Jerzy Włoch

Novel nitrogen-containing mesoporous carbons prepared from chitosan

In this study, synthesis of novel nitrogen-containing mesoporous carbons with the use of both colloidal silica as a template and chitosan as a new promising carbon precursor was performed. The prepared materials were characterized by adsorption of nitrogen, high-resolution transmission electron microscopy (HR-TEM), scanning electron microscopy, Raman spectroscopy, and elemental analysis. The use of the silica template makes it possible to achieve products of the pore volume as high as 4.31 cm3 g−1, with only insignificant contribution of microporosity. The present method enables the synthesis of nitrogen-containing carbons in a simple manner, using an inexpensive and readily available biopolymer.

MD simulation of organics adsorption from aqueous solution in carbon slit-like pores. Foundations of the pore blocking effect

The results of systematic studies of organics adsorption from aqueous solutions (at the neutral pH level) in a system of slit-like carbon pores having different sizes and oxygen groups located at the pore mouth are reported. Using molecular dynamics simulations (GROMACS package) the properties of adsorbent-adsorbate (benzene, phenol or paracetamol) as well as adsorbent-water systems are discussed. After the introduction of surface oxygen functionalities, adsorption of organic compounds decreases (in accordance with experimental data) and this is caused by the accumulation of water molecules at pore entrances. The pore blocking effect decreases with the diameter of slits and practically vanishes for widths larger than approx. 0.68 nm. We observed the increase in phenol adsorption with the rise in temperature. Moreover, adsorbed molecules occupy the external surface of the slit pores (the entrances) in the case of oxidized adsorbents. Among the studied molecules benzene, phenol and paracetamol prefer an almost flat orientation and with the rise in the pore width the number of molecules oriented in parallel decreases. The decrease or increase in temperature (with respect to 298 K) leads to insignificant changes of angular orientation of adsorbed molecules.

Al-MCM-41 modified with carbonaceous deposits : Characterisation by nitrogen adsorption measurements

Aluminosilicate MCM-41 samples in the as-prepared form and modified by deposition of carbonaceous compounds formed during conversion of cyclohexene were investigated by nitrogen adsorption. The amount of the deposits decreases with the reaction temperature and increases with the quantity of aluminium incorporated into the materials. The formation of coke occurs primarily in the aluminium-rich pores. The modification leads to a lowering of adsorption capacity, surface area, pore volume and relative pressure corresponding to the adsorption isotherm step that reflects the capillary condensation. The nitrogen adsorption measurements appeared to be a useful tool for characterisation of structural and surface properties of both the original and the novel surface-modified porous materials.

Water adsorption property of hierarchically nanoporous detonation nanodiamonds

The detonation nanodiamonds form the aggregate having interparticle voids, giving a marked hygroscopic property. As the relationship between pore structure and water adsorption of aggregated nanodiamonds is not well understood yet, adsorption isotherms of N2 at 77 K and of water vapor at 298 K of the well-characterized aggregated nanodiamonds were measured. HR-TEM and X-ray diffraction showed that the nanodiamonds were highly crystalline and their average crystallite size was 4.5 nm. The presence of the graphitic layers on the nanodiamond particle surface was confirmed by the EELS examination. The pore size distribution analysis showed that nanodiamonds had a few ultramicropores with predominant mesopores of 4.5 nm in average size. The water vapor adsorption isotherm of IUPAC Type V indicates the hydrophobicity of the nanodiamond aggregates, with the presence of hydrophilic sites. Then the hygroscopic nature of nanodiamonds should be associated with the surface functionalities of the graphitic shell and the ultramicropores on the mesopore walls.

Water nanodroplet on a graphene surface-a new old system.

The major subject of our study is the accuracy of contact angle calculations. Reporting new simulation data for graphene-water systems, we show that the majority of previously reported data should be treated with caution, since the proper contact angle can be recorded only after a sufficiently long simulation time. It has been proven that-if one wants to gain accuracy greater than 0.1°-long calculations (exceeding 50 ns) are required. Finally, we also show, using both a Groningen Machine for Chemical Simulations (GROMACS) package and our new molecular dynamics (MD) code, that the changes in the contact angle, caused by graphene bottom layer rotation, are within the range of calculation error. We also propose a novel definition of the bottom of the droplet as the height where the density is half the density of liquid water. This new definition is applied in the method of the contact angle calculation from the MD simulation data.

Nitrogen-containing carbon replicas of SBA-15 and MLV prepared from pyrrole as carbon precursor

The nitrogen-containing carbonaceous replicas of siliceous materials were prepared and studied with the nitrogen adsorption, TEM, TGA, XPS, and EDX methods. The carbons obtained using SBA-15 as a matrix exhibited well-developed and highly ordered porous structures. Those from the MLV material showed lower sorption capacities and 3-D structures less ordered as in the case of the SBA-15 replicas.

Al-MCM-48 as a template for synthesis of porous carbons-adsorption study

Porous carbons were prepared by polymerisation and subsequent carbonisation of furfuryl alcohol adsorbed on mesoporous Al-MCM-48 molecular sieves. The carbonaceous products were examined with XRD, TEM, and adsorption. The carbons exhibited a developed mesoporous structure with a contribution of micropores. The adsorption isotherms of nitrogen, benzene, ethanol, and water provided information on mechanisms of the adsorption processes.

Sorption properties and search for correlations between analytical parameters of sorption and content of metal in MeAPO-5 containing V or Zr

Abstract The sorption isotherms of H 2 O, C 6 H 6 and N 2 on large crystals of MeAPO-5 indicate that sorption characteristics of VAPO-5 containing V 4+ /V 5+ are similar to that of other derivatives with Me 2+ or Me 3+ . Higher contents of Zr 4+ cause formation of extraframework Zr phosphates at the external surface of the crystals and an apparent decrease of adsorption potentials. The dependence of the potentials on Me contents appears to be uniform for all studied Me n+ ions.

Equation of the sorption isotherme on zeolite Y including heterogeneity of the sorbent: a novel modification

The complex character of water vapour sorption on zeolite Y has been demonstrated. It has been found that the assumptions of the Dubinin theory of volume filling of micropores (TVFM) are applicable to the description of such water vapour sorption. An equation for the adsorption isotherm is given which describes the experimental data in a satisfactory manner and which includes both the heterogeneity of the zeolite surface and the size distribution of the micropores participating in the sorption process. The equation yields realistic values of the total micropore volume which are close to the experimental sorption capacities. A significant effect of the sodium counterions on the sorption of water vapour has been found.

Preparation and catalytic characterisation of Al-grafted MCM-48 materials

Samples of Al-MCM-48 were prepared by grafting Al onto the pure siliceous material and used as catalysts for cumene cracking and conversion of 2-propanol. The former reaction yielded mainly benzene and propene, which indicated the presence of strong Bronsted acid sites in the catalysts. The conversion of 2-propanol resulted mainly in dehydration of the substrate, yielding propene and diisopropyl ether. The catalytic activity of Al-MCM-48 grew with both the Al content and reaction temperature. The concentrations of the Bronsted and Lewis acid sites increased with the Al content of the material as well.