Adsorption and desorption behavior of water and organic vapor of allophanic soil<b>–</b>templated porous carbon materials

Abstract

We have synthesized several kinds of porous carbon material by template method using 2 kinds of natural allophanic soil purchased in Japan as template materials. To determine the hydroscopic properties of the templated porous carbon specimens, we measured their water adsorption and desorption isotherms around room temperature (283, 293 and 298 K). We also measured porous and chemical properties of the templated porous carbon specimens, and investigated the relationships between pore development and their water isotherms. The features of the isotherm curves of the templated porous carbon specimens were different from those of common activated carbon used as a reference, and the features in this study were dependent on template materials rather than carbon ingredients. Some of the templated porous carbon specimens had water adsorption isotherms that rose sharply at approximately 80% relative humidity (RH), and the desorption isotherms dropped off at 60% RH. The results indicate the possibility of application of these specimens as effective adsorbents that are not susceptible to moisture as compared with common activated carbon. The specimens are also assumed to be useful as humidity control materials.©2012 The Ceramic Society of Japan. All rights reserved.Key-words : Allophanic soil template, Hysteresis, Organic vapor adsorption, Porous carbon material, Relative humidity, Water isotherm [Received June 11, 2012; Accepted September 11, 2012] In both industrial applications and occupational hygiene, activated carbon is used as an adsorbent for various kinds of organic vapor. Particularly, coconut shell activated carbon is a commonly used material for gas adsorption in Japan. Also many other types of porous carbon product are produced from various raw materials with various configurations and specific surface areas, and they have preferable adsorption ability and capacity for typical organic vapors or gaseous compounds compared with other porous materials. The adsorption capacities of activated carbon are affected by temperature, flow rate of sampled air, concentrations of representative organic vapors and the moisture contents in both the airflow and the activated carbon. Among these factors, the moisture contents have been the focus of many quantitative studies, because in many cases moisture adsorption reduces the gaseous adsorption capacities. Accordingly, there have been many experimental reports regarding the moisture effect on activated carbon around room temperature (approximately 293298 K).1)12) With regard to various porous carbon materials, their water adsorption and desorption behavior and their mechanism are also attractive from the viewpoint of surface science. 13)17)In previous studies, 18)20) we synthesized templated porous carbon materials 21)27) using silica gels 20) and natural allophanic soils 18)20) or minerals 20) purchased in Japan as template materials. The templated porous carbon specimens each have unique pore size distributions and pore development characteristics based on template materi...