Abstract
Nitrogen-containing mesoporous carbons with the use of colloidal silica spheres of (14 nm) and chitosan as a carbon precursor were obtained. A removal of such small template particles from carbonized silica–chitosan composite is difficult and HF with a minimum concentration of 15 wt% should be used. By varying the silica-to-chitosan ratio, the porous characteristic of products is controlled. The modification by ZnCl2 with a molar Zn-to-C (in chitosan mass) ratio of ‘6’ results in the development of microporosity; however it is accompanied by a significant reduction of mesopore volume (Vmes). The addition of ZnCl2 in a ratio of ‘5.25’ and pH adjustment to 5.8 increase the volumes of micropores, small mesopores, BET surface area to 1975 m2/g, and preserve Vmes of 4.15 cm3/g. The novelty of the presented strategy is the creation of microporosity in the hard-templated materials by incorporating ZnCl2 into the mixture of Ludox HS-40 template and chitosan precursor, as well as the investigation on how the pH of synthesis influences the final porosity. The pH of a silica–chitosan–zinc solution, equal to 3.9, provides some coordination of Zn2+ by –OH and –NH2 groups, whereas pH adjustment to 5.8 results in the precipitation of a new template—Zn(OH)2.
Highlights
Hierarchical porous carbons are characterized by well-balanced and usually interconnected micro- and mesopores
The V t of this sample is 0.49 cm3/g (Table 2) only. It can be asked if an ordered structure with developed porosity is able to be created at the S iO2-to-chitosan mass ratio of 2.50? According to our previous results, concerning the synthesis of carbons using chitosan and Ludox AS-40 silica template [32] the S iO2-to-chitosan ratio above which the structure was overloaded with silica equaled 3.10
The smaller silica spheres of Ludox HS-40 can more effectively fill the space, as compared to Ludox AS-40, the more ordered porous system can be generated in the sample synthesized at SiO2-to-chitosan ratio of 2.5
Summary
Hierarchical porous carbons are characterized by well-balanced and usually interconnected micro- and mesopores. All pores of various widths and shapes usually play different roles in its practical application. The mesopores facilitate a rapid transport of ions in electrodes, while micropores provide a large surface area for the accommodation of the charge [1]. Doping carbon with heteroatoms, such as nitrogen, increases its conductivity and results in an improved. The use a colloidal silica template in the synthesis of carbon resulted in a material with a large pore volume and uniform mesopores. The beads of colloid silica are available over a wide range of diameters, e.g. For example Ludox colloidal silica is marketed as 7, 14, 24 nm-sized,
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