability. Meanwhile, the rGO sheets afford not only elastic buffer to alleviate the volume variations of Fe3O4 nanospheres, but also good ionic and electronic transport medium in the electrode.

Exceptional pseudocapacitive properties of hierarchical NiO ultrafine nanowires grown on mesoporous NiO nanosheets

Hierarchical NiO ultrafine nanowires grown on mesoporous NiO nanosheets with Ni foam as a substrate synthesized by a facile and effective hydrothermal method showed exceptional pseudocapacitive properties.

Effect of metal ion (Zn2+, Bi3+, Cr3+, and Ni2+)-doped CdS/halloysite nanotubes (HNTs) photocatalyst for the degradation of tetracycline under visible light

CdS/halloysite nanotube (HNT) samples doped with several metal ions (Mn+-CdS/HNTs, where Mn+ = Zn2+, Bi3+, Cr3+, and Ni2+) were synthesized using a facile and effective hydrothermal method. The as-prepared photocatalysts were characterized by scanning electron microscopy, transmission electron microscopy, X-ray energy dispersive spectroscopy, X-ray diffraction, UV–vis diffuse reflectance spectra, inductively coupled plasma-atomic emission spectroscope, X-ray photoelectron spectroscopy, and Fourier transform infrared. The photocatalytic activity of the Mn+-CdS/HNTs photocatalyst was evaluated by the degradation of tetracycline under visible-light irradiation. The optimum Mn+-doping amount was investigated in detail. At last, the possible photodegradation mechanism for metal-ion-doping photocatalyst was further discussed.

Control of Structure of Au@TiO2 Core–Shell Hollow Microspheres with Multiple Nanocores and Porous Shells

Abstract Au@TiO2 core–shell hollow microspheres with multiple nanocores and porous shells have been synthesized by a simple and effective hydrothermal method using TiF4 as TiO2 precursor. The size of microsphere can be controlled by changing synthetic conditions.

Low-Temperature Synthesis of Nanocrystalline ZnO Nanorods Arrays

In this present research, vertically aligned ZnO nanorods arrays were grown on silicon wafer (100) substrates from a zinc nitrate hexahydrate and hexamethylenetetramine solution by a cost effective and low temperature (90 °C) hydrothermal growth method. Field-emission scanning electron microscopy (FE-SEM) and X-ray diffraction (XRD) were used to analyze morphology, crystallinity and film thickness, respectively. It was demonstrated that when the seed layer thickness change from 18 to 200 nm, the nanowire density increased. Our result presented a scalable method for fabricating ZnO nanorods arrays with potential for a lots of application such as micro/nanosensors and the nanoelectronic devices.