Self-Assembly Mechanism of Folate-Templated Mesoporous Silica Rambabu Atluri, † Muhammad Naeem Iqbal, † Zoltan Bacsik, ‡ Niklas Hedin, ‡ Luis Angel Villaescusa, §,∥ and Alfonso E. Garcia-Bennett* ,⊥ † Nanologica AB, Drottning Kristinas Vä g 61, SE-114 28 Stockholm, Sweden ‡ Department of Materials and Environmental Chemistry, Berzelii Center EXSELENT on Porous Materials, Arrhenius Laboratory, Stockholm University, SE-106 91 Stockholm, Sweden § Departamento de Química, Universidad Polite ́ cnica de Valencia, Camino de Vera s/n, 46022 Valencia, Spain ∥ Centro de Reconocimiento Molecular y Desarrollo (IDM), Unidad Mixta Universidad Polite ́ cnica de Valencia−Universidad de Valencia, Camino de Vera s/n, 46022 Valencia, Spain ⊥ Department of Materials and Environmental Chemistry, Arrhenius Laboratory, Stockholm University, SE-106 91 Stockholm, Sweden * S Supporting Information ABSTRACT: A method to form ordered mesoporous silica based on the use of folate supramolecular templates has been developed. Evidence based on in situ small-angle X-ray scattering (SAXS), electron microscopy, infrared spectroscopy, and in situ conductivity measurements are used to investigate the organic−inorganic interactions and synthesis mechanism. The behavior of folate molecules in solution differs distinctively from that of surfactants commonly used for the preparation of ordered mesoporous silica phases, notably with the absence of a critical micellar concentration. In situ SAXS studies reveal fluctuations in X-ray scattering intensities consistent with the condensation of the silica precursor surrounding the folate template and the growth of the silica mesostructure in the initial stages. High-angle X-ray diffraction shows that the folate template is well-ordered within the pores even after a few minutes of synthesis. Direct structural data for the self-assembly of folates into chiral tetramers within the pores of mesoporous silica provide evidence for the in register stacking of folate tetramers, resulting in a chiral surface of rotated tetramers, with a rotation angle of 30°. Additionally, the self-assembled folates within pores were capable of adsorbing a considerable amount of CO 2 gas through the cavity space of the tetramers. The study demonstrates the validity of using a naturally occurring template to produce relevant and functional mesoporous materials. ■ INTRODUCTION Non-covalent interactions (e.g., hydrogen-bonding and aro- matic interactions) are of fundamental importance in the preparation of organic−inorganic supramolecular and macro- molecular structures. 1−3 Such interactions play a powerful role in biological systems, such as for example in the hydrogen- bonded base pairs of DNA and RNA and their supramolecular structures. Investigating these types of interactions continues to provide useful information to understand complex biological mechanisms, such as cellular receptor recognition or enzymatic reactions. Additionally, these studies also offer a justifiable route for the preparation of functional porous materials, relying on the specific character of hydrogen bonding. Of particular interest to this work are organic self-assembling structures capable of forming ordered motives of different dimensionalities in solution, because these may act as suitable structure-directing agents or templates for the formation of ordered inorganic materials with properties that are qualita- tively different from those synthesized by non-templated routes. After removal of an organic template, it is often possible to reveal a high-surface-area material with controllable textural properties for its use in a wide ranging number of applications, such as in catalysis, as adsorbents or drug delivery vehicles, and in dye inclusion or sensors. 4,5 This templating route has been demonstrated over the last few decades through the preparation of mesoporous silica and other metal oxide materials. Self- assembling amphiphilic surfactants are used to control the structural, textural, and morphological properties of meso- porous solid products with a large porous structural diversity. 6 Often co-structure-directing agents (CSDAs) may be added to promote the interaction between the template and the silica walls, for example, (3-aminopropyl)triethoxysilane (APTES). 7,8 Such silica precursors allow for the further fine-tuning of the synthesis of new mesoporous structures and their surface and textural properties. 9 Received: April 26, 2013 Revised: August 23, 2013 Article pubs.acs.org/Langmuir © XXXX American Chemical Society A dx.doi.org/10.1021/la401532j | Langmuir XXXX, XXX, XXX−XXX