Defect‐induced Ordered Mesoporous Titania Molecular Sieves: A Unique and Highly Efficient Hetero‐phase Photocatalyst for Solar Hydrogen Generation

Abstract

The conversion of solar energy into fuel has gained significant interest, particularly in photocatalytic water splitting, and the materials that efficiently generate hydrogen from water or aqueous solution using solar irradiation are highly desired for the hydrogen economy. Photocatalysts made of N‐doped TiO2 are frequently utilized for breaking of water molecules in the process of generating hydrogen. To achieve this target, a unique defect‐induced nitrogen‐doped highly organized 2D‐hexagonal periodic mesoporous titania, TiO2‐xNy with a well‐crystallized framework is synthesized in a reproducible way using structure‐directing agents, e. g., F108, F127, P123, and CTAB. The nitrogen is incorporated into these samples through a facile method involving the calcination of templated materials in an air. A systematic characterization of the resulting ordered mesoporous titania employing a battery of experimental techniques indicates the presence of considerable amounts of intrinsic defects, viz., trapped electrons in oxygen vacancy and/or Ti3+ centres via nitrogen‐doping in the titania matrix. These defects in turn promote the charge separation of photogenerated excitons, and therefore exhibit excellent photocatalytic activity for the hydrogen evolution reaction as compared to commercial titania such as Aeroxide®P‐25. The superior activity of the N‐doped mesoporous TiO2 is attributed to the synergistic effect of facile charge migration with high carrier density, unique phase composition (bronze and anatase), slow recombination of photo‐induced excitons, and enhanced absorbance from ultra‐violet to the visible region.

Ytterbium–nitrogen co-doped ordered mesoporous TiO2: an innovative hetero-phase photocatalyst for harnessing solar energy in green hydrogen production

“…67 As expected, and in agreement with our EPR studies, we also observed an additional shoulder located at around 457.5 eV, attributed to Ti 3+ defects, while such a feature is almost absent or only a weak signal can be noticed in the case of P-25 which is as per the literature. 32,68 Furthermore, it can also be seen from Fig. 10 that the peaks of trivalent titanium in Yb-doped samples, viz.…”

“…, N-OMTs, are also included. 32 It may, however, be noticed from these figures that, unlike the singly doped N-OMT materials, the doubly doped OMTs, i.e. , Yb/N-TMF-127, calcined under standard conditions, viz.…”

“…S12, ESI‡). Furthermore, a quantitative analysis was conducted using a standard procedure outlined in the literature 32 to determine the actual spin concentration in the samples under investigation, and the computed values are presented in Table 2. The table reveals that the Yb/N-OMT samples exhibit a substantial spin concentration, indicating the presence of a significant amount of Ti 3+ centre intrinsic defects in the mesoporous matrix.…”

“…Hence, they might serve as an intermedium, which after absorbing near-infrared (NIR) light, can transfer energy to titania to generate strongly oxidative holes and reductive electrons, which could help achieve a better photocatalytic activity. Similarly, Selvam and coworkers 30,32 reported a well-stabilized OMT and tested for photocatalytic oxidation and water-splitting reactions.…”

“…9–19 Furthermore, high-quality ordered mesoporous titania (OMT) including N-doped mesoporous titania (N-OMT) having high specific surface area and regular pore channels was also attempted for this purpose. 20–33…”