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Peas in a pod: A highly aligned Au(np)@TiO2 photocatalyst was formed by self-organizing anodization of a Ti substrate followed by dewetting of a gold thin film. This leads to exactly one Au nanoparticle (np) per TiO2 nanocavity. Such arrays are highly efficient photocatalysts for hydrogen generation from ethanol.

In the present work we introduce a technique to form a photocatalyst based on Pt nanoparticles suspended over the mouth of anodic TiO2 nanotubes. These structures are obtained by decorating the top end of highly ordered TiO2 nanotubes with a web of TiO2 nanofibrils, followed by sputter deposition of a minimum amount of Pt. A subsequent thermal dewetting step forms 3-6 nm-sized Pt nanoparticles along the nanofibrils. These structures, when compared to conventional Pt decoration techniques of TiO2 nanotubes, show strongly enhanced photocatalytic H2 evolution efficiency.

TiO2 nanotubes have been investigated in photoelectrochemistry and photocatalysis for more than a decade. However, up to now, a systematic investigation of different hole scavengers is still lacking. Here we investigate the effect of the most relevant sacrificial hole scavengers on the photoelectrochemical properties and photocatalytic H2 evolution performance of pristine and Pt-decorated anodic TiO2 nanotubes. We examine methanol, isopropanol, ethylene glycol, EDTA-Na2, as well as Na2SO3, and find that the incident photocurrent conversion efficiency (IPCE) of the TiO2 nanotubes in 0.1 M Na2SO4 electrolytes increases by 1.8-3.1 times, depending on the used hole scavenger. The efficiency increases in the sequence Na2SO3 < isopropanol < MeOH < ethylene glycol < EDTA-Na2. In presence of any hole scavenger, for nanotubes in the length-range of 2-10 µm, the photocurrent spectra and the ICPE magnitude are independent of the tube length. The photocurrent onset potential (optical flatband potential) is significantly affected by the different type of scavengers, in line with their red-ox potential. Under open circuit conditions (photocatalytic conditions), organic hole scavengers lead to a 10.0-28.8 times higher H2 production by TiO2 nanotubes than the scavenger-free case, with a sequence MeOH > i-PrOH > EDTA-Na2 > EG, while a detrimental effect of Na2SO3 is observed. These results are compared to results obtained for TiO2 particles, and discussed in terms of various concepts in the literature.

We report the fabrication of 3D hierarchical hetero-nanostructures composed of thin α-FeO nanoflakes branched on TiO nanotubes. The novel α-FeO/TiO hierarchical nanostructures, synthesized on FTO through a multi-step hydrothermal process, exhibit enhanced performances in photo-electrochemical water splitting and in the photocatalytic degradation of an organic dye, with respect to pure TiO nanotubes. An enhanced separation of photogenerated charge carriers is here proposed as the main factor for the observed photo-activities: electrons photogenerated in TiO are efficiently collected at FTO, while holes are transferred to the α-FeO nanobranches that serve as charge mediators to the electrolyte. The morphology of α-FeO that varies from ultrathin nanoflakes to nanorod/nanofiber structures depending on the Fe precursor concentration was shown to have a significant impact on the photo-induced activity of the α-FeO/TiO composites. In particular, it is shown that for an optimized photo-electrochemical structure, a combination of critical factors should be achieved such as (i) TiO light absorption and photo-activation vs.α-FeO-induced shadowing effect and (ii) the availability of free TiO surface vs.α-FeO-coated surface. Finally, theoretical analysis, based on DFT calculations, confirmed the optical properties experimentally determined for the α-FeO/TiO hierarchical nanostructures. We anticipate that this new multi-step hydrothermal process can be a blueprint for the design and development of other hierarchical heterogeneous metal oxide electrodes suitable for photo-electrochemical applications.

Most of existing solar thermal technologies require highly concentrated solar power to operate in the temperature range 300–600 °C. Here, thin films of refractory plasmonic TiN cylindrical nanocavities manufactured via flexible and scalable process are presented. The fabricated TiN films show polarization-insensitive 95% broadband absorption in the visible and near-infrared spectral ranges and act as plasmonic “nanofurnaces” capable of reaching temperatures above 600 °C under moderately concentrated solar irradiation (∼20 Suns). The demonstrated structures can be used to control nanometer-scale chemistry with zeptoliter (10–21 L) volumetric precision, catalyzing CC bond formation and melting inorganic deposits. Also shown is the possibility to perform solar thermal CO oxidation at rates of 16 mol h–1 m–2 and with a solar-to-heat thermoplasmonic efficiency of 63%. Access to scalable, cost-effective refractory plasmonic nanofurnaces opens the way to the development of modular solar thermal devices for sustainable catalytic processes.

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A technique is introduced to strongly ­reduce Pt use for photocatalytic hydrogen generation from TiO2 nanotubes. By site selectively depositing thin layers of Pt only at the “mouth” of the nanotubes, and with a subsequent thermal de­wetting step, an outstanding photocatalytic ­improvement with minimal amounts of cocatalyst is achieved.