Mesoporous Materials Controlled Synthesis of Highly Crystallized Mesoporous Mn 2 O 3 and Mn 3 O 4 by Using Anionic Surfactants Palani Raja Jothi, [a, b] Malay Pramanik,* [a] Cuiling Li, [a] Shanthi Kannan, [b] Victor Malgras, [a] Rahul R. Salunkhe, [a] and Yusuke Yamauchi* [a] Abstract: Mesostructured manganese oxide (Mn 3 O 4 ) is prepared by a soft-templating method employing sodium dodecyl sulfate (SDS) as a structure-directing agent. By re- moving the template from the as-prepared mesostruc- tured Mn 3 O 4 by extraction or calcination, we successfully synthesized highly crystallized mesoporous Mn 3 O 4 or Mn 2 O 3 , respectively, with different crystalline structures. Introduction The synthesis of mesoporous multivalent transition metal oxides (TMOs) with crystalline pore-wall has recently gained immense attention due to their unique properties applicable to catalysis, adsorption, sensors, and energy storage/conver- sion devices. [1–5] The crystalline mesoporous TMOs generally show promising electronic, optical, thermal, and photonic properties which cannot be achieved by other traditional mes- oporous materials (e.g., silica, carbon, metal). [6–8] Generally, two conventional synthetic methods (hard- and soft-templating) have been employed to prepare mesoporous TMOs. [9, 10] These above-mentioned techniques are relatively difficult and remain challenging due to the different coordination numbers and multivalent oxidation states of transition metals. [4, 11, 12] Manganese (Mn) oxides are considered as one of the most studied TMOs because of their unique characteristic features in various catalytic reactions. [13–15] The synthesis of mesoporous Mn oxides is much more complicated due to the existence of various stable oxidation states and different thermodynamical- ly stable polymorphs. [15, 16] There are only a few reports on the successful synthesis of mesoporous Mn oxides with crystalline pore-walls because the synthetic conditions are easily affected by the atmospheric conditions. Under atmospheric conditions, the oxidation state of manganese is generally not particularly set and can adopt various values. [17] It is well known that the soft-templating method leads to the successful formation of a mesophase which mainly depends on charge-density match- ing between the surfactant and the inorganic species. [1, 18] The mixed valence states of manganese, however, make it difficult to control the interaction between the inorganic precursors and the micelles. [19] For these reasons, most of the reported ordered mesopo- rous Mn oxides have been synthesized through the hard-tem- plating method. [4, 5, 20, 21] This method has some severe limita- tions due to its complicated and time-consuming synthetic process. [22] Only a few reports are available on mesoporous manganese oxides synthesized by a soft-templating strategy. Suib et al. prepared Mn oxide with a mesoporous structure by using a cetyltrimethylammonium bromide (CTAB) template under atmospheric conditions. [17] The same group also report- ed the synthesis of a crystalline/amorphous mesoporous man- ganese oxide using nonionic Pluronic P123 as structure-direct- ing agent. [19, 23] Until now, the soft-template synthesis of meso- porous Mn oxide have utilized only cationic or non-ionic sur- factants. [17, 19] It is believed, however, that the successful forma- tion of the mesostructure can be achieved through the interactions taking place between the negatively charged head group of the surfactants and the positively charged inorganic Mn precursors. Our target is to synthesize mesoporous Mn oxide with a single valence state by using an anionic surfac- tant. In this study, we synthesize mesostructured Mn 3 O 4 with crys- talline pore-walls through a one-step hydrothermal method using an anionic surfactant, sodium dodecyl sulfate (SDS), as a structure-directing agent. The organic template is removed from the mesostructured Mn 3 O 4 by extraction or a calcination process. When the mesostructured manganese oxide is cal- cined under atmospheric conditions, the Mn 3 O 4 phase is suc- cessfully converted into Mn 2 O 3 while maintaining the parent mesostructure. As mentioned above, several mesoporous Mn oxide materials have been reported, but in almost all cases the Mn oxides have mixed crystalline phases and the pore walls are not perfectly crystallized in a single phase. [17, 19, 23] Therefore, it is believed that the preparation of a single-phase crystallized mesoporous Mn oxide in an easy and economical way is a great achievement. Under our present synthetic conditions, [a] P.R. Jothi, Dr. M. Pramanik, Dr. C. Li, Dr. V. Malgras, Dr. R. R. Salunkhe, Prof. Y. Yamauchi World Premier International (WPI) Research Centre for Materials Nanoarchi- tectonics (MANA) National Institute for Materials Science (NIMS) 1-1 Namiki, Tsukuba, Ibaraki 305-0044 (Japan) E-mail : Pramanik.Malay@nims.go.jp Yamauchi.Yusuke@nims.go.jp [b] P. R. Jothi, Prof. S. Kannan Department of Chemistry Anna University Chennai 600 025 (India) Supporting information for this article is available on the WWW under http ://dx.doi.org/10.1002/asia.201501296. Chem. Asian J. 2016, 11, 667 – 673 # 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 667 Communication DOI: 10.1002/asia.201501296