RESUMO
This is the first work to investigate if and/or how changes in the surface structure/properties affect the charge transfer resistance (R CT) of anatase titania with decreasing particle size. It was accomplished by measuring the R CT (Ω) of same weight anatase titania pellets, with particle sizes ranging from 5.31 nm to 142.61 nm. Measurements were made using Electrochemical Impedance Spectroscopy (EIS) at each material's point of zero charge (PZC). Results demonstrated two regions of R CT. Above an average primary particle diameter of 23.54 nm, R CT remained essentially constant. Below, this diameter the R CT value first increased significantly, then decreased almost linearly toward zero. The projected average primary particle diameter where the materials R CT was projected to reach zero resistance is at a diameter of approximately 4.39 nm. A simple test was then developed to determine if at a small enough particle size the material would be affected by an external magnetic field. It was found that a sample with an average particle diameter of 12.689 nm, formed fine needles/threads of particles in deionized water, perpendicular to the settled powder at the base of the potash tube. This led to the development of a simple magnetic separation method to obtain strongly diamagnetic material from a parent population with an average primary particle diameter of 5.31 nm. A pellet consisting of these magnetically separated particles was then pressed at the same weight and pressure as the prior samples. The pellet's R CT was then measured using EIS under the identical conditions as the prior samples. EIS results of the magnetically separated particles in pellet form, under multiple conditions, resulted in Nyquist plots indicating the material exhibited no detectable R CT (i.e., superconductivity). Correlation of the shift in the materials R CT with known structure/property changes for each sample with decreasing particle size allowed the development of a model explaining: (1) the significant increase in diamagnetic strength of the magnetically separated particles and (2) the mechanism controlling the material's R CT.