Synthesis and stability of functionalized iron oxide nanoparticles using organophosphorus coupling agents

This paper describes syntheses of stable functionalized iron oxide nanoparticles through surface modification of magnetic iron oxide nanoparticles with tailor-made phosphonic acids of type X(CH2)nPO3H (where X = –COOH, –NH2). Iron oxide nanoparticles were synthesized by co-precipitation method and the surface modification process was achieved using ultrasonic probe. XRD analysis shows that the crystalline structure of iron oxide nanoparticle remains unaffected even after surface modification with phosphonic acid-based coupling molecules. FTIR and XPS studies indicate that phosphonic acid binds on iron oxides preferably through tridentate bonding mode. TEM analysis shows narrow size distribution and uniform morphology of phosphonoacetic acid and 2-carboxyethyl phosphonic acid modified particles. BET surface area and phosphorous content analysis show higher coverage by –COOH terminated phosphonic acids than –NH2 terminated phosphonic acids in the particular reaction condition. DLS study shows almost no change in hydrodynamic diameter of phosphonoacetic acid and 2-carboxyethyl phosphonic acid modified particles in a wide pH range.