"Nanotechnology and nanomaterials"

UV-spectroscopic and kinetic investigations of photodegradation of methyl orange in the presence of TiO2/β-cyclodextrin
Bardadym Yu. V., Kobrina L. V., Kobylinskyi S. M., Riabov S. V.
Institute of Macromolecular Chemistry of National Academy of Science of Ukraine, Kharkivske shose, 48, Kyiv-02160, Ukraine

Photocatalytic degradation is one of the most promising, safe and efficient method of purifying water from organic contaminants. Among all semiconductors titanium dioxide is well known and widely studied photocatalyst due to its non-toxicity, chemical stability and relatively low cost. Cyclodextrins (CDs) as cyclic oligosaccharides are able to form the inclusion complexes with various organic compounds. The combination of CDs and TiO2 is one of the possible methods to increase photocatalytic activity of TiO2.
The aim of this work is to study the influence of β-CD and some of its derivatives: 2-hydroxypropyl-, sulfobutyl-, carboxymethyl- and thexyl-β-cyclodex-trin on the photodegradation of methyl orange (MO) in aqueous solutions in the presence of TiO2. In present work various concentrations of MO (30–115 mg/l) and CD (0.09–0.5 g/l) at their molar ratio from 1:0.5 to 1:6 and constant concentration of TiO2 (1 g/l) were used. The UV irradiation of TiO2/CD-MO was performed in distilled, river and artesian waters at pH 2.5-6 under UV-A (365 nm) or UV-A/UV-C (365 nm/254 nm) light that provided by three lamps (8 W). It is shown that β-CDs accelerate the photodestruction of MO compared to neat TiO2 due to the oxidation of OH groups of CD, promoting the adsorption of inclusion complexes formed between them on the photocatalyst surface. It was found that sulfobutyl ether β-CD was slightly more efficient than other studied compounds in all tested environments. In general, photooxidation of MO in the presence of TiO2/CD strongly depends on medium acidity and it is the highest at pH 2.5, at which MO completely discolored for 20 - 25 min under UV-A or 10 min under UV-A/UV-C irradiation. The efficiency of photodestruction was revealed to maintain up to 8 - 10 cycles at MO:CD 1:3 and 1:6 (UV-A) or 1:1 under mixed light irradiation. The mechanism of MO degradation is considered on the base of UV data of investigated solutions, recorded after different irradiation time. It is shown that when applying of UV-A light the degradation of MO mainly occurs at the first stage, i.e., via the azo bond cleavage with p-aminobenzenesulfonic acid and N,N-dimethyl-p-diphenylamine formation. At the same time, exploring additional bactericidal lamp (UV-C) significantly increases the degradation efficiency. After 8 cycles of irradiation for 20 min each, only small amounts of degradation products like phenol, benzenesulfonic acid and p-benzophenone are present in the solution.