Photochemical properties and structure characterization of (BiO)2CO3 nanowires doped with alkaline-earth metal ions

Article abstract of DOI:10.1016/j.materresbull.2017.02.026

The photoluminescence (PL) properties and photocatalytic activities of pure (BiO)₂CO₃ nanowires and (BiO)₂CO₃ nanowires doped with alkaline-earth metal ions (Mg²⁺, Ca²⁺, and Sr²⁺

Full text of DOI:10.1016/j.materresbull.2017.02.026

Accepted Manuscript
Title: Photochemical Properties and Structure
Characterization of (BiO)2CO3 Nanowires Doped with
Alkaline-earth Metal Ions
Authors: Kuixin Cui, Yuehui He, Yujiao Guo, Shengming Jin
PII:
S0025-5408(16)32473-4
DOI:
Reference:
http://dx.doi.org/doi:10.1016/j.materresbull.2017.02.026
MRB 9172
To appear in:
MRB
Received date:
Revised date:
Accepted date:
13-12-2016
25-1-2017
15-2-2017
Please cite this article as: Kuixin Cui, Yuehui He, Yujiao Guo, Shengming
Jin, Photochemical Properties and Structure Characterization of (BiO)2CO3
Nanowires Doped with Alkaline-earth Metal Ions, Materials Research Bulletin
http://dx.doi.org/10.1016/j.materresbull.2017.02.026
This is a PDF file of an unedited manuscript that has been accepted for publication.
As a service to our customers we are providing this early version of the manuscript.
The manuscript will undergo copyediting, typesetting, and review of the resulting proof
before it is published in its final form. Please note that during the production process
errors may be discovered which could affect the content, and all legal disclaimers that
apply to the journal pertain.

Photochemical Properties and Structure Characterization of
(BiO)2CO3 Nanowires Doped with Alkaline-earth Metal
Ions
Kuixin Cui1,2,Yuehui He1, Yujiao Guo2, Shengming Jin2,3*
1. Powder Metallurgy Research Institute, Central South University, Changsha 410083,
P.R. China. E-mail: kxcui2010@csu.edu.cn
2. School of Minerals Processing and Bioengineering, Central South University,
Changsha 410083, P.R. China. Fax: +86-731-88710804; Tel: +86-731-88877204; E-mail:
shmjin@mail.csu.edu.cn
3. Key Laboratory for Mineral Materials and Application of Hunan Province, Central
South University, Changsha 410083, P.R. China.
1

Graphical abstract
Highlights
 Wire-like (BiO)2CO3 and alkaline-earth metal ions doped-(BiO)2CO3 were
prepared.
 The cell parameters of doped nanowires shifted from those of pure nanowires.
 TEM images show the doped ions introduced internal defects into (BiO)2CO3
nanowires.
 Doping ions altered PL emission intensity of (BiO)2CO3 nanowires.
 Alkaline-earth metal ions doped-(BiO)2CO3 had enhanced photocatalytic activity.
2

Abstract
The photoluminescence (PL) properties and photocatalytic activities of pure
(BiO)2CO3 nanowires and (BiO)2CO3 nanowires doped with alkaline-earth metal ions
(Mg2+, Ca2+, and Sr2+) were studied. X-ray diffraction (XRD) studies confirmed that the
as-prepared nanowires were orthogonal (BiO)2CO3 and the calculated cell parameters of
alkaline-earth metal ions doped-(BiO)2CO3 nanowires shifted from those of pure
(BiO)2CO3 nanowires. High-resolution transmission electron microscopy (HRTEM)
images demonstrated that numerous defects were introduced into (BiO)2CO3 nanowires
by the doped ions. PL observations showed that (BiO)2CO3 doping altered the relative
intensity of PL emissions, by particularly lowering the emission at 467 nm. The Sr2+ ions
and Ca2+ ions showed the strongest and weakest effect on the PL property of (BiO)2CO3
nanowires, respectively. The alkaline-earth metal ions doped nanowires had enhanced
photocatalytic activities, comparing to the pure nanowires. Therefore, the PL property
and photochemical performance of (BiO)2CO3 nanowires were expected to be adjusted by
doping with various cations.
Keywords: Photoluminescence; (BiO)2CO3 nanowires; alkaline-earth metal; ion-doped
(BiO)2CO3 nanowires; photocatalytic activity
3

1 Introduction
In recent years, bismuth-containing ternary compounds, such as BiOxXy (X=Cl, Br,
9
10
12
or I)1-3, BiVO44-6, Bi2WO67,8, Bi3NbO7 , BiPO4 , Bi6S2O1511, (BiO)2CO3 , et al., have
attracted a great of attention due to their outstanding properties13. Among them, bismuth
subcarbonate ((BiO)2CO3) has become one of the most popular researched
semiconductors in the past decade.14-16 Because of its unique layered structure and
tunable band gap, (BiO)2CO3 has potential applications as photocatalysts17-19, sensor
material20, anti-bacterial material14,21 and so on. (BiO)2CO3 with various morphologies,
size, and band gap has been prepared using the hydrothermal treatment or solvothermal
method, and its photocatalytic activities were widely studied.12 However, the
photocatalytic efficiency of pure (BiO)2CO3 remains low because of the broad band gap.
The band gap of a semiconductor is determined by its electronic structure and
microstructure. Besides, photoluminescence (PL) has been widely used to study the
electronic structures, surface defects, photo-induced charge carrier separation and
recombination processes of semiconductor nanomaterials because of its non-contact,
nondestructive features.22 Considering doping ions could modify the microstructures,
electrical structures, and surface defects of semiconductor materials, (BiO)2CO3 doped
with anions were prepared to improve their performance recently.23-26 Pure (BiO)2CO3
2-
microspheres (with a diameter of around 2µm) and CO3 self-doped (BiO)2CO3
microspheres showed a broad PL emission centered at 413 nm after excitation by a 250
4

2-
nm light. The PL intensity decreased with increasing CO3 content, while the
photocatalytic activity increased with increasing CO32- content.23 Chang et al. introduced
sulfur into (BiO)2CO3 to form Bi2O2(CO3)1-xSx, and their results showed Bi2O2(CO3)1-xSx
with different sulfur showed different UV-DRS property and photocatalytic activities.24
N-doped (BiO)2CO3 microspheres prepared by the hydrothermal method showed
enhanced photocatalytic activity towards removal of NO under visible light
irradiation.25,26 However, very little works about the PL properties and photocatalytic
activities of cations doped (BiO)2CO3 were reported. Zhang et al. prepared
(BiO)2CO3:Eu3+ microspheres and studied their PL property using an excitation
wavelength of 395 nm, results showed that three emission peaks appeared centering at
560, 592 and 613 nm and all the emission peaks corresponded to the specific emissions of
Eu3+ ions.27
Inspired by the achievements in the cations–doped Bi2WO6 photocatalysts28-30, it has
been accepted that cation doping can enhance the photocatalytic activity of the
photocatalysts. Alkaline-earth metal ions (Mg2+, Ca2+, and Sr2+) are widely employed as
dopants in modifying the electronic structures and properties of semiconductors. Doping
Mg into ZnO nanoparticles inhibited the growth of particles size, increased the band gap
and enhanced the PL emission.31 The photocatalytic performance of BiFeO3 nanofibers
can be improved by the Ca-doping.32 Sr-doped CdS–ZnS solid solution photocatalysts
showed enhanced photocatalytic activities compared with pure CdS–ZnS photocatalyst
because the doping metal ions induced defects, which could improve the separation of the
5

electrons and holes.33 It is believed that doping alkaline-earth metal ions (Mg2+, Ca2+, and
Sr2+) could modify the PL property of (BiO)2CO3 and improve the photocatalytic activity.
However, to the best of our knowledge, the photochemical properties of alkaline-earth
metal ions (Mg2+, Ca2+, and Sr2+)-doped (BiO)2CO3 nanowires have not been reported.
In order to understand the effect of cation-doping on the photochemical properties, it
is imperative to carry out systematic analysis on the photochemical properties of
(BiO)2CO3 with alkaline-earth metal ions doping. In this paper, pure (BiO)2CO3
nanowires and alkaline-earth metal ions (Mg2+, Ca2+, and Sr2+) doped-(BiO)2CO3
nanowires were prepared by hydrothermal method. The effect of alkaline-earth metal ions
(Mg2+, Ca2+, and Sr2+) on the microstructure and PL property of (BiO)2CO3 nanowires
was studied in detail. Moreover, their enhanced photocatalytic activity was demonstrated
by the decomposition of xanthate under visible light irradiation.
2 Experimental
2.1 Materials and methods
The bismuth trioxide powders (Bi2O3) were purchased from Changde Fine Chemical
Co. Ltd. Sodium chloride (NaCl) and sodium carbonate (Na2CO3) were bought from
Tianjin Kernel Chemical Reagent Co. Ltd. Magnesium chloride (MgCl2), calcium
chloride (CaCl2), and strontium chloride (SrCl2) were purchased from Xilong Chemical
Co., Ltd. All chemicals were used as they were received and without further purification.
6

Deionized water was used in the experiments.
In a typical synthesis of Mg2+-doped (BiO)2CO3 nanowires, 100 mmol NaCl, 0.5
mmol MgCl2 and 5 mmol Na2CO3 were first dissolved in 70 mL of deionized water, and
the solution was adjusted to pH 3.0 using 1 M HCl. Afterward, 5 mmol Bi2O3 was added
into the solution under magnetic stirring conditions and kept the stability of pH 3.0. Then,
the mixture was transferred into a 100-mL Teflon-lined stainless steel autoclave, stirred
magnetically for 6 h at 160 °C, and subsequently cooled to room temperature. Afterward,
the products were collected by filtration, washed several times with deionized water and
ethanol, and dried overnight in an oven at 60 °C. The procedure for the preparation of
Ca2+-doped, and Sr2+-doped (BiO)2CO3 nanowires were same as that for the preparation
of Mg2+-doped nanowires, except for the replacement of the MgCl2 with CaCl2 and SrCl2,
respectively.
2.2 Characterization
The phase composition of the as-synthesized (BiO)2CO3 nanowires was identified
by powder X-ray diffractometry (XRD, D/max, Rigaku, Japan) with Cu Kα as a radiation
source. The morphology was characterized by scanning electron microscopy (SEM,
Quanta 250 FEG, FEI, America), transmission electron microscopy (TEM, JEM-2100F,
JEOL, Japan) and high-resolution TEM (HRTEM, JEM-2100F, JEOL, Japan). PL
measurement was carried out by a fluorescence spectrometer (FLS980, Edinburgh
Instruments, UK) using an excitation wavelength of 250 nm at room temperature. The
7

photocatalytic activity was evaluated by decomposition of sodium isopropyl xanthate
solution under UV-visible light irradiation.
3 Results and Discussion
3.1 XRD characterization
The phase composition of alkaline-earth metal ions doped (BiO)2CO3 nanowires was
analyzed using XRD. Pure (BiO)2CO3 nanowires were employed for comparison. As
shown in Figure 1, all the diffraction peaks of pure (BiO)2CO3 nanowires could be
indexed to the orthorhombic phase with the lattice constants a = 3.865 Å, b = 3.862 Å,
and c = 13.675 Å ((BiO)2CO3, ICDD PDF card No. 09-4740). Most of the diffraction
peaks of alkaline-earth metal ions doped (BiO)2CO3 nanowires could be indexed to the
orthorhombic (BiO)2CO3, and the rest three peaks emerged at 14.9°, 25°, and 29° (2-theta)
could be assigned to BiO1.5 (ICDD PDF card No. 78-0736). Results apparently indicated
that the relative peak intensity varied from each other, intensity ratio of (002) to (013)
decreased, whereas the intensity ratio of (110) to (013) increased, suggesting that the
doped earth metal ions affected the growth orientation of (BiO)2CO3 nanowires.
The lattice parameters were calculated based on the XRD patterns to evaluate the
effect of dopants on the crystal structure, as listed in Table 1. The ironic radius ratio of
M2+/Bi3+ (M2+ = Mg2+, Ca2+, or Sr2+ ion) were also listed in Table 1. Results indicate that the
8

lattice parameters of as-synthesized pure (BiO)2CO3 nanowires greatly agree with the
standard values. Due to the presence of the doped ions, the lattice parameters of doped
nanowires were less than the theoretical lattice parameters, especially for the c value. The
calculated c value of nanowires increased with the sequence, Mg2+-doped (BiO)2CO3
nanowires < Ca2+-doped (BiO)2CO3 nanowires < Sr2+-doped (BiO)2CO3 nanowires after
doping with Mg2+, Ca2+, or Sr2+, indicating that doping by ions substituted Bi3+ and
deformed the structure along c-axis to some extent. In particular, the cell parameters of
Mg2+-doped (BiO)2CO3 nanowires were 3.845 × 3.842 × 13.396 Å, which were much
smaller than those of pure nanowires and the standard values because of the smaller ionic
radius of Mg2+ (0.72 Å) than Bi3+ (1.03 Å). On the contrary, the increase in a and b with
doping with Sr2+ can be attributed to the larger ionic radius of Sr2+ (1.18 Å) compared
with that of Bi3+.
3.2 SEM and TEM characterizations
In a typical hydrothermal environment, introducing impure ions may affect the
crystalline and growth orientation of nanostructures, resulting in different morphologies
and properties. As described in previous work, pure (BiO)2CO3 nanowires with uniform
diameter can be prepared using the hydrothermal method (Shown in Figure 2a).34 SEM
images (Figure 2a) shows the disordered wire-like morphology of the pure (BiO)2CO3,
resulting from the random diffusing of ions under the hydrothermal condition. It was
different from those orderly ITO nanowires on the surface of a substrate prepared by the
9

thermal evaporation methodology, which focused on the conductivity and light
absorption35. Herein, SEM images were used to evaluate the effects of alkaline-earth
metal ions on the morphologies of nanowires. As shown in Figure 2, the morphologies of
all samples maintained the wire-like 1D structure despite the separate introduction of
different alkaline-earth metal ions. In particular, all the Mg2+-doped, Ca2+-doped, and
Sr2+-doped (BiO)2CO3 nanowires showed several nanowires that were bonded together
with some nanosheets. Besides, the ratio of wire-like structure to sheet-like structure
differed, which was probably caused by the different ionic radii. The radius of Mg2+ is
0.72 Å, which is much smaller than the 1.03 Å radius of Bi3+. Thus, more sheet-like
structures appeared, as shown in Figure 2a. In contrast, fewer sheet-like nanostructures
emerged in the Sr2+-doped system, and nearly no sheet-like nanostructures could be
observed in the Ca2+-doped system due to their similar ionic radius (1.00 Å for Ca2+ and
1.18 Å for Sr2+). In other words, the ionic radius of introduced ions affected the formation
of nanowires during the hydrothermal treatment of Bi2O3, wherein increased mismatch
between the added ions and bismuth ions, resulted in the appearance of a more sheet-like
nanostructure.
TEM and HRTEM images of Mg2+-doped, Ca+-doped, and Sr2+-doped nanowires
were recorded to investigate how the doped ions affected the microstructure of
(BiO)2CO3 nanowires. As a comparison, TEM and HRTEM images of the pure
(BiO)2CO3 nanowires were shown in Figure 3a,3b, which grew along the b axis. Figures
3c and 3d show us the TEM and HRTEM images of Mg2+-doped nanowires. It could be
10

seen that the Mg2+-doped nanowires had diameters about 30 nm and a smooth surface.
Clear crystal fringes appeared in the HRTEM image. The spacing of adjacent fringes was
measured to be 0.1925 nm, which could be ascribed to (020) plane of (BiO)2CO3. It
indicated that Mg2+-doped (BiO)2CO3 nanowires grew along the b axis, just like pure
(BiO)2CO3 nanowires. According to Figure S1, Bi-O bonds expose on the surface of
(BiO)2CO3 nanowires when they grew along the b axis, so it was easy to substitute Bi
atom in the Bi-O layers of (BiO)2CO3 cells. As a result, the original Bi-O tetrahedrons
collapsed when smaller ions like Mg2+ located at the Bi lattice sites. Numerous
distortions could also be observed in the HRTEM image (shown as oval-shaped circles in
Fig. 3d). Combining the smaller measured d-value of (020) crystal plane and defects with
the XRD results, we concluded that Mg2+ intruded upon the original cell of (BiO2)CO3
resulting in a distorted cell. Figures 3e and 3f show the TEM and HRTEM images of
Ca2+-doped nanowires, respectively. The observed nanowires showed a more uniform
diameter of 20 nm or so. In Figure 3f, clearer crystal fringes and fewer defects could be
observed, comparing with that of Mg2+-doped nanowires. The spacing was measured to
be 0.1935 nm, which belonged to the (020) crystal planes, too. Similarly, some defects
existed on the surface of the nanowire because Sr2+ ions substituted some Bi3+ ions in the
(BiO)2CO3 nanowires (Figure 3h). Combining HRTEM analysis (enlarged d-spacing and
defects) with XRD results, Sr2+ was successfully introduced into the (BiO)2CO3 crystal
cell.
11

3.3 PL properties
The photoluminescence spectra of the as-prepared pure, Mg2+, Ca2+, and Sr2+-doped
(BiO)2CO3 nanowires were recorded at an exciting wavelength of 250 nm. For a better
comparison, all the spectra were normalized based on the emission peak at 467 nm, as
shown in Figure 4. The pure (BiO)2CO3 nanowires showed one sharp emission peak at
467 nm, and one weak broad emission region around 425 nm. The peak at 467 nm could
be ascribed to the surface defect-induced emission due to the high activity of surface
atoms (Bi atoms and O atoms) in (BiO)2CO3 nanowires, and the weak broad peak around
425 nm could be contributed to the intrinsic defect-induced emission. Oxygen vacancies
37
are the main defect in metal oxidant semiconductors, such as ZnO36, TiO2 , et al. For the
(BiO)2CO3 nanowires, Bi-O layers expose on the surface, which could also lead to
oxygen vacancies. These oxygen vacancies acted as recombination centers to show up the
467 nm emission peak in the PL spectrum. Compared to the PL spectrum of pure
(BiO)2CO3 nanowires, the surface defect-induced emission peak at 467 nm appeared
broader with a tail. At the same time, the intrinsic emission of (BiO)2CO3 at 394 nm
showed up, indicating the energy band structure and defect types of (BiO)2CO3 varied
from that of pure (BiO)2CO3 nanowires after doping with alkaline-earth metal ions.
Moreover, the intrinsic defect-induced emission peaks shifted to 428 nm in the PL spectra
of doped (BiO)2CO3 nanowires comparing with that of pure nanowires, suggesting that
doping alkaline-earth metal ions subtly altered the defect type. The generated Me-O
12

bonds are ionic bonds rather than covalent bonds of Bi-O because the electronegativities
of alkaline-earth metal ions are smaller than that of bismuth ion. As a result, the electron
cloud distribution and electronic structure of alkaline-earth metal ions doped-(BiO)2CO3
nanowires varied from that of pure (BiO)2CO3 nanowires, leading to the broadened
defect-induced PL emission with a tail.38, 39 It also could be observed that all the PL
emission peaks were located at same wavelength positions. Generally, a shift of the PL
emission peak occurs after the impure ions are doped in the crystal due to the energy level
splitting. However, no noticeable difference in the PL emission positions was observed
here, just like the PL features of Mg2+, Ca2+, and Sr2+ doped ZnO nanoparticles.40 Further
study is necessary to figure out the likely reasons. In order to have a better understanding
of the PL properties, we fitted all the PL spectra based on Gaussian-Lorentz (20:80)
calculation. A good fit with four emission peaks centered at 394, 428, 467 and 482 nm
was obtained for all of the PL spectra of the samples.
Table 2 shows PL intensity ratio of different chromophores to the total PL emission
intensity of pure nanowires and alkaline-earth metal ions-doped (BiO)2CO3 nanowires
based on the Gaussian-Lorentz simulation. The surface defect-induced PL emission made
up about 83.53% of the total PL emission, intrinsic defect-induced PL emission (9.63%)
and intrinsic PL emission (6.84%). For the Mg2+, Ca2+, and Sr2+-doped (BiO)2CO3
nanowires, the relative intensity of surface defect-induced emission dropped dramatically,
and the impurity defect-induced emissions at 482 nm were dominant because doping with
13

nonequivalent ions caused numerous impurity defects, which were different from that of
pure (BiO)2CO3 nanowires. The highest intensity of surface defect-induced emission
(14.68%) belonged to Ca2+-doped nanowires, followed by 8.87% of Mg2+-doped
nanowires, and 4.91% of Sr2+-doped nanowires. The electronegativity of Mg, Ca, Sr, Bi,
and O is 1.31, 1.0, 0.95, 2.02, and 3.44,41 respectively. While the ionic radius of Mg, Ca,
Sr, and Bi is 0.72, 1.0, 1.18 Å, and 1.03 for Mg2+, Ca2+, Sr2+ , and Bi3+ ions41, respectively.
For the geometrical part, the radius of Ca2+ is extremely close to that of Bi3+, leading to a
minimal structure change in the original crystalline cell of (BiO)2CO3. Given that the
ionic radius of Sr2+ was a little bigger than that of Bi3+, the intruded Sr2+ could enlarge the
original cell of (BiO)2CO3 and change the surface defect emission, leading to the lowest
surface defect-induced PL intensity. The radius of Mg2+ was much smaller than that of
Bi3+, the ions intruded into (BiO)2CO3 cells and resulted in shrunken crystal cells and
impurity defects. For the (BiO)2CO3 electronic structural part, the generated Me-O bonds
have a different strength after they replaced Bi in the crystal lattice. Based on the
electronegativity, the ionicity of an A-B bond is given by42:
fionic=1-exp[-(XA-XB)2/4]
Where XA and XB are the electronegativities of the elements A and B. So that the ratio of
the ionic bond is 0.678, 0.774, 0.787, and 0.396 in Mg-O, Ca-O, Sr-O and Bi-O bond,
respectively. The Bi-O bond is more covalent character than ionic character; meanwhile,
all the Me-O bonds are ionic bonds. The greater the difference in electronegativity
between Me and O, the stronger the ionic bond that will be formed between them. Hence,
14

the strength of the Me-O bond increase as the following order: Bi-O<Mg-O<Ca-O<Sr-O.
After Me had replaced Bi in the crystal lattice, the electron distribution between Me and
O shifted from the Bi-O bond, resulting in the shifting of the electronic structure of the
doped (BiO)2CO3 nanowires. Given that both the ionic radius and electronegativity of
doped alkaline-earth metal ions are different, the as-obtained PL results reflected the
interaction of ionic radius and electronegativity of doped ions. Therefore, doping with
alkaline-earth metal ions has a significant effect on the intrinsic defect PL emission and
impurity defect PL emission, but has little effect on the intrinsic PL emission of
(BiO)2CO3 nanowires.
3.4 Photocatalytic activity
The enhanced photocatalytic activity of Mg2+, Ca2+, and Sr2+-doped nanowires was
determined by degradation of sodium isopropyl xanthate in aqueous solution under
UV-visible irradiation using a 250 W mercury lamp as light source. As well, pure
(BiO)2CO3 nanowires were employed as a contrast. Figure 5 shows the plot of
degradation rate (A0-At)/A0%) of xanthate at different reaction time using Mg2+, Ca2+,
Sr2+-doped nanowires and pure (BiO)2CO3 nanowires as photocatalysts. Here, A0 is the
initial absorbance of sodium isopropyl xanthate, and At is the absorbance of sodium
isopropyl xanthate solution at a reaction time t. As shown in figure 5, the degradation rate
of sodium isopropyl xanthate was less than 5% without photocatalyst. As a contrast, the
xanthate was degraded very quickly once the photocatalysts were added into the xanthate
15

solution. At a time of 30 min without light irradiation, the degradation rate of xanthate by
Mg2+, Ca2+, and Sr2+-doped nanowires and pure nanowires was 97.9%, 66.7%, 88.9%,
and 52.4%, respectively. The results of UV-vis spectra of the xanthate-containing solution
indicated that sodium isopropyl xanthate decomposed into CS2 and C3H7OH under
UV-vis irradiation, which was in accordance with the previous results of pure (BiO)2CO3
nanowires.29 It might be caused by the different morphologies shown in Figure 2.
Mg2+-doped nanowires and Sr2+-doped nanowires contained lots of sheet-like
nanostructures, which might absorb xanthate quicker than the single wire-like
nanostructure. The decomposition rate increased with the increasing of the reaction time.
After 60 min of reaction, the degradation rate of xanthate was 98.9%, 98.5%, 95.9%, and
94.4% in the presence of Mg2+-doped, Ca2+-doped, Sr2+-doped nanowires, and pure
nanowires, respectively. The Mg2+-doped-nanowires showed the highest photocatalytic
activity, followed by Sr2+-doped nanowires, Ca2+-doped nanowires and pure nanowires,
which was in accordance with the PL results. The ions-doped nanowires also showed a
high stability of photocatalytic activity after three successive runs (Shown in Fig.S2).
4 Conclusions
In summary, pure and alkaline-earth metal ions (Mg2+, Ca2+, and Sr2+)-doped (BiO)2CO3
nanowires were successfully prepared using the hydrothermal method. The XRD results
confirmed that the as-prepared nanowires were of orthogonal (BiO)2CO3, and the
calculated cell parameters of doped-(BiO)2CO3 nanowires shifted from those of pure
16

(BiO)2CO3 nanowires because of the mismatched radii and valence between doped ions
and Bi3+. HRTEM images also demonstrated that numerous defects were introduced into
the (BiO)2CO3 nanowires by the doped ions. PL studies showed that the pure (BiO)2CO3
nanowires displayed one sharp emission at 467 nm, which was caused by surface defects.
Doping of (BiO)2CO3 altered the PL emission relative intensity. The Ca2+-doped
(BiO)2CO3 nanowires showed the similar PL property of pure (BiO)2CO3 nanowires,
followed by Mg2+-doped (BiO)2CO3 nanowires, and Sr2+-doped (BiO)2CO3 nanowires,
resulting from their different ionic radius and electronegativity. The closer of the radii
between the doping atom and Bi atom is, the more similar the PL spectrum of (BiO)2CO3
nanowires. The photocatalytic activity test demonstrated all the alkaline-earth metal ions
doped nanowires had an enhanced photocatalytic activity compared to the pure nanowires.
Therefore, the PL emission and photocatalytic activity of (BiO)2CO3 could be adjusted by
adding different impurities.
References
(1) Li, J.; Zhang, L.; Li, Y.; Yu, Y., Synthesis and Internal Electric Field Dependent
Photoreactivity of Bi3O4Cl Single-Crystalline Nanosheets with High {001} Facet
Exposure Percentages. Nanoscale 2014, 167-171.
(2) Kim, W. J.; Pradhan, D.; Min, B.; Sohn, Y., Adsorption/Photocatalytic Activity
and Fundamental Natures of BiOCl and BiOClxI1−X Prepared in Water and Ethylene
17

Glycol Environments, and Ag and Au-doping Effects. Appl. Catal. B 2014, 147, 711-725.
(3) Lin, X.; Huang, T.; Huang, F.; Wang, W.; Shi, J., Photocatalytic Activity of a
Bi-based Oxychloride Bi3O4Cl. J. Phys. Chem. B 2006, 110, 24629-24634.
(4) Tan, H. L.; Wen, X.; Amal, R.; Ng, Y. H., BiVO4 {010} and {110} Relative
Exposure Extent: Governing Factor of Surface Charge Population and Photocatalytic
Activity. J. Phys. Chem. Lett. 2016, 7, 1400-1405.
(5) Xiao, Q.; Gao, L.; Zhang, X., Synthesis and Characterization of Highly
Visible-Light Active Monoclinic Mesoporous BiVO4. J. Inorg. Mater. 2011, 1256-1260.
(6) Wang, M.; Xi, X.; Gong, C.; Zhang, X. L.; Fan, G., Open Porous BiVO4
Nanomaterials: Electronspinning Fabrication and Enhanced Visible Light Photocatalytic
Activity. Mater. Res. Bull. 2016, 74, 258-264.
(7) Zhang, G.; Lü, F.; Li, M.; Yang, J.; Zhang, X.; Huang, B., Synthesis of
Nanometer Bi2WO6 Synthesized by Sol–Gel Method and its Visible-Light Photocatalytic
Activity for Degradation of 4BS. J. Phys. Chem. Solids 2010, 71, 579-582.
(8) Xu, X.; Ge, Y.; Wang, H.; Li, B.; Yu, L.; Liang, Y.; Chen, K.; Wang, F., Sol–Gel
Synthesis and Enhanced Photocatalytic Activity of Doped Bismuth Tungsten Oxide
Composite. Mater. Res. Bull. 2016, 73, 385-393.
(9) Zhang, G.; Yang, J.; Zhang, S.; Xiong, Q.; Huang, B.; Wang, J.; Gong, W.,
Preparation of Nanosized Bi3NbO7 and its Visible-Light Photocatalytic Property. J.
Hazard. Mater. 2009, 172, 986-992.
(10) Xue, F.; Li, H.; Zhu, Y.; Xiong, S.; Zhang, X.; Wang, T.; Liang, X.; Qian, Y.,
18

Solvothermal Synthesis and Photoluminescence Properties of BiPO4 Nano-Cocoons and
Nanorods with Different Phases. J. Solid State Chem. 2009, 182, 1396-1400.
(11) Zhou, Y.; Grunwaldt, J.; Krumeich, F.; Zheng, K.; Chen, G.; Stötzel, J.; Frahm,
R.; Patzke, G. R., Hydrothermal Synthesis of Bi6S2O15 Nanowires Structural, in situ
EXAFS, and Humidity-Sensing Studies. Small 2010, 6, 1173-1179.
(12) Selvamani, T.; Asiri, A. M.; Al-Youbi, A. O.; Anandan, S., Emergent Synthesis
of Bismuth Subcarbonate Nanomaterials with Various Morphologies Towards
Photocatalytic Activities - an Overview. Mater. Sci. Forum 2013, 764, 169-193.
(13) Zhao, H.; Tian, F.; Wang, R.; Chen, R., A Review On Bismuth-Related
Nanomaterials for Photocatalysis. Rev. Adv. Sci. Eng. 2014, 3, 3-27.
(14) Chen, R.; So, M. H.; Yang, J.; Deng, F.; Che, C.; Sun, H., Fabrication of
Bismuth Subcarbonate Nanotube Arrays From Bismuth Citrate. Chem. Commun. 2006,
2265-2267.
(15) Liu, Y.; Wang, Z.; Huang, B.; Yang, K.; Zhang, X.; Qin, X.; Dai, Y., Preparation,
Electronic Structure, and Photocatalytic Properties ofPreparation, Electronic Structure,
and Photocatalytic Properties of Bi2O2CO3 Nanosheet. Appl. Surf. Sci. 2010, 257,
172-175.
(16) Huang, H.; Wang, J.; Dong, F.; Guo, Y.; Tian, N.; Zhang, Y.; Zhang, T., Highly
Efficient Bi2O2CO3 Single-Crystal Lamellas with Dominantly Exposed {001} Facets.
Cryst. Growth Des. 2015, 15, 534-537.
(17) Dong, F.; Lee, S. C.; Wu, Z.; Huang, Y.; Fu, M.; Ho, W.; Zou, S.; Wang, B.,
19

Rose-Like Monodisperse Bismuth Subcarbonate Hierarchical Hollow Microspheres:
One-Pot Template-Free Fabrication and Excellent Visible Light Photocatalytic Activity
and Photochemical Stability for NO Removal in Indoor Air. J. Hazard. Mater. 2011, 195,
346-354.
(18) Zhao, T.; Zai, J.; Xu, M.; Zhou, Q.; Su, Y.; Wang, K.; Qian, X., Hierarchical
Bi2O2CO3 Microspheres with Improved Visible-Light-Driven Photocatalytic Activity.
CrystEngComm 2011, 13, 4010-4017.
(19) Peng, S.; Li, L.; Tan, H.; Wu, Y.; Cai, R.; Yu, H.; Huang, X.; Zhu, P.;
Ramakrishna, S.; Srinivasan, M.; Yan, Q., Monodispersed Ag Nanoparticles Loaded On
the PVP-assisted Synthetic Bi2O2CO3 Microspheres with Enhanced Photocatalytic and
Supercapacitive Performances. J. Mater. Chem. A 2013, 1, 7630-7638.
(20) Zhou, Y.; Wang, H.; Sheng, M.; Zhang, Q.; Zhao, Z.; Lin, Y.; Liu, H.; Patzke,
G. R., Environmentally Friendly Room Temperature Synthesis and Humidity Sensing
Applications of Nanostructured Bi2O2CO3. Sens. Actuators B-Chem. 2013, 188,
1312-1318.
(21) Qin, F.; Li, G.; Wang, R.; Wu, J.; Sun, H.; Chen, R., Template-Free Fabrication
of Bi2O3 and (BiO)2CO3 Nanotubes and their Application in Water Treatment. Chem. Eur.
J. 2012, 18, 16491-16497.
(22) Gilliland, G. D., Photoluminescence Spectroscopy of Crystalline
Semiconductors. Mater. Sci. Eng. R-Rep. 1997, 18, 99-399.
(23) Huang, H.; Li, X.; Wang, J.; Dong, F.; Chu, P. K.; Zhang, T.; Zhang, Y.,
20

Anionic Group Self-Doping as a Promising Strategy: Band-Gap Engineering and
2-
Multi-Functional Applications of High-Performance CO3 -Doped Bi2O2CO3. ACS Catal.
2015, 5, 4094-4103.
(24) Chang, C.; Teng, F.; Liu, Z., Fully Understanding the Photochemical Properties
of Bi2O2(CO3)1–xSx Nanosheets. Langmuir 2016, 32, 3811-3819.
(25) Dong, F.; Xiong, T.; Zhao, Z.; Sun, Y.; Fu, M., Ammonia Induced Formation of
N-doped (BiO)2CO3 Hierarchical Microspheres: The Effect of Hydrothermal
Temperature On the Morphology and Photocatalytic Activity. CrystEngComm 2013, 15,
10522-10532.
(26) Dong, F.; Sun, Y.; Fu, M.; Ho, W.; Lee, S. C.; Wu, Z., Novel in Situ N-Doped
(BiO)2CO3 Hierarchical Microspheres Self-Assembled by Nanosheets as Efficient and
Durable Visible Light Driven Photocatalyst. Langmuir 2012, 28, 766-773.
(27) Zhang, N.; Xiong, H.; Liu, Y.; Li, R.; Leng, Z.; Gan, S., Novel Synthesis Route
to Uniform Nanosheet Bi2O2CO3:Eu3+ Crystals with Luminescence Properties. Appl. Surf.
Sci. 2015, 357, 255-261.
(28) Song, X. C.; Zheng, Y. F.; Ma, R.; Zhang, Y. Y.; Yin, H. Y., Photocatalytic
Activities of Mo-doped Bi2WO6 Three-Dimensional Hierarchical Microspheres. J.
Hazard. Mater. 2011.
(29) Guo, S.; Li, X.; Wang, H.; Dong, F.; Wu, Z., Fe-Ions Modified Mesoporous
Bi2WO6 Nanosheets with High Visible Light Photocatalytic Activity. J. Colloid Interf.
Sci. 2012, 369, 373-380.
21

(30) Li, W. T.; Huang, W. Z.; Zhou, H.; Yin, H. Y.; Zheng, Y. F.; Song, X. C.,
Synthesis and Photoactivity Enhancement of Ba Doped Bi2WO6 Photocatalyst. Mater.
Res. Bull. 2015, 64, 432-437.
(31) Arshad, M.; Meenhaz Ansari, M.; Ahmed, A. S.; Tripathi, P.; Ashraf, S. S. Z.;
Naqvi, A. H.; Azam, A., Band Gap Engineering and Enhanced Photoluminescence of Mg
Doped ZnO Nanoparticles Synthesized by Wet Chemical Route. J. Lumin. 2015, 161,
275-280.
(32) Feng, Y.; Wang, H.; Luo, Y.; Shen, Y.; Lin, Y., Ferromagnetic and Photocatalytic
Behaviors Observed in Ca-doped BiFeO3 Nanofibres. J. Appl. Phys. 2013, 113, 146101.
(33) Zhang, K.; Jing, D.; Chen, Q.; Guo, L., Influence of Sr-doping On the
Photocatalytic Activities of CdS–ZnS Solid Solution Photocatalysts. Int. J. Hydrogen
Energ. 2010, 35, 2048-2057.
(34) Cui, K.; He, Y.; Jin, S., Enhanced UV–Visible Response of Bismuth
Subcarbonate Nanowires for Degradation of Xanthate and Photocatalytic Reaction
Mechanism. Chemosphere 2016, 149, 245-253.
(35) Li, L.; Chen, S.; Kim, J.; Xu, C.; Zhao, Y.; Ziegler, K. J., Controlled Synthesis
of Tin-Doped Indium Oxide (ITO) Nanowires. J. Cryst. Growth 2015, 413, 31-36.
(36) Zeng, H.; Duan, G.; Li, Y.; Yang, S.; Xu, X.; Cai, W., Blue Luminescence of
ZnO Nanoparticles Based on Non-Equilibrium Processes: Defect Origins and Emission
Controls. Adv. Funct. Mater. 2010, 20, 561-572.
(37) Nowotny, M. K.; Sheppard, L. R.; Bak, T.; Nowotny, J., Defect Chemistry of
22

Titanium Dioxide. Application of Defect Engineering in Processing of TiO2-Based
Photocatalysts. J. Phys. Chem. C. 2008, 112, 5275-5300.
(38) Schubert, E. F.; Goepfert, I. D.; Grieshaber, W.; Redwing, J. M., Optical
Properties of Si-doped GaN. Appl. Phys. Lett. 1997, 71, 921-923.
(39) Qu, S. C.; Zhou, W. H.; Liu, F. Q.; Chen, N. F.; Wang, Z. G.,
Photoluminescence Properties of Eu3+-Doped ZnS Nanocrystals Prepared in a
Water/Methanol Solution. Appl. Phys. Lett. 2002, 80.
(40) Haja Hameed, A. S.; Karthikeyan, C.; Sasikumar, S.; Senthil Kumar, V.;
Kumaresan, S.; Ravi, G., Impact of Alkaline Metal Ions Mg2+, Ca2+, Sr2+ and Ba2+ On the
Structural, Optical, Thermal and Antibacterial Properties of ZnO Nanoparticles Prepared
by the Co-Precipitation Method. J. Mater. Chem. B 2013, 1, 5950.
(41) Pauling L., The Nature of the Chemical Bond, Cornell Univ., USA, 3rd ed.,
1960.
(42) Phillips, J. C., Bonds and Bands in Semicondutors; Academic Press: New York
and London, 1973.
23

Figure 1. XRD patterns of Mg2+-doped, Ca2+-doped, and Sr2+-doped (BiO)2CO3
nanowires and pure (BiO)2CO3 nanowires (solid circles: BiO1.5).
24

Figure 2. SEM images of (a) pure (BiO)2CO3 nanowires, (b) Mg2+-doped (BiO)2CO3
nanowires, (c) Ca2+-doped (BiO)2CO3 nanowires, and (d) Sr2+-doped (BiO)2CO3
nanowires
25

Figure 3. TEM and HRTEM images of (a, b) Pure -doped (BiO)2CO3 nanowires, (c, d)
Mg2+-doped (BiO)2CO3 nanowires, (e, f) Ca2+-doped (BiO)2CO3 nanowires, and (g, h)
Sr2+-doped (BiO)2CO3 nanowires
26

Figure 4. The normalized PL spectra of pure nanowires and doped nanowires
27

Figure 5. Photocatalytic activity of Mg2+-doped, Ca2+-doped, Sr2+-doped, and pure
nanowires for decomposition of xanthate
28

Table 1. Ion radius ratio, absolute ion radius difference between M2+ and Bi3+ and lattice
constants of pure (BiO)2CO3 nanowires and (BiO)2CO3 nanowires doped with Mg2+, Ca2+,
or Sr2+ ions
Absolute ion radius Ion radius
difference between ratio of
M2+/Bi3+*
a/ Å
b/ Å c/ Å
M2+ and Bi3+ /Å
Standard values
3.865
3.868
3.845
3.848
3.935
3.862 13.675
3.866 13.676
/
/
/
Pure (BiO)2CO3 nanowires
Mg2+-doped (BiO)2CO3 nanowires
Ca2+-doped (BiO)2CO3 nanowires
Sr2+-doped (BiO)2CO3 nanowires
/
3.842 13.396 0.31
3.841 13.439 0.03
3.846 13.455 0.15
0.699
0.971
1.140
* M2+ denotes Mg2+, Ca2+, and Sr2+ ion.
29