ENVIRONMENTAL SCIENCE AND TECHNOLOGY 2007 (II)DEVELOPMENT AND MONITORING OF MESOPOROUS VANADIUM CATALYSTS UNDERVISIBLE LIGHT
Yasuo Izumi, Kazushi Konishi, Dilshad Masih (Tokyo Institute of Technology, Yokohama, Japan)
Hideaki Yoshitake (Yokohama National University, Yokohama, Japan)
ABSTRACT: Ethanol photo-oxidation was investigated over mesoporous (template method), sol-gel,and conventional (mainly anatase) V+TiO2 catalysts. Under the illumination of visible light, mesoporous
V-TiO2 catalyst proceeded ethanol dehydration specific among all V+TiO2 catalysts tested. Initial
quicker water evolution suggested greater oxidation capability compared to other V+TiO2 catalysts. To
monitor the V sites in mesoporous TiO2 under on-reaction condition, state-sensitive V Kβ5,2-selecting V
K-edge X-ray absorption fine structure (XAFS) was applied. The red-ox states responsible for ethanol
dehydration were found to VIII and VIV over/in mesoporous TiO2 excited in visible light. The V Kβ5,2chemical shift between VIII and VIV states was 3.2 eV. Based on V Kβ5,2 emission and V Kβ5,2-selecting
XAFS spectra, the vanadium state was IV for fresh mesoporous V-TiO2 catalyst. Due to the dissociative
adsorption of ethanol under visible light, the vanadium sites were partially reduced but still in the energy
range for VIV state. Partially reduced vanadium sites re-oxidized in oxygen in visible light. Finally, 60%
of VIII state was extracted in the V Kβ5,2-selecting XAFS tuning the fluorescence spectrometer to 5456.3
eV among the mixture of VIII (minor) and VIV states (dominant) for the partially reduced mesoporous VTiO2.
INTRODUCTION
Utilization of solar energy is expected to be clean energy source. One of the technologicalpossibilities is photo-catalysis over TiO2-based catalysts. Because most of light wavelength absorbableby TiO2 lies in UV region, studies have been reported to shift the wavelength toward visible light region
by doping with V, Cr, Mn, Fe, Ni (Anpo, 2004), C, N, or S atom (Khan et al., 2002; Aita et al., 2004) toTiO2 to effectively utilize solar energy. Promoted catalysis by V doping on/in TiO2 were reported forethanol photo-oxidation (Klosek et al., 2001), degradation of crystal violet, methylene blue (Iketani et al.,
2004; Wu et al., 2004), methyl orange (Hou et al., 2006), and nitric oxide (Yamashita et al., 1999) under
the illumination of visible light.
In this paper, various V+TiO2 catalysts
were prepared via sol-gel/template synthesis anddirect/two-step
impregnation
of
V
over
anatase/rutile, and amorphous TiO2.
Ethanoloxidation reactions were studied over the series of
V+TiO2 catalysts under the illumination of visible
light. Further, molecular-level monitoring of the Vsites and substrates under on-reaction conditions
was performed to elucidate the specific dehydration
catalysis using selective X-ray spectroscopy.
MATERIALS AND METHODS
Mesoporous V-TiO2 catalysts wereprepared from V triisopropoxide oxide (1), Ti
tetraisopropoxide (2), and dodecylamine (3)(Yoshitake et al., 2003). The mixture of aqueous
solution was maintained at 333 K for 6 days andfiltered. Obtained powder was heated at 453 K for
10 days, and washed with p-toluenesulfonic acid in

FIGURE 1. Energy diagram of V Kβ 5,2 andV Kα1 emission processes and of catalysis
over mesoporous V-TiO2 under theillumination of visible light.

ISBN 978-0976885399© 2007 American Science Press

ENVIRONMENTAL SCIENCE AND TECHNOLOGY 2007 (II)ethanol. The powder was evacuated at 523 K for 2h. Specific surface area (SA) for template-washedsample was as much as 1200 m2g–1 and gradually decreased to 800 m2g–1 as the V loading increased to 3
wt% V. The loading was fixed to 3.0 wt% V throughout this paper. Mesopores with narrow size
distribution of ≈3 nm dominated. Following similar route, mesoporous TiO2 was synthesized fromcompounds 2 and 3. Mesoporous TiO2 was impregnated with compound 1 in 2-propanol.
Ethanol oxidation was performed in a closed circulating system (internal volume 132 ml)
equipped with quartz reaction cell illuminated with xenon arc lamp operated at 500 W (Ushio) and a UVcut filter (L42, Kenko). 55 µmol of ethanol and 110 µmol of oxygen were reacted with 100 mg ofcatalyst. Catalyst test in 55 µmol of ethanol in theabsence of O2 was also performed. Separately, 72µmol of water was interacted with mesoporous VTiO2 catalyst for 15 min, evacuated for 15 min, andthen 55 µmol of ethanol and 110 µmol of oxygen
were introduced to the catalyst all at 290 K.
In
additiontophysicochemical
characterization using XRD, HR-TEM, and BET,
UV-visible absorption and V Kβ5,2-selecting XAFS
were studied with the concept as illustrated in
Figure 1 (Izumi et al., 2007).
The X-raymeasurements were performed at KEK-PF 7C at
290 K. Si(111) monochromator was used and the
X-ray beam was fully tuned and focused at sample
position. The X-ray fluorescence from sample wasanalyzed by a homemade fluorescence spectrometerequipped with spherically-bent Johann-type
Ge(422) crystal (Izumi, Nagamori et al., 2005). VKβ5,2-selecting V K-edge XAFS spectrum wasmeasured by tuning the fluorescence spectrometerat fixed emission energies around V Kβ5,2 emission
peak.
In the V Kβ5,2-selecting XAFS, greaterchemical shifts are utilized for state discrimination
among VIII, VIV, and VV compared to V Kα1emission (Izumi, Kiyotaki et al., 2005).
RESULTS AND DISCUSSION
Ethanol Oxidation. Under visible light in ethanol
and O2, selective dehydration reaction of ethanol
proceeded over mesoporous V+TiO2 catalysts (23 –212 µmol h–1gcat–1) to form water and acetaldehyde(Figure 2B, C) compared to inactive mesoporous
TiO2 (2.3 – 16 µmol h–1gcat–1, Figure 2A) or
dehydrogenation over major anatase TiO2-based
catalysts (4.9 – 19 µmolacetaldehydeh–1gcat–1;
no/negligible water formation) (Masih et al., 2007).
Especially, water formation in the first 1h was
explosively faster (141 – 212 µmol h–1gcat–1) (Figure
2B, C) by more than one order of magnitude than420

FIGURE 2. Ethanol oxidation reaction as afunction time under the illumination ofvisible light on mesoporous TiO2 (A),mesoporous V-TiO2 (B), and V/mesoporousTiO2 catalysts (C) at 290 K. Ethanol (1.33
kPa) and O2 (2.67 kPa) were introduced in
the closed circulation system.

ENVIRONMENTAL SCIENCE AND TECHNOLOGY 2007 (II)steady acetaldehyde/water formation after 1h over mesoporous V-TiO2 and V/mesoporous-TiO2. The
steady reaction formula was
C2H5OH + 1/2O2  CH3CHO + H2O(1)

Comparative reaction only in ethanol was performed on mesoporous V-TiO2 catalyst under theillumination of visible light (Figure 3A). The formation rate of acetaldehyde was 1.7 µmol h–1gcat–1, only
7% of steady formation rate in ethanol + O2. No water formation was found. Hence, dehydration
reaction mechanism in ethanol + O2 was totally different from dehydrogenation reaction in the absence ofO2 over the catalyst.
Ethanol oxidation reaction was done after water adsorption on the catalyst (Figure 3B). The
formation rate of acetaldehyde was 7.0 µmol h–1gcat–1, 30% of steady formation rate for fresh catalyst.
Again, no water was produced. Thus, remarkably active V sites for explosive dehydration reaction may
be blocked by water molecules. The explosive, quick reaction in the first 1h may stabilize to constantstate (Figure 2B, C) due to the blocking effect of water molecules produced.
The
UV-visible Absorption Spectra.
wavelength of light absorption gradually shiftedto visible light region (beyond 400 nm) on goingfrom major anatase TiO2 or mesoporous TiO2 tomesoporous V-TiO2 and as the impregnated V
amount increased (Masih et al., 2007).
V Kβ 5,2 Emission Spectra.
The V Kβ5,2emission spectra were measured for mesoporous
V-TiO2 with the excitation energy set at 5484.1
eV. Intense peak top for fresh sample at 5462.1
eV shifted progressively toward lower-energy
side to 5461.6 eV in ethanol, then to 5461.0 eVin ethanol under visible light. After the visible
light was turned off, the peak top position
increased to 5461.6 eV. Then, sample was
exposed to oxygen and illuminated by visible
light. The peak top further increased to 5462.4
eV. These peak top energies corresponded to VIVstates (5460.5 – 5462.3 eV; Izumi et al., 2007).
A shoulder peak on lower energy side at 5456 –
5460 eV constantly appeared in these emission
spectra.
V Kβ 5,2-selecting XAFS Spectra Tuned to V
Kβ 5,2 Peak Top.
Next, V Kβ5,2-selecting
XANES (X-ray absorption near-edge structure)
spectra were measured for mesoporous V-TiO2
catalyst (Figure 4).
The tune energy offluorescence spectrometer was first fixed to eachpeak top to observe site structure changes
systematically under each catalytic condition.
For the fresh sample, the pre-edge peak

FIGURE 3. Ethanol oxidation reaction as afunction time under the illumination of visible
light on mesoporous V-TiO2 catalyst at 290 K.
(A) Only ethanol (1.33 kPa) was introduced.
(B) Ethanol (1.33 kPa) and O2 (2.67 kPa) wereintroduced after water (1.73 kPa) adsorption.
421

ENVIRONMENTAL SCIENCE AND TECHNOLOGY 2007 (II)and rising edge energy values were 5468.2 and 5479.7 eV,
respectively (Figure 4a). These were within the ranges ofcorresponding values, 5467.7 – 5469.4 and 5476.9 – 5479.8
eV, respectively, for VIV standard compounds, mesoporous VTiO2 (V Kα1-selecting XANES) (Izumi, Kiyotaki, et al., 2005),
and mesoporous TiO2 (Ti K-edge XANES shifted by +499.8
eV) (Yoshitake et al., 2002). In combination with the V Kβ5,2emission data, it was demonstrated that VIV sites substituted on
the Ti sites of amorphous TiO2 matrix for incipient catalyst(Figure 5a). This structure was supported by the curve fit
analyses for V K-edge EXAFS (extended XAFS) [N(V–O) = 4– 5] (Izumi, Kiyotaki, et al., 2005; Yoshitake et al., 2003).
With the introduction of ethanol, rising edge shifted
toward lower energy to 5478.0 eV (Figure 4b). A part ofvanadium sites were reduced from native IV state due to thedissociative adsorption of ethanol on VIV sites (Figure 4b). Preedge and post-edge peak positions and pattern were similar to
those for fresh sample (Figure 4a).
Next, when visible light was illuminated, the risingedge further shifted toward lower energy side to 5477.8 eV(Figure 4c). Because the rising edge positions were observed at5469.9 – 5474.7, 5476.9 – 5479.8, and 5478.0 – 5482.1 eV for
VIII, VIV, and VV standard inorganic compounds, respectively(Izumi, Kiyotaki et al., 2005; Wong et al, 1984), majority of V
sites were VIV state in this catalytic condition.
When the visible light was turned off, the edge position
increased to 5479.0 eV and the pre-edge peak intensity at
5468.0 eV became fairly weak (0.21) (Figure 4d). With theintroduction of oxygen under visible light, the X-ray absorption
edge further shifted up to 5479.9 eV (Figure 4e – f). Partiallyreduced V sites due to the dissociative adsorption of ethanol
and/or visible light illumination completely oxidized back to
VIV state in oxygen and/or visible light. Re-oxidized VIV sites
after the visible light was turned off were of relatively higher
symmetry based on mainly 1s→3d pre-edge peak intensity(Figure 4f, a).
In summary, V Kβ5,2-selecting XANES spectra undereach catalytic condition in Figure 4a, b, c, and f were assigned
to catalytic reaction states of Figure 5a, b, b + c, and a,
respectively.
V Kβ 5,2-selecting XAFS Spectra Tuned to Lower-energy
Shoulder of V Kβ 5,2. For partially reduced mesoporous VTiO2 sample for Figures 4d, the fluorescence spectrometer was
tuned to 5456.3 eV (lower-energy side shoulder) to specificallydiscriminate VIII state and compare to XANES spectrum tuned
to V Kβ5,2 peak top. The obtained V K-edge XANES spectrum
was depicted in Figure 6b in comparison with spectrum a tuned
to 5461.6 eV (a). The spectral pattern above 5473 eV was most422

FIGURE 4. V Kβ 5,2-detecting V
K-edge XANES spectra formesoporous V-TiO2 catalyst. (a)Fresh sample in argon, (b) in 2.1
kPa of ethanol, (c) in ethanol
under visible light illumination,(d) after the visible light was
turned off, (e) in 101 kPa of O2,and (f) in O2 under visible lightillumination. The tune energy
was 5462.1, 5461.6, 5461.0,
5461.6, 5462.4, and 5462.4 eV,
respectively.

ENVIRONMENTAL SCIENCE AND TECHNOLOGY 2007 (II)similar to the weighted sum of standard spectra for VIII and VIV with the mixing ratio 6:4 (Rf = 1.1%;
Figure 6, inset). The V sites for the two model compounds are surrounded with 5 – 6 O atoms similar tothe V site coordination for mesoporous V-TiO2. Thus, fully reduced VIII state by excited electrons undervisible light was not directly detected with this trial.
The V Kβ5,2-selecting XAFS measurements to directly detect VIII state with continuous feed ofsaturated pressure of ethanol gas under the illumination of visible light are in progress. When each
spectral data for VIII and VIV states will be available for mesoporous V-TiO2 catalyst, the population ofeach state can be determined under each catalytic condition.

FIGURE 6. V Kβ 5,2-detecting V Kedge XANES spectra for mesoporous
V-TiO2 catalyst after visible lightillumination in 2.1 kPa of ethanol. The
fluorescence tune energy was 5461.6(a) and 5456.3 eV (b). (Inset) R-factor
change of fit to spectrum b with thosefor VIII2O3 and VIVO(SO4)•nH2O. The
fits were performed in energy range
above 5473 eV.

FIGURE 5. Proposed reaction mechanism of
ethanol dehydration over mesoporous V-TiO2
catalyst under visible light (a – d).

CONCLUSIONSIn ethanol oxidation reaction under theillumination of visible light, ethanol dehydration anddehydrogenation proceeded on mesoporous V+TiO2 andV+TiO2(mainly anatase) catalysts, respectively. Distorted VIV sites were found to be highly active to
drastically evolve water in first 1h of reaction. The differences of specific SA and NHE for red-ox pair
VIV↔VIII (+0.337 V) compared to VV↔VIV for most of supported V catalysts (+0.958 V) may be also
critical. Ethanol dehydration reaction chosen as a simplified model reaction on mesoporous V-TiO2
catalyst will be extended to organic solvent/dye decomposition at C–O or C–N bond(s) to reduce
environmental risk.
Partial reduction of native VIV sites in mesoporous V-TiO2 was observed in V Kβ5,2 emission andKβ5,2-selecting XANES spectra in ethanol under visible light illumination. The V state oxidized back toinitial VIV state in oxygen and/or under visible light. The V site symmetry (coordination) slightly
increased after the photo-catalysis based on the decrease of V K pre-edge peak intensity.
The extraction of photo-reduced VIII states was 60% by tuning fluorescence spectrometer to5456.3 eV for partially reduced mesoporous V-TiO2 with smaller population of VIII state in dynamic
equilibrium with major VIV + photo-excited e– (≈102 ps; Martin et al., 1994).
V doping was effective to create VIV/III impurity energy level for visible light absorption between
relatively greater band gap of mesoporous TiO2 due to quantum size effect. Catalytic superiority of423

ENVIRONMENTAL SCIENCE AND TECHNOLOGY 2007 (II)ultimately exposed (catalytically available) native VIV sites was also suggested.
ACKNOWLEDGEMENTS
X-ray measurements were performed under the approval of the Photon Factory Proposal
Committee (2005P014, 2006G097). This work was financially supported from the Grant-in-aid on the
Priority Area "Molecular Nano-dynamics" (Y.I. 432-17034013).
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SIGNIFICANCE OF PASSIVE SAMPLERS (POCIS) FOR WATER MONITORING OF
THE RIVER TALL
Jaswinder Kaur (The Queens University of Belfast, Northern Ireland, United Kingdom)
Anthony Gravell (Environment Agency, Llanelli, United Kingdom)
Samuel H Mitchell (Agri-Food and Bioscience Institute, Belfast, Northern Ireland, United Kingdom)

Conventional water sampling techniques (grab sampling, spot sampling etc.) have serious limitations thatcan be overcome by more advanced passive sampling devices. The major drawbacks of these screening
techniques include poor representation of actual concentration due to short sampling period (fewminutes), availability of small samples (1-2L) for residue extraction and loss of pesticide residues duringmulti-step procedure of sample collection, storage, extraction and analysis. Alternatively, polar organic
chemical integrative sampler (POCIS) can provide a clear representation of the presence of polar
pesticides owing to their ability to monitor a water body for extended periods (days to weeks)
continuously adsorbing residues. POCIS can also provide episodic data over a longer period of time withless resource than conventional techniques.
During this project, we deployed POCIS (admixture) for 2-4 weeks at three different sites of theRiver Tall (Co. Armagh, Northern Ireland) at 6 different intervals. The disks were extracted using 1:1:8
methanol:toluene:dichloromethane solvent and residues were quantified by LC-MS/MS. The timeweighted average concentration (TWAC) for these contaminants were quantified on the basis of flow rate
data modelled for the River Tall from an analogous reference gauged catchment (River Callan, Co.
Armagh) using Flow Estimation Model. A few assumptions were made during flow rate estimation: 1)
geology, soil profile, land use, altitude and slope were homogenous across the gauged (Callan) andungauged (Tall) catchments, 2) rainfall distribution and intensity over the sampling periods were
homogenous, and 3) relationship between the observed flows on the gauged and ungauged catchments are
representative of the full range of flows exhibited. The data generated since May 2006 to Dec 2006
showed presence of atrazine, simazine, ethylene thiourea, terbutryn, carbendzim, diuron, isoproturon andmonuron at parts per trillion levels in the River Tall.

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