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INTRODUCTION
Synthetic dyes are one of the major water pollutants, with their presence in water even in low quantities highly visible and undesirable. The colour itself interferes with sunlight penetration and retards photosynthesis, thereby inhibiting the growth of plant biota (Wang et al. 2005). Direct discharge of dyes into the environment may also result in the formation of toxic carcinogenic breakdown products. The conventional methods for the treatment of wastewater containing dyes include chemical oxidation (Oguz & Keskinler 2007), liquid-liquid extraction (Muthuraman et al. 2008) and adsorption (Mohan et al. 2002). All these methods have certain limitations, which include low efficiency and limited scope. Adsorption has however been considered to be a better method because of its simplicity in design, operation and convenience. The extent of adsorption depends on the nature of adsorbent, especially its surface area and porosity, and in light of this, various adsorbents have been developed with different properties. Amongst the many adsorbents in use, activated carbon has been the most popular and widely used adsorbent (Bhatnagar & Minocha 2006). Methylene blue (MB) adsorption from aqueous solution has been successfully accomplished using activated carbon adsorbent prepared from different precursor materials, which include cotton stalk (Deng et al. 2009), pistachio shells (Attia et al. 2003) and Lupinus albus (Bağcı & Ceyhan 2015). The adsorption capacities found were high in some cases, such as 193.5 mg/g for cotton stalks.
Activated carbon is produced by a process which involves dehydration, carbonization and activation of the raw materials. Some of the most popular activating agents for the chemical process are zinc chloride (Makeswari & Santhi 2012), H3PO4 (Zhong et al. 2012), K2CO3 (Li et al. 2008) and H2SO4. Other chemicals, which include Na2CO3, NaOH, Ca(OH)2 and the chloride salts of magnesium, calcium, ferric iron and aluminium, have been used. The common feature in all these chemicals is their dehydrating nature. However, these different activating agents are affected by different parameters.
Some countries producing substantial quantities of tobacco have challenges concerning the disposal of remaining stalks after reaping the leaves. Clearly, this represents a huge and untapped resource since these stems are considered as waste and unusable. Tobacco stems have been applied in the form of tobacco dust (Qi & Aldrich 2008), tobacco stem ash (Ghosh &...