Photoinduced processes of adsorbed and associated dye molecules in mesoporous titania coatings

Abstract

Highlights • Sol-gel synthesis of mesoporous titania coatings with different pore structures • Dye association in pores depends on the pore sizes and pH of dye solution • Dye association influences the photodegradation process • Monomers show higher photodegradation rates than associated dye molecules

Thin layer photocatalysts of TiO2-Ag composites

“…For the photocatalysis tests one-sided samples were prepared using a laboratory made sample holder that covered one side of the substrate. The synthesis of precursor sols via acid catalysed hydrolysis and polycondensation of silicon-and titanium-alkoxides was similar to that reported previously [14,31]. Compact SiO 2 barrier layers were prepared from precursor sols with molar ratios of TEOS : EtOH : HCl : H 2 O -1 : 4.75 : 7.2 × 10 −4 : 4.00.…”

Effect of Silver Modification on the Photoactivity of Titania Coatings with Different Pore Structures

“…The kinetics of dye degradation was also investigated, by applying models from the literature. It was found, that monomer degradation can be described as two consecutive first order reactions (see Equation ( 1)), and a model first presented by Julson and Ollis could be applied, as described by equation 2 [17][18][19].…”

“…Ag modification of the samples caused a decrease or no significant change in the monomer degradation rates. The samples with higher Ag content showed lower trimer photodegradation rates, in part due to the initial trimerization under UV light, which process was found to be more prominent in the Quantum efficiency and quantum yield values for the first interval of R6G monomer photodegradation were determined for both UV and visible light tests: the detailed calculation is described in the Supporting information (in Supplementary Section 4) and in our previous publication [18], and the results can be seen in Table S5 in Supporting information. Generally, QE and QY values for the UV photodegradation were much higher compared to that of degradation under visible light, due to the different mechanism of dye degradation in these experiments.…”

“…In most experiments, the photodegradation process is investigated at the liquid–solid interface, in dye solutions [ 13 , 14 , 15 , 16 ]. However, in order to model the operating conditions of self-cleaning coatings, experiments at the air–solid interface are also very important, and less research has been conducted on this topic [ 17 , 18 , 19 ]. Studying the photoinduced wettability change of titania-based photocatalysts is also important: this commonly observed property of TiO 2 means that complete wetting (contact angle equals zero) can happen due to UV irradiation, and thus rain will facilitate the self-cleaning process in outdoor applications [ 10 , 20 ].…”

“…Refractive index (n), film thickness (d) and porosity (P) values of SiO 2 barrier layer on glass, and the different TiO 2 layers deposited on SiO 2 coated glass. Average pore size values (d pore ) are included from our previous publication[18], determined by ellipsometric porosimetry on samples prepared by dip-coating on Si wafers.…”