Separating type I heterojunction of NaBi(MoO4)2/Bi2MoO6 by TiO2 nanofibers for enhanced visible-photocatalysis

Article abstract of DOI:10.1016/j.chemphys.2020.110696

Among tremendous efforts for enhanced photocatalysis, construction of heterojunction has been deemed as an effective means. In comparison with type II heterojunction, type I heterojunction receives less attention due to accumulation and increased recombination of charge carriers in one side of heterojunction. Herein, we take NaBi(MoO₄)₂/Bi₂MoO₆ as an example of type I heterojunction and explore means to improve the photocatalytic performance of NaBi(MoO₄)₂/Bi₂MoO₆ heterojunction. We employ TiO₂ electrospun nanofibers as substrates and separately grow NaBi(MoO₄)₂ and Bi₂MoO₆ nanostructures on the skeleton of TiO₂. The characterization results show that TiO₂ changes type I heterojunction into multiheterojunction integrating two type II heterojunctions. Photocatalytic tests demonstrate that as-constructed multi-heterojunction is of higher activity than that of single type I or II heterojunction, respectively, where photogenerated electrons are accumulated on the surface of TiO₂ and photogenerated holes are accumulated on NaBi(MoO₄)₂ and Bi₂MoO₆, respectively. This study highlights the potential application of TiO₂ electrospun nanofibers in the construction of multiheterojunction for enhanced visible light photocatalysis.

Full text of DOI:10.1016/j.chemphys.2020.110696

Journal Pre-proofs
Separating Type I heterojunction of NaBi(MoO4)2/Bi2MoO6 by TiO2 Nanofibers
for enhanced visible-photocatalysis
Yuejun Li, Tieping Cao, Zemin Mei, Xiaoping Li, Dawei Sun
PII:
S0301-0104(19)31187-5
DOI:
https://doi.org/10.1016/j.chemphys.2020.110696
CHEMPH 110696
Reference:
Chemical Physics
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Revised Date:
Accepted Date:
3 October 2019
23 January 2020
23 January 2020
Please cite this article as: Y. Li, T. Cao, Z. Mei, X. Li, D. Sun, Separating Type I heterojunction of NaBi(MoO4)2/
Bi2MoO6 by TiO2 Nanofibers for enhanced visible-photocatalysis, Chemical Physics (2020), doi: https://doi.org/
10.1016/j.chemphys.2020.110696
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Separating Type I heterojunction of NaBi(MoO4)2/Bi2MoO6 by TiO2
Nanofibers for enhanced visible-photocatalysis
Yuejun Li, Tieping Cao,* Zemin Mei*, Xiaoping Li, Dawei Sun
Baicheng Normal University, Research Centre of nano-photocatalyst, Baicheng, Jilin,
137000
*Corresponding authors: bcctp2008@163.com; bczeminmei@163.com
Abstract:
Among tremendous efforts for enhanced photocatalysis, construction of
heterojunction has been deemed as an effective means. In comparison with type II
heterojunction, type I heterojunction receives less attention due to accumulation and
increased recombination of charge carriers in one side of heterojunction. Herein, we
take NaBi(MoO4)2/Bi2MoO6 as an example of type I heterojunction and explore
means to improve the photocatalytic performance of NaBi(MoO4)2/Bi2MoO6
heterojunction. We employ TiO2 electronspun nanofibers as substrates and separately
grow NaBi(MoO4)2 and Bi2MoO6 nanostructures on the skeleton of TiO2. The
characterization results show that TiO2 changes type I heterojunction into
multiheterojunction integrating two type II heterojunctions. Photocatalytic tests
demonstrate that as-constructed multi-heterojunction is of higher activity than that of
single type I or II heterojunction, respectively, where photogenerated electrons are
accumulated on the surface of TiO2 and photogenerated holes are accumulated on
NaBi(MoO4)2 and Bi2MoO6, respectively. This study highlights the potential
application of TiO2 electronspun nanofibers in the construction of multiheterojunction
for enhanced visible light photocatalysis.
Key words ： TiO2 nanofibers; type I, type II, multi-heterojunction, photocatalytic,
visible light
1. Introduction:
Heterojunction photocatalysis has been attracting increasing attention due to the
promoted charge separation, extended light absorption and boosted surface
reaction.[1-4] Therein, multiheterojunction is a more promising candidate of
photocatalyst than single heterojunction towards application in environment
purification and energy conversion[5,6]. It provides more choices for extended optical
absorption and promoted charge separation and hence enhanced photocatalytic
1

activity. In traditional photocatalyst, Staggered heterojunction[7, 8] has displayed its
advantage in inhibition of charge recombination, and whereas straddling
heterojunction is somehow inefficient for charge separation due to the growing charge
recombination in one side of heterojunction[9-11]. However, in the construction of
multiheterojunction, the type of heterojunction should be reconsidered because of the
increased contact interface between different components. With this regard, not only
components across type II but also type I heterojunction may be reactivated when
they meet another component in multi-component composites. Therefore, it deserves
particular attention on the re-assembly of multiheterojunction on the basis of type I
heterojunction.
Recent studies have witnessed that TiO2 electrospun nanofibers can serve as a
good substrate to build heterojunction due to their high surface area, large porosity
[13]
and interwoven architectures.[12] Many heterojunctions, such as TiO2/SnO2
TiO2/SrTiO3[14], TiO2/CeO2[15], TiO2/In2S3[16], TiO2/ZnO[17], TiO2/WO3/g-C3N4
,
,
[18]
BiVO4/TiO2[19], BiOBr/TiO2[20]and etc, have been built based on TiO2 electrospun
nanofibers and display higher photocatalytic activity due to promoted charge
separation by type II heterojunction as well as better ability of charge transfer along
one-dimensional nanofibers. Moreover, the potential of conduction band of TiO2
facilitates reduction of oxygen and the potential of valance band of TiO2 is more
positive than other visible light induced photocatalyst. Therefore, TiO2 is more
promising in formation of type II heterojunction with other visible light induced
photocatalyst and help transfer of electrons from other visible light induced
photocatalyst.
Besides, bismuth based compounds emerge as promising visible light induced
photocatalyst because of significant light absorption in the visible region and naturally
good charge separation by interlayer-built electric field[21-24]. In this study, we aim at
fabricating multiheterojunction from NaBi(MoO4)2, Bi2MoO6 and TiO2, respectively.
According to the position of energy band, NaBi(MoO4)2 and Bi2MoO6 form type I
heterojunction. However, when they grow on the surface of TiO2 nanofibers,
NaBi(MoO4)2/TiO2/Bi2MoO6
multiheterojunction
is
formed
instead
of
NaBi(MoO4)2/Bi2MoO6 heterojunction. Different from previous type I heterojunction,
2

multi-heterojunction is composed of two type II heterojunctions. Moreover,
NaBi(MoO4)2 and Bi2MoO6 can be evenly distributed on TiO2, which is beneficial for
charge transfer. Photocatalytic tests show that as-obtained dispersed
multiheterojunction is superior to single heterojunction, and the reason for the
enhanced activity will be discussed in detail.
2. Experimental Section
2.1 Reagents
Polyvinylpyrrolidone (PVP, Ms = 1300000) was purchased from Aladdin
Reagent Co., LTD. Butyl titanate, bismuth nitrate and ammonium molybdate are
purchased from National Medicine Group Chemical Reagent Co., LTD. Ethylene
glycol (EG), anhydrous ethanol and glacial acetic acid are purchased from Beijing
Chemical Factory; Ethylenediamine tetraacetic acid disodium salt (EDTA) was
purchased from Shanghai Research Industrial co., LTD.; All reagents are analytically
pure. Double distilled water was used in all experiments.
2.2 Preparation of multiheterojunction
TiO2
nanofibers
were
fabricated
as
reported
previously[25].
NaBi(MoO4)2/TiO2/Bi2MoO6 multiheterojunction was fabricated as following: 0.1769
g of (NH4)6Mo7O24·4H2O was dissolved in a 10 mL mixture of H2O and ethanol
(VH2O/Vethanol=1:1). 0.485g Bi(NO3)3·5H2O was dissolved in 20 mL of ethylene
glycol. Then the solution of (NH4)6Mo7O24·4H2O and Bi(NO3)3·5H2O was mixed and
stirred. During stirring, 5 mL of 0.2 M EDTA was added to the mixture. The pH of
the solution was adjusted to 10 by 1 M NaOH solution. After stirring for 30 mins, the
mixture was transferred to 50 mL autoclave. Meanwhile, 0.01 g TiO2 nanofibers were
immersed in the mixture. After sealing the autoclave, the autoclave was heated at 180
oC for 24 h. After cooling to room temperature, the product obtained in the autoclave
was rinsed with ethanol and water for several times, dried at 60 oC for 12 h and finally
obtained the colored nanofibers mat. For comparison, single heterojunction such as
NaBi(MoO4)2/TiO2 and TiO2/Bi2MoO6 was fabricated by simply changing the
ethanol/water mixed solvent to pure water and ethanol, respectively. Last,
NaBi(MoO4)2/Bi2MoO6
heterojunction
was
fabricated
as
that
for
NaBi(MoO4)2/TiO2/Bi2MoO6 multiheterojunction, the only change is no addition of
TiO2 nanofibers.
3

2.3 Characterization
X-ray diffraction (XRD) pattern was acquired at X'Pert3 powder instrument, Cu
Kα target（λ=0.154056nm）was equipped, pipe current and voltage was set at 40 mA
and 40 kV, respectively. Morphologies of samples were observed on Hitachi SU8010
scanning electron microscope (SEM). Growth and distribution of bismuth molydbate
on TiO2 nanofibers was observed on JEOL-JSM 2010 transmission electron
microscope (TEM). X-ray photoelectron spectroscopy (XPS) was collected on
PHI-5000 VersaProbe. UV-Vis-DRS spectra was collected on LAMBDA35.
Fluoresce spectra was obtained on Hitachi F-4500.
2.4 Photocatalytic test
The photocatalytic activity was evaluated by degradation of gaseous
acetaldehyde under visible light (λ ≥ 420 nm) with a 150 W Xe lamp. The light
intensity in the region of 420 nm to 800 nm was adjusted to 100 mW/cm2. The light
was irradiated from the top of the reactor. 0.1 g of photocatalyst was put in a 500 mL
reactor, then the reactor was fully filled with mixed gas of 20% O2/80% N2. Then, the
reactor was injected into gaseous acetaldehyde and the concentration of acetaldehyde
in the reactor was adjusted to 200 ppm. After irradiation for every 10 mins, the
concentration of acetaldehyde and CO2 was monitored by GC.
3. Results and discussion
Fig. 1. XRD patterns of different samples
4

Phase composition of single heterojunction as well as multiheterojunction were
detected by XRD. As shown in Fig. 1, TiO2 nanofibers are composed of mixed
anatase and rutile phases, which agrees our previous works. For sample BMT, the
pattern shows other 12 peaks in addition to TiO2 can be detected. These additional
peaks are in coincidence with orthogonal Bi2MoO6 (JCPDS card No. 72-1524). This
indicates that Bi2MoO6 can be obtained in the presence of ethanol as cosolvent in the
solvothermal reaction. For sample NBMT, the pattern shows other 9 peaks in addition
to TiO2 can be detected. These additional peaks are in coincidence with tetragonal
NaBi(MoO4)2 (JCPDS card No. 51-1508). This indicates that NaBi(MoO4)2 can be
obtained in the presence of water as cosolvent in the solvothermal reaction. For
sample NBMTBM, we can observe three sets of peaks corresponding to NBM, BM
and TiO2, respectively. In comparison with above three samples, we can conclude that
the as-adopted synthesis route in the presence of water/ethanol as cosolvent can
successfully produce mixture of NBM, BM and TiO2.
a
b
500nm
500nm
c
d
500nm
500nm
Fig. 2 SEM images of different samples: a, TiO2; b, NBMT; c, BMT; d,
NBMTBM
The morphology of different heterojunctions was observed by SEM. As shown in
Fig.2a, the pure TiO2 sample exhibits morphology of nanofibers, demonstrating
electrospinning technique is a powerful for producing nanofibers mat with either
organic or inorganic component. For sample NBMT, nanorods are evenly grown on
the surface of TiO2 nanofibers, indicating the formation of nanorods-nanofibers
heterojunction. The nanorods are of ca. 10 nm in diameter and ca. 30 nm in length. In
5

combination with above XRD results, it is deduced that the nanorods are composed of
NaBi(MoO4)2 phase. Similarly, for sample BMT, nanosheets are evenly distributed on
TiO2 nanofibers. The nanosheets are of ca.10 nm in thickness and ca. 30 nm in width.
The nanosheets are deduced to be composed of Bi2MoO6 phase. For sample
NBMTBM, morphologies including nanofibers, nanorods and nanosheets can be
simultaneously observed. Moreover, nanorods and nanosheets are uniformly grown
and distributed along the nanofibers. In combination with its XRD pattern and
morphology observation on single heterojunction, it is concluded that
multiheterojunction integrating TiO2, NaBi(MoO4)2 and Bi2MoO6 is fabricated. This
implies that NaBi(MoO4)2 and Bi2MoO6 can be separately or simultaneously grown
on TiO2 nanofibers, which provides a very feasible means to study
multiheterojunction and refer to that of single heterojunction. More importantly, the
control over the growth component can be realized by simple tuning the cosolvent
(ethanol or water or ethanol/water) in the precursor solution, which is easy for
experimental replication and drawing reliable conclusions.
a
b
(111)
0.31nm
0.35nm
TiO2
(101)
NaBi(MoO4)2
500 nm
5 nm
c
d
(101)
TiO2
0.35nm
0.32nm
(131)
Bi2MoO6
500 nm
5 nm
Fig. 3. TEM images of (a) NBMT and (c) BMT; HRTEM images of
(b) NBMT and (d) BMT
To have a further confirmation of formation of heterojunction, TEM and
HRTEM were performed and the images are shown in Fig. 3. As shown by TEM in
Fig. 3a, nanorods are deeply rooted in the skeleton of nanofibers. HRTEM in Fig. 3b
6

clearly shows the interface between nanorods and nanofibers. Lattice distances of
0.35 nm in the region of nanofibers stem can be ascribed to (101) facet of anatase
TiO2. Meanwhile, lattice distances of 0.31 nm can be ascribed to (111) facet of
NaBi(MoO4)2. These observations can safely prove the formation of NBMT
heterojunction. Similarly, for BMT shown in Fig. 3c, nanosheets can be vertically
rooted into the skeleton of nanofibers. HRTEM image in Fig. 3d show a lattice
distances of 0.32 nm corresponding to (131) facet of BM, proving the formation of
BMT heterojunction. The distribution of NBM and BM can also be evaluated by
EDS. As can be seen in Fig. S1, elements of Na, Bi, Mo and O are evenly distributed
without aggregation and in well accordance with the morphology of nanorods.
Accordingly, it can be again concluded that the as-adopted synthesis route can
selectively grow secondary NBM or BM on the surface and hence form
heterojunction.
Fig. 4 (a): XPS Survey spectra of different samples; High resolution XPS spectra of
(b): Bi4f ; (c): Mo3d ; (d): Ti2p ; (e): O1s ; (f): Na1s
The surface element composition and valence state of samples NBMT and BMT
were analyzed by XPS, and the results are shown in Fig. 4. As can seen in Fig. 4a,
NBMT and BMT are composed of Na, Bi, Mo, C, Ti, O and Bi, Mo, C, Ti, O
elements, respectively, where the binding energy is 283.18 eV. The C1s peak is
derived from the standard measurement method of the instrument and is corrected.
7

The other elemental compositions are in good agreement with the XRD and EDS
analysis results. Figures 4b-4f are the XPS high resolution spectra of Bi4f, Mo3d,
Ti2p, O1s and Na1s in the samples tested. Fig. 4b shows that Bi4f of sample NBMT
exhibits two asymmetric peaks at binding energies of 159.0 eV and 164.4 eV,
corresponding to Bi 4f7/2 and Bi 4f5/2, respectively, indicating that Bi is predominantly
present in Bi3+ form in the NBMT sample. The Bi4f photoelectron peak of sample
BMT is more complicated. After the peak deconvolution, in addition to the two
asymmetric peaks at 159.0 eV and 164.4 eV, two photoelectrons belonging to Bi5+
appear at 159.7 eV and 165.0 eV. The peak indicates that the Bi species of the BMT
sample exist in both Bi3+ and Bi5+ forms. According to the principle of electrical
neutrality, it can be speculated that oxygen vacancies exist in the BMT sample[26],
which will be beneficial to the improvement of photocatalytic activity of the sample.
As shown in Fig. 4c, the Mo3d of the two samples showed the same symmetric
photoelectron peak at 232.5 eV and 235.6 eV, corresponding to Mo3d5/2 and Mo3d3/2,
respectively, meaning that the Mo species in both samples were in the form of
Mo6+[27]. Fig. 4d shows the XPS spectrum of Ti2p. Two photoelectron peaks of
Ti2p1/2 and Ti2p3/2 appear at the binding energy of 464.4 eV and 458.6 eV in both
samples, and the peak positions are basically the same[28]. Fig. 4e is an XPS high
resolution spectrum of O1s in both samples. The photoelectron peak at a higher
binding energy of 531.7 eV is attributed to surface chemisorbed oxygen (Oα), while
the photoelectron peak at a lower binding energy of 529.7 eV is attributed to the
material lattice oxygen (Oβ) [29]. As shown in Fig. 4f, the sample NBMT showed a
Na1s photoelectron peak at 1072.3 eV[30].
Fig. 5a shows the UV-Vis-DRS spectra of different samples. The growth of
NBM can extend the absorption of TiO2 from UV to visible region as long as 500 nm.
As reported previously, NaBi(MoO4)2 is of yellow color and its band gap falls with
2.9 eV[31]. Herein, the red shift of absorption for NBMT in comparison with that of
pure TiO2 results from the narrower band gap of NaBi(MoO4)2. For BMT
heterojunction, the absorption can be extended to 600 nm, which is believed to be
induced by the compositing TiO2 with BM[32,33]. The more significant red shift over
BMT than NBMT is due to a smaller band gap of BM than that of NBM. As for the
NBMTBM multiheterojunction, the absorption is extended to 550 nm, which is a
synergistic effect of NBM and BM. In general, the fabrication of heterojunction can
8

effectively bring visible light absorption to TiO2, which is essential for endowing
photocatalytic activity under visible light.
Fig. 5. (a) UV-vis spectra of different samples; (b) PL spectra of different samples.
Fig. 5b shows the PL of different samples. The PL intensity follows an order:
NBMTBM < BMT < NBMT. It can be deduced that formation of BMT and NBMT
heterojunction can inhibit the charge recombination in TiO2. Moreover, BMT gives a
stronger ability for promoting charge separation than that of NBMT, which may be
related to the difference of matched degree of energy band position. Furthermore, in
comparison with single heterojunction, NBMTBM multiheterojunction shows the
lowest PL intensity, indicating the strongest ability for promoting charge separation
among all heterojunctions. This also implies that NBMTBM multiheterojunction is a
more promising candidate for photocatalysis under visible light.
Fig. 6. Times curves of (a) photocatalytic degradation of gaseous acetaldehyde
and (b) CO2 evolution over different samples.
9

Fig. 6 shows the photocatalytic test results of acetaldehyde degradation over
different samples. As can be observed, no activity can be observed in dark (curves
magnified in Fig. 6, inset) over all samples. Meanwhile, the decrease of acetaldehyde
and CO2 evolution can be hardly detected over pure TiO2, suggesting TiO2 is inactive
for degradation of acetaldehyde under visible light irradiation. Other three
heterojunctions display activity under visible light, the activity follows an order:
NBMTBM > BMT > NBMT. Notably, sample NBMTBM gives the highest activity.
There is no change of morphology and crystal phase after photocatalytic test (shown
in Fig. S1). Since the activity order is consistent with above PL analysis, it is believed
that the superior performance of NBMTBM originates from its best performance for
charge separation. In other words, the multi-heterojunction assembled by double type
II heterojunction promotes the electron transfer to O2 and hole transfer to H2O, as
shown in Scheme 2. Moreover, the advantages of charge separation by double
heterojunction outperforms sing heterojunction, resulting higher photocatalytic
activity towards degradation of acetaldehyde of NBMTBM than BMT and NBMT.
The performance of NBMTBM has also been compared with related works on
acetaldehyde degradation. As shown in Table S1, the photocatalytic activity is
comparable to other works, demonstrating the potential of NBMTBM in the
application of visible light induced photocatalysis.
To have a deep understanding on the enhanced activity over NBMTBM
heterojunction, Motto-Schottky curves are measured to compare the energy band
positions of the three components. As shown in Fig. 7a, the Mott-Schottky plots of all
samples have a positive slope, which agrees with their n-type semiconductor. The
Fermi levels of NaBi(MoO4)2, Bi2MoO6 and TiO2 are -1.13 V (vs. SCE), -1.04 V (vs.
SCE) and -0.94 V (vs. SCE), respectively. Because the flat-band potential of n-type
semiconductor lies very close to the bottom of the conduction band, it is inferred that
the conduction band position of NaBi(MoO4)2 is the highest, followed by Bi2MoO6,
and then TiO2. As is well reported, the bandgap of NaBi(MoO4)2, Bi2MoO6 and TiO2
is 2.9, 2.75 and 3.2 eV, respectively. It can be deduced that the valance band position
of TiO2 is the lowest, followed by NaBi(MoO4)2, and then Bi2MoO6[34]. Accordingly,
type I heterojunction can be formed between NaBi(MoO4)2 and Bi2MoO6, which is
worse for charge separation. When they are dispersed on TiO2 nanofibers, type II
10

heterojunction can be formed at the interface of NaBi(MoO4)2/TiO2 and
Bi2MoO6/TiO2, respectively, which is beneficial for charge separation. The schematic
illustration on the photocatalytic process over double heterojunction is shown in Fig.
7b.
a
b
5x109
4x109
3x109
2x109
1x109
NaBi( MoO )
4 2
Bi MoO
2
6
TiO
2
-1.1 -1.0 -0.9 -0.8 -0.7 -0.6 -0.5 -0.4 -0.3
E (V vs SCE)
Fig. 7: (a) Mott-Schottky curve of different samples, (b) schematic illustration of
photocatalytic process over NBMTBM heterojunction.
Last, the growth mechanism of NBM and BM on TiO2 is illustrated in Scheme 1.
On the basis of literature results and possible reaction between reactants[35,36], the
steps of chemical reaction are listed as following:
-
Bi(NO3)3 = Bi3+ + 3NO3
(1)
(2)
(3)
(4)
(NH4)6Mo7O24 + 14OH- = 7MoO42- + 6NH3↑ + 10H2O
Bi3+ + Na+ + 2MoO42- = NaBi(MoO4)2↓
2Bi3+ +4OH-+ MoO42- = Bi2MoO6↓ + 2H2O
At the initial stage, surface hydroxyl groups on TiO2 nanofibers react with
carboxyl group in EDTA molecular (step 1). Such reaction is similar to the
esterification between alcohol and organic acid[37,38]. This helps binding of EDTA
onto the surface of TiO2. Meanwhile, EDTA is a good chelating agent, which can
coordinate with Bi3+[39,40]. Accordingly, bismuth ion can be aggregated around the
surface of TiO2, which is beneficial for nucleation of bismuth related crystals on TiO2.
When water and ethanol are used as cosolvent, NaOH can react with (NH4)6Mo7O24
2-
and generate MoO4
ion (step 2). However, different cosolvent may induce a
different reaction pathway for the formation of heterojunction. When water is
presented as cosolvent, the solution media allows high concentration of both Na+ and
11

2-
Bi3+ ions (step 3). Therefore, MoO4 ion tends to react with Na+ and Bi3+ ions to
generate NaBi (MoO4)2 embryos on the surface of TiO2[41]. With the reaction
proceeds, NaBi(MoO4)2 nanorods gradually grow on the embryos and resulting in
NaBi(MoO4)2/TiO2 heterojunction. Differently, when ethanol is presented as
2-
cosolvent, MoO4 ion tends to react with Bi3+ in a solvothermal reaction due to hard
ionization and slow mobility of Na+ in organic solvent (step 4). Note that this reaction
is very common in most works Bi2MoO6 is obtained by similar solvothermal route.
In addition, it should be noted that EDTA plays a key role for the growth of
bismuth compounds on the surface of TiO2. We tried to synthesize NBMT and BMT
composites without the addition of EDTA, while other conditions are the same as that
for NBMT and BMT heterojunction. Fig. S2 shows the SEM images of samples
synthesized without EDTA. As can be seen, both NBM and BM form aggregates by
themselves rather evenly distribute on TiO2. Therefore, no heterojunctions are
obtained in the absence of EDTA. It is deduced that EDTA acts as a “molecular glue”
that binds TiO2 by esterification and capture Bi3+ and Na+ by coordination. This
EDTA-mediated synthesis route may work well in fabrication of other heterojunctions
on TiO2 or other semiconductor oxide supports.
EtOH+EG
pH=10
(B aq)
Bi3+
EDTA
Bi MoO /TiO2
H2O+EG
pH=10
TiO2
(A aq)
NaBi(MoO4)2/TiO
Scheme 1. Formation mechanism of NBMT and BMT.
4. Conclusions
In this work, by employing electrospun TiO2 nanofibers as the substrate, bismuth
nitrate as the bismuth source, and EDTA as the chelating agent, we successfully
prepared single heterojunction of Bi2MoO6/TiO2 and NaBi(MoO4)2/TiO2 as well as
double heterojunction NaBi(MoO4)2/TiO2/Bi2MoO6. Structural analysis demonstrates
the double heterojunction is more efficient for charge separation than single
12

heterojunction. Photocatalytic test via acetaldehyde degradation shows the best
performance of NaBi(MoO4)2/TiO2/Bi2MoO6 under visible light, benefiting from the
ultradispersion of heterojunction along TiO2 nanofibers. This study indicates that
electrospun inorganic nanofibers is promising candidate for fabrication of
multi-heterojunction.
Acknowledgements:
This work is supported by National Natural Science Foundation of China (21573003)
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Author Statement
Yuejun Li: Performing the experiment, Writing- Original draft
Tieping Cao: Propose the idea, Discussion on the raw data, Writing-Editing drfat
Zemin Mei: Discussion on the raw data
Xiaoping Li: Characterization on SEM, Photocatalytic Test
Dawei Sun: Characterization on XPS, Mott-Schottky
Graphical Abstract
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TiO2 nanofibers helps disperse type I heterojunction to two type II heterojunctions.
This leads to higher photocatalytic activity towards degradation of gaseous
acetaldehyde.
Highlights:
 NaBi(MoO4)2 and Bi2MoO6 can be grown on TiO2 nanofibers
 Type I heterojunction can be separated to two type II heterojunctions by TiO2
 Two type II heterojunctions are more active than type I heterojunction
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