1. INTRODUCTION

The presence of waste product in environmental is a worldwide problem and it has been highlighted by various environmentalist group. The organic effect produced in industrial such as textiles, paper, plastic, cosmetics, rubber, etc., impart intense color to the water bodies in which it is discharged. Discharging of dyes into water resources even in small amount can affect the aquatic life and the food web^1,2.

Today there are more 10,000 dyes available. Commercially most of which are not easy to biodegrade because of the stability towards light and oxidation also the dyes are resistant to aerobic digestion due to their complex aromatic molecular structure and synthetic origin. Such a large scale often poses pollution problems in waste water discharge into environment water bodies. Some dyes are known to the toxic are mutagenic and carcinogenic^1,2.

The adsorption process provides an attractive and alternative treatment especially the adsorbent is inexpensive and readily available such as Tectonagrandis L.F⁴, perlite⁵,walnut shell charcoal⁶, camel thorn plant⁷, Tectonagrandis bark powder⁸, water hyacinth root powder ⁹,wheat bran¹⁰, Agro-residues¹¹etc.,

The part of present study investigates the adsorption of Rhodamine-B (RDB) on a naturally occurring source of adsorbent namely Tectonagrandis bark powder (TGBP). The various parameters affecting the adsorption have been studied data have been filled to Langmuir and Freundlich adsorption isotherm and kinetic study in this paper for the adsorption of Rhodamine-B to activated carbon has also been respected.

2. MATERIAL AND METHODS:

2.1 Preparation of adsorbent

The present study on activated carbon prepared from the Tectonagrandis bark powder by acid treatment for carbonization. This step carried out at 500 °C for 2 hours in muffle furnace, after the carbon was removed and washed in distilled water again and again so that external of acids can be removed and the carbon is dried in 200 °C in oven for 2 hours. After carbon is ground and powdered to 75 mic size of Tectonagrandis bark powder (TGBP) and stored in plastic container which can be used further study of experiment.

2.2 Adsorbate

Rhodamine-B (C₂₈H₃₁N₂O₃Cl) was used for adsorbate in the present study in a cationic dye. The characteristics of Rhodamine-B dye are given as color index dye.

Formula weight 479.02, λ_max 543e (dm³mol¹cm⁻¹)-60000.0

2.3 Structure

Rhodamine-B

3. BATCH ADSORPTION EXPERIMENT:

It can be carried out in a batch process at 20 to 50 °C. The known weight of adsorbent was added to 50 mL of dye solution with the initial concentration of 2.5 to 25 ppm. The method of this study is using a mechanical shaker rotating at 120 rpm. The solution was filtered and the OD values are measured in calorimeter. The percentage of removal is noted in formula.

% Removal = (C₀-C_e) × 100

C₀

Where C_o = Initial dye concentration, C_e= Final dye concentration

The amount of adsorbed at equilibrium onto RDB, q_e(mg/g^-1) was then calculated using the formula

Amount of adsorbed = (Ci-Ct ) ×V

Where C_i = Initial dye concentration (mg/L⁻¹), C_t = Final dye concentration (mg/L⁻¹), V = volume (L) of the solution and W is the weight (g) of the adsorbent.

3.1 Effect of adsorbent dosage

The adsorbent dosage is taken from 5 mg to 30 mg/L in different aspects is mixed with 2.5 ppm (50 mL) of dye solution contained in mechanical shaker at 1hours is fixed in the 120 rpm. The various dosages can be determined adsorption values. The values are presented in Table 1. The graph is plotted for percentage removal efficiency against adsorbent dose is shown in figure 1.

Figure1 Effect of adsorbent dose on the adsorption of Rhodamine-B 2.5 ppm, contact time = 40 min; pH = 6, temperature = 20 °C using Tectonagrandis bark powder

Table1. Effect of adsorbent dose on the adsorption of Rhodamine-B on Tectonagrandis bark powder

Adsorbent(mg)	10	15	20	25	30
% Removal	43.75	50.00	56.26	68.75	78.57

3.2 Effect of Initial Dye concentration

The adsorption studies were conducted with various initial dye concentrations, the ranging from 2.5 to 30ppm, while adsorbent dosage is fixed with 50 mg/L. The percentage of removal dye value is decreased because of the values of dye concentration can be increased. This experiment is shown in the figure2 and Table-2

Figure 2 Effect of Initial dye concentration on the adsorption of RDB Adsorption dose=50mg/ 50ml; 2pH; Temperature=30°C; contact time=60mins

Table2.Effect of initial dye concentration of the adsorption of Rhodamine-B on Tectonagrandis bark powder

Initial conc. (ppm)	5	10	15	20	25	30
% Removal	81.93	69.88	60.12	39.76	38.56	35.00

3.3 Zero point charge [zpc]

It is necessary to determined ZPC of adsorbent³. The pH at the point of zero charge of Tectonagrandis bark powder was measured using the pH drift method. The pH of the solution was adjusted to between 2 to 10 by adding a 0.01M HCL or NaOH. The initial pH is stabilized. The adsorbent (50mg) was added to 7.5ppm of dye solution (50ml). After the pH was stabilized (after 24 hours).The final pH was recorded, the graph of final pH versus initial pH is used to determine ZPC of activated carbon. The initial and final pH values were equal shown in figure3.This point was taken as pH_zpc. In this study pH_zpcTectonagrandis was found to be 5.52.

Figure-3 Zero point charge (pH_zpc) of the used pressure during the adsorption experiment

Table3.Zero point charge of the adsorption of RDB on Tectonagrandis bark powder

Initial pH	2	4	6	8	10	12
After pH	2.22	5.4	5.48	6.73	7.1	7.62

3.4 Effect of pH

This experiment can be studied at different pH from the range of 2 to 10.This range can be maintained from the acetic and alkaline medium by adding the amount of 0.01 HCl and 0.01 NaOH is added. This experiment shows the table4.The graph is plotted using percentage of adsorption to initial pH. The effect of pH solution adsorption of uptake RDB ions at pH 8 of maximum obtained 2 to 8.After that there is a gradual decrease as seen in the figure4, and the values given in Table- 4.

Figure4- Effect of initial pH on the adsorption of Rhodamine-B

Contact time=40; adsorption dose=50mg/50ml, using 10ppm

Table4.Effect of pH for the adsorption of Rhodamine-B on Tectonagrandis bark powder.

Initial con	2	4	6	8	10	12
%Adsorbent	0.22	0.27	0.37	0.4	0.36	0.28

3.5 Effect of Temperature

The effect of temperature was studied in the range of 20 to 50°c.The adsorption of Rhodamine-B from 30mg to 60 (mg/L) on various dye concentration (5 to 25 ppm). The experimental temperature increased to 20 to 50°c and the dye adsorption also increases .Changing the temperature will change the equilibrium capacity of the adsorbent for particular adsorbate.

3.6 Effect of Time

The effect of contact time was studied to carry out from different dye concentration from 5 to 25 ppm. The contact time shows in figure5.The adsorption gradually increased to 10 to 40 minutes. The equilibrium data are collected in 50 to 60 min was efficient to achieve equilibrium and adsorption did not change with further increase in contact time. Therefore uptake and adsorbed dye concentration. The end of 50 mints is given as equilibrium values. These values are respectively in table5 and figure5.

Fig 5 Effect of contact time on adsorptions of Rhodamine-B; adsorbent dose=50mg/50ml

Table5.Effect of contact time for the adsorption of Rhodamine-B

Initial Dye concentration	10ppm	15ppm	20ppm	25ppm
% Removal	95.5	95.8	96.5	96.6
	96.2	96.13	96.65	96.76
	96.8	96.66	97	96.92
	97.4	97.46	97.65	97.12
	98	98	97.7	97.28
	98	98	97.7	97.28

4. ADSORPTION KINETICS:

Were kinetic study was carried out to determine the equilibrium time required for the uptake of dye (RDB) from aqueous solution. All adsorption reaction and mechanical model can apply for kinetic adsorption. This experiment can provided information about mechanism of the reaction between adsorbent and adsorbate. This is good useful to understand adsorption process, this model can be suggested for an adsorption including pseudo first order linear form as below

log (q_e-q_t ) = log q_e - ( k_t)/2.303

Where, q_e and q_t are amount of RDB adsorbed (mg/g) time and equilibrium respectively, and K is rate constant.

The pseudo first order adsorption process (min⁻¹). Figures (6 and 7) show a plot of linearized from of pseudo first order at all concentration study. The slopes were taken from the intercept of plot of log (q_e − q_t) and time. It is used to determine the first order rate constant k and equilibrium adsorption density q_e noted Table 6 for different concentration of RDB dye (20, 25) ppm on TGBP.

Figure-(6) pseudo first order adsorption kinetic of RDB for 20 ppm using Tectonagrandis bark powder.

Figure-(7) pseudo first order adsorption kinetic of RDB for 25ppm using Tectonagrandis bark powder.

The comparison of results with correlation coefficients is shows Table (6). The R² is approximately range (0.991, 0.996). The theoretical q_e values obtained from pseudo first order kinetic model to give reasonable values. The suggested that this adsorption system in first order reactions.

Table 6. k value of RDB from pseudo first order kinetic for 20, 25 ppm using Tectonagranadis bark powder

Initial dye concentration (ppm)	k value min¹ (× 10⁻³)	R² value
20.0	1.15	0.991
25.0	0.84	0.996

5. EQUILIBRIUM STUDIES:

The adsorption isotherm represents relation between the amount of adsorbed by the unit weight of solid adsorbent and the amount of adsorbate remained in the solution at equilibrium time using the Langmuir and Freundlich model

5.1 Langmuir model

Langmuir is based on mono layer adsorption of RDB dye on the surface of carbon sides and can explained in linear form of

C_e⁄q_e =1⁄(Q₀ b)+C_e⁄Q₀

C_e = concentration (mg/L)

Q_e=Amount of adsorbed at equilibrium (mg/g).The Langmuir constant Q_o(mg/g) represent the mono layer adsorption capacity and b Langmuir constant. A plot of c_e/q_e and c_e should indicate give slightly straight line slope 1/Q_o and intercept 1/ Q_ob. Show the figure (8). The adsorption of Rhodamine-B onto Tectonagrandis bark powder follows the Langmuir isotherm apply the linear form of correlation coefficient R²=0.992 model provided to straight line suggested model of adsorption system.

Figure-(8).Langmuir isotherm for adsorption of RDB (5 to 25 ppm), pH = 6, adsorbent=50mg/L

5.2 Freundlich model

Freundlich isotherm model is the earliest known the equation describing the adsorption process. It is in empirical equation and can be used to non ideal adsorption that involves heterogeneous adsorption. It can be derived assuming a logarithmic decreases in enthalpy of adsorption with increases the fraction of occupied sites. It gives the linear equation

Log q_e=log k_f+ 1/n log c_e

Log q_e= amount of adsorbate adsorbed

C_e= amount of adsorbate in solution at equilibrium

K_f can be defined as the adsorption (or) distribution coefficient and represent the quantity of dye adsorbed onto adsorbent for unit equilibrium concentration.1/n is adsorption intensity of dye onto the adsorbent.

Freundlich isotherm of RDB conducted at 60 minutes with 50mg/L at different concentration ranging at 5 to 25 ppm respectively. At pH 8, the intercept slopes linear plot of log q_e Vs log c_e resulting the adsorption process was investigated by correlation coefficient R²=0.975. The Table (8) shows that the data can be described the Langmuir and Freundlich is best fit for the isotherm.

Figure-(9) Freundlich isotherm for the adsorption of RDB by using Tectonagrandis bark powder.

6. CONCLUSION:

The present study is investigated the adsorption of basic dye Rhodamine-B onto Tectonagrandis bark powder , some of the following data at adsorbent dose, contact time, initial dye concentration, pH and temperature.

The percentage of dye removed increase with increasing adsorbent dosage and increase with increasing contact time and varied with dye solution pH. The adsorption rates increases with increasing temperatures. It can be achieved optimum contact time for equilibrium is occur in 1hours (60min). Rhodamine-B maximum adsorption occur in pH=8. The adsorption capacity increased in pH value upto 8 and after there is gradually decreased in adsorption. The equilibrium studies to give both Langmuir and Freundlich model can be best fits for adsorption equilibrium data. The adsorption kinetics study as followed as pseudo first order. The concentration range is 5 to 25 ppm. The presence studies conclude that Rhodamine-B could employed as adsorbent of Tectonagrandis bark powder.

7. REFERENCE:

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Received on 23.03.2015 Modified on 08.04.2015

Asian J. Research Chem 8(5): May 2015; Page 346-350

DOI: 10.5958/0974-4150.2015.00057.7