Manipulating the Size and Dispersibility of Zerovalent Iron Nanoparticles by Use of Carboxymethyl Cellulose Stabilizers

Abstract

Zerovalent iron (ZVI) nanoparticles of various sizes were synthesized by applying various types of carboxymethyl cellulose (CMC) as a stabilizer. At an initial Fe2+ concentration of 0.1 g/L and with 0.2% (w/w) of CMC (Mr = 90 000), nanoparticles with a hydrodynamic diameter of 18.6 nm were obtained. Smaller nanoparticles were obtained as the CMC/Fe2+ molar ratio was increased. When the initial Fe2+ concentration was increased to 1 g/L, only 1/4 of the CMC was needed to obtain similar nanoparticles. On an equal weight basis, CMC with a greater Mr or higher D.S. (degree of substitution) gave smaller nanoparticles, and lower the synthesizing temperature favored the formation of smaller nanoparticles. It is proposed that CMC stabilizes the nanoparticles through the accelerating nucleation of Fe atoms during the formation of ZVI nanoparticles and, subsequently, forms a bulky and negatively charged layer via sorption of CMC molecules on the ZVI nanoparticles, thereby preventing the nanoparticles from agglomeration through electrosteric stabilization. In agreement with the classical coagulation theory, the presence of high concentrations of cations (Na+ and Ca2+) promoted agglomeration of the nanoparticles. The strategy for manipulating the size of the ZVI nanoparticles may facilitate more effective applications of ZVI nanoparticles for in situ dechlorination in soils and groundwater.