Life cycle indicator comparison of copper, silver, zinc and aluminum nanoparticle production through electric arc evaporation or chemical reduction

Ways to produce metallic nanoparticles and the scale-up of these processes have seen increased interest as the industrial application of nanoparticles continues to grow. Their feasibility from an environmental point of view can be assessed by means of life cycle analysis (LCA). In this work two methods of metallic nanoparticle production, by evaporation/condensation of metal using electrical arc discharge reactors or by chemical reduction of metal salts in aqueous solutions or dry solid/solid mixtures, are evaluated based on the life cycle indicators. The evaporation of metal using electrical discharge reactors is a method studied in the European Commission 7th Framework Program “BUONAPART-E.” The environmental impact of the two different nanoparticle production approaches is here compared for four metals: copper, silver, zinc and aluminum. The chemical routes of producing nanoparticles require several different chemicals and reactions, while the electrical discharge routes use electricity to evaporate metal in a reactor under inert atmosphere. The nanoparticle production processes were modeled using “SimaPro” LCA software. Data for both the chemical production routes and the arc routes were taken from the literature. The choice of the best route for the production of each metal is strongly dependent on the final yield of the metallic nanoparticles. The yields for the chemical processes are not reported in the open literature, and therefore the comparisons have to be made with varying yields. At similar yields the electrical process has in general a lower environmental footprint than the studied chemical routes. The step or chemical with the greatest environmental impact varies significantly depending on process and metal being studied.Martin Slotte, Gregory Metha, Ron Zevenhove

Onset of carbon-carbon bonding in the Nb5Cy (y = 0-6) clusters: a threshold photo-ionisation and density functional theory study

We have used photo-ionisation efficiency spectroscopy to determine the ionisation potentials (IPs) of the niobium–carbide clusters, Nb5Cy (y = 0–6). Of these clusters Nb5C2 and Nb5C3 exhibit the lowest IPs. Complementary density functional theory calculations have been performed to locate the lowest energy isomers for each cluster. By comparing the experimental IPs with those calculated for candidate isomers, the structures of the Nb5Cy clusters observed in the experiment are inferred. For all these structures, the underlying Nb5 cluster has either a ‘prolate’ or ‘oblate’ trigonal bipyramid geometry. Both Nb5C5 and Nb5C6 are shown to contain carbon–carbon bonding in the form of one and two molecular C2 units, respectively

The optical spectrum of a large isolated polycyclic aromatic hydrocarbon: hexa-peri-hexabenzocoronene, C42H18

The first optical spectrum of an isolated polycyclic aromatic hydrocarbon large enough to survive the photophysical conditions of the interstellar medium is reported. Vibronic bands of the first electronic transition of the all benzenoid polycyclic aromatic hydrocarbon hexa-peri-hexabenzocoronene were observed in the 4080-4530 Angstrom range by resonant 2-color 2-photon ionization spectroscopy. The strongest feature at 4264 Angstrom is estimated to have an oscillator strength of f=1.4x10^-3, placing an upper limit on the interstellar abundance of this polycyclic aromatic hydrocarbon at 4x10^12 cm^-2, accounting for a maximum of ~0.02% of interstellar carbon. This study opens up the possibility to rigorously test neutral polycyclic aromatic hydrocarbons as carriers of the diffuse interstellar bands in the near future.Comment: 9 pages, 1 figure. Fixed a typo on the frequency of the 'b' ban

Guided Inquiry Learning in an Introductory Chemistry Course

Foundations of Chemistry (FoC), the University of Adelaide’s introductory chemistry pathway, recently underwent a complete restructure to assume no prior chemistry knowledge in order to better cater to students with little or no chemistry background. The restructure introduced Process-Oriented Guided Inquiry Learning (POGIL) style activities in lectures to deliver the majority of the course content and a new online learning platform for summative assessment. Three entirely new FoC courses were developed, one in each of semester 1 (FoC IA), semester 2 (FoC IB) and the University’s Summer Semester (FoC IS). Successful completion of all three courses provides students with a pathway into second year Chemistry in addition to the pathway provided by completing Chemistry IA and IB. To date, FoC IS has run from 2013 to 2015, with half of the students in each of these classes progressing to level II Chemistry courses. This paper outlines the restructure process that led to the creation of three new courses and how these developments have impacted student learning outcomes. Students have responded positively to the restructured courses, and end-of-semester results for FoC IA and IB have seen an increase in the proportion of Distinction and High Distinction grades

Development of POGIL-style introductory organic chemistry activities

Foundations of Chemistry IA (semester 1) and IB (semester 2) courses at the University of Adelaide are undertaken by Level I students pursuing a wide variety of degree programs that require a year of Chemistry study. As a consequence, many students who have never studied Chemistry in high school enrol in these courses. We have rewritten these courses for 2012 to cater to students with little or no Chemistry background, with group-based Process-Oriented Guided Inquiry Learning (POGIL) style activities used to deliver the majority of the course content. Early indications are that POGIL-style learning has been successful in improving student performance. We have been developing POGIL-style activities for all topics within both courses, but particularly in the area of introductory organic chemistry, for which few activities currently exist. Three organic chemistry activities were developed and subsequently tested in workshops run in November 2011 and April 2012. Student volunteers completed a survey consisting of Likert and open-ended questions related to the activities at the conclusion of each workshop. A focus group was also held at the conclusion of the second workshop. A summary of these responses and how they drove the development and revision process of the activities will be presented

Photoionization efficiency spectroscopy and density functional theory investigations of RhHo2On, (n=0-2) clusters

The experimental and theoretical adiabatic ionization energies (IEs) of the rhodium-holmium bimetallic clusters RhHo(2)O(n) (n=0-2) have been determined using photoionization efficiency spectroscopy and density functional theory (DFT) calculations. Both sets of data show the IE of RhHo(2)O to be significantly lower than the values for RhHo(2) and RhHo(2)O(2), which are found to be similar. This indicates that there are significant changes in electronic properties upon sequential addition of oxygen atoms to RhHo(2). The DFT investigations show that the lowest energy neutral structures are a C(2v) triangle for RhHo(2), a C(2v) planar structure for RhHo(2)O where the O atom is doubly bridged to the Ho-Ho bond, and a C(2v) nonplanar structure for RhHo(2)O(2), where the O(2) is dissociative and each O atom is doubly bridged to the Ho-Ho bond in the cluster above and below the RhHo(2) trimer plane. Good correlation between the experimental and computational IE data imply that the lowest energy neutral structures calculated are the most likely isomers ionized in the molecular beam. In particular, the theoretical adiabatic IE for the dissociative RhHo(2)O(2) structure is found to compare better with the experimentally determined value than the corresponding lowest energy O(2) associative structure.Alexander S. Gentleman, Matthew A. Addicoat, Viktoras Dryza, Jason R. Gascooke, Mark A. Buntine, and Gregory F. Meth

Chemically-synthesised, atomically-precise gold clusters deposited and activated on titania

Synchrotron XPS was used to investigate a series of chemically-synthesised, atomically-precise gold clusters Au(n)(PPh₃)(y) (n = 8, 9, 11 and 101, with y depending on cluster size) immobilized on titania nanoparticles. The gold clusters were washed with toluene at 100 °C or calcined at 200 °C to remove the organic ligand. From the position of the Au 4f₇/₂ peak it is concluded that cluster size is not altered through the deposition. From the analysis of the phosphorous spectra, it can be concluded that the applied heat treatment removes the organic ligands. Washing and calcination leads to partial oxidation and partial agglomeration of the clusters. Oxidation of the clusters is most likely due to the interaction of the cluster core with the oxygen of the titania surface after removal of ligands. The position of the Au 4f₇/₂ peak indicates that the size of the agglomerated clusters is still smaller than that of Au₁₀₁.David P. Anderson, Jason F. Alvino, Alexander Gentleman, Hassan Al Qahtani, Lars Thomsen, Matthew I. J. Polson, Gregory F. Metha, Vladimir B. Golovko and Gunther G. Andersso

The evolving SARS-CoV-2 epidemic in Africa: Insights from rapidly expanding genomic surveillance

INTRODUCTION Investment in Africa over the past year with regard to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) sequencing has led to a massive increase in the number of sequences, which, to date, exceeds 100,000 sequences generated to track the pandemic on the continent. These sequences have profoundly affected how public health officials in Africa have navigated the COVID-19 pandemic. RATIONALE We demonstrate how the first 100,000 SARS-CoV-2 sequences from Africa have helped monitor the epidemic on the continent, how genomic surveillance expanded over the course of the pandemic, and how we adapted our sequencing methods to deal with an evolving virus. Finally, we also examine how viral lineages have spread across the continent in a phylogeographic framework to gain insights into the underlying temporal and spatial transmission dynamics for several variants of concern (VOCs). RESULTS Our results indicate that the number of countries in Africa that can sequence the virus within their own borders is growing and that this is coupled with a shorter turnaround time from the time of sampling to sequence submission. Ongoing evolution necessitated the continual updating of primer sets, and, as a result, eight primer sets were designed in tandem with viral evolution and used to ensure effective sequencing of the virus. The pandemic unfolded through multiple waves of infection that were each driven by distinct genetic lineages, with B.1-like ancestral strains associated with the first pandemic wave of infections in 2020. Successive waves on the continent were fueled by different VOCs, with Alpha and Beta cocirculating in distinct spatial patterns during the second wave and Delta and Omicron affecting the whole continent during the third and fourth waves, respectively. Phylogeographic reconstruction points toward distinct differences in viral importation and exportation patterns associated with the Alpha, Beta, Delta, and Omicron variants and subvariants, when considering both Africa versus the rest of the world and viral dissemination within the continent. Our epidemiological and phylogenetic inferences therefore underscore the heterogeneous nature of the pandemic on the continent and highlight key insights and challenges, for instance, recognizing the limitations of low testing proportions. We also highlight the early warning capacity that genomic surveillance in Africa has had for the rest of the world with the detection of new lineages and variants, the most recent being the characterization of various Omicron subvariants. CONCLUSION Sustained investment for diagnostics and genomic surveillance in Africa is needed as the virus continues to evolve. This is important not only to help combat SARS-CoV-2 on the continent but also because it can be used as a platform to help address the many emerging and reemerging infectious disease threats in Africa. In particular, capacity building for local sequencing within countries or within the continent should be prioritized because this is generally associated with shorter turnaround times, providing the most benefit to local public health authorities tasked with pandemic response and mitigation and allowing for the fastest reaction to localized outbreaks. These investments are crucial for pandemic preparedness and response and will serve the health of the continent well into the 21st century

Pt Nanocluster Co-Catalysts for Photocatalytic Water Splitting

Degussa P25 is a benchmark form of TiO2 used worldwide in photocatalysis studies. Currently, no such benchmark exists for co-catalysts, which are essential for many photocatalytic reactions. Here, we present the preparation of Pt nanocluster co-catalysts on TiO2 using an unmodified commercial source and equipment that is commonly available. Transmission electron microscopy reveals that the procedure produces TiO2 decorated with Pt atoms and nanoclusters (1⁻5 atoms). Optical reflectance and X-ray diffraction measurements show that the procedure does not affect the TiO2 polymorph or ultraviolet-visible (UV-Vis) absorbance. Gas phase photocatalytic splitting of heavy water (D2O) shows that the Pt nanocluster-decorated TiO2 outperforms Pt nanoparticle (produced by photodeposition) decorated TiO2 in D2 production. Pt nanoclusters, produced directly from a commercial source, with high co-catalyst activity, are prime candidates to be used in benchmark photocatalytic reactions