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.