Increase Of Hydrothermal Time Research Articles

Ultrafine V-ZrSiO4 pigment prepared by a bottom-up approach: Particle size evolution and chromatic properties

To solve the contradiction between particle size and color performance, an ultrafine V-ZrSiO4 pigment was successfully synthesized by sol–gel-microemulsion-hydrothermal (S-G-M-H) method in this paper. Meanwhile, the effects of hydrothermal time on the chromatic parameter, particle size distribution, phase composition, valence bond species and microstructure of the precursor and pigment were systematically investigated. Moreover, the color deterioration mechanism of V-ZrSiO4 nano-grain pigment was also revealed. The results demonstrate that the median diameter (D50) of the obtained V-ZrSiO4 pigment is only 0.972 μm. Besides, the synthesized pigment has vivid blue hue and superior tinting strength. As the increase of hydrothermal time, the particle size of V-ZrSiO4 pigment decreases, while the color performance of the pigment deteriorates. The color deterioration mechanism is attributed to the dual effects of the reduction of vanadium content in the outer layers of pigment particles and the enhancement of visible light reflection intensity.

Hydrothermal Synthesis and Properties of SnO2 Nanopowder

The tin oxide nanopowder is synthesized by hydrothermal method and the hydrothermal time effect on its phase structure, morphology and optical properties are studied. The results show that the samples are all tetragonal rutile structure with high purity, and possess flowers-shaped morphology. The crystallites size increases as the hydrothermal time does. The sample obtained through 12 h hydrothermal time has excellent morphology, uniform size and great dispersibility. Photoluminescence spectra shows photoluminesce peak appear near 500 nm, which is related to the oxygen vacancy. With the increase of hydrothermal time, the photoluminesce peak has a blue shift and the peak intensity decreases.

Effects of mordenite zeolite catalyst synthesis conditions on dimethyl ether carbonylation

Effects of different mordenite (MOR) zeolite synthesis conditions, such as salt additive, hydrothermal time, hydrothermal temperature, and ultrasonic assistance, on dimethyl ether (DME) carbonylation were studied systematically in this work. Salt as additives being introduced into hydrothermal system obviously promoted the crystallinity and morphology of MOR. With the increase of hydrothermal time and temperature, a better crystallinity was obtained on the sample. However, a higher hydrothermal temperature of 180 °C led to a slightly decreased crystallinity. The MOR catalyst with NaCl as the additive and hydrothermal treatment at 130 °C for 48 h realized a better DME carbonylation activity with 50% DME conversion and almost 100% methyl acetate (MA) selectivity. In addition, H-MOR-UT, a MOR zeolite prepared with the assistance of ultrasonic treatment, showed a special morphology consisting of lots of MOR nanosheets with a width of around 70 nm. Here, this H-MOR-UT realized an enhanced catalytic stability and the highest DME conversion of 70%, about 5 times higher than the reference MOR zeolite prepared by traditional method. The strikingly excellent catalytic performance was attributed to its more acid content, stronger acid strength and smaller grain size.

Effects of Particle Size on the Structure and Photocatalytic Performance by Alkali-Treated TiO2.

Particle size of nanomaterials has significant impact on their photocatalyst properties. In this paper, TiO2 nanoparticles with different crystalline sizes were prepared by adjusting the alkali-hydrothermal time (0–48 h). An annealing in N2 atmosphere after hydrothermal treatment caused TiO2 reduction and created defects, resulting in the visible light photocatalytic activity. The evolution of physicochemical properties along with the increase of hydrothermal time at a low alkali concentration has been revealed. Compared with other TiO2 samples, TiO2-24 showed higher photocatalytic activity toward degrading Rhodamine B and Sulfadiazine under visible light. The radical trapping and ESR experiments revealed that O2•- is the main reactive specie in TiO2-24. Large specific surface areas and rapid transfer of photogenerated electrons are responsible for enhancing photocatalytic activity. The above findings clearly demonstrate that particle size and surface oxygen defects can be regulated by alkali-hydrothermal method. This research will deepen the understanding of particle size on the nanomaterials performance and provide new ideas for designing efficient photocatalysts.

Crystallization and phase transition of tobermorite synthesized by hydrothermal reaction from dicalcium silicate

AbstractIn this paper, tobermorite was hydrothermally synthesized from the dicalcium silicate (C2S) in sodium silicate solution, and the crystallization and phase transition process were investigated in detail using XRD, Raman spectra, and SEM. The tobermorite is difficult to synthesize when the temperature is lower than 160°C because it gets converted into xonotlite (without Na2O) or pectolite (with Na2O) when the temperature is higher than 180°C. The crystallization process of tobermorite shows “S” trend with the increase in time, which can be divided into three stages: the nucleation stage, rapid crystal growth stage, and perfect crystal forming stage. During the crystallization, 90% of the crystallization of tobermorite is completed in the stage of rapid crystal growth. Raman spectra and SEM analysis show that with the increase in hydrothermal time, the C2S of monomer (Q0) is first converted into the calcium silicate hydrate of sheet (Q2 and Q3), and then continues to convert into tobermorite of chain (Q2).

Adsorption and photodegradation behaviors of in-situ growth TiO2 films with various nano-structures

Adsorption and photodegradation performances of nanomaterials are significantly determined by their micro/nano-structures and crystal phase. Here, different nanostructures of TiO2 layer was produced on the pure titanium plates with H2O2/HCl solution and hydrothermally treatment. SEM, TEM and UV–Vis absorption spectra showed the TiO2 gel layer was dissolved and converted to anatase crystal with the increase of hydrothermal time. High specific surface area of the TiO2 layer displayed high adsorption capacity for methylene blue, however, excessive hydrothermal time led to the decline of the adsorption capacity. Moreover, high crystallinity and appropriate porosity were beneficial to catalytic efficiency.

Influence of microwave-assisted hydrothermal treatment time on the crystallinity, morphology and optical properties of ZnWO4 nanoparticles: Photocatalytic activity

In this work, zinc tungstate (ZnWO4) nanoparticles were obtained by microwave-assisted hydrothermal method at 140 °C and 2 atm. The hydrothermal treatment time was varied at 0, 5, 10, 30, 60 and 120 min. The nanoparticles were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscope (TEM), high-resolution transmission electron microscope (HRTEM), X-ray fluorescence (FRX), nitrogen adsorption by Brunauer-Emmett-Teller method (BET), UV–Visible spectroscopy (UV–Vis) and Photoluminescence (PL) properties. The adsorptive and photocatalytic properties were estimated against methylene blue (MB - cationic) and methyl orange (MO - anionic) dyes. The diffractograms show that the larger hydrothermal treatment time, anhigher the powders crystallinity. The BET and SEM analysis indicate that the increase in hydrothermal time does not interfere significantly in nanoparticles size but reduces their porosity. The change in the surface area is consistent with the adsorption tests, where the increase of the hydrothermal treatment time reduces the adsorption against the MB and MO dyes. However, increasing the hydrothermal treatment time provides an increase in photocatalytic activity.

Electrospinning preparation and dye adsorption capacity of TiO2@Carbon flexible fiber

Abstract TiO2@carbon flexible fiber was prepared by combining electrostatic spinning technology and hydrothermal synthesis method. The XRD, SEM, TEM and Zeta potential techniques were used to characterize the phase, microstructure and surface charge properties of the samples. The growth mechanism of TiO2 nanoarray on carbon flexible fiber with different morphologies was studied, and the dye adsorption capacity of the samples was evaluated by methylene blue (MB) degradation effect. The results showed that proper doping amounts of TiO2 particles improved the flexibility and the hydrophilic property of carbon fiber significantly, which was conducive to the deposition and growth of TiO2 on the carbon fiber. With the increase of hydrothermal time, the TiO2 nanoarray grew denser gradually along the [110] crystal surface. The negative charge on the surface of carbon fiber increased, which was benefited to the removal of MB. The dye adsorption capacity of TiO2@carbon fiber was resulted from the synergistic effect of physical adsorption (carbon fiber) and photocatalysis (TiO2) process.

The Influence of Electrode Microstructure on the Performance of Free-Standing Cathode for Aprotic Lithium-Oxygen Battery

Free-standing NiCo2O4@Ni cathodes for aprotic lithium-oxygen batteries were synthesized through a simple hydrothermal process followed by heat treatment in the air. The morphology of the NiCo2O4 deposit changed from nanosheet to nanowire with the increase of hydrothermal time. Further observation revealed that the nanosheet/nanowire NiCo2O4 were assembled by nanoparticles with a size of 10–20 nm. The directional assembly of the nanoparticles were not affected by the reaction time. The influence of catalyst microstructure on the electrochemical performance of Li-O2 batteries was studied. The results of battery tests in pure oxygen indicate that the cathode material with a high specific surface area, large pore volume and broad pore size distribution can facilitate the discharge reaction, leading to an improved cell performance. As a result, the cathode based on the NiCo2O4 nanowire array delivered a specific discharge capacity of 1682 mAh g−1 at 30 mA g−1 and a stable cyclability of 50 cycles with a capacity limitation of 500 mAh g−1.

Immobilization of flower-like ZnO on activated carbon fibre as recycled photocatalysts

ZnO was grown on the surface of activated carbon fibre (ACF) by a hydrothermal method to form a recyclable photocatalyst. With an increase in hydrothermal time from 1.5 to 3 h, ZnO particles deposited on the surface of ACF changed from sparse, random rod-like structures to dense, flower-like structures, which comprise many hexagonal ZnO nanorods. The results show that ZnO/ACF-3 has improved photocatalytic properties compared to ZnO/ACF-1.5 and ZnO, and the cause of this enhanced photocatalytic activity was also discussed. The cycling experiments demonstrated that ZnO/ACF-3 can be recycled without a remarkable decrease in photocatalytic activity.

Preparation of Electrode of Copper-Nickel Composite Material and Its Capacitance Performance

Nickel oxide/copper oxide composites are prepared. Then the composites were transferred into autoclave and thermal sinter under different temperature and different time. As-prepared composites were analyzed by XRD, and it was concluded that with the increase of hydrothermal time, content of NiO and Ni0.75Cu0.25O increases, but particles become smaller; it would improve the electrochemical activity. By SEM images directed lower crystallinity of composites, deeper porosity and rougher surface would have better electrochemical activity. The electrochemical performance was investigated by cyclic voltametry, AC impedance and galvanostatic charge-discharge. All results show that under the condition of 150°C 30 h, the electrochemical performance is the best. The specific capacitance was 225.67 F&middotg-1 at the charge-discharge current of 1 A&middotg-1.

Synthesis, Characterization of α-GaOOH Self-Assembly and Its Application in Removal of Perfluorinated Compounds.

This article discusses the hydrothermal synthesis of well-dispersed faceted α-GaOOH in the presence of sodium acetate by the self-assembly method. The synthesized α-GaOOH possesses a mixture of hexagonal and rectangular plates, cubic and diamond-like morphologies. The presence of ethanol as a co-solvent with water (1:1) facilitates scroll-like cylindrical morphology. The influences of sodium acetate concentration, hydrothermal temperatures, time and solvent on the formation of the above-mentioned morphologies were investigated. The synthesized α-GaOOH was characterized using X-Ray Diffraction (XRD), Field Emission Scanning Electron Microscopy (FE-SEM) and High-Resolution Transmission Electron Microscopy (HR-TEM), thermal analysis and nitrogen adsorption analysis. The XRD pattern confirmed the formation of orthorhombic α-GaOOH. The increase of the sodium acetate concentration from 0.031 mol/L to 0.250 mol/L facilitates the formation of more cubic and diamond-shaped particles than plate-like particles. The formation of faceted α-GaOOH is slow at 150 degrees C, and a further increase in hydrothermal temperature from 175 degrees C to 225 degrees C had no appreciable effect. Similarly, an increase in hydrothermal time from 5 h to 20 h at 200 degrees C facilitates hexagonal to cubic shaped plates. The solution pH strongly influenced the aspect ratio of the nanoplates. Hydrothermal temperature and time had no appreciable effect from 175 degrees C to 225 degrees C. The removal perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS) using the synthesized α-GaOOH was studied. A plausible mechanism for the formation of nanoplates is proposed.

Hydrothermal synthesis of TiO2 nanostructure films and their photoelectrochemical properties

In this study, anatase TiO2 nanostructured films were successfully prepared via Ti foil-assisted hydrothermal synthesis method without any surfactants. With the increase of hydrothermal time from 3 to 12h, the surface morphologies of the films changed from nanotubes to nanoflowers and the thickness of the films increased from 2.5 to 4.2μm. The nanoflowers were seated on a layer of oriented nanotubes and consisted of nanosheets. Both nanotubes and nanosheets were multi-walled, comprising interconnected [TiO6] octahedra. Ti foil and acid-treated Ti foil both formed pieces of thin films on the surface with nanotubes and nanoflowers, respectively. Photoelectrochemistry tests showed that the photocurrent response of the nanotube film was nearly 13.8μA/cm2, which was approximately three times higher than that of nanoflowers film. This indicates that the nanotubes more successfully transferred electrons to the surface of the film as a result of nanotubes providing direct pathways for electrons from the point of injection to the Ti foil electrode. The ultraviolet (UV)–visible–near infrared (NIR) absorption spectra indicated that the nanotube film had a narrower band gap as compared to the nanoflower film. In other words, a relatively low hydrothermal treatment temperature or relatively short hydrothermal treatment time is better for preparing excellent photocurrent response films.

Nanostructured copper and copper oxide thin films fabricated by hydrothermal treatment of copper hydroxide nitrate

Metallic copper and copper oxide thin films were fabricated on surface of glass slide substrates. Copper oxide thin films were prepared by a hydrothermal method using an α-phase layered hydroxide, copper hydroxide nitrate as a precursor. Morphology, thickness and crystallite size of the obtained copper oxide thin films changed by changing the time of hydrothermal treatment. Accordingly, the copper oxide thin films showed various water contact angles and optical band gaps. As, the optical band gap of the nanostructured copper oxide thin films increased with an increase in hydrothermal time from 1.85 to 2.95 eV. Moreover, the water contact angles changed from 16.4 to 38.8° by changing the hydrothermal time. By a reductive hydrothermal-treatment route, the copper oxide thin film was reduced to metallic copper thin film without any particle growth.

Preparation, characterization and photocatalytic performance of g-C3N4/Bi2WO6 composites for methyl orange degradation

The g-C3N4/Bi2WO6 composites have been synthesized and used as photocatalysts for degradation of methyl orange (MO) dye. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), infrared spectroscopy (IR), UV–visible diffuse reflection spectroscopy (DRS), and N2 physisorption isotherms were used to characterize the physicochemical properties of the materials. With the increase of hydrothermal time, the morphology of Bi2WO6 evolved from nanoparticles to microplates, flower-like and helix/tyre-like superstructures; in the meanwhile the g-C3N4 component was gradually dissolved. Such obtained g-C3N4/Bi2WO6 composites showed optical band gap in the range of 2.67–2.75eV. Photocatalytic results showed that g-C3N4/Bi2WO6 composites are more active than either pure Bi2WO6 or g-C3N4, and the weight ratio of g-C3N4 to Bi2WO6 and the hydrothermal time significantly affected the degradation efficiency of the materials. The optimum weight ratio of g-C3N4 to Bi2WO6 was 0.5:1, and that for hydrothermal time was 6h at 160°C.

Electrodeposition Combination with Hydrothermal Preparation of ZnO Films and Their Application in Dye-Sensitized Solar Cell

A suitable method is necessary for the high performance of dyes-sensitized solar cells (DSSCs). In this paper, photoanodes of DSSCs have been fabricated through electrodeposition and combination with hydrothermal method. The results of mix method showed better performance than the single one. After the second step electrodeposition, the ZnO films formed flack finally. With the increase of hydrothermal time, ZnO films become thicker and bigger, which can offer large surface area to absorb much more dyes. The short-circuit current (2.4 mA/cm2) and open-circuit voltage (0.67 V) were greater than the single one, alternating current impedance indicating that electrodeposition and hydrothermal mix are a more suitable method for high performance DSSCs. We expected to obtain higher conversion efficiency of DSSCs by this method.

Synthesis of Cobalt Sulfide Nanocrystallites via an Efficient Microwave Hydrothermal Process

Nanostructured cobalt sulfide(CoS) can be widely used as high energy density batteries, supercapacitors, solar photovoltaic materials and catalysts due to its excellent electronical, optical, magnetic and catalytic performance. In order to synthesize CoS crystallites in a efficient route, a facile microwave hydrothermal process was developed by using cobalt nitrate hexahydrate and thioacetamide(TAA) as source materials. The phase compositions and morphologies of the crystallites were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The influences of microwave hydrothermal temperature and time on the phase, grain size and morphology of the CoS nanocrystallites were particularly investigated. Results show that CoS crystallites can be obtained at the hydrothermal temperature of 180 °C. The as-synthesized CoS nanocrystallites are hexagonal phase that with the grain size of 10~30 nm. With the increase of hydrothermal time, the increase in particle size and the (102)-oriented growth are obviously.

Phase formation and composition of Mn–Zn ferrite powders prepared by hydrothermal method

Mn–Zn ferrite powders were prepared by hydrothermally aging the coprecipitates of compositional metal ions using ammonium hydroxide as a precipitant. R value (alkalinity) = (moles of added OH−)/[(moles of added Zn2+) × 2 + (moles of added Mn2+) × 2 + (moles of added Fe3+) × 3] was introduced to adjust the amount of added ammonia. The results show that the R value of starting suspension and hydrothermal time have similar and dominant effects on the composition, spinel ratio, and crystallite size of synthesized powders. From the analyses of x-ray diffraction (XRD) and inductively-coupled plasma (ICP), it notes that no α–Fe2O3 peak in the XRD patterns of powders synthesized at R = 2–3, 150 °C × 2 h, may be due to lower degree of crystallinity and less amount of α–Fe2O3 existing in these powders. Both the increase of hydrothermal time and of R value can promote the crystallinity of powders and also cause a significant loss of zinc, hinting that in the hydrothermal process, the loss of zinc may play a crucial role in the crystallinity of hydrothermally synthesized powders.