Rick C. Schroden

Hybrid Inorganic–Organic Mesoporous Silicates—Nanoscopic Reactors Coming of Age

This review describes methods of preparing hybrid inorganic–organic mesoporous silicates with uniform channel structures, as well as some of their applications. Both reactive and passive organic groups can be incorporated in the porous solids by grafting methods or by co-condensation under surfactant control. Functional groups have been placed selectively on the internal or external pore surfaces or even within the walls of the mesoporous solids. Organic functionalization of these solids permits tuning of the surface properties (hydrophilicity, hydrophobicity, binding to guest molecules), alteration of the surface reactivity, protection of the surface from attack, and modification of the bulk properties (e.g., mechanical or optical properties) of the material. Recent applications of hybrid mesoporous silicates are highlighted, including catalysis, sorption of metals, anions, and organics, reactors for polymerization, fixation of biologically active species, and optical applications.

Colloidal crystal templating of three-dimensionally ordered macroporous solids: materials for photonics and beyond

Abstract This review discusses strategies for the synthesis of three-dimensionally ordered macroporous (3DOM) solids (inverse opals) by colloidal crystal templating. Compositions of 3DOM structures include simple and ternary oxides, chalcogenides, non-metallic and metallic elements, hybrid organo-silicates, and polymers. A wide range of 3DOM synthesis techniques, including sol–gel chemistry, polymerization, salt-precipitation and chemical conversion, chemical vapor deposition, spray pyrolysis, ion spraying, laser spraying, nanocrystal deposition and sintering, oxide and salt reduction, electrodeposition, electroless deposition, fabrication from core-shell spheres, and patterning methods, as well as templating using inverse opal molds to produce new opal compositions are reviewed. Potential uses of 3DOM solids, including photonic crystal, optical, catalytic, and bioglass applications are briefly discussed.

Hybrid macroporous materials for heavy metal ion adsorption

Hybrid macroporous materials with thiol functional groups attached to titania and zirconia frameworks have been prepared via colloidal crystal templating techniques for use as heavy metal ion adsorbents. Synthesis procedures are described for the preparation of thiol–metal oxide materials containing either siloxane or sulfonate linkages. The hybrid macroporous materials were characterized by SEM, FT-IR, 29Si MAS NMR, elemental analysis, and nitrogen adsorption. The materials contained high levels of chemically anchored thiol groups and had uniform porous structures. The hybrid macroporous materials were effective adsorbents for the removal of heavy metal ions from solution, with adsorption capacities ranging from 0.33 to 1.41 mmol g−1 for mercury(II) ions and 0.27 to 1.24 mmol g−1 for lead(II) ions. The hybrid materials remained effective for metal ion adsorption after regeneration by an acid wash, with metal ion loading capacities of the recycled materials being on average two-thirds that of the original capacities. The metal ion adsorption capacity and reusability of hybrid macroporous materials makes them promising adsorbents for wastewater cleanup.

Designing Porous Solids over Multiple Pore Size Regimes

This chapter highlights some of the recent synthetic approaches to inorganic solids (especially silicates) with designed porosity on multiple levels, covering pore size ranges from a few Angstroms (micropores) through two to tens (mesopores) and hundreds (macropores) of nanometers. To achieve controlled porosity in these size regimes, molecular structure directors, supramolecular arrays of surfactants, block copolymers, emulsions, colloidal crystals, bacteria and porous carbon have been used as templates. Hierarchical porosity with bimodal or higher pore size distributions can be attained by employing combinations of these methods in multi-template processes.