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Supporting Information
Efficiently photocatalytic reduction of carcinogenic
contaminant Cr (VI) upon robust AgCl:Ag hollow
nanocrystals
Hongyan Li,a,c Tongshun Wu,a Bin Cai,a,c Weiguang Ma,a,c Yingjuan Sun,b,c
Shiyu Gan,a,c Dongxue Han* a and Li Niu a
a State Key Laboratory of Electroanalytical Chemistry, c/o Engineering Laboratory for Modern
Analytical Techniques, Changchun Institute of Applied Chemistry, Chinese Academy of
Sciences, Changchun, 130022, Jilin, China.
b State Key Laboratory of polymer physics and chemistry, Changchun Institute of Applied
Chemistry, Chinese Academy of Sciences, Changchun, 130022, Jilin, China.
c University of Chinese Academy of Sciences, Beijing, 100049, China
*Corresponding author: Prof. & Dr. Dongxue Han
Fax: +8643185262800
Tel: +8643185262425
E-mail: dxhan@ciac.ac.cn
Table of Contents
I. Experimental Procedure
1. Sample characterization instrument.
2. Photoelectric conversion experiments.
3. The calculation of apparent quantum efficiency.
II. Supplementary Results and Discussion
1. Typical SEM image of the NaCl crystal in the sythesis phase.
2. Additional SEM and TEM images of the as-prepared AgCl:Ag-Hollow NCs.
3. XRD results comparison of the AgCl:Ag-Hollow NCs and NaCl@AgCl.
4. The digital photographs of dispersion and desiccation of AgCl-Normal materials.
5. The surface mole ratios of Ag+ to Ag0 species.
6. Band-gap estimation for the semiconductor materials.
7. Electronic band structure calculation for the AgCl:Ag-Hollow NCs.
8. Barrett-Joiner-Halenda (BJH) pore distribution.
9. Typical photograph of color decay of concentration of hexavalent chromium.
10. Typical SEM and TEM images of AgCl:Ag-Hollow NCs after photoreduction reaction.
11. XRD results comparison of AgCl:Ag-Hollow NCs before and after photoreduction
reaction.
12. References.
I. Experimental Procedure:
1. Sample characterization instrument
Transmission electron microscopy (TEM) images were carried out on a Hitachi-600 TEM
with an accelerating voltage of 100 kV. The samples for TEM images were prepared by
dropping the dilute colloidal suspension (~0.05 mg mL-1) onto a carbon-covered copper grid
and dried in air at ambient temperature. High-resolution transmission electron microscopy
(HRTEM) and energy dispersive X-ray spectroscopy (EDX) measurements were performed
on a Tecnai G2 microscope at 200 kV. Field emission scanning electron microscope (FESEM)
images were performed on FE-SEM (Philips XL30 ESEM-FEG integrated with an EDAX
system) at an accelerating voltage of 10.0 kV. Gold-spraying was firstly carried out on the
surfaces of the samples before the SEM characterizations in order to protect the uniform
morphologies from decomposition under the high-energy electron beam. X-Ray photoelectron
spectroscopy (XPS) analysis was measured on an ESCALAB MKII X-ray photoelectron
spectrometer (VG Co.) with Al Kα X-rays radiation as the X-ray source for excitation. X-ray
diffraction (XRD) analysis was carried out on a D/Max 2500 V/PC X-ray diffractometer using
Cu (40 kV, 30 mA) radiation in the range of 10º-90º (2θ). Ultraviolet visible (UV-Vis)
absorption and UV-Vis diffuse reflectance spectra (using BaSO4 as the reference) were
recorded with a U-3900 HITACHI UV-Vis spectrophotometer. The bandgaps were calculated
by equation of Ahv = Φ(hv - Eg) n / 2, in which A, v, Φ, and Eg, respectively, signify the
absorption coefficient, light frequency, proportionality constant, and bandgap, n equals to 1 or
4, depending on whether the electron transition is direct or indirect. The nitrogen
adsorption-desorption measurements were performed on a Quantachrome ASiQwin-Autosorb
Iq Station 2 and the bath temperature was 77.35K (The outgas Temp. is 453.15K).
2. Photoelectric conversion experiments of AgCl: Ag-Hollow NCs
The photoelectric conversion properties were investigated in a conventional three-electrode
cell by using computer-controlled electrochemical workstation (CHI 660a electrochemical
analyzer: CH Instruments, Chenhua Co., Shanghai, China). Briefly, 50 mg catalysts were
suspended in 5 mL aqueous solution and the dispersion solution were ultrasonically scattered
to form a homogeneous solution. Then, 0.2 mL of the above solution was dropped onto the
Indium doped tin oxide (ITO) glass with fixed area. After evaporation in ambient
environment, the ITO glasses with catalysts were put into the bake oven (80℃) for overnight,
then the catalysts were found attached tightly onto the surface of ITO glass. The preparation
AgCl-Normal/ITO working electrode was followed with similar procedure that mentioned
above. A platinum wire was employed as counter electrode, Ag/AgCl (saturated KCl)
electrode as reference electrode, and 0.1 M sodium sulfate were used as the electrolyte. The
current-time (i-t) curves were collected as switching the light source (light off or on) every 10
seconds at the potential of 0.8 V. It needs to get rid of the oxygen with nitrogen for 30
minutes throughout the whole system before the test. The light source was a 3W LED lamp
with a UV cut off filter (λ > 420 nm) employed for the visible-light irradiation.
3. The calculation of apparent quantum efficiency
The photoreduction of carcinogen of Cr(VI) ion into Cr(III) undergoes a typical reaction
process as following:
Cr2O72- + 14H+ + 6e- → 2Cr3+ + 7H2O
Thus the apparent quantum efficiency could be calculated according to the following
equation 1, 2(1):
(1)
Where Nelectrons, Nphotons and NK2Cr2O7 represent the number of reacted electrons, incident
photons and the molecule number of generated potassium bichromate (K2Cr2O7), respectively.
The number of incident photons could be measured by the ferrioxalate actinometer method.3
In a typical procedure, 6 mL of 0.02 M Fe2(SO4)3 solution were mixed with 6 mL of 0.12 M
Na2C2O4 solution with irradiation for 20 s. Afterwards, 1 mL of the resulted mixture, 2 mL
1,10-phenanthrolin solution (0.2 wt %) and 0.5 mL of buffer solution (pH = 4.5, prepared by
dissolving 3.36 g CH3COONa to 50 mL H2SO4 solution (0.184 M)) were diluted to 100 ml
and subsequently kept in the dark under stirring for 30 min. After the reaction, the ferrous ion
concentration was subsequently determined via a UV-Vis spectrophotometric determination
of its phenanthroline complex at 510 nm. The blank value was measured using the similar
process just without irradiation. The number of incident photons per unit time was calculated
as following,
(2)
Where A and V signify absorbance at 510 nm and corresponding volume of the diluted
solution (1200 mL), respectively. NA=6.02×1023, ε=1.11×104 L mol-1 cm-1, L=1 cm, φ=1.21,
t=20 s. Results showed that the number of incident photons (n) was 7.26 × 1016 photons s-1.
2 2 7
K Cr O
electrons
photons photons
QE
N
N
NN
2
t 0 A
Fe
(A A ) V N
=εLt
n
II. Supplementary Results and Discussion
1. Typical SEM image of the NaCl crystal in the sythesis phase.
Fig. S1 Typical SEM image of the NaCl crystal morphology in sythesis phase. The inset
shows a well-defined cubic structure. The images obtained from the Phenon scanning electron
microscope Pro-x PW-100-011(part nr), 800-07333 (model nr) system (PHENON WORLD).
2. Additional SEM and TEM images of the as-prepared AgCl: Ag-Hollow
NCs
Fig. S2 SEM (a) and TEM (b) images of the as-prepared AgCl:Ag-Hollow NCs with high
magnification. Some pores and Ag0 species were found in the outer wall of the hollow
AgCl:Ag after water dissolution and bombardment of high energy electron beam from the
SEM and TEM images, respectively.
3. XRD results comparison of the AgCl: Ag-Hollow NCs and NaCl@AgCl.
Fig. S3 XRD patterns of the as-prepared AgCl:Ag-Hollow NCs and NaCl@AgCl. As
shown in the comparison diagram, the NaCl@AgCl displayed diffraction peaks (2θ) at 31.9°,
45.7°, 56.7°, 66.4° and 75.5°, which can be assigned to (200), (220), (222), (400) and (420)
crystal face respectively, corresponding to the crystal diffraction of NaCl4 (JCPDS file:
89-3615). It can be clearly seen that NaCl core were completely removed after the water
dissolution process. Meanwhile, a small quantity of metallic Ag was discovered due to the
visible light illumination. The diffraction peaks (2θ) at 38.1° (111), 44.3° (200) are ascribed to
the diffractions of the metallic Ag (JCPDS file: 65-2871).
4. The digital photographs of dispersion and desiccation of AgCl-Normal
materials.
Fig. S4 The digital photographs of dispersion and desiccation of AgCl-Normal materials.
5. The surface mole ratios of Ag+ to Ag0 species.
Fig.S5 XPS spectra of Ag 3d of AgCl:Ag-Hollow sample and AgCl-Normal materials. The
surface mole ratios of Ag+ to Ag0 species are calculated to be ca.7:1 and 13:1, respectively.
6. Band-gap estimation for the semiconductor materials.
Fig. S6 Band-gap evaluation from the plots of (Ahν)1/2 vs. the energy of the absorbed
photon.
The band-gap (Eg) energy of semiconductor could be estimated from the absorption edge and
more accurate to determine the value by using the following equation5 (1):
Ahν = Φ (hv-Eg)n/2 (1)
Where A, ν, Eg, and Φ are the absorption coefficient, light frequency, band gap energy and a
constant (Φ = 1), respectively. In the above equation, hν is the energy of the incident photons,
n depends on whether the transition constant is a direct (n = 1) or an indirect (n = 4)
semiconductor. For AgCl, the value of n is 4.6 The intercept of the tangent to the x-axis will
give a well approximation of the band gap energy for the as-prepared AgCl:Ag-Hollow NCs
from the plots of (Ahν)1/2 versus the photon energy (hν) (see Fig. S5).
7. Electronic band structure calculation for the AgCl:Ag-Hollow NCs.
The conduction band (CB) and valence band (VB) edge potentials of AgCl:Ag-Hollow NCs at
the point of zero charge can be calculated according to the empirical equations (1) and (2):7
ECB = χ – Ef – 0.5 Eg (1)
EVB = ECB + Eg (2)
Where χ is the absolute electronegativity of the semiconductor, which is defined as the
geometric mean of the absolute electronegativity of the constituent atoms, and herein, it can
be calculated by the arithmetic mean of the atomic electron affinity and the first ionization
energy.8 Ef is the energy of free electrons on the hydrogen scale (about 4.5 eV);9 Eg is the
band gap of the semiconductor which can be obtained from the Fig.S5. Meanwhile, ECB is the
conduction band potential and EVB is the valence band potential. Therefore, the band gap and
the χ value of AgCl:Ag-Hollow NCs are 2.01 eV and 6.07 eV, respectively. According to the
above equations, the top of the VB position and the bottom of the CB position of
AgCl:Ag-Hollow NCs are calculated to be 2.58 and 0.57 eV, respectively. It is noticed that
this method of calculation merely is based on the electronegativity.
8. Barrett-Joiner-Halenda (BJH) pore distribution.
Fig. S7 Barrett-Joiner-Halenda (BJH) pore distribution curves of AgCl:Ag-Hollow NCs and
AgCl-Normal materials.
9. Typical photograph of color decay of concentration of hexavalent
chromium.
Fig. S8 Typical digital photograph of the color decay from violet to pale before and during
the photoreduction of Cr(VI)-containing complex compound at 0 min to 10 min, which
indicated the successful conversion of Cr(VI).
10. Typical SEM and TEM images of AgCl: Ag-Hollow NCs after
photoreduction reaction.
Fig. S9 TEM and SEM images of the AgCl:Ag-Hollow NCs after several photocatalytic
reduction reactions. (a, c) low magnification, (b, d) high magnification. After the
photoreduction reaction, a great deal of metallic Ag0 species can be clearly detected on the
surface of the AgCl: Ag-Hollow NCs.
11. XRD results comparison of AgCl:Ag-Hollow NCs before and after
photoreduction reaction.
Fig. S10 XRD results comparison of AgCl:Ag-Hollow NCs before and after photoreduction
of the carcinogenic Cr (VI). As shown in the comparison diagram, the AgCl:Ag-Hollow NCs
also display similar diffraction peaks (2θ) at 27.7°, 32.2°,46.2°, 54.8°, 57.5°, 67.5°, 74.4°, and
76.7° corresponding to (111), (200), (220), (311), (222), (400), (331), (420) crystal face
respectively, which illustrates that the crystal structure did not significantly changed.
However, the content of metallic Ag increased due to the SPR-effect. The diffraction peaks
(2θ) at 38.1°(111), 44.3°(200), 64.5°(200) and 77.5°(331) are ascribed to the diffractions of
the metallic state of Ag (JCPDS file: 65-2871).
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