TiO₂ with Tunable Anatase-to-Rutile Nanoparticles Ratios: How Does the Photoactivity Depend on the Phase Composition and the Nature of Photocatalytic Reaction?

Abstract

We developed low-temperature (up to 200 °C) synthesis of TiO2 nanocomposites, which allows precise tuning of the anatase/rutile ratio. The materials were synthesized hydrothermally from strongly acidic solutions of Ti­(III) precursors and hydrogen peroxide. Two series of materials (A and B series) have been synthesized; the A series is characterized by smaller anatase particles, lower crystallinity, and higher specific surface area. The synthesized materials were examined in water oxidation, hydrogen peroxide reduction, photocurrent generation, and methanol-assisted water reduction. The optimal phase composition depends on the reaction typehigh contents of rutile or anatase should be considered for H2O2 reduction and water oxidation, respectively, while water reduction requires moderate contents of both polymorphs. The A series appeared more active in oxidation-controlled reactions, while the B series facilitated reduction-controlled processes. The DOS analysis confirmed that rutile is a significantly better reducer, whereas anatase is a better oxidant. Presented data show that a synergistic effect observed usually for anatase/rutile nanocomposites can result from both intrinsic and extrinsic factors. The intrinsic factors are responsible for the improved photocatalytic activity of the material related to its physicochemical properties, e.g., efficiency of charge separation, lifetime of photogenerated charges, absorption properties, redox characteristics, porosity, specific surface area, etc. The extrinsic factors are strongly related to the redox reactions to be performed at the photocatalyst surface, both oxidation and reduction. Therefore, we confirm hereby with presented experimental evidence that the design of the optimal photocatalyst must take into account both intrinsic and extrinsic factors.

Defective Grey TiO2 with Minuscule Anatase–Rutile Heterophase Junctions for Hydroxyl Radicals Formation in a Visible Light-Triggered Photocatalysis

“…Ullattil and Abdel-Wahab have recently developed self-oxygenated anatase-rutile phase junctions using a peroxide-assisted solvothermal strategy; it has been proven that anatase-rutile phase junctions are playing an important role in boosting the efficiency of photocatalysis [15]. Another version of TiO 2 has been developed by a hydrothermal method, where a very small amount of hydrogen peroxide, with reactants such as TiCl 3 and TiN, has been used to synthesize two sets of TiO 2 nanocrystallites with anatase-rutile phase junctions [27]. In both sets of solids, the temperature was set 200 • C. These materials were used in the photocatalytic hydroxylation of terephthalic acid and hydrogen generation [27].…”

“…Another version of TiO 2 has been developed by a hydrothermal method, where a very small amount of hydrogen peroxide, with reactants such as TiCl 3 and TiN, has been used to synthesize two sets of TiO 2 nanocrystallites with anatase-rutile phase junctions [27]. In both sets of solids, the temperature was set 200 • C. These materials were used in the photocatalytic hydroxylation of terephthalic acid and hydrogen generation [27].…”

Selective and efficient catalytic and photocatalytic oxidation of diphenyl sulphide to sulfoxide and sulfone: the role of hydrogen peroxide and TiO2 polymorph

“…Such anatase/rutile composites appeared also very active in photocatalytic transformations, both of Ph 2 S and Ph 2 SO, due to a synergistic effect of these phases reported in numerous publications on P25 and similar materials. [30][31][32][33][34] N100 and TRX_A appear more active catalytically, therefore, in a similar time window the second oxidation product, Ph 2 SO 2 , becomes the main product both in the dark and upon irradiation. The pure rutile phase, despite of its catalytic inactivity, appears the most active photomaterial.…”

Effects of Reaction Temperature on the Photocatalytic Activity of TiO2 with Pd and Cu Cocatalysts

“…The advantages of TiO 2 are high chemical stability, non-toxicity and low cost . Pd, Ag and Cu et al have been used as the cocatalysts of TiO 2 by facilitating electron transfer and therefore inhibiting electron-hole recombination, as well as by improving the photocatalytic response under the visible region [21,22,[26][27][28][29][30][31][32][33][34]. However, most of the studies on photocatalytic reaction were carried out at room temperature .…”