Optimization of boron-doping process of titania nanotubes via electrochemical method toward enhanced photoactivity
J Solid State Electrochem
Optimization of boron-doping process of titania nanotubes via electrochemical method toward enhanced photoactivity
Mariusz Szkoda 0 1
Anna Lisowska-Oleksiak 0 1
Katarzyna Siuzdak 0 1
0 Centre for Plasma and Laser Engineering, Szewalski Institute of Fluid Flow Machinery, Polish Academy of Science , Fiszera 14, 80-231 Gdańsk , Poland
1 Department of Chemistry and Technology of Functional Materials, Chemical Faculty, Gdańsk University of Technology , Narutowicza 11/12, 80-233 Gdańsk , Poland
In this work, we were focused on the development of the electrochemical approach resulting in a stable boron doping of titania nanotubes. The doping procedure concerns anodic polarization of as-anodized titania in a H3BO3 solution acting as n boron precursor. The series of attempts were taken in order to elaborate the most beneficial doping conditions. The parameters of electrochemical doping allowing to obtain boron-doped titania characterized by the highest photoconversion efficiency are as follows: reaction voltage 1.8 V, process duration 0.5 h, and the concentration of boric acid 0.5 M. Spectroscopy techniques such as UV-vis, X-ray diffraction, photoluminescence emission, and X-ray photoelectron spectroscopy were used to characterize the absorbance capability and the crystalline phase, to confirm the presence of boron atoms and to study the nature of chemical compounds, respectively. The well-ordered structure of titania and resistance of its morphology toward electrochemical treatment in H3BO3 were confirmed by scanning electron microscopy images. However, cyclic voltammetry and electrochemical impedance spectroscopy studies showed the significant difference in conductivity and capacitance between doped and pristine titania. Moreover, the photocurrent densities of the B-doped sample were about seven times higher in comparison with those generated by the pure titania nanotube electrode.
TiO2 nanotubes; Boron doping; Anodization; Photocurrent; Electrochemical doping
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In the last decades, the development of photochemical
systems capable of harnessing solar energy to produce electricity
or chemical fuels has attracted significant interest [1, 2]. The
most of research strategies focus on novel types of
semiconductors exhibiting photocatalytic activity [3]. In particular,
titanium dioxide is regarded as a promising semiconducting
material for photoelectrochemical applications due to its low
cost, non-toxicity, and stability against photocorrosion [4–6].
However, the activity of titania nanotubes in processes carried
out under illumination is limited by their wide bandgap
(Ebg = 3.2 eV) that corresponds to energy provided by
ultraviolet light [7, 8]. For this reason, many approaches have been
made to improve the activity of TiO2 that allows its efficient
utilization under natural light source—sun. The vast majority
of known strategies concerning material modification are
based on metal [9–12] and non-metal doping [13–16],
formation of organic-inorganic junctions [17], or surface
sensitization by dye molecules [18]. To initiate the visible-light-driven
activity of titania, doping with non-metal atoms (I, B, C, N,
and S) has been considered as a one of the most effective
approaches that results in stable material with improved
photoactivity compared to the unmodified sample [19, 20].
Recently, doping of TiO2 with boron has been widely
studied in terms of its effect on the surface and the bulk structure
which changes the ability of tailoring the bandgap, suppresses
electron-hole pairs from recombination, and improves
electron conductivity [21–23]. Some papers have reported that
B-doped TiO2 powders obtained by a modified sol-gel method
showed a red-shifted absorption spectrum [24, 25], while
other studies concern increase in the bandgap energy of TiO2
upon doping when H3BO3 was used as a boron precursor
because of the decrease of the crystal size after incorporation
of boron atoms [21]. According to Bettinelli et al. [21], boron
used as a titania dopant could favor the transformation of
anatase to rutile. On the other hand, Finazzi et al. [26] reported
that B atoms in the anatase crystal could occupy different
positions and promote changes in the electronic structure of
boron-doped TiO2 that is in accordance to the results of
density functional theory. In general, previous results on
borondoped titania nanoparticles suggest that preparation method
highly impacts on material properties, but simultaneous
decrease of bandgap energy value is not always observed.
In this work, we present a new boron doping of titania
nanotube (TiO2 NT) approach realized during an
electrochemical process carried out at constant voltage when as-anodized
titanium plate is immersed in electrolyte containing boric acid
as a boron precursor. This method could be regarded as a
simple, cheap, and fast doping procedure that enables control
of the photoactivity of obtained material. The series of
attempts were undertaken (...truncated)