Single-step Sol Gel Method Research Articles

A novel WO3/MoS2 photocatalyst applied to the decolorization of the textile dye Reactive Blue 198

A novel FTO/WO3 electrode decorated with MoS2 was constructed using two simple and low-cost techniques involving a modified single-step sol-gel method for the WO3 film together with the electrodeposition of amorphous MoS2. The photoelectrocatalytic performance of the material was investigated by monitoring the degradation of Reactive Blue 198 dye under visible-light irradiation. The FTO/WO3/MoS2 electrode exhibited excellent photocatalytic activity and afforded total decolorization of the dye after 90 min at low applied current density (5 mA cm−2). The results described herein support the view that MoS2 acts as a noble metal-free cocatalyst by promoting H2 evolution and assisting in the suppression of electron/hole pair recombination in the photocatalytic material (WO3), thereby improving the process of decolorization of the dye solution. The novel approach of combining of the WO3 and MoS2 materials shows particular promise and may prove to be very effective in the photocatalytic degradation of other hazardous organic compounds.

Poisoning effect of CaO on CeO2/TiO2 catalysts for selective catalytic reduction of NO with NH3

The effect of CaO on CeO2/TiO2 catalysts prepared by a single step sol-gel method for selective catalytic reduction of NO with NH3 was investigated. The results showed that CaO could severely deactivate the CeO2/TiO2 catalysts. Based on the characterization results obtained by BET, XRD, XPS, H2-TPR and NH3-TPD, the deactivation by CaO of CeO2/TiO2 catalysts should be attributed to pore blockage, lower concentration of Ce on catalyst surface, reduction of Ce3+ and surface adsorbed oxygen, degradation of redox ability and decrease in NH3 adsorption capacity. The theoretical DFT results demonstrated that Ca atom could strongly interact with cerium oxygen, which inhibits the formation and hydrogenation of oxygen vacancies on catalyst surface.

Preparation and Characterization of CeO2-MoO3/TiO2 Catalysts for Selective Catalytic Reduction of NO with NH3

ABSTRACTCeO2-MoO3/TiO2 catalysts were prepared by three methods: a single step sol-gel (SG), impregnation (IM) and coprecipitation (CP) method. These catalysts were investigated for selective catalytic reduction (SCR) of NO with NH3. The results indicate that the catalyst prepared by the SG method possessed the widest temperature window (about 250–475°C), best SCR activity below 450°C and resistance against 10% H2O and 1000 ppm SO2 at a gas hourly space velocity (GHSV) of 90,000 h–1. According to the results of BET, XRD, XPS, H2-TPR and TEM, it is found that larger BET surface area, more highly dispersed active species of Ce and Mo, presence of more Ce3+ and chemisorbed oxygen, synergistic effect among ceria, molybdenum and titania, and better redox ability can contribute to the better deNOx performance of the CeO2-MoO3/TiO2 catalyst prepared by the SG method, compared with those by the IM and CP methods.

One step synthesis and characterization of copper doped sulfated titania and its enhanced photocatalytic activity in visible light by degradation of methyl orange

This paper reports on the synthesis of copper doped sulfated titania nano-crystalline powders with varying (2.0%–10.0%, by mass) by single step sol gel method. The synthesized photo catalyst has been characterized by employing various techniques like X-ray Diffraction (XRD), Ultraviolet–Visible Diffuse Reflection Spectroscopy (UV–Vis DRS), X-ray Photoelectron Spectroscopy (XPS), Scanning Electron Microscopy (SEM), Energy Dispersive Spectrometry (EDS), Fourier Transform Infrared Spectroscopic Studies (FT-IR), and Transmission Electron Microscopy (TEM). From the XRD and TEM results, all the samples were reported in anatase phase with reduction in particle size in the range of 7 to 12nm. SEM indicated the change in morphology of the particles. The presence of copper in titania lattice was evidenced by XPS. From UV–Vis DRS and FT-IR studies indicated that prominent absorption shift is observed towards visible region (red shift), the entry of Cu2+ into TiO2 lattice as a substitutional dopant and SO42− ions were covalently bonded with Ti4+ on the surface of the copper doped titania respectively.The photocatalytic activity studies were investigated by considering methyl orange (MO) as dye pollutant in the presence of the visible light. The effect of various parameters like effect of dosage of the catalyst, dopant concentration, pH of the solution, and concentration of the dye was studied in detail.

MoO3 modified CeO2/TiO2 catalyst prepared by a single step sol–gel method for selective catalytic reduction of NO with NH3

A MoO3 modified CeO2/TiO2 catalyst was prepared by a single step sol–gel method for selective catalytic reduction of NO with NH3. The experimental results indicates that MoO3 modified CeO2/TiO2 catalyst exhibited higher SCR activity and resistance to 10% H2O and 1000ppm SO2. From the characterization results, it can be concluded that good physical properties, highly dispersed active species of Ce and Mo, more appearance of Ce3+ and chemisorbed oxygen, strong interaction among ceria, molybdenum and titania, and high oxygen storage capacity might contribute to the excellent deNOx performance of CeO2–MoO3/TiO2 catalyst prepared by a single step sol–gel method.

Synthesis of PbS–Al2O3 nanocomposites by sol–gel process and studies on their optical properties

PbS–Al2O3 nanocomposites were prepared by a single step sol–gel method starting from lead acetate, thiourea and aluminium isopropoxide. The crystallinity, shape of crystallites and optical properties of the nanocomposites were examined by various analytical techniques. X-ray diffraction indicates that the PbS–Al2O3 nanocomposites consist of small PbS crystallites (18.2–40.5nm). Transmission electron microscopy images show cube-like and flake-like morphology for pure PbS and Al2O3, respectively and TEM images of the nanocomposites indicate uniform distribution of PbS nanoparticles on the Al2O3 matrix. Diffuse reflectance spectral (DRS) studies on the nanocomposites indicate near infrared (NIR) absorption and the nanocomposites exhibit blue shift of the band gap of PbS compared to pure PbS nanoparticles. Photoluminescence studies show characteristic peak due to excitonic emission of PbS nanoparticles in the nanocomposites.

Activity and characterization of a Ce–W–Ti oxide catalyst prepared by a single step sol–gel method for selective catalytic reduction of NO with NH3

A Ce–W–Ti mixed oxide catalyst prepared by a single step sol–gel method exhibited excellent SCR activity and high resistance to H2O and SO2. The excellent catalytic performance might be attributed to the improved dispersion of Ce species on TiO2, the increase in the amount of Ce3+ and chemisorbed oxygen and the strong interaction among ceria, tungsten and titania owing to the addition of WO3.

Synthesis of mesoporous Ag/ZnO nanocrystals with enhanced photocatalytic activity

Mesoporous Ag/ZnO nanocrystals have been successfully synthesized at different Ag contents (0–10wt%) through a single-step sol–gel method in presence of triblock copolymer as a structure directing agent. The as-prepared hybrid materials were calcined at 450°C in air for 4h, subsequently, Ag nanoparticles have been photo-reduced from AgNO3 onto mesopores ZnO nanocyrstals. The XRD and Raman analysis revealed that well crystalline ZnO hexagonal wurtzite phase and face-centered cubic metallic Ag nanoparticles were formed. TEM images of mesoporous ZnO nanocrystals showed that synthesized materials composed of discrete ZnO nanoparticles agglomerated with worm-like mesoporous structure. The lattice fringes exhibit the typical distances, i.e., Ag(111) and ZnO(100) and the average Ag and ZnO nanoparticle diameters are ∼5 and 10nm, respectively. The photocatalytic performance of different prepared photocatalysts was evaluated by degradation of methylene blue (MB) under visible light irradiation. The results indicate that the photocatalytic efficiencies of mesoporous ZnO photocatalysts were remarkably enhanced by adding 1% Ag nanoparticles which completely degrade the target MB dye within 150min. The photodegradation rate was found to increase linearly with increasing the Ag contents from 0 to 1% and it is faster 2.2 times than undoped ZnO. From economic point of view, 1% Ag/ZnO photocatalyst contains optimum Ag content as there is no significant increase in the photocalatytic performance at higher Ag content.

Single-Step Synthesis of Silver-Doped Titanium Dioxide: Influence of Silver on Structural, Textural, and Photocatalytic Properties

The silver-doped titanium dioxide (Ag–TiO2) photocatalysts with varied silver content ranging from 0.75 at % to 3.5 at % were synthesized by a single-step sol–gel method. The role of silver content on the properties of photocatalyst has been studied. The doping of 0.75 at % silver in TiO2 produced thermally stable TiO2 anatase phase with smallest particle size, uniform particles size and morphology, high surface area and low-energy excitation characteristics. The Ag–TiO2 sample with 0.75 at % silver possesses predominantly finely dispersed silver species (Ag2O and AgO) on the surface. The proportion of surface agglomerated silver metal (Ag0) increases as the silver content in the Ag–TiO2 sample increases. The silver oxide species were observed to be responsible for better physicochemical and catalytic properties. The TiO2 with 0.75 at % silver was found to be an efficient photocatalyst showing enhanced photocatalytic activity for aqueous medium photocatalytic degradation of phthalic acid in the presence of UV radiation and air.

Low-temperature selective catalytic reduction of NO on CeO2–CuO/Al2O3 catalysts prepared by different methods

CeO2–CuO/Al2O3 catalysts were prepared by three different methods and their activities for selective catalytic reduction (SCR) of NO with NH3 were investigated. As can be seen from the experimental results, the catalyst prepared by the single-step sol–gel (SG) method showed the best SCR activity and resistance to SO2 and H2O. In order to investigate the relationship between the preparation method and the performance of SCR catalysts, the catalysts were characterized by using Brunauer–Emmett–Teller, X-ray diffraction, temperature programmed reduction with hydrogen, temperature programmed desorption with ammonia, X-ray photoelectron spectroscopy, Fourier transform infrared and thermo-gravimetric analysis techniques. It was found that the excellent performance of CeO2–CuO/Al2O3 catalyst prepared by the single-step SG method should be resulted from its large surface area, low crystallinity, high oxygen storage capacity, high NH3 adsorption capacity, high concentration of surface chemisorbed oxygen, weak sulphation process and weak water absorption.

Photocatalytic reduction of carbon dioxide with water vapors over montmorillonite modified TiO2 nanocomposites

Montmorillonite (MMT) modified TiO2 nanocomposites were synthesized by single step sol–gel method. The samples were characterized by XRD, FE-SEM, HR-TEM, FT-IR, N2-adsorption–desorption, UV–vis and photoluminescence (PL) spectroscopy. Modification of TiO2 with MMT controlled the crystal growth and produced anatase phase of delaminated TiO2 pillared montmorillonite. The size of TiO2 nanoparticles reduced from 18.73 to 13.87nm after adding MMT, while the surface area and pore volume increased. The UV–vis results identified blue shift in TiO2 band gap for the MMT modified samples. In addition, PL spectroscopy revealed significant inhibition in recombination of photogenerated electron–hole pairs. The performance of MMT modified TiO2 samples for reducing CO2 with H2O to hydrocarbon fuels was investigated. The effects of parameters such as MMT loading on TiO2, H2O/CO2 feed ratios, and reaction temperature on TiO2 photocatalytic activity was studied. Loading MMT on TiO2 enhanced the performance of TiO2 and markedly increased CO2 reduction to C1–C3 hydrocarbon fuels. The highest yield rates produced were 441.5 and 103μmolgcat−1h−1 for CH4 and CO, respectively under UV light irradiations at 20wt.% MMT loading, reactor pressure of 0.20 bars and 393K reaction temperature. These results revealed silicate layers of MMT dispersed in the given TiO2 sol system and vacant d-orbits of the MMT transition metal ions have obvious effect on the photocatalytic activity of TiO2. The possible pathways and reaction mechanisms of CH4 and CO productions were also suggested. Thus, MMT is a potentially attractive material to improve TiO2 as a photocatalyst for application in photocatalytic CO2 reduction.

Effect of preparation methods on the performance of CeO2/Al2O3 catalysts for selective catalytic reduction of NO with NH3

CeO2/Al2O3 catalysts prepared by three methods were investigated for selective reduction of NO with NH3. It was found that the catalyst prepared by the single step sol–gel method had the best SCR activity and SO2 resistance performance. From the results of BET, XRD, TPD and TPR, it can be concluded that large surface area, strong interaction, highly dispersed nano-crystalline ceria, high NH3 adsorption capacity and good redox ability might be the main reasons for the excellent performance of CeO2/Al2O3 catalyst prepared by the single step sol–gel method.

Methanation of carbon dioxide over mesoporous Ni–Fe–Ru–Al2O3 xerogel catalysts: Effect of ruthenium content

Mesoporous nickel (35wt%)–iron (5wt%)–ruthenium (x wt%)–alumina xerogel (denoted as 35Ni5FexRuAX) catalysts with different ruthenium contents (x=0, 0.2, 0.4, 0.6, 0.8, and 1.0) were prepared by a single-step sol–gel method for use in the methane production from CO2 and H2. Conversion of CO2, yield for CH4, metal surface area, and the amount of desorbed carbon dioxide of the catalysts showed volcano-shaped trends with respect to ruthenium content. Experimental results revealed that metal surface area and the amount of desorbed carbon dioxide of 35Ni5FexRu catalysts were well correlated with conversion of CO2 and yield for CH4.

Hydrogenation of CO to Methane Over Mesoporous Nickel–Iron–Alumina Xerogel Nano-Catalysts

Mesoporous nickel-iron-alumina xerogel ((40-x)Ni(x)FeAX) nano-catalysts with different iron content (x = 0, 2.5, 5, 7.5, and 10) were prepared by a single-step sol-gel method for use in the methane production from carbon monoxide and hydrogen. The effect of iron content on the catalytic performance of (40-x)Ni(x)FeAX catalysts was investigated. In the methanation reaction, yield for CH4 decreased in the order of 35Ni5FeAX > 32.5Ni7.5FeAX > 30Ni10FeAX > 37.5Ni2.5FeAX > 40Ni0FeAX. This indicated that optimal iron content of mesoporous nickel-iron-alumina xerogel nano-catalyst was required for maximum production of CH4 in the methanation reaction. Experimental results revealed that optimal CO dissociation energy and large H2 adsorption ability of the catalyst were favorable for methane production. Among the catalysts tested, 35Ni5FeAX catalyst, which retained the most optimal CO dissociation energy and the largest H2 adsorption ability, exhibited the best catalytic performance in terms of conversion of CO and yield for CH4 in the methanation reaction. CO dissociation energy and H2 adsorption ability of the catalyst played a key role in determining the catalytic performance of (40-x)Ni(x)FeAX in the methanation reaction.

Methanation of Carbon Dioxide Over Mesoporous Nickel–M–Alumina (M = Fe, Zr, Ni, Y, and Mg) Xerogel Catalysts: Effect of Second Metal

Mesoporous nickel (35 wt%)–M (5 wt%)–alumina xerogel (denoted as 35Ni5MAX) catalysts with different second metal (M = Fe, Zr, Ni, Y, and Mg) were prepared by a single-step sol–gel method for use in the methane production from carbon dioxide and hydrogen. In the carbon dioxide methanation reaction, yield for CH4 decreased in the order of 35Ni5FeAX > 35Ni5ZrAX > 35Ni5NiAX > 35Ni5YAX > 35Ni5MgAX. This indicated that the catalytic performance was greatly influenced by the identity of second metal in the carbon dioxide methanation reaction. Experimental results revealed that CO dissociation energy and metal-support interaction of the catalyst played key roles in determining the catalytic performance of 35Ni5MAX catalysts in the reaction. Among the catalysts tested, 35Ni5FeAX catalyst, which retained the most optimal CO dissociation energy and the weakest metal-support interaction, exhibited the best catalytic performance in terms of conversion of CO2 and yield for CH4. In the carbon dioxide methanation over mesoporous nickel–M–alumina xerogel catalysts with different second metal (M = Fe, Zr, Ni, Y, and Mg), yield for CH4 increased with decreasing TPSR peak temperature and with decreasing metal-support interaction of the catalyst.

Direct synthesis of dimethyl carbonate from methanol and carbon dioxide over Ga2O3-CeO2-ZrO2 catalysts prepared by a single-step sol-gel method: Effect of acidity and basicity of the catalysts

XGa2O3-CeO2-ZrO2 (X=0, 1, 3, 5, 7, and 9) catalysts were prepared by a single-step sol-gel method with a variation of Ga2O3 content (X, wt%) for use in the direct synthesis of dimethyl carbonate from methanol and carbon dioxide. The ratio of cerium oxide:zirconium oxide in the XGa2O3-CeO2-ZrO2 catalysts was fixed to be Ce0.6Zr0.4O2. Effect of acidity and basicity of XGa2O3-CeO2-ZrO2 on the catalytic performance in the direct synthesis of dimethyl carbonate from methanol and carbon dioxide was investigated using NH3-TPD and CO2-TPD experiments, respectively. Experimental results revealed that both acidity and basicity of the catalysts played important roles in determining the catalytic performance in the reaction. The amount of dimethyl carbonate increased with increasing both acidity and basicity of the catalyst. Among the catalysts tested, 3Ga2O3-CeO2-ZrO2, which retained the largest acidity and basicity, exhibited the best catalytic performance in the direct synthesis of dimethyl carbonate from methanol and carbon dioxide.

Impact of Pt loading methods over mesoporous-assembled TiO2–ZrO2 mixed oxide nanocrystal on photocatalytic dye-sensitized H2 production activity

In this work, the photocatalytic water splitting under visible light irradiation for hydrogen production was investigated by using Eosin Y-sensitized Pt-loaded mesoporous-assembled TiO2–ZrO2 mixed oxide nanocrystal photocatalysts. The mesoporous-assembled TiO2–ZrO2 mixed oxide with the TiO2-to-ZrO2 molar ratio of 95:5 (i.e. 0.95TiO2–0.05ZrO2) was synthesized by using a sol–gel process with the aid of a structure-directing surfactant. The Pt loading was comparatively performed via two different effective methods: single-step sol–gel (SSSG) and photochemical deposition (PCD). The synthesized photocatalysts were methodically characterized by N2 adsorption–desorption, XRD, UV–visible spectroscopy, SEM–EDX, TEM–EDX, TPR, and H2 chemisorption analyses. The results revealed that the Pt loading by the PCD method greatly enhanced the photocatalytic hydrogen production activity of the synthesized mesoporous-assembled 0.95TiO2–0.05ZrO2 mixed oxide photocatalyst more than that by the SSSG method. The optimum Pt loading by the PCD method was experimentally observed at 0.5wt.%, which was well associated with the maximum Pt dispersion. In addition, the PCD conditions, i.e. UV light irradiation time and UV light intensity, were investigated and optimized to be 2h and 44W, respectively.

Influence of temperature on structural and magnetic properties of Co0·5Mn0·5Fe2O4 ferrites

Co0·5Mn0·5Fe2O4 ferrites have been synthesized using a single-step sol-gel auto-combustion method in which the metal nitrate (MN)-to-citric acid (CA) ratio was adjusted to 0.5: 1 and pH to 7, respectively. The structural and magnetic properties of as-burnt and annealed samples were studied as a function of temperature. The inverse spinel structure was confirmed by X-ray diffraction (XRD) and crystallite size was estimated by the most intense peak (311) using Scherrer’s formula. Contrary to earlier studies reported in the literature, both as-burnt and annealed samples exhibit crystalline behaviour. Room temperature magnetic properties were studied using vibrating sample magnetometer (VSM) with field strengths up to ±10 kOe. Lattice constant and crystallite size increased as the annealing temperature was increased. However, the coercivity (H c) initially increased and then decreased with the increase of crystallite size. The variation in coercivity is ascribed to the transition from a multi-domain to a single-domain configuration.

Hydrogenation of carbon monoxide to methane over mesoporous nickel-M-alumina (M = Fe, Ni, Co, Ce, and La) xerogel catalysts

Mesoporous nickel(30 wt%)-M(10 wt%)-alumina xerogel (30Ni10MAX) catalysts with different second metal (M = Fe, Ni, Co, Ce, and La) were prepared by a single-step sol–gel method for use in the methane production from carbon monoxide and hydrogen. In the methanation reaction, yield for CH 4 decreased in the order of 30Ni10FeAX > 30Ni10NiAX > 30Ni10CoAX > 30Ni10CeAX > 30Ni10LaAX. Experimental results revealed that CO dissociation energy of the catalyst and H 2 adsorption ability of the catalyst played a key role in determining the catalytic performance of 30Ni10MAX catalyst in the methanation reaction. Optimal CO dissociation energy of the catalyst and large H 2 adsorption ability of the catalyst were favorable for methane production. Among the catalysts tested, 30Ni10FeAX catalyst with the most optimal CO dissociation energy and the largest H 2 adsorption ability exhibited the best catalytic performance in terms of conversion of CO and yield for CH 4 in the methanation reaction. The enhanced catalytic performance of 30Ni10FeAX was also due to a formation of nickel–iron alloy and a facile reduction.

Hydrogen production by steam reforming of liquefied natural gas (LNG) over mesoporous Ni–La–Al 2O 3 aerogel catalysts: Effect of La content

Mesoporous Ni–La–Al 2O 3 aerogel catalysts (denoted as (40- x)Ni xLa) with different lanthanum content ( x) were prepared by a single-step sol-gel method and a subsequent CO 2 supercritical drying method. The effect of lanthanum content on the physicochemical properties and catalytic performance of mesoporous (40- x)Ni xLa catalysts in the steam reforming of liquefied natural gas (LNG) was investigated. Physicochemical properties of (40- x)Ni xLa catalysts were strongly influenced by lanthanum content. Dispersion and reducibility of nickel aluminate phase in the (40- x)Ni xLa catalysts increased with increasing lanthanum content. Small amount of lanthanum addition was effective for dispersion of metallic nickel in the (40- x)Ni xLa catalysts, but large amount of lanthanum addition was not favorable for nickel dispersion due to the blocking of active sites. In the steam reforming of LNG, both LNG conversion and hydrogen yield showed volcano-shaped curves with respect to lanthanum content. Average nickel diameter of (40- x)Ni xLa catalysts was well correlated with LNG conversion and hydrogen yield over the catalysts. Among the catalysts tested, 36Ni4La (36 wt% Ni and 4 wt% La) catalyst with the smallest average nickel diameter exhibited the best catalytic performance and the strongest resistance toward carbon deposition in the steam reforming of LNG.