Functionalization of CNTS with maleic anhydride

The outstanding properties of carbon nanotubes (CNTs) [1] are mainly related with their unique structural features. However, the high π-π staking between the tubes is a major drawback for their manipulation and interaction with other materials. Chemical functionalization has been used as a convenient tool to improve their performance in various applications [2]. The work reports the functionalization of multi-wall carbon nanotubes (MWCNTs) with maleic anhydride via a Diels-Alder addition reaction, performed in dimethyl sulfoxide (190 ºC) or 2-chorotoluene (150 ºC) for 24 hours. The product was characterized by thermogravimetric analysis (TGA) and the weight loss at 800 ºC was 11.9 and 3.7 % respectively. Potentiometric titration suggests that CNTs modified at 190 ºC remain predominantly in the anhydride form, while for CNTs modified at 150 ºC, the extent of hydrolysis is approximately 40 %. Maleic anhydride was also reacted with a model compound (anthracene) in dimethyl sulfoxide (190 ºC) and the hydrolysis of the product (0.025 mmol in 650 µL of DMSO-d6) was followed by 1H RMN upon addition of 0.166 mmol of DCl (40 % weight in D2O) (graphic in figure). The anhydride 1 was easily regenerated from the dicarboxylic acid 2 when this compound was heated at 185 ºC for 10 minutes. A similar behavior is expected for the modified CNTs.Fundação para a Ciência e Tecnologi

Few-layer graphene aqueous suspensions for polyurethane composite coatings

Graphite nanoplates (GnP) have recently attracted attention as an economically viable alternative for the development of functional and structural nanocomposites. The incorporation of GnP into waterborne polyurethane (WPU) with loadings from 0.1 to 10 wt.% was studied. The mechanical properties of the composite films were assessed by tensile testing showing an increase of the Young’s modulus up to 48%. The electrical conductivity increased by 9 orders of magnitude and the water vapor permeability of the composite films decreased 57% for composites containing 5.0 wt.% of GnP.The authors acknowledge FCT, project PEst-C/CTM/LA0025/2015 and PhD grant SFRH/BD/87214/2012.info:eu-repo/semantics/publishedVersio

Electrochemical sensing using carboxylated multiwalled carbon nanotubes

Carbon nanotubes (CNTs) have demonstrated great advantages in electrochemistry. The application of CNTs most widely employed so far has been the construction of various detection devices, such as gas sensors, electrochemical detectors and biosensors [1]. The main advantage of their use is related to the increase of the electrodes surface area and of the electron transfer rates, improving sensors sensitivity. Besides, their sorption capability of different analytes can be used to improve sensors selectivity [2]. (...

Advanced electrically conductive adhesives for high complexity PCB assembly

Electronic packaging, or assembly of packed electronic components on printed circuit boards, present challenges that require innovative solder pastes and electrically conductive adhesives to face the increasing complexity of PCB assembly, with denser board occupation and demanding thermal management during assembly. Our aim is to prepare carbon particle based conductive adhesives. The first step to achieve this goal was to prepare composites with epoxy resin and a variety of nano to micron scale carbon particle, produced by mixing on a three roll mill. The percolation threshold for each particle type was determined as well as the conductivity level reached after percolation.This research is sponsored by the Portugal Incentive System for Research and Technological Development. Project in co-promotion nº 002814/2015 (iFACTORY 2015-2018)

Comportamento voltamétrico de perilenos bismides modificados em GCE e SPE

Uma das necessidades mais emergentes no planeta é a deteção e quantificação de diversos analitos prejudiciais aos seres vivos, presentes no meio ambiente, de uma forma rápida, com baixo custo e com elevada seletividade. Os screen printed electrodes (SPE) têm sido usados extensivamente como transdutores de sensores químicos para vários analitos importantes. A modificação da superfície dos SPEs com moléculas capazes de fazer o reconhecimento de diversos analitos traduz-se no aumento da seletividade do elétrodo, devido às interações entre as duas espécies [1]. Entre as técnicas de imobilização (covalente e não covalente) de moléculas na superfície dos SPE, destacamos a modificação não covalente, visto este ser um método rápido, com elevada reprodutibilidade, de baixo custo, e sem a necessidade de reações violentas para a superfície do sensor para formar a ligação covalente. A utilização de moléculas com estruturas capazes de formar ligações π com nanoestruturas de carbono [2] é uma vantagem, pois permite a adsorção de espécies que irão fazer o reconhecimento de analitos sem danificar a superfície da matriz principal mantendo assim as excelentes características das nanoestruras de carbono, como os nanotubos de carbono e as folhas de grafeno. (...

Screen printed electrodes modified with carboxylated multiwall carbon nanotubes for the analysis of hydroquinone and ascorbic acid

Carbon nanotubes (CNT) have demonstrated to be advantageous in electrochemical applications such as in energy storage devices and sensors. The presence of oxygenated carbon species, especially carboxylic acid moieties, together with metallic impurities are identified as chief factors for the catalytic properties of CNTs. The oxygen-containing groups are introduced randomly at the surface of CNTs by strong mineral acid treatment. These factors can be of extreme importance for the construction of biosensors based on carbon nanomaterials. In this study, multiwalled carbon nanotubes (MWCNTs) were chemically shortened and carboxylated by treatment with nitric acid for metal impurities removalusing a method described in the literature, originating MWCNT-COOH. Ethanol suspensions of MWCNT-COOH at different concentrations were used to modify the surfaces of commercially available screen-printed electrodes (SPEs). The SPEs modification with MWCNT-COOH was optimised and it was applied in order to obtain a reproducible electrochemical response. The morphology of the MWCNT-COOH modified SPEs was characterized by Scanning Electron Microscopy. Characterization of the CNT film generated on the surface of the working electrode and stability studies were carried out with potassium hexacyanoferrate. Results are compared with those obtained for commercially available carbon SPE and SPEMWCNT. Effect of solution acidity on the peak current and potential of the substances was studied at pH 3 and 7 where a correlation with the dissociation degree of carboxyl groups at the MWCNTs on the electrode surface occurs. The catalytic properties of the MWCNT-COOH-modified SPEs as well as their analytical advantages as voltammetric detectors are discussed through the analysis of ascorbic acid (AA) and hydroquinone (HQ)

The diels-alder cycloaddition reaction of 1,3-butadiene to MWCNTs

In this study the funtionalization of MWCNTs with 1,3-butadiene generated in situ from solfolene was investigated. The reaction was studded at two different temperatures (100ºC and 150ºC), mass ratios (CNTs:Sulfolene of 1:1 and 1:2) and different time reaction (2, 4 and 7 days). Thermogravimetric analysis (TGA) showed high degree of functionalization in a range of 10 % to 23 % in weight loss at 800 ºC. The acid properties of funtionalized materials were recorded by potentiometric titration that suggests some oxidation during the funtionalization process (Figure 1). In Figure 2 are summarized the results of weight loss obtained by TGA and respective acid properties of functionalized carbon nanotubes. The funtionalization was also evaluated by X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM).Fundação para a Ciência e a Tecnologia (FCT

Influence of the feedstock material on the compost maturity, stability and reactivity

Compost samples from different origins have been characterized in order to obtain information about their composition, humic-like substances content, maturity and stability. The composts used in the present study were obtained from manure (CAP), algae (CA), domestic waste (VCRU), sewage sludge (CT) and animal waste (CE). Different techniques have been used to gather physical-chemical parameters of the raw composts, their equilibrium solutions and the extracted humic-like substances. The analysis of the parameters collected in the characterization process allowed to stablish the degree of maturity and stability of the composts. Results indicate that the compost originated from algae exhibits the highest degree of maturity. Also, metal complexation was analyzed in the CE compost with the aim of assessing the contribution of the different fractions of dissolved organic matter.0366_RES2VALHUM_1_P - Valorização de resíduos orgânicos: produção de substâncias húmicas, cofinanciada pelo Fundo Europeu de Desenvolvimento regional (FEDER) através do Programa INTERREG V-A Espanha-Portugal (POCTEP) 2014-2020

Formation of graphene nanoribbons in solution

Recently, the formation of graphene by exfoliation of carbon nanotubes (CNT) has shown increasing interest. This process originates graphene nanoribbons (GNR) that are expected to present excellent electrical properties, depending on their width and on their edge shape [1]. Several methods for the unzipping of graphene from CNT were proposed along the past few years [2-6]. These methods often present some limitation, such as low yield of GNR, or extensively oxidized GNR without electrical conductivity. Recently, the formation of GNR was observed “in situ” by unzipping of carbon nanotubes under ultra-high vacuum scanning tunneling microscopy (UHV STM) [7]. The CNT under observation were functionalized by the 1,3-dipolar cycloaddition reaction [8]. This particular functionalization route seems to be responsible for the unzipping of the CNT under STM imaging conditions. The present work demonstrates the formation of GNR in solution by unzipping of functionalized CNT, in different solvents. The GNR thus formed were analyzed by UV-vis and Raman spectroscopy, and by transmission electron spectroscopy. GNR bundles were deposited from an ethanol solution and observed by TEM.Institute for Nanostructures, Nanomodelling and Nanofabrication (I3N

Simple strategies for stable aqueous suspensions of carbon nanotubes

Carbon nanotubes (CNT) are attractive nanoparticles for biological applications due to their broad absorption of light in the UV-Vis-NIR, NIR photoluminescence, unique Raman signature, photothermal response, and large surface area for the covalent and non-covalent conjugation of contrast agents and drugs, DNA/RNA. However, pristine CNT are highly hydrophobic and not biocompatible, requiring functionalization with hydrophilic molecules in order to form stable aqueous suspensions. Here, simple functionalization methods of perylene bisimides and pyrene, to render these polyaromatic molecules amphiphilic, will be presented. Bolaamphiphilic perylene bisimides (PBI) were prepared by the reaction of perylenetetracarboxylic dianhydride with -amino acids in good yield, using a simple protocol and avoiding complex purification methods. [1] Pyrene was modified by nitration followed by amination, and further reacted with maleic anhydride yielding carboxylic acid-functionalized pyrene. The CNT aqueous suspensions were studied by absorption and emission spectroscopy. Theoretical calculations were used to support the experimental observations. The possibility of CNT double functionalization (covalent and non-covalent) will be discussed based on CNT solubility studies in surfactant aqueous solutions. Pristine and covalently functionalized CNT, at different functionalization yields, were compared. The CNT were functionalized by the 1,3-dipolar cycloaddition of azomethine ylides. [2] The ability of CNT to adsorb surfactant molecules was reduced by the covalent functionalization. Nevertheless, depending on the extent of covalent functionalization, a high concentration of CNT in water could be attained, in comparison to that of pristine CNT.Fundação para a Ciência e a Tecnologia (FCT