Carbon-Based Nanomaterials.

Research on carbon-based nanomaterials, such as carbon nanotubes, graphene and its derivatives, nanodiamonds, fullerenes, and other nanosized carbon allotropes, has experienced sharp exponential growth over recent years [...].

Fluorescence Study of Riboflavin Interactions with Graphene Dispersed in Bioactive Tannic Acid.

The potential of tannic acid (TA) as a dispersing agent for graphene (G) in aqueous solutions and its interaction with riboflavin have been studied under different experimental conditions. TA induces quenching of riboflavin fluorescence, and the effect is stronger with increasing TA concentration, due to π-π interactions through the aromatic rings, and hydrogen bonding interactions between the hydroxyl moieties of both compounds. The influence of TA concentration, the pH, and the G/TA weight ratio on the quenching magnitude, have been studied. At a pH of 4.1, G dispersed in TA hardly influences the riboflavin fluorescence, while at a pH of 7.1, the nanomaterial interacts with riboflavin, causing an additional quenching to that produced by TA. When TA concentration is kept constant, quenching of G on riboflavin fluorescence depends on both the G/TA weight ratio and the TA concentration. The fluorescence attenuation is stronger for dispersions with the lowest G/TA ratios, since TA is the main contributor to the quenching effect. Data obey the Stern-Volmer relationship up to TA 2.0 g L-1 and G 20 mg L-1. Results demonstrate that TA is an effective dispersant for graphene-based nanomaterials in liquid medium and a green alternative to conventional surfactants and synthetic polymers for the determination of biomolecules.

Antibacterial Action of Nanoparticle Loaded Nanocomposites Based on Graphene and Its Derivatives: A Mini-Review.

Bacterial infections constitute a severe problem in various areas of everyday life, causing pain and death, and adding enormous costs to healthcare worldwide. Besides, they cause important concerns in other industries, such as cloth, food packaging, and biomedicine, among others. Despite the intensive efforts of academics and researchers, there is lack of a general solutions to restrict bacterial growth. Among the various approaches, the use of antibacterial nanomaterials is a very promising way to fight the microorganisms due to their high specific surface area and intrinsic or chemically incorporated antibacterial action. Graphene, a 2D carbon-based ultra-thin biocompatible nanomaterial with excellent mechanical, thermal, and electrical properties, and its derivatives, graphene oxide (GO) and reduced graphene oxide (rGO), are highly suitable candidates for restricting microbial infections. However, the mechanisms of antimicrobial action, their cytotoxicity, and other issues remain unclear. This mini-review provides select examples on the leading advances in the development of antimicrobial nanocomposites incorporating inorganic nanoparticles and graphene or its derivatives, with the aim of providing a better understanding of the antibacterial properties of graphene-based nanomaterials.

Synthesis and Applications of Biopolymer Composites.

In recent years, there has been a growing demand for a clean and pollution-free environment and an evident target to minimizing fossil fuel [...].

Materials for Photovoltaics: State of Art and Recent Developments.

In recent years, photovoltaic cell technology has grown extraordinarily as a sustainable source of energy, as a consequence of the increasing concern over the impact of fossil fuel-based energy on global warming and climate change. The different photovoltaic cells developed up to date can be classified into four main categories called generations (GEN), and the current market is mainly covered by the first two GEN. The 1GEN (mono or polycrystalline silicon cells and gallium arsenide) comprises well-known medium/low cost technologies that lead to moderate yields. The 2GEN (thin-film technologies) includes devices that have lower efficiency albeit are cheaper to manufacture. The 3GEN presents the use of novel materials, as well as a great variability of designs, and comprises expensive but very efficient cells. The 4GEN, also known as "inorganics-in-organics", combines the low cost/flexibility of polymer thin films with the stability of novel inorganic nanostructures (i.e., metal nanoparticles and metal oxides) with organic-based nanomaterials (i.e., carbon nanotubes, graphene and its derivatives), and are currently under investigation. The main goal of this review is to show the current state of art on photovoltaic cell technology in terms of the materials used for the manufacture, efficiency and production costs. A comprehensive comparative analysis of the four generations is performed, including the device architectures, their advantages and limitations. Special emphasis is placed on the 4GEN, where the diverse roles of the organic and nano-components are discussed. Finally, conclusions and future perspectives are summarized.

Quenching of fluorene fluorescence by single-walled carbon nanotube dispersions with surfactants: application for fluorene quantification in wastewater.

The fluorescence of fluorene in aqueous solutions of surfactants of different natures, anionic sodium dodecylsulphate (SDS), cationic cetyltrimethyl ammonium chloride (CTAC) and non-ionic polyoxyethylene-23-lauryl ether (Brij 35), as well as in single-walled carbon nanotube (SWCNT) dispersions in these surfactants, has been studied and compared. A fluorescence quenching phenomenon has been observed in the presence of SWCNT, the effect being stronger for dispersions in CTAC, related to the improved dispersion capability of this surfactant as revealed by microscopic observations and its stronger adsorption onto the SWCNT surfaces as inferred from the Raman spectra. SWCNT interact with fluorene causing a fluorescence quenching. The fluorescence intensity ratio, calculated in the absence and in the presence of SWCNT, follows the Stern-Volmer equation. For the CTAC concentration that provides the highest quenching effect, the analytical characteristics of the fluorimetric method like sensitivity, detection and quantification limits, repeatability, reproducibility and robustness have been calculated. Results demonstrate that it is possible to determine fluorene in a fortified wastewater sample in aqueous solutions of CTAC and SWCNT/CTAC dispersions, showing recoveries close to 100 %. The quenching effect found in this work could be useful for the development of an optical device that uses SWCNT-based receptors for fluorene detection and quantification in aqueous surfactant solutions. Graphical abstract Distribution of fluorene between single-walled carbon nanotubes and micelles.

Functional Nanomaterials in Biomedicine: Current Uses and Potential Applications.

Nanomaterials, that is, materials made up of individual units between 1 and 100 nanometers, have lately involved a lot of attention since they offer a lot of potential in many fields, including pharmacy and biomedicine, owed to their exceptional physicochemical properties arising from their high surface area and nanoscale size. Smart engineering of nanostructures through appropriate surface or bulk functionalization endows them with multifunctional capabilities, opening up new possibilities in the biomedical field such as biosensing, drug delivery, imaging, medical implants, cancer treatment and tissue engineering. This article highlights up-to-date research in nanomaterials functionalization for biomedical applications. A summary of the different types of nanomaterials and the surface functionalization strategies is provided. Besides, the use of nanomaterials in diagnostic imaging, drug/gene delivery, regenerative medicine, cancer treatment and medical implants is reviewed. Finally, conclusions and future perspectives are provided.

Fluorescence study of the influence of centrifugation on graphene oxide dispersions in water and in tannic acid.

Graphene oxide (GO) is acquiring a great interest in biomedicine, biotechnology and biochemistry due to its unique properties. However, GO layers are boundbyvan der Waals forces, which results in aggregation. An efficient dispersion of the aggregated nanostructures is crucial from an application viewpoint, hence eco-friendly procedures are pursued. In this work, the potential of tannic acid (TA) as a GO dispersant in water has been investigated for the first time. Transmission electronic microscopy (TEM) was used to visualize the degree of GO exfoliation in the dispersions. To further assess TA dispersant capability, a fluorescent biomolecule, riboflavin, has been selected. GO and TA cause a quenching effect on riboflavin fluorescence, which depends on the GO and TA concentration, the GO/TA weight ratio and the final centrifugation step that was found to be crucial. Multiple regression analysis has been used to determine the quenching constants for TA and GO simultaneously. The GO-riboflavin interaction weakens upon centrifugation. This step, traditionally used to remove the nanomaterial aggregates, should be avoided to obtain a high GO concentration in the dispersions. This study paves the way towards the use of environmentally friendly dispersant agents instead of conventional organic solvents or synthetic surfactants to attain high-quality dispersions of carbon nanomaterials in water.

Carbon-Based Polymer Nanocomposites for High-Performance Applications.

Carbon-based nanomaterials such as carbon nanotubes, graphene and its derivatives, nanodiamond, fullerenes, and other nanosized carbon allotropes have recently attracted a lot of attention among the scientific community due to their enormous potential for a wide number of applications arising from their large specific surface area, high electrical and thermal conductivity, and good mechanical properties [...].

Recent Progress in Antimicrobial Nanomaterials.

Bacterial infections are a well-known and serious problem in numerous areas of everyday life, causing death, pain, and huge added costs to healthcare worldwide [...].

Antimicrobial Polymer-Based Materials for Food Packaging Applications.

Antimicrobial packaging has recently attracted a great deal of interest from the food industry due to the boost in consumer demand for minimally-processed, preservative-free products.[...].

Tailorable Synthesis of Highly Oxidized Graphene Oxides via an Environmentally-Friendly Electrochemical Process.

Graphene oxide (GO) is an attractive alternative to graphene for many applications due to its captivating optical, chemical, and electrical characteristics. In this work, GO powders with a different amount of surface groups were synthesized from graphite via an electrochemical two-stage process. Many synthesis conditions were tried to maximize the oxidation level, and comprehensive characterization of the resulting samples was carried out via elemental analysis, microscopies (TEM, SEM, AFM), X-ray diffraction, FT-IR and Raman spectroscopies as well as electrical resistance measurements. SEM and TEM images corroborate that the electrochemical process used herein preserves the integrity of the graphene flakes, enabling to obtain large, uniform and well exfoliated GO sheets. The GOs display a wide range of C/O ratios, determined by the voltage and time of each stage as well as the electrolyte concentration, and an unprecedented minimum C/O value was obtained for the optimal conditions. FT-IR evidences strong intermolecular interactions between neighbouring oxygenated groups. The intensity ratio of D/G bands in the Raman spectra is high for samples prepared using concentrated H2SO4 as an electrolyte, indicative of many defects. Furthermore, these GOs exhibit smaller interlayer spacing than that expected according to their oxygen content, which suggests predominant oxidation on the flake edges. Results point out that the electrical resistance is conditioned mostly by the interlayer distance and not simply by the C/O ratio. The tuning of the oxidation level is useful for the design of GOs with tailorable structural, electrical, optical, mechanical, and thermal properties.

Impact of recovery correction or subjecting calibrators to sample preparation on measurement uncertainty: PAH determinations in waters.

The decision on the fitness of a measurement for its intended use and the interpretation of an analytical result requires the assessment of the measurement uncertainty. Frequently, the determination of analytes in complex matrices involves demanding sample preparations in which analyte losses are observed. These losses should be considered when reporting the results, which can be corrected for low recovery by taking the mean recovery observed in the analysis of reference items (e.g. spiked samples) or, alternatively, by subjecting calibrators to the same pre-treatment performed on the samples. In these cases, neat (NC) or adjusted (AC) calibrators are used, respectively. The way analyte losses are handled impacts on the measurement uncertainty. The top-down evaluation of the measurement uncertainty involves combining precision, trueness and additional uncertainty components. The trueness component is quantified by pooling various analyte recovery determinations. This work assesses and compares the uncertainty of polycyclic aromatic hydrocarbons (PAHs) measurements in water based on HPLC-FD calibrations with NC or AC. The trueness component is estimated by pooling mean recoveries observed from the analysis of different spiked samples to which mean recovery uncertainty and degrees of freedom are used to estimate a weighted mean recovery and respective uncertainty. The performance of measurements based on NC and AC are associated with equivalent uncertainty except when large analyte losses are observed, namely in the determination of Naphtalene. In this case, the processing of AC reduces the expanded relative uncertainty from 9.9% to 3.5%. The evaluated expanded uncertainty ranged from 3.5% to 12% of the measured value.

Antibacterial Nanocomposites Based on Thermosetting Polymers Derived from Vegetable Oils and Metal Oxide Nanoparticles.

Thermosetting polymers derived from vegetable oils (VOs) exhibit a wide range of outstanding properties that make them suitable for coatings, paints, adhesives, food packaging, and other industrial appliances. In addition, some of them show remarkable antimicrobial activity. Nonetheless, the antibacterial properties of these materials can be significantly improved via incorporation of very small amounts of metal oxide nanoparticles (MO-NPs) such as TiO2, ZnO, CuO, or Fe3O4. The antimicrobial efficiency of these NPs correlates with their structural properties like size, shape, and mainly on their concentration and degree of functionalization. Owing to their nanoscale dimensions, high specific surface area and tailorable surface chemistry, MO-NPs can discriminate bacterial cells from mammalian ones, offering long-term antibacterial action. MO-NPs provoke bacterial toxicity through generation of reactive oxygen species (ROS) that can target physical structures, metabolic paths, as well as DNA synthesis, thereby leading to cell decease. Furthermore, other modes of action-including lipid peroxidation, cell membrane lysis, redox reactions at the NP-cell interface, bacterial phagocytosis, etc.-have been reported. In this work, a brief description of current literature on the antimicrobial effect of VO-based thermosetting polymers incorporating MO-NPs is provided. Specifically, the preparation of the nanocomposites, their morphology, and antibacterial properties are comparatively discussed. A critical analysis of the current state-of-art on these nanomaterials improves our understanding to overcome antibiotic resistance and offers alternatives to struggle bacterial infections in public places.

Nanoparticle Reinforced Polymers.

The beginning of nanomaterials and nanoscience dates back to 1959 when the Nobel laureate in Physics Richard Feynman gave the famous lecture entitled "There's Plenty of Room at the Bottom [...].

Selected Papers from the 1st International Online Conference on Nanomaterials.

After decades of intense research, nanomaterials are now an integral part of many applications and enjoy the attention of a large research community [...].

Grafting of Polypyrrole-3-carboxylic Acid to the Surface of Hexamethylene Diisocyanate-Functionalized Graphene Oxide.

A polypyrrole-carboxylic acid derivative (PPy-COOH) was covalently anchored on the surface of hexamethylene diisocyanate (HDI)-modified graphene oxide (GO) following two different esterification approaches: activation of the carboxylic acids of the polymer by carbodiimide, and conversion of the carboxylic groups to acyl chloride. Microscopic observations revealed a decrease in HDI-GO layer thickness for the sample prepared via the first strategy, and the heterogeneous nature of the grafted samples. Infrared and Raman spectroscopies corroborated the grafting success, demonstrating the emergence of a peak associated with the ester group. The yield of the grafting reactions (31% and 42%) was roughly calculated from thermogravimetric analysis, and it was higher for the sample synthesized via formation of the acyl chloride-functionalized PPy. The grafted samples showed higher thermal stability (~30 and 40 °C in the second decomposition stage) and sheet resistance than PPy-COOH. They also exhibited superior stiffness and strength both at 25 and 100 °C, and the reinforcing efficiency was approximately maintained at high temperatures. Improved mechanical performance was attained for the sample with higher grafting yield. The developed method is a valuable approach to covalently attach conductive polymers onto graphenic nanomaterials for application in flexible electronics, fuel cells, solar cells, and supercapacitors.

The Effect of Hexamethylene Diisocyanate-Modified Graphene Oxide as a Nanofiller Material on the Properties of Conductive Polyaniline.

Conducting polymers like polyaniline (PANI) have gained a lot of interest due to their outstanding electrical and optoelectronic properties combined with their low cost and easy synthesis. To further exploit the performance of PANI, carbon-based nanomaterials like graphene, graphene oxide (GO) and their derivatives can be incorporated in a PANI matrix. In this study, hexamethylene diisocyanate-modified GO (HDI-GO) nanosheets with two different functionalization degrees have been used as nanofillers to develop high-performance PANI/HDI-GO nanocomposites via in situ polymerization of aniline in the presence of HDI-GO followed by ultrasonication and solution casting. The influence of the HDI-GO concentration and functionalization degree on the nanocomposite properties has been examined by scanning electron microscopy (SEM), Raman spectroscopy, X-ray diffraction (XRD), thermogravimetric analysis (TGA), tensile tests, zeta potential and four-point probe measurements. SEM analysis demonstrated a homogenous dispersion of the HDI-GO nanosheets that were coated by the matrix particles during the in situ polymerization. Raman spectra revealed the existence of very strong PANI-HDI-GO interactions via π-π stacking, H-bonding, and hydrophobic and electrostatic charge-transfer complexes. A steady enhancement in thermal stability and electrical conductivity was found with increasing nanofiller concentration, the improvements being higher with increasing HDI-GO functionalization level. The nanocomposites showed a very good combination of rigidity, strength, ductility and toughness, and the best equilibrium of properties was attained at 5 wt % HDI-GO. The method developed herein opens up a versatile route to prepare multifunctional graphene-based nanocomposites with conductive polymers for a broad range of applications including flexible electronics and organic solar cells.

Graphene/sepiolite mixtures as dispersive solid-phase extraction sorbents for the anaysis of polycyclic aromatic hydrocarbons in wastewater using surfactant aqueous solutions for desorption.

Different graphene/sepiolite (G/Sep) solid mixtures have been prepared and tested as nanometric sorbents for the analysis of polycyclic aromatic hydrocarbons (PAHs) using dispersive solid phase extraction (dSPE) and aqueous solutions of surfactants as environmentally friendly agents for desorption. Quantification of the PAHs was carried out by reversed-phase liquid chromatography (RP-HPLC) with fluorescence detection. The adsorption of four PAHs with increasing number of benzene rings into a G/Sep mixture (2/98, w/w) was investigated. A 100% retention was attained for phenanthrene (Phe), pyrene (Pyr) and benzo(a)pyrene (BaP), while for naphthalene (Nap) the maximum retention was close to 75%. The G/Sep mixtures can be used to remove the PAHs from wastewater. The desorption step was carried out using an aqueous surfactant solution: 100 mM non-ionic polyoxiethylen-23-lauryl eter (Brij L23). Considering the whole extraction process, the highest PAH recoveries (50, 92, 83 and 76% for Nap, Phe, Pyr and BaP, respectively) were obtained using 100 mM Brij L23. The developed method shows very high sensitivity, robustness and precision, as well as low limits of detection and quantification, and has been successfully applied to the analysis of PAHs in wastewater samples.

High-Performance PEDOT:PSS/Hexamethylene Diisocyanate-Functionalized Graphene Oxide Nanocomposites: Preparation and Properties.

Graphene oxide (GO) has emerged as an ideal filler to reinforce polymeric matrices owing to its large specific surface area, transparency, flexibility, and very high mechanical strength. Nonetheless, functionalization is required to improve its solubility in common solvents and expand its practical uses. In this work, hexamethylene diisocyanate (HDI)-functionalized GO (HDI-GO) has been used as filler of a conductive polymer matrix, poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS). The nanocomposites have been prepared via a simple solution casting method, and have been characterized by scanning electron microscopy (SEM), UV⁻Vis and Raman spectroscopies, X-ray diffraction (XRD), thermogravimetric analysis (TGA), tensile tests, and four-point probe measurements to get information about how the HDI-GO functionalization degree (FD) and the HDI-GO concentration in the nanocomposite influence the final properties. SEM analysis showed a very homogenous dispersion of the HDI-GO nanosheets with the highest FD within the matrix, and the Raman spectra revealed the existence of very strong HDI-GO-PEDOT:PSS interactions. A gradual improvement in thermal stability was found with increasing HDI-GO concentration, with only a small loss in transparency. A reduction in the sheet resistance of PEDOT:PSS was found at low HDI-GO contents, whilst increasing moderately at the highest loading tested. The nanocomposites showed a good combination of stiffness, strength, ductility, and toughness. The optimum balance of properties was attained for samples incorporating 2 and 5 wt % HDI-GO with the highest FD. These solution-processed nanocomposites show considerably improved performance compared to conventional PEDOT:PSS nanocomposites filled with raw GO, and are highly suitable for applications in various fields, including flexible electronics, thermoelectric devices, and solar energy applications.