Kinetics of Interlayer Expansion of a Layered Silicate Driven by Caffeine Intercalation in the Water Phase Using Transmission X-ray Diffraction

Abstract

The kinetics of caffeine uptake into the interlayer nanospace of silicate nanosheets modified with benzylammonium (BA) was evaluated by in situ monitoring the basal spacing in aqueous media using transmission X-ray diffraction. An interlayer spacing of 0.58 nm in water before caffeine uptake indicates a monomolecular layer of BA and a few water layers in each interlayer. The interlayer space expanded by 0.10 nm upon caffeine uptake (intercalation) and saturated even in the presence of excess caffeine. Time-course profiles of the interlayer spacing and the uptake amount after injection of caffeine into the water slurry were obtained. At the initial period, the plot for the basal spacing was located above that for the adsorbed amount, suggesting that the rate of the interlayer spacing change was faster than that to attain the adsorption equilibrium. A first-order kinetic simulation fitted to the profile also indicates that the basal spacing included a rapid expansion of 0.08 nm within a few minutes and a slow expansion of 0.02 nm over several hours. Regarding the slow component, the rate constant for the basal spacing was lower than that for the amount of caffeine adsorbed, meaning that a steady-state basal spacing is reached after the adsorption equilibrium.

Important Roles of Water Clusters Confined in a Nanospace as Revealed by a Synchrotron X-ray Diffraction Study

“…The basal spacing was linearly increased with the amount of adsorbed caffeine (d 001 = 0.14W + 1.52 nm, r 2 = 0.95), as previously reported for caffeine uptake on BA−KF. 48 The adsorbed amounts of caffeine (mmol/g) are stated in Figure 2b. Clearly, interlayer expansion was triggered by the intercalation of caffeine molecules.…”

“…Assuming that the change in basal spacing involves both rapid (d rapid ) and slow (d slow ) components, 48 we fitted the time-course plots obtained at different initial concentrations to first-order relaxation kinetics (see Figure 4b). Specifically, the time-course profile eq 4-1 was fitted by a double exponential (DE), described as the weighted sum of two first-order equations describing the kinetics of d rapid and d slow (eqs 4-2 and 4-3, respectively):…”

“…To this end, we perform structural characterization by conventional powder X-ray diffraction (c-XRD) and synchrotron radiation powder X-ray diffraction (SXRD) , and analyze the thermodynamics of the diffusionally averaged structure of water nanolayers (ordered water layers with the most probable molecular configuration) using humidity-controlled SXRD and water-vapor adsorption isotherms. As the interlayer expands very rapidly (within a few minutes to attain a steady state), we examined the caffeine intercalation kinetics using time-resolved SXRD ( t -SXRD) with high temporal resolution (minimum time = 50 ms) . Consequent to a survey on the presence of water over short time scales, we will gain better insight into the observed ordinary adsorption/intercalation phenomena for neutral polar organic molecules in 2D charged nanosheets in the aqueous phase.…”

Caffeine vehiculation into alpha-zirconium phosphate: a multifunctional intercalation product and its application for modified topical release

“…The water molecules are located in the zeolitic cavities of the interlayer region 21 . In the past, several authors have reported that caffeine can be successfully intercalated in lamellar solids reaching interesting goals [22][23][24][25][26][27]28 . Herein we report the first intercalation of CAF on ZrP, obtaining an intercalation product that has been successfully used to prepare a stable emulsion.…”

Direct Crystallization of Layered Silicates on the Surface of Amorphous Silica

“…The adsorptive properties of layered inorganic solids (interlayer space of the nanosheets) are of our currently research interests . The smectite group of layered clay minerals is, in particular, established host materials as molecular recognizable adsorbents by modifying the interlayer space (e. g., pillaring, organophilic modification), of the silicate layers (1 nm‐thickness in each) owing to their swelling and cation‐exchange abilities. Controlled morphology (particle size distribution and shape) is also a viewpoint to be focused on enhancing material's applicability.…”