Selective photocatalytic oxidation of glycerol and 3-pyridinemethanol by nanotube structured TiO2

In this thesis, nanotube structured TiO2 was formed on the Ti surface at different voltage (50-60 V) values by anodic oxidation methodand for different periods (3 and 5 hours). TiO2 powders were taken by ultrasonic method from the Ti electrodes as powdered form and calcined at different temperatures. TiO2 catalysts were characterized by XRD and SEM techniques. According to XRD analyses, by increasing the heat treatment temperature, both TiO2 crystallinity and primary particle sizes increased. While all the heat treated catalysts were only in the anatase phase up to 500 °C, both anatase and rutile phases were formed at 700 °C. SEM analyses prove that the prepared materials are in nanotube structure. The catalysts were photocatalytically tested for selective oxidation of glycerol and 3-pyridinemethanol under UVA irradiation under environmentally friendly conditions. Water was used as solvent and oxygen from air was used as oxidant, and the reactions were carried out at room temperature and at ambient pressure. In glycerol oxidation glyceraldehyde, 1,3-dihydroxyacetone and formic acid were determined as intermediate products, while the intermediate products of 3-pyridinemethanol oxidation were 3-pyridinmetanal and vitamin B3. Non-nanotube structured commercial TiO2 (Degussa P25 and Merck) and home-prepared rutile TiO2 catalysts were used for comparison. Low product selectivity values were observed in glycerol oxidation. On the other hand, the prepared NT-60V-5sa-250 catalyst showed both high activity and high product selectivity (total selectivity is over 90%) values for photocatalytic 3-pyridinmethanol oxidation. The TiO2 catalysts must be highly crystalline (calcined at 700 °C) for effective glycerol oxidation, while the optimum heat treatment temperature for selective and active 3-pyridinemethanol oxidation is 250 °C. The prepared catalysts have lower activity than Degussa P25, but they show higher product selectivity.