Fabrication of YxBi1-xVO4 solid solutions for efficient C2H4 photodegradation

Article abstract of DOI:10.1039/c4ta05872k

Photocatalytic oxidation of ethylene continues to be a challenge at the frontier of chemistry. Previous investigations have shown that BiVO₄ possesses strong photo-oxidative properties which can efficiently oxidize water and decompose organics in aqueous solutions; however, its conduction band minimum is too low to utilize the photo-generated electrons. Herein we report for the first time its effects on gaseous C₂H₄ photo-oxidation by fabricating Y_xBi_1-xVO₄ (x = 0.00-1.00) semiconductors with a polymeric method. Phase analysis identified that there are both a region of monoclinic and tetragonal phase coexistence (0.05 ≤ x ≤ 0.45) and a solid solution region (0.5 ≤ x ≤ 1.0). UV-visible diffusive reflectance spectra and Mott-Schottky analysis revealed that the incorporation of Y³⁺ widened the band gap by shifting upward the conduction band minimum as well as shifting downward the valance band maximum. Remarkable C₂H₄ photodegradation was obtained upon the Y_0.85Bi_0.15VO₄ photocatalyst and its superior performance is ascribed to the synergistic effect of C₂H₄ adsorption, active oxygen species O₂^- utilization, and relatively large surface area. The present study will be valuable for further investigation on both BiVO₄ and hydrocarbons (HC) degradation. This journal is

Full text of DOI:10.1039/c4ta05872k

Showcasing the work on band gap engineering of YxBi1-xVO4
solid solutions for efficient C2H4 photodegradation presented
by Ms. Peiqing Long and Prof. Zhiguo Yi, Fujian Institute of
Research on the Structure of Matter, Chinese Academy of
Sciences.
As featured in:
Title: Fabrication of YxBi1−xVO4 solid solutions for efficient
C2H4 photodegradation
C2H4 photo-oxidation upon YxBi1-xVO4 solid solutions with
tunable band edge positions. The introduction of yttrium
up-shifts the conduction band minimum of BiVO4, which
results in activation of oxygen molecules and thereby
boosts the photodegradation of ethylene.
See Zhiguo Yi et al.,
J. Mater. Chem. A, 2015, 3, 4163.
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Fabrication of YxBi1ꢀxVO4 solid solutions for
efficient C2H4 photodegradation†
Cite this: J. Mater. Chem. A, 2015, 3,
4163
*
Peiqing Long, Yaohong Zhang, Xuxing Chen and Zhiguo Yi
Photocatalytic oxidation of ethylene continues to be a challenge at the frontier of chemistry. Previous
investigations have shown that BiVO4 possesses strong photo-oxidative properties which can efficiently
oxidize water and decompose organics in aqueous solutions; however, its conduction band minimum is
too low to utilize the photo-generated electrons. Herein we report for the first time its effects on
gaseous C2H4 photo-oxidation by fabricating YxBi1ꢀxVO4 (x ¼ 0.00–1.00) semiconductors with a
polymeric method. Phase analysis identified that there are both a region of monoclinic and tetragonal
phase coexistence (0.05 # x # 0.45) and a solid solution region (0.5 # x # 1.0). UV-visible diffusive
reflectance spectra and Mott–Schottky analysis revealed that the incorporation of Y3+ widened the band
gap by shifting upward the conduction band minimum as well as shifting downward the valance band
maximum. Remarkable C2H4 photodegradation was obtained upon the Y0.85Bi0.15VO4 photocatalyst and
its superior performance is ascribed to the synergistic effect of C2H4 adsorption, active oxygen species
Received 31st October 2014
Accepted 8th December 2014
DOI: 10.1039/c4ta05872k
ꢀ
cO2 utilization, and relatively large surface area. The present study will be valuable for further
www.rsc.org/MaterialsA
investigation on both BiVO4 and hydrocarbons (HC) degradation.
last ten or more years.7–11 Compared with traditional treatments
such as activated carbon adsorption, micro-biological degra-
1. Introduction
dation and thermocatalysis, photocatalytic degradation has
several advantages, including low cost, the fact that it is envi-
ronmentally friendly and no waste disposal problem. The y in
the ointment is the development of highly active photocatalysts
for ethylene photo-oxidation remains a challenging task.12–18
AVO4 (A ¼ Bi, Y, etc.) compounds are a series of promising
photocatalysts and have received intensive research because of
their high efficiency in solar-driven water splitting as well as in
liquid-phase photo-degradation.19–23 As a visible light sensitive
photocatalyst, BiVO4 has three main crystalline phases: a zircon
structure type with tetragonal symmetry (z–t), and scheelite
structure types with monoclinic (s–m) and tetragonal (s–t)
symmetry, respectively.20 Among these the scheelite structure
BiVO4 with monoclinic symmetry has the highest photooxida-
tive activity, although its conduction band minimum is too low
to utilize the photo-generated electrons. YVO4 has a zircon
structure type with tetragonal symmetry (z–t) and shows high
UV light activity for solar driven water splitting.22,24 Making Yx-
Bi1ꢀxVO4 composites helps to engineer the band structures and
thus improves solar energy utilization efficiency in both solar
driven O2 and H2 generation reactions.22,25 However, the effect
of these semiconductors on C2H4 photodegradation is still
uncertain in light of the strong C–H bond energy as well as the
non-polar feature of ethylene molecule.
Ethylene (C2H4) is a gaseous volatile organic compound (VOC)
which has great inuence on both plant growth and the storage
of fresh produce.1,2 Ethylene released from natural sources,
fruits, vegetables and automotive exhausts can accelerate aging
and spoiling of plants. Even small amounts of C2H4 gas in the
atmosphere in a storage facility can induce undesirable reac-
tions in most fresh products, such as development of senes-
cence, bitter avors, chlorophyll loss, disease susceptibility and
physiological disorders. Consequently, the removal of trace
amounts of ethylene is imperative.
In light of the high bond energy of the C–H bond, strong
oxidizing chemicals, such as potassium permanganate and
ozone, and biological lters involving microorganisms, such as
bacteria and fungi, have been applied for the removal of
ethylene.3–6 However, undesirable byproducts, high production
costs and inefficiency in removing trace amounts of ethylene
were drawbacks of these methods. Taking into account the very
restrictive storage conditions for fresh products, photocatalytic
oxidation at ambient temperature appears to be a promising
alternative and has attracted considerable attention over the
Key Laboratory of Design and Assembly of Functional Nanostructures, Fujian Institute
of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou 350002,
China. E-mail: zhiguo@irsm.ac.cn
For photocatalytic degradation of orgaꢀnic pollutants,
† Electronic supplementary information (ESI) available: XRD patterns, SEM
images, Tauc plots, Mott–Schottky analysis, C2H4 degradation kinetics, ow
mode degradation of C2H4, and photocatalytic degradation of RhB. See DOI:
10.1039/c4ta05872k
the generation of the active oxygen species cO2 and cOH radi-
cals is
a
fundamentally important step.26,27 Developing
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semiconductors with a conduction band minimum higher than temperature using a Scan UV-vis-NIR spectrophotometer (Per-
the potential of O2/cO2ꢀ and valence band maximum lower than kinElmer Lambda 900) equipped with an integrating sphere
the cOH/OHꢀ potential may fulll the requirements of highly assembly using BaSO4 as a reectance sample. The surface
active photocatalysts for organic pollutant degradation. In this areas of the samples were measured by a TriStar II 3020-BET/
paper, we report the structural characteristics of a series of solid BJH Surface Area analyzer. In situ FTIR studies were performed
solutions of YxBi1ꢀxVO4 fabricated by a polymeric method and on the spectrometer Nexus FT-IR (Thermo Nicolet) by using a
their band edge potentials and ethylene photo-degradation diffuse reectance attachment equipped with
a reaction
activities.
chamber. 128 single beam spectra had been co-added at a
resolution of 4 cmꢀ1 and the spectra were presented as a
Kubelka–Munk function referred to adequate background
spectra. The background and sample spectra were taken (the
average of accumulated 32 scans) over the frequency range
2. Experimental section
2.1 Materials
4000–600 cmꢀ1
.
High purity chemicals bismuth(III) nitrate pentahydrate
(Bi(NO3)3$5H2O, 99.0%), ammonium metavanadate (NH4VO3,
99.0%), yttrium(III) nitrate hexahydrate (Y(NO3)3$6H2O, 99.0%),
sodium sulfate (Na2SO4, 99.0%), acetic acid (99.5%), acetylace-
tone (99.0%) and hexamethylene tetramine (HMTA, 99.0%)
were purchased from Sinopharm and used as received without
further purication.
2.5 Electrochemical measurements
The Mott–Schottky curves were measured by using an electro-
chemical workstation (CHI 660D, CH Instruments, Inc.). The
prepared lm electrodes were used as the working electrode,
with a platinum wire as the counter electrode and an Ag/AgCl
electrode as the reference electrode. The electrolyte was 0.5 M
Na2SO4 aqueous solution (pH ¼ 6.5), and the frequency was 1
kHz with a 5 mV AC (alternating current) amplitude.
2.2 Synthesis of YxBi1ꢀxVO4 powder photocatalysts
The YxBi1ꢀxVO4 (x
¼
0.00–1.00) powder photocatalysts
were prepared by a polymeric method.33 First, 5x mmol
Bi(NO3)3$5H2O and 5(1 ꢀ x) mmol Y(NO3)3$6H2O were dis-
solved in 50 mL deionized water, respectively, and then mixed
under constant stirring. The pH value of the solution was
adjusted to ꢁ2.0 by adding acetic acid drop by drop. Aer
stirring for 10 minutes, this solution was mixed with 50 mL
NH4VO3 (0.1 mol Lꢀ1). When a transparent solution of the
2.6 Photocatalytic degradation of C2H4
The photocatalytic oxidation of C2H4 was carried out in a Pyrex
reactor of 450 mL capacity. In a typical reaction, 0.15 g photo-
catalyst was dispersed uniformly on the bottom of the reactor,
the reactor was irradiated using a 300 W Xe lamp (the Xe lamp
spectrum is provided in Fig. S1†) from the upper part with a
light intensity of ꢁ240 mW cmꢀ2. The reactor was ushed with
N2 repeatedly in order to remove water and CO2 that adsorbed
on the catalyst and the inner wall of the reactor, and then 5 mL
O2 and 90 mL C2H4, respectively, were injected into the reactor
by micro-syringes. Prior to irradiation, the system was protected
from light for 2 h to reach an adsorption–desorption equilib-
rium of C2H4 on the photocatalyst. At certain time intervals, 4
mL gas was extracted from the reactor and the amount and type
of gases were analyzed by gas chromatography (GC9720 Fuli,
six-way valve gas sampler, and a ame ionization detector, a HP-
Plot/U capillary column, N2 as the carrier gas, and a thermal
conductivity detector, a molecular sieve 13ꢃ column, He as the
carrier gas).
mixed metal salts was obtained, 1 mL acetylacetone (1 mol Lꢀ1
)
and 2 mL HTMA (1 mol Lꢀ1) were added to adjust the subse-
quent polymeric process. The resulting solution was then
heated to reux for 1.5 hours under constant stirring. Aer that,
part of the viscous solution was dried in an oven at 100 ꢂC and
ꢂ
then treated at 550 C in atmospheric air for 3 hours.
2.3 Fabrication of YxBi1ꢀxVO4 thin lm electrodes
The rest of the viscous solution was used for thin-lm electrode
fabrication with a spin coating method. An FTO glass substrate
(15 U sqꢀ1) and the coating parameter (2000 rpm, 30 s) were
employed. The coated lms were further treated at 500 ꢂC
in atmospheric air for 30 minutes. The spin coating and the
calcinations were repeated 18 times. The thickness of
the resultant lms observed by scanning electron
microscopy (SEM) was about 530 nm. The active area of
YxBi1ꢀxVO4/FTO lms for the electrochemical measurement
was 1.5 cm ꢃ 1.5 cm ¼ 2.25 cm2.
3. Results and discussion
3.1 Structure and morphology of YxBi1ꢀxVO4 photocatalysts
Fig. 1 shows the XRD patterns of YxBi1ꢀxVO4 powder samples at
room temperature. Therein the patterns of the starting sample
BiVO4 are in full accord with a monoclinic scheelite structure
2.4 Physical characterization
Phase identication of the samples was determined by a Rigaku type.20 With the increase of Y3+ content, two additional peaks at
Miniex II X-ray diffractometer (XRD) with Cu Ka radiation 24.8ꢂ and 33.3ꢂ emerged (x ¼ 0.05) and became increasingly
(l ¼ 0.154178 nm). The morphology and microstructure of the stronger (x $ 0.10), whereas the peaks of the monoclinic
samples examined by scanning electron microscopy (SEM, JSM- scheelite structure type faded (x # 0.45) (see also Fig. S2†). The
6700F), transmission electron microscopy (TEM), and high- two additional peaks are identied, respectively, as the
resolution TEM (HRTEM) were taken on a JEM-2010. The UV-vis diffraction patterns of the (200) and (112) planes of the tetrag-
diffusive reection spectra (DRS) were collected at room onal zircon structure type28 of the end member sample YVO4.
4164 | J. Mater. Chem. A, 2015, 3, 4163–4169
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XRD patterns of the samples x # 0.10 were rened with
monoclinic symmetry, and the patterns of the samples 0.1 # x
# 0.35 were rened with both monoclinic and tetragonal
symmetries and the patterns of the samples x $ 0.40 were
rened with tetragonal symmetry, respectively. That the plots
of the lattice constants (x $ 0.50) fulll Vegard's law30 very well
(see the linear relation between the lattice constants and the x
values in Fig. 2) supported the conclusion that YxBi1ꢀxVO4
were solid solutions of tetragonal zircon structure type,
instead of the monoclinic scheelite structure type. When x #
0.45, the lattice constants obtained from the t of the tetrag-
onal and monoclinic symmetry varied slightly because of the
phases segregation.
The measurement of specic surface areas indicated that the
specic surface areas of the powder samples increase from
0.04 m2 gꢀ1 for BiVO4 and 1.56 m2 gꢀ1 for Y0.25Bi0.75VO4, to
10.46 m2 gꢀ1 for Y0.50Bi0.50VO4, 30.98 m2 gꢀ1 for Y0.85Bi0.15VO4
and 52.05 m2 gꢀ1 for YVO4, respectively, with an increase of Y3+
content.
Fig. 1 XRD patterns of the YxBi1ꢀxVO4 (0 # x # 1) powders collected at
room temperature.
Morphologies of the as-prepared YxBi1ꢀxVO4 powder
samples were observed using SEM (Fig. S3a–f†). The BiVO4
powder shows irregular sphere-like particles with a diameter
of 1–2 mm (Fig. S3a†). With the increase of Y3+ content, the
particle size reduced signicantly from less than 1 mm for
These phenomena indicated that there are both a region of
monoclinic and tetragonal phase coexistence (0.05 # x # 0.45)
and a solid solution region (0.5 # x # 1.0) in the YxBi1ꢀxVO4
materials. Notably, the 2q angles of crystalline planes of the
YVO4 are larger than the standard patterns of bulk YVO4, which
can be explained by the lattice contraction that results from the
additional pressure caused by the surface tension between the
nano YVO4 particles (Fig. S3e and f†) and the ambient atmo-
sphere.29 The smaller the crystallite size, the more intense the
incurred additional pressure and the larger the resulting lattice
contraction.
Y
0.25Bi0.75VO4 (Fig. S3b†) to less than 100 nm for Y0.85Bi0.15VO4
(Fig. S3c and d†) and YVO4 (Fig. S3e and f†), both showing
heavily aggregated states. TEM observations further conrmed
ne particles size distribution of the yttrium rich samples, as
the example of Y0.85Bi0.15VO4 shown in Fig. 3. Elemental
mapping analysis (Fig. S4 and S5†) indicated that the elements
Bi, Y, V and O have a uniform distribution throughout the
whole structures.
Fig. 2 shows a further analysis of lattice parameters of the
as prepared YxBi1ꢀxVO4 samples using program JADE 7.0. The
3.2 Mapping of band gaps as well as redox potentials of
YxBi1ꢀxVO4 photocatalysts
Fig. 4 shows UV-visible diffusive reectance spectra of the
YxBi1ꢀxVO4 powder photocatalysts. A sharp basal absorption
edge located at ꢁ500 nm is in good consistency with the
previous reports of monoclinic BiVO4.20 For the monoclinic
phase rich YxBi1ꢀxVO4 (0 # x # 0.35) samples, there is only a
slight shi for the absorption edge and the two-stage absorption
feature agrees well with the fact of two-phase coexistence. For
the tetragonal phase solid solution samples (x $ 0.50), the
absorption edge shied gradually toward a shorter wavelength
range because of weakening hybridization22,24 between Bi 6s and
O 2p orbitals with the increase of Y3+ content.
By using the Tauc equation,31 band gaps of the YxBi1ꢀxVO4
powder photocatalysts were calculated (Fig. S6†) and are shown
in Fig. 5. The smaller change of band gap of the monoclinic
scheelite phase and the gradually increased band gap of the
tetragonal zircon phase indicated that the band structure of the
tetragonal zircon phase is easier to regulate with increasing Y3+
content. The Mott–Schottky experiments introduced in the
following part indicated that both the negative shi of the
conduction band and the positive shi of the valance band with
Fig. 2 Lattice parameters of the YxBi1ꢀxVO4 powder samples.
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Fig. 5 Band gaps of the YxBi1ꢀxVO4 photocatalysts.
where 3 is dielectric constant of the semiconductor, e is electric
charge, 30 is the permittivity of vacuum, A is the surface area of
the semiconductor/electrolyte barrier, ND is the carrier
concentration of the semiconductor, E and EFB are the applied
potential and at-band potential of the sample, respectively,
and k is the Boltzmann constant. The at-band potential, EFB
,
can therefore be obtained from the point of intercept of the Cꢀ2
vs. E plot. The collected Mott–Schottky plots (Fig. S7†) indicated
that all the YxBi1ꢀxVO4 materials are n-type semiconductors.
Assuming that the gap between the conduction band minimum
and the at-band potential is negligible for an n-type semi-
conductor,34 the band edge positions of YxBi1ꢀxVO4 were map-
ped in Fig. 6 where the electrode potentials have been converted
to the reference normal hydrogen electrode (NHE) potential via
the formula:
Fig. 3 TEM images of the as prepared Y0.85Bi0.15VO4 powder.
ERHE ¼ EAg/AgCl + 0.059pH + EꢂAg/AgCl (EꢂAg/AgCl ¼ 0.209 V at
25 ꢂC),34
and the positions of the valance band maximum (EVB) were
determined by EVB ¼ ECB + E (band gap).35 With increasing Y3+
content, the negative shi of ECB as well as the positive shi of
EVB implied that the incorporation of Y3+ weakened the
Fig. 4 UV-visible diffusive reflectance spectra (DRS) of the YxBi1ꢀxVO4
powders.
increasing Y3+ content account for the band gap regulation of
YxBi1ꢀxVO4.
The relative band edge positions of YxBi1ꢀxVO4 were mapped
with Mott–Schottky analysis.32,33 The Mott–Schottky relation-
ship of capacitance (C) vs. applied potential (E) is:
Cꢀ2 ¼ 2(E ꢀ EFB ꢀ kT/e)/(330eNDA2),
Fig. 6 Band edge positions of the YxBi1ꢀxVO4 photocatalysts.
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hybridization of Bi 6s and O 2p orbitals22,24 and thus resulted in minimum of YVO4 is comparable to that of Y0.85Bi0.15VO4, the
the band gap widening of YxBi1ꢀxVO4.
band gap of it is much larger than that of Y0.85Bi0.15VO4 (Fig. 6),
which means less light can be utilized to drive the photoreac-
tions. During the photo-oxidation of C2H4, no other products
except CO2 were detected. That the CO2 yields, especially upon
the samples with x ¼ 0.50 and 0.85, were greater than that
which the C2H4 can generate shows obvious adsorption effects
of CO2 upon the samples.
The kinetics of C2H4 degradation upon the semiconductors
were investigated by applying the Langmuir–Hinshelwood
model.26 The reaction kinetic data for the highest performance
catalyst Y0.85Bi0.15VO4 were well tted with a two-stage linear
tting (Fig. S8†). The apparent rate constant k was 0.22 minꢀ1
for the larger slope line and the k value of the lower slope line
was 7.39 ꢃ 10ꢀ2 minꢀ1. Both were much higher than that of
BiVO4 (7.23 ꢃ 10ꢀ4 minꢀ1) and YVO4 (3 ꢃ 10ꢀ3 minꢀ1). To
determine the turnover number of ethylene photo-oxidation
upon the Y0.85Bi0.15VO4 sample, we further increased the C2H4
concentration during the catalytic reaction (Fig. S9†). Under ten
hours illumination, the turnover number for the ethylene
photo-oxidation was determined to be 3.96, indicating that the
reaction was truly driven by a catalytic process.
3.3 Photocatalytic performance of YxBi1ꢀxVO4
photocatalysts
Fig. 7a and b show, respectively, the time course of C2H4 photo-
degradation and CO2 evolution upon the YxBi1ꢀxVO4 powder
samples. In order to conrm the photocatalysis of the samples,
both the self-degradation of C2H4 as well as the adsorption
effects of C2H4 were measured. The results indicated that there
is no self-degradation effect of C2H4 under either dark or illu-
mination conditions. The YxBi1ꢀxVO4 (x ¼ 1.00 and x < 0.75)
samples showed less activity for C2H4 photo-degradation, and
the high photocatalytic activities of YxBi1ꢀxVO4 (x ¼ 0.75 < x ¼
0.90 < x ¼ 0.85) are partly attributed to their good adsorption
ability for C2H4. That the Y0.85Bi0.15VO4 sample exhibited the
highest activity for C2H4 photo-oxidation can be understood by
taking into account the following factors: rst, the ethylene
adsorption capacity of the Y0.85Bi0.15VO4 is highest among all
the samples. It is known that the adsorption of ethylene is a
prerequisite for its degradation, so a higher adsorption capacity
is benecial for a faster degradation rate. Second, the conduc-
tion band minimum of Y0.85Bi0.15VO4 is more negative than the
YxBi1ꢀxVO4 (x < ꢀ0.85) samples, which would facilitate the
formation of O2 radicals. Although the conduction band
In situ IR analysis was employed to investigate the possible
intermediates generated during the photocatalytic reactions. As
shown in Fig. 8, along with the decrease of the intensity of the
bands assigned to n(C–H) of ethylene, the bands assigned to the
characteristic mode of CO2 at ꢁ2340–2360 cmꢀ1 gradually
Fig. 8 In situ IR spectra of ethylene photo-oxidation upon the
Fig. 7 Time courses of (a) C2H4 degradation and (b) CO2 evolution Y0.85Bi0.15VO4 photocatalysts collected at different simulated sunlight
upon the YxBi1ꢀxVO4 photocatalysts.
illumination times.
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increased and the broad peak of the band at ꢁ3679 cmꢀ1 (which
corresponds to adsorbed water) enhanced aer light illumina-
tion.36 These results indicated that ethylene is oxidized to CO2
and H2O (C2H4 + 3O2 / 2CO2 + 2H2O) during the photocatalytic
reaction. In addition, the newly emerged typical n(C–O) band at
ꢁ1290–1300 cmꢀ1 for epoxy group36 vibration implies inter-
mediate species, such as epoxyethane, may be formed during
the ethylene photo-oxidation.
To investigate the stability of the highest activity photo-
catalyst Y0.85Bi0.15VO4, both cycle C2H4 photo-degradation
(Fig. 9) and ow C2H4 photo-degradation (Fig. S10†) were per-
formed. It was shown that under simulated sun light illumi-
nation, the C2H4 gas can be completely degraded within only 60
min under the cycle test and over 87% of C2H4 gas was degraded
under the ow gas mode. CO2 adsorption upon the photo-
catalyst accounts for the difference of its yield between the cycle
reactions. The ow mode test therefore provided more reliable
CO2 yield data, close to 100% (see Fig. S10†). Raman analysis
was further employed to probe possible structural changes of
the catalysts aer the photocatalytic reactions. Neither a new
Raman mode nor intensity changes of the existing Raman
modes were detected for the sample aer ve cycle reactions
(Fig. S11†), which indicates that the surface structures of the
catalysts are not changed aer the photoreactions.
Catalyst + hv / catalyst (h+) + catalyst (eꢀ)
Catalyst (eꢀ) + O2 / catalyst + cO2
Catalyst (h+) + OHꢀ (H2O) / catalyst + cOH
(1)
(2)
(3)
ꢀ
ꢀ
cO2 + cOH + organics / CO2 + H2O + other products (4)
Herein the generation of the active oxygen species cO2ꢀ and
cOH radicals was taken as a key step for the photodegradation of
organics. In the liquid phase photo-degradation, the catalysts
are surrounded by water and the photo-generated holes with a
strong oxidation power can thereby easily react with water to
generate cOH radicals. In our gas phase C2H4 degradation, cOH
radicals can hardly generate as almost no water is present in the
reaction system. Under such conditions, the generation of
ꢀ
active oxygen species cO2 becomes important. From the rela-
tive band edge positions of the YxBi1ꢀxVO4 semiconductors
shown in Fig. 6 where the redox potentials of O2/cO2ꢀ and cOH/
OHꢀ in aqueous solution42,43 as well as O2/cO2 in the gas
ꢀ
phase44–46 are all labeled schematically for comparison
purposes, we can conclude that the generation of the active
ꢀ
oxygen species cO2 played a more important role in the
gaseous C2H4 photodegradation whereas the generation of cOH
radicals accounted more for the liquid RhB photodegradation.
Liquid phase photodegradation of Rhodamine B (RhB) upon
the YxBi1ꢀxVO4 samples was carried out as well. The results
(Fig. S12†) indicated that the Y0.25Bi0.75VO4 photocatalyst
showed the highest activity instead. Although the photocatalytic
performance of a semiconductor is the result of a synergistic
effect that depends on the morphology, surface area, band gap,
band edge potentials and so on,37–39 the distinctions between
the gas phase photodegradation and the liquid phase photo-
degradation manifested themselves in the processes of
photocatalysis.
4. Conclusions
In summary, we have investigated the structural characteristics,
band edge potentials and C2H4 photodegradation activities of
YxBi1ꢀxVO4 semiconductors. Both the monoclinic and tetrag-
onal phase coexistence region (0.05 # x # 0.45) and the solid
solution region (0.5 # x # 1.0) were identied. With increasing
Y3+ content, the particle size of the samples decreased and the
BET surface increased signicantly. The band gaps and band
edge positions were mapped with careful UV-visible diffusive
reectance spectra and Mott–Schottky analysis. Efficient C2H4
photodegradation was obtained upon Y0.85Bi0.15VO4 photo-
catalysis and its superior performance is ascribed to thꢀe
synergistic effect of C2H4 adsorption, active oxygen species cO2
utilization, and a relatively large surface area. The present study
would be valuable for further investigation on both BiVO4 and
HC degradation.
We know that the following steps are generally involved in
the processes of organics photodegradation, though the
concrete reaction pathway and molecular mechanism still need
to be unraveled:40,41
Acknowledgements
This work was nancially supported by the National Key Project
on Basic Research (Grant no. 2013CB933203), the Natural
Science Foundation of China (Grant no. 21373224), the Natural
Science Foundation of Fujian Province (Grant no. 2012J01242),
the open project program of the State Key Laboratory of High
Performance Ceramics and Microstructures (Grant no.
SKL201202SIC), and the One Hundred Talents Program of the
Chinese Academy of Sciences.
Fig. 9 Stability test of C2H4 photodegradation upon the Y0.85Bi0.15VO4
photocatalyst (square: C2H4; circle: CO2).
4168 | J. Mater. Chem. A, 2015, 3, 4163–4169
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