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In this work, we evaluate the effect of Ni-doping LiMn2O4 spinels, LiNixMn2–xO4 (0.01 ≤ x ≤ 0.10) on the performance of lithium-ion hybrid supercapacitors (Li-HSCs) based on a mixture of 1 M lithiu...

This study aims to increase the knowledge on the interactions that occur at the electrode/electrolyte interface in carbon-based electric double-layer capacitors (EDLCs) when solvent-free ionic liquids are used as electrolytes. Many previous studies found in the literature are conducted using theoretical approaches, and they are unable to model all the variables and the complexity of an actual device with a complex carbon surface and an ionic liquid (IL). Here, the compatibility between imidazolium ionic liquids and different carbon materials-an activated carbon (AC), a mesoporous carbon (MES), multiwalled carbon nanotubes (MWCNTs), and reduced graphene oxide (RGO)-is empirically investigated applying synchronous chronopotentiometric tests to various symmetrical EDLCs. The study of the simultaneous evolution of the cell and electrode potentials of the various carbon/ILs cells, monitoring the evolution of specific capacitances and electrical resistances for each independent electrode, allows inferring about the ion-electrode compatibility, the limiting factors for charge accumulation, and its impacts on the performance of the global cell. The results indicate that the sp2 structures of MWCNTs and RGO favor interactions with the EMI+ cation on the negative electrode. In the positive electrodes, MES and AC favor interactions with the BF4- and TFSI- anions, respectively, yielding a higher specific capacitance and lower resistance., The authors thank the Conselho Nacional de Desenvolvimento Cienti ico e Tecnoló gico (CNPq)−Brazil for the financial support (PVE 2014, process number 400714/2014- 0), the Spanish Government and European Union (AEI/ FEDER, EU; project MAT2016-77114-R), N.Q.’s predoctoral contract (BES2017-082038), and Principado de Asturias (FEDER: IDI/2018/000121). The work was partially supported by the Brazilian Institute of Science and Technology (INCT) in Carbon Nanomaterials. P.F.R.O. acknowledges the Fundaca̧ o de Amparo a ̃ ̀Pesquisa do Estado de Minas Gerais (FAPEMIG)−Brazil (DOF no. 2720262/2018). P.F.R.O. and G. A.d.S. also acknowledge the scholarships received from CNPq. R.L.L. is a recipient of a fellowship from CNPq (grant number 313304/2017-3). P.F.R.O, G.G.S., and R.L.L. are members of the Rede Mineira de Quimica (RQ-MG) ́ −Brazil.

Naringin is a flavanone that has been studied due to its important properties, such as anti-inflammatory, anti-oxidant, anti-microbial, anti-viral, hypolipidemic, and anti-carcinogenic. Considering the extreme importance of the effects of this compound, the present work describes the development of a photoelectrochemical sensor for the determination of naringin at a zero-biased fluorine-doped tin oxide (FTO) electrode modified with cadmium sulfide (CdS) and titanium dioxide (TiO2) sensitized with chloroprotoporphyrin IX iron(III) (CPPI). The photoelectrochemical sensor was designated as CPPI-TiO2/CdS/FTO. A LED lamp of 20 W was used as irradiation source of the photoelectrochemical system. CdS film was electrodeposited on the electrode surface FTO and characterized by scanning electron microscopy. The composite CPPI-TiO2 was characterized by transmission electron microscopy. After optimization of experimental parameters, the sensor presented a detection limit of 0.03 μmol L−1 and a wide linear response range for the determination of the analyte, i.e., from 1 to 332 μmol L−1 at low potential (0 V vs. Ag/AgCl). The photoelectrochemical sensor was applied in citrus fruit juice samples presenting good accuracy and precision.

The use of nanofluids for industrial applications depends on its stability during transport and use. In this work, we demonstrate that graphene oxide (GO)-based aqueous nanofluids can remai...

There is no agreement regarding which solvent is more suitable to obtain sol–gel–derived titania (TiO2) samples with an enhanced photocatalytic behavior. Furthermore, the solvent effect on the preparation of TiO2-RGO (reduced graphene oxide) nanocomposites has not been published yet and could be an attractive experimental strategy to modulate structure and properties. On the basis of these observations, TiO2-RGO nanocomposites were fabricated in this study. It was evaluated for the influence of using either isopropyl (IsoprOH) or ethyl (EtOH) alcohol on the textural and photocatalytic properties of the prepared materials. The use of IsoprOH led to samples with smaller crystallite size, narrower apparent band gap, smaller isoelectric point, larger adsorption capacity, and higher photocatalytic activity. In addition, the incorporation of RGO into TiO2 greatly improved the adsorption capacity and photocatalytic activity of the latter. However, the optimal loading of RGO to prepare composites with enhanced photocatalytic activities was 1 wt%. This finding can be related to the stacking of RGO sheets when concentrations above 1 wt% are used, which could prevent UV light to reach the TiO2 particles and also decrease the photocatalytic capacity of the composites. Moreover, materials with RGO concentration above 1 wt% could exhibit a highly negatively charged surface, which may decrease the separation of the generated electron–hole pairs and lead to faster recombination rates of charge carriers.

CNPq - Conselho Nacional de Desenvolvimento Científico e Tecnológico FAPEMIG - Fundação de Amparo à Pesquisa do Estado de Minas Gerais CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível Superior INCT – Instituto nacional de ciência e tecnologia (Antigo Instituto do Milênio) This work deals with the preparation of reduced graphene oxide (RGO)-TiO2 composites by a one-step hydrothermal treatment. The effect of the RGO loading on both the structural properties and photocatalytic behavior of RGO-TiO2 is deeply addressed herein. The hydrothermal treatment promoted the reduction of graphene oxide, crystallization of TiO2 into anatase, and anchoring of TiO2 nanoparticles on RGO sheets. It was observed that the prepared anatase particles showed sizes below 10 nm, whereas the RGO sheets displayed thicknesses smaller than 1 nm. The use of RGO at concentrations up to 15 wt% greatly increased the specific surface area of RGO-TiO2. It was demonstrated that the combination of RGO and TiO2 gives rise to materials with improved photocatalytic properties and tailored structural properties. The composite with the highest photoactivity was the one containing an RGO loading of 1 wt%; this composite displayed a photocatalytic rate constant about 9.5 times higher than that evaluated for pure TiO2. This behavior may be related to the stacking of RGO nanosheets when its concentration is above 1 wt%. Moreover, the addition of RGO in excess may prevent the activation of the TiO2 surface by UV light and also decrease the lifetime of the photogenerated electron-hole pairs. Therefore, it appears that 1 wt% is the optimal loading of RGO to obtain a close interfacial contact between RGO and TiO2, leading to both an effective activation of TiO2 by UV radiation and an enhanced charge transfer between RGO and TiO2.

Molybdenum disulfide (MoS

Caffeic acid (CA) is an important phenolic compound of natural occurrence with antioxidant and anti-inflammatory activities as well as antimicrobial and cytotoxic properties that are of high importance for the human organism. Thus, the present work reports the development of a novel photoelectrochemical (PEC) sensor for CA determination based on titanium dioxide nanoparticles (TiO2), carbon nanotubes (CNTs), and cadmium telluride quantum dots (CdTeQDs) which form the TiO2/CNTs/CdTeQDs/FTO PEC sensor. The PEC sensor exhibited a high photocurrent in the presence of CA under the incidence of visible LED light when compared to each material used in the construction of the composite material. Characterization of the materials was performed by X-ray diffraction (XRD), scanning electron microscopy (SEM), linear scanning voltammetry (LSV), electrochemical impedance spectroscopy (EIS) and amperometry. Under optimized experimental and operational conditions, the photocurrent of the PEC sensor exhibited a linear relationship with the increase of CA concentration from 0.5 to 360 μmol L−1 and a detection limit of 0.15 μmol L−1. By using the standard addition method, the sensor was successfully applied for the determination of CA in samples of tea and soluble coffee. The PEC sensor presented average recovery values for CA in coffee and tea samples of 99.9% and 97.4%, respectively, suggesting good accuracy of the proposed method. In addition, the sensor demonstrated excellent precision, selectivity, and reproducibility for the determination of CA.

In this work we evaluated the influence of different gel electrolytes prepared with a synthesized poly(ionic liquid) – PIL matrix (PILTFSI) and two ionic liquids (ILs) 1-methyl-3-butylimidazolium bis(fluorosulfonyl)imide (MBIMFSI) and 1,2-dimethyl-3-propylimidazolium bis(trifluoromethylsulfonyl)imide (DPITFSI) on the electrochemical properties of solid-state supercapacitors. The synthesized PIL/IL gel electrolytes exhibited a conductivity of 3.2 × 10−3 S cm−1 (MBIMFSI) and 5.0 × 10−4 S cm−1 (DPITFSI) at 25 °C and electrochemical windows of 2.8 V and 3.0 V, respectively (obtained by linear sweep voltammetry). By using galvanostatic charge/discharge measurements carried out in a synchronous 2–3 electrode experiment, which allows the simultaneous registration of the voltage of the cell and the potential (versus a reference) of the positive and negative electrodes, we was able to evaluate in details the influence of each gel systems (focusing of the different ions of the IL) on the work voltage and capacitance of the cells. We have demonstrated that the working voltage of the cell (including the work potential of each electrode) should be determined using the complete cell instead of the electrochemical window of the electrolyte obtained with blocking electrodes. Additionally, we showed which gel was able to give to the supercapacitor the best performance, and we have described for the first time the asymmetry on the double layer formation in such PIL/IL solid-state supercapacitors prepared with a symmetrical configuration (same material and same mass in both electrodes).

Partially hydrolyzed polyacrylamide (HPAM) aqueous fluids in reservoirs produces a significant increase in the produced oil volume. However, the viscosity of these fluids is highly influenced by the temperature and salinity of the medium which is crucial in some reservoir conditions for the oil recovery. Thus, addition of nanomaterials in HPAM solutions to prepare nanofluids has been shown to be a promising alternative to increase viscosity and improve the performance in enhanced oil recovery. In this work, graphene oxide (GO) was prepared using modified Hummers method through the oxidation/exfoliation of expanded graphite while the aminated graphene oxide (GOA-EDA) was prepared using ethylenediamine in an ultrasonic bath. Spectroscopic techniques, elementary and thermogravimetric analyses confirmed the chemical composition of the produced nanomaterials. Images obtained by transmission electron microscope also confirmed the interfacial interactions between GO / GOA-EDA and HPAM. Rheological measurements were performed to determine the nanofluids viscosity as a function of concentration at high temperature (70 °C) under different salinity conditions. The results indicate that the viscosity increases promoted initially by the nanofluids prepared with GOA-EDA were smaller than those obtained by the nanofluids prepared with GO. In particular, the greatest increases in viscosity values occurs in the medium with the highest ionic strength ( η i % μ = 0.6 > η i % μ = 0.3 > η i % μ = 0.1 ). However, after 90 aging days, nanofluids prepared with GOA-EDA showed better performances reaching gains of up to 146% in viscositiy when compared to the HPAM reference fluids indicating that nanofluids prepared with GOA-EDA are more promising for application in enhanced oil recover.

2030 Interfacial or separate phase location of carbonaceous nanofillers (graphene and carbon nanotubes) in polymer blends with co-continuous phases can lead to double percolation behavior, significantly increasing rheological and electrical properties. The prediction of the morphology and the location of the nanofillers has been used as a tool to evaluate the proprieties of co-continuous polymer blends. This work aims to highlight the superior conductivity levels achieved using a low amount of carbon-based fillers, by the proper selection in a multiphase polymer matrix as a template for controlled dispersion and spatial distribution of the nanoparticles, offering a compromise between easy processability and enhanced performance. Here, two polymers (linear low-density polyethylene [LLDPE] and ethylene-co-methylacrylate [EMA]) and their co-continuous blend (LLDPE/EMA) were loaded with nanofillers (few-layer graphene [FLG], few-walled carbon nanotube [FWCNT]) via continuous melt mixing in twin-screw extrusion, separate and simultaneously. It was observed that the addition of the nanofillers changed the co-continuity of the blend, with the probable migration of the nanofillers from the EMA (hydrophilic) phase to the LLDPE (hydrophobic) phase. Rheological percolation occurred preferentially in blends containing FWCNT and FLG/FWCNT. Electrical conductivity was observed in all compositions, with higher electrical conductivity being noticed in hybrids

Hexagonal boron nitride (h-BN), graphene oxide (GO) and hybrid (GO/h-BN) nanosheets were employed as fillers in order to enhance the physical properties of the polymer matrix. Composites based in epoxy and these two-dimensional (2D) nanofillers were produced with different wt% and their microstructure, mechanical and thermal properties were investigated. Increases up to 140% in tensile strength, 177% in ultimate strain and 32% in elastic modulus were observed for the hybrid GO/h-BN composite with 0.5 wt% content. The hybrid nanofiller also contributed to the increase up to 142% on thermal conductivity with respect to the pure epoxy for GO/h-BN composite with 2.0 wt% content. Molecular dynamic simulation was used to predict the behavior of possible stacking arrangements between h-BN and GO nanosheets tensioned by normal and shear forces. The results showed that the hybrid GO/h-BN combination can prevent the re-stacking process of exfoliated layers, demonstrating the synergism between these nanostructures with the final effect of better dispersion in the composite material. The excellent thermal and mechanical performance of these hybrid composites engineered by the combination of different types of the 2D inorganic nanoparticles make them multifunctional candidates for advanced materials applications.

An effective nanofiller-matrix interaction is considered crucial to produce enhanced nanocomposites. Nevertheless, there is lack of experiments focused in the direct measurement of possible filler-matrix covalent linkage, which was the main goal of this work for a carbon nanotube (CNT)/epoxy system. CNT were functionalized with oxygenated (ox) functions and further with triethylenetetramine (TETA). An in-situ determination methodology of epoxy-CNTs heat of reaction was developed by Differential Scanning Calorimetry (DSC). Values of −(8.7 ± 0.4) and −(6.0 ± 0.6) J/g were observed for epoxy with CNT-ox and CNT-TETA, respectively. These results confirm the occurrence of covalent bonds for both functionalized CNTs, a very important information due to the literature generally disregard this possibility for oxygenated functions. The higher value obtained for CNT-ox can be attributed to a not complete amidation and to steric impediments in the CNT-TETA structure. The modified CNTs produced by DSC experiments were then characterized by X-Ray Photoelectron Spectroscopy, Transmission Electron Microscopy and Thermogravimetry, which confirmed the covalent linkage. This characterization methodology can be used to verify the occurrence of covalent bonds in various nanocomposites with a quantitative evaluation, providing data for better understanding of the role of CNT functional groups and for tailoring its interface with polymers.

Storage devices have been widely reported to satisfy the increase needs in the electronic and transportation areas. The easy access of the electrolyte ions to the surface of the electrodes of carbon nanomaterials is a challenge to be overcome in supercapacitors, especially in the case of ionic liquid electrolytes. Herein, the study of four different ionic liquids (IL) to select the one that exhibits better electrochemical properties in the presence of GO has been accomplished. Among the prepared IL composites, the one with [SET3][TFSI] showed an increase in the conductivity values and an electrochemical stability of over 3.5 V as measured by linear sweep voltammetry. The viscosity of composite [SET3][TFSI]-GO as a function of different concentrations of GO was discussed considering its effect on the conductivity mechanism. Furthermore, supercapacitors based on neat IL and IL-GO 0.1 wt% with reduced graphene oxide (rGO) were investigated. The best results obtained by cyclic voltammetry of the supercapacitor rGO/[SET3][TFSI]/rGO showed a capacitance value of 95.8 F g−1, whereas the supercapacitor rGO/[SET3][TFSI]-GO/rGO exhibited a capacitance of 125.3 F g−1, both at 5 mV s−1, working in a 2.5 V range; which demonstrates an increase of 31% in capacitance because of the presence of GO in the IL. TEM images indicated that the composite electrolyte increases the compatibility of the ionic liquid electrolyte with the rGO electrode, probably favoring the accessibility of the electrolyte ions to the electrode surface.

Both flexible energy harvesting and storage devices have been widely reported separately to satisfy part of the needs in the emerging areas, including wearable electronics, and low-density applications such as rooftop solar collectors. However, a flexible energy system with mechanical robustness and light-weight is the integrated device that will serve the real demand. Herein, a flexible printable dye-sensitized solar cell/supercapacitor integrated energy device has been designed, fabricated and characterized. This new device has several advantages: flexible, portable, high voltage capacity (up to 1.8 V), lightweight, environmental friendly and expanded indoor-use capabilities. The device demonstrated very stable performances under various extreme mechanical loading conditions in outdoor testing. This work paves way for future development of highly flexible integrated energy system for many potential applications.

Nowadays, hexagonal boron nitride nanosheets (h-BNNS) have shown promising results among 2D nanomaterials. A great effort has been made in recent years to obtain h-BNNS with a high-yield process to enable its large-scale application in industrial plants. In this work, we developed a mechanochemical method for obtaining h-BN nanosheets assisted by NaOH aqueous solution as process aid and aimed the ideal balance between yield, quality and process sustainability. Images obtained by transmission electron microscope suggested a great exfoliation of the h-BNNS in the range of 12–38 layers observed for well dispersed nanosheets. The macroscopic stability study, the polydispersity index, hydrodynamic diameter, and Zeta potential measurements suggested that material prepared in autoclave and ball milling followed by tip sonication process at 40 °C (h-BNNS-T40) could be considered the most promising material. The process used in this case reached a yield of about 37% of nanosheets with an optimal balance between quality and practicality. A hybrid lamellar material was also prepared by drop-casting and dip-coating techniques. An increase on thermal stability in oxidizing atmosphere was observed with respect to the pure graphene oxide (GO). Fourier transformation infrared spectroscopy and RAMAN suggested the presence of chemical interactions between h-BNNS and GO in the hybrid. This fact supports the interest of extending the study of this hybrid (which has an easy preparation method) to further explore its applicability.

In recent years, the use of supercapacitors with redox additives has been widely explored with the aim of maximizing energy density. However, the inclusion of such additives increases the complexity of the charge storage mechanisms, requiring more attention in quantifying performance parameters. Specific electrode capacities and capacitances are one of the most reported parameters and have been often overestimated or misinterpreted in relation to each other. Here, we evaluate these parameters considering the surface excess ( Γ * ) of redox additives adsorbed on electrode, which is obtained by current contribution separation from cyclic voltammetry (CV) measurements. Activated glassy carbon (AGC) electrodes in absence and presence of adsorbed methylene blue (MB) are studied by CV, chronopotentiometry and electrochemical impedance spectroscopy. The gravimetric normalization is obtained by means of Γ * and reveals specific capacity of 41.2±1.9 mAh g−1, around half of the theoretical for MB in 1e−-process. Finally, a comprehensive electrochemical discussion is done to assist the researcher community to improve performance metrics in supercapacitor electrodes in the presence of redox additives.

Two-dimensional (2D) nanomaterials as molybdenum disulfide (MoS2), hexagonal boron nitride (h-BN), and their hybrid (MoS2/h-BN) were employed as fillers to improve the physical properties of epoxy composites. Nanocomposites were produced in different concentrations and studied in their microstructure, mechanical and thermal properties. The hybrid 2D mixture imparted efficient reinforcement to the epoxy leading to increases of up to 95% in tensile strength, 60% in ultimate strain, and 58% in Young’s modulus. Moreover, an enhancement of 203% in thermal conductivity was achieved for the hybrid composite as compared to the pure polymer. The incorporation of MoS2/h-BN mixture nanofillers in epoxy resulted in nanocomposites with multifunctional characteristics for applications that require high mechanical and thermal performance.

In this article, a thermodynamic study of the methylene blue (MB) adsorption on carbon nanotubes (CNT), a known model system, was carried out by using a simple and rigorous experimental approach based on adsorption and isothermal titration calorimetry (ITC) experiments. Considering the thermodynamics of the process, the classical approach using the van’t Hoff approximation provided endothermic values for ΔadsH0 while the ITC measurements revealed that the adsorption of MB on both unmodified and acid-modified CNTs is an exothermic process. The thermodynamic parameters for the systems were obtained using the infinite dilution regime and ITC data: ΔadsH0 = −9.13 ± 0.02 kJ mol–1, ΔadsG0 = −21.18 ± 0.61 kJ mol–1, and ΔadsS0 = 40.42 ± 0.61 J K–1 mol–1 for u-CNT and ΔadsH0 = −11.49 ± 0.34 kJ mol–1, ΔadsG0 = −27.88 ± 0.18 kJ mol–1, and ΔadsS0 = 54.97 ± 0.38 J K–1 mol–1 for f-CNT. The process is both enthalpically and entropically driven, having a more negative ΔadsG0 for the system based on a modified nanotube. W...

Ultra high molecular weight polyethylene (UHMWPE) is one of the most important engineering materials owing to outstanding properties like impact strength and abrasion resistance. However, the relatively low Young´s modulus restricts some application and the use of fillers may be a suitable way to overcome this. The fillers can influence the photo stabilization of the compound, as it occurs to other polymers. Neat UHMWPE and its composites with 1 and 10% of iron ore fine were exposed to ultraviolet radiation for up to 33 days and then tested for mechanical properties. The stress-strain behaviour changed with degradation, with an evident necking and strain hardening region that was not observed before exposure, due to a reduction in entanglements density. From the tensile results, the filler may have a protection action against UV, particularly when a loading of 10% was present. Complementary analyses were performed, including X-ray diffraction, DSC and SEM.

Supercapacitor electrodes consisting of conjugated polymers (CP), metal oxides and graphene nanosheets have been explored as a strategy to achieve high specific capacitance, power, energy density, and stability. In this work, we synthesized a 3D structure composed of zirconia oxide nanoparticles (ZrO2), reduced graphene oxide (rGO) and polypyrrole (PPy), using a simple and easily scalable one-step chronopotentiometry method. Detailed characterization revealed that the addition of rGO and ZrO2 modified the morphology of the electrode material. The capacitance of the resulting architecture improved by up to a 100%. The ternary composite featured high stability, with an increase of 5% in capacitance after a thousand cycles. DFT and MD simulations were carried out in order to provide further insight on the role of zirconia.

A comprehensive study of a less harmful functionalization of multiwalled carbon nanotubes (MWCNT) was performed. The influence of ultrasonic cavitation and solid/liquid interface was indirectly evaluated by statistical characterization of MWCNT aspect ratio and degree of functionalization. MWCNT aspect ratio was determined through hundreds of electron microscopy images. Degree of functionalization of MWCNT was characterized by elemental analysis and thermogravimetry. Distribution of different oxygen-containing functional groups was assessed by potentiometric titration. MWCNT aqueous dispersions were evaluated by electrophoretic mobility and dynamic light scattering. An acid volume over 90% lower than usually reported in literature guaranteed MWCNTs with significantly larger aspect ratio, higher proportion of carboxylic groups and a more negative zeta potential in aqueous suspension. These results can be related to a more localized ultrasonic cavitation in MWCNTs/acid interface for reduced liquid volumes. This distinguished influence of ultrasonic cavitation may be a valuable contribution to more eco-friendly processes with nanomaterials.

In this article, we explore electrical double-layer capacitors (EDLCs) based on ionic liquids (IL), focusing on their stability and efficiencies (Coulombic and energetic). We analyze the conventional voltammetric methods to determine the electrochemical stability window, pointing out that a simple analysis of Coulombic efficiency, under different current and voltage conditions in galvanostatic experiments, has the advantage of being more representative for real cells, especially when studied together with energy efficiency. In addition, we study how IL-based EDLCs differ from aqueous and organic ones in terms of energy efficiency correlating with the physicochemical properties of electrolytes. Finally, we discuss the high resistance of this type of EDLC that has a detrimental effect on energy efficiency and cycling performance, even when the Coulombic efficiency is close to 100%., The authors would like to thank the Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPq)/Brazil for ́ the financial support (Process No. 458487/2014-7). The authors would like to acknowledge the Instituto Nacional de Ciencia e Tecnologia em Nanomateriais de Carbono (INCT ̂ Nanocarbono)/CNPq. R.L.L. is recipient of fellowship from CNPq (Grant No. 313304/2017 - 3). M.C.G.S. thankfully acknowledge the scholarship received from the Coordenaca̧ õ de Aperfeicoamento de Pessoal de Nivel Superior (CAPES) - Brazil.

Two series of polyurethane (PU) and carbon nanotubes (CNT) based composites with 0.0, 0.25, 0.5 and 1.0 mass% of CNT were obtained from diluting a commercial masterbatch with 30 mass% CNT and using two different dispersion methods. The quality of the dispersions was assessed using optical microscopy, and scanning and transmission electron microscopies. These tests showed that high controlled shear stress is necessary to produce composites with nanoscale dispersion: the elastic modulus improved by an average of 38% in the case of the high-shear dispersed materials in comparison with the neat polymer. A specific fatigue test conducted by dynamic mechanical analysis was first used in this work to compare the neat PU with the CNT/PU nanocomposites. The number of cycles to failure increased from 2700 for the neat polymer to 3200 for the 0.5 mass% CNT based nanocomposite; the elongation at failure increased by 145% in the test conditions.

In this work we have demonstrated how to prepare a novel gel polymer electrolyte (GPE) with remarkable adhesive characteristics by combining a synthesized poly(ionic liquid) consisting of poly(1-vinyl-3-propylimidazolium bis(fluorosulfonyl)imide) (poly(VPIFSI)) and a commercial ionic liquid: 1-ethyl-3-methyl imidazolium bis(fluorosulfonyl)imide (EMIFSI). For this purpose several PIL/IL-GPEs systems (considering the amount of IL) were subjected to electrochemical characterization. The influence of the PIL/IL-GPE (50 wt% of IL) on the properties of a flexible solid state supercapacitor was evaluated using electrochemical impedance spectroscopy, cyclic voltammetry and the galvanostatic charge/discharge technique that allows synchronous measurements of the cell voltage and the potential of the positive and negative electrodes. The influence of the ions on the formation of the electric double layer in the device during cycling employing different conditions and folding angles is discussed. The properties of the adhesive PIL/IL-GPE, such as high conductivity, good interaction between the PIL matrix and the IL liquid phase that prevents any leakage (thereby contributing to greater safety) together with the good adherability and wettability of the gel electrolyte on the electrode surface have produced a device with an improved rate capability and cyclability that undergoes hardly any changes in C,, E, and P of the cell when folded., The authors would like to thank the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq), Brazil, for the financial support received (Universal 2014, Process No. 458487/2014-7). The authors are also grateful to the Instituto Nacional de Ciência e Tecnologia em Nanomateriais de Carbono – INCT Nanocarbono and to profs. Dorila Piló Veloso and José Dias de Souza Filho (Department of Chemistry/UFMG/Brazil) for performing the NMR analysis. S.A.Alexandre also acknowledges the scholarship received from CNPq. R.L. Lavall is recipient of fellowship from CNPq (grant number 313304/2017-3). R. Santamaría would like to thank financial support from Ministerio de Economía, Industria y Competitividad (project MAT2016-77114-R).

Single-walled carbon nanotubes are oxidized in the presence of H2SO4/HNO3 mixtures containing distinct concentrations of the nitronium ion, [NO2+]. The spectroscopic analyses of the final samples suggest a higher structural disorder in the oxidized systems with increasing [NO2+]. This is due to a considerable oxygen amount on the tube surface, reaching up to 30%, depending on the reaction time and [NO2+]. Interestingly, if long reaction time is considered, the oxygen amount on the tube surface is maximum for low [NO2+] and reduces slightly for larger [NO2+]. On the other hand, the oxidation process occurs gradually at 4 h, allowing a fine control of the oxidation process. Therefore, if fine tuning of the oxidation degree is desirable, the reaction must be conducted during short time (4 h) using increasing [NO2+] as those obtained from 2:1, 2.5:1 and 3:1 H2SO4/HNO3 acid mixtures to produce increasing content of functionalization.

Smooth and optically transparent titania (TiO2) and TiO2-reduced graphene oxide (RGO) composite films were successfully prepared here. A nanocrystalline anatase suspension was initially prepared by combining the sol-gel process and hydrothermal treatment. Graphene oxide (GO) nanosheets were prepared following a route similar to the Hummers method. Glass slides were then dip-coated using mixtures of TiO2 and GO suspensions. The concentration of GO in the prepared coatings ranged from 1 to 5 wt%. The coated samples were air-dried, and then either calcined or irradiated with UVA light. It was observed that UVA light promoted the reduction of GO to RGO, which increased both the electrical conductivity and hydrophilicity of the composites. The heat treatment of as-prepared coatings also decreased the water contact angle (WCA) with its surface, which is related to the removal of organics residues, graphene burning, and the increase in surface energy. The superhydrophilicity of the prepared samples was investigated after keeping them in air for up to 60 days, followed by UVA illumination. It was also demonstrated that a hydrophilic behavior can be induced in the samples prepared here by applying a direct current (DC) voltage, which could allow their use as smart materials in several applications.

Two types of poly(3-hexylthiophene)-multi-walled carbon nanotubes (MWCNT) hybrids were prepared and their electrochemical properties were compared. A dispersion of MWCNT modified with monomeric thiophene derivative (MWCNT-thio) and the monomer 3-hexylthiophene (3HT) were allowed to react by in-situ oxidative polymerization to prepare a P3HTMWCNT covalent hybrid. The hybrid was synthesized with a 1:1 (polymer:MWCNTs) mass ratio and was easily dispersed in common organic solvents. Moreover, a second type of hybrid was obtained by polymerization of 3HT in the presence of MWCNT amine-functionalized with the same component ratio (non-covalent hybrid P3HT/MWCNT). The covalent hybrid (P3HTMWCNT) achieved an electrical conductivity of 4.6 × 10 −1 S cm −1 , which was 5 times higher than that of the hybrid produced with polymer adsorption on the MWCNT. This result provides a strong evidence of enhancement in charge transfer by covalent attachment between polymer and nanotubes. The chemical structure and morphology of the hybrids were compared with those of neat P3HT and neat MWCNTs. Moreover, the covalent hybrid was used as an electrode in a pseudocapacitor with an organic liquid electrolyte and this device was compared to a supercapacitor based only in electrodes of MWCNT (pure double layer capacitance). The device showed high performance with a specific capacitance of 239 F g −1 at a current density of 3 A g −1 , which is 585% higher than the supercapacitor based on MWCNT electrodes at 1 A g −1 (maximum current obtained). The results presented here demonstrating that a carbon nanotube-conjugated polymer hybrid with equivalent content of the components covalently linked can be a better choice for application in electrodes than the counterparts with adsorpted polymer or composites with polymer in excess.

This paper describes an integrated experimental and theoretical analysis for the synthesis and characterization of cisplatin/single-walled carbon nanotube inclusion complex (cDDP@SWCNT). Experimental data revealed the inclusion of cDDP into a short SWCNT, which was predicted to be energetically favorable by around −5.0 kcal mol −1 through quantum chemical calculations. The Raman spectra show that the ratio of intensity for G/D bands decreases from 10.9 (pristine SWCNT) to 4.8 (inclusion complex), suggesting an increase of structural disorder after the drug inclusion. Moreover, it was observed a decrease of the wavenumber in the spectral range of the radial breathing modes (RBM) by ∼9 cm −1 with the insertion of the cDDP molecules. As a continuation of the studies conducted by our group, through this theoretical and experimental work we expect to help experimentalists in the assignments of Raman spectra and contribute for characterization of such carbon-based drug delivery systems.

Carbon nanotubes (CNTs) were surface-modified by a glycodendrimer with four glucose units (4-Gl). Electrodes for supercapacitors based on CNT/4-Gl hybrids were used for the first time in this work. The preparation was conducted by casting eight alternating bilayers of two types of modified multiwalled carbon nanotubes (MWCNTs), MWCNT-COOH/4-Gl and MWCNT-NH/4-Gl, from aqueous dispersions (pH = 6). The electrodes showed good cohesion, dimensional stability, and a homogeneous nanoscale structure because the carbon nanotube/dendrimer layers interact electrostatically. The supercapacitor was stacked with a separator embedded with a 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ionic liquid electrolyte. The device with 20Â wt% of dendrimer with respect to CNT content in the electrodes achieved a remarkable increase of 600Â % in capacitance compared with the capacitance without the dendrimer., The authors are grateful to Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)—Brazil for the scholarship of João Paulo Campos Trigueiro and to the Centro de Microscopia/UFMG for the images provided. Pró-Reitoria de Pesquisa from UFMG (PRPq/UFMG) is acknowledged for financial support of the English revision. Rute C. Figueiredo extends gratitude to the Carolina Foundation for its scholarship program for the mobility of Brazilian teachers.

The data presented in this work show the preparation of an electrochemical double layer capacitor with improved capacitance employing an ionic liquid based composite gel polymer electrolyte containing nanostructured SiO 2 . The composite gel electrolyte has good self-standing characteristics, conductivity, electrochemical window and high thermal stability. The use of this electrolyte promotes an increase of about 72% in the device capacitance compared to a capacitor prepared with the gel electrolyte without SiO 2 at ambient temperature. The cell is very stable when cycled at a high current density (1.0 A g ⿿1 ) since it loses only 9% of its initial capacitance after 2000 cycles, with values of energy and power density of 32.2 Wh kg ⿿1 and 0.9 kW kg ⿿1 , respectively. Additionally, the SiO 2 -based electrolyte allows the capacitor to be used at high temperature (100 °C) with a superior performance without ionic liquid leakage. Therefore, the use of such composite gel electrolyte makes possible the construction of miniaturized, safe and completely solid state devices.

Flexible supercapacitors with large power and energy densities, long life cycles and good operational safety are necessary devices for various applications. In this work, we demonstrate the integration of a composite based on graphene nanosheets/multiwalled carbon nanotubes in an in-plane supercapacitor configuration by using a straightforward preparation involving the filtration of nanomaterials to produce an electrode film. Reduced graphene oxide (RGO) received 15 wt % carbon nanotubes to act as a conducting additive, which led to a flexible and transferable thin film (RGO/MW) with an average conductivity of 20.0 S cm −1 . Three ionic liquids were tested as electrolytes for the supercapacitor, among which 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMITFSI) was observed to exhibit the best performance. The specific capacitance of the supercapacitor based on RGO/MW-EMITFSI reached 153.7 F g −1 at a current density of 0.2 A g −1 and exhibited a capacitance retention of 88% after 2000 cycles. The maximum energy and power densities were calculated to be 41.3 Wh kg −1 and 3.5 kW kg −1 , respectively, for the RGO/MW-EMITFSI supercapacitor.

Few layers graphene oxide (GO), graphene oxide functionalized with diethylenetriamine (GO-DETA) and the hybrid of graphene oxide-diethylenetriamine and polyacrylamide (GO-DETA/PAM) hydrogel with high adsorption of methylene blue were prepared using microwave-assisted methods. TGA and XPS analysis were performed to confirm DETA molecules incorporation on GO and to identify an in-situ acrylamide polymerization with no usual chemical cross-linkers. The morphology and structure of the graphene derivative materials and hybrid gel were evaluated by TEM and SEM images. The obtained GO-DETA sheets played an important role as a cross-linker agent during the polymerization of PAM to form the hybrid GO-DETA/PAM. The results obtained showed that the GO-DETA influenced the swelling behavior and thermal properties of PAM, as well as improved its Tg, presenting a more stable PAM network in saline conditions. The hybrid hydrogel significantly improved the capacity to adsorb methylene blue (maximum adsorption capacity 205.4 mg g−1), compared to the neat PAM (maximum adsorption capacity 51.5 mg g−1). This feature demonstrates how this novel material can be used in the removal of emerging contaminants in water, for example, using a fast and reproducible synthetic method and lower quantities of adsorbent.

Nanocomposites based on graphene oxide (GO), hexagonal boron nitride (h-BN), and their hybrid GO/h-BN as nanofillers in polyurethane (PU) were prepared, and their structures and morphologies were studied. The efficient production of a few layers of nanofillers was completed using the direct liquid-phase exfoliation process. Mechanical and thermal tests were carried out to study the effect of the addition of GO, h-BN, and GO/h-BN at different wt% in the PU system. The tensile strength and Young's modulus showed an increase of up to 85% and 140%, respectively, for the composite containing 0.5 wt% of the hybrid GO/h-BN mixture. An impressive improvement of up to ~1450% in thermal conductivity was observed for the same sample when compared to neat polymer. In order to gain further insights regarding the mechanism behind the nanofiller dispersion and adhesion processes in PU, fully atomistic classical molecular dynamics simulations were carried out. Based on these simulations, it was possible to build structural models that help to explain the thermal and mechanical improvements in the hybrid GO/h-BN composites, with a focus on its stabilization energy.

The functionalization of carbon nanotubes has become a common approach to modify the surface properties of these materials for different applications such as in the formulation of polymeric composites, as electrodes of electrochemical devices and, mainly, in the removal of organic contaminants. On the other hand, these functionalization procedures generates oxidized polyaromatic fragments known as debris, which impacts the material properties. Unfortunately, most papers published in the literature disregard these effects or do not cite experimental procedures for debris removal, which are strongly adsorbed onto the surface of nanotubes. In this study, we evaluated the effects of debris – generated on multiwalled carbon nanotubes (MWCNT) subjected to acid oxidation – on the capacities, kinetics and adsorption mechanism. For this, three different MWCNTs were employed: a pristine unmodified MWCNT; an oxidized MWCNT (obtained by common procedure and without the removal of debris); and an oxidized MWCNT without debris (obtained after reflux in alkaline medium). In addition, methylene blue (MB) has been used as model adsorbate in these experiments. As a second goal, the effects of debris on MB faradic electron transfer at the MWCNT interface were also investigated using cyclic voltammetry and cyclic chronopotenciometry techniques. Finally, we have shown that debris impacts the adsorption capacity, kinetics and limits the performance of MWCNTs as electrodes.