A brief history and review of geopolymer technology is presented with the aim of introducing the technology and the vast categories of materials that may be synthesized by alkali-activation of aluminosilicates. The fundamental chemical and structural characteristics of geopolymers derived from metakaolin, fly ash and slag are explored in terms of the effects of raw material selection on the properties of geopolymer composites. It is shown that the raw materials and processing conditions are critical in determining the setting behavior, workability and chemical and physical properties of geopolymeric products. The structural and chemical characteristics that are common to all geopolymeric materials are presented, as well as those that are determined by the specific interactions occurring in different systems, providing the ability for tailored design of geopolymers to specific applications in terms of both technical and commercial requirements.

Geopolymer technology: the current state of the art

The Hydrothermal Synthesis of Zeolites: History and Development from the Earliest Days to the Present Time

The introduction of synthetic zeolites has led to a paradigm shift in catalysis, separations, and adsorption processes, due to their unique properties such as crystallinity, high-surface area, acidity, ion-exchange capacity, and shape-selective character. However, the sole presence of micropores in these materials often imposes intracrystalline diffusion limitations, rendering low utilisation of the zeolite active volume in catalysed reactions. This critical review examines recent advances in the rapidly evolving area of zeolites with improved accessibility and molecular transport. Strategies to enhance catalyst effectiveness essentially comprise the synthesis of zeolites with wide pores and/or with short diffusion length. Available approaches are reviewed according to the principle, versatility, effectiveness, and degree of reality for practical implementation, establishing a firm link between the properties of the resulting materials and the catalytic function. We particularly dwell on the exciting field of hierarchical zeolites, which couple in a single material the catalytic power of micropores and the facilitated access and improved transport consequence of a complementary mesopore network. The carbon templating and desilication routes as examples of bottom-up and top-down methods, respectively, are reviewed in more detail to illustrate the benefits of hierarchical zeolites. Despite encircling the zeolite field, this review stimulates intuition into the design of related porous solids (116 references).

Hierarchical zeolites: enhanced utilisation of microporous crystals in catalysis by advances in materials design.

The hydrothermal synthesis of zeolites: precursors, intermediates and reaction mechanism

New cements for the 21st century: The pursuit of an alternative to Portland cement

A mesoporous material based on aluminosilicate mixture was studied to investigate its ability to include drugs and then release them. Nonsteroidal anti-inflammatory agents such as diflunisal, naproxen, ibuprofen and its sodium salt have been used in this study. The preparation of the mesoporous material and its characterization by X-ray, N2 absorption-desorption isotherm, and thermogravimetry analysis have been described. Drug loading was performed by a soaking procedure. Drug-loaded matrices were characterized for entrapped drug amount, water absorption ability, and thermogravimetric behavior. Drug release studies also were performed at pH 1.1 and 6.8 mimicking gastrointestinal fluids. Experimental results showed that this type of matrix is able to trap the bioactive agents by a soaking procedure and, then, to release them in conditions mimicking the biological fluids. Also, the high affinity of these matrices for water makes them potentially biocompatible. Release data suggest that the matrix impregnated with diflunisal offers good potential as a system for the modified drug release.

Drug Delivery Devices Based on Mesoporous Silicate

Dissolution of high-silica zeolites in alkaline solutions II. Dissolution of ‘activated’ silicalite-1 and ZSM-5 with different aluminum content

Preparation of bifunctional hybrid mesoporous silica potentially useful for drug targeting

Zeolite-rich volcanic tuffs are widely distributed in almost every country of the world, where they are present in low-, medium-, or high-grade million-ton deposits. Even though the formation of the zeolite minerals may have followed different genetic paths, the zeolitic rocks have in common a matrix of finely crystalline zeolite that cements the other nonzeolitic particles and is responsible for the overall mechanical properties of the material. Zeolitic tuffs have been employed since pre-historic times in construction, mostly as dimension stone. This use is still the most common of natural zeolites in the building industry, although other applications have recently come to the forefront, such as lightweight aggregate or as additives for manufacturing blended cements.

Given the fact that much of this material is excavated and used locally and that the market demand is strongly affected by the trends of the building industry, estimates of the worldwide zeolitic tuff production for construction purposes are difficult to make. In Italy, where the use of zeolitic tuff as dimension stone is commonplace, about 75 quarries were reported in operation in 1992 with total production of about 3 x 106 tons per year (Aiello 1995). More recently, this production has decreased, due to the crisis of the building industry, and in 1998 it amounted to about 1.5 × 106 tons per year. In Japan, the production of tuff as dimension stone is currently about 4 × 105 tons per year (N. Kuchitsu, National Research Institute of Cultural Properties, Tokyo, Japan, pers. comm., 1996). Considering that zeolitic tuff is used as dimension stone in many other countries as well, e.g. Bulgaria, Cuba, Germany, Greece, Hungary, Mexico, Romania, and Turkey, the current worldwide zeolitic tuff consumption as dimension stone is about 3 × 106 tons per year.

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Use of Zeolitic Tuff in the Building Industry

Mesostructured films are an ideal material for incorporation of fluorescent dyes; controlling the doping process is, however, a critical step because the dyes will be constrained in a complex chemical environment. We have incorporated rhodamine 6G, a well-known fluorescent dye, in silica mesostructured 2d-hexagonal films at different concentrations. We have used dense silica films as reference material to compare the effect of incorporation of rhodamine 6G in mesostructured and dense materials. We have also prepared mesostructured films at different surfactant concentrations to compare the surfactant effect on dye aggregation state. The dye-doped films have been characterized by UV−vis absorption spectroscopy and emission and excitation fluorescence spectroscopy. At high dye concentrations, nonfluorescent sandwich H-type dimers are formed, but in mesostructured films the amount of this type of aggregates is reduced and the formation of fluorescent J-type dimers is favored. The presence of the surfactant w...

Rosario Aiello

Papers

Drug Delivery Devices Based on Mesoporous Silicate

Dissolution of high-silica zeolites in alkaline solutions II. Dissolution of ‘activated’ silicalite-1 and ZSM-5 with different aluminum content

Preparation of bifunctional hybrid mesoporous silica potentially useful for drug targeting

Use of Zeolitic Tuff in the Building Industry

Aggregation States of Rhodamine 6G in Mesostructured Silica Films