Characteristics and humidity control capacity of activated carbon from bamboo Toshihide Horikawa a, * , Yoshiyuki Kitakaze a , Tomoki Sekida a , Jun’ichi Hayashi b , Masahiro Katoh a a Department of Advanced Materials, Institute of Technology and Science, The University of Tokushima, 2-1 Minamijosanjima, Tokushima 770-8506, Japan b Department of Chemical, Energy and Environmental Engineering, Kansai University, 3-3-35 Kamiyamate, Suita, Osaka 564-8680, Japan article info Article history: Received 15 October 2009 Received in revised form 6 January 2010 Accepted 9 January 2010 Available online 4 February 2010 Keywords: Activated carbon Water vapor adsorption Surface functional groups Humidity control capacity abstract Activated carbons were prepared from bamboo by chemical activation with K 2 CO 3 or physical activation with CO 2 . The structural and surface chemical characteristics of the activated carbons were determined by N 2 adsorption–desorption and Boehm titration, respectively. The water vapor adsorption properties of the activated carbons with various pore structures (preparation conditions) were examined. The relation- ship between water vapor adsorption capacity and pore properties, and the humidity control capacity of the prepared activated carbons are also discussed. The water adsorption isotherms show a region of rap- idly increasing uptake of water vapor, and the relative humidity corresponding to those regions was dif- ferent according to the preparation conditions, especially activation temperature. Water vapor adsorption capacity was improved with larger pore volume and surface area, but the humidity control capacity in a certain specific humidity region differed greatly according to the relative humidity corre- sponding to the steeply rising regions of the isotherms. In the typical operating conditions of an adsorp- tion heat pump, RH 10–35%, the bamboo-sourced activated carbon that was prepared at 873 K by potassium carbonate activation with impregnation ratio 1.0 had the highest humidity control capacity. Ó 2010 Elsevier Ltd. All rights reserved. 1. Introduction Carbon materials such as activated carbons are well known as excellent adsorbents with high specific surface area and large pore volume, and are widely used in separation (Horikawa et al., 2002), purification (Caqueret et al., 2008), catalysis (Cabiac et al., 2008), and energy storage (Khomenko et al., 2008). Carbon materials, such as charcoal, have been used as humidity conditioning adsorbents since ancient times. Researchers have investigated the use of carbon materials in adsorption heat pumps (AHPs) or desiccant humidity conditioners (DHCs) as an adsorbent (Kawano et al., 2008), because water vapor adsorption on carbon materials has a sharp adsorption uptake accompanied by a clear adsorption hysteresis for desorption at medium or high relative humidity. AHP is a compressor-free machine that operates like an inverse Carnot cycle utilizing a low temperature energy source such as so- lar energy or waste heat. Consequently, AHP has been attracting much attention in recent years as an environmentally friendly technology for utilizing waste heat. The principle of AHP is to use the exothermic/endothermic changes associated with adsorption/ desorption of vapors on adsorbents (Wang et al., 2005). The characteristic pore properties of the adsorbent used have a great influence on the performance of the AHP. The ideal heat output of AHP of the water vapor type depends directly on the equilibrium adsorption ability of the adsorbent in the operational relative pres- sure range of AHP, Dq. There is a need for development of an inno- vative adsorbent with high adsorption capability for water vapor, prepared from environmentally friendly source materials such as biomass. Various agricultural sources of biomass have been investigated as source materials for preparing activated carbons, including nut- shells (Hayashi et al., 2002a), chickpea husk (Hayashi et al., 2002b), cherry stones (Olivares-Marín et al., 2006), olive stones (Ubago- Pérez et al., 2006), coffee endocarp (Nabais et al., 2008), and pine cones (Duman et al., 2009). Natural materials, which must be avail- able in large quantities, may have potential as inexpensive precur- sors for activated carbon production. Bamboo is an abundant and inexpensive natural resource in Japan. It is well known that bam- boo grows rapidly, so that it is possible to ensure a stable supply of bamboo as a source material. Activated carbon is commonly prepared by chemical activation (with ZnCl 2 , KOH, K 2 CO 3 , etc.) or physical activation (with CO 2 or H 2 O) under various conditions, to carefully control the develop- ment of pore structure. When a biomass is used as the source material to prepare activated carbon, the applicability of the acti- vation conditions should be verified because the ash composition is different in biomass species, and it can be different even in the same biomass species grown in different locations. In the present study, we have used bamboo to prepare activated carbon by chemical activation with K 2 CO 3 and physical activation 0960-8524/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.biortech.2010.01.032 * Corresponding author. Tel.: +81 (0)88 656 7426; fax: +81 (0)88 655 7025. E-mail address: horikawa@chem.tokushima-u.ac.jp (T. Horikawa). Bioresource Technology 101 (2010) 3964–3969 Contents lists available at ScienceDirect Bioresource Technology journal homepage: www.elsevier.com/locate/biortech