The bisorption of basic dye from aqueous solution on bamboo based activated carbon was studied in a batch system. The effect of various experimental parameters, such as pH, adsorbent dosage, temperature and initial dye concentration was investigated. The results showed that these parameters influenced the adsorption capacity. Higher solution pH favoured the adsorption of basic dye. Dye removal increased with increase in the initial concentration of basic dye. The adsorption of dye increased with increasing temperature of the solution from 25 to 45°C, indicating the process to be endothermic. Dye removal increased with increase in the initial concentration of the dye. As adsorbent concentration increased, the amount adsorbed per unit mass of adsorbent decreased. The equilibriumdata fitted very well to Langmuir and Freundlich models

Mordi, MI

Nwabanne, JT

English

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African Journal of Biotechnology Vol. 8 (8), pp. 1555-1559, 20 April, 2009     Available online at http://www.academicjournals.org/AJB ISSN 1684–5315 © 2009 Academic Journals      Full Length Research Paper  Equilibrium uptake and sorption dynamics for the removal of a basic dye using bamboo  J. T. Nwabanne* and M. I. Mordi  Department of chemical Engineering, Nnamdi Azikiwe University, P. M. B. 5025, Awka, Nigeria.  Accepted 3 January, 2009  The bisorption of basic dye from aqueous solution on bamboo based activated carbon was studied in a batch system. The effect of various experimental parameters, such as pH, adsorbent dosage, temperature and initial dye concentration was investigated. The results showed that these parameters influenced the adsorption capacity. Higher solution pH favoured the adsorption of basic dye. Dye removal increased with increase in the initial concentration of basic dye. The adsorption of dye increased with increasing temperature of the solution from 25 to 45°C, indicating the process to be endothermic. Dye removal increased with increase in the initial concentration of the dye. As adsorbent concentration increased, the amount adsorbed per unit mass of adsorbent decreased. The equilibrium data fitted very well to Langmuir and Freundlich models.  Key words: Activated carbon, bamboo, basic dye, isotherm, sorption.   INTRODUCTION  Dyes are used in many industries such as food, paper, carpets, rubbers, plastics, cosmetics, and textiles in order to colour their products (Bulut and Aydin, 2005). Effluents of these industries are highly coloured and the disposal of these wastes into receiving water causes damage to the environment as they may significantly affect photosyn-thetic activity in aquatic life due to reduced light pene-tration and may also be toxic to some aquatic life due to the presence of metals, chlorides, etc; in them (Aksu and Tezer, 2000). One of the major problems concerning textile wastewaters is coloured effluent (Hameed et al., 2006). The wastewater contains a variety of organic compounds and toxic substances, which are harmful to fish and other aquatic organisms (Ramakrishna and Viraraghavan, 1997; Lee et al., 1999; Kadirvelu et al., 2003; Kannan and Sundaram, 2001). Colour removal had been the target of significant attention in the last few years, not only because of its toxicity, but mainly due to its visibility problems (Aksu and Tezer, 2000; Yeh and Thomas, 1995; Morais et al., 1999; Correia et al., 1994). Equally, disposal of dying industrial effluents pose a major environmental problem because they contain pollutants that are especially resistant to  removal  by  the    *Corresponding author. E-mail: joe_nwabanne@yahoo.com. typical microbial population and may be toxic to the micro-organisms present in treatment plants (Otero et al., 2003). Various physicochemical and biological techniques can be employed to remove dyes from wastewaters (Suteu and Bilba, 2005; Bulut and Aydin, 2005). However, these processes are effective and economic only in cases where solute concentration are relatively high. Activated carbon is the most widely used adsorbent for the removal of colour and treatment of textile effluents but due to its high price it is not used on a great scale (Clarke and Anliker, 1980; El-Geundi, 1991; Lakshmi et al., 1994). This has led many researchers to search for the use of cheap and efficient alternative mate-rials such as coal, fly ash, palm-fruit bunch, rice husk, peat, activated clay, bagasse pits, cassava peel, palm tree cobs, date pits, fruit stones and nutshells (Mohan et al., 2002a; Mohan et al., 2002b; Wu et al., 2001; Nassar, 1997; Mckay, 1998; Girgis and El-Hendawy, 2002; Aygun et al., 2003 ). The use of agricultural by-products as raw material for manufacturing activated carbon is advantageous as these raw materials are renewable and potentially less expensive to manufacture (Hameed et al., 2006). Solid waste from bamboo is highly abundant in Nigeria. The objective of this work is to study the utilization of bamboo as adsorbent to remove basic dye from an aqueous solu- tion. Equilibrium and kinetic analysis  were  conducted  to 1556         Afr. J. Biotechnol.    understand sorption process.   MATERIALS AND METHODS  Adsorbate  The basic dye used is 2, 4 – dinitrophenylhydrazine. The stock solution of 1000 mg/l was prepared by diluting the stock solution with distilled water.   Adsorbent preparation  Bamboo used for this study was obtained from Nnamdi Azikiwe University, Awka. The bamboo was washed with distilled water, dried and grounded into powder. 100 g of bamboo powder was mixed with 100 ml of 0.1 M phosphoric acid. The mixture was oven dried at 110°C for 24 h. The oven dried mixture was carbonized in a muffle furnace (United Nations database 073050) at 450°C for 3 h. The carbonized sample was washed with distilled water until pH of 6.0 was obtained. The sample was thereafter dried in an electric oven for 4 h at 95°C and then kept in desiccators for use after crushing and sieving with 1.18 mm sieve.   Characterization of adsorbent  The surface area of the adsorbent was determined by iodine adsorption method (ASTM D 4607-86). Moisture content was determined using ASTM D 2867 – 91. Bulk density was determined using method of Okieimen et al. (2007). pH of the carbon was determined by immersing 1 g sample in 100 ml of distilled water and stirring for 1 h.   Batch adsorption experiment  The adsorption experiments were performed by batch method where samples of 1 g of bamboo based activated carbon were equilibrated with 250 ml of solution containing various amount of basic dye with intermittent stirring. The initial pH of solution was adjusted to 3, 5, 7 and 9 using 0.1 M NaOH or HCl. Effect of carbon dosage was studied by varying the amount of each adsorbent (1, 3, 5 and 7 g) per 20 ml of a concentration of 100 mg/l stock solution of basic dye. The effect of contact time was investigated for 30, 60, 90 and 120 min. at pH 6 and 1 g/100 ml sample dosage. The temperature of solutions (25, 30, 35 and 40°C) was controlled with a thermostatic bath. At the end of adsorption period, the various samples were filtered using filter paper and the supernatant liquid was analysed for the remaining dye using a UV spectrophotometer by monitoring the absorbance changes at a wavelength of maximum absorbance of 550 nm. The amount of dye adsorbed was calculated using the equation  qe  =  V(Co – Ce) / m                                         (1)  Where, qe is the amount adsorbed per gram of adsorbent, Ce is the equilibrium concentration of dye (mg/l), V is volume of solution (l) and m is mass of adsorbent used (g).   RESULTS AND DISCUSSION  Effect of carbon dosage on adsorption process  Adsorbent dosage  is  an  important  parameter  because                      	   Figure 1. Effect adsorbent (bamboo) dosage on the sorption of basic dye at 30°C.    this factor determines the capacity of an adsorbent for a given initial concentration of the adsorbate. The effect of adsorbent dosage was studied on basic dye removal by keeping all other experimental conditions constant. The result showed that as the adsorbent concentration increased, the amount adsorbed per unit mass of the adsorbent decreased considerably (Figure 1). The de-crease in unit adsorption with increasing dose of adsorbent is basically due to adsorption sites remaining unsaturated during the adsorption (Bulut and Aydin, 2006).   Effect of pH  The pH is one of the most important factors controlling the adsorption of dye onto adsorbent. The effect of pH in the adsorption of basic dye by bamboo is shown in Figure 2. The dye uptake was found to increase with increasing pH. The highest dye uptake was recorded at pH of 9.   Effect of temperature  Temperature has important effects on the adsorption process. As the temperature increases, rate of diffusion of adsorbate molecules across the external boundary layer and interval pores of the adsorbent particle increases (Waranusantigul et al., 2003). Figure 3 shows effects of different temperatures for basic dye removal on bamboo. The amount of basic dye adsorbed increased with increasing temperature of the solution from 25 to 45°C, indicating the process to be endothermic.   Effect of Initial dye concentration  The sorption capacity of powdered activated carbon for basic dye was determined at different initial dye concentrations. Figure 4 shows that  percentage  removal         Figure 2. Effect of pH on the sorption of basic dye at 30°C using bamboo as absorbent.                    °  Figure 3. Effect of temperature on the sorption of basic dye at30°C using bamboo as absorbent.    rate increased with an increase in dye concentration. Dye removal is highly concentration dependent. The increase in loading capacity of the adsorbent with relation to dye ions is probably due to a high driving force for mass transfer. In fact, the more concentrated the solution, the better the adsorption.   Characteristics of Bamboo based activated carbon  The characteristics of activated carbon synthesized from bamboo were determined and reported in Table 1. Nwabanne and Mordi        1557           Figure 4. Effect of initial dye concentration on its removal using bamboo as absorbent.    Table 1. Characteristics of bamboo based activated carbon.  Characteristic Value Surface area (m2/g) 364.24 Density (g/cm3) 0.65 pH 6.0 Moisture Content 0.038    Adsorption isotherm  The relationship between the amount of a substance adsorbed at constant temperature and its concentration in the equilibrium solution is called the adsorption isotherm. Several models have been published in the literature to describe experimental data of adsorption isotherms. The Langmuir and Freundlich are the most frequently used models. In this study, both models were employed to analyse the relationship between the amount of dye adsorbed and its equilibrium concentration.   Langmuir isotherm  The Langmuir adsorption isotherm assumes that adsorp-tion takes place at specific homogeneous sites within the adsorbent, and it has been used successfully for many adsorption processes of monolayer adsorption. The linearized Langmuir equation is represented as follows:  Ce/qe  =  1/Qb  +  (1/Q)Ce                                               (2)  where, Ce is the equilibrium concentration of the adsor-bate (mg/l), qe is the amount of adsorbate adsorbed per unit mass of adsorbate (mgg-1), and Q and b are Langmuir  1558         Afr. J. Biotechnol.      Figure 5. Langmuir isotherm for the sorption of basic dye at 30°C using bamboo as absorbent.    Table 2. Langmuir and Freundlich isotherm constants at 30°C using bamboo as absorbent.  Parameter Value Langmuir isotherm Q (mgg-1) 884.96 b (lmg-1) 0.026 RL 0.133 R2 0.996 Freundlich isotherm 1/n 0.641 KF  (mgg-1)   ( Lmg-1) 1/n 43.15 R2 0.997    constants related to adsorption capacity and rate of adsorption, respectively. Plotting Ce/qe against Ce gave straight line with slope, 1/Q (Figure 5), indicating that the adsorption of basic dye on activated carbon follows the Langmuir isotherm. The Langmuir constants ‘b’ and Q were evaluated from this isotherm and their values are recorded in Table 2. The fact that the Langmuir isotherm fits the experimental data very well may be due to the homogeneous distribution of active sites onto the bamboo surface, since the Langmuir equation assumes that the surface is homogeneous. The essential characteristics of the Langmuir isotherm can be expressed in terms of a dimensionless equilibrium parameter, RL (McKay et al., 1984) which is defined by:   RL  =  1/(1 + bCo)            (3)   Where, Co is the highest initial solute concentration, b the Langmuir’s adsorption constant (l/mg). The value of RL indicated the type of the isotherm to be either unfavourable (RL > 1), linear (RL= 1), favourable (0 < RL <       Figure 6. Freundlich isotherm for the sorption of basic dye 30°C using bamboo as absorbent.    1) or irreversible (RL = O). The value of RL was obtained as 0.026. This confirmed that the activated carbon from bamboo is favourable for adsorption of basic dye under the conditions used in this work.   Freundlich isotherm  The Freundlich isotherm is an empirical equation used to describe heterogeneous systems. The well-known logarithmic form of Freundlich model is given by the following equation:  Log qe =  log KF +  (1/n)log Ce           (4)  Where, KF and 1/n are Freundlich constants related to adsorption capacity and adsorption intensity of the sorbent, respectively. qe is the amount adsorbed at equilibrium (mgg-1), Ce is the equilibrium concentration of the adsorbate. The values of KF and 1/n are calculated from the intercept and slope respectively, and are recorded in Table 2. The plot of log qe versus log Ce gave straight line (Figure 6) with correlation coefficient of 0.997, which shows that the adsorption of basic dye follows the Freundlich isotherm.   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Equilibrium uptake and sorption dynamics for the removal of a basic dye using bamboo

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Equilibrium uptake and sorption dynamics for the removal of a basic dye using bamboo

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