Kinetic Analysis of the Cation Exchange in Nanorods from Cu2-xS to CuInS2: Influence of Djurleite's Phase Transition Temperature on the Mechanism.

In the syntheses of ternary I-III-VI2 compounds, such as CuInS2, it is often difficult to balance three precursor reactivities to achieve the desired size, shape, and atomic composition of nanocrystals. Cation exchange reactions offer an attractive two-step alternative, by producing a binary compound with the desired morphology and incorporating another atomic species postsynthetically. However, the kinetics of such cation exchange reactions, especially for anisotropic nanocrystals, are still not fully understood. Here, we present the cation exchange reaction from Cu-deficient djurleite Cu2-xS nanorods to wurtzite CuInS2, with size and shape retention. With reaction parameters in a broad temperature range between 40 °C and 160 °C, we were able to obtain various intermediates. Djurleite has a bulk phase transition temperature at 93 °C, which influences the cation exchange considerably. Below the phase transition temperature, indium is only incorporated into the surface of the nanorods, while, at temperatures above the phase transition temperature, we observe a Janus-type exchange mechanism and the formation of CuInS2 bands in the djurleite nanorods. The findings suggest that the diffusion above the phase transition temperature is strongly favored along the copper planes of the copper sulfide nanorods over the diffusion through the sulfur planes. This results in a difference of 37 kJ mol-1 in the activation energy of the cation exchange below and above the phase transition temperature.

Commercially available garden products as important sources of antibiotic resistance genes-a survey.

The dissemination of antibiotic resistance genes (ARGs) in the environment contributes to the global rise in antibiotic resistant infections. Therefore, it is of importance to further research the exposure pathways of these emerging contaminants to humans. This study explores commercially available garden products containing animal manure as a source of ARGs in a survey of 34 garden products, 3 recently landscaped soils, and 5 native soils. DNA was extracted from these soils and quantified for 5 ARGs, intI1, and 16S rRNA. This study found that both absolute and relative gene abundances in garden products ranged from approximately two to greater than four orders of magnitude higher than those observed in native soils. Garden products with Organic Materials Review Institute (OMRI) certification did not have significantly different ARG abundances. Results here indicate that garden products are important sources of ARGs to gardens, lawns, and parks.

X-ray-Based Techniques to Study the Nano-Bio Interface.

X-ray-based analytics are routinely applied in many fields, including physics, chemistry, materials science, and engineering. The full potential of such techniques in the life sciences and medicine, however, has not yet been fully exploited. We highlight current and upcoming advances in this direction. We describe different X-ray-based methodologies (including those performed at synchrotron light sources and X-ray free-electron lasers) and their potentials for application to investigate the nano-bio interface. The discussion is predominantly guided by asking how such methods could better help to understand and to improve nanoparticle-based drug delivery, though the concepts also apply to nano-bio interactions in general. We discuss current limitations and how they might be overcome, particularly for future use in vivo.

An in situ and real time study of the formation of CdSe NCs.

Magic Size Clusters (MSCs) have been identified in the last few years as intermediates in the synthesis of nanocrystals (NCs), and ever since there has been increased interest in understanding their exact role in the NC synthesis. Many studies have been focused on understanding the influence of precursors or ligands on the stability of MSCs and on whether the presence of MSCs influences the reaction pathway. However, their kinetic nature calls for an in situ temporal evolution study of the reaction, from the first seconds until the formation of regular nanocrystals, in order to unravel the role of MSCs in the formation of NCs. We have studied the synthesis of CdSe nanocrystals (NCs) in a continuous-flow reactor with in situ optical and small angle X-ray scattering characterization (SAXS). Our results show that MSCs are always formed, regardless the temperature, as necessary intermediates in the formation of CdSe NCs, and that their accumulation in solution depends only on the reaction time. These results explain why MSCs were, in some cases, not observed in some previous studies.

The Future of Colloidal Semiconductor Magic-Size Clusters.

Atomically defined, zero-dimensional magic-size clusters play pivotal roles in the nucleation and growth of semiconductor nanocrystals. Thus, they provide new opportunities to understand and to control nucleation and growth reactions beyond classical nucleation theory and to employ these reactions in the colloidal synthesis of increasingly complex and anisotropic nanomaterials with atomic level monodispersity. Both challenges require reliable determination of the exact structure and size of these ultrasmall and metastable nanoclusters. In this Perspective, we review and discuss the current challenges in analytics of magic-size clusters, in elucidating their formation mechanism, and in using them as next-generation reagents in colloidal chemistry.

Disparate Antibiotic Resistance Gene Quantities Revealed across 4 Major Cities in California: A Survey in Drinking Water, Air, and Soil at 24 Public Parks.

Widespread prevalence of multidrug and pandrug-resistant bacteria has prompted substantial concern over the global dissemination of antibiotic resistance genes (ARGs). Environmental compartments can behave as genetic reservoirs and hotspots, wherein resistance genes can accumulate and be laterally transferred to clinically relevant pathogens. In this work, we explore the ARG copy quantities in three environmental media distributed across four cities in California and demonstrate that there exist city-to-city disparities in soil and drinking water ARGs. Statistically significant differences in ARGs were identified in soil, where differences in blaSHV gene copies were the most striking; the highest copy numbers were observed in Bakersfield (6.0 × 10-2 copies/16S-rRNA gene copies and 2.6 × 106 copies/g of soil), followed by San Diego (1.8 × 10-3 copies/16S-rRNA gene copies and 3.0 × 104 copies/g of soil), Fresno (1.8 × 10-5 copies/16S-rRNA gene copies and 8.5 × 102 copies/g of soil), and Los Angeles (5.8 × 10-6 copies/16S-rRNA gene copies and 5.6 × 102 copies/g of soil). In addition, ARG copy numbers in the air, water, and soil of each city are contextualized in relation to globally reported quantities and illustrate that individual genes are not necessarily predictors for the environmental resistome as a whole.

Cl-capped CdSe nanocrystals via in situ generation of chloride anions.

Halide ions cap and stabilize colloidal semiconductor nanocrystal (NC) surfaces allowing for NCs surface interactions that may improve the performance of NC thin film devices such as photo-detectors and/or solar cells. Current ways to introduce halide anions as ligands on surfaces of NCs produced by the hot injection method are based on post-synthetic treatments. In this work we explore the possibility to introduce Cl in the NC ligand shell in situ during the NCs synthesis. With this aim, the effect of 1,2-dichloroethane (DCE) in the synthesis of CdSe rod-like NCs produced under different Cd/Se precursor molar ratios has been studied. We report a double role of DCE depending on the Cd/Se precursor molar ratio (either under excess of cadmium or selenium precursor). According to mass spectrometry (ESI-TOF) and nuclear magnetic resonance ((1)H NMR), under excess of Se precursor (Se dissolved in trioctylphosphine, TOP) conditions at 265 °C ethane-1,2-diylbis(trioctylphosphonium)dichloride is released as a product of the reaction between DCE and TOP. According to XPS studies chlorine gets incorporated into the CdSe ligand shell, promoting re-shaping of rod-like NCs into pyramidal ones. In contrast, under excess Cd precursor (CdO) conditions, DCE reacts with the Cd complex releasing chlorine-containing non-active species which do not trigger NCs re-shaping. The amount of chlorine incorporated into the ligand shell can thus be controlled by properly tuning the Cd/Se precursor molar ratio.

Interfacing quantum dots and graphitic surfaces with chlorine atomic ligands.

The performance of devices based on semiconductor nanocrystals (NCs) improves both with stronger interface interactions among NCs and between NCs and solid electrode surfaces. The combination of X-ray photoelectron spectroscopy (XPS) and solid (31)P CP/MAS NMR (cross-polarization/magic angle spinning nuclear magnetic resonance) shows that the selective substitution of long organic chains by chlorine atomic ligands during the colloidal synthesis by the hot injection method promotes the adsorption of CdSe NCs to carbon sp(2) surfaces, leading to the formation of well-ordered NC monolayers on graphitic materials.

Silane coupling agent structures on carbon nanofibers.

Carbon nanofibers (CNFs) are considered ideal materials for reinforcing polymers due to their excellent mechanical properties, among others. In order to obtain composites of optimal properties the clue is to enhance the interaction between reinforcement (CNFs) and polymer matrix. Surface modification of CNFs with silane coupling agents (SCAs) has revealed as one of the most interesting methods. The silanization process has been carried out mixing at room temperature and for one minute the hydrolysed silane with CNFs. We have use four different SCAs: 3-aminopropyltriethoxyxilane (APS), 3-aminopropyltrimethoxysilane (AMMO), N-(2-aminoethyl)-3-(aminopropyltrimethoxysilane) (DAMO), and 3-glycidoxypropyltrimethoxysilane (GLYMO), in order to elucidate the SCA-CNFs interaction and the silane structures formed on CNFs surface. XPS and FTIR-ATR techniques have pointed out that each silane adsorbs on CNFs surface through chemical bonding, forming multilayers. Silane nature determines the structure taken on CNFs surface. APS and AMO silanes adsorb taking vertical structures on CNFs surface, while DMO and GMO adsorb on CNFs taking horizontal structures, stabilized by zwitterions formed through H-bonds with hydroxyl groups from CNFs surface.