Supporting Information

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1 Supporting Information Photothermally-enabled Pyro-catalysis of BaTiO 3 Nanoparticles Composite Membrane at Liquid/air Interface Mengdie Min, Yanming Liu, Chengyi Song*, Dengwu Zhao, Xinyu Wang, Yiming Qiao, Rui Feng, Hao Wei, Peng Tao, Wen Shang, Jianbo Wu, Tao Deng* State Key Laboratory of Metal Matrix Composites, School of Materials Science and Engineering, Shanghai Jiao Tong University, 800 Dong Chuan Road, Shanghai , P.R.China. Corresponding author: dengtao@sjtu.edu.cn; chengyi2013@sjtu.edu.cn Table of Contents 1. Mechanical strength of PVDF-BTO membrane 2. Distribution of BTO NPs in the C-PVDF-BTO composite membrane 3. Electrostatic force microscope characterization of BTO NPs 4. Prolonged degradation experiment with C-PVDF membrane 5. Control experiment of RhB degradation with more porous C-PVDF membrane 6. Thermogravimetric analysis of PVDF-BTO membrane 7. RhB degradation experiments of PVDF-BTO membranes with different weight ratios 8. Supplementary Figures 9. Supplementary Table 10. References S-1

2 1. Mechanical strength of PVDF-BTO membrane As is well known, PVDF membrane is widely used in researches due to its outstand properties in thermal stability, chemical resistance, and high mechanical strength. 1-4 Hence, we used PVDF as a good binder for the BTO NPs in this work. The tensile stress-strain test of the PVDF-BTO composite membrane was conducted using a dynamic mechanical analyzer (DMA, Q800, TA Instruments). The as-prepared membrane was cut into 6 mm 2 cm pieces before testing. The stress-strain curve of PVDF-BTO membrane was shown in Figure S1. It showed that the tensile strength of 20.2 MPa with the elongation of 4.8%. We also compared our membrane with other pure PVDF or PVDF-based composite membranes reported by other groups, as shown in Table S1, which showed that our membrane had a relatively good tensile strength. 2. Distribution of BTO NPs in the C-PVDF-BTO composite membrane In order to investigate the distribution of BTO NPs in the membrane, we analyzed the energy dispersive spectrometry (EDS) mapping images with the individual elements of F, Ba and Ti, respectively (Figure S3). The F element indicates the absence of PVDF, while Ba and Ti elements indicate the distribution of BTO NPs. As show in EDS mapping, BTO NPs were homogeneously distributed in the PVDF-BTO composite membrane. 3. Electrostatic force microscope characterization of BTO NPs To further confirm the pyroelectric activity, the electrostatic force microscopy (EFM) was used to image and manipulate the ferroelectric polarization of BTO NPs. 5-6 The electric polarization of BTO was manipulated by applying a writing voltage V write on the atomic force microscopy (AFM) tip that scanned through the substrate in tap mode. After the local electric polarization is written onto the BTO NPs, the resulting polarization is probed using EFM with a lower voltage V probe by measuring the shift in the resonance frequency of the AFM tip. The topological AFM image of BTO NPs was shown in Figure S7a. A V write of -12 V was firstly applied on the tip, followed by a V probe of +2 V was applied to obtain the EFM image. As shown in Figure S7b, bright regions of BTO NPs were probed due to the strong attractive electrostatic interaction between the tip and BTO NPs. Then a V write of +12 V was applied on the tip, followed by applying a V probe of +2 V. Figure S7c reveals that the BTO NPs regions turned dark due to the variation of spontaneous polarization of BTO NPs driven by the reversed external electric field. The ferroelectricity of BTO NPs explains such change in the electrostatic force shown in EFM images. The ferroelectric response also indicates the pyroelectric property of BTO NPs. S-2

3 4. Prolonged degradation experiment with C-PVDF membrane The RhB degradation experiment with C-PVDF membrane was conducted for 9 more hours to determine the degradation rate under low RhB concentration. As shown in Figure S11, ~60% of RhB was degraded after 900 min. It can be observed a linear degradation rate at high RhB concentration. 7-9 The degradation rate on C-PVDF membrane tended to be slow and showed non-linear when the concentration of RhB solution decreased. 5. Control experiment of RhB degradation with more porous C-PVDF membrane A C-PVDF membrane with larger surface area (35.4 ± 0.5 m 2 g -1 ) was utilized to degrade RhB solution in comparison with the as-prepared C-PVDF-BTO composite membrane. As shown in Figure S13, the more porous C-PVDF membrane degraded ~40% of RhB, which was 5% higher than the original C-PVDF membrane due to the increase of surface area. However, compared to the C-PVDF-BTO membrane (75%), the degradation efficiency of more porous C-PVDF membrane was still much lower than C-PVDF-BTO membrane, indicating that BTO NPs were the dominant catalyst in the pyro-catalytic degradation of RhB. 6. Thermogravimetric analysis of PVDF-BTO membrane In order to investigate the amount of BTO NPs in the membrane after spin-coating, thermogravimetric analysis (TGA) and differential thermogravimetric (DTG) curves of the BTO-PVDF membrane was obtained with a heating rate of 20 C min -1 from 30 C to 900 C in air flow (Figure S14). It can be observed two steps in the weight loss process, which are attributed to the carbon-hydrogen scission and the formation of hydrogen fluoride (HF), followed by further loss of HF along the polymer chain resulting in a polyenic sequence. 10 After the temperature exceeded 800 C, PVDF was completely removed from the BTO-PVDF composite membrane. The TGA curve tended to be steady at ca. 21%, indicating the weight ratio of BTO NPs in the composite membrane. When we prepared the membrane, 30 wt% of BTO (0.6 g) was mixed with 2.0 g of PVDF. The theoretical weight ratio of BTO in the membrane was calculated to be ca. 23%, which was closed to the TGA result. S-3

4 7. RhB degradation experiments of PVDF-BTO membranes with different weight ratios In order to investigate the influence of the ratio of BTO and PVDF, we had prepared a series of membranes with the ratios of BTO to PVDF ranging from 10% to 100%, respectively. RhB degradation experiments were conducted using the as-prepared membranes, and the degradation results were compared with those in the original manuscript. As shown in Figure S15, when the mass ratio of BTO ranged from 0 to 50%, the degradation efficiency gradually increased as the ratio of BTO increased and the maximum efficiency reached 81% for the BTO: PVDF = 50%. The elevation of degradation efficiency was contributed to the addition of BTO NPs. However, the continuous addition of BTO NPs led to the decline of degradation efficiency and thus the degradation efficiency of BTO (mass ratio of BTO: PVDF = 100%) was slightly lower than BTO in the original manuscript (mass ratio of BTO: PVDF = 30%). The PVDF-BTO composite membrane with the BTO mass ratio of 30% presented good degradation property with relatively low amount, so we used 30% BTO as a representative concentration to verify the hypothesis. S-4

5 8. Supplementary Figures Figure S1. Stress-strain curve of PVDF-BTO composite membrane. S-5

6 Figure S2. Absorption spectrum of the C-PVDF-BTO membrane (CB side). S-6

7 Figure S3. SEM image of PVDF-BTO composite membrane and EDS mapping of F, Ba, and Ti elements. S-7

8 Figure S4. The SEM image of the PVDF-BTO membrane without water treatment. It reveals almost no connected 3D micro-porous structures. S-8

9 Figure S5. The SEM images of BTO NPs exposed on the membrane (a) and encapsulated BTO NPs in the membrane (b). S-9

10 Figure S6. The Raman spectrum of BTO NPs. S-10

11 Figure S7. (a) Topological AFM image of BTO NPs. b-c) EFM images of BTO NPs with V probe = +2 V after V write = -12 V and (b) V write = +12 V (c) were applied on the BTO NPs across the AFM tip. The scale bar is 1 μm. S-11

12 Figure S8. The temperature change of the solution away from the electric heater in the bulk NPs solution heating system. S-12

13 Figure S9. UV-vis absorption spectra of RhB solution at different time during the pre-adsorption process. S-13

14 Figure S10. FTIR spectrum of C-PVDF membrane. The characterized peaks (835, 1070, 1166 and 1231 cm -1 ) represent the typical β phase of PVDF, which exhibit pyro-electric activity. S-14

15 Figure S11. RhB degradation curve with C-PVDF membrane for prolonged time. S-15

16 Figure S12. The N 2 adsorption-desorption curve (a) and BET surface area plot (b) of pure PVDF membrane and PVDF-BTO composite membrane. S-16

17 Figure S13. Control experiment of RhB degradation with more porous C-PVDF membrane. S-17

18 Figure S14. Thermogravimetric analysis (TGA) and differential thermogravimetric (DTG) curves of the PVDF-BTO membrane. S-18

19 Figure S15. RhB degradation experiments with PVDF-BTO composite membranes of different weight ratios of BTO to PVDF. S-19

20 Figure S16. SEM images of PVDF-BTO composite membrane (a) and pure PVDF membrane (b). S-20

21 9. Supplementary Table Tensile strength (MPa) Thickness (μm) Reference This work Ref. (1) 5.92 ~100 Ref. (2) ~50 Ref. (3) Ref. (4) Table S1. Comparison of tensile strength, elongation and thickness between reference values and our work. S-21

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