| dc.description.abstract | Mesoporous carbons with the same structure (2D hexagonal p6mm and 3D cubic/tetragonal (Ia3 ̅d/ I41/a) ) were synthesized by the strategies of nanocasting and simple one-pot, and used for the adsorption of dyes. The goal was to compare the pore structure difference between the carbon materials synthesized by these two strategies, and investigate how these structure difference effect the adsorption of different dyes. Especially how the pore structure in two dimensions and three dimensions effected the adsorption of different molecule size dyes (such as small size methylene blue with 1D chain structure and large size victoria blue with 3D structure). In addition, we used another dye molecule with zero net charge, such as sudan red G, to investigate how the charge on the pore surface of mesoporous carbons effected the adsorption properties.
For the adsorption of methylene blue with 1D small molecule size, we found that no matter the pore structure of mesoporous carbons was in two dimensions or three dimensions, generally the bigger the pore surface area, the larger the adsorption capacity for the dye. After analyzing the adsorption isotherm data by the Langmuir and Freundlich models, we also found that they could be better described by the Langmuir model. The pore surface area of carbon materials was therefore the main factor for adsorption of small-size methylene blue.
In contrast, for the adsorption of victoria blue with 3D large molecule size, the adsorption capability was mainly dependent on the pore volume and the pore structure of the materials. The structure of 3D tetragonal (I41/a) mesoporous carbons all had different degree of phase transformation as revealed from XRD and N2 adsorption results, indicating that their pore structure were more complicated than the mesoporous carbons with 2D hexagonal (p6mm) symmetry. As a result, their adsoption capacities and adsorption velocities all dramatically decreased. On the other hand, due to phase transformation might produce more pores with much bigger size and result in bimodal porosity, our results also indicated that the higher the degree of bimodal porosity, the more complicated the pore structure, and therefore the less the adsorption capability for large-size victoria blue.
As for the adsorption of sudan red G with zero net charge on mesoporous carbons, it was found that the electrostatic attraction between the pore surface and dye molecules was the determinative factor for the better adsorption of last two dyes with positive charge, suggesting that the charge on the pore surface of carbon materials might greatly contribute to its adsorption capability for dyes.
In addition, after analyzing experimental data by the pseudo-first-order and pseudo-second-order kinetic models, we found that the adsorption of last three dyes on carbon materials all could be well depicted by the pseudo-second-order kinetic model. | en_US |