A quantum dot model for the surface charge density in ferrite-based ionic magnetic fluids

Calculation of the surface charge density in semiconductor metal-oxide quantum dots (QDs) dispersed in aqueous colloids, in a wide range of pH values (1-13), is presented. Surface charge density in the range +/- 0.4 C/m(2) was obtained for spherical nanoparticles in the typical diameter range. The shape of the calculated surface charge density curve as well as the range of the values obtained, in excellent agreement with the data reported in the literature, are obtained as long as a proton transfer. mechanism through the semiconductor-electrolyte interface takes place. The data reported here explain the stability found in ionic magnetic fluids at the usual lower/higher pH values. (C) 2002 Elsevier Science B.V. All rights reserved.