Hydrothermal Reaction Temperature Research Articles

Preparation of CdS nanorods on silicon nanopillars surface by hydrothermal method

Cadmium sulfide (CdS) nanorods are fabricated on Silicon (Si) nanopillars surface via hydrothermal reaction method for the first time. To optimize the growth condition, the thickness of CdS seed film, temperature and time of hydrothermal reaction are researched in this work. It is found that 30–60 nm seed layer at the 180 °C for 5 h is the optimal condition for CdS nanorods growth on Si nanopillars surface. The energy dispersive spectroscopy results show that Cd and S elements with a ratio of 1:1.02 is in agreement with the stoichiometric composition of CdS. The X-ray diffraction curves indicate that the CdS nanorods are well crystallized on Si nanopillars substrate. The CdS nanorods can reduce the reflection and increase the absorption of the incoming light obviously. And the CdS nanorods-Si nanopillars structure has obvious photosensitive effect, which has great potential in the field of photoelectric.

Controllable synthesis of MnO2 with different structures for supercapacitor electrodes

In this paper, MnO2 with four different structures (nanosandwiches, microsticks, nanowires and microflowers) are synthesized through varying reaction conditions, including the concentration of KMnO4 solution and hydrothermal reaction temperature. Through comparing experimental data, it can be concluded that the microstructure of MnO2 plays a vital role in electrochemical performance. Among the four structures, the microflower has the largest specific surface area for more electroactive sites, and thus demonstrates an excellent charge storage performance of 185 F/g at a current density of 0.5 A/g and cycling stability with a capacitance retention rate of 85% and a coulombic efficiency of nearly 100% after 10,000 charge-discharge cycles.

Effect of process factors on properties of high dispersion spherical α-Al2O3 particles prepared by hydrothermal method

Spherical α-Al2O3 powders were synthesized from a mixed solution consisting of Al2(SO4)3·18H2O, Al(NO3)3·9H2O and CH4N2O by hydrothermal method with muffle calcination and microwave calcination. Effects of raw material ratio, reaction temperature, and filling factor on properties of products were investigated. Properties of thermal behavior, functional groups, phase composition, microstructure and specific surface of precursors and products were characterized by DSC-TG, FT-IR, XRD, SEM and BET, respectively. Results show that SO42− plays an important role in the sphere formation of precursors and particle size can be changed by adding different proportion of NO3−. Precursors are amorphous spherical hydrated alumina containing SO42−, and the conversion of crystalline phase is from amorphous to γ-phase and then to α-phase at 1100 °C. Spherical morphology can be retained after crystallization to α-Al2O3. Compared with muffle furnace, Microwave calcination can increase calcining rate by three times and reduce insulation time by three quarters. When hydrothermal reaction temperature is 120 °C, the particles can be precipitated with good sphericity and narrow grain size distribution. If hydrothermal reaction temperature is too high or too low, spherical morphology can't be obtained. Size of the particles can be regulated by the different raw material ratio and filling factor from 800 nm to 3 μm, and specific surface area is in the range of 8 m2/g~15 m2/g.

Preparation of NH4+-loaded merlinoite for extracting potassium continuously at room temperature

The preparation of NH4+-loaded merlinoite (N-zeolite) for extracting potassium was studied systematically in seawater. N-zeolite was gained from K+-loaded merlinoite (K-zeolite), in which potassium ions were exchanged by ammonium ions. The amount of reagents, hydrothermal reaction temperature and reaction time were detailedly researched in order to obtain the optimized preparation conditions of N-zeolite. The experiment showed that the ion exchange between ammonium ions and potassium ions could be instantly completed at room temperature. The ion exchange equilibrium and property of N-zeolite for potassium extraction were studied in seawater at room temperature. The results indicated the ion exchange capacity for potassium reached equilibrium in about 50min. Since then, the maximum value of ion exchange capacity was 35.5mg/g. The ion exchange separation factors for KK+/Na+, KK+/Ca2+, KK+/Mg2+ were 21, 91 and 247, respectively. N-zeolite had good properties of reproducibility and reutilization through six times of repeated modified experiments. K-zeolite and N-zeolite revealed a reversible type-III isotherm characteristic by N2 adsorption–desorption experiments. The separation mechanism of N-zeolite for extracting potassium selectively was dominated by the memory function for a specific ion (K+) as well as the similar ion size.

Preparation and Photocatalytic Mechanism of Ag3PO4/SnO2 Composite Photocatalyst

A simple hydrothermal conversion method for the preparation of Ag3PO4/SnO2 composite photocatalyst has been developed. The morphological properties of the nanocomposites are studied using transmission electron microscopy (TEM), energy dispersive spectrometer (EDS), X-ray powder diffraction (XRD) and other methods. Different properties of catalysts are prepared by adjusting the temperature of hydrothermal reaction and the volume ratio. The prepared photocatalyst is tested by degradation of tetracycline solution under visible light show that the degradation rate of tetracycline can reach 74% when the initial [Ag3PO4]/[SnO2] molar ratio is 15 and the temperature is 140∘C. Moreover, by constructing Ag3PO4/SnO2 composite structure, the impedance and photocurrent of material are enhanced significantly according to the electrochemical characterization.

The influence of plasma treatment on the photovoltaic performance of DSSCs fabricated from hydrothermally prepared Zn2SnO4 nanoparticles

We synthesize high-quality Zn2SnO4 nanoparticles by means of hydrothermal method and then the influence of precursor concentration and precursor solution pH as well as hydrothermal reaction temperature on the structural properties of the resulting nanoparticles is investigated. Having synthesized the Zn2SnO4 nanoparticles with high-quality structural properties, the prepared nanoparticles are employed to construct the photoanodes. In the next step, the prepared photoanodes are treated with non-equilibrium atmospheric pressure plasma jet and the effect of plasma treatment duration on the photovoltaic properties of the fabricated Zn2SnO4-based dye-sensitized solar cells is studied. In comparison with untreated photoanode, the photoanode, treated for 12 min, exhibits maximum short-circuit current density and power conversion efficiency growth of about 27% and 32%, respectively. The increase in these values is ascribed to the improvement of dye-loading on the surface of photoanode. Furthermore, electrochemical impedance spectroscopy reveals that the charge transfer process at the interface of photoanode and electrolyte efficiently takes place which can be attributed to the interfacial properties improvement.

Fe-based ceramic nanocomposite membranes fabricated via e-spinning and vacuum filtration for Cd2+ ions removal

In this work, vacuum filtered and polymer mixed e-spinning membranes (ESPMs) made from or doped with Fe-based nanomaterials were successfully fabricated to remove Cd2+ ions from a neutral aqueous solution. The used Fe-based nanomaterials including FeOOH precursor Nanowires (NWs), α-Fe2O3 NWs and Fe3O4 nanoparticles (NPs) were synthesized by elevating the hydrothermal reaction temperature from 250 °C to 500 °C or doing post-heating treatment. The adsorption results showed that vacuum filtered membranes (VFMs) overall performed a better Cd2+ ions removal behavior than e-spinning ones. Among them, VFM made from Fe3O4 NPs has the highest adsorption capacity (qt) with the adsorption amount of Cd2+ ions reaching about 29.3 mg/g within only 2 min due to the high specific surface area of NPs. Models of pseudo-first-order, pseudo-second-order and intraparticle diffusion were used to study the kinetics of Cd2+ ions removal process, and a high correlation coefficient (R2) of 0.99 was obtained when pseudo-second-order model was used. It was calculated that the equilibrium rate constant of VFM made from Fe3O4 NPs has reached about 0.28 g mg−1 min−1, much smaller than those of other membranes, which indicated a high Cd2+ ions removal efficiency.

Synthesis and characterization of mesoporous bioactive glasses with highly ordered structures and high surface areas by a self-assembly process

Mesoporous bioactive glasses (MBGs) are considered to be outstanding bone-repairing materials. MBGs were prepared by a two-step acid-catalyzed self-assembly (TSACSA) process combined with a hydrothermal reaction. To synthesize the optimized texture organization, an orthogonal experiment was designed under the same conditions (acid concentration, calcination temperature, hydrothermal time and hydrothermal temperature). The MBGs were characterized by N2 adsorption analysis, SAXS and TEM. The in vitro bioactivity was investigated by XRD and FTIR after soaking in SBF for 3 and 6 h. The results illustrated that the calcination temperature was the key factor affecting pore volume and the specific surface area. The hydrothermal temperature had the greatest impact on pore size. Compared with MBG prior to hydrothermal treatment, MBG after hydrothermal treatment displays more highly ordered mesopores and more uniform cylindrical pores. In the in vitro bioactivity test, synthesized MBG presents hydroxyapatite (HA) mineralization activity within a short time. The optimal conditions of the synthetic process were 1 mol L−1 hydrochloride acid, a hydrothermal reaction temperature of 120 °C for 24 h and a calcination temperature of 500 °C. This resulted in a large pore volume (1.22 ± 0.06 cm3 g−1) and high specific surface (679 ± 32 m2 g−1).

A novel wet-mechanochemical pretreatment for the efficient enzymatic saccharification of lignocelluloses: Small dosage dilute alkali assisted ball milling

Achieving the capacity to produce fermentable sugars from lignocelluloses via green and efficient approaches is of strategic significance to an environmentally sustainable society. In this work, a novel wet-mechanochemical pretreatment approach was proposed using small amount of dilute alkali-assisted ball milling and subsequently hydrothermal pretreatment at mild conditions to enhance the enzymatic saccharification efficiency of bagasse and pennisetum. Effects of pretreatment conditions, such as NaOH concentration, hydrothermal reaction temperature and time, on the reducing sugars production were systematically evaluated. Parameters were optimized by statistical analysis and response surface methodology. Results showed that the existence of small amount of dilute alkali during ball milling can greatly facilitate the subsequent saccharification of bagasse and pennisetum, which can reduce the alkali dosage in comparison with traditional biomass pretreatment approach. The highest reducing sugars yield of 40.75% could be obtained from bagasse after pretreated by final concentration of 0.4% alkali in hydrothermal pretreatment process at 100 °C for 40 min. 55.74% of reducing sugars could be obtained from pennisetum treated by final concentration of 0.4% alkali in hydrothermal pretreatment process at 80 °C for 60 min. Compared with pretreatment temperature and time, NaOH concentration had more impact on the reducing sugars yield. Chemical composition of lignocelluloses also showed great influences on their saccharification efficiency. This work provides feasible theoretical basis and method for the efficient utilization of lignocelluloses.

Study on the electrical properties of nano ZnO/PET-ITO heterojunction prepared by hydrothermal method

The electrical properties of nano ZnO/PET-ITO heterojunction by the hydrothermal method were analyzed in detailed. The results showed that the average grain size increases with the rising of hydrothermal reaction temperature. It was observed that photoluminescence spectra of ZnO nanorods has belong to UV-violet emission band. By the means of current-voltage test, the nano ZnO/PET-ITO heterojunction presents fined rectification characteristics with the rising of hydrothermal reaction temperature. The leakage current decreased and the barrier height increased. This phenomenon can be explained by the reduction of oxygen vacancies due to the increase of hydrothermal reaction temperature, which weakens Fermi level pinning.

Hydrothermal synthesis of hematite (α-Fe2O3) nanoparticle forms: Synthesis conditions, structure, particle shape analysis, cytotoxicity and magnetic properties

In this work, we present the magnetic and structural properties of α-Fe2O3 nanoparticles synthesized by the hydrothermal synthesis method. XRD, FTIR and Raman spectroscopy indicate that the samples consist of single-phase α-Fe2O3 nanoparticles. A microstructural analysis by TEM and SEM shows: (i) irregular nanoparticles (∼50 nm), (ii) plate-like nanoparticles (with thickness t∼10 nm and diameter d∼50–80 nm) and (iii) microsized ellipsoid 3D superstructures (with length l∼3.5 and diameter d∼1.5 μm) composed of nanosized building blocks (∼50 nm). We used circularity, elongation and convexity measures to quantitatively analyze the shape of the particles. Irregular hematite nanoparticles were synthesized using a water solution of ferric precursor and sodium acetate during the hydrothermal reaction (reaction conditions: T = 180 °C, t = 12 h). The same hydrothermal reaction temperature, reaction duration and ferric precursor (without sodium acetate) were used for synthesizing hematite ellipsoid 3D superstructures. Addition of urea and glycine surfactants in hydrothermal reaction resulted in the formation of nanoplate hematite particles. The role of these surfactants on the structure and morphology of the particles was also investigated. Magnetic measurements at the room temperature displayed a wide range of coercivities, from HC = 73 Oe for irregular nanoparticles, HC = 689 Oe for nanoplates to HC = 2688 Oe for hematite ellipsoid 3D superstructures. The measured coercivity for the ellipsoid superstructure was about 35 times higher than in the case of irregular hematite nanoparticles and about 4 times than the coercivity of hematite nanoplates. Magnetic properties of synthesized samples were related to their structure and morphology. We conclude that shape anisotropy influenced enhancement of the coercivity in hematite nanoplates whereas hematite ellipsoid 3D superstructure (nanoparticle clusters) induced the formation of multidomain magnetic structure and highest coercivity revealing its superior structure for enhanced magnetic properties. The synthesized hematite nanoparticle structures exhibit low cytotoxicity levels on the human lung fibroblasts (MRC5) cell line demonstrating a safe use of these nanoparticles for practical applications.

Hydrothermal temperature effect on microstructure evolution and Fenton-like catalytic performance of spinel ferrite (Mg,Ni)(Fe,Al)2O4 synthesized from saprolitic nickel laterite

Metal-doped magnesium ferrites (Mg, Ni)(Fe, Al)2O4 were prepared by a hydrothermal method from saprolitic nickel laterite leaching solution. The effects of the hydrothermal reaction temperature (140–220 °C) and post calcination on the microstructure and catalytic performance of the as-prepared samples were investigated in detail. It is shown that higher hydrothermal temperature combined with calcination could promote the migration of Fe3+ from tetrahedral to octahedral sites almost exclusively located at the surface of the solid spinel ferrites, which was beneficial to improve the activity of formed MgFe2O4 catalysts. In addition, the calcined samples (hydrothermal synthesized at 180, 200 and 220 °C, then calcined at 500 °C (H180C, H200C and H220C)) exhibited excellent heterogeneous Fenton-like catalytic activity for decomposing Rhodamine B (about 97.0% degradation efficiency in 120 min). Moreover, reusability test results show that the reduction of degradation efficiency was less than 1.0% for the sample H200C, implying the as-prepared catalyst had good catalytic activity and excellent reusability. This study may provide a better understanding of relationships between microstructure and heterogeneous Fenton-like catalytic performance of spinel ferrites synthesized from natural minerals containing transition metals.

High-performance α-Fe2O3/C composite anodes for lithium-ion batteries synthesized by hydrothermal carbonization glucose method used pickled iron oxide red as raw material

The α-Fe2O3/C composites have been successfully synthesized by a facile hydrothermal carbonization glucose method using pickled iron oxide red as raw materials, which is the recycled product after treating the pickling wastewater. The NaOH is used as an additive to assist carbonization of glucose to obtain the high-quality carbon coating layer. X-ray diffraction, field emission scanning electron microscopy, and high-resolution transmission electron microscope are used to characterize the structure and morphology of the samples. To characterize the surface chemical composition and bonding configuration of α-Fe2O3/C, X-ray photoelectron spectroscopy is detected. The Electrochemical properties are optimized by the orthogonal tests, revealing that the hydrothermal reaction time has the most significant influence on the electrode capacity, followed by the hydrothermal reaction temperature, the amount of glucose added and the concentration of NaOH. As anode material for lithium ion battery, the initial discharge/charge capacity of α-Fe2O3/C electrode can reach 2640.1/2151.4 mAh g−1 with initial coulomb efficiency of 81.49% at a current density of 100 mA g−1, and even after 80 cycles maintain the capacity of 1529.5 mAh g−1, which far exceeds the theoretical capacity (1007 mAh g−1) of α-Fe2O3 electrode.

Zn3Ga2Ge2O10:Cr3+ Uniform Microspheres: Template-Free Synthesis, Tunable Bandgap/Trap Depth, and In Vivo Rechargeable Near-Infrared-Persistent Luminescence.

Near-infrared (NIR) emitting persistent phosphors of Cr3+-doped zinc gallogermanate have emerged for in vivo bioimaging with the advantage of no need for in situ excitation. However, it is challenging to synthesize well-dispersed and uniform spherical particles with high brightness, high resolution, and distinguished NIR long afterglow. In this work, Zn3Ga2Ge2O10:Cr3+ (ZGGC) monospheres were directly synthesized by a facile hydrothermal method with the assistance of citric anions (Cit3-), which emit an NIR emission at ∼696 nm and exhibit excellent NIR-persistent luminescence with rechargeability. Controlled experiments indicated that the shape evolution of the ZGGC product is significantly affected by Cit3-, solution pH, and the duration and temperature of hydrothermal reaction. Furthermore, compositional influence on the crystal structure, bandgap, trap depth, and luminescence characteristics of ZnyGa2Ge2O10-δ:Cr3+ (y = 2.8, 3.0, 3.2) were investigated in detail, which allows us to construct an energy level diagram of the ZGGC host, Cr3+ ions, and electron traps. It was found that the bandgap and conduction-band minimum (CBM) are significantly affected by the Zn content, while the valence-band maximum (VBM) is not. The y = 3.0 sample exhibited the best persistent luminescence, owing to its deepest defects. The ZGGC-NH2 prepared through surface functionalization of ZGGC spheres showed distinguished NIR long afterglow, low toxicity, and great potential for in vitro cell imaging and in vivo bioimaging in the absence of excitation. Moreover, the persistent luminescence signal from the ZGGC-NH2 can be repeated in vivo through in situ recharge with external excitation of a red LED lamp, indicating that the ZGGC-NH2 is suitable for applications in long-term in vivo imaging.

Novel insights into the properties of AgBiO3 photocatalyst and its application in immobilized state for 4-nitrophenol degradation and bacteria inactivation

This study focuses on the synthesis of novel AgBiO3 nanoparticles by the hydrothermal route and investigating its properties responsible for waste water treatment. The temperature and time of hydrothermal reaction was optimized to 150 °C and 24 h to obtain highly active crystalline nanoparticles, as determined by XRD. The oxidation state of each element in the material was determined from XPS analysis. The morphology and size of the nanoparticles was obtained from SEM and TEM analysis. The optical and electrochemical properties of the material were studied by UPS and Mott Schottky plot. AgBiO3 was found to have a low band gap that facilitates the absorption of higher wavelength range as confirmed by Tauc plots and UV–vis DRS analysis. The excellent photocatalytic activity of the immobilized material towards the degradation of 4-nitrophenol and inactivation of E. coli was confirmed from kinetic studies and stability tests. A maximum degradation of 90% was achieved for 4-NP and a 5-log reduction was observed for viable E. coli cells in 5 h and 1 h respectively. Scavenger studies were performed to identify that superoxide radicals were responsible for the photocatalytic activity of the material. To eliminate the cost of separation and ease the reusability of the material, the nanoparticles were immobilized on cellulose acetate. Leaching of Ag and Bi ions from immobilized as well as free AgBiO3 nanoparticles into water was obtained via ICP-MS analysis. The results indicated that the leaching of Ag and Bi was controlled to a considerable extent due to immobilization on cellulose acetate matrix.

Effect of Hydrothermal Reaction Temperature on Properties of Bismuth Nanoparticles and Its Properties as Modified Electrode for Pb Sensors

Heavy metal pollution is a common environmental problems. Therefore a versatile method that can be used to detect heavy metal ions on field is sought after. Electrochemical sensor is a promising method for heavy metal detection, however, electrodes modification is of interest to enhance sensitivity and specificity of sensors. In this work bismuth nanoparticles (BiNPs) was produced using hydrothermal method with varying hydrothermal reaction temperature. X-ray diffraction analysis showed pure-phase bismuth with a Rhombohedral structure was successfully produced. BiNPs/ITO had good CV properties in which BiNPs produced at 170°C has the highest respond current. However, BiNPs synthesized at 160°C showed the highest DPASV stripping current response due to high surface area and less agglomeration of particles. The BiNPs modified ITO was successfully fabricated as electrochemical Pb sensor. The modified BiNPs/ITO has LOD of 2.5 μg/L Pb with good specificity.

Surface-crumpled graphene hydrogels with macro- and microporous structures for ultrahigh-volumetric energy storage

Recent research has focused on three-dimensional graphene hydrogels with macroporous structure effectively applied for power supply. Here we report a novel surface-crumpled reduced graphene oxide hydrogel with hierarchical pores, through adjusting the temperature and time of hydrothermal reaction with the addition of 2-butanol molecules. Large amounts of micropores in the interior of the macroporous hydrogel skeleton, are attributed to the crispation on the edge of graphene sheets, forming the uniform tubes with the inner diameter of 1.74 nm confirmed by transmission electron microscopy. The pressed hydrogel electrode can provide an outstanding specific capacitance of 549 F cm-3 at 1.14 A cm−3 and high rate capability of 62.2% from 1.14 A cm−3 to 114 A cm−3. The assembled symmetric device can deliver a volumetric specific capacitance of 517 F cm-3 at 1.14 A cm−3, energy density of 71.9 Wh L−1 at 0.57 kW L−1, excellent cycling stability (98.6%) and coulomb efficiency (97.3%). The achievement of such remarkable performances can open up an exciting route to the hierarchically porous structure of graphene-based networks for highly efficient capacitive energy storage.

Mesoporous NiO with different morphology: Synthesis, characterization and their evaluation for oxygen evolution reaction

Mesoporous NiO samples with different morphology were synthesized by hydrothermal method, and they were studied as electrocatalysts for oxygen evolution reaction in alkaline solution. The NiO samples were characterized by X-ray diffraction, transmission electron microscopy, N2-adsorption, scanning electron microscopy and X-ray photoelectron spectroscopy. The critical synthesis parameters like hydrothermal reaction temperature, time and molar ratio of precursors were varied using Taguchi experimental method to investigate their effect on morphology and specific surface area of mesoporous NiO samples. The characterization data illustrated the formation of nanoplates, nanorods, and nanoparticles. All the NiO samples exhibited mesoporosity and the specific surface area values in the range of 88–156 m2/g. One of the synthesized mesoporous NiO samples, largely constituting of nanoplates and nanorods with high porosity, exhibited a Tafel slope of 62 mV/dec and achieved a current density of 41.6 mA/cm2 at 1.6 V (vs. RHE). It showed better electrocatalytic activity for oxygen evolution reaction than remaining samples.

In situ synthesis of hydrophobic calcium sulfate hemihydrate whiskers

A simple hydrothermal method was developed in this study to synthesize hydrophobic calcium sulfate hemihydrate whiskers in the presence of stearic acid. The morphology of the whiskers synthesized under different conditions was characterized by scanning electron microscopy, and their average aspect ratio was also estimated. The optimum synthesis conditions are determined as follows: the concentrations of Na2SO4 and CaCl2 solution for preparing the precursor are 1.1 mol L−1; the precursor content in the autoclave is 10 wt%; the hydrothermal reaction temperature is 150 °C; and the hydrothermal reaction time is 4 h, respectively. Glycol was used to promote the dispersion of stearic acid in the seriflux. The results show that the hydrophobic calcium sulfate hemihydrate whiskers can be obtained with stearic acid as surfactant, and their average aspect ratio can reach about 91.

Characterization and hydrothermal synthesis of nanocrystalline α-Fe2O3 with different morphologies

ABSTRACTThe nanocrystalline α-Fe2O3 was prepared using ferric(III) chloride and sodium hydroxide by a hydrothermal process. The effects of hydrothermal reaction temperature and time, concentration of sodium hydroxide on the morphology of α-Fe2O3 were studied. The prepared α-Fe2O3 products were characterized by powder X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results show that hydrothermal reaction temperature and time, concentration of sodium hydroxide have all effects on morphology of α-Fe2O3. When hydrothermal reaction temperature is raised from 140°C to 200°C, the morphologies of α-Fe2O3 samples are gradually converted from a needle-like mixture to a single flaky. When hydrothermal reaction time increased from 8 h to 24 h, the morphologies of α-Fe2O3 samples gradually changed from grain to flaky. And when concentration of sodium hydroxide increased from 1 mol/L to 6.5 mol/L, the morphologies of α-Fe2O3 samples changed from quasi-cubic to sheet.