Surfactant-free Hydrothermal Method Research Articles

Monoclinic–Tetragonal Heterostructured BiVO4 by Yttrium Doping with Improved Photocatalytic Activity

Yttrium-doped BiVO4 has been synthesized by means of a surfactant free hydrothermal method having good photoactivities under sun-like excitation for the degradation of Methylene Blue (MB). From the...

Shape-controlled synthesis of MnWO4 nanocrystals by a surfactant-free hydrothermal method

In this paper, we report the obtention of MnWO4 nanocrystals with different shapes, such as: nanospheres, nanorods, and urchin-like microspheres were synthesized by a surfactant-free hydrothermal method. The as-obtained powders were characterized by X-ray diffraction patterns and transmission electron microscopy. XRD patterns indicate that these crystals have a wolframite-type monoclinic structure without deleterious phases. The TEM images revealed that the pH values and precursors played a key role in the morphology-controlled synthesis of MnWO4 nanocrystals. This green method is an effective approach to the controlled growth of MnWO4 nanocrystals with different shapes, which are of interest for both theoretical investigations and practical applications. Finally, a possible growth mechanism for the formation of the MnWO4 microcrystals with different shapes was discussed in detail.

A facile surfactant-free method to prepare Ti0.95Er0.05O2 nanocrystal and its photocatalytic performance

The preparation of Ti0.95Er0.05O2 nanocrystal by a facile surfactant-free hydrothermal method was reported in this work. The obtained materials were investigated by means of HRTEM, SEM, EDS, XPS and XRD. The results indicated that Ti1−xErxO2 were obtained in uniform nanometer scale and very pure. According to the photocatalytic activity for the photocatalytic degradation of methylene blue, Ti0.95Er0.05O2 is nearly twice higher than that of the undoped sample. Furthermore, photoelectrochemical investigation has been carried out. The photocurrent intensity of Ti0.95Er0.05O2 is nearly twice higher than that of the undoped TiO2, which is in well accordance with their photocatalytic performance.

Preparation and electric-field response of novel tetragonal barium titanate

The tetragonal barium titanate (BaTiO3) particles with novel shapes were synthesized by a surfactant-free hydrothermal method and fully characterized by Raman, XRD, SEM and contact angle analysis. The shape of particles are dependent on reaction temperature, pH value and mineralization time. The tetragonal BaTiO3 particles with different morphology possess different tetragonality, surface hydrophilicity and dielectric property, and so they exhibit distinct electric-field response. The high tetragonality and good dielectric property of the particles are proposed as a main power of enhancing the electric response of tetragonal BaTiO3 dispersed in hydrous elastomer.

Erbium doped TiO2–Bi2WO6 heterostructure with improved photocatalytic activity under sun-like irradiation

Erbium doped TiO2–Bi2WO6 have been synthesized by means of a surfactant free hydrothermal method having good photoactivities under sun-like excitation for the degradation of Rhodamine B. From the structural and morphological characterization it has been stated that the presence of Er3+ induces a progressive russelite cell contraction due to its incorporation in the Bi2WO6 lattice in substitutional sites. The best photocatalytic performance was attained for the samples with 1at% of Er. From the study of the photocatalytic activity under different irradiation conditions it can be inferred that Er3+ presence induces a significant improvement of the photoactivity in the UV range. The evolution of band-gap values seems to be similarly related with the reaction rate progression. Thus, the higher band-gap values in lower Er doped systems would be the cause of a better electron hole separation under UV irradiation.

On the different photocatalytic performance of BiVO4 catalysts for Methylene Blue and Rhodamine B degradation

BiVO4 hierarchical structures were synthesized by means of a surfactant free hydrothermal method having good photoactivities for the degradation of Methylene Blue and Rhodamine B under UV–vis irradiation. From the structural and morphological characterization it has been stated that BiVO4 present the monoclinic crystalline phase with different morphologies depending on the pH value. For Methylene Blue the photodegradation rate is strongly affected by the crystallite size and higher (004) facet exposition. On the contrary, for Rhodamine B, the ζ-potential of the surface clearly determines the photocatalytic performance of BiVO4 catalyst.

One-step synthesis of crystalline anatase TiO2 nanospindles and investigation on their photocatalytic performance

Crystalline anatase TiO2 nanospindles were synthesized via a facile one-step and surfactant-free hydrothermal method without calcination procedure. The product was characterized by XRD, SEM and HRTEM, and the phase, morphology as well as the exposed facets was ascertained. Specific surface area of the as-synthesized TiO2 nanospindles was calculated based on N2 adsorption–desorption isotherms. The photocatalytic activities of both the TiO2 nanospindles and the commercial P25 TiO2 nanoparticles were examined via the photodegradation of organic dyes. The former sample exhibits a much higher photocatalytic activity and the origin is discussed. In addition, the stability of the as-synthesized TiO2 photocatalyst was studied through repeated use of the sample.

High-performance Er3+–TiO2 system: Dual up-conversion and electronic role of the lanthanide

Erbium-doped TiO2 materials are synthesized by means of a surfactant-free hydrothermal method having good photoactivities for the liquid-phase degradation of phenol and MB and the gas phase of toluene. From the structural and morphological characterization, it has been stated that the presence of Er3+ induces a progressive anatase cell expansion due to its incorporation in the TiO2 lattice. The best photocatalytic performance was attained for the samples with 2at% of Er3+ irrespective of the chemical degradation reaction essayed. From activity and optical studies under different irradiation excitation conditions, a dual-type mechanism is proposed to be at the origin of the photocatalytic activity enhancement. On one hand, the improvement observed under UV irradiation occurs by the effective charge separation promoted by Er3+ species which would act as electron scavenger. Besides, the up-conversion luminescence process of Er3+ allows profiting the NIR range of the lamp and transferring energy in the UV range to the TiO2. The dual action of Er ions located at anatase networks will open up a wide roadway for the developing of an integral solar active photocatalyst.

Manipulation of morphologies and magnetic properties for Bi4.2K0.8Fe2O9+δ nanostructures

In this paper, Bi4.2K0.8Fe2O9+δ nanostructures with different morphologies, such as dispersible nanobelts, urchin-like and floriated micronanostructures with dendrites in different sizes, were controllably synthesized by a surfactant-free hydrothermal method. The temperatures of the KOH solutions in the co-precipitation step and the hydrothermal reactions had great effects on not only the morphologies but also the magnetic properties of the products. It was found that the low-temperature-fabricated urchin-like samples had a higher magnetization value. The special cores of the urchin-like nanostructures may play a critical role in the enhanced magnetizations and spin-glass dynamic behaviors. These results provide a simple way to manipulate the morphology of low-dimensional Bi4.2K0.8Fe2O9+δ nanostructures as well as their related magnetic properties.

One-pot, high-yield synthesis of one-dimensional ZnO nanorods with well-defined morphology as a highly selective photocatalyst

One-dimensional (1D) semiconductor ZnO nanorods have been successfully prepared via a facile surfactant-free hydrothermal method. Their structure and properties have been characterized by a series of techniques, including X-ray diffraction (XRD), UV-vis diffuse reflectance spectra (DRS), field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), nitrogen adsorption–desorption, photoluminescence spectra (PL) and electron spin resonance spectra (ESR). It is found that ZnO nanorods with diameters around 20–30 nm and lengths up to several micrometers are well-distributed. ZnO nanorods have been used to photocatalyze the aerobic oxidation of alcohols to aldehydes under ambient conditions. The results show that ZnO nanorods exhibit a markedly enhanced photoactivity and selectivity compared to their precursor, commercial ZnO, which can be ascribed to the special 1D morphology of ZnO nanorods leading to its favorable, selective adsorptivity toward the reactant of alcohols instead of the product of aldehydes, and the efficient separation of photogenerated charge carriers. A possible reaction mechanism for the photocatalytic selective oxidation of alcohols over ZnO nanorods has also been proposed. Our present work not only provides a facile, high-yield and surfactant-free approach for the fabrication of ZnO nanorods, but also enriches the chemistry of morphology-dependent functional properties of ZnO materials in the application of heterogeneous photocatalytic selective oxidation, which therefore could open a new doorway to utilize 1D semiconductor materials such as nanorods, nanotubes and nanowires as photocatalysts in selective transformation under ambient conditions.

Controlled synthesis and thermal stability of hydroxyapatite hierarchical microstructures

Hydroxyapatite (HAp) hierarchical microstructures with novel 3D morphology were prepared through a template- and surfactant-free hydrothermal homogeneous precipitation method. Field emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HRTEM), and X-ray diffraction (XRD) were used to characterize the morphology and composition of the synthesized products. Interestingly, the obtained HAp with 3D structure is composed of one-dimensional (1D) nanorods or two-dimensional (2D) nanoribbons, and the length and morphology of these building blocks can be controlled through controlling the pH of the reaction. The building blocks are single crystalline and have different preferential orientation growth under different pH conditions. At low pH values, octacalcium phosphate (OCP) phase formed first and then transformed into HAp phase due to the increased pH value caused by the decomposition of urea. The investigation on the thermal stability reveals that the prepared HAp hierarchical microstructures are morphologically and structurally stable up to 800°C.

Interfacial oxidation–dehydration induced formation of porous SnO2 hollow nanospheres and their gas sensing properties

Abstract Uniform porous SnO 2 hollow nanospheres with average diameters of about 100–200 nm have been reproducibly synthesized via a facile template- and surfactant-free hydrothermal method, using hydrogen peroxide 30% and stannous sulfate as precursors. The morphology, composition and structure of the resultant products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy and nitrogen adsorption–desorption technique. Experimental results demonstrated that the formation of these porous SnO 2 nanostructures is ascribed to an interfacial oxidation–dehydration mechanism. H 2 O 2 usage has an important effect on both the morphology and purity of the final products. The gas sensing properties of the as-prepared porous SnO 2 hollow nanospheres were investigated. By comparative gas sensing tests, the porous SnO 2 hollow nanospheres exhibited superior gas sensing performances over commercial SnO 2 nanopowders toward some typical volatile organic compounds (VOCs), implying their promising applications in gas sensors.

Surfactant-free hydrothermal synthesis of flower-like Bi 2 WO 6 with enhanced solar-light-induced photocatalytic performance

Bi 2 WO 6 with a flower-like structure was successfully synthesised by a simple surfactant-free hydrothermal method. The flower-like structures were composed of many interweaved nanosheets to form an open porous structure. The BET results showed that flower-like Bi 2 WO 6 had a large surface area with 17.8 m 2 /g, which was 28 times higher than the Bi 2 WO 6 prepared by a solid state reaction (SSR-Bi 2 WO 6 ). A possible formation mechanism of the flower-like Bi 2 WO 6 is proposed. Owing to the higher surface area, porous structure and high surface-to-volume ratios, the flower-like Bi 2 WO 6 exhibited better photocatalytic activity than the SSR-Bi 2 WO 6 for the degradation of Rhodamine B.

One-Step, Surfactant-Free Hydrothermal Method for Syntheses of Mesoporous TiO2Nanoparticle Aggregates and Their Applications in High Efficiency Dye-Sensitized Solar Cells

A facile, one-step, template-less, surfactant-free hydrothermal process, using a metal salt as the precursor, is developed to prepare submicrometer sized mesoporous TiO2 nanoparticle aggregates (NPGs). The as-prepared TiO2 NPGs are crystalline of the anatase phase, with a high specific surface area of 166 m2/g, an average pore size of 8.9 nm, and an average NPG size of 840 nm. With these NPGs, a new form of composite photoanode, consisting of the mesoporous TiO2 NPGs and xerogels, is proposed for high efficiency dye-sensitized solar cells (DSSCs). TiO2 xerogels are incorporated into the TiO2 NPGs layer with an impregnation process to form the TiO2 NPGs/xerogels composite. A high power conversion efficiency of 8.41% is achieved for DSSCs based on the TiO2 NPGs/xerogels composite photoanode, representing a 38% efficiency boost over the efficiency of 6.11% achieved with a P25 TiO2 based cell. The success of the present composite TiO2 nanostructure can be attributed to the effective utilization of the inter-N...

A novel synthesis and characterization of 3D chrysanthemum-like β-In2S3 by surfactantfree hydrothermal method

β-In2S3 with 3D chrysanthemum-like superstructures has been successfully synthesized by a simple surfactantfree hydrothermal route. It was found that the effect of reaction temperature, sulfur source and solvent on the morphology and structure of In2S3 microspheres was obvious. The crystallization, morphology and composition of as-prepared β-In2S3 were characterized by XRD, SEM, Raman and EDS, respectively. It revealed that 3D chrysanthemum-like β-In2S3 was built from small 2D nanosheets with thickness of 40nm. Differential pulse voltammetry (DPV) and electrochemical impedance spectroscopy (EIS) were applied to investigate the electrochemistry performance of product. It was found that the synthesized 3D chrysanthemum-like β-In2S3 possessed the high electrocatalytic activity.

Controllable synthesis of CdWO<sub>4</sub> nanorods and nanowires via a surfactant-free hydrothermal method

Controllable synthesis of CdWO<sub>4</sub> nanorods and nanowires via a surfactant-free hydrothermal method

Dense layers of vertically oriented WO3crystals as anodes for photoelectrochemical water oxidation

Films of crystalline WO(3) nanosheets oriented perpendicular to tungsten substrates were grown by a surfactant-free hydrothermal method, followed by sintering. The films exhibit photoelectrochemical oxygen evolution at low overpotential.

Evidence of upconversion luminescence contribution to the improved photoactivity of erbium doped TiO2 systems

Er(3+)-TiO(2) synthesized by a surfactant free hydrothermal method exhibits good photoactivities under sun-like excitation for the degradation of phenol. The presence of Er(3+) does not affect the structural and morphological features of the TiO(2) significantly. The best photocatalytic performance was attained for the samples with 2 wt% of Er. Different photocatalytic runs indicated that the incorporation of the Er(3+) cation would be responsible for the enhanced photocatalytic activity, which participates in different mechanisms under UV and NIR excitation.

Hydrothermal synthesis of BiVO4: Structural and morphological influence on the photocatalytic activity

BiVO4 hierarchical heterostructures are synthesized by means of a surfactant free hydrothermal method having good photoactivities for the degradation of methylene blue under UV–vis irradiation. From the structural and morphological characterization it has been stated that BiVO4 present the monoclinic crystalline phase with different morphologies depending on the pH value, type of precipitating agent and hydrothermal temperature and treatment time. The best photocatalytic performance was attained for the samples with needle-like morphology.

Microstructures and Photoluminescence Properties of Three-Dimensional Multi-Layered ZnO Flowers by Surfactant-Free Hydrothermal Method

In this paper, a large-scale of three-dimensional multi-layered ZnO flowers constructed by porous nanosheets were fabricated on Zn foils through a surfactant-free hydrothermal method. The morphology and microstructures of precursors and the mesoporous ZnO flowers were revealed by scanning electron microscopy. Based on the urea hydrolyzation, a possible growth mechanism of etching-deposition was proposed. The quantities and sizes of ZnO petals can be turned by urea concentration variations. The optical properties of the multi-layered ZnO flowers prepared with variety urea contents were also investigated by room temperature photoluminescence spectroscopy and showed the lower urea added sample has better crystalline quality.