oxyhydroxidehydrate

Oxyhydroxidehydrate is a term used to describe a class of solid inorganic materials that consist of oxide and hydroxide groups of a metal combined with water molecules in the structure. These hydrated oxyhydroxides occur as interstitial, interlayer, or coordinated water within the solid and are found in both natural mineral systems and synthetic preparations. The water content can vary, leading to differences in stability, density, and reactivity.

Structurally, oxyhydroxidehydrates range from poorly crystalline or amorphous to semi-crystalline phases. Metal cations are linked by oxide and hydroxide bridges to form three-dimensional networks or layered structures, with water molecules occupying available sites within the framework. The hydrated form typically becomes less hydrated upon heating, undergoing dehydration and, in some cases, transformation toward oxide or more dehydroxylated phases. Common examples in nature and research include ferrihydrite and goethite, which are often discussed as hydrated iron oxyhydroxides.

Synthesis and transformation are driven by aqueous chemistry and aging conditions. They can be formed by precipitation of metal salts with base at controlled pH, hydrolysis of metal precursors, or oxidation under ambient conditions. The water content and crystallinity can be tuned by aging, temperature, and pH. Dehydration or thermal treatment generally yields an oxide or a less hydrated hydroxide, sometimes altering catalytic or sorptive properties.

Occurrence and significance: oxyhydroxidehydrates are abundant in soils, sediments, and weathering environments, where they influence nutrient and contaminant cycling due to high surface area and reactive sites. They are also studied as catalysts or catalyst supports and as pigments or functional materials in ceramics.