C, Volume 4, Issue 2 (June 2018) – 18 articles

MCM-41–Co catalysts were tested in the synthesis of single wall carbon nanotubes (SWCNTs) through methane chemical vapor deposition (CVD), varying total cobalt content, synthesis temperature, methane flow rate, and deposition time. All variables showed a relationship with total carbon deposition, graphitic quality according to Raman results. Cobalt content showed a maximum activity at 4%, but the structural quality is best at 3%. Flow rate does not affect the quality up to 300 cm³ min⁻¹, but deposition time leads to the formation of highly disordered carbon species passing methane for periods longer than 30 min, concluding that optimal variables are a methane deposition temperature of 800 °C, a 300 cm³ min⁻¹ methane flow rate, and a 30 min of methane injection time, leading to a 5.4% carbon mass content and 5.1 G/D area ratios. Full article

The earliest stages of annealing of graphitizable anthracene coke and non-graphitizable sucrose char were observed by rapid heating with a CO₂ laser. Structural transformations were observed with transmission electron microscopy. Anthracene coke and sucrose char were laser heated to 1200 °C and 2600 °C for 0.25–300 s. The transformations are compared to traditional furnace heating at matching temperatures for a 1 h duration. Traditional furnace and CO₂ laser annealing followed the same pathway, based upon equivalent end structures. Graphitizable anthracene coke annealed faster than non-graphitizable sucrose char. Sucrose char passed through a structural state of completely closed shell nanoparticles that opened upon additional heat treatment and gave rise to the irregular pore structure found in the end product. The observed curvature in sucrose char annealed at 2600 °C results from shell opening. The initial presence of curvature and loss by heat treatment argues that odd membered rings are present initially and not formed upon heat treatment. Thus, odd membered rings are not manufactured during the annealing process due to impinging growth of stacks, but are likely present in the starting structure. The observed unraveling of the closed shell structure was simulated with ReaxFF. Full article

Numerous adsorbent materials are developed and are able to face specific types of pollution, but none of them can manage the whole pollution. The purpose of this work is to develop a novel hybrid adsorbent, based on chitosan (CS) biopolymer, clay minerals and activated carbon (AC), having complementary adsorption properties and achieving a wide-spectrum water decontamination in a single treatment. Hybrid CS beads, containing dispersed clay and AC, were prepared from dispersions of solid adsorbents in a CS solution and its further coagulation in a basic medium. The porosity and the homogeneity of the hybrid beads were characterized by N₂ adsorption at 77 K and Cryo-Scanning Electron Microscopy respectively. The interaction between CS and clay was characterized using X-ray diffraction. Water content and the amount of each adsorbent in the hydrogel beads were determined by thermogravimetric analysis. Such a composite material was still porous and presented a wide adsorption spectrum. As shown by their adsorption kinetics, hydrophobic anionic clofibric acid (CBA) and cationic metoprolol (MTP) were well adsorbed on AC containing beads (21 and 26 mg/g), respectively. Clays containing beads showed interesting adsorption properties towards cationic Zn²⁺ and MTP. The obtained composite beads were able to adsorb all the pollutant types: Zinc cations, and hydrophobic-charged organic molecules, such as pharmaceutical derivatives (clofibric acid and MTP). Full article

Much recent work has focused on improving the performance of graphene by various physical and chemical modification approaches. In particular, chemical doping of n-type and p-type dopants through substitutional and surface transfer strategies have been carried out with the aim of electronic and band-gap tuning. In this field, the visualization of (i) The intrinsic structure and morphology of graphene layers after doping by various chemical dopants, (ii) the formation of exotic and new chemical bonds at surface/interface between the graphene layers and the dopants is highly desirable. In this short review, recent advances in the study of doped-graphenes and of the n-type and p-type doping techniques through transmission electron microscopy (TEM) analysis and observation at the nanoscale will be addressed. Full article

Laboratory-generated synthetic soot from benzene and benzene–thiophene was neodymium-doped yttrium aluminum garnet (Nd:YAG) laser and furnace annealed. Furnace annealing of sulfur doped synthetic soot resulted in the formation of micro-cracks due to the high pressures caused by explosive sulfur evolution at elevated temperature. The heteroatom sulfur affected the carbon nanostructure in a different way than oxygen. Sulfur is thermally stable in carbon up to ~1000 °C and thus, played little role in the initial low temperature (500 °C) carbonization. As such, it imparted a relatively unobservable impact on the nanostructure, but rather, acted to cause micro-cracks upon rapid release in the form of H₂S and CS₂ during subsequent traditional furnace heat treatment. In contrast, Nd:YAG laser heating of the sulfur doped sample acted to induce curvature in the carbon nanostructure. The observed curvature was the result of carbon annealing occurring simultaneously with sulfur evolution due to the rapid heating rate. Full article

Graphene is a monolayer of carbon atoms which exhibits remarkable electronic and mechanical properties. Graphene based nano-materials have gained a lot of interest for many applications. In this paper, inks with three different graphene concentrations (12.5, 25, and 33 wt % in graphene) were prepared and deposited by screen printing. A detailed investigation of films’ surface morphology using Scanning Electron Microscope (SEM) and Atomic Force Microscopy (AFM) revealed that the graphene films present a homogeneous dispersion of the filler with a comparatively lower surface roughness at higher concentrations and negligible agglomerates. The films were then printed between copper electrodes on FR-4 substrate (trade name for glass-reinforced epoxy laminate material), commonly used in Radio Frequency (RF) circuits, and the measured scattering parameters analyzed. Finally, the reflection coefficient of a patch antenna, fabricated on FR-4 substrate with and without a stub loaded by a thin film were measured. The difference of the resonant frequency due to the different interaction between graphene flakes and polymer binders shows attractive features of functionalized graphene films for chemical and bio-sensing applications. Full article

Lithium-ion capacitors (LICs) comprising capacitor-type and battery-type electrodes are promising electrochemical energy storage systems to effectively combine the merits of lithium-ion batteries (LIBs) and electrochemical capacitors (ECs). It is expected that the energy density of LICs can be improved by utilizing electrodes that are capable of providing high specific capacity. Herein, we demonstrate a graphene-based LIC with reduced graphene oxide-carbon nanotube (rGO-CNT) film as capacitor-type electrode and pre-lithiated rGO-CNT film as battery-type electrode using 1 M LiPF₆ in EC: EMC electrolyte. The rGO-CNT was prepared by electrostatic spray deposition (ESD), which offers advantages, such as simultaneous reduction and binder-free deposition of GO on a current collector and facile morphology control. The rGO-CNT shows high specific capacity and good cyclability as both capacitor-type and battery-type electrode materials. The rGO-CNT//lithiated rGO-CNT LIC delivered energy densities as high as 114.5 Wh Kg⁻¹ and maximum power density of 2569 W kg⁻¹. This indicates the promising potential of the ESD approach for the facile fabrication of graphene-based electrodes for high performance LICs. Full article

Aminated polyethersulfone (PES–NH₂) has been synthesized and used with carboxylated activated carbon (AC–COOH) as an adsorbent using two different methods: in situ and ex situ techniques. The chemical modification of polyethersulfone (PES) to introduce –NH₂ functions was used to overcome the hydrophobicity of PES which maximizes its use in water treatment applications whereas applying AC–COOH to this polymer provides a promising effective method as an adsorbent-separation technique to remove dye pollutants from wastewater. The structure and characterization of aminated polyethersulfone with carboxylated activated carbon (PES–NH₂–AC–COOH) were identified using proton nuclear magnetic resonance (¹H-NMR), Fourier transform infrared (FT-IR spectroscopy), X-ray diffraction (XRD), thermal analysis (TA), and a scanning electron microscopy (SEM). The performance of PES–NH₂ in situ and ex situ with AC–COOH was tested for the adsorption of cationic (methylene blue) and anionic (acid red 1) dyes from an aquatic environment. The results of the study showed a better thermal stability for the PES–NH₂ with 20% AC–COOH with both in situ and ex situ techniques as well as an excellent adsorption performance in comparison with the bare PES–NH₂. The resultant polymers displayed significantly high adsorption rates for the acid red dye (60% and 68%) and methylene blue dye (61% and 88%) by PES–NH₂ with AC–COOH using in situ and ex situ techniques, respectively, in comparison with the control (PES–NH₂) which showed lower adsorption rates for both dyes (21% for acid red and 33% for methylene blue). Lastly, the study experimental measurements found the most suitable model to describe the kinetic behavior of the acid red dye adsorption by our developed polymer (by PES–NH₂ with AC–COOH) to be the pseudo-second-order kinetic model. Full article

Early detection of pathogens requires methods that are fast, selective, sensitive and affordable. We report the development of a biosensor with high sensitivity and selectivity based on the low-cost preparation of organosiloxane (OSX) polymers imprinted with E. coli-GFP (green fluorescent protein). OSX polymers with high optical transparency, no cracking, and no shrinkage were prepared by varying several parameters of the sol–gel reaction. The unique shape and chemical fingerprint of the targeted inactivated E. coli-GFP were imprinted into bulk polymers by replication imprinting where the polymer solution was dropcast onto a bacteria template that produced a replica of the bacterial shape and chemistry on the polymer surface upon removal of the template. Capture performances were studied under non-laminar flow conditions with samples containing inactivated E. coli-GFP and compared to inactivated S. typhimurium-GFP. Capture selectivity ratios are dependent on the type of alkoxysilanes used, the H₂O:silane molar ratio, and the polymerization temperature. The bacteria concentration in suspension ranged from ~6 × 10⁵ to 1.6 × 10⁹ cells/mL. E. coli-imprinted OSX polymers with polyethylene glycol (PEG) differentiated between the targeted bacterium E. coli, and non-targeted bacteria S. typhimurium and native E. coli-GFP, achieving selectivity ratios up to 4.5 times higher than polydimethylsiloxane (PDMS) and OSX polymers without PEG. Full article

Carbon nanotubes (CNTs) are known for high thermal conductivity and have potential use as nano-radiators or heat exchangers. This paper focuses on the thermal performance of carpet-like arrays of vertically aligned CNTs on solid graphite substrates with the idea of investigating their behavior as a function of carpet dimensions and predicting their performance as thermal interface material (TIM) for electronic device cooling. Vertically aligned CNTs were grown on highly oriented pyrolytic graphite (HOPG) substrate, which creates a robust and durable all-carbon hierarchical structure. The multi-layer thermal analysis approach using Netzsch laser flash analysis system was used to evaluate their performance as a function of carpet height, from which their thermal properties can be determined. It was seen that the thermal resistance of the CNT array varies linearly with CNT carpet height, providing a unique way of decoupling the properties of the CNT carpet from its interface. This data was used to estimate the thermal conductivity of individual multi-walled nanotube strands in this carpet, which was about 35 W/m-K. The influence of CNT carpet parameters (aerial density, diameter, and length) on thermal resistance of the CNT carpet and its potential advantages and limitations as an integrated TIM are discussed. Full article

Porous graphite was prepared without the use of template by rapidly heating the carbonization products from mixtures of anthracene, fluorene, and pyrene with a CO₂ laser. Rapid CO₂ laser heating at a rate of 1.8 × 10⁶ °C/s vaporizes out the fluorene-pyrene derived pitch while annealing the anthracene coke. The resulting structure is that of graphite with 100 nm spherical pores. The graphitizablity of the porous material is the same as pure anthracene coke. Transmission electron microscopy revealed that the interfaces between graphitic layers and the pore walls are unimpeded. Traditional furnace annealing does not result in the porous structure as the heating rates are too slow to vaporize out the pitch, thereby illustrating the advantage of fast thermal processing. The resultant porous graphite was prelithiated and used as an anode in lithium ion capacitors. The porous graphite when lithiated had a specific capacity of 200 mAh/g at 100 mA/g. The assembled lithium ion capacitor demonstrated an energy density as high as 75 Wh/kg when cycled between 2.2 V and 4.2 V. Full article

In recent years, research efforts have focused on the development of safe and efficient H₂ generation/storage materials toward a fuel-cell-based H₂ economy as a long-term solution in the near future. Herein, we report the development of Pd nanoparticles supported on carbon nanofibers (CNFs) via sol-immobilisation and impregnation techniques. Thorough characterisation has been carried out by means of XRD, XPS, SEM-EDX, TEM, and BET. The catalysts have been evaluated for the catalytic decomposition of formic acid (HCOOH), which has been identified as a safe and convenient H₂ carrier under mild conditions. The influence of preparation method was investigated and catalysts prepared by the sol-immobilisation method showed higher catalytic performance (Pd_SI/CNF) than their analogues prepared by the impregnation method (Pd_IMP/CNF). A high turnover frequency (TOF) of 979 h⁻¹ for Pd_SI/CNF and high selectivity (>99.99%) was obtained at 30 °C for the additive-free formic acid decomposition. Comparison with a Pd/AC (activated charcoal) catalyst synthesised with sol-immobilisation method using as a support activated charcoal (AC) showed an increase of catalytic activity by a factor of four, demonstrating the improved performance by choosing CNFs as the preferred choice of support for the deposition of preformed colloidal Pd nanoparticles. Full article

Calcium phosphate and derivatives have been known for decades as bone compatible biomaterials. In this work, the chemical composition, microtexture, and structure of calcium phosphate deposits on carbon cloths were investigated. Three main types of deposits, obtained through variation of current density in using the sono-electrodeposition technique, were elaborated. At low current densities, the deposit consists in a biomimetic, plate-like, carbonated calcium-deficient hydroxyapatite (CDA), likely resulting from the in situ hydrolysis of plate-like octacalcium phosphate (OCP), while at higher current densities the synthesis leads to a needle-like carbonated CDA. At intermediate current densities, a mixture of plate-like and needle-like carbonated CDA is deposited. This established that sono-electrodeposition is a versatile process that allows the coating of the carbon scaffold with biomimetic calcium phosphate while tuning the morphology and chemical composition of the deposited particles, thereby bringing new insights in the development of new biomaterials for bone repair. Full article

An electrical double-layer capacitor (EDLC) is based on the physical adsorption/desorption of electrolyte ions onto the surface of electrodes. Due to its high surface area and other properties, such as electrochemical stability and high electrical conductivity, carbon materials are the most widely used materials for EDLC electrodes. In this work, we study an activated carbon felt obtained from sheep wool felt (ACF’f) as a supercapacitor electrode. The ACF’f was characterized by elemental analysis, scanning electron microscopy (SEM), textural analysis, and X-ray photoelectron spectroscopy (XPS). The electrochemical behaviour of the ACF’f was tested in a two-electrode Swagelok^®-type, using acidic and basic aqueous electrolytes. At low current densities, the maximum specific capacitance determined from the charge-discharge curves were 163 F·g⁻¹ and 152 F·g⁻¹, in acidic and basic electrolytes, respectively. The capacitance retention at higher current densities was better in acidic electrolyte while, for both electrolytes, the voltammogram of the sample presents a typical capacitive behaviour, being in accordance with the electrochemical results. Full article

To develop high capacity electrode materials for lithium-ion battery (LIB), dissimilar materials are mixed and, as a result, carbon nanofibers containing silicon (Si) nanoparticles and its components are successfully created by electrospinning method and some heat treatments. Tetraethoxysilane (TEOS) and Si nanoparticles are adopted as additives of carbon nanofibers because of their huge potential for obtaining high capacity. In this research, therefore, we develop TEOS/Si hybrid carbon nanofibers. Consequently, some samples obtain much higher charging/discharging capacity than the theoretical capacity for graphite (372 mAh/g, LiC₆) even after second cycle. Full article

The use of the Boehm titration (BT) method as an analytical tool for the quantification of oxygen-containing surface groups is systematically investigated for oxidized carbon black, carbon nanotubes and two active carbons with specific surface areas between 60 and 1750 m² g⁻¹. The accuracy of the BT method is quantitatively compared with results from elemental analysis (EA), temperature programmed desorption (TPD), and X-ray photoelectron spectroscopy (XPS). Overall, the results from TPD are in line with the values obtained by BT. Both show the equal ratio of the oxygen groups to each other. Within the series of carbon samples, all methods provide similar trends for the total oxygen content yet the absolute numbers are deviating significantly. Reasons for these discrepancies are discussed and linked to the specific characteristics of the different methods. As the BT method is a solution based method, it only probes the surface fraction of the carbon that is accessible to the base solution. That means, it probes the relevant fraction for applications where carbon is in contact to aqueous solutions. Overall, the BT method can be conveniently applied to a broad range of carbon materials as long as the samples are sufficiently hydrophilic and of the enough sample amount is provided. Full article

Practical aspects of the Boehm titration method are evaluated for obtaining reliable results in the quantification of oxygen-containing surface groups in a short time. Analytical criteria such as accuracy, repeatability, precision, and robustness are applied. Oxidized multi-walled carbon nanotubes (MWCNTs) are used as the model substance. Different reaction bases (NaHCO_3(aq), Na₂CO_3(aq), NaOH_(aq)) are applied and treatment times are studied. We also show that smaller amounts of carbon material can be reliably analyzed by using an autotitrator combined with a pH electrode. We find that indirect titration with Na₂CO₃ results in the highest titration precision and accuracy despite the lower base strength compared with NaOH. Therefore, CO₂ impurities do not have to be removed and only 7 min is necessary for one titration. The titration error with respect to the proposed method is 0.15% of the aliquot volume. The mixing method during the carbon treatment with bases (stirring, shaking, ultrasound treatment) has no influence on the result as long as one allows a few hours for the reaction to complete. Finally, we provide a standard operating procedure for obtaining results with high precision during Boehm titration. Full article

A sustainable and simple synthesis procedure involving the co-assembly of green phenolic resin and amphiphilic polymer template in water/ethanol mixture at room temperature to synthesize nitrogen doped mesoporous carbon is reported herein. Guanine is proposed as a novel nitrogen-based precursor which is able to create H-bondings both with the phenolic resin and the template allowing the formation of mesoporous carbons with nitrogen atoms uniformly distributed in their framework. The influence of the synthesis procedure, template amount and annealing temperature on the carbon textural properties, structure and surface chemistry were investigated. For several conditions, carbon materials with ordered pore size and high nitrogen content (up to 10.6 at %) could be achieved. The phase separation procedure combined with optimal amount of template favor the formation of ordered mesoporous carbons with higher specific surface area while the increase in the temperature induces a decrease in the surface area and amount of heteroatoms (N and O). The electrochemical performances as electrode in supercapacitors were evaluated in acidic medium and the capacitance was closely related to the material conductivity and surface chemistry. Full article