Antonio G. Souza Filho

Anti-adhesion and antibacterial activity of silver nanoparticles supported on graphene oxide sheets.

This work reports on the preparation, characterization and antibacterial activity of a nanocomposite formed from graphene oxide (GO) sheets decorated with silver nanoparticles (GO-Ag). The GO-Ag nanocomposite was prepared in the presence of AgNO3 and sodium citrate. The physicochemical characterization was performed by UV-vis spectroscopy, X-ray diffraction (XRD), thermogravimetric analysis (TGA), Raman spectroscopy and transmission electron microscopy (TEM). The average size of the silver nanoparticles anchored on the GO surface was 7.5 nm. Oxidation debris fragments (a byproduct adsorbed on the GO surface) were found to be crucial for the nucleation and growth of the silver nanoparticles. The antibacterial activity of the GO and GO-Ag nanocomposite against the microorganism Pseudomonas aeruginosa was investigated using the standard counting plate methodology. The GO dispersion showed no antibacterial activity against P. aeruginosa over the concentration range investigated. On the other hand, the GO-Ag nanocomposite displayed high biocidal activity with a minimum inhibitory concentration ranging from 2.5 to 5.0 μg/mL. The anti-biofilm activity toward P. aeruginosa adhered on stainless steel surfaces was also investigated. The results showed a 100% inhibition rate of the adhered cells after exposure to the GO-Ag nanocomposite for one hour. To the best of our knowledge, this work provides the first direct evidence that GO-Ag nanocomposites can inhibit the growth of microbial adhered cells, thus preventing the process of biofilm formation. These promising results support the idea that GO-Ag nanocomposites may be applied as antibacterial coatings material to prevent the development of biofilms in food packaging and medical devices.

Doped Carbon Nanotubes: Synthesis, Characterization and Applications

Various applications of carbon nanotubes require their chemical modification inorder to tune/control their physicochemical properties. One way for achieving thiscontrol is by carrying out doping processes through which atoms and moleculesinteract (covalently or noncovalently) with the nanotube surfaces. The aim of thischapter is to emphasize the importance of different types of doping in carbonnanotubes (single-, double- and multiwall). There are three main categories ofdoping: exohedral, endohedral and inplane doping. We will review the most efficientways to dope carbon nanotubes and discuss the effects on the electronic, vibrational,chemical, magnetic and mechanical properties. In addition, we will discuss thedifferent ways of characterizing these doped nanotubes using spectroscopictechniques, such as resonant Raman, X-ray photoelectron, electron energy lossspectroscopy and others. It will be demonstrated that doped carbon nanotubes couldbe used in the fabrication of nanodevices (e.g., sensors, protein immobilizers,field emission sources, efficient composite fillers, etc.). We will also presentresults related to the importance of inplane-doped nanotubes for attachingvarious metal clusters and polymers covalently using wet chemical routes.

Nanostructured silver vanadate as a promising antibacterial additive to water-based paints

In this article, we report the use of nanostructured silver vanadate as a promising antibacterial additive to water-based paints that has potential for applications in bathrooms, kitchens, and hospital environments. This hybrid nanomaterial was prepared by a simple and fast precipitation reaction involving silver nitrate and ammonium vanadate, dismissing the hydrothermal treatment. The preparation involved using Ag vanadate nanowires (β-AgVO(3)) with diameters ranging from 20 to 60 nm and decorated with silver (Ag) nanoparticles (NPs) with diameters ranging from 5 to 40 nm. Results of antibacterial tests show that this hybrid material has a promising antibacterial activity against several types of bacteria strains, such as methicillin-resistant Staphylococcus aureas (MRSA), Enterococcus faecalis, Escherichia coli, and Salmonella enterica Typhimurium. The evaluated material exhibits antibacterial activity 30 times larger than that of Oxacillin. In addition, this nanomaterial was tested as an antibacterial additive to water-based paints, and formulations with 1% show a 4-mm inhibition zone against a MRSA strain.

Unveiling the structure and composition of titanium oxide nanotubes through ion exchange chemical reactions and thermal decomposition processes

Neste trabalho reportamos reacoes de troca ionica e decomposicao termica em nanotubos de oxido de titânio, obtidos pelo tratamento hidrotermico de TiO 2 e NaOH. Considerando os resultados obtidos, sugerimos uma nova composicao quimica para os nanotubos: Na 2 Ti 3 O 7 ·nH 2 O. Os resultados tambem indicam que a estrutura da parede dos nanotubos seria isoestrutural as lamelas observadas para o Na 2 Ti 3 O 7 bulk. Dependendo da natureza da lavagem (agua deionizada ou solucao acida) executada no nanotubo apos o tratamento hidrotermico a concentracao de ions Na + pode ser modificada atraves de um processo de troca ionica do Na + por H + . Tais resultados permitem sugerir a seguinte formula quimica geral para os nanotubos obtidos: Na 2-x H x Ti 3 O 7 ·nH 2 O (0≤ x ≤2), sendo x dependente das condicoes de lavagens. In this paper we report the ion exchange reactions and the thermal decomposition of titanium oxide nanotubes, obtained by hydrothermal treatment of TiO 2 and NaOH. Based on these results we propose a new composition for the as-prepared nanotubes as Na 2 Ti 3 O 7 ·nH 2 O. Our results also suggest that nanotube walls have structure similar to those observed in the layer of the bulk Na 2 Ti 3 O 7 . Depending on how the washing process is performed on the nanotubes (water or acid solutions) the Na + content can be modified via the exchange reaction of Na

Structural and proactive safety aspects of oxidation debris from multiwalled carbon nanotubes

The removal of oxidation debris from the oxidized carbon nanotube surface with a NaOH treatment is a key step for an effective functionalization and quality improvement of the carbon nanotube samples. In this work, we show via infrared spectroscopy and ultrahigh resolution and accuracy mass spectrometry that oxidation debris obtained from HNO(3)-treated multiwalled carbon nanotubes is a complex mixture of highly condensed aromatic oxygenated carbonaceous fragments. We have also evaluated their cytotoxicity by using BALB/c 3T3 mouse fibroblasts and HaCaT human keratinocytes as models. By knowing the negative aspects of dissolved organic carbon (DOC) to the water quality, we have demonstrated the removal of these carbon nanotube residues from the NaOH solution (wastewater) by using aluminium sulphate, which is a standard coagulant agent used in conventional drinking water purification and wastewater treatment plants. Our results contribute to elucidate the structural and proactive safety aspects of oxidation debris from oxidized carbon nanotubes towards a greener nanotechnology.

Phonons in ferroelectric Bi2WO6: Raman and infrared spectra and lattice dynamics

Bi2WO6 ferroelectric single crystal was investigated by micro-Raman scattering and infrared spectroscopies. Symmetry of modes was established and the mode assignment was proposed.

Surface Chemistry in the Process of Coating Mesoporous SiO2 onto Carbon Nanotubes Driven by the Formation of SiOC Bonds

The deposition of mesoporous silica (SiO(2)) on carbon nanotubes (CNTs) has opened up a wide range of assembling possibilities by exploiting the sidewall of CNTs and organosilane chemistry. The resulting systems may be suitable for applications in catalysis, energy conversion, environmental chemistry, and nanomedicine. However, to promote the condensation of silicon monomers on the nanotube without producing segregated particles, (OR)(4-x)SiO(x)(x-) units must undergo nucleophilic substitution by groups localized on the CNT sidewall during the transesterification reaction. In order to achieve this preferential attachment, we have deposited silica on oxidized carbon nanotubes (single-walled and multiwalled) in a sol-gel process that also involved the use of a soft template (cetyltrimethylammonium bromide, CTAB). In contrast to the simple approach normally used to describe the attachment of inorganic compounds on CNTs, SiO(2) nucleation on the tube is a result of nucleophilic attack mainly by hydroxyl radicals, localized in a very complex surface chemical environment, where various oxygenated groups are covalently bonded to the sidewall and carboxylated carbonaceous fragments (CCFs) are adsorbed on the tubes. Si-O-C covalent bond formation in the SiO(2)-CNT hybrids was observed even after removal of the CCFs with sodium hydroxide. By adding CTAB, and increasing the temperature, time, and initial amount of the catalyst (NH(4)OH) in the synthesis, the SiO(2) coating morphology could be changed from one of nanoparticles to mesoporous shells. Concomitantly, pore ordering was achieved by increasing the amount of CTAB. Furthermore, preferential attachment on the sidewall results mostly in CNTs with uncapped ends, having sites (carboxylic acids) that can be used for further localized reactions.

Selection rules for one- and two-photon absorption by excitons in carbon nanotubes

Recent optical absorption and emission experiments showed that the lower energy optical transitions in carbon nanotubes are excitonic in nature, as predicted by theory. These experiments were based on the symmetry aspects of free electron-hole states and bound excitonic states. The present work shows, however, that group theory does not predict the selection rules needed to explain the two photon experiments. We obtain the symmetries and selection rules for the optical transitions of excitons in single-wall carbon nanotubes within the approach of the group of the wave vector, thus providing important information for the interpretation of theoretical and experimental optical spectra of these materials.

Suppression of the hemolytic effect of mesoporous silica nanoparticles after protein corona interaction: independence of the surface microchemical environment

Mesoporous silica nanoparticles are known to induce the hemolysis of human red blood cells (RBCs) when citotoxicity assays are performed in a phosphate buffer solution (PBS). However, in a more realistic approach, the presence of blood plasma biomolecules must be considered in any nanotoxicological evaluation of porous SiO2 nanoparticles when biomedical applications through intravenous administration are aimed. In this context, it is demonstrated in this work that porous silica nanoparticles do not induce any cytotoxic effect on RBCs when hemolysis assay is done in the presence of blood plasma, regardless the surface charge (positive or negative) of the nanoparticle. The absence of hemolysis is mainly associated with the adsorption of plasma proteins on the nanoparticle surface, which leads to the formation of a stable protein coating (called protein corona or PC) that shields the original microchemical environment of bare nanoparticles.

Funcionalização de nanotubos de Carbono

Carbon nanotubes are very stable systems having considerable chemical inertness due to the strong covalent bonds of the carbon atoms on the nanotube surface. Many applications of carbon nanotubes require their chemical modification in order to tune/control their physico-chemical properties. One way of achieving this control is carrying out functionalization processes where atoms and molecules interact (covalent or non-covalent) with the nanotubes. We review some of the progress that has been made in chemical functionalization of carbon nanotubes. Emphasis is given to chemical strategies, the most used techniques, and applications.