Bicrystalline TiO2 with controllable anatase–brookite phase content for enhanced CO2 photoreduction to fuels

Abstract

Among the three naturally existing phases of TiO 2 , brookite is the least studied as a photocatalyst. In this study, single-phase anatase and brookite, and mixed-phase anatase-brookite TiO 2 nanomaterials were synthesized through a hydrothermal method. The anatase-brookite phase content was controlled by adjusting the concentration of urea in the precursor solution. XRD, Raman spectroscopy, and highresolution TEM were used to confirm the crystal structures. SEM and TEM analyses demonstrated that anatase TiO 2 were nearly spherical nanoparticles while brookite TiO 2 were rod-shaped nanoparticles.UV-vis diffuse reflectance spectroscopy showed a blue shift in absorption spectra with increasing brookite content. The photocatalytic activities of the prepared bicrystalline TiO 2 were evaluated for CO 2 photoreduction in the presence of water vapor for production of solar fuels (CO and CH 4 ). The activities were compared with those of pure anatase, pure brookite, and a commercial anatase-rutile TiO 2 (P25).The results showed that bicrystalline anatase-brookite was generally more active than single-phase anatase, brookite, and P25. The bicrystalline mixture with a composition of 75% anatase and 25% brookite showed the highest photocatalytic activity, likely due to the enhanced interfacial charge transfer between anatase and brookite nanocrystals. In situ DRIFTS analysis showed that CO 2 À and HCO 3 À species were active reaction intermediates for CO 2 photoreduction while the accumulation of non-reactive CO 3 2À species on the TiO 2 surface may be detrimental.

Low-Temperature Sol-Gel Synthesis of Nitrogen-Doped Anatase/Brookite Biphasic Nanoparticles with High Surface Area and Visible-Light Performance

“…Moreover, the presence of brookite in the mixture can reduce the recombination of hole-electron pairs. The band gap was also widened with increasing brookite content [34]. This is why NA-165 (3.03 eV, 6% brookite content) and NA-185 (3.05 eV, 10% brookite content) exhibited similar MO photocatalytic degradation activity.…”

Brookite: Nothing New under the Sun?

“…Adapting the procedure reported by Zhao et al [45], some of us showed that pure brookite, anatase and rutile with a well-defined shape and dimension can be obtained using titanium (IV) bis(ammonium lactate) dihydroxide, Ti(NH 4 C 3 H 4 O 3 ) 2 (OH) 2 , and varying the concentration of urea in aqueous solution (0 to 7.0 M) at 160 • C for 24 h (Figure 2). Pure brookite nanorod formation was favored by higher urea concentrations, corresponding to higher pH values due to urea decomposition, in accordance with the literature [45,46].…”

Chelated Nitrogen-Sulphur-Codoped TiO2: Synthesis, Characterization, Mechanistic, and UV/Visible Photocatalytic Studies

“…Thermodynamically, rutile is the most stable phase while both anatase and brookite are metastable, transferring to rutile under heat treatment, typically at temperature ranging between 600 and 700°C [2]. Among the TiO 2 crystalline forms, anatase and rutile are the most widely investigated polymorphs, with anatase generally found to be more photocatalytically active than brookite and rutile, but some reports illustrate the synergistic effect found in the composite mixture of anatase-brookite and anatase-rutile to be responsible for the enhanced photocatalytic activity [3,4]. However, because of the large band gap, anatase (3.20 eV) begins to absorb UV light around 388.5 nm, and brookite (3.14 eV) absorbs at around 395 nm, whereas the absorption onset of rutile (3.02 eV) occurs around 411 nm [5].…”