Two novel hierarchical homogeneous nanoarchitectures of TiO2 nanorods branched and P25-coated TiO2 nanotube arrays and their photocurrent performances
Anzheng Hu
0
1
Cuixia Cheng
0
Xin Li
0
Jian Jiang
0
Ruimin Ding
0
Jianhui Zhu
0
Fei Wu
0
Jinping Liu
0
Xintang Huang
0
0
Institute of Nanoscience and Nanotechnology, Central China Normal University
, Wuhan 430079,
P. R. China
1
School of Physics and Electronic Engineering, Xiangfan University
, Xiangfan 441053, Hubei,
P. R. China
We report here for the first time the synthesis of two novel hierarchical homogeneous nanoarchitectures of TiO2 nanorods branched TiO2 nanotube arrays (BTs) and P25-coated TiO2 nanotube arrays (PCTs) using two-step method including electrochemical anodization and hydrothermal modification process. Then the photocurrent densities versus applied potentials of BTs, PCTs, and pure TiO2 nanotube arrays (TNTAs) were investigated as well. Interestingly, at -0.11 V and under the same illumination condition, the photocurrent densities of BTs and PCTs show more than 1.5 and 1 times higher than that of pure TNTAs, respectively, which can be mainly attributed to significant improvement of the light-absorbing and charge-harvesting efficiency resulting from both larger and rougher surface areas of BTs and PCTs. Furthermore, these dramatic improvements suggest that BTs and PCTs will achieve better photoelectric conversion efficiency and become the promising candidates for applications in DSSCs, sensors, and photocatalysis.
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Introduction
In current years, one-dimensional (1D) TiO2
nanostructure materials, especially nanotubular [1-3] and
hierarchical [4-7] nanoarchitecture TiO2 nanotube arrays
(TNTAs), have initiated increasing research interest
owing to their intriguing architectures because they
possess very high specific surface areas and a dual-channel
for the benefit of the electrons transportation from
interfaces to electrodes [7-13]. These nanostructure
materials have shown very promising applications in
dye-sensitized solar cells (DSSCs) [14-16], photocatalysis
[17-19], photosplitting water [20,21], sensors [22,23],
photoelectrochemical cells [24], and piezoelectronics
[25]. However, as far as we are concerned, tremendous
efforts have been conducted to improve the geometrical
factors of the nanotube layers [8-13,26], to convert
amorphous TiO2 nanotubes into different crystalline
forms (i.e., anatase or rutile phase, or mixture phases of
anatase and rutile) through high temperature annealing
for high performance applications [27-29], and also
many studies have devoted ones mind to change the
crystal structure or chemistry composition of the tubes
by modifying and doping [30-33]. There still remain
many challenges to prepare and discuss the
homogeneous modification of TNTAs, although the similar
synthesis method of growing branched ZnO nanowires
[34] and the decoration process of growing TiO2
nanoparticles on TiO2 nanotubes by a TiCl4 treatment [35]
have been reported. Therefore, it is particularly valuable
to seek some facile and high-efficiency method to
synthesize the modification of TNTAs nanostructures
for further specific surface area.
In this communication, we report for the first time the
synthesis of two novel hierarchical homogeneous
modification nanoarchitectures (i.e., P25-coated TNTAs,
PCTs; and TiO2 nanorods branched TNTAs, BTs) via
two-step method of electrochemical anodization and
hydrothermal modification approach. The main
precursors of modification are the P25 (Degussa,
Germany) and titanium(IV) isopropoxide (TTIP of 95%).
Erenow, the optimized nanoarchitecture TNTAs (with
bigger pore diameter, longer length, and larger space
among tubes) have been prepared by electrochemical
anodization method. Interestingly, the as-synthesized BTs and
PCTs with beautiful morphologies show both larger and
rougher surface area, and these properties result in
dramatic improvement of light-absorbing and
charge-harvesting efficiency, which has been shown through the UV-Vis
diffuse reflectance spectroscopic spectra and
photoelectrochemical performances in this article.
Experimental section
Fabrication of optimum nanoarchitecture TNTAs
In this article, TNTAs were prepared using a typical
anodization approach [13]. Briefly, the fabrication
process of the optimum nanoarchitecture TNTAs with
bigger pore diameter, larger space among tubes and longer
length was described as follows, Titanium foil samples,
about 200 m 2 cm 3.5 cm (Purity99.6%, from
ShengXin non-ferrous metal Co., LTD, Baoji, Shanxi,
China) were cleaned with soap, acetone, and
isopropanol before anodization. A two-electrode
configuration was used for anodization, with Ti foil as the anode,
and platinum foil as the cathode. A 99.7% pure Ti foil
(0.2 mm thickness, 2 3 cm2) was immersed in the
electrolyte containing 0.35 wt% NH4F (85% Lactic Acid) and
10 vol.% DMSO (dimethyl sulphoxide: purity 99.0%) at
a 45 V constant potential for 9 h. Thus we obtained the
amorphous TNTAs, and then the as-prepared TNTAs
were annealed at 400C for 1.5 h for further use.
Synthesis of hierarchical homogeneous
nanoarchitecture BTs
The BTs were obt (...truncated)