Preparation of hierarchic porous carbon mobolith without using templates

Abstract

Cabon monolith with hierarchical porous structure containing both interconnected macroporous and nanoporous structure are generally prepared by replicating from a hard template of inorganic material with similar porous structure. However, the preparing method is very complicate because of because the template removal is needed. Besides the porous structure of the carbon monolith is depended on the template.This research, therefore, focuses on the new effective method without using any templates for synthesis the monolithic carbon containing thehierarchical porous structure. Two effitive methods are introduced. The first method is an irradiation of ultrasonic wave at constant frequency of 20 kHz during sol-gel process of resorcinol-formaldehyde (RF) gel synthesis. Consequently, the RF monolith gel consisting of the interconnected macroporous structure can be obtained. Afterwards,the carbonization with N2 is performed in order to prepare the carbon monolith from the RF monolith gel. The cabonized carbon monolith not only consist with the interconnected macropores as well as the RF monolith, but also has the microporosities on the macropore wall. Additionally, the effect of sol-gel temperature, initial pH value of the resorcinol-formaldehyde solution and ultrasonic power on the interconnected macroporous structure of the carbonized carbon monolith are also investigated. These parameters strongly result in both the obtained monolith shape and the interconnected macropores of the carbon monolith. Moreover, the activated carbon monolith containing both bi-model microporosities on macropore structure and oxygenated functional groups can directly prepared at low retention time ( ̴30 min) by direct thermal activation with CO2 of the interconnected macroporous RF monolith gel, whereas the activated carbon monolith containing both tri-model micro-/meso-/ macropore structure and oxygenated functional groups can be prepared at low retention time by direct chemical activation by impregnation of Ca(NO3)2 followed by activating with CO2 The second method is an inducing the inverse-phase suspension of the RF solution at nearly complete gel-formation with adding water. The RF monolith gel with the interconnected macroporous structure can be obtained. Sol-gel keeping time and volume of adding water are the important key parameters for achievements of both obtained monolith shape and interconnected macropores. Afterwards, the direct thermal activation and the direct chemical activation are carried out under the same condition in order to generate the microporosities and mesoporosites in the obtained carbon monolith