J.M. Valente Nabais

Phenol removal onto novel activated carbons made from lignocellulosic precursors: influence of surface properties.

The adsorption of phenol from dilute aqueous solutions onto new activated carbons (AC) was studied. The novel activated carbon was produced from lignocellulosic (LC) precursors of rapeseed and kenaf. Samples oxidised with nitric acid in liquid phase were also studied. The results have shown the significant potential of rapeseed and kenaf for the activated carbon production. The activated carbons produced by carbon dioxide activation were mainly microporous with BET apparent surface area up to 1350 m(2)g(-1) and pore volume 0.5 cm(3)g(-1). The effects of concentration (0.1-2 mM) and pH (3-13) were studied. The phenol adsorption isotherms at 25 degrees C followed the Freundlich model with maximum adsorption capacities of approximately 80 and 50 mg g(-1) for the pristine and oxidised activated carbons, respectively. The influence of pH on the adsorption has two trends for pH below and above 10. It was possible to conclude that when phenol is predominantly in the molecular form the most probable mechanism is based on the pi-pi dispersion interaction between the phenol aromatic ring and the delocalised pi electrons present in the activated carbon aromatic structure. When phenolate is the major component the electrostatic repulsion that occurs at high pH values is the most important aspect of the adsorption mechanism.

Development of easy made low cost bindless monolithic electrodes from biomass with controlled properties to be used as electrochemical capacitors

The aim of the work now reported is the development of low cost electrodes in the monolithic shape without the need for a pos-production step with potential to be used in supercapacitors. The tested materials were activated carbon fibres prepared and activated carbons made from coffee endocarp. The main functional groups identified were quinone, lactone, Si-H, phenol, hydroxyl, carbonyl and ether for activated carbon samples and amine, amide, pyrone, lactone, carbonyl and hydroxyl for activated carbon fibres samples. The nanostructure of the materials is predominantly microporous but with a significant variety of porosity development with BET surface area and pore volume given by α(s) method range from 89 to 1050 m(2) g(-1) and 0.04 to 0.50 cm(3) g(-1), respectively. The electrochemical properties of the materials were investigated using classic cyclic voltammetry, chronopotentiometry and electrochemical impedance spectroscopy. The higher specific capacitance achieved was 176 F g(-1).

Characterisation of Surface Ionisation and Adsorption of Phenol and 4-Nitrophenol on Non-porous Carbon Blacks

The adsorption of phenol and 4-nitrophenol from aqueous solutions by carbon blacks was studied. Particular attention was paid to the characterisation of the surface chemistry and ionisation of the carbon blacks by use of a simple carbon surface ionisation model, as well as the use of a normalised form of the Freundlich equation for the analysis of the adsorption isotherms. The results indicated that the solutes interact directly with the graphene layers and that the adsorption is sensitive to the π-electron density. Phenol has a weaker interaction and is more sensitive to the system conditions. In particular, it is more sensitive to oligomerisation under certain conditions. Comparison of the results with those previously reported for activated carbons with similar points of zero charge prepared from cork confirms the existence of a significant micropore-narrowing effect in the adsorption of organic solutes by activated carbons and which can lead to up to a doubling of the value of the Freundlich exponent, nF.

Removal of Amitriptyline from Aqueous Media Using Activated Carbons

This paper reports the removal of amitriptyline, a widely used tricyclic anti-depressant, from aqueous solutions by six activated carbons produced from cork, coffee endocarp and eucalyptus pulp. The results of this study showed that samples from cork and eucalyptus pulp, activated at 800 °C, exhibited the highest adsorption capacity of 120 mg/g and 110 mg/g, respectively. Samples produced from coffee endocarp showed the lowest capacity. Amitriptyline adsorption was almost independent of the pH of the solution and occurred via three different mechanisms based on the dispersive and chemical interactions between amitriptyline molecules and the carbon surface.

Characterization of the surface of activated carbons produced from tire residues

The surface characterisation of new activated carbons produced from tire residues by activation with carbon dioxide was studied. The activated carbons produced were mainly basic with point of zero charge values above 8.8. The main surface functional groups identified by FTIR were ether, quinones, lactones, ketones, hydroxyls (free and phenol) and pyrones. The XRD analysis shows that the materials produced have a microstructural organisation with microcrystallite height around 1.5nm and width from 3 to 5.3nm. This analysis indicates also the possible presence of oxides (single or mixture) of the following heteroatoms: Fe, Al, Ca, Mg, Ti, Si, K, Pb, Cd, Ba, Zn and Sn. The results have shown the significant potential of this type of residues for activated carbon production. Furthermore, the environment friendly use of an industrial residue is also noteworthy.

Structural Characterisation and Mechanical Stability of Titanium Substituted Mesoporous Materials

Mesoporous silica and titanium SBA-15 samples with different Si/Ti molar ratio were prepared by direct one-step synthesis under strongly acidic hydrothermal conditions. The materials were characterised by X-ray diffraction, nitrogen adsorption at 77K. The Si/Ti values of the final calcined materials were determined by ICP analysis. It was found that all samples presented 2-D hexagonal structures with high degree of ordering. However, the metal content incorporated in all titanium mesoporous materials was very low, i.e., the Si/Ti molar ratio values of the final calcined samples are significantly different from the initial Si/Ti molar ratio in the synthesis gel. A study of mechanical stability in air was performed by exposing the calcined samples to a unidirectional external pressure in the range 74-814MPa. X-ray diffraction and nitrogen adsorption at 77K, on selected compacted samples, were used in order to evaluate the changes in mesoporous structure. It was found that, for all freshly calcined pure silica and titanium containing samples tested, the high quality SBA-15 structure is still observed after the application 148-370MPa of a unidirectional external pressure and the collapse of the pore structure occurs at around 814MPa.

Ordered Mesoporous Titanosilicate Materials Prepared at Room Temperature: Synthesis Conditions vs Structural Properties

Mesoporous titanosilicates were directly synthesised at ambient temperature and pressure, considering a wide range of metal content (0.01≤Ti/Si≤0.5) and using cationic surfactants of different alkyl chain length. It is shown that the use of tetradecyl-, hexadecyl- and octadecyltrimethylammonium bromide as structure-directing agents provide higher quality Ti-MCM-41 materials, than those prepared with surfactants of shorter alkyl chain. The pore volume and surface areas are gradually reduced by the increase of Ti content but up to Ti/Si=0.02 the alterations in the pore structural properties are negligible as compared with pure silica grades, becoming more noticeable for Ti/Si≥0.1. Nevertheless, for Ti/Si=0.1 the directly synthesised materials still have high pore volumes as well as high regularity and uniformity of the hexagonal pore array, with superior pore structural properties to those of materials prepared by post synthesis deposition of titanium on silica MCM-41, which did not provide a valid alternative for minimising the disruptive effect of high metal content on the hexagonal porous structure.

Development of Monolithic Materials with and without a Binder with Carbon Molecular Sieving Properties

In this work we studied the production of activated carbon fibres in monolith shape from a commercial textile acrylic fibre. The monoliths were produced with and without a binder. The binders tested were phenolic resin, polystyrene, polymethylmethacrylate and clay. We also tested the influence of using a solvent. The SEM analysis indicates that the monoliths are made of filaments that can be considered activated carbon fibres. The type of binder influences the fibre orientation, degradation and materials shrinkage, the worst results being obtained from the use of polymethylmethacrylate and polystyrene in toluene. The best results are obtained when the monoliths were produced only with acrylic fibre and with phenolic resin as binder. The use of solvents has opposite effects for the carbonised and activated samples. In the former case it seems that the water can be fibre protective but during activation the presence of water leads to an increase in the monolith’s burn-off. The methodology used leads to the formation of excellent samples for performing the gas separations O2/N2 and CO2/CH4. Some samples show maximum selectivity for the referred separations because N2 and CH4 are almost totally excluded from the porous structure which indicates a good potential to be utilised in PSA systems or for natural gas purification. The adsorption capacity is very dependent on the conditions used. Nevertheless, the best sample has a considerably high adsorption capacity (32cm3g-1 for CO2 and 4cm3g-1 for O2, after 200s contact time).