RESUMO
Waste of Mytella falcata shell was used as low-cost adsorbent to remove the biocide Basic Green 4 (BG4) from water. Shells were collected form trash nearby the lagoon were Mytella falcata is fished. After clean, dry and crushed, the powder was characterized by scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FT-IR), X-ray powder diffraction (XRD), and X-ray dispersive energy spectroscopy (EDS). Both kinetic and equilibrium adsorption tests are carried out. Adsorbent regenerability was tested during adsorption/desorption cycles, using a UV photo-regeneration process. The maximum adsorption capacity reached 539.24 mg.g-1 (60 °C), which was higher than those retrieved for other materials with similar origin. The kinetic results indicated that the process followed pseudo-second order model. Equilibrium data indicate an increase in BG4 adsorption capacity with temperature and Sips model had better fit for all the investigated temperatures (30, 40, 50 and 60 °C). The regeneration/reuse test indicated that the adsorbent is able to assure a BG4 removal above 70 % during five adsorption/desorption cycles evaluated. Thermodynamic parameters suggested that adsorption is spontaneous, endothermal, governed by chemisorption and with structural changes in the solid surface upon adsorption.
Assuntos
Desinfetantes , Poluentes Químicos da Água , Adsorção , Concentração de Íons de Hidrogênio , Cinética , Regeneração , Espectroscopia de Infravermelho com Transformada de Fourier , Termodinâmica , Águas Residuárias , Água , Poluentes Químicos da Água/análiseRESUMO
: In this study, the mechanisms of methylparaben adsorption onto activated carbon (AC) are elucidated starting from equilibrium and thermodynamic data. Adsorption tests are carried out on three ACs with different surface chemistry, in different pH and ionic strength aqueous solutions. Experimental results show that the methylparaben adsorption capacity is slightly affected by pH changes, while it is significantly reduced in the presence of high ionic strength. In particular, methylparaben adsorption is directly dependent on the micropore volume of the ACs and the π- stacking interactions, the latter representing the main interaction mechanism of methylparaben adsorption from liquid phase. The equilibrium adsorption data are complemented with novel calorimetric data that allow calculation of the enthalpy change associated with the interactions between solvent-adsorbent, adsorbent-adsorbate and the contribution of the ester functional group (in the methylparaben structure) to the adsorbateâ»adsorbent interactions, in different pH and ionic strength conditions. It was determined that the interaction enthalpy of methylparaben-AC in water increases (absolute value) slightly with the basicity of the activated carbons, due to the formation of interactions with π- electrons and basic functional groups of ACs. The contribution of the ester group to the adsorbate-adsorbent interactions occurs only in the presence of phenol groups on AC by the formation of Brønstedâ»Lowry acidâ»base interactions.
Assuntos
Adsorção/efeitos dos fármacos , Parabenos/química , Termodinâmica , Poluentes Químicos da Água/química , Calorimetria , Carbono/química , Carvão Vegetal/química , Fenóis/química , Solventes/química , Água/química , Poluentes Químicos da Água/toxicidadeRESUMO
In this work, equilibrium and dynamic adsorption tests of cadmium Cd (II) on activated carbons derived from different oxidation treatments (with either HNO3, H2O2, or NaOCl, corresponding to GACoxN, GACoxP, and GACoxCl samples) are presented. The oxidation treatments determined an increase in the surface functional groups (mainly the acidic ones) and a decrease in the pHPZC (except for the GACoxCl sample). A slight alteration of the textural parameters was also observed, which was more significant for the GACoxCl sample, in terms of a decrease of both Brunauer-Emmett-Teller (BET) surface area and micropore volume. Adsorption isotherms were determined for all the adsorbents and a significant increase in the adsorption performances of the oxidized samples with respect to the parent material was observed. The performances ranking was GACoxCl > GACoxP > GACoxN > GAC, likely due to the chemical surface properties of the adsorbents. Dynamic tests in a fixed bed column were carried out in terms of breakthrough curves at constant Cd inlet concentration and flow rate. GACoxCl and GACoxN showed a significantly higher value of the breakpoint time, likely due to the higher adsorption capacity. Finally, the dynamic tests were analyzed in light of a kinetic model. In the adopted experimental conditions, the results showed that mass transfer is controlled by internal pore diffusion, in which surface diffusion plays a major role.
Assuntos
Cádmio/química , Carvão Vegetal/química , Adsorção , Cátions Bivalentes/química , Cromatografia Líquida , Difusão , Concentração de Íons de Hidrogênio , Cinética , Modelos Químicos , Oxirredução , Porosidade , Solventes , Propriedades de Superfície , Temperatura , TermodinâmicaRESUMO
Paracetamol adsorption in acidic, neutral and basic media on three activated carbons with different chemistry surfaces was studied. A granular activated carbon (GAC) was prepared from coconut shell; starting from this sample, an oxidized activated carbon (GACo) was obtained by treating the GAC with a boiling solution of 6 M nitric acid, so to generate a greater number of oxygenated surface groups. In addition, a reduced activated carbon (GACr) was obtained by heating the GAC at 1173 K, to remove the oxygenated surface groups. Paracetamol adsorption was higher for GACr due to the lower presence of oxygenated surface functional groups. Moreover, adsorption was highest at neutral pH. The magnitude of the interactions between paracetamol molecules and activated carbons was studied by measuring the immersion enthalpies of activated carbons in solution of paracetamol at different concentrations and pH values and by calculating the interaction enthalpy. The highest value was obtained for GACr in a paracetamol solution of 1000 mg L-1 at pH 7, confirming that paracetamol adsorption is favoured on basic activated carbons at pH values near to neutrality. Finally, the Gibbs energy changes confirmed the latter result, allowing explaining the different magnitudes of the interactions between paracetamol and activated carbons, as a function of solution pH.