Urea-Assisted Synthesis and Characterization of Saponite with Different Octahedral (Mg, Zn, Ni, Co) and Tetrahedral Metals (Al, Ga, B), a Review.

Concepcion P Ponce,J Theo Kloprogge

doi:10.3390/life10090168

Concepcion P Ponce, J Theo Kloprogge

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https://doi.org/10.3390/life10090168

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Abstract

Clay minerals surfaces potentially play a role in prebiotic synthesis through adsorption of organic monomers that give rise to highly concentrated systems; facilitate condensation and polymerization reactions, protection of early biomolecules from hydrolysis and photolysis, and surface-templating for specific adsorption and synthesis of organic molecules. This review presents processes of clay formation using saponite as a model clay mineral, since it has been shown to catalyze organic reactions, is easy to synthesize in large and pure form, and has tunable properties. In particular, a method involving urea is presented as a reasonable analog of natural processes. The method involves a two-step process: (1) formation of the precursor aluminosilicate gel and (2) hydrolysis of a divalent metal (Mg, Ni, Co, and Zn) by the slow release of ammonia from urea decomposition. The aluminosilicate gels in the first step forms a 4-fold-coordinated Al3+ similar to what is found in nature such as in volcanic glass. The use of urea, a compound figuring in many prebiotic model reactions, circumvents the formation of undesirable brucite, Mg(OH)2, in the final product, by slowly releasing ammonia thereby controlling the hydrolysis of magnesium. In addition, the substitution of B and Ga for Si and Al in saponite is also described. The saponite products from this urea-assisted synthesis were tested as catalysts for several organic reactions, including Friedel–Crafts alkylation, cracking, and isomerization reactions.

Highlights

Clay minerals are a group of minerals that occur as colloidal crystals in sediments and soils.They consist mostly of hydrated aluminum phyllosilicates, which may contain variable amounts of iron, magnesium, alkali metals, alkaline earths, and other cations found on or near some planetary surfaces.They are abundant and widely distributed in nature showing a wide variety of structures, compositions, and properties
The use of urea, a compound figuring in many prebiotic model reactions, circumvents the formation of brucite, Mg(OH)2, in the final saponite product by slowly releasing ammonia thereby controlling the hydrolysis of magnesium [46]
Compared with the reduction temperatures observed for chrysocolla [Cu2 Si2 O5 (OH)2 ] [91,92], the reduction of the synthetic Cu2+ -containing saponite proceeded at higher temperatures

Summary

Introduction

Clay minerals are a group of minerals that occur as colloidal crystals in sediments and soils.They consist mostly of hydrated aluminum phyllosilicates, which may contain variable amounts of iron, magnesium, alkali metals, alkaline earths, and other cations found on or near some planetary surfaces.They are abundant and widely distributed in nature showing a wide variety of structures, compositions, and properties. Clay minerals are a group of minerals that occur as colloidal crystals in sediments and soils. They consist mostly of hydrated aluminum phyllosilicates, which may contain variable amounts of iron, magnesium, alkali metals, alkaline earths, and other cations found on or near some planetary surfaces. They are abundant and widely distributed in nature showing a wide variety of structures, compositions, and properties. Bernal was the first to point to the potential role of clay minerals in abiogenesis [1]. A few others have supported the importance of clays in the synthesis of simple and organic molecules that are the building blocks of life

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