Painting anatase (TiO2) nanocrystals on long nanofibers to prepare photocatalysts with large active surface for dye degradation and organic synthesis

Article abstract of DOI:10.1002/cctc.201200923

Anatase TiO₂ nanocrystals were painted on H-titanate nanofibers by using an aqueous solution of titanyl sulfate. The anatase nanocrystals were bonded solidly onto the titanate fibers through formation of coherent interfaces at which the oxygen atoms were shared by the nanocrystals and the fiber. This approach allowed us to create large anatase surfaces on the nanofibers, which are active in photocatalytic reactions. This method was also applied successfully to coat anatase nanocrystals on surfaces of fly ash and layered clay. The painted nanofibers exhibited a much higher catalytic activity for the photocatalytic degradation of sulforhodamineB and the selective oxidation of benzylamine to the corresponding imine (with a product selectivity >99%) under UV irradiation than both the parent H-titanate nanofibers and a commercial TiO₂ powder, P25. We found that gold nanoparticles supported on H-titanate nanofibers showed no catalytic activity for the reduction of nitrobenzene to azoxybenzene, whereas the gold nanoparticles supported on the painted nanofibers and P25 could efficiently reduce nitrobenzene to azoxybenzene as the sole product under visible light irradiation. These results were different from those from the reduction on the gold nanoparticles photocatalyst on ZrO₂, in which the azoxybenzene was the intermediate and converted to azobenzene quickly. Evidently, the support materials significantly affect the product selectivity of the nitrobenzene reduction. Finally, the new photocatalysts could be easily dispersed into and separated from a liquid because of their fibril morphology, which is an important advantage for practical applications.

Full text of DOI:10.1002/cctc.201200923

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DOI: 10.1002/cctc.201200923
Painting Anatase (TiO2) Nanocrystals on Long Nanofibers
to Prepare Photocatalysts with Large Active Surface for
Dye Degradation and Organic Synthesis
Zhanfeng Zheng, Jian Zhao, Hongwei Liu, Jiangwen Liu, Arixin Bo, and Huaiyong Zhu*[a]
Anatase TiO2 nanocrystals were painted on H-titanate nanofib-
ers by using an aqueous solution of titanyl sulfate. The anatase
nanocrystals were bonded solidly onto the titanate fibers
through formation of coherent interfaces at which the oxygen
atoms were shared by the nanocrystals and the fiber. This ap-
proach allowed us to create large anatase surfaces on the
nanofibers, which are active in photocatalytic reactions. This
method was also applied successfully to coat anatase nano-
crystals on surfaces of fly ash and layered clay. The painted
nanofibers exhibited a much higher catalytic activity for the
photocatalytic degradation of sulforhodamine B and the selec-
tive oxidation of benzylamine to the corresponding imine
(with a product selectivity >99%) under UV irradiation than
both the parent H-titanate nanofibers and a commercial TiO2
powder, P25. We found that gold nanoparticles supported on
H-titanate nanofibers showed no catalytic activity for the re-
duction of nitrobenzene to azoxybenzene, whereas the gold
nanoparticles supported on the painted nanofibers and P25
could efficiently reduce nitrobenzene to azoxybenzene as the
sole product under visible light irradiation. These results were
different from those from the reduction on the gold nanoparti-
cles photocatalyst on ZrO2, in which the azoxybenzene was
the intermediate and converted to azobenzene quickly. Evi-
dently, the support materials significantly affect the product se-
lectivity of the nitrobenzene reduction. Finally, the new photo-
catalysts could be easily dispersed into and separated from
a liquid because of their fibril morphology, which is an impor-
tant advantage for practical applications.
Introduction
TiO2 photocatalysts, especially the solids of anatase phase that
are the most studied photocatalyst materials, have drawn
great attention because of their ability to degrade organic pol-
lutants in wastewater and air completely and because of their
chemical and thermal stability.[1–3] Generally, a large active sur-
face of the photocatalyst is very important for photocatalytic
reactions because the photocatalytic reactions take place on
the surface.[4–8] Photocatalysts made of small particles have
large active surfaces but they suffer from particle aggregation
and a poor photocatalyst recovery for reuse.[9,10] A feasible ap-
proach is to immobilize the small active particles on a sub-
strate. By such an approach, one can effectively control particle
aggregation and achieve large active surfaces for catalytic reac-
tions. The large dimension of the substrate plays an important
role in the dispersion and stabilization of the discrete nanopar-
ticles. Generally, the recovery of catalysts obtained by such an
approach for reuse is much easier than that of small particles.
Thus, methods to immobilize small active particles are of sig-
nificant importance and have been widely studied.[11–14]
On the other hand, photocatalysis is, in principle, desirable
for the synthesis of organic chemicals as the process generally
proceeds at ambient temperature; and solid photocatalysts
may be readily recovered after use. Nonetheless, if used for or-
ganic synthesis, TiO2 photocatalysts exhibit poor product selec-
tivity, especially in aqueous solution, owing to the generation
C
of OH radicals and the autoxidation of the photogenerated
radicals.[4,15] These radicals have strong oxidation power and
can oxidize organic compounds completely. Recently, high se-
lectivity has been achieved in an organic solvent as the unse-
lective process driven by the radicals was inhibited.[15–19] If pho-
tocatalysts with a large active surface can be attained, they
may be efficient catalysts for the synthesis of organic chemi-
cals through selective oxidation. Moreover, the immobilized
TiO2 may also be a superior support of Au nanoparticle (NP)
photocatalysts. The metal oxide support with a large surface
area allows Au NPs to disperse into discrete NPs, which are
beneficial for their catalytic performance. Au NPs can strongly
absorb visible light because of the surface plasmon resonance
(SPR) effect, and the light absorption could induce the reaction
of the molecules on the NPs such as the selective reduction of
nitrobenzene under visible light irradiation.[20–22] The photoca-
talysis process follows a different pathway from that of a pro-
cess under elevated temperature and pressure using the Au
NP catalyst on TiO2.[23] The Au NP photocatalysts on transition
metal oxides usually exhibit much better activity than those on
other oxide supports.[20–21] A rational supposition is that the
[a] Dr. Z. Zheng, J. Zhao, Dr. H. Liu, Dr. J. Liu, A. Bo, Prof. H. Zhu
School of Chemistry, Physics and Mechanical Engineering
Queensland University of Technology
Brisbane, QLD 4001 (Australia)
Fax: (+61)7-3138-1804
E-mail: hy.zhu@qut.edu.au
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/cctc.201200923.
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support materials of the Au NP photocatalysts have important
influence on the catalyst performance.
In the present study we painted TiO2 nanocrystals (NCs) on
the surface of H-titanate nanofibers (NFs) using titanyl sulfate
(TiOSO4) as the Ti source, generating a large active anatase sur-
face on the inactive substrate of H-titanate. The large anatase
surfaces were adequately exposed to reactant molecules, and
the painted nanofibers could be easily dispersed into liquids
and be recovered from a liquid by filtration or sedimentation.
The fibril photocatalysts exhibited high activities in two reac-
tions: 1) the degradation of sulforhodamine B (SRB) under UV
light and 2) the selective oxidation of benzylamine to the cor-
responding imine under UV light. Au NPs as photocatalysts on
the painted NFs exhibited high activity for the photocatalytic
reduction of nitrobenzene to azoxybenzene under visible light.
The last two reactions are important in industry for producing
fine chemicals and pharmaceuticals and have been widely
studied.[15,21,24–26]
Results and Discussion
Surface, crystal structure, morphology, and UV/Vis absorp-
tion properties
N2 adsorption–desorption isotherms of H-titanate NFs and ana-
tase NCs painted NFs (TA-S12) are shown in Figure 1. The ana-
tase NC painting resulted in a dramatic increase in the specific
surface area, from 23 m2 gÀ1 for H-titanate to 166 m2 gÀ1 for
TA-S12. TA-S12 displayed type-IV adsorption isotherms typical
of mesoporous materials,[27] with average pore sizes in the 3–
6 nm range. These mesopores should be the intercrystal voids
within the NCs. In contrast, a type-II adsorption isotherm with-
out hysteresis loop is observed for the pristine H-titanate NFs,
indicating that the sample is a nonporous solid.[27]
Figure 1. a) N2 adsorption–desorption isotherms of H-titanate and TA-S12.
b) The Barrett–Joyner–Halenda (BJH) pore size distribution of TA-S12.
The XRD patterns of H-titanate NFs and TA-S12 are shown in
Figure 2a. The H-titanate NFs were indexed as H2Ti3O7,[28,29]
whereas the diffraction peak of anatase (011) is clearly ob-
served in TA-S12. There are diffraction peaks from both anatase
and titanate in TA-S12, indicating that the sample contained
the two phases. The TEM images in Figure 2 illustrate an inter-
esting morphological evolution of the TA-S12. The substrate H-
titanate NFs had a relatively smooth surface (Figure 2b). The
painting resulted in a very rough surface; anatase NCs with
sizes of approximately 6 nm can be clearly seen on the TA-S12
NFs (Figure 2c). This result also confirms that the mesopores of
the sample are the intercrystal voids among the NCs. In an
HRTEM image of an anatase particle (Figure 2d), the spacing
between the parallel fringes was 0.35 nm, consistent with the
lattice spacing of the anatase (011) plane. In our previous
work, large anatase crystals (sized at ꢀ40 nm) that covered H-
titanate NFs were obtained from the H-titanate NFs in a diluted
acid solution (0.05m HNO3) at moderate hydrothermal condi-
tions (1108C).[10] In the present study, the much smaller anatase
NCs on H-titanate NFs were obtained at a much lower temper-
ature and weaker acid conditions (808C, pH ꢀ2.6). No anatase
crystals formed when treating H-titanate NFs at the same acidi-
ty and temperature in the absence of TiOSO4.
If these nanofibers were used as supports for loading gold,
the Au NPs uniformly deposited on the two types of nanofib-
ers, as shown in Figure 2e and f. The Au particle size distribu-
tions are shown in Figure 2g. On both supports, the sizes of
Au NPs are mainly (>90%) distributed from 3 to 8 nm. For
comparison, Au NPs were also loaded on the reference P25
and the size of Au NPs on it was also mainly distributed in this
range (see the Supporting Information, Figure S1). The diffuse
reflectance UV/Vis spectra (Figure 3) of supported Au NPs all
exhibited a broad surface plasmon resonance peak at approxi-
mately 540 nm, which also confirmed the similar Au particle
size.[21,30–32]
Anatase NCs growth mechanism study
In Figure 4, the XRD patterns and Raman spectra of the solids
obtained from titanyl sulfate solution after treatment at 808C
for time periods from 1 h to 48 h in the absence of the H-tita-
nate NFs are shown. The patterns reveal the structural evolu-
tion of the precursor of the anatase NCs during the hydrother-
mal treatment at 808C. As seen from the Raman spectra, the
product obtained from 1 h treatment exhibited typical vibra-
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Figure 3. Normalized DRUV/Vis spectra of the supported Au NPs and the
corresponding supports.
Figure 2. Structure and morphology of the samples. a) XRD patterns of H-ti-
tanate and TA-S12. b) TEM image of H-titanate NFs. c) TEM and d) HRTEM
images of TA-S12. e) and f) TEM images of supported Au NPs on H-titanate
and TA-S12, respectively. g) Particle size distributions of Au NPs on H-titanate
and TA-S12.
[33,34]
tion peaks of a titanic acid
rather than the peaks of ana-
tase. The XRD pattern of this sample showed a broad hump,
indicating an amorphous state. TEM images also indicated the
change from amorphous particles (Figure S2a, 1 h product) to
nanocrystals (Figure S2b, 12 h product) on H-titanate NFs. The
amorphous solid formed first in the precursor and converted
to anatase seeds that grew into nanocrystals during the hydro-
thermal process according to the XRD patterns in Figure 4a.
An average crystallite size was estimated from XRD line broad-
ening of anatase at 25.38 employing the Scherrer equation.
The crystallite size at 1 h was 2.9 nm, increasing to 6.8 and
7.6 nm after the hydrothermal treatments of 12 h and 48 h, re-
spectively. This calculated crystallite size matched well with the
particle size observed in the TEM image (Figure 2c). For the
Figure 4. (a) XRD patterns and (b) Raman spectra of the solid samples pre-
cipitated from TiOSO4 solution after treatment at 808C for 1–48 h. The inset
in Figure 4b illustrates the increase of the anatase particle size during the
hydrothermal treatment.
sample, after 3 h hydrothermal reaction, six Raman active
modes of anatase crystals were clearly seen: A1g (515 cmÀ1),
2B1g (395 and 515 cmÀ1) and 3Eg (152, 199, and 639 cmÀ1).[35]
The blue shift of the strongest Eg mode from 144 cmÀ1 (for
bulk anatase) to 152 cmÀ1 also indicated the formation of small
anatase nanocyrstals.[36,37] The intensity increased slightly with
the increasing hydrothermal treatment time. In a titanyl sulfate
solution, TiO2+ [or Ti(OH)2+] is surrounded by H2O.[12,38,39] The
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isoelectric point (IEP) of H-tita-
nate was measured to be 5.4 at
258C, the detailed method is
shown in the Supporting Infor-
mation (Figure S3). At the acidic
conditions used for the anatase
NC painting (pH value below the
IEP of H-titanate), the H-titanate
NFs surfaces adsorb cations and
become positively charged, anal-
ogous to other metal oxide sur-
faces.[7,40,41] Therefore, at the be-
ginning of the hydrothermal re-
action, TiO2+ ions are adsorbed
on the surface of the H-titanate
Figure 6. A) HRTEM image showing a single nanocrystal of anatase on the surface of H-titanate. The inset is an
FFT image deduced from the red square area. B) Index of the FFT image in (A). The incident beam direction is
[111]A//[001]T. C) The corresponding IFFT image derived from the red square area in (A). “A” and “T” represent
anatase and H-titanate, respectively.
NFs with hydration water (as proven by Raman spectra). In the
subsequent step, the titanic acid loses the hydration water to
form more stable anatase NCs.
other reaction conditions identical to those for the preparation
of TA-S12. According to HRTEM (Figure 6a) and fast Fourier
transform analysis (FFT, Figure 6b), the anatase NCs were not
randomly stacked on the surface of H-titanate NFs. The (110)
planes in anatase NCs, (110)A, were almost parallel with the
(020) planes of the titanate fibers, (020)T, with only a small
angle divergence (less than 18). This observation means that
the anatase NC attached to the H-titanate fiber in such an ori-
entation that (110) planes of the NCs are parallel to the (020)
planes of the titanate, and thus the two phases can form
a closely matched interface, so-called coherent interfaces.[43–45]
The oxygen atoms at the interface are shared by two phases.
This interfacial match between anatase NCs and H-titanate NFs
lowers the surface energy, which permits the anatase NCs to
be bonded solidly onto the titanate fibers. The anatase NCs
will not fall off from the H-titanate NFs if used during the cata-
lytic reactions. This orientation of anatase NCs with respect to
the H-titanate was different from what was previously
observed.[46,47]
We found that anatase NCs could also be grown on other
oxide surfaces such as hollow spheres of fly ash (made largely
of silica and alumina) and a layered clay, laponite (Figure 5).
Photocatalytic degradation of sulforhodamine B (SRB)
The photocatalytic activity of TA-S12 was compared with that
of the well-known TiO2 photocatalyst P25 (Degussa) for the
degradation of the synthetic dye SRB under UV light (Figure 7).
If equal amounts of the photocatalyst (0.5 gLÀ1) were used, the
Figure 5. a, b) SEM images of fly-ash microballs and c, d) TEM images of la-
ponite, before and after anatase nanoparticles painting, respectively. The
insets in Figure 5a and 5b are enlarged SEM images.
Again, painting the anatase NC on laponite resulted in a signifi-
cant increase of the specific surface area (from 345 to
463 m2 gÀ1). These results demonstrate that anatase NCs can
be painted on a variety of oxide substrates. As most metal
oxides have IEPs higher than 3,[42] no further adjustment of the
pH was required during the hydrothermal reaction for painting
anatase NCs on the oxides by using titanyl sulfate solution.
In the TA-S12 sample, numerous anatase NCs were painted
on H-titanate NFs. It is difficult to observe how the NCs attach
onto the NFs by using HRTEM. Therefore, smaller amounts of
anatase NCs were painted on H-titanate NFs by using a solution
containing half as much of titanyl sulfate but maintaining
Figure 7. Photocatalytic degradation of SRB under UV light. The dashed line
for TA-S12 was calculated by using the equivalent amount of TiO2 in P25.
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activity of TA-S12 was much lower than that of P25 under UV
light irradiation. The H-titanate NFs exhibited negligible photo-
activity for the degradation of SRB, and the TiO2 content in TA-
S12 was much lower than in P25 (which contains ꢀ80% ana-
tase and ꢀ20% rutile). Anatase NCs accounted for approxi-
mately 26 wt% of the photocatalyst (calculated from the
weight increase after NC painting). However, the photocatalytic
activity of anatase NCs in TA-S12 was actually better than that
of P25. If the mass of TA-S12 was 3.85 times of that of P25, the
TiO2 content in TA-S12 sample was equal to the TiO2 content
in P25. Under these circumstances, the activity of the TA-S12
sample was better than that of P25 (see Figure 7). There were
two important factors influencing the activity: the amount of
active sites and the rate of the photogenerated charge recom-
bination.[13,14] The number of the active sites depended mainly
on the surface area of anatase and the more active sites the
better the activity. The specific surface area for TA-S12
(166 m2 gÀ1) was much larger than for P25 (51 m2 gÀ1). This
large specific surface area stemmed mainly from the anatase
NCs because the H-titanate NFs had a specific surface area of
23 m2 gÀ1. The recombination rate was mainly affected by the
crystal size. The smaller the crystal size, the faster the charge
recombination (and thus the lower the activity).[5,16,48] The size
of the anatase NCs in TA-S12 (ꢀ6 nm) was much smaller than
in P25 (ꢀ25 nm).[49] The large surface area of TA-S12 is an ad-
vantage for the reactant adsorption providing more active
sites for the reaction. However, the small sizes of anatase crys-
tals in TA-S12 caused rapid recombination of the photogener-
ated electrons and holes. If the mean crystal size was 6.8 nm,
the net result of the two offsetting factors was an improve-
ment of the photocatalytic activity.
use because the photocatalyst can absorb light irradiation and
contact with oxygen in air sufficiently and be readily separated
after reaction.
Selective oxidation of benzylamine
TA-S12 also exhibited a high photocatalytic activity (conversion
rate at 75% in 1 h) and product selectivity (to imine, >99%)
for the selective oxidation of benzylamine in acetonitrile sol-
vent under UV light illumination. This conversion rate was simi-
lar to that achieved with P25 (80%). Given that H-titanate was
not active under the reaction conditions in the present study,
the turnover frequency for the anatase NCs in TA-S12 (2.5ꢁ
10À3 sÀ1), calculated based on the total TiO2 content, was much
higher than that of P25 (6.9ꢁ10À4 sÀ1). Actually, if 150 mg of
TA-S12 (containing similar amounts of TiO2 to a 50 mg sample
of P25) was used for the reaction, TA-S12 showed a much
better photocatalytic activity (85% conversion in 25 min) than
P25 (80% conversion in 1 h). The reaction process involved
two steps: a selective oxygenation to generate the aldehydes
(the intermediate product, identified by GC–MS, Figure S5) and
a subsequent aldehyde–amine condensation reaction to yield
the imine:[15,17]
The high selectivity was achieved because of the use of the
inert solvent acetonitrile (to prevent the formation of OH· radi-
cals and unselective autooxidation reactions). The large surface
area of TA-S12 was an important factor contributing to the
high conversion rate for the photocatalytic oxidation of benzyl-
amine in the organic solvent.
In addition, the sedimentation of TA-S12 NFs was compared
with that of P25. As can be seen from Figure 8, the TA-S12 sus-
pension became clear after 2 h sedimentation, whereas the
P25 suspension was still turbid overnight. Thus, the TA-S12 NFs
can be recovered for reuse readily but P25 cannot.
The anatase NC painted floating spheres of fly ash were also
used for the degradation of SRB under UV light. The conver-
sion rate after 4 h was 93.7%. The TiO2 content on the painted
fly ash was ꢀ25 wt% according to the energy dispersive X-ray
measurement. The catalyst floated on the surface of the solu-
tion (Figure S4). This is an important advantage for practical
Selective reduction of nitrobenzene on supported Au NPs
The photocatalytic performance of Au NPs on different sup-
ports for the reduction of nitrobenzene is summarized in
Table 1. The photocatalyst exhibited activity only in the pres-
Table 1. Photocatalytic reduction of nitrobenzene using Au/TiO2 under
visible light.[a]
Product
Conversion Selectivity TOF[b]
[%]
[%]
[sÀ1
]
Au/TA-S12
Au/TA-S12 (no light) azoxybenzene 25
azoxybenzene 50
>99
>99
–
5.5ꢁ10À3
2.7ꢁ10À3
Au/H-titanate
TA-S12
–
–
0
0
–
–
–
Au/P25
Au/P25 (no light)
P25
azoxybenzene 76
azoxybenzene 55
>99
>99
–
8.3ꢁ10À3
6.0ꢁ10À3
–
–
0
[a] Reaction conditions: catalyst (100 mg), nitrobenzene (1.5 mmol), iso-
propanol (15 mL) as the solvent, 0.1m KOH/isopropanol (4.5 mL), reaction
in argon gas under visible light (0.43 WcmÀ2) at 408C for 5 h. [b] Turn-
over frequency.
Figure 8. Photographs showing the sedimentation difference between TA-
S12 and commercial P25: a) before and b) after 2 h sedimentation (concen-
tration: 1 gLÀ1 in water).
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H-titanate NFs (0.05 g). The mixture was kept at 808C for 12 h.
ence of Au NPs. Both Au/TA-S12 and Au/P25 exhibited high
conversions for the nitrobenzene reduction at 50% and 76%,
respectively, in 5 h reaction time. The reaction on Au/TA-S12
and Au/P25 also proceeded in the dark, achieving conversions
of 25% and 55%, respectively. An interesting finding was that
azoxybenzene was the sole product if the photocatalyst of Au
NPs on TiO2 supports were used, whereas in our previous
study, the azoxybenzene was the intermediate product and
converted to azobenzene quickly on Au/ZrO2.[21] Evidently, the
support materials significantly affect the product selectivity in
the nitrobenzene reduction. Therefore, this finding can be uti-
lized to prepare intermediate compounds, which are unstable
to be obtained if catalysts at elevated temperatures are used.
The photocatalyst of H-titanate supported Au NPs exhibited
no activity for this reaction, also demonstrating the importance
of the support materials on the performance of the photocata-
lyst. The phenomenon has not been fully understood yet, and
further studies on the influence of the support materials is
underway.
After the reaction, the precipitate was collected and washed thor-
2À
oughly with deionized water to remove residual SO4 ions. Then
the washed white solid was dried at 808C for 12 h. The sample
was labeled as TA-S12. TiO2 NCs were also painted on other materi-
als such as laponite clay or fly ash by using the same approach. To
prepare the Au NPs photocatalysts (3 wt%) on the fibril supports,
H-titanate or TA-S12 (2.5 g) was dispersed into 3.8ꢁ10À3 m HAuCl4
solution (100 mL), followed by addition of 0.53m lysine (20 mL)
under magnetic stirring. The stirring was prolonged for 30 min. To
this suspension, 0.35m NaBH4 solution (10 mL) was added gradual-
ly, followed by addition of 0.3m hydrochloric acid (10 mL). Then
the mixture was aged for 12 h. Finally, the solid was separated,
washed with deionized water and ethanol, and dried at 808C (la-
beled as Au/TA-S12).
Characterization
TEM was used to study the detailed structure of anatase NC paint-
ed H-titanate NFs. TEM and high-resolution TEM (HRTEM) were
conducted on a Techni F20 transmission electron microscope oper-
ating at 200 kV. XRD patterns of the sample powders were record-
ed on a Philips PANalytical X’Pert PRO diffractometer using CuKa ra-
diation (l=1.5418 ꢂ) operating at 40 kV and 40 mA with a fixed
slit. Diffuse reflectance UV/Vis (DRUV/Vis) spectra of the samples
were measured on a Varian Cary 5000 spectrometer. The Raman
spectra of the samples were measured on a Spectra-Physics model
127 He-Ne laser (633 nm) at a resolution of 2 cmÀ1. Nitrogen sorp-
tion isotherms were measured by the volumetric method on an
automatic adsorption instrument (Micromeritics, Tristar 3000) at
liquid nitrogen temperature (77 K). Zeta potential measurements
were conducted on a Malvern nano-ZS zetasizer connected with
a MPT-2 multipurpose titrator.
Conclusions
In summary, painting anatase nanocrystals (NCs) on a substrate
is an efficient method that can be applied to various oxide
substrates. It allowed us to achieve large photocatalytic active
surfaces and solve the problems of particle aggregation and
photocatalyst recovery. These two problems have seriously im-
peded the practical applications of the photocatalysts. The
anatase NCs covered on H-titanate nanofibers (NFs) exhibited
high activities for the degradation of sulforhodamine B, and
high activities and selectivities (>99%) for the benzylamine
oxidation (to imine). The photocatalysts of Au NPs on the ana-
tase NC painted titanate NFs or on P25 could efficiently reduce
nitrobenzene to azoxybenzene. Given that on Au NPs on ZrO2
support under the same reaction conditions, the azoxybenzene
is the intermediate product and quickly converts to azoben-
zene, the support material significantly affects the product se-
lectivity of this reaction. Therefore, we can optimize the prod-
uct selectivity by choice of the support materials. The photoca-
talysts with the nanofibril morphology are feasible for practical
applications because they can be easily dispersed into a solu-
tion and separated from a liquid by filtration, sedimentation or
centrifugation, because of their fibril morphology. The results
of this study could be used for developing superior photocata-
lysts and other delicate functional nanostructures.
Photocatalytic degradation of sulforhodamine B
Six parallel Hg lamps (20W, NEC, FL20SBL) were used as the UV
light source, and the peak of the wavelength was at approximately
350 nm. The catalyst concentration was 0.5 gLÀ1, and the initial
concentration (C0) of the SRB was 1.8ꢁ10À5 m. At designed irradia-
tion time intervals, specimens were taken from the reaction disper-
sion, and filtered through a Millipore filter (400 nm, Teflon) to
remove the catalyst particles prior to the analysis. The filtrate was
analyzed by UV/Vis spectra (Varian Cary 100 spectrometer) for the
absorbance intensity by using the reading at 565 nm.
Photocatalytic oxidation of benzylamine
The UV source was a 100 W Hg lamp. Reactions were conducted in
an oxygen atmosphere at 408C. In a typical reaction, benzylamine
(0.2 mmol) was dissolved in acetonitrile (5 mL), to which the pho-
tocatalyst (50 mg) was added. The liquid products were analyzed
by using an Agilent HP-6890 GC and GC–MS with an HP-5 column.
Experimental Section
Photocatalyst preparation
All the chemicals used in this study were analytical grade from
Sigma–Aldrich unless otherwise stated and all the solutions were
prepared by using high-purity deionized water (Millipore Corp.,
18.2 MWcm). H-titanate was prepared by using the method pub-
lished previously.[50] TiOSO4 solution was obtained by dissolving
TiOSO4·xH2O (1.35 g, Fluka) in H2O (10 mL). An aliquot of 0.5 mL of
the above solution was diluted to 50 mL with H2O and mixed with
Photocatalytic reduction of nitrobenzene
The reduction of nitrobenzene was conducted in an argon atmos-
phere at 408C. In a typical reaction, nitrobenzene (1.5 mmol) was
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[22] D. Tsukamoto, Y. Shiraishi, Y. Sugano, S. Ichikawa, S. Tanaka, T. Hirai, J.
Am. Chem. Soc. 2012, 134, 6309–6315.
[23] A. Grirrane, A. Corma, H. Garcꢃa, Science 2008, 322, 1661–1664.
[24] A. Corma, P. Concepciꢄn, P. Serna, Angew. Chem. 2007, 119, 7404–7407;
Angew. Chem. Int. Ed. 2007, 46, 7266–7269.
dissolved in isopropyl alcohol (15 mL), and a solution of KOH in
isopropyl alcohol (0.1m, 4.5 mL) and the catalyst (50 mg) were
added. Then, the reaction mixture was illuminated with incandes-
cent light (mainly visible light, 0.43 WcmÀ2) for 5 h under magnetic
stirring. The liquid products were analyzed by using an Agilent HP-
6890 GC with a HP-5 column.
[25] S. Patai, The Chemistry of the Hydrazo, Azo and Azoxy Groups, Vol. 2,
Wiley, Chichester, 1997.
[26] S.-I. Murahashi, Angew. Chem. 1995, 107, 2670–2693; Angew. Chem. Int.
Ed. Engl. 1995, 34, 2443–2465.
Acknowledgements
[27] K. S. W. Sing, D. H. Everett, R. A. W. Haul, L. Moscou, R. A. Pierotti, J. Rou-
querol, T. Siemieniewska, Pure Appl. Chem. 1985, 57, 603–619.
[28] Y. V. Kolen’ko, K. A. Kovnir, A. I. Gavrilov, A. V. Garshev, J. Frantti, O. I.
Lebedev, B. R. Churagulov, G. VanTendeloo, M. Yoshimura, J. Phys. Chem.
B 2006, 110, 4030–4038.
[29] D. Wu, J. Liu, X. N. Zhao, A. D. Li, Y. F. Chen, N. B. Ming, Chem. Mater.
2006, 18, 547–553.
[30] M. Quinten, Optical Properties of Nanoparticle Systems: Mie and beyond,
Wiley-VCH, Weinheim, 2011.
Financial Supports from the Australian Research Council (ARC) is
gratefully acknowledged. Prof Yingxin Xi and Dr Qin Zhou are
highly acknowledged for providing of the fly ash and laponite
samples. The authors acknowledge the facilities, and the scientific
and technical assistance, of the Australian Microscopy & Micro-
analysis Research Facility at the Centre for Microscopy and
Microanalysis, The University of Queensland.
[31] P. Mulvaney, Langmuir 1996, 12, 788–800.
[32] A. S. K. Hashmi, G. J. Hutchings, Angew. Chem. 2006, 118, 8064–8105;
Angew. Chem. Int. Ed. 2006, 45, 7896–7936.
[33] T. Gao, H. Fjellvag, P. Norby, Inorg. Chem. 2009, 48, 1423–1432.
[34] T. Beuvier, M. Richard-Plouet, L. Brohan, J. Phys. Chem. C 2010, 114,
7660–7665.
Keywords: gold · nanostructures · photochemistry · supported
catalysts · titanates
[35] T. Ohsaka, F. Izumi, Y. Fujiki, J. Raman Spectrosc. 1978, 7, 321–324.
[36] W. F. Zhang, Y. L. He, M. S. Zhang, Z. Yin, Q. Chen, J. Phys. D 2000, 33,
912–916.
[37] M. A. Cortꢅs-Jꢆcome, G. Ferrat-Torres, L. F. F. Ortiz, C. Angeles-Chavez, E.
Lopez-Salinas, J. Escobar, M. L. Mosqueira, J. A. Toledo-Antonio, Catal.
Today 2007, 126, 248–255.
[38] D. V. Bavykin, E. N. Savinov, P. G. Smirniotis, React. Kinet. Catal. Lett.
2003, 79, 77–84.
[39] Y. Ohya, Aqueous Precursors in Handbook of Sol-gel Science and Technol-
ogy: Processing, Characterization and Application, Vol. 1 (Ed.: H. Kozuka),
Kluwer, Boston, 2005, p. 108.
[40] J.-P. Jolivet, Metal Oxide Chemistry and Synthesis: From Solution to Solid
State, Wiley, New York, 2000.
[41] Case Studies of Nobel-Metal Catalysts. S. Soled in Synthesis of Solid Cat-
alysts, (Ed.: K. P. de Jong), Wiley-VCH, Weinheim, 2009, p. 355.
[42] M. Kosmulski, Chemical Properties of Material Surfaces, CRC Press, New
York, 2001.
[43] Y. Min, M. Akbulut, K. Kristiansen, Y. Golan, J. Israelachvili, Nat. Mater.
2008, 7, 527–538.
[44] G. Renaud, Surf. Sci. Rep. 1998, 32, 5–90.
[45] C. B. Eom, R. B. Vandover, J. M. Phillips, D. J. Werder, J. H. Marshall, C. H.
Chen, R. J. Cava, R. M. Fleming, D. K. Fork, Appl. Phys. Lett. 1993, 63,
2570–2572.
[46] H. W. Liu, Z. F. Zheng, D. J. Yang, X. B. Ke, E. Jaatinen, J. C. Zhao, H. Y.
Zhu, ACS Nano 2010, 4, 6219–6227.
[47] D. J. Yang, H. W. Liu, Z. F. Zheng, Y. Yuan, J. C. Zhao, E. R. Waclawik, X. B.
Ke, H. Y. Zhu, J. Am. Chem. Soc. 2009, 131, 17885–17893.
[48] M. Anpo, T. Shima, S. Kodama, Y. Kubokawa, J. Phys. Chem. 1987, 91,
4305–4310.
[49] T. Ohno, K. Sarukawa, K. Tokieda, M. Matsumura, J. Catal. 2001, 203, 82–
86.
[1] A. L. Linsebigler, G. Q. Lu, J. T. Yates, Chem. Rev. 1995, 95, 735–758.
[2] M. R. Hoffmann, S. T. Martin, W. Y. Choi, D. W. Bahnemann, Chem. Rev.
1995, 95, 69–96.
[3] M. A. Fox, M. T. Dulay, Chem. Rev. 1993, 93, 341–357.
[4] K. Masao, O. Ichiro, Photocatalysis: Science and Technology, Springer,
New York, 2003.
[5] Z. Zhang, C.-C. Wang, R. Zakaria, J. Y. Ying, J. Phys. Chem. B 1998, 102,
10871–10878.
[6] Z. F. Zheng, J. Teo, X. Chen, H. W. Liu, Y. Yuan, E. R. Waclawik, Z. Y.
Zhong, H. Y. Zhu, Chem. Eur. J. 2010, 16, 1202–1211.
[7] K. Takanabe, K. Domen, ChemCatChem 2012, 4, 1485–1497.
[8] R. Kydd, W. Y. Teoh, J. Scott, D. Ferri, R. Amal, ChemCatChem 2009, 1,
286–294.
[9] D. Beydoun, R. Amal, G. K. C. Low, S. McEvoy, J. Phys. Chem. B 2000, 104,
4387–4396.
[10] H. Y. Zhu, X. P. Gao, Y. Lan, D. Y. Song, Y. X. Xi, J. C. Zhao, J. Am. Chem.
Soc. 2004, 126, 8380–8381.
[11] S. Yamabi, H. Imai, Thin Solid Films 2003, 434, 86–93.
[12] S. Yamabi, H. Imai, Chem. Mater. 2002, 14, 609–614.
[13] E. V. Skorb, D. G. Shchukin, H. Moehwald, D. V. Sviridov, J. Mater. Chem.
2009, 19, 4931–4937.
[14] J. A. Byrne, B. R. Eggins, N. M. D. Brown, B. McKinney, M. Rouse, Appl.
Catal. B 1998, 17, 25–36.
[15] X. Lang, H. Ji, C. Chen, W. Ma, J. Zhao, Angew. Chem. 2011, 123, 4020–
4023; Angew. Chem. Int. Ed. 2011, 50, 3934–3937.
[16] M. Anpo, P. V. Kamat, Environmentally Benign Photocatalysts: Applica-
tions of Titanium Oxide-based Materials, Springer, London, 2010.
[17] X. Lang, W. Ma, Y. Zhao, C. Chen, H. Ji, J. Zhao, Chem. Eur. J. 2012, 18,
2624–2631.
[18] V. Augugliaro, T. Caronna, V. Loddo, G. Marci, G. Palmisano, L. Palmisa-
no, S. Yurdakal, Chem. Eur. J. 2008, 14, 4640–4646.
[19] S. Yurdakal, G. Palmisano, V. Loddo, V. Augugliaro, L. Palmisano, J. Am.
Chem. Soc. 2008, 130, 1568–1569.
[50] Z. F. Zheng, H. W. Liu, J. P. Ye, J. C. Zhao, E. R. Waclawik, H. Y. Zhu, J. Mol.
Catal. A: Chem. 2010, 316, 75–82.
[20] X. Chen, H. Y. Zhu, J. C. Zhao, Z. F. Zheng, X. P. Gao, Angew. Chem. 2008,
120, 5433–5436; Angew. Chem. Int. Ed. 2008, 47, 5353–5356.
[21] H. Y. Zhu, X. B. Ke, X. Z. Yang, S. Sarina, H. W. Liu, Angew. Chem. 2010,
122, 9851–9855; Angew. Chem. Int. Ed. 2010, 49, 9657–9661.
Received: December 14, 2012
Revised: January 17, 2013
Published online on && &&, 0000
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FULL PAPERS
Z. Zheng, J. Zhao, H. Liu, J. Liu, A. Bo,
H. Zhu*
&& – &&
Painting Anatase (TiO2) Nanocrystals
on Long Nanofibers to Prepare
Photocatalysts with Large Active
Surface for Dye Degradation and
Organic Synthesis
A porous paint: Anatase nanocrystals
with large surface areas that were paint-
ed on the surface of titanate nanofibers
bonded solidly. This process generated
a superior active surface for photocata-
lytic reactions, either serving as the
photocatalyst or Au catalyst support.
ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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8
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These are not the final page numbers!