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leveraging the capillary water flow to the hot zone for the evaporation at the surface. 35 .... also a pyroelectric material (Figure S10), the pyro-ca...
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Energy, Environmental, and Catalysis Applications

Photothermally-enabled Pyro-catalysis of BaTiO3 Nanoparticles Composite Membrane at Liquid/air Interface Mengdie Min, Yanming Liu, Chengyi Song, Dengwu Zhao, Xinyu Wang, Yiming Qiao, Rui Feng, Wei Hao, Peng Tao, Wen Shang, Jianbo Wu, and Tao Deng ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.8b03411 • Publication Date (Web): 05 Jun 2018 Downloaded from http://pubs.acs.org on June 5, 2018

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Photothermally-enabled Pyro-catalysis of BaTiO3 Nanoparticles Composite Membrane at Liquid/air Interface Mengdie Min†, Yanming Liu†, Chengyi Song*, Dengwu Zhao, Xinyu Wang, Yiming Qiao, Rui Feng, Wei Hao, 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 Dongchuan Rd, Shanghai, 200240, China KEYWORDS: pyro-catalysis, photothermal, solar energy, localized heating, barium titanate (BaTiO3) ABSTRACT: This paper reports the highly efficient pyroelectric nanomaterial-based catalytic degradation of waste dye under rapid temperature oscillation, which was achieved by periodical solar irradiation on a porous pyroelectric membrane that was floating at the liquid/air interface. Such membrane consists of the light-to-heat conversion carbon black film as top layer and the porous polyvinylidene fluoride (PVDF) film embedded with pyroelectric BaTiO3 nanoparticles (BTO NPs) as bottom layer. By using optical chopper, solar light can be modulated to periodically irradiate on the floating membrane. Due to the photothermal effect and low thermal conductivity of PVDF polymer, the generated heat is localized at the surface of membrane and increases substantially the surface temperature within a short period of time. When the solar light is blocked by the chopper, interfacial evaporation through porous membrane along with

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convective air cooling and radiative cooling leads to heat dissipation and then the temperature of membrane is rapidly decreased. Such efficient thermal cycle results in substantial rate of temperature change of membrane, which enhances its pyroelectric capability and subsequent pyro-catalysis. In contrast, the efficiency of pyro-catalysis through dispersed BTO NPs solution is about four times lower than that of BTO composite membrane. With the large heat capacity of aqueous solution and inevitable thermal loss due to bulk heating, the rate of temperature change of BTO NPs solution is much smaller than that of BTO composite membrane, and thus results in relatively small pyro-catalytic capability. Furthermore, the reusability and transferability of this newly developed composite membrane make it amenable to practical use in treating contaminated water. The findings in our report not only offer a new design strategy for efficient solar-enabled pyro-catalysis, but also pave a new way to rationally harvest solar-thermal energy in nature for various applications that involve pyroelectric materials.

INTRODUCTION Pyroelectric materials have been widely used as electricity generators to harvest thermal energy and convert it into electrical energy.1-7 The harvesting process is based on pyroelectric effect, which is owing to the generation of surface charges induced by the temperature oscillation-dependent spontaneous polarization. The induced surface charges can be represented by the pyroelectric current and mathematically described by the following Equation 1:8

‫ܫ‬௣ =

ୢொ೛ ୢ௧

= ܲ஺ · ‫· ܣ‬

ୢ் ୢ௧

(1)

where Ip represents the pyroelectric effect-induced current, Qp is the electrical charge, PA is the pyroelectric coefficient, A is the surface area of the pyroelectric crystal, and dT/dt is the rate of

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temperature change. Recently, pyroelectric materials were studied as pyro-catalysts by thermal excitation in the aqueous environments, which provides hydroxyl radical (·OH) for disinfection and degradation.9-12 For example, Meyer et al. studied LiNbO3 (LN) and LiTaO3 (LT) nano- and microcrystalline powders on the disinfection of bacterium Escherichia coli in aqueous solution under the thermal oscillation for 6 hours.12 In their study, one temperature cycle ran between 20 ℃ and 45 ℃ within 32 minutes with the average rate of temperature change at 0.026 ℃ s−1. Jia et al. reported dye degradation reaction catalyzed by dispersed pyroelectric BiFeO3 NPs under heating (38 ℃)-cooling (27 ℃) cycle within 16 minutes with the average rate of temperature change at 0.023 ℃ s−1.9 As revealed by Equation 1, both the increase in the surface area (A) of pyroelectric materials and the increase in the rate of temperature change (dT/dt) can result in large pyroelectric current and thus high catalytic efficiency. In the aforementioned systems, dispersed nanoparticles (NPs) solutions exhibit high surface area for catalytic reactions. Such thermal design with the bulk solution, however, results in overall low efficient due to the relatively low rate of temperature change. The high thermal heat capacity of water intrinsically limits the heating and cooling rate of the bulk solution, which subsequently limits pyroelectric conversion process. Hence, a rational and efficient thermal design for the pyro-catalysis system is needed for the continuous advancement in this field. Floating photothermal porous membranes were previously reported in localizing thermal energy at the air/water interface through highly efficient light-to-heat conversion process.13-19 Under solar light illumination, the surface temperature of floating membrane quickly increased by tens of degrees due to the accumulated heat restricted within the membrane.20-21 Once the light was off, the surface temperature of porous membrane went down quickly because of efficient heat dissipation through interfacial evaporation and the air cooling. By taking advantage

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of such heating and cooling processes, this work studied the design of a double layered membrane to achieve fast temperature oscillation rate for highly efficient pyro-catalytic reactions (Figure 1). In such design, barium titanate nanoparticles (BTO NPs) with the pyroelectric coefficient of 200 µC m−2K−18 were embedded throughout the porous polyvinylidene fluoride (PVDF) substrate which is a good binder of BTO NPs with good mechanical strength 25

22-

(Figure S1) as bottom layer for the pyro-catalysis. Carbon black (CB) powders were coated on

the other side of PVDF substrate as the light-to-heat conversion top layer.26-27 A homemade optical chopper was used for the modulation of the solar light. Such design enabled the fast temperature change of the membrane between 38.3 ℃ and 55.5 ℃ within 12 seconds in one cycle. Its average and instantaneous rate of temperature change could reach 3 ℃ s−1 and 13 ℃ s−1, respectively. Such instantaneous rate of temperature change is almost 11 times higher than that of bulk BTO NPs solution under similar condition. Under such enhanced pyroelectric capability at the liquid/air interface, ~75% degradation efficiency for Rhodamine B (RhB) dye was achieved in a period of 6 hours, much higher than that of bulk BTO NPs solution (10%) under the same energy input and thermal cycle. The recyclability of such pyroelectric membrane was also demonstrated in this work. The proposed concept of the floating pyroelectric composite membrane would not only expand the scope of application of localized heating at interface, but also pave a new way to efficiently harvest and rationally utilize solar energy for pyro-catalytic reactions.

RESULTS AND DISCUSSION

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Figure 2a schematically illustrated the fabrication process of the carbon-PVDF-BaTiO3 (CPVDF-BTO) composite membrane.28-29 BTO NPs were uniformly dispersed in the solution of PVDF/acetone and N, N-dimethylformamide (DMF), and such mixture was then spin-coated on a cleaned glass plate to form transparent PVDF-BTO polymer membrane. After thermal curing, the sample was incubated in a cold-water bath and the PVDF-BTO membrane was peeled off glass plate. The side of the composite film adhering to the glass plate was smooth, the other side with exposed BTO NPs was rough. Carbon black (CB) powder in the size of ~200 nm was dispersed in ethanol solution and sprayed over the smooth side of the PVDF-BTO membrane as a light-to-heat conversion layer, since the CB powder exhibits strong solar spectrum absorption (>82.5%) in the wavelength range from 250 nm to 2500 nm (Figure S2).27 The microscale surface roughness of CB film further improved the solar absorption of the membrane (Figure 2b).30 The cross-sectional view of SEM image reveals that the C-PVDF-BTO membrane with the thickness of ~8 µm consists of a CB layer and a PVDF-BTO layer (Figure 2c). By zooming in the SEM image of PVDF-BTO layer, numerous micro-pores were observed (Figure 2d), which was stemmed from immersion precipitation process.31-34 The energy dispersive spectrometry (EDS) mapping images with the individual elements of F, Ba and Ti were taken to depict the distribution of BTO NPs in the PVDF-BTO membrane (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 are homogeneously distributed in the PVDF-BTO membrane. After thermal curing of PVDF-BTO membrane sticking on the glass plate, organic solvent with low boiling point was evaporated, and a dense composite membrane was left (Figure S4). Such membrane was incubated in the water immediately, and the remaining DMF solvent blended with water, which led to the formation of numerous microporous structures within the PVDF

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film through immersion precipitation process (Figure 2d). Such porous structure is favorable for leveraging the capillary water flow to the hot zone for the evaporation at the surface.35 During the cooling process, heat is rapidly dissipated due to the large latent heat of vaporization of water and then a fast rate of decrease in temperature could be achieved15. A more rapid temperature oscillation can facilitate more free charge generated at the pyroelectric NPs surface, which can further help enhance the pyro-catalytic effect. Another advantage of the porous structure is the increased surface area of the C-PVDF-BTO membrane,36 which helps enhance the pyroelectric effect based on Equation 1. Further closely examining the PVDF-BTO layer, exposed BTO NPs cluster as well as encapsulated NPs were attached or embedded in the PVDF film (Figure S5). Raman spectrum was utilized to examine the characteristic peaks of the structures of BTO NPs. The sharp peaks positioned at 250 cm-1 [A1(TO)], 307 cm-1 [E, B1(TO+LO)], 513 cm-1 [E, A1(TO)], 709 cm-1 [E, A1(LO)] are assigned to the non-centrosymmetric tetragonal structure, which indicates the pyroelectric activity of BTO (Figure S6).28,

37-39

To further confirm the

pyroelectric activity, electrostatic force microscopy (EFM) was used to image and manipulate the ferroelectric polarization of BTO NPs (Figure S7).

40-41

The variation of the spontaneous

polarization of BTO NPs resulted from the reversed external electric field, indicating the presence of the pyroelectricity of BTO NPs. Figure 3a shows the schematic illustration of the localized heating of floating C-PVDF-BTO membrane at the liquid/air interface under modulated light illumination. To avoid the impact of photocatalytic effect of BTO under the ultraviolet light,42 a light filter with the transmitted wavelength ranging from 450 nm to 2000 nm was employed in this work. The PVDF-BTO layer was in contact with the solution to catalyze the degradation reaction. In the experiment, a chopper was used to achieve alternatively heating and cooling process by periodically blocking

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the incident solar light. One thermal cycle was about 12 seconds, including 6-second heating and 6-second cooling. To compare the rate of temperature change achieved by C-PVDF-BTO membrane with that of the bulk BTO NPs solution, an electric heater was utilized to heat up the sample solution. The heater, with the power input of 2 W, which is similar to the solar energy input on the membrane, was immersed into the RhB dye solution (10 mg L−1) and switched on (6 seconds) and off (6 seconds) by a circuit controller (Figure 3b). Figure 3c shows the changes of temperature with time for the floating BTO composite membrane under solar light illumination and bulk BTO NPs solution heated at the bottom via electric heater. The thermocouple was placed close to the heater to measure the temperature cycle of the solution with dispersed BTO NPs. The change of temperature increased from 46 ℃ to 50 ℃ in a 6-second heating process. In fact, the change of temperature of liquid away from the heater was much smaller than that of solution close to the heater (Figure 3c and Figure S8). An IR camera calibrated by thermocouple was used to measure the surface temperature of the floating membrane. Under the similar energy input, a substantial change of temperature (from 38.3℃ to 55.5 ℃) within 6 seconds for the floating membrane was observed. Owing to the low thermal conductivity of the membrane,43 the thermal diffusion, including both conduction and local convection, can be reduced. The most generated heat would be localized at the surface of membrane and leads to the rapid rise of temperature. Figure 3e and 3f depict the IR images of maximum temperature (55.5 ℃) and minimum temperature (38.3 ℃) for the C-PVDF-BTO membrane interfacially localized heating system. Through the calculation of the derivative of the curve from Figure 3c, we plotted the rate of temperature change (dT/dt) curves for the two systems in Figure 3d. For the interfacially localized heating system, the maximum rate of temperature change exceeded 13 ℃ s−1, while that for the bulk heating system was only 1.1 ℃ s−1. With the same energy input, the maximum rate of

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temperature change of interfacially localized heating system was almost 11 times higher than that of the bulk heating system. To compare the pyro-catalytic performance between the interfacially localized heating system and bulk solution heating system, the amount of dispersed BTO NPs in bulk solution was set to equal to the same amount of BTO particles used in the C-PVDF-BTO membrane. Pre-adsorption of all the degradation experiments were performed in the dark at room temperature for 2 hours until the catalysts and dye reached an adsorption-desorption equilibrium (Figure S9). As displayed in Figure 4a, during the interfacial degradation process, the UV-Vis spectra of the RhB solution at different time points were recorded. The maximum absorption peaks at ~553 nm continuously fell down with the degradation time. The inset optical picture shows the color decay of the RhB dye solution at different time points. Figure 4b displays the pyro-catalytic degradation efficiency of C-PVDF-BTO membrane, bulk BTO NPs solution, PVDF-BTO membrane and C-PVDF membrane for RhB dye decomposition. For the interfacially localized heating system, ~75% of RhB was degraded after 6 hours of continuous thermal cycles, while only ~10% of RhB was degraded in the bulk heating system after the same time and cycles. Such great difference in the degradation efficiency can be ascribed to the difference in the rate of temperature change as discussed above. RhB degradation experiment were conducted with the PVDF-BTO membrane to investigate the role of carbon layer in the pyro-catalytic effect. For the PVDF-BTO membrane, ~25% of RhB was degraded after 6 hours compared to the C-PVDFBTO membrane with the degradation efficiency of ~75%. The enhancement of the degradation efficiency on the C-PVDF-BTO membrane resulted from the carbon layer which absorbed and converted the light into the heat rapidly during the heating process. Since PVDF membrane is also a pyroelectric material (Figure S10), the pyro-catalytic property of C-PVDF membrane

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without the embedded BTO NPs was also examined at the water/air interface under the same condition (Figure S11). It showed that ~35% of RhB was degraded after 6 hours of continuous thermal cycles. To evaluate the absolute enhanced pyro-catalytic efficiency of doped BTO NPs in the PVDF membrane at the water/air interface, we subtracted the efficiency of the C-PVDF membrane from the C-PVDF-BTO membrane to obtain a new curve depicted in Figure 4b (dash line with red triangles). According to the result of subtraction, the pyro-catalytic efficiency of the BTO NPs in the C-PVDF-BTO composite membrane remained about 40%, which was still much higher than the bulk heating system (~10%) with the same amount of dispersed BTO NPs and energy input. Although some BTO NPs are encapsulated in the PVDF membrane, these embedded BTO NPs can also transfer the charges to the surface of PVDF membrane for the pyro-catalytic process.29, 44-46 Therefore, the pyro-catalytic effects of attached or embedded BTO NPs and PVDF membrane are coupled together to achieve the eventual degradation efficiency. Figure 4c demonstrated the stability and recyclability of C-PVDF-BTO membrane after performing 8 cycles of the pyro-catalytic degradation test. The appearance of the sample remained almost the same before and after the thermal cycles (Figure 4d). To distinguish the influence of surface area after adding the BTO NPs, we employed the Brunauer–Emmett–Teller (BET) method to measure the surface areas of pure PVDF membrane and PVDF-BTO composite membrane. The N2 adsorption-desorption curve and BET surface area plot were shown in Figure S12. The BET surface areas of pure PVDF membrane and PVDF-BTO composite membrane were 28.5 ± 2.0 and 29.2 ± 0.5 m2·g-1, respectively. The surface area was slightly increased due to the addition of BTO NPs. Since the surface area was almost the same before and after the addition of BTO NPs, the difference between the membrane surface areas played a minor role in the difference of the degradation performance. A control experiment with more porous C-PVDF

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membrane (measured surface area: 35.4 ± 0.5 m2·g-1) was also conducted to clarify the contribution of BTO NPs (see the details in the supporting information and Figure S13). Figure 5 depicts the working principle of the pyro-catalytic degradation activity through the interfacial effect from C-PVDF-BTO membrane. The enhanced degradation efficiency of RhB results from the rapid variation of temperature at the interface, which can be ascribed to two aspects: i) localized heating through an effective photothermal process under the light illumination, and ii) fast heat dissipation due to the interfacial-evaporation-induced quick cooling process when the membrane is blocked from the light. During the heating process, the generated heat were localized at the interface due to photothermal effect and low thermal conductivity of the membrane43, the surface temperature of membrane would dramatically increase, and subsequently decrease the level of spontaneous polarization (PS), leaving excess of compensation charges on the surface of BTO. To balance the decreased polarization, the extra compensation charges react with the surface-adsorbed species, such as OH— and O2, and form radical species11, which decompose the RhB molecules (Figure 5a).47 When the chopper blocks the light from illuminating on the C-PVDF-BTO membrane, the remaining heat results in the interfacial evaporation process, and heat would be rapidly dissipated leading to the temperature dropping. During the cooling process, the dipoles within the BTO NPs re-gain their orientation, leading to the increase in the level of spontaneous polarization. More compensation charges accumulate in the surface region of BTO to reach an equilibrium state, which is driven by the difference between the increased polarization and the shortage of compensation charges.11 Subsequently, different radicals are generated on the surface of BTO NPs (Figure 5b). In order to verify the pyro-catalytic mechanism of BTO NPs, we carried out the radical and hole trapping experiments on C-PVDF-BTO (CPB) composite membrane to determine the main active species. tert-Butyl

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alcohol (TBA, a hydroxyl radical scavenger), p-benzoquinone (BQ, a superoxide scavenger) and disodium ethylenediaminetetraacetate (EDTA, a hole scavenger) were added into the RhB solution, respectively.9, 48-49 As shown in Figure 5c, with the addition of TBA, the degradation efficiency of RhB was only decreased by 9% after 6 hours of thermal cycles, which indicates that ·OH radical was the primary reactive species during the degradation process. It can be observed that 17% of RhB was degraded after adding the BQ to capture ·O2-, which implies that ·O2 also played an important role in the degradation of RhB. The degradation efficiency of RhB showed slight suppression after the addition of EDTA, implying that the holes were the minor active species for the pyro-catalytic degradation.

CONCLUSION In this work, we couple the interfacially localized heating system with pyroelectric NPs to enhance the temperature oscillation rate for the pyro-catalysis. The composite membrane was fabricated by depositing the pyroelectric BTO NPs throughout the porous PVDF substrate as bottom layer for pyro-catalysis and coating carbon black powders on the one side as the photothermal conversion top layer. Periodical solar light illumination controlled by a chopper was used to heat up the membrane floating on the water/air interface, where fast average rate of temperature change of 3℃ s−1 and the instantaneous rate of 13 ℃ s−1 could be reached. Strong pyro-catalytic effect with ~75% degradation efficiency for RhB dye was achieved in this system within 6 hours, which shows greater advance in pyro-catalytic efficiency compared to the bulk pyroelectric NPs solution. The demonstrated reusability and transferability of composite membrane also makes it promising for large scale application. The findings in this work provide

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new insight of efficiently harvest and rationally utilize solar light and even waste heat for pyrocatalytic reactions.

EXPERIMENTAL METHOD Materials: All the chemicals were analytical grade and used without further purification. Acetone, N, N-Dimethylformamide (DMF), Rhodamine B (RhB), and BaTiO3 nanoparticles (BTO NPs) (∼100 nm in diameter) were purchased from Aladdin. Poly(vinylidene fluoride) (PVDF) powders were purchased from Shenzhen Tiancheng Technology Co., Ltd. Deionized water was produced by the Millipore Water Purification System (NANO pure, 18.2 MΩ). Fabrication of the C-PVDF-BTO composite membrane: 2.0 g of PVDF powders were mixed in 18 mL DMF and acetone solvent with volume ratio of 1:3. Such mixture was then incubated at 60 ℃ for 40 minutes in a beaker. After the powders were dissolved completely, solution was cooled down and stayed in room temperature for 30 minutes. 0.6 g of BTO NPs (mass ratio of BTO: PVDF = 30%) were added into the as-prepared PVDF solution and magnetically stirred for 2 hours. Thermogravimetric analysis (TGA) was used to estimate the amount BTO NPs in the PVDF-BTO composite membrane (Figure S14). The freshly prepared BTO/PVDF solution was spin-coated on a clean glass plate (5 cm × 5 cm) at 2000 rpm for 60 s and subsequently thermally cured in an oven at 80 ℃ for 1 hour. After heat treatment, the composite film along with glass slide was immediately immersed in the water bath of 10 ℃. The BTO/PVDF composite film with the weight of 100 mg was peeled off from the glass plate and dried at 60 ℃ in the oven. One side of the composite film adhere to the glass plate is smooth. A mixture of carbon black (CB) powders and ethanol solution (1.5 wt%) was sprayed on the smooth side of the BTO/PVDF

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composite membrane to obtain the Carbon-PVDF-BTO (C-PVDF-BTO) composite membrane sample. The amount of BTO NPs was an optimal usage as a representative to verify the interfacially pyro-catalytic effect with good degradation property (Figure S15). Fabrication of the C-PVDF membrane: The fabrication process of C-PVDF membrane was similar to the C-PVDF-BTO composite membrane. Briefly, the spin-coated PVDF membrane along with glass slide was immediately immersed in the water bath of 10 ℃ . The SEM characterization of this PVDF membrane was shown in Figure S16. A more porous PVDF membrane was prepared by immersing in the ice-water bath of 0 ℃. The membranes were peeled off and then sprayed carbon layer as the preparation of C-PVDF-BTO mentioned above. Pyro-catalytic property test: An aqueous RhB solution (10 mg L−1) was prepared and 5 mL of the such solution was injected into a 10-mL beaker. A 300-W Xe lamp (Shanghai Bilon Instrument Co., Ltd.) equipped with a Fresnel lens (Shenzhen Salens Technology Co., Ltd.) was used as the light source. And the electric hot plate was used as the heat source in the control experiment of bulk BTO NPs solution. The pre-adsorption experiment was performed to ensure an adsorption-desorption equilibrium between the catalysts and dye. The C-BTO-PVDF composite membrane and dispersed BTO NPs were kept in each of the RhB dye solution in the dark at room temperature for 2 hours before heating-cooling thermal cycles. After pretreatment, the quartz beaker with RhB solution and membrane sample was placed at the focal position of the Xe lamp and irradiated by the light with the filter (450 nm~2000 nm) from the top. The illumination power was maintained at ∼2.0 W during the irradiation, and the absorbance spectra of the sample solution were recorded every 1 hour using the spectrometer. The absorbance at 553 nm was used to estimate the concentration of RhB solution. The following Equation 2 was used to calculate the degradation degree (De) of RhB:19

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‫ܦ‬௘ =

஼೚ ି஼ ஼೚

× 100%

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(2)

where C0 is the initial concentration of RhB and C is the concentration at the irradiation time of t. Characterizations: The microstructures of the Carbon-PVDF-BaTiO3 (C-PVDF-BTO) composite membrane were characterized with a field-emission scanning electron microscopy (FESEM, FEI Sirion 200, 5 kV) equipped with equipped with energy dispersive spectroscopy (EDS, INCA X-Act, Oxford Instruments). A Raman spectrometer (LabRAM HR Evolution, Horiba) was used to measure the Raman spectrum of BTO NPs. Electrostatic force microscope (EFM) images of the BTO NPs were recorded by the same atomic force microscope (AFM, Multimode 8, Bruker) on a graphite substrate. A UV-Vis-NIR spectrometer (PerkinElmer, Lambda 750S) was used for the measurement of the optical absorption of the samples in the range of 200-800 nm. An IR camera (FLIR T620) was used to track the real-time thermal map of the C-PVDF-BTO composite membrane floating at the air/water interface during experiment. An Accelerated Surface Area and Porosimetry System (Micromeritics, ASAP 2020) was used for the measurement of BET surface area. Thermogravimetric analysis (TGA) of the BTO-PVDF membrane was obtained using a thermogravimetric analyzer (PerkinElmer, Pyris 1 TGA) with a heating rate of 20 °C·min-1 from 30 °C to 900 °C in air flow. A dynamic mechanical analyzer (DMA, Q800, TA Instruments) was employed to measure tensile stress-strain curve of PVDFBTO composite membrane. Calibration of Infrared Camera: An IR camera (FLIR T620) was used to measure the surface temperature of the floating C-PVDF-BTO membrane. With the heating of the C-PVDF-BTO membrane on water using a hot plate, the IR camera was calibrated by a thermocouple (Model:

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K-H-GGF; Beijing Qiaomu Automation Technology Company; uncertainty quoted from manufacturer: ~ 0.2 ℃).

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FIGURES

Figure 1. Schematic illustration of the setup used for the pyro-catalytic reaction at the liquid/air interface.

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Figure 2. (a) Fabrication process of the C-PVDF-BTO membrane. SEM images of (b) top view (CB side), (c) cross-sectional view, and (d) back view (BTO side) of C-PVDF-BTO membrane.

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Figure 3. Schematic illustration of (a) interfacially localized heating and (b) bulkheating. (c) The temporal temperature curve of the pyroelectric materials for the interfacial system and bulk solution system. (d) The temperature change rate (dT/dt) curve derived from (c). IR images of the maximum (e) and minimum (f) temperature in the interfacial system.

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Figure 4. (a) The UV-vis spectra of the RhB solution under the interfacial pyro-catalytic process with C-PVDF-BTO membrane. The inset optical picture shows the color change of the RhB dye solution. (b) Pyro-catalytic degradation efficiency of RhB as a function of time with different samples. (c) Repeated pyro-catalytic degradation of RhB for continuous 8 cycles. (d) The optical picture of the membrane before and after 8 cycles of the degradation experiment.

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Figure 5. Schematic illustration of pyro-catalytic mechanism of interfacial system under one thermal cycle: (a) localized heating through the photothermal conversion and (b) quick cooling due to the interfacial evaporation. (c) Radical and hole trapping experiments on C-PVDF-BTO (CPB) composite membrane with and without the addition of TBA, BQ, and EDTA.

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ASSOCIATED CONTENT Supporting Information The Supporting Information is available free of charge on the ACS Publications website at DOI: XXX. Additional figures include the absorption spectrum of C-PVDF-BTO membrane, the SEM characterization and EDS mapping, the Raman spectrum of BTO NPs, AFM and EFM characterizations, temperature change plot of bulk solution under electric heating, FTIR spectrum of C-PVDF membrane, BET surface area measurement, TGA analysis, supplementary RhB degradation curves, and stress-strain curve of PVDF-BTO membrane.

AUTHOR INFORMATION Corresponding Author *Chengyi Song Email: [email protected] *Tao Deng Email: [email protected] Author Contributions †Mengdie Min and Yanming Liu equally contributed to this paper. T. Deng, C. Song, P. Tao, W. Shang and J. Wu conceived the idea and designed the experiments. M. Min, Y. M. Liu, C. Song, and T. Deng conducted the experiments and wrote the manuscript. D. Zhao, X. Wang, Y. Qiao, R. Feng, C. Song, and T. Deng helped data analysis, discuss the results and comment on the manuscript.

Notes

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Any additional relevant notes should be placed here. ACKNOWLEDGMENT The authors thank the financial support from National Natural Science Foundation of China (Grant No: 21401129, 51521004, 51420105009 and 51403127), National Key R&D Program of China (No. 2017YFB0406000), Natural Science Foundation of Shanghai (Grant No: 14ZR1423300), the Zhi-Yuan Endowed fund from Shanghai Jiao Tong University. The authors thank Instrumental Analysis Center of Shanghai Jiao Tong University for access to SEM. The authors also thank State Key Laboratory of Metal Matrix Composites for access to UV/VIS/NIR Spectrometer.

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