Synthesis and characterization of nickel–copper hydroxide acetate, NiCu(OH)3.1(OCOCH3)0.9 · 0.9H2O

Nickel–copper hydroxide acetate with a chemical composition of NiCu(OH)3.1(OCOCH3)0.9 · 0.9H2O was synthesized by hydrothermal heating of an aqueous solution containing nickel acetate, copper acetate, and hydrogen peroxide to 423 K for 4 h. The crystal structure of this compound can be described as brucite-type octahedral (Ni,Cu)(OH)2 layers, where a part of OH sites are replaced by acetate ions located in the interlayer. This compound is stable below about 455 K except that the reversible dissociation and association of the water molecules from/with the interlayer acetate ions occur depending upon the surrounding conditions. Above 455 K, a part of the interlayer acetate ions are released from the solid phase. The solid phase is decomposed to nickel and copper oxides above about 500 K. The synthesized nickel–copper hydroxide acetate takes up little or no Cl− and NO3- but shows high selectivity for multivalent anions such as SeO32- and AsO43-. The uptake of multivalent anions proceeds on the basis of exchange with the acetate ions but may also involve exchange with the hydroxide ions in the matrix hydroxide layers.