Georgios N. Karanikolos

Water-based synthesis of ZnSe nanostructures using amphiphilic block copolymer stabilized lyotropic liquid crystals as templates

Simultaneous size and shape control of zinc selenide (ZnSe) nanostructures was achieved using lyotropic liquid crystal templates formed by the self-assembly of an amphiphilic block copolymer in the presence of water and a less polar organic solvent. ZnSe quantum dots, hollow nanospheres, nanotubes, and nanolaminates (parallel nanoplates or free-standing quantum wells) were grown at room temperature in the aqueous phase of a poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) block copolymer/water/p-xylene ternary system. The nucleation of ZnSe was facilitated by an irreversible reaction between zinc acetate dissolved in water and hydrogen selenide gas that was allowed to diffuse into the self-assembled template. The nanostructures exhibit good crystallinity under high-resolution transmission electron miscroscopy and quantum confinement effects in their photoluminescence spectra. The shape and size of nanocrystals can be precisely controlled by altering the structure of the templating phase, by tuning the size of the nanodomains, and by changing the concentration of the zinc precursor.

Ag and Cu Monometallic and Ag/Cu Bimetallic Nanoparticle–Graphene Composites with Enhanced Antibacterial Performance

Increased proliferation of antimicrobial resistance and new strains of bacterial pathogens severely impact current health, environmental, and technological developments, demanding design of novel, highly efficient antibacterial agents. Ag, Cu monometallic and Ag/Cu bimetallic nanoparticles (NPs) were in situ grown on the surface of graphene, which was produced by chemical vapor deposition using ferrocene as precursor and further functionalized to introduce oxygen-containing surface groups. The antibacterial performance of the resulting hybrids was evaluated against Escherichia coli cells and compared through a series of parametrization experiments of varying metal type and concentration. It was found that both Ag- and Cu-based monometallic graphene composites significantly suppress bacterial growth, yet the Ag-based ones exhibit higher activity compared to that of their Cu-based counterparts. Compared with well-dispersed colloidal Ag NPs of the same metal concentration, Ag- and Cu-based graphene hybrids display weaker antibacterial activity. However, the bimetallic Ag/CuNP-graphene hybrids exhibit superior performance compared to that of all other materials tested, i.e., both the monometallic graphene structures as well as the colloidal NPs, achieving complete bacterial growth inhibition at all metal concentrations tested. This striking performance is attributed to the synergistic action of the combination of the two different metals that coexist on the surface as well as the enhancing role of the graphene support.

Oriented CoSAPO‐5 Membranes by Microwave‐Enhanced Growth on TiO2‐Coated Porous Alumina

We thank Dr. Christopher Lew for assistance with diffuse reflectance UV/Vis experiments. Support from the NSF (grant NSF-NIRT CMMI 0707610) and the Petroleum Institute of Abu Dhabi through the ADMIRE partnership (Abu Dhabi-Minnesota Institute for Research Excellence) is appreciated. M.P. acknowledges CSIC for a JAE doctoral fellowship, A.C. would like to thank CONSOLIDER Ingenio 2010-MULTICAT, and G.N.K. acknowledges a European Marie Curie International Reintegration Grant (FP7, grant agreement no. 210947). Portions of this work were carried out in the Nanofabrication Center, part of the National Nanotechnology Infrastructure Network (NNIN) which receives support from the NSF, and in the Characterization Facility on the campus of the University of Minnesota-Twin Cities which receives partial support from the NSF through the MRSEC program.

Catalytic NOx removal by single-wall carbon nanotube-supported Rh nanoparticles.

Single-wall carbon nanotubes functionalized with polyethylene glycol and doped with Rh nanoparticles were prepared and tested as catalyst for NO(x) reduction. Gravimetric adsorption studies were employed to elucidate the mechanism of NO adsorption on the active surface sites and to determine the onset of the desorption of oxygen. These studies provided information about the reaction kinetics and the lifetime of the catalyst, as well as the NO scission onset temperature and abatement rate, thus making possible to predict the conversion and define the optimum reaction conditions for efficient NO removal. Catalytic experiments were performed under different operating conditions and feed compositions, such as under rich operation, in presence of oxygen, and in presence of reducing CO and hydrocarbons. The developed nanostructured catalyst exhibits enhanced activity at lower temperatures in comparison to that reported for other Rh-based catalytic systems, while data about feed composition effects and carbon support depletion provided operating conditions that suppress N(2)O formation and extent the catalyst lifetime.

Aligned Carbon Nanotubes with Ferromagnetic Behavior

ical and structural characteristics of CNTs. a) SEM image of alumina/CNT ely following CVD. b) SEM image of CNTs after alumina removal in NaOH. s after further purification in HNO3. d) Raman spectrum of purified CNTs. Magnetic graphite films have been realized through encapsulation of magnetic nanoparticles within graphitic layers. In addition to their uniquemagnetic characteristics, these core-shell structures exhibit remarkable stability owing to the resistant carbon shell around the functional particles that protects them against degradation and reduces interparticle magnetic coupling. Inspired by these advancements, we have induced magnetism into parallel-oriented carbon nanotubes (CNTs) by in situ inclusion of magnetic iron carbide nanocrystals inside the tube walls. The resulting ferromagnetic composite consisting of monodisperse, perfectly aligned, and inherently open-ended CNTs can open up new prospects in high-flux magnetic separations and microfluidics, bio-capturing, and controlled drug delivery and release, while the stability of the wall-encapsulated magnetic particles prolongs material durability and extends the limits of application conditions without compromising functionality. Doping of CNTs with magnetic particles proceeds through loading of the tube core, e.g., by capillary wettability, or by attachment onto the tube external surface after appropriate modification. Yet, although functionality has been demonstrated, the integrity of the resulting composites is often compromised by oxidation of the environmentexposed particles, agglomeration and detachment upon processing under a magnetic field, and non-uniform particle distribution caused by inefficient surface treatment and/or incomplete opening of the nanotube ends. In addition, the presence of particles blocks the tubes rendering thematerial inappropriate for applications where fast and uninterrupted flow of substances is desired. Biological separations, in particular, require high sample throughput and simultaneous processing of multiple samples in a fraction of the usual separation time. Most magnetic separation methods, however, while effective, operate in a batch rather than in a flow mode, making them too slow and inefficient for optimal use in a high-throughput setting. The use of magnetic CNTs can overcome this challenge as CNTs, when appropriately engineered, can exhibit extremely high permeability, owing to the inherent smoothness of the nanotube inner surfaces that provides nearly frictionless molecular transport. The morphological characteristics of the synthesized nanotubes are extracted from microscopy data shown in Figure 1. Figure 1a reveals that one CNT extends out of almost every

Poly(ethylene oxide)-b-Poly(propylene oxide) Amphiphilic Block Copolymer-Mediated Growth of Silver Nanoparticles and Their Antibacterial Behavior

Silver nanoparticles were grown in self-assembled amphiphilic poly(ethylene oxide)/poly(propylene oxide) (PEO/PPO) triblock copolymers in selective solvents. Ternary systems of block copolymer, water, and p-xylene were used, forming a dispersion of water droplets in oil (reverse micellar) as well as binary water/block copolymer solutions. Besides its stabilizing affect, the role of the copolymer as a reducing agent for the metal salt precursors was examined. It was found that block copolymer-enabled reduction, carried out mainly by the PEO blocks, could take place only under particular conditions mostly related to the metal precursor, the block copolymer concentration, and the self-assembled micellar configuration. The effect of the triblock copolymers on growth and stabilization of gold nanoparticles was also examined. The antibacterial effect of the silver nanoparticles was investigated against Escherichia coli cells, and their performance was evaluated through a series of parametrization experiments, including the effect of the metal concentration, stability, activity over time, and dosage, while particular emphasis was given on the role of ions versus nanoparticles on the antibacterial performance.