Comprehensive Magnetic Study of Nanostructured Mesoporous

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Comprehensive Magnetic Study of Nanostructured Mesoporous Manganese Oxide Materials and Implications for Catalytic Behavior Ehsan Moharreri, William A Hines, Sourav Biswas, David M Perry, Junkai He, Dustin Murray-Simmons, and Steven L. Suib Chem. Mater., Just Accepted Manuscript • DOI: 10.1021/acs.chemmater.7b05280 • Publication Date (Web): 10 Jan 2018 Downloaded from http://pubs.acs.org on January 11, 2018

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Chemistry of Materials

Comprehensive Magnetic Study of Nanostructured Mesoporous Manganese Oxide Materials and Implications for Catalytic Behavior Ehsan Moharreri†, William A. Hines‡, Sourav Biswas§, David M. Perry‡, Junkai He†, Dustin Murray-Simmons§, Steven L. Suib§,†,* † Institute of Materials Science, University of Connecticut

‡ Department of Physics, University of Connecticut § Department of Chemistry, University of Connecticut, 55 North Eagleville Road, Storrs, Connecticut 06269, * Corresponding author

ABSTRACT Magnetic behavior of nanostructured mesoporous manganese oxide materials, designated UCT-1 and UCT-18, were studied using a combination of superconducting quantum interference device (SQUID) magnetometry and 55Mn zero-field spin-echo nuclear magnetic resonance (NMR). Curie-Weiss fits to the magnetic susceptibility for the UCT-1 and UCT-18 samples calcined at 550 °C yielded paramagnetic moment values consistent with spin-only Mn3+ ions in the α-Mn2O3 phase (S = 2, 4.90 µB). However, the magnetization and NMR results reported here clearly identify a small amount of the Mn3O4 second phase (ferrimagnetic with TC ≈ 43 K) which does not appear in X-ray diffraction (XRD). The study resulted in the observation of fascinating magnetic behavior: (1) exchange bias, which occurs in cases where a ferromagnetic (or ferrimagnetic) phase forms a boundary with an antiferromagnetic phase and (2) a magnetic contribution attributed to uncompensated spins on the surfaces of the α-Mn2O3 nanoparticles. The presence of Mn3O4 and the interplay of Mn3+ and Mn2+ impact the catalytic properties.

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I.

INTRODUCTION The introduction of mesoporous silica and aluminosilicates (MCM-41 and M-

41S) by Mobile Oil Corporation researchers over two decades ago1 has resulted in considerable research activity,2–5 particularly in the application of mesoporous transition metal oxide materials as catalysts.6,7 Since that time, a variety of synthesis procedures, involving both soft and hard templates, chemical compositions, dopants, and promoter ions have been employed.6,8–10 The transition metal oxides can accommodate various cations either in the form of promoter ions on the surface or charge balancing ions in the structure.6,11,12 A unique type of mesoporous materials was developed by this group, recognized as UCT (University of Connecticut) materials.13 The UCT approach is a one-step synthetic process which relies on the use of sol-gel-based inverse micelles as soft templates along with unique NOx chemistry. The resulting nanoparticles are packed in a random close-packed structure to form micron-sized aggregates;14,15 the mesopores are created by the interconnected voids. The surface area and pore size of the mesoporous materials can be tuned efficiently by controlling the heat treatment cycles. This diverse synthesis method allows us to prepare mesoporous metal oxides from different parts of the periodic table. A major advantage the UCT process allows is the ability to synthesize mesoporous oxide materials involving the late transition metals (e.g., Mn, Co, Fe, and Ni). Mesoporous transition metal oxides prepared by this process were found to have broad applicability in a variety of catalytic reactions including water oxidation, lowtemperature CO oxidation, photocatalytic dye degradation, aerobic oxidation, and crosscoupling of organic compounds.6,7,16–20 Among the transition metals, Mn is particularly interesting since various valence states and five stable oxides (MnO, Mn2O3, Mn3O4, Mn5O8, and MnO2) exist with a wide range of technological applications.21–24 Furthermore, there has been recent emphasis to understand the behavior of the oxides at the nanoscale.25–28 Since the manganese ion can possess the valence states Mn2+, Mn3+, and Mn4+, various magnetic moment values occur (e.g., low spin-states of S = 5/2, 2, and 3/2, respectively). The oxides exhibit a variety of complex magnetic structures and behavior (antiferromagnetism, ferrimagnetism, and helical magnetic order). Moreover, the mixed valence nature of manganese gives it a

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wide range of catalytic applications in both the amorphous and crystalline states, which can be enhanced by the inclusion of other elements. In our previous study, we found that introduction of a minute amount ( TN(CoO). Since the oxides of many ferromagnetic transition metals are themselves antiferromagnetic, many of the early investigations involved nanoparticles consisting of a ferromagnetic core and an antiferromagnetic shell.42 However, Berkowitz et al.43 and Salazar-Alvarez et al.41 independently reported a “doubly inverted” core-shell system in which nanoparticles with an antiferromagnetic core (MnO) were surrounded with a ferrimagnetic shell (Mn3O4) shell and the magnetic ordering temperatures were such that TN(MnO) > TC(Mn3O4). The UCT-1 and UCT-18 materials studied here replicate a doubly inverted core-shell picture; i.e., nanoparticles with an α-Mn2O3 core having Mn3O4 inclusions or surface shells and TN(α-Mn2O3) ≈ 80 K > TC(Mn3O4) ≈ 43 K. Recently, electron energy loss spectroscopy (EELS) has provided a very advanced method in the characterization of nanostructured materials. An example is the study by Estradé et al.44 in which scanning transmission electron microscopy with EELS analysis (STEM-EELS) was used to identify the core/shell structure of the MnOx/MnOy nanoparticles. The Mn3O4 second

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phase in our samples may, however, exist in the form of small inclusions and not simply as well-defined shells. It is of particular importance to compare the magnetic phase composition of the UCT-1 and UCT-18 samples calcined at 250 °C. In earlier work, it was demonstrated the Cs-promoted UCT-18 (250 °C) had greatly enhanced catalytic activity compared to UCT1(250 °C).6 Although the Mn ion magnetic moment values are comparable as described above, the ZFC/FC and TRM curves show significant differences. As seen in Figs. 7(a) and 7(c) respectively, the UCT-1(250 °C) and UCT-18(250 °C) samples both show a peak in the ZFC at ≈ 22 K; however, the peak for the UCT-18(250 °C) is considerably broader. Although a weak first-order magnetic transition has been reported near 25 K for polycrystalline α-Mn2O3 45, the ZFC peaks seen in Figs. 7(a) and 7(c) are more likely due to the existence of a superparamagnetic blocking temperature. This would be possible for small α-Mn2O3 particles with uncompensated surface spins; however, the α-Mn2O3 phase has not been directly identified in any of the samples calcined at 250 °C. The suggestion of a superparamagnetic blocking temperature at 22K is based on the ac susceptibility measurements reported by Mukherjee et al.;46 however, a spin-glass-like transition cannot be completely ruled out.47 The ac susceptibility measurements were carried out on α−Mn2O3 nanocrystals (9-18 nm, similar to ours) dispersed in a silica matrix. From their analysis of the shift of the peak in χ’ with frequency, they conclude that the parameters are consistent with those obtained for superparamagnetic particles and well outside those for spin-glass systems. In any case there is a clear presence of Mn3O4 in the UCT-18(250 °C) sample as indicated by the bifurcation of the ZFC and FC curves at ≈ 46 K (Fig. 7(c)) which is not apparent with the UCT-1(250 °C) sample (Fig. 7(a)). This is also indicated in the corresponding TRM curves (Figs. 7(b) and 7(d)). These results were reproduced in the duplicate samples. The presence of Mn3O4 in the UCT-18(250 °C) samples and not the UCT-1(250 °C) samples provides a link to an understanding of the enhanced catalytic activity.6 From prior studies, we know that the mixed valence of manganese and easy mobility of labile oxygen are driving factors of catalytic activity. Mesoporous MnOx materials were correctly deemed to have "mixed Mn species", but rarely understood as mixed phase. Lattice size differences between α−Mn2O3 and Mn3O4 are rather challenging to pinpoint with HR-TEM. Here from a magnetic route, the

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coexistence of α−Mn2O3 and Mn3O4 provides another sign of interplay of Mn3+ and Mn2+ species. While Mn3+ is mostly the more active species even in non-oxidative reaction,20 with oxygen being required for its replenishment, the presence of Mn2+ is the consequence and the indicator of its activity. We showed that the secondary phase of Mn3O4 is oxidized during heat treatment (Fig. S6 (a) and S6 (b)) for a commercial α−Mn2O3 sample standard. The phase identification obtained from the magnetization measurements was supported by the

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Mn zero-field spin-echo NMR spectra. The uniqueness of NMR is

that this method can identify the actual phase of small magnetic inclusions, which are detected in magnetization measurements and, perhaps, not detected by XRD. NMR is also a useful technique in cases where there are two phases with similar structures that are difficult to distinguish by XRD or TEM. For UCT-1, characteristic spectra for both the principal α−Mn2O3 phase and the Mn3O4 second phase were observed for the samples calcined at 450 °C and 550 °C. These two phases were also observed in UCT-18(550 °C). A relatively strong 55Mn spectrum characteristic of Mn3O4 was observed in a 99.9% pure commercial sample of α−Mn2O3. Although the commercial is “pure” with regard to elemental impurities, this material is not completely phase pure. There are some previous reports in the literature concerning the magnetic properties of nanostructured manganese oxides, which are relevant to the work reported here. F. Jiao et al.8 first reported on a synthesis procedure for highly ordered mesoporous Mn3O4 with crystalline walls. The process involved an initial synthesis of highly-ordered mesoporous α−Mn2O3 using the hard template KIT-6 and then reducing it to form highly crystalline Mn3O4 retaining the ordered pore structure.

They observed a distinct

bifurcation of their ZFC/FC magnetization curves for the initial mesoporous α−Mn2O3 material just above 40 K and attributed this behavior to a trace amount (≈ 0.05%) of Mn3O4 in the sample, which was not detected in the XRD scans. T. Ahmad et al.48 have prepared a sample ≈ 50 nm α−Mn2O3 nanoparticles (along with samples of MnO and Mn3O4 nanoparticles) using a reverse micellar route followed by a heat treatment in air. They also observed a broad transition near 80 K due to the antiferromagnetic α−Mn2O3 as well as a “magnetic anomaly” near 45 K, which was attributed to ≈ 1% Mn3O4 impurity.

They were able to fit the magnetic susceptibility for their α−Mn2O3 18


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nanoparticles to the Curie-Weiss law 100 K ≤ T ≤ 300 K obtaining an effective moment value of 5.0 µB, which is consistent with the spin-only value for Mn3+, and Θ = −160 K. However, in their work, there is no mention of magnetic behavior related to uncompensated surface spins, probably due to the relatively large particle size. On the other hand, Mukherjee et al.46 have prepared much smaller α−Mn2O3 nanocrystals in a silica matrix using a sol-gel procedure followed by calcination.

Their α−Mn2O3

nanocrystals show weak ferromagnetic-like order for T ≤ 77 K along with the features of a superparamagnetic/ferromagnetic blocking temperature near 40 K. They rule out the presence of Mn3O4 nanocrystals and attribute all of the magnetic behavior to the uncompensated surface spins. Based on the results presented here, we suggest that this conclusion be revisited. In a recent work, Thota et al.49 prepared samples of MnO, Mn2O3, Mn5O8, and Mn3O4 nanoparticles by decomposing sol-gel produced manganese oxalate in oxygen, air, nitrogen, or oxygen at different temperatures. In particular, the α−Mn2O3 nanoparticles showed the antiferromagnetic transition at TN = 75 K along with a bifurcation in the ZFC/FC magnetization curves below 50 K. It is concluded that small amounts of the Mn3O4 phase is always present and cannot be completely eliminated in the preparation of various manganese oxide materials. Supporting Information The supporting information is available free of charge on the ACS Publications website. XRD patterns for UCT-18 samples Nitrogen sorption isotherms and pore size distribution for UCT-18 samples Scanning electron microscope images for UCT-1 and UCT-18 samples Transmission electron microscopy images for UCT-18 samples Thermoremanent magnetization curves for commercial and treated α-Mn2O3 samples Refinement analysis of XRD measurements of UCT-1 and UCT-18 Textural properties of mesoporous manganese oxide samples Parameters of refinement on XRD patterns

ACKNOWLEDGMENTS WH and DP would like to thank Richard Bibeault for assistance with the magnetization and NMR experiments. Authors EM, SB, JH and SS received funding from the Chemical,

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Geochemical and Biosciences Division of the Office of Basic Energy Sciences, Office of Science, U.S. Department of Energy for supporting this work under grant DE-FG0286ER13622-A000. We would like to thank the mentioned division for the support. The TEM studies were performed using the facilities in the UConn/Thermo Fisher Scientific Center for Advanced Microscopy and Materials Analysis (CAMMA).

REFERENCES (1)

(2)

(3)

(4)

(5)

(6)

(7)

(8) (9)

(10)

(11)

Kresge, C. T.; Leonowicz, M. E.; Roth, W. J.; Vartuli, J. C.; Beck, J. S. Ordered Mesoporous Molecular Sieves Synthesized by a Liquid-Crystal Template Mechanism. Nature 1992, 359 (6397), 710–712. Tüysüz, H.; Salabaş, E. L.; Bill, E.; Bongard, H.; Spliethoff, B.; Lehmann, C. W.; Schüth, F. Synthesis of Hard Magnetic Ordered Mesoporous Co 3 O 4 /CoFe 2 O 4 Nanocomposites. Chem. Mater. 2012, 24 (13), 2493–2500. Wang, G.; Liu, H.; Horvat, J.; Wang, B.; Qiao, S.; Park, J.; Ahn, H. Highly Ordered Mesoporous Cobalt Oxide Nanostructures: Synthesis, Characterisation, Magnetic Properties, and Applications for Electrochemical Energy Devices. Chem. - Eur. J. 2010, 16 (36), 11020–11027. Chen, C.-H.; Abbas, S. F.; Morey, A.; Sithambaram, S.; Xu, L.-P.; Garces, H. F.; Hines, W. A.; Suib, S. L. Controlled Synthesis of Self-Assembled Metal Oxide Hollow Spheres Via Tuning Redox Potentials: Versatile Nanostructured Cobalt Oxides. Adv. Mater. 2008, 20 (6), 1205–1209. Tian, B.; Liu, X.; Solovyov, L. A.; Liu, Z.; Yang, H.; Zhang, Z.; Xie, S.; Zhang, F.; Tu, B.; Yu, C.; Terasaki, O.; Zhao, D. Facile Synthesis and Characterization of Novel Mesoporous and Mesorelief Oxides with Gyroidal Structures. J. Am. Chem. Soc. 2003, 126 (3), 865–875. Biswas, S.; Poyraz, A. S.; Meng, Y.; Kuo, C.-H.; Guild, C.; Tripp, H.; Suib, S. L. Ion Induced Promotion of Activity Enhancement of Mesoporous Manganese Oxides for Aerobic Oxidation Reactions. Appl. Catal., B 2015, 165, 731–741. Biswas, S.; Dutta, B.; Mullick, K.; Kuo, C. H.; Poyraz, A. S.; Suib, S. L. Aerobic Oxidation of Amines to Imines by Cesium-Promoted Mesoporous Manganese Oxide. ACS Catal. 2015, 5 (7), 4394–4403. Jiao, F.; Harrison, A.; Hill, A. H.; Bruce, P. G. Mesoporous Mn2O3 and Mn3O4 with Crystalline Walls. Adv. Mater. 2007, 19 (22), 4063–4066. Biswas, S.; Mullick, K.; Chen, S.-Y.; Kriz, D. A.; Shakil, M.; Kuo, C.-H.; Angeles-Boza, A. M.; Rossi, A. R.; Suib, S. L. Mesoporous Copper/Manganese Oxide Catalyzed Coupling of Alkynes: Evidence for Synergistic Cooperative Catalysis. ACS Catal. 2016, 6 (8), 5069–5080. Wang, F.; Dai, H.; Deng, J.; Bai, G.; Ji, K.; Liu, Y. Manganese Oxides with Rod-, Wire-, Tube-, and Flower-Like Morphologies: Highly Effective Catalysts for the Removal of Toluene. Environ. Sci. Technol. 2012, 46 (7), 4034–4041. Escande, V.; Lam, C. H.; Coish, P.; Anastas, P. T. Heterogeneous SodiumManganese Oxide Catalyzed Aerobic Oxidative Cleavage of 1,2-Diols. Angew. Chem. 2017, 129 (32), 9689–9693.

20


Page 20 of 34

Page 21 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(12)

(13)

(14) (15)

(16)

(17)

(18)

(19)

(20)

(21)

(22)

(23)

(24)

Sato, H.; Enoki, T.; Yamaura, J.-I.; Yamamoto, N. Charge Localization and Successive Magnetic Phase Transitions of Mixed-Valence Manganese Oxides K1.5(H3O)xMn8O16. Phys. Rev. B 1999, 59 (20), 12836–12841. Poyraz, A. S.; Kuo, C.-H.; Biswas, S.; King’ondu, C. K.; Suib, S. L. A General Approach to Crystalline and Monomodal Pore Size Mesoporous Materials. Nat. Commun. 2013, 4, 1–10. Deljoo, B.; Jafari, T.; Suib, S. L.; Aindow, M. Studies of the Hierarchical Structure in UCT Manganese Oxides. Microsc. Microanal. 2017, 23, 1864–1865. Poges, S.; Dutta, B.; Khanna, H.; Moharreri, E.; Aindow, M.; Suib, S. L. Cross Sectional Analysis of Cation Doped Transition Metal Oxide Mesoporous Catalyst Materials. Microsc. Microanal. 2017, 23, 292–293. Kuo, C. H.; Mosa, I. M.; Poyraz, A. S.; Biswas, S.; El-Sawy, A. M.; Song, W.; Luo, Z.; Chen, S. Y.; Rusling, J. F.; He, J.; Suib, S. L. Robust Mesoporous Manganese Oxide Catalysts for Water Oxidation. ACS Catal. 2015, 5 (3), 1693– 1699. Song, W.; Poyraz, A. S.; Meng, Y.; Ren, Z.; Chen, S. Y.; Suib, S. L. Mesoporous Co3O4 with Controlled Porosity: Inverse Micelle Synthesis and High-Performance Catalytic Co Oxidation at -60 °c. Chem. Mater. 2014, 26 (15), 4629–4639. Jiang, T.; Poyraz, A. S.; Iyer, A.; Zhang, Y.; Luo, Z.; Zhong, W.; Miao, R.; ElSawy, A. M.; Guild, C. J.; Sun, Y.; Kriz, D. A.; Suib, S. L. Synthesis of Mesoporous Iron Oxides by an Inverse Micelle Method and Their Application in the Degradation of Orange II under Visible Light at Neutral pH. J. Phys. Chem. C 2015, 119 (19), 10454–10468. Dutta, B.; Biswas, S.; Sharma, V.; Savage, N. O.; Alpay, S. P.; Suib, S. L. Mesoporous Manganese Oxide Catalyzed Aerobic Oxidative Coupling of Anilines To Aromatic Azo Compounds. Angew. Chem., Int. Ed. 2016, 128 (6), 2211–2215. Dutta, B.; Sharma, V.; Sassu, N.; Dang, Y.; Weerakkody, C.; Macharai, J.; Miao, R.; Howell, A.; Suib, S. L. Cross Dehydrogenative Coupling of NAryltetrahydroisoquinolines (sp3 C-H) with Indoles (sp2 C-H) Using Heterogeneous Mesoporous Manganese Oxide Catalyst. Green Chem. 2017, 19 (22), 5350–5355. Qiu, Y.; Xu, G.-L.; Yan, K.; Sun, H.; Xiao, J.; Yang, S.; Sun, S.-G.; Jin, L.; Deng, H. Morphology-Conserved Transformation: Synthesis of Hierarchical Mesoporous Nanostructures of Mn2O3 and the Nanostructural Effects on Li-Ion Insertion/deinsertion Properties. J. Mater. Chem. 2011, 21 (17), 6346–6353. Jeong, D.; Jin, K.; Jerng, S. E.; Seo, H.; Kim, D.; Nahm, S. H.; Kim, S. H.; Nam, K. T. Mn5O8 Nanoparticles as Efficient Water Oxidation Catalysts at Neutral pH. ACS Catal. 2015, 5 (8), 4624–4628. Meng, Y.; Song, W.; Huang, H.; Ren, Z.; Chen, S.-Y.; Suib, S. L. Structure– Property Relationship of Bifunctional MnO 2 Nanostructures: Highly Efficient, Ultra-Stable Electrochemical Water Oxidation and Oxygen Reduction Reaction Catalysts Identified in Alkaline Media. J. Am. Chem. Soc. 2014, 136 (32), 11452– 11464. Kim, T.; Cho, E.-J.; Chae, Y.; Kim, M.; Oh, A.; Jin, J.; Lee, E.-S.; Baik, H.; Haam, S.; Suh, J.-S.; Huh, Y.-M.; Lee, K. Urchin-Shaped Manganese Oxide Nanoparticles as pH-Responsive Activatable T1 Contrast Agents for Magnetic

21



(25)

(26)

(27)

(28) (29) (30)

(31) (32)

(33)

(34) (35) (36) (37)

(38)

(39)

(40)

(41)

Resonance Imaging. Angew. Chem., Int. Ed. 2011, 50 (45), 10589–10593. Wei, W.; Cui, X.; Chen, W.; Ivey, D. G. Manganese Oxide-Based Materials as Electrochemical Supercapacitor Electrodes. Chem. Soc. Rev. 2011, 40 (3), 1697– 1721. Zhi, M.; Xiang, C.; Li, J.; Li, M.; Wu, N. Nanostructured Carbon–metal Oxide Composite Electrodes for Supercapacitors: A Review. Nanoscale 2013, 5 (1), 72– 88. Miller, D. R.; Akbar, S. A.; Morris, P. A. Nanoscale Metal Oxide-Based Heterojunctions for Gas Sensing: A Review. Sens. Actuators, B 2014, 204, 250– 272. Zhang, Z.; Yates, J. T. Band Bending in Semiconductors: Chemical and Physical Consequences at Surfaces and Interfaces. Chem. Rev. 2012, 112 (10), 5520–5551. Geller, S.; Espinosa, G. P. Magnetic and Crystallographic Transitions in Sc3+, Cr3+, and Ga3+ Substituted Mn2O3. Phys. Rev. B 1970, 1 (9), 3763–3769. Jo, E.; An, K.; Shim, J. H.; Kim, C.; Lee, S. Spin State of Mn3O4 Investigated by 55Mn Nuclear Magnetic Resonance. Phys. Rev. B Condens. Matter Mater. Phys. 2011, 84 (17), 1–4. Brunauer, S.; Emmett, P. H.; Teller, E. Adsorption of Gases in Multimolecular Layers. J. Am. Chem. Soc. 1938, 60 (2), 309–319. Barrett, E. P.; Joyner, L. G.; Halenda, P. P. The Determination of Pore Volume and Area Distributions in Porous Substances. I. Computations from Nitrogen Isotherms. J. Am. Chem. Soc. 1951, 73 (1), 373–380. Thommes, M.; Kaneko, K.; Neimark, A. V; Olivier, J. P.; Rodriguez-reinoso, F.; Rouquerol, J.; Sing, K. S. W. Physisorption of Gases , with Special Reference to the Evaluation of Surface Area and Pore Size Distribution ( IUPAC Technical Report ). Pure Appl. Chem. 2015, 87, 1051–1069. Selwood, P. W. Magnetochemistry; New York, 1956. Meiklejohn, W. H.; Bean, C. P. New Magnetic Anisotropy. Phys. Rev. 1956, 102 (3), 1413–1414. Jo, E.; Kim, C.; Lee, S. 55Mn Nuclear Magnetic Resonance for Antiferromagnetic α-Mn2O3. New J. Phys. 2011, 13, 1–6. Dho, J.; Kim, M.; Lee, S.; Lee, W.-J. The Enhancement Effect in the Domain and Domain Wall in Fe57 Nuclear Magnetic Resonance. J. Appl. Phys. 1997, 81 (3), 1362–1367. Kim, S. H.; Choi, B. J.; Lee, G. H.; Oh, S. J.; Kim, B.; Choi, H. C.; Park, J.; Chang, Y. Ferrimagnetism in γ-Manganese Sesquioxide (γ - Mn2O3) Nanoparticles. J. Korean Phys. Soc. 2005, 46 (4), 941–944. Shen, X. F.; Ding, Y. S.; Liu, J.; Han, Z. H.; Budnick, J. I.; Hines, W. A.; Suib, S. L. A Magnetic Route to Measure the Average Oxidation State of Mixed-Valent Manganese in Manganese Oxide Octahedral Molecular Sieves (OMS). J. Am. Chem. Soc. 2005, 127 (17), 6166–6167. Vasilakaki, M.; Trohidou, K. N.; Nogués, J. Enhanced Magnetic Properties in Antiferromagnetic-Core/Ferrimagnetic-Shell Nanoparticles. Sci. Rep. 2015, 5 (1), 1–7. Salazar-Alvarez, G.; Sort, J.; Suriñach, S.; Baró, M. D.; Nogués, J. Synthesis and Size-Dependent Exchange Bias in Inverted Core-Shell MnO|Mn3O4

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Page 22 of 34

Page 23 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(42) (43)

(44)

(45)

(46)

(47) (48)

(49)

Nanoparticles. J. Am. Chem. Soc. 2007, 129 (29), 9102–9108. Nogués, J.; Sort, J.; Langlais, V.; Skumryev, V.; Suriñach, S.; Muñoz, J. S.; Baró, M. D. Exchange Bias in Nanostructures. Phys. Rep. 2005, 422 (3), 65–117. Berkowitz, A. E.; Rodriguez, G. F.; Hong, J. I.; An, K.; Hyeon, T.; Agarwal, N.; Smith, D. J.; Fullerton, E. E. Antiferromagnetic MnO Nanoparticles with Ferrimagnetic Mn3O4 Shells: Doubly Inverted Core-Shell System. Phys. Rev. B Condens. Matter Mater. Phys. 2008, 77 (2), 1–6. Estradé, S.; Yedra, L.; López-Ortega, A.; Estrader, M.; Salazar-Alvarez, G.; Nogués, J.; Peiró, F. Distinguishing the Core from the Shell in MnO X /MnO Y and FeO X /MnO X Core/shell Nanoparticles through Quantitative Electron Energy Loss Spectroscopy (EELS) Analysis. Micron 2012, 43 (1), 30–36. Grant, R. W.; Geller, S.; Cape, J. A.; Espinosa, G. P. Magnetic and Crystallographic Transitions in the -Mn2O3-Fe2O3 System. Phys. Rev. 1968, 175 (2), 686–695. Mukherjee, S.; Pal, A. K.; Bhattacharya, S.; Raittila, J. Magnetism of Mn2O3 Nanocrystals Dispersed in a Silica Matrix: Size Effects and Phase Transformations. Phys. Rev. B 2006, 74 (10), 1–10. Winkler, E.; Zysler, R. D.; Mansilla, M. V.; Fiorani, D. Surface Anisotropy Effects in NiO Nanoparticles. Phys. Rev. B 2005, 72 (13), 1–4. Ahmad, T.; Ramanujachary, K. V; Lofland, S. E.; Ganguli, A. K. Nanorods of Manganese Oxalate: A Single Source Precursor to Different Manganese Oxide Nanoparticles (MnO, Mn2O3, Mn3O4). J. Mater. Chem. 2004, 14 (23), 3406– 3410. Thota, S.; Prasad, B.; Kumar, J. Formation and Magnetic Behaviour of Manganese Oxide Nanoparticles. Mater. Sci. Eng., B 2010, 167 (3), 153–160.

FIGURES

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(a)

* Mn2O3

RELATIVE INTENSITY

0.47

0.67

*

*

(b)

# MnO2

*

*

*

*

* * * * * * ** **** * *

550 C

* *

#

# * *

#*

* * * # # * * ** * * *

450 C

350 C

UCT-1 250 C 0

10

20

30

40

50

60

70

80

2θ

Fig. 1. (Color On-line) Powder x-ray diffraction patterns for the UCT-1 samples: (a) small angle – calcined at 450 °C; (b) wide angle – calcined at 250 °C (blue), 350 °C (red), 450 °C (green), and 550 °C (purple). *indicates peaks assigned to the α−Mn2O3 bixbyite phase (JCPDS #41-1442) and #indicates peaks assigned to the MnO2 phase (JCPDS #24-0735). The 250 °C and 350 °C sample are “XRD amorphous”.

(a)

100

(b)

UCT-1 250 C

DIFFERENTIAL PORE VOLUME (arb. units)

120

VOLUME ADSORBED (cm3/g)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 24 of 34

350 C 450 C

80

550 C

60 40 20 0 0

0.2

0.4

0.6

0.8

UCT-1 250 C 350 C 450 C 550 C

1

1

RELATIVE PRESSURE, P/Po

10 PORE DIAMETER (nm)

100

Fig. 2. (Color On-Line) (a) Nitrogen sorption isotherms and (b) pore size distribution curves for the UCT-1 samples: blue circles – calcined at 250 °C, red squares – calcined at 350 °C, green triangles – calcined at 450 °C, and purple diamonds - calcined at 550 °C. The BET surface areas, pore volumes, and BJH pore sizes are summarized in Table SI.

24


Page 25 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


25



Fig. 3. Transmission electron microscope images obtained from the UCT-1(550 °C) sample: (a) scale bar = 500 nm and (b) scale bar = 200 nm. The images show a random close-packed aggregation of nanoparticles (average diameter of the aggregate ≈ 200 nm). High-resolution TEM images obtained from the UCT-1 (550 °C) sample: (c) and (d) scale bar = 10 nm. The images show the single-crystalline nature of the nanoparticles. The resolved lattice fringes with d-spacings of 0.14 nm, 0.27 nm and 0.4 nm correspond to the (622), (222) and (211) planes for α-Mn2O3 bixbyite, respectively. 2.5

5

(b)

4

o

UCT-1(250 C)

MAGNETIZATION (emu/g)


(a)

3

2 100 K 150 K 200 K 250 K 300 K

1

0

2.0

1.5

1.0

0.5

0.0

0

10000

20000

30000

40000

o

UCT-1(250 C)

50000

H = 10,000 Oe

0

50

100

200

250

300

350

30000 1/(MAGNETIC SUSCEPTIBILITY) (g/emu)

20000 (c) o

16000

UCT-1(250 C)

12000

8000 H = 10,000 Oe isotherms

4000

0

150

TEMPERATURE (K)

MAGNETIC FIELD (Oe)

1/(MAGNETIC SUSCEPTIBILITY) (g/emu)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 26 of 34

-200

-100

0

100

200

(d)

25000

o

UCT-18(250 C)

20000 15000 10000

300

H = 10,000 Oe isotherms

5000 0

-300

-200

-100

0

100

200

300

TEMPERATURE (K)

TEMPERATURE (K)

Fig. 4. (Color On-line) Paramagnetic behavior (representative) for the UCT-1(250 °C) sample: (a) magnetization versus magnetic field isotherms at indicated temperatures 100 K ≤ T ≤ 300 K; (b) magnetization versus temperature for magnetic field H = 10,000 kOe; (c) Curie-Weiss fit to the magnetic susceptibility values obtained from the data in (a) and (b). (d) Curie-Weiss fit to the magnetic susceptibility values for the UCT-18(250 °C) sample. Parameters from the Curie-Weiss fits for the UCT-1 and UCT-18 samples calcined at 250 °C and 550 °C are summarized in Table I.

26


Page 27 of 34

6

0.2 (a)

(b)



4 2 0 -2 o

UCT-18(250 C) ZFC, T = 10 K

-4 -6 -60000 -40000 -20000

0

20000

40000

0.1

0.0

-0.1 o

UCT-18(250 C) ZFC, T = 10 K

-0.2 -2000

60000

-1000

MAGNETIC FIELD (Oe)

0

2000

0.2 (c)


(d)

0.1

0.0

-0.1

0.1

0.0

-0.1 o

o

-0.2 -2000

1000

MAGNETIC FIELD (Oe)

0.2


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


UCT-18(250 C) FC = +10 kOe, T = 10 K

-1000

0

1000

-0.2 -2000

2000

MAGNETIC FIELD (Oe)

UCT-18(250 C) FC = −10 kOe, T = 10 K

-1000

0

1000

2000

MAGNETIC FIELD (Oe)

Fig. 5. (a) Full magnetization loop obtained at 10 K after cooling in zero field for the UCT-18(250 °C) sample; (b) expansion of magnetization loop shown in (a) around the origin showing hysteresis behavior with Hc ≈ 500 Oe; (c) and (d) show a similar expansion around the origin for magnetization loops obtained after cooling in H = +10 kOe and −10 kOe, respectively. The shift of the magnetization loop along the magnetic field axis (Heb ≈ 310 Oe) is a signature of exchange bias. Hysteresis parameters for the UCT-1 and UCT-18 samples calcined at 250 °C and 550 °C are summarized in Table II.

27



2.0

0.20 (a)

(b)

0.15 MAGNETIZATION (emu/g)


1.5 1.0 0.5 0.0 -0.5 -1.0 o

UCT-1(550 C) ZFC, T = 10 K

-1.5 -2.0 -15000 -10000

-5000

0

5000

10000

0.10 0.05 0.00 -0.05 -0.10 o

UCT-1(550 C) ZFC, T = 10 K

-0.15 -0.20 -1000

15000

-500

MAGNETIC FIELD (Oe)

500

1000

0.20 (d)

(c)


0.15 0.10 0.05 0.00 -0.05 -0.10 o

-500

0

500

0.10 0.05 0.00 -0.05 -0.10 o

UCT-1(550 C) FC = −10 kOe, T = 10 K

-0.15

UCT-1(550 C) FC = +10 kOe, T = 10 K

-0.15 -0.20 -1000

0

MAGNETIC FIELD (Oe)

0.20

MAGNETIATION (emu/g)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 28 of 34

-0.20 -1000

1000

-500

0

500

1000

MAGNETIC FIELD (Oe)

MAGNETIC FIELD (Oe)

Fig. 6. (a) Full magnetization loop obtained at 10 K after cooling in zero field for the UCT-1 (550 °C) sample; (b) expansion of magnetization loop shown in (a) around the origin showing a very small hysteresis behavior with Hc ≈ 21 Oe; (c) and (d) show a similar expansion around the origin for magnetization loops obtained after cooling in H = +10 kOe and −10 kOe, respectively. The very small shift of the magnetization loop along the magnetic field axis (Heb ≈ 130 Oe) is a signature of exchange bias. Hysteresis parameters for the UCT-1 and UCT-18 samples calcined at 250 °C and 550 °C are summarized in Table II.

28


Page 29 of 34

0.016

0.35 o

0.012

0.008

Heating Cooling

0.004

o

UCT-1(250 C) FC = +10 kOe, H = 0



(b)

UCT-1(250 C) H = 50 Oe

(a)

0.25 0.20 0.15 Heating Cooling

0.10 0.05 0.00

0.000

0

20

40

60

80

100

120

140

160

0

20

TEMPERATURE (K)

40

60

100

120

0.20 o

o

UCT-18(250 C) H = 50 Oe

(c)

UCT-18(250 C) FC = +10 kOe, H = 0

(d)


0.008

0.006

0.004 Heating Cooling

0.002

0.000

80

TEMPERATURE (K)

0.010


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


0.12


0.04

0.00 0

20

40

60

80

100

120

140

160

0

TEMPERATURE (K)

20

40

60

80

100

TEMPERATURE (K)

Fig. 7. (a) and (c) are the ZFC (closed circles) and FC (open circles) magnetization versus temperature curves obtained at H = 50 Oe for the UCT-1(250 °C) and UCT18(250 °C) samples, respectively. (b) and (d) are the TRM heating (closed circles) and cooling (open circles) magnetization curves obtained for H ≈ 0 after cooling in +10 kOe magnetic field. The UCT-18(250 °C) sample shows a magnetic contribution due to Mn3O4 which is essentially absent in the UCT-1(250 °C) sample.

29


120


0.015

0.05

0.04

0.012

0.009


0.003

UCT-1(550 C) FC = +10 kOe, H = 0

(b)



o

o

UCT-1(550 C) H = 50 Oe

(a)

0.03


0.01

0.00 0.000

0

20

40

60

80

100

120

140

160

0

20

TEMPERATURE (K)

40

60

80

0.06

UCT-18(550 C) FC = +10 kOe, H = 0

(d)


0.016

0.012

0.008

Heating Cooling

0.004

120

o

o

UCT-18(550 C) H = 50 Oe

(c)

100

TEMPERATURE (K)

0.020


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 30 of 34

0.04 0.03 0.02 Heating Cooling

0.01 0.00

0.000

0

20

40

60

80

100

120

140

160

0

TEMPERATURE (K)

20

40

60

80

100

TEMPERATURE (K)

Fig. 8. (a) and (c) are the ZFC (closed circles) and FC (open circles) magnetization versus temperature curves obtained at H = 50 Oe for the UCT-1(550 °C) and UCT18(550 °C) samples, respectively. (b) and (d) are the TRM heating (closed circles) and cooling (open circles) magnetization curves obtained for H ≈ 0 after cooling in +10 kOe magnetic field. The arrow in (a) indicates the α-Mn2O3 antiferromagnetic transition at TN ≈ 80 K. In addition to the Mn3O4 ferrimagnetic transition at TC ≈ 43 K, the magnetic component for 44 K ≤ T ≤ 80 K is attributed to uncompensated α-Mn2O3 surface spins.

30


120

(CALIBRATED ECHO AMPLITUDE)/(FREQUENCY) (arb. units)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(CALIBRATED ECHO AMPLITUDE)/(FREQUENCY) (arb.units)

Page 31 of 34

1.2 o

(a)

1.0

black triangles - 350 C o

UCT-1 meso T = 4.2 K and H = 0

blue squares - 450 C o

red circles - 550 C

0.8 0.6 0.4

Mn2O3 phase

0.2 0.0

306 308 310 312 314 316 318 320 322 324 FREQUENCY (MHz)

1.2 (b) 1.0

o

black triangles - 350 C

UCT-1 meso T = 4.2 K and H = 0

o

blue squares - 450 C o

red circles - 550 C

0.8

0.6

0.4

Mn3O4 phase

0.2

0.0 245

250

255

260

265

270

275

FREQUENCY (MHz)

Fig. 9. (Color On-line) 55Mn zero field spin echo NMR spectra obtained at T = 4.2 K and H = 0 for the UCT-1 sample: black triangles – calcined at 350 °C; blue squares – calcined at 450 °C; red circles calcined at 550 °C. (a) α-Mn2O3 principal phase and (b) Mn3O4 second phase.

31


Page 32 of 34

1.2 blue squares

Mn2O3 phase

1.0

o

UCT-1 (550 C) black triangles

T = 4.2 K and H = 0

o

UCT-18 (550 C) red circles Commercial Mn2O3

0.8 0.6 0.4 0.2

(a)

0.0 305

310

315

320

325

FREQUENCY (MHz)


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60



1.2

blue squares

Mn3O4 phase

o

1.0

UCT-1 (550 C) black triangles

0.8

UCT-18 (550 C) red circles Commercial Mn2O3

T = 4.2 K and H = 0

o

0.6 0.4 0.2 0.0 245

(b)

250

255

260

265

270

275

FREQUENCY (MHz)

Fig. 10. (Color On-line) 55Mn zero field spin echo NMR spectra obtained at T = 4.2 K and H = 0: blue squares – UCT-1(550 °C) sample; black triangles – UCT-18(550 °C) sample; red circles – commercial α-Mn2O3 sample. (a) α-Mn2O3 principal phase and (b) Mn3O4 second phase.

32


Page 33 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


TABLES Table I. Curie-Weiss Law Fits Sample Calcin. Batch

Mn/g

C(emu-K/g)

Θ(K)

µ(µB) Range

UCT-1 250 oC

1st

7.63 × 1021

2.69 × 10−2

−183

4.12

100 ≤ T ≤ 300

UCT-1 250 oC

2nd

7.63 × 1021

2.44 × 10−2

−173

3.93

100 ≤ T ≤ 300

UCT-18 250 oC

1st

7.63 × 1021

2.32 × 10−2

−284

3.83

150 ≤ T ≤ 300

UCT-18 250 oC

2nd

7.63 × 1021

2.00 × 10−2

−237

3.39

150 ≤ T ≤ 300

UCT-1 550 oC

1st

7.63 × 1021

3.83 × 10−2

−153

4.91

100 ≤ T ≤ 300

UCT-18 550 oC

1st

7.63 × 1021

3.71 × 10−2

−167

4.84

100 ≤ T ≤ 300

Table II. Hysteresis Parameters Sample Calcin. Batch

Temp. (K)

Hc (Oe)

Heb (Oe)

UCT-1 250 oC

1st

60 10

− 570

− 15

UCT-1 250 oC

2nd

60 10

≈0 260

≈0 360

UCT-18 250 oC

1st

60 10

− 500

− 310

UCT-18 250 oC

2nd

60 10

− 400

− 340

UCT-1 550 oC

1st

60 10

7 21

14 130

UCT-18 550 oC

1st

60 10

− 52

− 47

33



Table of Content Graphic

34


Page 34 of 34

Comprehensive Magnetic Study of Nanostructured Mesoporous

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