Distinct Phase Formation Of BiREWO6 (RE = La-Yb) Nanoparticles By

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Distinct Phase Formation Of BiREWO6 (RE = La-Yb) Nanoparticles By A One Step Hydrothermal Synthesis And Their Photocatalytic Applications Pradeep P. Shanbogh, Diptikanta Swain, Chandrabhas Narayana, Ashok Rao, and Nalini G. Sundaram Cryst. Growth Des., Just Accepted Manuscript • DOI: 10.1021/acs.cgd.7b01774 • Publication Date (Web): 27 Feb 2018 Downloaded from http://pubs.acs.org on February 28, 2018

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Crystal Growth & Design

Distinct Phase Formation Of BiREWO6 (RE = LaYb) Nanoparticles By A One Step Hydrothermal Synthesis And Their Photocatalytic Applications Pradeep P. Shanbogh, †‡ Diptikanta Swain, Ἴ Chandrabhas Narayana,§ Ashok Rao,‡ and Nalini G. Sundaram,*† †

Functional Energy Nanomaterials group, Materials sciences Division, Poornaprajna Institute of

scientific Research, Devanahalli, Bengaluru-562110 E-mail: [email protected] ‡

Manipal Academy of Higher Education, Manipal. Karnataka-576104

Ἴ

§

Solid State and Structural Chemistry Unit, Indian Institute of Science, Bengaluru-560012

Chemistry and Physics of Materials Unit, Jawaharlal Nehru Centre for Advanced scientific

Research, Jakkur, Bengaluru-560064

Abstract: Under identical hydrothermal condition, remarkably, Aurivillius BiREWO6 nanoparticles crystallizes in an orthorhombic phase for RE=Ce and La, while the RE=Nd-Yb materials crystallize in the monoclinc phase. This kind of distinct phase formation in this series is not observed in solid state synthesis, where for all RE substitution, only the monoclinic phase is formed. Moreover formation of orthorhombic phase for BiLaWO6 and BiCeWO6 has been observed for the first time. Calcination of as synthesized BiLaWO6 and BiCeWO6 nanomaterials

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result in the monoclinc phase and this indicates that the formation of the orthorhombic phase is favoured only under mild reaction conditions . This could be attributed to the crucuial role of the ionic radii of RE3+ and Bi3+ ions in solution. Rietveld refinement confirms the BiCeWO6 and BiGdWO6 are isostrutural to the low temperature (LT) orthorhombic phase and monclinic high temperature (HT) phase of Bi2WO6 respectively. Additionally phase dependent distinct morphology and photocatalytic activity is observed. As a reprensentative example,it is observed that needle/plate shaped monoclinic BiGdWO6 nanoparticles show superior visible light driven photocatalytic activity for the congo-red dye degradation over the spherically agglomerated orthorhombic BiCeWO6 nanomaterial.

Aurivillius phases are well-known class of layered perovskite having general formula Bi2O2 (An-1BnO3n+1)1 and studied widely for

their ferroelectric2

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, oxide ion conductivity5,

photoluminescence6 and photocatalytic properties. Bi2WO6, the simplest compound among the Aurivillius family, has a fluorite [Bi2O2]2+ layer and a perovskite [WO4]2- layer stacked alternately7. This kind of structure favours efficient separation of photo induced electron-hole pairs, thus enhances the photocatalytic activity, which can be attributed to the generated internal electric fields between the stacked layers8. It exhibits interesting reversible phase transition as a function of temperature: a low temperature (LT) ferroelectric orthorhombic phase (Pca21) which undergoes displacive phase transformation at 650oC to form intermediate temperature (IT) ferroelectric orthorhombic phase (B2cb) and further undergoes reconstructive phase transformation at around 950oC to form a high temperature (HT) paraelectric monoclinic phase (A2/m)9. This phase transition from higher symmetry to lower symmetry is unusual and it is attributed to lone pair character of Bi 6S2 electrons10. It is known that volume occupied by the lone pair is equivalent to the volume of O2- or F- ions and occupies a position in crystal structure


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equivalent to these ions10, which influences the spatial distribution of the bonded electron pairs. This could induce a distortion at the central metal ion, resulting in altering the crystal symmetry and consequently the physical property of the materials11. In Bi2WO6 lone pair character in LT and IT phase is stereochemically dominant and it is constrained due to thermal energy in the HT phase, thus exhibiting a distinct ionic radius for Bi3+ at different conditions7. Interestingly, when a Rare earth is substituted at the Bi position (general formula Bi2-xRExWO6; ([Bi2-xRExO2]2+ [WO4]2-) by conventional solid state method, it shows polymorphism as a function of RE3+ concentration12: Solid solutions with the stoichiometry 0.3 < x < 1.3 crystallize in the (HT) monoclinic phase, while x < 0.3 composition crystallizes in the (LT) orthorhombic phase12. Therefore, the HT phase is stabilized by RE substitution and the reason for this is still unknown. Similar to the parent compound, Bi2-xRExWO6 also contains stereochemically dominant and constrained Bi 6s2 lone pairs for LT and HT phases respectively10. This implies a relationship between the ionic radius of Bi3+ induced by the nature of lone pair character and the phase formation in Bi2-xRExWO6 [RE = La-Yb] Aurivillius phases. The rich crystallographic features1 and presence of stereochemically active lone pair allows one to tune the multi-functionality of these materials for applications in the field of photocatalysis8, multiferroics13, high oxide ion conductors14 5, dielectrics15 etc. The formation of intra electric field between the layers of [(Bi/RE)O2]2+ [WO4]2- could improve the photo-generated electron-hole pair mobility16 and the possibility of absorption of visible and infrared spectrum by RE3+ ions makes these materials promising for photocatalytic applications17,18. In the past decade, soft chemistry approaches and low temperature solution based synthesis of the parent compound (Bi2WO6) have been extensively studied due to the ease of formation of homogeneous nanoparticles of different morphologies. In this context, hydrothermal synthesis, one of the versatile solution based


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approach is proven to be efficient in synthesizing phase pure multi metal oxide nanomaterials with superior properties. This method facilitates one step crystallization, good control over the particle size, morphology, phase purity, ability to stabilize metastable phases19 etc. Various morphologies of Bi2WO620 and associated heterostructured21 materials obtained by hydrothermal method have been extensively studied for several applications such as photocatalysis and phtoluminescent studies. However to the best of our knowledge, in the case of rare earth substituted Bi2WO6, only BiErWO6 nanoparticles in the monoclinic phase have been synthesized by the hydrothermal method17. In this communication, we present the hydrothermal synthesis of phase pure Bi2-xRExWO6 (RE = La-Yb; x =1) nanomaterials by facile hydrothermal method. Remarkably, under identical synthesis conditions, La & Ce substituted materials crystallize in the LT-orthorhombic phase (Figure 1a), while Nd, Eu, Gd, Tb, Dy, Er & Yb substitution results in the HT-monoclinic phase (Figure 1b). Phase purity of all materials were ascertained by powder XRD. It should be noted that BiLaWO6, along with the predominant LT Phase, shows a small amount of a secondary phase, identified as La2O3, while LT BiCeWO6 and HT BiREWO6 (RE = Nd to Yb) are single phase materials. An attempt has been made to address this distinct phase formation under identical hydrothermal conditions, through the stereochemical character of the Bi 6s2 lone pair and the ionic radii of the rare earth ion (RE3+). To the best of our knowledge this is the first time, crystallization of LT-orthorhombic phase of Bi2-xRExWO6 for RE = La & Ce; x =1 has been observed. Hence a detailed study of the hydrothermal reaction to follow the phase formation and crystal structure analysis through Rietveld refinement of X-ray data has been carried out. Reaction time and temperature controlled hydrothermal crystallization of both the phases shows that, the formation of the monoclinic BiREWO6 (RE = Nd-Yb) phase requires 200oC and


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around 8 hour of reaction time to form crystalline single phase material. Careful observation from XRD plots (Figure S1 & S2) clearly shows that the evolution of the monoclinic phase during the hydrothermal crystallization (mild conditions). Furthermore even by lowering the temperature and reaction time, BiREWO6 (RE=Nd-Yb) does not crystallize in the orthorhombic phase. Interestingly, pure crystalline BiCeWO6 crystallized in the orthorhombic phase in about 3 to 4 hours at 200oC (Figure S3) The obtained phase was stable for longer reaction times, confirming that, increasing longer reaction duration does not facilitate the phase transformation from LT to HT phase under hydrothermal conditions. Hence, further characterization and analysis have been carried out on the materials synthesized by the hydrothermal method at an optimum temperature and reaction time of 200oC and 8hours respectively for both the phases. Rietveld refinement of LT-BiCeWO6 and HT-BiGdWO6 phase on laboratory X-ray data (Bruker D2 Phaser) has been carried out using GSAS-EXPGUI suite22. BiCeWO6 is successfully refined in orthorhombic (Pca21) crystal system (Rwp= 3.89%) and BiGdWO6 in monoclinic (A2/m) crystal system (Rwp = 5.15%) (Figure 2 & Table S1), where LT-Bi2WO6 and HTBiNdWO6 were used as initial structural model for refinement of BiCeWO6 and BiGdWO6 respectively. Background was refined using shifted Chebyshev polynomial with 15 coefficients and the profile was fitted with pseudo-Voigt function. Positions, occupancy and thermal parameters of Bi and RE were constrained and all atoms including oxygen atoms in the general positions were reﬁned. Occupancy of RE and Bi were initially assumed to be equally distributed at both Bi1 and Bi2 sites and refinement of occupancy was carried out alternatively with thermal parameters of heavy atoms until convergence, while ensuring that the total occupancy was constrained. In presence of strong scatterer, RE/Bi and broad peak profile due to smaller particle size, initial refinement of oxygen positions were damped until convergence and later released.


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The O2 position in BiCeWO6 and O5 position in BiGdWO6 could not be refined to the convergence. Therefore it can be inferred that a neutron diffraction study would help in determining the exact position of oxygen atoms in these materials. Despite this limitation, we have deduced the gross structural features of orthorhombic BiCeWO6 and monoclinic BiGdWO6 phase (Figure S5). From the refinement it is observed that both Ce and Bi occupy the same site with slightly increased Bi fraction in both the sites. From this the resulting composition can be deduced to be Bi1.2Ce0.8WO6 (Table S2 & S3),while the composition of Gd substituted is found to be approximately Bi1Gd1WO6 (Table S2). Isomorphic substitution of RE3+ at Bi position is expected due to similarity in the ionic radius and charge. From the literature23 it is known that Ionic radius of Bi3+ in LT phase is 1.03 Å due to the stereochemically dominant lone pair (represented as Bi).However in the HT phase, where the lone pair is constrained, the Bi ionic radius is reduced to that of Nd3+ i.e., 0.98 Å7 (represented as Bi*).Therefore in the above reactions, we conjecture

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that under identical

hydrothermal condition, where low temperatures are employed, crystallization of La3+ (1.032 Å) and Ce3+ (1.01 Å) substituted materials in the LT (orthorhombic) phase is favored due to the similarity in the ionic radius of Bi and La3+/ Ce3+. However, the crystallization of [RE = Nd (0.983 Å), Eu(0.947 Å), Gd(0.938 Å), Tb(0.923 Å), Dy(0.912 Å), Er(0.89 Å) & Yb(0.868 Å)]23 in the HT (monoclinic) phase is attributed to the similar ionic radius of rare earth and Bi*. Conversely, in the solid state method24, the higher temperatures (700oC to 1100oC) drive the lone pair of Bi to be constrained, thus creating space for accommodating even the bigger La and Ce ion and facilitating the formation of HT (monoclinic) phase for all the rare earth ions. This hypothesis is further supported by calcination of as synthesized LT-Phase nanomaterials. On


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calcination at 1000oC for 16 hour, LT-BiCeWO6 undergoes an irreversible phase transformation from lone pair dominant LT to lone pair constrained HT phase (Figure S4). Phase formation also influences the morphology of the as synthesized materials; FE-SEM analysis shows a predominant needle/rod type morphology with dimensions of 20 to 60 nm width and length up to few microns for the HT phase with RE = Nd-Yb, along with plate type morphology observed in Gd. However, the LT-BiCeWO6 phase shows spherically agglomerated and flake type morphology with particle size distribution of 30 to 80 nm (Figure 3). Polydisperse particles with two or more morphologies in a single phase could be due to surfactant free synthesis conditions. Thus, the formation of distinct morphology for different crystal systems could indicate the relationship between crystal structure and morphology under identical hydrothermal conditions. Energy dispersive X-ray spectra (EDAX) of all materials confirmed the presence of Bi, W, O and corresponding RE and supports the composition of material to be Bi2xRExWO6

[x = ̴1], which is further corroborated by the Rietveld refinement results (Figure S6

& Table S3). X-ray photoelectron spectroscopy (XPS) characterization of as synthesized BiCeWO6 indicate the presence of both Ce3+ and Ce4+ in the material (Figure S7), Despite the presence of Ce4+, the material is isostructural to LT Bi2WO6. This is further supported by Raman (Figure S8), spectra, which shows characteristic stretching frequency matching to that of LT- Bi2WO6 orthorhombic phase25 with no signature of a secondary phase in the material. It is well known that Aurivillius phases retains their structure with divalent or tetravalent cation substitution at the Bi positions26 27 28

. These results suggest that the BiCeWO6 material might adopt oxygen deficient structure to

compensate the mixed valent Ce. A neutron diffraction measurement would help in resolving the oxygen stoichiometry.


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Further, preliminary work on photocatalytic activity of the LT-BiCeWO6 and HT-BiGdWO6 nanomaterial has been carried out for Congo-red dye degradation under visible light. The HTBiGdWO6 was found to be photocatalytically active while LT-BiCeWO6 and parent compound LT-Bi2WO6 showed no activity even for longer duration (Figure 4), this indicated a structure dependent photocatalytic response. However, there is no significant difference in the direct transition band gaps calculated by kubelka-munk function analysis on DRS spectra (Figure S9) are observed. Since LT phase contains corner linked chains of WO6 octahedra whereas HTphase contains edge shared WO6 octahedral dimers infers the structure dependent functionality, a more detailed analysis of the crystal structure and band structure to obtain insights on the structure property relationship is under progress. In summary we have demonstrated a general strategy to synthesize phase pure BiREWO6 (RE = Ce-Yb) materials via low temperature solution based hydrothermal synthesis. For the first time we have stabilized the LT orthorhombic phase of BiCeWO6. Additionally, The other BiREWO6 (RE = Nd-Yb) complex oxides crystallize in the HT monoclinic phase. The phase formation via hydrothermal synthesis is observed to be dependent on the ionic size of RE3+ and distinct ionic size of lone pair containing Bi3+ in different environments. In mild conditions, BiCeWO6 crystallizes in the LT phase and further calcination at higher temperature favors irreversible phase transformation to HT phase. The phase formation is observed to also dictate the morphology of the material under identical synthesis condition. Monoclinic phase is found to be a potential visible light photocatalyst over the orthorhombic phase for the Congo-red degradation. Extension of this work on the composition dependent synthesis of Bi2-xRExWO6 (x = 0.1 to 1.2) would help in getting more insights on the stereochemical nature of Bi 6s2 lone pair character. Accurate crystal structure analysis using synchrotron X-ray/neutron diffraction of both


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orthorhombic and monoclinic phase materials are under progress. Results from this work would give more insights in to the structure and properties in these series and could help in designing new multi-functional energy materials. Experimental Section Material Synthesis: Starting materials used for the hydrothermal synthesis of BiREWO6 nanomaterials are, bismuth nitrate pentahydrate (Bi(NO3)3.5H2O Alfa Aesar) and Sodium tungstate dihydrate (Na2WO6.2H2O; Alfa Aesar) as Bi and W source.Rare earth nitrate hydrates (RE(NO3)3.xH2O; RE = La, Ce, Nd, Eu, Gd, Tb, Dy, Er & Yb: from Alfa Aesar) were used as corresponding rare earth source. 1 m mol of Bi(NO3)3.5H2O and 1 m mol of RE(NO3)3 .xH2O were added to Millipore water, solution was acidified using concentrated HNO3 under constant magnetic stirring. To this mixture, 1 m mol of Na2WO4.2H2O was added and pH was adjusted to 7 to 7.5 by using 8M NaOH solution. Resulting solution was transferred in to 50 ml Teflon lined autoclave filled up to 80% of its volume and heated to 473 K for 8 hours. The obtained precipitate was washed several times with water and ethanol and dried at ambient conditions. Photocatalysis: The photocatalytic activity of the as synthesized materials were evaluated for the degradation of Congo red, an anionic dye (λmax = 498 nm). 50 mg of the as synthesized catalysts were dispersed in 100 ml of 2 x 10-5 M. The catalyst was dispersed uniformly throughout the solution by bubbling atmospheric air using aerator pump. Adsorption–desorption equilibrium of catalyst and dye molecule is attained by allowing the suspension in the dark and the resulting concentration was taken as the initial concentration. The experiment was carried out under visible light irradiation, generated by 500 W tungsten metal halide lamp. Aliquots were collected from the reaction cell at regular intervals of time. The catalyst particles were precipitated by centrifugation and the concentration of the solution was measured by UV-visible


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spectroscopy. The photocatalytic degradation of Congo red for Bi2WO6 was also carried out for comparison. Acknowledgements NGS acknowledges DST, India for funding and PPS is grateful for CSIR for fellowship. Authors wish to thank Dr. Parthasarathi Bera, CSIR−National Aerospace Laboratories, Bengaluru for the analysis of XPS data and Mr. Varadarajan, CeNSE, IISC, Bengaluru for FESEM and XPS measurements. ASSOCIATED CONTENT Supporting Information. P-XRD patterns of time and temperature driven hydrothermal synthesis and thermal treatment of BiREWO6 nanomaterials. Tables containing refined crystal structure data, EDAX analysis, XPS and Raman Spectral analysis of BiCeWO6 nanomaterial. Optical band gap calculation plots. Corresponding Author Nalini G. Sundaram (E-mail: [email protected]) References: 1. Pirovano, C.; Islam, M. S.; Vannier, R.N.; Nowogrocki, G.; Mairesse, G. Modelling the crystal structures of Aurivillius phases. Solid State Ionics 2001, 140 (1), 115-123. 2. Blake, S. M.; Falconer, M. J.; McCreedy, M.; Lightfoot, P. Cation disorder in ferroelectric Aurivillius phases of the type Bi2ANb2O9 (A= Ba, Sr, Ca). J. Mater. Chem. 1997, 7, 1609-1613. 3. Hervoches, C. H.; Snedden, A.; Riggs, R.; Kilcoyne, S. H.; Manuel, P.; Lightfoot, P. Structural behavior of the four-layer Aurivillius-phase ferroelectrics SrBi4Ti4O15 and Bi5Ti3FeO15. J. Solid State Chem. 2002, 164, 280-291. 4. Kennedy, B. J.; Zhou, Q.; Kubota, Y.; Kato, K. Cation disorder and phase transitions in the four-layer ferroelectric Aurivillius phases ABi4Ti4O15 (A= Ca, Sr, Ba, Pb). J. Solid State Chem. 2008, 181, 1377-1386.


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5. Kendall, K. R.; Navas, C.; Thomas, J. K.; zur Loye, H.-C. Recent Developments in Oxide Ion Conductors: Aurivillius Phases. Chem.Mater. 1996, 8, 642-649. 6. Ida, S.; Ogata, C.; Unal, U.; Izawa, K.; Inoue, T.; Altuntasoglu, O.; Matsumoto, Y. Preparation of a blue luminescent nanosheet derived from layered perovskite Bi2SrTa2O9. J. Am. Chem. Soc. 2007, 129, 8956-8957. 7. Watanabe, A. Polymorphism in Bi2WO6. J. Solid State Chem. 1982, 41, 160-165. 8. Mohn, C. E.; Stølen, S. Influence of the stereochemically active bismuth lone pair structure on ferroelectricity and photocalytic activity of Aurivillius phase Bi2WO6. Phys. Rev. B: Condens. Matter. 2011, 83. 9. Yanovskii, V.; Voronkova, V. Polymorphism and properties of Bi2WO6 and Bi2MoO6 Phys. Status Solidi A. 1986, 93, 57-66. 10. Watanabe, A. Stereochemical influence of the Bi3+ lone pair of electrons on polymorphism in Bi2WO6. Mater. Res. Bull. 1984, 19, 877-884. 11. Seshadri, R.; Hill, N. A. Visualizing the role of Bi 6s “lone pairs” in the off-center distortion in ferromagnetic BiMnO3. Chem.Mater. 2001, 13, 2892-2899. 12. Berdonosov, P. S.; Charkin, D. O.; Knight, K. S.; Johnston, K. E.; Goff, R. J.; Dolgikh, V. A.; Lightfoot, P. Phase relations and crystal structures in the systems (Bi,Ln)2WO6 and (Bi,Ln)2MoO6 (Ln=lanthanide). J. Solid State Chem.2006, 179, 3437-3444. 13. Khomskii, D. I. Multiferroics: Different ways to combine magnetism and ferroelectricity. J. Magn. Magn. Mater. 2006, 306, 1-8. 14. Boivin, J.-C. Structural and electrochemical features of fast oxide ion conductors. . International Journal of Inorganic Materials. 2001, 3, 1261-1266. 15. Santha, N.; Koshy, P.; Sebastian, M.; Ratheesh, R. Preparation and characterization of bismuth rare earth tungstate (BiREWO6) dielectric ceramics. J. Mater. Sci.-Mater. 2002, 13, 229-233. 16. Yao, W. F.; Xu, X. H.; Wang, H.; Zhou, J. T.; Yang, X. N.; Zhang, Y.; Shang, S. X.; Huang, B. B. Photocatalytic property of perovskite bismuth titanate. Appl. Catal., B: Environmental. 2004, 52, 109-116. 17. Zhang, Z.; Wang, W. Infrared-light-induced photocatalysis on BiErWO6. Dalton Trans. 2013, 42, 12072-4. 18. Zhang, Z.; Wang, W.; Zhou, Y. Hydrothermal synthesis of a novel BiErWO6 photocatalyst with wide spectral responsive property. Appl. Surf. Sci. 2014, 319, 250-255. 19. Gopalakrishnan, J. Chimie douce approaches to the synthesis of metastable oxide materials. Chem.Mater. 1995, 7, 1265-1275. 20. Li, Y.; Liu, J.; Huang, X.; Li, G. Hydrothermal synthesis of Bi2WO6 uniform hierarchical microspheres. Cryst. Growth Des. 2007, 7, 1350-1355. 21. Shang, M.; Wang, W.; Zhang, L.; Sun, S.; Wang, L.; Zhou, L. 3D Bi2WO6/TiO2 hierarchical heterostructure: controllable synthesis and enhanced visible photocatalytic degradation performances. J. Phys. Chem. C. 2009, 113, 14727-14731. 22. Toby, B. H. EXPGUI, a graphical user interface for GSAS. J. Appl. Crystallogr. 2001, 34, 210-213. 23. Shannon, R. t. Revised effective ionic radii and systematic studies of interatomic distances in halides and chalcogenides. Acta Crystallogr., Sect. A: Found. Crystallogr. 1976, 32, 751-767. 24. Watanabe, A. Synthesis and lattice parameters of rare earth bismuth tungstates, BiLnWO 6 and their solid solutions. Mater. Res. Bull. 1980, 15 (10), 1473-1477.


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25. Ma̧czka, M.; Macalik, L.; Hermanowicz, K.; Kȩpiński, L.; Tomaszewski, P. Phonon properties of nanosized bismuth layered ferroelectric material-Bi2WO6. Raman Spectrosc. 2010, 41, 1059-1066. 26. Millan, P.; Castro, A.; Torrance, J. The first doping of lead2+ into the bismuth oxide layers of the Aurivillius oxides. Mater. Res. Bull. 1993, 28, 117-122. 27. Millan, P.; Ramirez, A.; Castro, A. Substitutions of smaller Sb 3+ and Sn 2+ cations for Bi 3+ in Aurivillius-like phases. J. Mater. Sci. Lett. 1995, 14, 1657-1660. 28. Charkin, D.; Kazakov, S.; Lebedev, D. Study of cationic substitution in Bi2WO6 and derived structures in the framework of the modular approach. Russ. J. Inorg. Chem. 2010, 55, 1248-1256.


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Figure Caption: Figure 1: Powder XRD patterns of as synthesized BiREWO6 nanomaterials via hydrothermal method (a). BiLaWO6 and BiCeWO6, phase matching with the LT-Bi2WO6 (Standard Pattern), impurity peak in BiLaWO6 is identified as La2O3. (b). BiREWO6 (RE = Nd to Yb) materials, phase matching with the HT-Bi2WO6 (Standard Pattern). Figure 2: Observed (green), calculated (red) and difference (indigo) plots obtained by rieteld refinment of orthtorombic BiCeWO6 and monoclinic BiGdWO6 nanomaterials syntheszeid by hyrothermal method. Figure 3: FESEM images of as synthesized BiREWO6 (RE = Ce, Nd, Eu, Gd, Tb, Dy, Er & Yb) nanomaterials via hydrothermal method, where orthorhombic BiCeWO6 has spherically agglomerated and flake type morphology and monoclinic BiREWO6 (RE = Nd to Yb) materials are having rod and plate type morphology. Figure 4: Visible light induced photocatalytic Congo-red dye degradation plot monitored for Dark, LT-BiCeWO6, LT-Bi2WO6 and HT-BiGdWO6 nanomaterial.


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Figure 1: Powder XRD patterns of as synthesized BiREWO6 nanomaterials via hydrothermal method (a). BiLaWO6 and BiCeWO6, phase matching with the LT-Bi2WO6 (Standard Pattern), impurity peak in BiLaWO6 is identified as La2O3. (b). BiREWO6 (RE = Nd to Yb) materials, phase matching with the HT-Bi2WO6 (Standard Pattern).


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Figure 2: Observed (green), calculated (red) and difference (indigo) plots obtained by rieteld refinment of orthtorombic BiCeWO6 and monoclinic BiGdWO6 nanomaterials syntheszeid by

hyrothermal method.

Figure 3: FESEM images of as synthesized BiREWO6 (RE = Ce, Nd, Eu, Gd, Tb, Dy, Er & Yb) nanomaterials via hydrothermal method, where orthorhombic BiCeWO6 has spherically agglomerated and flake type morphology and monoclinic BiREWO6 (RE = Nd to Yb) materials are having rod and plate type morphology.


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Figure 4: Visible light induced photocatalytic Congo-red dye degradation plot monitored for Dark, LT-BiCeWO6, LT-Bi2WO6 and HT-BiGdWO6 nanomaterial.


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“For Table of Contents Use Only," Table of Content Distinct Phase Formation Of BiREWO6 (RE = La-Yb) Nanoparticles By A One Step Hydrothermal Synthesis And Their Photocatalytic Applications Pradeep P. Shanbogh, †‡ Diptikanta Swain, Ἴ Chandrabhas Narayana,§ Ashok Rao,‡ and Nalini G. Sundaram,*† †

Functional Energy Nanomaterials group, Materials sciences Division, Poornaprajna Institute of

scientific Research, Devanahalli, Bengaluru-562110 E-mail: [email protected] ‡

Manipal Academy of Higher Education, Manipal. Karnataka-576104

Ἴ

§

Solid State and Structural Chemistry Unit, Indian Institute of Science, Bengaluru-560012

Chemistry and Physics of Materials Unit, Jawaharlal Nehru Centre for Advanced scientific

Research, Jakkur, Bengaluru-560064


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Synopsis: Schematic representation of (a) ionic radii dependent phase formation in BiREWO6 series via hydrothermal method. Bi & Bi* stands for stereochemically dominant & constrained Bi 6S2 lone pair respectively (b). Congo-red dye degradation Plots monitored under visible light irradiation for as syntheszied photocatalysts.


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Distinct Phase Formation Of BiREWO6 (RE = La-Yb) Nanoparticles By

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