Accepted Manuscript Novel Magnetically Separable Ag3PO4@CuFe2O4 Micro-nanocomposite with Highly Enhanced Visible-light-driven Photocatalytic Activity Tianhong Zhou, Guozhen Zhang, Pengjun Ma, Xiaoli Qiu, Hongwei Zhang, Hao Yang, Gang Liu PII: DOI: Reference:
S0167-577X(17)31379-4 http://dx.doi.org/10.1016/j.matlet.2017.09.044 MLBLUE 23158
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Materials Letters
Received Date: Revised Date: Accepted Date:
1 June 2017 10 September 2017 12 September 2017
Please cite this article as: T. Zhou, G. Zhang, P. Ma, X. Qiu, H. Zhang, H. Yang, G. Liu, Novel Magnetically Separable Ag3PO4@CuFe2O4 Micro-nanocomposite with Highly Enhanced Visible-light-driven Photocatalytic Activity, Materials Letters (2017), doi: http://dx.doi.org/10.1016/j.matlet.2017.09.044
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Novel Magnetically Separable Ag3PO4@CuFe2O4 Micro-nanocomposite with Highly Enhanced Visible-light-driven Photocatalytic Activity Tianhong Zhou a, b, Guozhen Zhang a ∗, Pengjun Ma b, Xiaoli Qiu b, Hongwei Zhang a, Hao Yang a, Gang Liub a
School of environmental and municipal engineering, Lanzhou Jiaotong University, Lanzhou 730070, PR China
b
Research & Development Center for Eco-material and Eco-chemistry, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou 730000, PR China
Abstract: An effective visible-light-driven Ag3PO 4@CuFe2O4 Z-scheme magnetic micro-nanocomposite was successfully fabricated by a simple ion-exchange deposition method. The Ag3PO4@CuFe2O4 photocatalyst exhibited remarkably enhanced photocatalytic activity (degradation efficiency was ~99% within 30 min and kinetic constant reached 0.1423 min-1) as compared to Ag3PO4 and CuFe2O4 for the degradation of Rhodamine B (RhB). Comparing the activity results dependence with the characterization results, it was indicated that the dependence of the photocatalytic activity on the efficient separation of photogenerated h+-e- pairs. This study might provide a promising visible light responsive photocatalyst for the photocatalytic degradation of organic dyes in waste water. Keywords: Composite materials, Magnetic materials, Z-scheme, Visible photocatalytic, highly effective 1. Introduction In recent decades, environmental pollution due to the rapid industrial expansion and human population growth is one of the most important challenges facing all leaving beings worldwide[1]. Hence, developing effective, environmental-friendly, and low-cost technology for water treatment is one of the key issues[2]. Among various strategies, photocatalytic degradation has attracted much attention as a
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“green” technology, since photocatalysts can decompose organic pollutants under solar-light irradiation[3,4]. Recently, it has been reported that silver orthophosphate (Ag3PO4) is an efficient visible-light photocatalyst for the degradation organic dyes[5-7]. Its high-efficiency originates from a constructive effect of both the large dispersion of the conduction band and the inductive effect of PO43− owing to electron-hole pair separation[8]. Despite the fact that Ag3PO 4 demonstrates highly efficient visible-light photocatalytic performance, one disadvantage is the poor stability, which prohibits large-scale application. Therefore, the photocatalytic stability and recyclability of Ag3 PO4 needs to be further improved[8]. Hetero-coupling of the magnetic semiconductor materials are alternatives for addressing above-mentioned problems. CuFe2O4 is known to have high electromagnetic performance as well as excellent chemical stability[9]. Interestingly, CuFe2O4-based catalysts are magnetically separable in a suspension by virtue of their own magnetic properties. Moreover, this hetero-coupling magnetic composite could facilitate the immigration and separation of photogenerated electrons and holes, and indeed benefit the photocatalytic activity and stability. In this work, the visible-light-driven Ag3PO4@CuFe2O4 magnetic photocatalyst was successfully fabricated by a simple ion-exchange deposition method, and it showed remarkably enhanced photocatalytic activity as compared to Ag3PO 4 and CuFe2O4 for the degradation of RhB. Based on the characterization results of all samples, it was indicated that the dependence of the photocatalytic activity on the efficient separation of photogenerated h+-e- pairs. Moreover, the Ag3PO4@CuFe2O4 can easily recycle due to its magnetic property. Ag3PO4@CuFe2 O4 photocatalyst displays excellent photocatalytic activity for RhB degradation. Finally, a possible Z-scheme mechanism for organic contaminant degradation over the Ag3PO4@CuFe2O 4 photocatalyst is proposed. 2. Experimental 2
CuFe2O4 nanostructure was prepared by the sol-gel auto-combustion process according to the previous literature[10]. The Ag3PO4@CuFe2O4 composites were synthesized by related reference via a simple ion-exchange deposition[11], 1M ammonia solution was added into 180 ml AgNO3(0.03 mol) solution formed the silver ammonia solution. Then a certain amount of CuFe2O4 sample was added and sonicated for 10 min. Subsequently, 70 mL Na2HPO4 (0.2M) was added drop by drop to the above dispersion while mechanical agitation and then sonicated for another 20 min. The precipitates was collected by centrifugation, washed, and dried at 80°C. The different mass ratios of CuFe2O4 in Ag3PO4@CuFe2O4(10%) was evaluated. The details for relevant photocatalytic activity test and characterization are present in the Electronic Supplementary Information. 3. Results and discussion Fig. 1a shows the XRD patterns of CuFe2O4, Ag3PO4, and Ag3PO4@CuFe2O4 micro-nanocomposite. The peaks marked with ♥ over Ag3PO4 and Ag3PO4@CuFe2O 4 could be assigned to the body-centered cubic structure of Ag3PO4 (JCPDS 06-0505), respectively[12]. The peaks marked with ♣ over CuFe2O4 and Ag3 PO4 @CuFe2O4 belongs to (211), (312) and (224) facets of CuFe2O4 with tetragonal-type (JCPDS 34-0425), respectively[13]. This further illustrates that Ag3PO4@CuFe2O4 composite has been synthesized successfully. The UV-vis DRS of the samples is shown in Fig.1b, which suggests that the loading of Ag3PO 4 increase the absorption intensity in visible light. This result illustrates Ag3PO4@CuFe2O4 composite is a potentially good photocatalyst to degrade dye pollutants under visible light. The plots of (αhv)2 vs hv for Ag3PO4 and CuFe2O4 are shown in Fig.1b (inset). The Eg of Ag3PO4 and CuFe2O4 are 2.42 eV and 1.66 eV, respectively. The value is in agreement with early reports[14,15]. Fig. 2 displays the morphology and structure of as-synthesized samples. As shown in Fig. 2a and 2b, 3
Ag3PO4 is a cubic structure with the average diameter of 2-4 µm, and the CuFe2O4 nanoparticles disperse on the surface of the Ag3PO4. Fig. 2c presents the EDS image of Ag3 PO4 @CuFe2O4 composite from a selected area. It could be observed clearly that there is no other element existed except for Cu, Fe, O, Ag, and P. Moreover, the atom ratios of Ag/P and Cu/Fe are close to the stoichiometric ratios of 3/1 and 2/1. The HAADF-STEM and mapping of Cu, Fe, Ag, P and O are well-defined with sharp contrast in Fig. 2d-i. Mapping of Cu and Fe has the same shape and location, and the mapping of Ag and P has the same shape and location. All of above results indicates that CuFe2O4 nanoparticles are successfully combined with the Ag3PO4 and uniform dispersion. In addition, the chemical composition and state of the Ag3PO4@CuFe2O4(10%) was performed by XPS (as shown in Fig. S1). The photocatalytic degradation of RhB under visible light irradiation is applied as a probe reaction to evaluate the photocatalytic activity of the Ag3PO4, CuFe2O4, and Ag3PO4@CuFe2O4 samples. Obviously, the Ag3PO4@CuFe2O 4 composite manifests that approximately 99% of RhB is decomposed in 30 min irradiation; however, the photocatalytic activity of Ag3PO4@CuFe2O4 exceeds other samples under the same conditions (Fig. 3a). The apparent rate constants (k, min-1) determines from the first-order equation: ln(C/C0) =kt. As shown in Fig. 3b, the Ag3PO4@CuFe2O4 exhibites the higher rate constant (k=0.1423 min−1) than that of Ag3PO4, CuFe2O4. Clearly, the loading of CuFe2O4 on Ag3PO4 is conducive to increases the RhB photodegradation rate. The different loading of CuFe2O4 over Ag3PO4@CuFe2O4 was studied in Fig. S2. A detailed comparison of degradation efficiency in the Ag3PO4 based photocatalysts are shown in Table S1, which further confirming the outstanding catalytic behavior of Ag3PO4 @CuFe2O4. The stability experiments of RhB dyes have been performed (Fig.S3a). The crystal structure and chemical state of the used sample is characterized by XRD and XPS in Fig. S3b-S3c. To further examine the loading of CuFe2O4 in Ag3PO4@CuFe2O4 sample, we checked the atom concentration by SEM-mapping 4
and XPS method. The results show that the loading of CuFe2O4 in Ag3PO 4@CuFe2O4 sample is ca. 10% (as shown in Table S2-S3). The TOC suggests that 40% of RhB is mineralized in the photocatalytic system of Ag3PO4@CuFe2O4 composite within 35 min irradiation (Fig. 3c). To investigate the magnetic properties of all samples, the M-H loop is depicted in Fig. 3d. Ms of CuFe2O4 and Ag3PO4@CuFe2O4 composite are 17.70 and 2.19 emu g-1, respectively. The ferromagnetic property of as-synthesized catalysts ensures the convenient magnetic separation after used. Generally, •O2−, h+ and •OH play an important roles in degradation of organic dyes. To realize the underlying photocatalytic mechanism, various scavengers (1 mM EDTA-Na2 for holes, 1 mM isopropanol for •OH, and N2 for O2-) are added in the photocatalytic system[16]. In Fig. 3e, it is found that the degradation rate is drastically inhibited by the holes capture agent addition of EDTA-Na2, which further illuminates that the holes play an important role in the organic contaminant degradation process. A possible Z-scheme mechanism for organic contaminant degradation using the Ag3PO4@CuFe2O4 heterojunction photocatalyst is proposed, as shown in Fig. 3f and Fig. S4. The Z-scheme mechanism photocatalysts retain the stronger oxidation and reduction ability, which deeply contributes to the improvement of photocatalytic activity[17]. Under visible-light irradiation, both Ag3PO4 and CuFe2O4 could absorb visible light photons to produce photogenerated e- and h+. The photogenarated electrons in the CB of Ag3PO4 will migrate to the VB of CuFe2O4[18]. As a result, there are rich holes be generated in the VB of Ag3PO4, which can also interact with the H2O or OH- to yield highly reactive •OH radicals. At the same time, the electrons in the CB of CuFe2O4 reacts with the O2 yield •O2- radicals. These radicals (•OH and •O2-) and holes with strong oxidation can degrade RhB dye into nontoxic organic intermediate products. 5
4. Conclusion In summary, an effective visible-light-driven Ag3PO4@CuFe2O4 Z-scheme magnetic composite was successfully fabricated by a simple ion-exchange deposition method. Compared to Ag3PO4 and CuFe2O4, the Ag3PO 4@CuFe2O4 exhibited excellent photocatalytic activity and stability (degradation efficiency was ~99% within 30 min irradiation) for the photodegradation of RhB under visible light irradiation. A possible Z-scheme mechanism is proposed over the Ag3PO4@CuFe2O4. This study might provide a promising visible light responsive photocatalyst for the photocatalytic degradation of organic dyes in waste water. Acknowledgements This work was financially supported by the NSFC (Grant No. 51768031), and Program for Changjiang Scholars and Innovative Research Team in Chinese Universities (IRT - 14R25). References [1] L. Zhang, Y. M. He, Y. Wu, T. H. Wu, Mater. Sci. Eng. B 176 (2011) 1497-1504. [2] B. Bethi, S.H. Sonawane, B.A. Bhanvase, S.P. Gumfekar, Chem. Eng. Process. 109 (2016) 178-189. [3] H. Yin, X. Wang, L. Wang, Q. Nie, Y. Zhang, W. Wu, Mater. Res. Bull. 72 (2015) 76-83. [4] M. Zhou, H. Yang, T. Xian, R.S. Li, H.M. Zhang, X.X. Wang, J. Hazard. Mater. 289 (2015) 149-157. [5] S.S. Patil, M.S.Tamboli, V.G. Deonikar, G.G. Umarji, J.D Ambekar, M.V. Kulkarni, D.R. Patil, Dalton Trans. 44 (2015) 20426-20434. [6] V.G. Deonikar, S.S. Patil, M.S.Tamboli, J.D.Ambekar, M.V. Kulkarni, R.P. Panmand, D.R. Patil, Phys. Chem. Chem. Phys. 19 (2017) 20541-20550. [7] S.S. Patil, M.G. Mali, A. Roy, M.S. Tamboli, V.G. Deonikar, D.R. Patil, B.B. Kale, J. Energy Chem. 25 (2016) 845-853. [8] Z. Chen, W. Wang, Z. Zhang, X. Fang, J. Phys. Chem. C. 117 (2013) 19346-19352. [9] S. Hussain, S. Hussain, A. Waleed, M.M. Tavakoli, Z. Wang, S. Yang, M.A. Nadeem, ACS Appl. Mater. Interfaces. 8 (2016) 35315-35322. [10] T. Liu, L. Wang, P. Yang, B. Hu, Mater. Lett. 62 (2008) 4056-4058. 6
[11] G.Y. Zhao, L.J. Liu, J.R. Li, Q. Liu, J. Alloys Compd. 664 (2016) 169-174. [12] Y. Bi, S. Ouyang, N. Umezawa, J. Y. Cao, J. H. Ye, J. Am. Chem. Soc. 133 (2011) 6490-6492. [13] Y. Shen, Y.B. Wu, H.F. Xu, J. Fu, X.Y Li, Q.D. Zhao, Y. Hou. Mater. Res. Bull. 48 (2013) 4216-4222. [14] S. Hussain, A. Waleed, M.M. Tavakoli, Z.L. Wang, S.H. Yang, Z.Y. Fan, M.A. Nadeem, ACS Appl. Mater. Inter. 8 (2016) 35315-35322. [15] X.J. Chen, Y.Z. Dai, J. Guo, F.Z. Bu, X.Y. Wang, Mat. Sci. Semicon. Proc. 41 (2016) 335-342. [16] Y.S. Xu, W.D. Zhang, Dalton T. 42 (2013) 1094. [17] W. Chen, T.Y. Liu, T. Huang, Appl. Surf. Sci. 355 (2015) 379-387. [18] X.X. Chen, R. Li, X.Y. Pan, X.T. Huang, Z.G. Yi, Chem. Eng. J. 320 (2017) 644-652. Figure captions Fig. 1(a) XRD patterns of CuFe2O4, Ag3PO4@CuFe2O4 and Ag3PO4; (b) UV-vis diffuse absorbance spectra of the CuFe2O4, Ag3PO4@CuFe2O4, and Ag3PO4 and (b inset) plots of (αhv)2 vs hv of Ag3PO 4 and CuFe2O4. Fig. 2 SEM images of the sample for (a) CuFe2O4 and Ag3PO4, (b) Ag3PO4@CuFe2O 4 (c) EDS spectra of Ag3PO4@CuFe2O4, (d) HAADF-STEM, (e-i) The elemental mapping of Cu, Fe, Ag, P and O. Fig. 3 (a) Photocatalytic activity of Ag3PO4, CuFe2O4, and Ag3PO4@CuFe2O 4 composite for the degradation of RhB; (b) Regression curves of ln (C0/C) versus t for RhB; (c) TOC removal efficiency in the photodegradation of RhB over Ag3PO4@CuFe2O4 ; (d) the M-H loop of CuFe2O4 and Ag3PO4@CuFe2O4; (e) Plots of photogenerated carrier trapping in the photodegradation of RhB over Ag3PO4@CuFe2O4 composite;
(f)
Schematic diagram of the photocatalytic mechanism of
Ag3PO4@CuFe2O4 under visible-light irradiation.
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Figure 1
Figure 2
Figure 3 8
Highlights Ag3PO4@CuFe2O4 composite was synthesized by a simple ion-exchange deposition method. Ag3PO4@CuFe2O4 exhibited excellent photocatalytic activity of RhB degradation. Ag3PO4@CuFe2O4 showed the higher rate constant than that of Ag3PO4 and CuFe2O4. h+ play an important role in the RhB degradation rather than •OH and •O2- species. Z-scheme mechanism was discussed over Ag3PO4@CuFe2O4 photocatalyst.
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Graphical Abstract
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