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Published on the web May 28, 2011
Electrochemical and Photocatalytic Decomposition of Perfluorooctanoic Acid with a Hybrid
Reactor Using a Boron-doped Diamond Electrode and TiO2 Photocatalyst
Tsuyoshi Ochiai,*1,2 Hirofumi Moriyama,1,3 Kazuya Nakata,1,2 Taketoshi Murakami,1 Yoshihiro Koide,3 and Akira Fujishima1,2
1Kanagawa Academy of Science and Technology, 3-2-1 Sakado, Takatsu-ku, Kawasaki, Kanagawa 213-0012
2Division of Photocatalyst for Energy and Environment, Research Institute for Science and Technology,
Tokyo University of Science, 1-3 Kagurazaka, Shinjuku-ku, Tokyo 162-8601
3Department of Material and Life Chemistry, Faculty of Engineering, Kanagawa University,
3-27-1 Rokkakubashi, Yokohama, Kanagawa 221-8686
(Received April 5, 2011; CL-110283; E-mail: pg-ochiai@newkast.or.jp)
The efficient decomposition of environmentally persistent
perfluorooctanoic acid (PFOA) was achieved by a hybrid of
electrolysis and photocatalysis. The rate constant of PFOA
decomposition in the hybrid system was larger than the sum of
the constants in electrolysis-only and photocatalysis-only
systems. The hybrid system was able to accelerate the PFOA
decomposition by complementally support of two kinds of
reaction kinetics. These results could be useful for development
of a new continuous system for practical treatment of waste
water containing perfluorinated acids.
sampling
port
UV lamp
600 mW cm-2
@ 254 nm
Pt
BDD
current
density:
0.6 mA cm
quartz window
-2
glass vessel (0.5 L)
2.5 mM PFOA,
flow:
0.2 L min
0.1 M NaClO4, 1.5 wt% TiO2
-1
stirrer
pump
Perfluorinated acids have been widely used in industry (e.g.,
surfactants, surface treatment agents, and flame retardants).
However, some of them, particularly PFOA (C7F15COOH), have
been detected in the environment.1,2 Analytical studies have
revealed their toxicological properties and high stability.3 Thus,
techniques for decomposing them under mild conditions are
desirable. Recently, we reported the development of electro-
chemical and photocatalytic water treatment using a boron-
doped diamond (BDD) electrode and TiO2 photocatalyst.4 High-
level waste water containing environmentally persistent com-
pounds was converted to low-level waste water by the
electrolysis on BDD electrode. The low-level waste water was
then purified by photocatalysis on TiO2. Therefore, these two
methods for water treatment are complementary. We also
reported the electrochemical decomposition of PFOA by use
of a BDD electrode.5 From these results, here we report the
efficient electrochemical and photocatalytic decomposition of
PFOA with a hybrid reactor using a BDD electrode and TiO2
photocatalyst.
Figure 1. Schematic view of electrolysis-photocatalysis hy-
brid system.
(a)
(b)
1 cm
1 cm
Pt
BDD
Pt
BDD
Figure 2. Schematic illustrations of electrolysis unit (inside
the broken rectangle in Figure 1). (a) plate-type, (b) tube-type.
PFOA was obtained by Tokyo Kasei Kogyo Co., Ltd. TiO2
nanoparticles (P25) were obtained from Evonik Industries. A
schematic view of the hybrid system used for PFOA decom-
position is shown in Figure 1. The photocatalysis unit consists
of a glass vessel (inner diameter 133 mm © height 40 mm,
nominal volume, 0.5 L), equipped with a quartz window,
sampling ports, and a medium pressure ultraviolet (MPUV)
lamp (U46C18, Heraeus). The electrolysis unit consists of a
single compartment electrochemical flow cell using BDD and Pt
electrodes. In the present research, two types of reactor, plate
type and tube type, were used for electrolysis (Figure 2). The
plate reactor has been used for previous research.4 The tube
reactor consists of commercially available BDD electrode
(Element six) as the anode and a Pt foil as the cathode. Both
electrodes had area of 27 cm2, and the electrode gap was 1 cm. In
a typical run, an aqueous suspension (0.5 L) containing PFOA
(2.5 mM), NaClO4 (0.1 M), and P25 TiO2 nanoparticles (1.5
wt %) was filled into the photocatalysis unit and circulated
through the electrolysis unit by a pump at a flow rate of
0.2 L min¹1. The UV intensity for the photocatalysis and the
current density for the electrolysis were maintained at
600 mW cm (at 254 nm) and 0.6 mA cm (3.0 V), respective-
ly. For comparison, decomposition behaviors by electrolysis-
only and photocatalysis-only were evaluated. During the
reaction, the aqueous phase was analyzed by HPLC to quantify
the concentration of PFOA and to identify the decomposition
products in the aqueous phase. Analytical procedures have been
previously reported.5 The experiments were carried out at room
temperature and atmospheric pressure.
¹2
¹2
Figure 3 shows the electrolysis time dependence of the
survival rate of PFOA for plate and tube reactors without a
Chem. Lett. 2011, 40, 682-683
© 2011 The Chemical Society of Japan
Ochiai, Tsuyoshi
