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- Kronawitter, C. X., et al.
(författare)
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Titanium incorporation into hematite photoelectrodes : theoretical considerations and experimental observations
- 2014
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Ingår i: Energy & Environmental Science. - : Royal Society of Chemistry (RSC). - 1754-5692 .- 1754-5706. ; 7:10, s. 3100-3121
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Tidskriftsartikel (refereegranskat)abstract
- A theoretical and experimental perspective on the role of titanium impurities in hematite (alpha-Fe2O3) nanostructured photoelectrodes for solar fuel synthesis devices is provided. Titanium incorporation is a known correlate to efficiency enhancement in alpha-Fe2O3 cc photoanodes for solar water oxidation; here the relevant literature and the latest advances are presented and various proposed mechanisms for enhancement are contrasted. Available experimental evidence suggests that Ti incorporation increases net electron carrier concentrations in electrodes, most likely to the extent that (synthesis-dependent) charge compensating cation vacancies are not present. However, electron conductivity increases alone cannot quantitatively account for the large associated photoelectrochemical performance enhancements. The magnitudes of the effects of Ti incorporation on electronic and magnetic properties appear to be highly synthesis-dependent, which has made difficult the development of consistent and general mechanisms explaining experimental and theoretical observations. In this context, we consider how the electronic structure correlates with Ti impurity incorporation in alpha-Fe2O3 a from the perspective of synchrotron-based soft X-ray absorption spectroscopy measurements. Measurements are performed on sets of electrodes fabricated by five relevant and unrelated chemical and physical techniques. The effects of titanium impurities are reflected in the electronic structure through several universally observed spectral characteristics, irrespective of the synthesis techniques. Absorption spectra at the oxygen K-edge show that Ti incorporation is associated with new oxygen 2p-hybridized states, overlapping with and distorting the known unoccupied Fe 3d-O 2xp band of alpha-Fe2O3. This is an indication of mixing of Ti s and d states in the conduction band of alpha-Fe2O3. cc A comparison of spectra obtained with electron and photon detection shows that the effects of Ti incorporation on the conduction band are more pronounced in the near-surface region. Titanium L-2,L-3-edge absorption spectra show that titanium is incorporated into alpha-Fe2O3 as Ti4+ by all fabrication methods, with no long-range titania order detected. Iron L-2,L-3-edge absorption spectra indicate that Ti incorporation is not associated with the formation, of any significant concentrations of Fe2+, an observation common to many prior studies on this material system.
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- Mielke, Michelle M., et al.
(författare)
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The 32-year relationship between cholesterol and dementia from midlife to late life.
- 2010
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Ingår i: Neurology. - 0028-3878. ; 75:21, s. 1888-95
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Tidskriftsartikel (refereegranskat)abstract
- Background: Cellular and animal studies suggest that hypercholesterolemia contributes to Alzheimer disease (AD). However, the relationship between cholesterol and dementia at the population level is less clear and may vary over the lifespan. Methods: The Prospective Population Study of Women, consisting of 1,462 women without dementia aged 38–60 years, was initiated in 1968–1969 in Gothenburg, Sweden. Follow-ups were conducted in 1974–1975, 1980–1981, 1992–1993, and 2000–2001. All-cause dementia was diagnosed according to DSM-III-R criteria and AD according to National Institute of Neurological and Communicative Disorders and Stroke–Alzheimer's Disease and Related Disorders Association criteria. Cox proportional hazards regression examined baseline, time-dependent, and change in cholesterol levels in relation to incident dementia and AD among all participants. Analyses were repeated among participants who survived to the age of 70 years or older and participated in the 2000–2001 examination. Results: Higher cholesterol level in 1968 was not associated with an increased risk of AD (highest vs lowest quartile: hazard ratio [HR] 2.82, 95% confidence interval [CI] 0.94–8.43) among those who survived to and participated in the 2000–2001 examination. While there was no association between cholesterol level and dementia when considering all participants over 32 years, a time-dependent decrease in cholesterol over the follow-up was associated with an increased risk of dementia (HR 2.35, 95% CI 1.22–4.58). Conclusion: These data suggest that midlife cholesterol level is not associated with an increased risk of AD. However, there may be a slight risk among those surviving to an age at risk for dementia. Declining cholesterol levels from midlife to late life may better predict AD risk than levels obtained at one timepoint prior to dementia onset. Analytic strategies examining this and other risk factors across the lifespan may affect interpretation of results.
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