Obtaining of NiO/SiO2 by thermal decomposition of Ni(II) carboxylates formed within hybrid silica gels

Abstract

Nickel oxides nanoparticles were successfully obtained using a new sol–gel method approach which is based on the thermal decomposition of some carboxylate compounds formed within the pores of hybrid tetraethyl orthosilicate–diol gels. The Ni(II) carboxylate compounds were obtained in the redox reaction between diols (1,3-, 1,4-, and 2,3-butane diol, respectively) and NO 3 − anion of Ni(NO3)2·6H2O. The diol is the key component of the system by its simultaneous participation in the redox reaction as well as in the interaction with tetraethyl orthosilicate for the formation of the hybrid gels. There were synthesized gels with the three types of diol for compositions of 30, 50, and 70 % NiO/SiO2 in order to see what kind of crystalline species (Ni, NiO or mixtures) are formed within the silica matrix. The gels were thermally treated at different temperatures leading to single-phase, nanosized NiO/SiO2 crystallites, depending on the carboxylate radical, the morphology of the silica matrix, the sample composition, and the annealing temperatures of 350 and 800 °C. Thermal analysis is an excellent tool for the study of different thermal behavior of Ni(II) carboxylates based on the different diols used as reagents and the sample composition. The shape of the X-ray diffraction patterns evidenced the very fine nature of the samples and the nanometer size (5–25 nm) of the nickel oxide crystallites inside the silica matrix.