Nitrogen-Doped Titanium Dioxide as Visible-Light-Sensitive Photocatalyst: Designs, Developments, and Prospects

Achieving significantly enhanced visible-light photocatalytic efficiency using a polyelectrolyte: the composites of exfoliated titania nanosheets, graphene, and poly(diallyl-dimethyl-ammonium chloride)

A high-performance visible-light-active photocatalyst is prepared using the polyelectrolyte/exfoliated titania nanosheet/graphene oxide (GO) precursor by flocculation followed by calcination. The polyelectrolyte poly(diallyl-dimethyl-ammonium chloride) serves not only as an effective binder to precipitate GO and titania nanosheets, but also boosts the overall performance of the catalyst significantly. Unlike most titania nanosheet-based catalysts reported in the literature, the composite absorbs light in the UV-Vis-NIR range. Its decomposition rate of methylene blue is 98% under visible light. This novel strategy of using a polymer to enhance the catalytic performance of titania nanosheet-based catalysts affords immense potential in designing and fabricating next-generation photocatalysts with high efficiency.

Tertiary amine mediated aerobic oxidation of sulfides into sulfoxides by visible-light photoredox catalysis on TiO2

The selective oxidation of sulfides into sulfoxides receives much attention due to industrial and biological applications. However, the realization of this reaction with molecular oxygen at room temperature, which is of importance towards green and sustainable chemistry, remains challenging. Herein, we develop a strategy to achieve the aerobic oxidation of sulfides into sulfoxides by exploring the synergy between a tertiary amine and titanium dioxide via visible-light photoredox catalysis. Specifically, titanium dioxide can interact with triethylamine (TEA) to form a visible-light harvesting surface complex, preluding the ensuing selective redox reaction. Moreover, TEA, whose stability was demonstrated by a turnover number of 32, plays a critical role as a redox mediator by shuttling electrons during the oxidation of sulfide. This work suggests that the addition of a redox mediator is highly functional in establishing visible-light-induced reactions via heterogeneous photoredox catalysis.

Insights into How Fluorine-Adsorption and n-Type Doping Affect the Relative Stability of the (001) and (101) Surfaces of TiO2: Enhancing the Exposure of More Active but Thermodynamically Less Stable (001)

The stability of both the pure and fluorine (F)-adsorbed surface of TiO2 is examined on the basis of density functional calculations. For pure surfaces, both the beneficial local geometric structures and local potential strengthen the Ti-O binding in (101), rendering it the most stable surface. For F-adsorbed surfaces, F-adsorption significantly weakens the Ti-O bonds in (101) but strengthens them in (001), so that (001) becomes more stable than (101) for the F-adsorbed surfaces. On the basis of this observation, we further show that the n-type doping in TiO2 can significantly decrease the ability of F-adsorption in switching the relative stability of the two surfaces. The present work not only provides new insights into the physical and chemical properties about both pure and F-adsorbed surfaces of TiO2 and conclusively explains related experimental results but also suggests viable ways to prepare TiO2 samples with a high percentage of (001).

Amine-Functionalized Titanate Nanosheet-Assembled Yolk@Shell Microspheres for Efficient Cocatalyst-Free Visible-Light Photocatalytic CO2 Reduction

Exploiting advanced semiconductor photocatalyst with superior activity and selectivity for the conversion of CO2 into solar fuels and valuable chemicals is of worldwide interest. In this report, hierarchical amine-functionalized titanate nanosheets based yolk@shell microspheres were synthesized via one-pot organic amine mediated anhydrous alcoholysis of titanium(IV) butoxide. The selected organic amine, diethylenetriamine, played multiple roles. First, it was essential for the crystallographic, morphological and textural control of the synthesized titanate nanoarchitectures. Second, it was crucial for the in situ functionalization of titanate nanosheets by concurrent interlayer intercalation and surface grafting, which gave rise to the strong visible-light absorption ability and high CO2 adsorption capacity. As a consequence of the synergetic tuning in multilevel microstructures, an integrated engineering of the multifunctional modules of the titanate-based photocatalysts was achieved for efficient CO2 reduction toward solar fuels.

Advances and recent trends in heterogeneous photo(electro)-catalysis for solar fuels and chemicals

In the context of a future renewable energy system based on hydrogen storage as energy-dense liquid alcohols co-synthesized from recycled CO2, this article reviews advances in photocatalysis and photoelectrocatalysis that exploit solar (photonic) primary energy in relevant endergonic processes, viz., H2 generation by water splitting, bio-oxygenate photoreforming, and artificial photosynthesis (CO2 reduction). Attainment of the efficiency (>10%) mandated for viable techno-economics (USD 2.00-4.00 per kg H2) and implementation on a global scale hinges on the development of photo(electro)catalysts and co-catalysts composed of earth-abundant elements offering visible-light-driven charge separation and surface redox chemistry in high quantum yield, while retaining the chemical and photo-stability typical of titanium dioxide, a ubiquitous oxide semiconductor and performance "benchmark". The dye-sensitized TiO2 solar cell and multi-junction Si are key "voltage-biasing" components in hybrid photovoltaic/photoelectrochemical (PV/PEC) devices that currently lead the field in performance. Prospects and limitations of visible-absorbing particulates, e.g., nanotextured crystalline α-Fe2O3, g-C3N4, and TiO2 sensitized by C/N-based dopants, multilayer composites, and plasmonic metals, are also considered. An interesting trend in water splitting is towards hydrogen peroxide as a solar fuel and value-added green reagent. Fundamental and technical hurdles impeding the advance towards pre-commercial solar fuels demonstration units are considered.

Polymorphic phase study on nitrogen-doped TiO2 nanoparticles: effect on oxygen site occupancy, dye sensitized solar cells efficiency and hydrogen production

In this work we show that phase formation and oxygen substitution can be controlled by the source of nitrogen used during the synthesis of TiO₂ nanoparticles.

High photocatalytic activity of carbon doped TiO2 prepared by fast combustion of organic capping ligands

Carbon doped TiO₂ prepared by fast combustion of oleylamine ligands exhibit much higher photocatalytic activity for hydrogen production than those prepared by conventional methods.

Enhancing visible-light photocatalytic activity of g-C3N4by doping phosphorus and coupling with CeO2for the degradation of methyl orange under visible light irradiation

The efficient charge transfer at the interface of CeO₂/P-C₃N₄composite catalyst due to the synergistic effect between P-C₃N₄and CeO₂, which leads to an effective photogenerated electrons–hole pairs separation.

Adsorption properties of trifluoroacetic acid on anatase (101) and (001) surfaces: a density functional theory study

Trifluoroacetic acid adsorbs preferentially on the TiO₂(001) surface working as a growth control agent.

A high efficient graphitic-C3N4/BiOI/graphene oxide ternary nanocomposite heterostructured photocatalyst with graphene oxide as electron transport buffer material

A high efficient graphitic-C₃N₄/BiOI/graphene oxide ternary nanocomposite photocatalyst with graphene oxide as electron transport buffer material was synthesized.

S-doped Na2Ti6O13@TiO2 core–shell nanorods with enhanced visible light photocatalytic performance

S-doped Na₂Ti₆O₁₃@TiO₂ core–shell nanorods with exposed anatase {101} facets showed enhanced visible-light photocatalytic activity and stability for the degradation of methylene blue owing to the combined effect of hybridization, morphology engineering and S doping.

Improved light absorption and photocatalytic activity of Zn,N-TiO2−x rich in oxygen vacancies synthesized by nitridation and hydrogenation

Compared with N-TiO₂ and Zn,N-TiO₂ samples, Zn,N-TiO_2−x rich in oxygen vacancies demonstrates high photocatalytic activity.

Preparation of luminescent titania/dye hybrid nanoparticles and their dissolution properties for controlling cellular environments

Monodispersed titania/octadecylamine/fluorescein-isothiocyanate hybrid nanoparticles are synthesized to demonstrate a proof-of-concept for nanomedicines: an indirect molecular delivery system with no cytotoxicity.

Zinc oxide based photocatalysis: tailoring surface-bulk structure and related interfacial charge carrier dynamics for better environmental applications

Surface-bulk modification of zinc oxide for efficient photocatalysis.

A controlled solvothermal synthesis of CuS hierarchical structures and their natural-light-induced photocatalytic properties

A solvothermal synthesis of CuS hierarchical structures for the photodegradation of methylene blue (MB).

Visible light assisted photocatalytic hydrogen generation by Ta2O5/Bi2O3, TaON/Bi2O3, and Ta3N5/Bi2O3 composites

Bi₂O₃/TaON or Ta₃N₅ heterojunctions show significant enhancement in photocatalytic H₂ production under visible light irradiation compared to individual components.

Mesoporous titanium dioxide coating on gold modified silica nanotubes: a tube-in-tube titanium nanostructure for visible-light photocatalysts

A novel tube-in-tube structured titanium dioxide (TiO₂) based visible-light photocatalyst with non-metal doping and plasmonic metal decoration was fabricated and characterized.

A facile and general synthesis strategy to doped TiO2 nanoaggregates with a mesoporous structure and comparable property

A facile and general route was explored to fabricate porous metal-doped TiO₂ nanoaggregates from a titanium glycolate precursor and metal salts, and doping with Co or Ni is an effective approach to improve the photocatalytic efficiency.

Green synthesis of ZnO hollow sphere nanostructures by a facile route at room temperature with efficient photocatalytic dye degradation properties

The present work has prepared ZnO hollow spherical nanoparticles using a straightforward synthetic route and has innovatively made use of carbon spheres as a template at room temperature.

Hydrothermal assisted sol–gel synthesis and multisite luminescent properties of anatase TiO2:Eu3+ nanorods

The relationship between local structure of Eu³⁺ ions and luminescence properties were discussed through site-selective spectroscopy at 10 K.

Steering charge kinetics in photocatalysis: intersection of materials syntheses, characterization techniques and theoretical simulations

This review outlines the recent progress on probing and steering charge kinetics toward designing highly efficient photocatalysts.

Organophosphonate bridged anatase mesocrystals: low temperature crystallization, thermal growth and hydrogen photo-evolution

Tuning P-doping: phosphorus dendrimers enabled access, at 60 °C, to ultra-stable organophosphonate-bridged-anatase mesocrystals with a promising water-splitting photo-activity.

Origin of the increased photocatalytic performance of TiO₂ nanocrystal composed of pure core and heavily nitrogen-doped shell: a theoretical study

We have carried out a theoretical study to explain the photocatalytic performance of the newly synthesized special core (pure TiO2)-shell (heavily nitrogen (N)-doped TiO2) structure of TiO2 nanocrystal using advanced first-principles calculations. The conventional N doping models by maximizing the mutual distances between dopants are found to only introduce localized gap states irrespective of doping concentrations, which is in agreement with previous theoretical results but cannot explain the experimental results. In comparison, the electronically coupled N doping of TiO2, which is almost as stable as the conventional doping models and generally overlooked in previous works, can not only narrow the overall band gap but also decrease the carrier recombination rate. In particular, in the special core-shell structure of TiO2 nanocrystal, perfect type-II-like homojunction is formed, which can further decrease the carrier recombination rate. The present study conclusively accounts for the recent experimental results and indicates that the final electronic structures of doping system are very sensitive to the models used to conduct calculations, which can rationalize the distinct conclusions about N-doped TiO2 in previous theoretical works.