Fast Hydrothermal Method Research Articles

Study of the structural and magnetic properties of Pd-substituted CoFe2O4 materials obtained by a fast method

An efficient fast hydrothermal method was used to synthesize Co1-xPdxFe2O4 (x = 0, 0.05, 0.1 and 0.5) nanocrystalline powders, where Co2+ was substituted with Pd2+ ions. The materials crystallize within the spinel structure (Fd-3m) with crystallites sizes varying between 5.6 and 17.6 nm. The particles present a cubic shape for x = 0 and x = 0.1 samples and the presence of Pd in samples was confirmed by Energy-dispersive X-Ray spectroscopy (EDX) analysis. The magnetic hysteresis loops indicate that the saturation magnetization decreases with the increase once with of the Pd2+ amount substitution (from ~52 emu/g for x = 0–~7 emu/g for x = 0.5).

Catalytic use of TiO2 nanowires in the photodegradation of Benzophenone-4 as an active ingredient in sunscreens

Water contamination has compromised the quality of this resource during the last years with the presence of persistent organic pollutants. Because of the resistance of these compounds to degradation, several advance oxidation techniques have been proposed. In this study, we report the employment of an advance oxidation technique in the degradation of benzophenone-4 (BP-4), using TiO2 as catalyst, which was obtained following a fast-hydrothermal method. TiO2 nanowires (TiO2NWs) were fully characterized considering the morphology, elemental composition, oxidation states, vibrational modes and crystalline structure with SEM and TEM, EDS, XPS, FTIR and XRD, respectively. The photocatalytic degradation was carried out using a home-made photoreactor under slightly acidic conditions achieving an average of 90% removal. It was determined that the photocatalysis is the most probable route of degradation since the photolysis or catalysis procedures produce negligible contributions. An apparent kinetic constant of 1.29 × 10−2 min−1 was determined, according to a pseudo-first order reaction.

An accurate and rapid method to compare thermal insulation capacity of nine Gd-Yb-YSZ coatings

The conventional method to evaluate thermal insulation capacity (TIC) of thermal barrier coatings involves the measurement of three parameters, which incurred a large accumulative error. To solve this problem, a self-designed new experimental apparatus was used in this work to compare the TIC of nine ceramic coatings composed of nine ceramic powders with different contents of Gd, Yb, Y and Zr, respectively, synthesized by a new fast hydrothermal method. It was found that the insulation temperature (ΔT) of Yttria-stabilized Zirconia (YSZ) coating mainly depended on the material property and thus reflected the TIC of coating by using this new apparatus. The ΔT value was the temperature difference between a blank sample without coating and a coating sample. The measured ΔT values were found to be highly reproducible. Thus, comparing TIC of the nine Gd-Yb-YSZ coatings by measuring ΔT was more accurate and rapid than the conventional method. The measured ΔT values of nine Gd2O3 and Yb2O3 added YSZ (Gd-Yb-YSZ) coatings were about 10–20 °C higher than that of YSZ coating at 1050 °C. This indicated that the addition of Gd and Yb enhanced TIC of YSZ coating.

Tailoring Upconversion and Morphology of Yb/Eu Doped Y₂O₃ Nanostructures by Acid Composition Mediation.

The present study reports the production of upconverter nanostructures composed by a yttrium oxide host matrix co-doped with ytterbium and europium, i.e., Y2O3:Yb3+/Eu3+. These nanostructures were formed through the dissociation of yttrium, ytterbium and europium oxides using acetic, hydrochloric and nitric acids, followed by a fast hydrothermal method assisted by microwave irradiation and subsequent calcination process. Structural characterization has been carried out by X-ray diffraction (XRD), scanning transmission electron microscopy (STEM) and scanning electron microscopy (SEM) both coupled with energy dispersive X-ray spectroscopy (EDS). The acid used for dissociation of the primary oxides played a crucial role on the morphology of the nanostructures. The acetic-based nanostructures resulted in nanosheets in the micrometer range, with thickness of around 50 nm, while hydrochloric and nitric resulted in sphere-shaped nanostructures. The produced nanostructures revealed a homogeneous distribution of the doping elements. The thermal behaviour of the materials has been investigated with in situ X-Ray diffraction and differential scanning calorimetry (DSC) experiments. Moreover, the optical band gaps of all materials were determined from diffuse reflectance spectroscopy, and their photoluminescence behaviour has been accessed showing significant differences depending on the acid used, which can directly influence their upconversion performance.

A facile and green method for synthesis of ZnFe2O4@CMC as a new magnetic nanophotocatalyst for ciprofloxacin removal from aqueous media

This study aimed to synthesize a ZnFe2O4@carboxymethyl cellulose (CMC) nanophotocatalyst using a simple, facile, and green hydrothermal method for ciprofloxacin (CIP) removal from aqueous solutions. At first, ZnFe2O4@CMC was synthesized using the hydrothermal method, and then it was characterized. To assay the photocatalytic activity of ZnFe2O4@CMC, its ability was investigated in CIP and total organic carbon (TOC) removal by considering the effect of some variables such as initial CIP concentrations (5–30 mg/L), pH (3–11), nanophotocatalyst loading (0.1–0.5 g), and reaction time (20–120 min). The kinetic performance of the process was assessed by the pseudo-first order and Langmuir-Hinshelwood models. The concentration of CIP and TOC in the samples was determined using high performance liquid chromatography and a TOC analyzer, respectively. The influence of competitive compounds was examined on the efficiency of the nanophotocatalyst through its application for a real wastewater sample. Moreover, the reusability and chemical stability of ZnFe2O4@CMC were studied.Advantages of this technique are as follows:•ZnFe2O4@CMC as a high potent magnetically separable photocatalyst is designed by a green, simple, and fast hydrothermal method.•ZnFe2O4@CMC displays significant photocatalytic activity in photocatalytic degradation processes for ciprofloxacin removal.•ZnFe2O4@CMC exhibits good chemical stability and reusability.

Facile and rapid synthesis of highly crystalline mesoporous zeolite FAU

In this work, highly crystalline mesoporous zeolite FAU was synthesized via a fast hydrothermal method. Conventional microporous zeolite 13X and polyethylene glycol (PEG 400) were used as seed and polymeric solubilizer agents, respectively. The results of several characterization techniques such as nitrogen adsorption–desorption analysis, X-ray diffraction (XRD), scanning electron microscopy-energy dispersive X-ray (SEM/EDX) and Fourier transform infrared (FT-IR) spectroscopy demonstrated that obtaining well-developed zeolite crystals with mesopore size distribution of 2–10 nm could only be possible in the presence of both seeds and PEG. Seeding played a promoting role in zeolite FAU nucleation while PEG helped synthetic gel to crystallize well.

Synthesis and property of spinel porous ZnMn2O4 microspheres

Mesoporous ternary zinc manganese oxides on the Ti sheet substrate are prepared by easy and fast hydrothermal method for the first time. The obtained ZnMn2O4 materials with homogenously distributed pores have been characterized by XRD, SEM and Raman spectra, which show the good crystal phase and particles for improving supercapacitive performance. XRD and SEM images show that the as-prepared samples have good crystallinity, and ZnMn2O4 microsphere has an average diameter of 10μm. In addition, ZnMn2O4 are also characterized in 2M KOH solution using three-electrode system. In the work, we study that different substrates (Ti, carbon and nickel foam) have an important effect on the electrochemical performance of the samples. The research of cyclic voltammogram (CV) indicates that the obtained specific capacitance (155Fg−1) values on nickel foam substrate for the ZnMn2O4 microspheres are higher than the values reported for some inexpensive oxides. However, the specific capacitance of all ZnMn2O4 samples has almost no change at two different scan rates which shows good long-term cycling stability. The electrochemical impedance spectroscopy with a small resistance reveals that the as-synthesized samples have good frequency response characteristics. These results indicate that the unique ZnMn2O4 electrode would be a promising electrode for high-performance supercapacitor applications.

Low-Temperature Cathodoluminescence Investigations of High-Quality Zinc Oxide Nanorods.

We present results of cathodoluminescence (CL) investigations of high-quality zinc oxide (ZnO) nanorods obtained by an extremely fast hydrothermal method on a silicon substrate. A scanning electron microscopy (SEM) system equipped with CL allows direct comparison of SEM images and CL maps, taken from exactly the same areas of samples. Investigations are performed at a temperature of 5 K. An interlink between sample microstructure and emission properties is investigated. CL confirms a very high quality of ZnO nanorods produced by our method. In addition, the presence of super radiation effects in ZnO nanorod arrays is suggested.

Facile synthesis of α-MoO3 nanorods with high sensitivity to CO and intrinsic sensing performance

Orthorhombic molybdenum trioxide (α-MoO3) nanorods with well-defined morphology and high crystalline have been synthesized by a facile and fast hydrothermal method under 85°C for 1.5h without employing surfactants or templates. The controlling of stirring time, thermostatic time and HNO3 amount is crucial for the growth of α-MoO3 nanorods. The morphology and structure of α-MoO3 were characterized by field emission scanning electron microscopy (FESEM) and X-ray diffraction (XRD). The obtained α-MoO3 nanorods as a novel sensing material exhibit high sensitivity, the highest response to 40ppm CO is 239.6 at operating temperature of 292°C. The intrinsic sensing performance arises from the non-stoichiometry of the α-MoO3 due to the presence of Mo5+ in MoO3 lattice, that is, the molecular formula of MoO3 should be expressed as MoO3−x (x=0.08), which has been confirmed by X-ray photoelectron spectroscopic (XPS) analysis and room temperature photoluminescence (PL). The sensing mechanism of α-MoO3 to CO was also discussed in terms of lattice oxygen in MoO3.

Cobalt ferrite substituted with Mn: Synthesis method, characterization and magnetic properties

Mn substituted cobalt ferrite nanoparticles were successfully synthesized by a fast-hydrothermal method. The influences of substituent concentration and hydrothermal treatment conditions on the formation of crystalline phases, particle size, morphology and magnetic properties of the synthesized materials were investigated by XRD, SAED, TEM, HRTEM, EDX and magnetic measurements. The average crystallite size of the Co1−xMnxFe2O4 (where x=0; 0.05; 0.1; and 0.5) was between 12 and 18nm. The magnetic properties of the obtained materials are influenced by the substituent concentration; thus increasing the amount of substituent (Mn2+) leads to an increase of saturation magnetization (Ms), and to a decrease of the coercive field (Hc).

Micro Single Crystals of Hematite with Nearly 100% Exposed {104} Facets: Preferred Etching and Lithium Storage

The controlled synthesis of inorganic single crystals with a large percentage of exposed high-index facets has attracted much attention. However, high-index facets usually disappear during the early stage of crystal growth due to the minimization of surface energy and typically facet-controlling agents are employed. Here a facile fast hydrothermal method for the preparation of microsize α-Fe2O3 rhombohedra with nearly 100% exposed {104} facets was developed in a simple formulated solvent without any additives. The hydrothermal reaction time could be as short as 75 min, in contrast to typical hydrothermal reactions over days. The preferred etching edges along the diagonal axis of microsize rhombohedra by the self-generated ions was observed, which could be potentially extended to synthesize and tailor other transition metal oxides. The formation mechanism was revealed by ex situ FESEM observations of the samples prepared at different reaction times. Improved electrochemical performances in terms of cyclability, specific capacity, and high rate were achieved. The specific capacity was maintained at 550 mAh/g after 120 cycles at a rate of 200 mA/g. Experimental evidence clearly shows that the as-designed solid microsize α-Fe2O3 can effectively and reversibly store lithium ions with performance comparable to nanosize α-Fe2O3, suggesting electrode materials with particle size at the microscale will be worth further exploration.

Effect of the substitution element In in CoFe2−xInxO4 on morphology, magnetic and optical properties

Cobalt ferrite substituted with indium, CoFe2−xInxO4 (x = 0.05, 0.1 and 0.5 mol), was obtained by the original fast hydrothermal method and the effects of the substitution on morphology and magnetic and optical properties of cobalt ferrite were investigated. The obtained nanoparticle samples with different concentrations of the substitute (Fe3+ was substituted by In3+) were characterized by x-ray diffraction, bright field transmission electron microscopy, selected area electron diffraction, high-resolution transmission electron microscopy, energy dispersive x-ray, the conventional AC method, Fourier transform infrared spectroscopy and UV–Vis. The measurements confirmed the presence of indium in cobalt ferrite and showed a good degree of crystallization with diffraction peaks corresponding to the cubic spinel structure and crystallite sizes in the range of 11.8–17.6 nm. We observed that a single phase is formed when Fe3+ was substituted with In3+ at low concentrations (x = 0.05 and 0.1), and new peaks in XRD appear characteristic of the secondary phase of In2O3 for a high level of substitution (x = 0.5).

Behavior of sheet-like crystalline ammonium trivanadate hemihydrate (NH4V3O8×0.5H2O) as a novel ammonia sensing material

Abstract This work reports the use of ammonium trivanadate hemihydrate (NH 4 V 3 O 8 ×0.5H 2 O) as a novel sensing material for ammonia resistive sensors. It was prepared by a simple and fast hydrothermal method from V 2 O 5 as a precursor and characterized by SEM, FT-IR, XRD and TG techniques. The as-synthesized material showed a sheet-like morphology and was found thermally stable up to 250–280 °C. It reacted promptly and irreversibly when exposed to ammonia at room temperature. A full reversibility was instead registered undergoing the formed ammonia adduct at a temperature higher than 200 °C. A NH 4 V 3 O 8 ×0.5H 2 O-based resistive gas sensor was fabricated and its sensing properties were evaluated. Experimental results obtained have given a preliminary demonstration of the feasibility of using NH 4 V 3 O 8 ×0.5H 2 O as a novel ammonia sensing material since it yields several advantages including easy synthesis of the sensing layer, good sensitivity and reproducibility and fast response.

Development of a novel fast-hydrothermal method for synthesis of Ag-doped TiO 2 nanocrystals

Undoped and Ag-doped TiO 2 anatase nanocrystals were successfully prepared from titanium isopropoxide by a novel fast-hydrothermal method. The as-prepared TiO 2 nanocrystals were characterized by XRD, DRUV–VIS spectroscopy and SEM/EDX. The results show that the anatase TiO 2 has a particle size of around 4 nm from SEM and XRD results.

Reverse micelles template assisted fabrication of ZnO hollow nanospheres and hexagonal microtubes by a novel fast microemulsion-based hydrothermal method

ZnO hollow micro/nanostructures were fabricated by a novel fast hydrothermal method based on the microemulsion. The aqueous reverse micelles were used as templates and different amount of Zn2+ colloid was compelled to hydrolyze on its surface. Scanning electron microscopy indicates that the products grown in the solution with colloid volume concentration of 12.3 and 0.5 v.% are hollow nanospheres and hexagonal microtubes, respectively. It is believed that this difference should attribute to the initial shape of hydrolysate and the core/shell state of water/surfactant during hydrothermal treatment.