Mixed-component metal-organic frameworks (MC-MOFs) are metal-organic frameworks that have different linkers or metals with the same structural role. Many of these mixed-ligand or mixed-metal MOFs are ...solid solutions, in which the proportions of the ligands or metals can be adjusted or even controlled. These MC-MOFs can be prepared directly, using more than one metal or ligand in the synthesis, or formed by post-synthetic modification. A second class of MC-MOFs have core-shell structures, and these can be prepared through epitaxial growth of one MOF on the surface of another or post-synthetic modification of the crystal surfaces. This review describes the syntheses, structures and properties of mixed-ligand, mixed-metal and core-shell MOFs, and highlights some of the potential benefits in functionality that these materials have.
Since the development of simple, aqueous protocols for the synthesis of anisotropic metal nanoparticles, research into many promising, valuable applications of gold nanorods has grown considerably, ...but a number of challenges remain, including gold-particle yield, robustness to minor impurities, and precise control of gold nanorod surface chemistry. Herein we present the results of a composite fractional factorial series of experiments designed to screen seven additional potential avenues of control and to understand the seed-mediated silver-assisted synthesis of gold nanorods. These synthesis variables are the amount of sodium borohydride used and the rate of stirring when producing seed nanoparticles, the age of and the amount of seeds added, the reaction temperature, the amounts of silver nitrate and ascorbic acid added, and the age of the reduced growth solution before seed nanoparticles are added to initiate rod formation. This statistical experimental design and analysis method, besides determining which experimental variables are important and which are not when synthesizing gold nanorods (and quantifying their effects), gives further insight into the mechanism of growth by measuring the degree to which variables interact with each other by mapping out their mechanistic connections. This work demonstrates that when forming gold nanorods by the reduction of auric ions by ascorbic acid onto seed nanoparticles, ascorbic acid determines how much gold is reduced, and the amount of seeds determine how it is divided, yet both influence the intrinsic growth rates, in both width and length, of the forming nanorods. Furthermore, this work shows that the reduction of gold proceeds via direct reduction on the surface of seeds and not through a disproportionation reaction. Further control over the length of gold nanorods can be achieved by tuning the amount of silver nitrate or the reaction temperature. This work shows that silver does not directly influence rod length or width, and a new primary role for silver is proposed as a catalyst promoting the reduction of gold on the ends of forming nanorods. Furthermore, this silver catalyst is removed from the reaction by adsorption onto the surface of the growing nanorod. This work also demonstrates the importance of freshly prepared silver nitrate and ascorbic acid solutions, free from even a few hours of photodegradation, in preparing gold nanorods with high shape purity and gold yield.
Microplastics (1 - 5000 µm) are pervasive in every compartment of our environment. However, little is understood regarding the concentration and size distribution of microplastics in road dust, and ...how they change in relation to human activity. Within road dust, microplastics move through the environment via atmospheric transportation and stormwater run-off into waterways. Human exposure pathways to road dust include dermal contact, inhalation and ingestion. In this study, road dust along an urban to rural transect within South-East Queensland, Australia was analysed using Accelerated Solvent Extraction followed by pyrolysis Gas Chromatography-Mass Spectrometry (Pyr-GC/MS). Polypropylene, polystyrene, polyethylene terephthalate, polyvinyl chloride, poly (methyl methacrylate) and polyethylene were quantified. Microplastic concentrations ranged from ~0.5 mg/g (rural site) to 6 mg/g (Brisbane city), consisting primarily of polyvinyl chloride (29%) and polyethylene terephthalate (29%). Size fractionation (< 250 µm, 250–500 µm, 500–1000 µm, 1000–2000 µm and 2000–5000 µm) established that the < 250 µm size fraction contained the majority of microplastics by mass (mg/g). Microplastic concentrations in road dust demonstrated a significant relationship with the volume of vehicles (r2 = 0.63), suggesting traffic, as a proxy for human movement, is associated with increased microplastic concentrations in the built environment.
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•Street dust from Queensland, Australia was sampled in a city to rural transect.•Microplastics of PP, PS, PET, PVC, PMMA and PE were quantified using (pyr-GC/MS).•Concentrations ranged from ~0.5 mg/g (Rural) to 6 mg/g (City location).•Polyvinyl chloride (29%) and polyethylene terephthalate (29%) were the most abundant of all quantified microplastic.•Concentrations correlated with traffic volumes. (r2 = 0.63).
Anisotropic (nonspherical) metal nanoparticles are of widespread research interest because changing the shape of metals at the nanoscale can provide access to materials with unique optical, ...electronic, and catalytic properties. The development of seeded growth syntheses has provided researchers unprecedented access to anisotropic metal nanocrystals (particularly, gold, silver, platinum, and palladium nanocrystals) with precisely controlled dimensions and crystallographic features. The mechanisms by which the various reagents present in seeded growth syntheses accomplish shape control, however, have yet to be fully elucidated. Recently, the role halide ions play in controlling metal nanocrystal shape has become a subject of particular interest. There are many ways in which the halide ions may direct the anisotropic growth of metal nanocrystals, including modulating the redox potentials of the metal ions, acting as face-specific capping agents, and/or controlling the extent of silver underpotential deposition at the nanocrystal surface. In this Perspective, we examine recent progress in elucidating and articulating the role halide ions play in seeded growth with particular emphasis on gold nanoparticles.
•Archived biosolids from australia and UK from 1950 to 2016 analyzed for 7 plastics.•Increasing concentrations over time of PP, PS, PET, PMMA, PVC and PE.•Prior to the 1990s, leakage of plastics into ...biosolids was limited except for PS.•Leakage from 1990s driven by increased production and consumption of PE, PET, PVC.•Concentrations of plastics closely correlate with production and consumption.
Plastics are ubiquitous contaminants that leak into the environment from multiple pathways including the use of treated sewage sludge (biosolids). Seven common plastics (polymers) were quantified in the solid fraction of archived biosolids samples from Australia and the United Kingdom from between 1950 and 2016. Six plastics were detected, with increasing concentrations observed over time for each plastic. Biosolids plastic concentrations correlated with plastic production estimates, implying a potential link between plastics production, consumption and leakage into the environment. Prior to the 1990s, the leakage of plastics into biosolids was limited except for polystyrene. Increased leakage was observed from the 1990s onwards; potentially driven by increased consumption of polyethylene, polyethylene terephthalate and polyvinyl chloride. We show that looking back in time along specific plastic pollution pathways may help unravel the potential sources of plastics leakage into the environment and provide quantitative evidence to support the development of source control interventions or regulations.
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Midlatitude extreme weather events are responsible for a large part of climate‐related damage, yet our understanding of these extreme events is limited, partly due to the lack of a theoretical basis ...for midlatitude extreme weather. In this letter, the local finite‐amplitude wave activity (LWA) of Huang and Nakamura (2015) is introduced as a diagnostic of the 500 hPa geopotential height for characterizing midlatitude weather events. It is found that the LWA climatology and its variability associated with the Arctic Oscillation agree broadly with the previously reported blocking frequency in the literature. There is a strong seasonal and spatial dependence in the trends of LWA in recent decades. While there is no observational evidence for a hemispheric‐scale increase in wave amplitude, robust trends in wave activity can be identified at the regional scales, with important implications for regional climate change.
Key Points
Local finite‐amplitude wave activity (LWA) is an objective diagnostic of midlatitude weather events
The LWA climatology and its variability associated with the AO agree with the blocking frequency
Robust trends in wave activity can be identified at regional scale, but not at hemispheric scale
We present a homogeneous X-ray analysis of all 318 gamma-ray bursts detected by the X-ray telescope (XRT) on the Swift satellite up to 2008 July 23; this represents the largest sample of X-ray GRB ...data published to date. In Sections 2–3, we detail the methods which the Swift-XRT team has developed to produce the enhanced positions, light curves, hardness ratios and spectra presented in this paper. Software using these methods continues to create such products for all new GRBs observed by the Swift-XRT. We also detail web-based tools allowing users to create these products for any object observed by the XRT, not just GRBs. In Sections 4–6, we present the results of our analysis of GRBs, including probability distribution functions of the temporal and spectral properties of the sample. We demonstrate evidence for a consistent underlying behaviour which can produce a range of light-curve morphologies, and attempt to interpret this behaviour in the framework of external forward shock emission. We find several difficulties, in particular that reconciliation of our data with the forward shock model requires energy injection to continue for days to weeks.
Playing tag with MOFs: Zinc metal–organic frameworks with pendant aldehyde and methoxy groups are prepared. The aldehyde‐tagged MOF takes up 2,4‐dinitrophenylhydrazine, reacting to form a ...hydrazone‐functionalized MOF which is crystallographically characterized. Use of both aldehyde‐ and methoxy‐functionalized dicarboxylates leads to MOFs containing both ligands, of which the aldehyde groups can be selectively reacted.
The majority of short gamma-ray bursts (SGRBs) are thought to originate from the merger of compact binary systems collapsing directly to form a black hole. However, it has been proposed that both ...SGRBs and long gamma-ray bursts (LGRBs) may, on rare occasions, form an unstable millisecond pulsar (magnetar) prior to final collapse. GRB 090515, detected by the Swift satellite was extremely short, with a T90 of 0.036 ± 0.016 s, and had a very low fluence of 2 × 10−8 erg cm−2 and faint optical afterglow. Despite this, the 0.3–10 keV flux in the first 200 s was the highest observed for an SGRB by the Swift X-ray Telescope (XRT). The X-ray light curve showed an unusual plateau and steep decay, becoming undetectable after ∼500 s. This behaviour is similar to that observed in some long bursts proposed to have magnetars contributing to their emission. In this paper, we present the Swift observations of GRB 090515 and compare it to other gamma-ray bursts (GRBs) in the Swift sample. Additionally, we present optical observations from Gemini, which detected an afterglow of magnitude 26.4 ± 0.1 at T+ 1.7 h after the burst. We discuss potential causes of the unusual 0.3–10 keV emission and suggest it might be energy injection from an unstable millisecond pulsar. Using the duration and flux of the plateau of GRB 090515, we place constraints on the millisecond pulsar spin period and magnetic field.
Plastics are contaminants of emerging concern that can enter the environment from multiple sources, including via land application of treated sewage sludge (biosolids). Biosolids samples collected ...from 82 wastewater treatment plants (WWTPs) across Australia and covering 34% of the population during census week in 2016 were quantitatively analyzed to estimate the release of seven common plastics. Quantitative analysis was performed by pressurized liquid extraction followed by double-shot microfurnace pyrolysis coupled to gas chromatography mass spectrometry. Ninety nine percent of the samples contained plastics (Σ6plastics) at concentrations of between 0.4 and 23.5 mg/g dry weight (median; 10.4 mg/g dry weight), while polycarbonate was not detected in any sample. Per-capita mass loads of plastics (Σ6plastics) released were between 8 and 877 g/person/year across all investigated WWTPs. Polyethylene was the predominant plastic detected, contributing to 69% of Σ6plastics. Based on the concentrations measured, it was projected that around 4700 metric tons (Mt) of plastics are released into the Australian environment through biosolids end-use each year, equating to approximately 200 g/person/year, which represents 0.13% of total plastics use in Australia. Of this, 3700 Mt of plastics are released to agricultural lands and 140 Mt to landscape topsoil. Our results provide a first quantitative per-capita mass loads and emission estimate of plastic types through biosolids end-use.
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