Pore architecture affects photocatalytic activity of periodic mesoporous nanocrystalline anatase thin films

Abstract

We report the photocatalytic activity of periodic mesoporous nanocrystalline anatase thin films (denoted meso-nc-TiO 2 ) using Methylene Blue (denoted MB) as a probe of pore architecture effects on reactivity. Specifically, 2D hexagonal and 3D cubic mesoporous nanocrystalline anatase thin films (denoted h-meso-nc-TiO 2 and c-meso-nc-TiO 2 respectively) annealed at different temperatures were investigated to reveal the effects of different pore architectures on the photocatalytic activity. The adsorption behavior of MB on the films annealed at the same temperature signaled that c-meso-nc-TiO 2 has a larger accessible surface area but a lower adsorption surface affinity, compared to h-meso-nc-TiO 2 . In the case of the solid-state photodegradation of MB, the most efficacious photocatalyst was found to be c-meso-nc-TiO 2 annealed at 450 uC. For MB in solution, a 400 uC annealed c-meso-nc-TiO 2 was established to have the optimum photocatalytic activity among the samples investigated. The observed superior photocatalytic activity of c-meso-nc-TiO 2 relative to both h-meso-nc-TiO 2 and nc-TiO 2 is believed to originate from the higher photoactivity of anatase nanocrystallites comprising the more open cubic framework. as well as geometrical advantages, such as a larger surface area and less obstructed 3D diffusion paths of guest molecules. It is concluded that the photocatalytic efficiency of periodic mesoporous nanocrystalline anatase thin films depends on the pore architecture.

Block copolymer-templated synthesis of highly organized mesoporous TiO2-based films and their photoelectrochemical applications

“…Therefore, 3-D cubic mesoporous TiO 2 films shows much advance in photocatalysis because it holds greater accessibility and one more dimension for mass transfer of pollutant molecules and products. Similar results were also obtained when the adsorption ability and photocatalytic activity of 2-D and 3-D hexagonal mesoporous TiO 2 films were compared [127]. The accessible surface area of 3-D hexagonal mesoporous TiO 2 film estimated by the adsorption of methylene blue was found to be nearly twice as large as that of 2-D hexagonal one.…”

“…Despite their low crystallinity, mesoporous TiO 2 films have demonstrated remarkably high photocatalytic activities than the nonporous films in water splitting [126] and in complete degradation of organic contaminations, such as organic dyes [127][128][129], stearic acid [90], and lauric acid [76] in aqueous media, or gaseous pollutants such as acetone [46] and 2-propanol [91,130]. Excellent water disinfection property of mesoporous TiO 2 films was also found in killing Escherichia coli, a representative bacterium widely exists in the aquatic environment [131].…”

“…Thus, the calcination temperature has to be adjusted to balance these parameters in order to achieve a highest photocatalytic activity. Ozin's [127], Yu's [46], and Sanchez's [76] groups found that the films calcined at 400, 500 and 600 • C showed the highest photocatalytic activity, respectively. The difference in calcination temperature may be due to the difference in synthetic condition of mesoporous TiO 2 films and kinds of photocatalytic reactions.…”

Condensation‐ and Crystallinity‐Controlled Synthesis of Titanium Oxide Films with Assessed Mesopores

“…The size and connectivity of mesopores in the calcined films are important for effective diffusion of methylene blue (MB) molecules inside the films. [17,18] To understand the relationship between the mesostructure and photocatalytic performance of the titania films, we estimate the index for photocatalytic performance of the calcined films by multiplying three index values: crystallinity (see above), effective surface area, and diffusivity. The effective surface area of MB molecules is equivalent to the amount of MB adsorbed on the films at equilibrium.…”

Theoretical and experimental investigation into photoelectrocatalytic oxidation and reduction property of ZnFeTi mixed metal oxides

“…In our opinions, there were several factors which were very important for improving photocatalytic activity of the material, such as narrow band gap, high specific surface area (providing strong adsorption ability toward the target molecules and thus the generation of photoinduced electro-hole pairs of active sites are enhanced) [37], wide distribution of mesopores and macropores of materials (favorable for the transportation and diffusion of species), and small crystallite size of materials (not only can inhibit the recombination between photoelectrons and holes, but also effectively facilitate the rapid transfer of photoelectrons from bulk to the surface), and so on [38]. So, based on our results, we could conclude that ZnFeTi mixed metal oxides (MMO) showed narrower band gap, higher specific surface area and smaller crystallite size, were very efficient and effective for the photodegradation of p-chlorophenol.…”