This research develops an energy harvesting system based on CuFe2O4 (copper ferrite) ferrofluid with size control using oleic acid as surfactant. The synthesis of copper ferrite nanoparticles as ferrofluid filler was carried out using the sonochemical method with the main iron source material being iron sand from Sine Beach, Tulungagung. Copper ferrite nanoparticles were coated with oleic acid in various volumes to control their size. After being completely coated, the mixture is dispersed in olive oil to become a complete ferrofluid. A series of characterizations was carried out comprehensively to confirm the success of this research, including characterization of structure, morphology, functional groups, and electrical properties. The structure of copper ferrite nanoparticles was identified using an X-ray diffractometry (XRD) instrument. It was discovered that the size of copper ferrite nanoparticles was 9.7 nm, and the structure formed was spinel reverse cubic with the highest peak of the HKL (3 1 1) plane located at an angle of 35.5°. The morphology of copper ferrite nanoparticles was observed via scanning electron microscope (SEM). Based on the results obtained, copper ferrite nanoparticles appear to agglomerate with particle clusters reaching 52 nm and an average particle size distribution of 25.1 nm. Functional group characterization was carried out using Fourier transform infrared (FTIR). The results showed that all precursors in the ferrofluid system had successfully emerged and formed. Analysis of electrical characteristics was carried out through I-V testing, and it was obtained that the CF3 sample with a volume of 3.6 mL of oleic acid had the highest current values of 13.1 μA, however, the three samples showed a good response and were representative for use as an energy harvester, which is promising.
