Nanoporous Carbon Samples Research Articles

Increase in H2 storage capacity of nanoporous carbon fabricated from waste rice husk via improving the mode of the reaction mixture cooling down

Nanoporous carbon (NPC) with high hydrogen storage capacity was fabricated from rice husk. The rice husk was activated using KOH, and the cooling step during the KOH activation process was varied. The specific surface areas, pore size distributions, and hydrogen storage capacities of the fabricated NPC samples were determined. We found that while the specific surface area did not change with the choice of the cooling process, the pore size distribution did. Furthermore, in the case of rapid cooling, the maximum hydrogen storage capacity at 77 K was 7.2 wt%, while that for natural cooling was 5.5 wt%. Thus, it can be concluded that the cooling procedure used during the KOH activation process determines the hydrogen storage properties of the thus-fabricated NPC materials.

Preparation and characterization of metal organic framework-derived nanoporous carbons for highly efficient removal of vanadium from aqueous solution

The highly nanoporous carbon (NPC) materials were synthesized by carbonizing highly crystalline MOF-199 with addition carbon precursors and without any carbon precursors. In addition, a novel NPC@CNT was fabricated by the use of multi-walled carbon nanotubes (CNT) as carbon precursors and MOF-199 as the template. The morphology, structure, and surface properties of the synthesized NPC samples were characterized in detail. The NPC materials were employed as adsorbents for the removal of vanadium (V) from aqueous media by batch process. The effects of principal operational parameters on the adsorption of V ions are investigated, and the reaction mechanism for this treatment technology is also proposed. In order to determine the controlling mechanism of the adsorption process, the adsorption isotherms, kinetics and thermodynamics parameters were examined. The V adsorption onto NPC adsorbents can be best described with Langmuir isotherm points out the homogeneous surface sites of NPCs and also the monolayer formation of V ions on the adsorbent outer surface. The kinetic batch experiments revealed that more than the V ions were absorbed onto the synthesized NPCs within 15 min, and the pseudo-second-order kinetic model could explain the adsorption process. The thermodynamic study indicated that the adsorption process was exothermic and spontaneous and the system disorder increased during the adsorption process. The adsorbents showed preferential V ions adsorption with the existence of co-existing cation (Ni2+) and anions (SO42− and NO3−). The V adsorbed NPCs were regenerated with an efficiency of greater than 95% using 0.5 M sodium hydroxide.

Controlled synthesis of tunable nanoporous carbons for gas storage and supercapacitor application

A simple methodology has been developed for the synthesis of functional nanoporous carbon (NPC) materials using a metal–organic framework (IRMOF-3) that can act as a template for external carbon precursor (viz. sucrose) and also a self-sacrificing carbon source. The resultant graphitic NPC samples (abbreviated as NPC-0, NPC-150, NPC-300, NPC-500 and NPC-1000 based on sucrose loading) obtained through loading different amounts of sucrose exhibit tunable textural parameters. Among these, NPC-300 shows very high surface area (BET≈3119m2/g, Langmuir≈4031m2/g) with a large pore volume of 1.93cm3/g. High degree of porosity coupled with polar surface functional groups, make NPC-300 remarkable candidate for the uptake of H2 (2.54wt% at 1bar, and 5.1wt% at 50bar, 77K) and CO2 (64wt% at 1bar, 195K and 16.9wt% at 30bar, 298K). As a working electrode in a supercapacitor cell, NPC-300 shows excellent reversible charge storage thus, demonstrating multifunctional usage of the carbon materials.

Effects of various Carbonization Processes in the Preparation of Nanoporous Carbon Materials using Ipomoea Carnea Stem Waste for the Removal of Dyes from Textile Industrial Effluents

Nanoporous activated carbon materials were prepared from abundantly available Ipomoea Carnea stem waste. A series of five Nanoporous carbon samples were prepared by subjecting the carbon material to various chemical processes. The physico-chemical properties and adsorption capacities were compared. The adsorption capacity of selected derived carbon sample using Ipomoea Carnea stem waste prepared by Dolomite process was much greater than the capacities of the other carbons prepared by various processes viz., Acid process, ZnCl 2 process, Sulphate process and Carbonate process. The influence of surface area and porosity of the carbon samples on dye removal was analysed. The effects and influence of pKa values of dyes and isoelectricpoint (pH zpc ) of Nanoporous carbon materials were broadly studied and interpreted with dye adsorption onto Nanoporous carbon material. The results reveal that the prepared activated carbon could be employed as a lowcost alternative for removing toxic and carcinogenic dyes from the textile industrial waste water.

Electrical and galvanomagnetic properties of nanoporous carbon samples impregnated with bromine

Nanoporous carbon samples with a large specific surface area can be filled with heavier elements or their compounds, which makes it possible to investigate the interaction of their electronic subsystems with carbon. One of the elements convenient for filling pores of carbon materials is bromine. Impregnation of nanoporous carbon samples with bromine causes the occurrence of the processes of micropore filling, monolayer adsorption, and intercalation. It has been found that samples impregnated with bromine substantially change their electrical and galvanomagnetic properties, and these changes depend on the structure of the samples. It has been shown that, if in the skeleton of a porous carbon sample there is a fraction of graphite clusters, the impregnation of the sample with bromine increases the concentration of charged carriers (holes). But when the sample has a quasi-amorphous structure, the injection of bromine into the sample leads to the appearance of a certain concentration of electrons in addition to charged mobile holes of the initial sample; i.e., the electrical conductivity becomes bipolar. In the former case, bromine molecules intercalate graphite clusters and, since bromine is an acceptor during intercalation of graphite, the hole concentration in the carbon skeleton network increases. In the latter case, bromine molecules can only be adsorbed on pore walls. As a result, the adsorption interaction between the electron shells of bromine molecules and the carbon surface leads to the formation of a donor layer near the surface and to the generation of electrons in the carbon skeleton network.

Magnetism of palladium clusters in nanoporous carbon

To determine the electronic properties of metal-carbon clusters, palladium clusters are introduced into nanoporous carbon samples. The structural and magnetic properties of the nanocomposite thus obtained are investigated. A ferromagnetic resonance (FMR) component is observed in the electron spin resonance (ESR) spectra measured in a wide temperature range. The electron density of states (DOS) of clusters consisting of a palladium atom surrounded by carbon atoms is calculated, and it is shown that, due to the interaction between electronic terms of carbon and metal, such a cluster should exhibit magnetism. The investigation of the structures of the porous skeleton of nanoporous carbon and of palladium clusters has allowed us to reveal how carbon and palladium atoms are brought into close contact so that to give rise to the observed ferromagnetism.

Development of Anion Stereoselective, Activated Carbon Molecular Sieve Electrodes Prepared by Chemical Vapor Deposition

The electrochemical properties of nanoporous, activated carbon cloth electrodes in NaCl and NaNO3 solutions were investigated before and after carbon chemical vapor deposition (CVD) on the high surface area of nanoporous carbon samples. Different CVD reagents, temperatures, and pressures were employed. We achieved a sharp ion sieving effect for CDV-treated carbon samples/electrodes by selecting a given CVD reagent (namely, benzene) and a temperature that was too low to affect chemical decomposition of benzene in the gaseous phase, but sufficiently high to enable its decomposition on the outer surface of the carbon substrate, to form surface carbon deposits. The electroadsorption stereo selectivity achieved by optimized CVD treatment was so sharp that clear discrimination could be obtained even between anions of very similar dimensions, such as Cl− and NO3−. Here, the nitrate behaves as the smaller entity since, being a planar ion, it fits better into the carbon micropores known to have slit-shaped pores. The CVD treatment affects mainly the mouths of the pores and not their interior/volume. This was proven by adsorption experiments. From the gas phase, the stereoselectivity obtained by these CVD treatments was also demonstrated by discrimination between the adsorption of CO2 and N2 into the CVD-treated activated carbon.

Palladium clusters in nanoporous carbon samples: Magnetic properties

The magnetic properties of nanoporous carbon samples were studied. The samples were prepared from silicon and boron carbides and contained palladium clusters incorporated into pores. Electron spin resonance (ESR) studies over a wide temperature range (3–100 K) showed that the palladium clusters have a significant effect on the electrical and magnetic characteristics of composite samples. In particular, the ESR spectrum of samples with palladium has a narrow line whose intensity varies with temperature following the Curie law, which indicates the formation of an ensemble of localized spins. Therefore, the hole conductivity of the carbon skeleton is partially compensated. The ESR spectra of C(SiC): Pd have a ferromagnetic resonance line, which suggests that some Pd clusters in pores are magnetically ordered. This line is absent in C(B4C)B: Pd samples. However, the small variation of the resonance frequencies with temperature indicates that the C(B4C): Pd samples also contain small magnetic inclusions.

Palladium clusters in nanoporous carbon samples: Structural properties

The structure of nanoporous carbon samples (prepared from silicon and boron carbides) with incorporated palladium clusters was studied. X-ray and electron diffraction studies show that most Pd clusters have an fcc lattice. Using small-angle X-ray scattering measurements, the metal cluster sizes are determined under certain assumptions. The sizes are not very close to the cluster sizes (4–14 nm) that are found from photomicrographs obtained using a transmission electron microscope (TEM). The difference is likely due to the local character of the TEM measurements. Apart from relatively coarse clusters of the sizes indicated above, the samples contain very small clusters, which are smaller in size than a micropore. Such small clusters are particularly large in number in C(SiC)B: Pd, where they are 0.5–0.7 nm in size. The content of small clusters in C(B4C)B: Pd is substantially lower, and they are somewhat larger in size (1.2–1.6 nm). The possible reasons of the ferromagnetism observed in these samples are discussed. It is assumed that the magnetism may be due to the small clusters, which do not have cubic symmetry.

Metal incorporation into nanoporous carbon

AbstractNanoporous carbon films were deposited by 248 nm pulsed laser ablation of a graphite target in different background pressures of argon (PAr). The morphology changed from smooth, high-density amorphous carbon films at PAr = 20 mTorr to ultra-low density nanoporous material at PAr = 380 mTorr. Subsequently, the nanostructural, chemical and electrical properties of metal containing nanoporous carbon samples were investigated by ablating graphite targets containing known contents of Ni and Co. We demonstrate how the ablation plume dynamics affect both the nanostructure of the material and the incorporation of metal atoms. The suitability of these functionalised ultra-low density materials for gas sensing applications is discussed.

Magnetic properties of nickel clusters in nanoporous carbon

The magnetic properties of nanoporous carbon samples whose pores were loaded by nickel are described. It is shown that a sample becomes superparamagnetic for temperatures T < T C (Ni) only in the case where a noticeable fraction of Ni is contained in the nanopores. The nanopore size estimated from magnetic measurements coincides with the estimates derived earlier from small-angle x-ray scattering studies. © 2003 MAIK "Nauka/Interperiodica".

Electrophysical studies of nanoporous carbon materials prepared of silicon carbide powders

Measurements of the electrophysical properties of nanoporous carbon (NPC) samples (conductivity and Hall effect), as well as studies of the same samples using electron spin resonance (ESR), are summarized. Free holes are shown to play the major part in charge transport in such materials, thus permitting identification of the ESR signal with free holes. An analysis of the shape of the resonance lines, as well as of their dependence on temperature and the technology employed in sample preparation, established the ESR signals to consist of two superimposed resonance lines associated with carriers, free or localized to various extents, whose magnetic susceptibility obeys Pauli and Curie-Weiss laws, respectively. The temperature dependences of the ESR signal parameters were studied, and the experimental relations were compared with theory to determine the model-parameters. An analysis of the temperature behavior of these parameters suggests the conclusion that NPC samples are heterophase porous systems whose properties are dominated by structural characteristics.

Small-angle x-ray scattering in a carbon-sulfur nanocomposite produced from bulk nanoporous carbon

A new nanocomposite material containing approximately 50 vol % S is prepared by filling pores of bulk nanoporous carbon samples with sulfur. The initial nanoporous carbon samples are synthesized from polycrystalline α-SiC through the chemical reaction. A comparative investigation of small-angle x-ray scattering (SAXS) is performed for the prepared nanocomposite and the initial material. The possible changes in the scattering power of the initial material upon filling of its pores with sulfur are considered in the framework of a simple model. The regularities revealed are used to interpret the experimentally observed changes in the scattering power. The size distribution functions of incorporated sulfur nanoclusters in the nanocomposite (or filled nanopores in the initial material) are determined within the Guinier approximation. It is demonstrated that the smallest sized pores (8–16 A) remain unfilled, whereas the filling factor for larger sized pores can reach several ten percent by volume. The conditions favorable for small-angle x-ray scattering upon filling of the nanopores are analyzed.

On fractal nature of the structure of nanoporous carbon obtained from carbides

The curves describing small-angle x-ray scattering at npor-C nanoporous carbon samples obtained from polycrystalline α-SiC, TiC, and Mo2C and a 6H-SiC single crystal have been analyzed. An algorithm is developed for taking into account the corrections to experimental curves for the intensity of the primary beam transmitted through the sample and the height of the inlet slit in these measurements. Two systems of nanoclusters observed in the npor-C structure differ in the type of stacking of structural elements: small-scale mass fractals of a dimension 1<D 2<3 and a size L 2=50–90 A, which depend on the type of the initial carbide, and large-scale nanoclusters having a size L 1>550 A. In most samples, large-scale nanoclusters can be regarded as objects with a fractal surface and a dimension 2<D 1<13, which also depends on the type of the initial carbide. Large-scale nanoclusters in npor-C obtained from Mo2C prove to be mass fractals with a dimension D 1>2. Peculiarities of the structure formation of nanoporous carbon obtained from various carbides are discussed.

Structural studies of nanoporous carbon produced from silicon carbide

X-ray diffraction and small-angle scattering study of nanoporous carbon samples prepared from polycrystalline α SiC and single-crystal 6H SiC is reported. The distribution function of carbon nanoclusters in size was found. In α SiC samples, the small size (10–12 A) of nanoclusters is combined with their high size uniformity. Graphite-like nanoclusters 30–60 A in size were found in samples of both types. In 6H SiC samples, such clusters make up a notable fraction of the volume. The experimentally observed structural anisotropy of the samples is discussed.