Abstract: In this paper, the synthesis and acid-base properties of magnetite nanoparticles were studied. The testing results show that the surface of the magnetite nanoparticles possessed an obvious acid-base property. With increasing the amount of magnetite nanoparticles in the suspension, the pH buffer capacity of solution increased dramatically. There is a proportional relationship between the amount of magnetite nanoparticles added and solution pH buffer capacity. According to this, the adsorption quantity of proton on the surfaces can be determined. The effect of surface charge on the surface speciation was discussed by using computer program MEDUSA and WINSGW to establish the distribution diagram in magnetite suspension.

Key words: Fe₃O₄ nanoparticles, Surface acid-base properties, Gran plot