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Self-generation of reactive oxygen species on crystalline AgBiO3 for the oxidative remediation of organic pollutants Jianyu Gong, Chung-Seop Lee, Eun-Ju Kim, Jae-Hwan Kim, Woojin Lee, and Yoon-Seok Chang ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.7b06772 • Publication Date (Web): 14 Aug 2017 Downloaded from http://pubs.acs.org on August 17, 2017

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ACS Applied Materials & Interfaces

Self-generation of reactive oxygen species on crystalline AgBiO3 for the oxidative remediation of organic pollutants

Jianyu Gong a,b, Chung-Seop Lee b, Eun-Ju Kim b, Jae-Hwan Kim b, Woojin Lee b and Yoon-Seok Chang b,*

a School of Environmental Science and Engineering, Huazhong University of Science and Technology, Wuhan, 430074, China b Division of Environmental Science and Engineering, Pohang University of Science and Technology (POSTECH), Pohang, 37673, Republic of Korea.

*Corresponding author contact information: E-mail : [email protected] Phone: +82-54-279-2281; Fax: +82-54-279-829

Keywords: ROS, AgBiO3, self-production, lattice oxygen, oxidative degradation

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Abstract : In this study, we synthesized a novel perovskite nanomaterial consisting of AgBiO3 nanoparticles (NPs) via an ion-exchange method for remediation of polluted environments. The AgBiO3 NPs could self-produce significant amounts of reactive oxygen species (ROS) without light illumination or any other additional oxidant due to the controllable release of lattice oxygen from the crystalline AgBiO3, resulting in the formation of ROS somehow. The self-produced 1O2, O2•– and •OH were confirmed by electron spin resonance spectroscopy using a spin trap technique. We found that the AgBiO3 NPs could be reused for the mineraliztion of most recalcitrant organic compounds alone, including Rhodamine B (RhB), phenol, 4-chlorophenol, 2,4-dichlorophenol and bisphenol-A. After the repeated eight cycles of continious treatment of RhB, AgBiO3 NPs still achieved 79% of degradation after 30 min of treatment. Characterization results revealved that the lattice oxygen inside AgBiO3 was activated to form active oxygen (O*), which resulted in consecutive formation of ROS. This study provides a new insight on the lattice oxygen activation mechanism of silver bismuthate and its application to the remediation of polluted waters.

INTRODUCTION With the development of modern industrial production and the improvement of living standards, the problem of water pollution is a threat to human health and environmental ecosystems.1 Phenolic compounds, which are widely present in surface water and groundwater, are a kind of important organic pollutants. Due to its high stability and toxicity, phenolic compounds cannot be completely degraded by biodegradation or chemical reduction. Based on other studies, advanced oxidation technology could be utilized to treat phenolic pollutants, effectively, such as Fenton reaction, electro-Fenton system, photo-catalysis and so on.2 However, the problematic 2


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location of phenolic pollutants in groundwater restricts the application of an advanced oxidation process. Therefore, it is necessary to develop a novel type of high activity material which does not need the addition of chemicals, light or electricity supporting to produce ROS, independently and efficiently. The main reactive oxygen species (ROS) such as singlet oxygen (1O2), superoxide anion radical (O2•–) and hydroxyl radical (•OH) are playing a role key in oxidative degradation of organic compounds due to the high reactivity of ROS.3,4 For practical purpose, many researchers focused on how to produce ROS without any external support. Among those studies, iron based materials or methods have been widely considered. Choi et al. utilized zero valent iron (ZVI) to oxidative degradation of 4-chlorophenol (4-CP) in the presence of natural organic matter.5 Zhang et al. synthesized Fe@Fe2O3 nanowires to perform aerobic degradation of 4-CP.6,7 And, bismuth modified ZVI has been also synthesized for the oxidation of 4-CP based on the use of citric acid in our previous study.8 The mechanism of oxidative degradation of organic pollutants by iron-based materials could be explained by the generation of ROS or H2O2 quickly decomposed to form ROS. However, these systems are only feasible in the presence of copious amounts of oxygen or additives, which restrict its application to the remediation of polluted groundwater. Therefore, it is highly necessary to fabricate more specialized materials to treat this issue. Thus far, substantial efforts have been made for exploiting complex metal oxides based on a perovskite structure.9 The perovskite oxide structure is usually formed as ABO3 which can accommodate most of the metallic ions in the Periodic Table together. An ideal perovskite structure is a cubic crystal that is composed of a threedimensional framework of corner-sharing BO6 octahedra.10 Therefore, substitution of the A- or (and) B- sites by multiple cations would distort the compositional space, 3



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altering the symmetry of the pristine structure and the physical properties.11 Especially, the electronic properties of perovskite and its electronic dispersion, which are so important for the application of perovskite materials, would be significantly changed.12 In most cases, perovskite materials usually work as photocatalysts. However, the expensive external instruments and energy requirements have limited its application to the photocatalysts. In addition, insufficient dissolved oxygen molecules in the aqueous solution would also limit enough ROS production. Bismuthate is an interesting perovskite material because it can be stabilized in its exclusive electric structure of MBiO3 (M= Li, Na, Ba, Ca).13,14 Two different valences (Bi3+ and Bi5+) of bismuth exist in distorted octahedral (BiO6) structure.15 The excellent reactivity of these bismuthate oxides has also been reported due to the filled Bi 6s band of Bi3+ and the empty 6s band of Bi5+.16 Herein, silver bismuthate nanoparticles (AgBiO3 NPs) attracts an attention for it can self-produce large amounts of ROS without any chemicals, additives, and/or light illumination due to the lattice oxygen activation from the crystalline AgBiO3. Furthermore, to comprehensively understand its mechanism, the identification, quantification and kinetics evaluation of the ROS production on the AgBiO3 NPs have been investigated followed by utilization of this material in practical applications.

2. EXPERIMENTAL SECTION 2.1. Chemicals. Sodium bismuth (NaBiO3), silver nitrate, 5,5-dimethyl-1pyrroline N-oxide (DMPO), 2,2,6,6-tetramethyl-4-piperidinol (TMP), nitroblue tetrazolium (NBT), coumarin, Rhodamine B (RhB), 2,4-dichlorophenol (2,4-DCP), 4chlorophenol (4-CP), phenol, bisphenol-A (BPA) 1,4-benzoquinone (BZQ), isopropanol (IPA), sodium fluoride (NaF), sodium azide (NaN3) and furfuryl alcohol 4


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(FFA) were purchased from Sigma-Aldrich. Hydrochloric acid and absolute ethanol (ACS grade) were purchased from Merck. All chemical reagents were analytical grade and used without further purification. Ultrapure water (resistivity > 18 MΩ·cm) obtained from a water purification system (Millipore, France) was used in all experimental procedures. 2.2 Sample preparation. The synthesis of the AgBiO3 NPs was achieved via a simple ion-exchange method. Briefly, solid AgNO3 (0.17 g or desired amount) was dissolved in 100 mL water. Then, NaBiO3 (0.3 g or desired amount) was added. After 15 min of stirring, a black sediment was formed. Then, the resulting particles were separated by centrifugation, and washed with water and ethanol several times. Finally, these samples were collected after drying overnight at room temperature. 2.3. Characterization. HRTEM (JEOL JEM-2200FS) was employed to characterize the morphology of the nanomaterials and the related Fast Fourier Transform (FFT) observed. The Brunauer−Emmett−Teller (BET) surface area and pore size distribution were measured by N2 adsorption and desorption using an ASAP 2010 system at 77 K. The phase detection was accomplished using an XRD at 40 kV and 40 mA (MAC Science Co., Japan) using Cu Kα radiation and analyzed by Highscore program. The X-ray photoelectron spectra (XPS) analysis was conducted on a VG ESCALAB 220iXL. The fluorescence spectra were recorded on a Fluoromax-4 (HORIBA, France) fluorimeter. ROS and oxygen vacancy were detected with electron spin resonance (EPR) spectroscopy (Bruker A200). 2.4. Degradation experiments. Assessment of the AgBiO3 NPs was carried out by measuring the degradation of several organic pollutants, such as RhB (0.01 mM), 2,4-DCP (0.2 mM), 4-CP (0.2 mM), phenol (0.2 mM) and BPA (0.2 mM), in aqueous phases. All of these degradation experiments were carried out without adjustment of 5



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the initial pH by acid or alkali. The as-prepared AgBiO3 NPs (1 g L−1) were added to 50 mL of the pollutant solution. The contents were stirring at a constant speed throughout these reactions. A series of recycling degradation experiments were conducted to investigate the durability and efficiency of AgBiO3 and its potential for corrosion resistance during degradation. After the first cycle of degradation, these nanomaterials were collected by centrifugation and placed into fresh RhB solution again, and the process was repeated eight times. Here, we defined the AgBiO3 NPs that were only stirring in pure DI water for 4 h as aged AgBiO3 NPs. In addition, we named the samples that were re-used for four times and eight times of degradation as 4 runs AgBiO3 NPs and 8 runs AgBiO3 NPs, respectively. A series of active species trapping experiments were conducted by adding radical scavenging species, such as IPA, BZQ, NaF, and Na3N, to investigate the contributory roles of the respectively generated reactive •OHbulk, O2•–, •OH and 1O2 in the solution. Furthermore, the generation of 1O2 was analyzed by detecting the concentration of FFA (0.1 mM) with HPLC.17 NBT (2.5×10-2 mM), which easily reacted with O2•– and produced a purple precipitate, was selected as a molecular probe to test the concentration of O2•–.18 And, the production of •OH was tested based on the concentration of 7-hydroxycoumarin (7-HOC) in the fluorescence spectra because •OH can react with coumarin (0.1 mM) to produce 7-HOC.19 EPR is using to further identify the presence of ROS. TMP and DMPO are used for the identification of 1O2 and O2•– in ethanol and methanol, respectively. And, •OH is confirmed by the presence of DMPO in water. More details could be found in ESI. 2.5. Analytic methods. The quantitative analyses of organic compounds were performed using HPLC on an Agilent 1100 chromatograph (Agilent, USA) equipped with a C-18 column (250 mm × 4.6 mm). The eluent compositions were (a) 0.1% 6


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phosphoric acid aqueous solution and acetonitrile (70:30 v/v) for 4-CP, 2,4-DCP and FFA and (b) water and methanol (50:50 v/v) for RhB, phenol and BPA. GC/MSD studies were carried out using an Agilent-5973 gas chromatography containing a Carbowax capillary column. Helium was used as a carrier gas, and the flow rate was 1 mL/min. The initial column temperature was maintained at 70 °C for 2 min then increased to 310 °C at 10 °C min−1. The MS was operated in the scan mode with a scan range of m/z 50 to 1000.

3. RESULTS AND DISCUSSION 3.1. Materials Characterization. The fresh AgBiO3 NPs exhibited a block shape (Figure 1A) and were shown as a black powder (the inset of Figure 1A, top). The mapping results indicated a uniform distribution of Ag, Bi and O elements throughout the AgBiO3 NPs (Figure S1, Supporting Information). The Ag/Bi/O atomic ratio determined by EDX analysis (the inset of Figure 1A, bottom) was approximately 0.98:1:3 which was almost consistent with the design ratio of Ag/Bi/O (1:1:3). The surface area of the fresh AgBiO3 was 12 m2/g (BET) with a size distribution of nearly 250 nm (Figure S2 and its inset). HRTEM showed the solid states, and the planes of AgBiO3 (104) and NaBiO3 (002) were confirmed by the Fast Fourier Transform (FFT) patterns (Figure 1B and its two insets). The XRD analysis (Figure 1C) further confirmed that the fresh sample of the nanomaterial primarily contained AgBiO3 (JCPDS 01-089-9072). We used an ion-exchange method to synthesize AgBiO3 and there might be not washed NaBiO3 remained in the sample (JCPDS 00-001-0090). Nevertheless, the main component of the designed AgBiO3 was proved by the degradation efficiecny of RhB discussed later.

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3.2. Reactivity of AgBiO3. Figure 2A shows the decomposition rates of RhB on the different nanomaterials. RhB underwent rapid (kobs = 0.1979 min−1) and excellent decomposition in the presence of AgBiO3 NPs within 15 min. The inset of Figure 2A shows a decrease in the characteristic RhB absorption peak, as well as the images obtained from Ultraviolet–Visible (UV/Vis) spectroscopy. In addition, the effect of the atomic ratio of Ag-Bi on the degradation of RhB is shown in Figure S3. The maximum degradation of RhB was achieved using AgBiO3 with an atomic ratio of 1:1 (Ag:Bi). Therefore, this material was selected as the optimal nanomaterial for all further degradation studies. To assess the durability of AgBiO3 NPs against potential inactivation, the same concentration of RhB was repeatedly added to perform repeated RhB degradation tests for 30 min each, as shown in Figure 2B. After the 8th run, the activity of the recycled AgBiO3 NPs slightly decreased compared to that of freshly prepared AgBiO3 NPs; however, the recycled AgBiO3 NPs still achieved 79% removal of RhB, indicating that this nanomaterial was still durable and efficient. Furthermore, it seemed reasonable that AgBiO3 NPs would remain active and effective for further subsequent degradation cycles. Figure 2C clearly shows that the relative degradation efficiencies were significantly reduced to 30, 53, and 82% in the presence of NaN3, pbenzoquinone (BZQ), and NaF, respectively, indicating that 1O2 and O2•– are the most important oxidants responsible for the degradation of RhB, and that •OH provides a partial contribution to the degradation of RhB. On the other hand, the degradation efficiency of RhB was not significantly affected by the concentration of dissolved oxygen (Figure S4). We have tested a possibility that AgBiO3 NPs could also be repeatedly used for the degradation of some other organic compounds. To further demonstrate the 8


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superiority of AgBiO3 NPs, we have also carried out tests for the degradation of four organic pollutants (Figure S5). The pseudo-first-order rate constants for the degradation of these organic pollutants by AgBiO3 NPs are presented in Figure S6. The rate constants increased in the order of BPA (0.177 min−1) < phenol (0.254 min−1) < 4-CP (0.369 min−1) < 2,4-DCP (0.519 min−1). AgBiO3 NPs can be reused for the degradation of phenol, 4-CP and 2,4-DCP, while it cannot be reused for the degradation of BPA due to abrupt decrease of its reactivity by the repeated use of AgBiO3, indicating that BPA is more recalcitrant than other compounds. The amount of total ROS generated from the lattice oxygen of AgBiO3 was lower than that was rapidly consumed for the complete degradation of BPA. To comprehensively quantify and kinetically evaluate the ROS self-production on AgBiO3 NPs, we measured the concentrations of 1O2, O2•– and •OH generated from different nanomaterials by FFA, NBT and coumarin (Figure S7), respectively, and the results were summarized in Table 1. Furthermore, the presence of 1O2, O2•– and •OH were clearly confirmed using EPR (Figure 2D).20-22 The highest generation rates of ROS were achieved when using the fresh AgBiO3 NPs, followed by 4 runs and 8 runs of AgBiO3 NPs. This point towards the possibility that the production of ROS gradually decreases due to the deactivation of AgBiO3 NPs during the sequential recycling degradation of the pollutant (RhB). 3.3. Reaction mechanism. The crystal structure of AgBiO3 used for the degradation reactions was identified by XRD analysis. Figure 3A shows the XRD patterns of the re-used AgBiO3 NPs in the degradation of RhB. No significant changes in the aged AgBiO3 NPs were observed. However, for the 4th and 8th runs AgBiO3 NPs samples, new peaks at 2θ = 23.7, 30.1, 32.6, 42.2, and 46.8° were observed, which corresponded to Bi2(CO3)O2 (JCPDS 25-1464).23 Bi2(CO3)O2 is generally used 9



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as a photocatalyt and does not produce ROS in the dark.24,25 Therefore, the partial transformation of AgBiO3 to Bi2(CO3)O2 should cause slightly lower removal of RhB. The crystalline form of AgBiO3 was also further confirmed by the SEM and HRTEM images (Figure S8). A few plate-like structures appeared in the aged AgBiO3 NPs (Figure S8A-1). The interfringe spacing of 0.467 nm corresponded to the AgBiO3 (101) plane, which could also be confirmed in the FFT pattern (Figure S8A-2 and the inset). For the 4th runs of AgBiO3 NPs (Figure S8B-1), most of the particles were transformed into flower-like structures consisting of many short pieces due to the formation of Bi2(CO3)O2. The interfringe distance of 0.295 nm belonged to the Bi2(CO3)O2 (103) plane as shown in Figure S8B-2 and the inset. For the eight runs of AgBiO3 NPs, the flower-like structures were still maintained, however the particles appeared to be covered by the residual organic compounds during the degradation of RhB (Figure S8C-1). The interfringe distance of 0.417 nm belonged to the AgBiO3 (012) plane, and the distance of 0.372 nm corresponded to the Bi2(CO3)O2 (101) plane (Figure S8C-2 and the inset). The aforementioned observations were consistent with the XRD results. As we expected, the degradation efficiency of RhB was highly related to the cystalline transformation of AgBiO3. According to the calculation of the peak areas at the position of 2θ = 32.6°, after the 4th run for the degradation of different organic compounds by AgBiO3 NPs, the amount of Bi2(CO3)O2 generated increased in the order of 2,4-DCP < 4-CP < phenol < RhB < BPA (Figure 3B). This indicates that excessive amount of AgBiO3 NPs was transformed to Bi2(CO3)O2 during the degradation of BPA. Therefore, during the 4th run, AgBiO3 cannot further degrade BPA, while it still worked very well for the removal of RhB, phenol, 4-CP and 2,4-

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DCP even at 8th run. The result from the XRD patterns was consistent with those for degradation of several organic chemicals presented above. The XPS of the O 1s transition are shown in Figure 4A. For the fresh AgBiO3 NPs, the O 1s peak includes three distinct peaks with binding energies of 529.4, 530.4, and 532.5 eV. According to the literature, the O 1s featured at 529.4 eV is the characteristic of lattice oxygen,26 and no other changes for the aged AgBiO3 NPs were observed. The characteristic peak at 529.4 eV decreased after several continuous degradation runs (Figure 4A-d), indicating that the amount of oxygen present in the lattice of AgBiO3 gradually decreased during the reaction. The loss might be due to the conversion of lattice oxygen to ROS as the RhB underwent oxidative decomposition accompanied by the reduction of Bi and Ag ions. The peak at 530.4 eV typically corresponds to active oxygen or chemisorbed oxygen.27 The change in this oxygen signal indicates that the relative intensity of active oxygen increases significantly after the 4th and 8th degradation runs alongside the increase in the intensity of these peaks, resulting from the adsorbed oxygen being incorporated into the Bi2(CO3)O2 carbonate. The production of active oxygen increased during the 1st run of RhB degradation but gradually decreased with repeated runs. Figure 4B shows the spectra of Ag 3d. For the fresh AgBiO3 NPs, the binding energies of 367.2 and 373.1 eV were assigned to 3d5/2 and 3d3/2 of Ag, respectively, indicating the presence of Ag2+.28 For the 8 runs, the Ag 3d5/2 contained two main peaks at 367.5 and 368.9 eV, which were ascribed to Ag+ and Ag0, respectively,29 indicating that lower valence Ag species were gradually formed from the consecutive reduction of Ag2+ → Ag+ → Ag0 during the degradation of RhB. Therefore, this indicated that Ag ions existed as a mixture of both metallic silver (Ag0) and oxidized silver (Ag+ and Ag2+) in the reused AgBiO3 NP samples. 11



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In figure 4C, The XPS of Bi 4f exhibits large double peaks at 158.5 and 163.8 eV due to Bi 4f7/2 and Bi 4f5/2, respectively. In this figure, the Bi 4f7/2 and Bi 4f5/2 peaks gradually shift to higher binding energies because of the reduction of Bi5+ to Bi3+ and the continuous transformation of Bi2(CO3)O2 during the sequential degradation of RhB on AgBiO3 NPs. Figure 4D shows the XPS spectra of C 1s. The primary peak in the C 1s spectra of the fresh AgBiO3 and the aged AgBiO3 NPs was located at 284.8 eV corresponding to the C–C/C–H bonds from adventitious carbon. The other peak at 286.5 eV corresponds to C–OH/C–O–C groups resulting from CO2 adsorption.30 At the XPS spectrum of 8th run AgBiO3 NP sample, the peak at 288.8 eV corresponds to the C–O/C–O–Bi bonds of Bi2(CO3)O2, and the increased intensity of the peak at 285.8 was due to the presence of [CO3]2- groups in Bi2(CO3)O2. This can provide an excellent evidence for the transformation of Bi2(CO3)O2 during the degradation of the target organic. According to the above discussion, we could confirm that the lattice oxygen (O2-) was gradually released from the crystalline AgBiO3 to form ROS because of the reduction of Bi5+ to Bi3+ and Ag2+ to Ag+ and (or) Ag0 through the equations (1) and (2), respectively. This could be explained by following hypotheses. Firstly, AgBiO3 could be changed into Bi2(CO3)O2 only in the copresence of organic molecules accompanied with the reduction of Bi5+ to Bi3+. Due to the weak Bi-O bonds in the external [BiO6] layer, the Bi5+ cations could bind with carbon atoms through the chemisorption to form Bi2(CO3)O2. Therefore, the perovskite structure is unstable due to the electrostatic imbalance, which results in the release of lattice oxygen to reestablish its electrostatic balance. Consequently, the oxygen vacancies would be generated due to the release of lattice oxygen from the Bi-O bonds.31,32 The part of lattice oxygen is then transformed into active oxygen (O*), resulting in the generation 12


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of ROS.33,34 Thirdly, the high valence silver cations were reduced to metallic silver that could probably enhance the generation rate of ROS through the catalytic effect of noble metal. 2Bi5+ + O2- →Bi5+ + Bi3+ + Ovac + 0.5O2 (1) 4Ag2+ + 2O2- → Ag2+ + 2Ag+ + Ag0 + Ovac + 0.5O2 (2) The introduction of Ag into NaBiO3 may weaken the Bi-O bond strength and increases the amount of available lattice oxygen since the exchange of Na to Ag led to the accelerated oxygen diffusion and more available lattice oxygen. To unveil the presence of oxygen vacancy produced in the material, EPR was conducted, as shown in Figure S9. For the fresh AgBiO3, there was no EPR signal. However, obviously, it showed one strong EPR signal for 4 runs AgBiO3 and 8 runs AgBiO3, which could be ascribed to the presence of oxygen vacancies. The EPR results are in well agreement with the above mentioned degradation studies. The fresh AgBiO3 is almost stable in pure water since the structure is not being damaged, indicating no formation of oxygen vacancies. On the other hand, the ROS generation process was triggered by the formation of oxygen vacancies due to the presence of organic compounds. And, the reason behind the formation of ROS is due to the formation of oxygen vacancies from Bi-O bond.

4. CONCLUSIONS In summary, we successfully prepared a perovskite-structured nanomaterial (AgBiO3) and demonstrated the unique functionality for ROS production without light illumination or any other additional oxidant, leading to an excellent oxidizing reactivity. The lattice oxygen of AgBiO3 was activated to generate ROS in the presence of organic compounds. This unusual mechanism may open a new window 13



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for ROS production. Therefore, AgBiO3 should have great potential for the treatment of recalcitrant pollutants in various environmental matrices such as groundwater and soil. To be honest, some kind of organic molecules in the natural water system might also encourage slight release of lattice oxygen of AgBiO3, resulting in the oxidative degradation of the water pollutants. So, we are currently conducting more experiments with real environmental samples at field conditions, and the results will be reported separately in the near future.

ASSOCIATED CONTENT Supporting Information Additional descriptions, figures, and tables as mentioned in the text. This material is available free of charge via the Internet at http://pubs.acs.org. ACKNOWLEDGEMENTS This work was supported by the GAIA project by the Korea Ministry of Environment (RE201402059).

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Table Captions: Table 1 ROS generation rates for various AgBiO3 NPs.

Figure Captions: Figure 1 (A) SEM, (B) TEM and (C) XRD of AgBiO3.

Figure 2 (A) Degradation of RhB by (a) AgBiO3, (b) AgNO3, and (c) NaBiO3. The inset shows the UV/Vis spectral changes and color changes of RhB by AgBiO3. (B) The repeated runs of RhB degradation by AgBiO3 NPs. (C) Effects of different scavengers on the degradation of RhB by AgBiO3 NPs. (D) EPR spectra of (a) TMP1

O2 (in water), (b) DMPO-O2−• (in methanol) and (c) DMPO-•OH (in water) for fresh

AgBiO3 NPs in dark after 5 min of reaction.

Figure 3 (A) XRD patterns of (a) fresh, (b) aged, (c) 4 runs and (d) 8 runs AgBiO3 NPs on the degradation of RhB, and XRD patterns of (B) the 4 runs AgBiO3 NPs after treatment of (a) 2,4-DCP, (b) 4-CP, (c) phenol, (d) RhB and (e) BPA.

Figure 4 XPS spectra of (a) fresh AgBiO3 NPs, (b) aged AgBiO3 NPs, (c) 4 runs AgBiO3 NPs and (d) 8 runs AgBiO3 NPs for (A) O 1s transition, (B) Ag 3d transition, (C) Bi 4f transition and (D) C 1s transition after several repeated RhB degradation cycles.

20


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Table 1 ROS generation from various AgBiO3 NPs. Nanomaterials Fresh AgBiO3 Aged AgBiO3

1

O2 (mol)

O2•– (mol)

7 × 10-10

1.19 × 10-7 2.63 × 10-8

•OH (mol)

6.6 × 10-10 1.11 × 10-7 2.60 × 10-8

4 runs AgBiO3 5.5 × 10-10 0.95 × 10-7 2.52 × 10-8 8runs AgBiO3

4.8 × 10-10 0.82 × 10-7 2.27 × 10-8

21



(C) Intensity / a.u.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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NaBiO3

AgBiO3

10

20

30

40

50

2θ / degree

Figure 1

22


60

70

Page 23 of 26

(B) 1.0

C / C0

0.8 0.6 0.4 0.2 0.0 0

30

60

90

120

150

180

210

240

Reaction time / min Normal IPA 20 mM NaF 20 mM BZQ 2 mM NaN3 20 mM

0.8

(D) Intensity / a.u.

(C) 1.0

C / C0

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


0.6 0.4 0.2 0.0 0

5

10

15

20

Time / min

25

30

(c)

DMPO- •ΟΗ

(b)

DMPO-O2

(a)

TMP- Ο2

•−

1

3300 3320 3340 3360 3380 3400 3420 3440

Magnetic field / G

Figure 2

23



(B)

(110)

(103) (101)

(114) (200)

Intensity / a.u.

AgBiO3 NaBiO3 Bi2(CO3)O2 (d)

(A) Intensity / a.u.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(c)

(b) (012)

(110)

(018) (11-3)

(300) (208)

Page 24 of 26

Bi2(CO3)O2

(e) (d) (c)

(a)

(b) (a)

10

20

30

40

50

60

70

29

30

31

32

33

2θ / degree

2θ / degree

Figure 3

24


34

35

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(A)

367.3 367.5

(B)

531.5

531.3

368.9

532.7

529.6

373.5

373.2

374.6 d

d

367.2

530.8

367.3

373.2 373.4

368.2

374.3 c

c

367.2

529.4

373.1 b

b

532.5

Ag 3d5/2 O 1s

530.4

528

Ag 3d3/2 a

a

530

532

534

536

538 364

366

368

Binding energy / eV

(C)

159.0

164.3

160.0

370

372

159.7

284.9

288.8 285.6

164.9

163.9

284.9

289.1

b 158.5

156

158

160

164

c

284.8

Bi 4f5/2 163.8

162

d

b

166

Binding energy / eV

168

286.5

C 1s

a

154

378

286.1

c

Bi 4f7/2

376

285.3 285.8

(D)

165.4 d

158.6

374

Binding energy / eV

170 282

284

286

288

a

290

Binding energy / eV

Figure 4

25


292

294


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Self-Generation of Reactive Oxygen Species on ... - ACS Publications

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