Supplementary online Materials
Synthesis of Ag9(SiO4)2NO3 through a reactive flux method and its
visible-light photocatalytic performances
Xianglin Zhu, 1, Zeyan Wang 1,a Baibiao Huang 1,a Wei Wei, 2 Ying
Dai, 2 Xiaoyang Zhang, 1 and Xiaoyan Qin 1
1
State Key Laboratory of Crystal Materials , Jinan, 250100 (P.R. China)
2
School of Physics, Shandong University, Jinan, 250100 (P.R. China)
Experimental Section
Ag9(SiO4)2NO3 was synthesized through a reactive flux method, during which AgNO 3 was employed
as both a reactant and a flux. In a typical procedure, AgNO 3 and NaSiO3·9H2O with molar ratio of 8:1
were mixed and uniformly ground, and then the mixture were transferred into an alumina crucible and
heated to 220 °C (a rate of 5 °C/min) for 40 hrs. After the crucible was cooled down to room temperature,
the mixture was washed by deionized water thoroughly to remove the excess AgNO 3. And the reddish
brown Ag9(SiO4)2NO3 powders can be obtained after dried at room temperature overnight. Ag3PO4 was
synthesized by a facile precipitation method as following. 3 mmol AgNO3 was added into 100 ml
solution containing 1 mmol Na2HPO4 under constant stirring for 30 min, the yellow precipitation was
collected by filtration and washed with deionized water for three times. Finally, Ag 3PO4 can be
obtained after it was dried at room temperature.
Photocatalytic Experiments
The photocatalytic activity of as-prepared Ag9(SiO4)2NO3 was evaluated by the decolouration of
MB, MO, RhB dye and O2 production under visible light irradiation (λ>420 nm). In a typical dye
decomposition process, 50 mg Ag9(SiO4)2NO3 was dispersed in 50 mL organic dye solution (20 mg/L).
The mixed suspension was firstly kept in dark for 1 hr to establish adsorption-desorption equilibrium.
Then, it was put under 300 W Xe arc lamp equipped with a UV cut-off filter (λ > 420 nm). 3 mL of the
mixed suspension was taken every 3 minutes and centrifuged to remove the powders. The residual
concentration of organic dye solutions were determined by measuring the maximum absorption with a
UV-vis spectrophotometer (Shimadzu UV2550). The comparison experiment with Ag3PO4 was carried
out under identical conditions. Photocatalytic O2-production was carried out in presence of AgNO3 as
sacrificial agent. Typically, 200 mg catalyst was added into 50 mL deionized water containing 0.5g
AgNO3 and then the mixed suspension was placed under the 300 W Xe arc lamp equipped with a UV
cut-off filter (λ > 420 nm). O2 concentration was tested every 30 mins.
Characterizations
The X-ray diffraction patterns (XRD) of samples were obtained on Bruker D8-advanced X-ray powder
diffractometer with Cu Kα radiation λ=1.5418 Å. The scanning electron microscopy (SEM)
measurements were carried out by Hitachi S-4800 microscope. The elemental composition was
detected by X-ray photoelectron spectroscopy measurements (VG MicroTech ESCA 3000 X-ray
photoelectron spectroscope). UV-Vis diffuse reflectance spectra were recorded for the dry-pressed disk
samples by a Shimadzu UV2550 recording spectrophotometer in the wavelength range 200-800 nm.
The surface areas of the samples were measured by using the Brunauer–Emmett–Teller method with a
Builder 4200 instrument at liquid nitrogen temperature. The total of organic carbon (TOC) of RhB
solution was measured by using Total Organic Analyzer (TOC-VCPH, Shimadzu Corp.) and GC for the
measurement of O2.
Calculations of the VB and CB edges of Ag9(SiO4)2NO3
0
The CB edge of a semiconductor at the point of zero charge (ECB
) is empirically expressed as[1-3],
1
0
ECB
=χcomp - 2.30RT（pHzpc - pH）/F - Ee - Eg
2
(1)
In this formular R is the gas contant, T is temperature, and F is Faraday constant. Eg is the band gap of
the semiconductor, and Ee the energy of the free electrons on the hydrogen scale (i. e., Ee =4.5
eV).Under the reasonable assumption that the solution’s pH value at the zero point of charge, pH ZPC, is
very close to the solution’s pH value, pH, we obtain
1
0
ECB
≈ ECB ≈ χcomp - Ee - Eg
2
(2)
χcomp is the electronegativity of a compound which is given by the geometric mean of the
electronegativity of the constituent atoms, which expressed as the mean geometric of absolute
electronegativity of all the constituent atoms, Ee means the free electrons energy contrasting to the
hydrogen scale (4.5 eV vs NHE), Eg is the semiconductor band gap energy. that is 4,
N
p q
χcomp = √χ1r χs2 … χ3 χ4 ,
(3)
where χ and N are the electro negativity of the constituent atom, the number of the species, and the
total number of atoms in the compound, respectively . The superscripts r, s, p, ... , q refer to the
numbers of the atoms 1, 2, ... , n-1 and n, respectively in the molecule, respectively, so that r + s +∙∙∙∙∙∙+
p + q = N. From its UV/Vis diffuse reflectance spectrum, the band gap of Ag9(SiO4)2NO3 is estimated
to be 1.90 eV. The values of O, Si , Ag , N and are 7.54, 4.77, 4.44,6.7 respectively 5.
Thus, from Eq. 2, the CB edge of Ag9(SiO4)2NO3 is estimated to be 0.47 eV with respect to the normal
hydrogen electode (NHE), and -4.94 eV with respect to the absolute vacuum scale (AVS).Consequently,
on the basis of its band gap (1.90 eV), the VB edge of Ag9(SiO4)2NO3 is determined to be 2.37 eV with
respect to the NHE, and -6.52 eV with respect to the AVS
1
S. R. Morrison, Electrochemistry at Semiconductor and Oxidized Metal Electrodes, Plenum Press,
New York, 1980.
2
M. A. Butler, D. S. Ginley, J. Electrochem. Soc. 1978, 125, 228-232.
3
Y. Xu, M. Schoonen, Am. Mineral, 2000, 85, 543-556.
4
R. T. Sanderson, Chemical Periodicity, Reinhold, New York 1960.
5
D. Yu, Z.-D. Chen, F. Wang, S.-Z. Li, Acta Phys. Chim. Sin. 2001, 17, 15-22.
Calculation of bond dipole moments:
In crystal structure of Ag9(SiO4)2NO3, removing the NO3-, the other part is nearly centrosymmetric.
So we need only calculate the bond dipole moments of NO3-. For ease of calculation, the N atom is
putted at the center of coordinate system, O atom are placed keeping bond lengths and bond angles not
changed.
Table S1 bond lengths NO3-and atom sites
N–O1
1.248 Å
N-O2
1.529 Å
N-O3
1.197 Å
Atom
x
y
z
N
0
0
0
O1
0.002
0.005
1.248
O2
1.055
1.106
-0.047
O3
-0.622
0.651
-0.789
The follow five equation are used in calculation of bond dipole moments
(ni − Vi )r− = (nj + Sij )(R ij − r− )
（1）
ni r+ = nj (R ij − r+ )
（2）
Vi = ∑j Sij = ∑j exp[(R 0 − R ij )/B]
R = r+ + rμ = nR
（3）
（4）
（5）
ni and nj are electron number of atom i and j, while r+ and r- are the positive and negative center of i-j
perssad B = 0.37. Then, we get R, the difference between the “centroids” of positive and negative
charge.
Table 2 Bond valence sum (Vi) of NO3-.
Atom
O1
O2
O3
N
Rij
1.248 Å
1.529 Å
1.197 Å
Sij
0.7468
0.8299
0.8572
Vj
2.4339
Table 3 Bond dipole moments of NO3μx
μy
μz
NO1
0.1714
0.4245
106.9633
NO2
90.5807
94.9595
-4.0352
NO3
-53.4340
55.9253
-67.7805
μ
33.3181
151.3093
35.1297
∣μ∣
159.7536
FIG S1 Photodegradation of (a) MB dye solutions and (b) MO dye solution
FIG S2 XRD of Ag9(SiO4)2NO3with different reaction time.
FIG S3 Photodegradation of (a) RhB dye solutions over Ag 9(SiO4)2NO3 with different reaction
time.
Table S1 BET surface area of Ag9(SiO4)2NO3 prepared with different reaction time.
Sample
BET ( m2/g)
1 hr
5 hrs
20 hrs
171.516
154.011
30.180
Figure S4 Stability study of photocatalyst Ag9(SiO4)2NO3
FIG S5 Fluorescence lifetime measurements of Ag9(SiO4)2NO3 and Ag3PO4 which are excited
which 375 nm laser and the fluorescence is tested at 470 nm and 480 nm.
FIG S6 Electronic structure of Ag9(SiO4)2NO3 obtained from DFT calculations, plots of the total
density of states (TDOS)
FIG S7 Calculation XRD of Ag9(SiO4)NO3 according the structure and standard XRD of
Ag9(SiO4)NO3.