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Controlled synthesis of bimetallic Prussian blue analogues to activate peroxymonosulfate for efficient bisphenol A degradation
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Controlled synthesis of bimetallic Prussian blue analogues to activate peroxymonosulfate for efficient bisphenol A degradation Wuxiang Zhang, Hao Zhang, Xin Yan, Ming Zhang, Rui Luo, Junwen Qi, Xiuyun Sun, Jinyou Shen, Weiqing Han, Lianjun Wang, Jiansheng Li* Jiangsu Key Laboratory of Chemical Pollution Control and Resources Reuse, Key Laboratory of New Membrane Materials, School of Environmental and Biological Engineering, Nanjing University of Science and Technology, Nanjing, 210094, China
G R A P H I C A L A B S T R A C T
A R T I C LE I N FO
A B S T R A C T
Editor: Xiaohong Guan
Developing high-effective catalysts with tailored composition and structure has attracted extensive attention. In this work, a serious of shape-specific Fe/Co Prussian blue analogs (PBAs), including concave, core-shell and polygonal cubes were prepared by the one-step hydrothermal reaction, which were altered by adjusting the ratio of Fe/Co in the initial reaction system. The catalytic performance toward bisphenol A (BPA) degradation was significantly affected by the ultimate structure and Fe/Co composition. Benefiting from appropriate elemental proportions, unique elemental distribution (rich Co in the core and rich Fe in the shell) and high specific surface areas, the core-shell PBAs (CSPs) exhibits significantly higher peroxymonosulfate (PMS) activation performance toward bisphenol A (BPA) degradation (96 % of removal efficiency within 2 min). The stability of the CSPs catalyst test further indicates that the Fe shell can effectively protect and inhibit the leaching of cobalt ions. Electron paramagnetic resonance (EPR) and radical quenching experiments measurement exhibited that both SO4%− and %OH are the main active species in the degradation process. Our work expanded new ideas of designing novel PBAs with controllable shape and specific core-shell composition with excellent catalytic performance.
Keywords: Fe-Co bimetallic frameworks Complex nanostructures Core-shell Prussian blue analogs Bisphenol A degradation
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Corresponding author. E-mail address: [email protected] (J. Li).
https://doi.org/10.1016/j.jhazmat.2019.121701 Received 19 September 2019; Received in revised form 11 November 2019; Accepted 15 November 2019 0304-3894/ © 2019 Elsevier B.V. All rights reserved.
Please cite this article as: Wuxiang Zhang, et al., Journal of Hazardous Materials, https://doi.org/10.1016/j.jhazmat.2019.121701
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1. Introduction
catalytic efficiency was evaluated by BPA degradation experiments. Benefiting from unique elemental distribution (Co-containing in the core), high specific surface area (576.2 m2/g) and appropriate Fe/Co ratio (1:1.12), high-efficiency BPA degradation performance (96 % of removal efficiency in 2 min) will be confirmed in CSPs catalysts. More importantly, the unique element distribution of CSPs with rich Fe on the shell section can also effectively inhibit the leaching of cobalt ion (0.14 mg/L of cobalt leaching after 30 min). Finally, the SO4%− and %OH degradation mechanism is further verified by electron paramagnetic resonance (EPR) and radical quenching experiments.
The rapid development of urbanization and industrialization has accelerated the impact of human activities on the environment, especially water pollution that is closely related to the ecological system and human health. To date, various technologies have been developed to eliminate the recalcitrant contaminants in the water, such as physical adsorption (Al-Muhtaseb et al., 2011; Hou et al., 2019; Liu et al., 2008), membrane technology (Zhao et al., 2017a; Li et al., 2017), biological treatment (Bharti et al., 2019; Oller et al., 1993; Grandclement et al., 2017), and advanced oxidation process (AOPs) (Wang et al., 2019; Liu et al., 2019; Peng et al., 2019; Li et al., 2016a). Thereinto, AOPs technology based on sulfate radicals (SO4%−) reaction is one of the most efficient ways to remove organic contaminants in wastewater (Chen et al., 2017; Duan et al., 2019; Zhao et al., 2017b). In order to obtain highly active SO4%−, peroxymonosulfate (PMS) is usually employed as donor reagent (Chen et al., 2019a; Li et al., 2018). However, the acquisition of sulfate radicals is always invariably kinetic slow that from the single PMS in water. Usually, the activation of PMS is through a transition-metal catalyst such as Co, Fe, Ni, Cu, and Mn, etc (Ma et al., 2019; Cheng et al., 2019; Huang et al., 2017; Lin and Chen, 2017a). Particularly, many previous studies have established that the Co-based catalyst is the most excellent PMS activator to the degradation of organic pollutants, and complex cobalt-based bimetals can further improve the catalytic performance of advanced oxidation (Chen et al., 2017; Collier et al., 2009; Li et al., 2016b; Liang et al., 2012). However, the relatively high toxicity of discharged cobalt ions is detrimental to the environment and ecosystem. Therefore, developed a novel, highly efficient PMS-activated catalysts with the advantage of Co-element containing and eco-friendly is highly significant and indispensable. Prussian blue analogs (PBAs), an intriguing type of coordination polymer, which constructed by coprecipitation of M1 salt and [M2(CN)6] ion in the solution, the transition metal cations (Fe, Co, Mn, Ni, Cu, etc.) were represented by M1/M2 (Han et al., 2016; Li et al., 2015; Kaneti et al., 2017). PBAs with multiple compositions and structures has been established with a variety of advanced synthesis methods including soft/hard templating, acid and alkali etching, ion exchange and epitaxial growth, etc (Yu et al., 2017; Balamurugan et al., 2018; Liu et al., 2017a; Zhao et al., 2018). Additionally, high porosity, large surface areas, variable element construction, and unique coordination structure have attracted wide attention. Recently, the wellstructured PBAs catalysts based on high-efficiency SO4%− for AOPs technology have emerged. For instance, Zeng et al. presented that the high-efficiency core-shell PBAs@PmPDs catalysts to activate PMS to degrade Rhodamine B with low environmental toxicity (Zeng et al., 2019). Wu et al. reported the core-shell structural Fe/Mn PBA@PBAs catalysts and exhibited superior BPAs removal ability (Wu et al., 2018). Ding et al. confirmed that the hollow Co3O4@Fe2O3 heterogeneous catalysts have a high activity to activate PMS and high-efficiency degradation of norfloxacin (Chen et al., 2019b). Based on these previous studies, numerous similarities in high-active catalysts can be found: (i) specific structural advantages, (ii) synergistic effect of multi-metal, and (iii) more active sites. Therefore, ration designing high specific surface area and Co-containing bimetals PBAs with core-shells or complex cavities structure could be an interesting topic. However, previous studies on the specific structure of PBAs were usually prepared by complex and cumbersome procedures (Zhang et al., 2016a; Nai and Lou, 2018; Wang et al., 2017; Huang et al., 2018). Herein, developing a facile method to synthesize the special structure of PBAs are remains a top priority and highly desirable. Inspired by the above considerations, a one-step reduction-cation exchange strategy should be used to develop heterogeneous core-shell PBAs (CSPs) catalysts. In addition, to further investigate the effect of Fe/Co ratio on the final structure and composition of the nanoparticles, a series of shape-specific Fe-Co PBAs (concave and polygonal cube) with dissimilar Fe/Co ratios were fabricated. The corresponding
2. Experimental section 2.1. Materials Cobalt-nitrate hexahydrate (CoNO3·6H2O) and PMS were purchased from Sigma-Aldrich. Sodium hydroxide (NaOH), Potassium hexacyanocobaltate (III), Potassium hexacyanoferrate (III) were purchased from Sinopharm Chemical Reagent Co., Ltd. Polyvineypirrolydone (PVP, K30, MW∼40,000), BPA were purchased from Sinopharm Chemical Reagent Co., Ltd. Tertbutyl alcohol (TBA), anhydrous ethanol and methanol were purchased from Nanjing Chemical Reagent Co., Ltd. 5,5-dimethyl-1-pyrroline N-oxide (DMPO) was purchased from J&K Scientific. 2.2. Synthesis of materials The catalysts were synthesized based on our previous reports (Zhang et al., 2019a). For Fe-based PB (Fe-PB), 4.0 g of PVP were diffused in 40 mL of 0.1 M HCl solution, then added 0.13 g Potassium hexacyanoferrate in the solution. Then, placed the final solution into an electric oven and heated at 80 °C for 24 h. after washed and dried in a vacuum oven, the Fe-PB (Fe4[Fe(CN)6]3) were obtained. Synthesis of Co-based PB (Co-PB): 4.0 g of PVP were diffused in 40 mL of 0.1 M HCl solution, then added 0.14 g potassium hexacyanocobaltate (III) in the solution. After that, placed the final solution into an electric oven and heated at 80 °C for 24 h. The obtained Co-PB powder was centrifuged and washed with ethanol, and finally dried in a vacuum oven. Synthesis of Different Morphology of PBAs: PVP were dissolved in 0.1 M HCl solution, potassium hexacyanoferrate (3.25 g/L) was added into the above PVP solution (40 mL) (solution A). The 1.5 g/L, 3.5 g/L and 4.25 g/L of Co(NO3)3 were severally dissolved into the PVP solution (40 mL) under the stirring to obtain a clear solution (solution B). Then, slowly mixture two solutions into a beaker for stirring. Then, placed the final solution into an electric oven and heated at 80 °C for 24 h. The color of the solution changes during the hydrothermal process. Finally, the specific PBAs structure with concave cubes (CCPs), core-shell cages PBAs (CSPs) and polygonal cubes PBAs (PCPs) products were obtained, respectively. Washed with ethanol for several times, and dried to obtain the powders materials. 2.3. Characterization The morphology of the as-prepared PBAs was conducted by Fieldemission scanning electron microscopy (SEM) (FEI Quanta 250 F system) and Transmission electron microscopy (TEM) (FEI Tecnai G20 electron microscope). X-ray powder diffraction (XRD) patterns were collected on the Bruker D8 Advance at 40 kV and 40 mA (Bruker AXS, Germany). Nitrogen adsorption/desorption isotherm was recorded on Belsorp-MAX (Bel Japan, Inc.). The specific surface areas were calculated using the Brunauer-Emmet-Teller (BET) method. The measurements of X-ray photoelectron spectroscopy (XPS) were conducted on a photoelectron spectrometer (PHI Quantera II ESCA System). The concentration of iron and cobalt ion was quantified by An Inductive Coupled Plasma Atomic Emission Spectrometer (ICP-AES, Optima 2
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230 nm. The larger cavities on each surface can be observed clearly from SEM images as well. TEM technology was conducted to reveal the internal features of the CSPs. As shown in Fig. 2e, the large pores observed on all facets of the nanocages, resulting in a hollow shell about 80 nm. The element analysis on powder samples verified the Fe/Co ratio was 1:1.12 (shown in Fig. 2f and Table S1). The corresponding EDX line scanning analysis is exhibited in Fig. S1a confirmed that the intensity of cobalt in the interior of the cube is higher than that of iron, while the iron element mainly distributes in the edge of the cube. TEMmapping from Fig. S1b further revealed that the size proportion of Co is less than that of Fe, indicating that the heterogeneous component and Co element are contained in the core-shell structure. when 4.25 g/L of Co dosage is added, the external edges of products further etched, showing a polygonal cube structure (Fig. 2g and h). The element analysis on Fig. 2i and Table S1 confirmed the 1:1.28 of Fe/Co ratios of PCPs. The formation process of CCPs and PCPs was monitored during the different hydrothermal treatment times. As shown in Fig. S2, a solid cubic shape of PBAs was obtained in the room temperature (RT). As the hydrothermal reaction time increases, the CCPs is gradually formed with a contractive tendency on the surface of the cube, while PCPs shows thinner faces and edges. Interestingly, the element ratio (Fe:Co = 1:1.5) of CCPs and PCPs in PBAs-RT is not affected by the initial cobalt dosage (Fig. S2). In other words, cation exchange reactions can occur with the composition and structural changes in the hydrothermal reaction. It's worth mentioning that the CCPs, CSPs, and PCPs were obtained by the same experimental method, except that the initial dosage of Co ion was adjusted. Herein, it can be inferred that the initial number of cobalt ions can significantly influence the formation of Fe-Co PBAs. The final structure and composition of Fe-Co PBAs was controlled by the amount of Co(NO3)2. The crystallographic structures of the Fe-PB, CCPs, CSPs, PCPs, and Co-PB were conducted by powder X-ray diffraction (XRD) technique. As shown in Fig. 3a, In the case of the Fe-PB pattern, the several sharp peaks of 17.4°, 24.6°, 35.2° and 39.4° corresponding to the diffractions of (200), (220), (400) and (420) planes, respectively. The results are in good agreement with the reference data (JCPDS No. 73-0687) (Buser et al. (1977); Selvarani et al. (2008)). However, the lattice constants of PBAs depend on the Co/Fe ratios and the shoulders peaks are clearly seen with the increase of Co fractions, suggested that isomorphous replacement occurred (Zhang et al., 2019b). Analyze BET surface areas of products according to the N2 adsorption curves are shown in Fig. 3b. The Fe-PB and Co-PB were obtained in low BET surface areas of 3.88 m2/g and 17.7 m2/g, respectively. The higher BET surface areas of CCPs, CSPs, and PCPs were obtained for 338.7 m2/g, 576.2 m2/g, and 548.4 m2/g, respectively. The dramatic increase in specific surface area from PB to CSPs indicates that Co2+ has a significant contribution to pore structure. It demonstrates that the large specific surface area can
7000DV). The concentration of BPA was analyzed by high-performance liquid chromatography (HPLC, Agilent, 1260-Infinity), which had a C18 reversed-phase column and a detection wavelength was 230 nm. The mobile phase was methanol/water mixture (7:3, v/v) with a flow rate at 1 mL min−1. The radical signals were collected by EPR experiments (Bruker EMX 10/12). Excitation-Emission-Matrix (EEM) spectra was conducted by F-7000 FL 220−240 V. 2.4. BPA degradation The catalytic ability of catalysts was assessed by the activation of PMS to the degradation of organic contaminants of BPA. All degradation experiments were carried out at a set temperature in a 200 mL beaker with constant stirring at 400 rpm. A 100 mL solution containing 20 mg BPA and 20 mg PMS was prepared. The initial pH of the degradation system was adjusted by 0.2 M sodium hydroxide (range 5.0–10.0). Then, added the catalysts (20 mg) into above solution, and 0.8 mL of the reaction mixture was taken at selected time intervals for analysis. This samples were quenched with methanol (0.8 mL), filtered and analyzed by HPLC. For recycling experiments, the catalysts were recovered by centrifugation collected and rinsing five-times with distilled water, then drying out by vacuum oven. Each recovery is then evaluated under the same conditions. 3. Result and discussion 3.1. Characterization of materials The synthetic scheme was shown in Fig. 1. First, the Fe and Co transition metal ions self-assemble with ligands (cyanide bonds) in hydrothermal systems. Then, the core-shell Prussian blue (CSPs) was successfully fabricated by a reduction-cation exchange strategy (Zhang et al., 2019a). In addition, the concave cube Prussian blue (CCPs) and polygonal cube Prussian blue (PCPs) catalysts were established by adjusting the initial cobalt dose. The morphological structures of the prepared catalysts were characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The SEM images (shown in Fig. 2a) demonstrations that the surfaces of the CCPs shrink inward when 1.5 g/L of Co2+ is introduced into the synthetic system. The TEM images of Fig. 2b can also be observed that the faces shrinkage of the CCPs were about 30 nm, while the average cubic size remains constant about 230 nm. The inductively coupled plasma atomic emission spectra (ICP-AES) and energy dispersive X-ray (EDX) analysis of CCPs powder confirmed that the ratio of Fe/Co element was ∼1:0.56 (Fig. 2c and Table S1). The CSPs structure was obtained in the 3.5 g/L initial dosage of Co ion. The SEM images (shown in Fig. 2d) demonstrations that the uniform CSPs nanoparticles with a diameter of around
Fig. 1. Illustration of the preparation process of the shape-specific Fe/Co PBAs. 3
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Fig. 2. SEM, TEM images and EDX element analysis of CCPs (a–c), CSPs (d–f) and PCPs (g–i), respectively.
the single CSPs catalysts, confirming that large specific surface areas of the CSPs catalysts can adsorb a certain amount of PBA. In addition, about 15 % of BPA was degraded within 30 min when the presence of the single PMS, revealing that PMS can hardly generate active radicals in the absence of a catalyst. In comparison, when the catalyst and PMS are simultaneously employed to the reaction system, the removal efficiency of PBA can be remarkably improved compared with a single catalyst or PMS (shown in Fig. 4b). Despite the low concentration of the CSPs and PMS dose (0.2 g L−1), about 96 % of BPA removal efficiency
provide sufficient reactive sites as well as catalytic performance. Subsequently, the relationship between composition, structure and catalytic properties was conducted by the degradation experiments. 3.2. Catalytic performance The catalytic properties of synthetic catalysts were evaluated by the activation of PMS to the removal of BPA. Fig. 4a presents that approximately 10 % of BPA was removed with 30 min in the presence of
Fig. 3. (a) XRD patterns and (b) N2 adsorption-desorption isotherms of Fe-PB, Co-PB, CCPs, CSPs, and PCPs. 4
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Fig. 4. (a) removal of BPA rates in single system. (b) removal of BPA rates in different catalysts within 30 min (c) degradation efficiency and (d) rate constant of different catalysts. Reaction conditions: [BPA] =20 mg/L, [PMS] =0.2 g/L, catalyst =0.2 g/L, T =293 K, initial solution pH 7.0.
7.0, the removal efficiency presented a slowly decreasing trend, indicating that alkaline condition can slightly reduce degradation efficiency. The degradation rate constant k at different pH is calculated and shown in inset of Fig. 5a. The k value from 5 to 10 are 0.27, 0.45, 1.52, 1.26, 0.77 and 0.6 min−1, respectively. Herein, the initial pH about 7.0 achieved the best, and more than 90 % of BPA could be degraded at a wide pH value form 7–10 within 4 min, which verified that the highefficiency degradation capacity with a wide range of pH of the CSPs catalysts. Moreover, the effects of the CSPs catalysts, PMS, BPA dose and temperature on BPA removal efficiency were also studied in detail. Under the same PMS dose conditions, the degradation rate of BPA increased with the increase of catalyst dosage (shown in Fig. 5b). When the catalyst concentration is 0.10 and 0.15 g/L, the degradation efficiency of BPA can reach 80 % at 10 and 3 min, respectively. Increasing the catalyst concentration to 0.20 g/L can achieve 80 % BPA degradation efficiency in as little as 1 min. The results indicate that the increase of CSPs catalyst can improve the catalytic efficiency. Subsequently, the different PMS dosage (0.1∼0.2 g/L) are investigated, an analogical tendency can be observed in Fig. 5c. The efficiency of degradation accelerates along with the dose of PMS increases. Specifically, the degradation efficiency increased from 66 % (0.1 g/L PMS) to 82 % (0.15 g/L PMS) and completely degraded (0.2 g/L PMS) within 4 min, indicating that the higher PMS dose could speed up the production of free-radical. Conversely, increasing the concentration of organic contaminant (PBA) significantly reduces the catalytic ability (Fig. 5d), and 40 mg/L of BPA can be completely removed over a longer duration (15 min). This is because the free-radicals generated are not sufficient to degrade the excess PBA. In addition, the influence of reaction temperature on catalytic
can be achieved within only 2 min (shown in Fig. 4c), which displayed higher catalytic performance and the degradation rate compared to the single Fe-PB (11 %), single Co-PB (53 %), CCPs (16 %) and PCPs (81 %) at the same times, respectively. In addition, the degradation efficiency of the CSPs catalyst can approach 100 % within 4 min, which is a significant advantage over Fe-PB, Co-PB (30 min), CCPs and PCPs (10 min) catalysts (shown in Fig. 4b). The kinetic data of BPA degradation by different catalysts are was well fitted with pseudo-first order kinetics and calculated according to the first-order rate equation (Li et al., 2019; Liu et al., 2017b). As shown in Fig. 4d, the rate constant (k) of Fe-PB, CCPs, PCPs and Co-PB catalysts were calculated as 0.01, 0.03, 0.57 and 0.11 min−1, respectively, and the CSPs catalyst displays the highest catalytic performance (1.52 min−1). These results indicate that the CSPs catalysts are highly efficient in activating PMS due to an efficient synergistic effect of the Fe and Co, large surface areas with the enriching active sites, heterogeneous core-shell structure. Moreover, the performance of CSPs catalysts is superior to many reported metal-based catalysts (Table S2). Therefore, we further studied the degradation performance of BPA by CSPs catalysts. 3.3. Effects of performance The degradation efficiencies of CSPs catalysts were compared by the control experiments. Firstly, the influence of initial pH on BPA removal efficiency was studied in the PMS oxidation process. As shown in Fig. 5a, the degradation efficiency showed a significantly increased as the pH varied from 5.0–7.0, indicating that the weak inhibition efficiency to the degradation of BPA, which is possible because of the relative stability of PMS in acidic conditions. When the pH is more than to 5
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Fig. 5. Effects of (a) initial pH and (b) catalysts, (c) PMS, (d) PBA dosage (e) reaction temperature (f) antijamming capability on BPA removal efficiency. Reaction conditions: [BPA] =20 mg/L (for a, b, c, e and f), [PMS] =0.2 g/L (for a, b, d, e and f), catalyst =0.2 g/L (for a, c, d, e and f), initial pH = 7.0, T =298 K. The concentration of interfering ions and HA are 20 mM and 20 mg/L, respectively.
common anions could react with %OH or SO4%− radicals to form weaker radicals, thereby hindering BPA degradation (Lutze et al., 2015; Anipsitakis et al., 2006). Therefore, the anti-interference ability of CSPs catalysts in common anions (Cl−, HCO3−, and H2PO4−) and organic matter humic acid (HA) are also evaluated and shown in Fig. 5f, when 20 mM Cl− and H2PO4− was added to the degradation system, the negligible effect was observed. The inhibition effect of HCO3− ions is larger than that of Cl− and H2PO4− ions. However, the addition of Cl−, HCO3−, and H2PO4− did not cause an evident decrease in catalytic efficiency, indicating the excellent anti-interference ability of CSPs catalysts toward these common anions. Humic acid in the water can
performance is also included in Fig. 5e, a higher temperature can improve degradation efficiency due to the generation of active radicals’ reaction is accelerated. The reaction rate constants at 288, 298, 308 K were calculated according to the first-order rate equation, and correspond to the rate constants are 1.08, 1.52, 2.18 min−1, respectively. The activation energy was determined by calculating the degradation rate constant at different temperatures using the Arrhenius equation (inset of Fig. 5e). The activation energy of CSPs for the degradation of BPA was 27.4 kJ/mol with a good regression coefficient (R = 0.996). During the degradation of BPA by catalysts-activated PMS, the coexisting admixtures might impact the PMS activation. For instance, the
6
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Fig. 6. Fluorescence EEM profile for initial reaction time at (a) 0, (b) 2, and (c) 4 min, respectively. The EEM was divided as five (I–V) areas by dash line. Reaction conditions: [PBA] =20 mg/L, Catalysts =0.2 g/L, [PMS] =0.2 g/L, T =298 K.
catalysis. Catalyst recyclability is a key parameter in estimating the practical application. The experiments were carried out by recovering the catalyst and reusing them by the same conditions. Recycled experiments exhibited that more than 97 % are retained within 6 min after 5 cycles, indicating the highly active and recyclability of the CSPs catalysts (Fig. 7b). Hence, the CSPs catalysts are responsible for water treatment applications. To further determine the catalytic stability, the XRD and XPS characteristics of the CSPs catalyst can be compared before and after the reaction. No apparent structure change was observed by the XRD pattern (Fig. S5). This indicates that the stability structure of the CSPs catalysts. In addition, we further investigated the surface valence states of CSPs catalysts by XPS spectra. The high-resolution Fe 2p peaks (shown in Fig. 8a) exhibits the specific peaks at 708.4 eV (Fe2+ 2p3/2), and 710.2 eV (Fe3+ 2p3/2) are correspond to Fe2+ and Fe3+, respectively. A new shake-up satellite peak of 713.1 eV (Fe Sat.) were found after the catalytic reaction, which might be due to the Fe present in more than one coordination environment after the reaction (Du et al., 2016; Lin and Chen, 2017b). The high-resolution Co 2p spectrum can be assigned at 782.0 eV (Co 2p3/2), 786.8 eV (Co 2p3/2), indicating the existence of Co2+ (Fig. 8b). After the catalytic reaction, a new peak at 784.6 eV was detected indicates that the presence of Co3+, suggested the redox reaction has occurred.
effectively inhibit the degradation of PBAs process (Fig. 5f). When 20 mg/L HA is coexisted in the solution, a significant decline in degradation efficiency (80 % in 20 min). This result can be attributed to the generation of radicals that can be affected by organic substance, which was agreeing well with previous studies (Tan et al., 2017). The excitation-emission-matrix (EEM) spectra in Fig. 6 was also to study the degradation behavior of CSPs. The initial fluorescence intensity of BPA in the region I and region IV were measured to be 9623 (Ex = 230 nm) and 8378 in.(Ex = 275 nm), respectively. The fluorescence intensity of the I, II and IV regions were decreased as the catalytic reaction proceeds, which implied that the occurrence of catalytic reactions. After 4 min of catalytic reaction, the EEM intensity in the I, II and IV regions were significantly weaker and smaller than that of the initial sample, which indicated that the high-efficiency activation ability of the CSPs. 3.4. Stability experimental The Co and Fe leaching in the degradation process were exhibited by ICP-AES. As shown in Fig. 7a, less than 0.14 mg/L in Co ion and 0.03 mg/L Fe ion can be found in CSPs within 30 min, which exhibited excellent inhibition effect compared to pure Fe and Co-PB. Therefore, it can be concluded that Co leaching could be effectively suppressed due to the heterogeneous metal interactions (Cai et al., 2015; Yang et al., 2009). Moreover, Fe as a shell layer can effectively inhibit Co leaching in the PMS degradation system. The Co ion leaching concentrations after the reusability tests were further studied and shown in Fig. S3, the concentration of Co ion after five cycles decreased from 0.14 mg/L to 0.093 mg/L. To rule out the effects of homogeneous catalysis, the same concentration of Co2+ ion was used as the comparative catalyst. As shown in Fig. S4, only 40 % of the BPA decomposed in 20 min, demonstrating that the main contribution comes from heterogeneous CSPs
3.5. Degradation mechanism The Electron paramagnetic resonance (EPR) analysis were performed to detect the presence of free radicals. As shown in Fig. 9a, both hydroxyl and sulfate radicals were generated in BPA degradation, which indicated that the main reactive species were probably %OH and SO4%−. The degradation mechanism was further investigated by the radical quenching experiments to verify the main active substances in
Fig. 7. (a) Relationship between the dissolution of Co and Fe ions of different catalysts in 30 min (b) cycling stability of CSPs catalysts. Reaction conditions: [PBA] =20 mg/L, Catalysts =0.2 g/L, [PMS] =0.2 g/L, T =298 K. 7
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Fig. 8. Comparison of (a) High-resolution Fe 2p and (b) Co 2pperform between before and after the catalytic experiment.
intermediates of BPA degradation were identified by liquid chromatograph mass spectrometer (LC–MS), the main products being shown in Table S3, which is similar to the previous reports (Li et al., 2019; Luo et al., 2018). Therefore, based on the above results, a possible catalytic scheme is proposed and exhibited in Fig. 10. Specifically, the HSO5− species from PMS are reduced to SO4%− by activating Co(II) and Fe(II) (Redox potential of HSO5−/SO4%− was 2.5–3.1 V). At the same time, Co(III) and Fe(III) can react with HSO5− to form SO5%− by Eqs. (4 and 5) (Redox potential of HSO5−/SO5%− was 1.1 V) (Dong et al., 2019). In addition, the standard oxidation-reduction potential of Co(III)/Co(II) (1.81 V) is higher than that of Fe(III)/Fe(II) (0.77 V), which means that the Co(III) can be reduced by Fe (II) (Eq. (6)). The obtained Fe(III) or Co(II) by Eq. (6) further reacts with HSO5− and generates SO4%− and SO5%- by Eqs. (4 and 5) (Zeng et al., 2019; Zhang et al., 2016b). Then, SO5%- can be transformed into SO4%− and oxygen through Eq. (7). In addition, the hydrolysis of SO4%− can produce the %OH and SO42− through Eq. (8). Therefore, the large amounts of SO4%− and %OH radicals could degrade PBA into micromolecular intermediates or CO2 (Eq. (9)).
the decomposition process. Usually, ethanol (EtOH) acts as scavengers for %OH and SO4%−, while the tertbutyl alcohol (TBA) acts as a selective scavenger for %OH (Peng et al., 2013; Yang et al., 2019; Zhou et al., 2018; Wang et al., 2018; Qiao et al., 2019). A remarkable inhibiting effect was exhibited when the solution included 0.2 M EtOH (shown in Fig. 9b). Furthermore, when 0.2 M TBA was used during BPA degradation, the degradation efficiency showed a slight decline. The rate constants of kEtOH and kTBA were calculated to be 0.09 and 0.56 min−1, respectively. Here, each radical species reaction with BPA in the system is assumed to be pseudo-first-order kinetics. It is also assumed that the SO4%− and %OH are completely inhibited by EtOH and TBA. Therefore, the contribution of each active portion can be calculated by the equations Eqs. (1)–(3): k%OH + kSO4%− + kother= ktotal
(1)
kETOH= kother
(2)
kTBA= kSO4%−+ kother k%OH
(3)
and kSO4%− are rate SO4%−, respectively.
constants for the absence of inWhere ktotal, hibitors, %OH and The kother is the rate constant for all other active species. The contribution of the SO4%− and %OH were calculated according to kSO4%−/ktotal and k%OH /ktotal. Therefore, the contribution ratios of the SO4%− and %OH were 30.9 % and 63.1 %, respectively. The results confirmed that SO4%− and %OH act as the main active species in the CSPs system and the production of %OH may be due to a reaction between SO4%− and H2O or OH−. Furthermore,
Co(II)/Fe(II)+ HSO5− →Co(III)/ Fe(III) + SO4%−+ OH− Co(III)/ Fe(III) +
HSO5−→Co(II)/Fe(II)+
%
SO5 - + H
+
(4) (5)
Fe(II) + Co(Ш) → Fe(Ш) + Co(II)
(6)
SO5%−→SO4%−+O2
(7)
Fig. 9. (a) DMPO trapped EPR spectra in the reaction systems, (b) Effects of radical scavengers on PBA degradation, inset of (b) are the contribution percentage of different radicals. 8
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degradation and performed the analysis. Author 10: Lianjun Wang; Research and analysis of degradation mechanism. Author 11: Jiansheng Li: Project management and hosting; Conceived and designed the experiment; Wrote and revised the paper. Declaration of Competing Interest We declare that we do not have any commercial or associative interest that represents a conflict of interest in connection with the work submitted. Acknowledgments This work was financially supported by the National Natural Science Foundation of China (Grant No. 51878352), the priority academic program development of Jiangsu higher education institutions. Appendix A. Supplementary data Supplementary material related to this article can be found, in the online version, at doi:https://doi.org/10.1016/j.jhazmat.2019.121701. References Fig. 10. The proposed mechanism of PMS activation on CPSs for PBA degradation.
SO4%−+ H2O→SO42−+ %OH + H
+
SO4%−+ %OH + PBA→Degradation products
Al-Muhtaseb, A.A.H., Ibrahim, K.A., Albadarin, A.B., Ali-khashman, O., Walker, G.M., Ahmad, M.N.M., 2011. Remediation of phenol-contaminated water by adsorption using poly(methyl methacrylate) (PMMA). Chem. Eng. J. 168, 691–699. Anipsitakis, G.P., Dionysiou, D.D., Gonzalez, M.A., 2006. Cobalt-mediated activation of peroxymonosulfate and sulfate radical attack on phenolic compounds. Implications of chloride ions. Environ. Sci. Technol. 40, 1000–1007. Balamurugan, T.S.T., Mani, V., Hsieh, C.C., Huang, S.T., Peng, T.K., Lin, H.Y., 2018. Realtime tracking and quantification of endogenous hydrogen peroxide production in living cells using graphenated carbon nanotubes supported Prussian blue cubes. Sens. Actuators B: Chem. 257, 220–227. Bharti, V., Vikrant, K., Goswami, M., Tiwari, H., Sonwani, R.K., Lee, J., Tsang, D.C.W., Kim, K.-H., Saeed, M., Kumar, S., Rai, B.N., Giri, B.S., Rai, B.N., 2019. Biodegradation of methylene blue dye in a batch and continuous mode using biochar as packing media. Environ. Res. 171, 356–364. Buser, H.J., Schwarzenbach, D., Fetter, W., Ludi, A., 1977. The crystal structure of Prussian blue: Fe4[Fe(CN)6]3. xH2O. Inor. Chem. 16, 2704–2710. Cai, C., Zhang, H., Zhong, X., Hou, L., 2015. Ultrasound enhanced heterogeneous activation of peroxymonosulfate by a bimetallic Fe-Co/SBA-15 catalyst for the degradation of Orange II in water. J. Hazard. Mater. 283, 70–79. Chen, L., Cai, T., Sun, W., Zuo, X., Ding, D., 2017. Mesoporous bouquet-like Co3O4 nanostructure for the effective heterogeneous activation of peroxymonosulfate. J. Taiwan Inst. Chem. E. 80, 720–727. Chen, G., Zhang, X., Gao, Y., Zhu, G., Cheng, Q., Cheng, X., 2019a. Novel magnetic MnO2/ MnFe2O4 nanocomposite as a heterogeneous catalyst for activation of peroxymonosulfate (PMS) toward oxidation of organic pollutants. Sep. Purif. Technol. 213, 456–464. Chen, L., Zuo, X., Yang, S., Cai, T., Ding, D., 2019b. Rational design and synthesis of hollow Co3O4@Fe2O3 core-shell nanostructure for the catalytic degradation of norfloxacin by coupling with peroxymonosulfate. Chem. Eng. J. 359, 373–384. Cheng, M., Liu, Y., Huang, D., Lai, C., Zeng, G., Huang, J., Liu, Z., Zhang, C., Zhou, C., Qin, L., Xiong, W., Yi, H., Yang, Y., 2019. Prussian blue analogue derived magnetic Cu-Fe oxide as a recyclable photo-Fenton catalyst for the efficient removal of sulfamethazine at near neutral pH values. Chem. Eng. J. 362, 865–876. Collier, K.N., Jones, N.J., Miller, K.J., Qin, Y.L., Laughlin, D.E., McHenry, M.E., 2009. Controlled oxidation of FeCo magnetic nanoparticles to produce faceted FeCo/ferrite nanocomposites for rf heating applications. J. Appl. Phys. 105, 07A328. Dong, H., Chen, J., Feng, L., Zhang, W., Guan, X., Strathmann, T.J., 2019. Degradation of organic contaminants through activating bisulfite by cerium (IV): a sulfate radicalpredominant oxidation process. Chem. Eng. J. 357, 328–336. Du, Y., Ma, W., Liu, P., Zou, B., Ma, J., 2016. Magnetic CoFe2O4 nanoparticles supported on titanate nanotubes (CoFe2O4/TNTs) as a novel heterogeneous catalyst for peroxymonosulfate activation and degradation of organic pollutants. J. Hazard. Mater. 308, 58–66. Duan, X., Kang, J., Tian, W., Zhang, H., Ho, S.H., Zhu, Y.A., Ao, Z., Sun, H., Wang, S., 2019. Interfacial-engineered cobalt@ carbon hybrids for synergistically boosted evolution of sulfate radicals toward green oxidation. Appl. Catal. B: Environ. 117795. Grandclement, C., Seyssiecq, I., Piram, A., Wong-Wah-Chung, P., Vanot, G., Tiliacos, N., Roche, N., Doumenq, P., 2017. From the conventional biological wastewater treatment to hybrid processes, the evaluation of organic micropollutant removal: a review. Water Res. 111, 297–317. Han, L., Yu, X.Y., Lou, X.W., 2016. Formation of Prussian-blue-analog nanocages via a direct etching method and their conversion into ni-co-mixed oxide for enhanced oxygen evolution. Adv. Mater. 28, 4601–4605.
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4. Conclusion In summary, the concave, core-shell and polygonal cubes of Fe/Co PBAs were established by adjusting the initial cobalt dose in the reaction system. The core-shell PBA catalyst will be attracted due to the unique elemental distribution (Co-containing in the core and rich Fe in the shell), high specific surface area (576.2 m2/g) and appropriate ratio of Fe/Co element (1:1.12). In addition, the high catalytic capacity (96 % of removal efficiency in 2 min) by the degradation experiments also can be confirmed. The stability test further indicates that the rich Fe on the shell section can also effectively inhibit the leaching of cobalt ion (0.14 mg/L of cobalt leaching within 30 min). The %OH and SO4%− are have proven to be the main active species in the degradation process. Our work expanded new ideas of designing novel PBAs with controllable shape and specific elemental composition with satisfactory catalytic performance. Authors contribution Author 1: Wuxiang Zhang: Conceived and designed the catalyst; Synthesis nanomaterials; Collected and analysis data; Diagraph analysis; Wrote and revised the paper. Author 2: Hao Zhang: Synthesis nanomaterials; Collected the data. Author 3: Xin Yan: Characterization and analysis of TEM images. Author 4: Ming Zhang: Characterization the Electron paramagnetic resonance and performed the analysis. Author 5: Rui Luo: Characterization the mechanism of degradation and performed the analysis. Author 6: Junwen Qi: Discussion on XRD and BET analysis. Author 7: Xiuyun Sun: Characterization of the Inductive Coupled Plasma Atomic Emission Spectrometer. Author 8: Jinyou Shen; Characterization the mechanism of degradation and performed the analysis. Author 9: Weiqing Han; Discussion on the mechanism of 9
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mesochannels of ordered mesoporous silica for enhanced removal of bisphenol A from water. ACS Appl. Mater. Interfaces 11, 4328–4337. Peng, W., Liu, S., Sun, H., Yao, Y., Zhi, L., Wang, S., 2013. Synthesis of porous reduced graphene oxide as metal-free carbon for adsorption and catalytic oxidation of organics in water. J. Mater. Chem. A 1, 5854–5859. Qiao, J., Feng, L., Dong, H., Zhao, Z., Guan, X., 2019. Overlooked role of sulfur-centered radicals during bromate reduction by sulfite. Environ. Sci. Technol. 53 (17), 10320–10328. Selvarani, G., Prashant, S.K., Sahu, A.K., Sridhar, P., Pitchumani, S., Shukla, A.K., 2008. A direct borohydride fuel cell employing Prussian Blue as mediated electron-transfer hydrogen peroxide reduction catalyst. J. Power Sources 178, 86–91. Tan, C., Gao, N., Fu, D., Deng, J., Deng, L., 2017. Efficient degradation of paracetamol with nanoscaled magnetic CoFe 2 O 4 and MnFe2O4 as a heterogeneous catalyst of peroxymonosulfate. Sep. Purif. Technol. 175, 47–57. Wang, C., Kim, J., Malgras, V., Na, J., Lin, J., You, J., Zhang, M., Li, J., Yamauchi, Y., 2019. Metal–organic frameworks and their derived materials: emerging catalysts for a sulfate radicals‐based advanced oxidation process in water purification. Small 15, 1900744. Wang, J.G., Zhang, Z., Zhang, X., Yin, X., Li, X., Liu, X., Kang, F., Wei, B., 2017. Cation exchange formation of prussian blue analogue submicroboxes for high-performance Na-ion hybrid supercapacitors. Nano Energy 39, 647–653. Wang, N., Ma, W., Ren, Z., Du, Y., Xu, P., Han, X., 2018. Prussian Blue Analogues derived porous nitrogen-doped carbon microspheres as high-performance metal-free peroxymonosulfate activators for non-radical-dominated degradation of organic pollutants. J. Mater. Chem. A 6, 884–895. Wu, S., Zhuang, G., Wei, J., Zhuang, Z., Yu, Y., 2018. Shape control of core-shell MOF@ MOF and derived MOF nanocages via ion modulation in a one-pot strategy. J. Mater. Chem. A 6, 18234–18241. Yang, Q., Choi, H., Al-Abed, S.R., Dionysiou, D.D., 2009. Iron–cobalt mixed oxide nanocatalysts: heterogeneous peroxymonosulfate activation, cobalt leaching, and ferromagnetic properties for envi ronmental applications. Appl. Catal. B: Environ. 88, 462–469. Yang, M.T., Zhang, Z.Y., Lin, K.Y.A., 2019. One-step fabrication of cobalt-embedded carbon nitride as a magnetic and efficient heterogeneous catalyst for activating oxone to degrade pollutants in water. Sep. Purif. Technol. 210, 1–9. Yu, L., Wu, H.B., Lou, X.W., 2017. Self-templated formation of hollow structures for electrochemical energy applications. Acc. Chem. Res. 50, 293–301. Zeng, L., Xiao, L., Shi, X., Wei, M., Cao, J., Long, Y., 2019. Core-shell Prussian blue analogues@poly(m-phenylenediamine) as efficient peroxymonosulfate activators for degradation of Rhodamine B with reduced metal leaching. J. Colloid Interface Sci. 534, 586–594. Zhang, W., Zhao, Y., Malgras, V., Ji, Q., Jiang, D., Qi, R., Ariga, K., Yamauchi, Y., Liu, J., Jiang, J.S., Hu, M., 2016a. Synthesis of monocrystalline nanoframes of prussian blue analogues by controlled preferential etching. Angew. Chem. Int. Ed. Engl. 55, 8228–8234. Zhang, W., Song, H., Cheng, Y., Liu, C., Wang, C., Khan, M.A.N., Zhang, H., Liu, J., Yu, C., Wang, L., Li, J., 2019a. Core-shell prussian blue analogs with compositional heterogeneity and open cages for oxygen evolution reaction. Adv. Sci. 6, 1801901. Zhang, W., Zhang, H., Luo, R., Zhang, M., Yan, X., Sun, X., Shen, J., Han, W., Wang, L., Li, J., 2019b. Prussian blue analogues-derived bimetallic iron-cobalt selenides for efficient overall water splitting. J. Colloid Interface Sci. 548, 48–55. Zhang, S., Fan, Q., Gao, H., Huang, Y., Liu, X., Li, J., Xu, X., Wang, X., 2016b. Formation of Fe3O4@MnO2 ball-in-ball hollow spheres as a high performance catalyst with enhanced catalytic performances. J. Mater. Chem. A 4, 1414–1422. Zhao, X., Li, F., Li, B., Zhang, T., Teng, Q., Wang, L., Wang, H., Zhang, Y., 2018. Magnetic MnxCo3-xO4 microboxes fabricated from Prussian blue analogue templates for electrochemical applications. J. Phys. Chem. Solis. 113, 134–141. Zhao, S., Minier-Matar, J., Chou, S., Wang, R., Fane, A.G., Adham, S., 2017a. Gas field produced/process water treatment using forward osmosis hollow fiber membrane: membrane fouling and chemical cleaning. Desalination 402, 143–151. Zhao, Q., Mao, Q., Zhou, Y., Wei, J., Liu, X., Yang, J., Luo, L., Zhang, J., Chen, H., Chen, H., Tang, L., 2017b. Metal-free carbon materials-catalyzed sulfate radical-based advanced oxidation processes: a review on heterogeneous catalysts and applications. Chemosphere 189, 224–238. Zhou, Y., Jiang, J., Gao, Y., Pang, S.Y., Ma, J., Duan, J., Guo, Q., Li, J., Yang, Y., 2018. Oxidation of steroid estrogens by peroxymonosulfate (PMS) and effect of bromide and chloride ions: kinetics, products, and modeling. Water Res. 138, 56–66.
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Journal of Hazardous Materials journal homepage: www.elsevier.com/locate/jhazmat
Controlled synthesis of bimetallic Prussian blue analogues to activate peroxymonosulfate for efficient bisphenol A degradation Wuxiang Zhang, Hao Zhang, Xin Yan, Ming Zhang, Rui Luo, Junwen Qi, Xiuyun Sun, Jinyou Shen, Weiqing Han, Lianjun Wang, Jiansheng Li* Jiangsu Key Laboratory of Chemical Pollution Control and Resources Reuse, Key Laboratory of New Membrane Materials, School of Environmental and Biological Engineering, Nanjing University of Science and Technology, Nanjing, 210094, China
G R A P H I C A L A B S T R A C T
A R T I C LE I N FO
A B S T R A C T
Editor: Xiaohong Guan
Developing high-effective catalysts with tailored composition and structure has attracted extensive attention. In this work, a serious of shape-specific Fe/Co Prussian blue analogs (PBAs), including concave, core-shell and polygonal cubes were prepared by the one-step hydrothermal reaction, which were altered by adjusting the ratio of Fe/Co in the initial reaction system. The catalytic performance toward bisphenol A (BPA) degradation was significantly affected by the ultimate structure and Fe/Co composition. Benefiting from appropriate elemental proportions, unique elemental distribution (rich Co in the core and rich Fe in the shell) and high specific surface areas, the core-shell PBAs (CSPs) exhibits significantly higher peroxymonosulfate (PMS) activation performance toward bisphenol A (BPA) degradation (96 % of removal efficiency within 2 min). The stability of the CSPs catalyst test further indicates that the Fe shell can effectively protect and inhibit the leaching of cobalt ions. Electron paramagnetic resonance (EPR) and radical quenching experiments measurement exhibited that both SO4%− and %OH are the main active species in the degradation process. Our work expanded new ideas of designing novel PBAs with controllable shape and specific core-shell composition with excellent catalytic performance.
Keywords: Fe-Co bimetallic frameworks Complex nanostructures Core-shell Prussian blue analogs Bisphenol A degradation
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Corresponding author. E-mail address: [email protected] (J. Li).
https://doi.org/10.1016/j.jhazmat.2019.121701 Received 19 September 2019; Received in revised form 11 November 2019; Accepted 15 November 2019 0304-3894/ © 2019 Elsevier B.V. All rights reserved.
Please cite this article as: Wuxiang Zhang, et al., Journal of Hazardous Materials, https://doi.org/10.1016/j.jhazmat.2019.121701
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1. Introduction
catalytic efficiency was evaluated by BPA degradation experiments. Benefiting from unique elemental distribution (Co-containing in the core), high specific surface area (576.2 m2/g) and appropriate Fe/Co ratio (1:1.12), high-efficiency BPA degradation performance (96 % of removal efficiency in 2 min) will be confirmed in CSPs catalysts. More importantly, the unique element distribution of CSPs with rich Fe on the shell section can also effectively inhibit the leaching of cobalt ion (0.14 mg/L of cobalt leaching after 30 min). Finally, the SO4%− and %OH degradation mechanism is further verified by electron paramagnetic resonance (EPR) and radical quenching experiments.
The rapid development of urbanization and industrialization has accelerated the impact of human activities on the environment, especially water pollution that is closely related to the ecological system and human health. To date, various technologies have been developed to eliminate the recalcitrant contaminants in the water, such as physical adsorption (Al-Muhtaseb et al., 2011; Hou et al., 2019; Liu et al., 2008), membrane technology (Zhao et al., 2017a; Li et al., 2017), biological treatment (Bharti et al., 2019; Oller et al., 1993; Grandclement et al., 2017), and advanced oxidation process (AOPs) (Wang et al., 2019; Liu et al., 2019; Peng et al., 2019; Li et al., 2016a). Thereinto, AOPs technology based on sulfate radicals (SO4%−) reaction is one of the most efficient ways to remove organic contaminants in wastewater (Chen et al., 2017; Duan et al., 2019; Zhao et al., 2017b). In order to obtain highly active SO4%−, peroxymonosulfate (PMS) is usually employed as donor reagent (Chen et al., 2019a; Li et al., 2018). However, the acquisition of sulfate radicals is always invariably kinetic slow that from the single PMS in water. Usually, the activation of PMS is through a transition-metal catalyst such as Co, Fe, Ni, Cu, and Mn, etc (Ma et al., 2019; Cheng et al., 2019; Huang et al., 2017; Lin and Chen, 2017a). Particularly, many previous studies have established that the Co-based catalyst is the most excellent PMS activator to the degradation of organic pollutants, and complex cobalt-based bimetals can further improve the catalytic performance of advanced oxidation (Chen et al., 2017; Collier et al., 2009; Li et al., 2016b; Liang et al., 2012). However, the relatively high toxicity of discharged cobalt ions is detrimental to the environment and ecosystem. Therefore, developed a novel, highly efficient PMS-activated catalysts with the advantage of Co-element containing and eco-friendly is highly significant and indispensable. Prussian blue analogs (PBAs), an intriguing type of coordination polymer, which constructed by coprecipitation of M1 salt and [M2(CN)6] ion in the solution, the transition metal cations (Fe, Co, Mn, Ni, Cu, etc.) were represented by M1/M2 (Han et al., 2016; Li et al., 2015; Kaneti et al., 2017). PBAs with multiple compositions and structures has been established with a variety of advanced synthesis methods including soft/hard templating, acid and alkali etching, ion exchange and epitaxial growth, etc (Yu et al., 2017; Balamurugan et al., 2018; Liu et al., 2017a; Zhao et al., 2018). Additionally, high porosity, large surface areas, variable element construction, and unique coordination structure have attracted wide attention. Recently, the wellstructured PBAs catalysts based on high-efficiency SO4%− for AOPs technology have emerged. For instance, Zeng et al. presented that the high-efficiency core-shell PBAs@PmPDs catalysts to activate PMS to degrade Rhodamine B with low environmental toxicity (Zeng et al., 2019). Wu et al. reported the core-shell structural Fe/Mn PBA@PBAs catalysts and exhibited superior BPAs removal ability (Wu et al., 2018). Ding et al. confirmed that the hollow Co3O4@Fe2O3 heterogeneous catalysts have a high activity to activate PMS and high-efficiency degradation of norfloxacin (Chen et al., 2019b). Based on these previous studies, numerous similarities in high-active catalysts can be found: (i) specific structural advantages, (ii) synergistic effect of multi-metal, and (iii) more active sites. Therefore, ration designing high specific surface area and Co-containing bimetals PBAs with core-shells or complex cavities structure could be an interesting topic. However, previous studies on the specific structure of PBAs were usually prepared by complex and cumbersome procedures (Zhang et al., 2016a; Nai and Lou, 2018; Wang et al., 2017; Huang et al., 2018). Herein, developing a facile method to synthesize the special structure of PBAs are remains a top priority and highly desirable. Inspired by the above considerations, a one-step reduction-cation exchange strategy should be used to develop heterogeneous core-shell PBAs (CSPs) catalysts. In addition, to further investigate the effect of Fe/Co ratio on the final structure and composition of the nanoparticles, a series of shape-specific Fe-Co PBAs (concave and polygonal cube) with dissimilar Fe/Co ratios were fabricated. The corresponding
2. Experimental section 2.1. Materials Cobalt-nitrate hexahydrate (CoNO3·6H2O) and PMS were purchased from Sigma-Aldrich. Sodium hydroxide (NaOH), Potassium hexacyanocobaltate (III), Potassium hexacyanoferrate (III) were purchased from Sinopharm Chemical Reagent Co., Ltd. Polyvineypirrolydone (PVP, K30, MW∼40,000), BPA were purchased from Sinopharm Chemical Reagent Co., Ltd. Tertbutyl alcohol (TBA), anhydrous ethanol and methanol were purchased from Nanjing Chemical Reagent Co., Ltd. 5,5-dimethyl-1-pyrroline N-oxide (DMPO) was purchased from J&K Scientific. 2.2. Synthesis of materials The catalysts were synthesized based on our previous reports (Zhang et al., 2019a). For Fe-based PB (Fe-PB), 4.0 g of PVP were diffused in 40 mL of 0.1 M HCl solution, then added 0.13 g Potassium hexacyanoferrate in the solution. Then, placed the final solution into an electric oven and heated at 80 °C for 24 h. after washed and dried in a vacuum oven, the Fe-PB (Fe4[Fe(CN)6]3) were obtained. Synthesis of Co-based PB (Co-PB): 4.0 g of PVP were diffused in 40 mL of 0.1 M HCl solution, then added 0.14 g potassium hexacyanocobaltate (III) in the solution. After that, placed the final solution into an electric oven and heated at 80 °C for 24 h. The obtained Co-PB powder was centrifuged and washed with ethanol, and finally dried in a vacuum oven. Synthesis of Different Morphology of PBAs: PVP were dissolved in 0.1 M HCl solution, potassium hexacyanoferrate (3.25 g/L) was added into the above PVP solution (40 mL) (solution A). The 1.5 g/L, 3.5 g/L and 4.25 g/L of Co(NO3)3 were severally dissolved into the PVP solution (40 mL) under the stirring to obtain a clear solution (solution B). Then, slowly mixture two solutions into a beaker for stirring. Then, placed the final solution into an electric oven and heated at 80 °C for 24 h. The color of the solution changes during the hydrothermal process. Finally, the specific PBAs structure with concave cubes (CCPs), core-shell cages PBAs (CSPs) and polygonal cubes PBAs (PCPs) products were obtained, respectively. Washed with ethanol for several times, and dried to obtain the powders materials. 2.3. Characterization The morphology of the as-prepared PBAs was conducted by Fieldemission scanning electron microscopy (SEM) (FEI Quanta 250 F system) and Transmission electron microscopy (TEM) (FEI Tecnai G20 electron microscope). X-ray powder diffraction (XRD) patterns were collected on the Bruker D8 Advance at 40 kV and 40 mA (Bruker AXS, Germany). Nitrogen adsorption/desorption isotherm was recorded on Belsorp-MAX (Bel Japan, Inc.). The specific surface areas were calculated using the Brunauer-Emmet-Teller (BET) method. The measurements of X-ray photoelectron spectroscopy (XPS) were conducted on a photoelectron spectrometer (PHI Quantera II ESCA System). The concentration of iron and cobalt ion was quantified by An Inductive Coupled Plasma Atomic Emission Spectrometer (ICP-AES, Optima 2
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230 nm. The larger cavities on each surface can be observed clearly from SEM images as well. TEM technology was conducted to reveal the internal features of the CSPs. As shown in Fig. 2e, the large pores observed on all facets of the nanocages, resulting in a hollow shell about 80 nm. The element analysis on powder samples verified the Fe/Co ratio was 1:1.12 (shown in Fig. 2f and Table S1). The corresponding EDX line scanning analysis is exhibited in Fig. S1a confirmed that the intensity of cobalt in the interior of the cube is higher than that of iron, while the iron element mainly distributes in the edge of the cube. TEMmapping from Fig. S1b further revealed that the size proportion of Co is less than that of Fe, indicating that the heterogeneous component and Co element are contained in the core-shell structure. when 4.25 g/L of Co dosage is added, the external edges of products further etched, showing a polygonal cube structure (Fig. 2g and h). The element analysis on Fig. 2i and Table S1 confirmed the 1:1.28 of Fe/Co ratios of PCPs. The formation process of CCPs and PCPs was monitored during the different hydrothermal treatment times. As shown in Fig. S2, a solid cubic shape of PBAs was obtained in the room temperature (RT). As the hydrothermal reaction time increases, the CCPs is gradually formed with a contractive tendency on the surface of the cube, while PCPs shows thinner faces and edges. Interestingly, the element ratio (Fe:Co = 1:1.5) of CCPs and PCPs in PBAs-RT is not affected by the initial cobalt dosage (Fig. S2). In other words, cation exchange reactions can occur with the composition and structural changes in the hydrothermal reaction. It's worth mentioning that the CCPs, CSPs, and PCPs were obtained by the same experimental method, except that the initial dosage of Co ion was adjusted. Herein, it can be inferred that the initial number of cobalt ions can significantly influence the formation of Fe-Co PBAs. The final structure and composition of Fe-Co PBAs was controlled by the amount of Co(NO3)2. The crystallographic structures of the Fe-PB, CCPs, CSPs, PCPs, and Co-PB were conducted by powder X-ray diffraction (XRD) technique. As shown in Fig. 3a, In the case of the Fe-PB pattern, the several sharp peaks of 17.4°, 24.6°, 35.2° and 39.4° corresponding to the diffractions of (200), (220), (400) and (420) planes, respectively. The results are in good agreement with the reference data (JCPDS No. 73-0687) (Buser et al. (1977); Selvarani et al. (2008)). However, the lattice constants of PBAs depend on the Co/Fe ratios and the shoulders peaks are clearly seen with the increase of Co fractions, suggested that isomorphous replacement occurred (Zhang et al., 2019b). Analyze BET surface areas of products according to the N2 adsorption curves are shown in Fig. 3b. The Fe-PB and Co-PB were obtained in low BET surface areas of 3.88 m2/g and 17.7 m2/g, respectively. The higher BET surface areas of CCPs, CSPs, and PCPs were obtained for 338.7 m2/g, 576.2 m2/g, and 548.4 m2/g, respectively. The dramatic increase in specific surface area from PB to CSPs indicates that Co2+ has a significant contribution to pore structure. It demonstrates that the large specific surface area can
7000DV). The concentration of BPA was analyzed by high-performance liquid chromatography (HPLC, Agilent, 1260-Infinity), which had a C18 reversed-phase column and a detection wavelength was 230 nm. The mobile phase was methanol/water mixture (7:3, v/v) with a flow rate at 1 mL min−1. The radical signals were collected by EPR experiments (Bruker EMX 10/12). Excitation-Emission-Matrix (EEM) spectra was conducted by F-7000 FL 220−240 V. 2.4. BPA degradation The catalytic ability of catalysts was assessed by the activation of PMS to the degradation of organic contaminants of BPA. All degradation experiments were carried out at a set temperature in a 200 mL beaker with constant stirring at 400 rpm. A 100 mL solution containing 20 mg BPA and 20 mg PMS was prepared. The initial pH of the degradation system was adjusted by 0.2 M sodium hydroxide (range 5.0–10.0). Then, added the catalysts (20 mg) into above solution, and 0.8 mL of the reaction mixture was taken at selected time intervals for analysis. This samples were quenched with methanol (0.8 mL), filtered and analyzed by HPLC. For recycling experiments, the catalysts were recovered by centrifugation collected and rinsing five-times with distilled water, then drying out by vacuum oven. Each recovery is then evaluated under the same conditions. 3. Result and discussion 3.1. Characterization of materials The synthetic scheme was shown in Fig. 1. First, the Fe and Co transition metal ions self-assemble with ligands (cyanide bonds) in hydrothermal systems. Then, the core-shell Prussian blue (CSPs) was successfully fabricated by a reduction-cation exchange strategy (Zhang et al., 2019a). In addition, the concave cube Prussian blue (CCPs) and polygonal cube Prussian blue (PCPs) catalysts were established by adjusting the initial cobalt dose. The morphological structures of the prepared catalysts were characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The SEM images (shown in Fig. 2a) demonstrations that the surfaces of the CCPs shrink inward when 1.5 g/L of Co2+ is introduced into the synthetic system. The TEM images of Fig. 2b can also be observed that the faces shrinkage of the CCPs were about 30 nm, while the average cubic size remains constant about 230 nm. The inductively coupled plasma atomic emission spectra (ICP-AES) and energy dispersive X-ray (EDX) analysis of CCPs powder confirmed that the ratio of Fe/Co element was ∼1:0.56 (Fig. 2c and Table S1). The CSPs structure was obtained in the 3.5 g/L initial dosage of Co ion. The SEM images (shown in Fig. 2d) demonstrations that the uniform CSPs nanoparticles with a diameter of around
Fig. 1. Illustration of the preparation process of the shape-specific Fe/Co PBAs. 3
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Fig. 2. SEM, TEM images and EDX element analysis of CCPs (a–c), CSPs (d–f) and PCPs (g–i), respectively.
the single CSPs catalysts, confirming that large specific surface areas of the CSPs catalysts can adsorb a certain amount of PBA. In addition, about 15 % of BPA was degraded within 30 min when the presence of the single PMS, revealing that PMS can hardly generate active radicals in the absence of a catalyst. In comparison, when the catalyst and PMS are simultaneously employed to the reaction system, the removal efficiency of PBA can be remarkably improved compared with a single catalyst or PMS (shown in Fig. 4b). Despite the low concentration of the CSPs and PMS dose (0.2 g L−1), about 96 % of BPA removal efficiency
provide sufficient reactive sites as well as catalytic performance. Subsequently, the relationship between composition, structure and catalytic properties was conducted by the degradation experiments. 3.2. Catalytic performance The catalytic properties of synthetic catalysts were evaluated by the activation of PMS to the removal of BPA. Fig. 4a presents that approximately 10 % of BPA was removed with 30 min in the presence of
Fig. 3. (a) XRD patterns and (b) N2 adsorption-desorption isotherms of Fe-PB, Co-PB, CCPs, CSPs, and PCPs. 4
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Fig. 4. (a) removal of BPA rates in single system. (b) removal of BPA rates in different catalysts within 30 min (c) degradation efficiency and (d) rate constant of different catalysts. Reaction conditions: [BPA] =20 mg/L, [PMS] =0.2 g/L, catalyst =0.2 g/L, T =293 K, initial solution pH 7.0.
7.0, the removal efficiency presented a slowly decreasing trend, indicating that alkaline condition can slightly reduce degradation efficiency. The degradation rate constant k at different pH is calculated and shown in inset of Fig. 5a. The k value from 5 to 10 are 0.27, 0.45, 1.52, 1.26, 0.77 and 0.6 min−1, respectively. Herein, the initial pH about 7.0 achieved the best, and more than 90 % of BPA could be degraded at a wide pH value form 7–10 within 4 min, which verified that the highefficiency degradation capacity with a wide range of pH of the CSPs catalysts. Moreover, the effects of the CSPs catalysts, PMS, BPA dose and temperature on BPA removal efficiency were also studied in detail. Under the same PMS dose conditions, the degradation rate of BPA increased with the increase of catalyst dosage (shown in Fig. 5b). When the catalyst concentration is 0.10 and 0.15 g/L, the degradation efficiency of BPA can reach 80 % at 10 and 3 min, respectively. Increasing the catalyst concentration to 0.20 g/L can achieve 80 % BPA degradation efficiency in as little as 1 min. The results indicate that the increase of CSPs catalyst can improve the catalytic efficiency. Subsequently, the different PMS dosage (0.1∼0.2 g/L) are investigated, an analogical tendency can be observed in Fig. 5c. The efficiency of degradation accelerates along with the dose of PMS increases. Specifically, the degradation efficiency increased from 66 % (0.1 g/L PMS) to 82 % (0.15 g/L PMS) and completely degraded (0.2 g/L PMS) within 4 min, indicating that the higher PMS dose could speed up the production of free-radical. Conversely, increasing the concentration of organic contaminant (PBA) significantly reduces the catalytic ability (Fig. 5d), and 40 mg/L of BPA can be completely removed over a longer duration (15 min). This is because the free-radicals generated are not sufficient to degrade the excess PBA. In addition, the influence of reaction temperature on catalytic
can be achieved within only 2 min (shown in Fig. 4c), which displayed higher catalytic performance and the degradation rate compared to the single Fe-PB (11 %), single Co-PB (53 %), CCPs (16 %) and PCPs (81 %) at the same times, respectively. In addition, the degradation efficiency of the CSPs catalyst can approach 100 % within 4 min, which is a significant advantage over Fe-PB, Co-PB (30 min), CCPs and PCPs (10 min) catalysts (shown in Fig. 4b). The kinetic data of BPA degradation by different catalysts are was well fitted with pseudo-first order kinetics and calculated according to the first-order rate equation (Li et al., 2019; Liu et al., 2017b). As shown in Fig. 4d, the rate constant (k) of Fe-PB, CCPs, PCPs and Co-PB catalysts were calculated as 0.01, 0.03, 0.57 and 0.11 min−1, respectively, and the CSPs catalyst displays the highest catalytic performance (1.52 min−1). These results indicate that the CSPs catalysts are highly efficient in activating PMS due to an efficient synergistic effect of the Fe and Co, large surface areas with the enriching active sites, heterogeneous core-shell structure. Moreover, the performance of CSPs catalysts is superior to many reported metal-based catalysts (Table S2). Therefore, we further studied the degradation performance of BPA by CSPs catalysts. 3.3. Effects of performance The degradation efficiencies of CSPs catalysts were compared by the control experiments. Firstly, the influence of initial pH on BPA removal efficiency was studied in the PMS oxidation process. As shown in Fig. 5a, the degradation efficiency showed a significantly increased as the pH varied from 5.0–7.0, indicating that the weak inhibition efficiency to the degradation of BPA, which is possible because of the relative stability of PMS in acidic conditions. When the pH is more than to 5
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Fig. 5. Effects of (a) initial pH and (b) catalysts, (c) PMS, (d) PBA dosage (e) reaction temperature (f) antijamming capability on BPA removal efficiency. Reaction conditions: [BPA] =20 mg/L (for a, b, c, e and f), [PMS] =0.2 g/L (for a, b, d, e and f), catalyst =0.2 g/L (for a, c, d, e and f), initial pH = 7.0, T =298 K. The concentration of interfering ions and HA are 20 mM and 20 mg/L, respectively.
common anions could react with %OH or SO4%− radicals to form weaker radicals, thereby hindering BPA degradation (Lutze et al., 2015; Anipsitakis et al., 2006). Therefore, the anti-interference ability of CSPs catalysts in common anions (Cl−, HCO3−, and H2PO4−) and organic matter humic acid (HA) are also evaluated and shown in Fig. 5f, when 20 mM Cl− and H2PO4− was added to the degradation system, the negligible effect was observed. The inhibition effect of HCO3− ions is larger than that of Cl− and H2PO4− ions. However, the addition of Cl−, HCO3−, and H2PO4− did not cause an evident decrease in catalytic efficiency, indicating the excellent anti-interference ability of CSPs catalysts toward these common anions. Humic acid in the water can
performance is also included in Fig. 5e, a higher temperature can improve degradation efficiency due to the generation of active radicals’ reaction is accelerated. The reaction rate constants at 288, 298, 308 K were calculated according to the first-order rate equation, and correspond to the rate constants are 1.08, 1.52, 2.18 min−1, respectively. The activation energy was determined by calculating the degradation rate constant at different temperatures using the Arrhenius equation (inset of Fig. 5e). The activation energy of CSPs for the degradation of BPA was 27.4 kJ/mol with a good regression coefficient (R = 0.996). During the degradation of BPA by catalysts-activated PMS, the coexisting admixtures might impact the PMS activation. For instance, the
6
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Fig. 6. Fluorescence EEM profile for initial reaction time at (a) 0, (b) 2, and (c) 4 min, respectively. The EEM was divided as five (I–V) areas by dash line. Reaction conditions: [PBA] =20 mg/L, Catalysts =0.2 g/L, [PMS] =0.2 g/L, T =298 K.
catalysis. Catalyst recyclability is a key parameter in estimating the practical application. The experiments were carried out by recovering the catalyst and reusing them by the same conditions. Recycled experiments exhibited that more than 97 % are retained within 6 min after 5 cycles, indicating the highly active and recyclability of the CSPs catalysts (Fig. 7b). Hence, the CSPs catalysts are responsible for water treatment applications. To further determine the catalytic stability, the XRD and XPS characteristics of the CSPs catalyst can be compared before and after the reaction. No apparent structure change was observed by the XRD pattern (Fig. S5). This indicates that the stability structure of the CSPs catalysts. In addition, we further investigated the surface valence states of CSPs catalysts by XPS spectra. The high-resolution Fe 2p peaks (shown in Fig. 8a) exhibits the specific peaks at 708.4 eV (Fe2+ 2p3/2), and 710.2 eV (Fe3+ 2p3/2) are correspond to Fe2+ and Fe3+, respectively. A new shake-up satellite peak of 713.1 eV (Fe Sat.) were found after the catalytic reaction, which might be due to the Fe present in more than one coordination environment after the reaction (Du et al., 2016; Lin and Chen, 2017b). The high-resolution Co 2p spectrum can be assigned at 782.0 eV (Co 2p3/2), 786.8 eV (Co 2p3/2), indicating the existence of Co2+ (Fig. 8b). After the catalytic reaction, a new peak at 784.6 eV was detected indicates that the presence of Co3+, suggested the redox reaction has occurred.
effectively inhibit the degradation of PBAs process (Fig. 5f). When 20 mg/L HA is coexisted in the solution, a significant decline in degradation efficiency (80 % in 20 min). This result can be attributed to the generation of radicals that can be affected by organic substance, which was agreeing well with previous studies (Tan et al., 2017). The excitation-emission-matrix (EEM) spectra in Fig. 6 was also to study the degradation behavior of CSPs. The initial fluorescence intensity of BPA in the region I and region IV were measured to be 9623 (Ex = 230 nm) and 8378 in.(Ex = 275 nm), respectively. The fluorescence intensity of the I, II and IV regions were decreased as the catalytic reaction proceeds, which implied that the occurrence of catalytic reactions. After 4 min of catalytic reaction, the EEM intensity in the I, II and IV regions were significantly weaker and smaller than that of the initial sample, which indicated that the high-efficiency activation ability of the CSPs. 3.4. Stability experimental The Co and Fe leaching in the degradation process were exhibited by ICP-AES. As shown in Fig. 7a, less than 0.14 mg/L in Co ion and 0.03 mg/L Fe ion can be found in CSPs within 30 min, which exhibited excellent inhibition effect compared to pure Fe and Co-PB. Therefore, it can be concluded that Co leaching could be effectively suppressed due to the heterogeneous metal interactions (Cai et al., 2015; Yang et al., 2009). Moreover, Fe as a shell layer can effectively inhibit Co leaching in the PMS degradation system. The Co ion leaching concentrations after the reusability tests were further studied and shown in Fig. S3, the concentration of Co ion after five cycles decreased from 0.14 mg/L to 0.093 mg/L. To rule out the effects of homogeneous catalysis, the same concentration of Co2+ ion was used as the comparative catalyst. As shown in Fig. S4, only 40 % of the BPA decomposed in 20 min, demonstrating that the main contribution comes from heterogeneous CSPs
3.5. Degradation mechanism The Electron paramagnetic resonance (EPR) analysis were performed to detect the presence of free radicals. As shown in Fig. 9a, both hydroxyl and sulfate radicals were generated in BPA degradation, which indicated that the main reactive species were probably %OH and SO4%−. The degradation mechanism was further investigated by the radical quenching experiments to verify the main active substances in
Fig. 7. (a) Relationship between the dissolution of Co and Fe ions of different catalysts in 30 min (b) cycling stability of CSPs catalysts. Reaction conditions: [PBA] =20 mg/L, Catalysts =0.2 g/L, [PMS] =0.2 g/L, T =298 K. 7
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Fig. 8. Comparison of (a) High-resolution Fe 2p and (b) Co 2pperform between before and after the catalytic experiment.
intermediates of BPA degradation were identified by liquid chromatograph mass spectrometer (LC–MS), the main products being shown in Table S3, which is similar to the previous reports (Li et al., 2019; Luo et al., 2018). Therefore, based on the above results, a possible catalytic scheme is proposed and exhibited in Fig. 10. Specifically, the HSO5− species from PMS are reduced to SO4%− by activating Co(II) and Fe(II) (Redox potential of HSO5−/SO4%− was 2.5–3.1 V). At the same time, Co(III) and Fe(III) can react with HSO5− to form SO5%− by Eqs. (4 and 5) (Redox potential of HSO5−/SO5%− was 1.1 V) (Dong et al., 2019). In addition, the standard oxidation-reduction potential of Co(III)/Co(II) (1.81 V) is higher than that of Fe(III)/Fe(II) (0.77 V), which means that the Co(III) can be reduced by Fe (II) (Eq. (6)). The obtained Fe(III) or Co(II) by Eq. (6) further reacts with HSO5− and generates SO4%− and SO5%- by Eqs. (4 and 5) (Zeng et al., 2019; Zhang et al., 2016b). Then, SO5%- can be transformed into SO4%− and oxygen through Eq. (7). In addition, the hydrolysis of SO4%− can produce the %OH and SO42− through Eq. (8). Therefore, the large amounts of SO4%− and %OH radicals could degrade PBA into micromolecular intermediates or CO2 (Eq. (9)).
the decomposition process. Usually, ethanol (EtOH) acts as scavengers for %OH and SO4%−, while the tertbutyl alcohol (TBA) acts as a selective scavenger for %OH (Peng et al., 2013; Yang et al., 2019; Zhou et al., 2018; Wang et al., 2018; Qiao et al., 2019). A remarkable inhibiting effect was exhibited when the solution included 0.2 M EtOH (shown in Fig. 9b). Furthermore, when 0.2 M TBA was used during BPA degradation, the degradation efficiency showed a slight decline. The rate constants of kEtOH and kTBA were calculated to be 0.09 and 0.56 min−1, respectively. Here, each radical species reaction with BPA in the system is assumed to be pseudo-first-order kinetics. It is also assumed that the SO4%− and %OH are completely inhibited by EtOH and TBA. Therefore, the contribution of each active portion can be calculated by the equations Eqs. (1)–(3): k%OH + kSO4%− + kother= ktotal
(1)
kETOH= kother
(2)
kTBA= kSO4%−+ kother k%OH
(3)
and kSO4%− are rate SO4%−, respectively.
constants for the absence of inWhere ktotal, hibitors, %OH and The kother is the rate constant for all other active species. The contribution of the SO4%− and %OH were calculated according to kSO4%−/ktotal and k%OH /ktotal. Therefore, the contribution ratios of the SO4%− and %OH were 30.9 % and 63.1 %, respectively. The results confirmed that SO4%− and %OH act as the main active species in the CSPs system and the production of %OH may be due to a reaction between SO4%− and H2O or OH−. Furthermore,
Co(II)/Fe(II)+ HSO5− →Co(III)/ Fe(III) + SO4%−+ OH− Co(III)/ Fe(III) +
HSO5−→Co(II)/Fe(II)+
%
SO5 - + H
+
(4) (5)
Fe(II) + Co(Ш) → Fe(Ш) + Co(II)
(6)
SO5%−→SO4%−+O2
(7)
Fig. 9. (a) DMPO trapped EPR spectra in the reaction systems, (b) Effects of radical scavengers on PBA degradation, inset of (b) are the contribution percentage of different radicals. 8
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degradation and performed the analysis. Author 10: Lianjun Wang; Research and analysis of degradation mechanism. Author 11: Jiansheng Li: Project management and hosting; Conceived and designed the experiment; Wrote and revised the paper. Declaration of Competing Interest We declare that we do not have any commercial or associative interest that represents a conflict of interest in connection with the work submitted. Acknowledgments This work was financially supported by the National Natural Science Foundation of China (Grant No. 51878352), the priority academic program development of Jiangsu higher education institutions. Appendix A. Supplementary data Supplementary material related to this article can be found, in the online version, at doi:https://doi.org/10.1016/j.jhazmat.2019.121701. References Fig. 10. The proposed mechanism of PMS activation on CPSs for PBA degradation.
SO4%−+ H2O→SO42−+ %OH + H
+
SO4%−+ %OH + PBA→Degradation products
Al-Muhtaseb, A.A.H., Ibrahim, K.A., Albadarin, A.B., Ali-khashman, O., Walker, G.M., Ahmad, M.N.M., 2011. Remediation of phenol-contaminated water by adsorption using poly(methyl methacrylate) (PMMA). Chem. Eng. J. 168, 691–699. Anipsitakis, G.P., Dionysiou, D.D., Gonzalez, M.A., 2006. Cobalt-mediated activation of peroxymonosulfate and sulfate radical attack on phenolic compounds. Implications of chloride ions. Environ. Sci. Technol. 40, 1000–1007. Balamurugan, T.S.T., Mani, V., Hsieh, C.C., Huang, S.T., Peng, T.K., Lin, H.Y., 2018. Realtime tracking and quantification of endogenous hydrogen peroxide production in living cells using graphenated carbon nanotubes supported Prussian blue cubes. Sens. Actuators B: Chem. 257, 220–227. Bharti, V., Vikrant, K., Goswami, M., Tiwari, H., Sonwani, R.K., Lee, J., Tsang, D.C.W., Kim, K.-H., Saeed, M., Kumar, S., Rai, B.N., Giri, B.S., Rai, B.N., 2019. Biodegradation of methylene blue dye in a batch and continuous mode using biochar as packing media. Environ. Res. 171, 356–364. Buser, H.J., Schwarzenbach, D., Fetter, W., Ludi, A., 1977. The crystal structure of Prussian blue: Fe4[Fe(CN)6]3. xH2O. Inor. Chem. 16, 2704–2710. Cai, C., Zhang, H., Zhong, X., Hou, L., 2015. Ultrasound enhanced heterogeneous activation of peroxymonosulfate by a bimetallic Fe-Co/SBA-15 catalyst for the degradation of Orange II in water. J. Hazard. Mater. 283, 70–79. Chen, L., Cai, T., Sun, W., Zuo, X., Ding, D., 2017. Mesoporous bouquet-like Co3O4 nanostructure for the effective heterogeneous activation of peroxymonosulfate. J. Taiwan Inst. Chem. E. 80, 720–727. Chen, G., Zhang, X., Gao, Y., Zhu, G., Cheng, Q., Cheng, X., 2019a. Novel magnetic MnO2/ MnFe2O4 nanocomposite as a heterogeneous catalyst for activation of peroxymonosulfate (PMS) toward oxidation of organic pollutants. Sep. Purif. Technol. 213, 456–464. Chen, L., Zuo, X., Yang, S., Cai, T., Ding, D., 2019b. Rational design and synthesis of hollow Co3O4@Fe2O3 core-shell nanostructure for the catalytic degradation of norfloxacin by coupling with peroxymonosulfate. Chem. Eng. J. 359, 373–384. Cheng, M., Liu, Y., Huang, D., Lai, C., Zeng, G., Huang, J., Liu, Z., Zhang, C., Zhou, C., Qin, L., Xiong, W., Yi, H., Yang, Y., 2019. Prussian blue analogue derived magnetic Cu-Fe oxide as a recyclable photo-Fenton catalyst for the efficient removal of sulfamethazine at near neutral pH values. Chem. Eng. J. 362, 865–876. Collier, K.N., Jones, N.J., Miller, K.J., Qin, Y.L., Laughlin, D.E., McHenry, M.E., 2009. Controlled oxidation of FeCo magnetic nanoparticles to produce faceted FeCo/ferrite nanocomposites for rf heating applications. J. Appl. Phys. 105, 07A328. Dong, H., Chen, J., Feng, L., Zhang, W., Guan, X., Strathmann, T.J., 2019. Degradation of organic contaminants through activating bisulfite by cerium (IV): a sulfate radicalpredominant oxidation process. Chem. Eng. J. 357, 328–336. Du, Y., Ma, W., Liu, P., Zou, B., Ma, J., 2016. Magnetic CoFe2O4 nanoparticles supported on titanate nanotubes (CoFe2O4/TNTs) as a novel heterogeneous catalyst for peroxymonosulfate activation and degradation of organic pollutants. J. Hazard. Mater. 308, 58–66. Duan, X., Kang, J., Tian, W., Zhang, H., Ho, S.H., Zhu, Y.A., Ao, Z., Sun, H., Wang, S., 2019. Interfacial-engineered cobalt@ carbon hybrids for synergistically boosted evolution of sulfate radicals toward green oxidation. Appl. Catal. B: Environ. 117795. Grandclement, C., Seyssiecq, I., Piram, A., Wong-Wah-Chung, P., Vanot, G., Tiliacos, N., Roche, N., Doumenq, P., 2017. From the conventional biological wastewater treatment to hybrid processes, the evaluation of organic micropollutant removal: a review. Water Res. 111, 297–317. Han, L., Yu, X.Y., Lou, X.W., 2016. Formation of Prussian-blue-analog nanocages via a direct etching method and their conversion into ni-co-mixed oxide for enhanced oxygen evolution. Adv. Mater. 28, 4601–4605.
(8) (9)
4. Conclusion In summary, the concave, core-shell and polygonal cubes of Fe/Co PBAs were established by adjusting the initial cobalt dose in the reaction system. The core-shell PBA catalyst will be attracted due to the unique elemental distribution (Co-containing in the core and rich Fe in the shell), high specific surface area (576.2 m2/g) and appropriate ratio of Fe/Co element (1:1.12). In addition, the high catalytic capacity (96 % of removal efficiency in 2 min) by the degradation experiments also can be confirmed. The stability test further indicates that the rich Fe on the shell section can also effectively inhibit the leaching of cobalt ion (0.14 mg/L of cobalt leaching within 30 min). The %OH and SO4%− are have proven to be the main active species in the degradation process. Our work expanded new ideas of designing novel PBAs with controllable shape and specific elemental composition with satisfactory catalytic performance. Authors contribution Author 1: Wuxiang Zhang: Conceived and designed the catalyst; Synthesis nanomaterials; Collected and analysis data; Diagraph analysis; Wrote and revised the paper. Author 2: Hao Zhang: Synthesis nanomaterials; Collected the data. Author 3: Xin Yan: Characterization and analysis of TEM images. Author 4: Ming Zhang: Characterization the Electron paramagnetic resonance and performed the analysis. Author 5: Rui Luo: Characterization the mechanism of degradation and performed the analysis. Author 6: Junwen Qi: Discussion on XRD and BET analysis. Author 7: Xiuyun Sun: Characterization of the Inductive Coupled Plasma Atomic Emission Spectrometer. Author 8: Jinyou Shen; Characterization the mechanism of degradation and performed the analysis. Author 9: Weiqing Han; Discussion on the mechanism of 9
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