Facile synthesis of capped γ-Fe2O3 and Fe3O4 nanoparticles

Facile methods for the selective preparation of capped iron oxide nanoparticles (γ-Fe₂O₃, Fe₃O₄) are described. The magnetic oxides are obtained via oxidative transformation of an iron hydroxide gel using H₂O₂ or (NH₄)₂S₂O₈ solutions as oxidants. Capping with oleic or other aliphatic acids is established simultaneously in one step by adding a toluene solution of the capping agent and refluxing the resulting biphase system. The method is simple, soft and affords nanoparticles of γ-Fe₂O₃ or Fe₃O₄ of controlled size depending on the reaction conditions. The capped nanoparticles are readily soluble in organic or aqueous media according to the nature of the sheath surrounding the surface of the particles, providing stable and high concentration ferrofluids.     

Evaluation by Monte Carlo simulations of the power limits and bit-error rate degradation in wavelength-division multiplexing networks caused by four-wave mixing

Fiber nonlinearities can degrade the performance of a wavelength-division multiplexing optical network. For high input power, a low chromatic dispersion coefficient, or low channel spacing, the most severe penalties are due to four-wave mixing (FWM). To compute the bit-error rate that is due to FWM noise, one must evaluate accurately the probability-density functions (pdf) of both the space and the mark states. An accurate evaluation of the pdf of the FWM noise in the space state is given, for the first time to the authors' knowledge, by use of Monte Carlo simulations. Additionally, it is shown that the pdf in the mark state is not symmetric as had been assumed in previous studies. Diagrams are presented that permit estimation of the pdf, given the number of channels in the system. The accuracy of the previous models is also investigated, and finally the results of this study are used to estimate the power limits of a wavelength-division multiplexing system.     

Investigation of the thermal stability of 2-D patterns of Au nanoparticles

Nanoparticles can serve as useful components or sub-assemblies, i.e., building blocks, in the design and fabrication of more complex structures needed for rapid prototyping using layered nanofabrication (LNF) or for use in nanoelectromechanical systems (NEMS). This paper describes investigations of the thermal stability of simple 2-D patterns of thiol-coated, 5-nm gold nanoparticles deposited on the native oxide surface of a Si(100) single crystal substrate. The changes in the particle structure and location on the surface were probed by using atomic force microscopy (AFM) before and after heating in ambient air. Experiments were carried out on the as-deposited nanoparticles and on patterns of nanoparticles that had been pretreated (prior to heating) by a 10-min exposure in a UV-ozone ashing chamber. All individual particles and 2-D patterns were stable up to 550 degrees C. Higher temperatures caused first a reduction in particle height and eventually a loss of the particle from the field of view (presumably by rather long-range diffusion).     

Low Temperature Steam Reforming of Ethanol Over Supported Noble Metal Catalysts

The catalytic activity of M/Al₂O₃ catalysts for the reaction of steam reforming of ethanol has been investigated in the temperature range of 300–450 °C. It has been found that the catalytic performance varies in the order of Pt > Pd > Rh > Ru, with Pt exhibiting high activity and selectivity toward hydrogen production, as well as long term stability at low temperatures. It is shown that the reaction occurs in a bifunctional manner, with the participation of both the dispersed metallic phase and the support. Ethanol interacts strongly with the Al₂O₃ carrier, promoting mainly ethanol dehydration, while in the presence of Pt, catalytic activity is shifted toward lower temperatures. Ethanol decomposition and dehydrogenation reactions dominate at low temperatures, while reforming, water-gas shift and methanation contribute significantly to product distribution.     

Optically Active Spherical Polyelectrolyte Brushes with a Nanocrystalline Magnetic Core

The unique properties of magnetic nanocrystals have triggered intensive research towards their effective functionalization and application in many technological fields. Although synthesis of magnetic colloids is being thoroughly studied, there is limited knowledge on the synthesis, characterization, and properties of magnetic polyelectrolyte spherical brushes. In the present work, the preparation of such hybrids and the subsequent formation of stable aqueous colloids are described. The core of the spherical brush consists of a magnetic γ‐Fe₂O₃ nanocrystallite (faceted but mostly spherical‐like) with a mean diameter of 17 nm. The bioadhesive polyelectrolyte poly(sodium 4‐styrene sulfonate), forming the surrounding brush layer, was proven to be an effective covalently modifying macromolecule for the iron oxide surface, as Fourier transform IR spectroscopy revealed. Several observations on colloidal aspects are discussed and are successfully explained by models and experiments describing polyelectrolyte brushes with a soft polymeric core. Finally, the hybrids exhibit their multifunctional character and their technological importance by combining in a single and soluble product with magnetic and nonlinear optical properties.     

Evaluation of pesticides residues in Greek peaches during 2002–2007 after the implementation of integrated crop management

The incidence and levels of pesticide residues in peaches grown using Integrated Crop Management (ICM) methods in Pella and Imathia, districts of Macedonia, Northern Greece, are hereby presented. A total of 1150 peach samples were collected pre-harvest (June–September) and were analysed during the period of 2002–2007. Residual levels of selected insecticides, fungicides and acaricides were determined by Gas Chromatography-Mass Spectrometry following solid phase extraction. The monitoring program is extended up to 31 pesticides. Twenty-two of them were measured above detection limit, and 8 of them were found present every year. Insecticides represent the highest incidence amongst pesticide categories (654 positive samples, 56.9%) while chlorpyrifos is the most frequent within the category (491 positive samples). The incidence of pyrethrins was the highest in 2007 (26.8%) while bifenthrin was detected most frequently within this category (67 positive samples in 2007). Traceable levels of pesticides were lower than the Maximum Residues Limits (MRLs) in all peach samples. Variances in incidence and levels of pesticides are attributed to some extent to the weather conditions as well as due to abidance by the guidelines of agronomists during blowing and harvest period. Monitoring in agricultural products could be employed as the first step in a chain of biomonitoring studies in humans, and may also be proven to be a good and ample indicator of exposure.     

Mixed‐Valence Single‐Atom Catalyst Derived from Functionalized Graphene

Single‐atom catalysts (SACs) aim at bridging the gap between homogeneous and heterogeneous catalysis. The challenge is the development of materials with ligands enabling coordination of metal atoms in different valence states, and preventing leaching or nanoparticle formation. Graphene functionalized with nitrile groups (cyanographene) is herein employed for the robust coordination of Cu(II) ions, which are partially reduced to Cu(I) due to graphene‐induced charge transfer. Inspired by nature's selection of Cu(I) in enzymes for oxygen activation, this 2D mixed‐valence SAC performs flawlessly in two O₂‐mediated reactions: the oxidative coupling of amines and the oxidation of benzylic C? H bonds toward high‐value pharmaceutical synthons. High conversions (up to 98%), selectivities (up to 99%), and recyclability are attained with very low metal loadings in the reaction. The synergistic effect of Cu(II) and Cu(I) is the essential part in the reaction mechanism. The developed strategy opens the door to a broad portfolio of other SACs via their coordination to various functional groups of graphene, as demonstrated by successful entrapment of Fe^III/Fe^II single atoms to carboxy‐graphene.     

Non-van der Waals 2D Materials for Electrochemical Energy Storage

The development of advanced electrode materials for the next generation of electrochemical energy storage (EES) solutions has attracted profound research attention as a key enabling technology toward decarbonization and electrification of transportation. Since the discovery of graphene's remarkable properties, 2D nanomaterials, derivatives, and heterostructures thereof, have emerged as some of the most promising electrode components in batteries and supercapacitors owing to their unique and tunable physical, chemical, and electronic properties, commonly not observed in their 3D counterparts. This review particularly focuses on recent advances in EES technologies related to 2D crystals originating from non-layered 3D solids (non-van der Waals; nvdW) and their hallmark features pertaining to this field of application. Emphasis is given to the methods and challenges in top-down and bottom-up strategies toward nvdW 2D sheets and their influence on the materials’ features, such as charge transport properties, functionalization, or adsorption dynamics. The exciting advances in nvdW 2D-based electrode materials of different compositions and mechanisms of operation in EES are discussed. Finally, the opportunities and challenges of nvdW 2D systems are highlighted not only in electrochemical energy storage but also in other applications, including spintronics, magnetism, and catalysis.