Recent Advances in Processing and Characterization of Periodic Mesoporous MCM-41 Silicate Molecular Sieves

Abstract

The discovery of periodic mesoporous MCM-41 and related molecular sieves has attracted significant attention from a fundamental as well as applied perspective. They possess well-defined cylindrical/hexagonal mesopores with a simple geometry, tailored pore size, and reproducible surface properties. Hence, there is an ever-growing scientific interest in the challenges posed by their processing and characterization and by the refinement of various sorption models. Further, MCM-41-based materials are currently under intense investigation with respect to their utility as adsorbents, catalysts, supports, ion-exchangers, and molecular hosts. In this article, we provide a critical review of the developments in these areas with particular emphasis on adsorption characteristics, progress in controlling the pore sizes, and a comparison of pore size distributions using traditional and newer models. The model proposed by the authors for adsorption isotherms and criticalities in capillary condensation and hysteresis is found to explain unusual adsorption behavior in these materials while providing a convenient characterization tool.

Template-Based Synthesis of Nanoporous Hydroxyapatite

“…Surfactant-templated mesoporous materials have some specific features such as high surface areas and high adsorption capacities including the uniformity and periodicity of tunable mesopores [9][10][11], which are widely applicable to adsorbents and catalytic supports [12][13][14][15][16][17][18].…”

Coherent anti-Stokes Raman scattering microscopy for pharmaceutics

“…Figure 2 outlines schematically these formulation strategies; it is apparent that the basis of these stabilization strategies is physical separation with the API molecules separated from each other, thereby preventing crystallization. In some cases it has been shown that there is also a chemical interaction between the API and the excipients involved in the formulation [11].…”

“…However, a soliddispersion carrier is typically a large molecule such as a polymer or bile salt while a co-amorphous co-former is typically a small molecule such as citric acid [8], amino acids [15], and other drug molecules [7,11,16]. Methods used to prepare the coamorphous mixtures also vary with mechanical activation by cryo-milling the most common method used followed by quench cooling of the melt [14].…”

“…The amorphous form is a thermodynamically high energy state and has a tendency to crystallize which is a drawback for the drug development process. There is a large area of research in the field of amorphous form stabilization including solid dispersions [10,11], co-amorphous mixtures [12,13] and drug loaded silica [14,15] and silicon particles [16,17]. CARS microscopy is a third order non-linear optical imaging technique that probes the same molecular vibrational frequencies as spontaneous Raman scattering.…”

“…This is because standard dissolution techniques require the immersion of the drug (e.g. as a compact) in a flowing dissolution medium with samples of the dissolution medium removed and analyzed for dissolved drug concentration using UV absorption spectroscopy or HPLC [11].…”