Facile synthesis of cerium oxide nanoparticles decorated flower-like bismuth molybdate for enhanced photocatalytic activity toward organic pollutant degradation

Accepted Manuscript Facile synthesis of cerium oxide nanoparticles decorated flower-like bismuth molybdate for enhanced photocatalytic activity toward organic pollutant degradation Shijie Li, Shiwei Hu, Wei Jiang, Yu Liu, Yingtang Zhou, Jianshe Liu, Zhaohui Wang PII: DOI: Reference:

S0021-9797(18)30732-X https://doi.org/10.1016/j.jcis.2018.06.084 YJCIS 23775

To appear in:

Journal of Colloid and Interface Science

Received Date: Revised Date: Accepted Date:

12 April 2018 26 June 2018 26 June 2018

Please cite this article as: S. Li, S. Hu, W. Jiang, Y. Liu, Y. Zhou, J. Liu, Z. Wang, Facile synthesis of cerium oxide nanoparticles decorated flower-like bismuth molybdate for enhanced photocatalytic activity toward organic pollutant degradation, Journal of Colloid and Interface Science (2018), doi: https://doi.org/10.1016/j.jcis. 2018.06.084

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Facile synthesis of cerium oxide nanoparticles decorated flower-like bismuth molybdate for enhanced photocatalytic activity toward organic pollutant degradation Shijie Li1*, Shiwei Hu1, Wei Jiang1, Yu Liu1, Yingtang Zhou1, Jianshe Liu2, Zhaohui Wang2,3*

1

Key Laboratory of key technical factors in Zhejiang seafood health hazards, Institute of

Innovation & Application, Zhejiang Ocean University, Zhoushan, Zhejiang Province, 316022, China. 2

State Environmental Protection Engineering Center for Pollution Treatment and Control in

Textile Industry, College of Environmental Science and Engineering, Donghua University, Shanghai 201620, China. 3

International Center for Balanced Land Use (ICBLU), the University of Newcastle,

Callaghan, NSW 2308, Australia. * Email address: [email protected] (S. Li); [email protected] (Z. Wang)

1

Abstract: One of the great challenges in the field of photocatalysis is to develop novel photocatalysts with excellent solar-light-harvesting capacity and separation efficiency of photo-induced charge. Herein, novel CeO2/Bi2 MoO6 heterojunctions were fabricated through in-situ precipitation of CeO2 nanoparticles (size: ~26 nm) on the surface of flower-like Bi2MoO6 superstructures (diameter: 2.1‒3.5 μm) by a simple method. The as-prepared photocatalysts were systematically characterized by a range of techniques. The photocatalytic degradation of rhodamine B (RhB) dye, methyl orange (MO) dye and tetracycline (TC) antibiotic by this novel photocatalyst was investigated under visible-light irradiation. The CeO2/Bi2 MoO6 heterojunction with a CeO2/Bi2 MoO6 weight ratio of 0.05 (0.05Ce-Bi) exhibited the highest photocatalytic activity with the RhB degradation efficiency of 100% in 75 min, which was considerably higher than those of pristine CeO2 (26.8%) and Bi2MoO6 (80.3%) as well as their physical mixtures (74.8%). The more efficient separation of electronhole pairs was identified as the primary reason of the enhanced photocatalytic activity. Moreover, the synthesized material maintained satisfactory activity even after 6 recycling runs, indicating its high photocatalytic stability. Therefore, our finding offers a new avenue for development of stable and efficient heterojunction photocatalysts for environmental purification. Keywords: CeO2; Bi2MoO6; Heterojunction; Visible-light-driven; Antibiotics

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1. Introduction The increasing concerns about environmental deterioration fuel a booming search for semiconductor-based photocatalysts for the elimination of hazardous pollutants [1-4]. Significant progress has been made in ultraviolet-light-driven (ULD) catalysts [5-7]. However, the photocatalytic properties are still far from satisfactory owing to low solar utilization of these ULD catalysts [8]. Thus, the construction of highly efficient visible-lightdriven (VLD) photocatalysts has been a primary work [9-18]. Recently, Huge attention has been paid to bismuth (III)-based semiconductors such as Bi2WO6 [19], Bi2MoO6 [20] , BiPO4 [21] , Bi2O2CO3 [22] , BiOX (X= Cl, Br, I) [23], and BiVO4 [24] . Among them, Bi2MoO6, regarded as a typical VLD photocatalyst, has attracted much attention on photocatalytic removal of toxic pollutants [20, 25-27]. However, the practical application of Bi2MoO6 is severely constrained by its unsatisfactory performance, mainly resulting from the rapid electron-hole recombination and narrow range of visible-light photo-response. Encouragingly, various Bi2MoO6-based heterojunctions [28-35], such as RGO/Bi2 MoO6 [34], C3N4/Bi2MoO6 [31], Bi/Bi2 MoO6 [35], have been constructed to boost the charge separation rate and ameliorate the photocatalytic properties. Our research group has also designed a series of Bi2MoO6-based heterojunctions, which displayed superior VL photocatalytic properties [3, 36, 37]. Nowadays, CeO2 emerges as a good VLD photocatalyst in virtue of its excellent photocatalytic activity, nontoxicity and high durability [38-42]. More importantly, CeO2 may serve as a promising co-catalyst candidate to optimize the activity of Bi2MoO6 [33]. Thus, it is anticipated that the fabrication of hierarchical CeO2/Bi2 MoO6 heterojunctions is an ideal pathway to achieve highly efficient VLD photocatalysts for the removal of toxic organic pollutants. Here, aiming at the exploration of high-performance VLD Bi2 MoO6-based photocatalysts for toxic contaminant removal, hierarchical Ce 2O/Bi2MoO6 heterojunctions 3

with close interfacial contact have been synthesized via a facile method. The photocatalytic decomposition of rhodamine B (RhB) dye, methyl orange (MO) dye and tetracycline (TC) antibiotic were performed to assess the catalytic property of the novel photocatalysts under visible light irradiation. CeO2/Bi2MoO6 heterojunctions were much more active than pure Bi2MoO6 or CeO2. The plausible photocatalytic mechanism of Ce2O/Bi2MoO6 was also discussed.

2. Experiment 2.1. Chemicals Bismuth nitrate pentahydrate (Bi(NO3)3•5H2O, >99%), cerium nitrate hexahydrate (Ce(NO3)3·6H2O, >99%), sodium molybdate dihydrate (Na2MoO4•2H2O, >98%), rhodamine B (RhB, >99%), tetracycline hydrochloride (TC, >99%), methyl orange (MO, >99%), ammonium oxalate (AO, >99%), AgNO3, p-benzoquinone (BQ, >98%), iso-propanol (IPA, >99%), NH4OH (>99%), and ethylene glycol (>99%) were purchased from Shanghai Chemical Reagent factory (China). All the chemicals were used directly without further treatment. 2.2. Synthesis of catalysts Preparation of CeO2: Briefly, 4 g of Ce(NO3)3·6H2O was ultrasonically dissolved in ethylene glycol solution. Then 15 mL of NH4OH was slowly dropped into the above solution under ultra-sonication and the system was kept at 50 °C for 3 h. Finally the collected yellow precipitants were calcined at 400 °C for 1.5 h to obtain CeO2. Preparation of CeO2/Bi2MoO6: Typically, 0.5 mmol Bi(NO3)3•5H2O and 0.25 mmol Na2MoO4•2H2O were ultrasonically dissolved in the mixture containing 40 mL of ethylene glycol and 40 mL of ethanol. Subsequently, a certain amount of CeO2 was suspended in the 4

solution under ultra-sonication for 1 h. Then the solution was put into a 100 mL autoclave and kept at 160 °C for 24 h. Finally, the collected solids were calcined at 350 °C for 1 h to obtain the samples. The products with different CeO2/Bi2MoO6 weight ratios of 0.02/1, 0.05/1, 0.10/1, and 0.20/1 are labeled as 0.02Ce-Bi, 0.05Ce-Bi, 0.10Ce-Bi, and 0.20 Ce-Bi, respectively. 2.3. Characterization of catalysts The phases of samples were identified by Bruker D8 ADVANCE powder X-ray diffractometer (XRD). The morphologies were observed by Hitachi S-4800 scanning electron microscopy (SEM) and JEM-2100 JEOL transmission electron microscopy (TEM). The components were determined by using Bruker Quantax 400 energy-dispersive X-ray spectroscopy (EDS). The Brunauer-Emmett-Teller (BET) surface areas were acquired by using a Quantachrome Autosorb-iQ-2MP analyzer. UV‒Vis diffuse reflectance spectra (DRS) were recorded on a Shimadzu UV‒2600 spectrophotometer. Photoluminescence (PL) spectra of the samples were taken with a Hitachi RF-6000 spectrophotometer. 2.4. Photocatalytic tests The photocatalytic properties of CeO2/Bi2MoO6 heterojunctions were assessed by the removal of RhB, MO and TC under visible-light irradiation (λ > 400 nm), provided by 300 W xenon lamp. In each test, 50 mg of samples were suspended in 100 mL of RhB (10 mg L‒1), MO (5 mg L‒1) or TC (20 mg L‒1) solution, and then the solution was continuously stirred in the dark for 1 h. 2 mL of solution was collected from the reactor at certain time intervals. The concentrations of RhB, MO and TC were recorded by UV-2600 spectrophotometer. Total organic carbon (TOC) of the reaction solutions was determined on a Shimadzu TOC analyzer. All tests were performed in triplicate. 3. Results and discussion 3.1. Preparation and characterization 5

A series of CeO2/Bi2MoO6 heterojunctions with various CeO2/Bi2MoO6 weight ratios (0.02/1, 0.05/1, 0.10/1 and 0.2/1) were successfully synthesized and symbolized as 0.02Ce-Bi, 0.05Ce-Bi, 0.10Ce-Bi, and 0.20Ce-Bi, respectively. The crystal structures of Bi2MoO6, CeO2, and CeO2/Bi2MoO6 heterojunctions (0.02Ce-Bi, 0.05Ce-Bi, 0.10Ce-Bi, and 0.20Ce-Bi) were characterized by XRD technique (Fig. 1). The XRD patterns of Bi2MoO6 and CeO2 are well matched with orthorhombic Bi2MoO6 (JCPDS 76-2388) [3, 35] and cubic CeO2 (JCPDS 340394) [41, 42]. When the content of CeO2 is low, the XRD patterns of 0.02Ce-Bi, 0.05Ce-Bi, and 0.10Ce-Bi heterojunctions show similar diffraction peaks as the Bi2MoO6. No characteristic peaks of CeO2 are observed. As the CeO2 loading increases, 0.20Ce-Bi displays the diffraction peaks of both Bi2 MoO6 and CeO2, demonstrating the possible formation of CeO2/Bi2 MoO6 heterojunctions. The microstructures of Bi2MoO6 and CeO2/Bi2MoO6 heterojunctions were revealed by SEM images. The SEM images in Fig. 2a, b display that Bi2MoO6 possesses a flower-like structure constructed by randomly oriented nano-sheets, in agreement with the microstructure of pure Bi2MoO6 in our previous work [36]. All the CeO2/Bi2MoO6 heterojunctions display a hierarchical structure, similar to that of bare Bi2 MoO6. Representatively, 0.05Ce-Bi retains the structure of Bi2MoO6, whose surfaces are decorated by CeO2 nanoparticles (Fig. 2c-e). Moreover, the EDS spectrum further verifies the co-existence of Ce, Bi, Mo and O elements in the 0.05Ce-Bi heterojunction (Fig. 2f). The TEM images of 0.05Ce-Bi is shown in Fig. 3a, b, revealing that 0.05Ce-Bi is composed of Bi2 MoO6 hierarchical structures (diameter: ~2.6 μm) and CeO2 nanoparticles (size: ~19 nm). The HR-TEM image (Fig. 3h) shows a discernible crystalline structure and two sets of clear lattice fringes of ca. 0.37 and 0.27 nm, belonging to the (111) facet of Bi2MoO6 and the (200) facet of CeO2, respectively. It is worthy of note that CeO2 6

nanoparticles grow on Bi2MoO6, forming an intimate interfacial contact between them, in favor of the utilization of charge carriers [43-45]. The N2 adsorption/desorption isotherms of Bi2MoO6 and 0.05Ce-Bi are shown in Fig. 4. The Brunauer-Emmett-Teller (BET) specific surface area (43.8 m2 g‒1) of 0.05Ce-Bi is slightly higher than that (38.3 m2 g‒1) of bare Bi2 MoO6. In addition, there are numerous nanopores (~18 nm) in the samples (the inset of Fig. 4), which favors the photocatalytic reactions. In general, the sunlight absorption capability and band edge positions of a photocatalyst exert a significant effect on its photocatalytic performance. The UV-Vis absorption spectra of pure Bi2MoO6, CeO2, and CeO2/Bi2MoO6 heterojunctions are illustrated in Fig. 5. Bare Bi2MoO6 exhibits intense absorption from 200 nm to 470 nm, in line with the previous reports [3, 33]. CeO2 displays strong absorption from 200 nm to 460 nm, consistent with the reported values [40, 41]. Intriguingly, the introduction of CeO2 apparently ameliorates the absorption properties of Bi2MoO6. Thus, CeO2/Bi2MoO6 heterojunctions are expected to be good VLD candidates. 3.2. Photocatalytic performance The photocatalytic activity of CeO2/Bi2MoO6 heterojunctions was firstly assessed by the degradation of RhB under visible light (Fig. 6). The blank test performed in the absence of photocatalyst showed that almost no RhB was degraded after 90 min of irradiation. Only 28.9% or 89.8% of RhB was degraded by bare CeO2 or Bi2MoO6, owing to the rapid electron-hole recombination rate. When Bi2MoO6 was combined with CeO2, the activities of the asprepared heterojunctions were significantly enhanced. After 90 min of reaction, the degradation efficiencies of RhB by using 0.02Ce-Bi, 0.05Ce-Bi, 0.10Ce-Bi and 0.20Ce-Bi were 100%, 100%, 100%, and 93.3%, respectively, markedly higher than those by using the 7

bare CeO2, Bi2MoO6, and the physical mixture (4.8wt% CeO2 + 95.2wt% Bi2MoO6). Of note, 0.05Ce-Bi displayed the maximum photocatalytic activity. After 75 min of reaction, 100% of RhB was degraded (Fig. S2). This result demonstrates the central role of CeO2 in the activity enhancement. Additionally, the degradation of RhB over as-prepared samples followed the pseudofirst-order model (Fig. 6b), –ln(C/C0) = kt, where k represented the rate constant. It can be observed that 0.05Ce-Bi has the highest rate constant of 0.0527 min‒1, 13.6, 1.2, and 1.5 folds higher than pristine CeO2 (0.0036 min‒1), Bi2MoO6 (0.0237 min‒1), and the physical mixture (0.0208 min‒1). The effect of 0.05Ce-Bi catalyst dosage on the degradation of RhB was investigated (Fig. S3). The degradation efficiency of RhB increases with the increase of catalyst dosage from 25 mg to 75 mg. When the amount of catalyst dosage reaches 100 mg, the RhB degradation efficiency shows a slight decrease, probably due to the fact that part of the light may be shielded by the catalyst, resulting in a decrease of the formation of electron and holes [46, 47]. The influence of pH value of solutions on degradation efficiencies of RhB over 0.05Ce-Bi was also studied (Fig. S4). The degradation efficiency of RhB goes up as the pH value increases from 3 to 11. Additionally, the absorption capability of RhB increases with the increase of pH value (Table S1). Previous researches demonstrate that the degradation of organic pollutants is pH-dependent, which is primarily caused by the variation of surface charge of photocatalysts and molecule structure of the dye with pH [46, 48, 49]. The influence of ionic strength fixed by NaCl was further studied (Fig. S5). Apparently, the degradation efficiency of RhB goes down with the increase of ionic salt concentration in the solution, which can be attributed to two main reasons. First, the Cl– could shield the electrostatic attraction between RhB and the catalyst [6, 7]. Second, Cl– acting as a radical scavenger inhibits the photocatalytic degradation of RhB [6, 7, 49]. 8

The removal efficiency of RhB over CeO2/Bi2MoO6 (0.05Ce-Bi) was further compared with those by using other sorbents or catalysts previously reported [50-54]. As shown in Table 1, CeO2/Bi2MoO6 can be categorized as one kind of the most active photocatalysts for the removal of RhB dye. The widely used antibiotic TC or industrial dye MO was employed as a target pollutant to further evaluate the catalytic performance of 0.05Ce-Bi (Fig. 7). The TC degradation rate over 0.05Ce-Bi is up to 78.7% after 120 min of reaction, greatly higher than that over CeO2 (5.7%), Bi2MoO6 (55.4%), or a physical mixture (50.8%) (Fig. 7a and Fig. S6). Moreover, 0.05Ce-Bi was also effective in the degradation of MO (Fig. 7b and Fig. S7). Overall, 0.05Ce-Bi belongs to a type of high-efficiency VLD photocatalyst, which shows robust removal activity towards toxic pollutants (RhB, TC, and MO). For testing the mineralization ability of the catalyst, the TOC removal during the photocatalytic degradation of RhB (50 mg L–1, 150 mL) by 0.05Ce-Bi (200 mg) was measured. It was observed that the TOC removal efficiency of RhB over 0.05Ce-Bi finally reached 82.1% after 5 h of visible light irradiation, indicating that RhB dye could be effectively mineralized by 0.05Ce-Bi. For assessing the stability of CeO2/Bi2 MoO6, six successive runs in the RhB removal by using 0.05Ce-Bi as a catalyst were performed. The RhB degradation efficiency maintains 93.6% after the sixth runs (Fig. 9a). Moreover, there are no apparent changes in the XRD pattern (Fig. 9b) and morphology (Fig. S1) of the used 0.05Ce-Bi compared with those of the fresh one (Fig. 9b), confirming the good stability and durability of 0.05Ce-Bi. 3.3. Origin of the improved performance Photoluminescence (PL) technique was applied to illustrate the transfer and recombination processes of charge carriers in Bi2 MoO6 and 0.05Ce-Bi (Fig. 10). Generally, a weaker PL intensity represents the higher separation capacity of photo-generated carriers [35, 9

43]. As depicted in Fig. 10, pristine Bi2MoO6 has a strong emission peak centered at ~470 nm, in agreement with the reported cases. Apparently, 0.05Ce-Bi exhibits weaker intensity than that of Bi2MoO6, verifying that the nano-junction between Bi2MoO6 and CeO2 remarkably suppresses the recombination rate of charge carriers. To identify the primary active species responsible for pollutant degradation over CeO2/Bi2 MoO6, a series of tests were performed through the degradation of RhB in the presence of various scavengers over 0.05Ce-Bi (Fig. 11). The addition of IPA (scavenger of •OH) shows no apparent influence on RhB removal. This signifies that •OH is not the active species. By contrast, the RhB removal efficiency is substantially declined when BQ (quencher of O2•–) or AO (quencher of h+) is added, indicating that O2•– and h+ are responsible for the RhB removal over CeO2/Bi2 MoO6. The band gaps of CeO2 and Bi2 MoO6 can be determined by the Tauc’s equation: (αhν) =A(hν-Eg)n/2. As illustrated in Fig.S2, the Eg of CeO2 and Bi2MoO6 are approximately 2.66 eV and 2.59 eV, respectively. The band edge positions (EVB/ECB) of CeO2 and Bi2 MoO6 can be calculated by the empirical formula: EVB = X – E0 + 0.5Eg

(1)

ECB = EVB –Eg

(2)

where the X values for CeO2 and Bi2MoO6 are 5.57 eV [40] and 5.5 eV [3], respectively. E0 value equals to ~4.5 eV. From the formula, The EVB and ECB of CeO2 were estimated to be -0.03 and 2.68 eV, while those of Bi2MoO6 are -0.32 and 2.34 eV. The outstanding activities of the heterojunctions own a well-matched band-structure, contributing to fast separation of charge carriers at the interfaces [55, 56]. On the basis of CB/VB edge potentials, the schematic diagram of band structure is illustrated in Fig. 12. Under visible-light illumination, both CeO2 and Bi2MoO6 can be driven by visible-light photons, leading to the excitation of electrons to the CB while holes stay in the VB. Since the 10

CB and VB potentials of CeO2 are more negative than those of Bi2MoO6, the photo-induced e– in the CB of Bi2MoO6 may flow into that of CeO2. Simultaneously, the h+ are injected easily from the VB of CeO2 to the VB of Bi2MoO6. In such a way, the electron-hole pairs can be effectively separated, in agreement with the result of PL spectra of Bi2MoO6 and CeO2/Bi2 MoO6 (Fig. 10). Considering the CB band potential of Bi2MoO6 is more negative than E (O2/O2•–) (+0.13 eV) [57], the e– on the CB of Bi2 MoO6 can react with O2 to produce active O2•–, decomposing RhB/MO/TC pollutants. Meanwhile, Since the VB potential of Bi2MoO6 is equal to E (•OH/H2O) (+2.68 eV), •OH can be produced. However, the radical quenching test confirms that •OH is not one of the major active species in the reaction. The h+ enriched on the VB of CeO2 and Bi2MoO6 can directly oxidize RhB/MO/TC pollutants.

4. Conclusions In summary, innovative CeO2/Bi2MoO6 heterojunction photocatalysts have been prepared via a facile procedure. The CeO2/Bi2MoO6 heterojunctions, especially the 0.05Ce-Bi possessed optimal photocatalytic properties toward the removal of toxic pollutants (RhB, MO, and TC) in contrast with bare CeO2 and Bi2MoO6. The CeO2 anchored on Bi2 MoO6 can lead to effective separation of charge carriers, primarily contributing to the activity enhancement. The holes and O2•– account for the efficient removal and mineralization of the industrial dye. Therefore, the CeO2/Bi2 MoO6 heterojunction could serve as a promising VLD catalyst for water pollution remediation. This work may offer a promising platform for the fabrication of stable and efficient Bi-based heterojunction photocatalysts for wastewater treatment.

Acknowledgments

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This work has been financially supported by the National Natural Science Foundation of China (51708504 and 31501573), the Science and Technology project of Zhoushan (2017C41006, 2016C41012, 2015C21014, 2015C21013) and National Key Research and Development Program of China (2016YFC0400501/2016YFC0400509). Appendix A. Supplementary material Supplementary data associated with this article can be found, in the online version.

References [1] J.B. Pang, A. Bachmatiuk, Y. Yin, B. Trzebicka, L. Zhao, L. Fu, R.G. Mendes, T. Gemming, Z.F. Liu, M.H. Rummeli, Adv. Energy Mater. 8 (2018) 1702093. [2] H.J. Li, W.G. Tu, Y. Zhou, Z.G. Zou, Adv. Sci. 3 (2017) 1500389. [3] S.J. Li, X.F. Shen, J.S. Liu, L.S. Zhang, Environ. Sci.: Nano 4 (2017) 1155-1167. [4] M. Mousavi, A. Habibi-Yangjeh, S.R. Pouran, J Mater Sci: Mater. Electron. 29 (2018) 1719-1747. [5] H.R. Rajabi, O. Khani, M. Shamsipur, V. Vatanpour, J. Hazard. Mater. 250-251 (2013) 370-378. [6] H.R. Rajabi, M. Farsi, Mater. Sci. Semicon. Proc. 48 (2016) 14-22. [7] H.R. Rajabi, M. Farsi, J. Mol. Catal. A: Chem. 399 (2015) 53-61. [8] M. Pirhashemi, A. Habibi-Yangjeh, S.R. Pouran, J Ind Eng Chem 62 (2018) 1-25. [9] J. Liu, Y. Li, J. Ke, S.B. Wang, L.D. Wang, H.N. Xiao, Appl. Catal. B 224 (2018) 705714. [10] W. Han, Z. Li, Y. Li, X. Fan, F. Zhang, G. Zhang, W. Peng, Front. Chem. 5 (2017) 84. 12

[11] Y. Liu, H. Zhang, J. Ke, J. Zhang, W. Tian, X. Xu, X. Duan, H. Sun, M.O. Tade, S. Wang, Appl. Catal. B 228 (2018) 64-74. [12] S.J. Li, S.W. Hu, K.B. Xu, W. Jiang, Y. Liu, Z. Leng, J.S. Liu, J. Colloid Interface Sci. 504 (2017) 561-569. [13] L.V. Bora,R.K. Mewada, Renew. Sustain. Energy Rev. 76 (2017) 1391-1421. [14] S.J. Li, S.W. Hu, K.B. Xu, W. Jiang, J.S. Liu, Z.H. Wang, Nanomaterials 7 (2017) 22-34. [15] A. Akhundi, A. Habibi-Yangjeh, J. Colloid Interface Sci. 504 (2017) 697-710. [16] M. Mousavi, A. Habibi-Yangjeh, J. Colloid Interface Sci. 465 (2016) 83-92. [17] S. Asadzadeh-Khaneghah, A. Habibi-Yangjeh, M. Abedi, Sep. Purif. Technol. 199 (2018) 64-77. [18] M. Mousavi, A. Habibi-Yangjeh, J. Mater. Sci. 53 (2018) 9046-9063. [19] J. Wang, L. Tang, G. Zeng, Y. Liu, Y. Zhou, Y. Deng, J. Wang, B. Peng, ACS Sustainable Chem. Eng. 5 (2017) 1062-1072. [20] C. Yu, Z. Wu, R. Liu, D.D. Dionysiou, K. Yang, C. Wang, H. Liu, Appl. Catal. B 209 (2017) 1-11. [21] Y.Y. Zhu, Q. Ling, Y.F. Liu, H. Wang, Y.F. Zhu, Appl. Catal. B 187 (2016) 204-211. [22] X. Feng, W. Zhang, Y. Sun, H. Huang, F. Dong, Environ. Sci.: Nano 4 (2017) 604-612. [23] H.F. Cheng, B.B. Huang, Y. Dai, Nanoscale 6 (2014) 2009-2026. [24] M. Xie, Z. Zhang, W. Han, X. Cheng, X. Li, E. Xie, J. Mater. Chem. A 5 (2017) 1033810346. [25] B. Zhang, J. Li, Y. Gao, R. Chong, Z. Wang, L. Guo, X. Zhang, C. Li, J. Catal. 345 (2017) 96-103. 13

[26] Y. Ma, Y. Jia, L. Wang, M. Yang, Y. Bi, Y. Qi, J. Power Sources 331 (2016) 481-486. [27] J.L. Li, X.J. Liu, Z. Sun, Y. Sun, L.K. Pan, J. Colloid Interface Sci. 452 (2015) 109-115. [28] Y. Ma, Z. Wang, Y. Jia, L. Wang, M. Yang, Y. Qi, Y. Bi, Carbon 114 (2017) 591-600. [29] D. Ma, J. Wu, M. Gao, Y. Xin, Y. Sun, T. Ma, Chem. Eng. J. 313 (2017) 1567-1576. [30] S.N. Lou, J. Scott, A. Iwase, R. Amala, Y.H. Ng, J. Mater. Chem. A 4 (2016) 6964-6971. [31] J. Li, Y.C. Yin, E.Z. Liu, Y.N. Ma, J. Wan, J. Fan, X.Y. Hu, J J. Hazard. Mater. 321 (2017) 183-192. [32] M.Y. Zhang, C.L. Shao, J.B. Mu, Z.Y. Zhang, Z.C. Guo, P. Zhang, Y.C. Liu, Crystengcomm 14 (2012) 605-612. [33] W.L. Dai, X. Hu, T.Y. Wang, W.W. Xiong, X.B. Luo, J.P. Zou, Appl. Surf. Sci. 434 (2018) 481-491. [34] J. Ke, X. Duan, S. Luo, H. Zhang, H. Sun, J. Liu, M. Tade, S. Wang, Chem. Eng. J. 313 (2017) 1447-1453. [35] Z.W. Zhao, W. Zhang, Y.J. Sun, J.Y. Yu, Y.X. Zhang, H. Wang, F. Dong, Z.B. Wu, J. Phys. Chem. C 120 (2016) 11889-11898. [36] S.J. Li, S.W. Hu, J.L. Zhang, W. Jiang, J.S. Liu, J. Colloid Interface Sci. 497 (2017) 93101. [37] S.J. Li, S.W. Hu, W. Jiang, Y.P. Liu, Y.T. Zhou, Y. Liu, L.Y. Mo, J. Colloid Interface Sci. 521 (2018) 42-49. [38] S. Sultana, S. Mansingh, K.M. Parida, J. Phys. Chem. C 122 (2018) 808-819. [39] K. Saravanakumar, R. Karthik, S.-M. Chen, J.V. Kumar, K. Prakash, V. Muthuraj, J. Colloid Interface Sci. 504 (2017) 514-526. 14

[40] S. Issarapanacheewin, K. Wetchakun, S. Phanichphant, W. Kangwansupamonkon, N. Wetchakun, Catal. Today 278 (2016) 280-290. [41] S. Ijaz, M.F. Ehsan, M.N. Ashiq, T. He, Catal. Sci. Technol. 5 (2015) 5208-5215. [42] H. Guo, Y.Y. Guo, L.X. Liu, T.T. Li, W. Wang, W.W. Chen, J. Chen, Green Chem. 16 (2014) 2539-2545. [43] S.J. Li, S.W. Hu, W. Jiang, Y. Liu, J.S. Liu, Z.H. Wang, J. Colloid Interface Sci. 501 (2017) 156-163. [44] G.G. Zhang, Z.A. Lan, X.C. Wang, Angew. Chem. Int. Ed. 55 (2016) 15712-15727. [45] H.W. Huang, Y. He, X. Du, P.K. Chu, Y.H. Zhang, ACS Sust. Chem. Eng. 3 (2015) 3262-3273. [46] H.R. Rajabi, M. Farsi, Mater. Sci. Semicon. Proc. 31 (2015) 478-486. [47] M. Shamsipur, H.R. Rajabi, Spectrochim. Acta Part A 122 (2014) 260-267. [48] L.S. Zhang, K.-H. Wong, Z.G. Chen, J.C. Yu, J.C. Zhao, C. Hu, C.-Y. Chan, P.-K. Wong, Appl. Catal. A 363 (2009) 221-229. [49] H.R. Rajabi, F. Karimi, H. Kazemdehdashti, L. Kavoshi, J. Photochem. Photobiol B. 181 (2018) 98-105. [50] Y. Jiao, C. Wan, W. Bao, H. Gao, D. Liang, J. Li, Carbohyd. Polym. 189 (2018) 371-378. [51] V.S. Lacerda, J.B. López-Sotelo, A. Correa-Guimarães, S. Hernández-Navarro, M. Sánchez-Báscones, L.M. Navas-Gracia, P. Martín-Ramos, J. Martín-Gil, J. Environ. Manage 155 (2015) 67-76. [52] J. He, J. Li, W. Du, Q. Han, Z. Wang, M. Li, J. Alloys Compd.750 (2018) 360-367. [53] X.N. Liu, Q.F. Lu, J.H. Liu, J. Alloys Compd. 662 (2016) 598-606. 15

[54] S. Li, S. Hu, W. Jiang, Y. Liu, Y. Liu, Y. Zhou, L. Mo, J. Liu, Front. Chem. 2018, doi: 10.3389/fchem.2018.00255 [55] S.J. Li, S.W. Hu, W. Jiang, Y. Liu, J.S. Liu, Z.H. Wang, Mol. Catal. 435 (2017) 135-143. [56] R. Marschall, Adv. Funct. Mater. 24 (2014) 2421-2440. [57] Y.J. Chen, G.H. Tian, Y.H. Shi, Y.T. Xiao, H.G. Fu, Appl. Catal. B 164 (2015) 40-47.

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Fig. 1. XRD patterns of Bi2MoO6, CeO2, and CeO2/Bi2MoO6 heterojunctions.

17

Fig. 2. SEM images of Bi2MoO6 (a, b); SEM images (c-e) and EDX (f) spectrum of 0.05CeBi.

18

Fig. 3. TEM (a, b) and HRTEM (c) images of 0.05Ce-Bi

19

Fig. 4. N2 adsorption/desorption isotherms of Bi2 MoO6 and 0.05Ce-Bi.

Fig. 5. UV-vis absorbance spectra of pure Bi2MoO6, CeO2, and CeO2/Bi2MoO6 heterojunctions, the inset is the resulting Tauc plots of CeO2 and Bi2 MoO6.

20

Fig. 6 (a) The photocatalytic degradation of RhB (10 mg L‒1, 100 mL) over different samples (50 mg) under visible light (λ > 400 nm) irradiation. (b) Kinetic fitting for RhB degradation over all samples.

21

Fig. 7. The photocatalytic degradation of TC (20 mg L‒1, 100 mL) (a) and MO (5 mg L‒1, 100 mL) (b) over 0.05Ce-Bi (50 mg), CeO2 (50 mg), Bi2MoO6 (50 mg), and a physical mixture (50 mg).

22

Fig. 8. TOC removal profile of RhB (50 mg L–1, 150 mL) over 0.05Ce-Bi (200 mg).

23

Fig. 9 (a) Recycling experiments; (b) XRD patterns of 0.05Ce-Bi before and after six runs.

24

Fig. 10. Photoluminescence (PL) spectra of bare Bi2MoO6 and 0.05Ce-Bi under 300 nm excitation.

25

Fig. 11. Comparison of the photocatalytic activity of 0.05Ce-Bi (50 mg) for the RhB removal (10 mg L‒1, 100 mL) in the presence of various agents (isopropyl alcohol (IPA), ammonium oxalate (AO), and benzoquinone (BQ)).

26

Fig. 12. Photocatalytic mechanism scheme over CeO2/Bi2MoO6.

27

Table 1 Performance of some typical methods for removal of RhB

System Fe3O4/CA/H 2O2 AC/removal MnBTB/remov al ZnO/Bi2WO 6/UVVis(350 w) Ag3VO4/Bi2 O2CO3/ Vis(300w) CeO2/Bi2M oO6/Vis (300 w)

Amount of sample

Max decolorization (%)

Time (min)

Volume and concentration of RhB

3 g/L 4 g/L

100 98

3840 360

100 mL/10 mg/L 80 mg/L

[48] [49]

0.4 g/L

20

120

10 mL/12 mg/L

[50]

1.5 g/L

90.4

150

40 mL/10 mg/L

[51]

0.05 g/L

98.4

60

80 mL/5 mg/L

[52]

0.05 g/L

100

75

100 mL/10 mg/L

BTB = 1,3,5-tris(4-carboxyphenyl)benzene acid) CA= Cellulose aerogel AC=Activated carbon

28

Ref.

This paper

29