Sonochemical synthesis and characterization of magnetic separable Fe3O4–TiO2 nanocomposites and their catalytic properties

A novel sonochemical method is described for the preparation of Fe₃O₄–TiO₂ photocatalysts in which nanocrystalline titanium dioxide particles are directly coated onto a magnetic core. The Fe₃O₄ nanoparticles were partially embedded in TiO₂ agglomerates. TiO₂ nanocrystallites were obtained by hydrolysis and condensation of titanium tetraisopropyl in the presence of ethanol and water under high-intensity ultrasound irradiation. This method is attractive since it eliminated the high-temperature heat treatment required in the conventional sol–gel method, which is important in transforming amorphous titanium dioxide into a photoactive crystalline phase. In comparison to other methods, the developed method is simple, mild, green and efficient. The magnetization hysteresis loop for Fe₃O₄–TiO₂ nanocomposites indicates that the hybrid catalyst shows superparamagnetic characteristics at room temperature. Photocatalytic activity studies confirmed that the as-prepared nanocomposites have high photocatalytic ability toward the photodegradation of RhB solution. Furthermore, the photodecomposition rate decreases only slightly after six cycles of the photocatalysis experiment. Thus, these Fe₃O₄–TiO₂ nanocomposites can be served as an effective and conveniently recyclable photocatalyst.     

P123 assisted morphology-engineered and hierarchical TiO<Subscript>2</Subscript> microspheres for enhanced photocatalytic activity

In this study, hierarchical titanium dioxide (TiO₂) microspheres with controlled morphology derived from calcination treatment of hierarchical titanate microspheres were fabricated. The obtained hierarchical TiO₂ microspheres with diameters of 1 to 2 µm were composed of polycrystalline anatase nanosheets with thickness of 10 nm. The morphology was manipulated by simply adjusting the molar ratio of tetrabutyl titanate/P123. At a low molar ratio of 17.04, TiO₂ microspheres composed of a large number of nanosheets closely packed together were obtained. At a high molar ratio of 34.08, TiO₂ hybrid architectures with polycrystalline anatase hierarchical microspheres and single-crystal anatase mesoporous (approximately 5 nm) nanospheres were obtained. Investigations on evolution formation revealed that P123 played a key role in the formation of a well-defined hierarchical structure. The photocatalytic performances of the obtained samples were investigated by the degradation of methylene blue and papermaking wastewater. When compared with commercial P25, the obtained hierarchical TiO₂ microspheres exhibit superior photocatalytic activity, high degradation efficiency, and good reproducibility. The product with hybrid architectures exhibited the highest photocatalytic activity. The chemical oxygen demand and the chroma removal rate of papermaking wastewater achieved 85.5 and 100%, respectively, after 12 h of photodegradation.     

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.     

Fly ash supported photocatalytic nanocomposite poly(3,4‐ethylenedioxythiophene)/TiO2 for azo dye removal under simulated solar irradiation

The main objective of this study was to develop a supported photocatalyst for wastewater treatment with extended efficiency under solar light. For that purpose titanium dioxide (TiO₂) was immobilized by sol–gel synthesis on the surface of the waste fly ash (FA). On such prepared composite material, conductive polymer poly(3,4‐ethylenedioxythiophene) was grafted by in situ chemical oxidative polymerization with different oxidants, ammonium persulfate (APS), and iron(III) chloride, FeCl₃. Characterization was performed by Fourier transform infrared spectroscopy, scanning electron microscopy, X‐ray diffraction, thermogravimetric analysis, and gas sorption analysis. Photocatalytic activity of composite photocatalyst was evaluated by testing removal efficiency of C.I. Reactive Red 45 (RR45) azo dye in three consecutive photocatalytic cycles under different pH. Discoloration of RR45 was measured using UV/Vis spectroscopy. It was determined that oxidant type plays major role in structure of composite as sample synthesized with APS had higher fraction of polymer and largest pore volume. The same composite had much better photocatalytic efficiency than sample synthesized with FeCl₃ oxidant. It was also determined that there is a very strong adsorption of dye molecules on the surface of photocatalyst that quickly causes saturation of photocatalyst and efficiency drop after first cycle. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46316.     

Synthesis of TiO<Subscript>2</Subscript> nanoparticles from sprayed droplets of titanium tetrachloride by the gas-phase detonation method

Nanostructured polycrystalline titanium dioxides are produced by gas-phase detonation and pyrohydrolysis. Titanium tetrachloride (TiCl₄) is used as a precursor in the gas phase, and a premixed gas (O₂ and H₂) is used as a source of energy. The product is a mixture of TiO₂ crystals in the rutile phase (80%) and anatase phase (20%). __________ Translated from Fizika Goreniya i Vzryva, Vol. 44, No. 5, pp. 112–116, September–October, 2008.     

Synthesis of Ni,N co-doped TiO<Subscript>2</Subscript> using microwave-assisted method for sodium lauryl sulfate degradation by photocatalyst

A titanium dioxide (TiO₂) photocatalyst was modified with nickel (Ni) and nitrogen (N) in titanium tetra-isopropoxide (TTIP) as a precursor through a microwave-assisted method. The Ni and N dopants led to a decrease in the TiO₂ band gap and made it able to function with visible light irradiation. The results of X-ray diffraction analysis demonstrated that the crystalline size of Ni–N–TiO₂ was 13.275 nm in anatase form with a specific peak in 2θ = 25.32°. Ni–N–TiO₂ was analyzed by scanning electron microscopy, which showed the smaller morphology and thin particles, and this was further supported by energy-dispersive X-ray data regarding the elemental composition of Ni and N being 4.50 and 2.39%, respectively. Fourier transform infrared spectroscopy results demonstrated the absorption spectrum in wavenumbers of 1197 and 1149 cm^?1, indicating an N–TiO₂ bond, a Ti–O bond at 648 cm^?1, and an Ni–O bond at 469 cm^?1. TiO₂ modified by Ni and N exhibited a decrease in the band gap at 1.95 eV, suggesting the Ni and N dopants successfully inserted onto the TiO₂ crystalline surface to be visualized with visible light. Photoactivity testing was carried out to degrade sodium lauryl sulfate surfactants under visible irradiation, where the degradation efficiency was 93.75%.     

Photoreduction of CO<Subscript>2</Subscript> into CH<Subscript>4</Subscript> using Bi<Subscript>2</Subscript>S<Subscript>3</Subscript>-TiO<Subscript>2</Subscript> double-layered dense films

Nano-sized bismuth sulfide (Bi₂S₃) and titanium dioxide (TiO₂) with the orthorhombic and anatase tetragonal structures, respectively, were synthesized for application as catalysts for the reduction of carbon dioxide (CO₂) to methane (CH₄). Four double-layered dense films were fabricated with different coating sequences—TiO₂ (bottom layer)/Bi₂S₃ (top layer), Bi₂S₃/TiO₂, TiO₂/Bi₂S₃: TiO₂ (1 : 1) mix, and Bi₂S₃: TiO₂ (1 : 1) mix/Bi₂S₃: TiO₂ (1 : 1) mix—and applied to the photoreduction of CO₂ to CH₄; the catalytic activity of the fabricated films was compared to that of the pure TiO₂/TiO₂ and Bi₂S₃/Bi₂S₃ doubled-layered films. The TiO₂/Bi₂S₃ double-layered film exhibited superior photocatalytic behavior, and higher CH₄ production was obtained with the TiO₂/Bi₂S₃ double-layered film than with the other films. A model of the mechanism underlying the enhanced photoactivity of the TiO₂/Bi₂S₃ double-layered film was proposed, and it was attributed in effective charge separation.     

Synthesis and characterisation of novel titania impregnated kaolinite nano-photocatalyst

Nano-sized titanium dioxide (TiO₂) has received a great attention in the field of research and development as a promising photocatalyst to promote the degradation of organic contaminants in water. One of the key technical challenges involved in separation and recovery of the photocatalyst particles from the water treatment system makes this technology unviable as an industrial process. A novel titania impregnated kaolinite (TiO₂/K) photocatalyst was synthesized by a modified two step sol–gel method: hydrolysis of titanium(IV) butoxide and heterocoagulation with pre-treated kaolinite (K) clay. The TiO₂/K photocatalysts were characterised using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and BET specific surface area measurements (BET). The photocatalytic activity was evaluated by the degradation of Congo red in aqueous solution. The TiO₂/K photocatalyst had a rigid porous layer structure and promising nano-size properties, and demonstrated an enhanced adsorption and photocatalytic ability for the removal of Congo red. The TiO₂/K photocatalyst can be easily separated and recovered from the water treatment system. The TiO₂/K photocatalyst is expected to deliver a true engineering solution for an industrial water/wastewater treatment process.     

A novel synthesis route of titanium dioxide with (NH4)0.3TiO1.1F2.1 as by-product

This work explores a new route for the synthesis of titanium dioxide using scraps and titanium chips, which are typically discarded as waste, as the precursor materials. The band-gap energy of the synthesised materials was determined using diffuse reflectance spectroscopy. The morphology, elemental analysis, crystallinity, and chemical structure of the synthesised materials were determined by scanning electron microscopy, energy dispersive spectroscopy, X-ray diffractometry, and infrared and Raman spectroscopies, respectively. The X-ray and Raman analyses confirmed the formation of titanium dioxide in its tetragonal (anatase) crystalline form after heat treatment (400 °C, 2 h). Moreover, a mixture of (NH₄)_0,3TiO_1,1F_2,1 and anatase TiO₂ was obtained as a by-product. After heat treatment, this by-product was converted into fluorine-doped titanium dioxide, also in anatase crystalline form. The apparent crystallite size (L_c) of anhydrous titanium dioxide was found to be smaller than that of the calcined by-product. The diffuse reflectance spectroscopy analysis revealed that the calcined by-product has a significantly higher absorption capacity at higher wavelengths, as well as a lower band-gap energy value. The scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) analyses showed large particulates on which smaller particles are deposited and good dispersion of the elemental components. The anhydrous titanium dioxide sample presents a smaller particle size than the calcined by-product.     

Experimental study of the influence of sodium salts as additive to NO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>OUT process

An experimental study of the SNCR process with urea as reducing agent and sodium salts as additive has been carried out, and detailed analysis of the reaction mechanism has been given here. In the temperature range of 800–975 °C, NO concentration decreases at first and then increases while the concentration of N₂O increases at first and then decreases with the increasing of temperature, and the turning point is 900 °C. With increasing of normalized stoichiometric ratio of reduction nitrogen to NO _x (NSR), NO removal efficiency increases, while the concentration of N₂O also increases, which decreases overall NO _x removal efficiency. With sodium salts as additive, the concentration of N₂O decreases with increasing of sodium salts addition at all temperatures, while the concentration of NO decreases at first and then increases at low-temperature side of the temperature window and increases at high-temperature side with additional increasing, whose changing extent is smaller than N₂O. Since sodium salts as additive can remove N₂O effectively and have no large influence on the removal of NO, the effect of sodium salts as additive is the combined effect of the production of active radicals and the removal of HNCO produced by the decomposition of urea through neutralization reactions, which is more important. To achieve the same effect under each condition, the needed addition of NaOH and CH₃COONa is less than that of Na₂CO₃ counting as Na atom. For the decomposition of CH₃COONa can produce CH₃COO, its addition can promote the reduction of NO more obviously at the lower temperature than Na₂CO₃ or NaOH. Overall NO _x removal efficiency at 900 ‡C with NSR=1.5 had been improved from about 30% to 70.45% through the addition of sodium salts. Sodium salts as additive caused the flue gas to become alkaline gas, but it was not serious for sodium salts existing as NaNCO.     

Preparation of zeolitic adsorbents from waste coal fly ash

Power plants burning coal generate a large amount of fly ash as waste matter. The objective of this study is to produce zeolitic adsorbents that possesses high adsorptive capacity for toxic cations. The sample was first pretreated with a High Intensity Magnetic Separator for the removal of iron and magnetic materials (mainly Fe₂O₃ and TiO₂). The zeolitic adsorbents were prepared under the various conditions of NaOH concentration (1–5 N), reaction time from 3 to 96 hours and at the various temperatures of 60, 80 and 100°C. The results of the experiment showed that the coal fly ash should be synthesized with 4 N NaOH for 48 hours at 100°C in order to have good adsorptive capacity. The zeolitic adsorbents showed higher cation exchange capacity values than the natural zeolite in removing NH ₄ ⁺ , Pb²⁺, Ca²⁺and Cd²⁺ions.     

Mössbauer analysis of iron phases in brown coal ash and fireside deposits

The iron phases present in an electrostatic precipitator ash, an uncooled ash deposit and a cooled superheater ash deposit from Hazelwood Power Station, Australia, burning Morwell brown coal has been examined using Mössbauer spectroscopy. The principal iron phase in the precipitator ash and the uncooled ash deposit from a hot gas offtake was calcium aluminoferrite (Ca₂Fe_{2 ? x}Al_xO₅). Minor amounts of hematite (α-Fe₂O₃) and magnetite (Fe₃O₄) were also detected in the precipitator ash. The cooled superheater ash deposit contained a (Mg, Fe, Al) oxide spinel as the primary iron phase; small quantities of hematite were also detected in this deposit close to the heat exchanger interface. The formation of these iron phases has been rationalized on the basis of the average composition of coal delivered to the power station and supplementary ash chemistry data obtained from other techniques. The evidence suggests that the calcium aluminoferrite in the precipitator ash is derived from inorganic constituents (distributed throughout the coal organic matrix) and the hematite and magnetite are of mineral origin (discrete particles).     

Emulsifier‐free miniemulsion polymerization of styrene and the investigation of encapsulation of nanoparticles with polystyrene via this procedure using an anionic initiator

Emulsifier‐free miniemulsion polymerization of styrene was investigated in the presence of potassium persulfate (KPS) as an anionic initiator and cetyl alcohol as a costabilizer using ultrasonic irradiation and comparison of this procedure with conventional emulsifier‐free emulsion polymerization showed that this method has a remarkably higher polymerization rate (R_p), smaller size of particles, and narrower molecular weight distribution via gravimetric measurement, transmission electron microscopy (TEM), and gel permeation chromatography techniques, respectively. Then, the encapsulation of magnetite (Fe₃O₄) and titanium dioxide (TiO₂) nanoparticles with polystyrene was investigated using this procedure. Attempt to encapsulate magnetite nanoparticles failed; however, the encapsulation of titanium dioxide nanoparticles was successfully carried out via this procedure using KPS in both cases. TEM proved the presence of TiO₂ nanoparticles in polymer particles, and thermogravimetric analysis was used to determine the percentage of TiO₂ in the products. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

57Fe Mössbauer spectroscopic studies of fly ash from coal-fired power plants and bottom ash from lignite-natural gas combustion

A series of four fly ashes, representing a variety of geological origins, and a bottom ash sample derived from the combustion of lignite-natural gas mixtures have been studied by ⁵⁷Fe Mössbauer spectroscopy. The ashes are separated into magnetic and non-magnetic fractions to facilitate a study of the chemical state of the iron contained in the ash. The bottom ash contains no magnetic fraction whereas the magnetic fractions of the fly ashes range from 1.1 to 7.3%. The magnetic fractions contained iron in the form of magnetite, Fe₃O₄. Iron in the non-magnetic fly ash fractions occur as Fe⁺¹ and Fe⁺² mullites, and Fe⁺³ and Fe⁺² silicates. Only Fe⁺³ silicates are found in the bottom ash.     

Al-doped TiO<Subscript>2</Subscript> mesoporous materials: synthesis and photodegradation properties

Aluminium-doped TiO₂ mesoporous material was successfully fabricated by solid-state reaction with cetyltrimethylammonium bromide as a template agent and tetrabutyl orthotitanate as a precursor. The characteristic results from low-angle and wide-angle X-ray diffraction, high resolution transmission electron microscopy and energy dispersive spectroscopy, N₂ absorption–desorption, Fourier transform infrared spectroscopy, Raman spectroscopy, ultraviolet visible light spectroscopy and X-ray photoelectron spectroscopy (XPS) clearly showed that the mesoporous architecture of aluminium-doped TiO₂ was composed of crystal wall and micro-/mesopore formed gradually by the mesopore degradation of anatase TiO₂, and aluminium had been doped into the framework of anatase TiO₂. The mesoporous Al-doped TiO₂ material, not only possessed high thermal stability hexahedral mesostructure, large BET surface area and narrow distribution of pore size, but also showed excellent photodegradation behavior for Congo Red. Furthermore the medium UV–Vis absorption peak of mesoporous aluminium-doped TiO₂ in the range 210–370 nm was the absorption peak of aluminium oxide nanoparticles locating the extraframework of TiO₂. A small quantity of aluminium doped into anatase TiO₂ could obviously improve photodegradation activity, and the photodegradation activity of aluminium-doped TiO₂ was higher than that of pure TiO₂.     

Photocatalytic membrane reactor for degradation of acid red B wastewater

Nano-titanium dioxide (TiO₂) photocatalyst was prepared by acid–sol method using tetrabutyl titanate and ethanol, which appeared to be anatase by XRD analysis. The wastewater containing azo dye acid red B was then subjected to photocatalytic degradation with photocatalyst TiO₂ and UV as light source in a slurry photocatalytic membrane reactor, which included a double layer cylindrical photocatalytic reaction zone and a plate frame membrane separation part. Two kinds of ultrafiltration (UF) membranes PVDF700 and PAN700 were applied and the combined process with photocatalysis was operated by a continuous re-circulating mode during treatment. At first, the adsorption characteristic of the titanium dioxide catalyst under different pH values was analyzed and the optimal operation condition of the photocatalytic process was achieved by changing TiO₂ dose and initial concentration of the dye. Then the performance of photocatalyst separation process by ultrafiltration (UF) was investigated. It was found that the degradation of acid red B was followed by first-order kinetics and the efficiency of photocatalysis can be evaluated by the initial reaction rate. Finally, the conglomeration and hydrophilizion phenomena by TiO₂ in the coupling system and its effect to different ultrafiltration membranes were analyzed.     

Preparation of photo-catalytic copolymer grafted asymmetric membranes (N-TiO<Subscript>2</Subscript>-PMAA-g-PVDF/PAN) and their application on the degradation of bentazon in water

Nitrogen-doped titanium dioxide (N–TiO₂) was prepared and supported on a novel copolymer grafted membrane matrix to avoid the problems associated with the removal of spent photocatalyst from treated water. Membranes of poly (methacrylic acid) grafted onto poly (vinylidene difluoride) and blended with poly (acrylonitrile) (PMAA-g-PVDF/PAN) were prepared through a dry–wet phase inversion technique. Methacrylic acid side chains were grafted onto an activated PVDF backbone by the method of reversible addition fragmentation chain transfer polymerization and then the novel photocatalytic asymmetric membranes of N–TiO₂–PMAA-g-PVDF/PAN were prepared. The casting solutions were blended with 1–5 % N–TiO₂ before immersion into the coagulation bath. PVDF and PAN offer several advantages which include: mechanical strength and toughness, chemical resistance, unaffected by long-term exposure to UV radiation, low weight, and thermal stability. N–TiO₂ was prepared through sol-gel synthesis. The photocatalytic membranes were evaluated by degradation process of herbicide bentazon in water. Photodegradation studies revealed that the optimum photocatalyst loading was 3 % N–TiO₂ and the optimum pH was 7 for the degradation of bentazon in water. UV–Vis, TOC and LC–MS analyses confirmed the successful photodegradation of bentazon. A bentazon removal efficiency of 90.1 % was achieved at pH 7. N–TiO₂–PMAA-g-PVDF/PAN membranes were successfully prepared and characterized. These photocatalytic membranes showed great potential as a technology for the effective removal of pesticides from water. According to literature, N–TiO₂–PMAA-g-PVDF/PAN asymmetric photocatalytic membranes have not been prepared before for the purpose of treating agricultural wastewater.     

Effect of surfactant in a modified sol on the physicochemical properties and photocatalytic activity of crystalline TiO<Subscript>2</Subscript> nanoparticles

This study describes the effect of amphiphilic organic molecules (surfactants) in a sol on the physicochemical properties and photocatalytic activity of crystalline TiO₂ nanoparticles prepared via a simple sol–gel route at high temperatures from 400 to 800 °C. Addition of polyoxyethylenesorbitan surfactant and polyethylene oxide and polypropylene oxide triblock copolymer as particle size inhibitors and pore directing agents into a stable titania sol affected the physicochemical properties of TiO₂ nanoparticles such as their crystallographic structure, morphology, and defect structure. With the addition of the surfactants, the ratio of anatase and rutile crystal phases of TiO₂ was controlled and an active anatase crystal phase was maintained during heat treatment up to 800 °C. Decrease in the sintering rate and inhibition in crystal growth were also observed, which resulted in higher surface area and inhibition of crystallite aggregation. Bulk defects in TiO₂ were reduced while surface defects were increased as a result of the addition of surfactants. These physicochemical properties of TiO₂ nanoparticles were correlated with photocatalytic degradation of 4-chlorophenol in water. The results revealed that high crystallinity, anatase crystal phase, high specific surface area, surface defects, and segregated morphology of TiO₂ nanoparticles, which were induced by the addition of surfactants, were more advantageous for enhancing photocatalytic destruction of the model organic compound tested in the study.     

Preparation of titania/carbon nanotube composites using supercritical ethanol and their photocatalytic activity for phenol degradation under visible light irradiation

Titanium dioxide (anatase, TiO₂) nanoparticles have been successfully deposited onto multi-walled carbon nanotubes (MWCNTs) via hydrolysis of titanium isopropoxide in supercritical ethanol. The as-prepared composites were characterized by X-ray diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy. It was demonstrated that the MWCNTs were decorated with well-dispersed anatase nanoparticles less than 7 nm in diameter. The size and loading content of the nanoparticles on MWCNTs could be tuned by manipulating the ratio of precursor to MWCNTs, and the formation mechanism of the composites was also discussed. The absorbance spectrum of the resultant TiO₂/MWCNT composites extended to the whole UV-visible region due to the decoration of TiO₂ on MWCNTs. The TiO₂/MWCNT composites were used as photocatalyst for phenol degradation under irradiation of visible light, which showed higher efficiency compared to a mixture of TiO₂ and MWCNTs.