Nanoporous metal organic framework materials for hydrogen storage

Hydrogen is expected to play an important role in future transportation as a promising alternative clean energy source to carbon-based fuels.One of the key challenges to commercialize hydrogen energy is to develop appropriate onboard hydrogen storage systems,capable of charging and discharging large quantities of hydrogen with fast enough kinetics to meet commercial requirements.Metal organic framework (MOF) is a new type of inorganic and organic hybrid nanoporous particulate materials.Its diverse networks can enhance hydrogen storage through tuning the structure and property of MOFs.The MOF materials so far developed adsorb hydrogen through weak disperston interactions,which allow significant quantity of hydrogen to be stored at cryogenic temperatures with fast kinetics.Novel MOFs are being developed to strengthen the interactions between hydrogen and MOFs in order to store hydrogen under ambient conditions.This review surveys the development of such candidate materials,their performance and future research needs.     

Predicting thermal conductivity of liquid suspensions of nanoparticles (nanofluids) based on rheology

A methodology is proposed for predicting the effective thermal conductivity of dilute suspensions of nanoparticles (nanofluids) based on rheology.The methodology uses the rheological data to infer microstructures of nanoparticles quantitatively,which is then incorporated into the conventional Hamilton-Crosser equation to predict the effective thermal conductivity of nanofluids.The methodology is experimentally validated using four types of nanofluids made of titania nanoparticles and titanate nanotubes dispersed in water and ethylene glycol.And the modified Hamilton-Crosser equation successfully predicted the effective thermal conductivity of the nanofluids.     

Acetone adsorption on ice investigated by X-ray spectroscopy and density functional theory

Using a combination of X-ray photoemission and near-edge X-ray absorption spectroscopy (NEXAFS) as well as density-functional theory (DFT), we have investigated the adsorption of acetone on ice in the temperature range from 218 to 245 K. The adsorption enthalpy determined from experiment (45 kJ mol(-1)) agrees well with the adsorption energy predicted by theory (41 to 44 kJ mol(-1)). Oxygen K-edge NEXAFS spectra indicate that the presence of acetone at the ice surface does not induce the formation of a pre-melted layer at temperatures up to 243 K. DFT calculations show that the energetically most favored adsorption geometry for acetone on ice is with the molecular plane almost parallel to the surface.     

Substrate changes associated with the chemistry of self-assembled monolayers on silicon

Alkylsiloxane self-assembled monolayers (SAMs) are used in the semiconductor industry and, more recently, as proxies for organics adsorbed on airborne mineral dust and on buildings and construction materials. A number of methods have been used for removing the SAM from the substrate after reaction or use, particularly plasmas or piranha (H2SO4/H2O2) solution. However, when the substrates are reused to make new SAMs, the impact of the cleaning methods on the chemistry of subsequently formed SAMs on the surface is not known. Here we report atomic force microscopy, X-ray photoelectron spectroscopy, Auger electron spectroscopy, and Fourier transform infrared studies of changes in a silicon substrate upon repetitive deposition and removal of SAMs by these two methods. It is shown that a thicker layer of silicon oxide is formed, and the surface becomes irregular and roughened, particularly after the piranha treatment. This layer of silica impacts the structure of the SAMs attached to it and can serve as a reservoir for trace gases that adsorb on it, potentially contributing to the subsequent reactions of the SAM. The implications for the use of such surfaces as a proxy for reactions of organics on airborne dust particles and on structures in the boundary layer are discussed.     

Effects of the Sagittarius dwarf tidal stream on dark matter detectors

The Sagittarius dwarf tidal stream may be showering dark matter onto the solar neighborhood, which can change the results and interpretation of direct detection searches for weakly interacting massive particles (WIMPs). Stars in the stream may already have been detected in the solar neighborhood, and the dark matter in the stream is (0.3-25)% of the local density. Experiments should see an annually modulated steplike feature in the energy recoil spectrum that would be a smoking gun for WIMP detection. The total count rate in detectors is not a cosine curve in time and peaks at a different time of year than the standard case.