Electronic Supplementary Material (ESI) for

Oxygen Vacancies Induced Selective Silver Deposition

on the {001} Facets of BiOCl Single-Crystalline

Nanosheets for Enhanced Cr(VI) and Sodium

Pentachlorophenate Removal under Visible Light

Hao Li and Lizhi Zhang *

Key Laboratory of Pesticide & Chemical Biology of Ministry of Education, Institute

of Environmental Chemistry, College of Chemistry, Central China Normal

University, Wuhan 430079, P. R. China

Preparation of photocatalysts.

I. BiOCl single-crystalline nanosheets (SCNSs) were prepared by modifying the

method reported by our group. In a typical procedure, 1 mmol of Bi(NO3)3∙5H2O and

1 mmol of KCl were added in distilled water at room temperature with continuous

stirring, and the pH value was adjusted to 1 or 6 before poured into a 20 mL Teflon-

lined stainless autoclave. The autoclave was allowed to be heated at 220 °C for 24 h

under autogenous pressure, and then air cooled to room temperature. The resulting

precipitates were collected and washed with deionized water and ethanol and dried at

60 °C in air. The BiOCl SCNSs obtained under pH = 1 were {001} facets exposed

* To whom correspondence should be addressed. E-mail: zhanglz@mail.ccnu.edu.cn. Phone/Fax: +86-27-6786 7535

Electronic Supplementary Material (ESI) for Nanoscale.This journal is © The Royal Society of Chemistry 2014

(BOC-001) and the BiOCl SCNSs synthesized under pH = 6 were {010} facets

exposed (BOC-010).

II. For the microwave synthesis of selective silver loaded Ag-BiOCl composites,

0.1 g of BiOCl (BOC-001 or BOC-010) SCNSs were dispersed in 30 mL of ethylene

glycol (EG), then AgNO3 with a weight ratio of 5% was added into the mixture. The

above solution was irradiated under microwave at 160 oC for 10 minutes. The

corresponding composite containing BOC-001 and BOC-010 SCNSs were denoted as

Ag-BOC-001 and Ag-BOC-010, respectively. Time dependent synthesis experiments

were conducted through simply adjusting the microwave irradiation time.

III. For the solvothermal synthesis of Ag-BiOCl composites, the above

AgNO3/EG/BiOCl mixture in preparation method II was poured into an 80 mL

Teflon-lined stainless autoclave and was allowed to be heated at 160 oC for 10 min

under autogenous pressure. The as-obtained products with BOC-001 and BOC-010

SCNSs were denoted as Ag-SV-BOC-001 and Ag-SV-BOC-010.

IV. For the EG treated BiOCl under microwave irradiation, 0.1 g of BOC-001 or

BOC-010 SCNSs were dispersed in 30 mL of EG and then irradiated under

microwave irradiation at 160 oC for 2 h. The products obtained with BOC-001 and

BOC-010 SCNSs were denoted as BOC-MW-001 and BOC-MW-010, respectively.

For the EG treated BiOCl with solvothermal method, the above EG/BiOCl mixture

was poured into an 80 mL Teflon-lined stainless autoclave and then heated at 160 oC

for 2 h under autogenous pressure. The products obtained with BOC-001 and BOC-

010 SCNSs were denoted as BOC-SV-001 and BOC-SV-010, respectively.

V. For the preparation of Ag randomly deposited Ag-BiOCl composites

employing NaBH4 as the reducing agent. In a typical synthesis, 0.1 g of BOC-001 or

BOC-010 SCNSs were well dispersed in 20 mL of distilled water containing AgNO3

with a weight ratio of 5% in an ultrasonic bath, then stoichiometric amount of 0.01

mol/L NaBH4 (about 10 % in excess) was added into the above solution drop by drop

under magnetic stirring and after that, the reaction continued for 2 h in the dark to

ensure the total reduction of AgNO3. The resultant precipitate was collected and

washed with deionized water and ethanol and dried at 60 °C in air. The resulting

products with Ag randomly deposited on BOC-001 and BOC-010 SCNSs were

denoted as Ag-BOC-B-001 and Ag-BOC-B-010, respectively.

VI. To prove that oxygen vacancies could in situ react with AgNO3, 0.05 g of

BOC-MW-001 SCNSs containing oxygen vacancies were dispersed into 20 mL of EG,

and then 10 mL of EG containing 5 wt% AgNO3 was added in the above mixture drop

by drop, and finally was allowed to react in the dark for 12 h at room temperature.

The resulting product was denoted as Ag-OV-BOC-001.

VII. As XPS spectra revealed that the weight ratios of Ag to BiOCl were

respectively 4.8% and 3.0% for Ag-BOC-001 and Ag-BOC-010. To prepare

Ag/BiOCl composites with different amount of silver randomly deposited onto the

{001} facets of BiOCl SCNSs, 0.1 g of BOC-001 SCNSs were well dispersed in 20

mL of distilled water containing Ag+ with a weight ratio of 0.5, 1, 3 and 5%, then

stoichiometric amount of 0.01 mol/L NaBH4 (about 10 % in excess) was added into

the above solution drop by drop under magnetic stirring and after that, the reaction

continued for 2 h in the dark to ensure the total reduction of AgNO3. The resultant

precipitate was collected and washed with deionized water and ethanol and dried at 60

°C in air. The resulting products were denoted as Ag/BOC-001-x (x= 0.5, 1, 3 and 5)

according to the ration of added Ag+. Accordingly, Ag/BOC-010-x (x= 0.5, 1, 3 and 5)

composites with silver randomly deposited onto the {010} facets of BiOCl SCNSs

were prepared in the same way.

Characterization. The powder X-ray diffraction (XRD) were recorded on a Rigaku

D/MAX-RB diffractometer with monochromatized Cu Kα radiation (λ = 0.15418 nm).

The scanning electron microscope (SEM) images and energy-dispersive X-ray

spectrum (EDS) were obtained with a JEOL 6700-F field-emission scanning electron

microscope. The transmission electron microscopy (HRTEM) images were obtained

by JEOL JSM-2010 high-resolution transmission electron microscopy. UV-visible

absorbance spectra of the samples were obtained using a UV-visible

spectrophotometer (UV-2550, Shimadzu, Japan). Electron paramagnetic resonance

(EPR) spectra were conducted on a Bruker EMX EPR Spectrometer (Billerica, MA).

X-ray photoelectron spectroscopy (XPS) was obtained with Perkin-Elmer PHI 5000C

and all binding energies were calibrated by using the contaminant carbon (C1S = 284.6

eV) as a reference. Raman spectra were obtained by a confocal laser micro-Raman

spectrometer (Thermo DXR Microscope, USA) with a 532 nm laser. In situ diffuse

reflectance FTIR spectra were recorded by Nicolet iS50FT-IR spectrometer (Thermo,

USA) with a 10 oC/min heating rate and 30 min maintaining time. Total organic

carbon (TOC) content of the prepared NaPCP solution was determined by a Shimadzu

TOC-V CPH analyzer.

Photocatalytic activity test. All photocatalytic activity experiments were conducted

at ambient temperature using a 500 W Xenon lamp with two 420 nm cutoff filter as

the light source. Typically, 0.05 g of photocatalyst was added into 50 mL of 10 mg·L-

1 sodium pentachlorophenate (NaPCP) or Cr(VI) aqueous solution in a container. The

mixture was continuously stirred in the dark for 60 min to ensure an adsorption-

desorption equilibrium before the lamp was turned on. Five milliliters of the solution

was taken out each 1 h and after centrifuged to remove the photocatalyst,

concentration of NaPCP or Cr(VI) was monitored by colorimetry with a Hitachi U-

3310 UV-vis spectrometer. Active species trapping experiments were conducted by

adding the corresponding scavenger (0.01 mol/L) to the mixture before the lamp was

turned on.

Photocurrent measurements. To prepare Ag-BiOCl electrodes, the Ag-BiOCl

composites were dispersed in chitosan solution to form a 10 mg∙mL-1 solution. Then,

0.3 mL of colloidal solution was dip-coated on the pretreated ITO surface and was

allowed to dry under vacuum conditions for 24 h at room temperature. Photocurrent

measurement was conducted on CHI660D Instruments in a standard three-electrode

system with the Ag-BiOCl composites as the working electrode, Pt foil as the counter

electrode, saturated calomel electrode as the reference electrode and 0.5 mol/L

Na2SO4 aqueous solution as the electrolyte.

Figure S1. (a) SEM image of BOC-001 SCNSs and (b, c) atomic structure of the

{001} facets: (b) top view; (c) side view. (d) TEM image, (e) SAED pattern and (f)

HRTEM image of the BOC-001 SCNS.

By increasing the hydrothermal reaction temperature to 220 oC, BiOCl single-

crystalline nanosheets of a well-defined decahedron shape were obtained. SEM

images revealed that BOC-001 SCNSs consisted of large-scale nanosheets with

widths of 4~8 μm and thickness of 500~800 nm (Figure S1). The TEM diffraction

spots and corresponding SAED of BOC-001 SCNSs were indexed as the [001] zone

of tetragonal BiOCl and the displayed (110) and (200) planes with an angle of 45o was

in agreement to the theoretical value (Figures S1d and S1e). The lattice fringe spacing

of 0.73 nm on the HRTEM image of vertical nanosheet was assigned to the (001)

planes of BOC-001 SCNSs (Figure S1f).

Figure S2. (a) SEM image of BOC-010 SCNSs and (b, c) atomic structure of the

{010} facets: (b) top view; (c) side view. (d) TEM image, (e) SAED pattern and (f)

HRTEM image of the BOC-010 SCNS.

The BOC-010 SCNSs consisted of nanosheets with width of 1~3μm and

thickness of 100~300 nm (Figure S2a, d). The corresponding SAED pattern was

indexed as [010] zone. The displayed (002) and (102) planes with an angle of 43.4o

was close to the theoretical value (Figure S2e). The (002), (102) atomic planes with a

lattice spacing of 0.37 and 0.27 nm revealed that the BOC-010 SCNSs were exposed

with {010} facets (Figure S2f).

Figure S3. SEM images of (a) Ag-BOC-001 and (b) Ag-BOC-010. (c) TEM image of

Ag-BOC-010 and (d) the corresponding SAED pattern and (f) HRTEM image.

As shown in Figure S3d, the set of diffraction spots of Ag-BOC-010 could still be

indexed as the [010] zone of tetragonal BOC-010, while no other diffraction spots

indexed to Ag could be found, indicating the purity of {010} facet.

Figure S4. (a) SEM image of Ag-BOC-001. (b, c) EDS spectra on different sites of

Ag-BOC-001. (d) Proportion of relevant elements detected in figure S4c.

Figure S5. (a) SEM image of Ag-BOC-010. (b, c) EDS spectra on different sites of

Ag-BOC-010. (d) Proportion of relevant elements detected in figure S5c.

To further verify the selectivity, energy-dispersive X-ray spectrum (EDS)

analysis was first used to detect the element composites on the selected areas. When

the monitoring spot was located on the smooth surface of Ag-BOC-001, no trace of

element Ag was detected (Figure S4b); when the monitoring spot was located on the

small nanocube, a distinct Ag element signal appeared (Figure S4c). Similarly, the

smooth top facet of Ag-BOC-010 confirmed no existence of element Ag (Figure S5b),

while a relative weaker signal of element Ag was confirmed on the rough lateral {001}

facet (Figure S5c). The appearance of Au signal was due to the Au spraying onto

BiOCl before SEM characterization.

Figure S6. (a) High-resolution XPS spectra of element Bi and Ag of the as-prepared

samples. (b) XRD and (c) UV-visible absorbance spectra of the as-prepared samples.

Two peaks at 165.6 and 160.2 eV in high-resolution Bi 4f spectrum of BOC-001

and BOC-010 SCNSs were assigned to the binding energies of Bi 4f5/2 and Bi 4f7/2,

respectively, which are characteristic energies of Bi3+ in BiOCl (Figure S6a). After

coupled with Ag, no measurable binding energy shifts were observed for Bi 4f.

X-ray diffraction (XRD) characterization showed that the intensity ratios of (002)

and (020) peaks were respectively 4.38 and 0.93 for BOC-001 and BOC-010 SCNSs,

which indirectly reflected the different facet exposure of these two samples. After the

Ag deposition, the intensity ratios of (002) and (020) peaks were 2.72 and 0.97 for

Ag-BOC-001 and Ag-BOC-010. XRD patterns of the as-prepared samples with

BiOCl could be indexed to JCPDF #85-861 and metallic could be indexed to JCPDF

#04-0783.

Figure S7. SEM images of (a) BOC-001 SCNSs and Ag-BOC-001 with reaction time

of (b) 30 s and (c) 60 s. SEM images of (d) BOC-010 SCNSs and Ag-BOC-010 with

reaction time of (e) 3 min and (f) 5 min.

The dynamic nucleation processes of Ag on the {001} facets of BOC-001 and

BOC-010 were observed by adjusting the microwave irradiation time. Figure S7a

shows the regular shape of a BOC-001 SCNS with a smooth surface. After the

reaction system was exposed to microwave irradiation for 30 s, tiny Ag nanograins

with an average size of 5 nm appeared (Figure S7b). Further increase the irradiation

time to 60 s, Ag nanograins grew bigger (Figure S7c). However, nucleation of Ag on

the lateral {001} facets of BOC-010 seemed to be much slower. Trace amount of Ag

nanograins were found exclusively on the {001} lateral facets when the irradiation

time reached 3 min (Figure S7e), which was 6 times longer than that on BOC-001

SCNSs. Only after 5 min of reaction, we were able to observe aggregation of

nanoparticles on the lateral facets of BOC-010 (Figure S7f).

Figure S8. Diffuse reflectance FTIR spectra of BOC-001 and BOC-010 SCNSs under

30 oC.

Figure S9. In situ diffuse reflectance FTIR spectra of surface hydroxyl groups of (a)

BOC-001 and (b) BOC-010 SCNSs with temperature increase.

At 30 oC, both samples exhibited a single-component surface hydroxyl group

signal at 3560 cm-1. To eliminate the influence of adsorbed H2O, we recorded the IR

spectra of the two samples heated up to different temperatures (200, 250, 300, and 400

oC) and found the absorbance of surface hydroxyl groups decreased slightly at 200 oC

and maintained their stability up to 300 oC, but decreased drastically at 400 oC. In all

cases, the signals of surface hydroxyl groups were much stronger than those of BOC-

010 SCNSs, confirming that BOC-010 SCNSs were terminated with more oxygen

atoms than BOC-010 SCNSs.

Figure S10. Solvothermal synthesis of Ag-BiOCl composites: (a) Ag-SV-BOC-001

and (b) Ag-SV-BOC-010.

Figure S11. (a) Diffuse reflectance FTIR spectra of surface hydroxyl of BOC-001,

BOC-010, BOC-MW-001 and BOC-MW-010 at 200 oC. (b) Color change of BOC-

001 and BOC-010 SCNSs after being reacted with ethylene glycol under microwave

irradiation. (c) UV-vis absorbance spectra of BOC-MW-001 and BOC-MW-010. (d)

EPR spectra of the BOC-MW-001&010 and BOC-SV-001 and BOC-SV-010. (d)

Schematic illustration oxygen vacancies-rich {001} facets of BOC-MW-001 and

BOC-MW-010.

The traditional solvothermal method was employed to evaluate the role of

microwave irradiation. In the absence of microwave irradiation, Ag could not be

selectively deposited onto the {001} facets of BiOCl SCNSs (Figure S10b). Then the

BiOCl SCNSs/EG mixture were allowed to react through solvothermal method or

microwave-assisted method at 160 oC for 2 h. We found that no obvious oxygen

vacancy signal appeared in the case of sovothermal treatment, while, a significant

oxygen vacancy signal appeared for BOC-001 SCNSs synthesized under microwave

irradiation (Figure S11d). Meanwhile, no measurable oxygen vacancy signal was

found on BOC-MW-010, probably due to the lower proportion of {001} facets.

Figure S12. SEM images of Ag-BiOCl composites synthesized via the NaBH4

reduction route: (a) Ag-BOC-B-001 and (b) Ag-BOC-B-010. High-resolution XPS

spectra of element Bi and Ag of silver randomly deposited Ag/BiOCl composites: (c)

Ag-BOC-B-001 and (d) Ag-BOC-B-010. SEM images of BiOCl SCNSs reacted with

AgNO3 in H2O under microwave irradiation: (e) BOC-001 SCNSs and (f) BOC-010

SCNSs. SEM image of (g) Ag-OV-BOC-001 and (h) schematic illustration of the in

situ redox reaction between oxygen vacancies on {001} facets and AgNO3 in the dark

at room temperature.

Figure S13. (a) The Cr(VI) reduction, (b) NaPCP oxidation and (c) transient

photocurrent responses over the unselective silver loaded Ag/BOC-x composites

under visible light. (d) Comparison of the maximum transient photocurrent density of

the as-prepared Ag-BiOCl composites. (e) Photocatalytic reduction of Cr(VI) and (f)

oxidation of NaPCP over Ag/BOC-010-x.

Figure S14. (a) The Cr(VI) reduction, (b) NaPCP oxidation with Ag/BOC-001-3

before and after (denoted as Ag/BOC-001-3-M) being irradiated with microwave in

EG.

Figure S15. XRD patterns of the Ag-BiOCl composites after 5th cycle.

Figure S16. (a) Photocatalytic reduction of Cr(VI) and (b) oxidation of NaPCP over

Ag-BOC-010 in the presence of different scavengers

Figure S17. Change of TOC over the degradation of NaPCP by Ag-BOC-001 and

Ag-BOC-010 under visible light.

Figure S18. Photocatalytic removal of (a) methyl orange, (b) rhodamine B, (c) orange

G and (d) salicylic acid with different samples under visible light.

Table S1 Textural and photocatalytic properties of the different samples

Sample Ag-BOC-001 Ag-BOC-010 Ag/BOC-001-3

Degradation in 3 h 65% 86% 19%Cr(VI)

k (h-1) 0.35 0.67 0.07

Degradation in 3 h 62% 80% 16%NaPCP

k (h-1) 0.32 0.53 0.06

* k represent the kinetic constants of the photocatalytic reduction or oxidation reaction,

which is based on pseudo-first-order reaction.

Table S2 Average molar ratio of Ag:Bi before and after the recyclability test of the

Ag-BiOCl nanocomposites.

Sample Ag-BOC-001 Ag-BOC-010 Ag/BOC-001-3

Before 0.102:1 0.088:1 0.079:1

After 0.093:1 0.080:1 0.027:1Molar ratio of

Ag:BiDecrease

percentage8.8% 9.0% 65.8%