Luiz H. S. Gasparotto

Investigation of Various Ionic Liquids and Catalyst Materials for Lithium-Oxygen Batteries

Abstract We report about the use of different ionic liquids and catalyst materials in lithium-oxygen batteries. Different types of oxygen electrodes such as self-supporting oxygen electrodes and catalyst-coated separators were prepared by hot-pressing and spray-coating procedures, respectively. Porous carbon material such as Ketjen Black, binder material and different metal oxides were used to prepare the cathodes. Self-supporting oxygen electrodes and catalyst-coated separators consist of a carbon material loading of 10 and 1.5 mg/cm2, respectively. Electrolyte systems based on lithium bis-(trifluoromethylsulfonyl) imide (LiTFSI) in ionic liquids and lithium hexafluorophosphate (LiPF6) in carbonate solvents were investigated in lithium-oxygen batteries. 1-butyl-1-methyl-pyrrolidinium bis-(trifluoromethylsulfonyl) imide and 1-butyl-1-methyl-pyrrolidinium tetracyanoborate as well as 1-ethyl-3-methyl-imidazolium bis-(trifluoromethylsulfonyl) imide, thi oisocyanat and dicyanamide were tested. The cell potential recorded for ionic liquids ranged from 2 to 2.5 V during the discharge process. At a current density of 0.1 mA/cm2geom discharge capacities were found to be higher for lithium-oxygen cells using imidazolium-based ionic liquids compared to pyrrolidinium-based ionic liquids. Discharge voltages between 2.7 and 2.8 V were observed for the carbonate-based solvents. The discharge potentials observed were independent of the metal oxide used, but the charge potentials were highly dependent on the catalyst materials employed. Good reversibility was obtained when the corresponding lithium-oxygen cells were cycled at 20–40% of their maximum capacity (mA h/g C).

Doxycycline conjugated with polyvinylpyrrolidone-encapsulated silver nanoparticles: a polymer's malevolent touch against Escherichia coli

The emergence of multi-resistant pathogens has necessitated the investigation of new strategies to cope with this ever-increasing threat to public health. In this context, we combined silver nanoparticles (AgNPs) with doxycycline (DO), an antibiotic from the class of tetracyclines, to evaluate the potentiality of this hybrid as a bactericidal agent against E. coli. Polyvinylpyrrolidone (PVP) was used as a stabilizer to prevent the excessive growth and agglomeration of AgNPs. Interestingly, DO bound directly to PVP and had its concentration increased around the particle as a consequence of this interaction. As a result, the AgNPs/DO conjugates presented enhanced bactericidal properties compared to the individual components. Stabilizing agents are generally unwanted on the surfaces of nanoparticles because of their potential to block adsorption surface sites. However, we have shown that PVP played a paramount role in concentrating DO around the particle, which culminated in an increased bactericidal activity towards E. coli.

A low-cost microcontrolled photometer with one color recognition sensor for selective detection of Pb2+ using gold nanoparticles

The present work describes a microcontrolled photometer based on light-emitting-diodes (LEDs) for detection of Pb2+ using gold nanoparticles (AuNPs). The photometer makes use of a single LED as a light source, a sensor TCS230 (TAOS, USA) and an Arduino electronic card as an acquisition system. On the sensor, the light from the three closely adjoined red, green, and blue LEDs composing the “white” light source LED is contact-coupled to the map-illumination pointed toward the detection cell. To maintain a constant light intensity, a common white-color LED (emitting a 450–620 nm continuous spectrum) was employed as a controllable light source. Software was written in C++ to control the photometer through a USB interface and for data acquisition. Pb2+ measurements are based on the color change of AuNPs due to their aggregation provoked by Pb2+. The method showed excellent selectivity for Pb2+ compared to other 19 metal ions (Ag+, Al3+, Ba2+, Ca2+, Cd2+, Co2+, Cr3+, Cu2+, Fe2+, Hg+, K+, Li+, Mg2+, Mn2+, Na+, Ni2+, Sn2+, Sr2+, and Zn2+). Pb2+ was detected with the photometer and also monitored via UV-Vis. Solutions containing Pb2+ in the concentration range from 0.6 to 10 mmol L−1 were employed to construct the analytical curves, proving a limit of detection (LOD) of 0.89 mmol L−1. The sensitivity was compared to that obtained with a UV-Vis spectrophotometer at 520 nm. A repeatability of 4.11% (expressed as the relative standard deviation of 10 measurements) was obtained. The proposed method was successfully applied to detect Pb2+ in spiked water samples.

Layer-by-layer assembly of poly(vinylpyrrolidone)-embedded gold nanoparticles with carbon nanotubes for glycerol electro-oxidation

In the present study, poly(vinylpyrrolidone) (PVP) served as reducing and capping agents for the synthesis of gold nanoparticles (AuNPs) in alkaline medium. The PVP-AuNPs were then combined with carbon nanotubes (CNTs) to assemble thin films onto ITO via the layer-by-layer (LbL) technique. The PVP-AuNPs/CNTs LbL films were analyzed with UV–Vis spectroscopy and atomic force microscopy (AFM). The latter technique revealed that the PVP-AuNPs/CNTs LbL films took over the entire ITO surface homogeneously, which positively impacted the magnitude of the anodic currents for glycerol electro-oxidation. Such results indicated that the combination PVP-AuNPs with CNTs in an adequate LbL fashion nanostructure may be feasible for applications in various fields such as catalysis, fuel cells, and sensing.

Electrogeneration of platinum nanoparticles in a matrix of dendrimer–carbon nanotubes

Hybrid materials with enhanced properties can now be obtained by combining nanomaterials such as carbon nanotubes and metallic nanoparticles, where the main challenge is to control fabrication conditions. In this study, we demonstrate that platinum nanoparticles (PtNps) can be electrogenerated within layer-by-layer (LbL) films of polyamidoamine (PAMAM) dendrimers and single-walled carbon nanotubes (SWCNTs), which serve as stabilizing matrices. The advantages of the possible control through electrogeneration were demonstrated with a homogeneous distribution of PtNps over the entire surface of the PAMAM/SWCNT LbL films, whose electroactive sites could be mapped using magnetic force microscopy. The Pt-containing films were used as catalysts for hydrogen peroxide reduction, with a decrease in the reduction potential of 60 mV compared to a Pt film deposited onto bare ITO. By analyzing the mechanisms responsible for hydrogen peroxide reduction, we ascribed the enhanced catalytic activity to synergistic effects between platinum and carbon in the LbL films, which are promising for sensing and fuel cell applications.

How the interaction of PVP-stabilized Ag nanoparticles with models of cellular membranes at the air-water interface is modulated by the monolayer composition

The antimicrobial property of silver nanoparticles (AgNPs) is believed to be associated to their interaction with biointerfaces such as microbial cell membranes, encouraging research on the identification of membrane sites capable of AgNPs binding. Although significant progress has been made in that regard, the exact molecular mechanism of action is yet to be fully understood. In this study, AgNPs dispersed in aqueous media and stabilized with polyvinylpyrrolidone were incorporated in Langmuir monolayers of selected lipids that served as cell membrane models. Results from pressure-area isotherms, vibrational spectroscopy and Brewster angle microscopy revealed condensation of glycoside-free lipid monolayers, evidencing that the AgNPs interact mostly with the lipid hydrophilic head groups. In contrast, the monolayers of systems containing glycoside derivatives were found to expand upon AgNPs incorporation, indicating that the glycosidic compounds might facilitate the incorporation of these nanoparticles in cellular membranes. These data can be therefore correlated with the possible toxicity and microbicide effect of AgNPs in lipidic surfaces of mammalian and microbial membranes.

Dual Role of a Ricinoleic Acid Derivative in the Aqueous Synthesis of Silver Nanoparticles

We show that sodium 9,10-epoxy-12-hydroxytetradecanoate (SEAR), an epoxidized derivative of ricinoleic acid, simultaneously functioned as reducing and stabilizing agents in the synthesis of silver nanoparticles in alkaline aqueous medium. The advantage of using SEAR is its biodegradability and nontoxicity, which are important characteristics for mitigation of environmental impact upon discharge of nanoparticles into terrestrial and aquatic ecosystems. The SEAR concentration was found to impact considerably the size distribution of silver nanoparticles (AgNPs). A concentration below the SEAR critical micelle concentration (CMC) generated 23 nm sized AgNPs with 10 nm standard deviation, while 50 nm sized AgNPs ( nm) were obtained at a concentration above the SEAR CMC. FTIR analysis revealed that the carboxylate that constitutes the SEAR hydrophilic head binds directly to the AgNPs surface promoting stabilization in solution. Finally, AgNPs turned into Ag2S upon contact with wastewater samples from Wastewater Treatment Plant at Federal University of Rio Grande do Norte (UFRN), Brazil, which is an interesting result, since Ag2S is more environmentally friendly than pure AgNPs.

Near Infrared Spectroscopy as an Emerging Tool for Forensic Entomotoxicology

Leomir Aires Silva de Lima, Tainá C. Baia, Renata A. Gama, Luiz Henrique da Silva Gasparotto and Kássio M.G. Lima Universidade Federal do Rio Grande do Norte, Instituto de Química, Programa de Pós-Graduação em Química, Grupo de Pesquisa em Química Biológica e Quimiometria, CEP 59072–970 – Natal, RN, Brazil. E-mail: kassiolima@gmail.com.br Universidade Federal do Rio Grande do Norte, Departamento de Microbiologia e Parasitologia, CEP 59072–970 – Natal, RN, Brazil

On the synergy between silver nanoparticles and doxycycline towards the inhibition of Staphylococcus aureus growth

In a previous paper (RSC Adv., 2015, 5, 66886–66893), we showed that the combination of silver nanoparticles (NanoAg) with doxycycline (DO) culminated in an increased bactericidal activity towards E. coli. Herein we further investigated the metabolic changes that occurred on Staphylococcus aureus upon exposure to NanoAg with the help of attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) coupled with multivariate data analysis. It has been discovered that the combination of DO with NanoAg produced metabolic changes in S. aureus that were not simply the overlap of the treatments with DO and NanoAg separately. Our results suggest that DO and NanoAg act synergistically to impede protein synthesis by the bacteria.

Spherical neutral gold nanoparticles improve anti-inflammatory response, oxidative stress and fibrosis in alcohol-methamphetamine-induced liver injury in rats

ABSTRACT This study aimed to elucidate the anti‐inflammatory, anti‐oxidant and antifibrotic effects of gold nanoparticles (GNPs) in rats subjected to liver injury with ethanol and Methamphetamine (METH). The liver injury was induced by gavage administrations of 30% alcoholic solution (7g/kg) once a day during 28days, followed by METH (10mg/kg) on the 20th and 28thdays of treatment. GNPs treatment (724.96&mgr;g/kg) during the ethanol and METH exposure was associated with reduced steatosis, hepatic cord degeneration, fibrosis and necrosis. Furthermore, there was a reduction in biochemical markers of liver damage and oxidative stress, and pro‐inflammatory cytokines IL‐1&bgr; and TNF‐&agr;, compared to ethanol+METH group alone. A decrease of FGF, SOD‐1 and GPx‐1 expression was also observed. GNPs down‐regulated the activity of Kupffer cells and hepatic stellate cells affecting the profile of their pro‐inflammatory cytokines, oxidative stress and fibrosis through modulation of signaling pathways AKT/PI3K and MAPK in ethanol+METH‐induced liver injury in a rat model.