Interactions of iron-oxide filled carbon nanotubes with gas molecules.

This work presents a study on iron-oxide filled carbon nanotubes (CNTs) and their interaction with the surrounding atmosphere. Theoretical and experimental methods were employed to determine the interaction mechanism between the CNTs and some gases, such as O2 and N2. The electrical behavior of these CNTs under different atmospheric conditions was studied through resistance measurements, and for comparison, similar studies were conducted on non-filled carbon nanotubes. The iron-oxide filled CNTs were found to be more sensitive to the presence of O2 than the non-filled carbon nanotubes. This behavior was confirmed by the first-principles simulations based on density functional theory with local spin density approximations for CNTs filled with hematite and magnetite iron-oxides. The theoretical study on the interactions of iron-oxide filled CNTs with gas molecules demonstrated a physisorption regime between the nanotube and the surrounding atmosphere, resulting in modifications of the electronic properties of this material.

Metal-doped carbon nanotubes interacting with vitamin C.

In this paper, the structural, electronic and magnetic properties of carbon nanotubes doped with Al, Fe, Mn and Ti atoms interacting with vitamin C molecules are studied through first principles simulations based on the density functional theory. The charge transfers are obtained from the vitamins into the tubes for adsorption and substitutional doping cases. The highest binding energies of vitamin C molecules are calculated for the Al substitutional and Ti adsorbed cases, with values of about 1.20 and 3.26 eV, respectively. The results demonstrated that, depending on doping, the spin polarizations and the conductance characters of the systems can change, which could be relevant to improve the molecule adsorption on carbon nanostructures.

Adsorption of Reactive Blue 4 dye from water solutions by carbon nanotubes: experiment and theory.

Multi-walled and single-walled carbon nanotubes were used as nanoadsorbents for the successful removal of Reactive Blue 4 textile dye from aqueous solutions. The adsorbents were characterised by infrared and Raman spectroscopy, N(2) adsorption/desorption isotherms and scanning and transmission electron microscopy. The effects of pH, shaking time and temperature on adsorption capacity were studied. In the acidic pH region (pH 2.0), the adsorption of the dye was favourable using both adsorbents. The contact time to obtain equilibrium isotherms at 298-323 K was fixed at 4 hours for both adsorbents. The general order kinetic model provided the best fit to the experimental data compared with pseudo-first order and pseudo-second order kinetic adsorption models. For Reactive Blue 4 dye, the equilibrium data (298 to 323 K) were best fitted to the Liu isotherm model. The maximum sorption capacity for adsorption of the dye occurred at 323 K, attaining values of 502.5 and 567.7 mg g(-1) for MWCNT and SWCNT, respectively. Simulated dyehouse effluents were used to check the applicability of the proposed nanoadsorbents for effluent treatment (removal of 99.89% and 99.98%, for MWCNT and SWCNT, respectively). The interaction of Reactive Blue 4 textile dye with single-walled carbon nanotubes (SWCNTs) was investigated using first principles calculations based on density functional theory. Results from ab initio calculations indicated that Reactive Blue 4 textile dye could be adsorbed on SWCNT through an electrostatic interaction; these results are in agreement with the experimental predictions.

Ab initio simulations of black and blue phosphorene functionalised with chemical groups for biomolecule anchoring.

Black and blue phosphorene (2D-dimensional allotropes of phosphorus) have shown fascinating electronic, optical, and magnetic properties, with promising technological applications. In this work, we studied the adsorption of amine, hydroxyl, amide, and carboxyl groups onto both black and blue phosphorenes, in order to analyse the effects of biomolecule anchoring on the structural and electronic properties of phosphenes, using density functional simulations. Analyses were carried out of six different configurations for each chemical group functionalised on black and blue phosphorene. We observed that the radicals interacted via a chemisorption regime with the nanostructures, with binding energies that varied from 1.42 to 3.78 eV. The electronic properties showed that the presence of the chemical groups altered the energy gaps for both black and blue phosphorenes, due to a presence of a half-filled level when a single radical was adsorbed. We were able to observe that functionalised two-dimensional phosphorene showed promising characteristics in terms of anchoring molecules, and particularly those of biological interest, due to its high surface area, strong coupling between phosphorene and chemical groups, and the possibility of chemically manipulating radicals.

Functionalization of single-wall carbon nanotubes through chloroform adsorption: theory and experiment.

The interaction of chloroform (CHCl(3)) with single-wall carbon nanotubes (SWCNT) is investigated using both first principles calculations based on Density Functional Theory and vibrational spectroscopy experiments. CHCl(3) adsorption on pristine, defective, and carboxylated SWCNTs is simulated, thereby gaining a good understanding of the adsorption process of this molecule on SWCNT surfaces. The results predict a physisorption regime in all cases. These calculations point out that SWCNTs are promising materials for extracting trihalomethanes from the environment. Theoretical predictions on the stability of the systems SWCNT-CCl(2) and SWCNT-COCCl(3) are confirmed by experimental TGA data and Fourier Transform Infrared Spectroscopy (FT-IR) experiments. Results from resonance Raman scattering experiments indicate that electrons are transferred from the SWCNTs to the attached groups and these results are in agreement with the predictions made by ab initio calculations.

Density functional theory study of π-aromatic interaction of benzene, phenol, catechol, dopamine isolated dimers and adsorbed on graphene surface.

We analyze the influence of different groups on the intermolecular energy of aromatic homodimers and on the interaction between a single aromatic molecule and a graphene surface. The analysis is performed for benzene, phenol, catechol, and dopamine. For calculating the energies, we employ density functional theory within the local density approximation (LDA-DFT). Our results show that the lowest intermolecular energies between the aromatic molecules are related to the T-shaped configurations. This lower energy results from the quadrupole interaction. In the case of the interaction between the graphene sheet and the aromatic molecules, the lowest energy configuration is the face to face. The adsorption energy of a molecule on a graphene surface involves π - π interactions that explain the face to face arrangement. These results provide insight into the manner by which substituents can be utilized in crystal engineering, supramolecular chemistry, bioinspired materials, formation of various molecular clusters, parameterization of force fields suitable for classical simulations, and design of novel sensing, drug delivery, and filters based on graphene.

A simulation environment for polymeric nanoparticles based on multi-agent systems.

Production and characterization of polymeric nanoparticles, as colloidal dispersions, are processes that require time and technical skills to make the results accurate. Computational simulations in nanoscience have been used to help in these processes and provide agility and support to reach results: stability and quality in dispersions. Multi-Agent System for Polymeric Nanoparticles (MASPN) is an innovative and original simulation environment with features to demonstrate interactions of particles from physical-chemical parameters, ensuring Brownian motion of particles and attractive and repulsive behaviour. The MASPN environment has been designed and has been built according to the feature-driven development (FDD), as software methodology, and a multi-agent systems approach. In addition, we have used the event-driven simulation package algs4, the JASON agent building environment, all integrated by Java language. This paper aims to present the relation of the algs4 package and the JASON tool, both integrated into the MASPN environment to generate Brownian motion with elastic and inelastic collisions. The MASPN environment as a simulation tool emerges as a result, including the following features: graphical interface; integrated physical-chemical parameters; Brownian motion; JASON and algs4 integration; and distribution charts (size, zeta potential, and pH).

Natural lipid nanoparticles containing nimesulide: synthesis, characterization and in vivo antiedematogenic and antinociceptive activities.

Lipid nanoparticles are drug delivery systems able to increase bioavailability of poorly soluble drugs. They can be prepared with different lipid materials, especially natural lipids. Shea butter is a natural lipid obtained from the Butyrospermum parkii seed and rich in oleic and stearic acids. Nimesulide is a COX 2 selective anti-inflammatory that is poorly soluble in water. The purpose of this study was to develop and characterize shea butter lipid nanoparticles using a new technique and evaluate the in vivo activity of these nanoparticles. Lipid nanoparticles were prepared by melting shea butter and mixing with an aqueous phase using a high shear mixer. The nanoparticles presented pH of 6.9 +/- 0.1, mean particle size of 90 nm and a narrow polydispersity (0.21). Zeta potential was around -20 mV and the encapsulation efficiency was 97.5%. Drug release was evaluated using dialysis bags and presented monoexponential profile with t50% of 4.80 h (free drug t50% was only 2.86 h). Antinociceptive activity was performed by the acetic acid model. Both nimesulide and nimesulide-loaded nanoparticles presented significant activity compared to the control. The in vivo anti-inflammatory activity was evaluated by paw edema and was statistically different for the nanoparticles containing nimesulide compared to free nimesulide, blank nanoparticles and saline. In conclusion, the use of shea butter as encapsulating lipid was very successful and allowed nanoparticles to be prepared with a very simple technique. The nanoparticles presented significant pharmacological effects that were not seen for free drug administration.

Adsorption of Reactive Red M-2BE dye from water solutions by multi-walled carbon nanotubes and activated carbon.

Multi-walled carbon nanotubes and powdered activated carbon were used as adsorbents for the successful removal of Reactive Red M-2BE textile dye from aqueous solutions. The adsorbents were characterised by infrared spectroscopy, N(2) adsorption/desorption isotherms and scanning electron microscopy. The effects of pH, shaking time and temperature on adsorption capacity were studied. In the acidic pH region (pH 2.0), the adsorption of the dye was favourable using both adsorbents. The contact time to obtain equilibrium at 298K was fixed at 1h for both adsorbents. The activation energy of the adsorption process was evaluated from 298 to 323K for both adsorbents. The Avrami fractional-order kinetic model provided the best fit to the experimental data compared with pseudo-first-order or pseudo-second-order kinetic adsorption models. For Reactive Red M-2BE dye, the equilibrium data were best fitted to the Liu isotherm model. Simulated dyehouse effluents were used to check the applicability of the proposed adsorbents for effluent treatment.

Nicotine adsorption on single wall carbon nanotubes.

This work reports a theoretical study of nicotine molecules interacting with single wall carbon nanotubes (SWCNTs) through ab initio calculations within the framework of density functional theory (DFT). Different adsorption sites for nicotine on the surface of pristine and defective (8,0) SWCNTs were analyzed and the total energy curves, as a function of molecular position relative to the SWCNT surface, were evaluated. The nicotine adsorption process is found to be energetically favorable and the molecule-nanotube interaction is intermediated by the tri-coordinated nitrogen atom from the nicotine. It is also predicted the possibility of a chemical bonding between nicotine and SWCNT through the di-coordinated nitrogen.

Titanium monomers and wires adsorbed on carbon nanotubes: a first principles study.

In this work a theoretical study of Ti monomers and wires interacting with an (8, 0) semiconductor single-wall carbon nanotube (SWNT), by inside as well as outside faces, is presented. Spin-polarized total-energy ab initio calculations, based on the density functional theory, are used to describe the structural, electronic and magnetic properties of the studied systems. The most stable configurations for monomers are found to be over the centre of a C-C bond for inside and over the midpoint of the centre of the hexagonal site for outside. Considering that the Ti atoms on the tube surface tend to form continuous wires, to allow a comprehensive view of the interaction of the Ti wires with the SWNT surface, we present a complete understanding, both from inside and outside the nanotube. Our calculations have shown that the most stable configuration is with the wire inside the tube, with the resulting electronic structures showing a metallic system with high hybridization between the Ti and C atoms and a large charge transfer from Ti to C atoms. For Ti wire adsorbed inside the tube the low spin configuration is shown to be more stable than high spin configuration and the opposite behaviour is observed for the corresponding outside case. These novel results are relevant for the understanding of Ti atoms covering and filling SWNTs, demonstrating the high stability of these systems and suggesting that they can be useful for future use in nanodevices, in particular for spintronics and nanosensors.

Silicon adsorption in defective carbon nanotubes: a first principles study.

The electronic and structural properties of an (8, 0) single-walled carbon nanotube (SWNT) with a single vacancy and interacting with a Si atom are studied using first principles calculations based on the density-functional theory. Initially, the Si atom is positioned in the site above the vacancy, with its position fixed until the nanotube geometry is fully relaxed. After that, the Si atom approaches the tube and it is shown that one C atom is displaced outwards forming a bump. The final configuration, as well as each step of the process, is studied in detail and the resulting band structures and the total charge densities are systematically analysed.