Hierarchically porous TiO2/SiO2 fibers with enhanced photocatalytic activity

Article abstract of DOI:10.1039/c4ra02285h

While TiO₂ nanoparticles are one of the most promising photocatalysts, their applications have been greatly hindered by easy aggregation. One of the effective routes to solve this problem is to incorporate them on/in a solid carrier. In this paper, we report the fabrication of hierarchically porous TiO₂/SiO₂ fibers via an electrospinning technique combined with subsequent high-temperature calcination treatment, in which the hierarchically porous SiO₂ fibers confer a platform to assemble TiO₂ nanoparticles with a uniform spatial distribution. The resultant hierarchically porous TiO₂/SiO ₂ fibers have shown an enhanced photocatalytic activity with ～95% degradation of rhodamine B as compared to ～75% using our synthesized TiO₂ nanoparticles and ～77% using commercially available Degussa P25 after 120 min illumination.

Full text of DOI:10.1039/c4ra02285h

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Hierarchically porous TiO2/SiO2 fibers with
enhanced photocatalytic activity†
Cite this: RSC Adv., 2014, 4, 19939
b
b
b
b
a
Huilin Hou,ab Lin Wang, Fengmei Gao, Guodong Wei, Jinju Zheng, Bin Tang
*
b
*
and Weiyou Yang
While TiO2 nanoparticles are one of the most promising photocatalysts, their applications have been greatly
hindered by easy aggregation. One of the effective routes to solve this problem is to incorporate them on/in
a solid carrier. In this paper, we report the fabrication of hierarchically porous TiO2/SiO2 fibers via an
electrospinning technique combined with subsequent high-temperature calcination treatment, in which
the hierarchically porous SiO2 fibers confer a platform to assemble TiO2 nanoparticles with a uniform
spatial distribution. The resultant hierarchically porous TiO2/SiO2 fibers have shown an enhanced
photocatalytic activity with ꢀ95% degradation of rhodamine B as compared to ꢀ75% using our
synthesized TiO2 nanoparticles and ꢀ77% using commercially available Degussa P25 after 120 min
illumination.
Received 16th March 2014
Accepted 17th April 2014
DOI: 10.1039/c4ra02285h
www.rsc.org/advances
and attendant dispersion of catalyst functions, and superior
mass transport.10 The key point is to select a proper material as
1. Introduction
the carrier support. SiO2 could be an excellent one owing to its
chemical inertia, thermal stability, and high transmissivity to
the UV radiation.11 Up to date, a rich variety of methods have
been exploited for the fabrication of porous SiO2 bers.12
However, the inner structures of the reported SiO2 porous bers
are ordinary solid.
In present work, we report the fabrication of hierarchically
porous TiO2/SiO2 via electrospinning technique, in which the
hierarchically porous SiO2 ber framework services as the ideal
platform to assemble. As compared to the reported work,13 the
present TiO2/SiO2 bers possessed a novel hierarchically hollow
structure and the TiO2 nanoparticles were well dispersed on/in
the amorphous SiO2 matrix. The photodegradation of rhoda-
mine B (RhB) as a simulate reaction were investigated and the
electrospun TiO2/SiO2 hierarchically porous bers show a
signicantly enhanced photocatalytic activity compared to TiO2
nanoparticles and Degussa P25.
Titanium dioxide (TiO2) is considered as one of the most
promising semiconductor photocatalysts due to its high effi-
ciency, low cost, chemical inertness, and photo-stability.1 In
particular, nanoscale TiO2 particles exhibit a high photo-
catalytic activity due to their high specic surface areas.2
However, TiO2 nanoparticles could be easily aggregated to
reduce their surface areas, thus greatly lowering their perfor-
mance. Moreover, suspended TiO2 nanoparticles are difficult to
be separated from the reaction solution aer the photocatalytic
process, which inevitably brings the second pollution to the
treated water. Typically, surface modication,3 size-controlled
TiO2 nanoparticles4 and assembling nanosized photocatalyst
on/in a solid carrier5 are oen used to overcome these short-
comings. Among these strategies, the third one is regarded as
the promising effective route, and thus many efforts have been
devoted to assemble TiO2 nanoparticles on/in various supports
such as thin lms,6 nanotubes,7 porous bers,8 dendrimers,9
and so forth.
Hierarchically porous bers are deemed as an excellent
candidate for catalyst supports, owing to their high surface area
2. Experimental procedure
TiO2/SiO2 porous bers were synthesized via calcination of
electrospinning polyureasilazane (PSN), polyvinylpyrrolidone
(PVP) and tetrabutyl titanate (TBOT) hybrid bers. In a typical
experimental procedure, 5.0 g of PSN (Ceraset, Kion Corpora-
tion, USA), 4.0 g of PVP (MW z 30 000, Ares, Scientic Instru-
ments Company, Ningbo, China) and 2.5 g TBOT (Aladdin,
Reagent Company, Shanghai, China) were commercially were
commercially available and directly used without further puri-
cation. For electrospinning of polymeric precursor bers,
9.5 ml of absolute ethyl alcohols were used as the solvent. The
aResearch Institute of Surface Engineering, Taiyuan University of Technology, Taiyuan
City, 030024, P.R. China. E-mail: tangbin@tyut.edu.cn
bInstitute of Materials, Ningbo University of Technology, Ningbo City, 315016, P.R.
China. E-mail: weiyouyang@tsinghua.org.cn; Fax: +86-574-87081221; Tel: +86-574-
87080966
† Electronic supplementary information (ESI) available: (1) SEM images of the
electrospun polymer precursor bers, pure TiO2 nanoparticles and P25; (2) XRD
pattern and EDS analysis of the pure TiO2 nanoparticles and P25. (3) The
spectra changes of RhB in dark and over P25 photocatalyst. See DOI:
10.1039/c4ra02285h
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mixtures of PSN/PVP/TBOT were rstly vigorous stirred for 12 h,
and then transformed into a plastic syringe with a stainless steel
nozzle (anode, diameter: 0.2 mm). The tip of the stainless steel
nozzle was placed in the front of a metal cathode (collector) with
a xed distance of 20 cm between the nozzle and the collector.
An electrical potential of 20 kV was applied for electrospinning
PSN/PVP/TBOT bers. The resultant polymeric bers were
located in an Al2O3 crucible (99% purity) with a piece of graphite
paper as the cover, and then placed at the centre of a tube
furnace. Subsequently, the samples were pyrolyzed in air at the
desired temperature of 900 ꢁC for 2 h with a heating rate of 5 ꢁC
minꢂ1, followed by furnace-cool to ambient temperature. For
comparison, TiO2 nanoparticles were prepared via the tradi-
tional sol–gel process combined with subsequent calcination
treatment. Typically, 2.0 g of TBOT was rstly mixed with an
amount of deionized water and vigorous stirred for 12 h for the
formation of TiO2 gelatin, which were dried by an incubator and
subsequently calcinated with the similar pyrolysis procedure of
the TiO2/SiO2 porous bers as mentioned above. Degussa P25
was commercially available, and used directly for the photo-
catalytic activity characterization (Aladdin, Reagent Company,
Shanghai, China).
3. Results and discussion
3.1 SEM and TEM characterizations of the as-prepared
products
The as-spun precursor bers are ranged in the size of several to
dozens millimeters in length and averagely sized in ꢀ2.5 mm in
diameters with smooth surfaces (Fig. S1(a), ESI†) and circular
solid cross-sections (Fig. S1(b), ESI†). Fig. 1 displays the typical
SEM images of the calcinated bers under different magni-
cations. The products are of high yields with well-dened ber
shapes (Fig. 1(a)). Fig. 1(b) shows the resultant bers under a
high magnication, suggesting that the bers are averagely
sized in ꢀ1.6 mm in diameter with rough surfaces. Closer
observation (Fig. 1(c)) of the ber bodies under a higher
magnication reveals that numerous tiny nanoparticles are
assembled uniformly in the ber matrix. Notably, the bers
possess a thoroughly porous structure throughout the entire
bodies (Fig. 1(d and e)). As compared to the reported works on
the fabrication of porous SiO2 bers,12 our bers exhibit a novel
hierarchically porous structure. Their typical XRD pattern
(Fig. 1(f)) discloses that the bers are composed by major
phases of amorphous SiO2 and rutile TiO2 (JCPDS card no. 21-
1276). The minor peaks detected at ꢀ28ꢁ and ꢀ32ꢁ are attrib-
uted to the tiny SiO2 nanoparticles, which might be transformed
partly from the amorphous SiO2 caused by the high pyrolysis
temperature.
Fig. 2(a) is a typical TEM image of the obtained bers under
a low magnication, clearly suggesting that the bers possess
a thoroughly porous structure. A closer observation displays
that a large amount of tiny nanoparticles are uniformly
assembled in the porous ber frameworks (Fig. 2(b)). Fig. 2(c)
provides a typical selected area electron diffraction (SAED)
pattern recorded from the marked area of A in Fig. 2(b),
implying that the bers are composed by amorphous phase
and crystalline rutile TiO2. Fig. 2(d) presents a representative
HRTEM image of the as-synthesized bers, suggesting that
TiO2 nanoparticles are irregularly shaped and typically sized
in just several nanometers, which are isolatedly and homo-
geneously assembled in the amorphous framework matrix.
The blue marked areas refer to the crystalline TiO2
nanoparticles.
The obtained products were characterized with X-ray powder
diffraction (XRD, D8 Advance, Bruker, Germany) with Cu Ka
˚
radiation (l ¼ 1.5406 A), eld emission scanning electron
microscopy (SEM, S-4800, Hitachi, Japan) and high-resolution
transmission electron microscopy (HRTEM, JEM-2100, JEOL,
Japan) equipped with energy dispersive X-ray spectroscopy
(EDS).
The photocatalytic activity of the resultant products was
evaluated for degradation of rhodamine B (RhB). The photo-
catalytic reaction is performed in an inner-irradiation quartz
annular reactor with a Xenon lamp (l > 320 nm, CEL-Hx F300,
Beijing) and a water-cooled condenser. Typically, 90 mg of RhB
and 800 mg of the as-prepared TiO2/SiO2 porous bers were
dispersed in 100 ml deionized water (the mole fraction of RhB is
3.5 ꢃ 10ꢂ4). Prior to irradiation, the suspensions were
magnetically stirred in dark for 30 min to ensure the estab-
lishment of an adsorption–desorption equilibrium between the
photocatalyst and the RhB dye. An aliquot (3 ml) of the solution
was taken at a certain time interval (10 min) during the reaction
and analyzed on the UV-visible spectrophotometer (UV-3900,
Hitachi, Japan). The change in RhB absorbance in the solution
was used to monitor the extent of reaction at given irradiation
time intervals. For comparison, 60 mg of as-prepared TiO2
nanoparticles and P25 were also used as the photocatalyst for
degradation of RhB with the same concentration and light
conditions. Here, 60 mg TiO2 nanoparticles is to keep the
identical dosages of these two TiO2 photocatalysts for the
degradation of RhB, which is calculated based on the EDS
results (Fig. 3). According to the EDS analysis, the atomic ratio
of Si to Ti is: 29.07 : 1.84 ¼ 15.8. Then the weight ratio of SiO2 to
TiO2 within the porous bers can be calculated as: 15.8 ꢃ (28 +
The EDS analysis shows that the bers mainly consist of Si,
O, Ti (Fig. 3(a)). The detected C and Cu come from the carbon
lm and copper grid used to support the TEM sample, respec-
tively. The atomic ratio of Si to O, within the experimental limit,
is close to 1 : 2, implying that the amorphous matrix frame-
works are SiO2 (Fig. 3(b), ESI†). The element mappings conrm
that the assembled TiO2 nanoparticles exhibit a very uniform
spatial distribution within the porous SiO2 frameworks
(Fig. 3(c)–(e)).
3.2 The proposed formation mechanism
16 ꢃ 2) : 1 ꢃ (44 + 16 ꢃ 2) ¼ 948 : 76 ¼ 12.5 : 1. As for 800 mg The possible mechanism for the formation of inner porous
porous TiO2/SiO2 bers used as the photocatalysts, the dosage structure is schematically illustrated in Fig. 4. Before electro-
of TiO2 nanoparticles should be xed at: 800 ꢃ 1/(12.5 + 1) ¼ 60 spinning, TBOT will be easily hydrolyzed in ethanol via the
(mg).
reaction as bellow:
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Fig. 1 (a and b) Typical SEM images of the hierarchically porous TiO2/SiO2 fibers under different magnifications. (c) Closer observation of the
fiber surface. (d and e) Typical SEM images of the destroyed body and cross-section of the products, showing their hierarchically porous nature
throughout the entire fibers. (f) A respective XRD pattern of the as-synthesized hierarchically porous TiO2/SiO2 fibers.
under calcination at 900 ꢁC, and Ti(OH)4 would be transformed
Ti(O–Bu)4 + H2O / Ti(OH)4 + C4H9OH
(1)
to rutile TiO2, which consequently make TiO2 nanoparticles be
assembled in SiO2 hierarchically porous bers.
As a result, Ti(OH)4 would exist as a droplet phase and
dispersed in the PVP/PSN solutions, which favors the formation
of a microemulsion. The dispersed droplet phase experiences
3.3 Photocatalytic activity
only by the acting surface forces from the continuous phase of The photodegradation of rhodamine B (RhB) used as a simu-
PVP/PSN solution sucked into the jet due to the electric forces. late reaction was investigated to explore the photocatalytic
Thus, in the case of the electric force strong enough, a jet will be activity of the hierarchically porous TiO2/SiO2 bers. Prior to
stretched from the PVP/PSN and Ti(OH)4 drop tip, making the irradiation, the mixture is maintained in dark and no obvious
formation of a discontinued jet and, ultimately, discontinued photodegradation can be observed aer 120 min (Fig. S3, ESI†),
bers.14 The resultant discontinued structure plays as the suggesting that the reaction should be photocatalytic rather
template for the formation of the hierarchically porous bers by than physical adsorption. As disclosed in Fig. 5(a), the UV-
the convention of Ti(OH)4 to TiO2 caused by the calcination in visible adsorption peaks centered at ꢀ554 nm of RhB over TiO2/
air. Additionally, the formation of the hierarchically porous SiO2 porous bers undergoes a fairly evolution with the
bers can be attributed to the selective evaporation–calcination increase of the irradiation time, suggesting the dye concen-
process due to the distinctively different thermal properties trations decreased during the photocatalysis process.16
between PVP and PSN.15 Thus, PSN would be converted to SiO2 However, the spectra changes of RhB (Fig. 5(b)) over TiO2
and retained for constructing the hierarchically porous bers nanoparticles (SEM image and XRD pattern of the fabricated
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Fig. 4 Schematic illustration for the formation of hierarchically porous
TiO2/SiO2 fibers.
Fig. 2 (a and b) Typical TEM images of the obtained fibers under
different magnifications. (c) A typical SAED pattern of the fiber recor-
ded from the marked area of A in (b). (d) A representative HRTEM image
of the fiber recorded form the marked area of B in (b).
nanoparticles aer long time work induced by the minimiza-
tion of the surface energy, which results in the photocatalyst
deactivation. The aggregation of nanoparticles would lead to
following negative inuences: (i) inhibit the interparticle
charge transfer; (ii) lower the capacity of the adsorption of
reactants and desorption of products, ultimately result in the
TiO2 nanoparticles, see Fig. S2, ESI†) exhibit an evolution quite
different from that of TiO2/SiO2 porous bers. Notably, the deactivation of the photocatalysis behavior. Furthermore, for
adsorption peaks experience a gradually decrease at the early comparison, the photocatalytic efficiency of commercial TiO2
nanoparticles (Degussa P25) (SEM image and EDS pattern, see
Fig. S4, ESI†), which are a widely used standard photocatalyst,
is also measured under the same experimental conditions. The
stage of the reaction time of ꢀ70 min, whereas there is negli-
gible changes with the further increase of the irradiation time.
This could be ascribed to the aggregation of the TiO2
Fig. 3 (a) A typical EDS spectrum of the porous fibers. (b) Detailed chemical compositions (at%) of the porous fiber. (c–e) The element mapping
of Si, O, and Ti within the honeycomb mesoporous fibers.
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Fig. 6 Schematic illustration for RhB photodegradation over SiO2/
TiO2 porous fibers under light irradiation.
These results conrm the enhanced photocatalytic activities of
hierarchically porous TiO2/SiO2 bers as compared to TiO2
nanoparticles.
3.4 The proposed photodegradation mechanism
The mechanism of RhB photodegradation over the hierarchi-
cally porous TiO2/SiO2 bers is schematically illustrated in
Fig. 6. Typically, current theory has pointed out that the reaction
process of RhB photodegradation can divide into two types. One
is deethylation with the obvious adsorption peak shis, and the
other is cycloreversion with insignicant peak transformation.17
Based on the present UV-visible adsorption (Fig. 5(a) and (b)),
the reaction can be attributed to the second type. In general,
TiO2 particles rstly absorb the UV light to generate electron/
hole pairs once the energies are higher than the band gap
energy. Then, part of the valence band holes (h+) will directly
cleavage the chromophore structure (cycloreversion) of RhB.
Anther part of the holes will be trapped by the surface bound
HOꢂ (or by H2O) to yield cOH radicals and H+ cations.
Concomitantly, the conduction band electrons (eꢂ) are scav-
enged by the adsorbed oxygen molecules to yield superoxide
radical anions (O2cꢂ) and combine with H+ cations to generate
cOOH radicals. Subsequently, cOH and cOOH radicals would
attack on the positions of highest electron density in RhB
molecules through photooxidation.
Fig. 5 (a and b) Temporal UV-visible adsorption spectral of the RhB
solution with the irradiation time over TiO2/SiO2 porous fibers and
TiO2 nanoparticles, respectively. (c and d) Digital pictures of the color
changes with the irradiation time of TiO2/SiO2 porous fibers and TiO2
nanoparticles, respectively. (e and f) Photocatalytic activities and the
first order kinetic plots of TiO2/SiO2 porous fibers, TiO2 nanoparticles
and P25, respectively. The black line in (e) responds to the photo-
catalytic activity of TiO2/SiO2 porous fibers in dark.
results suggest that the photocatalytic activity of P25 is similar
to our present TiO2 nanoparticles (Fig. 5(d) and (e) and S5(a),
ESI†), implying the P25 photocatalyst also can not work steadily
with high-efficiency. That is to say, the hierarchically porous
SiO2 bers have been serviced as a good carrier for TiO2
nanoparticles to limit their aggregation, which, in turn,
enhances their photocatalytic activities. Fig. 5(c and d) and
S5(b), ESI† show the color changes of RhB solutions by using
these three photocatalysts corresponding to the UV-visible
adsorption changes, respectively. It seems that the colors of the
suspensions catalyzed by TiO2/SiO2 porous bers (Fig. 5(c))
changed gradually from pink to almost colorless, suggesting
the nearly complete photodegradation of RhB. Nevertheless,
4. Conclusions
the suspensions catalyzed by TiO2 nanoparticles (Fig. 5(d)) and In summary, we have demonstrated the fabrication of hierar-
P25 (Fig. S5(b), ESI†) still show an obvious light pink color aer chically porous TiO2/SiO2 bers via electrospinning polymeric
120 min illumination. Fig. 5(e) presents the time-dependent precursor containing polyureasilazane, polyvinylpyrrolidone
degradations of RhB of these three photocatalysts (C and C0 and butyl titanate combined with subsequent high-temperature
refer to the real time RhB concentration and initial RhB calcination treatment. The obtained bers are composed of
concentration, respectively). As for TiO2/SiO2 porous bers, it hierarchically porous SiO2 frameworks and tiny TiO2 nano-
exhibits a favorable linear relevance with a degradation quan- particles. The results suggest that the hierarchically porous SiO2
tity of ꢀ95% aer 120 min illumination. Otherwise, the ber frameworks could confer an ideal platform to assemble the
degradation quantities of TiO2 nanoparticles and P25 are TiO2 nanoparticles with a uniform spatial distribution. The
ꢀ75% and ꢀ77%, respectively. Fig. 5(f) shows the rst order resultant hierarchically porous TiO2/SiO2 bers exhibit an
constants of k derived form the linear tting of the plots. The k enhanced photocatalytic activity with ꢀ95% degradation of
of the photocatalysts of TiO2/SiO2 porous bers, TiO2 nano- rhodamine B as compared to ꢀ75% of our synthesized TiO2
particles and P25 are cal. 0.0227, 0.0125 and 0.017, respectively. nanoparticles and ꢀ77% of commercial available P25. It is
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´
5 (a) S. D. Burnside, V. Shklover, C. Barbe, P. Comte,
expected that current work could provide a facile strategy for the
exploration of photocatalysts with high performance.
¨
F. Arendse, K. Brooks and M. Gratzel, Chem. Mater., 1998,
10, 2419; (b) T. Kamegawa, D. Yamahana and
H. Yamashita, J. Phys. Chem. C, 2010, 114, 15049.
6 S. D. Burnside, V. Shklover, C. Barb, P. Comte, F. Arendse,
K. Brooks and M. Grtzel, Chem. Mater., 1998, 10, 2419.
7 S. Lee and W. M. Sigmund, Chem. Commun., 2003, 6, 780.
8 B. Ding, J. Kim, E. Kimura and S. Shiratori, Nanotechnology,
2004, 15, 913.
9 S. Khaled, R. Sui, P. A. Charpentier and A. S. Rizkalla,
Langmuir, 2007, 23, 3988.
10 (a) C. M. Parlett, K. Wilson and A. F. Lee, Chem. Soc. Rev.,
2013, 42, 3876; (b) M. M. Gao, K. N. Peh, W. L. Ong and
G. W. Ho, RSC Adv., 2013, 3, 13169.
Acknowledgements
This work was supported by 973 program (Grant no.
2012CB326407), National Natural Science Foundation of China
(NSFC, Grant no. 51072084, 51002083 and 51372123), Founda-
tion of Educational Commission in Zhejiang Province of China
(Grant no. Y201327895), Taiyuan University of Technology
Innovation Fund for Graduate Students (Grant no. 2012310012)
and Outstanding Innovation Project for Graduate Student in
Shanxi Province (Grant no. 20133040).
11 (a) R. Wang, X. Wang and J. H. Xin, ACS Appl. Mater.
Interfaces, 2009, 2, 82; (b) W. Li and D. Zhao, Adv. Mater.,
2013, 25, 142.
References
1 (a) A. Fujishima, T. N. Rao and D. A. Tryk, J. Photochem.
Photobiol., C, 2000, 1, 1; (b) D. Yang, H. Liu, Z. Zheng,
Y. Yuan, J. Zhao, E. R. Waclawik, X. Ke and H. Zhu, J. Am.
Chem. Soc., 2009, 131, 17885; (c) H. Hu, H. Irie and
K. Hashimoto, J. Am. Chem. Soc., 2011, 132, 6898; (d)
D. Feng, W. Luo, J. Zhang, M. Xu, R. Zhang, H. Wu, Y. Lv,
A. Asiri, S. B. Khan, M. M. Rahman, G. Zheng and D. Zhao,
J. Mater. Chem. A, 2013, 1, 1591; (e) J. Lu, F. Su, Z. Huang,
C. Zhang, Y. Liu, X. Ma and G. Gong, RSC Adv., 2013, 3,
720; (f) L. Li, X. Liu, Y. Zhang, P. A. Salvador and
G. S. Rohrer, Int. J. Hydrogen Energy, 2013, 38, 6948; (g)
L. Zhang, D. Jing, X. She, H. Liu, D. Yang, Y. Lu and
L. Guo, J. Mater. Chem. A, 2014, 2, 2071.
12 (a) F. Kleitz, F. Marlow, G. D. Stucky and F. Schth, Chem.
Mater., 2001, 13, 3587; (b) J. Wang, J. Zhang, B. Y. Asoo
and G. D. Stucky, J. Am. Chem. Soc., 2003, 125, 13966; (c)
Y. Yang, M. Suzuki, H. Fukui, H. Shirai and K. Hanabusa,
Chem. Mater., 2006, 18, 1324; (d) A. C. Patel, S. Li,
J. M. Yuan and Y. Wei, Nano Lett., 2006, 6, 1042.
13 (a) B. Ding, H. Kim, C. Kim, M. Khil and S. Park,
Nanotechnology, 2003, 14, 532; (b) M. Jin, X. Zhang,
A. V. Emeline, Z. Liu, D. A. Tryk, T. Murakami and
A. Fujishima, Chem. Commun., 2006, 43, 4483; (c)
A. S. Nair, Z. Peining, V. J. Babu, Y. Shengyuan, P. Shengjie
and S. Ramakrishna, RSC Adv., 2012, 2, 992.
14 (a) Z. Zhang, X. Li, C. Wang, L. Wei, Y. Liu and C. Shao, J.
Phys. Chem. C, 2009, 113, 19397; (b) H. Chen, J. Di,
N. Wang, H. Dong, J. Wu, Y. Zhao, J. Yu and L. Jiang,
Small, 2012, 7, 1779.
15 H. Hou, F. Gao, G. Wei, M. Wang, J. Zheng, B. Tang and
W. Yang, Cryst. Growth Des., 2012, 12, 536.
16 (a) J. Yu, Q. Xiang, J. Ran and S. Mann, CrystEngComm, 2010,
12, 872; (b) W. Shi, J. Shi, S. Yu and P. Liu, Appl. Catal., B,
2013, 138, 184.
17 (a) S. Horikoshi, H. Hidaka and N. Serpone, Environ. Sci.
Technol., 2002, 36, 1357; (b) X. Li and J. Ye, J. Phys. Chem.
C, 2007, 111, 13109; (c) J. Zhuang, W. Dai, Q. Tian, Z. Li,
L. Xie, J. Wang, P. Liu, X. Shi and D. Wang, Langmuir,
2010, 26, 9686.
2 (a) C. Burda, Y. Lou, X. Chen, A. Samia, J. Stout and J. L. Gole,
Nano Lett., 2003, 3, 1049; (b) I. Robel, M. Kuno and
P. V. Kamat, J. Am. Chem. Soc., 2007, 129, 4136; (c) L. Li,
G. S. Rohrer and P. A. Salvador, J. Am. Ceram. Soc., 2012,
95, 1414; (d) L. Zhang, Y. Li, Q. Zhang and H. Wang,
CrystEngComm, 2013, 15, 1607; (e) C. Lin, Y. Song, L. Cao
and S. Chen, Nanoscale, 2013, 5, 4986.
3 (a) O. V. Makarova, T. Rajh, M. C. Thurnauer, A. Martin,
P. A. Kemme and D. Cropek, Environ. Sci. Technol., 2000,
34, 4797; (b) G. Ramakrishna, A. Das and H. N. Ghosh,
Langmuir, 2004, 20, 1430.
4 (a) S. Y. Chae, M. K. Park, S. K. Lee, T. Y. Kim, S. K. Kim and
W. I. Lee, Chem. Mater., 2003, 15, 3326; (b) M. Pal, J. Garci,
P. Santiago and U. Pal, J. Phys. Chem. C, 2007, 111, 96.
19944 | RSC Adv., 2014, 4, 19939–19944
This journal is © The Royal Society of Chemistry 2014