Poly(ethylene oxide)-Poly(butylene oxide)-Poly(ethylene oxide)- Templated Synthesis of Mesoporous Alumina: Effect of Triblock Copolymer and Acid Concentration Kelly L. Materna, Stacy M. Grant, and Mietek Jaroniec* Department of Chemistry and Biochemistry, Kent State University, Kent, Ohio 44242, United States ABSTRACT: Mesoporous alumina was synthesized via a one-pot self- assembly of aluminum isopropoxide and poly(ethylene oxide)-poly(butylene oxide)-poly(ethylene oxide) triblock copolymer in an acidic ethanol solution. The effects of the polymer concentration and nitric acid concentration, independently, on the adsorption properties (such as surface area, pore volume, microporosity, mesoporosity, and pore width) were studied. An increase in the specific surface area and the pore volume was seen for the samples containing a polymer/aluminum isopropoxide wt. ratio up to 0.71 and a polymer/acid wt ratio of 0.88. Titania isopropoxide was also added to the synthesis to illustrate the extension of this approach to alumina-based mixed metal oxides. KEYWORDS: mesoporous alumina, metal oxides, soft-templating, aluminum titanium oxide ■ INTRODUCTION Alumina is commonly used in a variety of applications such as catalysis, 1-4 optical 5 and biomedical 6 purposes, ceramics, 7,8 and adsorption. 9-11 The addition of supplementary metal oxides, such as titania (used extensively in catalysis and photo- catalysis 12,13 ), brings further applications to these materials. Titania-alumina materials can be used in automotives and aeronautics, 14 dental implants and orthopedics, 15 and the decontamination of chemical warfare agents. 16 Therefore, control of the properties such as surface area, pore width and porous structure of these materials, has attracted much attention. Mesoporous alumina (MA) has been synthesized through several routes, including the sol-gel method, 17,18 nonionic templating, 19 a reverse cation-anion double hydrol- ysis method (CADH), 20 and evaporation-induced self-assembly (EISA) with block copolymers. 21,22 Among various synthesis routes, the templating methods, especially those involving self- assembly, are particularly interesting because they allow for achieving high surface area of alumina samples and for tuning their porosity and surface properties. 2 A detailed comparison of different methods used for synthesis of templated mesoporous aluminas is presented in recent review, 2 which contains several tables listing experimental conditions and properties of these materials. Niesz et al. reported a breakthrough in the block copolymer- templated synthesis of ordered mesoporous alumina (OMA) by showing the possibility of obtaining highly ordered alumina but at strict experimental conditions. 23 More recently, much attention has been directed toward block copolymer-templating synthesis because some of these polymers such as poly- (ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) [(EO) n (PO) m (EO) n ] known as Pluronics are inexpensive, biodegradable, commercially available and produce materials with large and uniform mesopores. 24 Another triblock copolymer, poly(ethylene oxide)-poly(butylene oxide)-poly- (ethylene oxide), Vorasurf 504 (EO) 38 (BO) 46 (EO) 38 , has been used in the synthesis of FDU-1 mesoporous silica producing siliceous materials with high surface areas (<714 cm 3 /g) 25 and mesoporous alumina in a revised EISA synthesis, producing disordered materials with surface areas equal to 300 cm 3 /g. 26 In addition, adjustment of the acid concentration in a one- pot triblock copolymer-templated synthesis of mesoporous alumina permitted a good control of its structural parameters; 27 in this synthesis Pluronic P123 triblock copolymer (EO) 20 (PO) 70 (EO) 20 was used and the nitric acid concen- tration was varied to determine the effect acid concentration on the materials’ adsorption characteristics. It was reported that the optimal range of nitric acid for the synthesis of mesoporous alumina with high surface areas (up to 467 m 2 /g) and pore volume (0.74 cm 3 /g) was 1.2-3.0 mols per one mol of aluminum isopropoxide; 27 this superior characteristics of mesoporous alumina stimulated us to study the acid concentration effect for another block copolymer template such as (EO) 38 (BO) 46 (EO) 38 . This block copolymer has almost twice longer poly(ethylene oxide) blocks than those in Pluronic P123 but its middle block, poly(butylene oxide), is more hydrophobic than poly(propylene oxide) block in the Received: May 15, 2012 Accepted: June 15, 2012 Published: June 15, 2012 Research Article www.acsami.org © 2012 American Chemical Society 3738 dx.doi.org/10.1021/am3008642 | ACS Appl. Mater. Interfaces 2012, 4, 3738-3744