Stable Co‐Catalyst‐Free Photocatalytic H 2 Evolution From Oxidized Titanium Nitride Nanopowders

Plasmon assisted synthesis of TiN-supported single-atom nickel catalysts

We report the deposition of single atom nickel catalyst on refractory plasmonic titanium nitride (TiN) nanomaterials supports using the wet synthesis method under visible light irradiation. TiN nanoparticles efficiently absorb visible light to generate photoexcited electrons and holes. Photoexcited electrons reduce nickel precursor to deposit Ni atoms on TiN nanoparticles' surface. The generated hot holes are scavenged by the methanol. We studied the Ni deposition on TiN nanoparticles by varying light intensity, light exposure time, and metal precursor concentration. These studies confirmed the photodeposition method is driven by hot electrons and helped us to find optimum synthesis conditions for single atoms deposition. We characterized the nanocatalysts using high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), energy dispersive X-ray spectroscopy (EDX), and X-ray photoelectron spectroscopy (XPS). We used density functional theory (DFT) calculations to predict favorable deposition sites and aggregation energy of Ni atoms on TiN. Surface defect sites of TiN are most favorable for single nickel atoms depositions. Interestingly, the oxygen sites on native surface oxide layer of TiN also exhibit strong binding with the single Ni atoms. Plasmon enhanced synthesis method can facilitate photodeposition of single atom catalysts on a wide class of metallic supports with plasmonic properties.

Probing the formation and optical properties of Ti3+–TiO2 with (001) exposed crystal facet by ethanol-assisted fluorination

(001)-faceted TiO₂ with Ti³⁺ defects that are exclusively embedded in the bulk lattice near the surface was synthesized.

Hydrogen-Location-Sensitive Modulation of the Redox Reactivity for Oxygen-Deficient TiO2

Hydrogenated black TiO₂ is receiving ever-increasing attention, primarily due to its ability to capture low-energy photons in the solar spectrum and its highly efficient redox reactivity for solar-driven water splitting. However, in-depth physical insight into the redox reactivity is still missing. In this work, we conducted a density functional theory study with Hubbard U correction (DFT+U) based on the model obtained from spectroscopic and aberration-corrected scanning transmission electron microscopy (AC-STEM) characterizations to reveal the synergy among H heteroatoms located at different surface sites where the six-coordinated Ti (Ti_6C) atom is converted from an inert trapping site to a site for the interchange of photoexcited electrons. This in-depth understanding may be applicable to the rational design of highly efficient solar-light-harvesting catalysts.

Photocatalysis with Reduced TiO2: From Black TiO2 to Cocatalyst-Free Hydrogen Production

Black TiO₂ nanomaterials have recently emerged as promising candidates for solar-driven photocatalytic hydrogen production. Despite the great efforts to synthesize highly reduced TiO₂, it is apparent that intermediate degree of reduction (namely, gray titania) brings about the formation of peculiar defective catalytic sites enabling cocatalyst-free hydrogen generation. A precise understanding of the structural and electronic nature of these catalytically active sites is still elusive, as well as the fundamental structure-activity relationships that govern formation of crystal defects, increased light absorption, charge separation, and photocatalytic activity. In this Review, we discuss the basic concepts that underlie an effective design of reduced TiO₂ photocatalysts for hydrogen production such as (i) defects formation in reduced TiO₂, (ii) analysis of structure deformation and presence of unpaired electrons through electron paramagnetic resonance spectroscopy, (iii) insights from surface science on electronic singularities due to defects, and (iv) the key differences between black and gray titania, that is, photocatalysts that require Pt-modification and cocatalyst-free photocatalytic hydrogen generation. Finally, future directions to improve the performance of reduced TiO₂ photocatalysts are outlined.

A Facile Approach to Prepare Black TiO₂ with Oxygen Vacancy for Enhancing Photocatalytic Activity

Black TiO₂ has triggered worldwide research interest due to its excellent photocatalytic properties. However, the understanding of its structure–property relationships and a more effective, facile and versatile method to produce it remain great challenges. We have developed a facile approach to synthesize black TiO₂ nanoparticles with significantly improved light absorption in the visible and infrared regions. The experimental results show that oxygen vacancies are the major factors responsible for black coloration. More importantly, our black TiO₂ nanoparticles have no Ti³⁺ ions. These oxygen vacancies could introduce localized states in the bandgap and act as trap centers, significantly decreasing the electron–hole recombination. The photocatalytic decomposition of both rhodamine B and methylene blue demonstrated that, under ultraviolet light irradiation, better photocatalytic performance is achieved with our black TiO₂ nanoparticles than with commercial TiO₂ nanoparticles.

Exploitation of the synergistic effect between surface and bulk defects in ultra-small N-doped titanium suboxides for enhancing photocatalytic hydrogen evolution

The work utilizes the “double-faced” roles of surface and bulk defects in engineering photocatalytic activity.

One-step synthesis of nonstoichiometric TiO2 nanorod films for enhanced photocatalytic H2 evolution

Nonstoichiometric TiO₂ nanorod films with high stability and excellent H₂ generation activities have been obtained by a facile one-step sputtering method.

Noble-Metal-Free Photocatalytic Hydrogen Evolution Activity: The Impact of Ball Milling Anatase Nanopowders with TiH2

Ball milling TiO₂ anatase together with TiH₂ can create an effective photocatalyst. The process changes the lattice and electronic structure of anatase. Lattice deformation created by mechanical impact combined with hydride incorporation yield electronic gap-states close to the conduction band of anatase. These provide longer lifetimes of photogenerated charge carriers and lead to an intrinsic cocatalytic activation of anatase for H₂ evolution.

Transparent Nb-doped TiO2 films with the [001] preferred orientation for efficient photocatalytic oxidation performance

[001]-Oriented Nb-TiO₂ films via topotactic transformation from [100]-oriented Nb-TiN exhibit efficient photoactivity due to highly-reactive-facet exposure and increased surface-reactive sites.