Improving the photocatalytic reduction of CO2 to CO through immobilisation of a molecular Re catalyst on TiO2.

The photocatalytic activity of phosphonated Re complexes, [Re(2,2'-bipyridine-4,4'-bisphosphonic acid) (CO)3(L)] (ReP; L = 3-picoline or bromide) immobilised on TiO2 nanoparticles is reported. The heterogenised Re catalyst on the semiconductor, ReP-TiO2 hybrid, displays an improvement in CO2 reduction photocatalysis. A high turnover number (TON) of 48 molCO molRe(-1) is observed in DMF with the electron donor triethanolamine at λ>420 nm. ReP-TiO2 compares favourably to previously reported homogeneous systems and is the highest TON reported to date for a CO2-reducing Re photocatalyst under visible light irradiation. Photocatalytic CO2 reduction is even observed with ReP-TiO2 at wavelengths of λ>495 nm. Infrared and X-ray photoelectron spectroscopies confirm that an intact ReP catalyst is present on the TiO2 surface before and during catalysis. Transient absorption spectroscopy suggests that the high activity upon heterogenisation is due to an increase in the lifetime of the immobilised anionic Re intermediate (t50% >1 s for ReP-TiO2 compared with t50% = 60 ms for ReP in solution) and immobilisation might also reduce the formation of inactive Re dimers. This study demonstrates that the activity of a homogeneous photocatalyst can be improved through immobilisation on a metal oxide surface by favourably modifying its photochemical kinetics.Financial support from the EPSRC (EP/H00338X/2 to E.R.; studentship and Doctoral Prize to C.D.W.; DTP scholarship to E.P.), the Christian Doppler Research Association (Austrian Federal Ministry of Science, Research and Economy and the 28 National Foundation for Research, Technology and Development) and the OMV Group (to E.R.), the ERC (project Intersolar to J.D.) and the European Commission Marie Curie CIG (PCIG10-GA-2011-303650 to A.R.) is gratefully acknowledged.This is the final published version. It first appeared in Chemistry - a European Journal, 2015, 21, 3746 – 3754, DOI: 10.1002/chem.20140504

Reexamination of the long-range Potts model: a multicanonical approach

We investigate the critical behavior of the one-dimensional q-state Potts model with long-range (LR) interaction $1/r^{d+\sigma}$, using a multicanonical algorithm. The recursion scheme initially proposed by Berg is improved so as to make it suitable for a large class of LR models with unequally spaced energy levels. The choice of an efficient predictor and a reliable convergence criterion is discussed. We obtain transition temperatures in the first-order regime which are in far better agreement with mean-field predictions than in previous Monte Carlo studies. By relying on the location of spinodal points and resorting to scaling arguments, we determine the threshold value $\sigma_c(q)$ separating the first- and second-order regimes to two-digit precision within the range $3 \leq q \leq 9$. We offer convincing numerical evidence supporting $\sigma_c(q)Comment: 18 pages, 18 figure

From low-conflict polity to democratic civil peace: Explaining Zambian exceptionalism

An absence of civil war and other significant sub-state violence makes Zambia an exceptional although not unique case in central-southern Africa. The literature devoted to explaining civil war has grown dramatically in recent years, but while it pays much attention to sub-Saharan Africa only rarely does it investigate counterfactual cases like Zambia. Similarly the growing field of research into post-conflict reconstruction fails to capture the distinct features of persistently low-conflict situations where many of the predisposing conditions for violent conflict might seem to be present. This paper examines Zambia’s experience against a background of general theories that try to explain conflict. It is an “interpretative case study”. The paper proceeds by substantiating Zambia’s claim to a relatively peaceful record and introduces ideas of conflict and conflict theories, before arguing that no single general theory dwelling on just one primary “cause” will suffice to explain Zambian exceptionalism. The precise mix of arguments differs for each one Zambia’s three republican eras, as the potential threats to peace have themselves evolved over the period since independence. The paper’s main theoretical claim is that over time the explanation is both multi-layered and dynamic. That said, certain features do stand out, most notably an inherited political culture that is predisposed against the violent resolution of conflict and continues to insulate the country against social and economic traumas and democratic shortcomings

Synthesis, Structures, and Optical Properties of Ruthenium(II) Complexes of the Tris(1-pyrazolyl)methane Ligand

Four new complex salts [Ru^(II)Cl(Tpm)(L^A)_2][PF_6]_n [Tpm = tris(1-pyrazolyl)methane; n = 1, L^A = pyridine (py) 1 or ethyl isonicotinate (EIN) 2; n = 3, L^A = N-methyl-4,4′-bipyridinium (MeQ^+) 3 or N-phenyl-4,4′-bipyridinium (PhQ^+) 4] have been prepared and characterized. Electronic absorption spectra show intense d → π^* metal-to-ligand charge-transfer (MLCT) absorption bands, while cyclic voltammetry reveals a reversible Ru^(III/II) wave, accompanied by quasireversible or irreversible L^A-based reductions for all except 1. Single crystal X-ray structures have been obtained for 1•Me_2CO, 2, and 3•Me_2CO. For 2–4, molecular first hyperpolarizabilities β have been measured in acetonitrile solutions via the hyper-Rayleigh scattering (HRS) technique at 800 nm. Stark (electroabsorption) spectroscopic studies on the MLCT bands in frozen butyronitrile allow the indirect estimation of static first hyperpolarizabilities β_0. The various physical data obtained for 3 and 4 are compared with those reported previously for related cis-{Ru^(II)(NH_3)_4}^(2+) species [Coe, B. J. et al. J. Am. Chem. Soc. 2005, 127, 4845]. TD-DFT calculations on the complexes in 1–4 confirm that their lowest energy absorption bands are primarily Ru^(II) → L^A MLCT in character, while Ru^(II) → Tpm MLCT transitions are predicted at higher energies. DFT agrees with the Stark, but not the HRS measurements, in showing that β_0 increases with the electron-accepting strength of L^A. The 2D nature of the chromophores is evidenced by dominant β_(xxy) tensor components

Rejets de tritium dans l’environnement et impact : évolutions récentes et perspectives

Plusieurs publications ont suscité des interrogations en France sur le comportement du tritium dans l’environnement et sur son impact sur la santé de l’homme. En 2008, l’ASN a demandé à deux groupes d’experts de faire le point de l’état de l’art sur le sujet. Un plan d’action découlant des recommandations exprimées a été présenté dans le Livre Blanc du Tritium publié en 2010. Depuis, le comité chargé de son suivi a abordé périodiquement les sujets identifiés. Les avancées métrologiques, les travaux de recherche concernant le transfert et le niveau d’activité du tritium dans l’environnement ont été étudiés. La compréhension de sa toxicité a progressé. Les exploitants des INB ont caractérisé les formes physico-chimiques des effluents tritiés existantes dans les rejets de leurs installations. Chaque année, l’ASN met à jour sur le site du Livre Blanc l’inventaire des rejets de tritium des INB et INBS et des impacts dosimétriques associés. Les actions du comité relatives aux sujets de recherche encore en cours étant maintenant limitées, l’ASN a proposé de clore les travaux du comité sous sa forme actuelle et de traiter les travaux de recherche non encore finalisés lors d’une journée dédiée qui sera organisée par l’IRSN