A e na y E
3+
-BiVO
4
/TiO
2
complex he e os uc u e
wi h excellen pho oca aly ic pe o mance
S. Ob eg´
on and G. Col´
on*
Te na y e bium doped BiVO
4
/TiO
2
complexes a e syn hesized by means o a simple imp egna ion me hod
wi h good pho oac i i ies unde sun-like exci a ion o he deg ada ion o phenol. F om he s uc u al
and mo phological cha ac e iza ion i has been s a ed ha he p esence o E
3+
induces a sligh
s abiliza ion o he e agonal phase p obably due o i s inco po a ion in he BiVO
4
la ice. The e o e a
e na y he e os uc u ed ma e ial has been ob ained. The bes pho oca aly ic pe o mance was a ained
o he samples wi h 1 w % o E
3+
-doped BiVO
4
con en wi h espec o TiO
2
. The occu ence o a
complex s uc u al mix u e wi h he adequa e band posi ion leads o effec i e cha ge pai sepa a ion
which induces highe pho oca aly ic ac i i ies.
1. In oduc ion
Visible-ligh -induced semiconduc o pho oca alys s ha e
e ealed g ea po en ial applica ions in elimina ion o o ganic
pollu an s.
1
Howe e , mos o he p oposed semiconduc o
pho oca alys s a e clea ly es ic ed by hei poo efficiency.
Wi hin his amewo k, bismu h anada e (m-BiVO
4
) has been
p oposed as a no el al e na i e o TiO
2
-based pho oca alysis.
Thus, in he las ew yea s, many s udies desc ibed he in e -
es ing pe o mances o BiVO
4
o o ganic con aminan s deg a-
da ion as well as O
2
e olu ion eac ions unde isible-ligh
i adia ion.
2–6
I has been widely epo ed ha he pho oca aly ic pe o -
mance o BiVO
4
is s ongly dependen on i s mo phology and
mic os uc u e.
7–10
Diffe en syn he ic ou es leads o BiVO
4
in wo c ys alline phases: monoclinic (space g oup I2/b)and
e agonal (space g oup I4
1
/a) scheeli e.
11,12
Among he abo e
c ys al phases, he monoclinic BiVO
4
is he bes isible-ligh -
d i en pho oca alys . The esul s epo ed by Yu e al. demon-
s a ed ha he c ys alline s uc u e is he i al ac o con olling
MB deg ada ion and O
2
e olu ion eac ions.
13
In he same
di ec ion, Tokunaga e al. epo ed ha monoclinic s uc u e
shows much highe ac i i y han a e agonal one o O
2
e olu ion eac ion.
14
F om DFT calcula ions i is p oposed ha
he effec i e hyb idiza ion o Bi6s s a e and he O2p s a e a he
op o he alence band would be he esponsible o he lowe
band gap alue exhibi ed by m-BiVO
4
(ca. 2.4 eV) (Scheme 1).
15,16
On he basis o he wide epo ed esul s, he pho oca aly ic
ac i i y o e agonal BiVO
4
appea s almos negligible
17–19
while
he pho oca aly ic ac i i y o m-BiVO
4
is s ill sca ce due o he
poo cha ge- anspo cha ac e is ics and he weak su ace
adso p ion p ope ies o his ma e ial.
20,21
The e o e, i is
necessa y o de elop effec i e s a egies o imp o e he cha ge
sepa a ion efficiency and enhance isible-ligh pho oca aly ic
ac i i y o BiVO
4
pho oca alys s.
Fo he pho oac i i y imp o emen sake, diffe en
app oaches ha e been p oposed which include he e ojunc ion
s uc u e o ma ion,
20,22,23
co-ca alys s loading,
24,25
and impu i y
doping.
26,27
Among hese app oaches, he co-exis ence o
monoclinic- e agonal he e os uc u e appea s as a new way o
be conside ed. Recen ly, i has been s a ed ha he exis ence o
a mixed-phase BiVO
4
clea ly show highe pho oca aly ic
ac i i y.
28
The imp o ed pho oca aly ic pe o mance o m–
he e os uc u ed BiVO
4
has been associa ed o p omo ion
pho oinduced elec on–hole pai s sepa a ion.
29
Wi hin his
amewo k, Ob eg´
on e al. epo ed he unexpec ed enhanced
pho oca aly ic ac i i y o e agonal s abilized Ln-doped
BiVO
4
.
30,31
Mo eo e , by changing he p ecu so addi ion
sequence in he syn hesis ou e, we ha e ob ained a monoclinic-
Scheme 1 Schema ic band s uc u es o he -BiVO
4
and m-BiVO
4
.
Ins i u o de Ciencia de Ma e iales de Se illa, Cen o Mix o CSIC-Uni e sidad de
Se illa, C/Am´
e ico Vespucio, 49, 41092 Se illa, Spain. E-mail: [email protected];
Tel: +34 954489536
Ci e his: RSC Ad .,2014,4, 6920
Recei ed 12 h No embe 2013
Accep ed 23 d Decembe 2013
DOI: 10.1039/c3 a46603e
www. sc.o g/ad ances
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e agonal he e os uc u ed E
3+
-BiVO
4
exhibi ing no ably a
high pho oac i i y unde sun-like i adia ion.
32
Fo his sys em,
we ha e s a ed ha he p esence o e bium p o okes a signi-
can ly highe pho oac i i y ha could be ela ed o a double
complex mechanism. Fi s ly, he o ma ion o he igh in e -
ace m– he e os uc u e could be he esponsible o a mo e
effec i e cha ge sepa a ion. And secondly, bu no less impo -
an , he con ibu ion o ex a-pho ons gene a ed by a coope -
a i e luminescence p ocess in he o e all mechanism due an
ene gy ans e p ocess om e bium ions o -BiVO
4
and m-
BiVO
4
could enhance he pho on efficiency o he pho oca aly ic
p ocess.
Thus, as he o ma ion o he e ojunc ion can signican ly
educe he ecombina ion and speed up he sepa a ion a e o
pho ogene a ed cha ge ca ie s, coupling BiVO
4
wi h o he
semiconduc o s a e oen used as an effec i e modica ion
me hod. Wi hin his ame, Long e al. p oposed he Co
3
O
4
/
BiVO
4
composi e pho oca alys ash a p–n he e ojunc ion semi-
conduc o . These au ho s showed ha he composi e pho o-
ca alys p esen ed much highe pho oac i i y han pu e BiVO
4
in he deg ada ion o phenol unde isible ligh i adia ion.
33
Mo eo e , o he au ho s epo ed a V
2
O
5
/BiVO
4
composi e
exhibi ing he enhanced pho oca aly ic pe o mance.
34,35
Finally, he pho oca aly ic p ope ies o coupled TiO
2
/BiVO
4
ha e been also ecen ly in es iga ed demons a ing he in e es
o BiVO
4
based he e ojunc ions.
36,37
Howe e , in hese la e
cases m-BiVO
4
has been conside ed. Taking in o accoun m-
BiVO
4
conduc ion and alence bands posi ion wi h espec o
TiO
2
, i is clea ha an un a ou able si ua ion is aking place. In
he p esen pape we p esen a e na y complex he e os uc u e
o med by TiO
2
ana ase and monoclinic- e agonal BiVO
4
by
e bium doping. The pho oca aly ic ac i i ies we e e alua ed by
he pho odeg ada ion o phenol unde simula ed sun-ligh
i adia ion and he possible elec onic mechanism esponsible
o he enhanced pho oca aly ic ac i i ies o E
3+
-doped BiVO
4
/
TiO
2
composi e pho oca alys s was also discussed.
2. Expe imen al
2.1 Samples p epa a ion
TiO
2
sample was ob ained by means o a hyd o he mal me hod
elsewhe e desc ibed.
38
In b ie , a TiO
2
colloidal solu ion was
ob ained by adding ce ain amoun o Ti
4+
–isop opanol solu-
ion o 400 mL o dis illed wa e a pH ¼2 achie ed by means o
ace ic acid. Ae TTiP addi ion a whi e p ecipi a e is ob ained
ha upon s i ing a oom empe a u e o one week e ol e o a
milky homogeneous solu ion. A ce ain amoun o ie hyl-
amine (TEA) was hen added d op wise o he Ti-solu ion aliquo
ill he pH alue was 9. Ae wa ds, he ob ained whi e p ecipi-
a e suspension was hen placed in a Teon ecipien inside o
s ainless s eel au ocla e eac o . The hyd o he mal ea men
was pe o med a 120 C, 20 hou s. The as ob ained p ecipi a e
was hen l e ed, epea edly washed and d ied o e nigh a
120 C. Then TiO
2
powde was submi ed o a u he calcina-
ion ea men a 300 C o 2 hou s.
On he o he hand, o he p epa a ion o E
3+
doped BiVO
4
,
we ha e ollowed he me hod p e iously epo ed.
32
B iey,
5 mmol o Bi(NO
3
)
3
$5H
2
O was dissol ed in 10 mL o glacial
ace ic acid a oom empe a u e. A second aqueous solu ion was
p epa ed by dissol ing he co esponding s oichiome ic
amoun o NH
4
VO
3
and he co esponding amoun o E (NO
3
)
3
(0.75 a .%) in 60 mL o ho dis illed wa e . A milky colloidal
suspension is ob ained which could indica e he o ma ion o
small E VO
4
pa icles. Ae wa ds, he ammonium me a-
anada e solu ion was added o he bismu h ni a e aqueous
solu ion and he p ocess was accompanied wi h a igo ous
s i ing. The pH o he ob ained suspension was adjus ed o 9.0
by adding concen a ed NH
4
OH (13 mol L
1
). The slu y was
encased in a Teon essel and hea ed unde mic owa e i adi-
a ion using a mic owa e eac o . The empe a u e was xed a
140 C wi h a maximum a iable powe o 195 W du ing 30 min.
The ob ained p ecipi a e was hen cooled un il oom empe a-
u e, l e ed and epea edly washed and d ied o e nigh a
120 C. Ae wa ds, hus ob ained samples we e submi ed o a
u he calcina ion ea men a 300 C o 2 h.
Hyb id composi es we e achie ed by simple imp egna ion
me hod p e iously desc ibed.
39
In a ypical p ocedu e, he
app op ia e amoun s o TiO
2
and E -BiVO
4
we e added in o
me hanol and sonica ed sepa a ely o 30 min. Then, hese wo
solu ions we e mixed and s i ed a oom empe a u e o 24 h.
Ae wa ds, he composi e pho oca alys s we e ob ained by
e apo a ing he me hanol a 80 C. E -BiVO
4
con en s anged
om 0.5 w % o 5 w % wi h espec o TiO
2
.
2.2 Ma e ials cha ac e iza ion
BET su ace a ea and po osi y measu emen s we e ca ied ou
by N
2
adso p ion a 77 K using a Mic ome i ics 2010
ins umen .
X- ay diff ac ion (XRD) pa e ns we e ob ained using a
Siemens D-501 diff ac ome e wi h Ni l e and g aphi e
monoch oma o . The X- ay sou ce was Cu Ka adia ion
(0.15406 nm). The diff ac ion pa e ns we e eco ded om 2q
10 o 80wi h s ep o 0.05and 120 s pe s ep. C ys alli e sizes
we e ob ained om Rie eld enemen .
The UV diffuse eec ance spec a we e measu ed using an
UV- is spec opho ome e equipped wi h an in eg a ing sphe e
(JASCO V-570). The e e ence sample used was a BaSO
4
coa ed
s anda d pa e n.
Mic o-Raman measu emen s we e pe o med using a Lab-
RAM Jobin Y on spec ome e equipped wi h a mic oscope.
Lase adia ion (l¼532 nm) was used as exci a ion sou ce a
5 mW. All measu emen s we e eco ded unde he same
condi ions (2 s o in eg a ion ime and 30 accumula ions) using
a 100magnica ion objec i e and a 125 mm pinhole.
Field emission scanning elec on (FE-SEM) and T ans-
mission elec on mic oscopy (TEM) was pe o med by using a
Hi achi S 4800 and Philips CM 200 mic oscopes, espec i ely.
The samples we e dispe sed in e hanol using an ul asonica o
and d opped on a ca bon g id.
2.3 Pho oca aly ic es s
The pho oca aly ic ac i i y o he samples was es ed by means
he deg ada ion o phenol unde simula ed sola condi ions. In
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a ypical p ocedu e, 0.05 g o pho oca alys was placed in a
ba ch eac o con aining 50 mL o phenol whose ini ial
concen a ion was 30 mg L
1
. The suspension was main ained
unde da k condi ions o 15 min in o de o achie e he
adso p ion–deso p ion equilib ium o he dye on he pho o-
ca alys su ace. Ae wa ds, he suspension was i adia ed wi h
simula ed sola ligh by means a sola simula o PEC-L01,
Peccell. Samples o 1 mL we e aken a gi en in e al imes and
he pho oca alys was sepa a ed using a nylon l e . The
concen a ions we e moni o ed by checking he abso p ion
spec um o each sample h ough i s abso p ion band
maximum (270 nm) using an UV- is spec opho ome e
(MECASYS Op izen 2120UV).
3. Resul s and discussion
We ha e p epa ed a simple he e os uc u e based on TiO
2
and
E -BiVO
4
sys ems. The s uc u al cha ac e iza ion o bo h was
al eady epo ed by us.
32,38
The sol–gel hyd o he mal p epa a-
ion o TiO
2
om colloidal suspension leads o ana ase phase
sys em wi h calcula ed c ys alli e size o ca. 15 nm (Table 1). On
he o he hand, i has been s a ed ha he inco po a ion o E
3+
in he BiVO
4
s uc u e induces he s abiliza ion o he e ag-
onal s uc u e (Fig. 1).
Such s uc u al s abiliza ion has been explaining by
conside ing he o ma ion o small E VO
4
seeds du ing he
syn he ic p ocedu e, p e ious o he BiVO
4
o ma ion.
32
E VO
4
is
no mally ob ained in he e agonal zi con s uc u e.
40
These
small seeds would ac as s uc u e-di ec ing agen condi ioning
he o ma ion o he e agonal BiVO
4
. Thus, a mix u e o
monoclinic and e agonal phase is ob ained, being he e ag-
onal he p edominan one (70% e agonal s. 30% monoclinic).
The XRD pa e ns o composi e sys ems deno e he p esence o
o me s uc u es, ana ase TiO
2
and he co esponding g owing
ac ion o e agonal-monoclinic mix u e o E -BiVO
4
(Fig. 1).
The BET su ace a ea o TiO
2
is ound o be signican ly
high, ca. 102 m
2
g
1
. On he con a y and as widely epo ed in
he li e a u e, o BiVO
4
he su ace a ea alues a e conside ably
low, always below 1–2m
2
g
1
(Table 1).
41,42
The occu ence o
he e agonal phase clea ly induces a ce ain inc ease in his
ea u e.
30,32
The e o e, he e os uc u ed composi es show a
sligh ly lowe su ace a ea wi h espec o p is ine TiO
2
.
F omRamanspec oscopyi ispossible oob ainin e -
es ing in o ma ion om he s uc u al poin o iew (Fig. 2).
Fo ba e TiO
2
we ha e ound he ypical Raman bands asso-
cia ed o ana ase s uc u e: 150 (e.g. (1)), 196 (e.g. (2)), 396
(A
1g
/B
1g
), 516 (A
1g
), and 640 cm
1
(e.g. (3)). Single BiVO
4
sys em shows Raman bands a ound 158, 208, 324, 362, 710,
and 826 cm
1
we e obse ed o all samples, which a e ypical
ib a ional bands o monoclinic BiVO
4
(inse in Fig. 2).
43,44
Raman bands a 324 and 366 cm
1
a e assigned o he
asymme ic and symme ic de o ma ion modes o he VO
43
e ahed on, espec i ely.
Addi ionally, he Raman bands a 822 cm
1
co esponds o
he symme ic V–O s e ching mode wi h A
g
symme y. When
e agonal phase is p esen , i can be obse ed a no ably shio
his la e band owa d highe equencies (ca. 850 cm
1
). Thus
in ou case, in which BiVO
4
appea s composed by a mix u e o
e agonal and monoclinic phase, wi h he o me as he main
c ys alline phase, only he 850 cm
1
is clea ly obse able.
Table 1 Su ace, s uc u al and pho oca aly ic cha ac e iza ion o
TiO
2
/E -BiVO
4
he e os uc u ed ca alys s
Samples C ys alli e size
a
(nm) BET (m
2
g
1
) Band gap (eV)
TiO
2
14 (a) 102 3.14
E -BiVO
4
0.5% 15 (a) 99 3.14
E -BiVO
4
1.0% 15 (a) 91 3.13
E -BiVO
4
2.0% 15 (a) 90 3.13
E -BiVO
4
3.0% 15 (a) 92 3.07
E -BiVO
4
4.0% 15 (a) 89 3.05
E -BiVO
4
5.0% 15 (a) 90 2.80
E -BiVO
4
52 ( s) 3 2.80 + 2.35
BiVO
4
48 (ms) 1 2.35
a
(a: ana ase, s: e agonal scheeli e; ms: monoclinic scheeli e).
Fig. 1 XRD pa e ns o TiO
2
/E -BiVO
4
he e os uc u es wi h diffe en
E -BiVO
4
con en .
Fig. 2 Raman spec a o TiO
2
/E -BiVO
4
he e os uc u es wi h
diffe en E -BiVO
4
con en .
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In addi ion he abo e s uc u al cha ac e iza ion, i can be
s a ed a se o bands in he ange 400–700 nm ha could be
a ibu ed o he isible uo escence emission in E -doped
sys ems (inse in Fig. 2). Such isible luminescence upon g een
exci a ion has been widely epo ed o E based phospho s
ma e ials. As we ha e p e iously shown, such emission is
ela ed o he p esence o e agonal phase.
30
The E -doping
on o BiVO
4
s uc u e is achie ed by an effec i e E subs i u ion
in Bi
3+
si es o he e agonal s uc u e. Wi hin his si ua ion, a
s ong luminescence emission is obse ed. The e o e, he
addi ional bands obse ed in he he e os uc u ed composi e
spec a co espond o such isible luminescence p ocess.
The mo phology o BiVO
4
has ex ensi ely epo ed o be
dependen on he p epa a ion ou e.
45
In ou case, ba e BiVO
4
shows a squa e od-like mo phology.
30
The mo phology o E -
doped sys ems clea ly deno es he e agonal-monoclinic
s uc u al mix u e (Fig. 3a). Thus, bo h mo phologies (squa e
ods and needle-like pa icles) clea ly cohabi in his sys em.
He e os uc u ed composi es a e o med by E -BiVO
4
effec i ely
co e ed by TiO
2
(Fig. 3b and c). Addi ionally, i can be no iced
la ge TiO
2
agg ega es o med by small pa icles o abou 10–15
nm size (inse Fig. 3c and EDS spec a).
Rega ding o UV- is abso p ion p ope ies, he diffuse
eec ance UV- is spec a o diffe en composi es a e shown in
Fig. 4. As i can be no iced h ee abso p ion edges can be ound,
co esponding o TiO
2
ana ase and monoclinic and e agonal
mix u e o E -BiVO
4
(inse Fig. 4). The calcula ed band gap
alues (Table 1) a e in acco dance o he he e os uc u ed
assembly o TiO
2
and E -BiVO
4
sys ems. I is wo hy o no e ha
due o he low doping le el, i is no possible o de ec he
exci a ion bands o E
3+
species. In spi e o his, he s ong
uo escence bands obse ed in Raman spec a would indica e
he impo an luminescence p ocess which is aking place.
The pho oca aly ic pe o mance o he E -doped sys ems was
s udied o phenol deg ada ion unde sola -like i adia ion
(Fig. 5). The  s poin ha is wo hy o men ion is ha he e -
os uc u ed composi e sys ems lead o highe pho oac i i ies
han ba e TiO
2
. Thus, as E -BiVO
4
con en inc eases i can be
no ice a p og essi e aise in he eac ion a es ill E -BiVO
4
con en eaches 1 w % alue (Fig. 5b). F om his alue, he
Fig. 3 SEM and TEM s udy o he e os uc u ed sys ems: (a) SEM image o E -BiVO
4
; (b) SEM image o TiO
2
/E -BiVO
4
(1% E -BiVO
4
) he e o-
s uc u es; (c) TEM image o TiO
2
/E -BiVO
4
(1% E -BiVO
4
) he e os uc u e including EDS analysis o diffe en posi ions in he he e os uc u e
in e ace (inse : TEM image o p is ine TiO
2
).
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eac ion a e s a s o dec ease eaching a simila alue as
p is ine TiO
2
o 5 w %.
The pho oca aly ic pe o mance o he p oposed complex
he e os uc u e clea ly o e comes he al eady published BiVO
4
–
TiO
2
sys ems.
36,37
Thus, Hu e al. p oposed a band congu a ion
in which upon isible exci a ion BiVO
4
would ac as sensi ize .
Based on he posi ion o BiVO
4
and TiO
2
conduc ion bands he
pho ogene a ed elec on ans e om BiVO
4
o TiO
2
is ene -
ge ically o bidden. So, a diffe en elec onic mechanism
should be conside ed in his case. Mo eo e , Zhang e al.
showed an in e es ing syne gis ic effec aking in o accoun
he double UV and isible pho oac i i y o he BiVO
4
/TiO
2
he e os uc u e.
37
Howe e , hese au ho s we e able o dis-
colo a e Rhodamine B ae 6 hou s o i adia ion. Thus, he
esul s p esen ed he e clea ly su pass he abo e men ioned
published ones.
In o de o en isage a possible mechanism, we ha e also
pe o med he pho oac i i y s udies o he e os uc u e
composi e o med by TiO
2
and undoped m-BiVO
4
(Fig. 6).
Fi s ly, i is wo hy o no e ha m-BiVO
4
showed a lowe pho-
oac i i y han E -BiVO
4
o which a mix u e o e agonal and
monoclinic phase is p esen . This ac was al eady s a ed by us
and explained by conside ing a double coope a i e pho onic
and elec onic mechanism in ol ed.
30,32
Rega ding o he e os uc u ed composi e sys ems, i is clea
ha he TiO
2
/m-BiVO
4
assembly, hough inc eases he pho o-
ac i i y wi h espec o TiO
2
, shows a eac ion a e s ill ai ly
lowe han TiO
2
/E -BiVO
4
he e os uc u e. Taking in o accoun
he low E doping le el in he TiO
2
/E -BiVO
4
composi e (0.75
a .% E -BiVO
4
is p esen in 1 w % o he composi e), o hese
he e os uc u e i would be expec ed ha he up-con e sion
luminescen p ocess migh be almos negligible. So, he
enhanced pho oca aly ic ac i i y mus be associa ed o he
p esence o an effec i e in ima e he e ojunc ion. Thus, an
Fig. 4 Diffuse eflec ance spec a o TiO
2
/E -BiVO
4
he e os uc u es
wi h diffe en E -BiVO
4
con en s.
Fig. 5 (a) E olu ion o phenol concen a ion (C
0
¼50 ppm) wi h pho odeg ada ion ime; (b) calcula ed eac ion a es o TiO
2
/E -BiVO
4
he -
e os uc u es wi h diffe en E -BiVO
4
con en .
Fig. 6 Compa ison o phenol pho odeg ada ion eac ion a es o
diffe en ba es and he e os uc u ed ma e ials.
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effec i e spa ial cha ge sepa a ion would be he esponsible o
he pho oca aly ic ac i i y enhancemen (Scheme 2).
I we conside he band posi ions o diffe en phases, he
diffe ence in he obse ed band gap alues o monoclinic and
e agonal s uc u es lays on he pa icipa ion o Bi6s o bi als in
he monoclinic alence band hyb idiza ion.
16
The pa icipa ion
o Bi6s o bi al in he band hyb idiza ion would s abilize he
alence band op h ough coupling Bi6s–O2p an ibonding s a e
wi h Bi6p s a e.
2,46
Mo eo e , he s e ically ac i e Bi6s
2
lone pai
would play a key ole in aising up he O2p s a es and educing
he band gap.
15
F om he calcula ed ene gies o BiVO
4
alence
and conduc ion bands,
47
he ollowing scheme can be en is-
aged: m-BiVO
4
alence band op is posi ioned a sligh ly lowe
ene gy wi h espec o he TiO
2
one, while he co esponding o
-BiVO
4
is loca ed a sligh ly highe ene gy posi ion (Scheme 2).
On his basis, i could be expec ed ha upon UV exci a ion, -
BiVO
4
would ac as elec on sink while holes will be de i ed o
TiO
2
. In he case o TiO
2
/m-BiVO
4
he cha ge pai s ow in he
m-BiVO
4
di ec ion. Fo his eason, he eac ion a e o TiO
2
/m-
BiVO
4
appea s compa able han ha ob ained o TiO
2
. Thus, i
can be assumed ha he occu ence o a s uc u al mix u e in
he BiVO
4
wi h p edominan e agonal phase would also help
o enhanced cha ge sepa a ion. In addi ion o his p oposed
syne gis ic mechanism in a lowe ex en , he occu ence o a
e agonal-monoclinic he e os uc u ed BiVO
4
has been also
demons a ed o ha e be e pho oca aly ic pe o mances.
31
F om he ela i e band posi ions o e agonal and monoclinic
s uc u es an effec i e cha ge sepa a ion can be also consid-
e ed. The e o e, his addi ional in e ac i e p ocess, hough in
lowe le el due o he small BiVO
4
con en , migh be also
conside ed in he o e all pho oca aly ic mechanism.
4. Conclusions
We ha e ob ained a complex he e os uc u ed sys em by a
simple imp egna ion me hod, showing imp o ed pho oac i i y
unde sola -like i adia ion. F om his me hod we ha e
ob ained an effec i e co e age o la ge E -BiVO
4
pa icles wi h
15 nm size TiO
2
. F om he s uc u al poin o iew we ha e
s a ed ha he exis ence o a phase mix u e in BiVO
4
leads o
be e pho oca aly ic pe o mance o he he e ojunc ion. F om
he esul s ob ained, i would be p oposed ha he concu ence
o TiO
2
and E
3+
-BiVO
4
complex he e os uc u e would induce
an imp o ed pe o mance due o an op imized cha ge sepa a-
ion p ocess.
Acknowledgemen s
The nancial suppo by p ojec s P09-FQM-4570 and ENE2011-
24412 is ully acknowledged. S. Ob eg´
on hanks CSIC o he
concession o a JAE-P e g an .
Re e ences
1 A. Kubacka, M. Fe n´
andez-Ga c´
ıa and G. Col´
on, Chem. Re .,
2012, 112, 1555–1614.
2 A. Kudo, K. Omo i and H. Ka o, J. Am. Chem. Soc., 1999, 121,
11459–11467.
3 J. Yu and A. Kudo, Ad . Func . Ma e ., 2006, 16, 2163–2169.
4 Y. Sasaki, A. Iwase, H. Ka o and A. Kudo, J. Ca al., 2008, 259,
133–137.
5 G. Xi and J. Ye, Chem. Commun., 2001, 1893–1895.
6 S. Na al´
on, A. Dhkshinamoo hy, M. Al a o and H. Ga c´
ıa,
ChemSusChem, 2013, 6, 562–577.
7 L. Zhou, W. Z. Wang, L. S. Zhang, H. L. Xu and W. Zhu,
J. Phys. Chem. C, 2007, 111, 13659–13664.
8 Y. Zhao, Y. Xie, X. Zhu, S. Yan and S. X. Wang, Chem. –Eu . J.,
2008, 14, 1601–1606.
9 H. Jiang, H. Dai, X. Meng, L. Zhang, J. Deng, Y. Liu and
C. T. Au, J. En i on. Sci., 2012, 24, 449–457.
10 H. Jiang, X. Meng, H. Dai, J. Deng, Y. Liu, L. Zhang, Z. Zhao
and R. Zhang, J. Haza d. Ma e ., 2012, 217–218,92–99.
11 A. R. Lim, S. H. Choh and M. S. Jang, J. Phys.: Condens.
Ma e , 1995, 7, 7309–7324.
12 G. Li, Y. Bai and W. F. Zhang, Ma e . Chem. Phys., 2012, 136,
930–934.
13 J. Yu, Y. Zhang and A. Kudo, J. Solid S a e Chem., 2009, 182,
223–228.
14 S. Tokunaga, H. Ka o and A. Kudo, Chem. Ma e ., 2001, 13,
4624–4628.
15 Z. Zhao, Z. Li and Z. Zou, Phys. Chem. Chem. Phys., 2011, 13,
4746–4753.
16 Y. Pa k, K. J. McDonald and K. S. Choi, Chem. Soc. Re ., 2013,
42, 2321–2337.
17 X. Zhang, Z. Ai, F. Jia, L. Zhang, X. Fan and Z. Zou, Ma e .
Chem. Phys., 2007, 103, 162–167.
18 Y. Liu, B. Huang, Y. Dai, X. Zhang, X. Qin, M. Jiang and
M.-H. Whangbo, Ca al. Commun., 2009, 11, 210–213.
19 H. M. Zhang, J. B. Liu, H. Wang, W. X. Zhang and H. Yan,
J. Nanopa . Res., 2008, 10, 767–774.
20 S. J. Hong, S. Lee, J. S. Jang and J. S. Lee, Ene gy En i on. Sci.,
2011, 4, 1781–1787.
21 W. Yao, H. Iwai and J. Ye, Dal on T ans., 2008, 1426–1430.
22 M. Long, W. Cai and H. Kisch, J. Phys. Chem. C, 2008, 112,
548–554.
23 X. Zhang, Y. Gong, X. Dong, X. Zhang, C. Ma and F. Shi,
Ma e . Chem. Phys., 2012, 136, 472–476.
Scheme 2 P oposed elec onic mechanism upon UV- is exci a ion
o diffe en TiO
2
–BiVO
4
he e os uc u es.
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View A icle Online
24 N. Mu akami, N. Takebe, T. Tsubo a and T. Ohno, J. Haza d.
Ma e ., 2012, 211–212,83–87.
25 D. Wang, R. Li, J. Zhu, J. Shi, J. Han, X. Zong and C. Li,
J. Phys. Chem. C, 2012, 116, 5082–5089.
26 W. J. Luo, Z. S. Li, T. Yu and Z. G. Zou, J. Phys. Chem. C, 2012,
116, 5076–5081.
27 K. P. S. Pa ma , H. J. Kang, A. Bis , P. Dua, J. S. Jang and
J. S. Lee, ChemSusChem, 2012, 5, 1926–1934.
28 G. Tan, L. Zhang, H. Ren, S. Wei, J. Huang and A. Xia, ACS
Appl. Ma e . In e aces, 2013, 5, 5186–5193.
29 H. Fan, T. Jiang, H. Li, D. Wang, L. Wang, J. Zhai, D. He,
P. Wang and T. Xie, J. Phys. Chem. C, 2012, 116, 2425–2430.
30 S. Ob eg´
on, S. W. Lee and G. Col´
on, Dal on T ans., 2014, 43,
311–316.
31 S. Usai, S. Ob eg´
on, A. I. Bece o and G. Col´
on, J. Phys. Chem.
C, 2013, 117, 24479–24484.
32 S. Ob eg´
on and G. Col´
on, submi ed.
33 M. Long, W. Cai, J. Cai, B. Zhou, X. Chai and Y. J. Wu, J. Phys.
Chem. B, 2006, 110, 20211–20216.
34 H. Jiang, M. Nagai and K. Kobayashi, J. Alloys Compd., 2009,
479, 821–827.
35J.Su,X.X.Zou,G.D.Li,X.Wei,C.Yan,Y.N.Wang,J.Zhao,
L.J.ZhouandJ.S.Chen,J. Phys. Chem. C, 2011, 115, 8064–8071.
36 Y. Hu, D. Li, Y. Zheng, W. Chen, Y. He, Y. Shao, X. Fu and
G. Xiao, Appl. Ca al., B, 2011, 104,30–36.
37 L. Zhang, G. Tann, S. Wei, H. Ren, A. Xia and Y. Luo, Ce am.
In ., 2013, 39, 8597–8604.
38 M. C. Hidalgo, M. Aguila , M. Maicu, J. A. Na ´
ıo and
G. Col´
on, Ca al. Today, 2007, 129, 50.
39 S. Ob eg´
on and G. Col´
on, J. Pho ochem. Pho obiol., A, 2013,
253, 16.
40 C. T. Au and W. D. Zhang, J. Chem. Soc., Fa aday T ans., 1997,
93, 1195–1204.
41 H. Jiang, H. Dai, X. Meng, K. Ji, L. Zhang and J. Deng, Appl.
Ca al., B, 2011, 105, 326–334.
42 S. Ob eg´
on, A. Caballe o and G. Col´
on, Appl. Ca al., B, 2012,
117–118,59–66.
43 J. Liu, H. Wang, S. Wang and H. Yan, Ma e . Sci. Eng., B,
2003, 104,36–39.
44 J. Yu and A. Kudo, Chem. Le ., 2005, 34, 850–851.
45 L. Ren, L. Ma, L. Jin, J. B. Wang, M. Qiu and Y. Yu,
Nano echnology, 2009, 20, 405602.
46 K. E. Kweon and G. S. Hwang, Phys. Re . B: Condens. Ma e ,
2012, 86, 165209.
47 J. Yang, D. Wang, X. Zhou and C. Li, Chem. –Eu . J., 2013, 19,
1320–1326.
6926 |RSC Ad .,2014,4, 6920–6926 This jou nal is © The Royal Socie y o Chemis y 2014
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