Supporting Information

Charge separation and interfacial selectivity induced by

synergistic effect of ferroelectricity and piezoelectricity

on PbTiO3 monocrystalline nanoplates

Yawei Feng,a,b,c Mengjiao Xu,a Hui Liu,a Wei Li,d Hexing Li,a and Zhenfeng Biana,*

a MOE Key Laboratory of Resource Chemistry and Shanghai Key Laboratory of Rare

Earth Functional Materials, Shanghai Normal University, Shanghai, 200234, P.R.

China

b CAS Center for Excellence in Nanoscience, Beijing Key Laboratory of Micro-Nano

Energy and Sensor Beijing Institute of Nanoenergy and Nanosystems, Chinese

Academy of Sciences, Beijing, 100083, P.R. China

c School of Nanoscience and Technology, University of Chinese Academy of

Sciences, Beijing, 100049, P.R. China

d Laboratory of Advanced Materials, Shanghai Key Lab of Molecular Catalysis and

Innovative Materials and iChEM, Department of Chemistry, Fudan University,

Shanghai, 200433, P.R. China

*Email: bianzhenfeng@shnu.edu.cn

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S2

Chemicals:The raw materials are nano TiO2 (Degussa P25), potassium hydroxide (KOH, aladdin,

99.99%), lead(III) acetate trihydrate (PbC4H6O4·3H2O, Macklin, 99.99%),

Palladium(II) chloride (PdCl2, J&K Chemical, Pd: 59.8%), chloroplatinic acid

hexahydrate (H2PtCl6·6H2O, aladdin, Pt: 37.5%), chloroauric Acid (HAuCl4·4H2O,

Shanghai Fine Chemical Materials Institute, Au: 47.8%), sodium borohydride

(NaBH4, Tianjin Damao Chemical Reagent Factory, 98%), Nitric acid (HNO3,

Changshu Zhitang Fine Chemical Co., Ltd, 65%). Alcohol (99.7%), hydrochloric acid

(HCl, 36%) were purchased from RichJoint Chemical Reagent Co., Ltd. Home-made

deionized water was used throughout the process.

Prepare of PbTiO3:Hydrothermal method was use to prepare PbTiO3 single crystal. The Pb/Ti molar ratio

was set at 1.25:1, KOH was used as the mineralizer. Before hydrothermal treatment,

Ti precursor (P25, 0.3 g) was aged in KOH solution (12.5 mL, 8 M) for 2 hours, then

the concentration of KOH was adjusted to 4 M using deionized water after Pb

precursor was being added. The hydrothermal treatment was performed in an

autoclave at 200 for 20 h. The resultant products were washed with 0.3 M nitric℃

acid, deionized water, and ethanol for several times, finally dried at 70 in air for a℃

night.

Facet-depended deposition of noble metal nanoparticles:The photo-reduction deposition of the noble metal was achieved using H2PtCl6 or

PdCl2 as the precursor. H2PtCl6, PdCl2 was dissolved in diluted the mixture of 48 mL

water and 2 mL hydrochloric acid to form the solution with the Au concentration of

10 mg/mL, Pd concentration of 2.5 mg/mL. In a typical procedure, 100 mg PbTiO3

sample was suspended in the mixture of 80 mL deionized water and 20 mL ethanol.

After ultrasonic treatment (20 kHz, 500 W) for 30 min, metal precursor added

dropwise and the suspension was then irradiated by a Xe lamp (CEL-HXF300, 1050

mW·cm-2) under a constant stirring (800 rpm). After 1 h irradiation, the suspension

was centrifuged in deionized water and ethanol, respectively, and dried at 70 for℃

12 h in a vacuum oven.

NaBH4-reduction of Pt, Pd, Au:

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The NaBH4-reduction deposition of Pt, Pd or Au was achieved by adding NaBH4

solution dropwise into PbTiO3-dispersed solution at 20 . To make sure metal℃

precursor was totally reduced, the mount of NaBH4 was much exceeded (NaBH4 :

metal = 20 : 1 at molar ratio) and the mixture kept in the beaker under stirring for 30

min. After the suspension was dried by a rotatory evaporator at 100 , the powder℃

was centrifuged in deionized water and ethanol, then dried at 70 for 12 h in a℃

vacuum oven.

Characterization:The morphology was characterized with a scanning electron microscope (SEM,

Hitachi S4800) and a transmission electron microscope (TEM, FEI Tecnai G2 F20 S-

TWIN). X-ray diffractometer (XRD, Panalytical Xpert 3 powder, Cu Kα radiation)

was used to analyze the crystal structure of obtained powder. Atomic force

microscope (AFM, Asylum Research MFP-3D-SA) was applied to obtain the 3D

morphology of PMNs in AC mode and piezoresponse in Switching Spectroscopy

PFM (SS-PFM) mode using a Ti/Pt-coated silicon tip (Asylum Research AC240TM-

R3). UV−vis diffuse reflectance spectra (DRS) were obtained by using a

spectrophotometer (Shimadzu UV 3600) with an integrating sphere attachment and

with BaSO4 as reflectance standard. X-ray photoelectron spectroscopy (XPS, Versa

ProbePHI 5000) was employed to determine surface electronic states.

Photoelectrochemical measurement:Photoelectrochemical measurements were carried out in a conventional three-

electrode cell on an electrochemical station (CHI 660D). The catalyst-loaded ITO

glass electrodes were prepared by the following procedures: ethanol dispersion of

PbTiO3 or P25 (~2 mg/mL) was treated under ultrasonic process (20 min, 20 kHz, 500

w) to form a homogenous suspension, then 20 μL the above suspension was dipped

onto ITO glass (20 mm·20 mm). Being dried at room temperature, the glass was

calcined at 450 for 1 h. Pt sheet (10 mm *10 mm) and saturated calomel electrode℃

(SCE) were used as counter and reference electrodes, respectively. Saturated KCl

solution was used as the electrolyte. For photoelectrochemical experiments, the

working electrode was irradiated by a UV monochromator (Lamplic GUV-310, 85

mW·cm-2, irradiation area: 0.8 cm2) with zero bias voltage. The electric poling was

carried out in saturated KCl solution on the electrochemical station by applying a bias

voltage via the electrochemical station for 5 min.

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Photocatalytic degradation:For typical photocatalytic runs, photocatalyst dispersion (2.0 g/L) containing RhB or

other organics (MB, MO, AR50, BPA) was sonicated for 15 s, and then transferred

into a quartz reactor. The photocatalytic reaction was initiated by a UV LED (CEL-

LED100, 365 nm, 15 mW/cm2) at a certain stirring velocity applied by a magnetic

stirrer. After UV illumination, the sample was centrifuged at 9000 rpm to remove the

photocatalyst particles. The concentration of remaining organics was analyzed by a

UV spectrophotometer (UV 7504/PC) at the characteristic wavelength.

Photocatalytic H2 generation:30 mg photocatalyst was suspended in 30 mL water solution with alcohol (20 vol%)

in 50 mL quartz cell and the suspension was sonicated for 15 s. Then, the cell was

sealed and purged with Ar gas for 20 min. The sample was irradiated with a UV

monochromator (Lamplic GUV-310; 85 mW·cm-2, irradiation area: 0.8 cm2) with

constant magnetic stirring at room temperature. After irradiation, 1 mL of gas was

analyzed using a gas chromatograph (CEAULIGHT, GC-7900) equipped with an MS-

5A column and a thermal conductivity detector.

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Figure S1. (a) The band structure of a general semiconductor, ferroelectrics without and with the compressive stress modulation. EC, EV, Ef represent the conduction band, valence band and Fermi level of the given ferroelectric semiconductor, respectively. (b) The proposed principle of facet-depended photocatalysis on PMNs by coupling of ferroelectricity and piezoelectricity.

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Figure S2. XPS of P25 and PMNs. High-resolution XPS spectra of (a) C 1s, (b) O 1s,

(c) Ti 2p recorded on P25 and PMNs. High-resolution spectrum of (d) Pb 4f for

PMNs is also shown.

Figure S3. XRD pattern of PMNs.

Figure S4. SEM image of a large-scale PMNs.

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Figure S5. AFM topography. (a) The topographic image of a single PMN, (b) shows

the corresponding line profile of the PMN in (a).

Figure S6. A simulation diagram for the orientation of PMNs crystal.

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Figure S7. Absorbance spectrum. Absorbance spectrum of PMNs as the function of

(a) wavelength and (b) photon energy. The spectrum was obtained by converting the

UV-vis diffused reflectance spectrum using Kubelka-Munk function.

Suppose the PMNs can be well contacted to ITO glass, the probability of [001]

zone axis of PMNs facing to and backing to ITO glass are equal, thus the band

structure of PMNs is symmetric (Figure S6a). Before any electric poling, the electrode

gives the current output of 4.5 μA/cm2 under UV irradiation (Figure 3a), implying the

obtained PMNs with good response for UV light. After electric poling, the band

structure of PMNs was modulated by the residual polarization due to the ferroelectrics

PMNs are electret. Under the driven of residual polarization, photo-excited hole-

electron pairs can be separated effectively. As for the positive poling (Figure S6b), the

downward band of PMNs at the interface of IFO is more favorable for the migration

of electron to ITO, thus the photocurrent output increases to 5.2 μA/cm2 (Figure 3a).

However, the upward band of PMNs at the interface of IFO (Figure S6c) is less

advantage for the migration of electron to ITO, thus the output decreases to 4.0

μA/cm2 after the electrode being negatively polarized.

Figure S8. Schematic energy band diagrams. Energy band of PMNs (a) at the original

state, (b) being positively polarized and (c) negatively polarized, respectively.

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Figure S9. Photocurrent output from P25 electrode before and after poling.

Figure S10. RhB concentration change in PMNs and RhB (10 mg/L) aqueous mixture

in the static state.

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Figure S11. RhB degradation over PMNs in the dark condition. (a) Degradation

performance of RhB induced by piezocatalysis under different stirring speeds and (b)

the fitted quasi-first-order dynamic curve.

Figure S12. The (a) photocatalytic RhB (10 ppm) degradation and (b) quasi-first-

order dynamic curves of under static and stirring state (200 rpm).

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Figure S13. RhB degradation over PMNs. (a) The structure illustration of RhB

molecule and (b) the degradation performance of 10 mg/L RhB upon PMNs under

different stirring conditions.

Figure S14. Active species capturing. Degradation performance of RhB under UV

illumination and stirring at 800 rpm with the addition of radical scavenger. (5 mg/L

RhB, 1 mM EDTA-2Na, 1 mM t-BuOH and 1 mM AgNO3 was added, N2 bubbling

for 60 min) The addition of tert-butanol (t-BuOH) as hydroxyl radicals (·OH)

scavenger, EDTA-2Na as holes (h+) scavenger, AgNO3 as electrons (e-) scavenger and

N2 to inhibit the formation of superoxide anions (·O2-).

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N

SN N

Figure S15. Structure illustration of MB molecule.

Figure S16. BPA degradation over PMNs. (a) The structure illustration of BPA

molecule. It implies BPA molecule is not ionic molecule. (b) The degradation

performance of 10 mg/L BPA upon PMNs under different stirring conditions.

Structure illustration of molecule.

Figure S17. AR50 degradation. (a) The structure of AR50 molecule and (b) the

degradation performance of 5 mg/L AR50 upon PMNs under different stirring

conditions.

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0 20 40 60 800

2

4

6

8

10M

O c

once

ntra

tion

(mg/

L)

Time (min)

200 rpm 800 rpm

Figure S18. MO degradation. Degradation performance of 10 mg/L MO on 1 wt%

Au-loaded PMNs under different stirring conditions, showing the trend of decreasing

degradation activity can be reduced but cannot be eliminated.

Figure S19. SEM images of PMNs with photo-deposited Pd nanoparticles. The

contents of deposited Pd are (a-c) 1 wt% and (d-f) 2.5 wt%, respectively.

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Figure S20. SEM images of PMNs with photo-deposited Pt nanoparticles. The

contents of deposited Pt are (a-c) 3 wt% and (d-f) 5 wt%, respectively.

Figure S21. SEM images of PMNs with NaBH4-reduced Pd nanoparticles. (a-b) The

contents of deposited Pd are 2.5 wt%.

Figure S22. SEM images of PMNs with NaBH4-reduced Pt nanoparticles. (a-b) The

contents of deposited Pt are 3wt%.

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Figure S23. XPS spectra of Pt. Fine XPS scan of (a) Pt 4f7 and (b) Pt 4d5 recorded

on PMNs loaded with Pt nanoparticles reduced by NaBH4 and photo method.

Figure S24. Photocatalytic H2 generation at 1600 rpm as a function of irradiation time

in (a) water and (b)20 vol% alcohol aqueous solution over PMNs with Pt loaded by

photo reduction method (red line) and by NaBH4 reduction method (dark line). The

content of Pt is 1 wt%.

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1 2 3 4 5 60

20

40

60

80

H2

gene

ratio

n (μ

mol

)

Cycled number

Figure S25. The durability for H2 generation after each 1 h at 1600 rpm in 20 vol%

alcohol aqueous solution over PMNs with Pt loaded by photo reduction method. The

content of Pt is 1 wt%.

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