Midgap levels for wide gap TiO 2 have become increasingly important because they can be used to capture solar light efficiently for photocatalysis as demonstrated by black TiO 2 in a recent paper [Chen, X., et al. Science 2011, 331 (6018), 746−750]. However, a method for systematically characterizing the midgap state energy levels is still lacking. We proposed an optical method, i.e., transient infrared (IR) absorption − excitation energy scanning spectrum, by recording nanosecond time-resolved transient IR absorption from the excited electrons either in the conduction band or at the excited localized states below the conduction in combination with midgap excitation energy scanning. We demonstrate that both the electron trap states beneath the Fermi level and those excited localized states below the conduction band as well as the Fermi level of TiO 2 nanoparticles can unambiguously be determined by this method, which has great potential for characterizing the midgap trap states of various semiconductor nanomaterials other than TiO 2 . ■ INTRODUCTIONWide bandgap oxide semiconductor TiO 2 is still considered one of the best materials for photocatalysis and solar energy conversion, 1 while the anatase form is usually considered to be more active in photocatalytic and photovoltaic applications. The large bandgap of TiO 2 ensures the photogenerated electrons within the conduction band (CB) have a strong reducing ability and the holes in the valence band have a strong oxidizing ability. 2 Either in photocatalysis or in the photovoltaic process, nanophase TiO 2 has been used for its highly effective surface area as well as its large number of surface binding sites. However, the number of surface and interstitial defects known as trap states also increases substantially in the nanoparticles versus the number in the single crystals. These trap states with their energy levels lying in the bandgap act as carrier traps in competition with the fast carrier recombination in the bulk during photoexcitation, which enhances the photoactivity of the nanoparticles. On the other hand, the deep trap states reduce the photocatalytic activities when their chemical potentials are considered. 3 Because of its wide bandgap, TiO 2 absorbs light only in the UV range, which accounts for only 3−5% of the total sunlight; 4 this leads to a low light conversion efficiency in the solar spectral region. Therefore, extending the absorption of TiO 2 to the visible range would be an effective means of increasing its overall efficiency. One way to increase solar energy absorption efficiency is to narrow the bandgap by anion doping such as nitrogen doping. 5 At present, nitrogen-doped TiO 2 exhibits the strongest response to solar radiation, 6 but its absorption in the visible and infrared region remains insufficient.In contrast to the cation-doped TiO 2 , the surface and interstitial defects usually known in a form of Ti 3+ such as selfdoping 7 act as color centers; these color centers in principle would not narrow the bandgap but would provide a cha...

The Escherichia coli DegP has been reported to function both as molecular chaperone and protease for the quality control of outer membrane protein biogenesis. Activation of the inactive DegP hexamers was believed to occur via their disassembly into trimeric units and subsequent reassembly into larger oligomers (12-mers and 24-mers). Here, we analyzed the thermal stability and the unfolding dynamics of the different secondary structure components of the DegP hexamers using Fourier transform infrared spectroscopy and temperature-jump nanosecond time-resolved IR difference absorbance spectroscopy. We found that the interfacial secondary structure components possess a degreed thermal stability, with the disassembly of the DegP hexamers follows a “proteinquake” manner, such that the fully exposed parts of the interfacial β-sheets serving as the temperature sensor and epicenter to drive the sequential unfolding/disassembly process that finishes within about 134 ns at room temperature.

Knowledge of dynamical structure of protein is an important clue to understand its biological function in vivo. Temperature-jump (T-jump) time-resolved transient mid-IR absorbance spectroscopy is a powerful tool in elucidating the protein dynamical structures and the folding/unfolding kinetics of proteins in solution. A home-built setup of T-jump time-resolved transient mid-IR absorbance spectroscopy with high sensitivity is developed, which is composed of a Q-switched Cr, Tm, Ho:YAG laser with an output wavelength at 2.09 μm as the T-jump heating source, and a continuous working CO laser tunable from 1580 to 1980 cm(-1) as the IR probe. The results demonstrate that this system has a sensitivity of 1 × 10(-4) ΔOD for a single wavelength detection, and 2 × 10(-4) ΔOD for spectral detection in amide I' region, as well as a temporal resolution of 20 ns. Moreover, the data quality coming from the CO laser is comparable to the one using the commercial quantum cascade laser.