Enhanced Photocatalytic Activity by Particle Morphology: Preparation, Characterization, and Photocatalytic Activities of Octahedral Anatase Titania Particles

Abstract

Titania samples containing octahedral anatase particles (OAPs) were prepared by the ultrasonicationhydrothermal process of partially proton-exchanged potassium titanate nanowires. It was found that increase in the ultrasonication time changed the product morphology, with other structural properties such as specific surface area, crystalline size, and crystallinity remaining almost constant. The results of photocatalytic activity tests for those samples suggested higher activity of a sample with higher OAP content, especially for reactions in the presence of oxygen.Titanium(IV) oxide (titania) has been used extensively for many years as a photocatalyst, mainly owing to its redox ability, stability, and nontoxicity.1,2 Though a large number of papers have been published on titania photocatalysis, the essence of its photocatalytic activity, e.g., the reason of various levels of photocatalytic activity of samples with various properties and polymorphic composition, has not been clarified. 3 Recently, crystallite morphology, which has been widely studied for reactions occurring on a titania single crystal (mainly rutile (110)) 4 but neglected for particulate photocatalysts, has been considered as one of the crucial factors affecting the photocatalytic activity of particulate titania on the basis of the results of studies performed using facetted octahedral 57 and decahedral 810 anatase particles. We have recently developed an ultrasonication (US)hydrothermal reaction (HT) process 11 to prepare octahedral anatase particles (OAPs), exposing eight themodynamically most stable equivalent {101} facets, with enhanced photocatalytic activity, especially for the oxidation of acetic acid in aerated aqueous solutions, compared with many commercial titania samples with similar properties. However, proof of higher activity only owing to OAP morphology has not yet been obtained, because particles with the same structural properties except for morphology could not be prepared. In order to prove the effect of particle morphology on the photocatalytic activity, we examined various preparation conditions. In this paper, we present the results of sample preparation using different OAP contents and with other structural properties that remain almost constant; we also show a comparison of their photocatalytic activities.The samples were fabricated by the USHT process (for details, see SI)12 using partially proton-exchanged potassium titanate nanowires (TNW; Earthclean Tohoku Co., Ltd.) prepared by the HT reaction of Evonik P25 (Nippon Aerosil) in a potassium hydroxide solution (17 mol L ¹1) at 383 K for 20 h, followed by washing with dilute hydrochloric acid. 13 The controlled parameters were the US time (04 h), HT reaction time (348 h), and HT temperature (413473 K). The products were collected by centrifugation and vacuum dried (353 K, 12 h).Specific surface areas of the products were estimated by nitrogen adsorption at 77 K using the BrunauerEmmettTeller (BET) equation. Crystallinity (anatase content) as well as crystallite size and ...

Morphology- and Crystalline Composition-Governed Activity of Titania-Based Photocatalysts: Overview and Perspective

“…Although DAP particles have shown extremely high photocatalytic activity for both oxidation and reduction reactions (even higher than famous P25) [78], single-facet titania seems to be very attractive for mechanism study. For example, octahedral anatase particles (OAP) with eight {101} facets showed very high photocatalytic activity for the oxidation of acetic acid [128,129]. Although, various reports (as also shown in this review) have claimed that faceted morphology was beneficial for photocatalytic activity, the direct proof was not presented until the study by Wei et al [128,129].…”

Noble metal-modified octahedral anatase titania particles with enhanced activity for decomposition of chemical and microbiological pollutants

“…Octahedral anatase particles (OAPs), which expose eight equivalent and thermodynamically stable (1 0 1) facets, exhibit a very high level of photocatalytic activity, probably due to the preferential distribution of shallow electron traps (ETs) rather than deep ETs that results in a low rate of recombination of charge carriers [55], [56]. Although OAPs have a high level of photocatalytic activity, they are inactive under visible light (as is bare titania).…”

Decahedral-shaped anatase titania photocatalyst particles: Synthesis in a newly developed coaxial-flow gas-phase reactor

“…In addition, the difference in surface energies of the conduction and valence bands of different crystal facets of titania can promote the separation of electrons and holes [12]. The shape of an anatase titania single crystal, which determines the type of the exposed crystal facet, has recently been recognized as a potential key factor influencing photocatalytic efficiency and selectivity [13][14][15][16].…”