Sonochemical preparation of PbWO4 crystals with different morphologies

PbWO₄ was prepared from Na₂WO₄·2H₂O and Pb(OAc)₂·3H₂O in a solution containing a cationic surfactant (N-cetyl pyridinium chloride) using the sonochemical process (ultrasonic irradiation). The product morphologies, characterized using scanning electron microscopy (SEM) and transmission electron microscopy (TEM), were controlled by the surfactant, pH values and ultrasonic irradiation times. X-ray diffraction (XRD) and selected area electron diffraction (SAED) studies revealed diffraction patterns in good agreement with the simulation model, along with Fourier transform infrared (FTIR) and Raman analyses showed a W–O stretching band consistent with tetragonal PbWO₄. Photoluminescent properties of the pine tree shaped products were also investigated.     

Synthesis of micro-and nanosized PbS with different morphologies by the hydrothermal process

PbS micro- and nanostructures with different morphologies and particle sizes were obtained via a simple hydrothermal reaction between lead oxalate, Pb(C₂O₄)₂, and thioglycolic acid (TGA) as Pb²⁺ and the sulfur source and the capping agent, respectively. Products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), ultraviolet–visible (UV–vis) spectroscopy and Fourier transform infrared (FT-IR) spectra. The effects of temperature, reaction time and the type of Pb²⁺ source on the morphology and particle sizes of products were investigated.     

硫化铅薄膜材料的合成及应用研究进展

综述了PbS薄膜材料的合成方法、应用现状,结合薄膜材料的发展需求提出了电子束辐射法、超声法、微波法等几种高效合成均匀致密PbS薄膜的新方法,展望了PbS薄膜材料的发展前景。     

超临界水热合成制备纳米微粒材料

简述了超临界水热合成法制备纳米微粒材料技术的微粒形成机理、过程基本工艺及目前所取得的研究成果。讨论了未来需要解决的问题。     

Comparative hydrothermal synthesis of hydroxyapatite by using cetyltrimethylammonium bromide and hexamethylenetetramine as additives

Comparative synthesis ways for preparing HA (Ca₁₀(PO₄)₆(OH)₂) nanoparticles in presence of hexamethylenetetramine (HMTA) and cetyltrimethylammonium bromide (CTAB) were carried out. The reactions were performed in a Teflon-lined stainless-steel reactor at 120 °C during 12 h. The effects of the additive concentration and the cooling mode (fast and slow) were analyzed. The obtained powders were characterized by X-ray Diffraction (XRD), Raman Spectroscopy, Dynamic Light Scattering (DLS) and Scanning Electron Microscopy (SEM). The two hydrothermal ways carried out for preparing HA nano powders produced a pure crystalline phase of HA. When the fast cooling mode was used, the obtained particles exhibited smaller mean particle sizes. The highest concentrations of used additives (HTMA or CTAB) resulted in opposite effect on the obtained mean particle size of HA particles. These observations were associated to the different behavior of these additives in the HA formation processes.     

A CTAB-assisted hydrothermal and solvothermal synthesis of ZnO nanopowders

ZnO nanopowders were synthesized by hydrothermal and solvothermal method by using CTAB as surfactant, and the effects of CTAB on the morphologies of ZnO nanopowders were investigated. The results showed that the presence of CTAB could greatly vary the shape of the ZnO crystals. ZnO nanorods were prepared from the hydrothermal system without CTAB and flowers-like ZnO nanostructures were produced from hydrothermal system with 0.4 M and 0.5 M CTAB. Low concentration of CTAB in ethanol was conducive to the formation of ZnO nanorods, but the concentration continued to increase, the morphology of sample transformed into hexagonal bipyramid, and then transformed into spherical. The synthesis mechanism of ZnO powders with different morphologies has been presented.     

Hydrothermal synthesis of orthorhombic LiMnO2 nano-particles

Orthorhombic LiMnO₂ nano-particles were successfully prepared under mild hydrothermal conditions from KMnO₄ and MnCl₂ sources. Transmission electron microscopy (TEM) and X-ray diffraction (XRD) were used to characterize the LiMnO₂ particles. The influence of the molar ratio of Li/Mn and of the holding temperature was studied. The synthesized nano-particles were found to be highly crystallized with a diameter of 50-100 nm.     

Influence of hydrothermal synthesis conditions on BNT-based piezoceramics

The Bi_0.5Na_0.5TiO₃ perovskite (BNT) is a very promising lead-free candidate for piezoelectric applications. Nevertheless a low reproducibility is commonly reported for the solid state synthesized BNT. In this work, the hydrothermal synthesis was investigated to improve the BNT ceramics characteristics reproducibility. The synthesis conditions were studied in order to control more particularly the BNT grain size, crystallinity and stoichiometry.Thanks to the slow hydrolysis of titanium isopropoxide with bismuth nitrate pentahydrate, well crystallized BNT-based powder was synthesized at 265 °C. Nevertheless this powder exhibited secondary amorphous phases. Such secondary phases synthesis was limited and prevented by both lowering the temperature synthesis down to 160 °C and optimizing the washing conditions of the powder. The BNT was finally made free of any amorphous phase by using a hydrochloric solution. The BNT sinterability was improved and BNT-based piezoceramics exhibiting a d₃₃ as high as 60 pC/N were successfully produced.     

Pre-treatment of raw materials for the hydrothermal synthesis of hydrotalcite-like compounds

Hydrotalcite-like compounds are layered materials with anionic exchange and adsorption properties. Alternatively, this material is synthesized by hydrothermal treatment of magnesium oxide (MgO) and aluminium trihydroxide (ATH). Since this synthesis deals with solid raw materials, and the reaction proceeds through a solution mediated dissolution–precipitation process, it is a challenge to enhance the reactivity of the raw materials. This research aims to investigate the effect of four different pre-treatments: blending, ultrasound treatment, and wet grinding on the conversion rate. In experiments at 80 °C, only 3R₁ polytype HTlc was formed, while a mixture of 3R₁ and 3R₂ polytypes was found in the experiments at 170 °C. All the pre-treatment techniques cause a decrease in particle size of the raw materials whereby wet grinding induced the strongest effect. Experimentally the fastest conversions at both synthesis temperatures were achieved by wet grinding. A reaction mechanism is proposed which explains the observed conversions as a function of the particles size of the reactants, the exposure time of the MgO to water and the reaction temperature. Two important parameters to be taken into account in the synthesis are thus exposure to water prior to the reaction and the particle size of the raw materials.     

Cellulose in lithium chloride/N,N-dimethylacetamide, optimisation of a dissolution method using paper substrates and stability of the solutions

Activation and dissolution in lithium chloride/N,N-dimethylacetamide (LiCl/DMAc) of cellulose from paper substrates are studied. The importance of the multiple parameters involved such as salt concentration, sample source and preparation is shown in a literature review. The experiments are carried out in order to perfect the method of activation and dissolution of paper containing different kinds of additives, typically found in historic papers. The suitability and efficiency obtained in the different trials are evaluated. The final procedure involves the activation by solvent exchange, with a water/methanol/DMAc sequence, followed by dissolution in 8% LiCl/DMAc at 4 °C. A study of the stability of the cellulose solutions in the experimental conditions showed that no degradation nor aggregation occurred during the solvation process and even after several months and confirmed the non-aggressiveness of LiCl/DMAc.     

Morphology-controlled synthesis and characterization of bismuth sulfide crystallites via a hydrothermal method

Bismuth sulfide (Bi₂S₃) crystallites with various morphologies have been successfully synthesized via a hydrothermal process assisted by KOH mineralizer. X-ray diffraction (XRD) and scanning electron microscopy (SEM) indicated that the mineralizer played a key role in the crystallization and morphology-controlled synthesis of Bi₂S₃ crystallites. The room temperature photoluminescence spectra (PL) showed that uniform rod-shape morphology resulted in better luminescence.     

SAPO-11分子筛的水热合成及其金属负载改性的研究进展

简述了SAPO-11分子筛的结构和合成原理,介绍了传统水热合成方法。通过几种方法对其进行改进,比较了改进前后分子筛的结构和性能。同时归纳和总结了金属负载改性对SAPO-11分子筛应用于烷烃异构化性能的影响。     

Lithium-ion battery anode properties of TiO2 nanotubes prepared by the hydrothermal synthesis of mixed (anatase and rutile) particles

From mixed (anatase and rutile) bulk particles, anatase TiO₂ nanotubes are synthesized in this study by an alkaline hydrothermal reaction and a consequent annealing at 300-400 °C. The physical and electrochemical properties of the TiO₂ nanotube are investigated for use as an anode active material for lithium-ion batteries. Upon the first discharge-charge sweep and simultaneous impedance measurements at local potentials, this study shows that interfacial resistance decreases significantly when passing lithium ions through a solid electrolyte interface layer at the lithium insertion/deinsertion plateaus of 1.75/2.0 V, corresponding to the redox potentials of anatase TiO₂ nanotubes. For an anatase TiO₂ nanotube containing minor TiO₂(B) phase obtained after annealing at 300 °C, the high-rate capability can be strongly enhanced by an isotropic dispersion of TiO₂ nanotubes to yield a discharge capacity higher than 150 mAh g⁻¹, even upon 100 cycles of 10 C-rate discharge-charge operations. This is suitable for use as a high-power anode material for lithium-ion batteries.     

Effect of substrate surface treatment on the hydrothermal synthesis of zinc oxide nanostructures

In this investigation, ZnO nanostructures were coated via hydrothermal process on glass substrate surfaces, which were treated by acidic and alkaline solutions. Furthermore, the ZnO structure was doped by different amounts of Al⁺³ ions to investigate the microstructural variation. Characteristics of the samples by XRD and SEM analyses confirmed the formation of different morphologies and various crystal sizes for the nanostructured ZnO on the substrates including nanoflower, nanorod, and nanopanel morphologies. Furthermore, XRD results showed that the Zn²⁺ concentration was a crucial factor in changing the grain size. EDS analysis confirmed the uniform distribution of Al dopant, while the FTIR spectra revealed the presence of Al–O and Zn–O stretching bonds in the coatings. The results confirmed that the sample, which was etched by fused NaOH had a uniform and compacted structure. Moreover, it was evident the proposed treatment and synthesis process was successful in the formation of uniform nanostructured ZnO film on the glass substrate without the requirement for seed layer deposition.     

A facile galvanostatic method for the synthesis of quinoxalinediones

Electrochemical oxidation of catechols (1a-d) has been studied in the presence of N,N-dimethylethylendiamine (3) as a nucleophile in aqueous solutions, using cyclic voltammetry, constant-current coulometry and controlled-potential coulometry. The results indicate that the quinones derived from catechols (2a-d) participate in Michael addition reactions with N,N′-dimethylethylendiamine (3) via the ECECE mechanism to form the corresponding quinoxalinedione derivatives (6a-c).     

The hydrothermal synthesis and structure of a one-dimensional Fe(II)molybdophosphate

A new one-dimensional Fe(II)molybdophosphate of the formula, [(C₁₀H₈N₂)H₂]₂[Fe₄^(II)Mo₁₂^(V)(HPO₄)₆(PO₄)₂(H₂O)₈(OH)₆O₂₄]·8H₂O, (1), has been synthesized by employing hydrothermal methods and characterized by single crystal X-ray diffraction. The structure consists of a network of MO₆ (M = Fe, Mo) octahedra and (H)PO₄ tetrahedra linked through their vertices. The connectivity between the polyhedral units gives rise to one-dimensional chains with eight-membered apertures. The hydrogen bonded interactions between the chains form pseudo two-dimensional layers. Extensive hydrogen bonding also exists between the amine molecule, 4,4^′-bipyridine, water molecule and framework oxygen atoms. Crystal data for 1: monoclinic, space group = P2₁ (no. 4), a=12.549(3) (Å), b=23.496(5) (Å), c=14.551(3) (Å), β=114.87(3)°, , and Z=2.     

Modified hydrothermal synthesis of SnOy-SiO2 for lithium-ion battery anodes

A modified hydrothermal method was developed to synthesize tin oxide doped with highly dispersed silicon oxide. The microstructure, morphology and electrochemical performance of the mixtures were analyzed by X-ray diffraction (XRD), infra-red (IR), scanning electron microscopy (SEM) and electrochemical methods. The average size of the particles is about 30 nm. Silicon oxide as matrix should be able to support the anode changes accompanied by the formation of lithium-tin alloys, thus an improvement of the cycleability of the Li-ion battery would be expected. The electrochemical results showed that addition of silicon oxide reduces the irreversible capacity during the first discharge/charge cycle. The material delivers a charge capacity of more than 750 mAh g⁻¹. The capacity loss per-cycle is about 0.9% after cycling 20 times. The electrochemical performance indicates that silicon oxide is an appropriate matrix and these composites are good anode candidates for application in lithium-ion batteries.     

Morphology controlled hydrothermal synthesis and photocatalytic properties of ZnFe2O4 nanostructures

The present work is focused on studying morphology dependent catalysis of spinel ZnFe₂O₄ nanostructures. Different morphologies i.e. porous nanorods, nanoparticles, nanoflowers and hollow microspheres were designed hydrothermally. The as prepared nanomaterials were characterized using Fourier Transform Infra-Red (FTIR), field emission scanning electron microscopy (FE-SEM), high resolution transmission electron microscopy (HR-TEM), powder X-ray diffraction (XRD), vibrating sample magnetometer (VSM), Brunauer–Emmett–Teller (BET) technique and UV–visible spectrophotometer. The results confirmed formation of desired morphologies of cubic spinel ZnFe₂O₄ with high surface areas (92–138 m²/g) and narrow band gaps (1.76–1.97 eV). It suggested the use of ZnFe₂O₄ nanostructures as potential visible light photocatalysts. Therefore, the application of synthesized ZnFe₂O₄ nanostructures was studied in photo-Fenton degradation of dyes. The results indicated shape dependent relationship with photocatalytic activity as the degradation of dyes followed the order porous nanorods>nanoparticles>nanoflowers>hollow microspheres. The role of main active species in the reaction i.e. ^∙OH was also confirmed. All the materials exhibited stability and magnetic separability hence could act as potential photo-Fenton catalysts for wastewater treatment.     

Sodium niobates and protonic niobates nanowires obtained from hydrothermal synthesis: Electrochemical behavior in aqueous electrolyte

Niobium-based oxides can be used in several applications due to a diverse set of properties. In this work, Na₂Nb₂O₆.H₂O sodium niobate nanowires were obtained by hydrothermal synthesis at low temperature. Dehydrated sodium niobate (Na₂Nb₂O₆) and sodium niobate with perovskite structure (NaNbO₃) were obtained by submitting Na₂Nb₂O₆.H₂O to heat treatment (350 °C and 500 °C, respectively). To obtain protonic niobates, sodium niobates were immersed in nitric acid in order to promote ion exchange reactions. From this procedure, protonic niobates (H₃O)₂Nb₂O₆.H₂O and (H₃O)₂Nb₂O₆ were obtained. The sample NaNbO₃ did not undergo any transformation. Cyclic voltammetry tests carried out in a neutral aqueous solution 1 M Na₂SO₄ showed a wide potential window for both niobates (sodium and protonic). However, the protonic niobate samples (H₃O)₂Nb₂O₆.H₂O and (H₃O)₂Nb₂O₆ presented much higher current density values than the sodium niobates. This result can be related to a structural rearrangement that allowed a significant increase in the intercalation of sodium Na ⁺ ions from the electrolyte into the structure of these protonic niobates, when polarized. Therefore, in this work, it was demonstrated that it is possible to obtain protonic niobates from sodium niobates, as well as, it was verified the distinct electrochemical behavior between these materials.     

Citrate-assisted hydrothermal synthesis of vanadium dioxide textured films with metal-insulator transition and infrared thermochromic properties

The present study reports the fast synthesis of VO₂ (М₁) oriented films on the r-Al₂O₃(012) substrates by the hydrothermal method using citric acid and vanadium (V) oxide as precursors with post deposition annealing in inert atmosphere. The effects of synthesis parameters (solution concentration and autoclave filling factor) on the films composition, morphology and electric properties are considered using XRD, Raman spectroscopy, AFM and SEM. The obtaining VO₂(M₁)/r-Al₂O₃ films show a metal-insulator transition with resistivity change of ~3.5 orders of magnitude and excellent thermochromic properties in the long-wavelength IR region. This work demonstrates a promising technique to promote the commercial implementation of VO₂ as material for design of infrared (IR) switch devices.