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Feb 5, 2016 - Novel Bi12O15Cl6 Photocatalyst for the Degradation of Bisphenol A under Visible-Light Irradiation. Chu-Ya Wang, Xing Zhang, Xiang-Ning ...
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Novel Bi12O15Cl6 Photocatalyst for the Degradation of Bisphenol A under Visible-Light Irradiation Chu-Ya Wang, Xing Zhang,* Xiang-Ning Song, Wei-Kang Wang, and Han-Qing Yu* CAS Key Laboratory of Urban Pollutant Conversion, Department of Chemistry, University of Science & Technology of China, Hefei 230026, China S Supporting Information *

ABSTRACT: Bisphenol A (BPA), a typical endocrine-disrupting chemical, is widely present in water environments, and its efficient and cost-effective removal is greatly needed. Among various physicochemical methods for BPA degradation, visible-light-driven catalytic degradation of BPA is a promising approach because of its utilization of solar energy. Bismuth oxychloride (BiOCl) is recognized as an efficient photocatalyst, but its band gap, >3.0 eV, makes it inefficient for solar energy utilization, especially for degrading nondye pollutants like BPA. Thus, preparation and application of bismuth oxychloride photocatalysts with an increased visible-light activity are essential. In this work, inspired by density functional theory calculations, a novel bismuth oxychloride photocatalyst, Bi12O15Cl6, was designed. The nanosheets were successfully synthesized using a facile solvothermal method followed by a thermal treatment route. The prepared Bi12O15Cl6 nanosheets had a favorable energy band structure and thus exhibited a superior visible-light photocatalytic activity for degrading BPA. The BPA degradation rate by the Bi12O15Cl6 was determined to be 13.6 and 8.7 times faster than those for BiOCl and TiO2 (P25), respectively. The photogenerated reactive species and degradation intermediates were identified, and the photocatalytic mechanism was elucidated. Furthermore, the as-synthesized Bi12O15Cl6 nanosheets remained stable in the photocatalytic process and could be used repeatedly, demonstrating their promising application in the degradation of diverse pollutants in water and wastewater. KEYWORDS: Bi12O15Cl6, nanosheet, degradation, photocatalysis, visible light, bisphenol A (BPA)

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light applications.7 Thus, it is necessary to prepare and apply new visible-light-responsive photocatalysts. Recently, bismuth oxyhalides, a novel ternary oxide semiconductor, have attracted great interests for their potential application in photocatalysis. Their uniquely layered structures, with an internal static electric field perpendicular to each layer, can induce an effective separation of the photogenerated electron−hole pairs, and thus achieve high photocatalytic performance.8−19 Among the ternary oxide semiconductors, BiOCl is similar to TiO2 and has a 3.3 eV band gap with a strong absorption in the ultraviolet light region (the absorption edge is 376 nm).20 In recent years, great efforts have been made to reduce the band gap of BiOCl to harvest a larger portion of the sunlight.14,21,22 Different approaches for narrowing the band gap have been pursued to increase the visible light absorption. The most common method is the introduction of oxygen vacancies on the surface of BiOCl.23 Thus, thin BiOCl nanoplates with a high oxygen atom surface density on the {001} facets exhibited an enhanced CO2 trapping capability and an enhanced electron−hole pair separation efficiency, which led

INTRODUCTION Bisphenol A (BPA), which is associated with the epoxy resins, polycarbonate, unsaturated polyester−styrene resins, and flame retardants, is a typical endocrine-disrupting chemical.1 With its wide applications, BPA is widely present in water environments, and thus has raised great concerns about its impact on human health.2 However, BPA could not be decomposed effectively and completely by biological treatment methods because of its stable chemical structure.3 Thus, efficient physicochemical methods are highly desired for the cost-effective and efficient removal of BPA from water and wastewater.4 Among various physicochemical methods, because visible light-driven photocatalytic degradation is environmentally friendly, capable of complete mineralization, low cost, nontoxic, and easily available, it has been recognized as such an approach for BPA degradation.5 To optimize the use of solar energy and reduce costs and energy consumption for photocatalytic water purification, we require efficient and stable photocatalysts that are capable of harvesting visible light.6 Over recent decades, oxide-based semiconductors, such as TiO2, have been widely used for the photocatalytic degradation of pollutants. However, the band gap of the TiO2 limits its photoactivity to the visible region of the spectrum, making it an inefficient photocatalyst for solar © XXXX American Chemical Society

Received: December 11, 2015 Accepted: February 5, 2016

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DOI: 10.1021/acsami.5b12092 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX

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ACS Applied Materials & Interfaces to the photocatalytic CO2 reduction.22 Although several recent studies have reported the achievement of visible light activity by using this method, it is difficult to increase the visible-light activity by further narrowing the band gap of BiOCl via the introduction of oxygen vacancies. Therefore, another route to reduce the band gap of bismuth oxychloride is still needed. Density functional theory (DFT) calculations of bismuth oxychloride indicate that its valence band (VB) is mainly composed of hybridized Bi 6s, O 2p and Cl 3p, whereas the conduction band (CB) is based on the Bi 6s and Bi 6p orbitals.24,25 This calculation suggests that an effective way to decrease the band gap of bismuth oxychloride is to adjust the relative amounts of bismuth, oxygen and chloride. For example, Bi24O31Cl10, has a narrow band gap of 2.80 eV and has exhibited excellent visible light photocatalytic activity toward the degradation of Rhodamine B.25 Also, it was reported that the intrinsic conductivity could be switched from p-type BiOCl to n-type Bi12O15Cl6 by vacuum annealing step.26−28 The exploration of photocatalytic mechanism and potential application of the n-type Bi12O15Cl6 are highly needed.29 Therefore, in this work, a simple and facile solvothermal method followed by a thermal treatment was proposed to synthesize the Bi12O15Cl6 nanosheets with a narrowed band gap. Their photocatalytic activity under visible light was examined for the degradation of BPA in comparison with BiOCl and TiO2 (P25). Based on the identified reactive species and the degradation intermediates, the photocatalytic mechanism of the Bi12O15Cl6 nanosheets for BPA degradation was elucidated. In addition, the stability of the as-synthesized Bi12O15Cl6 nanosheets during the photocatalytic reaction was evaluated. In this way, an efficient and cost-effective photocatalyst was developed for the pollutant degradation in water and wastewater treatment.

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valence state of the constituent elements were analyzed with X-ray photoelectron spectroscopy (XPS) (ESCALAB250, Thermo Fisher Inc., USA). The diffuse reflectance spectra (DRS) were measured using a UV/vis spectrophotometer (Solid 3700, Shimadzu Co., Japan). The electron paramagnetic resonance (EPR) (JES-FA200, JEOL Co., Japan) was used to detect reactive radicals. A liquid chromatographytwo stage tandem mass spectrometry (LC-MS/MS) (Thermo Fisher Scientific Inc., USA) was used to determine the intermediate products from BPA degradation. The total organic carbon (TOC) concentration was measured using a TOC analyzer (Muti N/C 2100, Analytik Jena AG, Germany). Photocatalytic Degradation of BPA. The photocatalytic degradation of BPA by the Bi12O15Cl6 nanosheets was conducted at ambient temperature using a 350 W Xe arc lamp with a 420 nm cutoff filter as the light source and the radiation flux was 82 mW cm−2. Prior to the experiment, 10 mg of the Bi12O15Cl6 nanosheet photocatalyst was added to the 40 mL aqueous solution containing 10 mg L−1 BPA, followed by stirring in the dark for 60 min to ensure sufficient adsorption/desorption equilibrium. Then, during the light irradiation and continuous magnetic stirring, the samples were collected at given time intervals, and the concentrations of BPA and its degradation products were measured using an HPLC (1260 Infinity, Agilent Co., USA) with an Agilent Eclipse XDB-C18 column (4.6 × 150 mm) and the column temperature of 30 °C. To measure the concentrations of BPA and 4′-hydroxy-acetophenone, 50% acetonitrile and 50% deionized water (containing 0.1% formic acid) were used as the mobile phase at a flow rate of 1.0 mL min−1, and the detection wavelength was 273 nm. To determine the phenol concentration, we used 40% acetonitrile and 60% deionized water (without formic acid) as the mobile phase at a flow rate of 0.5 mL min−1, and the detection wavelength was 254 nm.

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RESULTS AND DISCUSSION Morphology and Microstructure of Bi12O15Cl6 Nanosheets. Figure 1 shows the XRD patterns of the prepared

EXPERIMENTAL SECTION

Synthesis of Bi12O15Cl6 Nanosheets. To prepare the nanosheets, we added 0.485 g of Bi(NO3)3·5H2O (1 mmol) to 10 mL of EG. Upon vigorous stirring and sonication for 10 min, the mixture was dispersed to form a homogeneous solution. Meanwhile, 0.018 g of NH4Cl (0.33 mmol) was added to 35 mL of distilled water while vigorously stirring for 5 min to form a homogeneous solution. Then, the above two solutions were mixed, and a white suspension was formed immediately, and was transferred to a 50 mL autoclave with a Teflon liner. It was heated at 160 °C for 12 h, and then allowed to cool to room temperature. The resulting powder was collected via centrifugation and washed with distilled water and alcohol three times to remove the residual ions. The products were then dried at 80 °C for 6 h prior to characterization. Then, the solid powder was calcined in the Muffle Furnace at 400 °C for 5 h. For comparison, BiOCl was also prepared with 0.485 g of Bi(NO3)3·5H2O (1 mmol) and 0.054 g of NH4Cl (1 mmol) using the same procedure. All chemicals used in this work were of analytical grade and purchased from Shanghai Chemical Reagent Co., China without further purification. Physicochemical Characterization of the Catalysts. The X-ray powder diffraction (XRD) patterns of the samples were obtained on a Philips X’Pert PRO SUPER diffractometer equipped with graphite monochromatized Cu Kα radiation (λ = 1.541874 Å). The scanning electron microscopy (SEM) images of the samples were acquired with an X-650 scanning electron microanalyzer and a JSM-6700F field emission SEM (JEOL Co., Japan). The transmission electron microscopy (TEM) images of the samples were recorded on a TEM (JEM-2011, JEOL Co., Japan), using a 100 kV electron kinetic energy. The high-resolution transmission electron microscopy (HRTEM) images were produced with a HRTEM (2010, JEOL Co., Japan) at a 200 kV acceleration voltage. The chemical composition and the

Figure 1. XRD patterns of Bi12O15Cl6 nanosheets.

samples. All of the identified peaks could be assigned to Bi12O15Cl6 (JCPDS card No. 70−0249). It is interesting to see that some strongest peaks were different from the standard card. The main XRD diffraction peak at 2θ = 30.16° corresponds to the (413) planes, demonstrating that the (413) planes were preferential orientated. In addition, no other crystalline impurities were detected, suggesting that the products were composed of the single phase Bi12O15Cl6. The morphology of the Bi12O15Cl6 product was observed with SEM and TEM. The SEM images (Figure 2a, b) reveal that the sample possessed a large scale sheet-like structure with a diameter ranging from 100 to 600 nm. More than 80% of Bi12O15Cl6 nanosheets had a size range of 250−500 nm (Figure S1). The TEM images (Figure 2c) further confirmed a sheetlike structure with an approximately 20 nm sheet thickness. The detailed structure of the sample was further characterized using B

DOI: 10.1021/acsami.5b12092 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX

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198.9 eV, corresponding to the Cl 2p3/2 and Cl 2p1/2 of Cl−, respectively (Figure 3d).30 All of the above results demonstrate that the formed nanostructures were mostly composed of Bi12O15Cl6. The photocatalytic activity of the photocatalyst is closely related to its band structure feature. Typically, the optical absorption of a crystalline semiconductor near the band edge follows the relationship below31 α(hν) = A(hν − Eg )n /2

(1)

Eg = E VB − ECB

(2)

where α, hν, Eg, A, EVB, and ECB are the absorption coefficient, photon energy, band gap, a constant, the valence band position potential, and the conduction band position potential, respectively, and n depends on the characteristics of the transition in the semiconductor. For BiOX, n is 4 for its indirect transition. Figure 4b displays the UV−vis diffuse reflection spectra (UV−vis DRS) of the as-prepared samples, while Figure 4c

Figure 2. (a, b) SEM images, (c) TEM image, and (d) HRTEM image of Bi12O15Cl6 nanosheets.

HRTEM. The HRTEM image (Figure 2d), which was taken from the edge of a single nanosheet, reveals highly crystalline and clear lattice fringes. The continuous lattice fringes with an interplanar lattice spacing of 0.30 nm, as marked in the image, matched well with the (413) atomic planes of Bi12O15Cl6. This further confirms that the (413) peak was different from the standard card. The XPS analysis was performed to explore the surface composition and the chemical state of the as-prepared Bi12O15Cl6 nanosheets. From the full scan spectrum (Figure 3a), the peaks of the Bi, O, Cl, and C elements could be

Figure 4. (a) Images of the Bi12O15Cl6 nanosheets and BiOCl, (b) UV−vis diffuse reflectance spectrum, (c) the band gap values, estimated from the plotted curve of (αhν)1/2 versus hν, and (d) XPS valence band spectrum for Bi12O15Cl6 and BiOCl.

shows the Tauc plots ((αhv)1/2 vs. hv) of the as-prepared Bi12O15Cl6 nanosheets and BiOCl. These results demonstrate that the semiconductor band gap was governed by the linear Tauc region, which was just above the optical absorption edge.32 Extrapolation of this line to the photon energy axis yields the semiconductor band gap. Thus, the Eg of Bi12O15Cl6 nanosheets was determined to be approximately 2.36 eV, and the Eg of BiOCl approximately 3.37 eV. The results indicate that the Bi12O15Cl6 nanosheets had a narrower band gap in the visible-light region. The colors of the corresponding Bi12O15Cl6 and BiOCl products were light yellow and white (Figure 4a), respectively, which is in agreement with the UV−vis DRS spectra result. The VB values of both the Bi12O15Cl6 nanosheets and the BiOCl were measured by the XPS valence spectra, as shown in Figure 4b. The Bi12O15Cl6 nanosheets and the BiOCl displayed a VB with a maximum energy edge at approximately 1.85 eV. Thus, according to the optical absorption spectrum, the CB minimum of the Bi12O15Cl6 nanosheets and BiOCl were −0.51

Figure 3. XPS spectra of for Bi12O15Cl6 nanosheets: (a) survey spectrum; (b) Bi 4f, (c) O 1s, and (d) Cl 2p.

identified. The XPS spectra were corrected for specimen charging by referencing the C 1s peak to 284.60 eV. The Bi 4f XPS spectrum (Figure 3b) shows two main peaks with binding energies at 159.8 and 165.2 eV (with the splitting energy Δ = 5.4 eV), corresponding to the Bi 4f7/2 and Bi 4f5/2 of Bi3+, respectively. The O 1s core level spectrum (Figure 3c) fit well with the peak at 529.4 eV, which belonged to O2− from a bismuth−oxygen bond in Bi12O15Cl6. The Cl 2p XPS spectrum exhibits two main peaks with binding energies at 194.5 and C

DOI: 10.1021/acsami.5b12092 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX

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ACS Applied Materials & Interfaces and −1.52 eV, respectively. Thus, the CB minimum of the Bi12O15Cl6 nanosheets down-shifted by 1.01 and occurred at −0.51 eV, compared to that of BiOCl. Degradation of BPA by Bi12O15Cl6 Nanosheets. The photocatalytic activity of the prepared Bi12O15Cl6 nanosheets was examined for the degradation of BPA,33 which is a colorless, endocrine-disrupting molecule in water.34 Figure 5a

Figure 5. (a) Photocatalytic degradation of BPA with Bi12O15Cl6, BiOCl, TiO2 (P25), and blank test under visible-light irradiation; and (b) kinetic curves of Bi12O15Cl6, BiOCl, TiO2 (P25), and blank test.

Figure 6. (a) BPA and 4′-hydroxy-acetophenone during photodegradation, (b) standard specimen of 4′-hydroxy-acetophenone, (c) 4′-hydroxy-acetophenone, BPA and phenol in the photodegradation, and (d) standard specimen of phenol.

shows the evolution of the visible spectrum of BPA as a function of time in the presence of the photocatalysts. The results reveal that the BPA could not be self-degraded under visible light irradiation in the absence of the photocatalysts, and BPA could be almost completely degraded by the Bi12O15Cl6 nanosheets within 6 h. It exhibited the greatest photocatalytic activity compared with only ∼10% BPA degradation for BiOCl and 20% for TiO2 (P25). To further compare the photocatalytic capacities of the Bi12O15Cl6 nanosheets, BiOCl, and TiO2 (P25), we calculated the kinetic constants for these photocatalysts and the blank sample by plotting the kinetic curves. The degradation kinetics of BPA was investigated by fitting the experimental data to the Langmuir−Hinshelwood model when Bi12O15Cl6 nanosheets, BiOCl, and TiO2 (P25) were respectively used.35 Because the reactant concentration was low, the following pseudo first-order kinetics equation was used36 −ln(C t /C0) = kt

BPA. An increasing peak that occurred at 3.9 min appeared from the second BPA solution sample, which was taken 30 min after the beginning of the visible light irradiation. However, no peaks were found in the curve of the first sample, which was acquired just before the irradiation. This result indicates that the species was one of the BPA degradation products by Bi12O15Cl6 nanosheets, which was in agreement with the peak occurring at 3.9 min. A series of 4′-hydroxy-acetophenone standard solutions with different concentrations were then tested with HPLC under the same conditions. The 4′-hydroxyacetophenone peak occurred at 3.9 min (Figure 6b), which is in accordance with the degraded product of BPA. The samples of BPA solution before and after visible light irradiation at different times (5 samples in total) were analyzed by LC-MS/MS to obtain more information about the reaction intermediates and the mechanism. Each irradiated sample exhibited an obvious peak at m/z 136, while no peak at m/z 136 was observed for the sample before irradiation. Then, MS/ MS spectrogram of the molecule with m/z 136 was tested (Figure S3) and 4′-hydroxy-acetophenone was identified as one of the products. To find more information about the photocatalytic degradation products, each sample was detected immediately by HPLC with another measurement wavelength and mobile phase. This time, apart from the peaks of BPA (12.9 min) and 4′-hydroxy-acetophenone (3.8 min), another degraded product, phenol, was also detected in each irradiated sample, whose characteristic peak occurred at 5.9 min (Figure 6c) and is in consistent with the standard specimen of phenol (Figure 6d). This result indicates that phenol was another degradation product. Furthermore, a TOC removal of 50% was achieved under visible light irradiation (Figure S4). Photocatalytic BPA Degradation Mechanisms. To verify the presence of •O2− and •OH, we used terephthalic acid (TPA) and nitroblue tetrazolium (NBT) to capture •OH and •O2−, respectively.21 The presence of the •O2− species was confirmed by a decrease in the maximum absorbance of NBT in the UV−vis spectra (Figure S5a). This result is in accordance with the inference regarding the band structure of Bi12O15Cl6. Bi12O15Cl6 is able to produce •O2− by the photogenerated electron (e−) because CB occurs at −0.51 eV and is more

(3)

where C is BPA concentration and k is the apparent rate constant. The reaction kinetics of all of the samples could be fitted well by the pseudo first order rate model with high correlation coefficients (Figure 5b). The calculated k value for the Bi12O15Cl6 nanosheets was 0.368 h−1, which was 13.6 and 8.7 times higher than that of BiOCl and TiO2 (P25), respectively. The BET values were 7.4, 5.9, and 42.3 m2 g−1 for Bi12O15Cl6, BiOCl, and TiO2 (P25), respectively (Figure S2). The surfacearea-normalized photocatalytic activity of Bi12O15Cl6 (0.0497 g h−1 m−2) was substantially higher than that of BiOCl (0.0046 g h−1 m−2) and TiO2 (P25) (0.0001 g h−1 m−2) samples. Thus, the Bi12O15Cl6 nanosheets exhibited a great photocatalytic activity under visible light irradiation, which was attributed to the narrower band gap of Bi12O15Cl6 nanosheets (2.36 eV) than BiOCl (3.37 eV), rather than the surface area. Degradation Products of BPA by Bi12O15Cl6 Nanosheets. To explore the photocatalytic degraded products of the BPA, we detected the reaction intermediates during the photocatalytic process using HPLC. Figure 6a shows the process of the degradation of BPA as observed with HPLC, in which the decreasing peak that occurred at 7.8 min represented D

DOI: 10.1021/acsami.5b12092 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX

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ACS Applied Materials & Interfaces negative than that of O2/•O2− (−0.33 eV). Figure S5b indicates the existence of •OH because the 420 nm peak in the fluorescence spectra increased over time,37 and EPR test (Figure S6) further proved the •OH generation as the four characteristic peaks of •OH were observed in the EPR spectrogram with an intensity ratio of 1:2:2:1. Thus, •OH was generated indirectly from e− via •O2−, rather than h+ directly. The h+ of Bi12O15Cl6 could not produce •OH because the VB of Bi12O15Cl6 occurred at 1.85 eV and was less positive than that of OH−/•OH (2.3 eV). For comparison, NBT and TPA were also used to measure the reactive oxygen species (ROS) generated over Bi12O15Cl6 and BiOCl. The peak value changes show that much more •O2− was generated by Bi12O15Cl6 than by BiOCl (Figure S5c), and that •OH at a certain level of was generated by Bi12O15Cl6, while almost no •OH was generated by BiOCl (Figure S5d). These results indicate a higher activity of Bi12O15Cl6 than BiOCl under visible-light irradiation. To identifiy the role of the active species responsible for the degradation of BPA within the Bi12O15Cl6 nanosheets under visible light irradiation, scavenger experiments were carried out by adding various scavengers. The scavengers included sodium oxalate (Na2C2O4) for photogenerated hole (h+), tert-butyl alcohol (TBA) for •OH, p-benzoquinone (PBQ) for •O2−, and N2 for dissolved oxygen.38,39 The degradation of BPA was greatly suppressed by the addition of these scavengers (Figure 7a). The inhibition efficiencies for the removal of BPA were

Thus, the photocatalytic degradation of BPA was likely to occur through the oxidation by h+, •OH, and •O2−, which were generated from O2 in the following series of reactions40 Bi12O15Cl 6 + hν → h+ + e−

(4)

O2 + e− → •O2−

(5)

•O2− + •O2− + 2H+ → H 2O2 + O2 −

H 2O2 + e → •OH + OH +

−

−

BPA + h , •OH or • O2 → degraded products

(6) (7) (8)

As shown in Figure 8b, BPA and O2 molecules were initially adsorbed on the surface of the Bi12O15Cl6 nanosheets, followed by the photoinduced electron−hole pair generation under visible light irradiation. •O2− was generated from the activation of the chemisorbed O2 through a one-electron transfer via the conduction band of Bi12O15Cl6 excitation. Then, •O2− reacted with H+ and generated H2O2, which was excited by e− and changed into •OH. Finally, •OH, as the main active species, could efficiently oxidize BPA into 4′-hydroxy-acetophenone and phenol under visible-light irradiation. Additionally, the photoinduced holes in the valence band also played an equivalent role in the BPA degradation under visible-light irradiation. Stability and Reusability of Bi12O15Cl6 Nanosheets for BPA Photodegradation. To evaluate the reusability of the assynthesized Bi12O15Cl6 nanosheets, we collected the sample powders at the end of the photocatalytic reaction and were reused six times under the same conditions. The SEM images of the Bi12O15Cl6 sample after the photocatalytic reactions reveal that its morphological structure remained unchanged (Figure 9a). As shown in Figure 9b, the Bi12O15Cl6 nanosheets

Figure 7. (a) Photocatalytic degradation of BPA with Bi12O15Cl6 by adding various scavengers, and (b) kinetic curves of Bi12O15Cl6 by adding various scavengers.

estimated to be 81% for sodium oxalate, 45% for TBA, 55% for PBQ, and 67% for the dissolved oxygen, respectively. The results show that the reaction kinetics of all of the samples fitted well with the pseudo first order rate model with high correlation coefficient values (Figure 7b). The calculated k values for the Bi12O15Cl6 nanosheets with the addition of the scavengers were 0.0008, 0.0023, 0.0019, and 0.0014 h−1 for Na2C2O4, TBA, PBQ, and N2-purging, respectively (Figure 8a).

Figure 9. (a) SEM of the Bi12O15Cl6 nanosheets after 6 cycles, and (b) recycling properties of the photocatalytic degradation of BPA over Bi12O15Cl6 nanosheets.

were highly stable and maintained their high photocatalytic performance over the six reaction cycles. Therefore, the

Figure 8. (a) Kinetic constant of each scavenger, and (b) the schematic of BPA degradation. E

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Bi12O15Cl6 photocatalyst is stable in the photocatalytic degradation of organic pollutants, which is very important for its practical applications.

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CONCLUSIONS The designed and as-synthesized Bi12O15Cl6 nanosheets exhibit a favorable energy band structure. Thus, they have a superior photocatalytic activity for the degradation of BPA under visible light irradiation with a reaction rate of 13.6 and 8.7 times faster than those for BiOCl and TiO2 (P25), respectively. Additionally, Bi12O15Cl6 nanosheets remain stable in the photocatalytic process and can be used repeatedly. The photogenerated reactive species and degradation intermediates are identified, and a photocatalytic mechanism is proposed. This work demonstrates that the Bi12O15Cl6 nanosheets can act as an excellent photocatalyst for the degradation of BPA. Our findings indicate promising applications for the bismuth oxychloride photocatalysts in water and wastewater treatment and help expand the use of this catalyst for the degradation of diverse pollutants under visible-light irradiation.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsami.5b12092. Figures S1−S6 (PDF)

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AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected]. Fax: +86-551-63601592. *E-mail: [email protected]. Fax: +86-551-63601592. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work is supported by the Natural Science Foundation of China (51538011), the Program for Changjiang Scholars and Innovative Research Team in University and the Collaborative Innovation Center of Suzhou Nano Science and Technology of the Ministry of Education of China, and the Open Project of State Key Laboratory of Urban Water Resource and Environment (QA201402).

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DOI: 10.1021/acsami.5b12092 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX