Abstract
The synthesis of Mg-Al, Ca-Al, Zn-Al and Cu-Al layered double hydroxides (LDHs) was investigated with a one-step wet mechanochemical route. The research aims to expand on the mechanochemical synthesis of LDH using a mill designed for wet grinding application. A 10% slurry of solids was added to a Netzsch LME 1 horizontal bead mill and milled for 1 h at 2000 rpm. Milling conditions were selected according to machine limitations and as an initial exploratory starting point. Precursor materials selected consisted of a mixture of oxides, hydroxides and basic carbonates. Samples obtained were divided such that half was filtered and dried at 60 °C for 12 h. The remaining half of the samples were further subjected to ageing at 80 °C for 24 h as a possible second step to the synthesis procedure. Synthesis conditions, such as selected precursor materials and the MII:MIII ratio, were adapted from existing mechanochemical methods. LDH synthesis prior to ageing was successful with precursor materials observably present within each sample. No Cu-Al LDH was clearly identifiable. Ageing of samples resulted in an increase in the conversion of raw materials to LDH product. The research offers a promising ‘green’ method for LDH synthesis without the production of environmentally harmful salt effluent. The synthesis technique warrants further exploration with potential for future commercial up-scaling.
Highlights
Layered double hydroxides (LDHs) are clay-like minerals commonly referred to as anionic clays with a wide range of physical and chemical properties
The particle size of the raw material mixtures as well as that of the sample obtained is depicted in Tables 1 and 2, respectively
Implementation of ageing resulted in more complete conversion of raw materials to LDH product
Summary
Layered double hydroxides (LDHs) are clay-like minerals commonly referred to as anionic clays with a wide range of physical and chemical properties. They are represented by the general formula [MII 1−x MIII x (OH)2 ][Xq− x/q ·H2 O] in which MII and MIII represent the selected divalent and trivalent metal elements and [Xq− x/q ·H2 O] denotes the interlayer composition. LDHs often find application in pharmaceuticals, as polymer additives, as additives in cosmetics, and in catalysis This is due to having variable layer charge density, reactive interlayer space, ion exchange capabilities, a wide range of chemical compositions and rheological properties [1].
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