TiOxNy Modified TiO2 Powders Prepared by Plasma Enhanced Atomic Layer Deposition for Highly Visible Light Photocatalysis

Synthesis of TiOxNy oxynitrides with a tunable nitrogen content

TiOxNy is a solid solution of cubic TiN and cubic TiO, with the ability to adjust its physical and chemical properties by modifying the O/N ratio, thus making it suitable for various applications. However, the synthesis of TiOxNy remains a significant challenge for inorganic chemists. In this work, we have successfully synthesized TiOxNy nanoparticles using the layered oxide Cs0.68Ti1.83O4 as the precursor and urea as the nitrogen source. The synthesis process was conducted within a temperature range of 800 to 1200 °C, leading to the transformation of the nitrided products from a two-dimensional layered precursor structure to a three-dimensional structure as the temperature increased. By varying the reaction temperature, the O/N ratio can be controlled. The experimental findings demonstrate that the nitrogen content in TiOxNy nanoparticles increases with rising temperature, ranging from TiO0.8N0.2 at 800 °C to TiO0.25N0.75 at 1200 °C. This work highlights the potential of the solid-state method in tailoring the properties of TiOxNy nanoparticles and presents a novel approach for synthesizing oxynitrides.

Modulation of Structural, Electronic, and Optical Properties of Titanium Nitride Thin Films by Regulated In Situ Oxidation

Epitaxial titanium nitride (TiN) and titanium oxynitride (TiON) thin films have been grown on sapphire substrates using a pulsed laser deposition (PLD) method in high-vacuum conditions (base pressure <3 × 10^-6 T). This vacuum contains enough residual oxygen to allow a time-independent gas phase oxidation of the ablated species as well as a time-dependent regulated surface oxidation of TiN to TiON films. The time-dependent surface oxidation is controlled by means of film deposition time that, in turn, is controlled by changing the number of laser pulses impinging on the polycrystalline TiN target at a constant repetition rate. By changing the number of laser pulses from 150 to 5000, unoxidized (or negligibly oxidized) and oxidized TiN films have been obtained with the thickness in the range of four unit cells to 70 unit cells of TiN/TiON. X-ray photoelectron spectroscopy (XPS) investigations reveal higher oxygen content in TiON films prepared with a larger number of laser pulses. The oxidation of TiN films is achieved by precisely controlling the time of deposition, which affects the surface diffusion of oxygen to the TiN film lattice. The lattice constants of the TiON films obtained by x-ray diffraction (XRD) increase with the oxygen content in the film, as predicted by molecular dynamics (MD) simulations. The lattice constant increase is explained based on a larger electrostatic repulsive force due to unbalanced local charges in the vicinity of Ti vacancies and substitutional O. The bandgap of TiN and TiON films, measured using UV-visible spectroscopy, has an asymmetric V-shaped variation as a function of the number of pulses. The bandgap variation following the lower number of laser pulses (150-750) of the V-shaped curve is explained using the quantum confinement effect, while the bandgap variation following the higher number of laser pulses (1000-5000) is associated with the modification in the band structure due to hybridization of O_2p and N_2p energy levels.

Nanoporous TiN/TiO2/Alumina Membrane for Photoelectrochemical Hydrogen Production from Sewage Water

An aluminum oxide, Al2O3, template is prepared using a novel Ni imprinting method with high hexagonal pore accuracy and order. The pore diameter after the widening process is about 320 nm. TiO2 layer is deposited inside the template using atomic layer deposition (ALD) followed by the deposition of 6 nm TiN thin film over the TiO2 using a direct current (DC) sputtering unit. The prepared nanotubular TiN/TiO2/Al2O3 was fully characterized using different analytical tools such as X-ray diffraction (XRD), Energy-dispersive X-ray (EDX) spectroscopy, scanning electron microscopy (SEM), and optical UV-Vis spectroscopy. Exploring the current-voltage relationships under different light intensities, wavelengths, and temperatures was used to investigate the electrode's application before and after Au coating for H2 production from sewage water splitting without the use of any sacrificing agents. All thermodynamic parameters were determined, as well as quantum efficiency (QE) and incident photon to current conversion efficiency (IPCE). The QE was 0.25% and 0.34% at 400 mW·cm-2 for the photoelectrode before and after Au coating, respectively. Also, the activation energy was 27.22 and 18.84 kJ·mol-1, the enthalpy was 24.26 and 15.77 J·mol-1, and the entropy was 238.1 and 211.5 kJ-1·mol-1 before and after Au coating, respectively. Because of its high stability and low cost, the prepared photoelectrode may be suitable for industrial applications.

Facile Synthesis of Potassium-Doped Titanium Oxide Nanostructure (KTiOxs)/AlO(OH) Composites for Enhanced Photocatalytic Performance

Generally, nanoparticles (NPs) are used as photocatalysts, which sometimes results in difficulties in the separation and recycling of photocatalysts from suspensions after their application in water and wastewater treatment, which hinders industrial applications of NPs that are too fine to be removed by gravitational settling. This can be solved by using support NPs to overcome these problems. -OH enrich AlO(OH), which is produced by a steam coating process, has been could be used as a possible support, because the -OH groups on the surface can interact with foreign molecules; thus, various composite functional materials can be prepared. Potassium doped titanium oxide NPs, which are produced by a wet corrosion process, namely KTiOxs, have been selected as photocatalysts, because KTiOxs have sufficient K+ ions, thereby expecting the chemical bonding with -OH group from AlO(OH). This study fabricated a novel photocataysis system made by combining KTiOxs as catalysts and AlO(OH) as the catalysts’ support, namely KTiOxs/AlO(OH) composites. The KTiOxs nanowires, obtained from 10 mol/L of a KOH solution treated with Ti and AlO(OH) at 280 °C for 24 h through a steam coating process, yielded the highest surface area and the highest photocatalytic performance.

Surface Modification of Catalysts via Atomic Layer Deposition for Pollutants Elimination

In recent years, atomic layer deposition (ALD) is widely used for surface modification of materials to improve the catalytic performance for removing pollutants, e.g., CO, hydrocarbons, heavy metal ions, and organic pollutants, and much progress has been achieved. In this review, we summarize the recent development of ALD applications in environmental remediation from the perspective of surface modification approaches, including conformal coating, uniform particle deposition, and area-selective deposition. Through the ALD conformal coating, the activity of photocatalysts improved. Uniform particle deposition is used to prepare nanostructured catalysts via ALD for removal of air pollutions and dyes. Area-selective deposition is adopted to cover the specific defects on the surface of materials and synthesize bimetallic catalysts to remove CO and other contaminations. In addition, the design strategy of catalysts and shortcomings of current studies are discussed in each section. At last, this review points out some potential research trends and comes up with a few routes to further improve the performance of catalysts via ALD surface modification and deeper investigate the ALD reaction mechanisms.

Recent Developments of Advanced Ti3+-Self-Doped TiO2 for Efficient Visible-Light-Driven Photocatalysis

Research into the development of efficient semiconductor photocatalytic materials is a promising approach to solving environmental and energy problems worldwide. Among these materials, TiO2 photocatalysts are one of the most commonly used due to their efficient photoactivity, high stability, low cost and environmental friendliness. However, since the UV content of sunlight is less than 5%, the development of visible light-activated TiO2-based photocatalysts is essential to increase the solar energy efficiency. Here, we review recent works on advanced visible light-activated Ti3+-self-doped TiO2 (Ti3+–TiO2) photocatalysts with improved electronic band structures for efficient charge separation. We analyze the different methods used to produce Ti3+–TiO2 photocatalysts, where Ti3+ with a high oxygen defect density can be used for energy production from visible light. We categorize advanced modifications in electronic states of Ti3+–TiO2 by improving their photocatalytic activity. Ti3+–TiO2 photocatalysts with large charge separation and low recombination of photogenerated electrons and holes can be practically applied for energy conversion and advanced oxidation processes in natural environments and deserve significant attention.

Atomic Layer Deposition on Dispersed Materials in Liquid Phase by Stoichiometrically Limited Injections

Atomic layer deposition (ALD) is a well-established vapor-phase technique for depositing thin films with high conformality and atomically precise control over thickness. Its industrial development has been largely confined to wafers and low-surface-area materials because deposition on high-surface-area materials and powders remains extremely challenging. Challenges with such materials include long deposition times, extensive purging cycles, and requirements for large excesses of precursors and expensive low-pressure equipment. Here, a simple solution-phase deposition process based on subsequent injections of stoichiometric quantities of precursor is performed using common laboratory synthesis equipment. Precisely measured precursor stoichiometries avoid any unwanted reactions in solution and ensure layer-by-layer growth with the same precision as gas-phase ALD, without any excess precursor or purging required. Identical coating qualities are achieved when comparing this technique to Al₂ O₃ deposition by fluidized-bed reactor ALD (FBR-ALD). The process is easily scaled up to coat >150 g of material using the same inexpensive laboratory glassware without any loss in coating quality. This technique is extended to sulfides and phosphates and can achieve coatings that are not possible using classic gas-phase ALD, including the deposition of phosphates with inexpensive but nonvolatile phosphoric acid.

Visible-Light-Induced Photocatalytic and Antibacterial Activity of TiO2 Codoped with Nitrogen and Bismuth: New Perspectives to Control Implant-Biofilm-Related Diseases

Biofilm-associated diseases are one of the main causes of implant failure. Currently, the development of implant surface treatment goes beyond the osseointegration process and focuses on the creation of surfaces with antimicrobial action and with the possibility to be re-activated (i.e., light source activation). Titanium dioxide (TiO₂), an excellent photocatalyst used for photocatalytic antibacterial applications, could be a great alternative, but its efficiency is limited to the ultraviolet (UV) range of the electromagnetic spectrum. Since UV radiation has carcinogenic potential, we created a functional TiO₂ coating codoped with nitrogen and bismuth via the plasma electrolytic oxidation (PEO) of titanium to achieve an antibacterial effect under visible light with re-activation potential. A complex surface topography was demonstrated by scanning electron microscopy and three-dimensional confocal laser scanning microscopy. Additionally, PEO-treated surfaces showed greater hydrophilicity and albumin adsorption compared to control, untreated titanium. Bismuth incorporation shifted the band gap of TiO₂ to the visible region and facilitated higher degradation of methyl orange (MO) in the dark, with a greater reduction in the concentration of MO after visible-light irradiation even after 72 h of aging. These results were consistent with the in vitro antibacterial effect, where samples with nitrogen and bismuth in their composition showed the greatest bacterial reduction after 24 h of dual-species biofilm formation ( Streptococcus sanguinis and Actinomyces naeslundii) in darkness with a superior effect at 30 min of visible-light irradiation. In addition, such a coating presents reusable photocatalytic potential and good biocompatibility by presenting a noncytotoxicity effect on human gingival fibroblast cells. Therefore, nitrogen and bismuth incorporation into TiO₂ via PEO can be considered a promising alternative for dental implant application with antibacterial properties in darkness, with a stronger effect after visible-light application.

Structural-Controlled Synthesis of Highly Efficient Visible Light TiO2 Photocatalyst via One-Step Single-Mode Microwave Assisted Reaction

TiO₂ with different chemical structures are successfully synthesized via a one-step single-mode magnetic microwave (SMMW) assisted process, during where Ti selectively oxidizes in magnetic field under Ar-O₂ mixed atmosphere. The chemical state and band structure of the as-prepared TiO₂ are well-controlled by changing the volume fraction of O₂ (φO₂) during SMMW synthesis. Ti³⁺ self-doped TiO₂ (TiO_2−x, 0 < x < 2) is synthesized under lower φO₂, while TiO₂ with specific core/shell structure (TiO_2+y core/TiO_2−x-TiO_2+z shell) is observed under higher φO₂. The as-synthesized TiO₂ with controlled structures show sufficient light absorption in visible region and quite narrow bandgap (2.05 eV∼), whose value can be also tuned by φO₂ during SMMW synthesis. In addition, the synthesized TiO₂ exhibits highly efficient photocatalytic performance towards the degradation of Rhodamine B under UV and visible light irradiation. The formation mechanism for different structural TiO₂ can be attributed to the specific rapid heating and cooling dynamics induced by SMMW irradiation.