| Particulate systems are encountered in many technological applications, including chemical, catalytic and environmental processes; microelectronics; sensors; pigments; coatings; separations; biological applications and nanotechnology. There is a need for methods that can probe the morphology and the physicochemical properties of particles with nanoscale resolution. This work demonstrates the ability of Atomic Force Microscopy (AFM) to probe directly the structure and reactivity of submicron particles, achieving resolution that can be comparable to that of HRTEM.; We have developed novel AFM-based methods to image particles with high resolution, and to study the photoreactivity of oxide and metal-decorated oxide particles. Our efforts focused on submicron titanium dioxide particles, used as catalysts and photocatalysts in environmental applications, and as pigments and sizing agents in paints and plastics. The photocatalytic activity of these systems is strongly structure-sensitive and there is therefore a need to characterize and control these materials on the nanometer scale. The photocatalytic reduction of Ag+ to metallic Ag on the surfaces of TiO2 particles, by transfer of a photoexcited electron from TiO2, was used to probe the spatial distribution of photoreactive sites on the titania particle surfaces. We developed protocols to study directly the same titania particle before and after reaction. Such studies can link directly the surface structure of titania particles and their photoreactivity. These protocols were used to quantify the effect of different factors, such as TiO2 bulk and surface structure and photoreduction conditions, on the spatial and size distribution of the Ag nanoparticles, so as to define the optimum conditions for metal deposition. We have used these techniques to probe potential methods for manipulating the performance of TiO2 particles, such as metal doping, surface sensitization by organometallic dyes and surface passivation by silica/alumina coatings.; Despite the several limitations of SPM in studies of particulate systems, AFM can provide unique insights into the chemical and physical properties of such systems. AFM-based methods could help to elucidate a variety of problems in particle science and technology, and could lead to the rational design of particle surfaces for applications where the reactivity needs to be characterized and controlled on the nanoscale. |
