• Energy Research

AbstractThe role of molecular simulations in (i) the structure determination of existing porous Metal-Organic Framework (MOF) materials, (ii) the fundamental understanding of their structural behaviors upon diverse stimuli, and (iii) the discovery of novel architectures is illustrated through recent advances our group has made in this field.

MIL-91(Ti) is shown to be one of the very few MOFs of real interest for CO2capture.

A novel and water stable Fe(iii) based porous coordination polymer was discovered. Due to its interesting features for CO2 capture, this material was used as an inorganic filler for the processing of composite membranes in CO2/N2 separation.

The discovery of more-efficient and stable water adsorbents for adsorption-driven chillers for cooling applications remains a challenge due to the low working capacity of water sorption, high regeneration temperature, low energy efficiency under given operating conditions and the toxicity risk of harmful working fluids for the state-of-the-art sorbents. Here we report the water-sorption properties of a porous zirconium carboxylate metal–organic framework, MIP-200, which features S-shaped sorption isotherms, a high water uptake of 0.39 g g−1 below P/P0 = 0.25, facile regeneration and stable cycling, and most importantly a notably high coefficient of performance of 0.78 for refrigeration at a low driving temperature (below 70 °C). A joint computational–experimental approach supports that MIP-200 may be a practical alternative to the current commercially available adsorbents for refrigeration when its water adsorption performance is combined with advantages such as the exceptional chemical and mechanical stability and the scalable synthesis that involves simple, cheap and green chemicals.

MOFs offer great potential in the photocatalytic hydrogen release from liquid organic carriers: towards the use of on-board H2as a transportation fuel.

Context. NGC 253 is one of only two starburst galaxies found to emit γ-rays from hundreds of MeV to multi-TeV energies. Accurate measurements of the very-high-energy (VHE; E > 100 GeV) and high-energy (HE; E > 60 MeV) spectra are crucial to study the underlying particle accelerators, probe the dominant emission mechanism(s) and to study cosmic-ray interaction and transport. Aims. The measurement of the VHE γ-ray emission of NGC 253 published in 2012 by H.E.S.S. was limited by large systematic uncertainties. Here, the most up to date measurement of the γ-ray spectrum of NGC 253 is investigated in both HE and VHE γ-rays. Assuming a hadronic origin of the γ-ray emission, the measurement uncertainties are propagated into the interpretation of the accelerated particle population. Methods. The data of H.E.S.S. observations are reanalysed using an updated calibration and analysis chain. The improved Fermi–LAT analysis employs more than 8 yr of data processed using pass 8. The cosmic-ray particle population is evaluated from the combined HE–VHE γ-ray spectrum using NAIMA in the optically thin case. Results. The VHE γ-ray energy spectrum is best fit by a power-law distribution with a flux normalisation of (1.34 ± 0.14stat ± 0.27sys) × 10−13 cm−2 s−1 TeV1 at 1 TeV – about 40% above, but compatible with the value obtained in Abramowski et al. (2012). The spectral index Γ = 2.39 ± 0.14stat ± 0.25sys is slightly softer than but consistent with the previous measurement within systematic errors. In the Fermi energy range an integral flux of F(E > 60 MeV) = (1.56 ± 0.28stat ± 0.15sys) × 10−8 cm−2 s−1 is obtained. At energies above ∼3 GeV the HE spectrum is consistent with a power-law ranging into the VHE part of the spectrum measured by H.E.S.S. with an overall spectral index Γ = 2.22 ± 0.06stat. Conclusions. Two scenarios for the starburst nucleus are tested, in which the gas in the starburst nucleus acts as either a thin or a thick target for hadronic cosmic rays accelerated by the individual sources in the nucleus. In these two models, the level to which NGC 253 acts as a calorimeter is estimated to a range of fcal = 0.1 to 1 while accounting for the measurement uncertainties. The presented spectrum is likely to remain the most accurate measurements until the Cherenkov Telescope Array (CTA) has collected a substantial set of data towards NGC 253.