Anatase-Wrapped Rutile Nanorods as an Effective Electron Collector in Hybrid Photoanodes for Visible Light-Driven Oxygen Evolution

Arrays of single crystal TiO2 rutile nanorods (RNRs) appear highly promising as electron-collecting substrates in hybrid photoanodes as the RNRs offer direct charge carriers transport pathways, contrary to the conventional electrodes prepared from TiO2 powders that suffer from the numerous charge traps at the grain boundaries. However, the specific surface area of the nanorods is highly limited by their smooth morphology, which might be detrimental in view of utilizing the RNR as a substrate for immobilizing other functional materials. In this study, we developed a novel anatase-wrapped RNR (ARNR) material fabricated by a facile seed layer-free hydrothermal method. The ARNR comprises polycrystalline anatase nanoparticles formed on the surface of RNR, resulting in a large surface area that provides more deposition sites compared to the bare nanorods. Herein, we functionalize ARNR and RNR electrodes with polymeric carbon nitride (CNx) coupled with a CoO(OH)x cocatalyst for dioxygen evolution. The anatase wrapping of the rutile nanorod scaffold is found to be crucial for effective deposition of CNx and for improved photoanode operation in visible light-driven (λ > 420 nm) oxygen evolution, yielding a significant enhancement of photocurrent (by the factor of ∼3.7 at 1.23 V vs. RHE) and faradaic efficiency of oxygen evolution (by the factor of ∼2) as compared to photoanodes without anatase interlayer. This study thus highlights the importance of careful interfacial engineering in constructing photoelectrocatalytic systems for solar energy conversion and paves the way for the use of ARNR-based electron collectors in further hybrid and composite photochemical architectures for solar fuel production.

The impact of hydrogenation conditions on the physical properties of the degenerated Ni/Al co-doped diluted magnetic semiconductor anatase nanoparticles

: Anatase (TiO2) nanoparticles co-doped with Ni/Al ions were synthesized by a thermo-precipitation method. The samples were characterized by using X‐Ray diffraction and optical absorption spectroscopy. The structural/optical investigations established the development of substitutional solid solutions: TiO2:Ni:Al. The magnetization investigations were performed to study the generated stable ferromagnetic properties of the samples due to the Ni2+ doping. To boost the created ferromagnetic properties, Al ions co-dopings were employed to supply/densify the itinerant electrons. It was planned to decide the suitable hydrogenation conditions and temperature (TH), which are necessary to create appreciable strength of ferromagnetic properties in the host co-doped samples based on TiO2 for practical uses. The results established that the ferromagnetic energy (Umag) was increased by ~240% and the saturation magnetization by ~140% with increasing of TH from 400 oC to 500oC. The obtained Msat was higher by ~50 times than that previously attained for Ni-doped TiO2. Such novel results were discussed and explained through the spin-spin Heisenberg interactions.

Heterostructural transformation of mesoporous silica–titania hybrids

Mesoporous silica (SBA-15 with the BJH pore size of 8 nm) containing anatase nanoparticles in the pore with two different titania contents (28 and 65 mass%), which were prepared by the infiltration of the amorphous precursor derived from tetraisopropyl orthotitanate into the pore, were heat treated in air to investigate the structural changes (both mesostructure of the SBA-15 and the phase and size of the anatase in the pore). The mesostructure of the mesoporous silica and the particle size of anatase unchanged by the heat treatment up to 800 °C. The heat treatment at the temperature higher than 1000 °C resulted in the collapse of the mesostructure and the growth of anatase nanoparticles as well as the transformation to rutile, while the transformation of anatase to rutile was suppressed especially for the sample with the lower titania content (28 mass%). The resulting mesoporous silica-anatase hybrids exhibited higher benzene adsorption capacity (adsorption from water) over those heated at lower temperature, probably due to the dehydroxylation of the silanol group on the pore surface. The photocatalytic decomposition of benzene in water by the present hybrid heated at 1100 °C was efficient as that by P25, a benchmark photocatalyst.

TiO2 Nanotubes Transformation Into 4nm Anatase Nanoparticles

The scope of this work shows novel experimental findings on preparing anatase TiO2 nanoparticles, first anodizing titanium into an organic media for obtaining TiO2 nanotubes, and using these as a photocatalytic active electrode in treating water polluted with organic contaminants. The substrates were grit blasted to obtain mechanical fixation of the generated nanotubular TiO2 structure. This was successfully achieved without diminishment of the nanotubes order and with a self-leveling of the outer surface. A new phenomenon has been investigated consisting of the process of oxidation of the nanotubes in water after anodizing. Along this process, methyl orange added to the aqueous solution was discolored as part of the redox reaction involved. The final state of the modified layer was composed of conglomerates of almost completely crystalline TiO2 nanoparticles, around 4 nm in size, consisting of anatase. SEM and TEM images show the transition of the amorphous nanotubes (atomic disorder/nanometric order) to crystalline disordered particles (atomic order/nanometric disorder).