Single-crystalline rutile TiO2 nano-flower hierarchical structures for enhanced photocatalytic selective oxidation from amine to imine

Article abstract of DOI:10.1039/c5ra23428j

Single-crystalline rutile TiO₂ nano-flower hierarchical structures were synthesized via a one-pot solvent-thermal method, and they are demonstrated to be ordered three dimensional (3D) hierarchical structures with single-crystalline rutile TiO<

Full text of DOI:10.1039/c5ra23428j

View Article Online
View Journal
RSC Advances
This article can be cited before page numbers have been issued, to do this please use: J. Bu, J. Fang, W.
R. Leow, K. Zheng and X. Chen, RSC Adv., 2015, DOI: 10.1039/C5RA23428J.
This is an Accepted Manuscript, which has been through the
Royal Society of Chemistry peer review process and has been
accepted for publication.
Accepted Manuscripts are published online shortly after
acceptance, before technical editing, formatting and proof reading.
Using this free service, authors can make their results available
to the community, in citable form, before we publish the edited
article. This Accepted Manuscript will be replaced by the edited,
formatted and paginated article as soon as this is available.
You can find more information about Accepted Manuscripts in the
Information for Authors.
Please note that technical editing may introduce minor changes
to the text and/or graphics, which may alter content. The journal’s
standard Terms & Conditions and the Ethical guidelines still
apply. In no event shall the Royal Society of Chemistry be held
responsible for any errors or omissions in this Accepted Manuscript
or any consequences arising from the use of any information it
contains.
www.rsc.org/advances

Please do not adjust margins
RSC Advances
Page 1 of 6
View Article Online
DOI: 10.1039/C5RA23428J
Journal Name
ARTICLE
Single-crystalline rutile TiO2 nano-flower hierarchical structures
for the enhanced photocatalytic selective oxidation from amine to
imine
Received 00th January 20xx,
Accepted 00th January 20xx
Jing Bu,a Jun Fang,*,b Wan Ru Leow,a Kaihong Zheng,a Xiaodong Chen*, a
DOI: 10.1039/x0xx00000x
Single-crystalline rutile TiO2 nano-flower hierarchical structures were synthesized via a one-pot solvent-thermal method, it
is demontrated to be an ordered three dimensional (3D) hierarchical structures with single-crystalline rutile TiO2 nanorods
as its buliding blocks. They exhibited enhanced photocatalytic activity for the selective oxidation from benzylamine to N-
benzylidenebenzylamine (N-BIBL) with high yield under visible light irradiation. Such remarkable performance could
attribute to the rapid photocharges separation and inhibition of charges recombination due to the unique hierarchical
structures of this single-crystalline rutile TiO2 nano-flower. The facilely prepared single-crystalline rutile TiO2 nano-flowers
are promising materials in the field of photocatalytic fine chemical conversions and other photocatalytic applications.
www.rsc.org/
single crystalline rutile TiO2 3D hierarchical architectures are
still rare.18
Introduction
Herein, we report a facile method to synthesize nano-
TiO2 (titaium dioxide), as one of the typical transition metal
oxides, has been widely studied during the past decades due
to its low cost, nontoxicity, and high chemical stability, and its
application has been extended to various fields, such as
photovoltaic cells,1 photocatalysis,2 Li-ion battery materials,3
sensors4 and so on. Generally, the performances of these
materials are highly dependent on their crystal phases, particle
sizes and the exposed facets.5-10 Ruitle TiO2, as one of the
common phases of titania, was well investigated in its
mophology-control growth, one of the representative
examples is the rutile TiO2 nanorods11 used for DSSCs.12
Although significant achievements have been made in
synthesis of this isolated 1D nanostructure in the past decades,
the well controlled synthesis of complex nanostrucutures such
as ordered 3D hierarchical nanostructure with both
appropriate designed building blocks and well-defined overall
shape still remains great challenge. Compared to 1D nano-
materials, three dimensional (3D) hierarchically structured
counterparts could provide larger suface area, extend
dispersion of active sites at different length scales and shorten
diffusion path, it could also allow mutiple light reflections and
scatterings. All of these could contribute to remarkbaly
improved performances of these materials. To date, 3D
materials with hierarchical architectures have attracted
inceasing attention.13-17 However, reports on the synthesis of
flower-like rutile TiO2 hierarchical structures, the building
blocks of such nano-flower structures are single-crystalline
rutile TiO2 nanorods. To the best of our knowledge, the novel
photocatalytic activity toward the selective oxidation from
benzylamine to N-BIBL by this rutile TiO2 nano-flower structure
has not been reported yet. Such excellent photocatalytic
performance and the rapid synthesis strategy for the single-
crystalline rutile TiO2 nano-flower structures offer the great
potentials in the synthesis of such 3D ordered hierarchical
strucutures and their promising applications in photocatalytic
fine chemical conversions.
Results and Discussion
Fig 1A and Fig 2B are the typical SEM images of the rutile TiO2
nano-flower structure. The as-synthesized materials are
composed of substantial nano-flower-like assemblies. The
ordered hierarchical nano-structure was obtained with high
yield and uniformity, the diameter of the nano-flowers is ca.
1.2 μm, and the building blocks are these radially oriented
single nanorods. Fig 1C and Fig 1D show TEM images of the
rutile TiO2 nano-flower structure under different
magnifications, one nano-flower composed of the nanorods
bundles could be observed under TEM in Fig 1C. The HRTEM
image in Fig 1D focused on one tip of the nano-flower, the
lattice fringe of d = 0.32 nm could be measured in Fig 1D,
which could be assigned to rutile TiO2 (110) facet. The SAED
pattern present in the inset image of Fig 1D demonstrates that
the nano-flowers are single-crystalline, in which the incident
electron beam was examined along the [110] zone axis. Thus,
TEM and SAED results indicates that the growth direction of
a.School of Materials Science and Engineering, Nanyang Technological University,
50 Nanyang Avenue, Singapore 639798, Singapore
b.State Key Laboratory of Materials-Oriented Chemical Engineering, College of
Chemical Engineering, Nanjing Tech University, No. 5 Xin Mofan Road, Nanjing
210009 (P.R. China)
E-mail: fangjun@njtech.edu.cn (Jun Fang) Tel: +862583172232
chenxd@ntu.edu.sg (Xiaodong Chen) Tel: +6565137350
Electronic Supplementary Information (ESI) available
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 1
Please do not adjust margins

Please do not adjust margins
RSC Advances
Page 2 of 6
View Article Online
DOI: 10.1039/C5RA23428J
ARTICLE
Journal Name
Fig. 1 (A, B) SEM images of the rutile TiO2 nano-flower structure under different
magnification; (C, D) TEM images of the rutile TiO2 nano-flower structure under
different magnification; (Inset of D) Selected area electron diffraction (SAED) pattern of
rutile TiO2 nano-flower structure.
the nanorod is along [001] axis, so the (110) facet was exposed
as the side walls.
Fig 2 shows the typical characterizations of the rutile TiO2
nano-flower structure. The XRD pattern of the rutile TiO2
nano-flower structure is present in Fig 2A. All of the diffraction
peaks of the as-synthesized nano-flower structure could be
indexed to rutile TiO2 (JCPDS. 21-1276), which indicates that
pure rutile TiO2 phase could be synthesized under this solvent-
thermal condition. The Raman spectrum of the rutile TiO2
nano-flower structure is shown in Fig 2B. Two characteristic
peaks with the Raman shift at 442 cm-1 and 606 cm-1 could be
attributed to the scattering mode of pure rutile TiO2, which are
assigned to Eg and A1g mode.19 No additional Raman bands
assigned to other TiO2 phases are observed, which further
confirms the single rutile phase feature of the TiO2 samples.
Thus the XRD pattern and Raman spectrum of the rutile TiO2
nano-flower structure indicate that the as-synthesized TiO2
nanostructure is composed of pure rutile phase. Fig 2C displays
the UV-Vis diffuse reflectance spectrum of rutile TiO2 nano-
flower structure, distinct from the typical TiO2 rutile poly-
crystalline structure, which presents a mono absorption edge
at ca. 400 nm with the band gap ca. 3.0 eV, the spectrum of
our rutile TiO2 nano-flower structure exhibits a step in the UV
region at ca. 380nm, which implies the unique geometric
structure may be present. Furthermore, a plot of the modified
Kubelka-Munk function [F(R∞)E]1/2 vs the energy of absorbed
light E was used to calculate the values of these two band
gaps, and Egap1 = 3.0 eV and Egap2 = 3.5 eV were obtained. The
multiple band gaps presented in the nano-flower structure
should be resulted from the quantum confinement of the
electrons in these rutile nanorods which are the building
blocks for this hierarchical structure. It is reported that for 1D
anatase TiO2 nanowires (NWs), when the diameter of the NW
Fig. 2 (A) XRD pattern of the rutile TiO2 nano-flower structure; (B) Raman spectrum of
rutile TiO2 nano-flower structure; (C) UV-Vis diffuse reflectance spectrum of rutile TiO2
nano-flower structure; (D) Transformed UV-Vis diffuse reflectance spectrum of rutile
TiO2 nano-flower structure; (E) The N2 adsorption desorption isotherm of rutile TiO2
nano-flower structure; (F) The pore size distributions of rutile TiO2 nano-flower
structure.
reduced to 40 nm, the quantum confinement could occur,
along with the arising of multiple band-edge absorptions in
UV-Vis spectra for such TiO2 NWs.20 Due to the similar
morphology between the 1D TiO2 NWs and the TiO2 nanorods
in this case, which are the building blocks for the nano-flower
structure, it is reasonable to deduce that such absorption step
in the UV-vis reflectance spectra (Fig 2C) could be attributed to
the quantum confinement in our rutile TiO2 nano-flowers. The
N2 adsorption desorption isotherm of rutile TiO2 nano-flower
structure is shown in Fig 2E, the shape of the isotherm
indicates that the rutile TiO2 nano-flower shows mesoporous
structures, the hysteresis loop in the isotherms is type H2,
which could usually be observed in the pores with narrow
necks and wider bodies (ink-bottle pores).21 Pore size
distributions were analyzed with the BJH method from the
desorption branch of the isotherm (Fig 2F), The nano-flower
structure showed a maximum pore diameter at 4.0 nm. The N2
adsorption desorption isotherm and the pore size distributions
of P25 was present in Fig S5, which showed distinct features
compared with these of rutile TiO2 nano-flowers.P25
possessed a hysteresis loop of type H3, associated with
aggregates of platelike particles giving rise to slitlike pores, and
2 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Please do not adjust margins
RSC Advances
Page 3 of 6
View Article Online
DOI: 10.1039/C5RA23428J
Journal Name
ARTICLE
the pore size distribution was much broadened.Table S1 also different hydrophilic/hydropobic ends, and its stereo
summarizes the BET surface area, pore volume, and average configuration restrained its formation of densed micelle and
pore size calculated from the isotherms both for rutile TiO2 packed closely at the interface of water/toluene. So the nano-
nano-flower structure and P25. Rutile TiO2 nano-flower flower structure composed of TiO2 nanorods could be
structure showed much smaller pore size than that of P25 and obtained using TDAB and CTAB as the surfactant rather than
much narrowed pore size distribution, which suggests the TOAB.
integrity of the nano-flower structure rather than the random
packed nanoparticles of P25. And this could play important applied for the synthesis of all samples. And the amount of
role in charge diffusion in photocatalytic processes. CTAB using in the synthesis process was also evaluated. As
In this paper, CTAB was selected as the solo surfactant
Based on the synthesized protocol, several parameters shown in Fig. S3, only when the molar ratio between CTAB and
were adjusted to examine their influence on the growth of Ti precursor achieved 1:1, the nano-flower structure with
such hierarchical nanostructures. Non-polar solvent toluene uniform size distribution could be obtained. Otherwise, when
was replaced by polar solvent ethanol, as the result, none of the ratio is less than 1:1, the SEM images of the as-synthesized
an ordered nanostructure was observed (Fig. S1), implying that samples are present in Fig. S3 (Fig. S3A to Fig. S3D). It could be
the interface between polar and non-polar substances are observed that without the fully protection of CTAB for the
crucial for the vectorial growth of TiO2 nanorods, and their samples during the synthesis process, the uniform nano-flower
self-assembly procedure. It is the interface between the trace structure could not be obtained, both larger aggregates with
water in HCl and toluene before the TiO2 crystal nucleus, then spherical shape and small bundles of nanorods could be
the interface between hydrophilic TiO2 and toluene induced formed (Fig. S3). This indicates CTAB showed significant
the growth of TiO2 nanorods.12 Specifically, the trace water contribution to the morphology control of the samples, both in
from the HCl solution is immiscible with the nonpolar toluene, the constituent nanostructure of each nano-flower and the
initially, water in HCl was uniformly distributed in toluene highly ordered hierarchical structure in overall scale for all the
phase, forming micro-emulsion. Ti precursor could hydrolyze nano-flowers.
at the water/toluene interfaces and transform into TiO2
For the effective synthesis, temperature is another crucial
nucleus. After the generation of the crystalline nucleus, a new parameter, and as shown in Fig. S4, only when the reaction
interface between the hydrophilic TiO2 and toluene is formed, temperature retained at 180 oC, the uniform nano-flower
with continuous hydrolysis and subsequent growth- structure could be fully grown. With the increasing
crystallization. HCl used was to slow down the hydrolysis rate temperature, to minimize system energy, water in this
of Ti precursor by preserving the low pH value of the solution. immiscible water/toluene mixture is diffusing away from the
Such interface in this micro-emulsion system could not be high-energy water/toluene interface, with Ti4+ precursor
found in water/ethanol mixture solution as they are totally hydrolyzed simultaneously. The higher of the temperature, the
miscible, and therefore, only random packed nanoparticles faster of the diffusing speed of water. Due to the rapid mass
with non-uniform size distribution was synthesized (Fig. S1).
transfer at high temperature during the synthesis process,
Besides the solvent, the influence of surfactant in the thinner nanorods bundles could be obtained, rather than the
synthesis of the hierarchical rutile TiO2 was also examined. In thick nanorods with a short longitudinal length synthesized at
this case, three organic ammonium salts, tetraoctylammonium low temperature (80 oC, Fig. S4A). The samples obtained at the
bromide (TOAB), tetradecyltrimethylammonium bromide temperature between 80 oC and 180 oC clearly showed the
(TDAB) and cetyltrimethylammonium bromide (CTAB) were morphology evolution from thick nanorods to uniform nano-
selected for the orientation growth of the TiO2 nanostructure. flowers (Fig. S4B to Fig. S4D).
The morphology of the as-prepared TiO2 samples were shown
Based on all the characterizations aforementioned, a
in Fig. S2, respectively, and the inset images are the molecular proposed growth mechanism of the rutile TiO2 nano-flower
structures of these surfactants, accordingly. It could be structure is present in Scheme 1. In this micro-emulsion
observed that both TDAB and CTAB could induce the system composed of water/toluene phase, CTAB was used as
formation of the nano-flower structure, whereas using TOAB the surfactant forming micelles at the interfaces of two
as the surfactant, only a large domain with the size over 5 μm phases. Firstly, Ti precursor could hydrolyze at the
was obtained, without any ordered hierarchical structure (Fig. water/toluene interfaces and transform into TiO2 nucleus,
S2A). It is known that TDAB and CTAB both show a long mono- where the trace water are from HCl. It is reported that the
chain structure of carbon, with one hydrophilic (amine group) interface between two immiscible liquids could guide the
and one hydrophobic (methyl group) double ends. Therefore, growth and assembly of nanoparticles, due to nanoparticles
the surfactants prefer to be assembled at the interface of were tended to be trapped at the liquids’ interface to minimize
water and toluene, forming a micelle. As the proposed growth the Gibbs free energy of the system.22 A so-called Pickering
mechanism of the nano-flower structure aforementioned, emulsion was one of these typical examples which consists of
surfactants were selectively adsorbed on TiO2 (110) facet oil, water and nanoparticles at their interface. And in this case,
preferentially, lowering down the surface energy of TiO2 (110) we have demonstrated that the interface between toluene
facet, promoting the anisotropic growth of the TiO2 nano- and water played a key role for the formation of TiO2 nano-
flower structure. However, for TOAB surfactant, its molecular flower hierarchical structures, especially at the initial stage.
structure of branch carbon chains with the absence of two
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 3
Please do not adjust margins

Please do not adjust margins
RSC Advances
Page 4 of 6
View Article Online
DOI: 10.1039/C5RA23428J
ARTICLE
Journal Name
After the generation of the crystalline nucleus, a new interface by TiO2 photocatalysts under visible light, an oxygenation
b e t w e e n
t h e
h y d r o p h i l i c pathway was demonstrated to be the key steps for this
selective oxidation reaction, rather than the generation of
Table 1 Photocatalytic reactivity for the oxidation of benzylamine to imine under visible
light by rutile TiO2 nano-flower and P25.
Scheme 1. Proposed mechanism of the self-assembly to produce the rutile TiO2 nano-
flower hierarchical structures.
TiO2 and toluene is formed, with continuous hydrolysis and
subsequent growth-crystallization. The adding of concentrated
HCl provided an acidity environment for the synthesis of TiO2
samples, and TiCl4 in the precursor and HCl itself provided
plenty of Cl- ions to the system, the presence of Cl- ions and
low pH value both are demonstrated to favor the growth of
the rutile phase rather than anatase phase.22 Besides, some
calculation results have revealed that rutile TiO2 {110} showed
the lowest surface energy of 1.78 J·m-2 among all the rutile
facets.23 Moreover, in this case, the selective adsorption of Cl-
ions on (110) crystal faces favored the growth of rutile
nanorods along the [001] direction. The surfactant CTAB would
preferentially enhanced the oriented growth process, with the
stabilization of CTAB, TiO2 nanorods showed vectorial growth
along [001] direction, mainly exposed (110) facet as the side
walls of the nanorods. In this acidic solution, all the nanorods
are protonated, after the formation of single thin rutile
nanorod, the agglomeration of these nanorods were
promoted, which attributed to the hydrogen bonding between
neighboured protonated nanorods. So in this case, the rutile
nanorods could attach to each other in an oriented fashion to
further reduce the surface energy of the system and finally,
these nanorods self-assembled into nano-bundles. As a result,
these assembled nanorods are constructed into ordered
nanorod-based 3D nano-flowers. As the photocatalyst, the
activity of these rutile TiO2 nano-flower samples utilized in
photocatalytic oxidation from benzylamine to imine would be
examined.
OH· radical and autooxidation of amines in H2O, thus high yield
of imines could be achieved. Thus, the photo-reactivity of the
rutile TiO2 nano-flower catalysts was evaluated by
photocatalytic oxidation of amines to imines. And in the
meantime, P25 was the control sample, by which the reactions
were conducted under the identical conditions, and the results
were shown in Table 1. Benzylamine was used as the model
compound for the selective oxidation process. N-
benzylidenebenzylamine (N-BIBL) was the target product after
the selective oxidation. The reaction results indicate that the
rutile TiO2 nano-flower catalysts exhibited superior activity
than that of commercial P25 nano-powders. After 4 h reaction,
the conversion of benzylamine by nano-flower catalysts
approached to 99.9% and the selectivity to N-BIBL was 73.3%,
so the total yield of N-BIBL achieved 73.2%. For the identical
reaction time, the conversion of benzylamine by P25 only
reached 78.1% and the yield of N-BIBL was only 57.0 %, which
is much lower than that by single-crystalline rutile nano-flower
catalysts. The reaction time was prolonged to 6 h, and the
conversion by P25 finally achieved 98.7%, and the yield of N-
BIBL was 72.6%. Besides, the blank experiment was also
conducted, in which the yield of N-BIBL was examined under
the identical reaction conditions without adding any
photocatalyst. The conversion of benzylamine is extremely low
(0.78%) in this control experiment, which addressed the
significance of rutile TiO2 nano-flower photocatalyst for
remarkably promoting such selective oxidation reaction. The
proposed mechanism for this selective oxidation reaction from
amine to imine under visible light is illustrated in Scheme 2. At
first, benzylamine was adsorbed on the surface of TiO2,
forming a complex, as shown in Scheme 2; this complex could
act as the visible light absorber. Upon the excitation of visible
light, photo-electrons and holes were generated; photo-
generated holes could transfer to the substrate for the
oxidation process, produce a free radical (Scheme 2), and
electrons are retained in the lattice of TiO2, generate Ti (III)
center, so the effective separation of photo-generated charges
is achieved. The photogenerated free radicals shown in
Imine derivatives are very important starting materials in
chemical industry to produce various value-added fine
chemicals.24 The conventional route to synthesize imines is
from the condensation of amines and carbonyl compounds.
However, it is often suffered from the low efficiency due to the
over oxidation problems. Recently, an alternative route of the
direct oxidation of amines was developed which offers a new
strategy to produce imines, that is the photocatlytic
conversion route based on TiO2 photocatlysts.25, 26 In this new
method, O2 or O2 in the air was used as the oxidant, which
makes the reaction facile and green. Usually, the selective
photooxidation by TiO2 in H2O is very hard to control due to its
strong oxidation capability under UV light illumination, the
products often end up to CO2 and H2O for many organic
reactants. However, it is been demonstrated that the highly
selective oxidation by TiO2 in H2O could be achieved by
avoiding the generation of OH· radicals and unselective
autooxidation.27-30 And in the conversion of amines to imines
4 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Please do not adjust margins
RSC Advances
Page 5 of 6
View Article Online
DOI: 10.1039/C5RA23428J
Journal Name
ARTICLE
Scheme 2 could be easily oxidized by dioxygen dissolved in selective oxidation from benzylamine to N-BIBL. The results
acetonitrile to generate benzaldehyde. At meantime, the suggest the great potential of this 3D highly ordered
electron in conduction band of TiO2 would also complete the hierarchical structure in photocatalytic fine chemical
transfer to O species for the recovery of Ti(IV) center. After conversions. And this work offered the great opportunities to
explore the promising prospect of the rational designed
complex ordered nanostructures and their diverse applications
in photocatalysis.
Acknowledgements
This work was financially supported by the Singapore National
Research Foundation (NRF-RF2009-04).
Notes and references
1 B. O’Regan and M. Gratzel, Nature, 1991, 353, 737.
2 A. Fujishima and K. Honda, Nature, 1972, 238, 37.
3 (a) V. Subramanian, A. Karki, K. I. Gnanasekar, F. P. Eddy and B. Rambabu, J.
Power Sources, 2006, 159, 186. (b) Y. X. Tang, Y. Y. Zhang, J. Y. Deng, J. Q. Wei, H. L.
Tam, B. K. Chandran, Z. L. Dong, Z. Chen and X. D. Chen, Adv. Mater., 2014, 26,
6111.
4 N. Wu, S. Wang and I. A. Rusakova, Science, 1999, 285, 1375.
5 X. B. Chen and S. S. Mao, Chem. Rev., 2007, 107, 2891.
Scheme 2. Proposed mechanism for the generation of N-BIBL from benzylamine by
rutile TiO2 nano-flower hierarchical structures under visible light irradiation.
this, the nucleophilic attack on benzaldehyde by the unreacted
benzylamine would yield the corresponding N-BIBL. Thus the
reaction occurred with high selectivity and high yield of target
product. The enhanced photocatalytic activity of the rutile
TiO2 nano-flower structure can be attributed to their three-
dimensional (3D) hierarchical nanostructures and ordered
single-crystalline rutile nanorods as the building blocks
exposed (110) facets. 3D hierarchical nanostructures are
usually considered to have advanced structures than 0D and
1D architectures because of the diffusion of active sites at
different length scales on the surface of 3D nanostructures.
And the single-crystalline rutile nanorods facilitate the
vectorial transfer of the photo-generated electrons inside TiO2
from conduction band to the surface active sites and shorten
the mean diffusion length of the electrons (Scheme 2), this
advanced nanostructure facilitate the charge separation and
transfer, avoiding the excessive charge recombination which
occurred in P25 due to randomness. So the rutile TiO2
nanoflower exhibits superior activity in the oxidation process
than P25. Furthermore, The complex of the 3D hierarchical
nanostructures allow the multiple light reflections and
scatterings, leading to improved light absorption by this
nanostructure, all of these factors mentioned above resulted
in the promotion of the reactivity by TiO2 nano-flower
structure in the selective photocatalytic oxidation from
benzylamine to N-BIBL.
6 H. G. Yang, C. H. Sun, S. Z. Qiao, J. Zou, G. Liu, S. C. Smith, H. M. Cheng and G. Q.
Lu, Nature, 2008, 453, 638.
7 S.W. Liu, J. G. Yu andM. Jaroniec, J. Am. Chem. Soc., 2010, 132, 11914.
8 A. Selloni, Nat. Mater., 2008, 7, 613.
9 X. Y. Ma, Z. G. Chen, S. B. Hartono, H. B. Jiang, J. Zou, S. Z. Qiao and H. G. Yang,
Chem. Commun., 2010, 46, 6608.
10 J. Fang, F. Wang, K. Qian, H. Z. Bao, Z. Q. Jiang and W. X. Huang, J. Phys. Chem. C,
2008, 112, 18150.
11 B. Liu and E. S. Aydil, J. Am. Chem. Soc., 2009, 131, 3985.
12 X. J. Feng, K. Shankar, O. K. Varghese, M. Paulose, T. J. Latempa and C. A.
Grimes, Nano Lett., 2008, 8, 3781.
13 E. Hosono, S. Fujihara and T. Kimura, Electrochim. Acta, 2004, 49, 2287.
14 L. Xiao, Y. Yang, J. Yin, Q. Li and L. Zhang, J. Power Sources, 2009, 194, 1089.
15 F. Lu, W. Cai and Y. Zhang, Adv. Funct. Mater., 2008, 18, 1047.
16 (a) X. F. Yang, J. L. Zhuang, X. Y. Li, D. H. Chen, G. F. Ouyang, Z. Q. Mao, Y. X. Han,
Z. H. He, C. L. Liang, M. M. Wu and J. C. Yu, ACS Nano, 2009,
Y. X. Tang, X. F. Liu, Z. L. Dong, H. H. Hng, Z. Chen, T. C. Sum, X. D. Chen, Small,
2013, , 996.
3, 1212. (b) Y. Y. Zhang,
9
17 X. F. Yang, J. Chen, L. Gong, M. M. Wu and J. C. Yu, J. Am. Chem. Soc., 2009, 131,
12048.
18 X. F. Yang, C. J. Jin, C. L. Liang, D. H. Chen, M. M. Wu and J. C. Yu, Chem.
Commn., 2011, 47, 1184.
19 W. G. Su, J. Zhang, Z. C. Feng, T. Chen, P. L. Ying and C. Li, J. Phys. Chem. C, 2008,
112, 7710.
20 P. Chinnamuthu, A. Mondal, N. K. Singh, J. C. Dhar, K. K. Chattopadhyay and S.
Bhattacharya, J. Appl. Phys., 2012, 112, 054315.
21 K. S. W. Sing, D. H. Everett, R. A. W. Haul, L. Moscou, R. A. Pierotti, J. Rouquerol
and T. Siemieniewska, Pure Appl. Chem., 1985, 57, 603.
22 C. H. Wang, X. T. Zhang, C. L. Shao, Y. L. Zhang, J. K. Yang, P. P. Sun, X. P. Liu, H.
Liu, Y. C. Liu, T. F. Xie and D. J. Wang, J Colloid Interface Sci., 2011, 363, 157.
23 P. M. Oliver, G. M. Watson, E. T. Kelsey and C. P. Stephen, J. Mater. Chem.,
1997, 7, 563.
24 S. I. Murahashi, Angew. Chem. Int. Ed. Engl., 1995, 34, 2443.
25 X. J. Lang, H. W. Ji, C. C. Chen, W. H. Ma and J. C. Zhao, Angew. Chem. Int. Ed.,
2011, 50, 3934.
26 X. J. Lang, W. R. Leow, J. C. Zhao and X. D. Chen, Chem. Sci., 2015, 6, 1075.
27 F. Parrino, A. Ramakrishnan and H. Kisch, Angew. Chem. Int. Ed., 2008, 47, 7107.
28 Y. Shiraishi, N. Saito and T. Hirai, J. Am. Chem. Soc., 2005, 127, 12820.
29 S. H. Zhan, D. R. Chen, X. L. Jiao and Y. Song, Chem. Commn., 2007, 2043.
30 Q. J. Xiang, J. G. Yu and M. Jaroniec, Chem. Commn., 2011, 47, 4532.
Conclusions
To summarize, nano-flower like rutile TiO2 hierarchical
structures have been synthesized by a one-pot solvent-thermal
method. And the building blocks of such nano-flower
structures are single-crystalline rutile TiO2 nanorods with their
growth along [001] axis and exposed (110) facet on nanarods’
side walls. Owing to this hierarchical nanostructure, this rutile
TiO2 displayed enhanced photocatalytic activity for the
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 5
Please do not adjust margins

Please do not adjust margins
RSC Advances
Page 6 of 6
View Article Online
DOI: 10.1039/C5RA23428J
ARTICLE
Journal Name
Table of Contents
One-pot synthesized single-crystalline 3D rutile TiO2 nano-flower
hierarchical structures exhibited superior reactivity toward photocatalytic
selective oxidation from amine to imine.
6 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins