Bismuth(V)-Containing Semiconductor Compounds and Applications in Heterogeneous Photocatalysis

Abstract

Heterogeneous photocatalysis technology has become a promising approach to solve energy and environmental problems since 1972. The exploration and search for active semiconductor photocatalysts specially for solar energy appli- cations is one of the most challenging tasks. The bismuth(V)-containing photocata- lysts have gained great significance due to their unique electronic/energy band structures. The preparation techniques, physical–chemical properties, photocata- lytic activities, and photostabilities of the bismuth(V)-containing photocatalysts (as represented by ilmenite-type NaBiO3) are reviewed in this chapter. Some of these photocatalysts have excellent catalytic performance in water purification, disinfec- tion of water as well as splitting of water for H2 production. But nevertheless, their instabilities under light exposure during photocatalysis process have been gradually realized and further studied. The trend of bismuth(V)-containing photocatalyst research is also prospected in the end of this chapter.

Full text

343
H. Li and Z.M. Wang (eds.), Bismuth-Containing Compounds, Springer Series
in Materials Science 186, DOI 10.1007/978-1-4614-8121-8_15,
© Springer Science+Business Media New York 2013
Abstract Heterogeneous photocatalysis technology has become a promising
approach to solve energy and environmental problems since 1972. The exploration
and search for active semiconductor photocatalysts specially for solar energy appli-
cations is one of the most challenging tasks. The bismuth(V)-containing photocata-
lysts have gained great significance due to their unique electronic/energy band
structures. The preparation techniques, physical–chemical properties, photocata-
lytic activities, and photostabilities of the bismuth(V)-containing photocatalysts (as
represented by ilmenite-type NaBiO3) are reviewed in this chapter. Some of these
photocatalysts have excellent catalytic performance in water purification, disinfec-
tion of water as well as splitting of water for H2 production. But nevertheless, their
instabilities under light exposure during photocatalysis process have been gradually
realized and further studied. The trend of bismuth(V)-containing photocatalyst
research is also prospected in the end of this chapter.
Chapter 15
Bismuth(V)-Containing Semiconductor
Compounds and Applications
in Heterogeneous Photocatalysis
Xiaofeng Chang, Mohammed Ashraf Gondal, Zain Hassan Abdallah Yamani,
and Guangbin Ji
X. Chang (**-L
Department of Applied Chemistry, College of Materials Science and Technology,
Nanjing University of Aeronautics and Astronautics, Nanjing 211100, China
e-mail: changxf@nuaa.edu.cn; gbji@nuaa.edu.cn
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e-mail: magondal@kfupm.edu.sa
Z.H.A. Yamani
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e-mail: zhyamani@kfupm.edu.sa

344
15.1 Introduction
15.1.1 Fundamental of Heterogeneous Photocatalysis
Heterogeneous photocatalysis process has become a promising technology to solve
energy and environmental problems since 1972 [1]. The dream for “low-carbon and
green life,” as well as the pioneer achievements by scholars [2–4] in this field, is
inspiring and instigating great enthusiasm to develop highly efficient photocatalysts
to improve the quantum efficiency under visible light (380–780 nm) which repre-
sents around 40 % of the total light spectrum of the solar radiations [5].
The principle of semiconductor photocatalysts is illustrated in Fig. 15.1 [, 7].
An electron–hole pair is, respectively, generated in the conduction and valence
bands (CB, VB) after absorption of the photon with photo energy equal or higher
than the band gap value (Eg) of semiconductor. The photogenerated electron and
hole could immigrate to the reactive surface sites followed by reduction process
(reduce an acceptor) or oxidation process (oxidize a donor), respectively (process c
and d in Fig. 15.1).
In a typical photocatalyst, the surface-bound OHads radical is produced through
the oxidation of OH− (a.q.) which can effectively oxidize the adsorbed pollutants.
The CB of the semiconductor has a certain potential and hence the electrons possess
certain reduction capacity which depends on the band edge potential. The photogen-
erated electron are picked up by the oxygen thus producing peroxy radical, hydroxyl
radical, and a series of species possessing strong oxidation capacity, which can oxi-
dize the organics present in water.
Fig. 15.1 Schematic illustration of the main processes on an irradiated photocatalyst particle
(reprinted from ref. [7])
X. Chang et al.

345
Such photocatalytic process can be adopted in splitting of water for H2 production
and CO2 reduction as well [8, 9], but requires photogenerated electrons with higher
energy than the electrochemical potential of H2 evolution and CO2 conversion.
However, the practical quantum efficiency for CO2 reduction during a photocata-
lytic process is very low (usually less than 1 %), because of the possible process
such as the recombinations of the carries by the attractive force between them (pro-
cess a in Fig. 15.1) and by the defects in the semiconductor, as well as the trapping
in reactive surface sites which might take 10–100 ns for holes and some hundreds
of picoseconds for electrons [] (process b in Fig. 15.1). But recently, it has been
realized that the low solar photocatalytic efficiency is not associated with light
absorption but more likely with the charge transfer kinetics [9]. Therefore, the
exploration and search for active semiconductor photocatalysts remains to be one of
the most challenging tasks for solar energy utilization.
15.1.2 Motivations for Developing Bismuth(V)-Containing
Semiconductor
In an oxide semiconductor, it is well known that the metal orbits which contribute
to the CB, determines the band gap of the semiconductor, as the band edge potential
of the VB (which is composed of O2p states) has the fixed energy at around 3 eV. For
example, the CV and VB of anatase TiO2, which is thought to be one of the most
typical oxide semiconductor, is composed of Ti3d (at approximately −0.2 eV) and
O2p (at appr oximately 3 eV), therefore the band gap energy of anatase TiO2 is 3.2 eV [10].
$FFRUGLQJWRWKH3ODQFN·VHTXDWLRQDQDWDVH7L22 could work under UV light with
wavelength shorter than 387 nm. It should be noted that only around 4 % of the UV
exposure can reach to the surface of the earth because of the blocking effect by the
ozone layer in the upper atmosphere. However, the visible light which spans 380–
780 nm represents around 40 % of the total light spectrum of the solar radiations
DQGWKHUHPDLQGHU LVLQIUDUHGZKLFKDFFRXQWVIRUa 7KXVH[SORUDWLRQDQG
development of visible-light response photocatalysts attract a lot of attention of
research community worldwide (IR-response semiconductor is not considered to be
working efficiently because of small band gap which may not facilitate the separa-
tion of photogenerated carries).
On the basis of the abovementioned facts, the substitution of metal atom in the
VHPLFRQGXFWRULVHVVHQWLDOWRFRQWUROWKHEDQGJDSHQHUJ\([SORULQJPHWDOFDWLRQV
filled with s2 might be a suitable strategy for the development of visible-light
response photocatalysts because of the following advantages (as shown in Fig. 15.2):
(1) the broad hybrid orbital composed of metal cations filled with s2 and O2p can
have “narrow” the band gap of the corresponding semiconductor; (2) as the ns orbit-
als of such metal cations could form the top of VB by overlapping with O2p orbital
thus increase the VB width so that improve the photogenerated hole mobility and
lifetime [11].
15 Bismuth(V)-Containing Semiconductor Compounds and Applications…


3UHYLRXVO\ WKH %L,,, FRQWDLQHG R[LGH VHPLFRQGXFWRU KDV EHHQ ZLGHO\
investigated as the broad hybrid orbital composed of Bis and O2p. The preparation
and photocatalytic activity of such catalysts, like BiVO4 [12], Bi2WO [13, 14], and
CaBi2O4 [15] photocatalysts, have been widely studied. The vast majority of elec-
trons in these Bi(III) are in the total movement to become a part of the VB of the
respective semiconductor. However, compared to those empty d-orbital of the tran-
VLWLRQPHWDOFDWLRQVWKHHPSW\s orbital has a much lower energy, and Bi5+ ion with
WKHs orbital has a significant impact on the CB of the corresponding semiconduc-
tor. The research progress of Bi(V)-containing semiconductors and their application
in heterogeneous photochemistry is comprehensively reviewed.
15.2 Microstructure and Optical Property
15.2.1 Microstructure
15.2.1.1 Ilmenite-Type
There are two kinds of ilmenite-type oxides with formula of ABO3 in different com-
binations of metal cations, i.e., A2+M4+O3 and A+M5+O3. The weak magnetic iron
titanium oxide (FeTiO3) crystal is a typical ilmenite-type oxide which belongs to the
former combination of A2+M4+O3. Two typical Bi(V)-containing semiconductors of
NaBiO3 and AgBiO3 belong to the latter one of A+M5+O3 which is not as common as
the former one. The reports on crystal structure characterization of AgBiO3 are rare.
Fig. 15.2 Schematic diagram
showing the electronic
structure of Bi3+/Bi5+-
modified semiconductor
oxide (adapted from ref. [11])
X. Chang et al.

347
%\XVLQJSRZGHUQHXWURQGLIIUDFWLRQ31'GDWDWKH1D%L23 and AgBiO3 structures
were refined as ilmenite-type under an ambient condition and the details of NaBiO3
crystal structure were described by Kumada et al. [], that is, the NaO (AgO)
octahedra and BiO octahedra are stacked alternately along the c axis in a layered
structure (as displayed in Fig. 15.3).
The chemical formula of commercial NaBiO3 VXFK DV :DNR 3XUH &KHPLFDO
,QGXVWULHV/WG-DSDQ KDVEHHQFRQÀUPHG DV1D%L23·2H2O by X-ray diffraction
(XRD) method. A few investigations clearly proved that the hydrated NaBiO3
changes to the ilmenite-type structure after dehydration over 140 °C [18, 19], and it
can be found that the strong XRD peak at ~12 °C (Cu Kα irradiation) disappears
after dehydration. Recently, Dias et al. [20] further determined the crystal structure
of NaBiO3 by measuring the phonon spectra via Raman and infrared spectroscopies.
The conducted group theory calculations confirm the trigonal R3 to be the most pos-
sible space group to describe such perovskite oxides but with highly distorted struc-
ture because of the very small tolerance factor (t = 0.793) [20]. By means of density
functional theory (DFT), it was predicted by Liu et al. [21] that the phase of NaBiO3
can be transformed from ilmenite phase (R-3 No. 148) to the orthorhombic phase
3QPD1RXQGHUK\GURVWDWLFSUHVVXUH
15.2.1.2 Perovskite Structure (BaBiO3)
In a typical perovskite oxide structure with the chemical formula of ABO3, the
A and B sites cations often consist of an alkaline-earth metal element (a rare earth
element) and transition-metal element, respectively. It is well known that an ideal
Fig. 15.3 Crystal structure of NaBiO3 from different view directions (reprinted from refs.
[, 17])
15 Bismuth(V)-Containing Semiconductor Compounds and Applications…

348
perovskite structure should have stoichiometry as well as cubic structure consisting
of corner-sharing BO octahedra [22], as shown in Fig. 15.4. The structural stability
RISHURYVNLWHR[LGHVFDQ EHHYDOXDWHGE\FDOFXODWLQJWKH*ROGVFKPLGW·VWROHUDQFH
factor (t) which describes the deviation of the perovskite cubic structure,
trA rO
rB rO
=
+
+
() ()
(( )())2
where r(A), r(B), and r(ODUHLRQLFUDGLLRIWKHUHVSHFWLYHLRQVEXWWKH6KDQQRQ·V
ionic radii have been widely employed for the tolerance factor determination.
An ideal cubic structure can be expected if 0.79 < t < 1.1 [3]. It is worth noticing that
in the case of BaBiO3VHPLFRQGXFWRUWKHUDGLLRI%LLRQVDUHDQGcIRU
Bi3+LRQZLWKFRRUGLQDWLRQQXPEHURIDQG%L5+LRQZLWKFRRUGLQDWLRQQXPEHURI
[24]. According to the crystal structure characteristic as reported by Tang et al. [23],
WKH*ROGVFKPLGW·VWROHUDQFHIDFWRURI%D%L23 can be calculated at 0.904, indicating
the relative stability of such BaBiO3 oxides.
The thermal stability of such perovskite oxide has been studied systematically as
well. The crystal phase of BaBiO3 transforms from monoclinic at room temperature
to rhombohedral at 300 °C and to cubic at ~500 °C. Further temperature increasing
IURP  WR & OHDGV WR WKH R[\JHQ ORVW LQ %D%L23 and the formation of
oxygen- deficient phases such as BaBiO2.88, BaBiO2.83, BaBiO2.75, and BaBiO2.55 [25].
The X-ray photoelectron spectrum of the Bi4f7/2 levels in BaBiO3 was examined
by Kostikova et al. as well [@,WZDVIRXQGWKDWWKH;36RI%Lf7/2 levels contains
two lines at 158.4 and 157.5 eV, respectively, indicating the ordering of trivalent and
pentavalent bismuth atoms in BaBiO3.
The Fourier transform-infrared spectroscopy (FT-IR) characterization is an effi-
cient way to reveal the ordering existence of Bi3+–O2−–Bi5+ cross-linkages in BaBiO3
crystal. The IR absorption by both the Bi3+–O2− bonds and Bi5+–O2− bonds are
Fig. 15.4 Left: Ideal cubic perovskite structure for ABO3 (the red, blue, and green spheres repre-
sent O-atoms, B-atoms, and A-atoms, respectively); right: crystal structure of BaBiO3 perovskite
(reprinted from ref. [22, 23])
X. Chang et al.

349
almost the same because of the indiscernible valence states of Bismuth cations in IR
spectroscopy [27]. Yaremchenko et al. [28] detected only one strong IR absorption
EDQGFHQWHUHGDWQPLQWKHLU%D%L23 sample, which is attributed to the stretch-
ing vibration of the Bi–O bonds coming from the Bi3+–O2−–Bi5+. However, the band
DWQPGLVDSSHDUHGDQGDQHYROYLQJEDQGFDQEHREVHUYHGDW²FP−1 after
substituting Bi3+ with La3+, which is thought to be the Bi5+–O2− bonds coming from
Bi3+–O2−–La3+ERQG0HDQZKLOHDIWHU VXEVWLWXWLQJ %LDWRPZLWK3U4+ in BaBiO3,
WZRDEVRUSWLRQEDQGVFDQEHGHWHFWHGDW²DQG²FP−1, which is attrib-
uted to the Bi–O stretching vibrations in Bi3+–O2−–Bi5+ and Bi5+–O2−²3U4+, respec-
tively. The similar trend was observed by Lakshminarasimhan et al. [11] as well.
It was found that new IR absorption bands span from 540 to 520 cm−1 appeared after
substituting Bi3+ with La3+, which is considered as the district stretching vibration of
O2−–Bi5+ in Bi5+O octahedron.
15.2.1.3 Tunnel Structures
KBiO3 and LiBiO3 exhibit tunnel structures and isostructure with KSbO3, which are
different from ilmenite oxides of ABiO3(A=Na, Ag). However, both the KBiO3 and
LiBiO3 with tunnel structures and ilmenite-type oxides of ABiO3(A=Na, Ag) are
formed by edge-sharing octahedra. Such structures consist of BiO octahedra pairs
which are edge-shared to form Bi2O10 clusters, resulting in the formation of tunnel
structure (as shown in Figs. 15.5 and ). For KBiO3, the potassium ion partially
RFFXSLHV WKUHH VLWHV LQ WKH WXQQHO VWUXFWXUH 7KHUPDO JUDYLPHWULF 7* DQDO\VLV
results indicated that a sudden weight loss takes place above 500 °C, suggesting the
decomposition of KBiO3 into K2O and Bi2O3 [29@7KH*ROGVFKPLGW·V WROHUDQFH
Fig. 15.5 Crystal structure of KBiO3 (shaded circles represent potassium atoms located along the
[111] direction, reprinted from [29]); right: oxygen atoms are at the corner of the octahedron
around Bi5+ while K+ cations reside within the tunnels, reprinted from ref. [30]
15 Bismuth(V)-Containing Semiconductor Compounds and Applications…

350
factor (t) of KBiO3 and LiBiO3ZDV FDOFXODWHG DW DQGDVVKRZQ LQ
Fig. 15.7), respectively, indicating that only KBiO3 can be considered as a stable
perovskite oxide.
Up to now, four kinds of lithium bismuth oxides containing pentavalent bismuth
have been discovered, that is, Li3BiO4 [32], Li7BiO [33], Li5BiO5 [34], and LiBiO3 [31].
Among them, LiBiO3 has attracted more attention due to its potential applications
in heterogeneous photocatalysis. By means of neutron powder diffraction data, the
structure of LiBiO3 oxides with high purity was characterized and reported for the
ÀUVWWLPHLQ7KHDVSUHSDUHG/L%L23 crystal which crystallizes in the ortho-
rhombic system was found to have the isostructure with LiSbO3, because of the fact
that array of hexagonally close-packed oxygen atoms with cations occupying two-
thirds of the octahedral sites can be observed in both structures. Thermal gravimet-
ULF DQG GLIIHUHQWLDO WKHUPDO DQDO\VLV 7*'7$ UHVXOWV VKRZ WKDW /L%L23 is
decomposed to LiBiO2 after heating up to 300 °C [31].
15.2.1.4 Trirutile and Lead Antimonite Structure [35]
Figure 15.8GHSLFWVWKHWULUXWLOHDQGOHDGDQWLPRQLWH 3E6E2O) structure with the
same chemical formula of ABi2O where A is a divalent cation. In trirutile structure
(such as MgBi2O and ZnBi2O), the two crystallographic sites with similar chemi-
cal environments are for the oxygen atoms which are coordinated to two Bi cations
and one A cation (such as Mg2+ and Zn2+), meanwhile retaining the planar coordina-
WLRQ VWUXFWXUH 7KH WULUXWLOH VWUXFWXUH KDV WKH VDPH VSDFH JURXS ZLWK UXWLOH 32/
mnm) but has a tripled c-axis in the unit cell.
Fig. 15.6 Crystal structures of LiBiO3 with different view directions (reprinted from ref. [31])
X. Chang et al.

351
,Q3E6E2O type structure (such as SrBi2O, BaBi2ODQG3E%L2O), planar layers
are composed of edge-sharing BiO octahedra, where two out of every three octahe-
dral holes are filled. One out of every three octahedral holes in adjoining layers is
also occupied by A cations (such as Sr2+, Ba2+DQG3E2+) and the octahedral holes
are filled by A cations by sitting above and below the vacant octahedral site in the
Bi2O layers (Table 15.1).
Fig. 15.7 Calculated
*ROGVFKPLGW·VWROHUDQFH
factors of various pentavalent
bismuthates
Fig. 15.8 Crystal structures of the trirutile oxides (left) and lead antimonite-type oxides (right).
The A and Bismuth cations are shown as larger light gray spheres and smaller black spheres
within the octahedra, respectively. The oxide ions are shown as smaller spheres at the vertices of
the octahedra (reprinted from ref. [35])
15 Bismuth(V)-Containing Semiconductor Compounds and Applications…

352
15.2.2 Optical Absorption Performance
Since it is difficult to measure the transmission spectroscopy of metal oxide materi-
als, diffuse reflectance spectroscopy (DRS) has been widely adopted to evaluate the
optical absorption properties. The optical absorption near the absorption edge for a
semiconductor usually obeys the following equation [40]:
Table 15.1 Reported crystal data for typical Bi(V)-containing crystals
Formula Crystal system Lattice parameters
Characterization
method References
LiBiO3Orthorhombic a c 31' [31]
b c
c c
Li5BiO5Monoclinic a c TOF-NDa,
XRD
[34]
b c
c c
α = β = 109.49(2)°
NaBiO3Hexagonal a c 31' []
c c
α-Na3BiO4Monoclinic a = 5.87(1) XRD []
b 
c 
β = 109.8°
Na0.75Bi0.25O4
(β-Na3BiO4)
Hexagonal a c HR-XRD []
c c
KBiO3Cubic a c XRD [29]
AgBiO3Hexagonal a c 31' []
c c
BaBiO3Monoclinic a c XRD [23]
b c
c c
β 
BaBi3+0.5 − xLa3+xBi5+0.5O3
(x = 0, 0.1 and 0.3)
Monoclinic c≤ a ≤c XRD [11]
c≤ b ≤c
c≤ c ≤c
89.8° ≤ β ≤90.2°
Na(Bi0.08Ta0.92)O3Orthorhombic a c XRD [37]
b c
c c
Na0.04 Sr0.48BiO3·0.48H2O Hexagonal a c XRD [38]
c c 7*'7$
Na1 − 2xBaxBiO3·nH2O
(0.11 ≤ x ≤
Hexagonal c≤ a ≤c XRD [38]
c≤ c ≤c 7*'7$
MgBi2OTetragonal a c XRD [39]
c =c
ZnBi2OTetragonal a c XRD [39]
c c
aTime-of-flight neutron diffraction
X. Chang et al.

353
KhvE ahv
n
()
-=
g
in which h, ν, α, and KDUHWKH3ODQFNFRQVWDQWOLJKWIUHTXHQF\DEVRUSWLRQFRHIÀ-
cient, and constant, respectively. The exponent n depends on the transition involved
and is defined for crystalline semiconductors as follows:
n = 1 for allowed direct transitions
n = 3/2 for forbidden direct transitions
n = 2 for allowed indirect transitions
n = 3 for forbidden indirect transitions
The values of n can be confirmed by plotting ln (αhv) vs. ln (hv − Eg) (lg (αhv) vs.
lg (hv − Eg), using the approximate Eg value) because n is the slope of the straightest
(tangent) line near the absorption edge. Therefore the band gap (Eg) of as-prepared
semiconductor can be determined by plotting (αhv)1/n vs. (hv) as the Eg is the inter-
cept on the hv axis. The reported Eg data of various Bismuth(V)-containing semi-
conductors are summarized in Table 15.2.
15.3 Preparation Technique
15.3.1 Ion-Exchange Reaction
,RQH[FKDQJH,(SURFHVVKDVEHHQHPSOR\HGWRSUHSDUHYDULRXVSHQWDYDOHQWELV-
muthates with chemical formula of ABO3, by using ilmenite-type NaBiO3 as the ion
exchanger which is a kind of cation exchanger that can exchange positively charged
ions such as Ag+, Li+, Sr2+, and Ba2+.
Kumada et al. [, 18, 31] carried out a variety of investigations on the synthesis
and microstructure characterization of ilmenite-type pentavalent bismuthates (such
as AgBiO3 and LiBiO3). It was found that AgBiO3 can be prepared during one day
WKURXJKDYHU\VLPSOH,(SURFHVVDW&DQGDPELHQWSUHVVXUHE\XVLQJ1D%L23
and AgNO3 as the ion exchanger and silver cation source (with a molar ratio of Ag/
Bi = 2–4), respectively. Recently, Yu et al. [45] used similar reaction process but
different molar ratio of Ag/Bi (≈0.93), reaction temperature (R.T.), it was found that
the black colored solid which is composed of metallic silver and Bi2O2CO3 was
produced very quickly (complete in seconds), indicating that molar ratio of Ag/Bi,
where reaction temperature and reaction time may play an important role in the
preparation of AgBiO3.
LiBiO3 oxides with ilmenite structure was once tried to be prepared by ion-
exchange method in 1993 by stirring NaBiO3·nH22LQ0/L&,VROXWLRQDW&
however, it was not very successful because the ion-exchanged products were
partially decomposed to Bi2O3 in the reaction. However, after 3 years, the prepara-
tion of LiBiO3 compound with high purity was reported by this group. LiBiO3
crystals with similar structure of LiSbO3 were successfully prepared through
15 Bismuth(V)-Containing Semiconductor Compounds and Applications…

354
hydrothermal- induced ion-exchange process, using NaBiO3 and LiOH as the raw
materials. A few current investigations clearly show that various pentavalent bis-
muthates with the chemical formula of both ABO3-like (such as Na0.04
Sr0.48BiO3·0.48H2O) and AB2O (such as SrBi2O), can be prepared by such similar
,(SURFHVVEXWXQGHUK\GURWKHUPDOFRQGLWLRQV
Table 15.2 The transition type and determined band gap values of
Bismuth(V)-containing semiconductors
Semiconductor Transition type Eg/eV References
LiBiO3N.A.  [10]
N.A. 1.8 [30]
N.A. 1.7 [41]
NaBiO3aN.A.  [17]
N.A. 2.53 [10]
Indirect 2.45 [19]
N.A. 2.7 [35, 42]
NaBiO3·nH2O Indirect  [43]
Direct 2.71
NaBiO3·nH2ObIndirect 1.92
Direct 
NaxBiO3Indirect 1.50
Direct 1.77
NaxBiO3cIndirect 1.45
Direct 2.03
KBiO3N.A. 2.04 [10]
N.A. 2.1 [30]
KBiO3·1.45H2O Indirect 1.9 [43]
Direct 2.1
KBiO3·1.45H2OdIndirect 1.82
Direct 2.15
AgBiO3N.A. 0.87 [10]
N.A. 0.8 [35]
Indirect 2.5 [44]
BaBiO3Indirect 2.05 [23]
Na(Bi0.08Ta0.92)O3N.A. 2.88 [37]
MgBi2ON.A.  [10]
N.A. 1.8 [35, 39, 42]
SrBi2ON.A. 1.93 [10]
N.A. 2.0 [35, 42]
BaBi2ON.A. 1.93 [10]
N.A.  [35, 42]
ZnBi2ON.A. 1.53 [10]
N.A. 1.7 [35, 39, 42]
3E%L2ON.A. 1.92 [10]
aAfter heating commercialized NaBiO3·2H2O at 175 °C for 2 h
bAfter acidification
cAfter acidification
dAfter the acidification
X. Chang et al.

355
15.3.2 Oxidation–Reduction Process
3DQHWDO>] prepared NaBiO3 of powder with high purity through oxidation–
reduction (O–R) reaction route by using Bi(OH)3 and NaClO as a reducing and
oxidizing agent, as shown in the reaction below:
2
33
22
333
NaOH Cl NaClONaClHO
Bi OH NaOH Bi OH NaNO
Bi OH
+= ++
+= +() ()
())
33
2
2++
=+
NaClONaOHNaBiO ONaClgH
The purity of NaBiO3 can be determined based on the reaction between BiO3−
and Fe2+ shown as below:
BiOFeHBi Fe
HO
3
233
2
26
23
-+++ +
++=+ +
Thus the purity of NaBiO3 can be confirmed by potassium dichromate titration
process (for Fe2+ determination).
The preparation of anhydrous KBiO3ZDVÀUVWUHSRUWHGE\-DQVHQ>47]. In his
SURFHVVKHXVHG²&DQGDQR[\JHQSUHVVXUHRI²DWPWRREWDLQ
potassium bismuthate as a red powder. Here, KBiO3·nH2O compound was prepared
in liquid phase through oxidation of bismuth nitrate by bromine in hot KOH [48, 49].
Similar approach was proved to be available for the preparation of NaBiO3E\(EHUO
as well (but with a little intermediates of excess sodium and remaining Bi(III)-
content [42]). Thus it might be considered a general method for the preparation of
various pentavalent bismuthates including NaBiO3 and KBiO3. The general prepa-
ration process can be illustrated as follows:
Heating to boiling
temperature
Bi2O3
(or bismuth salt)
AOH (A=Na, K)
+
Adding Br2
(E (Br
2
/Br−)=1.066V)
ABiO3
Scheme 15.1 Schematic illustration for the preparation process of ilmenite-type pentavalent bis-
muthates (NaBiO3 and KBiO3)
Chen et al. [50] prepared NaBiO3 crystals through another O–R route under
solventhermal process by using Bi(OR)3DQG1D255 3UL&0H2(W&+2CH2OCH3)
as the starting materials. It is well known that the oxidation of Bi(III) into Bi(V) is
difficult because of the weak reduction ability of Bi(III). But in their reaction pro-
cess, the reduction ability of Bi(III) was considered to be improved due to the strong
basic condition caused by the starting materials. Meanwhile, the solventhermal
environment could be benefits for the oxidation process which is difficult to take
place at ambient temperature and pressure.
15 Bismuth(V)-Containing Semiconductor Compounds and Applications…


15.3.3 Solid State Reaction
The solid state (SS) reaction is one of the most widely adopted routes for the
preparation of complex oxides from a mixture of starting materials (such as oxides
or carbonate) as the solid can react together under high temperature. This method
had been widely used for the preparation of Bi(V)-containing compounds. The solid
reactants for the preparation are usually adopted as the nitrites/carbonate salts and
oxides (peroxides). The bismuth source is usually adopted as Bi2O3 or Bi(NO3)3,
indicating that a reduction–oxidation process occurs in the solid state route.
15.3.4 Complex Sol–Gel Process
&RPSOH[VRO²JHO&6*PHWKRGKDVDOVREHHQDWWHPSWHGWRSUHSDUH%D%L23 with
perovskite structure [23@ E\ XVLQJ HWK\OHQHGLDPLQHWHWUDDFHWLF DFLG ('7$ DQG
citric acid (CIT) as the chelating agent for Bi3+ and Ba2+, respectively. As illustrated
in Scheme 15.2, the complex sol–gel process involves the preparation of sol and
xerogel, dissociation of ligand and complex (endothermic reaction), and finally the
formation of perovskite phase at high temperature (exothermic reaction).
$VDPHPEHURIWKHSRO\DPLQRFDUER[\OLFDFLGIDPLO\RIOLJDQGV('7$4− which
possesses six dissociation equilibrium in total (pK1 = 0.9, pK2  SK3 = 2.0,
pK4 SK5  SK = 10.24) has been widely selected to bind to a metal
FDWLRQE\LWVDPLQHVDQGFDUER[\ODWHV('7$LVDFDQGLGDWHOLJDQGIRUFKHODWLQJ%L3+
DVZHOOEHFDXVHRIWKHVWDELOLW\FRQVWDQWVOJ.RI('7$4−–Bi3+ can reach to as high
as 27.9 [51].
,QFRPSOH[VRO²JHOSURFHVVWKHH[FHVVDPRXQWRI('7$LVQHFHVVDU\WRSUHSDUH
WKH('7$%LFRPSOH[VROEHFDXVHRIWKHDFLGHIIHFWFRHIÀFLHQWZKLFKLVGHÀQHGDV
IROORZVLQFDVHRI('7$
aYH
Y
Y
YHYHYHYHYHYH
()
[]
[]
[][][][][][][
=′=++ ++++
−− −− +43
2
2
3456
YY
Y
H
K
H
KK
H
KK
H
KKKK
H
2
4
6
2
65
3
654
4
6543
1
+
−
++ ++
=+ ++ ++
]
[]
[][] [] [] [
K
+
++
+
][
]
5
65432
6
6543
21
KKKKK
H
KKKKKK
EDTA4−−Bi3+ CIT−Ba2+
Stabilized sol Xerogel
Mixing
Calcination
BaBiO3
Pyrolysis
Scheme 15.2 Schematic illustration for the preparation process of perovskite-type BaBiO3
X. Chang et al.

357
in which [Y@LVWKHFRQFHQWUDWLRQRI('7$4− ion and [Y′] is the total concentration
RIERWK('7$4− ion and its six kinds of protonated forms. aY(H) will be equal to 1 if
all the protons are dissolved; however, the effective chelating process takes place
only between Y4− and metal cation. Therefore the coefficient of aY(H) should be less
than 1 in practical situation. Since Bi3+ is very easy to hydrolyze and the solubility
product constant of Bi(OH)3 is extremely low (Ksp = 4 × 10−31), Bi3+ cannot exist in
the aqueous solution unless strong acid conditions exist. But after the chelate com-
SOH[IRUPDWLRQRI('7$4+–Bi3+, Bi3+ can be very stable in aqueous solution near
neutral pH condition. CIT is also thought to be an excellent chelating agent, even if
the stability constants (lg K) of CIT-based complex (lg K = 11–15) is much lower
WKDQWKDWRI('7$EDVHGFRPSOH[
15.3.5 Electrochemical Process
The pentavalent bismuthates of β-Na3BiO4 [] and KBiO3 [29] were prepared via
similar electrochemical process, i.e., the crystals were obtained on platinum anode
through electrooxidation of alkali hydroxide melts containing Bismuth(III) oxide
Bi2O3, meanwhile a sacrificial reductant (such as ZnO, ZnCl2, and CuCl) is essential
LQWKHHOHFWURFKHPLFDO(&SURFHVVWREDODQFHWKHHOHFWURQLQYHQWRU\RIWKHZKROH
oxidation–reduction process (Table 15.3).
15.4 Electronic/Band Structure
15.4.1 Typical Bismuth(V)-Containing Semiconductors
15.4.1.1 ABO3 Type
As one of the most typical Bismuth(V)-containing materials, the energy band structure
(%6DQGGHQVLW\RIVWDWHV'26RI1D%L23 were investigated by Liu et al. [21],
during their study on the pressure-induced phase transition of NaBiO3. By means of
the DFT using the generalized gradient approximation, their DOS results (including
SDUWLDOGHQVLW\RIVWDWHV3'26RI1D%L23 (at ambient pressure) indicated that the
s/p orbitals from Bismuth and the p orbital from Oxygen are the main constituents
of the covalent bond and CB. Kako et al. [17] also found that there is a large disper-
sion in the hybridized sp orbitals in the CB of NaBiO3, which might be beneficial
for the high mobility of photogenerated electrons on the sp bands. Li et al. [35]
reported the photocatalytic hydrogen production (from aqueous methanol) enhance-
ment by substitution of Ta5+ with Bi5+ in NaTaO3 photocatalyst. It was deduced
DERXWWKHIRUPDWLRQRIDORZHUHQHUJ\RI&%DVZHOODVWKHK\EULGL]DWLRQRI%Ls/
%Lp and Ta5dRUELWDOV7KLVFRXOGKDSSHQWKDWWKH%Ls%Lp mainly contribute to
15 Bismuth(V)-Containing Semiconductor Compounds and Applications…

358
Table 15.3 3UHSDUDWLRQWHFKQLTXHVIRU%LVPXWK9FRQWDLQLQJVHPLFRQGXFWRUFRPSRXQGV
Compound
3UHSDUDWLRQ
technique Starting materials Reaction condition References
LiBO3,( NaBiO3·nH2O, LiOH Hydrothermal at 120–200 °C, 7 days [30, 31, 41]
(Li–Na)BiO3,( NaBiO3·nH2O, LiCI solution &DWP [18]
NaBiO3O–R Bi(OH)3, NaClO, NaOH 20 °C–30 °C, 1 atm []
Bi2O3, NaOH, Br21 atm, T: N.A. [43]
Bi(OR)31D255 3UL&0H2(W
CH2CH2OCH3)
Solventhermal at 240 °C [50]
α-Na3BiO4SS Na2O2, Bi2O3T²&22 flow), 12 h []
β-Na3BiO4(& Bi2O3, NaOH, LiOH, ZnO 330–350 °C constant current density = 1 mA/cm−2, 18–42 h []
Na0.04 Sr0.48BiO3·0.48H2O,( NaBiO3·nH2O, SrCl2Hydrothermal at 90 °C, 2–20 days [38]
Na1 − 2xBaxBiO3·nH2O
(0.11 ≤ x ≤
,( NaBiO3·nH2O, BaCl2Hydrothermal at 90 °C, 2–20 days [38]
KBiO3O–R Bi2O3, KOH, Br2Boiling point of 50 % KOH a.q. (~125 °C), 1 atm [30, 43]
(& KOH, Bi2O3, ZnCl2 (CuCl), Working potential = 1.1 or 0.8 V [29]
AgBiO3,( NaBiO3, AgNO370 °C, 1 atm, ≥24 h [, 44]
NaBiO3·nH2O, AgNO3Hydrothermal at 70 °C [10]
BaBiO3&6* Ba(NO3)2, Bi(NO3)3&,7('7$ dried at 393 K for 10 h and calcined at 923 K for 5 h [23]
SS Ba(NO3)2, Bi(NO3)3·5H2O 850 °C, 24 h [11]
Bi(NO3)3·5H2O, BaCO31,070 ± 1,270 K, 15 ± 30 h [28]
Ba(NO3)2, Bi2O3700 °C, 9 h [25]
BaO2/Ba(NO3)2, Bi2O3900–1000 °C, 24 h, [52]
Ba1 − xMxBiO3 (M=K, Rb) SS BaCO3, K2CO3, Rb2CO3, Bi2O3900 °C, 2 h [53]
BaBi1 − xMxO3 = δ0 /D3U SS Bi(NO3)3, La(NO3)33UO11, BaCO31,070 ± 1,270 K, 15 ± 30 h [28]
SrBi2O,( NaBiO3·nH2O, SrCl2Hydrothermal at 90–130 °C, 1 week [10]
BaBi2O,( NaBiO3·nH2O, BrCl2Hydrothermal at 90–130 °C, 1 week [10]
3E%L2O,( NaBiO3·nH223E123)2R.T., 1 atm [10]
MgBi2O,( NaBiO3·nH2O, MgCl2Hydrothermal at130 °C [10, 54]
ZnBi2O,( NaBiO3·nH2O, Zn(NO3)2Hydrothermal at 90 °C [10, 54]
X. Chang et al.

359
the bottom of CB in Na(Bi0.25Ta 0.75)O3, which was confirmed also by their DOS
results. The lower CB and hybrid orbitals were considered as the main reason for
the smaller band gap of the series of solid-solution Na(BixTa 1 − x)O3 (x = 0 − 0.10)
compared with NaTaO3.
Besides NaBiO3 WKH (%6 DQG '26 RI RWKHUV W\SLFDO %LVPXWK9FRQWDLQLQJ
semiconductors (i.e., AgBiO3, LiBiO3, KBiO3) have been investigated as well.
According to the results from Takei et al. [10], the CB and VB of these bismuthate
are mainly composed of O2pDQG%Ls orbitals. But the details of their DOS results
are not similar for different compounds. For the DOS results of AgBiO3, the broad
Ag4d orbital above the O2p is considered as the main reason for the electronic
conductivity of AgBiO3. For LiBiO3 crystal, it is interesting to find that the hybrid
RUELWDOVZKLFKDUHFRPSRVHGRI%Ls and O2p) do not emerge. For KBiO3, the rela-
tive low CB was found as the formation of the hybrid orbital which is composed of
%Ls and O2p. The lower CB might be the main reason for the photodegradation
performance over KBiO3. But more importantly, it was observed from the DOS
plots that two types of oxygen atoms (edge-shared and corner-shared oxygen) can
be found because of the splitting of O2p. This might be another reason for the low
band gap of red-colored KBiO3 (Eg = 2.04 eV).
15.4.1.2 AB2O6 Type
The DOS results of Bismuth(V)-containing semiconductors with the AB2O type
(e.g., SrBi2O, MgBi2O, ZnBi2O, BaBi2O DQG3E%L2O) have been reported by
Mizoguchi et al. [35] and Takei et al. [10] in 2004 and 2011.
For the semiconductors with lead antimonite structure (SrBi2O, BaBi2O, and
3E%L2OWKHRUELWDORI3Es could be observed at around −2 eV, which is the pos-
sible reason of the lowest band gap among these three kinds of semiconductors
(Eg3E%L2O) = 1.92 eV, Eg(SrBi2O) = Eg(BaBi2O) = 1.93 eV). For the semiconduc-
tors with trirutile structure (MgBi2O and ZnBi2O), a broad VB was found from the
DOS plots of ZnBi2O, possibly resulting the lower band gap (1.53 eV) than MgBi2O
H9,WZDVUHSRUWHGE\0L]RJXFKLHWDO>35] that the electronic structure of
MgBi2O is qualitatively very similar to MgSb2O and ZnSb2O with trirutile crystal
structures. By the linear muffin-tin orbital (LMTO) calculations with the atomic
sphere approximation (ASA) including the combined correction (CC), the energy
UDQJHVRIIRXU%Ls to O2p σDQG%Ls to O2p σ* bands were, respectively, found to
EHïWRïH9 DQG²H9LQGLFDWLQJWKHLUPXFKPRUHQDUURZHUHQHUJ\
ranges compared with MgSb2O which possibly caused by the improved overlap of
%Ls and O2p with respect to that of Sb5s and O2p orbitals.
15.4.2 Mixed-Valence Bismuth Containing Semiconductors
The development of mixed-valence Bismuth (Bi3+ and Bi5+) containing photocata-
lyst is now considered to be another efficient way to improve the mobility and
15 Bismuth(V)-Containing Semiconductor Compounds and Applications…


lifetime of the photogenerated carries in the corresponding semiconductor, because
of the effective modification of CB (to decrease band gap by forming a lower the CB
position) and VB (to improve the hole mobility by the increase in the width of VB)
by Bi3+ and Bi5+, respectively. On the other hand, basically, the spatial orientation of
the suborbitals (such as s, p, and d orbitals) has great effect on the photogenerated
electron transfer process from VB to CB as well. Therefore, it can be deduced that
the existence of Bi3+%Ls) and Bi5+%Ls) in the semiconductor might be beneficial
for the migration of the photogenerated carries as the less localized characteristics.
However, such report on the mixed-valence Bismuth containing photocatalysts
which Bi3+ and Bi5+ coexist in the same crystal lattice is rare, even imagine that such
PDWHULDOVKDGEHHQSUHSDUHGDQGFKDUDFWHUL]HGDOPRVW\HDUVDJR>55].
Tang et al. [23@UHSRUWHGWKH(%6DQG'26RI%D%L23 for the first time in early
7KHLU '26UHVXOWVSURYHGWKDWWKH%LsDQG%Ls%Lp are the predominant
composition of the top of the VB and the bottom of the CB. Moreover, their density
contour maps for the LUMO (corresponding to CB) and HOMO (corresponding to
9%IXUWKHUFRQÀUPWKHH[LVWHQFHRI%Ls in both LUMO and HOMO (as shown in
Fig. 15.9). Not only such unique characteristics could narrow the band gap, improve
mobility and life time of the photogenerated carries, but facilitate the electron tran-
sition because of the much lower barrier formed, which should be the possible rea-
son for the excellent photocatalytic performance of BaBiO3.
Fig. 15.9 (a) Density
contour maps of the bottom
orbital of the conduction
band (LUMO) and (b)
density contour maps of the
top orbital of the VB
(HOMO) for BaBiO3
(reprinted from ref. [23])
X. Chang et al.


From the contrary view point, Lakshminarasimhan et al. [11] demonstrated the
significance of mixed-valence Bismuth in the photocatalytic activity enhancement.
Their DOS results clearly show that the partial substitution of Bi3+ with La3+ in
BaBi3+0.5Bi5+0.5O3FU\VWDOFDQUHGXFHWKH%Ls contribution to the top of VB and the
CB band width, leading to a lower mobility of photogenerated carries, and there-
fore, a lower photocatalytic activity of La3+ substituted BaBi3+0.5Bi5+0.5O3 crystal.
15.5 Photocatalytic Applications
15.5.1 Removal of Various Contaminates from Aqueous
Solution
In early 2004, Zou et al. [] publicized the photocatalytic application in the removal
of methyl blue on pentavalent bismuthates (NaBiO3, LiBiO3, and AgBiO3) from
aqueous solution in their patent registered in China. The results reported in their
patent that three kinds of pentavalent bismuthate photocatalysts demonstrated
excellent decomposition activity to methyl blue under visible light irradiation.
When the wavelengths of the irradiated light from Xenon lamp is greater than λx
(λx = 420, 480, 500, and 580 nm), the time for the complete decomposition of methyl
blue was less than 40 min. The shortest time required was just 8 min under optimal
conditions at λx = 420 nm by NaBiO3 photocatalyst, indicating the potential
application of NaBiO3 in heterogeneous photocatalysis.
As a matter of fact, the possible application in chemical synthesis of NaBiO3 was
reported for the first time in early 1950. A few fission process with good yield on
NaBiO3 (as oxidant) was discovered such as the fission of αβ-glycols to aldehydes
or ketones [57]. Recently NaBiO3 has been applied in organic compound synthesis
such as glycol cleavage, conversion of acyloins to α-diketones, oxidative halogena-
tion, and chemoselective oxidation [58–].
The first formal report on NaBiO3 photocatalyst in academic journal was pub-
lished by Kako et al. [17]. Dehydrated NaBiO3 was prepared by heating commercial
product of NaBiO3·H2O for 5 h. The calculated band gap value of as-prepared
NaBiO3VKRZVVPDOOHUYDOXHRIH9LQGLUHFWEDQGJDSFRPSDUHGZLWKW\SLFDO
trivalent bismuthates compound such as (2.8–2.9 eV), Bi2WO (2.8 eV), and
Bi2W2O9 (3.0 eV). Their photocatalytic decomposition of 2-propanol and methy-
lene blue was investigated from air and aqueous solution, respectively. It was inter-
esting to find that NaBiO3 can convert 2-propanol into acetone effectively under full
arc or visible light irradiation (irradiated from Xenon lamp), but cannot mineralize
2-propanol into CO2 and H2O at irradiation time less than 1 h, which might be due
to the degradation pathway. On the other hand, NaBiO3 exhibits superior photooxi-
dation activity to methylene blue than N-doped TiO2 and BiVO4 photocatalysts
which are considered to be the most popular photocatalysts to date.
3RO\F\FOLFDURPDWLFK\GURFDUERQV3$+VDUHSURGXFHGPDLQO\E\WKHEXUQLQJ
RI IRVVLO IXHOV VXFK DV FURSV DQG RWKHU QDWXUDO VXEVWDQFHV 3DUWV RI WKH 3$+V
15 Bismuth(V)-Containing Semiconductor Compounds and Applications…


UHSUHVHQWHG E\ FKORULQDWHG SRO\F\FOLF DURPDWLF K\GURFDUERQV &O3$+V ZLGHO\
presented in the environment, are considered as a great potential threat to human
health. Kou et al. [19@ UHSRUWHG WKH SRVVLEOH SKRWRFDWDO\WLF DSSOLFDWLRQ RI 3$+V
removal on NaBiO3 from aqueous phase under visible light irradiation, by selecting
anthracene (ANT) and benzo[a]anthracene (Bz[a]A) as target pollutants. It was
found that under certain conditions, photocatalytic conversion rates of ANT and
Bz[a]A on NaBiO3 can reach to over 50 % and up to 100 % within 8 and 1 h, respec-
tively. During the process of photocatalytic conversion of ANT and Bz[a]A, the
intermediate products were detected and each contain compounds of anthraquinone
(the main degradation product), anthrone,1-hydroxy-anthracene and anthracene-
GLRQH HWF XVLQJ JDV FKURPDWRJUDSK\²PDVV VSHFWURPHWU\ *&06 7KH
results also showed that there is a similar degradation pathway in the NaBiO3 pho-
tocatalytic conversion process of ANT and Bz[a]A (as shown in Fig. 15.10).
Yu et al. [] studied the photocatalytic degradation pathway and mechanism of
Rhodamine B dye on NaBiO3 under visible light irradiation. They separated and
confirmed all intermediate products of N-bit de-ethylation and other small- molecule
FRPSRXQGVE\PHDQVRIKLJKSHUIRUPDQFHOLTXLGFKURPDWRJUDSK\+3/&OLTXLG
FKURPDWRJUDSK\²PDVV²PDVVVSHFWURPHWU\/&0606DQG*&067ZRNLQGVRI
Fig. 15.10 Degradation pathway of ANT and Bz[a]A in NaBiO3 suspended solution under visible
light irradiation (reprinted from ref. [19])
X. Chang et al.


isomers of different contents (N,N-dimethylamino-rhodamine DR and N-dimethyl-
N′GLPHWK\OUKRGDPLQH ((5 JHQHUDWHG LQ SKRWRFDWDO\WLF UHDFWLRQ PLJKW EH
related to the electron density of the dye molecules. Chromophore split and N-bit
de-ethylation effect may be two competing mechanisms in the process of Rhodamine
%SKRWRFDWDO\WLFGHFRPSRVLWLRQ<XHWDO·VH[SHULPHQWVFRQÀUPHGWKHGLYLVLRQSURFHVV
of chromophore was more dominant compared with N-bit de-ethylation effect.
3HQWDFKORURSKHQRO3&3DQGLWVVRGLXPVDOW3&31DKDGEHHQZLGHO\XVHG
as the insecticide to protect wood and textile worldwide; however, its toxicity,
HQGRFULQH('&DQGRUJDQLVPJDWKHULQJHIIHFWFDXVHGSHRSOH·VDWWHQWLRQ3UHYLRXV
VWXGLHVKDYHVKRZQWKDWFRPPHUFLDOJUDGH3&31DFRQWDLQHGPRUHWR[LFSRO\FKOR-
rinated dibenzo-pGLR[LQV 3&'' DQG SRO\FKORULQDWHG GLEHQ]RIXUDQV 3&')
We previously [] carried out a systematic study on the kinetics of NaBiO3 pho-
WRFDWDO\WLFNLQHWLFVRI3&31DRQ1D%L23 in visible light and conducted a prelimi-
QDU\DQDO\VLVDQGGLVFXVVLRQDERXWLWVSKRWRFDWDO\WLFPHFKDQLVPEDVHGRQWKH(%6
of NaBiO3. It was found that photocatalytic process of NaBiO3 decomposing
3&31D REH\HG WKH /DQJPXLU+LQVKHOZRRG ÀUVWRUGHU NLQHWLFV SURFHVV 7KH
DPRXQWRIFDWDO\VWLQLWLDOS+YDOXHRI3&31DDTXHRXV VROXWLRQDQGWKHLQLWLDO
concentration produced a significant impact on the kinetic process. At the same
time, we noticed experimentally that, there is almost no obvious impact on the
photocatalytic kinetic process purged with nitrogen. It is indicated by theoretical
calculation that the CB edge potential of NaBiO3 is closer to the electrochemical
potential of O2/O2−, thus the overpotential of oxygen anions produced by photo-
generated electron reduction of O2 is smaller, resulting in the photocatalytic
GHFRPSRVLWLRQSURFHVVWKHUHIRUHR[\JHQDQLRQV·R[LGDWLRQRUJDQLFVLV QRW WKH
leading step in the whole process.
Apart from NaBiO3, other pentavalent bismuthates such as LiBiO3, KBiO3, and
AgBiO3 have also been attempted in the heterogeneous photocatalytic application.
Kikugawa et al. [41] investigated the photocatalytic degradation of methylene blue
over as prepared LiBiO3 under white fluorescent light exposure. Their results show
that methylene blue can be completely decolorized after 4-h reaction, and the min-
eralization efficiency can be reached to 70 %. The highest apparent photoefficiency
3(RIFRXOGEHREWDLQHGXQGHUQPPRQRFKURPDWLFOLJKWLUUDGLDWLRQ
The photocatalytic activity of LiBiO3 was further confirmed by Ramachandran et al.
[30]. Two cationic dyes of Rhodamine B and Methylene blue have been used as
model compounds. Under UV and solar radiations, it was found that LiBiO3 exhib-
its better photocatalytic activity of Methylene blue than Rhodamine B in terms of
both degradation efficiency and reaction kinetics constant.
7KHSKRWRFDWDO\WLFGHJUDGDWLRQRI YDULRXV DQLRQLFG\HVLH2UDQJH*2*
$PLGREODFN%$%%$OL]DULQF\DQLQHJUHHQ$&*,QGLJRFDUPLQH,&
and Coomassie brilliant blue R 250 (CBBr) over KBiO3 from aqueous phase were
investigated by Ramachandran et al. [30] as well. It was found that the overall pho-
WRFDWDO\WLFGHJUDGDWLRQRI&%%UDQG$&*DUHKLJKHUWKDQWKDWRI2*DQG$%%
SRVVLEO\EHFDXVHRIWKHPRUHUHDFWLYHRI&%%UDQG$&*ZKHUHVXOIRQ\OJURXSLV
attached to the benzene ring, but less reactive naphthalene leads to the less reactive
RI2*DQG$%%
15 Bismuth(V)-Containing Semiconductor Compounds and Applications…


2Q WKH FRQWUDU\ LW ZDVIRXQG E\ (EHUO WKDW QR SKRWRFDWDO\WLF GHJUDGDWLRQ RI
4-Chlorophenol [43]. KBiO3 did not exhibit the photocatalytic mineralization
performance, and powder sample after exposure changed into yellow.
In recent years, Bi(III)/Bi(V)-containing mixed-valence semiconductor com-
SRXQGVZLWKDVLQJOHSKDVHVWUXFWXUHKDYHDOVRGUDZQSHRSOH·VDWWHQWLRQ&RPSDUHG
with the semiconductor compound simply containing Bi(V), the energy band/electron
VWUXFWXUHRIWKLVNLQGRIFRPSRXQGFRXOGLPSURYHWKHFDUULHU·VPRELOLW\DQGOLIHWKXV
increase the heterogeneous photocatalytic activity. Tang et al. [23] prepared BaBiO3
photocatalyst containing mixed-valence Bi(III)/Bi(V) by complex sol–gel method.
The result shows that the photocatalytic activity of BaBiO3 is superior to other
Bi-containing visible light photocatalysts such as ZnBi12O20 and CaBi2O4. By select-
ing acetaldehyde and methyl blue as model compound, after 1-h reaction under the
lighting conditions of λ ≥ 440 nm and λ ≥ 420 nm, the photocatalytic decomposition
efficiency can reach to 80 % and 100 %, respectively. For its reason, mainly because
crystal Bi(III) and Bi(V) effectively controlled the VB and CB of semiconductor,
respectively. Theoretical calculation based on the electron structure in semiconductor,
it was found that photogenerated electrons and holes all have better mobility because
of better dispersion of CB and VB in the crystal which can then improve the lifetime
of the carrier. Transitions of photogenerated electrons from VB to CB are influenced
by the sub-shell electron orbital orientation to a great extent. During the photocata-
lytic process of BaBiO3WKHSKRWRHOHFWURQMXPSVIURPs orbit of Bi3+WRs orbit of
Bi5+. Therefore the energy barrier of s–s transition is the lowest as the ball symmetri-
cal characteristic of s orbit. Thus it can promote the photocatalysis reaction.
(EHUO>43] applied NaxBiO3 (the content of Bi(V) accounted for more than 90 %)
to the photocatalytic decomposition experiment of 4-Chlorophenol and it showed
that 4-Chlorophenol was completely mineralized within 1 h under the lighting con-
dition of λ > 455 nm. It is probably because of the fact that the common existence of
Bi(III) and Bi(V) in photocatalytic materials made photogenerated electron–hole
JHWPRUHHIIHFWLYHVHSDUDWLRQDQGWKHQLPSURYHWKHFDUULHU·VOLIH
Lakshminarasimhan et al. [11] prepared BaBi3+0.5 − xLaxBi5+0.5O3 photocatalyst
which Bi3+ was partly displaced by La3+ (x = 0, 0.1 and 0.3, the ionic radius of La3+
and Bi3+ZHUH$DQG$$OORIWKHVHFDWDO\VWVZHUHGDUNEURZQ,WZDV
IRXQGWKDWDEVRUSWLRQEDQGFHQWHUHGDWQPDERXWH9LQWKHGLIIXVHUHÁHF-
tion spectrum of BaBi3+0.5Bi5+0.5O3 disappeared due to the displacement of less con-
tent of La3+ (namely, x  $FFRUGLQJWR0L]RJXFKL·VSRLQWRIYLHZ>], this
absorption band might be attributed to the carrier transition from Bi3+s2) to Bi5+
s0). Thus it is not difficult to find, the displacement of La3+ which can hinder
the differentiation of Bi3+–O2−–Bi5+ valence bond. This conclusion is also con-
firmed by Fourier transform-infrared absorption spectroscopy (FT-TR). By using
4-Chlorophenol as a target pollutant, the photocatalytic investigation showed that
the photocatalytic activity of BaBi3+0.5 − xLaxBi5+0.5O3 weakened with the increase of
the amount of displacement of La3+, and BaBi3+0.5 − xLaxBi5+0.5O3 with no substitution
showed the highest photocatalytic activity because the photogenerated hole had
stronger oxidation capacity. The displacement between Bi3+ and La3+ destroyed the
valence bond differentiation, which led to the decrease of photocatalytic activity.
X. Chang et al.


15.5.2 Disinfection from Water
Up to now, to the best of our knowledge, there is no report on the photocatalytic
removal of contaminants on AgBiO3 compound (a visible light-responsive cata-
lyst that absorbs strongly in the visible light spectrum) from air or aqueous
phase. However a new attempt, that is, the photocatalytic inhibition of the
growth of cyanobacteria on AgBiO3 under natural light irradiation was made by
Yu et al. [44].
Microcystis (blue-green algae) is one of the most common toxic cyanobacteria in
fresh water which includes the harmful algal bloom Microcystis aeruginosa.
Microcystis bloom which is one of the most objectionable characteristics of eutro-
phication in tropical and subtropical waters is thought to harm the ecological envi-
ronment, local economies, and even human health besides its unfavorable effects on
the landscape. Yu et al. [44] found that the as-prepared AgBiO3 compound which is
imagined to be able to produce more hydroxyl radicals than NaBiO3, can effectively
inhibit the growth of M. aeruginosa meanwhile damaged its cell walls and mem-
branes, resulting to the electrolyte and cytoplasmic leakage and finally the death of
the bacteria (as shown in Fig. 15.11).
Fig. 15.11 7(0RIM. aeruginosa with or without AgBiO3 ((a) control sample; (b–d) AgBiO3
treatment sample, reprinted from ref. [44])
15 Bismuth(V)-Containing Semiconductor Compounds and Applications…


15.5.3 Photocatalytic Hydrogen Production
The photocatalytic splitting of water requires a higher (more negative) CB band
edge potential of semiconductor compared with H+ reduction potential. However,
the report on the relevant application of Bismuth(V)-containing semiconductor is
rare, due to the lower CB band edge potential of such semiconductor. Ultraviolet
SKRWRHOHFWURQVSHFWURVFRS\836>] and flatband potential determination-based
photoelectrochemical techniques [–] were two important methods to test the
electrochemical potentials of CB and VB. Recently, a theoretical method based on
the absolute (Mullikan) electronegativity was widely used to predict band position
of semiconductors and such simple method is in good agreement with the experi-
mental results for semiconductor compounds [23, 70–72]. The CB and VB band
edge (ECB/EVBYVVWDQGDUGK\GURJHQHOHFWURGH6+(RIWKHVHPLFRQGXFWRUDWWKH
point of zero charge can be calculated by the equation as follows (the error of this
method is around 0.2 eV [73]):
EXEEEE E
CB
C
gVBC
Bg
=- --=
1
2
where X is the absolute electronegativity of the semiconductor which can be
calculated as the geometric mean of the Mulliken electronegativity of the constitu-
ent atoms. EC is the energy of free electrons on hydrogen scale (≈4.5 eV) and Eg is
the band gap of the semiconductor which can be calculated by DRS measurements.
(YHQLIWKHFDOFXODWHGECBH9YVYDFXXPï9YV6+(LVFORVHWRWKH+2
evolution potential, however, no H2 evolution was observed by Tang et al. [23], pos-
sibly due to the practical CB is lower than H2 evolution potential or the overpotential
of the material is not enough for H2 production.
Li et al. [37] investigated the H2 production from aqueous methanol solutions
over Bi(V) substituted NaTaO3 solid-solution (Na(BixTa1 − x)O3) under visible light
irradiation (λ > 400 nm). No H2 evolution was found for NaTaO3 under visible light
irradiation because of the relative wide band gap value (3.91 eV). The substitution
of Bi(V) in NaTaO3 could decrease the band gap as well as the CB band edge; there-
fore, over amount substitution might not be beneficial for the H2 production because
a much lower CB band edge will be formed. The Na(Bi0.08Ta0.92)O3 photocatalyst
which was considered to be the optimal composition in the solid-solution exhibited
the highest activity of H2 evolution (59.48 mmol h−1 g−1) under visible light irradia-
tion (Table 15.4).
15.6 Photostability
The photostability evaluation of any catalyst is of great importance in fundamental
study as well as due to other engineering aspects. Up to now, however, such investi-
gations and discussions on the possible corrosion mechanism are very rare.
X. Chang et al.

Table 15.4 3KRWRFDWDO\WLFGHJUDGDWLRQFRQYHUVLRQRIYDULRXVFRQWDPLQDWHVRQ%LVPXWK9FRQWDLQLQJSKRWRFDWDO\VWV
3KRWRFDWDO\VW Target pollutant Light source
Reaction condition Activity evaluation
ReferencesCcataC0bt
Degradation/
conversion % k/min−1
TOC removal
72&RU3(
LiBiO3Methylene blue White fluorescent
OLJKWP:FP2
0.3 g/100 mL 13.2 mg/L 4 h ~100 % N.A. TOC% ≈ 70 %
3( 
(420 nm)
[31]
Methylene blue Xenon lamp 300 W 3 g/L PJ/ 40 min ~100 % N.A. N.A. [10]
3KHQRO λ > 420 nm N.A. 2 h N.A. N.A. TOC% ≈ 72 %
Rhodamine B High pressure mercury
vapor lamp 125 W
0.1 g/100 mL 50 mg/L 2 h 57 % 0.00513
(first 20 min)
N.A. [30]
Methylene blue 20 mg/L ~83 % 0.00102
(first 20 min)
N.A.
Rhodamine B Solar radiation ~975 W/m250 mg/L ~34 % 0.0024 N.A.
Methylene blue 20 mg/L ~97 % 0.01473 N.A.
NaBiO33URSDQROJ Xenon lamp ~3 mW 0.4 g SSP 1 h N.A. (~47 ppm
acetone evolved)
N.A. N.A. [17]
Methylene blue Xenon lamp 300 W 0.3 g/100 mL PJ/ 10 min ~100 % 0.42 N.A.
Methylene blue Xenon lamp 300 W 3 g/L PJ/ 40 min ~100 % N.A. N.A. [10]
3KHQRO λ > 420 nm N.A. 2 h N.A. N.A. TOC% ≈ 82 %
Sodium
pentachlorophenate
Xenon lamp 500 W 0.1 g/150 mL 50 mg/L 1 h 90.50 %  N.A. []
λ > 400 nm
4-t-Octylphenol Xenon lamp 500 W 0.3125 g/L 29 mg/L 1 h ~90 % ~0.03741 N.A. [74]
λ > 400 nm
4-Chlorophenol Xenon lamp 150 W 0.9 g/L 2.5×10−4 mol/L 2 h N.A. N.A. TOC% ≈ [43]
λ > 455 nm 950 ± 100 W/m2
Anthracene Xenon lamp 300 W JP/ 3 mg/(20 mL
H2O+40 mL
Actone)
10 h ~85 % N.A. N.A. [19]
Benz[a]anthracene λ > 420 nm P/ 80 min ~100 % N.A. N.A.
Rhodamine B Xenon lamp
750 W
1 g/L 20 mg/L 30 min ~100 % N.A. N.A. []
λ > 400 nm
(continued)

3KRWRFDWDO\VW Target pollutant Light source
Reaction condition Activity evaluation
ReferencesCcataC0bt
Degradation/
conversion % k/min−1
TOC removal
72&RU3(
KBiO3Methylene blue Xenon lamp 300 W 3 g/L PJ/ 40 min ~100 % N.A. N.A. [10]
3KHQRO λ > 420 nm N.A. 2 h N.A. N.A. TOC% ≈ 55 %
2UDQJH* High pressure mercury
vapor lamp 125 W
0.1 g/100 mL 50 mg/L 2 h a 0.00144 N.A. [30]
Amido black 10B ~22 % 0.0017 N.A.
N.A.
Alizarin cyanine green ~49 % 0.00102 N.A.
N.A.
Indigo carmine a  N.A.
Coomassie brilliant
blue R 250
15 mg/L ~80 % 0.01043 N.A.
2UDQJH* Solar radiation ~975 W/m250 mg/L ~0 % 0 N.A.
Amido black 10B ~28 % 0.00345 N.A.
N.A.
Alizarin cyanine green ~55 % 0.00958 N.A.
N.A.
Indigo carmine ~94 % 0.02319 N.A.
Coomassie brilliant
blue R 250
15 mg/L a 0.01585 N.A.
4-Chlorophenol Xenon lamp (150 W) λ > 455 nm
950 ± 100 W/m2
N.A. 2.5 × 10−4 mol/L N.A. ~0 % 0 % 0 % [43]
BaBiO3Methylene blue Xenon lamp 300 W 0.3 g/100 mL 15.3 mg/L 2 h ~100 % N.A. N.A. [23]
λ > 420 nm
Acetaldehyde Xenon lamp 300 W
λ > 440 nm
0.8 g 837 ppm 40 min N.A. N.A. TOC% > 80 %
3( 
QP
3.3 h ~100 % N.A. N.A.
4-Chlorophenol Xenon lamp 300 W 0.5 g/L 100 μM 4 h ~27 % N.A. N.A. [11]
λ > 420 nm
a3KRWRFDWDO\VWGRVDJH
bInitial concentration of target contaminant
Table 15.4 (continued)


By using methylene blue as model compound, Kako et al. [17] found that the
photooxidation activity of NaBiO3 declined only a little bit after the reaction was
F\FOHGIRUWLPHV ZKLFKZDVGHPRQVWUDWHGE\ ;5'PHDVXUHPHQWV DVWKHUHZDV
almost no significant changes observed in the catalyst sample after the reaction.
On the basis of photooxidation to methylene blue, it was found by Kako et al.
[17] that the photodegradation of methylene blue on NaBiO3 decreased slightly
after six subsequent cycling reaction and the corresponding XRD signals of NaBiO3
were still detectable after recycling, indicating the good photostability of the NaBiO3
catalyst. Another investigation reported by Yu et al. is that little decrease in photo-
activity can be found after five subsequent cycling degradation of Rhodamine B
over NaBiO3 and the corresponding XRD peaks of NaBiO3 were detectable after
recycling. Similar conclusions were made by Yu et al. as well [].
But unfortunately, the instability of NaBiO3·nH2O under long time exposure
ZDVIRXQGE\(EHUO>43]. It was found that the color of NaBiO3 gradually changes
from yellow to brown as the time of the photocatalytic reaction was extended. XRD
results showed that after a long time (about 20 h) of photocatalytic reaction,
NaBiO3·nH2O was transformed into (BiO)2CO3 crystal finally. Moreover,
6HSXOYHGD*X]PDQHWDO·VVWXG\DOVRVKRZHGWKHSRRUVWDELOLW\RI1D%L23 under
HOHFWURQ EHDP H[SRVXUH 6HOHFWHG $UHD (OHFWURQ 'LIIUDFWLRQ 6$(' UHVXOWV
showed that NaBiO3 can be partially reduced to metallic Bismuth particles under
electron beam irradiation [75].
(EHUO·VLQYHVWLJDWLRQ>43] on the photostability of NaxBiO3 under light exposure
showed that the problem of poor stability of this photocatalyst still exists. It was
found that the mineralization rate of 4-Chlorophenol was close to 0 after photoreac-
WLRQF\FOHGPRUHWKDQKDQGα-Bi2O3 was thought as a possible corrosion product
by XRD analysis.
Our previous study [74] also clearly suggested that NaBiO3 crystal was extremely
unstable under acid conditions in photocatalysis. Different degrees of NaBiO3 cor-
rosion in 4-t-Octylphenol solution (target contaminant) containing hydrogen chlo-
ride were found under visible light irradiation. XRD results showed that after 1 h
photocatalytic reaction, NaBiO3 crystal was corroded into compounds including
Bi3+ such as Bi2O3 when the initial pH is 4.29 and finally was corroded into BiOCl
with tetragonal system structure when the initial pH is around 2.13. Additionally, it
was found by our group that NaBiO3 can react with hydrogen halide aqueous solu-
tion (HCl, HBr, and HI a.q.) very easily at ambient conditions, meanwhile producing
the oxidation product of hydrogen halide were proved to be the corresponding halo-
gen gas (Cl2 and Br2) or solid (I2). Therefore it can be preliminary concluded that
NaBiO3·nH2O should be neglected as a suitable photocatalyst driven by visible light.
The stability of the BaBiO3 in photocatalytic decomposition of acetaldehyde gas
was tested by Tang et al. [23] under exposure to air for 2 months and cycling the
catalytic reaction for 10 times (each time exposure duration of 2 days). It was found
that there is no apparent change in its photocatalytic activity and the bulk crystal
structure and optical absorption, indicating the excellent photostability of as-
prepared BaBiO3 in photocatalysis from air. However, they found that such complex
oxide material exhibits far better stability in organic solvent compared with that in
aqueous solution.
15 Bismuth(V)-Containing Semiconductor Compounds and Applications…

370
15.7 Future Directions and Prospectus
Although so far, there are a lot of research reports about Bi(V)-containing photo-
catalysts, some basic scientific problems, especially the basic structure-activity role
of Bi(V) in the photocatalyst, still remains to be studied deeply by means of in-
depth experiments and theories. According to the previous literature reports, most
Bi(V)-containing photocatalysts have better photocatalytic activity in visible light,
but the instability of this kind of catalysts in the photocatalytic process greatly hin-
ders the long-term practical applications. Therefore restraining the chemical insta-
bility of the catalyst in water environment and photocatalytic reaction, while making
IXOOXVHRIWKHDGYDQWDJHRI%L9IRUHOHFWURQ(%6LQVHPLFRQGXFWRUVZLOOEHDQHZ
problem for researchers in material physics, material chemistry, catalytic chemistry,
and other areas in the coming years.
Acknowledgements 7KH VXSSRUW E\ .LQJ )DKG 8QLYHUVLW\ RI 3HWUROHXP DQG 0LQHUDOV LV
gratefully acknowledged. Xiaofeng Chang likes to extend his thanks to undergraduate students
Mr. Qi Su and Ms. Yaling Chen (from College of Materials Science and Technology, Nanjing
University of Aeronautics and Astronautics) for their help in manuscript preparation.
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WKH KLJKWHPSHUDWXUH VXSHUFRQGXFWRU %D3E1-xBixO3 5XVV - *HQ &KHP 71, 1010–1012
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GH+DLU7:%ODVVH*'HWHUPLQDWLRQRIWKHYDOHQF\VWDWHRIELVPXWKLQ%D%L23 by infrared
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5DPDFKDQGUDQ 5 6DWKL\D 0 5DPHVKD . 3UDNDVK $6 0DGUDV * 6KXNOD $.
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%ODVVH * 2Q WKHVWUXFWXUHRIVRPH FRPSRXQGV /L3Me5+O4, and some other mixed metal
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*UHDYHV & .DWLE 60$ 7KH VWUXFWXUHV RI /L5BiO5 and Li5SbO5 from powder neutron
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15 Bismuth(V)-Containing Semiconductor Compounds and Applications…

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6KHHWV:&6WDPSOHU(6.DEERXU+%HUWRQL0,&DULR/0DVRQ720DUNV7-
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degradation of rhodamine B over NaBiO3SDWKZD\VDQGPHFKDQLVP-3K\V&KHP$113,
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