Preparation of activated carbon derived from Jatropha curcas fruit shell by simple thermo-chemical activation and characterization of their physico-chemical properties

Abstract

High surface area activated carbons were prepared by simple thermo-chemical activation of Jatropha curcas fruit shell with NaOH as a chemical activating agent. The effects of the preparation variables, which were impregnation ratio (NaOH:char), activation temperature and activation time, on the adsorption capacity of iodine and methylene blue solution were investigated. The activated carbon which had the highest iodine and methylene blue numbers was obtained by these conditions as follows: 4:1 (w/w) NaOH to char ratio, 800 °C activation temperature and 120 min activation time. Characterization of the activated carbon obtained was performed by using scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR) and nitrogen adsorption isotherm as BET. The results present that the activated carbon possesses a large apparent surface area (S_BET = 1873 m²/g) and high total pore volume (1.312 cm³/g) with average pore size diameter of 28.0 Å.

Introduction

Activated carbons are the most versatile and commonly used adsorbents because of their extremely high surface areas micropore volumes, large adsorption capacities, fast adsorption kinetics, and relative ease of regeneration. The most precursors used for the production of activated carbons are organic materials that are rich in carbon (Prahas et al., 2008). Agricultural wastes are the one, which considered being a very important feed stock for activated carbon preparation because there are renewable sources and low-cost materials. With many earlier studies, an agricultural wastes such as corn cob (Tsai et al., 1998), coconut shell (Hu and Srinivasan, 1999), palm shell (Daud et al., 2000), grain sorghum (Diao et al., 2002), pistachio nut shell (Lua and Yang, 2005), olive stones and walnut shell (Martınez et al., 2006), cherry stones (Olivares-Marin et al., 2006), rice bran (Suzuki et al., 2007), jackfruit shell waste (Prahas et al., 2008) and oil palm shell (Tan et al., 2008) have been found to be suitable precursors owing to their high carbon and low ash contents. From previous studies, the quality and characteristics of activated carbons not only depended on physical and chemical properties of the starting materials but also depended on the preparation conditions (Ahmadpour and Do, 1996, Molina-Sabio and Rodriguez-Reinoso, 2004, Lillo-Rodenas et al., 2004).

Due to successful use of Jatropha curcas oil in biodiesel production, it promotes the heavy cultivation of this plant in many countries (Sarin et al., 2007, Tapanes et al., 2008, Hawash et al., 2009, Lu et al., 2009). From this point of view, it may lead to the problem with its associated waste as J. curcas fruit shell (JS). It contains low nutrient, which is not suitable for use as an agriculture fertilizer, but it is abundant in cellulose, hemicelluloses and lignin resulting in difficult to digest or degrade. Thus, a possible solving of this waste is converting it into value-added activated carbon, which is one of the most widely used materials because of its exceptional adsorbent properties.

In general, the process for manufacturing of activated carbons involves two steps, carbonization of raw carbonaceous materials in an inert atmosphere followed by the activation of the carbonized product. The activation process can be provided by two types, either by physical activation or chemical activation. However, chemical activation is now widely applied for the activation because of its lower activation temperature and higher product yield compared with the physical one (Guo and Rockstraw, 2007). Based on the literature reviewed, it was found that alkaline hydroxides (KOH and NaOH) (Lillo-Rodenas et al., 2007) can be used to prepare the activated carbon, which gave high specific surface area in the range of 2318–3500 m²/g (Macia-Agullo et al., 2004, Yoshizawa et al., 2002, Tseng, 2006). Moreover, sodium hydroxide was also shown to be more particularly interesting because NaOH activation can reduce chemical activation cost and environmental load when compared with KOH activation (Perrin et al., 2004).

The aims of this work were to utilize J. curcas fruit shell, biomass waste, for the preparation of activated carbon by simple thermo-chemical activation using NaOH as an activating agent. The effects of impregnation ratio of reagent to char, activation temperature and activation time on iodine and methylene blue numbers of the activated carbon were studied in order to obtain high adsorption capacity and surface area of the product. Subsequently, the physico-chemical characteristics of the activated carbon, obtained by optimum conditions, were also determined.