Surface structure of organoclays as examined by X-ray photoelectron spectroscopy and molecular dynamics simulations

Abstract

Organoclays are sorbent materials prepared from clays by exchanging inorganic with organic cations. Their properties depend on the loading and conformational structure of the organic cations, but little information is available about the surface structures of organoclays. In this work, X-ray photoelectron spectroscopy (XPS) and classical molecular dynamics (MD) simulations are combined to characterize the external interface of an organoclay prepared from hexadecylpyridinium (HDPy+) and bentonite. The XPS survey spectra show well the varying elemental composition of the surface with increasing amount of surfactant, showing a decreasing contribution of clay-derived elements with increasing organic coverage. The high-resolution C 1s XPS spectra depict sensitively the surface arrangement of the surfactant. In combination with MD simulations, the results implied a monolayer coating for low surfactant coverage and a disordered bilayer arrangement at high surfactant uptakes. Molecular dynamics simulations showed that for very high cation uptake a quasi-paraffin-like configuration is also possible. The combination of experimental and modelling methods yielded congruent information on the molecular-scale arrangement of organic cations at the organoclay surfaces and the controlling mechanisms.

The multilayer model of soil mineral–organic interfaces—a review

“…Computer modeling is useful in investigating the three-dimensional structure of soil OM, metal-OM complexes, and MOA, of which the properties like surface area, polarity, and stability can be estimated by minimizing the potential energy of conformations via geometric optimization. Molecular modeling coupled with computational chemistry can help to understand the formation and dynamic process of MOA and the involved mechanisms (Schulten and Leinweber, 2000;Sutton and Sposito, 2006;Schaumann and Thiele-Bruhn, 2011;Schampera et al, 2015Schampera et al, , 2016. However, molecular models only represent a simplified reality.…”

The Interaction between Surfactants and Montmorillonite and its Influence on the Properties of Organo-Montmorillonite in Oil-Based Drilling FluIDS

“…Oxygen is the element most exposed on the surface of Mnt and TOT layers. The C 1s spectra ( Figure 10) of surfactants can be distinguished as two parts: C-C groups corresponding to a binding energy of 284.8 eV and C-N groups corresponding to 285.9 eV (C18) and 286.0 eV (DC18) (He et al, 2007;Schampera et al, 2015).…”

Adsorption Kinetics of Malachite Green and Methylene Blue from Aqueous Solutions Using Surfactant-modified Organoclays

“…18 Clay minerals are appropriate for adsorption process because of their specific surface area and nanometer-scale size. 19 Recent progress in the synthesis of nanostructured materials offers a broader spectrum to change surface properties of naturally occurring clays in order to increase their adsorption properties. The organoclays (OCs) are set up by introducing cationic surfactant molecules (e.g.…”