Article pubs.acs.org/cm
Amphiphilic Block Copolymer Templated Synthesis of Mesoporous Indium Oxides with Nanosheet-Assembled Pore Walls Yuan Ren,† Xinran Zhou,† Wei Luo,‡ Pengcheng Xu,∥ Yongheng Zhu,†,§ Xinxin Li,∥ Xiaowei Cheng,† Yonghui Deng,*,†,∥ and Dongyuan Zhao† †
Department of Chemistry, State Key Laboratory of Molecular Engineering of Polymers, Shanghai Key Laboratory of Molecular Catalysis and Innovative Materials, iChEM (Collaborative Innovation Center of Chemistry for Energy Materials), Fudan University, Shanghai 200433, China ‡ College of Materials Science and Engineering, Donghua University, Shanghai 201620, China § College of Food Science and Technology, Shanghai Ocean University, Shanghai 201306, China ∥ State Key Lab of Transducer Technology, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, Shanghai 200050, China S Supporting Information *
ABSTRACT: A solvent evaporation induced coassembly approach combined with a comburent CaO2-assisted calcination strategy was employed for the synthesis of ordered mesoporous indium oxides by using lab-made high-molcular weight amphiphilic diblock copolymer poly(ethylene oxide)-b-polystyrene (PEO-b-PS) as a template, indium chloride as an indium source, and THF/ethanol as the solvent. The obtained mesoporous indium oxide materials exhibit a large pore size of ∼14.5 nm, a surface area of 48 m2 g−1, and a highly crystalline In2O3 nanosheets framework, which can facilitate the diffusion and transport of gas molecules. By using an integrated microheater as the chemresistance sensing platform, the obtained mesoporous indium oxides were used as sensing materials and showed an excellent performance toward NO2 at a low working temperature (150 °C) due to their high porosity and unique crystalline framework. The limit of detection (LOD) of the microsensor based on mesoporous indium oxides can reach a concentration as low as 50 ppb of NO2. Moreover, the microsensor shows a fast response-recovery dynamics upon contacting NO2 gas and fresh air due to the highly open mesoporous structure and the large mesopores of the crystalline mesoporous In2O3. tures, and special optical, electronic properties.10−16 Compared to their counterparts with solid structure, metal oxide semiconductors with porous structure, especially mesoporous structure, have attracted considerable research interest.17−21 However, it remains a great challenge to synthesize mesoporous metal oxides with the crystalline framework by using commercial amphiphilic surfactants triblock copolymers as templates,22,23 for the two well-known reasons. One is that the hydrolysis and condensation of their precursors (usually salts or alkoxides) is very fast and difficult to control. The other is that, during calcination for removal of the template or posttreatment for crystallization of the pore wall, metal oxides usually undergo an intense reorganization, which results in an undesired collapse of mesostructures. Particularly, the synthesis of mesoporous transition metal oxides such as ZnO, In2O3, Fe2O3, and NiO remains particularly challenging due to their relative lower crystallization temperature (300−400 °C).24 Recently, Wiesner and co-workers reported mesoporous Nb2O5
1. INTRODUCTION Ever since the discovery by Mobil researchers, ordered mesoporous materials (OMMs) have been receiving everincreasing research interest in multidisciplinary fields covering chemistry, materials, biomedicine, physics, etc.1−6 OMMs are a kind of porous materials with a pore size of 2.0−50 nm which are aligned in two- or three-dimensional arrays throughout the materials. Their synthesis is usually accomplished by coassembly of surfactant molecules or amphiphilic block copolymers (i.e., the template molecules or structure directing agent) and specific inorganic/organic precursors through molecular interaction in sol−gel chemistry, followed by the cosolidification of the nanocomposites and the removal of template molecules via calcination or solvent extraction.7−9 The resultant mesoporous materials have outstanding physicochemical properties, including tunable pore size, high surface area, large pore volume, and controllable framework composition, which endow them with great application potential in fields such as catalysis, adsorption, controlled release, fuel cell, sensor, and electrode materials. Semiconducting metal oxide nanomaterials have been extensively studied in various fields including catalysis, sensing, energy storage for unique micro-, nanostruc© 2016 American Chemical Society
Received: September 3, 2016 Revised: October 16, 2016 Published: October 19, 2016 7997
DOI: 10.1021/acs.chemmater.6b03733 Chem. Mater. 2016, 28, 7997−8005
Article
Chemistry of Materials
micelles; while the most widely used Pluronic copolymers suffer drawbacks of low glass transition temperature (
