Research Article www.acsami.org
Sustainable Mesoporous Carbons as Storage and Controlled-Delivery Media for Functional Molecules Dipendu Saha,† E. Andrew Payzant,‡ Amar S. Kumbhar,§ and Amit K. Naskar*,† †
Carbon and Composites Group, Materials Science and Technology Division, and ‡Chemical & Engineering Materials Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States § Institute for Advanced Materials, NanoScience and Technology, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, United States S Supporting Information *
ABSTRACT: Here, we report the synthesis of surfactanttemplated mesoporous carbons from lignin, which is a biomass-derived polymeric precursor, and their potential use as a controlled-release medium for functional molecules such as pharmaceuticals. To the best of our knowledge, this is the first report on the use of lignin for chemical-activation-free synthesis of functional mesoporous carbon. The synthesized carbons possess the pore widths within the range of 2.5−12.0 nm. In this series of mesoporous carbons, our best result demonstrates a Brunauer−Emmett−Teller (BET) surface area of 418 m2/g and a mesopore volume of 0.34 cm3/g, which is twice the micropore volume in this carbon. Because of the dominant mesoporosity, this engineered carbon demonstrates adsorption and controlled release of a representative pharmaceutical drug, captopril, in simulated gastric fluid. Large-scale utilization of these sustainable mesoporous carbons in applications involving adsorption, transport, and controlled release of functional molecules is desired for industrial processes that yield lignin as a coproduct. KEYWORDS: mesoporous carbon, lignin, soft-templating, drug delivery, sustainable materials template” technique has been developed.9−15 In it, mesoporous carbon is synthesized by cross-linking organic resins in the presence of some sacrificial surfactants, followed by pyrolysis, leading to removal of the surfactant and carbonization in the same step. Amphiphilic block copolymeric surfactants form selfassembled structures of micelles as a consequence of repulsive interactions between the covalently bonded polymer segments.16 One segment interacts with resin and forms a miscible system, while the other phase tends to form nanometer-sized immiscible domains in the precursor resin matrix. The majority of the precursors employed to synthesize mesoporous carbons are phenolic resins such as cross-linked phenol,9−11 resorcinol,12,13 phloroglucinol,7,14 and hexaphenol.15 These resins form a very strong hydrogen bond between phenolic hydroxyl groups and the miscible segment of the surfactant macromolecule. Lignin, the third most abundant natural polymer next to cellulose and chitin, contains an abundance of aliphatic and phenolic hydroxyl groups. Although lignin-based activated
1. INTRODUCTION Lignin has a wide range of uses, as a low-value fuel, a dispersing agent for chemicals, a modifier for polymers, and a precursor for activated carbon. Activated carbon produced from lignin does not exhibit controlled mesoporosity; usually, microporosity (pore width
