Facile Template-free Hydrothermal Method Research Articles

Synthesis of one-dimensional porous Co3O4 nanobelts and their ethanol gas sensing properties

In this paper, one-dimensional porous Co3O4 nanobelts were synthesized via a facile template-free hydrothermal method and subsequent the thermal decomposition. Their microstructures and morphologies were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, thermogravimetric analysis, fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and N2 adsorption–desorption techniques. The results indicate that the reaction parameters such as the molar ratio of Co(NO3)2·6H2O to C2H4N4, the amount of Co(NO3)2·6H2O, the hydrothermal temperature and time play crucial rules in controlling the microstructures and morphologies of the as-prepared cobalt precursors. A possible formation mechanism was proposed. Moreover, the obtained porous Co3O4 nanobelts exhibit ethanol gas sensing properties superior to the commercial Co3O4 powders at a working temperature of 200°C, suggesting their potential applications as nanosensors.

Nanorod-like Fe2O3/graphene composite as a high-performance anode material for lithium ion batteries

In this study, a nanorod-like Fe2O3/graphene nanocomposite is synthesized by a facile template-free hydrothermal method and a following calcination in air at 300 °C for 2 h. The Fe2O3 nanorods with diameter of 15–30 nm and length of 120–300 nm are homogenous distributed on both sides of graphene. The morphologies of intermediates at different hydrothermal reaction times are investigated by transmission electron microscopy (TEM) characterization, and a possible growth mechanism of this one-dimensional structure is proposed. It is shown that the α-FeOOH rodlike precursors are formed through a rolling-broken-growth (RBG) model, then the α-FeOOH is transformed into α-Fe2O3 nanorods during calcinations, preserving the same rodlike morphology. Electrochemical characterizations demonstrate that the Fe2O3 nanorod/graphene composites exhibit a very large reversible capacity of 1063.2 mAh/g at the charge/discharge rate of 0.1 C.

Template-free synthesis of a CdSnO3⋅3H2O hollow-nanocuboid photocatalyst via a facile microwave hydrothermal method

A CdSnO3⋅3H2O hollow-nanocuboid photocatalyst was successfully synthesized via a facile template-free microwave hydrothermal method for the first time. The as-prepared samples were characterized by x-ray diffraction, UV–vis diffuse reflectance spectroscopy, Brunauer–Emmett–Teller (BET) surface area analysis and x-ray photoelectron spectroscopy. Moreover, samples prepared under different reaction times were analyzed by transmission electron microscopy to investigate the formation process of the CdSnO3⋅3H2O hollow-nanocuboids. Based on this result, a possible mechanism for the formation process was proposed. The sample prepared at 160 ° C for 2 h at pH 11 exhibited the best photocatalytic activity and stability for the degradation of gaseous benzene under UV irradiation (λ = 254 nm) as compared with the other samples. The conversion and mineralization rates of benzene were about 12.5% and 67%, respectively. The mineralization rate was twice as high as that of commercial TiO2 (Degussa Co.). Furthermore, the excellent stability for the benzene decomposition was attributed to the positive charge on the catalyst surface, which was analyzed both by electron spin resonance and Zeta-potentials.

Synthesis of SnO2 single-layered hollow microspheres and flowerlike nanospheres through a facile template-free hydrothermal method

SnO2 single-layered hollow microspheres and SnO2 flowerlike nanospheres have been fabricated by one step template-free hydrothermal reaction with the help of PEG400. The concentration of NaOH plays an important role in the formation of SnO2 nanostructure. When the molar ratio of SnCl4/NaOH is 1:6, the nanostructure of SnO2 turns out to be a single-layered hollow microsphere. And it will be a flowerlike nanosphere when molar ratio of SnCl4/NaOH is 1:8. These single-layered hollow microspheres with diameters of 1–5μm have a very thin shell thickness of about 200nm. These flowerlike nanospheres with diameters of 0.5–1μm are composed of SnO2 submicron rods with diameters of 200–300nm. A possible growth mechanism is proposed.

Morphology change and band gap narrowing of hierarchical TiO2 nanostructures induced by fluorine doping

A series of TiO2 hierarchical nanostructures were synthesized by a facile template-free hydrothermal method in the presence of sodium fluoride (NaF) using titanium tetrachloride (TiCl4) as precursor. The pompon-like and football-like TiO2 hierarchical microspheres are composed of aligned rutile and anatase nanoparticles. The TiO2 nanostructures are comprised of oriented anatase nanoparticles. It is found that the doping concentration of NaF plays an important role in controlling the morphology and structure of the hierarchical nanoarchitectures. A sequential phase transition is observed with increasing dopant concentration: rutile → rutile + anatase → anatase. X-ray photoelectron spectroscopy (XPS) and X-ray absorption near edge structure (XANES) results indicated that F ions physically absorbed on the surface of TiO2 and incorporated into TiO2 crystal lattice. For the first time, a sequential red shift of absorption band edge of F-doped TiO2 is observed with increasing the concentration of NaF as compared to pure TiO2. The band gap could be tuned from 3.0 eV to 2.2 eV, which depends on the fluorine doping concentration. It is found that F-doped TiO2 nanostructures exhibit higher photocatalytic activity than that of pure TiO2 under visible light irradiation.

Shape evolution, photoluminescence and degradation properties of novel Cu2O micro/nanostructures

Three kinds of novel cuprous oxide (Cu2O) micro/nanostructures are synthesized via a facile template-free hydrothermal method. Two factors are critical for the growth process of typical samples: the concentration of copper ions (Cu(II)) and the addition of Polyvinylpyrrolidone (PVP) as surfactant. It is found that the application of ethanol as solvent speeds up the reduction rate of Cu(II), and it promotes the aggregating of Cu2O nanocrystals at the preliminary stage to form irregular spherical structures. Photoluminescence (PL) properties of the three kinds of samples and their photocatalytic activities for degradation of Methyl Orange (MO) are also measured. The sample with higher concentration of copper vacancy (V Cu) defects has better photocatalytic ability, indicating that besides the morphology of Cu2O nano/microcrystals, the defects in crystalline structures can also influence their electrical characteristics, and thus change their photocatalytic activity. This provides a potential method to improve the photocatalytic performances of Cu2O crystals.

Zn-doped In2O3nanostructures: preparation, structure and gas-sensing properties

Novel Zn-doped In2O3 nanocages and hollow spindle-like nanostructures (HSNs) have been prepared by calcining precursors obtained via a facile template-free hydrothermal method. The change in morphology, size, and phase compositions in a controlled synthesis of the Zn-doped In2O3 nanostructures are achieved by simple adjustments of the amount of water. The result of this formation mechanism investigation reveals that the amount of water and the reaction time make significant contributions to the growth of Zn-doped In2O3 nanostructures. The driving forces for the formation of the nanostructures are the precipitation–dissolution–renucleation–growth and Ostwald ripening processes based on time-dependent experimental results. The gas-sensing properties of Zn-doped In2O3 nanocages and HSNs have shown high sensitivity toward formaldehyde (HCHO) vapor at a relatively low operating temperature. Note that the gas sensor fabricated with Zn-doped In2O3 HSNs exhibit a higher and faster response than those fabricated with Zn-doped In2O3 nanocages due to the larger surface area and the decreasing size of the particle.

Facile synthesis of single-crystalline mesoporous α-Fe2O3 and Fe3O4 nanorods as anode materials for lithium-ion batteries

In this work, single-crystalline α-FeOOH nanorods with a length of 400–700 nm and a diameter of 20–80 nm were successfully synthesized via a facile template-free hydrothermal method. Single-crystalline mesoporous α-Fe2O3 and Fe3O4 nanorods could be obtained from these α-FeOOH precursors after calcining at 350 °C in air and 500 °C in nitrogen, respectively. The as-prepared single-crystalline mesoporous α-Fe2O3 and Fe3O4 nanorods exhibited a large specific surface area and porosity, effectively enhancing the electrochemical reaction area and accommodate the strain during the charge–discharge cycling process.

Facile hydrothermal synthesis of InVO4 microspheres and their visible-light photocatalytic activities

Self-assembled three-dimensional InVO4 microspheres consisting of nanoparticles were synthesized by a facile template-free hydrothermal method. The resulting InVO4 microspheres had high crystallinity, and were of about 4.5μm in diameter. The band-gap energy estimated from the main absorption edges of the UV–vis diffuse reflectance spectrum was 2.4eV. Compared to the same material created via a solid-state reaction method, the InVO4 microspheres exhibited enhanced photocatalytic activities in the degradation of Rhodamine B(RhB) under visible light irradiation, which was mainly attributed to their higher surface area, and improved light-absorbing ability resulting from their unique morphology and variation of their crystal structure.

Template-free synthesis of SnO2 hollow microspheres as anode material for lithium-ion battery

SnO2 hollow microspheres were synthesized by a facile template-free hydrothermal method combining with an annealing process, and sodium stannate trihydrate was used as precursor. The diameter of microspheres which were composed of nanoparticles with size of about 10nm was in the range of 200–500nm. As anode materials for lithium ion batteries, the initial reversible capacity of SnO2 hollow microspheres electrodes reached 997mAh g−1. The electrodes revealed a capacity of 406.5mAh g−1 up to 65 cycles exhibiting high lithium storage capacity and coulomb efficiency. The superior performance of the SnO2 hollow microspheres can be mainly attributed to hollow structure and small size of SnO2 nanoparticles, which reduce volume expansion and lithium diffusion length.

Template-Free Hydrothermal Synthesis of ZnIn2S4 Floriated Microsphere as an Efficient Photocatalyst for H2 Production under Visible-Light Irradiation

A series of ZnIn2S4 floriated microspheres consisting of flakes were synthesized by a facile template-free hydrothermal method. The obtained ZnIn2S4 products were characterized by X-ray diffraction...

Template-free synthesis of hollow α-Fe2O3 microspheres

Nearly monodisperse hollow α-Fe2O3 microspheres composed of nanoparticles have been successfully synthesized through a facile template-free hydrothermal method. The products were characterized by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. It is shown that the hollow α-Fe2O3 microspheres consist of well-aligned α-Fe2O3 nanoparticles with a mean diameter of about 15 nm. This facile reaction route presents an efficient method for mass production of monodisperse hollow magnetic nanomaterials. The final α-Fe2O3 microspheres exhibit special magnetic properties with a small remnant magnetization of 0.09 emu g−1 and a high coercivity of 1121.67 Oe at room temperature.

Alkaline- and template-free hydrothermal synthesis of stable SnO 2 nanoparticles and nanorods for CO and ethanol gas sensing

SnO 2 nanoparticles and nanorods are synthesized via a facile template-free hydrothermal method, using SnCl 2·2H 2O and deionized water without any alkaline solution. The influences of the hydrothermal reaction time in the range of 5–48 h and temperatures of 130 and 160 °C and also calcination temperature on the size and morphological and gas-sensing properties of SnO 2 particles were investigated. The SnO 2 samples were characterized by X-ray diffraction analysis (XRD), surface area analyzer (using BET method) and scanning electron microscopy. The response of the SnO 2 nanostructures sensors to ethanol and various concentrations of CO were measured in an automated flow setup at different temperatures. As the hydrothermal synthesis temperature and time increases, the crystallite sizes enlarge nonlinearly and morphology of SnO 2 nanostructures changes from nanoparticles to nanorods. The most SnO 2 samples are thermally stable at calcination temperature of 350 °C. SnO 2 nanoparticles as small as 3.1 nm with the highest specific surface area of 254 m 2/g are hydrothermally synthesized at 130 °C in 5 h. This sample shows the highest response of 30 and 2565 to 1000 ppm CO and ethanol at 200 and 250 °C, respectively.

Hydrothermal synthesis of ultralong single‐crystalline α‐Ni(OH)2 nanobelts and corresponding porous NiO nanobelts

AbstractUltralong α‐Ni(OH)2 nanobelts with uniform size have been prepared on large scale via a facile template‐free hydrothermal method. The as‐prepared nanobelts were single crystals, with several tens of microns in length and about 100 nm in width. For the whole process, a novel nucleation–aggregation–dissolution–seed‐directed growth mechanism was proposed based on the experimental results. The roles of aqueous ammonia and hydrothermal temperature were also discussed. Furthermore, porous NiO nanobelts were obtained by annealing the as‐prepared Ni(OH)2 nanobelts. This facile, template‐free, and low cost method might feasibly be scaled up for industrial production. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Synthesis of SnO2 hollow microspheres with core-shell structures through a facile template-free hydrothermal method

Abstract SnO 2 hollow microspheres with core-shell structures were fabricated by a template-free hydrothermal reaction of a simple aqueous solution containing SnCl 4 and NaOH. This process was carried out under mild conditions and required no high-temperature heat treatment. By simply adjusting the molar ratio of SnCl 4 to NaOH, hollow microspheres, hollow core-shell microspheres and nanoparticles can be selectively synthesized. The products were characterized by powder X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and nitrogen BET measurements. The as-prepared SnO 2 hollow core-shell microspheres present a high Brunauer-Emmett-Teller surface area of 122.4 m 2 /g and a mesoporous structure. A possible formation mechanism for this kind of core-shell structure was proposed.

Template-Free Hydrothermal Synthesis and Formation Mechanism of Hematite Microrings

Hematite microrings with an outer diameter ∼12 μm, inner diameter ∼4 μm, and thickness ∼500 nm have been successfully synthesized by a facile template-free hydrothermal method using K3Fe(CN)6 and NaOH as reagents through a redox reaction. The influence of the reaction time, reaction temperature, concentration of K3Fe(CN)6, and NaOH on the evolution of shape and structures has been studied in detail. The optimal condition for preparation of the microrings is 180 °C for 5 h, the NaOH concentration is 4 M, and the K3Fe(CN)6 concentration is 0.02 M. The possible hollowing growth mechanism for the hematite microrings has been discussed. Magnetic hysteresis measurement revealed that hematite microrings after calcination at 700 °C for 4 h display a magnetic behavior with remanent magnetization of 0.211 emu/g and coercivity of 2005 Oe at room temperature.

Bi2WO6 Nanocrystals with High Photocatalytic Activities under Visible Light

Visible-light-induced photocatalyst Bi2WO6 with the size of ca. 30 nm has been synthesized via a facile template-free hydrothermal method. The effects of the pH values of the precursor suspensions and hydrothermal time on the photocatalytic activities of the Bi2WO6 nanoplates have been investigated in detail. The photocatalytic activity of as-prepared Bi2WO6 was about 8−10 times higher than that of the product prepared by solid-state reaction, which was evaluated by the degradation of RhB dye in water under visible light irradiation. Even under the illumination of a compact fluorescent lamp, the nanosized Bi2WO6 also exhibited high photocatalytic activity.

Controlled Synthesis of SnO2 Hollow Microspheres via a Facile Template-free Hydrothermal Route

Abstract Hollow rutile-like SnO2 microspheres were synthesized via a facile template-free hydrothermal method at 160 °C for 5–28 h. The as-prepared samples were characterized with XRD, SEM, and PL. A possible formation mechanism of the hollow spheres is briefly discussed.