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This work shows the possibility of using plasma nitriding under ultra-high-vacuum conditions to introduce nitrogen into a titanium dioxide structure in the form of nanotubes with a diameter of about 110 nm. Nanotubes were produced by the anodic oxidation of Ti foil in a solution based on glycerine and water with the addition of ammonium fluoride at a voltage of 25 V. Based on experimental evidence obtained by X-ray photoelectron spectroscopy (XPS, in situ), it has been shown that alternating nitriding and annealing processes at 450 °C leads to formation of Ti-N-O, Ti-N, and Ti-O-N chemical bonds in the TiO2 crystal structure (anatase). The observed changes were identified as interstitial or substitutional admixtures or variations of these. The spectrophotometric and spectrophotoelectrochemical tests performed showed that the photoactivity of the photoanodes doped with nitrogen and annealed at 450 °C in the UV–vis range was significantly greater than that of the photoanodes without nitrogen. The highest maximum photocurrent density, of about 30.0 μA·cm–2 at a wavelength of λ = 350 nm, was obtained for the double-nitrided and once-annealed sample, where nitrogen was mainly incorporated in the interstitial positions in the TiO2 lattice. For the materials not nitrided as well as annealed only at 450 °C and pristine, the worse photoresponse was received at the levels of ∼16 and ∼0.2 μA·cm–2, respectively. The thermo-chemical treatment applied also effectively extended the operational range of the photoanodes toward visible light, where a wide maximum of light absorption was observed from ∼400 to ∼700 nm, with a maximum wavelength of 550 nm and an estimated bandgap energy of 2.5 eV. Our investigations confirmed that photoelectrochemical (PEC) performance for TiO2 NT-based photoanodes was achieved by the optimum annealing condition and concentration of nitrogen, where the narrowed bandgap was observed by generating a new N 2p energy level above the O 2p valence band. The following research techniques were used to identify the changes taking place in the materials produced: XPS spectroscopy, UV–vis spectroscopy, PEC measurements, X-ray diffraction structural measurements, and scanning electron microscopic observations. [ABSTRACT FROM AUTHOR]

Heterojunction engineering enables more versatile and higher performance systems than single components. In parallel with heterojunction engineering, defect engineering has emerged as a means of tailoring the optoelectronic properties of photoelectrodes. However, constructing effective and stable hybrid semiconductor heterojunctions is a challenging task under the strict requirements of band alignment, vacancy characteristics, and interface properties. Herein, the photoelectrochemical (PEC) reduction of CO2 to methanol is augmented by a novel approach explored by modeling the Fermi level in a multi‐interface architecture. The excellent PEC CO2 reduction activity is attributed to the formation of a high‐performance, energetically aligned multi‐interface system of CuO/Cu2O||rGO|h‐WO3|rGO (rGO = reduced graphene oxide layer). The overall performance of this hybrid, system strongly depends on the number of oxygen groups in rGO and the structural properties of rGO. Therefore, to construct an effective PEC system, numerous postsynthetic treatments are explored for their practicality and usefulness. The results reported herein clearly show that the best performance toward the CO2 photoreduction currents of 3 mA/cm2 at 0.00.1 V versus reversable hydrogen electrode (more than double that of the CuO/Cu2O system) has been reached for the semiconductor architecture containing two layers of rGO. [ABSTRACT FROM AUTHOR]

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Nanostructured WO3 photoanodes with crystallographic orientation along the [001] direction were fabricated via doctor blading nanoparticles synthesized through a microwave-assisted nonaqueous sol–gel route. Monoclinic WO3 platelets with a size ranging from 20 to 40 nm and a thickness of 3 nm were obtained after a short reaction time of 10 minutes under microwave irradiation. The films consisted of a porous network of nanoparticles and their photoelectrochemical activity was tested. After cathodic polarization of the photoanodes in the dark which led to a significant increase of 65% of the photocurrent, the films exhibited initially a maximum photocurrent of 2.7 mA cm−2 at 1 V vs. reversible hydrogen electrode (RHE) in 3 M H2SO4 under simulated AM 1.5 G illumination (100 mW cm−2) comparable to the best photocurrents reported for WO3 photoanodes. However oxygen evolution measurements showed that the faradaic efficiency dropped after the cathodic polarization and other products than O2 might be formed. In comparison to the chemical solution growth of films from molecular precursors, the use of preformed nanoparticles in the form of powders is not only more robust and easier to up-scale, but also offers many opportunities to improve the photoelectrochemical performance by tailoring the nanoparticle size, the shape, and their arrangement on the substrate. [ABSTRACT FROM AUTHOR]

The structural and chemical modification of TiO 2 nanotubes (NTs) by the deposition of a well-controlled Au deposit was investigated using a combination of X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), Scanning Transmission Electron Microscopy (STEM), Raman measurements, UV-Vis spectroscopy and photoelectrochemical investigations. The fabrication of the materials focused on two important factors: the deposition of Au nanoparticles (NPs) in UHV (ultra high vacuum) conditions (1-2 × 10 -8 mbar) on TiO 2 nanotubes (NTs) having a diameter of ∼110 nm, and modifying the electronic interaction between the TiO 2 NTs and Au nanoparticles (NPs) with an average diameter of about 5 nm through the synergistic effects of SMSI (Strong Metal Support Interaction) and LSPR (Local Surface Plasmon Resonance). Due to the formation of unique places in the form of "hot spots", the proposed nanostructures proved to be photoactive in the UV-Vis range, where a characteristic gold plasmonic peak was observed at a wavelength of 580 nm. The photocurrent density of Au deposited TiO 2 NTs annealed at 650 °C was found to be much greater (14.7 μA cm -2 ) than the corresponding value (∼0.2 μA cm -2 ) for nanotubes in the as-received state. The IPCE (incident photon current efficiency) spectral evidence also indicates an enhancement of the photoconversion of TiO 2 NTs due to Au NP deposition without any significant change in the band gap energy of the titanium dioxide ( E g ∼3.0 eV). This suggests that a plasmon-induced resonant energy transfer (PRET) was the dominant effect responsible for the photoactivity of the obtained materials., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)