Adsorption Isotherms, Kinetics and thermodynamic studies of Vat Brown 16 Dye using ZnO and Nano-ZnO Particles

 

Barakat A. F. Kamel*, Amel S. Mahdi, Athraa A. Ahmed, Dina A. Ali and Kafi M. Dawood

Department of Chemistry, College of Science, University of Al-Mustansiriyah, Iraq

 

ABSTRACT:

In this research the adsorption of Vat Brown 16 Dye on ZnO and Nano-ZnO particles  were investigated, the effect of changing the contact times, the effect of changing the initial concentrations of the dye were applied, The adsorption kinetics of dye studied and found that the reaction was ( Pseudo-second order), the effect of changing the temperatures studied to apply the adsorption isotherms ( Langmuir and freundlich) models which are calculated the isotherm constants to calculate the thermodynamic parameters ( ΔH, ΔG and ΔS). The negative values of ΔH indicate that the adsorption of Vat Brown16 Dye on ZnO and Nano-ZnO was exothermic, the positive values of ΔS reflects good affinity of Vat Brown16 Dye towards ZnO and Nano-ZnO. The results have established good potentiality for Nano-ZnO particles to remove the polutant dye from the water better than ZnO particles. 

 

 

1. INTRODUCTION:

Unlike most organic compounds, dyes possess color because they 1) absorb light in the visible spectrum (400–700 nm), 2) have at least one chromophore (colour-bearing group), 3) have a conjugated system, i.e. a structure with alternating double and single bonds, and 4) exhibit resonance of electrons, which is a stabilizing force in organic compounds. When any one of these features is lacking from the molecular structure the colour is lost. [1]. They are produced either chemically or from plants. An interesting point about them is that unlike paint, they do not build up on the surface of the fibre but are absorbed into the pores of the material. This becomes possible because of two reasons. First, the size of the dye molecules is smaller than the size of the pores in the fibre. The dye molecules have a shape like narrow strips of paper, that is having length and breadth but relatively little thickness[2]. Industrial dye effluents, such as paper, plastics, leather, pharmaceutical, food, cosmetics, dyestuffs, and textiles[3], have always been a

 

serious environmental problem,  Lots of dyes are toxic and may cause direct destruction to aquatic communities[4]. vat dyes are one of two main classes which are derivatives of indigo and anthraquinone, the latter type being most popular. Vat dyes produce dyeings which display the highest overall fastness properties of all dyes used on cellulosic fibres[5], they contain at least two, conjugated carbonyl groups ( - C = O) that enable the dye to be converted, by means of reduction under alkaline conditions, to the corresponding water-soluble ionized  leuco compound [6].  Adsorption process is an attractive and effective alternative treatment for dye removal from wastewater. There are many advantages of adsorption process, such as less land area (half or a quarter of what is required in a biological system), lower sensitivity to diurnal variation, not getting affected by toxic chemicals, greater flexibility in the design and operation and superior removal of organic contaminants[7]. The conventional methods for removal of dyes from industries effluent are coagulation, filtration, floatation, ion exchange, chemical oxidation, photo degradation, solvent extraction and membrane separation etc. These methods have some drawback such as high cost, operating required sensitive conditions, and less efficiency [8].  In this work Vat Brown 16 Dye was used in the adsorption on ZnO and Nano-ZnO particles.

 

EXPERIMENTAL

Materials and methods:

All chemical materials used in this work were purchased from Merck: vat brown 16 (C₄₉H₂₀ClN₃O₇,  C.I.70910) , Distilled water, ZnO and Nano-ZnO particles.

 

 

Fig.1. The structure of Vat Brown16 Dye

 

Calibration Curve Determination:

The determination of calibration curve was carried out for Vat Brown 16 dye by preparation of several solutions in different concentrations at constant wave length (λmax= 281nm). The relation between absorbance and concentration was carried out according to (Bear-Lambert Law): (A=ε. b. C), which showed a linear relation, its slope represents the molar absorbance coefficient (ε = 0.025). Fig. 2 shows this relation:

 

 

Fig. 2. Calibration Curve of Vat Brown16 Dye   

 

Adsorption Experiments:

In each adsorption experiment, 10 ml of dye solution with a concentration (30ppm) was added to 0.1 g of Zno or Nano-ZnO in a 250 ml glass-stopper flask at 30 ± 0.5 0C, and the mixture was stirred on a mechanical shaker (Model: BS-11 degetal, JEIO Korea, TECH.)  at 182 min^-1. The samples were withdrawn during stirring at preset time intervals, and the adsorbent was separated from the solution by filtration papers. The absorbance of the supernatant solution was estimated to determine the residual dye concentration, and was measured before and after treatment with double beam  spectrophotometer (Hitachi U 2000 Spectrophotometer). The initial dye concentration in the test solution and the adsorbent dosage were varied to investigate their effect on the adsorption kinetics. The adsorption studies were carried out at different temperatures (303, 313,323 and 333)K. This is used to determine the thermodynamic parameters. The amount of equilibrium adsorption q_e (mg /g) was calculated using the following equation:

 

q_e = ( C_o – C_t ) V / m                        …………..(1)

 

Where,  C_t (mg. L^-1) is the liquid phase concentrations of dye at any time, C₀ (mg. L^-1) is the initial concentration of the dye in solution, V is the volume of the solution (ml) and m is the mass of dry adsorbent (g).

 

RESULTS AND DISCUSSION:

IR Spectroscopy:

The IR spectra of Vat Brown 16 dye in figure 3 shows the peaks at 1325cm^-1 ( C-N stretching of C-N-H), 1589cm^-1 ( C=C stretching of aromatic rings), 1662cm^-1 ( C=O stretching of quinine), 3064cm^-1 ( C-H stretching of aromatic rings) and 3387cm^-1 ( N-H stretching of  amine)[10].  

 

Fig.3. IR spectra of Vat Brown16 Dye

 

UV-Vis. Spectroscopy:

The UV-Vis. Spectra of Vat Brown16 Dye in figure 4 shows peaks at 204nm, 231nm and 281nm.

 

Fig. 4. UV Spectra of Vat Brown16 Dye

Adsorption study:

Effect of Contact Time and Temperature

 

 

(a)

 

(b)

Fig. 5. Effect of Contact Time at Different Temperatures on The Adsorption of  Vat Brown16 Dye on (a) ZnO and  (b) Nano-ZnO particles.

 

The influence of contact time on the amount of Vat Brown16 Dye adsorbed on ZnO and Nano-ZnO particles was investigated at different temperature as shown in figure 5. Its seen that the amount of adsorption increased with increasing of contact time and with increasing of temperatures.                                                                                                                                                                                                                                                                                   

Adsorption Isotherms:

The adsorption data were analyzed to see whether the isotherm obeyed the Langmuir [11] or freundlich isotherms equations:

 

C_e / q_e = (1 / q_m k_L) + C_e / q_m              …………..(2)                                                                                  …………………(2)

 

Where, q_e, the monolayer capacity of the adsorbent (mg/g); k_L, the Langmuir constant (L/mg) and q_m, the theoretical saturation capacity (mg/g). the Langmuir plots between (C_e / q_e) and C_e  as shown in figure 6:

 

 

 

 

Fig. 6. Langmuir Isotherm Model for The Adsorption of  Vat Brown16 Dye on (a) ZnO and (b) Nano-ZnO particles.

 

log q_e = log k_L + n log C_e                       …………...(3)

 

Where k_F  and n are freundlich constants, associated and heterogeneity factor respectively. The Freundlich plots between log qe and log Ce for the adsorption of dye. Values of heterogeneity factor (n<1) indicates Freundlich isotherm as favourable isotherm[12] as shown in figure 7:

 

 

 

Fig. 7. Freundlich Isotherm Model for The Adsorption of  Vat Brown16 Dye on (a) ZnO and (b) Nano-ZnO particles.

 

Table 1. shows the adsorption parameters of Vat Brown16 dye on ZnO and Nano-ZnO particles according to Langmuir and freundlich isotherms.

 

Adsorption Kinetics:

In order to investigate the controlling mechanism of the adsorption processes such as mass transfer and chemical reaction, the pseudo-first-order and pseudo – second order equations are applied to model the kinetics of Vat Brown 16 Dye adsorption on Zno and Nano-ZnO particles. Lagergren proposed a pseudo-first order kinetic model. The integral form of the model is:

 

ln ( q_e – q_t ) = ln q_e – k₁t                                                                                                           ………………(4)

 

where qe is the amount of dye adsorbed onto the adsorbent at equilibrium (mg/g), qt is the amount of dye adsorbed onto the adsorbent at any time t (mg/g), and k₁ (min^-1) is the rate constant of the pseudo-first-order adsorption which can be calculated from the slope of the linear plot of ln (qe – qt) vs. t  (slope= k₁, qe = exp intercept) [13] as in figure 8. the adsorption kinetic of Vat Brown 16 Dye may also described by Pseudo-second order according to following equation:

 

t / q_t = 1 / k₂ q_e² + ( 1 / q_e ) t                                                                                                   ………………..(5)

 

Where q_e and q_t are the amount of dye adsorbed (mg . g⁻¹) at equilibrium and at time t, respectively,  k₂ is the rate constant of pseudo-second order. The plots between t/q_t and t [14] is shown in Figure 8.

 

 

 

 

 

Fig . 8. (a)  Pseudo –first order (b) Pseudo-second order for the adsorption of Vat Brown 16 Dye on ZnO and Nano-ZnO particles

 

Table 2 shows the parameters for adsorption kinetics of Vat Brown 16 Dye on ZnO  and  Nano-ZnO particles.

 

 

 

Table1. Langmuir and Freundlich Parameters for adsorption of Vat Brown16 Dye on ZnO and Nano-ZnO particles

 

 

Table2. The Kinetic Parameters for Adsorption of Vat Brown16 Dye on ZnO and Nano-ZnO Particles

 

From the figure 8 and table 2 showed that the adsorption of Vat Brown 16 Dye on ZnO and Nano-ZnO particles is pseudo-second order reaction.

 

Adsorption Thermodynamic:

The thermodynamic parameters that must be considered to determine the process are Gibbs free energy change (ΔG°) , enthalpy of adsorption (ΔH°) and entropy change (ΔS°).  These parameters were calculated using the following equations[15]:

ΔG^o = − R T ln k                                                                                                                           ……………(6)

 

ln k = (ΔS^o / R) – (ΔH^o / RT)       …………….(7)

 

Where, R is the ideal gas constant (8.314 × 10−3 kJ·mol⁻¹·K⁻¹), k the isotherm constant (L·mol⁻¹), ΔG° the change in Gibbs free energy (kJ·mol⁻¹), ΔH° the enthalpy of adsorption (kJ·mol⁻¹) and ΔS° the entropy of adsorption (J·mol⁻¹·K⁻¹). The results of the thermodynamic calculations for the adsorption of Vat Brown16 Dye on ZnO and Nano-ZnO particles are shown in Table3. ΔH° and ΔS° can be determined from the slope and the intercept of the linear plot of ln k vs. 1/T, as shown in Figure 9:

 

 

 

Fig. 9. Van ̓t Hoff plot for The Adsorption of Vat Brown16 Dye on (a) ZnO and (b) Nano-ZnO Particles

 

Table3. Thermodynamic Parameters for The Adsorption of Vat Brown16 Dye on ZnO and Nano-ZnO Particles

 

 

 

The thermodynamic parameters showed that the adsorption of Vat Brown16 Dye on ZnO and Nano-ZnO particles was exothermic reaction.

 

CONCLUSIONS:

We concluded that the use of Nano-ZnO gives better results than ZnO particles in the adsorption of water-contaminated dyes and that the reaction was pseudo-second order and exothermic reaction.                                                                                                                     

 

 

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Accepted on 20.10.2018        © RJPT All right reserved

Research J. Pharm. and Tech 2018; 11(10): 4613-4618.