Macroporous Titania Research Articles

The application of Langmuir–Blodgett technique in preparation of the macroporous titania coatings

The aim of this work was preparation of the macroporous titania coatings with the use of the sol–gel process and poly(methylmetacrylate) beads as a template. The effectiveness of the Langmuir–Blodgett (LB) and dip-coating (DC) methods in deposition of polymer beads on the silicon wafers was compared. Resulted polymer layers and final porous titania coatings were analyzed with the use of the atomic force microscope. It was found, that application of the LB is possible only when arachidic acid is present in the subphase. It should be highlighted, that the application of the LB method is the novelty between the methods of the polymer beads arrangement having the diameter of 200–300 nm. Main factors which influence the structure and the arrangement of polymer templates were the concentration of the polymer suspension and the rate of the substrate immersion/withdrawal from the suspension. We established, that the optimal concentrations for preparation of polymer templates, exhibiting good arrangement of individual beads, were 0.5 and 6 % for LB and DC methods, respectively. The size of pores of the obtained macroporous titania (200–330 nm) corresponds well with the size of the polymer beads used as the template (200–235 nm).

Significant photocatalytic activity enhancement of titania inverse opals by anionic impurities removal in dye molecule degradation

The photocatalytic behavior in dye molecule degradation of highly ordered three dimensional macroporous titania inverse opals prepared by the polystyrene spheres templating method has been investigated. The sulfate impurity stemming from K2S2O8 used as initiator for the styrene polymerization and remaining in the final materials in a form of sulfate anions was found to strongly inhibit the photocatalytic process of titania inverse opals. The mechanism of the negative effect of sulfate anionic impurity has been studied by the theoretical calculations and the comparison of samples subject to a wash process or not, the artificial addition of sulfate anions to the reaction medium and cycle experiments of samples without the washing process. Raman spectroscopy confirmed that in TiO2 inverse opal structures, sulfate ions are present in divalent forms. However, in aqueous photocatalytic medium, monovalent hydrosulfate anions can also be present. Theoretical calculations on the interaction of sulfate (mono and divalent) anions and Rhodamine B (RhB) with TiO2 inverse opal indicated that the adsorption binding energy of divalent sulfate anions on the titania surface (168kcal/mol) is over four times as that of the Rhodamine B (36kcal/mol) in the photocatalytic system and that of hydrosulfate anions is around 53–57kcal/mol, still much higher than that of Rhodamine B. The strong adsorption of the anionic sulfate impurity on the surface of titania inverse opals would block the active sites and thus strongly affect the photocatalytic performance. A model of the negative action of sulfate anions has been proposed. This work leads to a new physic-chemical insight on the behavior of sulfate anions in the photocatalytic degradation of RhB and revealed that a single washing process to remove the impurity suggested significant promotion effect of the photocatalytic reaction without any surface modulations. This washing process dramatically suppressed the adsorption effect induced by the sulfate impurity and simplified the procedures, improving the photocatalytic performance.

Hydrothermal and surfactant treatment to enhance the photocatalytic activity of hierarchically meso–macroporous titanias

The photocatalytic activities of various hierarchically meso–macroporous titanias, obtained via a spontaneous self-formation process using titanium isopropoxide, have been investigated by comparing each materials’ capability to photodegrade Rhodamine B. Three synthesis routes have been developed to synthesize hierarchically meso–macroporous titania materials: (A) in water without and (B) with hydrothermal treatment and (C) in a surfactant Brij 56 aqueous solution with hydrothermal treatment, respectively. These results show that the introduction of surfactant Brij 56 and a hydrothermal treatment in the synthesis system greatly improve the crystallinity of the anatase phase in hierarchically meso–macroporous titanias and their thermal stability, resulting in a remarkable enhancement of their photocatalytic activity. Furthermore, the effect of calcination on hierarchically porous structure and their photocatalytic activity has also been investigated in detail. The properties of the products were characterized by XRD, SEM and N2 adsorption-desorption measurements.

Fabrication of Scattering Spheres-Embedding Three-Dimensional Ordered Macroporous Titania and Application in Dye-Sensitized Photoanode

Scattering spheres-embedding three-dimensional ordered macroporous (3DOM) titania(TiO2) was fabricated, by the route of colloidal spheres self-assembly, infiltration and template removal. The procedures of 3DOM structure preparation were characterized by transmission electron microscope (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD). The silica@PMMA core-shell spheres were prepared and self-assembled into colloidal crystal template. Solid material was deposited in the colloidal crystal template by spin-coating of titania nanoparticle dispersions. Subsequently, the samples were heated to 400 °C to form anatase TiO2and to remove the polymer of template, which resulted in macroporous structure with a silica sphere in each lattice pore. The conventional TiO2film, 3DOM TiO2photoanodes were also fabricated. It was found that SiO2-embedding 3DOM photoanode has the higher photocurrent efficiency than both of TiO2 film and 3DOM, because there are scattering spheres in its lattice pores which enhance the light scattering and improve the light harvest of the dye.

A facile approach to fabricate three-dimensional ordered macroporous rutile titania at low calcination temperature

Although ordered macroporous rutile titania is seldom successfully fabricated because it is hard to maintain its integrated structure at the high calcination temperature, we herein describe a facile approach to obtain inverse rutile titania opals under a relatively mild condition. By employing SnO2 as the additive for enhancing the phase transformation from anatase to rutile, we investigated various kinds of differences (pore size, backbone filling fraction, reflection peaks, etc.) between the macroporous structures with the two different kinds of crystalline phases (anatase and rutile), which were hardly stressed in other reports because the two phases could not be obtained separately under the same calcination condition if using other approaches.

Rapid atmospheric plasma spray coating preparation and photocatalytic activity of macroporous titania nanocrystalline membranes

Macroporous TiO 2 nanocrystalline (NC) membranes with average pore size of 0.35 μm were successfully fabricated by coating on an alumina support via a rapid atmospheric plasma spraying (APS) approach. The as-prepared TiO 2 and P25 membranes were first tested for photocatalytic activity using Reactive Black-5 (RB5) dye in a batch reactor with UV light irradiation, respectively. RB5 dyes were completely decomposed with an irradiation time of 70 min, and the rate constants for the photocatalytic reactions using TiO 2 and P25 membranes were determined to be approximately 0.076 and 0.071 min −1, respectively. The photocatalytic activity of the as-prepared TiO 2 NC membranes was slightly better than P25 membranes, indicating the APS-fabricated TiO 2 NC membranes were with a high photocatalytic activity. The TiO 2 membranes were further used for the photodegradation of dextran and humic acid (HA), and the permeate fluxes of dextran and HA increased when the membranes were exposed to UV light irradiation. The dominant filtration resistances of the dextran and HA solutions were pore and cake resistances, respectively, which were reduced by a photocatalytic TiO 2 NC membrane under UV light illumination. The removal percentages of HA at an initial concentration of 2 ppm were 58% and 90% in the dark and under UV light irradiation, respectively. The increase in the HA removal resulted from the photodegradation of HA by the photocatalytic TiO 2 NC membrane. In this work, a rapid process of APS coating was first used for the preparation of macroporous TiO 2 NC membranes with high photocatalytic activities, which can be applied for water treatment, for example, in the photodegradation of bio-organisms and protein under UV light irradiation.

Exotemplating synthesis of nitrogen-doped carbon materials with hierarchically porous structure and their application for lysozyme adsorption

Nitrogen-doped carbon materials with hierarchically porous structure were prepared by employing meso-/macroporous titania (MMT) as exotemplate with the use of Vitamin B6 (VB6) as both the carbon precursor and the nitrogen source for elemental doping. The synthesized materials were characterized by N 2 sorption, scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. The obtained N-doped carbon materials have a multi-scaled porous hierarchy with pore sizes ranging from micropores, mesopores to macropores, and their morphology can be easily tuned through a simple adjustment of the weight ratio of VB6 to MMT. The different chemical state (pyridine-like N, quaternary N and oxidized N) and the content of nitrogen were analyzed by XPS. The prepared materials were used as the adsorbents for lysozyme. The effect of nitrogen doping on the lysozyme adsorption capability was investigated by comparison of the lysozyme adsorption behavior on the nitrogen-doped and nitrogen-free carbon materials with a similar pore structure. It was found that the nitrogen-containing carbon had higher adsorption capacity of lysozyme than that of the nitrogen-free carbons.

Three‐Dimensionally Ordered Macroporous Titania with Structural and Photonic Effects for Enhanced Photocatalytic Efficiency

The three dimensional photonic crystals concept has been employed for photocatalysis. Slow photons observed in photonic crystal structures will enhance the absorption of materials when the photon energy matches the absorbance of the materials, which would improve the photocatalytic efficiency. In this work, three dimensionally ordered macroporous (3DOM) titania was prepared by applying the colloidal templating method with a range of pore diameters. Calcination at different temperatures to remove the templates resulted in different crystalline phases. The structural and photonic properties were characterized and their effects on photocatalytic activity are presented as well. A strong effect of the pore diameter on the photocatalytic activity was observed and correlated with the photon energy involved in the photodegradation process of organics. A very interesting phenomenon was also observed: the sample prepared by using PS spheres of 250 nm had a high photocatalytic efficiency, which mismatched the effect of pore diameter, probably owing to the slow photon effect.

The stability of nonporous and macroporous titania thin films in aqueous electrolyte solutions

A simple electrochemical approach was used to evaluate the stability and porosity of titania and silica thin films spin coated on electrode surfaces. This approach involved monitoring the magnitude of the Faradaic current of diffusing redox probes at the modified electrode surfaces over the course of a week to 4.5 months. Relatively nonporous films were examined as well as films templated with polystyrene latex spheres. The results show that templated titania films were significantly more porous compared to non-templated films. After the defect sites in the templated films were blocked, their long-term stability in aqueous electrolyte was evaluated. For titania, blocking was done by spin coating a dilute titania sol on the top of the film whereas for silica, the film was soaked in octyltrimethoxysilane. Both types of titania films (templated and non-templated) were found to be significantly more stable than the corresponding silica films, showing no signs of deterioration in simple electrolyte solutions during the entire evaluation period. In contrast, silica films showed significant deterioration in as little as 3 days. The enhanced stability of the titania films relative to silica films in near neutral electrolyte solutions was attributed to the differences in the point of zero charge of the oxide films.

Random lasing from localized modes in strongly scattering systems consisting of macroporous titania monoliths infiltrated with dye solution

We have prepared random lasers that consist of macroporous titania monoliths infiltrated with dye solution and that operate close to light localization regime. When the excitation pulse energy exceeds a threshold, discrete spectral lines ascribed to laser oscillation appear on a featureless emission peak. No pulse-to-pulse variation was observed in the spectral positions of lasing lines, indicating that the lasing modes are localized in the medium. We demonstrated selective excitation of lasing modes by pumping at different positions on the sample.

Microwave-Assisted Self-Organization of Colloidal Particles Inside Water-in-Oil Emulsions

Commercial amidine polystyrene microspheres were self-organized to obtain colloidal microclusters from water-in-oil emulsion droplets as confining geometries. For demulsification process, microwave was irradiated to remove water droplets selectively resulting in the shrinkage of water droplets which induces inward capillary pressure for the particle self-assembly. The amidine polystyrene clusters were coated with silica nanospheres or titania nanoparticles by co-organizing the mixed particle suspensions inside water droplets by microwave heating. Titania-coated polystyrene clusters were calcined to produce hollow macroporous titania powders. Finally, sulfate-coated polystyrene microspheres were self-assembled with silica nanoparticles to generate polystyrene/silica composite clusters by microwave irradiation method.

Phosphorus and nitrogen co-doped titania photocatalysts with a hierarchical meso-/macroporous structure

Visible light-active phosphorus and nitrogen co-doped meso-/macroporous titania materials were prepared by a simple two-step approach of the direct phosphation with the use of phosphoric acid solution and the succedent nitridation with the use of the urea solution. The prepared materials were characterized by UV–vis, solid-state 31P MAS NMR, FT-IR, XPS, XRD, SEM, TEM, and N2 adsorption analysis. Direct synthesis of phosphorus-doped meso-/macroporous titania materials could inhibit the formation of brookite phase and increase the surface area significantly, resulting in the hierarchical porous framework of nanocrystalline anatase phase with enhanced thermal stability and large porosity, and these features retained during the subsequent nitridation. The incorporation of P and N in the anatase titania lattice in the form of O–Ti–N, O–P–N, and Ti–O–P linkages was evidenced, and the extension of the absorption edges into the visible region and the corresponding narrowing of band gaps were observed in these N and P co-doped meso-/macroporous titanias, giving a higher photocatalytic activity in the degradation of Rhodamine B dye under visible-light irradiation than the samples doped with only N or P. The beneficial effect of hierarchical meso-/macroporous structure is also examined.

Shear Induced Formation of Patterned Porous Titania with Applications to Photocatalysis

Patterned macroporous titania (TiO2) materials have been synthesized via a shear-aligned rigid crystalline surfactant mesophase. The macropores inherit the hexagonal geometry of the water channels of the template. Scanning electron microscopy (SEM) and cut-section transmission electron microscopy (TEM) images show that the macropores templated by the sheared mesophase attain considerably greater alignment than pores templated by the nonsheared mesophase. The mean pore diameter, the crystalline size of TiO2 particles, and the photoactivity of the materials increase with the increase of water content in the template. The sheared TiO2 samples exhibit higher photocatalytic activity for the degradation of Rhodamine B than the corresponding materials synthesized in the nonsheared template. The improvement in photocatalytic activity of the sheared TiO2 materials is attributed to its higher photoabsorption efficiency and the patterned channels which facilitate the diffusion and transport of reactant molecules within the frameworks. Such patterned porous materials may have promise as advanced catalytic supports and photocatalytic materials.

Macroporous anatase titania particle: Aerosol self-assembly fabrication with photocatalytic performance

An anatase titania particle with a honey-comb-like pore structure (200 nm-pore size) and a controllable outer diameter (0.2–1 μm) was successfully prepared using a spray-drying method. As a precursor, an anatase nanoparticle (5 nm) and a polystyrene particle (200 nm) were used as a titania source and a colloidal template, respectively. The outer diameter could be controlled by varying the precursor concentration. The photocatalytic performance of a porous particle was faster than that of a dense particle (with a similar outer diameter).

Fluorine and Carbon Codoped Macroporous Titania Microspheres: Highly Effective Photocatalyst for the Destruction of Airborne Styrene under Visible Light

Airborne styrene is a suspected human carcinogen commonly present in industries where resins are used. Traditional ways of abating this pollutant include the use of various adsorbents (activated carbon or zeolites) or thermal treatment. The earlier method is simply a temporary containment of the pollutant, requiring spent-adsorbents to be regenerated frequently, while the latter is energy-intensive. Work involving the photodegradation of airborne styrene is limited in recorded literature. This study uses a well-characterized combined fluorine/carbon codoped macroporous-titania catalyst, capable of destroying airborne styrene using irradiation in the visible range. A fluidized-bed photoreactor, combined with high-flow rates relative to the minimum fluidization velocity (Umf) of the catalysts, is utilized in the photooxidation process. The effects of varying relative humidity (RH, 0 or 20%) are investigated in using both UV (248nm) and visible (400−700nm) irradiation. It is found that RH levels of 20% promote the complete degradation of 300 ppmV airborne styrene under both types of irradiation. Reaction intermediates on the surface of the used catalysts are probed by high-performance liquid chromatography (HPLC).

Synthesis of titania monoliths for chromatographic separations

Titania monoliths inside capillary columns were prepared from a mixture of titanium propoxide, hydrochloric acid, formamide and water. Several synthesis parameters such as hydrolysis ratio, porogen type, precursor concentration, and drying step have been identified and controlled in order to obtain a macroporous titania monolith, efficient for liquid chromatography, inside a silica capillary. Pure titania monolith with a 10 times higher permeability as compared to a classical packed column was produced, and was able to separate a xanthine test mixture in the LC mode. Even if direct observations with scanning electron microscopy cannot be performed in wet conditions, the homogenous structure of the monolith was demonstrated by the plate height observed during chromatographic separation of xanthines in hydrophilic interaction liquid chromatography.

Highly Crystalline Inverse Opal Transition Metal Oxides via a Combined Assembly of Soft and Hard Chemistries

A combined assembly of soft and hard chemistries is employed to generate highly crystalline three-dimensionally ordered macroporous (3DOM) niobia (Nb2O5) and titania (TiO2) structures by colloidal crystal templating. Polystyrene spheres with sp2 hybridized carbon are used in a reverse-template infiltration technique based on the aqueous liquid phase deposition of the metal oxide in the interstitial spaces of a colloidal assembly. Heating under inert atmosphere as high as 900 degrees C converts the polymer into sturdy carbon that acts as a scaffold and keeps the macropores open while the oxides crystallize. Using X-ray diffraction it is demonstrated that for both oxides this approach leads to highly crystalline materials while heat treatments to lower temperatures commonly used for polymer colloidal templating, in particular for niobia, results in only weakly crystallized materials. Furthermore it is demonstrated that heat treatment directly to higher temperatures without generating the carbon scaffold leads to a collapse of the macrostructure. The approach should in principle be applicable to other 3DOM materials that require heat treatments to higher temperatures.

Photocatalytic oxidation of gaseous 1,2-dichlorobenzene using photonic titania (inverse opal) on optical fibers in a monolith configuration

Macroporous photonic band-gap titania with inverse opal topology was fabricated on optical fibers using polystyrene templates and sol–gel chemistry. The photonic character of the inverse opal titania was characterized using X-ray diffraction and UV absorbance measurements. The fibers were bundled into a monolith reactor and used to degrade a gaseous pollutant, 1,2-dichlorobenzene (DCB). The process was conducted in a semi-batch system with UV radiation being conducted through optical fibers. Experimental parameters such as polystyrene template size, UV light intensity, fiber distribution pattern and feed flow rates were varied. The reaction rate constant increased with increasing feed flow rate and UV intensity. Rate constants were reaction-limited above a flow rate of 50 mL/min and the intrinsic rate constant reached at asymptotic value above the UV intensity of 60 mW/cm 2 in the lab-scale reactor. Computational fluid dynamic (CFD) simulations identified flow bypassing in the reactor, which was rectified by rearranging the fibers within the reactor.

Biomimetic apatite induction of P-containing titania formed by micro-arc oxidation before and after hydrothermal treatment

Phosphorous (P)-containing titania films were prepared by micro-arc oxidation (MAO) of titanium (Ti) in an electrolyte containing β-glycerol phosphate disodium salt pentahydrate (β-GP, C 3H 7Na 2O 6P .5H 2O), and their apatite inducing ability in a simulated body fluid (SBF) was investigated. Macro-porous titania films were formed, consisting of only anatase phase, and the P content in the films increased up to 8 at.% with an increasing applied voltage. During hydrothermal treatment, the P in the films was diffused out to the surface and hydrolyzed to form the hydrogen phosphate (HPO 4 2−) group. When immersed in SBF, no apatite was induced in any of the P-containing MAO specimens for up to 28 days. However, after a hydrothermal treatment at 250 °C, apatite was induced on the titania surfaces as early as 9 h immersion, and the entire exposed surface was covered with the apatite globules after 36 h immersion, which was much faster than the apatite induction on Ca-containing titania. The higher apatite-inducing ability of P-containing titania after hydrothermal treatment was believed to be due to the crystal structure (anatase) and presence of HPO 4 2− group on the surface.

Degradation of Methylene Blue by Three-Dimensionally Ordered Macroporous Titania

Accelerated photodegradation of methylene blue (MB) over three-dimensionally ordered macroporous (3DOM) titania (pore sizes: 0.5 and 1 microm) is demonstrated. The catalysts were synthesized by colloidal crystal templating against polystyrene spheres using a metal alkoxide precursor. The 3DOM titania walls which are predominantly anatase (> 98%) were decorated homogeneously with gold nanoparticles (5-7 nm) by pH-controlled precipitation of Au from HAuCl4 using sodium hydroxide. A combination of powder X-ray diffraction (XRD), analytical transmission electron microscopy (ATEM) and X-ray photoelectron spectroscopy (XPS) confirmed the deposition of Au(0) on the 3DOM titania macroporous walls. Photocatalytic activity was monitored by following the degradation of MB with activity benchmarked against commercial P25 (Degussa) and powdertitania prepared by hydrolysis of titanium ethoxide. Macroporous 3DOM titania with pore diameter 0.5 microm had the highest first-order rate constant of 0.042 min(-1) for decomposition of MB, compared to 0.025 min(-1) for P25 titania. Deposition of gold on the 3DOM titania surfaces decreased the reaction rate by covering the surface active sites.