Hydrothermal Synthesis Technique Research Articles

Enhanced photocatalytic activity of Fe3O4/SnO2 magnetic nanocomposite for the degradation of organic dye

Composite photocatalysts composed of semiconductor and magnetic matters are of great concern due to their excellent catalytic and recyclable performances. In this work, hydrothermal synthesis technique was employed to prepare magnetic Fe3O4/SnO2 nanocomposites (FS1, FS2, and FS3) of different molar ratios. The nanocomposites material was characterized by powder X-ray diffraction (XRD), high resolution scanning electron microscopy (HRSEM), energy-dispersive X-ray spectroscopy (EDS) and UV–vis diffuse reflectance spectroscopy (UV–vis DRS), Vibrating sample magnetometer (VSM) analysis. The SnO2 optical absorption was extended into visible region after coupling with Fe3O4. The magnetic features of Fe3O4/SnO2 nanocomposites offer simply separable method for reusability of the material in photocatalytic application. The catalytic activity of as prepared magnetically separable nanocomposites was inspected based on photodegradation of crystal violet as model organic pollutant. The extent of variation of field-dependent photo and dark current of the samples were determined from photoconductivity studies. The photoconductivity studies revealed the ohmic nature of the samples with a linear increase in both dark and photocurrent with a corresponding increase with increase in the applied field. The nanocomposite FS1 depicted good photocatalytic activity due to enlarged photoresponsive range and increase in charge separation rate. From the results, we suggest an attractive physical property and an efficient and a recyclable nanocomposite catalyst active under UV light irradiation for use in wastewater treatment to control water pollution.

Solvent-exfoliation of transition-metal dichalcogenide MoS2 to provide more active sites for enhancing photocatalytic performance of BiOIO3/g-C3N4 photocatalyst

The ternary complex photocatalysts of BiOIO3/g-C3N4/MoS2 by solvent-exfoliation method was synthesized for the first time. In the typical procedure, the BiOIO3/g-C3N4 was obtained via hydrothermal synthesis technique, and then the BiOIO3/g-C3N4/MoS2 photocatalysts were prepared via ultrasonic solvent-exfoliation method from bulk commercial MoS2 in the alcohol solution. The samples of BiOIO3/g-C3N4/MoS2 were analyzed by PL, XRD and other characterization analysis methods. The photocatalytic activity of the as-prepared samples was investigated by removing gas phase mercury irradiation under visible light. The as-prepared BCM-0.3 exhibits excellent photocatalytic performance, being with the highest efficiency of 70.58%. Owing to the electronic channels of field-effect, an internal electric field was formed through the corresponding band-gap engineering, improving photocatalytic reaction. Besides, the excellent activity of the ternary photocatalysts BiOIO3/g-C3N4/MoS2 is attributed to heterostructure between BiOIO3/g-C3N4 and MoS2, which enlarges spectral response and improved separation efficiency of charge carriers, and MoS2-composing, which provides more active sites for catalytic oxidation. In addition, the as-prepared samples with excellent photocatalytic performance also offer a perspective insight into the hydrogen evolution, CO2 conversion and degradation of organic pollutants.

Synthesis of Zeolite Na-LSX from Iraqi Natural Kaolin using Alkaline Fusion Prior to Hydrothermal Synthesis Technique

The synthesis of zeolite materials by hydrothermal transformation of kaolin using an alkaline fusion prior to hydrothermal synthesis method was investigated. The kaolin clay used in the present investigation was supplied from Iraq. The physical and chemical characterization of the starting kaolin and produced zeolite Na-LSX samples were carried out using different analytical techniques such as Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS), X – Ray Diffraction (XRD), X – Ray Fluorescence (XRF), Thermogravimetric Analysis (TGA), Fourier Transform Infrared (FT-IR) Spectroscopy and Inductively Coupled Plasma-Optical Emission Spectrometer (ICP-OES). An alkaline fusion method was introduced prior to the hydrothermal treatment while kaolin clay powder was mixed manually with NaOH powder (ratio = 1/1.2 in weight). The metakaolinisation phase was achieved by calcining the mixture in air at 600 oC for 1hr. The result from this route shows that zeolite Na-LSX with cubic rounded edge crystal habit have been successfully synthesised. Finally, The kinetic study indicated the suitability of the zeolite Na-LSX for the removal of Cu2+, Fe3+, Pb2+ and Zn2+ ions from synthetic wastewater.

Synthesis of Pure and High Surface Area Sodalite Catalyst from Waste Industrial Brine and Coal Fly Ash for Conversion of Waste Cooking Oil (WCO) to Biodiesel

The ravaging environmental menace of coal utilization in power generation and high cost of biodiesel production had recently resulted to global energy discourse. Non-waste-derived heterogeneous catalysts prepared from waste materials could reduce production cost of biodiesel and thus make it economical and environmentally sustainable. In this preliminary study, coal fly ash and industrial waste brine of South African origin were beneficiated for synthesis of waste-derived solid Hydroxy Sodalite (HSOD) catalyst. Non-waste-derived catalysts are not economical and environmentally sustainable. However, hydrothermal synthesis technique was employed to synthesize the catalysts used to produce biodiesel in a batch reactor. The physicochemical properties of the catalysts were studied using Fourier transform infrared spectroscopy (FT-IR), X-ray diffractometer (XRD), Scanning electron microscopy equipped with Energy-dispersive X-ray spectroscopy (SEM-EDS). Textural property of the catalyst was obtained via nitrogen physisorption at 77 K. The catalyst was tested for producing biodiesel from waste cooking oil using these conditions: methanol-to-waste cooking oil ratio of 15:1, 3 wt % of catalysts, and agitation speed of 300-500 rpm, 8 h reaction time and temperature of 60 o C. The biodiesel yield for waste-derived catalyst and non-waste-derived catalyst were 89.4 and 85.0 % respectively, at a maximum waste cooking oil conversion of 97.0 %. Results of the BET analysis reveal that the surface areas of waste-derived and non-waste derived catalysts were 33.05 m 2 g -1 and 0.1645 m 2 g -1 , respectively.

Characterization of nickel cobalt oxide: a potential material for supercapacitor

Hydrothermal synthesis technique is used to synthesize nanosized NiCo2O4 particles. The as-synthesized nanosized particles are structurally characterized by Raman spectroscopy. The nanostructure and morphology of the prepared nanoparticles are studied by Field Effect Scanning Electron Microscopy and Raman spectroscopy. DC electrical conductivity has been measured in the temperature range 303–402 K and the activation energy has been calculated. The absorbance of the nanoparticles in the UV–Visible range is recorded. The absorption spectrum analysis shows that the material possesses two direct band gaps, one corresponding to 1.74 eV and the other corresponding to 2.2 eV. The changes in AC conductivity and dielectric constant with a variation of frequency are studied. The AC conductivity exhibits Jonscher’s power law. From the dielectric studies, it is seen that with increasing frequency, the dielectric constant reduces. Also, the dielectric constant value of the nanoparticles is very high which indicates its supercapacitive behaviour. The small dielectric loss (0.32 at 3.5 kHz) shows a very small delay (relaxation time ∼4.54 × 10−5 s) in molecular polarization along with the varying electric field which reveals that the energy losses are less. The AC impedance spectroscopy also exhibits that the synthesized material has the potential as a good supercapacitive material.

Fluidizable Fe–Co/Ce–ZrO2 Catalysts for Steam Reforming of Toluene as a Tar Surrogate in Biomass Gasification

The Ce–ZrO2 composite based catalysts were successfully synthesized using a hydrothermal synthesis technique. The Fe–Co metals were incorporated on the Ce–ZrO2 composite to enhance its catalytic performance during steam reforming of toluene. X-ray diffraction revealed the crystalline phases of the catalysts. The addition of Fe and Co improved the acidity (NH3-temperature programmed desorption) as well as the specific surface area (Brunauer–Emmett–Teller analysis) of the catalysts. The catalytic performance of the fluidized catalysts was evaluated under the realistic conditions in a CREC riser simulator at three different temperatures (600, 650, and 700 °C). The Fe–Co promoted Fe–Co/Ce–ZrO2 catalysts exhibited better performance for long-term operation in the steam reforming of toluene, while the Ce–ZrO2 composite catalyst stimulates CO2 reforming of methane. Moreover, Fe–Co/Ce–ZrO2 showed the highest H2 production (i.e., 63%) at 700 °C. Thus, Fe–Co/Ce–ZrO2 catalysts hold great promise in producing high-qu...

Chemical, Morphological, Structural, Optical, and Magnetic Properties of Transition Metal Titanium (Ti)-Doped LaFeO3 Nanoparticles

In the present work, pure and transition metal titanium (Ti)-doped LaFe1−xTixO3(x = 0.0, 0.2, 0.4, and 0.6) nanoparticles have been successfully synthesized by hydrothermal synthesis technique for various molar ratios of 0.2, 0.4, and 0.6. The prepared samples were grinned and annealed in furnace at 600 ∘C/4 h. The X-ray diffraction (XRD) analysis confirms the phase orthorhombic formation of LaFeO3 and Ti-doped LaFeO3. The stoichiometric analysis was performed through energy-dispersive X-ray studies (EDX). The micro-structural features of surface morphology were examined by field emission scanning electron microscopy (FESEM). Further, surface nanocrystalline of the titanium (Ti)-doped LaFe1−xTixO3 was also investigated through high-resolution transmission electron microscopic (TEM) analysis. The enhancement of room temperature magnetization value has been observed from the M–H curve which is measured using vibrating sample magnetometer (VSM).The weak ferromagnetic behavior was observed from hysteresis loop. From hysteresis loop, saturation takes place when the applied magnetic field intensity is 15 kOe.

Hierarchical zinc oxide nanorings with superior sensing properties

Morphology controlled hydrothermal synthesis techniques have been realised to produce hierarchical zinc oxide (ZnO) nanostructures with high surface-to-volume ratios and more exposed polar facets. Hierarchical ZnO nanorings (HNRs) were produced by growing secondary nanowires (NWs) on initial mono-morphological nanodisks (NDs). In the two steps of growth process, zinc sulphate and zinc nitrate were used as the source of zinc ions, respectively. In comparison with NWs and NDs, the grown HNRs showed more enhanced performance as gas sensors. HNRs were substantially sensitive and faster in responding to acetone. This high performance in gas sensing is due to the increased surface-to-volume ratio and small size of the NW building blocks as well as the increased proportion of (0001) polar facets. This work represents a guide to structure induced improvement of sensing properties by controlling the morphology of nanostructures.

Nanothermite colloids: A new prospective for enhanced performance

Abstract Nanothermites (metal oxide/metal) can offer tremendously exothermic self sustained reactions. CuO is one of the most effective oxidizers for naonothermite applications. This study reports on two prospectives for the manufacture of CuO nanoparticles. Colloidal CuO particles of 15 nm particle size were developed using hydrothermal synthesis technique. Multiwalled carbon nanotubes (MWCNTs) with surface are 700 m2/g was employed as a substrate for synthesis of CuO-coated MWCNTs using electroless plating. On the other hand, aluminium particles with combustion heat of 32000 J/g is of interest as high energy density material. The impact of stoichiometric nanothermite particles (CuO/Al & Cuo-coated MWCNTs/Al) on shock wave strength of Al/TNT nanocomposite was evaluated using ballistic mortar test. While CuO-coated MWCNTs decreased the shock wave strength by 15%; colloidal CuO enhanced the shock wave strength by 30%. The superior performance of colloidal CuO particles was correlated to their steric stabilization with employed organic solvent. This is the first time ever to report on fabrication, isolation, and integration of stablilized colloidal nanothermite particles into energetic matrix where intimate mixing between oxidizer and metal fuel could be achieved.

Analysis of interfaces in Bornite (Cu5FeS4) fabricated Schottky diode using impedance spectroscopy method and its photosensitive behavior

In this report, we have synthesized Bornite (Cu5FeS4) material by hydrothermal synthesis technique. The interface characteristics of Al/Cu5FeS4/FTO Schottky barrier diode (SBD) are investigated by using ac impedance spectroscopy (IS) analysis (under dark condition) and dc current-voltage (I–V) measurements (under dark and light both condition). IS is a powerful tool to identify the interface regions of SBDs. Ac impedance spectra of Al/Cu5FeS4 SBD are recorded in the frequency range 40 Hz-20 MHz during dc bias scanning from -0.6 V to 0.6 V under dark condition. The diode parameter including ideality factor and barrier height is calculated from the conventional I–V measurement based on thermionic emission (TE) theory. Space charge limited current (SCLC) theory has been employed to further exemplify the improved performance of Cu5FeS4 based SBD, which points out that the carrier mobility is enhanced ∼2-fold after irradiation of light.

Interface Controlled Growth of Single-Crystalline PbTiO3 Nanostructured Arrays

PbTiO3 (PTO) ferroelectric perovskite has appealing electromechanical characteristics such as low aging rate of the dielectric constant, a high pyroelectric coefficient, a high piezoelectric voltage constant (gij), and a high Curie temperature of 490 °C. However, the high tetragonality of PTO ceramics makes them difficult to be synthesized via conventional high-temperature techniques. Here, a novel synthesis methodology is reported that results in epitaxial growth of a vertically aligned array of PTO nanofibers on a Ti metal substrate. High quality single crystal PTO nanofibers oriented along the [001] PTO direction were obtained on a (110) oriented TiO2 seed layer using a low-temperature hydrothermal synthesis technique. Fundamental understanding of the nucleation and growth criterion is provided through a combination of modeling of the geometric matching of crystal surfaces and experiments detailing the role of underlying TiO2 phase and interplanar atomic configuration. Crystal matching revealed good co...

Iron- and Cobalt-Doped Ceria–Zirconia Nanocomposites for Catalytic Cracking of Naphtha with Regenerative Capability

Series of nanosized iron- and cobalt-doped ceria–zirconia nanocomposites were prepared using a hydrothermal synthesis technique at 180 °C for 24 h, with the successful novel incorporation of both Co and Fe on ceria–zirconia, for n-hexane catalytic cracking. Effects of dopant ions on the improvement of intrinsic properties of ceria–zirconia nanocomposites were investigated using disparate characterization techniques. The synthesized ceria–zirconia nanocomposites exhibited similar X-ray diffraction (XRD) patterns, indicating full fusion of the metal ions into the ceria–zirconia lattice structure. The synthesized nanocomposite catalysts were tested for n-hexane cracking over 10 h time-on-stream, with no previous study or report for catalytic cracking of hexane via ceria–zirconia nanocomposites. Relatively high ethylene and propylene selectivity (both >62%) was obtained over CZ, FeCoCZa, and FeCoCZb over time-on-stream. Comparatively, the best catalytic activity and stability was exhibited by FeCoCZa with hig...

Band gap engineering of niobate composites through incorporation of Ni2+ metal ions and its property evaluation

A simple low cost, two step synthesis route, based on hydrothermal and wet chemical synthesis techniques, has been successfully adopted to prepare pure and Ni2+ doped potassium niobate-sodium niobate (KNi x Nb1-x O3-NaNbO3, x = 0, 0.02, 0.1, 0.25, 0.50) composites (by equal weight percentage). The synthesized materials have been thoroughly analyzed through XRD, FTIR, and HRTEM techniques. Further, morphological analyses through FESEM have revealed existence of mixed morphology, comprising of rod-shaped and irregular spherical structures, in the system. Diffuse Reflectance (DR) UV-Vis spectroscopy has been used to analyze the band gap values of the synthesized materials, and it has been observed that Ni2+ doping has significantly reduced the band gap values of the composites. Methylene Blue (MB) photodegradation analyses under UV irradiation have revealed absence of significant variation in the photodegradation efficiency values of the materials (photocatalysts) on doping. Dielectric studies have revealed low dielectric constant (ɛr) and loss tangent (tan δ) values, indicating an alteration to the perovskite structure of the composite materials, which in effect leads to a possible intensification of the cento-symmetric nature of the individual constituent niobate materials and thus, weakens the dielectric response of the composites in the process.

Ce-Based Catalysts for the Selective Catalytic Reduction of NOx in the Presence of Excess Oxygen and Simulated Diesel Engine Exhaust Conditions

A family of various cerium oxide-based catalysts were synthesized by adopting flame aerosol (FSP), coprecipitation, wet impregnation, and hydrothermal synthesis techniques. The resulting catalysts were explored for the selective catalytic reduction (SCR) of NOx using NH3 as reductant. In our studies, both the preparation method and the Ce/W ratios were found to be critical variables for successful catalyst promotion. For the industrial realization, we have scaled up the SCR activity tests. The microreactor catalytic formulations at simulated diesel engine exhaust conditions revealed that the Ce–W (1:1 atomic ratio) and Ce–W/TiO2 catalysts showed high deNOx activity, while the other catalysts’ activity was found to be rather low. Of interest is the finding that the Ce–W/TiO2/cordierite and Ce–W (1:1 atomic ratio)/cordierite formulations show impressive deNOx performance and high N2 selectivity with respect to a commercial vanadia based reference currently used for mobile applications. To gain fundamental i...

Sustainable steric stabilization of colloidal titania nanoparticles

A route to produce a stable colloidal suspension is essential if mono-dispersed particles are to be successfully synthesized, isolated, and used in subsequent nanocomposite manufacture. Dispersing nanoparticles in fluids was found to be an important approach for avoiding poor dispersion characteristics. However, there is still a great tendency for colloidal nanoparticles to flocculate over time. Steric stabilization can prevent coagulation by introducing a thick adsorbed organic layer which constitutes a significant steric barrier that can prevent the particle surfaces from coming into direct contact. One of the main features of hydrothermal synthesis technique is that it offers novel approaches for sustainable nanoparticle surface modification. This manuscript reports on the sustainable steric stabilization of titanium dioxide nanoparticles. Nanoparticle surface modification was performed via two main approaches including post-synthesis and in situ surface modification. The tuneable hydrothermal conditions (i.e. temperature, pressure, flow rates, and surfactant addition) were optimized to enable controlled steric stabilization in a continuous fashion. Effective post synthesis surface modification with organic ligand (dodecenyl succinic anhydride (DDSA)) was achieved; the optimum surface coating temperature was reported to be 180–240°C to ensure DDSA ring opening and binding to titania nanoparticles. Organic-modified titania demonstrated complete change in surface properties from hydrophilic to hydrophobic and exhibited phase transfer from the aqueous phase to the organic phase. Exclusive surface modification in the reactor was found to be an effective approach; it demonstrated surfactant loading level 2.2 times that of post synthesis surface modification. Titania was also stabilized in aqueous media using poly acrylic acid (PAA) as polar polymeric dispersant. PAA-titania nanoparticles demonstrated a durable amorphous polymeric layer of 2nm thickness. This manuscript revealed the state of the art for the real development of stable colloidal mono-dispersed particles with controlled surface properties.

Urea-Assisted Room Temperature Stabilized Metastable β-NiMoO4: Experimental and Theoretical Insights into its Unique Bifunctional Activity toward Oxygen Evolution and Supercapacitor.

Room-temperature stabilization of metastable β-NiMoO4 is achieved through urea-assisted hydrothermal synthesis technique. Structural and morphological studies provided significant insights for the metastable phase. Furthermore, detailed electrochemical investigations showcased its activity toward energy storage and conversion, yielding intriguing results. Comparison with the stable polymorph, α-NiMoO4, has also been borne out to support the enhanced electrochemical activities of the as-obtained β-NiMoO4. A specific capacitance of ∼4188 F g-1 (at a current density of 5 A g-1) has been observed showing its exceptional faradic capacitance. We qualitatively and extensively demonstrate through the analysis of density of states (DOS) obtained from first-principles calculations that, enhanced DOS near top of the valence band and empty 4d orbital of Mo near Fermi level make β-NiMoO4 better energy storage and conversion material compared to α-NiMoO4. Likewise, from the oxygen evolution reaction experiment, it is found that the state of art current density of 10 mA cm-2 is achieved at overpotential of 300 mV, which is much lower than that of IrO2/C. First-principles calculations also confirm a lower overpotential of 350 mV for β-NiMoO4.

Bright Green Frequency Upconversion in Catechin Based Yb3+/Er3+ Codoped LaVO4 Nanorods upon 980 nm Excitation

A series of Yb3+–Er3+ codoped LaVO4 phosphors using catechin as a chelating agent and phase director have been prepared by the low temperature hydrothermal synthesis technique. The sample exists in two different crystalline phases, i.e., monoclinic and tetragonal, depending on the concentration of dopants. Structural, optical, and thermal characterizations have been done by using X-ray diffraction, EDX, FE-SEM, UV–vis diffuse reflectance, FTIR, and TGA analysis. Upconversion emission (UC) based imaging and drug delivery systems have been proposed to overcome some significant drawbacks of existing systems. Though fluorides are better hosts for UC, their harmful character has forced researchers to look at alternatives including oxides. The frequency upconversion emission (UC) study upon excitation at 980 nm has been performed in this particular host (m-LaVO4) which is not an ideal upconverting host. The sample emits bright green color upconversion emission, along with relatively weak emissions in the blue, ...

Corrosion‐Resistant Superhydrophobic Coatings on Mg Alloy Surfaces Inspired by Lotus Seedpod

Superhydrophobic surfaces are widely found in nature, inspiring the development of excellent antiwater surfaces with barrier coatings isolating the underlying materials from the external environment. Here, the naturally occurring superhydrophobicity of lotus seedpod surfaces is reported. Protective coatings that mimic the lotus seedpod are fabricated on AZ91D Mg alloy surfaces with the synergistic effect of robust superhydrophobicity and durable corrosion resistance. The predesigned titanium dioxide films are coated on AZ91D by an in situ hydrothermal synthesis technique. Through sonication assisted electroless plating combined with a self‐assembling method, the densely packed Cu‐thiolate layers are uniformly plated with robust adhesion on the Mg alloy substrate, which function as a superhydrophobic barrier that can hold back the transport of water and corrosive ions contained such as Cl−. Notably, the two extreme wetting behaviors (superhydrophilicity and superhydrophobicity) as well as corrosion resistance and improved corrosion resistance can be easily controlled by removal of the hydrophobic materials (n‐dodecanethiol) at elevated temperature (350 °C) and modifying them at room temperature for 18 cycles, indicative of exceptional adhesion between the superhydrophobic coating and the underlying AZ91D Mg alloy.

The lattice stiffening transition in UO2 single crystals

The effective Debye temperatures () of the surface region of UO2 single crystals, prepared by the hydrothermal synthesis technique, were obtained from temperature-dependent x-ray photoemission in the temperature range of 300 K–623 K. A lattice stiffening transition, characterized by different regions of different effective Debye temperature, 500 ± 59 K below 475 K and 165 ± 21 K above 475 K is identified. A comparison of the temperature dependence of the effective UO2 Debye temperature, with the changes in the lattice expansion coefficient for UO2, support strong lattice-phonon interaction arising from the Jahn–Teller distortion.

Hydrothermal Synthesis and Magnetic Characterization of the Quaternary Oxide CoMo2Sb2O10.

The new quaternary layered oxide CoMo2Sb2O10 was synthesized by hydrothermal synthesis techniques, and its structure was determined from single-crystal X-ray diffraction data. CoMo2Sb2O10 crystallizes in the monoclinic space group C2/c with one Sb3+, Mo6+, and Co2+ atom site per unit cell, respectively. The crystal structure contains building units consisting of [Co2O8]n, [Mo2O8]n, and [SbO2]n chains. These are connected through corner sharing to form charge-neutral [CoMo2Sb2O10]n layers. Thermal decomposition of CoMo2Sb2O10 starts at 550 °C. The magnetic susceptibility follows a Curie-Weiss law above 50 K with a Curie constant of C = 3.46 emu·K·mol-1 corresponding to an effective moment of μeff = 5.26 μB per cobalt atom and a Curie-Weiss temperature θ = -13.2 K. Short-range anti-ferromagnetic ordering dominates below 5 K. Magnetic susceptibility and heat capacity data can be successfully modeled by the predictions from an Ising linear chain with an intrachain spin exchange of ca. -7.8 K.