First Synthesis of Highly Crystalline, Hexagonally Ordered, Uniformly

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First Synthesis of Highly Crystalline Hexagonally Ordered Uniformly Mesoporous TiO2-B and Its Optical and Photocatalytic Properties Md. Kamal Hossain, Agni Raj Koirala, Umme Sarmeen Akhtar, Mee Kyung Song, and Kyung Byung Yoon Chem. Mater., Just Accepted Manuscript • DOI: 10.1021/acs.chemmater.5b01800 • Publication Date (Web): 09 Sep 2015 Downloaded from http://pubs.acs.org on September 9, 2015

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First Synthesis of Highly Crystalline, Hexagonally Ordered, Uniformly Mesoporous TiO2-B and Its Optical and Photocatalytic Properties Md. Kamal Hossain, Agni Raj Koirala, Umme Sarmeen Akhtar, Mee Kyung Song, and Kyung Byung Yoon* Korea Center for Artificial Photosynthesis, Center for Nanomaterials, Department of Chemistry, Sogang University, Seoul 121-742, Korea

-------------------------------------------------------------------------------------------------------------------ABSTRACT: Out of the eleven different phases of titanium dioxide, TiO2-B is unique in that it contains crystalline voids, which can readily intercalate small cations. Because of this property, TiO2-B is receiving great attention as an electrode material for energy storage devices, dye sensitized solar cells, and supercapacitors, as well as a photocatalyst for hydrogen production and dye decomposition. Applications in the above arenas are expected to increase significantly if this substance can be prepared in the form of ordered, uniformly mesoporous TiO2-B. In the current study, we developed the first method for synthesis of hexagonally ordered, uniformly mesoporous TiO2-B (houm-TiO2-B) with a high degree of purity on a large scale (>10 g). The results show that the band gap energy of houm-TiO2-B is 0.36 eV less than that of the corresponding nanoparticle. Importantly, houm-TiO2-B displays a higher performance than the corresponding nanoparticles as a photocatalyst in hydrogen production from aqueous methanol and in the photodecomposition of 4-chlorophenol (4-CP) and methylene blue (MB). Effect of the crystalline interconnection (Eg decrease)

TiO2-B

P25 K.-M. Value

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Chemistry of Materials

5 nm Hexagonally Ordered Uniformly Mesoporous TiO2-B (houm-TiO2-B)

rutile

houm-TiO2-B TiO2-B nanoparticle anatase 390

420 λ , nm

450

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■ INTRODUCTION Titanium dioxide (TiO2) is one of the most important metal oxides and is widely used in industrial applications. Among the eleven phases that it can exist in,1 TiO2-B is unique in that it contains crystalline voids which intercalate small cations.2-17 TiO2-B was first synthesized in 1980 by Marchand et al. through a pathway involving calcination of protonated layered titanate H2Ti4O9 at 500 °C.18 We term this pathway as the dry H-titanate calcination route.8,12-15,18-21 The dry H-titanate calcination route has been widely utilized for the preparation of TiO2-B in various forms such as nanobelts,12 nanotube clusters,13 nanowires,19 nanoribbons,20 nanotubes,22 microfloweres,8 mesoporous microspheres,15,16 and as well as bulk materials.18 For some time, it was believed that TiO2-B was a purely synthetic material, but a later discovery showed that it also exits in nature.23 Another route for preparation of TiO2-B involves treatment of a gel consisting of Ti powder, hydrogen peroxide, aqueous ammonia solution, glycolic acid, and sulfuric acid, under hydrothermal conditions at temperatures between 110 and 230 °C.4,24 The final method for fabrication of TiO2-B follows a solvothermal route involving the treatment of a gel containing a Ti source (TiCl3, TiCl4, or titanium isopropoxide), an organic solvent (ethylene glycol or octadecene) with an acid or a base catalyst (autogenously produced HCl, oleic acid, or NH4OH).9,14,25 Because TiO2-B is now being utilized as an electrode material in energy storage systems,2-17 dye sensitized solar cells,17,26-28 supercapacitors,29 smart window applications,17 and photocatalysts for hydrogen production and dye decomposition,25,30,31 other methods have been developed for its synthesis on electrodes. For example, in one approach randomly mesoporous TiO2-B films supported on electrodes is prepared by dip coating electrodes in a gel consisting of a Ti source, mixed acid catalyst (HCl and H3PO4), Pluronic P123 diblock copolymer and nbutanol, followed by calcination at 350 °C17 for 2 h. Alternatively, electrodes can be coated using a slurry of TiO2-B nanoparticles dispersed in a mixture of organic solvents (ethanol and THF) and Pluronic P123 diblock copolymer, followed by heating at 500-550 °C.3,17 Uniformly mesoporous metal oxides (um-MOx) and uniformly mesoporous mixed metal oxides (um-MAMBOx) contain uniformly and symmetrically arranged mesopores with pore sizes ranging between 2 and 10 nm.32-35 Following the discovery of um-silica (um-SiO2), a large number of non-siliceous um-MOx and um-MAMBOx materials have been prepared which now comprise a 2 ACS Paragon Plus Environment

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large class of um-metal oxide materials. These oxides have been widely used as catalysts, catalyst supports, adsorbents, as well as nanocasts for the preparation of other um-materials, such as um-metals, um-carbon, um-polymers, um-metal oxides, um-sulfides, um-phosphates, and umceramics.32-34 One of the important characteristics of um-materials is that their physicochemical properties depend on whether they have crystalline, semicrystalline or amorphous frameworks. Crystalline um-materials are rare (anatase,36 rutile,37 Fe3O4,38 γ-Fe2O3,38 γ-Al2O3,39 and CuO,40 Ta2O5,41 Nb2O542) because their structures have a strong tendency to collapse during the crystallization process. Among the various um-MOx oxides that have been prepared thus far, applications of crystalline um-TiO2 have received greatest attention owing to its important properties. To date, out of eleven phases of crystalline TiO2, only anatase and rutile have been generated in um-forms. However, owing to the reasons mentioned above, TiO2-B is currently receiving increasing attention. In this regard, um-TiO2-B (Figure 1a,b) is expected to have better properties than do randomly mesoporous (rm-TiO2-B, Figure 1c) and individual nanoparticle (np-TiO2-B, Figure 1d) forms. Firstly, the diffusion rates of ions and molecules within um-TiO2-B are expected to be uniform owing to the uniformity of the channel sizes. Secondly, the diffusion rates of incorporated ions and molecules within this material are expected to be larger than those in rm-TiO2-B as a consequence of the larger channel sizes. Thirdly, unlike in rm-TiO2-B, all sites within rm-TiO2-B are expected to be accessible to incorporated ions and molecules as a result of the complete openness of the channels. Fourthly, the rates of carrier (electron and hole) transport along the walls of or frameworks in TiO2-B are expected to be faster in um-TiO2-B than in rm-TiO2-B as a result of the presence of three-dimensional (3D) crystalline interconnections. Fifthly, the optical and electronic properties of the TiO2-B walls and frameworks are expected to be constant within um-TiO2-B because of a uniform wall thickness within the material. Finally, as observed for umanatase,26 the electronic absorption onset of um-TiO2-B is expected to be red-shifted with respect to that of np-TiO2-B. As a consequence, its photocatalytic activity in various processes promoted by solar light is expected to be enhanced. In spite of the potential advantages summarized above, no methods to prepare um-TiO2-B have been developed during the last 25 years. In the investigation described below, we devised the first method for synthesis of highly pure, hexagonally ordered um-TiO2-B (houm-TiO2-B) in a large scale manner (>10 g). In addition, we have demonstrated that this material has a smaller 3 ACS Paragon Plus Environment


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band gap energy than do the corresponding nanoparticles and that it displays superior performances in photocatalytic applications than do TiO2-B nanoparticles.

■ EXPERIMENTAL SECTION Synthesis. The TiO2-B nanoparticles (5-7 nm) used in this study were prepared by using the known procedure.3,22 The methodologies utilized for the preparation of houm-TiO2-B are termed evaporation-induced self-assembly (EISA, Figure 2, top)35,43 and combined assembly of soft and hard (CASH, Figure 2, bottom) template36,42,44-46 methods. These methods have been developed by many research groups36,42,44-46 for the synthesis of hexagonally ordered uniformly mesoporous anatase (houm-anatase). EISA Method. In a typical procedure, 10 g of Pluronic P123 (Aldrich) was dissolved in 300 g ethanol (99.9%) at room temperature. A mixture of concentrated H2SO4 (98.08% 5.5 g) and concentrated HCl (35-37%, 15 g) was added to the ethanol solution, which was then stirred for 3 h at 40 °C. TIP (99%, 36 g) was added to the acidic ethanol solution, which was then vigorously stirred for 10 h. The mixed solution (gel) was transferred to a petri dish, which was subsequently let stand in a humidity (50-60%) controlled chamber for 24-48 h at 40 °C and then in an oven at 100 °C oven for 12 h to remove all volatile components and give surfactant-filled amorphous houm-TiO2). CASH. The surfactant-filled amorphous houm-TiO2 was calcined at 300 °C for 1 h under a continuous flow of N2. This process involving carbonizing the channel-filling surfactant gave carbon-lined amorphous houm-TiO2. The carbon-lined amorphous houm-TiO2 was then calcined at 450 °C for 5 h to produce houm-TiO2-B. Measurement of photocatalytic activity. Photocatalytic degradation reactions of methylene blue (MB, >82%) and 4-cholorophenol (4-CP, 99%) were carried out using an Oriel 200 W arc Hg lamp (Oriel CA-9015) as the light source. Each catalyst (0.05 g) was introduced into an aliquot (50 mL) of a MB or 4-CP solution (10 ppm, mg/L). Prior to irradiation, each heterogeneous solution was kept in the dark for 1 h with stirring. Absorbance changes of the methylene blue and 4-CP containing solutions taking place during photoirradiation were monitored at 660 nm and and 225 nm, respectively.


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Hydrogen production experiments were performed using an air tight continuous flow stainless reactor connected to an online gas chromatograph (GC) system. Typically, into a vial containing 0.1 g of a sample 20 mL of water and 4 mL of methanol were added. The sample solution in the dark was flushed with Ar (99.9999%) at a flow rate of 6 mL/min for variable periods of time until all oxygen was removed. The solution was irradiated under the continuous flow of Ar with a standard AM-1.5 solar simulated light (HAL-302 Asahi) with the power of 72 mW cm-2. The intensity of the light was adjusted using a 1-sun checker (CS-20, Asahi Spectra Co., Ltd.). The area of irradiation was 6 cm2. The amounts of hydrogen gas generated in the processes were determined using an on-line GC and are reported as nano mole (nmol) per unit area (1 cm2) per hour (nmol cm-2 h-1). Instrumentation. Small-angle X-ray (SAX) and wide-angle X-ray (WAX) diffraction patterns of the samples were recorded using a Rigaku D/MAX-2500/pc diffractometer, with Cu-Kα radiation (200 kV, 40 mA for WAX and 250 kV, 50 mA for SAX). N2 sorption isotherms were determined at 77 K using a BELSORP-max. Prior to these measurements, samples were degassed under vacuum at 200 °C for 6 h. The Brunauer–Emmett–Teller (BET) method was used to calculate surface areas. Pore size distributions were determined using the BJH method. TEM images were recorded employing a JEOL 2011 microscope operated at 200 kV. Diffuse reflectance spectra were converted into the Kubelka-Munk (K-M) formalism. Elemental analyses were performed utilizing a Thermo Scientific Elemental Analyzer (Flash EA 1112 series). UV-vis absorption spectra of the methylene blue and 4-cholorophenol solutions were recorded using a Scinco (S-3100) diode array UV-vis spectrophotometer. The analyses of the hydrogen generated from water was performed using a Young Lin (YL-6000) gas chromatograph equipped with a flame ionization detector (FID) and fitted with DB-624 column (Agilent), a pulsed discharged detector (PDD) fitted with a Carboxen column (Supelco), and a capillary injector.

■ RESULTS AND DISCUSSION Preparation of Highly Pure, Hexagonally Ordered, Uniformly Mesoporous TiO2-B (houmTiO2-B). The TiO2 material utilized in this investigations was prepared by using the evaporationinduced self-assembly method (EISA, Figure 2). The small-angle X-ray (SAX) diffraction pattern of the material contains a diffraction peak at 2θ = 0.68° (d = 12.9 nm) (Figure 3a), indicating that it is comprised of an ordered array with large d-spacing. The wide angle X-ray 5 ACS Paragon Plus Environment


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(WAX) diffraction pattern of the material is comprised of featureless broad peaks centered at 2θ = ca. 26°, ca. 48°, and 60° (Figure 3b), showing that it is an amorphous TiO2 material. In addition, the TiO2 material possesses hexagonally ordered uniform mesopores as revealed by inspection of the low resolution transmission electron microscope (TEM) image (Figure 3c). The high resolution TEM image of the material displays no lattice fringes of TiO2, confirming that it is amorphous. Although its pores are not yet open owing to the presence of pore-filling template molecules, it has a rigid amorphous TiO2 mesoporous framework. As a result, we refer to this material as template filled hexagonally ordered uniformly mesoporous amorphous (houmamorphous) TiO2. White template-filled houm-amorphous-TiO2 turns black upon calcination at 300 °C for 1 h under a flow of N2, indicating that the channel-filling P123 is carbonized and lines the surface. The SAX diffraction pattern of the carbon-lined houm-amorphous-TiO2 contains a diffraction peak (Figure 4a) at 2θ = 0.76° (d = 11.6 nm). The WAX pattern contains weak diffractions at 2θ = 25.1, 37.5, 48.2, 54.5, and 63.0° together with a broad weak peak at 2θ = ca. 26°. Because the diffractions at 2θ = 25.1, 37.5, 54.5, and 63.0º correspond to the (110), (401), (020), (113) and (313) planes of crystalline TiO2-B,7,8 it appears that a small fraction of the TiO2 wall in the surfactant-filled houm-amorphous-TiO2 has crystallized to generate to TiO2-B during carbonization. The low magnification TEM image (Figure 4c) of carbon-lined houm-amorphous TiO2 displays a much more vivid contrast of the hexagonally ordered channels owing to the disappearance of the channel-filling, P123 polymer. Finally, inspection of the high resolution TEM image (Figure 4d) reveals that the majority of the TiO2 wall remains amorphous. The SAX diffraction pattern of the carbon-lined houm-amorphous TiO2, calcined at 450 °C for 6 h under air, contains a strong peak at 2θ = 0.82° (d = 10.7 nm) (Figure 5a). Remarkably, the WAX diffraction pattern of the sample contains only diffraction lines that are typical for crystalline TiO2-B. Specifically, the observed diffraction peaks at 2θ = 14.2, 25.1, 28.5, 33.2, 37.5, 44.0, 48.2, 54.5, 57.5, 62.5, and 67.5° correspond to the (001)/(200), (110), (002), (310), (401), (003), (020), (113), (022), (313), (023) planes of crystalline TiO2-B (Figure 5b). This finding unambiguously demonstrates that the material produced in the manner described above is highly crystalline pure houm-TiO2-B. The low magnification TEM image of this material (Figure 5c) displays a vivid contrast of the hexagonally ordered channels, indicating that the channels are well-preserved, uniform in size and hexagonally ordered over a long range. Inspection of a 6 ACS Paragon Plus Environment

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selected area electron diffraction of the low magnification TEM image (Figure 5d) confirms the existence of the (001)/(200), (110), (002), (310), and (401) planes of TiO2-B.15 The high resolution TEM image (Figure 6) also demonstrates the presence of vivid lattice fringes of TiO2B as well as the well preserved hexagonally ordered mesopores. This observation also demonstrates that the material is pure houm-TiO2-B with a wall thickness of ca. 5 nm. This thickness matches the wall thickness of houm-TiO2-B (5.6 nm) estimated by utilizing the Scherrer equation to analyze the (002) peak in the powder diffraction pattern (Figure 5b). Moreover, a prefect match of the Raman bands of the material with those reported for bulk TiO2B particles21 and a TiO2-B film17 and the absence of other bands (Figure 7) further show that the material is highly pure houm-TiO2-B. Producing highly pure TiO2-B, regardless whether it is in nanoparticles or uorm-TiO2-B forms, has been a difficult task. A careful analysis of the literature shows that many (ca. 70%) attempts have led to generation of TiO2-B that contains anatase as well. Moreover, the difficulty of producing pure TiO2-B without anatase and a method to assay the purity of TiO2-B has been addressed previously.21 Careful inspection of the literature reports shows that attempts using the solvothermal route, including the hydrothermal method, generally yield impure TiO2-B, owing presumably to the lower temperatures (10 g), by combining the EISA and CASH methods. In addition, we found that the amount of sulfuric acid and crystallization temperature play crucial roles for the success of the houm-TiO2-B synthesis process. Moreover, the results of photophysical studies show that the band gap energy of houm-TiO2-B is 0.36 eV lower than that of the corresponding nanoparticles, a phenomenon that is associated with interconnections of the 5-nm thick TiO2-B nanoparticles into the highly extended three-dimensional polycrystalline TiO2-B framework. The feature gives rise to formation of large polycrystalline TiO2-B possessing uniformly mesoporous channels. houm-TiO2-B displays much higher activities than TiO2-B nanoparticles in



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photocatalytic hydrogen production from methanolic water, and the photodecomposition of 4chlorophenol (4-CP) and methylene blue (MB). Until now, out of the eleven phases of TiO2, only anatase and rutile have been prepared in the houm forms and their physicochemical properties have been elucidated. In this respect, the results of the studies described above contribute significantly to applications of the crystalline TiO2.

■ UV-lights are hazardous. ■ AUTHOR INFORMATION Corresponding Author *E-mail: [email protected]

Notes The authors declare no competing financial interest.

■ ACKNOWLEDGMENTS This study was financially supported by the Korea Center for Artificial Photosynthesis, located at Sogang University and funded by the Ministry of Science, ICT and Future Planning through the National Research Foundation of Korea, No. 2009-0093886. We also thank J. Y. Lee for help with drawing Figures.


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Page 17 of 27

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


oum-TiO2-B

b

a

Hexagonally ordered uniformly mesoporous TiO2-B (houm-TiO2-B)

Cubically ordered uniformly mesoporous TiO2-B

np-TiO2-B

rm-TiO2-B

d

c

Randomly mesoporous TiO2-B

Individual TiO2-B nanoparticles

Figure 1. Schematic illustrations of four possible forms of TiO2-B, including houm-TiO2-B (a), cubically ordered uniformly Mesoporous TiO2-B (b), randomly mesoporous TiO2-B (c), and TiO2-B nanoparticles in various shapes such as spheres, plates, rods and belts (d).



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1. EISA (Evaporation Induced Self-Assembly) Evaporation Humid chamber (50-60%) 40 °C / 24 - 48 h

houm-amorphous-TiO2

Pluronic P123 H2SO4 + HCl (1:3) Ti(OiP)4 Ethanol

Surfactant template

2. CASH (Combined Assembly of Soft and Hard Templates) houm-crystalline-TiO2-B

houm-amorphous-TiO2 Step 1

Step 2

300 °C, N2, 1 h

450 °C Air, 6 h

~10 g

Surfactant template

Carbon lining

Figure 2. Schematic illustration of the method used to prepare hexagonally ordered, uniformly mesoporous TiO2-B (houm-TiO2-B) that combines the EISA (top) and CASH (bottom) methods.


Page 19 of 27

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


a

100

b

= 2000 CPS

0.8

1.2

10

= 500 CPS

20

30

2 θ (degree)

40

50

60

70

2 θ (degree)

c

d

100 nm

5 nm

c Figure 3. SAX (a) and WAX (b) diffraction patterns and low (c) and high (d) resolution TEM images of the surfactant-filled houm-amorphous-TiO2.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

a

Page 20 of 27

b

100

= 2000 CPS

0.8

1.2

= 500 CPS

10

20

2 θ (degree)

c

30

40

50

60

70

2 θ (degree)

d

100 nm

5 nm

Figure 4. SAX (a) and WAX (b) diffraction patterns and low (c) and high (d) resolution TEM images of the carbon-lined houm-amorphous-TiO2.


Page 21 of 27

b

100

(110)

a

= 2000 CPS

0.8

1.2

10

20

30

40

50

60

(313)

(023)

(020)

(113) (022)

200

(401)

(002) (310)

110

(003)

= 500 CPS (001) / (200)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


70

2 θ (degree)

2 θ (degree)

d

c

001/200 110 002 301 401

100 nm

Figure 5. SAX (a) and WAX (b) diffraction patterns and low (resolution TEM image (c) and the selected area electron diffraction (d) of the highly crystalline houm-TiO2-B.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 6. HR-TEM image of houm-TiO2-B showing the presence of a highly crystalline TiO2-B framework.


Page 22 of 27

Page 23 of 27

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houm-TiO2-B synthesized in this work np-TiO2-B synthesized by ref 21

200

400

600 800 -1 Frequency / cm

1000

1200

Figure 7. Raman spectra of houm-TiO2-B (solid) and pure crystalline TiO2-B nanoparticle (npTiO2-B) synthesized by Richard-Plouet, Brohan and coworkers (ref 21), showing the exact match of Raman bands.



150 % of Optimum Amount

Intensity , a . u

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Page 24 of 27

Optimum amount

50 % of Optimum Amount

No H2SO4

10

20

30 40 50 2 θ ( degree )

60

70

Figure 8. WAX diffraction patterns of various TiO2 materials generated by using the procedure shown in Figure 2 with gels containing different amounts of H2SO4 (as indicated, without changing other parameters).


Page 25 of 27

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Figure 9. N2 adsorption-desorption isotherms (a-c) and pore size distributions (d-f) of surfactantfilled houm-amorphous-TiO2 (a,d), carbon-lined houm-amorphous-TiO2 (b,e) and crystalline houm-TiO2-B (c,f).



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Page 26 of 27

Figure 10. Diffuse reflectance UV-vis spectra of anatase, rutile, Degussa P25, TiO2-B nanoparticles (np-TiO2-B), and houm-TiO2-B. (a) intensity normalized, (b) in the 380-470 nm region (c) normalized diffuse reflectance UV-vis spectra of houm-TiO2-B before and after ball milling (d) Diffuse reflectance UV-vis spectra of anatase, Degussa P25, TiO2-B nanoparticles (np-TiO2-B), and houm-TiO2-B along with the spectrum of solar simulated light used in theH2 production experiment. The inset in c shows the WAX diffraction patterns of houm-TiO2-B before and after ball milling.


Page 27 of 27

b

H2 Production

1.0

houm-TiO2-B

C / Co

C / Co

np-TiO2-B

P25

0.6 0.4 0.2

P25, anatase

houm-TiO2-B 0.0

1

2

3

0

4

t (h)

20

np-TiO2-B

40 60 t (min)

1.0

np-TiO2-B 0.5

0

f

0.9

0.25

houm-TiO2-B

np-TiO2-

20

40 t (min)

60

80

houm-TiO2-B

0.6

0.3

np-TiO2-B

P25 anatase

0.20

0.15

0.10

0.05

P25 anatase 0.0

0.0

houmTiO2-B

-1

1.5

P25

0.0

e houm-TiO2-B

anatase

0.4

80

-1

2.0

0.6

0.2

0.0

0

none

0.8

anatase

4.0

MB Decomposition

1.0

none

0.8

2.0

c

4-CP Decomposition

Rate const. ( min )

6.0

Rate const. ( min )

Initial rate x 10-5 ( mol h-1 g-1)

H2 Yield x 10-5 ( mol h-1 g-1)

1 2 3 4 5 6a 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 d 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


np-TiO2-B

P25 anatas

0.00

Figure 11. Comparison of the photocatalytic activities of anatase, Degussa P25, np-TiO2-B, and houm-TiO2-B for water reduction (a), 4-CP decomposition (b), and MB decomposition (c). The corresponding comparison of the initial reaction rates for each reaction (d-f) for the period of 60 min (d,e) and 20 min (f). Solar simulated light (AM 1.5, 1 sun) was used for the H2 production reaction (a,d) and an Oriel 200 W arc Hg lamp was used for photodecompositions of MB and 4CP (b,c,e,f).


First Synthesis of Highly Crystalline, Hexagonally Ordered, Uniformly

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