Anatase TiO 2 nanocrystals (aTiO 2 ) of a uniform size have been synthesized and were subject to a successive hydrogenation under a H 2 gas flow at elevated temperatures (500−700 °C). We found that the concentration of Ti 3+ defects, such as Ti 3+ interstitials and oxygen vacancies, and their distribution between surface and bulk varied significantly, depending on the hydrogenation temperature and time. Such changes in defects were found to be critical in enhancing the photoactivity of the hydrogenated TiO 2 (H-aTiO 2 ) by an order of magnitude. In our case, H-aTiO 2 nanocrystals hydrogenated at 600 °C for longer than 10 h showed 10 times higher photoactivity than aTiO 2 , which was explained from a high surface-to-bulk defect ratio and a nonuniform distribution of defects between bulk and surface due to a preferential diffusion of bulk defects to the surface. Our study showed that a kinetically controlled hydrogenation condition could be used not only to control the surface/bulk defects but also to enhance the photoactivity of oxide nanocrystals.

A series of NH(3) temperature-programmed desorption (TPD) spectra were taken after dosing NH(3) at 70 K on rutile TiO(2)(110)-1 × 1 surfaces with oxygen vacancy (V(O)) concentrations of ~0% (p-TiO(2)) and 5% (r-TiO(2)), respectively, to study the effect of V(O)s on the desorption energy of NH(3) as a function of coverage, θ. Our results show that in the zero coverage limit, the desorption energy of NH(3) on r-TiO(2) is 115 kJ mol(-1), which is 10 kJ mol(-1) less than that on p-TiO(2). The desorption energy from the Ti(4+) sites decreases with increasing θ due to repulsive NH(3)-NH(3) interactions and approaches ~55 kJ mol(-1) upon the saturation of Ti(4+) sites (θ = 1 monolayer, ML) on both p- and r-TiO(2). The absolute monolayer saturation coverage is determined to be about 10% smaller on r-TiO(2) than that on p-TiO(2). Additionally, the trailing edges of the NH(3) TPD spectra on the hydroxylated TiO(2)(110) (h-TiO(2)) appear to be the same as that on r-TiO(2) while those on oxidized TiO(2)(110) (o-TiO(2)) shift to higher temperatures. We present a detailed analysis of the results and reconcile the observed differences based on the repulsive adsorbate-adsorbate dipole interactions between neighboring NH(3) molecules and the surface charge associated with the presence of V(O)s.

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This study investigated how three levels of arousal affected performance of a 3-back working memory task. Ten female and ten male university students participated in this experiment. With pictures selected from a group test, three levels of arousal were induced--i.e., tense, neutral, and relaxed emotions. Each subject was run through the procedure three times, once for each arousal level. The procedure consisted of six phases for each arousal condition: (1) Rest 1 (2 min), (2) Picture 1 (presenting emotion arousing photos for 2 min), (3) 3-back working memory task 1 (2 min), (4) Picture 2 (presenting emotion-arousing photos for 2 min), (5) 3-back working memory task 2 (2 min), and (6) Rest 2 (2 min). The skin conductance level of electrodermal activity was also measured during all phases of the experiment. The accuracy rate of 3-back working memory task performance was the highest at a neutral emotional state, followed by relaxed and then tense emotional states. There were no significant differences in reaction time.

The interaction of N2O with oxygen vacancies (VO’s) on a partially reduced rutile TiO2(110)-1×1 surface was investigated using temperature-programmed desorption (TPD). Contrary to a common belief that VO on a rutile TiO2(110) is a dissociation site for N2O, our results indicate that N2O does not dissociate to form N2(g) and O(a). In TPD, N2O desorption shows two peaks with maxima at 135 and 175 K that are assigned to N2O desorption from Ti4+ and VO sites, respectively, with absolute coverages determined to be 5.4 × 1014 N2O/cm2 and 2.3 × 1013 N2O/cm2, respectively, on the TiO2(110)-1×1 surface used (VO concentration of 5%, 2.6 × 1013/cm2). When VO’s are passivated by dissociative adsorption of H2O, the N2O desorption peak at 175 K disappears, evidencing that the peak is related to VO-bonded N2O. The absence of N2O dissociation on VO’s is supported by a number of observations. First, the integrated amount of N2O desorbed from the substrate during TPD vs the amount of N2O dosed at 70 K shows a straight line with no offset, indicating no loss of N2O due to the N2 formation. Second, N2O scattering experiments at 300–350 K indicate no change in the VO concentration as determined from the H2O TPD spectra. Third, N2O uptake experiments at 70–90 K show that the N2 desorption feature is observed from TiO2(110) surfaces without VO’s, suggesting a possible contribution from background N2 adsorption. On the basis of the above observations, we conclude that N2O does not dissociate on VO sites on TiO2(110), in contrast with the currently accepted view.