RESUMEN
Nitrogen-containing porous carbons prepared by the pyrolysis of adequate biopolymer-based precursors have shown potential in several electrochemical energy-related applications. However, it is still of crucial interest to find the optimal precursors and process conditions which would allow the preparation of carbons with adequate porous structure as well as suitable nitrogen content and distribution of functional groups. In the present work we suggested a straightforward approach to prepare N-doped porous carbons by direct pyrolysis under nitrogen of chitosan : coffee blends of different compositions and using KOH for simultaneous surface activation. The synthetized carbon materials were tested for the electrochemical oxygen reduction to hydrogen peroxide (H2O2). A higher fraction of chitosan in the precursor led to a decrease in meso- and nano-porosity of the formed porous carbons, while their activity towards H2O2 generation increased. The nitrogen species derived from chitosan seem to play a very important role. Out of the synthesized catalysts the one with the largest content of pyridinic nitrogen sites exhibited the highest faradaic efficiency. The faradaic efficiencies and current densities of the synthesized materials were comparable with the ones of other commercially available carbons obtained from less renewable precursors.
RESUMEN
In the present work, we report for the first time an in-depth study of the factors influencing porous cellulose film structure formation during the nonsolvent-induced phase separation (NIPS) process from biopolymer solutions in ionic liquid-based solvents. The length of the alkyl chain of the ionic liquid's cation, the solvent/co-solvent ratio, and the type of the cellulose precursor used were found to have great influence both on cellulose solution formation and properties and to the NIPS process with water acting as nonsolvent. In the undiluted form, both studied ionic liquids proved to dissolve almost equally well the cellulose; however, due to differences in viscosities of the formed biopolymer solutions and due to differences in miscibility with water of the two ionic liquids, the used ionic liquid had a strong influence on the film's porous structure formation. The use of increasing amounts of an aprotic co-solvent, here dimethylsulfoxide, improved biopolymer solubilization and also led to the formation of a more pronounced macroporous structure during the NIPS process. The cellulose type also affected the porous structure generation during the NIPS process: with the increase of the molecular weight of the precursor, the viscosity of the formed biopolymer solution increased and the tendency to generate macroporous structures decreased.
RESUMEN
A series of cellulose/chitosan blend porous spheres were prepared by dropping cum phase separation from 1-butyl-3-methylimidazolium acetate/dimethylformamide based solutions via coagulation in water. Special attention was given to the investigation of the phase separation process initiated with water in relation with the different chitosan content in polymer solutions. The increase of the chitosan fraction in the biopolymer solution led to a destabilization of the solutions by lower amounts of water. Both viscosity of the polymer and stability of the solution played a very important role to the spheres structure formation. It was observed that the SBET seems to decrease at the increase of the chitosan content in the porous material. Despite the decrease of porosity, the increase of the chitosan fraction in the blend had a beneficial influence on the adsorber properties of the spheres, due to the amino groups in the chitosan units.
