Wireless Rotating Disk Electrode (wRDE) for assessing Heterogeneous Water Oxidation Catalysts (WOCs)

A novel method for assessing the activity of a powdered water oxidation catalyst (WOC) is described, utilising an easily-prepared wireless rotating disc electrode of the WOC, thereby allowing its activity to be probed, via the observed kinetics of water oxidation by Ce(iv) ions, and so provide invaluable electrochemical information.</p

The P25 TiO2/4-chlorophenol photocatalytic system: Spectral sensitivity or lamp artefact?

The photocatalysed mineralisation of 4-chlorophenol, 4-CP, by P25 TiO2 is a well-studied photocatalytic system. A previous paper (Emeline et al., J. Phys. Chem. B, 2000, 104, 11202) reported an action spectrum, i.e. photonic efficiency, η, vs. excitation wavelength, λ(ex), for the P25/4-CP system, that exhibited a series of peaks and troughs which, it was proposed, provided evidence of P25 spectral sensitivity. However, in this re-examination it is shown that the peaks and troughs in the action spectrum occur in the regions of the troughs and peaks in the emission spectrum of the Xe/Hg lamp used by these researchers. The dependencies of η, and quantum yield, ϕ, upon incident light intensity, ρ, in semiconductor-sensitised photocatalytic systems are considered and a rationale provided that suggests the action spectrum reported by Emerline et al. is actually due to the variation in ρ in the emission spectrum of the Xe/Hg lamp. In order to test the latter hypothesis, the action spectrum of the same P25/4-CP system is determined, but this time using a Xe lamp; the latter action spectrum has no peaks and troughs and corresponds closely to that of the diffuse reflectance spectrum of the P25 dispersion as expected if there is no spectral sensitivity. This action spectrum, and similar results reported by others for this and other test pollutants, provides strong evidence that the claim of spectral sensitivity for the P25/4-CP system is unjustified, based on the reported action spectrum of Emeline et al., since the latter is due to the spectral variation in irradiance of the Xe/Hg excitation source employed in the original study. © 2017 Elsevier B.V.1

Action Spectra in Semiconductor Photocatalysis

Action spectra are an increasingly important part of semiconductor photocatalyst research, and comprise a plot of photonic efficiency, η, versus excitation wavelength, λ. The features and theory behind an ideal photocatalytic system are discussed, and used to identify: (i) the key aspect of an ideal action spectrum, namely: it is a plot of η vs. λ which has the same shape as that of the fraction of radiation absorbed by the semiconductor photocatalyst, f, versus λ and (ii) the key requirement when running an action spectrum, namely, that the initial rate of the photocatalytic process is directly proportional to incident photon flux, ρ, at wavelengths where η &amp;gt; 0. The Pt/TiO2/MeOH system is highlighted as an example of a photosystem that yields an ideal action spectrum. Most photocatalytic systems exhibit non-ideal action spectra, mostly due to one or more of the following: light intensity effects, crystal phase effects, dye-sensitisation, dye photolysis, charge transfer complex, CTC, formation and localized surface plasmon radiation, LSPR, absorption by a deposited noble metal catalyst. Each of these effects is illustrated using examples taken from the literatures and discussed. A suggested typical protocol for recording the action spectrum and absorption/diffuse reflectance spectrum of a photocatalytic system is described. The dangers of using a dye to probe the activity of a photocatalysts are also discussed, and a possible way to avoid this, via reductive photocatalysis, is suggested. © 2017 The Royal Society of Chemistry.1

China's Foreign Conventional Arms Acquisitions: Background and Analysis

This report examines the major, foreign conventional weapon systems that China has acquired or has committed to acquire since 1990, with particular attention to implications for U.S. security concerns. It is not the assumption of this report that China’s military, the People’s Liberation Army (PLA), will engage in conflict with other forces in Asia. Nonetheless, since the mid-1990s, there has been increasing concern about China’s assertiveness in Asia and greater threats against Taiwan