Mixed Oxide Nanocomposites Research Articles

Microwave assisted synthesis of polycinnamamide Mg/Al mixed oxide nanocomposite and its application towards the removal of arsenate from aqueous medium

Microwave assisted synthesis of polycinnamamide Mg/Al mixed oxide nanocomposite was carried out and its ability for the removal of arsenate from water through adsorption has been investigated in the present study. Characterization of the nanocomposite was made by FE-SEM, EDX, TGA/DSC, FTIR, XRD and elemental analysis (CHNS) techniques. The effect of various parameters viz. contact time, pH (6–12), initial arsenate concentration (1–50mg/l), interfering anions, etc. has been investigated to determine the adsorption capacity of PCMA. Adsorption kinetic study showed that the adsorption process followed the first order kinetics and the data revealed that the uptake rate of arsenate was rapid at the beginning and equilibrium was established after 60min. The Lagergren rate constants and intraparticle diffusion rate constant (at 25°C) were found to be 0.069 and 0.41 respectively. The maximum adsorption capacity calculated from Langmuir isotherm model was found to be 11.54mg/g at 25°C. The mean free energies calculated from D.R. adsorption isotherm were found to be 15.2, 15.5 and 15.8kJmol−1 at 25, 35 and 45°C respectively. Thermodynamic study indicated an endothermic nature of the adsorption and a spontaneous and favorable process. The interfering anions reduced the arsenate adsorption in the order of, carbonate>bicarbonate>phosphate>chloride>sulfate>nitrate.

The Growth and Gas Sensing Properties of Mixed Oxide Nanocomposite Thin Film Derived from Anodically Oxidized Al/Ti Metal Layers

Abstract A method is described for forming nanostructured thin solid films consisting of regularly mixed titanium-aluminium oxide nanocomposites, with the self-organized root-like inner and column-like outer structures, derived from anodically oxidized Al/Ti bilayers sputter-deposited onto oxidized silicon wafers. The morphology, crystal structure and phase composition of the anodic films can be controlled and tailored during the film growth. The films are promising as fast-response NO2 sensing layers, the response and recovery times being as short as about 1 min.

MnO x /ZrO2 gel-derived materials for hydrogen peroxide decomposition

Manganese-yttrium-zirconium mixed oxide nanocomposites with three different Mn loadings (5, 15 and 30 wt%) were prepared by sol–gel synthesis. Amorphous xerogels were obtained for each composition. Their structural evolution with the temperature and textural properties were examined by thermogravimetry/differential thermal analysis, X-ray diffraction, diffuse reflectance UV–vis spectroscopy and N2 adsorption isotherms. Mesoporous materials with high surface area values (70–100 m2 g−1) were obtained by annealing in air at 550 °C. They are amorphous or contain nanocrystals of the tetragonal ZrO2 phase (T-ZrO2) depending on the Mn amount and exhibit Mn species with oxidation state higher than 2 as confirmed by temperature programmed reduction experiments. T-ZrO2 is the only crystallizing phase at 700 °C while the monoclinic polymorph and Mn3O4 start to appear only after a prolonged annealing at 1,000 °C. The samples annealed at 550 °C were studied as catalysts for H2O2 decomposition in liquid phase. Their catalytic activity was higher than that of previously studied Mn/Zr oxide systems prepared by impregnation. Catalytic data were described by a rate equation of Langmuir type. The decrease of catalytic activity with time was related to dissolution of a limited fraction (up to 15%) of Mn into the H2O2/H2O solution.

Photo‐assisted hetero‐Fenton decolorization of azo dye from contaminated water by Fe–Si mixed oxide nanocomposite

An aerogel of silica gel dopeyd with 2.86 wt% Fe was prepared by an alkoxide sol–gel method and using tetraethyl orthosilicate as a precursor material. The synthesized aerogel was calcined at 500 °C to produce nanoparticle solids, and was characterized by XRD, FT‐IR and SEM. The nanosized iron–silica gel mixed oxide was tested in the photooxidation of the azo dye Acid Red 14 (AR 14) using 30% aqueous hydrogen peroxide as oxidant and UV light. The 2.86 wt% Fe‐loaded SiO2 showed very good efficiency in the decolorization of AR 14. The effects of various parameters including solution pH, catalyst, oxidant and initial dye concentrations on photodegradation were investigated and the optimum conditions were determined. The catalyst was resistant to leaching and could be recycled several times without appreciable loss of activity.

Synthesis and characterization of Ni-Si mixed oxide nanocomposite as a catalyst for carbon nanotubes formation

Ni-Si mixed oxide nanocomposite was prepared by co-precipitation method with Ni(NO3)2 · 6H2O and tetraethylorthosilicate (TEOS) at pH = 10.5 under reflux condition for 6 days. It was then used as a catalyst for the formation of carbon nanotubes (CNTs) by CVD procedure. Characterization of the catalyst and the CNTs was carried out using X-ray diffractometry (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. The results showed that Ni-Si mixed oxides nanorods with the average diameter of 3 to 4 nm play a key role in CNTs formation.

Iron and chromium mixed-oxide nanocomposites

Mixed oxides nanocomposites of the type xCr2O3-(1-x)α-Fe2O3 (x = 0.0–1.0) were synthesized using hydrothermal technique and characterized by X-ray diffraction (XRD) and Mossbauer spectroscopy. The same characterization methods were applied to a set of samples annealed at 600°C for 2 h. High chromium content correlated with occurrence of amorphization effects and onset of superparamagnetism in the as-obtained samples. The structure and properties of the thermally annealed samples, however, are dominated by the equilibrium of two phases, Cr:Fe2O3 and Fe:Cr2O3. The final (x = 1.0) particle size of the nanocomposite is close to 19 nm.

Sol-gel method of synthesis and characterization of some mixed-oxide nanocomposites

Nanosized crystallites of the mixed oxides BaCuO 2 (1), BaNiO 2 (2), Ba 2 Co 4 O 7,8 (3) and Ba 2 CuCe 2 O 7 (4) were synthesized by comparatively inexpensive route: Sol-Gel method. The particle size and morphology were studied by Scanning Electron Microscopy (SEM). The crystallinity, average crystalline size and phase purity of the prepared nanocomposites were analyzed by powder X-ray diffraction technique (XRD). The results indicated that all the samples had good crystallinity and composed of multiple phases with the exception of BaNiO 2 . The average crystalline sizes were found to be in the range 29-44 nm. Impedance measurements in the temperature range 303-363 K reveal decrease of bulk resistance (R b ) with increase of temperature upto 333 K, indicating semiconducting behaviour in this temperature range. The energy gap (Eg) measurements via Four-Probe setup instrument reveal that they fall in the range 0.15-2.15 eV.

Structure of SrCo0.5Fe0.5O3 − δ-based composites prepared by sol-gel and mechanochemical processes

X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, and Mossbauer spectroscopy have been used to investigate the structural phase transformations of SrCo0.5Fe0.5O3 − δ-based mixed-oxide nanocomposites containing fine iron oxide particles. The nanocomposites have been prepared using sol-gel and mechanochemical processes. The addition of iron(III) oxide sol to SrCo0.5Fe0.5O3 − δ xerogel is shown to enhance the thermal stability of the resultant cubic perovskite phase. The stabilization is due to partial shielding of the perovskite surface with a thin Fe2O3 layer, which hinders cobalt diffusion to the surface, preventing Co3O4 formation.

Gel derived niobium–silicon mixed oxides: Characterization and catalytic activity for cyclooctene epoxidation

Abstract Niobium–silicon mixed oxide nanocomposites, containing 7–37 wt.% Nb, were synthesized by a new sol–gel route and characterized for textural and acid properties by N 2 adsorption, NH 3 TPD and FTIR of adsorbed acetonitrile. The materials were tested as catalysts for epoxidation of cyclooctene with H 2 O 2 . High surface areas (>150 m 2 g −1 ), decreasing with Nb content, were found for materials containing up to 23.0 wt.% Nb. FTIR and TPD measurements evidenced the presence of both Bronsted and Lewis acid sites with different strength. The amount of strong acid sites, relative to those of low or moderate strength, increased with Nb content. The materials containing up to 23.0 wt.% Nb were active and stable catalysts for the epoxidation of cyclooctene. The highest activity and H 2 O 2 selectivity was found for the catalyst with the lowest Nb content, that showed also high stability in reuse. Catalytic properties were related to acid sites and to the presence of NbO x species with different coordination.

TPR/TPO characterization of cobalt–silicon mixed oxide nanocomposites prepared by sol–gel

Cobalt–silicon mixed oxides with Co/Si ratio of 10/90 (10Co), 20/80 (20Co) and 30/70 (30Co) were prepared by a modified sol–gel method. The materials treated in air at 400 and 600 °C were characterized by SEM and TPR/TPO techniques. TPR measurements showed that in all samples only a fraction of Co was present as Co 3O 4 and as amorphous silicate and was reducible by H 2 within 800 °C, while a part was not reducible under TPR conditions. The fraction of Co not reducible decreased with increasing Co content. A TPO/TPR cycle gave rise to an increase of the fraction of not reducible Co.

Cobalt–silicon mixed oxide nanocomposites by modified sol–gel method

Cobalt–silicon mixed oxide materials (Co/Si=0.111, 0.250 and 0.428) were synthesised starting from Co(NO 3) 2·6H 2O and Si(OC 2H 5) 4 using a modified sol–gel method. Structural, textural and surface chemical properties were investigated by thermogravimetric/differential thermal analyses (TG/DTA), XRD, UV–vis, FT-IR spectroscopy and N 2 adsorption at −196 °C. The nature of cobalt species and their interactions with the siloxane matrix were strongly depending on both the cobalt loading and the heat treatment. All dried gels were amorphous and contained Co 2+ ions forming both tetrahedral and octahedral complexes with the siloxane matrix. After treatment at 400 °C, the sample with lowest Co content appeared amorphous and contained only Co 2+ tetrahedral complexes, while at higher cobalt loading Co 3O 4 was present as the only crystalline phase, besides Co 2+ ions strongly interacting with siloxane matrix. At 850 °C, in all samples crystalline Co 2SiO 4 was formed and was the only crystallising phase for the nanocomposite with the lowest cobalt content. All materials retained high surface areas also after treatments at 600 °C and exhibited surface Lewis acidity, due to cationic sites. The presence of cobalt affected the textural properties of the siloxane matrix decreasing microporosity and increasing mesoporosity.

Sol–gel synthesis and structural characterization of niobium-silicon mixed-oxide nanocomposites

(Nb2O5) x ·(SiO2)1−x gels of four different compositions with x = 0.025 (2.5Nb), 0.050 (5Nb), 0,10 (10Nb) and 0.20 (20Nb) were synthesized at room temperature from niobium penta-chloride and tetra-ethoxysilane and their structural evolution with the temperature was examined by X-ray diffraction, thermogravimetry/differential thermal analysis, Raman and IR spectroscopy (Fourier transform). The synthesis procedure tuned in this work allowed to obtain for each studied composition transparent chemical gels in which the niobium dispersion resulted to be strongly dependent on the Nb2O5 loading: it was on the atomic scale for the 2.5Nb and 5Nb gel samples whereas the gel structure of the 10Nb and 20Nb appears formed by phase separated niobia-silica nanodomains. All dried gels keep their amorphous nature up to 873 K, while at higher temperatures crystallization of T- and H-Nb2O5 polymorphs were observed according to the Nb2O5 loading: at low loading T-Nb2O5 was the main crystallising phase, whereas at higher one the H-Nb2O5 prevails. Particularly, T-Nb2O5 was the sole crystallising phase in the whole explored temperature range for the 2.5Nb, keeping its nanosize up to 1273 K for all samples except for the 20Nb.

A versatile sol–gel synthesis route to metal–silicon mixed oxide nanocomposites that contain metal oxides as the major phase

The general synthesis of metal–silicon mixed-oxide nanocomposite materials, including a variety of both main group and transition metals, in which the metal oxide is the major component is described. In a typical synthesis, the metal-oxide precursor, MClx·yH2O(x=2–6,y=0–7), was mixed with the silica precursor, tetramethoxysilane (TMOS), in ethanol and gelled using an organic epoxide. The successful preparation of homogeneous, monolithic materials depended on the oxidation state of the metal as well as the epoxide chosen for gelation. The composition of the resulting materials was varied from M/Si=1–5 (mol/mol) by adjusting the amount of TMOS added to the initial metal-oxide precursor solution. Supercritical processing of the gels in CO2 resulted in monolithic, porous aerogel nanocomposite materials with surface areas ranging from 100–800m2g−1. The bulk materials are composed of metal oxide/silica particles that vary in size from 5–20nm depending on the epoxide used for gelation. Metal oxide and silica dispersion throughout the bulk material is extremely uniform on the nanoscale. The versatility and control of the synthesis method will be discussed as well as the properties of the resulting metal–silicon mixed oxide nanocomposite materials.

Silicon oxide in an iron(III) oxide matrix: the sol–gel synthesis and characterization of Fe–Si mixed oxide nanocomposites that contain iron oxide as the major phase

The synthesis of Fe–Si mixed oxide nanocomposite materials in which the iron(III) oxide is the major component is described. In a typical synthesis, the iron oxide precursor, FeCl 3 · 6H 2O, was mixed with a silica precursor, tetramethyl- or tetraethylorthosilicate, in ethanol and gelled using an organic epoxide. The composition of the resulting materials was varied from Fe/Si (mol/mol)=1–5 by adjusting the amount of silica precursor added to the FeCl 3 · 6H 2O solution. Further processing of the gels in supercritical CO 2 resulted in monolithic, porous aerogel nanocomposite materials with surface areas ranging from 350–450 m 2/g. The bulk materials are composed of iron(III) oxide/silica particles that vary in size from 5–20 nm depending on the epoxide used for gelation. Iron(III) oxide and silica dispersion throughout the bulk material is extremely uniform on the nanoscale. The synthesis method presented is general for the synthesis of several other metal oxide/silicon oxide nanocomposite materials.