TiO₂ Nanoparticles‐Photocatalytic Oxidation of Selected Cycloalkanols

Abstract

Photocatalytic oxidation of cyclohexanol (1), cyclopentanol (2), and cycloheptanol (3) was investigated by using titanium dioxide (Degussa P25) as a semiconductor photocatalyst .The effect of different operational parameters such as the catalyst, the solvent, time, and oxidant was also studied. Results showed a high percentage of conversion for 1-3 (71.6%, 94.2%, and 100%, resp.) and that the primary photocatalytic oxidation products are the corresponding cycloalkanones (4-6). They were formed with high selectivity (>85%). Several other products were also identified using GC, GC/MS techniques and authentic samples. The photocatalytic activity is explained by a photoinduced electron transfer mechanism through the formation of electron-hole pair at the surface of the semiconductor particles. A first-order kinetic model was observed for the photocatalytic oxidation of the investigated cycloalkanols.

Ag‐doped TiO2 enhanced photocatalytic oxidation of 1,2‐cyclohexanediol

“…Decomposition of 1 d and 1 e would be expected to occur rapidly to form the cyclic oxidation products 2 , 3 , 4 , and 5 . Formation of 4 could be expected via dehydration of 2 . A multistep process (scheme 20) may be proposed for the formation of 5 from 2 .…”

“…The use of water‐free acetonitrile solvent rules out the participation of hydroxyl radicals in the photocatalyzed oxidation process and the elimination of the metal (Ag) by photocorrosion. Acetonitrile, as a polar nonhydroxylic solvent, represents the best solvent for controlling the oxidation reactivity at the interface, between a liquid reaction and a solid irradiated photocatalyst . Also, direct photolysis is excluded as the λ max of 1,2‐cyclohexanediol was observed at 224 nm ( Є = 2.28 mV), whereas the maximum emission of the used 450‐Wt medium pressure Hg lamp is in the range 296.7–578.0 nm.…”

“…).The distance between the sample cell and the radiation source is 5 cm. The system was covered with aluminum foil served as light reflector to decrease light loss, and the apparatus was set up in a metallic cabinet …”

“…Heterogeneous photocatalysis has been started with the pioneer findings of Fujishima and Honda . Application of photocatalytic oxidation (PCO), as one of the promising technologies, in water recycling, air pollution treatment, as well as in organic synthesis, has been a great interest. The need for sustainable green chemistry technology to obtain valuable chemicals appears today of primary importance.…”

“…Continuing our interest on PCO of cyclic and acyclic alcohols, as well as other interests on PCO of biomolecules, the present article embraces PCO of 1,2‐cyclohexanediol ( 1 ). Cyclohexane moiety represents the base structure of many biomolecules such as sterols and estrogens hormones (estriol).…”