Nickel(III) containing layered double hydroxides with hydrotalcite structure

Synthesis of layered double hydroxides (LDH) was carried out by the method of coprecipitating of components from the solution at room temperature and variable pH, followed by aging at 98 °C for 2 days. During the synthesis the following compositions were specified: M2+6M3+1.5Ni3+0.5, where M2+ is Mg, Cu or Ca, M3+ is Al, Fe, or Co. In order to convert nickel cations to oxidation state +3, an oxidizing agent – sodium hypochlorite – was introduced into the reaction system. It is shown that the use of this method of synthesis allows to obtain layered double hydroxides containing aluminum and nickel or iron and nickel in the positions of triply charged cations in the structure of brucite-like layers. The formation of hydrotalcite-like structure was confirmed by XRD. The synthesized materials had morphology typical for layered double hydroxides. According to transmission electron microscopy, the samples consisted of aggregates of plate-like particles. The behavior during heat treatment was studied by thermogravimetric analysis. It was shown that the replacement of aluminum with iron cations in the structure of nickel-containing LDH led to a slight decrease in thermal stability of LDH. The thermal destruction of the obtained samples occured in two stages. The first stage, observed in the temperature range from 20 to 220 °C, included the loss of physically sorbed and crystalline water. In the second stage, when heated above 220 °C, simultaneous dehydroxylation of brucite-like layers and removal of carbonate anions from the interlayer space were observed, which resulted in the destruction of the layered structure. Heat treatment at 500 °C led to the transformation of layered double hydroxides into a mixture of corresponding oxides.