טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentNussbaum Milka
SubjectSurface Modification of Photocatalysts
DepartmentDepartment of Nanoscience and Nanotechnology
Supervisor Professor Yaron Paz
Full Thesis textFull thesis text - English Version


Abstract

Hazardous organic wastes represent one of the greatest challenges for mankind. Photocatalytic degradation of organics in water and air seems to have a number of advantages over other techniques. This study dealt with two aspects of surface modification of photocatalysts for achieving unique properties in the photocatalysis process.

The first aspect is a study on the photocatalytic degradation of contaminants (salicylic acid and stearic acid) on titanium dioxide films over-coated with a few monolayers of silica. A rather uncommon situation was observed, where the presence of the thin silica layers decreased the degradation rate of stearic acid yet increased that of salicylic acid. The results were explained by tendency of silica films to ease desorption of intermediate products formed during the degradation of salicylic acid. This finding, which may apply also to other aromatic compounds, may have important implications on the design and operation of photocatalytic devices for indoor applications, since ultrathin layers of silica are known to be formed over time on the photocatalyst.

            It was found that the thickness of the silica sub-nanometer layer affected the degradation rate of salicylic acid. This was explained in terms of gradual changes in the isoelectric point. If optimized, this effect can be utilized to precisely control adsorption or desorption and accordingly to induce specificity in photocatalytic degradation of contaminants.   A methodology for preparing molecularly imprinted photocatalyst with and without an inert ultrathin layer in between the imprinted sites was presented. It was found that over-coating the area in between the imprinted sites preserved the benevolent effect of imprinting. While at present the imprinting effect was moderate, there is a reason to believe that this effect can be improved considerably by controlling the type of inert overlayer.

            The second aspect of surface modification relates to the developing of new photoactive compounds that absorb in the visible range of the spectrum. Here, the preparation, characterization and photocatalytic activity of bismuth-containing oxides are reported. These materials are usually formed by a high-temperature solid state reaction that produces materials with very low surface area that consequently limits the photocatalytic activity. Here we studied a novel room-temperature technique, which eventually led to heavily doped crystalline BiOCl having large surface area (100 m2g-1). This group of materials was found to be highly photocatalytically active.