Adsorptive removal of Direct Red 81 dye from

Sustainable Environment Research 26 (2016) 117e123

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Sustainable Environment Research journal homepage: www.journals.elsevier.com/sustainableenvironment-research/

Original research article

Adsorptive removal of Direct Red 81 dye from aqueous solution onto Argemone mexicana Shraddha Khamparia a, *, Dipika Jaspal b a b

Symbiosis Centre of Research and Innovation, Symbiosis International University, Pune 412115, India Department of Applied Science, Symbiosis International University, Pune 412115, India

a r t i c l e i n f o

a b s t r a c t

Article history: Received 13 May 2015 Received in revised form 13 October 2015 Accepted 21 January 2016 Available online 12 April 2016

A low cost adsorbent has been tested for its adsorption ability to remove a hazardous dye from textile wastewater. The present paper assesses the results pertaining to the investigation conducted on removal of a di azo sulphonated dye, Direct Red 81 by adsorption onto a natural adsorbent, Argemone mexicana. Adsorption studies were carried out in both batch and column mode to examine the influence of various parameters on the removal efficiency of the uncharted natural adsorbent. A fixed-bed column has been designed and necessary parameters have been calculated by applying mass transfer kinetic approach. The data obtained have been successfully used to equate different adsorption isotherm models. Isothermal data were found to fit well with Langmuir adsorption model. The estimated mean adsorption energy from the DeR isotherm model has been obtained as 1.34 104 J mol1 further conferring to the chemical process of the adsorption. The adsorption interaction of direct dye on to A. mexicana obeyed pseudo second-order rate equation. Intraparticle diffusion studies revealed the dye adsorption interaction was complex and intraparticle diffusion was not only the rate limiting step. Column operations depicted good adsorption leading with 98% saturation of dye. © 2016 Chinese Institute of Environmental Engineering, Taiwan. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/bync-nd/4.0/).

Keywords: Adsorption Argemone mexicana Textile dye Decolorization

1. Introduction Tremendous amounts of different synthetic dyes are being formulated globally which are remarkably consumed by color industry [1,2]. Amongst different kinds of dyes, azo dyes accounts for nearly half of the total dyes consumed in the textile industries [3e5]. During the dyeing process, about 10e15% of unfixed dye is lost in water which comes out as a colored effluent from the industries [6]. Hence it is essential to completely remove these toxic dyes from wastewater effluents [7]. Several researchers have embraced the adsorption approach to treat the textile wastewater by means of natural and synthetic adsorbents. Present study aimed at economic removal of Direct Red 81 using a low cost natural adsorbent by adopting adsorption technique. Direct Red 81, a toxic sulphonated azo-based dye, known for its carcinogenic nature and toxicity towards animals and humans is selected as a synthetic model dye solution for experimentation which is widely used in * Corresponding author. E-mail address: [email protected] (S. Khamparia). Peer review under responsibility of Chinese Institute of Environmental Engineering.

many industries [8e10]. Ingestion of significant amount of this dye results in gastro-intestinal discomfort producing nausea and vomiting. It also has harmful effect on skin and eyes. Presence of double azo linkage along with sulphonic acid group, makes the dye easily soluble in water [11,12]. Earlier researches have been carried out with modified Silk Maze [13], native and citric acid modified bamboo sawdust [14], Chamomilla plant [15] and Sonchus fruit plant [16] for removal of Direct Red 81 using these modified agricultural wastes. Argemone mexicana seeds utilized in this work belongs to the family of Papaveraceae which is widely available all over the globe. It is commonly known as Mexican prickly poppy. In India it is known as ‘Satyanashi’ meaning devastating and is phytotoxic to many other crop species [17,18]. The present investigation is aimed at studying the kinetics and adsorption isotherms of the adsorption of Direct Red 81 with an objective to explore optimum conditions for the removal of the dye by adsorption technique using A. mexicana as a novel low cost adsorbent. Since very few research have been carried out with unmodified natural material to treat Direct Red 81, present study will unveil the pristine low cost natural adsorbent in the field of textile wastewater treatment.

http://dx.doi.org/10.1016/j.serj.2016.04.002 2468-2039/© 2016 Chinese Institute of Environmental Engineering, Taiwan. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

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S. Khamparia, D. Jaspal / Sustainable Environment Research 26 (2016) 117e123

2. Experiments

The experiment was performed by varying several parameters like pH, dye concentration, contact time, amount of adsorbent, particle size, and temperature.

2.1. Materials and methods Direct Red 81, a sulphonated azo dye, disodium; (3E)-7benzamido-4-oxo-3-[[4-[(4-sulfonatophenyl)diazenyl]phenyl]hydr azinylidene]naphthalene-2-sulfonate, having molecular formula C29H19N5Na2O8S2 and molecular weight 676 g mol1 was procured from SigmaeAldrich. The structure is shown in Fig. 1. Maximum absorption wavelength of the dye is 508 nm. Dye stock solution of concentration 103 M was prepared in distilled water. All solutions were prepared by diluting the stock solution with distilled water. 2.2. Material development For experimentation, the natural adsorbent opted for this study was collected from Lavale road, near the Symbiosis International University Campus Pune, were it was available in plenty. The seed capsules were separated from the thorny plant carefully and dried in sunlight for about 48 h. Seeds were separated from the capsules and were further dried in a Labline Hot air oven for 4 h at 110 C. Moisture free seeds were then cleaned and finally grounded in a grinder to get a fine powder. Subsequently the fine powder was sieved by using a sieve set and then was collected in the range of 600e425, 425e300 and 300e125 mm particle size respectively. The particle size of the adsorbent was determined by sieve analysis using Standard test sieves as per IS-460 (Indian standards). Fourier transform infrared spectroscopy (FTIR) analysis was also carried out in order to find out the morphology and characterization. 2.3. Batch adsorption studies To access the propensity of adsorption process, batch studies were carried out by varying different physiochemical conditions. Batch adsorption studies were conducted by taking 25 mL of dye solution in 100 mL of volumetric flask at 30, 40 and 50 C using suitable sieve size and definite amount of adsorbent. The test solution was intermittently shaken with a speed of 100 rpm in an orbital shaker BTI-05 for 1 h and then was kept for 24 h for saturation. Thereafter the supernatant liquid was filtered through Whatman filter paper no. 41 (pore size 20 mm) and final equilibrium concentrations of the dye in solution were measured spectrophotometrically at a wavelength of 508 nm, using a Systronic double beam spectrophotometer model no. 2203. Amount of dye adsorbed is calculated as per Eq. (1) below.

qe ¼

ðCo Ce ÞV m

(1)

2.3.1. pH pH is one of the pivotal factors influencing not only the surface charge (ionization/dissociation) of the adsorbent, but also the solution dye chemistry. The effects of initial pH on Direct Red 81 solution using A. mexicana seeds were evaluated within a range between 1 and 10. The pH of the test solutions were adjusted by using HCl and NaOH with an Equiptronics digital pH meter EQ-610. 2.3.2. Amount of adsorbent In order to study the variation in adsorption of Direct Red 81 on the basis of amount of adsorbents, various amounts ranging from 0.02 to 0.12 g of the adsorbent was taken in 100 mL volumetric flask and experiments were performed at three different temperatures 30, 40 and 50 C, keeping other parameters constant. 2.3.3. Particle size Another influential factor during adsorption is size of the particle. In order to study the effect of particle sizes, batch adsorption experiments were conducted at three sieve sizes, i.e., 600, 425 and 300 mm. 2.3.4. Concentration The effect of concentration on adsorption of Direct Red 81 by A. mexicana seeds was investigated keeping other experimental parameters (pH, particle size and adsorbent dosage) constant. After undergoing meticulous experimental procedures, a desired concentration range of 1 105 to 10 105 M was selected and fixed amount of adsorbent (0.1 g) was added to these solutions. 2.3.5. Contact time Contact time study aided in acquiring the optimum time duration for adsorption during the experiment. Fixed amount of adsorbent was taken in single concentration solution for duration of about 360 min and shaken at a speed of 100 rpm at three different temperatures i.e., 30, 40 and 50 C. The supernatant solution was observed after every 30 min. 2.4. Adsorption isotherms For optimization of adsorption process, the results obtained from the adsorption of Direct Red 81 dye onto A. mexicana seeds were analyzed by well-known isotherm models of Langmuir, Freundlich, DubinineKaganereRadushkevich (DeR) and Temkin. In the present paper adsorption isotherm models were extended to describe experimental isotherm data and identify the mechanism of the adsorption process. 2.4.1. Langmuir isotherm According to the Langmuir adsorption isothermal model, maximum adsorption corresponds to the formation of a saturated monolayer of dye molecules on adsorbent surface which stipulates the chemisorption of the process and aids in assessing the adsorption capacity of the adsorbent [19]. Langmuir model, may be expressed as Eq. (2)

1 1 1 ¼ þ qe Qo bQo Ce

Fig. 1. Structure of Direct Red 81 dye.

(2)

The key feature of Langmuir adsorption isotherm can be exhibited in terms of a dimensionless constant separation parameter (RL), expressed by the following Eq. (3) [20].


RL ¼

1 1 þ bCo

(3)

On equating the above relation, the RL values were investigated for the above dye-adsorbent system [21]. 2.4.2. Freundlich isotherm At equilibrium conditions, Freundlich adsorption [22] isotherm model can be predicted by given Eq. (4).

1 log qe ¼ log Kf þ log Ce n

(4)

Generally, Freundlich model was used to describe non-specific adsorption that involves heterogeneous surfaces. 2.4.3. Temkin isotherm Temkin isotherm (Eq. (5)) based on the assumption that the heat of adsorption of all the molecules in the layer increases linearly with coverage due to adsorbate specieseadsorbent interactions, and adsorption is characterized by a uniform distribution of binding energies, up to some maximum binding energy [23].

qe ¼ B ln AT þ B ln Ce

(5)

2.4.4. DeR isotherm The DeR model [24] estimates the characteristic porosity of the adsorbent and the apparent energy of adsorption. The linear form of the model can be given as Eq. (6)

ln Cads ¼ ln Xm bε2

(6)

where Xm is provided by the intercept, b is obtained from slope of the straight line plot of ln Cads vs 32 and 3 can be evaluated by the following Eq. (7)

1 ε ¼ RT ln 1 þ Ce

(7)

The apparent energy of adsorption was related to the activity coefficient generally termed as mean adsorption energy, which was equated using Eq. (8).

E¼

1 √2b

(8)

requirement for attainment of equilibrium during the adsorption process investigations were carried out in air tight 100 mL volumetric flask with 25 mL of dye solution of known concentration. A definite pH of 7.0 was maintained and 0.1 g of powdered A. mexicana seeds were brought in contact with the adsorbate at different temperatures 30, 40 and 50 C, with periodic shaking. The solutions were then filtered at fixed time intervals using Whatman filter paper no. 41 and evaluated spectrophotometrically for the dye uptake. 3. Results and discussion 3.1. Adsorbent characterization FTIR spectroscopy of the sieved adsorbent was done using JASCO FT/IR 6100, Department of Physics, Pune University, India. Fig. 2 shows the FTIR spectrum of the A. mexicana investigated in this study. Evidence of intense peak in the range of 700e1300 cm1 indicates the presence of CeC stretching bonds. A number of peaks are found in the range of 1200e1500 cm1 indicating methylene and hydroxyl bonds in the adsorbent. A peak at 3272 cm1 confirms the presence of hydroxyl group. Further the occurrence of carboxylic group is noticed by a peak in the range of 1700e1800 cm1. Aliphatic CeH stretching absorption bands are also evident in the range of 2750e3000 cm1. The presence of saturated and unsaturated carbon derivatives is indicated by a broad absorption peak between 600 and 700 cm1. 3.2. Batch adsorption studies 3.2.1. Effect of pH From the set of experiments conducted, it was found, that pH influences the surface - dye binding sites and the dye chemistry in water. Results showed that maximum adsorption took place at pH 2 which decreased with the increase in pH. At low pH, the adsorbent surface is surrounded by the hydronium ions (Hþ) facilitating high electrostatic attraction between the positively charged adsorbent surface and the dye molecules. While at higher pH a negatively charged adsorbent surface retards the adsorption of dye molecules thereby resulting in decreased adsorption [25]. Maximum adsorption for Direct Red 81 was observed at low pH, but due to the fact that almost all water bodies have pH in range of 6e8 and this system will be useful in natural conditions [26], for the further studies pH 7 was chosen, giving an idea of adsorption capacity in neutral conditions.

2.5. Column studies In column experiment a glass column (1 cm internal diameter and 30 cm length) was filled with suitable amount of A. mexicana seeds on glass wool support. Adsorbent was fed into the column in the form of slurry to avoid air entrapment. Direct Red 81 dye solution of known concentration at 30 C and pH 7 was percolated through the column at a fixed flow rate. To obtain the breakthrough curve, the effluent was collected and analyzed. Column studies were terminated when the column reached exhaustion. After complete adsorption, desorption studies were carried out using 1 N NaOH solution as an eluent. 2.6. Kinetic studies To determine the kinetics i.e., the influence of concentration and temperature on rate of reaction and to evaluate the time

119

Fig. 2. FTIR spectrum of A. mexicana seeds.


3.2.2. Effect of amount of adsorbent With increase in amount of adsorbent, adsorption was found to increase, i.e., from 3.4, 5.4, 8.4 to 7.9, 8.2 and 8.9 106 mol g1 at 30, 40 and 50 C respectively. It was observed that the Direct Red 81 removal increased initially and then became almost constant. This increase in the adsorption with the adsorbent dosage was attributed to greater surface area and the availability of more binding sites for dye molecules [14]. It was evident that the dye removal efficiency increased rapidly with increasing dosage of adsorbent until it reached the value of 0.1 g. On the other hand, further increase in the adsorbent dosage up to 0.12 g did not show significant change in adsorption. This was due to the binding of almost all dye ions to surface of adsorbent and the maintenance of equilibrium between the dye molecules on the adsorbent and those present in the solution [27]. Hence 0.1 g of adsorbent was selected as optimized dose for further studies. 3.2.3. Effect of particle size Results showed that with decrease in particle size the amount adsorbed increased. On an average the amount of dye adsorbed increased from 0.75 to 0.85 mol g1 for the studied system for sieve sizes, i.e., 600, 425 and 300 mm. The reason behind the increased adsorption was due the increase in surface area of the adsorbent with decrease in particle size [28]. The above result is further supported by the rate constant and half-life values obtained in each case. Impact of temperature along with change in particle size was also investigated. The study was carried out at three different temperatures which again showed that with increase in temperature, rate of reaction also increases i.e., from 0.05, 0.06, 0.06 to 0.07, 0.07 and 0.09 g mg1 min1 with decrease in particle size at 30, 40 and 50 C respectively. The increase in adsorption was due to an increased surface activity and increased kinetic energy of the dye molecule [29]. 3.2.4. Effect of concentration With an increase in concentration of the dye, adsorption increased at all temperatures. Experimental data unveiled the direct relation between temperature and adsorption in the present case. Higher temperature provides greater mobility to the ionized dye molecules, thereby leading to an increased adsorption. Moreover, with increasing the concentration, adsorption increased suggesting a better adsorption at higher concentrations. Results indicated increase in adsorption efficiency i.e. from 0.025, 0.13, 0.18 to 1.3, 1.8, 2.2 105 mol g1 with increase in concentration from 1 105 M to 10 105 M at 30, 40 and 50 C respectively which was due to an increase in the number of active sites on the adsorbents [30]. However, with further increasing the concentration of dye solution, saturation of the adsorbent sites occurred, which did not allow further adsorption of dye molecules at all the temperature ranges under investigation.

3.3. Adsorption isotherms 3.3.1. Langmuir isotherm A linear plot was obtained from the Langmuir adsorption graph between 1/qe and 1/Ce, at three different temperatures (Fig. 3). The linearity of the plot suggested the applicability of the isotherm model with experimental data showing the formation of a monolayer of dye molecule at the adsorbent surface [32]. Qo and b were computed from the slope and intercept of the Langmuir plots, respectively at 30, 40 and 50 C (Table 1). In the present research work, RL values have been found to be 0.67, 0.66 and 0.55 at 30, 40 and 50 C respectively. As evident, magnitude of the RL values lied in between 0 and 1, indicating adsorption to be favorable for the adsorbate-adsorbent system. The maximum equilibrium adsorption capacity (Qo) values were determined as 2.4 3.3 and 6.9 mol g1 at 30, 40 and 50 C. As seen Langmuir isotherm fits the experimental data which may be attributed to the homogenous distribution of active sites on the A. mexicana seeds. 3.3.2. Freundlich isotherm Fig. 4 represents the plot for Freundlich isotherm for the adsorbateeadsorbent system. Values of n and Kf were obtained from intercept and slope of the plot log Ce vs log qe. The value of n, obtained lied in the range of 1e10, indicating favorable adsorption. Value of Kf is 0.02, 0.03 and 0.3 at 30, 40 and 50 C respectively. The values obtained from Freundlich model showed an increase in of adsorption capacity with increase in temperature with an average adsorption capacity of 0.13 mol g1 showing favorable adsorption. 3.3.3. Temkin isotherm The slopes and intercepts obtained from the graphical plot (Fig. 5) were used to calculate the Temkin constants (Table 1). The mean values of energy constant (AT) was found to be 8.5 104 M1. Examination of the data shows that the Temkin isotherm fits well to the adsorption data for A. mexicana seeds. Correlation coefficients R2 obtained from Temkin model were comparable to that obtained for Langmuir equation which was a better fit than Freundlich isotherm, explaining the applicability of Temkin model to the adsorption of Direct Red 81 onto A. mexicana seeds. 3.3.4. DeR isotherm DeR model constants b and Xm were calculated from the slopes and intercept from Fig. 6 respectively. Xm, maximum sorption capacity was determined to be 8.6 mmol g1 and mean adsorption 400000 R² = 0.9574 350000 300000 R² = 0.9843

250000

1/Ce (M-1)

120

200000 150000

3.2.5. Effect of contact time It was found that with increase in temperature and time adsorption increases. It was found that amount of dye adsorbed increased in the time of 0.025e0.85 105 mol g1 from 30 to 50 C respectively on varying the contact time from 30 to 270 min. Initially due to numerous active sites present over the adsorbent surface, adsorption rapidly increased which after some time reached at equilibrium due to unavailability of fresh site for adsorbate and adsorbent bonding [31].

100000

R² = 0.9118

30 ⁰C 40 ⁰C

50000

50 ⁰C

0

0

50000

100000

150000

200000

250000

300000

1/qe (g mol-1) Fig. 3. Langmuir adsorption isotherm for Direct Red 81- A. mexicana seeds system (adsorbent dose ¼ 0.1 g, sieve size ¼ 300 mm and pH 7.0).

S. Khamparia, D. Jaspal / Sustainable Environment Research 26 (2016) 117e123 Table 1 Langmuir, Freundlich, Temkin and DeR constants for removal of Direct Red 81 by Argemone mexicana seeds system (adsorbent dose ¼ 0.1 g, sieve size ¼ 300 mm, pH 7.0). Parameters

Fruendlich Temkin DeR

R² = 0.9643

3

Temperature

Qo 105 (mol g1) b 104 (M1) n Kf AT (M1) b (mol2 J2) Xm (mmol g1) E (J mol1)

Langmuir

4 3.5

2.5

30 C

40 C

50 C

2.4 1.6 1.29 0.02 1.2 105 8 109 7.2 0.79 104

3.3 2.5 1.34 0.03 1.2 105 5 109 5.8 1.0 104

6.9 2.6 1.12 0.3 0.22 105 1 109 12 2.2 104

In Cads

Isotherm

121

2

R² = 0.9687

1.5 30 ⁰C

1 R² = 0.9877

0.5

40 ⁰C 50 ⁰C

0 500000000

700000000

900000000

1.1E+09

1.3E+09

ε2 Fig. 6. DeR adsorption isotherm for Direct Red 81- A. mexicana seeds system (adsorbent dose ¼ 0.1 g, sieve size ¼ 300 mm and pH 7.0).

-6 R² = 0.9505

-5.8 -5.6

R² = 0.9701

-5.4

DSo ¼

log qe

-5.2 R² = 0.8817 -5 -4.8 -4.6

30 ⁰C

-4.4

40 ⁰C

-4.2

50 ⁰C

-4 -4.2

-4.4

-4.6

-4.8

-5

-5.2

-5.4

-5.6

log Ce Fig. 4. Freundlich adsorption isotherm for Direct Red 81- A. mexicana seeds system (adsorbent dose ¼ 0.1 g, sieve size ¼ 300 mm, pH 7.0).

0.00006 0.00005

R² = 0.9842

0.00004 0.00003

qe (mol g-1 )

DHo DG0

0.00001

R² = 0.9883

0 30 ⁰C

-0.00001

40 ⁰C

-0.00002

50 ⁰C

-0.00003 -13

-12.5

-12

-11.5

In Ce

-11

-10.5

-10

-9.5

-9

Fig. 5. Temkin adsorption isotherm for Direct Red 81- A. mexicana seeds system (adsorbent dose ¼ 0.1 g, sieve size ¼ 300 mm, pH 7.0).

energy as 1.3 104 J mol1 which suggest the process to be chemical adsorption since the values lied between 8e16 104 J mol1. 3.3.5. Calculation of thermodynamic parameters In order to describe the thermodynamic behavior several thermodynamic parameters were calculated including DG⁰, DH⁰ and DS⁰ from the following Eqs. (9)e(11) [33].

DGo ¼ RT ln b

DH o ¼ R

T2 T1 b ln 2 T2 T1 b1

(11)

where T is the absolute temperature (K), b, b1 and b2 were obtained from slopes and intercepts of Langmuir isotherms. The negative values of DG⁰ ( 26 kJ mol1) suggested that the adsorption is spontaneous and feasible at all the studied temperatures. Moreover, adsorption process is expected to be exothermic in general but the positive value of DH⁰ (20 kJ mol1) indicates the adsorption reaction endothermic. This uncommon behavior of anionic dyes has been noted by several researchers [34]. The positive value of DS⁰ (147 J mol1 K1) shows that adsorption of Direct Red 81 originates a new order in the surrounding water molecules, conditioning by the affinity of A. mexicana seeds for the dye during adsorption [35]. It also suggests decrement in the number of water molecules surrounding the dye molecules and points out towards the increased randomness at adsorbate and adsorbent interface during the adsorption process. 3.4. Column studies

R² = 0.9639

0.00002

T

(9) (10)

3.4.1. Column adsorption In this study, a solution of concentration 10 105 M of the dye was percolated through the column at a constant flow rate. When the effluent concentration exceeded 99% of the initial level, the column operation was suspended and desorption study was made by rinsing the respective columns with NaOH solution at the same flow rate as that of adsorption process. Fig. 7 represents a typical breakthrough curve between concentration and eluted volume attained during column operation of dye-adsorbent system as well as the desorption curve for the studied system. It was found that about 4 mg of the dye adsorption took place from the dye present in the solution. Parameters such as d, tx, td, tf, f, Fm, Ms and percent saturation of column at break point were calculated by using following Eqs. (12)e(16).

tx ¼

Vx Fm

(12)

td ¼

Vx Vb Fm

(13)

td td ðVx Vb Þ ¼ ¼ t x tf tx þ td ðf 1Þ Vb þ f ðVx Vb Þ

(14)

d D

¼

122


Concentra on × 10-5 (M)

12

10 8 6 4 2

Adsorption Desorption

0 0

50

100

150

200

250

F¼

Volume of effluent (mL) Fig. 7. Adsorption (Breakthrough curve) and Desorption of Direct Red 81 from A. mexicana seeds.

f ¼1

tf Ms ¼ td ðVx Vb ÞCo

Percentage saturation ¼

(15) D þ dðf 1Þ 100 D

(16)

Length of column, D was 2 cm for the system. The breakthrough curve was used to find out the values of Vb, Vx, Cb and Cx, which were then applied to calculate values of tx, tf, td, f and d for the studied system. Fm was found to be 0.03 mg cm2 min1 for the selected adsorbent. 3.4.2. Desorption study The recovery of Direct Red 81 dye was achieved by eluting the dye using NaOH through the exhausted fixed-bed. Fig. 7 describes the trend of collected volume of the eluent versus concentration of recovered amount of dye. It is evident from the graph that maximum attrition of the column took place with first 10 mL of NaOH and rest of the Direct Red 81 was desorbed by eluting ten increments of 10 mL each. Total percentage recovery of the dye was about 80%.

Qt Q∞

The kinetic adsorption data were processed to understand the dynamics of the adsorption reaction in terms of the order of the rate constant. Pseudo first order and second order rate equations were applied to Direct Red 81-A. mexicana seeds system. Equations (17) and (18) given below summarize the Lagergren's pseudo first order and second order equation respectively.

(19)

Here the Qt and Q∞ are amount adsorbed after time t and after infinite time, respectively. Bt values were obtained from Reichenberg's table using values of F, which was further used to plot graph between Bt values and time (plot not shown), which helped to distinguish between film diffusion and particle diffusion. It was seen that linearity was maintained at lower temperatures rather than in higher ones suggesting involvement of film diffusion and particle diffusion mechanisms as the rate-controlling step at lower and higher temperatures respectively. Also it may be concluded that surface adsorption and intra-particle diffusion were synchronously operating during the Direct Red 81-adsorbent interactions. It was observed from the graph that the straight line did not pass through the origin which further indicated that intraparticle diffusion was not solely the controlling rate step but rather was a complex process involving both boundary layer and intraparticle diffusion. At temperatures 30, 40 and 50 C, the values of Di for Direct Red 81 in the adsorbent phase were calculated using Eqs. (20) and (21) which was found to be 1.1 106, 6.1 107 and 3.5 107 m2 s1 at 30, 40 and 50 C respectively.

Ea Di ¼ Do exp RT Do ¼

3.5. Rate constant study

qt ¼ qe 1 expkads t

3.5.1. Rate expression and treatment of data For absolute interpretation of the kinetic data, it is imperative to identify the adsorption process steps, which govern the overall removal adsorption rate. The intuitive mathematical treatment by Boyd et al. [36] was employed to differentiate between particle diffusion and film diffusion. When external transport is greater s to surface than internal transport, i.e., adsorbate molecules attache only, film diffusion takes place, while particle diffusion takes place when adsorbate goes inside the pores of adsorbent making internal transport higher than external transport. The fractional attainment F of equilibrium at time t was calculated by Eq. (19).

s 2:72d2 kT DS exp h R

(20)

(21)

The 1/T versus log Di plot (not shown) was found linear with positive slope thereby indicating a decrease in the mobility of ions and an increase in the retarding forces acting on the diffusing ions with the temperature. The negative value of DSs obtained for the adsorption reflected no significant change occurring in the internal structure of elected adsorbent during the adsorption process as reported in literature [37].

(17) 4. Conclusions

qt ¼

k2 q2e t

1 þ k2 qe t

(18)

In the above equations qe and qt denotes the amount adsorbed at equilibrium and at any time t in g, respectively. kads and k2 are the equilibrium rate constants for pseudo first and second order kinetic models respectively. Nonlinear curves were plotted between qt and time for both the models and compared with the obtained experimental values. Nonlinear regression method was used to calculate the kinetic parameters using solver add-in function which dictated the closeness of experimental data with pseudo second order kinetic model. Also the obtained R2 values were close to unity was indicative of the fact that the ongoing reaction proceeded via pseudo second order mechanism rather than pseudo first order mechanism.

A. mexicana seeds were successfully employed for the removal of a di azo sulphonated textile dye. Results showed that the adsorption of Direct Red 81 dye increased with increasing adsorbent dosage, and decreasing the particle size. It was also noticed that adsorption capacity was strongly dependent on the temperature. A. mexicana seeds showed good removal at acidic pH. In neutral conditions, the minimum equilibration time of the dye was obtained after 4.5 h of contact between dye and adsorbent. Study of correlation coefficients of various adsorption isotherm models showed the satisfactory applicability to the adsorption process. The adsorption of Direct Red 81 onto A. mexicana was found to be a physio-chemical process. The study showed that the adsorption kinetics followed the pseudo-second order rate. Thermodynamic


investigation revealed that the adsorption was spontaneous and feasible at all the studied temperatures. Also the system was endothermic in nature without any significant change in internal structure of adsorbent. Breakthrough studies indicated the quantitative recovery of the dye using NaOH. The employed adsorbent was found to be efficient for dye removal and proved to be a promising solution towards dye wastewater treatment. Acknowledgement One of the Authors (SK) is thankful to the financial support provided by Symbiosis International University to carry out this research under Junior Research Fellowship programme. The fellowship was awarded on 28th January 2014 via notification no. SIU/28/430 dated 26th April 2013. References [1] Palmieri G, Cennamo G, Sannia G. Remazol Brilliant Blue R decolourisation by the fungus Pleurotus ostreatus and its oxidative enzymatic system. Enzyme Microb Technol 2005;36:17e24. [2] Saratale RG, Saratale GD, Chang JS, Govindwar SP. Bacterial decolorization and degradation of azo dyes: a review. J Taiwan Inst Chem Eng 2011;42:138e57. [3] Deveci T, Unyayar A, Mazmanci MA. Production of Remazol Brilliant Blue R decolourising oxygenase from the culture filtrate of Funalia trogii ATCC 200800. J Mol Catal B Enzym 2004;30:25e32. [4] Sponza DT, Isik M. Decolorization and inhibition kinetic of Direct Black 38 azo dye with granulated anaerobic sludge. Enzyme Microb Technol 2004;34: 147e58. [5] Puvaneswari N, Muthukrishnan J, Gunasekaran P. Toxicity assessment and microbial degradation of azo dyes. Indian J Exp Biol 2006;44:618e26. [6] Forgacs E, Cserhati T, Oros G. Removal of synthetic dyes from wastewaters: a review. Environ Int 2004;30:953e71. [7] Kamboh MA, Bhatti AA, Solangi IB, Sherazi STH, Memon S. Adsorption of Direct Black-38 azo dye on p-tert-butylcalix[6]arene immobilized material. Arab J Chem 2014;7:125e31. [8] Sivakumar B, Karthikeyan S, Kannan C. Film and pore diffusion modeling for the adsorption of Direct Red 81 on activated carbon prepared from Balsamodendron caudatum wood waste. Dig J Nanomater Bios 2010;5:657e65. [9] Little LW, Lamb III JC. Acute Toxicity of 46 Selected Dyes to the Fathead Minnow, Pimephales Promelas. Dyes and the Environment e Reports on Selected Dyes and Their Effects. New York: American Dye Manufacturers Institute, Inc.; 1973. [10] Junnarkar N, Murty DS, Bhatt NS, Madamwar D. Decolorization of diazo dye Direct Red 81 by a novel bacterial consortium. World J Microbiol Biotechnol 2006;22:163e8. [11] Sharma N, Tiwari DP, Singh SK. Efficiency of chemically treated potato peel and Neem bark for sorption of Direct Red-81 dye from aqueous solution. Rasayan J Chem 2014;7:399e409. [12] Solmaz SKA, Ustun GE, Birgul A, Yonar T. Advanced oxidation of textile dyeing effluents: Comparison of Feþ2/H2O2, Feþ3/H2O2, O3 and chemical coagulation processes. Fresenius Environ Bull 2009;18:1e11. [13] Heravi MM, Ardalan P, Vafaie A. Equilibrium and kinetic studies of Direct Red 81 biosorption onto modified silk maze as an economical biosorbent. J Chem Health Risks 2014;4:63e73. [14] Ali I, Dahiya S, Khan T. Removal of Direct Red 81 dye from aqueous solution by native and citric acid modified bamboo sawdust e kinetic study and equilibrium isotherm analyses. Gazi Uni J Sci 2012;25:59e87. [15] Heravi MM, Kodabande A, Bozorgmehr MR, Ardalan T, Ardalan P. Kinetic and thermodynamic studies on biosorption of Direct Red 81 from aqueous solutions by Chamomilla plant. J Chem Health Risks 2012;2:37e44. [16] Heravi MM, Abasion Z, Morsali A, Ardalan P, Ardalan T. Biosorption of Direct Red 81 dye from aqueous solution on prepared sonchus fruit plant, as a low cost biosorbent: thermodynamic and kinetic study. J Appl Chem 2015;9: 17e22. [17] Brahmachari G, Gorai D, Roy R. Argemone mexicana: chemical and pharmacological aspects. Rev Bras Farmacogn 2013;23:559e75. [18] Shaukat SS, Siddiqui IA, Khan GH, Zaki MJ. Nematicidal and allelopathic potential of Argemone mexicana, a tropical weed. Plant Soil 2002;245:239e47. [19] Langmuir I. The adsorption of gases on plane surfaces of glass, mica and platinum. J Am Chem Soc 1918;40:1361e403. [20] Hall KR, Eagleton LC, Acrivos A, Vermeulen T. Pore- and solid-diffusion kinetics in fixed-bed adsorption under constant-pattern conditions. Ind Eng Chem Fundam 1966;5:212e23. [21] Sankar M, Sekaran G, Sadulla S, Ramasami T. Removal of diazo and triphenylmethane dyes from aqueous solutions through an adsorption process. J Chem Technol Biotechnol 1999;74:337e44. [22] Freundlich HMF. Over the adsorption in solution. J Phys Chem 1906;57: 385e470.

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Nomenclature qe: amount of dye adsorbed (mol g1) Co: initial dye concentration (M) Ce: dye concentration at equilibrium (M) m: mass of adsorbent (g) V: volume of dye solution (L) Qo: maximum adsorption capacity (mol g1) n: Freundlich constants related to adsorption intensity Kf: adsorption capacity AT: Temkin isotherm energy constant (M1) B: Temkin isotherm constant Cads: amount of dye adsorbed per unit weight of the adsorbent (mg g1) Xm: maximum sorption capacity provided by the intercept (mmol g1) 3 : Polanyi potential R: universal gas constant in (kJ mol1 K1) DGo: Gibb's free energy (J mol1) DHo: change in enthalpy (J mol1) DSo: change in entropy (J K1 mol1) b, b1 and b2: Langmuir constants at 30, 40 and 50 C d: length of primary adsorption zone (cm) tx: time involved in establishing the primary adsorption zone (min) td: time required by primary adsorption zone to move down its length (min) tf: time of initial formation of primary adsorption zone (cm) f: fractional capacity of the prepared column Fm: mass rate of flow to the adsorbent (mg cm2 min1) Ms: amount of adsorbate adsorbed in the primary adsorption zone from break point to exhaustion (mol g1) Di: effective diffusion coefficient (m2 s1) b: activity coefficient (mol2 J2) DSs: entropy of activation (J K1 mol1) D: length of the column bed (cm) Vx: volume of effluent at 90% adsorption (mL) Vb: volume of effluent at 2% adsorption (mL) Cb: concentration of dye solution at 2% adsorption (M) Cx: concentration of dye solution at 90% adsorption (M)