Artur P. Terzyk

The influence of activated carbon surface chemical composition on the adsorption of acetaminophen (paracetamol) in vitro: Part II. TG, FTIR, and XPS analysis of carbons and the temperature dependence of adsorption kinetics at the neutral pH

Abstract The presented paper is the subsequent one of the series concerning the results of the influence of carbon surface chemical composition on paracetamol adsorption from water solutions. The non-modified de-ashed commercial carbon D43/1, (Carbo-Tech, Essen, Germany) as well as modified ones (using conc. nitric acid, fuming sulphuric acid, ammonia, and modified via ionic exchange process with Cu2+) were used as adsorbents. For these, characterised previously, carbons the results of some additional measurements, i.e. thermogravimetry in He and in air, FTIR, and XPS are reported, to expose the type of carbon surface groups created by chemical modifications. The results of kinetic measurements (performed at three temperatures: 300, 310 and 320 K) are reported. They were described using very simple kinetic equation proposed by Korta and co-workers; moreover, this equation has been modified in the current paper. It is shown that, up to the relative adsorption value equal to 0.5 the kinetics of the process of paracetamol adsorption is determined by the hydrophilicity of carbon surface. The rate of this process increases linearly with the values of the enthalpy of carbon immersion in water. Moreover, for all the carbons, except for the modified one with Cu2+, the rate of adsorption is determined by the presence of surface groups and it increases with the total acidity of carbon.

Estimation of the pore-size distribution function from the nitrogen adsorption isotherm. Comparison of density functional theory and the method of Do and co-workers

A comparative analysis of the results for the estimation of the pore-size distribution based on the methods of Do and co-workers (ND) and density functional theory (DFT) is given. A new algorithm (ASA, Adsorption Stochastic Algorithm) is adopted and it is shown that this algorithm can be successfully applied for the determination of the PSD curve from the ND method. The obtained results show that, generally, the ND and DFT methods lead to almost the same PSD curves and this similarity is observed for carbons of different origin and possessing different pore structures. However, if the contribution of micropores to the PSD increases, the differences in the fit of ND and DFT to the experimental data are more pronounced.

Thermally modified active carbon as a support for catalysts for NH3 synthesis

The effect of thermal treatment of a typical active carbon at 1300 °C and 1900 °C on its structural properties was investigated. It has been found that only a high-temperature heating (1900 °C) produced substantial changes in the structure of the carbon used: a disappearance of a considerable part of open micropores and formation of a turbostratic structure. The prepared materials were used as a support in catalysts for NH3 synthesis. The precursor of the active phase was Fe(NO3)3 · 9H2O. The iron nitrate deposited on the raw amorphous carbon decomposes to finely dispersed, hardly reducible iron oxides on heating to 470 °C in a H2 + N2 mixture. Even if reduced to more than 33%, iron is inactive in NH3 synthesis (400–470 °C, p = 10MPa). When deposited on the turbostratic, low-surface area carbon, iron forms, however, well developed crystallites (~60 nm), and is active in ammonia synthesis. Potassium activates strongly the surface of Fe, and, in the case of the amorphous support, it stimulates the reduction of iron oxides.

What kind of pore size distribution is assumed in the Dubinin-Astakhov adsorption isotherm equation?

Abstract Two most sophisticated methods of carbon porosity characterization (high resolution αs-plot and the procedure proposed by Nguyen and Do, (ND)) were utilized for the assessment of porosity from the series of numerically generated adsorption isotherms. Basing on the Dubinin–Astakhov (DA) adsorption isotherm equation, two series of adsorption isotherms of nitrogen (T=77.5 K) were generated for constant E0 and different n values, and for constant n and different E0. They were described by the both above-mentioned methods. The types of obtained αs-plots as well as the pore size distribution curves (PSD) lead to suggestions about the basic features of the DA and the meaning of the parameters of this adsorption isotherm equation.

The influence of activated carbon surface chemical composition on the adsorption of acetaminophen (paracetamol) in vitro: The temperature dependence of adsorption at the neutral pH

Abstract The in vitro adsorption and desorption of acetaminophen from water solution on four activated carbons at three temperatures (300, 310 and 320 K) and at the neutral pH (7) were investigated. The carbons were characterized using the low temperature nitrogen adsorption, the mercury porosimetry, Bachmann’s method, Boehm’s method as well as the water immersion calorimetry. As an initial adsorbent, the de-ashed-commercial, ‘non-modified’ carbon D43/1 (Carbo-Tech, Essen, Germany) was applied. To change the chemical composition of its surface, concentrated nitric and sulfuric acids as well as gaseous ammonia were applied as chemical modificators. The acetaminophen adsorption and desorption isotherms on the ‘non-modified’ as well as on the chemically modified carbons were measured, together with the enthalpy of immersion in paracetamol solution. It is shown that, generally, for all the investigated carbons, acetaminophen adsorption increases with temperature. A slightly marked hysteresis on adsorption–desorption isotherms was observed at higher adsorption values. Among the applied procedures of the changing of carbon surface chemical composition, the modification with fuming sulphuric acid leads to the increase in paracetamol adsorption, whilst the opposite effect is observed for the carbon modified with concentrated nitric acid. The modification in the stream of ammonia practically does not change the adsorption properties towards paracetamol. The changes in the adsorption properties of carbons after modification are analysed using isotherms, adsorbability, relative enthalpy of displacement as well as the values of the integral enthalpy of adsorption. To calculate this enthalpy the solubility of acetaminophen in the investigated range of temperatures was determined, and the enthalpy of solution at infinite dilution was calculated using Abraham’s method.

Developing the solution analogue of the Toth adsorption isotherm equation

The well-known Toth adsorption isotherm equation developed formerly for adsorption of vapors is converted into its solution analogue. It is shown that this equation can be successfully applied to the description of adsorption data of organics on activated carbons.

Catalytic conversion of ethanol on carbon catalysts

The decomposition of ethanol was studied using carbon catalysts with a different nature of the surface. They were prepared from poly(furfuryl alcohol). The catalytic tests were performed in a flow reactor in the temperature range 323–633 K. Dehydration and dehydrogenation of ethanol, as well as acetal formation, occur under the conditions applied. The products are ethene plus diethyl ether, acetaldehyde and l,l′-diethoxyethane, respectively. The study supports previous findings that oxidation with nitric acid enhances dehydration activity and selectivity, whereas introduction of Ni2+ ions increases dehydrogenation activity and selectivity. The supported Ni2+ cations, in the hydrated form, act as additional active centers for dehydrogenation. In addition, both these surface modifications also enhance carbon catalytic activity and selectivity for the acetal formation. The acetal results from a secondary reaction between the formed acetaldehyde and ethanol on acidic centers located on the outer surface of the catalyst.

Can carbon surface oxidation shift the pore size distribution curve calculated from Ar, N2 and CO2 adsorption isotherms? Simulation results for a realistic carbon model

Using the virtual porous carbon model proposed by Harris et al, we study the effect of carbon surface oxidation on the pore size distribution (PSD) curve determined from simulated Ar, N(2) and CO(2) isotherms. It is assumed that surface oxidation is not destructive for the carbon skeleton, and that all pores are accessible for studied molecules (i.e., only the effect of the change of surface chemical composition is studied). The results obtained show two important things, i.e., oxidation of the carbon surface very slightly changes the absolute porosity (calculated from the geometric method of Bhattacharya and Gubbins (BG)); however, PSD curves calculated from simulated isotherms are to a greater or lesser extent affected by the presence of surface oxides. The most reliable results are obtained from Ar adsorption data. Not only is adsorption of this adsorbate practically independent from the presence of surface oxides, but, more importantly, for this molecule one can apply the slit-like model of pores as the first approach to recover the average pore diameter of a real carbon structure. For nitrogen, the effect of carbon surface chemical composition is observed due to the quadrupole moment of this molecule, and this effect shifts the PSD curves compared to Ar. The largest differences are seen for CO(2), and it is clearly demonstrated that the PSD curves obtained from adsorption isotherms of this molecule contain artificial peaks and the average pore diameter is strongly influenced by the presence of electrostatic adsorbate-adsorbate as well as adsorbate-adsorbent interactions.

The comparative characterization of structural heterogeneity of mesoporous activated carbon fibers (ACFs)

The comparative analysis of the most widely used methods of mesoporosity characterization of two activated carbon fibers is presented. Not only the older methods are used, i.e. Barrett, Joyner and Halenda (BJH), Dubinin (the so-called first variant-D-1ST and the so-called second variant-D-2ND), Dollimore and Heal (DH), and Pierce (P) but the recently developed ones, i.e. the method of Nguyen and Do (ND) and that developed by Do (Do) are also applied. Additionally, the method of the characterization of fractality is put to use (fractal analog of FHH isotherm). The results are compared and discussed

Pillared graphene as a gas separation membrane

Graphene and carbon nanotubes are considered as future materials in various fields, including adsorption, accumulation and separation processes, and so are hybrid materials combining their properties. This paper reports our study on separative abilities of 3-D network structures consisting of graphene planes pillared with nanotube fragments. Results of molecular dynamics simulations confirm that such materials can be successfully applied as membranes in relation to noble gas mixtures. A simple explanation of the mechanism underlying the process is proposed.