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

Ti-O-O coordination bond caused visible light photocatalytic property of layered titanium oxide

The layered titanium oxide is a useful and unique precursor for the facile and rapid preparation of the peroxide layered titanium oxide H_1.07Ti_1.73O₄·nH₂O (HTO) crystal with enhanced visible light photoactivity. The H₂O₂ molecules as peroxide chemicals rapidly enter into the interlayers of HTO crystal, and coordinate with Ti within TiO₆ octahedron to form a mass of Ti-O-O coordination bond in the interlayers. The introduction of these Ti-O-O coordination bonds result in lowering the band gap of HTO, and promoting the separation efficiency of the photo induced electron–hole pairs. Meanwhile, the photocatalytic investigation indicates that such peroxide HTO crystal has the enhanced photocatalytic performance for RhB degradation and water splitting to generate oxygen under visible light irradiating.

Giant Enhancement of Internal Electric Field Boosting Bulk Charge Separation for Photocatalysis

Incorporating carbon into Bi3 O4 Cl enhances its internal electric field by 126 times, which induces a bulk charge separation efficiency (ηbulk ) of 80%. This ultrahigh ηbulk value presents a state-of-the-art result in tuning the bulk charge separation. The generated C-doped Bi3 O4 Cl has a noble-metal- and electron-scavenger-free water-oxidation ability under visible light, which is difficult to achieve with most existing photocatalysts.

Photocatalytic conversion of CO2 over graphene-based composites: current status and future perspective

The continuous rise in the atmospheric CO₂ level and the ever-increasing demand of energy have raised serious concerns about the ensuing effects on the global climate change and future energy supply. Photocatalytic conversion of CO₂, which uses solar light energy to recycle CO₂ into fuels and chemicals, provides a promising and straightforward strategy to simultaneously reduce the atmospheric CO₂ level and fulfil the future energy demand. However, the lack of substantial development of state-of-the-art materials remains a major bottleneck of this technology. In recent years, graphene-based composite photocatalysts have gained increasing interest in CO₂ conversion due to the introduction of graphene with a series of unique physicochemical properties, which has shown to play a significant role in promoting the photocatalytic solar energy conversion efficiency. In this review, we comprehensively summarize the typical literature reports on graphene-based composites for photocatalytic conversion of CO₂ to produce solar fuels and chemicals. The main types of the reported graphene-based composites and the role of graphene in the composites in improving the photocatalytic performance have been elaborated. In particular, we have highlighted the possible role of graphene in tuning the product selectivity of photocatalytic reduction of CO₂. Finally, perspectives on the existing problems and future research on graphene-based composites toward photocatalytic conversion of CO₂ are critically discussed.

Facile synthesis of surface N-doped Bi2O2CO3: Origin of visible light photocatalytic activity and in situ DRIFTS studies

Bi2O2CO3 nanosheets with exposed {001} facets were prepared by a facile room temperature chemical method. Due to the high oxygen atom density in {001} facets of Bi2O2CO3, the addition of cetyltrimethylammonium bromide (CTAB) does not only influence the growth of crystalline Bi2O2CO3, but also modifies the surface properties of Bi2O2CO3 through the interaction between CTAB and Bi2O2CO3. Nitrogen from CTAB as dopant interstitially incorporates in the Bi2O2CO3 surface evidenced by both experimental and theoretical investigations. Hence, the formation of localized states from NO bond improves the visible light absorption and charge separation efficiency, which leads to an enhancement of visible light photocatalytic activity toward to the degradation of Rhodamine B (RhB) and oxidation of NO. In addition, the photocatalytic NO oxidation over Bi2O2CO3 nanosheets was successfully monitored for the first time using in situ diffuse reflectance infrared Fourier-transform spectroscopy (DRIFTS). Both bidentate and monodentate nitrates were identified on the surface of catalysts during the photocatalytic reaction process. The application of this strategy to another relevant bismuth based photocatalyst, BiOCl, demonstrated that surface interstitial N doping could also be achieved in this case. Therefore, our current route seems to be a general option to modify the surface properties of bismuth based photocatalysts.

Atomic Layer Deposition-Confined Nonstoichiometric TiO2 Nanocrystals with Tunneling Effects for Solar Driven Hydrogen Evolution

Ti(3+) self-doped TiO2 nanocrystals (TNCs) confined with controllable atomic layer deposition (ALD) amorphous layers were developed to provide a novel model of metal-insulator-semiconductor (MIS) photocatalysts for hydrogen generation in the ultraviolet to near-infrared region. Photoexcitation of optimized MIS nanostructures consisting of a metal cocatalyst (Pt), electron tunneling layer (ALD TiO2), and photoactive nonstoichiometric core (Ti(3+)-doped TNC) exhibited efficient hydrogen generation (52 μmol h(-1)·g(-1)), good reusability (16 h), and long-term stability (>7 d). The charge-transfer dynamics were examined using transient absorption spectroscopy to clarify the relationship between the photocatalytic activity and the tunneling effect. Our strategies highlight defect engineering in fabricating MIS photocatalysts with improved charge separation and tailored solar energy conversion properties.

Recent advances in 2D materials for photocatalysis

Two-dimensional (2D) materials have attracted increasing attention for photocatalytic applications because of their unique thickness dependent physical and chemical properties. This review gives a brief overview of the recent developments concerning the chemical synthesis and structural design of 2D materials at the nanoscale and their applications in photocatalytic areas. In particular, recent progress on the emerging strategies for tailoring 2D material-based photocatalysts to improve their photo-activity including elemental doping, heterostructure design and functional architecture assembly is discussed.

In Situ Fluorine Doping of TiO2 Superstructures for Efficient Visible-Light Driven Hydrogen Generation

With the aid of breakthroughs in nanoscience and nanotechnology, it is imperative to develop metal oxide semiconductors through visible light-driven hydrogen generation. In this study, TiOF2 was incorporated as an n-type F-dopant source to TiO2 mesocrystals (TMCs) with visible-light absorption during the topotactic transformation. The crystal growth, structural change, and dynamic morphological evolution, from the initial intermediate NH4 TiOF3 to HTiOF3, TiOF2, and F-doped TMCs, were verified through in situ temperature-dependent techniques to elucidate the doping mechanism from intermediate TiOF2. The visible-light efficiencies of photocatalytic hydrogen were dependent on the contents of the dopant as compared with the pure TMC and a controled reference. Using femtosecond time-resolved diffuse reflectance spectroscopy, the charge-transfer dynamics were monitored to confirm the improvement of charge separation after doping.

Photochemistry of the α-Al₂O₃-PETN Interface

Optical absorption measurements are combined with electronic structure calculations to explore photochemistry of an α-Al₂O₃-PETN interface formed by a nitroester (pentaerythritol tetranitrate, PETN, C₅H₈N₄O₁₂) and a wide band gap aluminum oxide (α-Al₂O₃) substrate. The first principles modeling is used to deconstruct and interpret the α-Al₂O₃-PETN absorption spectrum that has distinct peaks attributed to surface F⁰-centers and surface—PETN transitions. We predict the low energy α-Al₂O₃ F⁰-center—PETN transition, producing the excited triplet state, and α-Al₂O₃ F⁰-center—PETN charge transfer, generating the PETN anion radical. This implies that irradiation by commonly used lasers can easily initiate photodecomposition of both excited and charged PETN at the interface. The feasible mechanism of the photodecomposition is proposed.

Au/BiOCl heterojunction within mesoporous silica shell as stable plasmonic photocatalyst for efficient organic pollutants decomposition under visible light

A new mesoporous silica protected plasmonic photocatalyst, Au/BiOCl@mSiO2, was prepared by a modified AcHE method and a subsequent UV light induced photodeposition process. The surfactant-free heterojunction allows the electrons spontaneously flow from Au to nearby BiOCl surface, leading to the accumulation of positive charges on Au surface, and negative charges on Bi species under visible light. Au/BiOCl@mSiO2 exhibits high visible light photocatalytic efficiency in complete oxidation of aqueous formaldehyde and Rhodamin B. We showed that a positive relationship exists between the LSPR effect and rate enhancements, and leads to a hypothesis that the metallic Au LSPR enhances the photocatalytic rates on nearby semiconductors by transferring energetic electrons to BiOCl and increasing the steady-state concentration of active OH species by a multi-electron reduction of molecular oxygen. The OH species is the main oxidant in photocatalytic transformations, whose intensity is greatly enhanced in the dye-involving systems due to the synergetic effect between LSPR and dye sensitization processes. In addition, the mesoporous SiO2 shell not only inhibits the over growth of BiOCl nanocrystals within the silica frameworks, but also protects the dissolution of chloride or Au species into aqueous solution, which ultimately makes the Au/BiOCl@mSiO2 catalysts rather stable during photocatalysis.

Cellulose-Rich Nanofiber-Based Functional Nanoarchitectures

Surface self-assembly of functional molecules or nanoscale building blocks is an effective strategy for the syntheses of advanced materials. Natural cellulose-rich substances have unique macro-to-nano hierarchical structural features. The fabrication of nanoarchitectures, employing specific guest species on the surfaces of the fine structures of such substances, results in corresponding artificial nanomaterials that possess the chemical functionalities and physical properties of both sides. Metal oxide thin film coatings with nanometer precision on the nanofibers of bulk cellulose-rich substances not only yield replicas of nanostructured materials, but also make it possible for further assemblies of functional units on the surfaces. Hence, nanostructured metal oxides and further composites, as well as surface-functionalized cellulose-based composites are fabricated by employing cellulose-rich substances as templates or scaffolds. The three-dimensional cross-linked porous structures, with the high surface area of the resultant nanomaterials or composites, lead to superior performance when employed as photocatalysts, electrode materials, and sensing matrices, on which this report is focused.

Band gap and morphology engineering of TiO2 by silica and fluorine co-doping for efficient ultraviolet and visible photocatalysis

Silicon and fluorine co-doped anatase TiO₂ (Si–F–TiO₂) photocatalysts with enhanced photocatalytic activity were successfully prepared via a facile two-step synthetic method by using SiO₂ powders and (NH₄)₂TiF₆ as the precursors.

Nitrogen-doped titanium dioxide (N-doped TiO2) for visible light photocatalysis

Energy level diagrams for undoped and N-doped TiO₂ for visible light induced photocatalytic application.

Synthesis and characterization of BiPO4/g-C3N4 nanocomposites with significantly enhanced visible-light photocatalytic activity for benzene degradation

BiPO₄/g-C₃N₄ nanocomposites were fabricated by a hydrothermal method including calcination and showed high photocatalytic activity under visible light.

Materials for selective photo-oxygenation vs. photocatalysis: preparation, properties and applications in environmental and health fields

Photosensitizing materials made of organic dyes embedded in various supports are compared to usual supported TiO₂-based photocatalysts.

Accurate quantification of tio2 nanoparticles collected on air filters using a microwave-assisted acid digestion method

Titanium dioxide (TiO(2)) particles, including nanoparticles with diameters smaller than 100 nm, are used extensively in consumer products. In a 2011 current intelligence bulletin, the National Institute of Occupational Safety and Health (NIOSH) recommended methods to assess worker exposures to fine and ultrafine TiO(2) particles and associated occupational exposure limits for these particles. However, there are several challenges and problems encountered with these recommended exposure assessment methods involving the accurate quantitation of titanium dioxide collected on air filters using acid digestion followed by inductively coupled plasma optical emission spectroscopy (ICP-OES). Specifically, recommended digestion methods include the use of chemicals, such as perchloric acid, which are typically unavailable in most accredited industrial hygiene laboratories due to highly corrosive and oxidizing properties. Other alternative methods that are used typically involve the use of nitric acid or combination of nitric acid and sulfuric acid, which yield very poor recoveries for titanium dioxide. Therefore, given the current state of the science, it is clear that a new method is needed for exposure assessment. In this current study, a microwave-assisted acid digestion method has been specifically designed to improve the recovery of titanium in TiO(2) nanoparticles for quantitative analysis using ICP-OES. The optimum digestion conditions were determined by changing several variables including the acids used, digestion time, and temperature. Consequently, the optimized digestion temperature of 210°C with concentrated sulfuric and nitric acid (2:1 v/v) resulted in a recovery of >90% for TiO(2). The method is expected to provide for a more accurate quantification of airborne TiO(2) particles in the workplace environment.

Earth-abundant stable elemental semiconductor red phosphorus-based hybrids for environmental remediation and energy storage applications

The photocatalytic generation of hydrogen and the photodegradation of organic dyes in wastewater using solar light, preferably visible light, have attracted considerable interest because they are clean, low-cost, and environmentally friendly processes.

S-doped mesoporous nanocomposite of HTiNbO5 nanosheets and TiO2 nanoparticles with enhanced visible light photocatalytic activity

S-doped mesoporous TiO₂/HTiNbO₅ nanocomposite showed dramatically enhanced visible-light photocatalytic activity and stability owing to the combined effects of nano-heterojunction, S doping and morphology engineering.

Inorganic perovskite photocatalysts for solar energy utilization

This review specifically summarizes the recent development of perovskite photocatalysts and their applications in water splitting and environmental remediation.

Characterization of a highly efficient N-doped TiO2 photocatalyst prepared via factorial design

The preparation of a highly efficient N-doped TiO₂ photocatalyst was optimized by factorial design and the resulting powder was fully characterized.

Three way electron transfer of a C–N–S tri doped two-phase junction of TiO2nanoparticles for efficient visible light photocatalytic dye degradation

C–N–S tridoped TiO₂nanoparticles were synthesized by a sol–gel method using thiourea as a compound source of carbon (C), nitrogen (N) and sulphur (S).

Application of photo degradation for remediation of cyclic nitramine and nitroaromatic explosives

Photo degradation is a rapid and safe remediation process and advances in continuous-flow photochemistry can scale-up yields of photo degradation.

Synthesis of MoS2 nanosheet supported Z-scheme TiO2/g-C3N4 photocatalysts for the enhanced photocatalytic degradation of organic water pollutants

MoS₂ nanosheets loaded with Z-scheme TiO₂/g-C₃N₄ photocatalysts were prepared using a wetness impregnation method.

Facile synthesis of TaOxNy photocatalysts with enhanced visible photocatalytic activity

N-doped TaO_xN_y is prepared using ethylenediamine as the nitrogen source by a sol–gel method.

Facile preparation of a novel SnO2@UiO-66/rGO hybrid with enhanced photocatalytic activity under visible light irradiation

An effective ternary composite of SnO₂@UiO-66/rGO was designed and synthesized.

Y. S. One step solvothermal synthesis of ultra-fine N-doped TiO2 with enhanced visible light catalytic properties

Herein, we report the one-step solvothermal synthesis of nitrogen doped TiO₂ using N-methyl-2-pyrollidone as solvent cum dopant. The method leads to higher surface area, highly crystalline anatase TiO₂ with improved visible light response.

Double-hole codoped huge-gap semiconductor ZrO2 for visible-light photocatalysis

Anionic codoping pairs make the huge-gap semiconductor ZrO₂ a promising catalyst for solar-driven water splitting.

A new cadmium-doped titanium–oxo cluster with stable photocatalytic H2 evolution properties

A new Cd-doped titanium–oxo cluster (TOC) with good H₂ evolution ability and high catalytic stability has been prepared and characterized.

Facile preparation of N-doped TiO2at ambient temperature and pressure under UV light with 4-nitrophenol as the nitrogen source and its photocatalytic activities

This article reports the facile preparation of N-doped TiO₂(P25) in aqueous media at ambient temperature and pressure under inert conditions with 4-nitrophenol as the nitrogen source.

Coating a N-doped TiO2 shell on dually sensitized upconversion nanocrystals to provide NIR-enhanced photocatalysts for efficient utilization of upconverted emissions

An efficient NIR-enhanced photocatalyst was developed by coating a N-doped TiO₂ shell on dually sensitized core–shell upconversion nanocrystals.