Removal of malachite green from aqueous solution using activated nerium oleander leaves.
Synthetic dyes are more commonly used in industries like textiles, paper and pulp, food, cosmetics, plastics and pharmaceuticals to incorporate colour to their products. Such industries discharge huge loads of coloured effluents into fresh water resources. These coloured effluents reduce the sunlight penetration, photosynthetic activity, oxygen dissolution in water and pose great threats to the aquatic biodiversity that makes it unfit for their survival in such contaminated water. The health risks associated with dyes include carcinogenesis, mutagenesis, teratogenesis and respiratory toxicity. The incomplete decomposition of the dyes produces toxic amines  that are harmful to the aquatic environment. Though conventional methods are available for waste water treatment such as sedimentation, flocculation, aeration, precipitation, ultra filtration and disinfection, adsorption technique stands superior over conventional methods due to easy availability of adsorbent, simple method and high adsorption efficiency.
The biomaterial serves as a low cost precursor for the preparation of adsorbents. It not only proves to be economical but also solves the problem of waste management. Thus use of biosorbent has become the growing field of interest for researchers against the commercially available adsorbents which are cost prohibitive and exhibit lower adsorption efficiency. Several biomaterial are used for adsorption of dyes from aqueous medium namely apricot stones , oil palm shells , The vetia Peruviana , Mahogany saw dust  and rice husk .
Nerium Oleander is a flowering plant found in the tropical region bearing needle like leaves. These leaves are used as precursor to prepare activated carbon for the removal of malachite green dye from aqueous solution.
Malachite Green dye is a direct dye used on wool, jute, silk, cotton, leather and paper. It also finds application in aquaculture and food industry . However, it is ecotoxic and cause chromosomal fractures and has histopathological effects like multi-organ tissue injury . Thus treatment of Malachite Green dye is of greater concern.
A. Preparation of adsorbent:
The dried fallen leaves of Nerium Oleander were collected from the local grounds near Tamilnadu Agricultural University, Coimbatore. They were washed well with double distilled water, sun dried and used. The cleaned leaves were activated chemically by soaking them in 1:1 sulphuric acid  (Qualigens, Mumbai) overnight. The partially activated carbon obtained from oleander leaves were washed with double distilled water and were soaked in 10% NaHC[O.sub.3] (E-Merck India Limited, Mumbai) overnight. It was subjected to thermal activation in a muffle furnace at 5000C for 2 hours and then cooled to room temperature. The finely ground and sieved activated carbon (125 micron sieve) was stored in air tight bottles and used as adsorbent.
B. Preparation of Adsorbate:
100 mg of malachite green dye(AR grade, Loba Chemie Ltd.,Mumbai) was dissolved in 1000ml of double distilled water and 100 ppm of stock solution was prepared. A range of test solutions were prepared of desired concentrations from the stock. A calibration curve was drawn from the obtained results which were used to calculate residual dye concentration; amount of dye adsorbed and dye removal percentage.
C. Batch mode studies:
Experiments were carried out in batches to test the adsorption of malachite green onto NOAC. Initial concentration (10-100mg/l), adsorbent dose (0.01-0.1g), pH (1.0-9.0) and contact time (30-150 min) were fixed to investigate adsorption. All experiments were performed at room temperature (30 [+ or -] 1[degrees]C, 303 [+ or -] 1 K). A known weight of adsorbent was added to 50 ml of dye solution of desired concentration and shaken in Bench top incubator cum orbital shaker (model: NEOLAB OSI 261) for a prefixed time interval. After equilibrium, the test solution was filtered with Whatman 42 filter paper and the residual dye concentration was measured using UV/Vis spectrophotometer.
RESULTS AND DISCUSSION
A. Characterization of adsorbent:
Activated carbon prepared from Nerium oleander leaves was characterized for its physical properties and is summarized as:
PH 6.41 Moisture 1.57% Volatile matter 1.79% Ash 2.30%
The FTIR spectra of NOAC and MG dye loaded NOAC are shown in figure 2 and 3 respectively. In figure 2, a sharp band can be observed at 1100 [cm.sub.-1] that represents C-O stretching in alcohol, carboxylic acid, ester or ether. Some weak bands at 2343 [cm.sup.-1] ascribe to C = N stretching of nitriles and between 750-600 [cm.sub.-1] correspond to phenolic alcohol.
In figure 3, the peak around 1150 [cm.sub.-1] corresponding to C-O stretching in alcohol, carboxylic acid, ester or ether is broad and got shifted from 1100 [cm.sub.-1] (figure 2) due to adsorption of dye to NOAC. A sharp band at 1550 [cm.sub.-1] indicates C=C stretching involved in benzene rings (aromatic systems) and N-H bending of amines present in the dye. Some bands beyond 3500 [cm.sub.-1] represent O-H stretching of carboxylic acid group of MG dye adsorbed on NOAC .
Experiments were performed and the results were consolidated to understand the adsorption behaviour of NOAC.
Some of the adsorption parameters are calculated as follows:
Removal efficiency, % = [C.sub.0] - [C.sub.e]/[C.sub.0] X 100 (1)
Amount of dye adsorbed, qe = [C.sub.0] - [C.sub.e]/M X V (2)
where [C.sub.e], mg/l is the concentrations of dye at equilibrium [C.sub.0] (mg/l) is the initial concentration of the dye in solution. V (l) is the operating volume of the solution M (mg) is the mass of dry adsorbent
IV. Effect of initial dye concentration and adsorbent dose:
The amount of dye adsorbed onto adsorbent depends on its initial concentration. At lower concentration, all the dye molecules tend to occupy the surface sites of the NOAC (99.5 % removal for 10 ppm). For subsequently higher concentrations, dye removal was found to be more than 75% and gradually drops down as shown in fig. with increase in concentration for the same amount of NOAC. This is due to the unavailability of surface voids on NOAC for the higher concentrations of the dye. Thus the number of surface sites on the adsorbent can be increased with increase in adsorbent dose. Lower doses of NOAC shows less dye removal. However, at higher NOAC dose (0.02-0.06 g), more number of surface sites is created that attracts dye molecules. Beyond 0.07 g of NOAC, removal percentage remains constant because of equilibrium established between the dye on the adsorbent and the dye in the test solution. Such results are reported in earlier literature .
V. Effect of ph and contact time interval:
The pH of the dye solution was adjusted using 0.1M HCl and 0.1M NaOH. This changes the polarity on the adsorbent and thus varies its adsorption behaviour. It was observed that at extremely low (pH 1) and high pH (pH >=10), the colour of the test solution fades without the support of the adsorbent. However, studies were performed at the pH 2-9. Similar observation was noted for pH 2 (97.8% removal) where the dye fades which makes the observation insignificant. At lower pH the dye is prorogated that gets strongly repelled by the positive surface sites that shows less adsorption. However, dye gets deprotonated at subsequently higher pH and increases negative charge density on the dye thereby creating a thrust for cations . This enhances the electrostatic force of attraction between the dye and the surface sites of the adsorbent that results in more dye removal percentage. The dye removal also depends on adsorbate--adsorbent interaction with respect to time. The adsorbate--adsorbent interaction is driven by the time of contact. The interaction increases with the extension of time. In the beginning dye uptake is less as its takes time for all the dye molecules to get adsorbed to the surface voids of NOAC. With the extension of time interval all the dye molecules get adsorbed to NOAC accounting for more dye removal. However, above 120 minutes equilibrium is reached and removal percentage remains constant because of attainment of saturation between dye and NOAC.
VI. Adsorption isotherms:
Adsorption isotherms relates the adsorbate--adsorbent interaction at equilibrium. Langmuir and Freundlich adsorption isotherms were evaluated and expressed as
Langmuir isotherm: [C.sub.e]/[q.sub.e] = [C.sub.e]/[q.sub.m] + 1/[K.sub.L][q.sub.m] (3)
Freundlich isotherm: log [q.sub.e] = log [K.sub.F] + (1/n) log [C.sub.e] (4)
where [C.sub.e] is the dye concentration at equilibrium [q.sub.e] ia the amount of dye adsorbed per g of adsorbent [q.sub.m] is the monolayer adsorption capacity [K.sub.L] is Langmuir adsorption constant n is Freundlich constant [K.sub.F] is Freundlich Coefficient
A straight line for Langmuir plot shows that adsorption follows Langmuir's isotherm and [q.sub.m] and [K.sub.L] can be determined from the slope and intercept of the plot respectively. The applicability of isotherm models is decided by correlation coefficient, [r.sup.2].
Fig. 7 indicated linear plot thus obeying Langmuir isotherm that correspond to a saturated monolayer adsorption of the dye onto the homogeneous surface of NOAC. The Langmuir adsorption fits well with the data with the correlation coefficient of 0.9802.The values of [K.sub.L] and [q.sub.m] are given in Table 7.
The separation dimensionless parameter [R.sub.L] values indicate the applicability of isotherm model. Langmuir isotherm is favorable if 0 < [R.sub.L] < 1, unfavorable if [R.sub.L] > 1, linear if [R.sub.L] = 1, or irreversible if [R.sub.L] = 0 . It is calculated as,
[R.sub.L] = 1 / (1 + [K.sub.L] x [C.sub.e]) (5)
From Langmuir plot, [R.sub.L] values were obtained between 0.706 and 0.002 which confirms that adsorption is favorable.
Freundlich isotherm exhibits an empirical relationship of adsorption of adsorbate to the adsorbent. The plot between log [q.sub.e] versus log [C.sub.e] did not give a straight line which implied that adsorption did not obey Freundlich isotherm. The values of n and [K.sub.F] are given in Table 7. Though the value of 1/n = 0.16 (i.e. 1/n < 1) indicate favourable adsorption condition , the correlation coefficient, [r.sup.2] = 0.8498 which is very poor compared to Langmuir model.
VII. Adsorption kinetics:
The rate of adsorption and the mechanism of adsorbate--adsorbent interaction depends on the ionic nature of adsorbate and adsorbent surfaces. These can be investigated using Lagergren equations.
Pseudo first order equation: log ([q.sub.e] - [q.sub.t]) = log [q.sub.e] - [k.sub.1] t/2.303 (6)
Pseudo second order equation: t /[q.sub.t] = 1/[k.sub.2] [qe.sup.2.sub.+] t/qe (7)
where [q.sub.e] and [q.sub.t] are the amounts of dye absorbed at equilibrium and at any time t
[k.sub.1] is the reaction rate constant in [s.sup.-1] of pseudo first order
[k.sub.2] is the rate constant of pseudo second order
Pseudo first order model interprets the rate of adsorption as the function of difference in saturated concentration and amount of dye adsorbed with time . This is expressed by the equation no. 8.
[dq.sub.t] / dt = [k.sub.1] ([q.sub.e] - [q.sub.t]) (8)
The plot of log([q.sub.e] - [q.sub.t]) versus t at different concentrations is given by figure 9. The plot should give a straight line from which the kinetic parameters [k.sub.1] and [q.sub.e] can be calculated for the slope and intercept respectively. The graph shows straight lines for some concentrations which implies that pseudo first order kinetics fits well and there is a good correlation in equilibrium attained.
The applicability of pseudo second order kinetics can be understood by the linear line of the plot between t /[q.sub.t] versus t for different initial dye concentration. From such plot the rate constant [k.sub.2] and qe can be calculated from the intercept and slope respectively. Figure 10 did not indicate straight lines for any of the initial dye concentrations and implies that pseudo second order kinetic model is not a good fit for the obtained experimental data for the adsorption of MG dye onto NOAC. The values of rate constants and [q.sub.e] (cal) and correlation coefficient [r.sup.2] for different initial dye concentrations are summarized in Table 8.
Although kinetics models depicts the rate of adsorption and its dependent factors, it is not suitable to predict the diffusion mechanism . The solute from the liquid travel to the surface of the adsorbent and get diffused into the voids. The mechanism behind such behaviour of MG dye onto NOAC is analysed by intra particle diffusion model.
Intraparticle diffusion model was developed by Weber and Morris, Mekay and Poots  and is represented by equation no. 9.
[q.sub.t] = [k.sub.i] [t.sup.1/2] + C (9)
where [k.sub.i] is the intra-particle diffusion rate constant
C is the intercept
Figure 11 shows a plot of [q.sub.t] versus [t.sup.1/2] in which some of the lines are linear for some concentrations but does not pass through the origin. This implies that the diffusion mechanism of MG dye onto NOAC is operated by pore diffusion which is the only rate controlling step and not film diffusion. The values of [k.sub.i] and [r.sub.2] are consolidated in Table 8.
A low cost activated carbon was prepared from Nerium oleander leaves and tested for the adsorption of malachite green dye from the aqueous medium. The amount of MG dye adsorbed onto NOAC increased from 19.9 mg/g to 70 mg/g for dye concentrations 10-100 mg/l, from 15.59 mg/g to 51.5mg/g for the adsorbent dose 10-100 mg, from 25 mg/g to 57.9 mg/g for the pH 3-9and from 42.8 mg/g to 166.7 mg/g for the contact time 30-150 minutes. Adsorption isotherm investigations indicated that Langmuir isotherm best fits the obtained experimental data. This is supported by dimensionless parameter [R.sub.L] (0 < [R.sub.L] < 1). Kinetic studies confirmed that rate of adsorption followed pseudo first order and intra particle diffusion model proved that MG dye adsorption onto NOAC followed pore diffusion rather than film diffusion.
The authors J.Sheeja and K.Sampath acknowledge the laboratory support offered by Chemistry departments of Sri Ramakrishna Engineering College and Kumaraguru College of Technology, Coimbatore and material characterization support offered by Nanoscience and Technology department, Sri Ramakrishna Engineering College, Coimbatore.
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(1) J. Sheeja and (2) K. Sampath
(1) Department of Chemistry, Sri Ramakrishna Engineering College, Coimbatore, India.
(2) Department of Chemistry, Kumaraguru College of Technology, Coimbatore, India.
Received 28 February 2017; Accepted 22 May 2017; Available online 6 June 2017
Address For Correspondence:
J. Sheeja, Department of Chemistry, Sri Ramakrishna Engineering College, Coimbatore, India.
Caption: Fig. 1: Structure of malachite green dye
Caption: Fig. 2: FTIR spectrum of NOAC
Caption: Fig. 3: FTIR spectrum of NOAC loaded with MG dye
Caption: Fig. 3: Effect of initial concentration on adsorption
Caption: Fig. 4: Effect of adsorbent dose on dye Dye adsorption
Caption: Fig. 5: Effect of pH on dye removal
Caption: Fig. 6: Effect of contact time on dye removal
Caption: Fig. 7: Langmuir plot of MG dye onto NOAC
Caption: Fig. 8: Freundlich plot of MG dye onto NOAC
Caption: Fig. 9: Pseudo first order plot for MG dye to NOAC
Caption: Fig. 10: Pseudo second order plot for MG dye to NOAC
Caption: Fig. 11: Intra particle diffusion mechanism for MG dye to NOAC
Table 1: Effect of initial concentration on dye removal Concentration, Eq. Rem. amount mg/l concentration Eff,% adsorbed, mg/g 10 0.05 99.5 19.9 20 3.1 84.5 33.8 30 7.25 75.8 45.5 40 16.15 59.63 47.7 50 21.5 57 57 60 28.15 53.08 63.7 70 38.45 45.07 63.1 80 45 43.75 70 90 57.85 35.72 64.3 100 74.25 25.75 51.5 Table 2: Effect of adsorbent dose on dye removal Carbon Eq Rem Amt dose, g concentration Eff,% Adsorbed, mg/g 0.01 74.25 25.75 51.5 0.02 52.05 47.95 47.95 0.03 41.45 58.55 39.03 0.04 35.75 64.25 32.13 0.05 31.55 68.45 27.38 0.06 26.35 73.65 24.55 0.07 22.15 77.85 22.24 0.08 22.15 77.85 19.46 0.09 22.1 77.9 17.31 0.1 22.05 77.95 15.59 Table 3: Effect of pH on dye removal pH Eq. Rem Amt concentration Eff,% adsorbed, mg/g 2 0.65 97.8 58.7 3 17.5 41.67 25 4 14.05 53.17 31.9 5 12 60 36 6 6.25 79.17 47.5 7 5.15 82.83 49.7 8 3.25 89.17 53.5 9 1.05 96.5 57.9 Table 4: Effect of contact time on dye removal Time 10 20 30 40 50 interval, rem rem rem rem rem min eff, % eff, % eff, % eff, % eff, % 30 23.5 37.25 35.5 44.63 45.2 60 99.5 84.5 75.8 59.63 57 90 99.5 90 79.83 67 67.4 120 99.5 91.75 83.3 83.9 82.1 150 99.5 95 89 84 82.5 Time 60 70 80 90 100 interval, rem rem rem rem rem min eff, % eff, % eff, % eff, % eff, % 30 43.97 46.07 38.75 30.7 21.4 60 53.08 52.14 43.75 35.7 25.75 90 70.97 65.29 56.25 51.27 47.4 120 82.58 82.8 82.93 83.5 82.65 150 83.92 85.07 85 83.61 83.35 Table 5: Langmuir isotherm parameters Concentration, Eq.concentration Rem. amount Ce/qe mg/l ([C.sub.e]), mg/l Eff,% adsorbed, mg/g 10 0.05 99.5 19.9 0.003 20 3.1 84.5 33.8 0.09 30 7.25 75.8 45.5 0.16 40 16.15 59.63 47.7 0.34 50 21.5 57 57 0.38 60 28.15 53.08 63.7 0.44 70 38.45 45.07 63.1 0.61 80 45 43.75 70 0.64 90 57.85 35.72 64.3 0.9 100 74.25 25.75 51.5 1.44 Table 6: Freundlich isotherm parameters Concentration, Eq. concentration, Rem. amount mg/l mg/l Eff,% adsorbed, mg/g 10 0.05 99.5 19.9 20 3.1 84.5 33.8 30 7.25 75.8 45.5 40 16.15 59.63 47.7 50 21.5 57 57 60 28.15 53.08 63.7 70 38.45 45.07 63.1 80 45 43.75 70 90 57.85 35.72 64.3 100 74.25 25.75 51.5 Concentration, Ce/qe log log mg/l Ce qe 10 0.003 -1.3 1.3 20 0.09 0.49 1.53 30 0.16 0.86 1.9 40 0.34 1.2 1.7 50 0.38 1.33 1.76 60 0.44 1.45 1.8 70 0.61 1.6 1.8 80 0.64 1.65 1.85 90 0.9 1.76 1.81 100 1.44 1.87 1.71 Table 7: Langmuir and Freundlich adsorption parameters Time Langmuir parameters Freundlich parameters interval, min qm KL r2 1/n KF r2 30 142.9 0.01 0.3593 0.488 7.08 0.7108 60 50 0 0.9768 0.176 31.35 0.7736 90 100 0.2 0.9837 0.327 27.54 0.9442 120 200 0.11 0.7591 0.644 22.9 0.9446 150 200 0.142 0.8100 0.521 33.11 0.9461 Table 8: Kinetic equilibrium parameters Initial Pseudo first order concentration, mg/l qe(exp) qe(cal) k1 r2 10 19.9 5.75 0.005 0.9142 20 33.8 9.77 0.005 0.9352 30 45.5 16.6 0.005 0.9165 40 47.7 24.7 0.0046 0.8746 50 57 31.6 0.0046 0.9085 60 63.7 37.15 0.0055 0.9183 70 72.9 50.11 0.0053 0.9043 80 70 38.9 0.007 0.9103 90 64.3 30.9 0.01 0.9289 100 51.5 20.9 0.014 0.9193 Initial Pseudo second order concentration, mg/l qe(exp) qe(cal) k2 10 19.9 58.8 6.45 x [10sup.-4] 20 33.8 58.8 8.11 x [10sup.-4] 30 45.5 76.9 6.04 x [10sup.-4] 40 47.7 100 7.3 x [10sup.-4] 50 57 111.1 6.8 x [10sup.-4] 60 63.7 142 5.9 x [10sup.-4] 70 72.9 166 5.1 x [10sup.-4] 80 70 250 4.25 x [10sup.-4] 90 64.3 500 3.9 x [10sup.-4] 100 51.5 4.1 x [10sup.-4] Initial Intra particle diffusion concentration, mg/l r2 ki r2 10 0.4757 1.963 0.7738 20 0.9411 3.095 0.8629 30 0.9597 4.279 0.8952 40 0.9888 4.877 0.9846 50 0.9876 5.935 0.9848 60 0.9649 7.821 0.9800 70 0.9649 8.919 0.9710 80 0.8574 12.239 0.9477 90 0.6574 16.073 0.9411 100 -0.0334 21.039 0.9439
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|Author:||Sheeja, J.; Sampath, K.|
|Publication:||Advances in Natural and Applied Sciences|
|Date:||Jun 1, 2017|
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