Hydrothermal Synthesis Parameters Research Articles

Preparation of ZSM-5 molecular sieve by diatomaceous earth in-situ crystallization

ABSTRACTWith diatomaceous earth as raw material and sodium aluminate as aluminum source by adopting TBAB template, ZSM-5 molecular sieve was synthesized by hydrothermal method of in-situ crystallization which shall be reacted in alkali liquor. The influence of silicon-aluminum ratio, pH value, hydro-thermal crystallization temperature, crystallization time and other factors during the synthesis process on crystallized product were systematically observed by combining XRD, SEM and BET. In addition, it was determined that optimized process parameters of hydro-thermal synthesis of molecular sieve were: the usage amount of sodium aluminate was 6% of purified diatomaceous earth; the system pH value was 13.50; crystallization temperature was 170°C and crystallization time was 48 h. Compared with raw material of diatomaceous earth, the shape of ZSM-5 molecular sieve was changed from disk into clustered crystal; the specific surface area was increased from 7.247 m2/g to 199.280 m2/g; and pore volume was increased by nearly twice. The process of composing ZSM-5 molecular sieve with cheap diatomaceous earth as silicon source has great value in application.

The Influence of Sulfates on Tobermorite Formation in Lime-Ash Composite

Autoclaved aerated concrete is an ecological building material with suitable properties and long-time tradition. The research of secondary raw materials usage and technology optimization is needed in order to increase the efficiency and sustainability of its production. It is important to focus on development of mineralogical composition while studying the influence of input materials and the parameters of hydrothermal synthesis on the properties of final product. This is especially important in case of tobermorite formation as the bearer of strength in the structure. Main focus of this paper is applicability of fly ash (silica component) and admixture of energo-gypsum (sulfate component) in production of lime-ash composite in hydrothermal conditions. The research was focused on autoclaving of samples at temperature of 170°C in three various isothermal sustains. Final samples were analyzed by XRD and SEM in order to proof the influence of input materials. Results show that 5% admixture of energo-gypsum had positive influence on tobermorite formation.

Solar Light Responsive Poly(vinyl alcohol)-Assisted Hydrothermal Synthesis of Immobilized TiO2/Ti Film with the Addition of Peroxymonosulfate for Photocatalytic Degradation of Ciprofloxacin in Aqueous Media: A Mechanistic Approach

This study is focused on the synthesis of a solar light driven novel poly(vinyl alcohol) (PVA)-assisted TiO2/Ti film via a facile one pot hydrothermal technique and then its photocatalytic applications by adding with peroxymonosulfate (PMS) for efficient degradation of ciprofloxacin (CIP). The key hydrothermal synthesis parameters like PVA-content, hydrothermal time (HT), and pH were optimized. The best photocatalytic performance of the synthesized material was observed when prepared with the conditions of PVA = 8 mg, HT = 3 h, and pH = 2.62. Results showed that 98.3% of CIP was degraded within 60 min by PVA-assisted TiO2/Ti film with 0.5 mM PMS added, compared to 89.38% and 88.86% degradation with 0.5 mM persulfate (PS) and 0.5 mM hydrogen peroxide (H2O2), respectively. The photocatalytic degradation of CIP by PVA-assisted TiO2/Ti film with PMS added was dependent on the [PMS]0 and increased with increase in [PMS]0. The kapp values at [PMS]0 of 0.2, 0.5, 0.8, and 1.0 mM were 0.029, 0.0582, 0.068, and 0.1...

Controlling Oriented Attachment and in Situ Functionalization of TiO2 Nanoparticles During Hydrothermal Synthesis with APTES

Understanding growth mechanisms and the role of surface functionalization is of key importance to control shape and morphology of nanoparticles and their properties. Here, we describe the growth mechanism and the effect of hydrothermal synthesis parameters (pH, time, and precursor/functionalization agent ratio) during in situ functionalization of anatase TiO2 nanoparticles with 3-aminopropyltriethoxysilane. Elongated crystallographically oriented TiO2 nanoparticles were formed by oriented attachment mechanism in addition to spherical nanoparticles. The growth mechanism is determined by a combination of ex situ techniques such as high-resolution transmission electron microscopy combined with in situ synchrotron X-ray diffraction and density functional theory calculations. Oriented attachment induced by the functionalization agent is shown to be the origin of the elongation of the nanoparticles, as only spherical nanoparticles were formed in the absence of surface functionalization. Finally, it was shown th...

Insights into the multistep transformation of titanate nanotubes into nanowires and nanoribbons

Abstract Different types of titanate one-dimensional nanostructured materials were synthesized and characterized using scanning and transmission electron microscopy, X-ray diffraction and Raman spectroscopy. The results presented in this work unquestionably showed dependence of morphology and structure of the titanate nanopowders on parameters of hydrothermal synthesis. It was found that nanotubes, nanowires and nanoribbons are three unavoidable kinetic products of hydrothermal reaction. Moreover, increasing temperature of reaction or hydrothermal treatment duration results in acceleration of nanotube-nanowire-nanoribbon transformation. However, the sequence of titanate morphology transformation is invariable. The detailed studies further revealed that the crystal structure of hydrothermally prepared nanotubes and nanowires are indistinguishable but the determination of the exact structure is practically impossible. Because of higher crystallinity, the structure of nanoribbons can be established. It was shown that it corresponds to the monoclinic layered trititanic acid H2Ti3O7 and is isostructural with sodium derivatives Na2_xHxTi3O7.nH20 (with x near 2).

Piezopotential‐Induced Schottky Behavior of Zn1−xSnO3 Nanowire Arrays and Piezophotocatalytic Applications

This article presents the piezotronic‐ and piezophototronic effect‐enhanced photocatalysis (piezophotocatalysis) of Zn1−xSnO3 (ZTO) nanowires fabricated through a two‐step hydrothermal reaction. The highlights of this research include (1) tailoring hydrothermal synthesis parameters to obtain well‐aligned LN‐type single‐crystalline ZTO nanowire arrays; (2) exploring the piezopotential‐driven piezotronic and piezophototronic effects of ZTO nanowires; (3) identifying Schottky barrier height variations; and (4) exploiting synergistic piezophotocatalysis for decomposing methylene blue (MB). Transmission electron microscopy, electron probe energy‐dispersive spectroscopy, and X‐ray photoelectron spectroscopy analyses reveal highly crystalline Zn‐deficient ZTO nanowires. The band gap is estimated to be approximately 3.8 eV. The ZTO nanowires exhibit piezopotential‐modulated piezotronic and piezophototronic effects. The corresponding Schottky barrier height variation is calculated using thermionic emission‐diffusion theory. The calculated photodegradation rate constant k of the sample, under pressure from ultrasonic vibration and a piece of glass, is approximately 1.5 × 10−2 min−1, approximately four times higher than that of ZTO nanowires in the absence of stress. The observed synergistic piezophotocatalysis is attributed to (1) band bending of ZTO nanowires; (2) application of alternating ultrasonic vibration; (3) MB mass transfer enhancement; and (4) abundant active reaction sites generated from ZTO nanowire surface sweeping.

Optimal hydrothermal synthesis of hierarchical porous ZnMn2O4 microspheres with more porous core for improved lithium storage performance

ZnMn2O4 spinel is a promising anode material for lithium-ion batteries (LIBs) which can utilize both conversion reaction and alloying reaction to provide its lithium storage capacity. In this study, we developed hierarchical porous ZnMn2O4 microspheres with more porous interior as high-performance anode for LIBs by adjusting the parameters of hydrothermal synthesis (e.g., temperature and time). With increasing hydrothermal temperature, the morphology of the microspheres progressively changed from a hollow interior to a porous interior, while the thickness of the more dense shell was reduced. The crystallinity of the spinel phase increased with hydrothermal temperature and time. The resultant morphologies of the samples indicate the dominant formation of hollow microspheres at 140 and 160°C and porous microspheres with more dense shell at 180°C. N2 adsorption-desorption isotherms reveal the dominant presence of mesopores and increased porosity with increasing temperature and time durations. Tested in a coin-type half-cell with Li counter electrode, a sample with optimized hydrothermal condition at 180°C for 9hours provides the optimal anode performance, retained 726mAhg−1 capacity after 90 cycles at 500mAg−1 current discharge rate.

TiO2beads as photocatalyst and photoelectrode for dye-sensitized solar cells synthesized by a microwave-assisted hydrothermal method

In this study, a two-step process involving a sol–gel and microwave-assisted hydrothermal (MH) techniques has been used to synthesize a novel TiO2 structure, namely, TiO2 mesoporous beads. Various hydrothermal synthesis parameters were investigated to study their effects on the resulting beads. It was found that within the processing conditions used, the TiO2 beads have similar sizes (~325 nm) and contain uniform-sized anatase TiO2 nanoparticles (<10 nm), which are single crystals. Crystalline TiO2 beads are obtained in as short as 15 min at a low temperature of only 140 °C without any post-process calcination. Less surface oxygen vacancies was obtained at a higher MH temperature. Compare to the commercial P-25 TiO2 powders and conventional hydrothermal synthesized TiO2 beads, MH synthesized TiO2 beads exhibit much higher values of specific surface areas, pore volumes, and porosities. The use of TiO2 beads as photocatalyst and photoelectrode for dye-sensitized solar cells has also been investigated. Copyright © 2015 John Wiley & Sons, Ltd.

Synthesis and Characterization of Zeolite NaY Using Kaolin With Different Synthesis Methods

AbstractThe benefits of using kaolin as a source of aluminosilicate in zeolite synthesis to obtain lowercost catalysts, adsorbents, or ion exchangers are widely known. Previous attempts to produce zeolite from natural Iranian kaolin resulted in the formation of zeolites A, X, and HS. Zeolite Y plays an important role in the petrochemical industry due to its application in the area of fluidized catalytic cracking; ~40% of gasoline production is obtained using this process.In the present study, different methods were used to prepare pure zeolite NaY from the Iranian kaolin available. The effects of different parameters such as aging time, crystallization time, kaolin calcination and crystallization temperature, and starting-material composition were investigated in order to obtain improved properties and maximize phase purity. In all cases, the crystal structure and microstructure were studied using X-ray diffraction and scanning electron microscopy. Among different synthesis approaches, the ‘guide-agent method’ resulted in the formation of zeolite NaY. The synthesis was generally sensitive to changes in kaolin calcination temperature and in hydrothermal synthesis parameters. The optimum parameters to prepare pure zeolite NaY were: kaolin calcination temperature = 680°C, aging time of guide agent = 48 h without an overall gel aging step, and crystallization at 90°C for 36 h.

Zeolite micromembrane fabrication on magnetoelastic material using electron beam lithography

In the present study, electron beam lithography (EBL) is employed in the manufacturing of patterns of continuous Linde Type A (LTA) zeolite membranes. The patterns are down to the micrometer scale and they are composed of LTA micromembranes having all three dimensions in the micrometer scale. The control of the size and location of zeolite films or membranes onto specific substrates, will lead to new aspects for their use in microsensing, microelectronics and microreactor applications. Our focus is on the microsensing field, where a magnetoelastic ribbon (Metglas) is used as the sensing platform, since the Metglas/zeolite film composite has been successfully used for the detection of gases and VOCs in the past. Here we report on the first LTA zeolite micromembrane attached onto a previously EBL patterned PMMA coated Metglas substrate. The sensing ability of such a sensor could be significantly improved by using lower amount of zeolite film since it could lead to shorter response and recovery times. The conditions for the manufacturing of the LTA micromembranes onto the Metglas substrate are investigated and discussed in terms of EBL, seeding and hydrothermal synthesis parameters.

Investigations on hydrothermal synthesis parameters in preparation of nanoparticles of LTA zeolite with the aid of TMAOH

Abstract In this work, nanocrystals of LTA zeolite with crystallite sizes ranging from 30 to 70 nm were synthesized successfully. Tetramethylammonium hydroxide (TMAOH) was used as template. The effects of organic and inorganic cations as well as crystallization conditions including aging time, synthesis time, and synthesis temperature on size of the zeolites were studied. The crystallite size was adjusted by varying the compositions of synthesis gel and also crystallization conditions. The final products were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The obtained results showed that zeolite size decreases significantly and zeolite size distribution becomes narrow by increasing aging time, and organic cation content. Moreover, the zeolite crystallite size increases significantly by increasing inorganic cation content. It was found that reaction time has a great effect on crystallinity of the synthesized zeolites. It was indicated that nucleation is completed after 3 days and no further nucleation occurs after.

Controllable growth of flowerlike ZnO nanostructures by combining laser direct writing and hydrothermal synthesis

A method combing laser direct writing (LDW) and hydrothermal growth was developed for the synthesis of flowerlike three-dimensional (3D) ZnO nanostructures. By controlling the parameters of hydrothermal synthesis (reaction time and reaction temperature) and laser irradiation (pulse energy, irradiated time, and focus conditions), different sizes of flowerlike ZnO nanostructures are synthesized. Our results indicate that annealing the samples could reduce nonradiative related defects and greatly increase luminescence efficiency. The formation mechanisms of flowerlike ZnO nanostructures are also discussed. Such a mild synthesis route can be extended to fabricate complex 3D architectures of other materials.

Hydrothermal synthesis of xonotlite from carbide slag

Carbide slag was used as the calcareous materials for the first time to prepare xonotlite via dynamic hydrothermal synthesis. The effects of influential factors including different calcination temperatures, pretreatment methods of the carbide slag and process parameters of hydrothermal synthesis on the microstructure and morphology of xonotlite were explored using XRD and SEM techniques. The results indicate that the carbide slag after proper calcination could be used to prepare pure xonotlite; and different calcination temperatures have little effect on the crystallinity of synthesized xonotlite, but have great impact on the morphology of secondary particles. The different pretreatment methods of the carbide slag pose great impact on the crystallinity and morphology of secondary particles of xonotlite. Xonotlite was also synthesized from pure CaO under the same experimental conditions as that prepared from calcined carbide slag for comparison. Little amount of impurities in carbide slag has no effect on the mechanism of hydrothermal synthesizing xonotlite from carbide slag.

Hydrothermal synthesis and photocatalytic activity of highly dispersed ZnO powders

Considerable attention of researchers in Russia and abroad has been given recently to the design and study of materials based on zinc oxide. This high interest is due to the unique electrophysical properties of these materials. Zinc oxide can be used as a component of gas sensors, transparent conductors, luminescent materials, solar cells, UV lasers, piezoelectric devices, and others [1]. Special attention is given to studies of the photocatalytic activity of ZnO. Photocatalytic purification of sewage has several advantages over presently used ozonation, chlorination, electrochemical oxidation, and decomposition by hydrogen peroxide and potassium permanganate [2‐4]. A possibility to prepare ZnO samples with photocatalytic activity comparable with that of commercial TiO 2 samples has been shown [5 − 8]. Thus, zinc oxide is considered as a cheaper alternative to TiO 2 . Highly dispersed zinc oxide is presently prepared by different methods: ceramic technology, sol‐gel process, pyrolysis of aerosols, and others [9]. Here we used the hydrothermal method to synthesize zinc oxide. This method makes it possible to vary the micromorphology of the synthesized materials through changing the synthesis parameters. Other advantages of the method are its ecological safety, economy, and relative simplicity [10]. The purpose of this work is to study the micromorphology and photocatalytic activity of ZnO as dependent on the hydrothermal synthesis parameters.

The influence of γ-Al2O3 and Na2O on the formation of gyrolite in the stirring suspension

Influence of γ-Al2O3, Na2O and hydrothermal synthesis parameters on the gyrolite formation process was established at 200 °C. The molar ratios of primary mixtures were CaO/(SiO2 + Al2O3) = 0.66 and Al2O3/(SiO2 + Al2O3) = 0 or 0.025. The amount of NaOH, corresponding to 5% of Na2O from the mass of dry materials, added in the form of solution. It was determined that in the stirred suspensions under favourable synthesis conditions (active SiO2 component, dispersive starting materials) gyrolite already forms after 16 h of isothermal curing at 200°C. The stirring affects the sequence of intermediate compounds: gyrolite crystallizes together with Z-phase. γ-Al2O3, as the additive in gyrolite synthesis is not usable, because it stimulates other calcium silicate hydrates formation. Na2O additive positively affects gyrolite synthesis because the duration of gyrolite synthesis shortens almost 2–3 times (6 h, 200°C) to compare with pure mixtures. However, gyrolite is not stable in the mixture with Na2O and begins to turn into pectolite already after 16 h of isothermal curing. Moreover, the presence of (Na2O + γ-Al2O3) additive stabilizes gyrolite and prevents its transformation to pectolite. Obtained results were confirmed by XRD, DSC and SEM/EDS analysis methods.

Rapid synthesis of silicalite-1 seeds by microwave assisted hydrothermal treatment

The objective of this work was to evaluate the use of microwave (MW) heating for the rapid synthesis of small and homogeneous silicalite-1 seeds. The influence of the chemical composition of the starting sol, the sol stirring time at room temperature and the hydrothermal synthesis conditions on the characteristics of the derived seeds have been studied. The silicalite-1 seeds were characterized by their size, shape, homogeneity, aggregation and yield. The TPAOH template concentration was an important parameter for the reaction yield, as well as particle size and aggregation. Starting from an optimized formulation (SiO 2:0.4TPAOH:19.5H 2O:4C 2H 5OH), we first demonstrated that MW heating drastically shortens the synthesis duration time because long sol ageing ( maturation–nucleation) times are not required in this case. On the other hand the hydrothermal synthesis parameters (MW power, temperature, duration, number of synthesis steps) have been optimized in order to control the morphological characteristics and yield of the silicalite-1 crystals. Although an original fibrous morphology was obtained for very short MW assisted hydrothermal synthesis times (10–30 min), very small individual seed (size of ≈50–60 nm) were obtained after only 110–150 min, starting from sols aged for either 1 or 264 h.

Synthesis and sintering behaviour of hydrothermally synthesised YTZP nanopowders for ion-conduction applications

The influence of hydrothermal synthesis parameters (pH, temperature, initial Zr concentration) on the chemical composition, crystalline structure, crystallite sizes and grain sizes of 4 mol% YTZP powders was investigated. Tetragonal, cubic, and monoclinic phases were formed as a function of the synthesis conditions. Tetragonal zirconia was formed as major phase at lower pH, in correlation with the synthesis parameters and precipitate chemical composition. Hydrothermal temperature increases the crystallization degree and crystallite sizes while decreasing particle sizes, particle sizes also decreasing with decreasing pH. The analysis of sintering curves revealed that a densification process takes place in the temperature range 800–1300 °C with a well-defined maximum around 1100 °C, leading to the formation of ceramic materials with fine equal grains. The dense sintered pellets obtained were used to study the oxygen transport properties in zirconia nanomaterials.