TiO 2 is one of the most promising candidate materials for clean-energy generation and environmental remediation. However, the larger-than 3.1 eV bandgap of perfectly crystalline TiO 2 confines its application to the ultraviolet (UV) range. In this study, the electronic and the optical properties of undoped mixed-phase TiO 2 nanoparticles were investigated using UV and inverse photoemission, low intensity Xray photoelectron (XP), and diffused reflectance spectroscopy methods. The facile solution-phase synthesized nanoparticles exhibited a midgap-states-induced energy gap of only ∼2.2 eV. The diffused reflectance spectrum showed sub-bandgap absorption due to the existence of a large Urbach tail at 2.2 eV. The UV photoemission spectrum evidenced the presence of midgap states. The 2.2 eV energy gap enables the nanoparticles to be photoactive in the visible energy range. The gas-phase CO 2 photoreduction test with water vapor under visible light illumination was studied in the presence of the synthesized TiO 2 nanoparticles which resulted in the production of ∼1357 ppm gr −1 (catalyst) CO and ∼360 ppm gr −1 (catalyst) CH 4 , as compared to negligible amounts using a standard TiO 2 (P25) sample. The synthesized nanoparticles possessed a Brunauer−Emmett−Teller (BET) surface area of ∼131 m 2 gr −1 , corresponding to a Langmuir surface area of ∼166 m 2 gr −1 . The determined interplanar distances of atomic planes by highresolution transmission electron microscopy (HR-TEM) and X-ray diffraction (XRD) methods were consistent. A detailed elemental analysis using XPS and inductively coupled plasma mass spectrometry (ICP-MS) demonstrated that the synthesized catalyst is indeed undoped. The catalytic activity of the undoped synthesized nanoparticles in the visible spectrum can be ascribed to the unique electronic structure due to the presence of oxygen vacancy related defects and the high surface area.

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The growing demand for nonfossil fuel-based energy production has drawn attention to the utilization of natural proteins such as photosynthetic reaction center (RC) protein complexes to harvest solar energy. The current study reports on an immobilization method to bind the wild type Rhodobacter sphaeroides RC from the primary donor side onto a Au electrode using an immobilized cytochrome c (cyt c) protein via a docking mechanism. The new structure has been assembled on a Au electrode by layer-by-layer deposition of a carboxylic acid-terminated alkanethiol (HOOC (CH2)5S) self-assembled monolayer (SAM), and layers of cyt c and RC. The Au|SAM|cyt c|RC working electrode was applied in a three-probe electrochemical cell where a peak cathodic photocurrent density of 0.5 μA cm–2 was achieved. Further electrochemical study of the Au|SAM|cyt c|RC structure demonstrated ∼70% RC surface coverage. To understand the limitations in the electron transfer through the linker structure, a detailed energy study of the SAM and cyt c was performed using photochronoamperometry, ellipsometry, photoemission spectroscopy, and cyclic voltammetry (CV). Using a simple rectangle energy barrier model, it was found that the electrode work function and the large barrier of the SAM are accountable for the low conductance in the devised linker structure.

Post-deposition annealing effects on nanomechanical properties of granular TiO 2 films on soda-lime glass substrates were studied. In particular, the effects of Na diffusion on the films' mechanical properties were examined. TiO 2 photocatalyst films, 330 nm thick, were prepared by dip-coating using a TiO 2 sol, and were annealed between 100°C and 500°C. Film's morphology, physical and nanomechanical properties were characterized by atomic force microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, differential thermo-gravimetric analysis, and nanoindentation. Contrary to expectations, the maximum film hardness was achieved for 300°C annealing, with a value of 0.69 ( 0.05 GPa. Higher annealing temperatures resulted in inferior mechanical properties. No pile-up or sink-in effects were observed with minimal creep for the 300°C annealed sample. Considerable decrease in the amount of chemisorbed water was found with increasing annealing temperature, causing gel films densification, explaining the increasing trend of hardness with annealing temperature between 100°C and 300°C. DTA/TGA results also confirmed the weight loss and the endothermic reaction due to desorption of chemisorbed water. Decrease in hardness above 300°C annealing is attributed to thermal diffusion of Na ions from the glass substrate, confirmed by nanoindentation tests on TiO 2 films deposited on fused quartz, which did not exhibit hardness decrease after 300°C annealing.