Hydrothermal synthesis of vanadium pentoxide nanostructures and their morphology control

Different morphologies of vanadium pentoxide (V₂O₅) from 1D to 3D, including nanospheres, nanowires, urchin-like and flower-like nanostructures, have been synthetized by a simple hydrothermal method. Some parameters, such as the reaction temperature, the volume of polyvinyl pyrrolidone (PVP) and possible formation mechanisms of different V₂O₅ nanostructures were discussed. The results demonstrate that PVP and the reaction temperature play a critical role on the morphology of vanadium pentoxide.     

铂纳米花的控制合成

以氯铂酸钾（K2PtCl6）为前驱体、聚乙烯吡咯烷酮（PVP）为稳定剂及还原剂,在一定量溴化钾（KBr）的存在下,采用水热法制备了铂纳米花。考察了n（K2PtCl6）∶n（PVP）∶n（KBr）、反应温度、反应时间对产物形貌的影响。结果表明,在n（K2PtCl6）∶n（PVP）∶n（KBr）为1∶10∶15、反应温度为130℃、反应时间为3h的条件下,制备出形貌规则、大小均匀的花形自组装铂纳米颗粒。利用透射电子显微镜、X-射线光电子能谱和X-射线粉末衍射对产物进行了表征。所制备的铂纳米花由零价态的铂原子组成,具有面心立方（fcc）结构。     

Hydrothermal synthesis and characterizations of 2D and 3D 4ZnO·B2O3·H2O nano/microstructures with different morphologies

2D and 3D nano/microstructures of 4ZnO·B₂O₃·H₂O with different morphologies have been successfully synthesized by a hydrothermal route in the presence of surfactant polyethylene glycol-300 (PEG-300). Lamellar-like nanoparticles and microsphere organizations of nano and microrods are fabricated by varying the reaction conditions. The products have been characterized by XRD, FT-IR, TG-DTA and SEM. The XRD data indicate the as-prepared samples present at pure phase 4ZnO·B₂O₃·H₂O with monoclinic symmetry. The SEM results reveal that the lamellar-like particles are about 30 nm in thickness and around several hundred nanometers in diameter. The microsphere organizations have different diameters, and the secondary structures are made from rod-like particles with different size and mode, respectively. The morphologies of products strongly depend on surfactant, hydrothermal temperature and time.     

Synthesis and characterization of CeO2 nano-rods

We report a synthesis of two types of CeO₂ nano-rods via the facile and efficient hydrothermal process free from any surfactant and template. The synthesized nano-rods are chemically identified as CeO₂ with the standard fluorite structure but their morphologies are different. The nano-rods prepared with cerium nitrate hexahydrate and sodium phosphate are thicker and shorter with diameter of ∼30 nm and length of ∼100 nm, and those prepared with cerium acetate hydrate and dibasic sodium phosphate are thinner and longer with ∼10 nm in diameter and ∼400 nm in length. Microstructural analyses reveal that the two species of nano-rods have low-energy {111} surfaces and grow along the 〈112〉 direction. As a consequence of their morphologies, the two types of synthesized nano-rods exhibit excellent UV-absorption ability in comparison to the irregular CeO₂ nanoparticles.     

Effect of substrate (ZnO) morphology on enzyme immobilization and its catalytic activity

In this study, zinc oxide (ZnO) nanocrystals with different morphologies were synthesized and used as substrates for enzyme immobilization. The effects of morphology of ZnO nanocrystals on enzyme immobilization and their catalytic activities were investigated. The ZnO nanocrystals were prepared through a hydrothermal procedure using tetramethylammonium hydroxide as a mineralizing agent. The control on the morphology of ZnO nanocrystals was achieved by varying the ratio of CH₃OH to H₂O, which were used as solvents in the hydrothermal reaction system. The surface of as-prepared ZnO nanoparticles was functionalized with amino groups using 3-aminopropyltriethoxysilane and tetraethyl orthosilicate, and the amino groups on the surface were identified and calculated by FT-IR and the Kaiser assay. Horseradish peroxidase was immobilized on as-modified ZnO nanostructures with glutaraldehyde as a crosslinker. The results showed that three-dimensional nanomultipod is more appropriate for the immobilization of enzyme used further in catalytic reaction.     

Synthesis of highly dispersed MnOx–CeO2 nanospheres by surfactant-assisted supercritical anti-solvent (SAS) technique: The important role of the surfactant

In this work, highly dispersed mesoporous MnO_x–CeO₂ hollow nanospheres have been prepared using a surfactant-assisted supercritical anti-solvent (SAS) technique. The phase equilibria of methanol–CO₂, precursor-methanol–CO₂ and surfactant, precursor-methanol–CO₂ systems were measured to preliminarily screen suitable surfactants. The MnO_x–CeO₂ particles were characterized using N₂ adsorption/desorption, transmission electron microscopy (TEM) and X-ray diffraction (XRD). Polyvinylpyrrolidone (PVP) and poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) (P123) both efficiently reduced the interconnectivity and agglomeration of MnO_x–CeO₂ particles and led to the formation of highly dispersed particles with higher specific surface areas, more uniform pores and larger pore volumes. The effects of the SAS process parameters including the surfactant to precursor mass ratio, the temperature and the pressure, on the morphology, particle size, particle size distribution, specific surface area and pore volume of the particles were also investigated. In addition, the catalytic activities of the synthesized hollow nanospheres for the low temperature denitrification (deNO_x) in the presence of NH₃ were evaluated. Over the entire experimental temperature range (100–220 °C), NO conversions of the MnO_x–CeO₂ particles prepared by introducing PVP or P123 during SAS were much higher than those for MnO_x–CeO₂ particles prepared without surfactants.     

The role of Eu2O3 and CeO2 on the phase formation,infrared emission and magnetic properties of Co0.6Zn0.4Fe2O4 ceramics by a solvothermal method

Nanosized Eu₂O₃ and CeO₂ co-addition CoZn ceramics have been achieved via a hydrothermal method by adjusting the mol ratios of Eu and Ce. The as-prepared samples were characterized by X-ray diffraction (XRD), Transmission electron microscopy (TEM), Fourier transform infrared (FTIR), Vibrating sample magnetometer (VSM) and Infrared emission measurement (IRE-2). The particle morphologies of the as-prepared samples evolve from spherical, to self-assembled nanoparticles, and irregular nanoparticles when the mol ratios (x) of Eu and Ce was changed from 0:10 to 10:0. Correspondingly, the main phases of the as-prepared samples change from both cubic spinel CoFe₂O₄ and CeO₂, pure cubic cerianite CeO₂, to amorphous. Meanwhile, the as-prepared samples appear transformed from a ferromagnetic behavior with a saturation magnetization 66.4 emu/g to a paramagnetic behavior with a saturation magnetization of 0.55 emu/g at turning point x=3.5:6.5. While the infrared emissivity is increasing as the x from 0:10 to 3.5:6.5, reach the maximum at 3.6:6.4, and then remain stable when further increasing x till 10:0. Those may be due to the amorphous tendency rising and the particle sizes gradual decreasing with x increasing from 0:10 to 10:0. What is more important is that the solvothermal method is proved to be an efficient way to prepare CoZn nano-ceramics in this study which may open new pathways to magnetic and far infrared therapy.     

Unique polyhedron CeO2 nanostructures for superior formaldehyde gas-sensing performances

Highly exposed surface area CeO₂ polyhedral nanostructures were successfully prepared via a two-step hydrothermal route for gas-sensing applications. The surface chemistry and formation of polyhedral nanostructures was attributed to the interaction between polyvinylpyrrolidone and ammonium bicarbonate surfactants with parent ceria. The synthesized polyhedron CeO₂ structures were characterized using XRD, XPS, BET, SEM, EDS and TEM, respectively. The polyhedrons exhibited a high specific surface area 98.76?m²/g. For gas-sensing applications, the CeO₂ polyhedrons were exposed to different gases at various temperatures, from a low to high concentration range (1–150?ppm). At an optimal temperature 220?°C, superior gas-sensing response towards formaldehyde was observed than other target gases. The enhanced sensor response was attributed to multifaceted polyhedral nanostructures. The polyhedral structure based sensors have great potential in industrial sensing applications.     

Preparation of Pt/CeO2/HCSs anode electrocatalysts for direct methanol fuel cells

Hollow carbon spheres (HCSs) were prepared through a simple hydrothermal method using silica particles and glucose as the template and carbon precursor, respectively. HCSs used as supports for platinum catalysts deposited with cerium oxide (CeO₂) were prepared for application as anode catalysts in direct methanol fuel cells. The composition and structure of the samples were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), energy dispersive spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). The electrocatalytic properties of the as-prepared catalysts for methanol oxidation were investigated by cyclic voltammetry (CV). The Pt/CeO₂/HCSs catalyst heated at 550 °C for 1 h exhibited the best catalytic activity for methanol oxidation.     

γ-Bi2MoO6 nanoplates: Surfactant-assisted hydrothermal synthesis and optical properties

γ-Bismuth molybdate (Bi₂MoO₆) nanoplates were successfully fabricated on a large scale at 180 °C for 12 h by one-step hydrothermal method with the use of surfactant poly(vinyl pyrrolidone) (PVP). X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to characterize the product, and the results indicated that as-prepared Bi₂MoO₆ product had a typical plate-like structure with a thickness range of 100–150 nm. UV–vis spectroscopy was employed to estimate the band gap energy of γ-Bi₂MoO₆ nanoplates, and it exhibited significant absorption from the visible region to near infrared region, in addition to the absorption band in the UV region. The method provides a facile, one-step and low-cost route for the synthesis of nanostructures of multicomponent metal oxides with potential optical applications.     

Controllable synthesis and flame retardant properties of bunch-, chrysanthemum-, and plumy-like 4ZnO·B2O3·H2O nanostructures

Three kinds of new 4ZnO·B₂O₃·H₂O nanostructures of bunch-, chrysanthemum-, and plumy-like morphologies have been synthesized under hydrothermal conditions at 140 °C in the presence of ethanol. The as-synthesized products were characterized by the chemical analysis, TG, XRD, FT-IR, SEM and TEM. All the synthesized 4ZnO·B₂O₃·H₂O nanostructures consist of nanoribbons. A series of control experiments confirmed that the morphologies of the products were influenced by the reaction time, temperature, and the presence of the surfactant of PEG-300. Furthermore, the flame retardant properties of the synthesized 4ZnO·B₂O₃·H₂O nanostructures were investigated by the thermal analysis method, demonstrating that they had the better behaviors than the non-nanostructure sample.     

Synthesis and characterization of In2S3 nanostructures via ultrasonic method in the presence of thioglycolic acid

In the present study, nanocrystalline In₂S₃ with different morphologies and particle sizes were obtained via an ultrasonic method by employing InCl₃·4H₂O, thioglycolic acid (TGA) and propylene glycol as In³⁺, sulfur source and solvent agent, respectively. Besides, the effects of preparation parameters such as time and power of ultrasonic irradiation, solvent, and surfactant on the morphology and particle size of the products were studied. The synthesis procedure is simple and facile for the preparation of structures with various morphologies. The morphology, structure, and composition of the as-synthesized nanostructures have been investigated by X-ray diffraction (XRD), energy dispersive X-ray analysis (EDX), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Optical properties of the as-prepared sample were investigated by photoluminescence (PL) and ultraviolet–visible (UV–vis) spectroscopy.     

Hydrothermal synthesis and mechanism of triangular prism-like monocrystalline CeO2 nanotubes via a facile template-free hydrothermal route

Monocrystalline CeO₂ tablet-like nanostructures and triangular prism-like nanotubes were synthesized by thermal conversion of cerium carbonate hydroxide (CeOHCO₃) precursors prepared by a simple template-free hydrothermal method using Ce(NO₃)₃·6H₂O as cerium source, CO(NH₂)₂ as both precipitator and carbon source and polyvinylpyrrolidone (PVP) as surfactant. X-ray diffractometer (XRD) images inferred that the as-synthesized Ce(CO₃)(OH) has a hexagonal structure, and the CeO₂ obtained by calcining the Ce(CO₃)(OH) at 500 °C for 5 h has a cubic fluorite structure. Scanning electron microscope (SEM) was employed to reveal the transformation from tablet-like to triangular prism-like structures, and then to triangular prism-like nanotubes with the increase of temperature from 120 up to 200 °C. Monocrystalline structure was revealed by high resolution transmission electron microscope (HRTEM) and select area electron diffraction (SAED) patterns. The thermal decomposition process of the as-synthesized Ce(CO₃)(OH) was investigated by thermo-gravimetric differential thermal analysis (TG–DTA) apparatus, and the possible formation mechanism of CeO₂ has been discussed. The spectral properties were characterized by Fourier transform infrared spectrum (FT-IR), Raman scattering, Photoluminescence (PL) spectra and UV–vis spectroscopy. There is a red-shifting in the band gap of the material compared to bulk one, which is mainly attributed to the influences of the Ce³⁺ ions, oxygen vacancies and the change of morphology.     

Morphology-controlling synthesis of ZnS through a hydrothermal/solvthermal method

Different morphologies of ZnS have been synthesized by a solvothermal process, through the reaction of Zn(CH₃COO)₂·2H₂O and SC(NH₂)₂ in different mixed solvents, changing the density of the surfactant (C₁₂H₂₅SO₃Na). The samples were characterized by the X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive X-ray analysis (EDAX) techniques. The results show that the as-prepared ZnS have different morphologies, such as lamellar ZnS, smooth microspheres, roughen microspheres, plate-like ZnS and so on. So far, to our knowledge, lamellar ZnS have not been synthesized by solvothermal route before.     

Green synthesis of aniline by phosphorus-doped titanium dioxide polymorphs

Phosphor doping in association with a heterostructure not only modifies the band structure of titanium dioxide (TiO₂) to make it more responsive to visible light, but it also suppresses its charge recombination and causes TiO₂ to have enhanced photoactivity. In this paper, we report on the controlled synthesis of phosphor-doped binary and ternary TiO₂ nanostructures through a hydrothermal method. The phase and morphology of the samples can be tuned by simply changing the hydrothermal time. Also, the visible-light photoactivity of the samples was evaluated by the reduction of nitrobenzene. The as-prepared catalysts exhibit enhanced photocatalytic activity in comparison to P₂₅ and the undoped counterpart, and the selected catalyst shows high photostability and photoactivity after reuse five times. These new TiO₂ nanostructures present a promising candidate for application in photocatalysis, photochemistry, sensors, and solar cells.     

Preparation of Highly Crystalline TiO<Subscript>2</Subscript> Nanostructures by Acid-assisted Hydrothermal Treatment of Hexagonal-structured Nanocrystalline Titania/Cetyltrimethyammonium Bromide Nanoskeleton

Highly crystalline TiO₂ nanostructures were prepared through a facile inorganic acid-assisted hydrothermal treatment of hexagonal-structured assemblies of nanocrystalline titiania templated by cetyltrimethylammonium bromide (Hex-ncTiO₂/CTAB Nanoskeleton) as starting materials. All samples were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The influence of hydrochloric acid concentration on the morphology, crystalline and the formation of the nanostructures were investigated. We found that the morphology and crystalline phase strongly depended on the hydrochloric acid concentrations. More importantly, crystalline phase was closely related to the morphology of TiO₂ nanostructure. Nanoparticles were polycrystalline anatase phase, and aligned nanorods were single crystalline rutile phase. Possible formation mechanisms of TiO₂ nanostructures with various crystalline phases and morphologies were proposed.     

Transformation of CeO2 into a mixed phase CeO2/Ce2O3 nanohybrid by liquid phase pulsed laser ablation for enhanced photocatalytic activity through Z-scheme pattern

Cerium-based nanohybrids have attracted considerable attention in photocatalytic research owing to their remarkable potential in the photodegradation of environmental pollutants. However, the process of nanohybrid formation suffers from complex operations with specialized equipment, extreme conditions, long durations, and low yields, making it infeasible for efficient utilization. Considering the above obstacles, we herein describe the first pulsed laser ablation (PLA) for the synthesis of oxygen vacancy affluent CeO₂/Ce₂O₃ nanohybrids, as an alternative to hydrothermal and calcination methods. The microstructures and optical properties of the nanocomposites are characterized by TEM, XRD, XPS, and DRS analysis. The photocatalytic activity of the CeO₂/Ce₂O₃ nanohybrid showed an MB dye degradation rate superior to that of bare CeO₂ nanostructures. The enhanced performance of CeO₂/Ce₂O₃ was attributed to an oxygen-vacancy-driven Z-scheme mechanism, where efficient separation of the photogenerated charge carriers significantly contributed to photocatalytic enhancement. This was further evidenced by both PL and scavenger experiment results. Moreover, the synthesized CeO₂/Ce₂O₃ nanocomposites exhibit a strong blue emission, which could have potential applications in LED manufacturing.     

Effect of copper on improving the electrochemical storage of hydrogen in CeO2 nanostructure fabricated by a simple and surfactant-free sonochemical pathway

Introducing high-performance compounds for hydrogen sorption is of interest because of their advantages for substantial applications such as energy storage. Here, the role of copper addition on hydrogen storage capability and Coulombic efficiency of CeO₂ nanostructure (fabricated by an easy and surfactant-free sonochemical pathway) was examined, for the first time. Nanostructured oxides were fabricated with loading various percentages of copper (4 wt% and 40 wt%) inside CeO₂. Nanostructured copper-ceria binary oxides were checked by diverse analyses. The hydrogen storage performance as well as Coulombic efficiency of the nanostructured copper-ceria binary oxides and the net CeO₂ were checked through chronopotentiometry charge−discharge pathway in the alkaline medium. The outcomes exhibited that the hydrogen storage capacity of CeO₂ nanostructure could be enhanced with adding the proper dosage of copper as a beneficial low-cost solution. Self-assembled copper-doped CeO₂ hierarchical nanostructures could display the most appropriate performance than the net CeO₂ and nanostructured Cu₂O–CeO₂. The discharge capacity for the self-assembled copper-doped CeO₂ hierarchical nanostructures (fabricated by adding 4 wt% copper) could rise to 5070 mAh/g at 22nd cycle. Appropriate porosity, special architecture and unique morphology as well as convenient surface area of the self-assembled copper-doped CeO₂ hierarchical nanostructures render they can be very beneficial compounds in the energy storage.     

Ultra-thin cerium oxide nanostructures through a facile aqueous synthetic strategy

In this work, synthesis of ultra-thin 2D CeO₂ nanoribbons is reported for the first time along with rod-shaped nanostructures via a surfactant free aqueous method. CeO₂ nanoribbons of length >100 nm have been synthesised through a mild reaction route involving ammonia precipitation and subsequent heating and ageing at 0 °C. 2D nanostructures are proposed to be formed as a result of self-assembly of CeO₂ molecules. The ribbons exhibited amorphous X-ray diffraction pattern and TEM showed a ribbon like morphology with crystal facets of ～0.33 nm spacing corresponding to (1 1 1) plane of CeO₂. HR-TEM confirmed that the nanorods are enclosed by {1 1 1} planes and have preferentially grown in {1 1 0} direction. The surface area of the powder containing majority nanorods is 82 m²/g and their average pore size is ～3 nm. The nanostructures exhibited optical band gaps dominated by the regular quantum confinement effect as well as presence of defects.     

A CTAB-assisted hydrothermal synthesis of VO2(B) nanostructures for lithium-ion battery application

Nanostructured VO₂(B) was synthesized via a combined hydrothermal method using V₂O₅ as a source material and oxalic acid powder as a reductant. Especially, cetyltrimethylammonium bromide (CTAB) was used as template and then three different morphologies of the VO₂(B): nanobelts, nanoflowers and nanoflakes were obtained through the change of the experimental conditions. The morphology and crystalline structure of the prepared products were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR). Furthermore, the electrochemical charge–discharge cycling properties of the VO₂(B) nanostructures in lithium-ion battery were investigated. The results indicated that the belt-like, flower-like and flake-like VO₂(B) nanostructures have the initial specific discharge capacity of 205.2, 254.0 and 56.0 mA h g⁻¹, and that the morphology of VO₂(B) nanostructures can deeply affect the service performance of batteries. According to the experiments, this CTAB-assisted hydrothermal method provides an insight into the preparation and application of nanostructured VO₂(B) as cathode material in lithium-ion battery.