Well Shaped Mn₃O₄ Nano‐octahedra with Anomalous Magnetic Behavior and Enhanced Photodecomposition Properties

Abstract

Very uniform and well shaped Mn₃O₄ nano-octahedra are synthesized using a simple hydrothermal method under the help of polyethylene glycol (PEG200) as a reductant and shape-directing agent. The nano-octahedra formation mechanism is monitored. The shape and crystal orientation of the nanoparticles is reconstructed by scanning electron microscopy and electron tomography, which reveals that the nano-octahedra only selectively expose {101} facets at the external surfaces. The magnetic testing demonstrates that the Mn₃O₄ nano-octahedra exhibit anomalous magnetic properties: the Mn₃O₄ nano-octahedra around 150 nm show a similar Curie temperature and blocking temperature to Mn₃O₄ nanoparticles with 10 nm size because of the vertical axis of [001] plane and the exposed {101} facets. With these Mn₃O₄ nano-octahedra as a catalyst, the photodecomposition of rhodamine B is evaluated and it is found that the photodecomposition activity of Mn₃O₄ nano-octahedra is much superior to that of commercial Mn₃O₄ powders. The anomalous magnetic properties and high superior photodecomposition activity of well shaped Mn₃O₄ nano-octahedra should be related to the special shape of the nanoparticles and the abundantly exposed {101} facets at the external surfaces. Therefore, the shape preference can largely broaden the application of the Mn₃O₄ nano-octahedra.

Polyetheramide Templated Synthesis of Monodisperse Mn3O4 Nanoparticles with Controlled Size and Study of the Electrochemical Properties

“…Among them, hydrothermal/solvothermal method possesses advantages of mild reaction condition and well-controlled size, morphology and structures, which has been adopted successfully in the synthesis of various nanometer-sized oxides, metals, semiconductors and magnetic compos-ites [14,15].…”

Engineering High‐Energy Interfacial Structures for High‐Performance Oxygen‐Involving Electrocatalysis

“…X-ray photoelectron spectra (XPS) were recorded to check surface and interfacial structures of the materials.T he main peak at 532.1 eV on the O1s XPS spectrum of hi-Mn 3 O 4 ( Figure 2a)isassigned to the lattice oxygen of Mn-O-Mn, and the weak peak might originate from other oxygen species such as Mn-O-H. [15] After coupling with CoO to form CoO/hiMn 3 O 4 ,e xcept the peaks from Mn-O-Mn and Co-O-Co (529.8 eV), [16] another peak centered at 530.9 eV is observed, which is not found on the spectrum of apure CoO and should be associated with interfacial Mn-O-Co species.M oreover, the binding energy of Mn-O-Co species in CoO/hi-Mn 3 O 4 is higher than that in CoO/Mn 3 O 4 ,s uggesting the formation of ah igh-energy interfacial structure.T he binding energy of Co2p 3/2 is 780.3 eV as can be seen on the Co2p spectrum of CoO ( Figure S9), and the spin orbit splitting values between the main peak and its corresponding satellite peak for Co2p 3/2 and Co2p 1/2 are 5.9 and 6.7 eV,respectively,which agrees with the data reported for CoO. [17] After coupling CoO with hi- positively Synchrotron-based near edge X-ray absorption fine structure (NEXAFS) technique was further used to explore the origin of the high-energy structure of CoO/hi-Mn 3 O 4 .The NEXAFS spectra of Mn L-edge that is sensitive to the oxidation state are shown in Figure 2b.B efore deposition of CoO,h i-Mn 3 O 4 presents two groups of peaks,t he peak at 640.2 eV corresponding to Mn II ,a nd the peaks (a 1 and a 2 ) from 641.0 to 643.0 eV for Mn III .…”

2D Atomic Mapping of Oxidation States in Transition Metal Oxides by Scanning Transmission Electron Microscopy and Electron Energy-Loss Spectroscopy

“…Many interesting and unique properties of Mn 3 O 4 warrant its applications in fields like catalysis, molecular adsorption, ion exchange, supercapacitors, magnetic applications and batteries [25][26][27]. The fact that it is a mixed valence compound at room temperature also makes it an ideal candidate to demonstrate valence state mapping at atomic resolution.In this work, 150 nm octahedral single crystals of Mn 3 O 4 were studied using atomic resolution STEM-EELS [25]. The octahedral morphology of the nanocrystals allows a careful selection of the sample thickness, while the minimal presence of an amorphous surface layer enables acquisition of high-contrast images and maps [28].…”

“…It has a spinel structure with lattice parameters a ¼ 5:762 A and c ¼ 9:4696 A and space group I41=amd. Many interesting and unique properties of Mn 3 O 4 warrant its applications in fields like catalysis, molecular adsorption, ion exchange, supercapacitors, magnetic applications and batteries [25][26][27]. The fact that it is a mixed valence compound at room temperature also makes it an ideal candidate to demonstrate valence state mapping at atomic resolution.…”

“…In this work, 150 nm octahedral single crystals of Mn 3 O 4 were studied using atomic resolution STEM-EELS [25]. The octahedral morphology of the nanocrystals allows a careful selection of the sample thickness, while the minimal presence of an amorphous surface layer enables acquisition of high-contrast images and maps [28].…”