Temperature Hydrothermal Growth Research Articles

Influence of growth temperature on structural, optical, morphological and photoelectrochemical characteristics of vertically aligned hydrothermally synthesized TiO2 nanorods

Herein, vertically oriented TiO2 nanorods were prepared on FTO substrate using hydrothermal synthesis. The influence of growth temperature on structural, optical, morphological and photoelectrochemical characteristics were analyzed. The FESEM and AFM results validated the formation of TiO2 nanorods. XRD spectra revealed the formation TiO2 tetragonal crystal structure with the rutile phase. UV–vis data showed an increase in the visible light absorption and a narrowing of the energy band gap with increasing in reaction temperature. Based on PEC studies, all the samples showed good light response and pronounced photocurrent density under light conditions. The highest possible photocurrent density of 78.8 μA/cm2 at 1.2V vs Ag/AgCl was recorded from TiO2 film with hydrothermal growth temperature of 200°C for 3 h s. This performance is attributed to narrow bandgap (2.89eV) and longer lifetime of carriers (0.3s). This result was validated by data from EIS, whereby the fast separation and transfer of photogenerated charge carriers were demonstrated.

Morphological Control of Supported ZnO Nanosheet Arrays and Their Application in Photodegradation of Organic Pollutants.

Supported nanostructured photocatalysis is considered to be a sustainable and promising method for water pollution photodegradation applications due to its fascinating features, including a high surface area, stability against aggregation, and easy handling and recovery. However, the preparation and morphological control of the supported nanostructured photocatalyst remains a challenge. Herein, a one-step hydrothermal method is proposed to fabricate the supported vertically aligned ZnO nanosheet arrays based on aluminum foil. The morphologically controlled growth of the supported ZnO nanosheet arrays on a large scale was achieved, and the effects of hydrothermal temperature on morphologic, structural, optical, and photocatalytic properties were observed. The results reveal that the surface area and thickness of the nanosheet increase simultaneously with the increase in the hydrothermal temperature. The increase in the surface area enhances the photocatalytic activity by providing more active sites, while the increase in the thickness reduces the charge transfer and thus decreases the photocatalytic activity. The influence competition between the area increasing and thickness increasing of the ZnO nanosheet results in the nonlinear dependence between photocatalytic activity and hydrothermal temperature. By optimizing the hydrothermal growth temperature, as fabricated and supported ZnO nanosheet arrays grown at 110 °C have struck a balance between the increase in surface area and thickness, it exhibits efficient photodegradation, facile fabrication, high recyclability, and improved durability. The RhB photodegradation efficiency of optimized and grown ZnO nanosheet arrays increased by more than four times that of the unoptimized structure. With 10 cm2 of as-fabricated ZnO nanosheet arrays, the degradation ratio of 10 mg/L MO, MB, OFL, and NOR was 85%, 51%, 58%, and 71% under UV irradiation (365 nm, 20 mW/cm2) for 60 min. All the target pollutant solutions were almost completely degraded under UV irradiation for 180 min. This work offers a facile way for the fabrication and morphological control of the supported nanostructured photocatalyst with excellent photodegradation properties and has significant implications in the practical application of the supported nanostructured photocatalyst for water pollution photodegradation.

Effect of growth temperature on the nanostructure and electrochemical properties of in-situ deposited WO3 thin films

Thin films of tungsten trioxide (WO3) have widespread applications such as in photocatalysis, electrochromism, photochromism, etc. Tuning the nanostructure of WO3 thin films has a notable impact on their electro/photocatalytic properties. In this work, WO3 thin films were prepared on FTO glass employing the in-situ hydrothermal method. Amongst other parameters of thin-film growth, the hydrothermal growth temperature is crucial toward WO3 thin film characteristics. The reaction temperature for the preparation of WO3 thin films in this study varied from 120 to 180 °C. XRD analysis revealed that WO3 thin films prepared at reaction temperatures of 120 (W120) and 150 °C (W150) have a hexagonal structure, whereas thin film prepared at 180 °C (W180) has a mixed hexagonal and monoclinic structure. The morphology of thin films changed with reaction temperature, as evidenced by FE-SEM analysis. Cyclic voltammetry analysis indicated that W120 exhibited fast Li+ ions insertion and extraction kinetics as compared to thin films synthesized at other temperatures. Finally, a correlation was made between the better electrochemical performance of W120 with its structure and morphology.

Influence of growth temperature on light trapping properties of ZnO:Al nanorods grown on seed layers with crater-like structures

We report the growth and characterization of textured ZnO:Al (AZO) films with excellent optoelectronic properties. The surface morphology depended strongly on growth temperature; in particular, the effect of hydrothermal growth temperature on the optoelectronic properties and light trapping abilities of AZO nanorods grown on the crater-like AZO seed layers was investigated systematically. The AZO nanorods grown at 110°C were relatively dense, indicating that hydrothermal growth temperature can promote the growth of AZO nanorods along the direction perpendicular to the substrates. The difference in the height and orientation of AZO nanorods prepared at 100°C resulted in significant enhancement of light trapping abilities. In addition, the textured AZO films maintained low sheet resistance and high total transmittance.

Hydrothermal temperature effect on the growth of h-MoO3 thin films using seed layers and their photoluminescence properties

In this work, thin films of molybdenum trioxide were successfully deposited via the facile and cost-effective hydrothermal technique. The films were grown at different temperatures of 50, 80, 110, and 130 °C on glass substrates. The growth temperature effects on the optical, morphological, and structural properties of samples were studied. X-ray diffraction (XRD) pattern analysis and Raman spectroscopy revealed that all deposited MoO3 thin films were crystallized in a hexagonal crystal structure. Field emission scanning electron microscope (FESEM) images exhibited that MoO3 thin films were coated by well-shaped hexagonal micro-rods. Also, the diameter of the micro-rods was decreased from 8.95 to 3.60 μm by increasing the hydrothermal growth temperature. At 130 °C, micro-rods were accumulated in the form of micro-flowers. By increasing the growth temperature, the estimated optical bandgap of films was increased from 2.94 to 3.04 eV, respectively. All h-MoO3 fabricated thin films showed photoluminescence (PL) emission at room temperature, and increasing the growth temperature caused the enhancement of the PL intensity. This study provides a simple and low-cost synthesis route at low temperatures to deposit h-MoO3 films for further investigations as in gas sensing and optoelectronic applications.

Hollow ZnO microspheres self-assembled from rod-like nanostructures: morphology-dependent linear and Kerr-type nonlinear optical properties

Hollow nanostructures have attracted attention because of their unique physiochemical properties and broad potential applications in electronics, optics and photonics. In this study, a facile hydrothermal approach was developed to fabricate hollow ZnO microspheres via self-assembled rod-like nanostructures. The morphology-controlled synthesis was conducted by altering hydrothermal treatment temperature (150, 200 and 250 °C) in solutions containing zinc acetate dihydrate precursor and glycerol as the stabilizing agent. The morphological observations indicated that hydrothermally grown ZnO architectures could be reasonably adjusted by modulating hydrothermal reaction temperature. Possible growth routes are proposed to elucidate the formation process of ZnO microspheres with the rod-like nanostructures. Morphology-dependent absorbance and emission along with red-shifts with improved crystalline qualities were observed with increasing hydrothermal growth temperature. Kerr-type nonlinear optical characteristics examined using single-beam Z-scan technique in the near infrared spectral range under nanosecond Nd-YVO4 laser pulses showed positive values of nonlinear refraction providing an evidence of self-focusing behaviors at the excitation wavelength of 1064 nm in all the samples studied. The highest Kerr-type nonlinear susceptibility was estimated to be 2.31 × 10–6 esu for hollow ZnO microspheres grown at 250 °C, suggesting synergistic effects of surface morphologies on optical nonlinearities.

Controlled hydrothermal synthesis and solar light photocatalysis properties of branched Bi2S3/TiO2 nano-heterostructure

In this work, we used two simple and inexpensive hydrothermal steps to synthesize Bi2S3 nanoflowers branched on TiO2 nanorod heterostructure. The nanoscale morphology of Bi2S3 deposited on TiO2 nanorods was optimized by controlling the hydrothermal growth temperature of bare Bi2S3 nanoparticles. Under solar lighting, the structural and optical properties, also the photocatalytic performance was systematically evaluated for the bare Bi2S3, bare TiO2 and Bi2S3/TiO2 heterostructures synthesized under optimized conditions. The Bi2S3/TiO2 heterostructures showed an enhanced visible-light absorption ability and photocatalytic efficiency comparing to bare TiO2. Photoluminescence and electrochemical impedance spectroscopy measurements suggest that Bi2S3/TiO2 heterostructures promoted the separation of electron-hole pairs and then enhanced the photocatalytic degradation performance for organic pollutant. The prepared heterostructures showed great stability and reusability. It also displayed enhanced photocatalytic performance for MB degradation, presenting 90% removal efficiency for 240 min, under solar light irradiation. The improved photocatalytic performance was attributed to the large Bi2S3 nanowires branched like nanoflowers structure on TiO2 nanorod arrays. This performance has obviously led to a better separation of electron-hole pair and an improvement in the absorption of light in the visible-light region.

Effect of Temperature and Growth Time on Vertically Aligned ZnO Nanorods by Simplified Hydrothermal Technique for Photoelectrochemical Cells.

Despite its large band gap, ZnO has wide applicability in many fields ranging from gas sensors to solar cells. ZnO was chosen over other materials because of its large exciton binding energy (60 meV) and its stability to high-energy radiation. In this study, ZnO nanorods were deposited on ITO glass via a simple dip coating followed by a hydrothermal growth. The morphological, structural and compositional characteristics of the prepared films were analyzed using X-ray diffractometry (XRD), field emission scanning electron microscopy (FESEM), and ultraviolet-visible spectroscopy (UV-Vis). Photoelectrochemical conversion efficiencies were evaluated via photocurrent measurements under calibrated halogen lamp illumination. Thin film prepared at 120 °C for 4 h of hydrothermal treatment possessed a hexagonal wurtzite structure with the crystallite size of 19.2 nm. The average diameter of the ZnO nanorods was 37.7 nm and the thickness was found to be 2680.2 nm. According to FESEM images, as the hydrothermal growth temperature increases, the nanorod diameter become smaller. Moreover, the thickness of the nanorods increase with the growth time. Therefore, the sample prepared at 120 °C for 4 h displayed an impressive photoresponse by achieving high current density of 0.1944 mA/cm2.

Bipolar resistive switching and memristive properties of hydrothermally synthesized TiO2 nanorod array: Effect of growth temperature

In the present work, the hydrothermal approach is employed to develop 1D-TiO2 nanorod array memristive devices and the effect of hydrothermal growth temperature on TiO2 memristive devices is studied. X-ray diffraction (XRD) analysis suggested that the rutile phase is dominant in the developed TiO2 nanorod array. Field emission scanning electron microscopy (FESEM) images show well adherent and pinhole free one dimensional (1D) TiO2 nanorods. The presence of titanium and oxygen in all the samples was confirmed by energy dispersive X-ray spectroscopy (EDS). Furthermore, growth of the 1D TiO2 nanorods depends on the growth temperature and uniform growth is observed at the higher growth temperatures. The well-known memristive hysteresis loop is observed in the TiO2 nanorod thin films. Furthermore, resistive switching voltages, the shape of I-V loops and (non)rectifying behavior changed as the growth temperature varied from 140 °C to 170 °C. The biological synapse properties such as paired-pulse facilitation and short-term depression are observed in some devices. The detailed electrical characterizations suggested that the developed devices show doubled valued charge-magnetic flux characteristic and charge transportation is due to the Ohmic and space charge limited current.

Flower-like nanostructures of WO3: Fabrication and characterization of their in-liquid gasochromic effect

A hydrothermal method based on ammonium oxalate was developed to grow colloidal suspensions of WO3 flower-like structures at different temperatures. PdCl2 solution was added as a hydrogen catalytic source to the suspensions in order to develop a gasochromic response. Transmission electron microscopy (TEM) revealed the presence of spherical 50–200nm palladium nanoparticles on the WO3 surfaces. X-ray diffraction patterns (XRD) showed a phase transformation from orthorhombic WO3·(H2O)0.33 to monoclinic WO3 by increasing the hydrothermal growth temperature from 100 to 180°C. The effect of post-annealing on the WO3 structure was also investigated. Fourier transform infrared spectroscopy (FTIR) was used to identify functional groups, hydroxyl ions and chemical bonds in the WO3. The in-liquid gasochromic effect when a 1:9 hydrogen:argon gas mixture was bubbled through the suspension, showed a color change from clear to blue, with the sample prepared at 150°C showing the best response. The gasochromic reactions of these hydrothermal samples are compared to those obtained by pulsed laser ablation and anodizing methods.

Hydrothermal Synthesis Effect on Growth of Zinc Oxide Structure

The properties and performances of Zinc Oxide (ZnO) film have made the material spread widely in several applications such as in providing energy to consumers in which it is harvest energy from the sun rays. By using hydrothermal method in order to fabricate ZnO films is one of the process that consume less energy and lower temperature compare to the other methods. In this research, the seed layer of ZnO was deposited on Fluorine doped Tin Oxide (FTO) substrate and heat treated at 100 °C for 10 min prior to the hydrothermal growth. Hydrothermal growth temperature was varies at 70 °C, 90 °C and 110 °C for 12 hours. The ZnO-coated FTO films were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and energy disperse spectroscopy (EDS). The I-V characteristic of the ZnO-coated FTO films was characterized with solar simulator. The experimental results reveal that the hydrothermal growth temperature exerts a strong influence on the properties of the ZnO-coated FTO films. The effects of the hydrothermal growth temperature are discussed.

Effect of Hydrothermal Growth Temperature on the Morphology and Structural Properties of Synthesized TiO<sub>2</sub> Nanowires

Titanium dioxide nanowires have successfully prepared by hydrothermal method. The effect of hydrothermal growth temperature on the morphology and structural properties of TiO2 nanowires have been investigated. It was observed that at low temperature of 100 °C, the formation of nanowires was at early stage, while hydrothermal treatment at 130 °C showed the TiO2 precursor acquired enough energy for formation of the nanowires. Increased the temperature to 200 °C was formed the bundle of nanowires in microsize. The diameter of nanowires increased as the temperature increased. The TiO2 nanowires produced at temperature of 150 °C and annealed at 500 °C showed highest crystallinity with anatase phase.

Effect of hydrothermal growth temperature on structural and optical properties of TiO2 nanoparticles

TiO2 nanoparticles have been prepared by hydrothermal method at different temperatures. The X-ray diffraction results showed that anatase TiO2 nanoparticles with grain size in the range of 7–27 nm has been obtained. HRTEM images show the formation of TiO2 nanoparticles with grain size ranging from 7 to 26 nm. The Raman spectra exhibited peaks corresponding to the anatase phase of TiO2. Optical absorption studies reveal that the absorption edge shifts towards longer wavelength (red shift) with increasing hydrothermal temperature.

Fabrication of Novel Hierarchical β-Ni(OH)2 and NiO Microspheres via an Easy Hydrothermal Process

Hierarchical β-Ni(OH)2 microspheres with 6−8 μm diameter assembled from nanoplate/nanosheet building blocks were successfully fabricated via a hydrothermal process in the presence of an anion surfactant poly(ethylene glycol) 4-nonylphenyl 3-sulfopropylether potassium salt. The factors influencing the formation of hierarchical Ni(OH)2 microspheres were monitored by using SEM characterizations. The effect of hydrothermal growth temperature on the Ni(OH)2 morphology was also investigated. NiO microspheres assembled from nanoplate/nanosheet were also obtained by thermal decomposition of the as-synthesized β-Ni(OH)2 at 320 °C for 3 h in air. HRTEM and SAED results reveal that the Ni(OH)2 and NiO nanosheets are single crystalline. Nitrogen adsorption−desorption measurements of the BET surface area and pore size of NiO microspheres were 160 m2/g and 30−50 nm, respectively. It is anticipated that these novel hierarchical microsphere structures of Ni(OH)2 and NiO will have great applications in Ni-based batteries,...

The effect of hydrothermal growth temperature on preparation and photoelectrochemical performance of ZnO nanorod array films

Highly oriented ZnO nanorod arrays with controlled diameter and length, narrow size distribution and high orientation consistency have been successfully prepared on ITO substrates at different growth temperatures by using a simple hydrothermal method. XRD results indicate that the nanorods are high-quality single crystals growing along [001] direction with a high consistent orientation perpendicular to the substrate. SEM images show that the nanorods have average diameters of about 30–70 nm by changing growth temperature. The thin films consisting of ZnO nanorods with controlled orientation onto ITO substrates allow a more efficient transport and collection of photogenerated electrons through a designed path. For a sandwich-type cell, the relatively high overall solar energy conversion efficiency reaches about 2.4% when the growth temperature is at 95 °C.

Core–shell structure of strontium titanate self-grown by a hydrothermal processfor use in grain boundary barrier layers

A perovskite shell of strontium titanate (SrTiO3)has been successfully self-grown on the surface of a titanium (Ti) particleby a hydrothermal process using Sr(OH)2·8H2Oand Ti powder with or without alkaline (NaOH) solutionat a temperature of 150–200°Cfor 3 h. The obtained strontium titanate (ST) shell contained sphericalgrains. The shells’ crystallinity, thickness and grain size increased with anincrease in the hydrothermal growth temperature. The obtained shellgrain size was estimated by transmission electron microscopy to be inthe range 50–120 nm. The thickness of the spherical grain shell wasabout 400 nm for 3 h hydrothermal growth at 180°Cand 600 nm for 3 h at 200°C.There was a transition zone of about 200 nm between the ST shell and the Ticore. The results are ascribed to diffusion of the Sr ions through the shell into thecore to react with dissolved Ti ions in an oxygen-deficient environment. Theself-grown ST–Ti was annealed in air after sintering at 1350°Cin a reducing C/CO atmosphere. This produced a core–shell structure with an STgrain boundary barrier layer. The sintered and annealed body exhibited the goodnonlinear resistance properties of a varistor.

Mesoporous TIO2 Electrodes for Photovoltaic Applications

AbstractDuring the past five years, we have developed in our laboratory a new type of solar cell based on a photo-electrochemical process. A respectable photovoltaic efficiency (i.e. 10%) is obtained by the use of mesoporous, nanostructured films of anatase particles. We will show how the TiO2 electrode microstructure influences the photovoltaic response of the cell. More specifically, we will focus on how processing parameters such as hydrothermal growth temperature, binder addition and sintering conditions influence the film porosity, pore size distribution, and consequently affect the solar cell efficiency.