Influence of microwave and ultrasonic treatment on the formation of CoFe2O4 under hydrothermal conditions

The formation of CoFe2O4 nanocrystals under hydrothermal conditions at a temperature of 130°C is investigated. The average size of CoFe2O4 particles varies from 6 to 11 nm depending on the synthesis time. The hydrothermal medium is heated by two different methods, i.e., the microwave (with a synthesis time from 1 min to 2 h) and conventional (with a synthesis time from 30 min to 45 h) methods. It is demonstrated that the use of microwave heating considerably accelerates the formation of CoFe2O4 particles. Preliminary ultrasonic treatment for 3 min increases the phase formation rate in the case of microwave heating and hardly affects the occurrence of the process upon conventional heating. It is revealed that the exposure of the initial mixture (preliminarily treated with ultrasound) to room temperature for 2 h or longer almost completely reduces the efficiency of the action of ultrasonic treatment on the phase formation process under hydrothermal conditions.