Article pubs.acs.org/JPCC
Multiscale Investigation of a Bioresidue as a Novel Intercalant for Sodium Montmorillonite Ellie H. Fini,*,† Bjarke Høgsaa,‡ Jesper de Claville Christiansen,‡ Catalina-Gabriela Sanporean,‡ Erik Appel Jensen,‡ Masoumeh Mousavi,† and Farideh Pahlavan† †
North Carolina A&T State University, 1601 East Market Street, Greensboro, North Carolina 27411, United States Materials Science and Engineering Research group, Department of Mechanical and Manufacturing Engineering, Aalborg University of Denmark, Fibigerstraede 16, 9220 Aalborg East, Aalborg, Denmark
‡
S Supporting Information *
ABSTRACT: This paper investigates the efficacy of a novel bioresidue (made from biomass) for organic modification of sodium montmorillonite clay. To this end, montmorillonite was biomodified using a solution-intercalation processing technique. The results of experiments, carried out using techniques of XRD, FTIR, TGA, and oscillatory rheometry, showed that strong interactions exist between certain molecular species of bioresidue (e.g., amide and carboxyl groups) and silicate platelets of montmorillonite clay, leading to a highly intercalated clay structure. An atomic-level analysis using density functional theory (DFT) was also employed to study the effect of the bioresidue’s polar functional groups on the basal d-spacing of montmorillonite. On the basis of DFT results, the overall increase in the gallery spacing observed for amide and carboxyl intercalants could be attributed to the ion− dipole and dipole−dipole interactions and, most importantly, reduction in positive charge of the gallery space. This reduction of positive charge promotes the steric repulsive interactions between the montmorillonite layers that is manifested in an increase of the basal d-spacing.
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INTRODUCTION
have enabled scientists to design materials with tailored properties.5,12−17 Sarrier et al. demonstrated that the long-chain fatty acids octadecanoic acid and dodecanaoic acid, pretreated with sodium salts, could be used as stable low-cost surfactants for organic modification of sodium montmorillonite (Na-MMT).18 In another study conducted by Rooj et al., MMT was intercalated with long-chain fatty acids with different lengths of carbon atoms; it was documented that the polar carboxyl group (−COOH) of the fatty acids was attracted to the backbone of the modified montmorillonite, causing the nonpolar chain to intercalate into the clay gallery spacing. This in turn led to an expansion of the gallery spacing.19 They further reported that fatty acids with the longer carbon chains led to higher interlayer expansion.19 A drawback to the utilization of long-chain fatty acids as surfactants is the relatively high degradation rate of fatty acids by clay catalysts, which negatively impacts the thermal stability of the resulting organoclay. Amides are among other functional groups that can promote dipole−dipole interactions with hydroxyl groups of Na-MMT.
The silicate-layered structure of montmorillonite (MMT) with its high surface area and particular cation-exchange capacity has turned it into a proper target to be intercalated by water and small organic molecules. Almost all MMT-modification methods are engineered based on the expansive nature of MMT nanoclay. Introducing the alkyl ammonium cations into MMT interlayers and replacing the small exchangeable cations, and consequently expansion of the basal spacing, is among the MMT-modification approaches which has been thoroughly examined.1−5 Most recently, functionalization of MMT nanoclay by polar organic compounds to modify the physicochemical properties of MMT and render novel environmentally friendly forms of nanoclay particles has received attention from several scientists.6−8 A plausible mechanism for the expansion of MMT-interlayer spacing under the influence of polar/ionic compounds is through promotion of dipole/ion−dipole interactions between the silicon oxide groups of the nanoclay and functional groups of the modifier (such as hydroxyl, carboxyl, amine, and amide).9−11 Fortunately, the recent increase in computing power and modern simulation techniques not only have provided a better insight into the nature of prevalent interactions in laminar composites, but also © XXXX American Chemical Society
Received: November 28, 2016 Revised: January 1, 2017 Published: January 2, 2017 A
DOI: 10.1021/acs.jpcc.6b11966 J. Phys. Chem. C XXXX, XXX, XXX−XXX
Article
The Journal of Physical Chemistry C
Montmorillonite. Cloisite Na+, a commercial natural sodium montmorillonite, was acquired from Southern Clay Products Inc. The clay had an average dry particle size (d50) of
