Photoelectron diffraction: from phenomenological demonstration to practical tool

The potential of photoelectron diffraction—exploiting the coherent interference of directly-emitted and elastically scattered components of the photoelectron wavefield emitted from a core level of a surface atom to obtain structural information—was first appreciated in the 1970s. The first demonstrations of the effect were published towards the end of that decade, but the method has now entered the mainstream armoury of surface structure determination. This short review has two objectives: First, to outline the way that the idea emerged and the way this evolved in my own collaboration with Neville Smith and his colleagues at Bell Labs in the early years: Second, to provide some insight into the current state-of-the art in application of (scanned-energy mode) photoelectron diffraction to address two key issue in quantitative surface structure determination, namely, complexity and precision. In this regard a particularly powerful aspect of photoelectron diffraction is its elemental and chemical-state specificity

Probing spatial correlations in a system of polarizable nanoparticles via measuring its optical extinction spectrum

It is shown that quantitative information on spatial correlations in a system of polarizable particles can be extracted directly from its experimentally measurable optical spectra. For a collection of metallic nanoparticles (NPs), it is demonstrated that the degree of shortrange correlation in NP’s positions can be evaluated by an appropriate numerical analysis of the extinction spectrum in the surface plasmon resonance region, given the polarizability of an individual NP. The spectrum analysis consists in the evaluation of a single number, which is the derivative of the ensemble response function in the vanishing polarizability limit, using the Tikhonov regularization method. This number has to be compared to pre-calculated values for a model NP system with given density and correlation parameters.Financial support from the Portuguese Foundation for Science and Technology (FCT) through Projects PTDC-FIS-113199-2009. PEst-C/FIS/UI0607/2011 and PEst-C/MAT/UI0013/2011 is gratefully acknowledged

Disposal of chemical agents and munitions stored at Pine Bluff Arsenal, Pine Bluff, Arkansas. Final phase 1, Environmental report

The Pine Bluff Arsenal (PBA) near Pine Bluff, Arkansas, is one of eight continental United States (CONUS) Army installations where lethal unitary chemical agents and munitions are stored and where destruction of agents and munitions is proposed under the Chemical Stockpile Disposal Program (CSDP). The chemical agent inventory at PBA consists of approximately 12%, by weight, of the total US stockpile. The destruction of the stockpile is necessary to eliminate the risk to the public from continued storage and to dispose of obsolete and leaking munitions. In 1988 the US Army issued a Final Programmatic Environmental Impact Statement (FPEIS) for the CSDP that identified on-site disposal of agents and munitions as the environmentally preferred alternative (i.e., the alternative with the least potential to cause significant adverse impacts). The purpose of this report is to examine the proposed implementation of on-site disposal at PBA in light of more recent and more detailed data than those on which the FPEIS is based. New population data were used to compute fatalities using the same computation methods and values for all other parameters as in the FPEIS. Results indicate that all alternatives are indistinguishable when the potential health impacts to the PBA community are considered. However, risks from on-site disposal are in all cases equal to or less than risks from other alternatives. Furthermore, no unique resources with the potential to prevent or delay implementation of on-site disposal at PBA have been identified

Disposal of chemical agents and munitions stored at Pine Bluff Arsenal, Pine Bluff, Arkansas

The Pine Bluff Arsenal (PBA) near Pine Bluff, Arkansas, is one of eight continental United States (CONUS) Army installations where lethal unitary chemical agents and munitions are stored and where destruction of agents and munitions is proposed under the Chemical Stockpile Disposal Program (CSDP). The chemical agent inventory at PBA consists of approximately 12%, by weight, of the total US stockpile. The destruction of the stockpile is necessary to eliminate the risk to the public from continued storage and to dispose of obsolete and leaking munitions. In 1988 the US Army issued a Final Programmatic Environmental Impact Statement (FPEIS) for the CSDP that identified on-site disposal of agents and munitions as the environmentally preferred alternative (i.e., the alternative with the least potential to cause significant adverse impacts). The purpose of this report is to examine the proposed implementation of on-site disposal at PBA in light of more recent and more detailed data than those on which the FPEIS is based. New population data were used to compute fatalities using the same computation methods and values for all other parameters as in the FPEIS. Results indicate that all alternatives are indistinguishable when the potential health impacts to the PBA community are considered. However, risks from on-site disposal are in all cases equal to or less than risks from other alternatives. Furthermore, no unique resources with the potential to prevent or delay implementation of on-site disposal at PBA have been identified

Sol-immobilized vs deposited-precipitated Au nanoparticles supported on CeO2 for furfural oxidative esterification

The non-edible nature of lignocellulose makes this an important raw material for future biorefineries. This work concerns the oxidative esterification of furfural (a C5 compound) to alkyl furoates, which find applications in the fine chemical industry. RESULTS: Very efficient Au/CeO2 catalysts for furfural oxidative esterification were prepared by deposition of gold colloids using polyvinyl alcohol as protective agent. The catalysts provided complete conversion and selectivity without the presence of a base. Sol-immobilized catalysts displayed better catalytic performances than Au/CeO2 prepared by deposition–precipitation (74% conversion). It was proposed that polyvinyl alcohol molecules act not only as gold stabilizer, but they leave ceria support uncovered and available for catalysis. The reaction is extremely sensitive to temperature, but can be carried out at very low pressures. Sol-immobilized catalysts do not require any preliminary calcination to be activated and can be recovered by simple filtration: no oxidation of the exhausted catalyst is required for at least six catalytic runs. CONCLUSION: The new catalyst is active, selective, recyclable and suitable for an industrial chemistry application based on renewable resources. Furoate ester can be obtained with optimal yields by a greener process than is presently used

Supported Gold Nanoparticles for Furfural Valorization in the Future Bio-based Industry

Gold nanoparticles prepared by sol immobilization using PVA as protecting agent were supported over different oxides (CeO2, ZrO2 and TiO2). The activity of the gold catalysts was tested in the oxidative esterification of furfural by an efficient and sustainable process. The samples supported on ceria and zirconia (AuCe and AuZr) have shown complete conversion and selectivity under mild reaction conditions. The catalytic performances are better than those obtained with the reference commercial AuTiWGC. The DR UV–Vis spectroscopic results indicate that gold nanoparticles that give rise to similar plasmonic band, as in the case of AuCe and AuZr, are very active and highly selective. The extent of crystallinity of the gold particles seems to have no influence on the activity of the sol immobilized catalysts. The null selectivity of the catalyst supported on titania is probably due to the presence of residual sulphate groups. The effect of the oxygen pressure on the furfural conversion is almost negligible for all the samples and, despite of the oxygen pressure lowering, it is possible to obtain always high conversion and selectivity. The selectivity of the process is unaffected by using air instead of oxygen, even at very low pressures. On the contrary, the presence of PVA seems to influence the conversion when working in air at low pressures, due to a dilution effect of the oxidant atmosphere. This is confirmed by the results obtained for a sample synthesized by deposition precipitation of gold on zirconia, where the high metal dispersion and the absence of the protecting agent allowed to reach high conversion even in low air pressure