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Browsing Bioenergia - UB by Subject "Acetaminophen adsorption"
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- Carbon-based materials prepared from pine gasification residues for acetaminophen adsorptionPublication . Galhetas, M.; Mestre, A. S.; Pinto, Moisés L.; Gulyurtlu, Ibrahim; Lopes, Helena; Carvalho, A. P.Fly ash, a residue produced frompine gasification,was used as precursor of carbon-basedmaterials assayed in acetaminophen adsorption. Materials prepared by activation with K2CO3, presented high porosity development (ABET 1200m2 g1) and samples calcined at 900 C presented high volumes of large micropores and mesopores. Kinetic and equilibrium acetaminophen adsorption data showed that the process obeys to the pseudo-second order kinetic equation and Langmuir model, respectively. The rate of acetaminophen adsorption depends of the presence of larger micropores. For the lab-made samplesmonolayer adsorption capacities attained values similar to those of commercial carbons. The influence of themicropore size distribution of the carbons in the acetaminophen adsorption process justified the lower adsorption affinities of the lab-made carbons. The importance of pores of a specific dimension (0.7 nm) to enhance the affinity of the molecule towards the carbon surfacewas demonstrated. The increase of temperature lead to highermonolayer adsorption capacities, most likely due to the easier accessibility of the acetaminophen species to the narrowest micropores.
- Chars from gasification of coal and pine activated with K2CO3: Acetaminophen and caffeine adsorption from aqueous solutionsPublication . Galhetas, M.; Mestre, A. S.; Pinto, Moisés L.; Gulyurtlu, Ibrahim; Lopes, Helena; Carvalho, A. P.The high carbon contents and low toxicity levels of chars from coal and pine gasification provide an incentive to consider their use as precursors of porous carbons obtained by chemical activation with K2CO3. Given the chars characteristics, previous demineralization and thermal treatments were made, but no improvement on the solids properties was observed. The highest porosity development was obtained with the biomass derived char (Pi). This char sample produced porous materials with preparation yields near 50% along with high porosity development (ABET 1500 m2 g1). For calcinations at 800 C, the control of the experimental conditions allowed the preparation of samples with a micropore system formed almost exclusively by larger micropores. A mesopore network was developed only for samples calcined at 900 C. Kinetic and equilibrium acetaminophen and caffeine adsorption data, showed that the processes obey to a pseudo-second order kinetic equation and to the Langmuir model, respectively. The results of sample Pi/1:3/800/2 outperformed those of the commercial carbons. Acetaminophen adsorption process was ruled by the micropore size distribution of the carbons. The caffeine monolayer capacities suggest a very efficient packing of this molecule in samples presenting monomodal micropore size distribution. The surface chemistry seems to be the determinant factor that controls the affinity of caffeine towards the carbons.
- The influence of the textural properties of activated carbons on acetaminophen adsorption at different temperaturesPublication . Galhetas, M.; Andrade, Marta A.; Mestre, A. S.; Kangni-foli, Ekoé; Brito, Maria J. Villa de; Pinto, Moisés L.; Lopes, Helena; Carvalho, A. P.The influence of temperature (20–40 °C) on the acetaminophen adsorption onto activated carbons with different textures was studied. Different temperature dependences, not explained by kinetic effects, were observed for carbons with different micropore size distribution patterns: adsorption capacity increased for pine gasification residues (Pi-fa) derived carbons and decreased for sisal based materials. No significant variation was seen for carbon CP. The species identified by 1H NMR spectroscopy on the back-extraction solution proved that during the adsorption process exist the conditions required to promote the formation of acetaminophen oligomers which have constrained access to the narrow microporosity. The rotation energy of the dihedral angle between monomers (estimated by electronic DFT methods) showed that conformations in the planar form are less stable than the non-planar conformation (energy barrier of 70 and 23 kJ mol-1), but have critical dimensions similar to the monomer and can access most of the micropore volume. The enthalpy change of the overall process showed that the energy gain of the system (endothermic) for Pi-fa samples (˜40 kJ mol-1) was enough to allow a change in the dimer, or even a larger oligomer, conformation to the planar form. This will permit adsorption in the narrow micropores, thus explaining the uptake increase with temperature. Non-continuous micropore size distributions centered at pore widths close to the critical dimensions of the planar form seem to be crucial for a positive evolution of the adsorption capacity with temperature.