DOI: 10.1002/cssc.201100082

Three-Dimensionally Ordered Macroporous Titania withStructural and Photonic Effects for EnhancedPhotocatalytic EfficiencyMin Wu,[a] Yu Li,[b] Zhao Deng,[b] and Bao-Lian Su*[a, b]

Introduction

Titania is recognized as the most efficient photocatalyst, andhas been widely used in environmental applications, such asthe photodegradation of organic pollutants and the purifica-tion of water and air.[1] The physicochemical properties of tita-nia strongly determine its photocatalytic activity. These proper-ties include crystallite size,[2] surface area,[3] crystalline struc-ture,[4] and lattice facet exposure.[5] As the crystallite size de-creases, the ratio of surface-area-to-volume increases, thus in-creasing the fraction of atoms on the surface and enhancingthe photocatalytic activity. Also, the anatase crystal structure isbelieved to have a higher photocatalytic activity than the rutilephase owing to its higher adsorption affinity for organic com-pounds[6] and lower electron–hole recombination rate.[7] Theeffect of the lattice facet during nanocrystal growth on thephotocatalytic activity has been investigated as well.[5] Basedon these studies, titania nanomaterials with an abundance ofanatase phase are strongly preferred in photocatalysis studies.

Three-dimensionally ordered macroporous (3DOM) materialshave drawn much attention recently, because the periodicpore structure, with its large porosity and high surface area,promotes the diffusion rates of ions and molecules. A commonsynthesis strategy for 3DOM materials is the colloidal crystaltemplating method.[8] The colloidal crystals are first self-assem-bled from monodisperse spheres [e.g. , polystyrene, poly(meth-yl methacrylate), or silica] into a face-centered close-packed, oropal, arrangement. A liquid precursor of titania penetrates theopal and fills the voids of the templates. After solidification ofthe precursor, the colloidal templates are removed by calcina-tion or wet etching, yielding an inverse opal replica of thearray of ordered spheres. The resulting solid skeleton is sur-rounded by air holes originating from the spheres prior to re-moval. Where the original spheres made contact, the macro-pores are interconnected by windows. Different sizes and

shapes of these interconnected macropores and different porewall thicknesses alter the photonic band gap and change thelight-scattering properties.[9] Moreover, the wall morphology ofthese titania skeletons can potentially tune the photonic bandstructure.[10] In addition, the growth of nanocrystals is confinedto the voids between the templates, resulting in uniformlysized crystallites. The method is suitable for fabricating 3DOMmaterials as both thin films[11] and in bulk powder form[12] fordifferent applications. By this method, the properties of nano-particles (e.g. , high surface-area-to-volume ratio and confine-ment effects) are transferred to the 3DOM materials.

3DOM structures have also been prepared to investigate theslow photon effect. Increasing the path length of light hasbeen reported to enhance the light absorption of a materialand improve its photoreaction efficiency as well.[13] Slow pho-tons found in materials with 3DOM structures, known as pho-tonic crystals, are capable of achieving this goal. Photonic crys-tals have periodic modulations of the refractive index on thelength scale of the light wavelength, thus forbidding certainwavelengths of light to propagate through the materials andresulting in a stop-band reflection because of coherent Braggdiffraction. The stop-band reflection frequencies depend onthe periodicity and dielectric contrast of the photonic crystal.

[a] Dr. M. Wu, Prof. B.-L. SuLaboratory of Inorganic Materials Chemistry (CMI)University of Namur (FUNDP), Namur, 5000 (Belgium)Fax: (+ 32) 81725414E-mail : bao-lian.su@fundp.ac.be

[b] Prof. Y. Li, Dr. Z. Deng, Prof. B.-L. SuState Key Laboratory of Advanced Technology forMaterials Synthesis and ProcessingWuhan University of TechnologyWuhan, Hubei, 430070 (PR China)

The three dimensional photonic crystals concept has been em-ployed for photocatalysis. Slow photons observed in photoniccrystal structures will enhance the absorption of materialswhen the photon energy matches the absorbance of the mate-rials, which would improve the photocatalytic efficiency. In thiswork, three dimensionally ordered macroporous (3DOM) titaniawas prepared by applying the colloidal templating methodwith a range of pore diameters. Calcination at different tem-peratures to remove the templates resulted in different crystal-

line phases. The structural and photonic properties were char-acterized and their effects on photocatalytic activity are pre-sented as well. A strong effect of the pore diameter on thephotocatalytic activity was observed and correlated with thephoton energy involved in the photodegradation process oforganics. A very interesting phenomenon was also observed:the sample prepared by using PS spheres of 250 nm had ahigh photocatalytic efficiency, which mismatched the effect ofpore diameter, probably owing to the slow photon effect.

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Slow photons appearing in photonic structures could increasethe path length of the light, as the group velocity of light atthe edge of these wavelengths decreases dramatically. For ap-plications in photocatalysis, it is expected that overlap of theenergy of slow photons and the absorbance of the materialwill enhance the materials’ lightabsorption. This possible en-hancement opens an alternativeand attractive route to increasethe photocatalytic efficiency. Pre-vious reports[14] described thatthe macropore diameters arecorrelated to the photonic stop-band, and that the photodegra-dation activity of 3DOM titaniacould be enhanced only if theaccording photonic stop-bandedge matches the irradiationwavelength.

In this work, we demonstratethe combined effects of thestructural and photonic proper-ties of different pore diametersand calcination temperatures onphotocatalytic reactions. 3DOMtitania is synthesized by infiltrat-ing ordered arrays of home-prepared polystyrene (PS) sphereswith titanium isopropoxide precursors and removing the tem-plates by calcination after solidification of the precursor, leav-ing inverse replicas of the sphere arrays. To find the optimalsize for photocatalysis, the pore diameter is tuned between130 and 450 nm by varying the template size. 3DOM titaniamaterials with different pore sizes are calcined at 550, 700, and900 8C to investigate the influence of the calcination tempera-ture. The effects of the crystalline phase, morphology, surfacearea, band-gap energy, and arrangement of the pore structureare also discussed.

Results and Discussion

Preparation and structural characterization of 3DOM titaniawith different pore diameters

PS spheres with different diameters were used to prepare3DOM titanias, with pore sizes ranging from 130 nm to450 nm. The home-prepared PS spheres were dispersed inwater. When drying the suspension in an oven, the PS spheresself-assembled into a close-packed arrangement as the waterevaporated. The titanium alkoxide precursor was then added,filling the voids of the templates. This step is crucial, becauseit determines the final pore size. After solidification and calci-nation, various 3DOM titanias with different pore sizes wereobtained. Their crystallography, morphology, and surface areawere characterized by using X-ray diffraction (XRD), scanningelectron microscopy (SEM), transmission electron microscopy(TEM), and N2 adsorption, respectively (Table 1).

The XRD patterns of all the samples are shown in Figure 1.All of the samples revealed good crystallinity. The diffractionpeak intensities gradually increased, and the peaks becamenarrower as the calcination temperature rose from 550 8C to900 8C, indicating a further crystallization. The crystallite size

was calculated by using Scherrer’s equations,[15] and the crys-tallite grain sizes were found to grow gradually with increasingcalcination temperature (Table 1). A higher degree of crystallini-ty means less bulk defects and imperfections in the titaniastructure (which act as the recombination centers for electron–hole pairs) and results in a higher photocatalytic activity.

The anatase phase was the only crystalline phase observedat calcination temperatures below 700 8C. However, when thesamples were calcined at 900 8C, the anatase phase was partial-ly transformed to the rutile phase as shown in the XRD pat-tern. The (101) crystal plane of anatase is obviously dominantin all of these samples. The diffraction peaks of anatase and

Table 1. Structural properties of 3DOM titanias prepared with templates of different pore sizes.

Entry Sample[a] PS diameter[nm]

Calcinationtemperature [8C]

3DOM titania[b]

pore diameter [nm]Band gap[c]

energy [eV]BET surfacearea [m2 g�1]

Crystallite[d]

size [nm]

1 250nm700C 250�10 700 ~130 3.13 16 ~202 350nm550C 350�10 550 ~250 3.14 38 ~103 350nm700C 350�10 700 ~250 3.15 25 ~234 350nm900C 350�10 900 n.d.[e] 2.97 10 ~325 480nm550C 480�10 550 ~370 3.13 36 ~96 480nm700C 480�10 700 ~370 3.21 29 ~167 480nm900C 480�10 900 n.d.[e] 2.93 3 ~348 550nm550C 550�10 550 ~450 3.14 28 ~109 550nm700C 550�10 700 ~450 3.2 18 ~19

10 550nm900C 550�10 900 n.d.[e] 2.89 5 ~4411 P25 N/A[f] N/A 2.98 41 n.d.[e]

[a] Sample names refer to template size and calcination temperature. [b] Pore diameter measured from SEMimages. [c] Band gap energy values were calculated from the UV/Vis reflectance measurements, performed byusing the Kubelka–Munk correction. [d] Crystallite sizes were calculated from the dominant (101) peak in theXRD patterns by using Scherrer’s equation. [e] Not determined. [f] Not available.

Figure 1. XRD patterns of 3DOM titania prepared by using different tem-plate diameters. The samples from top to bottom are a) commercial P25, fol-lowed by the titania samples b) 550nm700C, c) 480nm900C, d) 480nm700C,e) 480nm550C, f) 350nm700C, and g) 250nm700C. The anatase and rutilephases are labeled as “ + ” and “o”, respectively.

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B.-L. Su et al.

rutile are labeled “ + ” and “o”, respectively, in Figure 1. In ac-cordance with our previous work,[16] the PS spheres could befully removed by calcination at 500 8C.

Representative SEM images of 3DOM titanias with differentpore diameters are shown in Figure 2. The dark areas of thestructures indicate the air voids, whereas the lighter areas indi-cate the solid skeleton. The images show three dimensional in-verse opal structures with well-ordered macropores and inter-connected pore walls, and a regular periodicity. The highly or-dered macroporous structures were found to extend over tens

of micrometers in large fractions of the samples. Notably, thesamples prepared at a calcination temperature of 900 8C tem-perature comprised mostly stacked nanoparticles instead of or-dered macropores, because the high temperature resulted inthe collapse of the 3DOM morphology and induced aggrega-tion of the nanoparticles. Approximate measurements of thepore sizes were performed by measuring the distance betweentwo neighboring macropores from the SEM images. Thesemacropores are usually smaller (ca. 100 nm) than the initialtemplates owing to shrinkage of the PS spheres by meltingduring calcination. The pore size is obviously determined andtuned by the size of the PS spheres. A few discontinuous or-dered areas can be seen in the 3DOM structures. This may becaused by incomplete penetration of the precursor in the PStemplates. In these areas, hydrolysis and solidification of pre-cursors occurred on the surface of the templates before theliquid had properly infiltrated the void spaces between thespheres.

In contrast to the SEM images, the darker areas of the struc-tures in the TEM images of samples prepared from 480 nm PStemplates and calcined at 550 8C (Figure 3 a), 700 8C (Figure 3 c),and 900 8C (Figure 3 f). represent the solid framework, whereasthe lighter areas are representative of the air voids. Clearly, thethree dimensionally ordered structure is not well maintainedupon calcination at 900 8C, as only nanoparticles are observed

in the image (consistent with the SEM results). Moreover, theuniformity of the crystallite size is comparably poor. By con-trast, the samples calcined at 550 8C and 700 8C exhibit excel-lent periodicity: Figures 3 a and c reveal that the nanocrystalsare of uniform size and evenly distributed in the macroporousstructure. Figures 3 b and d are high-resolution TEM images ofthe 480nm550C and 480nm700C samples. The lattice fringessuggest that the samples are highly crystalline and that thesize of the nanocrystals is comparably uniform. The insetshows a fast Fourier transform (FFT) pattern, obtained fromthe white, square area, with arrays of diffraction spots indicat-ing a single-crystalline structure of the sample. The latticespacing (Figure 3 e) was measured to be 0.35 nm, which corre-sponds to the (101) crystal planes of anatase.

The specific surface area is a critical factor in photocatalysisapplications for 3DOM materials. A larger specific surface areawill facilitate adsorption and diffusion of the molecules andlead to a higher photocatalytic activity. However, the surface isa defective site, on which electrons and holes recombine

Figure 2. Representative SEM images of the titania samples a) 350nm550C,b) 350nm700C, c) 480nm550C, d) 480nm700C, e) 480nm900C, f) 550nm550C,g) 550nm700C, and g) 550nm900C.

Figure 3. a) Representative TEM images of Titania 480nm550C and high-res-olution TEM (HRTEM) images of the titania b) 480nm550C, c 480nm700C,d) 480nm700C [the white square in (d) is magnified for lattice spacing meas-urements (e)] , and f) 480nm900C. The inset in (d) is the FFT image of thewhite square.

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Titania with Enhanced Photocatalytic Efficiency

easily. Hence, larger specific surface areas result in faster elec-tron–hole recombination rates and reduce the photocatalyticperformance as a consequence.[17] Meanwhile, the calcinationtemperature also affects the surface area because of thegrowth of the crystallite size and sintering. Higher calcinationtemperatures lead to lower surface areas. Surface area data arelisted in Table 1. The Brunauer–Emmett–Teller (BET) resultsshow that the specific surface areas decrease as the calcinationtemperature increases.

Photonic properties

Three dimensional photonic crystals can block light in a certainwavelength range, allowing the confinement and manipulationof photons in the materials. According to the modified Bragg’slaw, the photonic stop-band wavelength can be adjusted bycontrolling the pore size, according to Equations (1–3):[18]

lmax ¼ 2d111

ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi

n2eff � sin2 q

p

ð1Þ

neff ¼ nTiO2f þ nairð1� f Þ ð2Þ

d111 ¼ffiffiffiffiffiffi

2=3

q

D ð3Þ

In these equations, nTiO2and nair are the refractive indices of

titania and air, respectively, whereas the volume fraction f isusually equal to 0.74 for a face-centered cubic structure, and Dis the pore size. The photonic stop-band wavelength of thesample prepared from a 250 nm diameter template was calcu-lated by using the above equations to be close to the photo-catalysis irradiation wavelength of approximately 370 nm.When the stop bands of 3DOM titania are in the UV range, UVlight would be trapped in the structure, enhancing light ab-sorption by the material and the photochemical process. Al-though the surface area of this sample is relatively low, thephotocatalytic activity could be compensated to some extentby the periodic effect of the 3DOM structure. This was furtherproven by the photocatalytic activity test.

In this work, the photonic properties of the 3DOM titaniawere further characterized by recording the UV/Vis absorptionspectrum. Figure 4 presents the UV/Vis absorption spectrumobtained from reflectance measurements. Notably, the bandgap of the anatase form is a broad stop band instead of a fullband gap.[8f] Contrarily, in Figure 4 a the band gap energies ofsamples prepared at temperatures below 700 8C are shifted toshorter wavelengths, which is correlated to the decrease incrystallite size compared to the commercial P25. Figure 4 b re-veals that the absorption spectra of samples prepared byusing different template diameters and calcined at tempera-tures under 700 8C are similar. The band gap energy can be es-timated from the intersect point between the tangent line ofthe steep curve and the wavelength axis after the original re-flectance data has been subjected to Kubelka–Munk transfor-mation. The transformed reflectance K was calculated by usingEquation (4), in which R is the original reflectance:

K ¼ ð1�RÞ2=2R ð4Þ

Then the wavelength is converted into photon energy Ephot

(eV). Figure 5 is a plot of (KEphot)1/2 versus Ephot, from which the

band gap energy was determined by extrapolation from thetangent at the band edge. All the band-gap energy values arelisted in Table 1. When the crystallite size of the sample issmaller than that of the commercial P25, the band-gap energyis higher, which may be attributable to quantum size effects.However, it is interesting to find that the samples calcined at700 8C always have a higher band-gap energy, even if the crys-tallite size is increased. It may be related to crystal structure al-

Figure 4. UV/Vis absorption spectra compared to commercial P25. a) Varyingcalcination temperature, and b) variation of the template diameter.

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terations during the calcination process. Confirmation of thisrequires further experimental work.

Photocatalytic activity

3DOM titania with different pore diameters were examined byphotodegrading Rhodamine B to correlate structural and pho-tonic properties with the photocatalytic activity. Figures 6 a–clist the first-order degradation rate curves of samples synthe-sized by using three different PS template spheres (350, 480,and 550 nm) and calcined at 550, 700, and 900 8C in compari-son with that of the commercial P25. Figure 6 d presents theinfluence of PS template size variation under the same calcina-tion conditions. Obviously, all samples calcined at 700 8C dis-play the best photocatalytic performance and can fully photo-degrade the organic pollutants within 15 min.

The kinetics of the photoreaction can be described as beingof pseudo first-order ln(C/C0) = kt. C0 and C correspond to theconcentrations at t = 0 and after time “t”, respectively. The deg-radation rate constant k was obtained by plotting ln(C/C0)versus the reaction time. Figures 7 a and b display the first-order degradation rate constant k (min�1), determined fromFigure 6, of all the samples, and the optimal photocatalytic ac-tivity efficiency (the error is �0.01). At first, the degradationrate constant increased, when the samples were calcined attemperatures in the range from 550–700 8C. But when thesamples were calcined at 900 8C, the degradation rate constantdecreased. The initial increase may attributable to an improve-ment in crystallinity as the temperature was increased from550 8C to 700 8C, because there were less imperfections anddefects in the structure, which could act as a recombinationcentre for the electron–hole pairs. Increasing the specific sur-face area to improve the diffusion of and the contact area be-tween photocatalyst and reactant would be beneficial for theenhancement of the photocatalytic activity. However, althoughthe surface area was higher at 550 8C (see Table 1), the photo-catalytic efficiency was still lower than that observed for sam-ples calcined at 700 8C, which had a lower surface area. Whenthe sample was calcined at 900 8C, aggregation of nanoparti-

Figure 5. Plots of (K � Ephot)1/2 versus Ephot used for the calculation of the band

gap energy for the titania samples 480nm550C (black), 480nm700C (red),480nm900C (blue), and p25 (green).

Figure 6. First-order degradation rate curves of titania samples prepared byusing different templates and calcination temperatures compared to com-mercial P25. a) 350 nm, (b) 480 nm, c) 550 nm (&: P25; ^: 550 8C; ~: 700 8C;!: 900 8C). d) Comparison of crushed (&) and original (^) 3DOM Titania pre-pared by using the 480 nm temperature after calcination at 700 8C.

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Titania with Enhanced Photocatalytic Efficiency

cles occurred, leading to the loss of 3DOM structure, and thesurface area and the amount of anatase phase were stronglydecreased, which resulted in a poorer photocatalytic perfor-mance.[19] To further prove the effect of the 3DOM structure, acontrol experiment was performed by crushing the480nm700C sample and remeasuring the photocatalytic per-formance (see Figure 6 d). Obviously, when the 3DOM structurewas completely destroyed by crushing, the photocatalytic ac-tivity dropped dramatically, which clearly confirms the effect ofthe 3DOM structure in enhancing the photocatalytic activity.The photocatalysis results indicate that the 3DOM titaniaformed by using 480 nm templates and calcining at 700 8C ex-hibit the best photocatalysis activity, which is even higher thanthe commercial P25. For different samples calcined at 700 8C,the photocatalytic activity revealed a dependence on the porediameter, which is shown in Figure 7 b. Initially, the photocata-lytic performance was improved by increasing the templatesize from 350 to 480 nm, whereas the performance deteriorat-ed when the template size was increased further.

The degradation rate constant of the sample prepared byusing the 250 nm PS template did not fit the trend. The250 nm PS template formed 3DOM titania with approximately130 nm pore size, which reflected light near the UV wave-length according to Equations (1–3) and enhanced the photonabsorption during the photocatalysis process. As a result, thephotodegradation rate of the sample prepared by using the250 nm template was higher than that prepared from a350 nm template, which is in contrast to the observed trend.

When the reflection wavelength of the ordered macroporousstructure was within the visible range, the slow photon effectin the UV photocatalysis process would be small. From theXRD, SEM, and TEM results, the sample prepared by using the480 nm template and calcined at 700 8C revealed a high crys-tallinitity and anatase phase volume with uniformly sized nano-crystals, which were preferred to achieve a high photocatalyticactivity. In addition, the surface area of the 480nm700C samplemay reach an optimum value, which probably contributes tothe improvements in the photocatalytic performance. An in-crease in the band-gap energy in combination with a decreasein the crystallite size may potentially enhance the redox poten-tial of holes in the valence band and electrons in the conduc-tion band, resulting an improved photoredox process.[17] Thiscould also partially explain the high photocatalytic activity ofthe sample prepared by using a 480 nm template at 700 8C.

Conclusions

Highly 3D ordered macroporous (3DOM) titania with differentpore diameters were prepared by employing the colloidal tem-plating method. The effect of pore diameter and calcinationtemperature on photonic properties and photocatalytic activityrevealed that the sample synthesized by using the 480 nmtemplate and calcined at 700 8C presented a higher perfor-mance than the other samples. This is probably owed to anoptimal balance of uniformly sized nanocrystals, an excellentcrystalline structure, specific surface area, a well-ordered mac-roporous structure, and the band-gap energy. A very interest-ing phenomenon was also observed for the sample preparedby using PS spheres of 250 nm diameter. Its higher photocata-lytic efficiency stemmed from the fact that the prepared 3DOMconsisted of pores of 130 nm size, which reflect light near theUV wavelength and enhance the photon absorption in thephotocatalysis process. These photonic crystal structured mate-rials have great potential in future applications, including pho-tocatalysis and photochemical synthesis. In addition, their ex-cellent performance in degrading dyes might allow couplingof 3DOM titania with dye-sensitized photoelectrochemical cellsin the future.[20]

Experimental Section

Materials

Styrene, titanium(IV) isopropoxide, and hydrogen chloride acid(HCl) were purchased from Aldrich. Anhydrous ethanol was ob-tained from Acros and used without further purification.

Synthesis of polystyrene spheres and template preparation

Polystyrene (PS) spheres were prepared by applying an emulsionpolymerization method without addition of a surfactant. Firstly, sty-rene was washed three times by using NaOH (2 m) to remove theinhibitors. For example, polystyrene spheres of 250 nm diameterwere prepared as follows: prewashed styrene (5 mL) and water(120 mL) were heated to 70 8C in an oil bath under a N2 atmos-phere. K2S2O8 (0.07 g) was added as the initiator for the polymeri-

Figure 7. First-order degradation rate constant for the photodegradation ofRhodamine B. a) Comparison of different calcination temperatures for porediameters of 250, 370, and 450 nm, and b) comparison of different pore di-ameters for a calcination temperature of 700 8C.

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B.-L. Su et al.

zation. The reaction was stopped after 4 h by cooling the contain-er. The amount of styrene, water, and initiator as well as the reac-tion time were optimized according to the sphere diameter. PS col-loidal template was obtained directly by oven drying PS spheresmonodispersed in water at 60 8C and crushed to a powder prior tobe used as a template.

Synthesis of 3DOM titania

The method for preparing the 3DOM titania was according to typi-cal literature reports.[8] The precursor was composed of a mixtureof ethanol (5 mL), hydrochloric acid (HCl, 1 mL), titanium(IV) iso-propoxide (5 mL), and water (2 mL). The mixture was added to avial and stirred at room temperature for several minutes. Dried PSsphere powder was placed on a filter paper in a B�chner funnel,and the precursor was added dropwise to the PS templates duringsuction applied to the B�chner funnel. The amount of precursorsolution was equal to the template by mass. After air drying themixture of precursor and template for 24 h, the template was re-moved by calcination in air using a heating rate of 2 8C min�1. Thesample was stabilized at 300 8C for 2 h, 400 8C for 2 h, and 550 8Cfor 2 h. For samples calcined at 700 and 900 8C, the calcinationswere continued to 700 8C for 2 h and 900 8C for 2 h, respectively.All the samples appeared to be visibly white powders. The final di-ameters of 3DOM titania prepared from 250, 350, 480, and 550 nmPS spheres were 150, 250, 380, and 450 nm, respectively, as mea-sured by using scanning electron microscopy (SEM). All sampleswere washed with water to remove impurities and oven dried forphotocatalysis application.

Characterization

Powder X-ray diffraction (XRD) patterns were collected by using aPhilips PW-170 diffractometer, equipped with a Cu anode X-raytube (Cu Ka X-rays, l= 1.5418 �). SEM observations were per-formed by using a Hitachi S-4800 microscope. Transmission elec-tron microscopy (TEM) images of the samples were recorded oncarbon coated copper grids by using a JEM-2100F microscope.Samples were degassed under vacuum at 373 K before nitrogenadsorption measurement was performed by applying Micromerit-ics. The surface area was measured by using the Brunauer–Emmet–Teller (BET) method. The UV/Vise absorption spectra wereobtained from reflectance measurements on bulk oriented powderby using the Lamda 35 UV/Vis spectrometer (Perkin–Elmer Instru-ments).

Photocatalytic testing

3DOM titania (0.05 g) was added to Rhodamine B (50 mL, 10 mm).The suspension was poured into a quartz tube and inserted into areactor surrounded by UV lamp with the emission wavelength ofl= 370 nm. The mixture was magnetically stirred at 700 rpmduring the photocatalysis process. An aliquote of approximately2 mL was collected at certain time intervals after photocatalysiswas started. All aliquots were centrifuged at 9000 rpm for 30 minto fully separate the solution from the powder and then injectedinto the quartz cell for the UV/Vis absorption spectrum measure-ments.

Acknowledgements

This work was realized in the framework of an Interuniversity At-traction Poles Program (Inanomat-P6/17)-Belgian State-BelgianScience Policy and the project “Redugaz”, which was financiallysupported by the European community and the Wallon govern-ment in the framework of Interreg IV (France-Wallonie). B.L. Suacknowledges the Chinese Central Government for an “Expert ofthe State” position in the program of “Thousand talents” and theChinese Ministry of Education for a Changjiang Scholar positionat the Wuhan University of Technology. The fruitful suggestionsfrom Dr. J. Li and Dr. X. Y. Yang are highly appreciated.

Keywords: macroporous materials · photocatalysis · photoniccrystals · template synthesis · titanium

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Received: February 14, 2011Revised: May 17, 2011Published online on August 24, 2011

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