Enhanced degradation of organic pollutants over Cu-doped LaAlO3 perovskite through heterogeneous Fenton-like reactions

Accepted Manuscript Enhanced degradation of organic pollutants over Cu-doped LaAlO3 perovskite through heterogeneous Fenton-like reactions Huihui Wang, Lili Zhang, Chun Hu, Xiangke Wang, Lai Lyu, Guodong Sheng PII: DOI: Reference:

S1385-8947(17)31557-7 http://dx.doi.org/10.1016/j.cej.2017.09.058 CEJ 17643

To appear in:

Chemical Engineering Journal

Received Date: Revised Date: Accepted Date:

22 May 2017 7 September 2017 8 September 2017

Please cite this article as: H. Wang, L. Zhang, C. Hu, X. Wang, L. Lyu, G. Sheng, Enhanced degradation of organic pollutants over Cu-doped LaAlO3 perovskite through heterogeneous Fenton-like reactions, Chemical Engineering Journal (2017), doi: http://dx.doi.org/10.1016/j.cej.2017.09.058

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Enhanced degradation of organic pollutants over Cu-doped LaAlO3 perovskite through heterogeneous Fenton-like reactions Huihui Wang,ab Lili Zhang,*a Chun Hu,acd Xiangke Wang,be Lai Lyu,acd and Guodong Shengf a

Key Laboratory of Drinking Water Science and Technology, Research Center for

Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China b

College of Environmental Science and Engineering, North China Electric Power University, Beijing 102206, China c

School of Environmental Sciences and Engineering, Guangzhou University, Guangzhou 510006, China d

e

University of Chinese Academy of Sciences, Beijing 100049, China

NAAM Research Group, Faculty of Science, King Abdulaziz University, Jeddah 21589, Saudi Arabia

f

College of Chemistry and Chemical Engineering, Shaoxing University, Zhejiang 312000, P.R. China *Corresponding author. Tel: +86-10-62844150; fax: +86-10-62923541 E-mail address: [email protected] (L. Zhang);

Abstract Cu-doped LaAlO3 perovskite (LaAl1−xCu xO3) was synthesized via a Pechini-type sol-gel process for the oxidative degradation of persistent organic compounds. The characterization results show that Cu was incorporated into the structure of sphere-like LaAlO3 and formed the bond of La/Al-O-Cu. LaAl0.95Cu 0.05O3 performed 1

excellent activity and stability for the degradation and mineralization of various organic pollutants through heterogeneous Fenton-like reactions. In the practical reaction process, at the organic pollutant initial concentration of 25 mg L−1, 1.0 mol H2O2 produces 1.8 mol HO• radicals within 60 min and 1.0 mol H2O2 still produces 1.3 mol HO• radicals after reaction time of 240 min. The results of ESR and active species trapping experiments indicated that HO• radicals acted the dominant role during the degradation of pollutants in LaAl0.95Cu0.05O3/H2O2 system. Combining with in-situ Raman analysis and the XPS results of LaAl0.95Cu 0.05O3 before and after reaction, H2O2 was predominantly reduced to HO• on the electron-rich Cu center, and H2O2/H2O can be dissociated on oxygen vacancies (OVs) to enhance formation of HO• on the surface of LaAl0.95Cu0.05O3, resulting in the high catalytic activity of LaAl0.95Cu0.05O3. This efficient material can potentially be used as a promising catalyst for the efficient degradation of organic pollutants in environmental pollution cleanup. Keywords: Cu-doped LaAlO3 perovskite; Fenton-like reaction; Active species; Organic pollutants 1. Introduction With the rapid development of chemical industry, different kinds of persistent aromatic pollutants, such as phenols, pesticides, pharmaceuticals, endocrine disruptors, were produced and unavoidably released into the natural environment, which could cause serious environmental effects and biohazard [1]. During the past few years, many researchers have focused on the efficient elimination of organic pollutants from 2

aqueous solutions, and various techniques have been adopted such as adsorption [2, 3], flocculation [4, 5], Advanced Oxidation Processes (AOPs) [6-8] and bio-contact oxidation [9]. Among these methods, AOPs as a useful technique for dealing the persistent pollutants has been widely applied in the treatment of industrial wastewater. The strong chemical species (HO•, HO2•, etc.) generated from AOPs [10-12] are highly reactive and can mineralize most organic substances into inorganic compounds and small molecules. As one of AOPs, the classic Fenton reaction has attracted worldwide attention recently due to its high performance, simplicity and environmental friendly [13-15]. However, the widespread application of Fenton reaction is still limited by the narrow working pH range (pH = 2.5 - 3.5), the production of sludge (mainly iron-containing, a secondary pollutants) and the catalyst lost continuously. In addition, heterogeneous catalysts still neutral and acidic conditions were more effective. However, in many cases, industrial effluents are formed at basic pH conditions [16]. Therefore, it is essential to develop highly active and stable Fenton catalysts at extensive pH range. It is well known that perovskite-type oxides (ABO3) have been applied to industrial reactions as important heterogeneous catalysts [17-19]. With the high tolerance factor, various sizes of cations can be dissolved in both A- and B-site cation sublattices. Consequently, oxygen vacancies (OVs) are generated to compensate the charge of substituting ions [20]. LaAlO3 as a combination of rocksalt-LaO with rutile-AlO2 structure has attracted the intense interest of the scientific society [21]. Recently, different kinds of Cu-based materials have been synthesized 3

extensively in the field of catalysis, especially as Fenton catalysts, such as Cu-doped metal oxide [22, 23], Cu-doped goethite [24] and Cu-doped magnetic porous carbon [25]. While the utilization efficiency of H2O2 ranged from 10% to 60% in Cu-based systems were reported [26]. Meanwhile, different kinds of perovskite materials have been studied as Fenton catalysts, such as a series of LaBO3 perovskites (B = Ti, Fe,) [27, 28], the influence of the A-site cation in AFeO3 (A = La, Bi) perovskite-type oxides [29, 30] and a mesoporous SBA-15 host support for the perovskite [31, 32]. However, to gain applications in practice and the catalytic efficiency of these oxides have to be improved. Therefore, the H2O2 utilization efficiency has to be enhanced and the formation rate of hydroxyl radicals (HO•) has to be accelerated during the Fenton reaction process, which is critical to increase the catalytic efficiency of Fenton reaction. Herein, the Cu-doped LaAlO3 perovskite catalyst was successfully synthesized by a sol-gel route. Several ubiquitous aromatic pollutants, including phenol, pharmaceuticals (such as diphenhydramine (DP), ciprofloxacin (CIP), ibuprofen (IBU), and phenytoin (PHT)), pesticides (such as 2-chlorophenol (2-CP), 2,4-dichlorophenoxyacetic acid (2,4-D)), and endocrine disrupting chemicals (such as bisphenol A (BPA)), were selected as representative pollutants to evaluate the oxidation degradation activity of the catalyst under different experimental conditions. The catalyst was characterized by high-resolution transmission electron microscopy (HRTEM), field emission scanning electron microscope (SEM), X-ray diffraction (XRD), The Fourier-transform infrared spectroscopy (FTIR), Raman spectroscopy, 4

X-ray photoelectron spectroscopy (XPS) and extended X-ray absorption fine structure (EXAFS)

spectroscopy.

Additionally,

the

interaction

processes

between

LaAl0.95Cu0.05O3 and hydrogen peroxide (H2O2) were detected by electron spin resonance (ESR) and in-situ Raman spectroscopy, and a complex mechanism of Cu-doped LaAlO3 (LaAl1−xCu xO3) heterogeneous Fenton-like reactions was proposed from the analytical results. 2. Experimental 2.1. Reagents Eight contaminants (phenol, DP, CIP, IBU, PHT, 2-CP, 2,4-D and BPA) were purchased from Acros (Geel, Belgium). Lanthanum nitrate (La(NO3)3·6H2O), aluminium nitrate (Al(NO3)3·9H2O), copper nitrate trihydrate (Cu(NO3)2·3H2O) and H2O2 (30%, w/w) were purchased from Sinopharm Chemical Reagent Co., Ltd. Citric acid and polyethylene glycol (PEG, molecular weight =10000) were obtained from Beijing Chemical Co. Ltd. 5,5-Dimethyl-1-pyrroline-N-oxide (DMPO) was supplied by Sigma Ltd. All chemicals were analytical grade. 2.2. Catalyst synthesis LaAl1−xCu xO3 perovskite (x = 0.0 - 0.1) composites were synthesized via a Pechini-type sol-gel process (Fig. 1). In a typical procedure [33, 34], the required amounts of La(NO3)3·6H2O, Al(NO3)3·9H2O and Cu(NO3)2·3H2O were dissolved in 20 mL solvent (ethanol: deionized water = 7:1). Thereafter, citric acid and PEG were added into the nitrate precursors as the chelating agent and the molar ratio of the citric acid and metal ions was 2:1. The resultant mixtures were stirred for 1 h at room 5

temperature and condensed at 75 °C in a water bath for 6 h to evaporate water until dry gels formed, and then dried at 110 °C overnight. The gels were well ground and prefired at 450 °C for 4 h. Thus treated samples were fully ground and fired at 800 °C for 3h. The x values of initial synthesis mixtures were fixed to 0, 0.01, 0.02, 0.05 and 0.1. 2.3. Characterization The HRTEM images of the samples were recorded using a JEOL-2100 TEM with an acceleration voltage of 200 kV. The SEM images were measured by a SU8020 FESEM instrument (Hitachi), which was operated at the accelerating voltage of 20 kV and the detector current of 10 mA. The XRD patterns were collected with a Scintag-XDS-2000 diffractometer with Cu Kα radiation (λ = 1.540598 Å) operating at 40 kV and 40 mA. The XPS data were taken on an AXIS-Ultra instrument (Kratos) using monochromatic Al Kα radiation (225 W, 15 mA, 15 kV) and low-energy electron flooding for charge compensation. The ESR spectra were obtained using a Bruker A300-10/12 ESR spectrometer (center field: 3480.00 G; microwave frequency: 9.79 GHz; and power: 5.05 mW). The Raman spectra were scanned on a LabRAM HR Evolution (HORIBA, France) with 40 mW 532 nm laser light irradiation. The Cu K-edge EXAFS spectra at 8.979keV were measured at room temperature in transmission mode at the beam lines (i.e., BL14W1) of Shanghai Synchrotron Radiation Facility (SSRF), China. The Fourier-transform infrared spectroscopy (FTIR) spectra were recorded on a Nicolet 8700 FTIR spectrophotometer (Thermo Fisher Scientific Inc., USA). 6

2.4. Procedures and analysis Eight contaminants (phenol, DP, CIP, IBU, PHT, 2-CP, 2,4-D and BPA) were selected to evaluate the activity and properties of the catalyst. In a typical experiment, 0.05g catalyst powders was placed in 50 mL aqueous solution to achieve the catalyst content of 1.0 g L−1 and the pollutant concentration of 10 mg L−1. The suspension was constantly stirred for about 30 min to establish an adsorption/desorption equilibrium between the contaminant and the catalyst. Then, the required amounts of H2O2 was added to achieve the H2O2 concentration of 10 mmol L−1 as an oxidant under continuous stirring. At given time intervals, 3 mL aliquots was withdrew and filtered through a Millipore filter (pore size 0.45µm) to remove the catalyst powders for pollutant concentration analysis. The pH was adjusted to the targeted value by using 0.1 M H2SO4 or 0.1 M NaOH. More details about the experimental procedures and analysis were provided in the supporting information (SI). 3. Result and discussion 3.1 Characterization of catalysts The typical SEM images of the as-prepared LaAl1−xCu xO3 perovskites (Fig.2A, 2C and Fig.S1) showed the sphere-like morphology with an average size of 80-100nm. The energy dispersive spectroscopy (EDS) (Fig.2B) and SEM elemental mapping analysis (Fig.2D) of these samples were detected to explore the elemental distribution. The EDS spectra indicated the existence of La, Al and O in LaAlO3, while La, Al, O and Cu appear in LaAl0.95Cu0.05O3. According to the rough atomic percentage of these samples shown in Table S1, the percentage of Al decreased after Cu was doped in 7

LaAlO3. The SEM elemental mapping of LaAl0.95Cu0.05O3 revealed that the component elements of La, Al, O and Cu were uniformly distributed over the surface. TEM images (Fig. 2E) revealed that LaAl0.95Cu 0.05O3 had a sphere-like morphology, consistent with the results observed with SEM. The HRTEM image (Fig. 2F) showed the lattice space of 2.68 Å corresponding to the (110) planes of the rhombohedral-phase of LaAlO3 (JCPDS 70-4109) in LaAl0.95Cu0.05O3. The results suggested that the lattice of the LaAlO3 was not destroyed obviously during the Cu-doping process. The XRD patterns of LaAl1−x Cu xO3 (x = 0.0 - 0.1) perovskite samples (Fig. 3A and Fig. S2) showed that the synthesized perovskite samples are pure phase of LaAlO3 (JCPDS 70-4109), and no diffraction peaks of copper oxide (CuOx) were observed in these samples, suggested a high dispersion of Cu species on LaAlO3. To determine the electronic properties of Cu species in these catalysts, an ESR investigation was undertaken. As shown in Fig. 3B, LaAlO3 sample was ESR inactive, the intensity of the ESR signals was substantially larger for the sample containing more Cu. The Cu incorporated samples exhibited signals characteristic of Cu (II) at g = 2.084, suggested that the isolated copper species were responsible for the spectrum component in the LaAl0.95Cu 0.05O3 sample [35]. The detailed FTIR spectra analysis for LaAl1−xCu xO3 was described in SI. The results of FT-IR analysis also indicated that the structure of LaAlO3 was not destroyed during the Cu-doping process (Fig. S3). Fig. 3C showed the Raman spectra of LaAl1−xCu xO3 perovskites. Two strong peaks at 124 and 485 cm−1 in the sample of 8

LaAlO3 (curve a) were assigned to O-O rotation and bending modes in the rhombohedral phase, respectively [36]. The band at 150 cm−1 was assigned to oxygen-metal-oxygen bending modes [37, 38]. With the doping of Cu, two new peaks appeared at 595 and 708 cm−1, which were attributed to Cu-O vibrations [39]. In combination with the results of XRD analysis, Cu was confirmed to be doped in LaAlO3 very well and the structure of LaAlO3 was not destroyed. In the typical XPS survey spectra of LaAlO3 and LaAl0.95Cu0.05O3 (Fig. S4A), the peak of Cu 2p was detected in LaAl0.95Cu0.05O3. The small position change of La 3d in LaAlO3 and LaAl0.95Cu0.05O3 suggested that the cohesive energy of La was changed slightly during the Cu-doping process (Fig. S4B). Two peaks were detected in the O1s XPS spectrum of LaAlO3 (Fig. 3D), the first peak P1 at 529.3 eV was attributed to the lattice oxygen, and the second one P2 at 531.5 eV denotes O 1s lateral structure, corresponded to two components (i.e., Al-O-La and O-H) [40]. Comparing to LaAlO3 sample, the ratio of P1 and P2 decreased from 1.53:1 to 1:1 in LaAl0.95Cu 0.05O3 sample, which attributed more OVs were generated due to the incorporation of Cu into the LaAlO3 structure for the LaAl0.95Cu0.05O3 sample. According to previous method [41], OVs increased by 28 mol% with the incorporation of Cu. The Al 2p spectrum (Fig. S4C) at around 73 eV was fitted with two peaks assigned to the bond of Al-O-Al and Al-O-La in LaAlO3 [42], while the Al 2p peak consisted of the peak of Al3+ (around 72.5 eV), Cu 3p 3/2 (around 74.9 eV), and Cu 3p 1/2 (77.2 eV) peaks of Cu+ [43]. According to previous report [23, 42], the binding energies (BEs) were assigned to Al−O−Al/La and Al−O−Cu, respectively. In the Cu 2p3/2 spectrum (Fig. 3E), the peak 9

at ca. 932.5 eV corresponded to the reduced state of copper species (i.e., Cu+), and the peak at ca. 933.6 corresponds to the oxidation state of the copper species (i.e., Cu 2+) [44]. The “shake-up” peak at around 942.6 eV was attributed to the Cu 2+ satellite. The auger parameter at 1847.1 eV confirmed the existence of Cu+ based on the auger electron spectroscopy measurement. These results indicated that both Cu+ and Cu 2+ existed in LaAl0.95Cu0.05O3, and the atomic ratio of Cu+:Cu2+ was 3.8:1. The Cu K-edge EXAFS K2χ(R) functions and their Fourier transform (FT) of LaAl1−xCu xO3 were shown in Fig. S5 and Fig. 3F. The FT shapes for the three LaAl1−xCu xO3 samples were different from the reference samples of Cu 2O and CuO. The existence of the secondary phases (e.g., CuO and Cu 2O) can be excluded in the samples. The EXAFS oscillations were distinct in the spectra up to a high k value that showed the magnitude of the Fourier transforms |FT(k2χ(R))| of the experimental EXAFS spectra of samples between Rmin =1 to Rmax = 12 Å−1 [45, 46]. The main peaks in FT denoted the contribution of the backscattering of photoelectrons emitted at Cu site from neighboring atoms. Table 1 showed the local coordination structure of Cu species in various catalyst, two Cu-O shells were observed over all samples with coordination number of about 4.2 and 1.9 at the bond distance of 1.98 ± 0.02 Å and 2.36 ± 0.03 Å. In the second shell, the Cu-Cu subshells fitted well to the experimental results, indicating a Cu-Cu coordination number of about 1.3 at a bond distance of 2.92 ± 0.03 Å. The Cu-Al/La interaction was located at ~3.24 Å, confirmed that Cu was incorporated into LaAlO3 and La/Al-O-Cu bonds formed. Moreover, with the increase of the doping amount of Cu, the coordination number of the Cu-Al/La shell 10

from 1.4 changed to 1.7. The result indicated that the local environment of Al and La was affected by the incorporation of Cu, and due to the similar atom radius of Cu and Al, the position of Al was partly replaced by Cu to form La/Al-O-Cu bond. 3.2 Catalytic activity and stability of LaAl0.95Cu0.05O3 The catalytic activity of LaAl1-xCu xO3 was evaluated based on the degradation of 2-CP and the corresponding TOC removal (Fig. 4A and 4B). 11% of 2-CP was adsorbed on the surface of LaAlO3 within 30 min adsorption/desorption equilibrium experiment, 30% of 2-CP was degraded and the corresponding TOC removal was 15% in LaAlO3 suspension within 120 min. With the increase of Cu doping, the degradation rate of 2-CP greatly increased. 12% of 2-CP was adsorbed on the surface of LaAl0.95Cu0.05O3 in the part of adsorption/desorption equilibrium experiment, while 2-CP was completely removed and the corresponding TOC removal reached up to 62% in LaAl0.95Cu0.05O3 suspension within 120 min. Elemental analysis result indicates the carbon element of the probable adsorbed species on the surface of fresh LaAl0.95Cu0.05O3 and LaAl0.95Cu0.05O3 after reaction is 0.1405 and 0.209%, respectively. After correcting, about 11.8% of TOC was adsorbed on the surface of LaAl0.95Cu0.05O3 after reaction, which means the TOC of the probable adsorbed species on the surface was not significant. However, with a higher Cu content, the degradation of 2-CP was not significant increasing, the concentration of total dissolved Cu from LaAl0.9Cu 0.1O3 (1.05 mg L−1) was double of that from LaAl0.95Cu0.05O3 (0.523 mg L−1). Therefore, well-crystallized LaAl0.95Cu0.05O3 with a pure LaAlO3 phase was selected to be used in the following Fenton-like reactions. In 11

addition, only about 10% of TOC was removed within 120 min in the homogeneous Fenton reaction (Cu2+ concentration 0.523 mg L−1) in the absence of LaAl0.95Cu0.05O3, which was much lower than that in LaAl0.95Cu0.05O3 suspension, indicated that the released Cu2+ ions was not dominant for the degradation of pollutants. Based on the standard < 1.3 mg L−1 of drinking water in USA regulations and the standard < 2 mg L−1 in EU directives, 0.523 mg L−1 Cu2+ release is already within the acceptable range [47]. Additionally, according to the XRD analysis (Fig. 3C), the structure of LaAl0.95Cu0.05O3 before and after Fenton reaction did not change significantly. The results suggested that the catalyst was effective and stable for heterogeneous Fenton reactions. The effects of H2O2 concentration on the catalytic activity and the corresponding TOC removal in the presence of LaAl0.95Cu0.05O3 were investigated (Fig. S6). Only 5% of 2-CP was degraded after reaction time of 120 min without H2O2. The degradation of 2-CP was significantly accelerated in the presence of H2O2. With the addition of 5 mmol L−1 H2O2, about 80% of 2-CP was degraded within 120 min, while it could be completely removed within 120 min with the addition of 10 mmol L−1 H2O2. However, at the H2O2 concentration higher than 10 mmol L−1, a slight increase in the substrate degradation of 2-CP and no increase in TOC removal were observed due to an unprofitable consumption of H2O2. The effects of LaAl0.95Cu0.05O3 concentration on the catalytic activity in the presence of H2O2 were investigated (Fig. S7). In the absence of catalyst, only 8% of 2-CP was degraded after reaction time of 120 min. The degradation efficiency 12

improved with the increasing catalyst concentration, and about 80% of 2-CP were degraded within 120 min at a catalyst concentration of 0.5 g L-1. They were degraded completely within 90 min at a catalyst concentration of 1.0 g L-1. A higher concentration of 1.5 g L-1 did not cause much improvement of the degradation efficiency. In addition, the effect of the initial 2-CP concentration on its degradation by LaAl0.95Cu0.05O3 was determined (Fig. S8). At higher concentration of 2-CP, 63% of 2-CP was removed with initial 2-CP concentration 50 mg L-1 and 28% of 2-CP was removed with initial 2-CP concentration 100 mg L-1 after reaction time of 120 min. Furthermore, the degradation of 2-CP in LaAl0.95Cu 0.05O3 suspension exhibited a high catalytic activity at initial neutral pH range, and no significant difference was found at initial pH 5.0 and 9.0. At initial pH 10.0 about 50% of 2-CP was degraded within 120 min, but only 12% of 2-CP was removed at initial pH 11.0 and 8% of 2-CP was removed at initial pH 12.0 (Fig. 4C and 4D). The results indicated that LaAl0.95Cu0.05O3 exhibited a high catalytic activity at pH of 5.0-9.0, and the catalytic activity of LaAl0.95Cu0.05O3 was decreased to some extent at pH of 10.0, and the catalytic activity was decreased significantly at pH of 11.0-12.0. In addition, for seven other pollutants (phenol, PHT, BPA, 2,4-D, IBU, CIP and DP) at initial concentration of 10 mg L−1, they were degraded completely after 60 min for Phenol, 30 min for PHT and BPA, 90 min for 2,4-D and CIP, 120 min for IBU and DP (Fig. S9A), and the corresponding TOC removals were 75%, 52%, 62% 67%, 38%, 51%, and 45% within 120 min (Fig. S9B), respectively. These results were compared to previous reports for non-catalytic and catalytic processes [48-50]. Comparing to the Fenton 13

process at acid pH and initial circumneutral pH, the degradation efficiency of DP was higher than that with Fe2+ as catalyst with the TOC removal 19.5% at pH 2.8 and 31% at pH 6.2 [48]. The results obtained achieved higher degradation than the degradation of BPA in non-catalytic ozonation with the maximum TOC removal of 12 % after 75 min of reaction at pH 5.9 [49]. In contrast with that of practical wastewater treatment process at basic pH in peroxone non-catalytic processes, phenol could be completely degraded by LaAl0.95Cu0.05O3 as catalyst within 60 min, superior to the non-catalytic process in which ＞99% of phenol was degraded after 180 min [50]. 3.3 H2O2 utilization efficiency As Luo et al. reported [51], H2O2 utilization efficiency (η) was defined as the ratio of the amount of H2O2 consumption ([∆H2O2]S) for the degradation of pollutants to the actual H2O2 consumption ([∆H2O2]A). Accordingly, when H2O2 utilization efficiency reached up to 100%, which is equivalent to one mol HO• radicals was generated by the reacted per mol H2O2. Based on the calculation method of Navalon et al. [52], 8.164 equiv of H2O2 consumed for degradation 68% of BPA within 60 min, and 11.2 equiv of H2O2 consumed for complete disappearance of BPA. H2O2 utilization efficiency reached up to 180% after reaction time of 60 min, and the utilization efficiency of H2O2 was ~130% after the reaction time of 240 min in LaAl0.95Cu0.05O3/H2O2 system (Fig. 4E). Which equals to 1.8 mol HO• radicals was generated after reaction time of 60 min and still 1.3 mol HO• radicals was generated after reaction time of 240 min by the reacted per mol H2O2. According to previous report [26], the utilization efficiency of H2O2 usually ranged from 10% to 60% in 14

Cu-based systems, which means only 0.1 to 0.6 mol HO• radicals was generated by the reaction of per mol H2O2. The quantitative relationship of H2O2 and HO• radicals was further detected using the terephthalic acid (TPA) probe method (Fig. 4F). The amount of generated HO• radicals was nearly twice the consumption of H2O2 within 15 min and the amount of HO• radicals generated was much higher than the consumption of H2O2 within 25 min. At the beginning of reaction, the amount of HO• radicals was accurately determined due to the HO• radical predominantly reacted with TPA. With the increase of reaction time, the HO• radical reacted with other substances (i.e., the intermediates of the reacted TPA, HO• radicals itself and H2O2), resulting in the lower HO• radicals measurement. The result indicated that the amount of HO• radicals was nearly twice as that of the reacted H2O2 in the practical reaction process, in line with the result of H2O2 utilization efficiency. 3.4. Reaction mechanism The decomposition of H2O2 in different suspensions was shown in Fig. 5A. H2O2 was barely decomposed in LaAlO3 suspension, whether BPA was present or not. In LaAl0.95Cu0.05O3 suspension, 85% of H2O2 was decomposed in the absence of BPA within 240 min, while only 16.5% of H2O2 was decomposed in the presence of BPA at the same condition. These results indicated that the decomposition of H2O2 was inhibited effectively in the presence of BPA, whereas in the absence of pollutants the radicals generated from H2O2 would react with H2O2 again to result in the decomposition of H2O2 quickly because H2O2 acted as a scavenger to remove the active species from the reaction media [28, 53]. In addition, Cu2+ on the surface of 15

LaAl0.95Cu0.05O3 can chelate with the phenolic OH group to form phenoxo-Cu(II) complexes and orbital interactions in the phenoxo-Cu(II) complexes improve the electronic polarity of the benzene ring, resulting in H2O2 directly reacted with the aromatic ring to form HO• radicals[54, 55]. And due to the charge transfer from the benzene ring to Cu(II), Cu(II) in the phenoxo-Cu(II) complexes was reduced to Cu(I), and the oxidation of H2O2 was inhibited significantly. DMPO spin-trap ESR was performed to detect the reactive oxygen radicals (ROS) generated in different dispersions of the corresponding samples with H2O2. The DMPO-HO2•/O2•− radicals are detected in methanol because the HO2•/O2•− radicals in water are very unstable [56]. The sextet peaks of DMPO-HO2•/O2•− adducts were observed in LaAl0.95Cu0.05O3/H2O2 system (Fig. 5C), and the peaks are higher than that without adding H2O2 and LaAlO3/H2O2 system. Accordingly, four characteristic peaks of DMPO-HO• radicals are detected in the LaAl0.95Cu 0.05O3/H2O2 system (Fig. 5D, while no significant characteristic peaks was appeared in LaAlO3/H2O2 system. The results indicated that H2O2 was decomposed into HO• and HO2•/O2•− radicals by the redox reaction with LaAl0.95Cu0.05O3. It is noteworthy that the intensity of DMPO-HO• was much higher than that of DMPO-HO2•/O2•− at the same measurement condition in the LaAl0.95Cu0.05O3/H2O2 system. Above results shown that H2O2 was predominantly reduced to HO• on the surface of LaAl0.95Cu0.05O3 Free-radical scavenger was added independently during the degradation of BPA in the presence of H2O2 in LaAl0.95Cu0.05O3 suspension to explore the anomalous 16

phenomena of the utilization efficiency of H2O2 (Fig. 5B). After the HO2• radicals were scavenged, the degradation activity decreased in some extent, while after the HO• radicals were scavenged, the degradation activity decreased significantly (i.e., only about 10% of BPA was degraded after the reaction time of 120 min). The result indicated that HO• radicals played the essential role in the degradation of BPA. The interaction processes of LaAlO3 and LaAl0.95Cu 0.05O3 powders with H2O2 are detected by in-situ Raman spectroscopy (Fig. 6). The peaks at 550 and 1100 cm−1 are attributed to the satellite. In LaAlO3 suspension whether BPA was present or not (Fig. 6A and 6B), no significant peaks appeared before adding H2O2 (curve a), while a strong peak appeared at 876 cm−1 after adding H2 O2 (curve b). According to previous studies [57, 58], the peak at 876 cm−1 attributed to H2O2 and there is positive correlation between the peak intensity and the H2O2 concentration. The peak intensity did not change obviously with the increase of contact time, indicating H2O2 was hard to decompose in LaAlO3 suspension. The peak of H2O2 in LaAl0.95Cu 0.05O3suspension (Fig. 6C and 6D) was weaker than in LaAlO3 suspension, which may ascribe to the interaction between H2O2 and LaAl0.95Cu0.05O3. First, H2O2 can form transient complexes with, Cu 2+ on the surface of LaAl0.95Cu0.05O3 [59] and H2O2 can be adsorbed and dissociated on OVs of LaAl0.95Cu0.05O3 [60], resulted in weakening the strength of H2O2. In LaAl0.95Cu0.05O3 suspension, the peak intensity was weakened with the increase of contact time in the absence of BPA (Fig. 6C), while not change significantly in the presence of BPA (Fig. 6D). These results were in line with the decomposition of H2O2 in different suspensions (Fig. 5A), indicated that the 17

decomposition of H2O2 was quick in water solution, but slow in the presence of BPA. Besides, three new bonds at 695, 1406 and 1605 cm−1 attributed to C=O deformations, and CH3 deformation mode [61], and the vibration of C=C bond stretching in the aromatic ring [62], respectively, were detected in Fig. 6D. The intensities of the new bonds increased with the increase of contact time, means these new bonds corresponding to the degradation products of BPA. The interaction of H2O2 and Cu species on the surface of LaAl0.95Cu0.05O3 was further confirmed by the XPS spectra of Cu 2p on the surface of LaAl0.95Cu 0.05O3 after reaction time of 120 min and 24 h (Fig. S11). After reaction time of 120 min, the ratio of Cu +:Cu2+ was decreased to 2.1: 1 from approximately 3.8:1 before reaction. While after reaction time of 24 h, the ratio of Cu+:Cu 2+ returned back to 3.9:1. These results indicated that the interfacial electron cycle of Cu + and Cu2+ occurred on the surface of LaAl0.95Cu0.05O3 by the redox reaction with H2O2 . Meanwhile, active species (HO•, HO2•/O2•−, etc.) were formed in the process from the redox of H2O2 by Cu2+/Cu + cycles. The H2O2 dissociation on OVs of LaAl0.95Cu0.05O3 was further proved by the XPS spectra of O 1s on the surface of fresh LaAl0.95Cu0.05O3 and LaAl0.95Cu0.05O3 after reaction (Fig. 7A). Comparing to fresh LaAl0.95Cu0.05O3 sample, the ratio of P1 and P2 decreased from 1:1 to 0.8:1 in LaAl0.95Cu 0.05O3 after reaction. According to Li et al.’s report, the change was intrinsically attributed to the H2O2 dissociation on OVs of LaAl0.95Cu 0.05O3, where surface-bound HO• formed. Since OVs possess an electron-rich character for the small molecules activation or dissociation, the 18

sufficient charge back-donation from OVs of LaAl0.95Cu0.05O3 to adsorbed H2O2, which results in the O-O elongation of H2O2 to enhance the formation of HO• (OV + H2O2 → HO• + OH-) [60]. In addition, the formation of HO• from H2O oxidation on OVs of LaAl0.95Cu0.05O3 was observed by DMPO spin-trap ESR. Four characteristic peaks of DMPO-HO• were detected in the aqueous dispersions of LaAl0.95Cu 0.05O3 (Fig. 7D), and the sextet peaks of DMPO-HO2•/O2•− were observed in LaAl0.95Cu0.05O3 methanol dispersions (Fig. 7B), while no such signals appeared in LaAlO3 suspensions and blank experiment. The larger electronegativity of Cu than La and Al and the existence of OVs resulted in the electron-rich Cu center [63, 64], which could reduce O2 to O2•−. Additionally, OVs could offer a possibility to enhance the thermodynamics toward water oxidation, which was mainly due to the activation of adsorbed water via their localized electrons [60, 65], Therefore, Cu center donated electrons to O2 and simultaneously withdrawing electrons from OVs that induce molecular adsorption H2O to produce HO•. This electron transfer cycle was further evidenced by the solid ESR spectra of LaAl0.95Cu0.05O3 before and after reacting with O2 in Fig. 7C. The ESR signals were no significant change, which indicated the electrons transfer cycle was occurred around the Cu center of LaAl0.95Cu0.05O3 [66]. Based on the above analysis, a complex mechanism was proposed in Fig. 8. The amount of HO• radicals was twice as that of the reacted H2O2 in the process of practical reaction, which was attributed to the interaction process on the surface of LaAl0.95Cu0.05O3. Three possible ways to generate HO• radicals were proposed. First, 19

the redox of H2O2 by the interfacial electron cycle of Cu+ and Cu2+ on the surface of LaAl0.95Cu0.05O3 to form HO•. Second, the O-O bond of H2O2 was broken on the OVs of LaAl0.95Cu0.05O3 enhanced formation of HO•. Third, the molecular adsorption H2O on OVs of LaAl0.95Cu0.05O3 was induced to produce HO•. 4. Conclusions In summary, the sphere-like LaAl0.95Cu0.05O3 was synthesized with the high dispersion of Cu species in the LaAlO3 structure. An efficient mineralization of persistent organic compounds was obtained over the LaAl0.95Cu 0.05O3 catalyst in the presence of H2O2 at ambient condition. Twice the amount of HO• radicals as that of the consumed H2O2 was generated, which was attributed to the interface reaction between LaAl0.95Cu0.05O3 and H2O2. The generation of HO• radicals was confirmed from the redox of H2O2 by Cu2+/Cu + cycles on the surface of LaAl0.95Cu0.05O3, and enhanced by H2O2/H2O dissociated on OVs of LaAl0.95Cu 0.05O3. The high catalytic activity and H2O2 utilization efficiency of LaAl0.95Cu0.05O3 at pH of 5.0-9.0 in heterogeneous Fenton-like reactions make it a promising catalyst in industrial wastewater treatment. Acknowledgments This work was supported by the National Natural Science Foundation of China (Grant Nos. 21407165, 51538013), and the National Key Research and Development Plan (2016YFA0203204). We thank the BL14W1 beamline at the Shanghai Synchrotron Radiation Facility (SSRF, China) for providing the beam time.

20

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30

Figure and Table Captions Table 1. Curve fitting results of Cu K-edge EXAFS for various samples. Fig. 1. The schedule illustration of the synthesis processes. Fig. 2. (A) SEM image of LaAlO3; (B) Energy Dispersive Spectrum (EDS) of LaAlO3 and LaAl0.95Cu0.05O3; (C) SEM image of LaAl0.95Cu0.05O3; (D) SEM elemental mapping of LaAl0.95Cu 0.05O3; (E) TEM image of LaAl0.95Cu 0.05O3; (F) HRTEM image of LaAl0.95Cu0.05O3. Fig. 3. (A) XRD patterns of the fresh LaAl0.95Cu0.05O3 and LaAl0.95Cu0.05O3 after Fenton reaction; (B) The ESR spectra of the LaAl1-xCu xO3 powders. (C) Raman spectra of the various LaAl1-xCuxO3 powders; (D) XPS spectra of LaAlO3 and LaAl0.95Cu0.05O3 powders; (E) XPS spectra of Cu 2p3/2 for LaAl0.95Cu0.05O3. Inset shows Cu LMM X-ray induced Auger parameter for the sample; (F) Fourier transform (FT) spectra of Cu K-edge EXAFS for the various LaAl1-xCuxO3 powders. Fig. 4. (A and B) Effect of Cu incorporated amount on 2-CP (10 mg L−1) degradation in the presence of H2O2 (10 mmol L−1) in various LaAl1-xCu xO3 suspension (1g L−1) and the corresponding TOC removal; (C and D) Effect of initial pH on 2-CP (10 mg L−1) degradation in the presence of H2O2 (10 mmol L−1) in LaAl0.95Cu0.05O3 suspensions (1g L−1) and the corresponding TOC removal of initial pH on 2-CP degradation; (E) The utilization efficiency and decomposition of H2O2 in the presence of H2O2 (10 mmol L−1) in LaAl0.95Cu0.05O3 (1g L−1) suspensions, degradation and TOC removal of BPA (25 mg L−1); (F) The quantitative relation between H2O2 (10 mmol L−1) consumption and HO• radicals generation in LaAl0.95Cu 0.05O3 suspensions 31

(1g L−1) during the reaction. Fig. 5. (A) Effect of different solutions on H2O2 decomposition in the LaAl0.95Cu0.05O3 suspensions. (Initial pH 6.8, initial H2O2 concentration 10 mmol L−1 catalyst concentration 1.0 g L−1). (B) Effect of different free-radical scavenger on BPA (25 mg L−1) degradation in the presence of H2O2 (10 mmol L−1) in LaAl0.95Cu0.05O3 suspensions (1 g L−1). (tert-butyl alcohol (100 mmol L−1) was added to quench HO• radicals and p-benzoquinone (1 mmol L−1) was added to quench HO2• radicals.); (C) DMPO spin-trapping ESR spectra for DMPO-HO2•/O2•− in various methanol dispersions with H2O2. (D) DMPO spin-trapping ESR spectra for DMPO-HO• in various aqueous suspensions with H2O2. Fig. 6. In-situ Raman spectra for different catalysts aqueous dispersions: (A) LaAlO3 in water dispersions; (B) LaAlO3 in aqueous dispersions with BPA (100 mg L−1); (C) LaAl0.95Cu0.05O3 in water dispersions; (D) LaAl0.95Cu0.05O3 in aqueous dispersions with BPA (100 mg L−1). For all panels (a) before adding H2O2, and after adding H2O2: (b) 2 min, (c) 4 min, (d) 6 min and (e) 8 min. Fig. 7. (A) The XPS spectra of O1s for LaAl0.95Cu0.05O3 before and after Fenton reaction; (B) DMPO spin-trapping ESR spectra for DMPO-HO2•/O2•− in various methanol dispersions without H2O2. (C) ESR spectra of LaAl0.95Cu 0.05O3 and LaAlO3 solid samples before and after the reaction with O2. (D) DMPO spin-trapping ESR spectra for DMPO-HO• in various aqueous suspensions without H2O2.

32

Fig. 8. The schematic illustration for the interaction of Cu-doped LaAlO3 perovskite with H2O2.

33

Table 1. Curve fitting results of Cu K-edge EXAFS for various samples. Sample

Cu2O

shell

R(Å)

CN

σ2 (Å2)

First shell Cu-O

1.90(3)

1.7(3)

0.008(2)

3.39(3)

5.1(3)

0.016(4)

2.95(2)

1.5(2)

0.029(3)

1.96(5)

2.1(3)

0.019(2)

2.89(3)

1.7(5)

0.018(4)

2.93(3)

0.8(4)

0.027(3)

First shell (Cu-O)

1.98(2)

4.1(4)

0.009(4)

2.37(1)

1.9(2)

0.010(5)

Second shells (Cu-Al/Cu/La)

2.91(4)

1.2(3)

0.023(2)

3.23(2)

1.4(1)

0.027(3)

First shell (Cu-O)

1.99(3)

4.3(1)

0.006(5)

2.35(4)

1.9(2)

0.012(4)

Second shells (Cu-Al/Cu/La)

2.93(2)

1.3(5)

0.034(3)

3.22(4)

1.6(2)

0.025(3)

First shell (Cu-O)

1.98(2)

4.2(4)

0.009(2)

2.37(1)

2.1(2)

0.011(4)

Second shells (Cu-Al/Cu/La)

2.91(3)

1.3(1)

0.041(2)

3.25(4)

1.7(1)

0.036(3)

Second shells Cu-Cu

CuO

First Cu-O shell Second shells Cu-Cu

LaAl0.99Cu0.01O3

LaAl0.95Cu0.05O3

LaAl0.9Cu0.1O3

R: Bond distance, CN: Coordination number, σ2: Debye-Waller factor.

34

Fig. 1. The schedule illustration of the synthesis processes.

35

Fig. 2. (A) SEM image of LaAlO3; (B) Energy Dispersive Spectrum (EDS) of LaAlO3 and LaAl0.95Cu0.05O3; (C) SEM image of LaAl0.95Cu0.05O3; (D) SEM elemental mapping of LaAl0.95Cu 0.05O3; (E) TEM image of LaAl0.95Cu 0.05O3; (F) HRTEM image of LaAl0.95Cu0.05O3.

36

(A)

(110)

Intensity (a.u.)

(B)

LaAl0.99Cu0.01O3

(202) (024) (300) (200) fresh LaAl0.95Cu0.05O3

LaAl0.98Cu0.02O3

Intensity(a.u.)

(012)

LaAlO3

LaAl0.95Cu0.05O3 LaAl0.9Cu0.1O3

LaAl0.95Cu0.05O3 used

20

30

40

50

60

2 theta (degree)

70

80

P1:P2=1.53:1

(D)

P2:O1s lateral structure 531.4

LaAl0.95Cu0.05O3

LaAlO3

LaAl0.98Cu0.02O3

P'1:P'2=1:1

LaAl0.99Cu0.01O3

P'2:O1s lateral structure 531.1

124 485

LaAlO3

1200

800

+

2+

Cu LMM-Auger + (Cu ) 1847.1

534

532

530

528

Binding Energy (eV)

526

(F)

+

-3

(Cu ) 932.5

Cu2O

|FTK χ(R)|Å

CuO

2

1852 1850 1848 1846 1844 1842 1840

Auger Parameter (eV)

2+

536

(E)

Cu : Cu =3.8:1

(Cu satellite) 942.6

P'1:lattice oxygen 528.9

LaAl0.95 Cu0.05O3

400

-1

Wavenumber (cm )

Cu 2p3/2

P1:lattice oxygen 529.3

150

LaAl0.9Cu0.1O3

1600

2.5 2.0 1.5 Magnetic Filed (G)

(C)

708 595

Intensity (a.u.)

90 3.0

2+

(Cu ) 933.6

LaAl0.99Cu0.01O3 LaAl0.95Cu0.05O3 LaAl0.9Cu0.1O3

948

944

940

936

Binding Energy (eV)

0

932

2

4

Radial distance (Å)

6

8

Fig. 3. (A) XRD patterns of the fresh LaAl0.95Cu0.05O3 and LaAl0.95Cu0.05O3 after Fenton reaction; (B) The ESR spectra of the LaAl1-xCu xO3 powders. (C) Raman spectra of the various LaAl1-xCuxO3 powders; (D) XPS spectra of LaAlO3 and LaAl0.95Cu0.05O3 powders; (E) XPS spectra of Cu 2p3/2 for LaAl0.95Cu0.05O3. Inset

37

shows Cu LMM X-ray induced Auger parameter for the sample; (F) Fourier transform (FT) spectra of Cu K-edge EXAFS for the various LaAl1-xCuxO3 powders. 1.0

(A)

1.0

LaAlO3 LaAl0.99Cu0.01O3

C/C0

LaAl0.98Cu0.02O3 LaAl0.95Cu0.05O3

0.4

LaAl0.9Cu0.1O3

0.2

0.8

TOC removal

0.6

0.0 0

30

60

90

Time (min)

0.6

0.6

0.4

0.4

0.2

0.2

0.0

0.0

O O O O LaAlO 3 l Cu 0.01 3 l Cu 0.02 3 l Cu 0.05 3 Al 9Cu 0.1 3 La 0. LaA 0.99 LaA 0.98 LaA 0.95

120

1.0

(C)

TOC removal

0.8

C/C0

0.6 pH=5 pH=6.8 pH=9 pH=10 pH=11 pH=12

TOC removal

0.6 0.4 0.2

0.0

0.0

60

Time (min)

2.0

90

120

H2O2 utilization efficiency (E)

C/C0

1.5 H2O2 decomposition

1.0

1.0

TOC removal

0.5

0.5

BPA

0

60

120

Time (min)

180

240

5

6.8

9

pH

10

11

12

0.6 (F)

[H2O2]S/[H2O2]A

1.5

2.0

0.0

C (mmol L )

30

-1

0

0.0

(D)

0.8

0.2

0.8

Sample

1.0

0.4

1.0

TOC removal Cu leaching

Cu leaching (mg/L)

0.8

(B)

0.4

OH ∆Η2Ο2

0.2 0.0

-0.2

0

6

12

18

24

30

Time (min)

Fig. 4. (A and B) Effect of Cu incorporated amount on 2-CP (10 mg L−1) degradation in the presence of H2O2 (10 mmol L−1) in various LaAl1-xCu xO3 suspension (1g L−1) and the corresponding TOC removal; (C and D) Effect of initial pH on 2-CP (10 mg L−1) degradation in the presence of H2O2 (10 mmol L−1) in LaAl0.95Cu0.05O3 suspensions (1g L−1) and the corresponding TOC removal of initial pH on 2-CP 38

degradation; (E) The utilization efficiency and decomposition of H2O2 in the presence of H2O2 (10 mmol L−1) in LaAl0.95Cu0.05O3 (1g L−1) suspensions, degradation and TOC removal of BPA (25 mg L−1); (F) The quantitative relation between H2O2 (10 mmol L−1) consumption and HO• radicals generation in LaAl0.95Cu 0.05O3 suspensions (1g L−1) during the reaction.

39

1.0

(A)

1.0

0.8

0.8

C/C0

C/C0

LaAl0.95Cu0.05O3 in water

no scavenger

0.4

LaAlO3 in BPA

0.4

•ΟΗ scavenger HO2• scavenger

0.6

LaAl0.95Cu0.05O3 in BPA

0.6

LaAlO3 in water

0.2

0.2

0.0

0.0

0

1.5x10

7

1.0x10

7

5.0x10

6

60

120

180

Time (min)

0

240

(C) LaAl0.95Cu0.05O3+DMPO+H2O2

Intensity (a.u.)

Intensity (a.u.)

(B)

LaAlO3+DMPO+H2O2

1.5x10

7

1.0x10

7

5.0x10

6

DMPO

0.0

60

Time (min)

90

120

(D)

LaAl0.95Cu0.05O3+DMPO+H2O2

LaAlO3+DMPO+H2O2

DMPO

0.0

3480

30

3500

3520

Magnetic Filed (G)

3540

3480

3500

3520

3540

Magnetic Filed (G)

Fig. 5. (A) The decomposition of H2O2 in different suspensions. (Initial pH 6.8, initial H2O2 concentration 10 mmol L−1 catalyst concentration 1.0 g L−1). (B) Effect of different free-radical scavenger on BPA (25 mg L−1) degradation in the presence of H2O2 (10 mmol L−1) in LaAl0.95Cu0.05O3 suspensions (1 g L−1). (tert-butyl alcohol (100 mmol L−1) was added to quench HO• radicals and p-benzoquinone (1 mmol L−1) was added to quench HO2• radicals.); (C) DMPO spin-trapping ESR spectra for DMPO-HO2•/O2•− in various methanol dispersions with H2O2. (D) DMPO spin-trapping ESR spectra for DMPO-HO• in various aqueous suspensions with H2O2.

40

(A)

(B)

876

876

Intensity (a.u.)

Intensity (a.u.)

e d c b a

e d

c b a

1800

1500

1200

900-1

Wavenumber (cm )

600

1800

1605

876 e

Intensity (a.u.)

Intensity (a.u.)

1200

900-1

600

Wavenumber (cm )

(D)

(C)

d c b a

1800

1500

e

876

695

1406

d c b a

1500

1200

900-1

Wavenumber (cm )

600

1800

1500

1200

900-1

Wavenumber (cm )

600

Fig. 6. In-situ Raman spectra for different catalysts aqueous dispersions: (A) LaAlO3 in water dispersions; (B) LaAlO3 in aqueous dispersions with BPA (100 mg L−1); (C) LaAl0.95Cu0.05O3 in water dispersions; (D) LaAl0.95Cu0.05O3 in aqueous dispersions with BPA (100 mg L−1). For all panels (a) before adding H2O2, and after adding H2O2: (b) 2 min, (c) 4 min, (d) 6 min and (e) 8 min.

41

P1(528.9)

P1:lattice oxygen P2:O1s lateral structure

(A)

Fresh LaAl0.95Cu0.05O3

P'1(529.3)

P'1:P'2=0.8:1

P'2(531.5)

Intensity (a.u.)

P1:P2=1:1

P2(531.1)

532

530

6

LaAlO3+DMPO

1x10

528

3480

526

3520

3540

(D)

(C)

DMPO

Before reaction with O2

0 3460

3500

Magnetic Filed (G)

Intensity(a.u.)

LaAl0.95Cu0.05O3+DMPO

DMPO

0

Binding Energy (eV)

6

2x10

Intensity (a.u.)

534

LaAlO3+DMPO

6

1x10

LaAl0.95Cu0.05O3 after reaction

536

(B)

LaAl0.95Cu0.05O3+DMPO

6

2x10

After reaction with O2

3480

3500

3520

3540

Magnetic Filed (G)

3.0

3560

2.5

2.0

Magnetic Filed (G)

1.5

Fig. 7. (A) The XPS spectra of O1s for LaAl0.95Cu0.05O3 before and after Fenton reaction; (B) DMPO spin-trapping ESR spectra for DMPO-HO• in various aqueous suspensions

without

H2O2.

(C)

DMPO

spin-trapping

ESR

spectra

for

DMPO-HO2•/O2•− in various methanol dispersions without H2O2. (D) ESR spectra of LaAl0.95Cu0.05O3 solid sample before and after the reaction with O2.

42

Fig. 8. The schematic illustration for the interaction of Cu-doped LaAlO3 perovskite with H2O2.

43


Cu was incorporated into the sphere-like LaAlO3 structure with La/Al-O-Cu bond.
Cu-doped LaAlO3 showed excellent activity and stability for the pollutants removal.
The generated amount of HO• radicals was nearly twice as that of the reacted H2O2.
H2O2 was predominantly reduced to HO• on the electron-rich Cu center.
The generation of HO• radicals was enhanced on oxygen vacancies.

44

Graphical Abstract

45