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The low penetration depth of UV light in mammalian tissue is the critical limitation for the use of TiO2-based photocatalysis in biomedical applications. In this work, we develop an effective near-infrared (NIR)-active photocatalytic platform that consists of a shell structure of upconversion nanocrystals decorated on a core of Au/dark-TiO2. The heart of this system is the strong photocatalytic activity in the visible region enabled by the gold surface-plasmon resonance on dark TiO2(D-TiO2). Simulation and experiment demonstrate for an optimized Au/D-TiO2combination a highly enhanced light absorption in the visible range. Using ampicillin sodium (AMP) as model drug, we exemplify the effective use of this principle by demonstrating a NIR light-triggered photocatalytic payload release. Importantly, the photocatalytically generated reactive oxygen species can effectively inactivate AMP-resistant bacteria strains, thus maintaining an antibacterial effect even after all drug is released. Overall, we anticipate that the here-introduced NIR-light-active photocatalytic cascade can considerably widen TiO2-based photocatalysis and its applications into the infrared range.

The primary focus of the paper is the fabrication of nanotubes viaa two steps anodizing procedure on a TiZr substrate followed subsequent annealing treatments and their effect on surface and biocompatibility. The two step anodizing process is optimized for obtaining uniform and ordered nanotubular structures, that are then annealed in air or reduced in an Ar/H2environment. The high aspect ratio nanotubular structures (diameter 160 nm, length 9.4 μm) maintained their morphology after annealing or reduction. While the thermal treatments burned-off the fluoride, they converted the tubes to ZrTiO4(annealing in air) or (Zr0.333Ti0.666)O2(reducing). Surface roughness and adhesion forces evaluation of the nanostructures was included in the AFM investigations, and show that these properties can be tuned. In vitrocell response to TiZr substrate and nanotubular coatings were analyzed using HGF-1gingival fibroblasts cell line and LDH, nitric oxide (NO) and reactive oxygen species (ROS) tests. Regarding the hydrophilic balance of the studied samples, as expected it decreased after annealing and but increased after reduction, with only small change in the cell response. The results suggest that these coatings are biocompatible with human gingival fibroblast and can be used in biomedical applications without generating any considerable inflammatory process.

We induce solid-state dewetting of thin Au films (nominal thickness of 0.5–10 nm) on flat TiO2surfaces to produce Au nanoparticles with an average size tunable in the 3–200 nm range. Such Au-decorated TiO2surfaces enable plasmonic photoelectrochemical water splitting under visible light illumination (450–750 nm), with a photon-to-current conversion efficiency that reaches a maximum for TiO2surfaces decorated with ∼30 nm sized Au particles. Optical measurements show, as expected, a red shift of the plasmon resonance with the increasing Au nanoparticle size. More interestingly, the photocurrent is found to peak for every photoanode at ∼600 nm regardless of the Au nanoparticle size, i.e., the wavelength of maximum photocurrent is size-independent. Such a remarkable observation can be ascribed to a hot electron injection cutoff effect, i.e., can be explained in terms of the interband versus intraband transition scenario.

Photoelectrochemical water splitting on n-type semiconductors is highly dependent on catalysis of the rate-determining reaction of O2evolution. Conventionally, in electrochemistry and photoelectrochemistry O2evolution is catalyzed by metal oxide catalysts like IrO2and RuO2, whereas noble metals such as Pt are considered unsuitable for this purpose. However, our study finds that Pt, in its single-atom form, exhibits exceptional cocatalytic properties for photoelectrochemical water oxidation on a TiO2photoanode, in contrast to Pt in a nanoparticle form. The decoration of Pt single atoms onto TiO2yields a remarkable current density of 5.89 mA cm–2at 1.23 VRHE, surpassing bare TiO2(or Pt nanoparticle decorated TiO2) by 2.52 times. Notably, this enhancement remains consistent over a wide pH range. By accompanying theoretical work, we assign this significant enhancement to an improved charge transfer and separation efficiency along with accelerated kinetics in the oxygen evolution reaction facilitated by the presence of Pt single atoms on the TiO2surface.

Compared to many other metal oxides, anatase TiO2shows relatively lower reactivity toward carboxylic acid anchor groups. The latter is crucial for applications, for example, in dye-sensitized solar cells (DSSCs), where the most used dyes bind to the metal oxide surface through carboxylic acid terminations. To improve the surface reactivity, metal–phosphate bilayers of Ni or Co were synthesized on anatase TiO2compact oxide and nanotubes. In both cases, time-of-flight secondary ion mass spectrometry (ToF-SIMS) and X-ray photoelectron spectroscopy (XPS) results showed that the bilayers were successfully formed and that the phosphate layer works as an intermediate between TiO2and the other species. ToF-SIMS depth profiles of modified nanotubes showed that Ni and Co are present through the whole tube length and reduce in content after heat treatment, in agreement with XPS results. Phosphate groups, on the other hand, are more present in the tubes’ depth, and their content on the surface is reduced upon exposure to temperature. The reactivity of the modified surfaces toward carboxylic acid-terminated molecules, as stearic acid and Ru-based N719 dye, was evaluated. Contact angle measurements together with dye desorption experiments demonstrated that the Co–phosphate bilayers heat-treated at 300 °C resulted in the largest enhancement compared to the reference. Bilayer-modified compact anatase TiO2and anatase TiO2nanotubes were utilized as photoanodes in DSSCs. An increase in efficiency was observed for all modified electrodes with phosphate–Co treatment, leading to the highest JSCvalues and an efficiency improvement of 48%.

TiS2 nanotubular structures were synthesized by a high temperature H2S treatment of anodized TiO2 nanotube layers, and their electrochemical activity for a use as counter electrodes in dye sensitized solar cells (DSSCs) was evaluated. During conversion to TiS2 compositional, morphological and structural transformations were monitored. The fully converted TiS2 nanostructures show a high electrocatalytic activity for the I[?]/I3[?] oxidation comparable to a nanoparticular platinum layer. For a simplified model a DSSC solar cell efficiency of 6.1% was obtained using the TiS2 nanotube layer as counter electrode, which is very close to values obtained for a Pt reference (6.2%).

Noble metal cocatalysts are conventionally a crucial factor in oxide-semiconductor-based photocatalytic hydrogen generation. In the present work, we show that optimized high-temperature hydrogenation of commercially available strontium titanate (SrTiO3) powder can be used to engineer an intrinsic cocatalytic shell around nanoparticles that can create a photocatalyst that is highly effective without the use of any additional cocatalyst for hydrogen generation from neutral aqueous methanol solutions. This intrinsic activation effect can also be observed for SrTiO3[100] single crystal as well as Nb-doped SrTiO3[100] single crystal. For all types of SrTiO3samples (nanopowders and either of the single crystals), hydrogenation under optimum conditions leads to a surface-hydroxylated layer together with lattice defects visible by transmission electron microscopy, electron paramagnetic resonance (EPR), and photoluminescence (PL). Active samples provide specific defects identified by EPR, PL, and electron-energy loss spectroscopy as Ti3+states in a defective matrix—this is in contrast to the inactive defects formed in other reductive atmospheres. In aqueous media, active SrTiO3samples show a significant negative shift of the flatband potential (in photoelectrochemical as well as in capacitance data) and a lower charge-transfer resistance for photoexcited electrons. We therefore ascribe the remarkable cocatalyst-free activation of the material to a synergy between thermodynamics (altered interface energetics induced by hydroxylation) and kinetics (charge transfer mediation by suitable Ti3+states).

Au and Pt do not form homogeneous bulk alloys as they are thermodynamically not miscible. However, we show that anodic TiO2nanotubes (NTs) can in situ be uniformly decorated with homogeneous AuPt alloy nanoparticles (NPs) during their anodic growth. For this, a metallic Ti substrate containing low amounts of dissolved Au (0.1 atom %) and Pt (0.1 atom %) is used for anodizing. The matrix metal (Ti) is converted to oxide, whereas at the oxide/metal interface direct noble metal particle formation and alloying of Au and Pt takes place; continuously these particles are then picked up by the growing nanotube wall. In our experiments, the AuPt alloy NPs have an average size of 4.2 nm, and at the end of the anodic process, these are regularly dispersed over the TiO2nanotubes. These alloyed AuPt particles act as excellent co-catalyst in photocatalytic H2generation, with a H2production rate of 12.04 μL h–1under solar light. This represents a strongly enhanced activity as compared to TiO2NTs decorated with monometallic particles of Au (7 μL h–1) or Pt (9.96 μL h–1).

The use of bioactive glass (BG) particles as a filler for the development of composite electrospun fibers has already been widely reported and investigated. The novelty of the present research work is represented by the use of benign solvents (like acetic acid and formic acid) for electrospinning of composite fibers containing BG particles, by using a blend of PCL and chitosan. In this work, different BG particle sizes were investigated, namely nanosized and micron-sized. A preliminary investigation about the possible alteration of BG particles in the electrospinning solvents was performed using SEM analysis. The obtained composite fibers were investigated in terms of morphological, chemical and mechanical properties. An in vitromineralization assay in simulated body fluid (SBF) was performed to investigate the capability of the composite electrospun fibers to induce the formation of hydroxycarbonate apatite (HCA).

Ordered TiO2 through-hole membranes were obtained effectively by the repeated use of a Ti substrate with ordered concaves. A combined process involving the formation of two-layer structures with different solubilities through an intermediate heat-treatment, and selective dissolution of the bottom part of the oxide allows the repeated use of the Ti substrate with an ordered array of concaves, which act as initiation sites for hole development during the subsequent anodization. For the repeated use of the Ti substrate with ordered concaves, the oxide layer must be removed selectively without the dissolution of the Ti substrate. A mixed solution of HF and CrO3 was found to be effective for selective dissolution. Ordered TiO2 through-hole membranes obtained by this process can be used in various applications requiring an ordered hole arrangement.

In the present work we report on TiO2nanotube arrays (TNTAs) that were converted to a conductive scaffold established via an optimized reduction treatment in Ar/H2. These conductive TNTAs are then employed for RuO2nanoparticle decoration. The effect of the Ar/H2treatment is evaluated by electron energy loss spectroscopy (EELS) and electron paramagnetic resonance (EPR). The results show that, under ideal conditions, buried Ti3+states are formed, with a higher concentration in the inner shell of the nanotube. Together with the capacitive and conductive performance, investigated by solid-state conductivity and electrochemical measurements, we find that 20 μm long TNTAs, annealed at 550 °C in Ar/H2, yield an optimized and stable structure that provides a remarkably low resistivity of 13.5 KΩ/tube (vs. 70.2 MΩ for non-treated nanotubes). In cycling experiment, with a loading of only 0.048 mg cm−2RuO2a specific capacitance of 1297 F g−1can be reached. The reason for this highly efficient use of RuO2is that the conducting core-shell scaffold provides a unique, well dispersed RuO2nanoparticle structure (∼2.8 nm), which is responsible for the high specific capacitance, and moreover yields an excellent long-term cycling stability.

TiO2used as a light‐absorbing semiconductor represents the classic benchmark for photocatalytic solar energy conversion and many other photocatalytic reactions. Various strategies are developed to improve the photoresponse of TiO2‐based materials, such as bandgap engineering or surface sensitization in combination with nanostructuring and geometry optimization. The present feature article is focused on direct and indirect approaches involving bulk or surface fluorine used to tune the surface chemistry, electronic structure, and the morphology of TiO2photocatalysts. A comprehensive overview is provided on fluorine effects on TiO2, involving morphology modifications, and how surface or bulk fluorine affect the photocatalytic performance of TiO2. After outlining some basic interaction principles of F and TiO2, characterization techniques for different fluorine species are discussed. It is reviewed how fluorine during crystal growth mediates the morphology of TiO2; then how surface fluorination and doping fluorine effects can be beneficially utilized in photocatalysis are discussed. Finally, synergistic effects between fluorine and cocatalyst are discussed, for example, the use of lattice fluorine species to stabilize Pt single‐atom cocatalysts. Finally, the challenges and outlook on further advancing the development of fluorine effects are highlighted. TiO2semiconductors are very promising photocatalysts in solar energy conversion and increasing its solar conversion efficiency is greatly demanded. Fluorine species involved in the design of TiO2is capable of tuning the structural properties of TiO2. This perspective summarizes the direct and indirect effect of fluorine on photocatalytic performance of TiO2, along with future needs and opportunities in this field.