Sol-gel Hydrothermal Method Research Articles

PREPARATION AND CHARACTERIZATION OF Cu-Fe/TiO2 PHOTOCATALYST FOR VISIBLE LIGHT DEEP DESULFURIZATION

A photooxidative system for deep desulfurization of model diesel fuel was explored. Nanoparticles of anatase titania (TiO2) were synthesized via sol-gel hydrothermal method. The TiO2 was further modified with bimetallic Cu-Fe using wet-impregnation method followed by calcination process in order to extend the activity region of the photocatalyst to visible-light. A series of bimetallic 2.2 wt% Cu-Fe/TiO2 photocatalysts with different Cu:Fe mass compositions were characterized for their physical, chemical and optical properties using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), high resolution transmission electron microscopy (HRTEM), diffuse reflectance UV-visible spectroscopy (DR-UV-Vis), Fourier Transform Infrared Spectroscopy (FTIR) and Brunauer–Emmett–Teller (BET) surface area analysis. The performance of the photocatalysts was evaluated for photooxidation of dibenzothiophene (DBT) as the sulfur species from model oil in the presence of hydrogen peroxide, H2O2 under 500 W visible light illumination. The highest sulfur conversion of 82.36 % was observed for photocatalyst with 10:1 Cu:Fe mass composition.

Experimental study of forced convection and subcooled flow boiling heat transfer in a vertical annulus using different novel functionalized ZnO nanoparticles

In this study the effect of different ZnO-nanoparticles synthesis methods on thermal performance of prepared nanofluids has been investigated. The study has been accomplished in two parts. At first, four types of ZnO nanoparticles were synthesized by sol-gel hydrothermal method. The surfaces of these nanoparticles were functionalized and then the characterization tests were performed. At the second step, forced convective and subcooled flow boiling heat transfer coefficients of the synthesized water-based nanofluids were experimentally studied. The experiments were conducted in a closed loop in which the working fluid passed through a vertical cylindrical annulus. The experiments were performed at different levels of operating variables such as subcooling temperature (30–50°C), volume flow rate (2–4 L/min), heat flux (8–110kW/m2) and nanoparticle concentration (0.005–0.02vol%). The results indicated that nanorod-nanotube ZnO nanoparticles which were surface modified by silica gel and UV radiation had the best thermal performance.

Photocatalytic degradation of alprazolam in water suspension of brookite type TiO2 nanopowders prepared using hydrothermal route

Two series of nanocrystalline brookite-type powders have been synthesized by using combined sol–gel–hydrothermal method with titanium tetrachloride (TiCl4) as a precursor and hydrothermal temperature and reaction time varied in the range of 120–200 °C and 12–48 h, respectively. The effects of chosen synthesis parameters on structural, morphological and optical properties of synthesized powders have been investigated by the XRPD, SEM, EDS and BET measurements, as well Raman spectroscopy and spectroscopic ellipsometry. The XRPD results have shown that pure brookite phase, with mean crystallite size of ∼33 nm, has been obtained only in the sample synthesized at 200 °C, after 24 h of hydrothermal process. In all other samples anatase phase also appears, whereas rutile and sodium titanate phases have been noticed in the samples synthesized at lower temperatures. The presence of different titania phases has also been confirmed and analyzed by Raman scattering measurements. The SEM measurements have shown spindle-like particles in brookite-rich samples synthesized at 200 °C, whereas BET measurements have detected mesoporous structure in these samples. The properties of synthesized powders have been correlated to their photocatalytic efficiency, tested in degradation of alprazolam, one of the 5th generation benzodiazepines. The sample consisted of pure brookite has shown the highest efficiency in the photodegradation of alprazolam, practically equal to the activity of Degussa P25.

Sol–gel-hydrothermal synthesis of Er3+:Y3Al5O12/Pt–TiO2 membrane and visible-light driving photocatalytic hydrogen evolution from pollutants

A novel visible-light photocatalyst, Er3+:Y3Al5O12/Pt–TiO2 membrane, was prepared via sol–gel–hydrothermal method on glass substrates as a support. X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDX) were used to reveal the crystallinity, surface morphology and chemical composition of the prepared Er3+:Y3Al5O12/Pt–TiO2 membrane. The catalytic activity of Er3+:Y3Al5O12/Pt–TiO2 membrane was examined through the photocatalytic hydrogen evolution from some pollutants, including phenol, glycerol and Na2S/Na2SO3, which were used as electron donors, under visible-light irradiation. Furthermore, some influence factors, such as mass ratio, pre-treatment temperature and used times, on the photocatalytic activity of Er3+:Y3Al5O12/Pt–TiO2 membrane were studied. The experimental results showed that the Er3+:Y3Al5O12/Pt–TiO2 membrane is a good and broad-spectrum photocatalyst in visible-light photocatalytic hydrogen evolution with simultaneous pollutant solution treatment.

Fabrication of ZnO Nanorods on Silicon Substrates by Sol-gel Hyrdothermal Methods

ZnO nanorods were deposited on silicon substrate using sol-gel hydrothermal methods. The seed layer was first grown by sol-gel methods and then annealed at temperatures of 300ºC, 400ºC, 500ºC and 600ºC. Multiple material and optical analyses including field-emission scanning electron microscope, energy dispersive X-ray spectroscopy, X-ray diffraction, photoluminescence spectra, and Raman spectra were conducted to examine the growth orientation and material properties. Results indicate that the ZnO nanorods annealed at a proper temperature of 400ºC could enhance orientation and material quality.

In situ growth of porous ZnO nanosheet-built network film as high-performance gas sensor

Porous ZnO nanosheet-built network film was in situ grown on the surface of the Al2O3 ceramic tube as gas sensor via sol–gel hydrothermal method. The film was characterized by X-ray diffraction analysis, field emission scanning electron microscopy and transmission electron microscopy. The results demonstrate that the porous ZnO network film is of hexagonal wurtzite and mesoporous structure. The gas sensing property was also studied. The results indicate that the sensor shows high sensitivity and fast response to acetone and ethanol at 400°C operating temperature, to H2S at 200°C operating temperature, and to humidity at 25°C operating temperature, respectively. Moreover, it also exhibits nice selectivity to H2S and humidity at its corresponding operating temperature, which makes the sensor have promising applications in gas detector.

Morphological, Structural and UV Sensing Properties of Fe-Doped ZnO Nanorods

Iron (Fe) doped ZnO nanorods were synthesized on glass substrate using a sol-gel hydrothermal growth method by adopting various concentration ratios of 0.8 at% Fe, 1 at% Fe and 3 at% Fe respectively. The X-ray diffraction (XRD) analysis show that all the grown ZnO nanorods have a hexagonal wurtzite structure and are preferentially oriented along the c-axis perpendicular to the substrate surface. At 3 at% Fe-doping, the crystalline quality and the preferential orientation of ZnO nanorods are improved and below 3 at% Fe-doping concentration crystalline quality and the preferential orientation of ZnO nanorods is weakened in turn. The surface morphology analysis of the samples show that the ZnO nanorods are grown vertically to the substrate surface and highly interconnected. Such interconnected network will facilitates the electron transport along the nanorods axis. Current-voltage and current-time characterization under the exposure of UV light ON/OFF sates with exhibited excellent current gain of 1.12 and good response/recovery time of 30 and 10 s showed that the fabricated device can be used for UV sensing applications.

Scandium and gadolinium co-doped BaTiO3 nanoparticles and ceramics prepared by sol–gel–hydrothermal method: Facile synthesis, structural characterization and enhancement of electrical properties

A facile sol–gel–hydrothermal process was used to synthesize Scandium and Gadolinium co-doped BaTiO3 nanocrystals in this paper. Similar to the previous studies, a single-phase solid-solution structure is hard to achieve for BaTiO3 materials doped with rare-earth ions like Sc- and Gd- via solid-state method. Here, uniform Ba1−xTi1−xGdxScxO3 (0≤x≤0.04) nanoparticles (NPs) with single-phase solid-solution cubic structure and average particle size of 30–40nm were obtained and Ba1−xTi1−xGdxScxO3 pellets prepared from as-synthesized nanopowders can be sintered at a lower temperature of 1150°C. The internal structures, chemical constitution and morphology were characterized by FT-IR spectra, XRD, TEM, HRTEM, Raman spectra and SEM analysis. The results clearly demonstrated that Sc3+ and Gd3+ have entered into the BaTiO3 lattice and led to structural distortion in a short range and all samples were single-phase tetragonal structure at room temperature. Additionally, the dielectric temperature stability was enhanced with Sc3+ and Gd3+ as dopants, since the single-phase BaTiO3 ceramics exhibited broadened dielectric peaks, decline of Curie temperature as well as low dielectric loss below 0.02. Ceramics containing 3mol% Sc3+ and Gd3+ can exhibit the best dielectric behaviour of εr ~1700 and Tc=32°C in this work.

Ultraviolet radiation detection by barium titanate thin films grown by sol–gel hydrothermal method

Ultraviolet (UV) photodetector using ferroelectric barium titanate, BaTiO3 thin film has been prepared successfully. BaTiO3 (BTO) this film is deposited by sol–gel hydrothermal (SG-HT) method. The deposited BTO films were found to be polycrystalline having a band gap of about 3.51eV. The photoconductive gain (K=Ion/Ioff) of bare BTO based photodetector was found to be 8.36×102 for UV radiation (λ=365nm and intensity=24μW/cm2). The modifier, tungsten (W) in the form of both thin overlayer and uniformly distributed circular dotted structures (600μm diameter) were integrated with the surface of BTO thin film by rf-magnetron sputtering technique to improve the photoresponse characteristics. The photoconductive gain was enhanced to about two orders of magnitude (1.84×104) after integration of W modifier in the form of circular dots. The significant enhancement in photoresponse for W(dots)/BTO photodetector is related to the twin effect of (1) reduction in dark current (Ioff) due to formation of schottky junction between the oxide (BTO) and metal (W), and (2) enhancement in photocurrent (Ion) due to high absorption of UV radiation on the detector surface.

Photooxidative–extractive deep desulfurization of diesel using Cu–Fe/TiO2 and eutectic ionic liquid

Abstract An efficient photooxidative–extractive system for deep desulfurization of model fuel and actual diesel fuel was explored. A series of bimetallic Cu–Fe/TiO2 photocatalysts was synthesized using sol–gel hydrothermal method and characterized using thermogravimetric analysis (TGA), X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) coupled with energy dispersive X-ray analysis (EDX), high resolution transmission electron microscopy (HRTEM) and diffuse reflectance UV–visible spectroscopy (DR-UV–Vis). The photocatalysts were evaluated for photooxidative–extractive deep desulfurization of model oil (100, 300 and 500 ppm dibenzothiophene in dodecane) and actual diesel fuel. 2.0 wt% Cu–Fe/TiO2 photocatalyst was identified as the most efficient photocatalyst for the conversion of sulfur species under mild conditions in the presence of hydrogen peroxide (H2O2:S molar ratio of 4) as oxidant and eutectic based ionic liquid as extractant. The sulfur conversion in both model oil and actual diesel fuel reached 100%. The removal of sulfur species from both model oil and actual diesel fuel was done by two times extraction with a removal of 97.06% and 78.93%, respectively in the first run and 2.94% and 21.07%, respectively in the second run. The photocatalyst was able to be recycled for six cycles with an average performance of 99.75%.

SnO₂(β-Bi₂O₃)/Bi₂Sn₂O₇ nanohybrids doped with Pt and Pd nanoparticles: applications in visible light photocatalysis, electrical conductivity and dye-sensitized solar cells.

Bi2O3-SnO2 nanocomposites formed at a nominal molar ratio of 3 : 1 and loaded with Pd/Pt nanoparticles synthesized by a sol gel-hydrothermal method with the aid of a template were thoroughly characterized by X-ray diffraction, TEM-EDX, N2 sorptiometry, diffuse reflectance UV-Vis, FTIR, photoluminescence and electrical conductivity. It has been shown that Pd and Pt stimulate the existence of β-Bi2O3 and SnO2, respectively together with the key component Bi2Sn2O7. The photocatalytic results indicate that Pd/β-Bi2O3-Bi2Sn2O7 revealed a remarkable performance for the degradation of methylene blue (MB) dye as compared to the Pt/SnO2-Bi2Sn2O7 and Bi2O3-SnO2 samples in both the UV and visible regions. The enhanced photocatalytic activity of the Pd/β-Bi2O3-Bi2Sn2O7 nanocomposite is primarily attributed to the broad contact between the β-Bi2O3 and Bi2Sn2O7 phases, which indicates high mesoporosity and heterojunction structures resulting in separation efficacy between photo-induced electron-hole pairs. Specifically, the photosensitive β-Bi2O3 is easily excited and released electrons to be accepted by Bi2Sn2O7 and Pd that might be deposited in the interlayer between β-Bi2O3 and Bi2Sn2O7. The degradation mechanism of MB over Pd/β-Bi2O3-Bi2Sn2O7 in the visible region showed that the dye degradation proceeds through evolution of ˙O2(-) and ˙OH radicals as evaluated using photoluminescence and free radical trapping experiments. An insight into the electrical properties including the dielectric constant and impedance of the materials indicates that Pd/β-Bi2O3-Bi2Sn2O7 has the highest conductivity based on increasing the ionic transport and defects at the β-Bi2O3/Bi2Sn2O7 heterojunction. This material displayed an improved photocurrent response of a higher power conversion efficiency, exceeding that of Pt/SnO2-Bi2Sn2O7 and SnBi3 by 50% and 250%, respectively, in dye-sensitized solar cells. Picosecond-resolved photoluminescence (PL) and polarization gated PL anisotropy measurements were combined to clarify the process of FRET from the excited Pd/β-Bi2O3-Bi2Sn2O7 to SD N719. This indicates that the latter structure can be proposed as a multifunctional candidate for use in dye-sensitized solar cells, as an electrical material and as an efficient photocatalyst based on its versatile structure.

Sol–gel hydrothermal synthesis of microstructured CaO-based adsorbents for CO2capture

A novel 3D hierarchical CaCO3hollow microspherical adsorbent composed of 1D spike-shaped nanorods was synthesized by a sol–gel hydrothermal method for CO2capture.

Comparative Studies of Multiferroic BiFeO<sub>3</sub> Powders Prepared by Hydrothermal Method versus Sol-Gel Process

Multiferroic BiFeO3 powders were synthesized by two methods: sol-gel process and hydrothermal method. The synthesized powders were characterized by X-ray diffraction (XRD), field emission scanning electron microscope (SEM) and particle size distribution analysis. The results obtained by XRD, which is consistent with 86-1518 JCPDS card, show that powders prepared by hydrothermal method are composed of the single phase with the trigonal structure (perovskite-type). It can be found by particle size distribution analysis that the particle size of the samples prepared by sol-gel process is finer and more uniform than that of the samples synthesized by the hydrothermal method. The SEM images of samples depicts that the synthesized BiFeO3 powders are united and the average grain size of hydrothermal processed samples is significantly large as compared to the sol-gel derived sample.

Effect of H3PW12O40 impregnation on Sn-MCM-41 mesoporous molecular sieves and their physico-chemical properties

Si-Sn-MCM-41 (Si/Sn=110) mesoporous molecular sieve was synthesized by hydrothermal sol–gel method using cetyltrimethylammonium bromide (CTAB) as surfactant and SnCl4·5H2O as a metal source. To generate surface acidity of Si-Sn-MCM-41, 12-tungstophosphoric acid (HPWA) is impregnated on it. The acidity of HPWA loading on Sn-MCM-41 was investigated by temperature programmed desorption of NH3. The diffused reflectance spectra of ultraviolet radiation, Raman spectra, FT-IR, 29Si-MAS NMR and 31P-MAS NMR techniques revealed the intact of α-Keggin anions on Sn-MCM-41. The wide angle XRD results showed that the HPWA is well dispersed on the support. The total acidity was enhanced with increase in loading of H3PW12O40. The catalytic activity was examined in desulfurization of dibenzothiophene in vapor phase system. Among the catalysts 18% HPWA loaded Sn-MCM-41 showed good catalytic activity in desulfurization at 325°C. The HPWA/Sn-MCM-41 are a suitable solid acid catalyst for converting organic sulfur into insoluble sulfone.

Graphene-supported CoPc/TiO2 synthesized by sol-gel–hydrothermal method with enhanced photocatalytic activity for degradation of the typical gas of landfill exhaust

This work was focused on the enhanced photocatalytic activity of cobalt phthalocyanine (CoPc)/TiO2 under visible light irradiation supported on reduced graphene oxide (RGO). A series of RGO/CoPc/TiO2 nanocomposites were synthesized via sol-gel–hydrothermal method. The photocatalysts were characterized by X-ray diffraction, BET surface area, Scanning electron microscopy, Raman spectra, Fourier transform infrared spectra, UV–Vis spectra and Photoluminescence spectra. The results demonstrated that the TiO2 existed as anatase phase both of CoPc/TiO2 and RGO/CoPc/TiO2 composites, and the absorption range in visible light of RGO/CoPc/TiO2 composites were broadened further. The photodegradation results of diethyl sulfide, the typical gas of landfill exhaust, under visible light revealed that RGO/CoPc/TiO2 nanocomposites exhibited much higher photocatalytic activity than CoPc/TiO2 and pure TiO2, indicating the ideal amount of RGO was 7.5wt.%, the optimal amount of 7.5% RGO/CoPc/TiO2 composite on each plat was 0.3g and the degradation efficiency of diethyl sulfide was about 90%.Implications: Over the past decades, air pollution has become more and more serious, many countries have reported that the complaints of odor problems related to urban garbage and industry are increasing. This study is beneficial for the exhaust governance of some landfills. Moreover, the process doesn’t involve any expensive oxidizing chemicals and can be performed under normal conditions of temperature and pressure.

Exploring the Origin of Enhanced Activity and Reaction Pathway for Photocatalytic H2 Production on Au/B-TiO2 Catalysts

Gold-embedded boron-doped TiO2 (Au/B-TiO2) photocatalysts were synthesized by a sol–gel hydrothermal method. The TEM images display that the gold nanoparticles were embedded into the B-TiO2 framework. Hydrogen evolution under light irradiation showed that doping of boron into TiO2 enhanced the photocatalytic activity. A further remarkable improvement of the activity was observed over the Au/B-TiO2. Evidenced by B 1s XPS and 11B MAS NMR spectra, the embedment of Au nanoparticles contributes to the formation of more interstitial boron species in B-TiO2. In turn, it gives rise to surface or near-surface states facilitating the embedment of Au nanoparticles, as demonstrated by the Au 4f XPS spectra, which indicates the strong interaction between gold and the B-TiO2 framework. This specific synergy significantly contributes to the enhancement of photocatalytic activity. For the first time, the isotopic tracer studies using a gas chromatograph isotope ratio mass spectrometer along with a series of control experiments reveal that the produced hydrogen originated mainly from water rather than methanol, whereas the direct oxidation of methanol did not lead to hydrogen generation. Acting as a sacrificial reagent, methanol could be oxidized to formaldehyde by protons/water under oxygen-free conditions.

Performance of TiO<sub>2</sub> Nanoparticles Synthesized at pH 2 as Photoelectrode in Dye Solar Cell

Nanocrystalline TiO2 was prepared using sol-gel hydrothermal method to be used as photoelectrode material for dye solar cells (DSC) employing continuous stirring of titanium tetrachloride (TiCl4) with hydrochloric acid (HCl) and deionized water at 70 oC for 6 hours. TiO2 nanopowder was obtained after calcinations in air at 400 oC. The samples were characterized using FESEM, TEM, XRD, BET and UV-Vis optical absorption. This paper discusses the effect of surfactant on the physicochemical properties and the efficiency of the synthesized TiO2 photoelectrode to convert light into electricity.

Monodisperse hollow perovskite BaTiO3 nanostructures prepared by a sol–gel–hydrothermal method

A sol–gel–hydrothermal method was developed to prepare single-crystal BaTiO3 (BT) hollow nanoparticles, where acetylacetone (acac) was used as a modifier in TiO2 sol. The products were characterized by XRD, Raman spectroscopy, SEM, TEM and Nitrogen adsorption. The results show that the monodisperse hollow BT nanoparticles have an average size about 86.7nm in diameter. Based on the results of the time-dependent experiment, a possible formation mechanism was proposed, which involves a pathway that is an aggregation–realignment–fusion process. The synthesized approach and the proposed growth mechanism could provide new insights into the designing and controlled preparation of hollow architectures of other perovskite oxides.

Shape control of nanostructured TiO2 using a Schiff base ligand via sol–gel hydrothermal method

Employing a Schiff base ligand in a hydrothermal sol–gel method for preparation of TiO2 nanostructures was studied. The as-prepared products were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectrum, electron dispersive X-ray spectroscopy and ultraviolet–visible spectroscopy. It is shown that in the controlled reaction conditions, a Schiff base ligand containing hard atoms is capable of driving the growth mechanism in a way that anisotropic shapes of TiO2 nanostructures are formed. Considering the structure of the Schiff base ligand, the possible growth mechanism of TiO2 nanostructures is proposed. The optical studied as well as calculated molecular orbital structure of ligand by density functional theory is done.

Ultraviolet Radiation Detection by Barium Titanate Thin Films Grown by Sol-gel Hydrothermal Method

Ferroelectric Barium titanate, BaTiO 3 (BTO) thin film has been prepared successfully by sol-gel hydrothermal method (SG-HT) which combines the basic sol-gel process with hydrothermal treatment. High resolution X-ray diffraction (HR-XRD) study reveals single phase polycrystalline tetragonal structure of the prepared BTO thin film. Optical properties were studied using UV- Visible spectroscopy and band gap was found to be 3.51 eV. The I–V characteristics revealed a low dark current (I off ) of 6.07 × 10 -9 A for the prepared BTO thin film which increases to 4.06 × 10 -6 A (I on ) by almost three orders of magnitude when illuminated with UV radiation (λ = 365 nm, Intensity = 24 μW/cm 2 ). The photoconductive gain (K = I on /I off ), was found to be 6.7 × 10 2 . It can be clearly seen that the prepared BTO film can be utilized as an efficient Ultraviolet photodetector.