Synthesis, characterization, catalytic activity and adsorption properties of new nanosized cobalt-magnesium spinel ferrites for water treatment processes

Nitrophenols are carcinogenic, non-biodegradable pollutants in wastewaters from textile, paper and other industries. Cost-effective and environmentally friendly photocatalysts for degradation of such toxicants are magnetic nano-sized spinel ferrites. The research was aimed at establishing the effect of structure and cations distribution in tetrahedral and octahedral sublattices of ferrite spinels on adsorption-catalytic activity of CoFe₂O₄ (CF), Co_0.5Mg_0.5Fe₂O₄ (CMF), MgFe₂O₄ (MF) in photocatalysis and Fenton-like oxidation reactions. Nanosized spinels were synthesized by citrate combustion method and characterized by XRD, Mossbauer spectroscopy, FTIR, SEM, energy dispersive analysis and BET nitrogen adsorption-desorption technique. Oxidative degradation of 2,4-dinitrophenol by hydrogen peroxide was used to evaluate catalytic activity of spinels under differentiation of contributions of sorption, photocatalysis and Fenton-like reactions to overall degradation process. The reaction followed pseudo-first-order kinetic model with degradation efficiency of 79.5 and 98.3 % for CF and MF, respectively. The highest degree of pollutant degradation after four catalysis cycles without regeneration was characteristic of CMF. The observed stability of CF, CMF and MF in several cycles demonstrate their high catalytic potential for treatment of wastewaters containing phenolic compounds. Additionally, the study illustrated the possibility of synthesized spinels application as sorbents of inorganic toxicants from aqueous medium. The sorption capacity for heavy metal ions, activity of sorption sites per unit surface area, efficiency of purification increased in the order CF < CMF < MF allowing to extract from 19 to 58 mg/g of Cu²⁺ from water. The investigated materials reached sorption equilibrium within 20-80 min, successfully operated in several sorption cycles both without and under regeneration conditions, and were easily isolated for reuse and regeneration by external magnetic field.