Weakly Ferromagnetic Ordered Mesoporous Co₃O₄ Synthesized by Nanocasting from Vinyl‐Functionalized Cubic Ia3d Mesoporous Silica

Abstract

Mesostructured metal oxides whose framework structures are engineered from materials other than silica make attractive research subjects. However, direct synthesis of these kinds of mesoporous materials using surfactants is quite difficult because, compared to silica, the surfactant/oxide composite precursors are often more susceptible to lack of condensation, redox reactions, or phase transitions accompanied by thermal breakdown of the structural integrity.[1] The nanocasting method for carbon, [2] pioneered by the group of Ryoo, [3] is an attractive alternative to the cooperative assembly routes, but using it to prepare non-carbon frameworks seems to be difficult. Previously, focus has mainly been on the creation of noble-metal replicas of small sections of the pore systems, which are then used to visualize their connectivity. [4] In this work we have explored the possibility of synthesizing frameworks of novel composition using silica-based templates. Spinel-type cobalt oxide (Co 3 O 4 ) was selected as a model because it is potentially useful for applications in catalysis, sensors, magnetic materials, and energy storage. For instance, Poizot et al. [5] proposed nanometer-sized transition-metal oxides as a new class of anode materials for lithium-ion batteries. Among them, cobalt oxides demonstrated the best electrochemical properties as lithium storage materials in lithiumion cells. Zhao's group has recently been successful in using microwave-digested (MWD) mesoporous silica (specifically, the two-dimensional hexagonal mesoporous silica, SBA-15, and the three-dimensional caged mesoporous silica, SBA-16) to synthesize nanowires and nanospheres of different metal oxides.[6] We show here that it is possible to create cubic Ia3dCo 3 O 4 using vinyl-functionalized, ordered, mesoporous silica [7] as a template, and demonstrate that the bulk antiferromagnet shows weak ferromagnetism at low temperatures. Following the synthesis procedure given in the Experimental section, a mesoscopically ordered array of Co 3 O 4 was obtained. Figure 1a shows the low-angle X-ray diffraction COMMUNICATIONS

Fabrication of mesoporous Co3O4 oxides by acid treatment and their catalytic performances for toluene oxidation

“…Bruce's work also confirmed that mesoporous Co 3 O 4 , Cr 2 O 3 , Fe 2 O 3 , Mn 2 O 3 , and Mn 3 O 4 catalysts exhibited high catalytic reactivity for CO oxidation [22]. Transition metal oxides are more susceptible to hydrolysis, redox or phase transition reactions, and they simultaneously possess different coordination modes as well as multiple oxidation states, hence, it is difficult to obtain their mesoporous structures [23][24][25][26][27][28]. Modified approaches such as the use of soft or hard templates, hydrothermal or microemulsion strategies have been reported for the synthesis of mesoporous materials [21,25,[29][30][31].…”

Magnetic Nanoparticles: Synthesis, Protection, Functionalization, and Application

“…[31][32][33][34] Since this situation effectively corresponds to the presence of a ferromagnet in close proximity to an antiferromagnet, additional effects, such as exchange bias, can result (see Section 2.2.2).…”

Nanocasting Synthesis of Mesostructured Co3O4 via a Supercritical CO2 Deposition Method and the Catalytic Performance for CO Oxidation

“…However, bulk Co 3 O 4 usually possesses a low surface area (*20 m 2 /g) which is unfavorable to its applications either as a catalyst or as a catalyst support. Mesoporous Co 3 O 4 , on the other hand, possessing the advantages of large surface areas ([100 m 2 /g) and tunable pore structures, has attracted much attention both in material science and in catalysis [10][11][12][13][14][15]. It has been shown that mesoporous Co 3 O 4 exhibited much better catalytic performance than bulk Co 3 O 4 in CO oxidation [15,16] and in VOC removal [13].…”