Effect of Cu and Zr Co-doped SiO<Subscript>2</Subscript> Nanoparticles on the Stability of Phases (Quartz-Tridymite-Cristobalite) and Degradation of Methyl Orange at High Temperature

SiO₂ nanoparticles doped by 10 mol% Zr and 10 mol% Cu were prepared via the sol-gel method in a controled process. The effects of doping and calcination temperature on the structural and photo-catalytic properties of SiO₂ nanopowders were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and UV-Vis absorption spectroscopy. The phases of cristobalite, quartz and tridymite were found at a calcinations temperature range of 800 to 1000 ^°C and only cristobalite phase was formed at a temperature of 1200 ^°C. The degradation of methyl orange was examined under visible light radiation indicating that the effect of doped elements (Zr, Cu) on SiO₂ reduces the band gap effectively.     

Optical and Structure Properties of Nanocrystalline Titania Powders with Cu Dopant

TiO₂ nanopowders doped by Cu were prepared by the sol–gel method. The effects of Cu doping on the structural, optical, and photo-catalytic properties of titania nanopowders have been studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and UV–Vis absorption spectroscopy. XRD results suggest that adding impurities has a significant effect on anatase phase stability, crystallinity, and particle size of TiO₂. Titania rutile phase formation in the system (Ti–Cu) was promoted by Cu²⁺ doped TiO₂. The photo-catalytic activity was evaluated by photo-catalytic degradation kinetics of aqueous methylene orange (MO) under visible radiation. The results show that the photo-catalytic activity of the 5 %Cu doped TiO₂ nanopowders has a larger degradation efficiency than pure TiO ₂ under visible light. Also, the minimum band gap was estimated to be ～ 1.9–2 eV from UV–Vis spectra.     

Microstructure,mechanical properties,and high-temperature oxidation resistance of AlN/SiO<Subscript>2</Subscript> nanomultilayer coatings

The microstructure, mechanical properties, and high-temperature oxidation resistance of AlN/SiO₂ nanomultilayer coatings with various SiO₂ layer thicknesses were investigated using X-ray diffractometry, high-resolution transmission electron microscopy, scanning electron microscopy, and nanoindentation. The results revealed that SiO₂ formed wurtzite-typed hexagonal pseudo-crystal structures and grew epitaxially with AlN when its thickness was less than 0.6 nm. Meanwhile, the multilayer coatings yielded superhardness effect with a maximum hardness of 29.0 GPa. A minute increase in SiO₂ thickness from 0.6 to 0.9 nm would decrease the hardness of the nanomultilayer coatings due to the formation of amorphous SiO₂ and destruction of epitaxial structure. The high hardness of superhard coatings was sustained after high-temperature annealing treatment of up to 800°C. However, a further increase in annealing temperature to 900°C caused severe oxidation of AlN and thus degradation of coating’s hardness.     

Effect of heat treatment on crystal phase and photocatalytic activity of Tm doped TiO2 nanoparticles

Abstract

Abstract

Tm doped TiO₂ nanoparticles have been synthesised by hydrolysis-precipitation method. The effect of heat treatment on the crystal phase and photocatalytic activity of Tm doped TiO₂ nanoparticles has been studied. The prepared samples were characterised by transmission electron microscopy, X-ray diffraction, Fourier transformed infrared and diffuse reflection spectrum analysis. The results show that Tm³⁺ doping can effectively inhibit the phase transformation from antase to rutile and decrease the crystallite size of nano-TiO₂ particles. There is an optimal Tm doping (1·4?mol.-%) after calcination at 550°C for the photocatalytic activity of methylene blue degradation.     

Preparation of oriented SiO32− doped TiO2 film and degradation of methylene blue under visible light irradiation

SiO₃^2? doped TiO₂ films with oriented nanoneedle and nanorectangle block structure has been firstly synthesized by hydrothermal synthesis method. The prepared samples are characterized, X-ray diffraction (XRD) results demonstrate that the SiO₃^2? doped TiO₂ films are rutile and brookite phases. The scanning electron microscope (SEM) analysis reveals that the quantity of O₂ affects the morphology of the SiO₃^2? doped TiO₂ films (SiTiA films prepared with unmodified substrate). The SiO₃^2? doped TiO₂ films (SiTiB films prepared with modified substrate) display two layers, one is porous structure, the other is nanoneedle structure. UV–vis, IR, transmission electron microscopy (TEM) and energy-dispersive X-ray (EDX) microscopy all prove that SiO₃^2? have been doped in the TiO₂ crystal structure. They have remarkable red shift and higher photocatalytic activity of degradation of methylene blue than P-25 under visible light (λ > 420 nm) irradiation. Besides, photocatalytic activity of the film is stable during 4 times recycling.     

Purity-controllable growth of bamboo-like multi-walled carbon nanotubes over copper-based catalysts

The growth of bamboo-like multi-walled carbon nanotubes (CNTs) without the formation of amorphous carbons was performed using copper-based catalysts by catalytic chemical vapour deposition (CVD) with diluted ethylene at 700–900 °C. The as-grown CNT soot was characterised by transmission electron microscopy, thermogravimetric analysis and Raman spectroscopy. The weak metal–support interaction of a sulphate-assisted copper catalyst (CuSO₄/SiO₂) can provide high-purity growth with remarkable yields of CNTs (2.24–6.10 CNT/g Cu·h) at 850–900 °C. Additionally, hydrogen-assisted CVD can activate inert copper catalysts, e.g., Cu(NO₃)₂/SiO₂ or Cu(CH₃COO)_2/SiO₂, for the growth of CNTs.     

Preparation and photocatalytic activity of BiOI/MnxZn1-xFe2O4 magnetic photocatalyst

BiOI/Mn_xZn_1-xFe₂O₄ magnetic photocatalysts were successfully prepared for the first time. With the degradation of simulated RhB wastewater as a pointer to the photocatalytic reaction and combined with Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), UV–visible diffuse reflectance spectroscopy (UV–vis DRS), and vibrating sample magnetometer (VSM), the reasons influencing the photocatalytic performance of the magnetic photocatalysts were further explored. The excessive or insufficient Mn-Zn ferrite both leads to a relatively low photocatalytic activity. When the calcination temperature reaches to 200 and 400?°C, the photocatalytic activity is enhanced significantly, but the main active component in the photocatalysts has changed from BiOI to Bi₅O₇I at 400?°C. The nanocomposites prepared under alcohol water environment with hollow microspheres morphology possess a highly photocatalytic efficiency, and the RhB degradation rate within 4?h in the ethanol water environment is significantly higher than that in pure water (98% vs. 59%).     

Synthesis and photocatalytic performance of hollow sphere particles of SiO2-TiO2 composite of mesocellular foam walls

Hollow Microspheres of SiO₂-TiO₂ photocatalysts whose walls are made up of mesoporous cellular foams were synthesized with the aid of hexane as a swelling agent and P123 as a pore template by an emulsion templating method. Pore structure of materials and crystal phase of titanium oxide was tailored by hydrothermal and calcination temperature during synthesis of samples. The samples were characterized with field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), N₂ adsorption–desorption experiments, X-ray photoelectron spectroscopy (XPS) and X ray diffraction (XRD) techniques. The effect of pore structure and titania phase on photoactivity were evaluated by methylene blue (MB) degradation test under UV light as well. Results showed that hydrothermal temperature during synthesis process has a significant effect on pore and window sizes of mesostructured cellular foam. Interestingly, for the sample hydrothermally treated at higher temperature (130 °C), anatase to rutile transformation was avoided after calcination treatment as high as 800 °C. The highest photocatalytic activity was detected from the sample hydrothermally treated at 130 °C and calcined at 800 °C for which the highest degree of crystallinity and anatase phase as well as enhanced pore connectivity was obtained.     

Novel‐doped zinc oxide sorbents for low temperature regenerable desulfurization applications

Eight metal oxide sorbents including transition metal doped ZnO/SiO₂ sorbents and ZnO/SiO₂ were prepared by incipient wetness impregnation for regenerable desulfurization applications at low temperatures (i.e. room temperature). Among them, copper‐doped sorbent (Cu‐ZnO/SiO₂) demonstrated the highest saturation sulfur capacity of 0.213 g sulfur/g ZnO (54% of the theoretical capacity), which is twice that of ZnO/SiO₂ sorbent. Compared with ZnO/SiO₂, Cu‐ZnO/SiO₂ demonstrated superior desulfurization performance in a wide temperature range of 20–400°C. Due to the use of porous SiO₂ support, Cu‐ZnO/SiO₂ is highly regenerable. It can be easily regenerated in air at low temperatures, ca. 300–550°C, which are much lower than the typical regeneration temperatures of commercial ZnO sorbents. Cu‐ZnO/SiO₂ maintained its sulfur capacity during 10 cycles of regeneration/sulfidation. © 2010 American Institute of Chemical Engineers AIChE J, 2010     

Transparent zinc silicate/ zinc oxide crystallized glass-ceramics for water remediation application under visible light

The present study focuses on taking advantage of both Zinc Silicate (Zn₂SiO₄) and Zinc Oxide (ZnO) crystals in the glass matrix for enhancing photocatalytic activity. The fabricated samples were used as a photocatalyst for degrading ～ 5 mg/L concentrated “Methylene Blue” (MB) and “Rhodamine B” (RB) dye separately under visible light. For this, 44 SiO₂:11 Al₂O₃:35 ZnO:10 K₂O compositions were prepared via the traditional melt quench process followed by heat treating at a temperature of 750 °C at 2, 4, and 6 h. Scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS) was employed to characterize the fabricated samples. The bandgap measured from Differential reflectance spectroscopy (DRS) was found to decrease with an increase in the heat treatment duration. 44 SiO₂:11 Al₂O₃:35 ZnO:10 K₂O composition heat-treated at 750 °C for 2 h degraded ～59% and ～71% of Rhodamine B (RB) dye and Methylene Blue (MB) dye under visible light in 4 h.     

Effect of Fe<Superscript>3+</Superscript> doping on the performance of TiO<Subscript>2</Subscript> mechanocoated alumina bead photocatalysts

Ferric ion was introduced to the commercial photocatalyst P25 (Degussa) by ultrasonic wet impregnation technique. The concentration of the dopant was varied from 0.0 to 3.0% Fe/Ti ratio. The doped TiO₂ was then loaded to alumina balls using mechanical coating technique and followed by calcination in air at 400, 450, 500 and 550 °C. The fabricated photocatalyst was characterized by X-ray diffraction, N₂ adsorption-desorption isotherms, scanning electron microscopy, UV-Vis diffuse reflectance spectroscopy, X-ray adsorption near edge structure and photoluminescence spectroscopy. The photocatalytic activity was tested by following the degradation of methylene blue (MB). It was found that the Fe³⁺ doped TiO₂/Al₂O₃ has a combination of anatase and rutile phase and free of iron oxide phases. The optimum calcination temperature is 400 °C with 0.1% Fe³⁺ concentration. The catalyst addresses the entrainment in photocatalytic reactors, eliminating the need for a post filtration process.     

Thermal evolution and structural study of 2:1 mullite from monophasic gels

Single phase mullite gels with composition 2Al₂O₃·SiO₂ (2:1) were prepared by the slow hydrolysis method using aluminium nitrate nonahydrate and tetraethylorthosilicate as reagents. The evolution to mullite from gels was studied by infrared (IR) spectroscopy and X-ray diffraction (XRD). Gels thermally treated under fast schedules showed mullite formation below 900 °C. Compositional and microstructural changes in 2:1 mullites through the range of temperature from 900 to 1600 °C were determined by the measurement of lattice parameters and field emission scanning electron microscopy. The alumina-rich mullites formed at low temperatures become almost the nominal 2:1 at 1600 °C. This result is consistent with available thermodynamic data for mullite formation from alumina and silica. Microstructural examination indicated an almost constant grain size for mullite from 900 to 1600 °C.     

Synthesis and field emission properties of carbon nanotubes/nanofibers grown on pyrolyzed polyaniline–SiO2 substrates

Pyrolyzed polyaniline–SiO₂ substrates with the rough surface containing some holes were prepared by the pyrolysis of polyaniline–SiO₂ composites at temperature of 900 °C. Carbon nanotubes/nanofibers (CNTs/CNFs) were grown on the rough surface and inside the holes using a CVD method with a xylene–ferrocene mixture as a carbon and catalyst precursor source. The structural and morphological properties of CNTs were characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results indicated that the SiO₂ content of the substrates was responsible to the diameter and electron field emission properties of CNTs.     

Photocatalytic degradation of dyestuff wastewater under visible light irradiation using micron‐sized mixed crystal TiO2 powders

A phase transformation of micron‐sized TiO₂ powder from anatase to rutile was attempted by heat‐treatment in order to generate a new mixed crystal TiO₂ with high associated photocatalytic activity. Heat‐treated micron‐sized TiO₂ powders at different transition stages were characterized by X‐ray diffraction analysis (XRD), Fourier transform infrared spectroscopy (FT‐IR) and transmission electron microscopy (TEM) methods. The tests of photocatalytic activity of the heat‐treated micron‐sized TiO₂ powders were conducted by the photocatalytic degradation of Rhodamine B and Acid Red B under visible light irradiation. The results indicate that mixed crystal TiO₂ photocatalyst heat‐treated at 400 °C for 60 min shows the highest photocatalytic activity. It can effectively decompose the Rhodamine B and Acid Red B in aqueous solution after 6 h visible light irradiation. A remarkable improvement in photocatalytic activity of TiO₂ is caused by the formation of combined rutile–anatase phases and separation of photogenerated electron–hole pairs. Copyright © 2007 Society of Chemical Industry     

High‐Selectivity Y2O3‐Doped SiO2 Nanocomposite Membranes for Gas Separation in Steam at High Temperatures

Asymmetric structures were fabricated by depositing Y₂O₃‐doped SiO₂ (Si/Y) membranes onto γ‐Al₂O₃ supported by tubular α‐Al₂O₃. The thickness of the Y₂O₃‐doped SiO₂ deposits was approximately 100 nm. The deposits/membranes have micropores with a pore diameter ~ <0.40–0.55 nm. Pore size distribution measurements were conducted directly on the membranes before and after hydrothermal treatment with a nano‐permporometer. The gas permeance properties of the membranes were measured in the temperature range 100°C–500°C. The Y‐doped SiO₂ membrane (Si/Y = 3/1) was found to exhibit asymptotically stable permeances of 2.39 × 10^?7 mol/m²/s/Pa for He and 6.19 × 10^?10 mol/m²/s/Pa for CO₂, with a high selectivity of 386 (He/CO₂) at 500°C for 20 h in the presence of steam. The Y‐doped silica membranes exhibit very high gas permeances for molecules with smaller kinetic diameters. The apparent activation energies of the H₂ permeance at 400°C were 24.2 ± 0.2 and 21.3 ± 0.7 kJ/mol for SiO₂ and Si/Y, respectively.     

Template-assisted hydrothermal synthesis and photocatalytic activity of novel TiO2 hollow nanostructures

TiO₂ hollow nanostructures were successfully synthesized by a controlled hydrothermal precipitation reaction using Resorcinol–Formaldehyde resin spheres as templates in aqueous solution, and then removal of the RF resins spheres by calcination in air at 450 °C for 4 h. The obtained TiO₂ hollow spheres were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, N₂ adsorption–desorption analysis, and UV–visible diffuse reflectance spectroscopy. The photocatalytic activity of the as-prepared samples was evaluated by photocatalytic decolorization of rhodamine B aqueous solution at ambient temperature under UV illumination. The results indicated TiO₂ hollow nanostructures exhibit the excellent photocatalytic activity probably due to the unique hollow micro-architectures.     

Effect of sintering temperature on the microstructure and transparency of Nd,Y:CaF2 ceramics

1 at% Nd, 3 at% Y doped CaF₂ transparent ceramics were obtained by hot pressing at the sintering temperature varing from 500 to 800 °C under vacuum environment with co-precipitated CaF₂ nanopowders. Transmission electron microscopy (TEM) and X-ray diffraction (XRD) analysis showed that the obtained nanoparticles were single fluorite phase with grain size around 26 nm. Scanning electron microscopy (SEM) observations of the Nd, Y: CaF₂ ceramics indicated that the mean grain size of the ceramic sintered at 800 °C was about 748 nm. The influence of the temperature on the grain size, microstructure and optical transmittance was investigated. For the ceramic sintered at 800 °C, the transmittance was 85.49% at the wavelength of 1200 nm. The room temperature emission spectra of Nd: CaF₂ and Nd, Y: CaF₂ ceramics were measured and discussed.     

Effect of Thermal Treatment on the Photocatalytic Activity in Visible Light of TiO<Subscript>2</Subscript>-W Flame Spray Synthesised Nanopowders

Effect of W doping as well as a thermal treatment on the structural and photocatalytic properties of TiO₂ produced by flame spray synthesis (FSS) were the subject of investigation. Structural properties were studied by means of X-ray diffraction (XRD), BET adsorption isotherm and transmission electron microscopy (TEM). The surface condition was investigated by X-ray photoelectron spectroscopy (XPS) and differential scanning calorimetry (DSC) and differential thermal and thermogravimetric analysis (DTA-TGA). The photocatalytic properties were studied by optical measurements and photodecomposition of methylene blue under visible irradiation. It was found that the photoactivity in the visible region was enhanced significantly by the W-doping as well as by additional thermal treatment of those nanopowders. The obtained TiO₂-W nanopowders exhibited higher performance under visible light than P25.     

Photocatalytic activity of undoped and sulfur-doped TiO2 films grown by MOCVD for water treatment under visible light

Titanium dioxide ceramic coatings have been used as catalysts in green technologies for water treatment. However, without the presence of a dopant, its photocatalytic activity is limited to the ultraviolet radiation region. The photocatalytic activity and the structural characteristics of undoped and sulfur-doped TiO₂ films grown at 400 °C by metallorganic chemical vapor deposition (MOCVD) were studied. The photocatalytic behavior of the films was evaluated by methyl orange dye degradation under visible light. The results suggested the substitution of Ti⁴⁺ cations by S⁶⁺ ions into TiO₂ structure of the doped samples. SO₄^2? groups were observed on the surface. S-TiO₂ film exhibited good photocatalytic activity under visible light irradiation, and the luminous intensity strongly influences the photocatalytic behavior of the S-TiO₂ films. The results supported the idea that the sulfur-doped TiO₂ films grown by MOCVD may be promising catalysts for water treatment under sunlight or visible light bulbs.     

Enhanced photocatalytic activity of TiO2/SiO2 by the influence of Cu-doping under reducing calcination atmosphere

Cu-doped titania photocatalyst supported on silica beads (Cu-TiO₂/SiO₂) were prepared under different Cu-ion concentration and under different calcination atmosphere. The properties and performance of Cu-TiO₂/SiO₂ were compared with undoped TiO₂/SiO₂ photocatalyst. The effect of Cu-doping and calcination atmosphere on photocatalytic degradation of phenol under both black light and visible light irradiation were investigated, where in both cases the degradation rate of phenol by Cu-doped catalyst prepared under reducing calcination atmosphere was found to be higher than the undoped catalyst or Cu-doped catalyst prepared under air atmosphere. This may be attributed to increase in visible light absorption and lengthening of photogenerated electron–hole pair recombination time. The photocatalytic beads were characterized by X-ray diffraction (XRD), UV-Vis absorption spectroscopy and SEM/EDAX analysis.