Hydrothermal preparation and characterization of TiO2:AC composites

A new photocatalyst titania:activated carbon (TiO₂:AC) composite was prepared by impregnating anatase type TiO₂ nanoparticulates onto the activated carbon surface through a mild hydrothermal route. A varied ratio of TiO₂ to AC was considered for impregnation. As-prepared TiO₂:AC composite was characterized by various techniques such as powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), BET surface area and positron annihilation lifetime spectroscopy (PALS). Powder XRD results showed the persisting nature of anatase phase of TiO₂ deposited on the activated carbon surface. The BET, FTIR and PALS results revealed the impregnation threshold. The TiO₂ particulates were well adhered and uniformly dispersed on the carbon surface as confirmed by SEM.     

Antimicrobial activity of composite nanoparticles consisting of titania photocatalytic shell and nickel ferrite magnetic core

Reverse micelle and hydrolysis have been combined to synthesize composite nanoparticles consisting of anatase–titania photocatalytic shell and nickel ferrite magnetic core. The average particle size of the composite nanoparticles was in the range of 10–15 nm. The photocatalytic shell of titania is responsible for the photocatalytic and anti-microbial activity and nickel ferrite magnetic core is responsible for the magnetic behavior, studied by superconducting quantum interference device. The anatase TiO2 coated NiFe₂O₄ nanoparticles retains the magnetic characteristics of uncoated nanocrystalline nickel ferrites, superparamagnetism (absence of hysteresis, remanence and coercivity at 300 K) and non-saturation of magnetic moments at high field. The magnetic measurements results encourage their application as removable anti-microbial photocatalysts. Bacterial inactivation with UV light in the presence of titania-coated NiFe₂O₄ nanoparticles is faster than the action with UV light alone.     

Photocatalytic activity of vanadium-doped titania-activated carbon composite film under visible light

A V-doped titania-activated carbon composite film was prepared by a modified sol-gel method under mild condition. X-ray diffraction analysis revealed that the titania was a pure anatase phase. From scanning electron microscopy and N₂ adsorption-desorption measurements, we found that the composite film was porous since it formed a micro-nano structure. The photocatalytic activity of such film was evaluated through degradation of azo-dye Reactive Brilliant Red under visible light, and was compared to commercially available TiO₂, pure titania and vanadium-doped titania films. Results showed that the photocatalytic activity was enhanced a lot. It was due to expansion of the absorption edge by vanadium doping, and the synergistic effect of activated carbon with titania. Furthermore, the hydrophilic property of the as-prepared composite film was superior to other samples.     

Comparison of magnetic-nanometer titanium dioxide/ferriferous oxide (TiO<Subscript>2</Subscript>/Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>) composite photocatalyst prepared by acid–sol and homogeneous precipitation methods

Novel magnetic-nanometer titanium dioxide/ferriferous oxide (TiO₂/Fe₃O₄) composite photocatalyst was prepared using acid–sol and homogenous precipitation methods. The photocatalyst particle was made of a Fe₃O₄ core covered with nanocrystal anatase TiO₂, without a high-temperature heat-treatment step. The catalyst has been characterized by X-ray diffraction, transmission electron microscopy, differential thermal analysis measurements, and ultraviolet spectrum. The results suggested that titania was mainly presented as anatase and Fe₃O₄ did not appear on the surface of the composite particles when the molar ratio of TiO₂/Fe₃O₄ increased to 20:1 in the acid–sol method, but 5:1 in the homogeneous precipitin method. The size of the crystal was ranged from 2.4 to 3.6 nm prepared by both methods. In the catalytic test, the composite particles, which were prepared by acid–sol, had higher catalytic activity than that prepared by homogenous precipitation method due to the size difference of the composite particles.     

Percolation threshold for electrical resistivity of Ag-nanoparticle/titania composite thin films fabricated using molecular precursor method

To find the percolation threshold for the electrical resistivity of metallic Ag-nanoparticle/titania composite thin films, Ag-NP/titania composite thin films, with different volumetric fractions of silver (0.26 ≤ φ_Ag ≤ 0.68) to titania, were fabricated on a quartz glass substrate at 600 °C using the molecular precursor method. Respective precursor solutions for Ag-nanoparticles and titania were prepared from Ag salt and a titanium complex. The resistivity of the films was of the order of 10⁻² to 10⁻⁵ Ω cm with film thicknesses in the range 100–260 nm. The percolation threshold was identified at a φ_Ag value of 0.30. The lowest electrical resistivity of 10⁻⁵ Ω cm at 25 °C was recorded for the composite with the Ag fraction, φ_Ag, of 0.55. X-ray diffraction (XRD), field-emission scanning electron microscope (FE-SEM), and transmission electron microscopic (TEM) evaluation of the effect of the morphology and the nanostructures of the Ag nanoparticles in the composite thin films on the electrical resistivity of the film revealed that the films consist of rutile, anatase, and metallic Ag nanoparticles homogeneously distributed in the titania matrix. It could be deduced that the electrical resistivity of the thin films formed at 600 °C was unaffected by the anatase/rutile content within the thin film, whereas the shape, size, and separation distance of the Ag nanoparticles strongly influenced the electrical resistivity of the Ag-nanoparticle/titania composite thin films.     

Deposition of anatase titania onto carbon encapsulated magnetite nanoparticles

A novel magnetically separable photocatalyst (titania-coated carbon encapsulated magnetite: TCCEF) was prepared. The prepared composite photocatalyst was characterized with an x-ray diffractometer (XRD), a transmission electron microscope (TEM), a Fourier transform infrared spectrometer (FT-IR) and a vibrating sample magnetometer (VSM). The photocatalytic activity of the samples was determined by degrading model contaminated water, a phenol aqueous solution. The results were compared with single-phase titania (pure titania and Degussa P25) and Fe(3)O(4)/TiO(2), and enhanced photocatalytic activity was obtained. It is suggested that the enhanced photocatalytic activity is ascribed to two major factors. First, the encapsulation of magnetite into the carbon layer may inhibit the direct electrical contact of titania and magnetite, hence preventing the photodissolution of the iron oxide phase. Second, the enhanced hydroxyl groups on TCCEF may inhibit the recombination of electron-hole pairs. On the other hand, the magnetic photocatalyst can be easily recovered from a slurry with the application of an external magnetic field.     

Preparation and photocatalytic characteristics of core-shell structure TiO2/BaFe12O19 nanoparticles

A core-shell structure TiO₂/BaFe₁₂O₁₉ composite nanoparticles that can photodegrade organic pollutants in the dispersion system effectively and can be recycled easily by a magnetic field is reported in this paper. The obtained samples were characterized by energy dispersive X-ray spectroscopy (SEM-EDS), X-ray diffraction (XRD) and transmission electron microscopy (TEM). The TiO₂/BaFe₁₂O₁₉ magnetic photocatalyst is composed of two parts: (1) TiO₂ shell used for photocatalysis and (2) BaFe₁₂O₁₉ core for separation by the magnetic field. The photocatalytic activity of the as-prepared magnetic photocatalyst increased with increasing the thickness of TiO₂ coating layer. On the other hand, the saturation magnetizations of titania-coated BaFe₁₂O₁₉ nanoparticles decreased with increasing thickness of the titania coating, while the coercivity does not show any change after coating.     

Poly(methyl methacrylate)-TiO<Subscript>2</Subscript> nanocomposite obtained by non-hydrolytic sol–gel synthesis

Poly(methyl methacrylate) (PMMA)/titanium dioxide (TiO₂) nanocomposites were prepared by means of in situ generation of TiO₂ through a non-hydrolytic sol–gel process (NHSG), starting from titanium chloride, as titania precursor, benzyl alcohol, as oxygen donor, and commercial PMMA. TiO₂ nanoparticles (average size of 30 nm) were obtained in the anatase and amorphous forms. The in situ generation led to a very homogeneous distribution of particulate fillers within the polymeric matrix avoiding the problems related to distributive and dispersive mixing of conventional compounding methods (top down approach). A slight increase of glass transition temperature was observed for all prepared composites with respect to the pristine PMMA. The NHSG process did not affect the molecular weight of the polymers indicating the absence of any degradation reaction for PMMA. The presence of titania in the anatase phase increases the photodegradation of the PMMA matrix due to UV irradiation.     

An investigation on synthesis and photocatalytic activity of polyaniline sensitized nanocrystalline TiO<Subscript>2</Subscript> composites

Polyaniline (PAn) sensitized nanocrystalline TiO₂ composite photocatalyst (PAn/TiO₂) with high activity and easy separation was facilely prepared by in situ chemical oxidation of aniline from the surfaces of the TiO₂ nanoparticles. The morphology, structure, and light absorption properties of composite photocatalyst were examined in term of its application to photocatalysis. The photocatalytic activity of PAn/TiO₂ nanocomposites for the degradation of methylene blue (MB) aqueous solution was investigated and compared with pure TiO₂. The spectra analyses illustrated that, when PAn deposited on the surface of TiO₂, the crystalline behavior of PAn was hampered and the degree of crystallinity decreased, and the characteristic peaks of the PAn were shifted indicating that there was a strong interaction between PAn and TiO₂ nanoparticles. PAn was able to sensitize TiO₂ efficiently and the composite photocatalyst could be activated by absorbing both the ultraviolet and visible light (λ = 190–800 nm), whereas pure TiO₂ absorbed ultraviolet light only (λ < 400 nm). Photocatalytic experiments showed that under natural light irradiation, MB could be degraded more efficiently on the PAn/TiO₂ than on the pure TiO₂, due to the charge transfer from PAn to TiO₂ and efficient separation of e⁻-h⁺ pairs on the interface of PAn and TiO₂ in the excited state. More significantly, the PAn/TiO₂ composite photocatalyst exhibited easy separation and less deactivation after several runs. The advantages of the obtained PAn/TiO₂ composite photocatalyst revealed its great practical potential in wastewater treatment.     

Photocatalytic decomposition of methylene blue on nanocrystalline titania prepared by different methods

Nanocrystalline particles of pure anatase titania were prepared by two different methods. One is the sol-gel method at ambient temperature using ultrasonication (TiO₂-SG-US) and conventional stirring method (TiO₂-SG-S) and the other by surfactant assisted hydrothermal synthesis (TiO₂-HT). More uniform distribution/dispersion of the nanoparticles (SEM), marginally higher surface area, better thermal stability and phase purity are some of the advantages of preparation of nanocrystalline titania by sol gel ultrasonication method and hydrothermal synthesis method. The behavior of anatase titania in photocatalytic decomposition of methylene blue in aqueous medium was studied as a function of the method of preparation and the crystallite size. The nanoparticles prepared by ultrasonication method were more effective than both, the sample prepared by conventional stirring method and commercial Degussa P-25. The higher photocatalytic activity of TiO₂-SG-US is attributed to the more uniform size of the particles as compared to TiO₂-SG-S samples. Both TEM and XRD data on TiO₂-HT samples reveal a uniform and nanocrystalline TiO₂ particles, which showed photocatalytic activity in both UV and visible region although brookite phase was also present.     

A new method to prepare high-surface-area N-TiO2/activated carbon

A new method, combining impregnation and vapor-hydrolysis, was developed to prepare hybrid photocatalyst: nitrogen doped TiO₂ coated activated carbon (N-TiO₂/AC). The activated carbon (AC) was impregnated into titanium tetraethoxide/urea/methanol solution, and then the impregnated AC powder was kept in water vapor at 90 °C for 3 h for hydrolysis. Then it was calcinated to fabricate N-TiO₂/AC. Transmission electron microscopy (TEM) results showed that the nitrogen doped TiO₂ (N-TiO₂) in the as-synthesized hybrid was anatase TiO₂ powder with 10-20 nm in grain size, and the bandgap was about 3.08 eV. Moreover, the hybrid photocatalyst (8 wt.% N-TiO₂) had high specific surface area that was up to 1321 m²/g. The hybrid photocatalyst is expected to have high photocatalytic performance with visible irradiation.     

Study on crystallinity and morphology controlling of titania using acrylamide gel method and their photocatalytic properties

In this study, polyacrylamide gel method was used for preparation of pure and mixed phase TiO₂ nanoparticles. The influence of synthesis conditions on the physicochemical properties of products was investigated. It was found that the type of acid, which was used for acidifying the precursor solution together with calcination temperature can affect the phase structure, crystalline size, morphology and thereby photocatalytic activity of obtained TiO₂ nanoparticles. Different trends were observed during the phase transformation, particle growth, shift in energy of band gap with the change in tensile strain to compressive strain of the prepared TiO₂ nanomaterial. X-ray diffraction (XRD) showed that prepared nanocrystals, which were calcined at 450 °C have pure anatase and anatase–rutile mixed structures. The prepared samples having crystallite size between 5 nm and 60 nm were observed at different calcination temperatures. In addition, the photocatalytic activities of the prepared samples were evaluated by monitoring the degradation of Cresol Red (CR). The results show that the photocatalyst (TEC_I), exhibits the highest photocatalytic efficiency where 94.7% of CR can be decomposed after UV exposure for 75 min.     

Preparation of SiO2/TiO2 composite fibers by sol-gel reaction and electrospinning

Submicron scale composite fibers of SiO₂/TiO₂ with various compositions have been prepared by electrospinning a sol-gel precursor of tetraethyl orthosilicate(TEOS) and titanium(IV) isopropoxide(TiP), followed by calcination. Any gelator or binder has not been used in this direct preparation process for composite fibers, and the maximum amount of titania for suitable fiber formation was about 50 mol%. The sintered composite fibers were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), and Fourier transform infrared (FT-IR) spectroscopy. Our results show that the surface morphology and crystallization behavior of electrospun fibers are largely influenced by the calcination temperature and the content of TiO₂. XRD results also reveal that the anatase phase in composite fibers can be preserved even after high temperature processing at lower content (x = 0.1, 0.2) of titania.     

In-situ growth of titania nanoparticles in electrospun polymer nanofibers at low temperature

In-situ growth of titania nanoparticles in poly (ethylene terephthalate) (PET) nanofibers has been successfully achieved by combining sol-gel method and electrospinning process. Titania precursor, tetra-n-butyl titanate (TBT), was firstly hydrolyzed in trifluoroacetic acid (TFA), and then blend with a solution of PET in mixture of trifluoroacetic acid/dichloromethane (TFA/DCM) to form a homogeneous solution for electrospinning. Titania nanoparticles in-situ generated in the electrospun nanofibers via a hydrothermal treatment process at 70 °C-90 °C. The morphology and crystallinity of PET/TiO₂ hybrid nanofibers were investigated using TEM and DSC. The results showed that titania nanoparticles of anatase phase with an average diameter of about 10 nm in-situ generated both inside and on the surface of PET electrospun nanofibers. The reversible networks formed between titania nanoparticles and PET macromolecular chains led to considerable decrease of PET crystallinity.     

Macroporous TiO2/carbon composites prepared via a simple soaking process

A new-type composite photocatalyst of three-dimensional ordered macroporous (3DOM) TiO₂/C was prepared and tested in this paper. 3DOM carbon materials were first prepared by colloidal crystal templating process, and then the sols of TiO₂ from tetrabutyl titanate were infiltrated in the macroporous structures via capillary force. After calcinations at nitrogen flow, TiO₂/C composite materials were prepared. The obtained samples were analyzed by SEM, TEM, XRD and BET. The results indicated that macroporous TiO₂/C can remain the three-dimensional ordered structure and TiO₂ nanoparticles distributed in the interior of macropores uniformly. Eventually, 3DOM TiO₂/C materials were used as a new-type photocatalysts to decompose the methyl orange solution under ultraviolet light, which displayed excellent catalytic activity and regenerative ability.     

Preparation of magnetic photocatalyst nanoparticles—TiO2/SiO2/Mn–Zn ferrite—and its photocatalytic activity influenced by silica interlayer

A magnetic photocatalyst, TiO₂/SiO₂/Mn–Zn ferrite, was prepared by stepwise synthesis involving the co-precipitation of Mn–Zn ferrite as a magnetic core, followed by a coating of silica as the interlayer, and titania as the top layer. The particle size and distribution of magnetic nanoparticles were found to depend on the addition rate of reagent and dispersing rate of reaction. The X-ray diffractometer and transmission electron microscope were used to examine the crystal structures and the morphologies of the prepared composites. Vibrating sample magnetometer was also used to reveal their superparamagnetic property. The UV–Vis spectrophotometer was employed to monitor the decomposition of methylene blue in the photocatalytic efficient study. It was found that at least a minimum thickness of the silica interlayer around 20 nm was necessary for the inhibition of electron transference initiated by TiO₂ and Mn–Zn ferrite.     

Evaluating the potential of a new titania precursor for the synthesis of mesoporous Fe-doped titania with enhanced photocatalytic activity

Mesoporous Fe (III) doped TiO₂ nanoparticles with an anatase phase were prepared by using a stable precursor potassium hexafluorotitanate as Ti source for the first time and its physical as well as photocatalytic properties were compared with that of Fe doped titania prepared from the most common Ti source titanium isopropoxide. FeSO₄·7H₂O and Fe (NO)₃·9H₂O were used for doping titania with Fe (III). Physicochemical properties of the samples were characterized by XRD, XPS, FTIR, Raman spectroscopy, N₂ adsorption–desorption isotherms, UV–vis diffuse reflectance spectroscopy. EDX confirms the presence of Fe. DRS and TEM reveals that doping has taken place. It was found that Fe-doped nanostructured titania prepared from potassium hexafluorotitanate was much more effective in the photocatalytic decomposition of bromocresol green than undoped nanostructured titania as well as commercial titania.     

Facile two-step preparation of polystyrene/anatase TiO2 core/shell colloidal particles and their potential use as an oxidation photocatalyst

Titania and materials containing titania have received considerable attention due to their technological importance in many areas. In this study, anatase crystalline titania (TiO₂) coated polystyrene (PS) colloidal particles were successfully prepared in two easy steps. First, a one pot synthesis of the colloidal particles was produced via an emulsifier-free emulsion copolymerization of styrene (S) and 2-(dimethylamino)ethyl methacrylate (DMA) at pH 4.0. In the second step, the synthesized particles were coated by titania using a sol–gel process in-situ hydrolysis and a condensation reaction of titanium(IV) isopropoxide in an acidic aqueous solution. In this way, anatase crystalline titania, rather than the usual amorphous form, was obtained as a shell on the PS colloidal particles. Both the PS colloidal particles and the polystyrene/anatase titania (PS/TiO₂) core/shell colloidal particles had monodisperse morphology and were characterized using SEM, Zetasizer, FTIR, XRD and TGA techniques or measurements. In addition, the photocatalytic activity of the PS/TiO₂ core/shell particles was tested for the first time in an oxidation reaction, in the oxidation of 4-methoxybenzyl alcohol (MBA) with O₂ in water. Much higher selectivities of the target product, p-anisaldehyde (AA), were obtained with the PS/TiO₂ core/shell particles than with a commercial anatase crystalline TiO₂.     

Low-temperature synthesis of magnetically recoverable,superparamagnetic, photocatalytic,nanocomposite particles

A new, simple, low-temperature method for the synthesis of superparamagnetic, photocatalytic, nanocomposite particles for applications in the decomposition of pollutants in water is presented. The method is based on the coating of clusters of superparamagnetic maghemite (γ-Fe₂O₃) nanoparticles with a photocatalytic anatase layer using the hydrolysis of aqueous TiOSO₄. The clusters of an appropriate size between 100 and 200 nm form by the simultaneous agglomeration of the aminopropyl-triethoxy-silane-grafted maghemite nanoparticles with a size of approximately 15 nm in a suspension of diluted TiOSO₄. During a sudden increase of pH with the addition of NaOH the titania is heterogeneously nucleated at the cluster surfaces. If the hydrolysis was conducted at an elevated temperature of 90 °C, the titania layer was nanocrystalline anatase. The composition of the nanocomposite particles, i.e., the thickness of the anatase layer, can be controlled simply by changing the starting TiOSO₄/Fe₂O₃ ratio for low titania contents, and by multiple coatings to get high titania contents. The photocatalytic activity of the nanocomposites was evaluated in the photocatalytic decomposition of formic acid. The activity seems to increase with an increase in the thickness and the crystallinity of the anatase coating, whereas it decreased after the calcination of the as-synthesized nanocomposite. The coating of the maghemite nanoparticles with a thin layer of insulating silica also slightly improves the photocatalytic activity.     

Synthesis and characterization of Ce-doped mesoporous anatase with long-range ordered mesostructure

The effect of cerium cation on the formation of titania crystallites using H⁺ as catalyst under mild condition has been investigated. The results indicated that the presence of cerium cation can improve the selectivity of producing anatase crystallites and inhibit the growth of crystallites. The Ce-doped mesoporous titania with highly crystallized pore walls consisting of anatase nanoparticles was synthesized by anatase crystallites assembly. The long-range ordered mesostructure was characterized by low angle and wide angle X-ray diffraction (XRD), N₂ adsorption-desorption, transmission electron microscopy (TEM) and selected area electron diffraction (SAED).