In this study, Ni-doped iron oxide (NixFe3-xO4) materials were synthesized via the 1,2-epoxypropane assisted sol-gel method by varying the molar concentration of Ni from x=0.2 to 1. Sol-gel derived NixFe3-xO4 gels were dried and the dried powder was further calcined upto 600 degrees C in air for 90 min. Obtained calcined NixFe3-xO4 powders were further analyzed to determine the phase composition, crystallite size, specific surface area, pore volume, and morphology via powder X-ray diffraction (PXRD), BET surface area analysis (BET), as well as scanning and transmission electron microscopy (SEM and TEM). The obtained results in the synthesis and characterization section indicate formation of NixFe3-xO4 nanoparticles with high specific surface area. Thermal reduction and re-oxidation of the sol-gel synthesized NixFe3-xO4 materials were determined by using the high temperature thermogravimetry. Obtained results indicate that the amount of O-2 released during the thermal reduction step (at 1400 degrees C) and quantity of CO produced during the CO2 splitting step (at 1000 degrees C) increases as the concentration of Ni inside the iron oxide crystal structure increases. The highest amounts of O-2 released (221.88 mu mol/g) and CO produced (375.01 mu mol/g) in case of NiFe2O4 (NF10 material).