Preparation of superfine down particles derived from down fiber wastes and their application as an efficient adsorbent toward acid brilliant scarlet 3R

Abstract

Low-cost superfine down particles (SDP) were evaluated as an adsorbent for the removal of acid brilliant scarlet 3R (ABS-3R) dye from aqueous solutions. Scanning electron microscopy, particle size distribution, Brunauer–Emmett–Teller specific surface area, X-ray diffraction, Fourier transform infrared spectroscopy, and amino-acid analysis were used to characterize the structural characteristics of the adsorbent material. The effects of adsorption process parameters, including initial pH, adsorbent dose, initial dye concentration, adsorption time, and temperature, were systematically studied in batch adsorption experiments. Further, adsorption equilibrium data were modeled by Langmuir, Freundlich, and Dubinin–Radushkevich isotherms. The adsorption process followed the Langmuir isotherm model and the maximum adsorption capacity was 158.23 mg/g at 318 K. Kinetic studies at different temperatures showed that the pseudo-second-order kinetic model fitted well in correlation to the experimental results in comparison to the pseudo-first-order model. The activation energy of the adsorption process was 59.52 kJ/mol, using the Arrhenius equation, which indicated the chemisorption nature of ABS-3R adsorption onto SDP. Thermodynamic study showed that adsorption of ABS-3R was a spontaneous and endothermic process. In summary, SDP was found to be an efficient and eco-friendly adsorbent, which might be suitable for the removal of dyes from aqueous solutions.

Keywords

superfine down particle adsorption isotherm kinetics thermodynamics

Synthetic dyes are widely used in a number of industries such as textiles, leather, paper, printing, food, cosmetics, paints, pigments, petroleum, solvents, rubber, plastics, pesticides, wood preserving chemicals, and pharmaceuticals. Consequently, large volumes of dyestuffs wastewater are generated every year.^1,2 The discharge of such wastewater into the hydrosphere without proper treatment not only affects living organisms owing to its carcinogenicity, genotoxicity, mutagenicity, teratogenicity, and toxic nature, but also interferes with the transmission of sunlight into the hydrosphere, resulting in a reduction in the photosynthesis action. Most importantly, the hazardous effects of synthetic dyes may be passed on to future generations.³ Therefore, the development of methods for the removal of dyes from the industrial wastewater is crucial.

Over the past few decades, many techniques, such as chemical oxidation,^4–7 ion exchange,⁸ coagulation/flocculation,^9,10 electrochemical,¹¹ photochemical treatment,^12–16 biodegradation,^17,18 and adsorption,^19–25 have been applied for the removal of dyes from industrial effluents. Among them, the adsorption process is considered to be one of the most efficient and economically viable treatment methods, owing to its simple design, ease of operation, low initial investment costs and energy consumption, insensitivity to toxic substances, and complete removal of pollutants even from dilute solutions.¹⁹ However, a number of previously published studies have shown that many of the high-performance and high-efficiency adsorbents are expensive and difficult to regenerate. While industrial wastes and byproducts, such as luffa cylindrical,²⁶ teak leaves,²⁷ sewage sludge,²⁸ waste apricot,²⁹ rice husk,³⁰ orange peel,^31,32 carbon nanotubes,^33,34 activated carbon,³⁵ and de-oiled soya and bottom ash,^36–39 have been used as cost-effective adsorbents for the removal of dyes, their adsorption capacities are limited. Therefore, new cost-effective, easily available, and high-performance adsorbents are still being investigated. Mittal et al. employed hen feathers as a biological adsorbent for the removal of brilliant yellow, amido black 10B, brilliant blue FCF, malachite green, and erythrosine from colored wastewater.^40–44 Hen feathers act as an effective adsorbent for such a wide variety of dyes, owing to the large number of functional groups (carboxyl, hydroxyl, and amine groups) both on the backbone and side chains of the polypeptide molecules present in the hen feathers.⁴⁵ However, their low adsorption capacity has limited their practical commercial applications.

In the present study, we have prepared superfine down particles (SDP) from the down fibers of ducks, which are expected to have higher adsorption capabilities than hen feathers.

The aim of this work is to explore the possibility of utilizing SDP for the removal of acid brilliant scarlet 3R (ABS-3R) from aqueous solutions. To understand the mechanism of adsorption of ABS-3R onto the surface of SDP, equilibrium adsorption isotherms and kinetic processes were studied by using conventional theoretical methods.

Materials and methods

Materials

The down fibers of ducks were collected from a local poultry farm in Wuhan, China, where they were available in abundance as a waste material, with no economic value. ABS-3R was purchased from Tianjing Jiedi Co. Ltd., Tianjing, China, and used without further purification. Detailed information on the properties of ABS-3R used in this study is provided in Table 1. The water used for the experiments was purified using a Milli-Q Plus185 water purification system (Millipore, Bedford, MA) and had a resistivity of 10–16 MΩ cm.

Table 1.

Details of the dye used in this study

Dyestuff	Acid brilliant scarlet 3R
Commercial name	Acid red R
Appearance	Red crystalline powder
Molecular formula	C₂₀H₁₁N₂Na₃O₁₀S₃
Molecular weight (g/mol)	604.48
Molecular structure
λ_max	505 nm

Preparation of SDP

The SDP used as the adsorbent in this study were prepared from the down fibers of ducks by a four-step fabrication process. In the first step, the collected down fibers were washed thoroughly (3–4 times) with deionized water to remove any dirt and other granular impurities. In the second step, the washed fibers were cut into short pieces (about 3 mm in length each) with a rotary blade. In the third step, the fiber pieces were placed in 30% hydrogen peroxide solution (analytical reagent grade; Sinopharm Chemical Reagent Co., Ltd) at room temperature for 24 h. The soaked pieces were then washed with deionized water and dried at 383 K for 3 h. Finally, the fiber pieces were pulverized under the mechanical action using a machine developed previously.⁴⁶ The SDP thus prepared were stored in a closed bottle for use in the subsequent adsorption studies.

Characterization of SDP

The surface morphologies of the down fibers and SDP were observed by a scanning electron microscope (SEM; JSM5610LV and JSM7600F, JEOL Ltd, Japan) at an electron acceleration voltage of 25kV. Prior to scanning, the adsorbent was mounted on a stainless steel stab with double stick tape and coated with a thin layer of gold in a high vacuum condition. The particle size distribution of SDP was recorded by a laser particle analyzer (Malvern Corporation, England). The porous structures of SDP were determined by adsorption/desorption of nitrogen at 77K using a Micromeritics ASAP 2020 analyzer (Mike Corporation, USA). X-ray diffraction (XRD) analysis of the SDP was carried out using a Miniflex XRD spectrometer with a Cu K_α radiation source at 30 kV and 15 mA; diffraction angles ranged from 5° to 60° with a scan speed of 5°/min. Fourier transform infrared (FTIR) spectra were recorded using a Nicolet 5700 FTIR spectrometer (Thermo Nicolet Corporation, United States) in the wavenumber range 4000–400 cm⁻¹ at ambient conditions. Amino-acid analysis was carried out with a Hitachi 835-50 amino-acid analyzer at CCTCC (China Centre for Type Culture Collection).

Adsorption studies

All of the adsorption experiments were conducted in the batch mode. The effects of various factors such as pH, adsorbent dosage, initial dye concentration and contact time on the adsorption characteristics of the down-fiber particles were evaluated. The experiments were conducted in 50 mL conical flasks with 25 mL of working volume. The flasks were agitated at a constant speed of 200 r/min in a SHZ-82 isothermal water-bath shaker. The pH values of the solutions were adjusted using 0.1 mol/L HCl or NaOH and the adsorption experiments were carried out at temperatures of 298, 308, and 318 K.

The supernatant liquid was separated from the solution by centrifugation at 12,000 r/min for 10 min at predetermined time intervals. The residual dye concentrations in the supernatant liquid sample were determined using a UV/visible spectrophotometer (Shimadzu, UV-2550) by measuring the absorbance at a wavelength of 505 nm. The dye removal percentage (%) was calculated using the following equation:

Removal = \frac{(C_{0} - C_{e})}{C_{0}} \times 100 %

(1)

where C₀ and C_e (mg/L) represent the initial and equilibrium concentrations of the dye in the solutions, respectively. The adsorption capacity (q_e, mg of dye/g of adsorbent) at equilibrium was calculated using

q_{e} = \frac{(C_{0} - C_{e}) \times V}{m}

(2)

where V (L) is the volume of the solution and m (g) is the mass of N SDP.

In order to ensure the reproducibility of results, all the experiments were conducted three times and the average values were used in data analysis.

Results and discussion

Characterization of the SDP

The morphologies and structures of down fibers and SDP are presented in Figure 1.

Figure 1.

SEM image of down fiber (a, b), photograph of SDP (c), and SEM image of SDP (d).

It can be seen that down feathers are highly ordered, hierarchical branched structures, which contain short or vestigial rachis (shaft), few barbs, and barbules that lack hooks (Figure 1(a) and (b)). Meanwhile, we noted that the SDP exhibit a white color just like that of natural down fiber (Figure 1c), which suggests that the native properties of down fiber was not damaged and preserved well during the manufacturing process. Figure 1(d) shows that SDP are an irregular sphere; the surface of SDP is very rough and has many pores, which could provide a large exposed surface area for the adsorption of dyes.

The particle size distribution and parameters related to pore structure of the SDP are presented in Figure 2.

Figure 2.

The particle size distribution and pore structures parameters of SDP.

The particle size of the SDP was found to be in the narrow range of 0.2–18 μm, with 80% of the particles being smaller than 4 μm. The average particle size was around 2.34 ± 0.26 μm, which agreed well with the results obtained by the SEM image (Figure 1). Furthermore, the Brunauer–Emmett–Teller (BET) specific surface area of SDP and the average pore size from the N₂ adsorption/desorption isotherms were determined to be 0.7277 m²/g and 9.88 nm, respectively, which suggests that SDP comprise a mesoporous adsorbent material.

To investigate the crystalline nature and the functional groups present on the surface of SDP, XRD and FTIR measurements were carried out and the results are as shown in Figure 3.

Figure 3.

XRD pattern (a) and FTIR spectrum (b) of SDP.

In the XRD patterns, two distinct peaks (Figure 3(a)) characteristic of semi-crystalline keratin were observed at 2θ values of 9.3° and 19.5°. The diffraction peak at 9.3° corresponds to the α-helix conformation of the protein molecule present in the SDP, while the peak at 19.5° originates from the β-sheet crystalline structure. The results of the XRD analyses were consistent with those previously reported in the literature.⁴⁷ Several adsorption peaks were seen in the FTIR spectrum (Figure 3(b)). The absorption peaks at 3300, 3080, 2963, and 1078 cm⁻¹ correspond to the stretching vibrations of N–H and O–H, –C=CH₂, –C–H, and –C–O, respectively, whereas, the absorption peaks at 1655 (amide I), 1536 (amide II), and 1237 cm⁻¹ (amide III) were characteristic of the down keratin II structure. The absorption peaks at 1237 (amide III) and 698 cm⁻¹ (amide V) were attributed to the random coil conformation. In order to investigate the chemical composition of SDP, the amino acids of SDP were also tested and the results are presented in Table 2.

Table 2.

The chemical composition of SDP

Chemical composition	Average content, wt %	Chemical composition	Average content, wt %	Chemical composition	Average content, wt %
Glycine	6.4	Valine	6.1	Serine	11.5
Histidine	0.9	Proline	4.6	Leucine	6.4
Alanine	3.5	Tyrosine	1.8	Threonine	4.6
Cysteine	2.9	Phenylalanine	3.8	Isoleucine	4.0
Lysine	1.7	Glutamic acid	9.1	Methionine	0.4
Arginine	6.0	Aspartic acid	6.2

As can be seen from Table 2, SDP contains almost all the amino acids that are present in plants and animal bodies; the proportion of basic amino acids accounted for 51.19% of total amino acids, which provide a potential possibility for the adsorption of dyes.

Effect of various operating parameters on adsorption

The adsorbent dose, pH, initial dye concentration, and contact time are very important factors that can affect the dye adsorption process. Figure 4(a) shows the effect of the initial solution pH on the dye removal percentage by the adsorption of ABS-3R onto SDP. It can be seen that the adsorption of ABS-3R was strongly dependent on pH in the range 2.0–5.0, as is evident from the sharp decline in the dye removal percentage with an increase in pH from 2.0 to 5.0. On the other hand, the dye removal percentage was independent of pH in the range 5.0–10.0. In the range of pH values studied, the maximum dye removal percentage of 98.52% was achieved at a pH of 2.0. Hence, the optimal pH for the adsorption of ABS-3R on SDP was determined to be 2.0 and this value was used in subsequent studies. The higher adsorption of the ABS-3R at lower pH may be due to enhanced protonation by neutralization of negative charge at the surface of the SDP. This helps in the preferential adsorption of the dye over active sites and facilitates the diffusion process in the working solution.⁴²

Figure 4.

Effect of different operating parameters on adsorption of the ABS-3R onto SDP at different temperatures. (a) pH (experimental conditions: C_{0, ABS-3R}: 500 mg/L; adsorbent dose: 5 g/L; adsorption time: 6 h; temperature: 298 K; agitation speed: 200 r/min). (b) Adsorbent dose (experimental conditions: C_{0, ABS-3R}: 500 mg/L; pH: 2; adsorption time: 6 h; agitation speed: 200 r/min). (c) Initial dye concentration (experimental conditions: pH: 2; adsorbent dose: 5 g/L; adsorption time: 6 h; agitation speed: 200 r/min). (d) Adsorption time (experimental conditions: C_{0, ABS-3R}: 600 mg/L; pH: 2; adsorbent dose: 5 g/L; agitation speed: 200 r/min).

Figure 4(b) shows the effect of adsorbent dose on the adsorption of ABS-3R onto SDP. The dye removal percentage was found to increase with an increase in the adsorbent dose, which could be attributed to the increase in the surface area of the adsorbent and greater availability of adsorption sites. Maximum dye removal percentage was observed at an adsorbent dose of 5 g/L. Further increase in the adsorbent dose did not significantly change the adsorption yield, which might be due to the binding of almost all of the dye molecules to the adsorbent surface and the establishment of adsorption equilibrium in the solution.⁴⁹ Therefore, the optimal adsorbent dosage of 5 g/L was used in the subsequent studies.

Dye adsorption experiments with initial dye concentrations of 100–800 mg/L were carried out at 298, 308, and 318 K. As shown in Figure 4(c), the amount of dye adsorbed on SDP increased with an increase in the initial dye concentration, since the initial dye concentration provides the driving force required to overcome the resistances for the mass transfer of the dye molecules between the adsorbent and adsorption medium, until the adsorbent is saturated.⁵⁰ In contrast, once the adsorbent surface is saturated above a certain dye concentration, the adsorption of the dye leveled off, owing to the limited availability of active sites. In addition, when the concentration of the dye in the solution was high and, the active sites of the adsorbent were surrounded by a large number of dye molecules, the adsorption phenomenon occurred more efficiently. Consequently, the value of q_e increased with an increase in the initial dye concentration.⁵¹ Meanwhile, the adsorption of ABS-3R onto SDP was also found to increase with an increase in temperature, indicating that the adsorption process was endothermic in nature. The effect of adsorption time on adsorption of the ABS-3R onto SDP at different temperatures is presented in Figure 4(d). The amount of dye adsorbed per unit mass of SDP increased sharply with an increase in the adsorption time and temperature. Rapid adsorption in the initial stages was probably due to the availability of a large number of vacant sites at the beginning of the process as well as the large concentration gradient in the solution. However, the rate of adsorption decreased slowly with increasing time until equilibrium was reached, owing to the limited mass transfer of the dye molecules from the bulk solution to the surface of the adsorbent, and a subsequent slower internal mass transfer within the adsorbent. The equilibrium time for maximum dye adsorption capacity is 3 h at 298 K, whereas it was achieved at 2 h at a temperature of 318 K. After this equilibrium period, the amount of dye adsorbed does not show time-dependent change.

Adsorption isotherms

Adsorption isotherms describe the equilibrium relationship between the adsorbate concentration in the solution and on the surface of the adsorbent under given conditions. They form the thermodynamic basis for the adsorption separation processes and determine the extent to which a material can be adsorbed onto a particular surface under specific conditions. In order to optimize the design of an adsorption system for the adsorption of dye, it is necessary to establish the most appropriate correlations for the equilibrium curves. Figure 5 illustrates the ABS-3R adsorption isotherms on SDP. The adsorption capacity of ABS-3R on SDP exhibited a sharply increase-firstly, and then reached a plateau with an increase in the equilibrium concentration of dye solutions.

Figure 5.

The adsorption isotherms of SDP in the temperature range 298–318 K.

To further investigate the adsorption isotherms of ABS-3R dye molecules, adsorption isotherm models were used to describe the equilibrium adsorption data. While different theoretical adsorption isotherm models have been developed for describing the adsorption equilibrium relationships, no single model is universally applicable, since all the models involve assumptions that may or may not be valid in particular cases. In order to improve our understanding of the adsorption of ABS-3R on SDP, the experimental equilibrium data were fitted to Langmuir, Freundlich, and Dubinin–Radushkevich (D-R) models. The linear form of the Langmuir isotherm can be expressed by:⁵²

\frac{C_{e}}{q_{e}} = \frac{C_{e}}{q_{m}} + \frac{1}{K_{L} q_{m}}

(3)

where q_m is the maximum adsorption capacity (mg/g), C_e is the equilibrium adsorbate concentration in the solution (mg/L), and K_L is the Langmuir adsorption equilibrium constant (L/mg), which is related to the free energy of adsorption. The values of q_m and K_L were calculated from the slope and intercept of the linear plot of C_e/q_e versus C_e and their values at different temperatures are listed in Table 3.

Table 3.

Adsorption isotherm constants for adsorption of ABS-3R onto SDP at different temperatures

T (K)	Langmuir isotherm			Freundlich isotherm			D-R isotherm
T (K)	q_m (mg/g)	K_L (L/mg)	R²	K_F (mg/g) (L/mg)^1/n	n	R²	β (mol²/J²)	q_m (mg/g)	E (kJ/mol)	R²
298	147.71	0.02	0.975	9. 48	1.97	0.945	−3.72 × 10⁻⁹	70.29	11.60	0.861
308	155.04	0.03	0.991	9.62	1.92	0.959	−3.17 × 10⁻⁹	70.71	12.56	0.847
318	158.23	0.06	0.982	10.64	1.90	0.972	−2.19 × 10⁻⁹	73.15	15.12	0.905

The experimental results indicate that the adsorption of ABS-3R onto SDP follows the Langmuir model.

Next, the experimental data were fit to the Freundlich isotherm model. The linear form of the Freundlich isotherm can be expressed by the following equation:

\log q_{e} = \log K_{F} + \frac{1}{n} \log C_{e}

(4)

In the above equation, K_F (mg/g) (l/mg)^1/n and n are the Freundlich adsorption equilibrium constants related to the adsorption capacity and adsorption intensity, respectively. As indicated by the correlation coefficients R², the dye adsorption process follows the Langmuir isotherm. The Freundlich adsorption equilibrium constants, K_F and n were also calculated and their values at different temperatures are summarized in Table 3.

In order to estimate the porosity apparent free energy and the characteristics of adsorption, the D-R isotherm was also applied to analyze the adsorption data. The D-R equation can be defined by:^53,54

\ln q_{e} = \ln q_{m} - β ξ^{2}

(5)

where β is the D-R constant (mol²/J²), which is related to the adsorption energy, q_m is the D-R monolayer capacity (mg/g), and ξ is the Polanyi potential (J m/mol), which is given by

ξ = RT \ln (1 + \frac{1}{C_{e}})

(6)

where R is the universal gas constant (8.314 J/(mol K)) and T is the temperature in kelvin. The slope and intercept of the plot of ln q_e versus ξ² yield the values of β and q_m, respectively.

The free energy of adsorption (E, kJ/mol) may be estimated from the value of β using:⁵⁵

E = \frac{1}{\sqrt{- 2 β}}

(7)

The values of the parameters obtained using the above equations are summarized in Table 3. The adsorption capacity (q_m) increased as the temperature was increased from 298 to 318 K. The E values were in the range 11–16 kJ/mol, which indicates that the adsorption process may be dominated by chemisorption.⁵⁶

It can be seen that the Langmuir isotherm fits the data better than Freundlich and D-R isotherms, which can be attributed to the predominantly homogeneous distribution of active sites on the SDP surfaces, since the Langmuir equation assumes that the adsorbent surface is energetically homogeneous.⁵⁷ This is also confirmed by the high value of correlation coefficients in the case of the Langmuir model. The maximum monolayer adsorption capacity was 158.23 mg/g at 318 K. The maximum adsorption capacities of various low-cost adsorbents reported in the literature, including SDP, are compared in terms of monolayer adsorption capacity in Table 4.

Table 4.

Comparison of the maximum monolayer adsorption capacities of various low cost adsorbents reported in the literature including SDP at ambient temperature

Adsorbent	Temperature (K)	q_m (mg/g)	References
Lemon peel	305	43.45	Kumar⁵⁶
Peanut hull	293	68.03	Gong et al.⁵⁸
Indian clayey soil	303	78.57	Saha et al.⁵⁹
Hen feathers	303	75.29	Chakraborty et al.⁶⁰
Hen feathers	313	78.62	Chakraborty et al.⁶⁰
Rubber seed shell	ambient temperature	82.64	Oladoja et al.⁶¹
Activated carbon	303	102.04	Basar²⁹
	313	113.64
	323	136.98
Pineapple stem	303	119.05	Hameed et al.⁶²
Meranti sawdust	303	120.48	Ahmad et al.⁶³
Meranti sawdust	313	117.64	Ahmad et al.⁶³
Neem leaf powder	300	133.60	Bhattacharyya and Sarma⁶⁴
SDP	298	147.71	Present study
	308	155.04
	318	158.23

As listed in Table 4, it can be seen that SDP showed the higher adsorption capacity compared with other low-cost adsorbents due to the porous and irregular surface texture of the adsorbent. This fact suggests that ABS-3R could be easily adsorbed on SDP. Therefore, SDP are an efficient, eco-friendly, and promising adsorbent for the removal of ABS-3R from aqueous solutions.

Adsorption kinetics

In order to investigate the mechanism of the adsorption process and determine the rate-controlling steps, kinetic models (i.e. pseudo-first-order and pseudo-second-order models) were applied to analyze the experimentally determined equilibrium data.

The pseudo-first-order equation, which is widely used for describing the adsorption of a solute from a liquid solution,⁶⁵ is represented by

\log (q_{e} - q_{t}) = \log q_{e} - \frac{k_{1}}{2.303} t

(8)

In the above equation, q_e and q_t are the adsorption capacities of the adsorbent (mg/g) at equilibrium and at time t (h), respectively, and k₁ (h⁻¹) is the rate constant for the pseudo-first-order adsorption equation. Linear plots of log(q_e − q_t) versus t were constructed at temperatures of 298, 308, and 318 K (Figure 6(a)) and the values of k₁, determined from the slope of the plots, are summarized in Table 5. From the values of the linear correlation coefficient (R²), it was evident that the pseudo-first-order equation did not accurately fit the experimental data.

Figure 6.

The kinetics for adsorption of ABS-3R onto SDP at different temperatures. (a) Pseudo-first-order; (b) Pseudo-second-order.

Table 5.

Kinetic parameters for adsorption of ABS-3R onto SDP

T(K)	q_exp (mg/g)	Pseudo-first order kinetic model			Pseudo-second-order kinetic model
T(K)	q_exp (mg/g)	q_e (mg/g)	k₁ (h⁻¹)	R²	q_e (mg/g)	k₂ (g/mg h)	R²
298	157.55	154.38	0.51	0.952	158.89	2.46 × 10⁻³	0.996
308	154.63	145.59	0.59	0.877	153.85	6.49 × 10⁻³	0.992
318	143.88	140.50	1.09	0.949	143.47	1.50 × 10⁻²	0.998

The pseudo-second-order equation based on the adsorption capacity can be expressed as follows:

\frac{t}{q_{t}} = \frac{1}{k_{2} {q_{e}}^{2}} + \frac{t}{q_{e}}

(9)

In the above equation, k₂ (g/(mg h)) is the rate constant from the pseudo-second-order adsorption equation.

The q_e and k₂ values were estimated from the slope (1/q_e) and intercept (1/k₂ $q_{e}^{2}$ ) of the linear plots of t/q_t versus t at different temperatures (Figure 6(b)). The values of these parameters are also summarized in Table 5.

From Table 5, it is evident that the experimental data fit excellently to the pseudo-second-order equation at all the temperatures studied. Further, the equilibrium q_e values calculated using this kinetic model were close to the experimental q_e values. Therefore, it may be concluded that the adsorption process follows the pseudo-second order mechanism and not the pseudo-first-order mechanism. The good fit to the pseudo-second-order kinetics also implies that the rate limiting step of the adsorption process may be chemisorption involving valence forces from the sharing or exchange of electrons.⁶⁶ In addition, the values of k₂ calculated from the experimental data increased as the temperature increased, indicating that the adsorption of ABS-3R onto the surface of SDP was an endothermic process.

Adsorption thermodynamic parameters

Activation energy

From the pseudo-second-order rate constant k₂ values (Table 5), the activation energy (E_a) for the adsorption of ABS-3R onto SDP was determined using the Arrhenius equation:

\ln k_{2} = \ln A - \frac{E_{a}}{RT}

(10)

where A is the Arrhenius frequency factor, R is the ideal gas constant (8.314 J/(mol K)), and T is the adsorption temperature in kelvin. The activation energy calculated from the slope of the linear plot of ln k₂ versus 1/T, was estimated to be 59.52 kJ/mol, as shown in Table 4. According to the literature,⁶⁷ activation energies (E_a) value greater than 40 kJ/mol indicate that chemisorption is the predominant adsorption mode. This result confirms that the nature of ABS-3R adsorption onto SDP is chemisorption.

Thermodynamic parameters

To determine the effect of temperature on ABS-3R adsorption, the thermodynamic behavior of adsorption of ABS-3R onto SDP was evaluated in terms of thermodynamic parameters such as Gibbs free energy change (ΔG⁰), enthalpy change (ΔH⁰), and entropy change (ΔS⁰). The parameters were calculated using the following equations:

Δ G^{0} = - RT \ln K_{c}

(11)

K_{c} = \frac{C_{a}}{C_{e}}

(12)

where q_e is the equilibrium dye concentration (mg/L) on the surface of the SDP, C_e is the equilibrium concentration (mg/L) of the dye in the solutions, and K_c is the distribution coefficient for the adsorption. The enthalpy change (ΔH⁰) is obtained from van 't Hoff equation:⁶⁶

ln K_{c} = \frac{Δ S^{0}}{R} - \frac{Δ H^{0}}{RT}

(13)

where R is the ideal gas constant (8.314 J/(mol K)) and T is the adsorption temperature in kelvin. From the slope and the intercept of the plot of ln K_c versus 1/T, as presented in Figure 7, ΔH⁰ and ΔS⁰ values were calculated. The parameters calculated by using the above equations are presented in Table 6.

Figure 7.

Plot of ln K_c versus 1/T.

Table 6.

Thermodynamic parameters for adsorption of ABS-3R onto SDP

E_a (kJ/mol)	ΔG⁰ (kJ/mol)			ΔH⁰ (kJ/mol)	ΔS⁰ (J/mol K)
E_a (kJ/mol)	298 K	308 K	318 K	ΔH⁰ (kJ/mol)	ΔS⁰ (J/mol K)
59.52	−8.24	−8.66	−9.45	18.95	76.07

As can be seen in Table 6, ΔG⁰ values for adsorption of ABS-3R onto SDP were found to be −8.24, −8.66, and −9.45 kJ/mol for 298, 308, and 318 K, respectively. The negative value of ΔG⁰ at all temperatures confirms the spontaneous nature of ABS-3R adsorption onto SDP. The positive value of enthalpy change (ΔH⁰) indicated that the adsorption was an endothermic process, which is consistent with the conclusions made from the Langmuir monolayer capacity results. The positive value of ΔS⁰ revealed that the adsorption caused increased randomness at the solid/solution interface with some structural changes in the adsorbate and adsorbent. They also suggested good affinity of SDP towards the ABS-3R dye.

Conclusions

In this study, SDP, which were prepared from the down fibers of ducks, were evaluated as an adsorbent for the removal of ABS-3R from aqueous solutions. The adsorbent was characterized using SEM, particle size distribution, BET specific surface area, XRD, FTIR spectroscopy, and amino-acid analysis. The effects of various operating parameters on the adsorption process were investigated systematically in batch adsorption experiments and the results indicate that the adsorption was strongly dependent on initial pH, adsorbent dose, initial dye concentration, adsorption time, and temperature. The adsorption equilibrium data obtained at different temperatures provided a best fit with the Langmuir isotherm model, indicating monolayer adsorption on a homogeneous surface. The maximum adsorption capacity was found to be 158.23 mg /g at 318 K, which is considerably higher than that of many other adsorbent materials reported in the literature. Kinetic studies at different temperatures showed that the adsorption of ABS-3R onto SDP followed a pseudo-second-order rate equation. The activation energy calculated using the Arrhenius equation further confirmed that the adsorption involved chemisorption. Thermodynamic study showed that adsorption of ABS-3R was a spontaneous and endothermic process. In summary, the results suggest that SDP can be used as an efficient, economical, and eco-friendly adsorbent for the removal of ABS-3R from aqueous solutions.

Footnotes

Acknowledgements

The authors are grateful to Ph.D. Dongzhi Chen (School of Materials Science and Engineering, Wuhan Textile University) for English language editing.

Declaration of Conflicting Interests

The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The authors disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This work was supported by the National Science Fund for Distinguished Young Scholars (grant number 51325306), the National Natural Science Foundation of China (grant number 51203124), the Program for Middle-aged and Young Talents from Educational Commission of Hubei Province (grant number Q20120103).

References

Chowdhury

Mishra

Saha

. Adsorption thermodynamics, kinetics and isosteric heat of adsorption of malachite green onto chemically modified rice husk. Desalination 2011; 265: 159–168.

Mondal

. Methods of dye removal from dye house effluent: an overview. Environ Eng Sci 2008; 25: 383–396.

Mittal

Kurup

. Adsorption isotherms, kinetics and column operations for the removal of hazardous dye, tartrazine, from aqueous solutions using waste materials, bottom ash and de-oiled soya, as adsorbents. J Hazard Mater 2006; 136: 567–578.

Körbahti

. Response surface optimization of electrochemical treatment of textile dye wastewater. J Hazard Mater 2007; 145: 277–286.

Tunc

Duman

Gürkan

. Monitoring the decolorization of Acid Orange 8 and Acid Red 44 from aqueous solution using Fenton's reagents by on-line spectrophotometric method: effect of operation parameters and kinetic study. Ind Eng Chem Res 2013; 52: 1414–1425.

Karthikeyan

Gupta

Boopathy

. A new approach for the degradation of high concentration of aromatic amine by heterocatalytic Fenton oxidation: kinetic and spectroscopic studies. J Mol Liq 2012; 173: 153–163.

Gupta

Ali

Saleh

. Chemical treatment technologies for waste-water recycling: an overview. RSC Adv 2012; 16: 6380–6388.

Sarı

Akgöl

Karatas

. Reversible immobilization of catalase by metal chelate affinity interaction on magnetic beads. Ind Eng Chem Res 2006; 45: 3036–3043.

Meriç

Selçuk

Belgiorno

. Acute toxicity removal in textile finishing wastewater by Fenton's oxidation, ozone and coagulation–flocculation processes. Water Res 2005; 39: 1147–1153.

10.

Phalakornkule

Polgumhang

Tongdaung

. Electrocoagulation of blue reactive, red disperse and mixed dyes, and application in treating textile effluent. J Environ Manage 2010; 91: 918–926.

11.

Shen

Yang

. Methods to improve electrochemical treatment effect of dye wastewater. J Hazard Mater 2006; 131: 90–97.

12.

Guettai

Amar

. Photocatalytic oxidation of methyl orange in presence of titanium dioxide in aqueous suspension. Part I. Parametric study. Desalination 2005; 185: 427–437.

13.

Zainal

Lee

Hussein

. Electrochemical-assisted photodegradation of dye on TiO₂ thin films: investigation on the effect of operational parameters. J Hazard Mater 2005; 118: 197–203.

14.

Gupta

Jain

Mittal

. Photo-catalytic degradation of toxic dye amaranth on TiO₂/UV in aqueous suspensions. Mater Sci Eng C 2012; 32: 12–17.

15.

Gupta

Jain

Nayak

. Removal of the hazardous dye-Tartrazine by photodegradation on titanium dioxide surface. Mater Sci Eng C 2011; 31: 1062–1067.

16.

Saleh

Gupta

. Photo-catalyzed degradation of hazardous dye methyl orange by use of a composite catalyst consisting of multi-walled carbon nanotubes and titanium dioxide. J Colloid Interface Sci 2012; 371: 101–106.

17.

Chang

Chou

Lin

. Kinetic characteristics of bacterial azo-dye decolorization by Pseudomonas luteola. Water Res 2001; 35: 2841–2850.

18.

Tan

NCG

Prenafeta-Boldu

Opsteeg

. Biodegradation of azo dyes in cocultures of anaerobic granular sludge with aerobic aromatic amine degrading enrichment cultures. Appl Microbiol Biotechnol 1999; 51: 865–871.

19.

Xiong

Chen

Yan

. The adsorption of dibenzothiophene using activated carbon loaded with cerium. J Porous Mater 2012; 19: 713–719.

20.

Chen

Xiong

Cai

. Adsorption of Direct Fast Scarlet 4BS dye from aqueous solution onto natural superfine down particle. Fiber Polym 2015; 16: 73–78.

21.

Zhang

Xiao

Yang

. Preparation of hemicellulose-containing latex and its application as absorbent toward dyes. J Mater Sci 2015; 50: 1673–1678.

22.

Ayranci

Duman

. In-situ UV–visible spectroscopic study on the adsorption of some dyes onto activated carbon cloth. Sep Sci Technol 2009; 44: 3735–3752.

23.

Duman

Tunc

Polat

. Determination of adsorptive properties of expanded vermiculite for the removal of C.I. Basic Red 9 from aqueous solution: kinetic, isotherm and thermodynamic studies. Appl Clay Sci 2015; 109-110: 22–32.

24.

Saleh

Gupta

. Column with CNT/magnesium oxide composite for lead(II) removal from water. Environ Sci Pollut R 2012; 19: 1224–1228.

25.

Jain

Gupta

Bhatnagar

. A comparative study of adsorbents prepared from industrial wastes for removal of dyes. Sep Sci Technol 2003; 38: 463–481.

26.

Altınısık

Gür

Seki

. A natural sorbent, Luffa cylindrica, for the removal of a model basic dye. J Hazard Mater 2010; 179: 658–664.

27.

Ajmal

Rao

Ahmad

. Adsorption studies on teak leaves (Tectona grandis): removal of lead ions from wastewater. J Environ Sci Eng 2008; 50: 7–10.

28.

Martin

Artola

Balaguer

. Activated carbons developed from surplus sewage sludge for the removal of dyes from dilute aqueous solutions. Chem Eng J 2003; 94: 231–239.

29.

Basar

. Applicability of the various adsorption models of three dyes adsorption onto activated carbon prepared waste apricot. J Hazard Mater 2006; 135: 232–241.

30.

Guo

Zhao

Zhang

. Use of rice husk-based porous carbon for adsorption of rhodamine B from aqueous solutions. Dyes Pigm 2005; 66: 123–128.

31.

Crini

. Nonconventional low cost adsorbents for dye removal: a review. Bioresour Technol 2006; 97: 1061–1085.

32.

Gupta

Nayak

. Cadmium removal and recovery from aqueous solutions by novel adsorbents prepared from orange peel and Fe₂O₃ nanoparticles. Chem Eng J 2012; 180: 81–90.

33.

Gupta

Agarwal

Saleh

. Synthesis and characterization of alumina-coated carbon nanotubes and their application for lead removal. J Hazard Mater 2011; 185: 17–23.

34.

Khani

Rofouei

Arab

. Multi-walled carbon nanotubes–ionic liquid–carbon paste electrode as a super selectivity sensor: application to potentiometric monitoring of mercury ion (II). J Hazard Mater 2010; 183: 402–409.

35.

Gupta

Srivastava

Mohan

. Design parameters for fixed bed reactors of activated carbon developed from fertilizer waste for the removal of some heavy metal ions. Waste Manage 1997; 17: 517–522.

36.

Mittal

Malviya

. Decoloration treatment of a hazardous triarylmethane dye, Light Green SF (Yellowish), by waste material adsorbents. J Colloid Interface Sci 2010; 342: 518–527.

37.

Mittal

Kaur

Malviya

. Adsorption studies on the removal of coloring agent phenol red from wastewater using waste materials as adsorbents. J Colloid Interface Sci 2009; 337: 345–354.

38.

Mittal

Malviya

. Adsorptive removal of hazardous anionic dye “Congo red” from wastewater using waste materials and recovery by desorption. J Colloid Interface Sci 2009; 340: 16–26.

39.

Mittal

Malviya

. Removal and recovery of Chrysoidine Y from aqueous solutions by waste materials. J Colloid Interface Sci 2010; 344: 497–507.

40.

Mittal

Thakur

Gajbe

. Evaluation of adsorption characteristics of an anionic azo dye Brilliant Yellow onto hen feathers in aqueous solutions. J Environ Sci Pollut Res 2012; 19: 2438–2447.

41.

Mittal

Thakur

Gajbe

. Adsorptive removal of toxic azo dye Amido Black 10B by hen feather. J Environ Sci Pollut Res 2013; 20: 260–269.

42.

Mittal

. Use of hen feathers as potential adsorbent for the removal of a hazardous dye, Brilliant Blue FCF, from wastewater. J Hazard Mater 2006; 128: 233–239.

43.

Mittal

. Adsorption kinetics of removal of a toxic dye, Malachite Green, from wastewater by using hen feathers. J Hazard Mater 2006; 133: 196–202.

44.

Gupta

Mittal

Kurup

. Adsorption of a hazardous dye, erythrosine, over hen feathers. J Colloid Interface Sci 2006; 304: 52–57.

45.

Villarreala

IAA

Petriciolet

Montoya

. Batch and column studies of Zn²⁺ removal from aqueous solution using chicken feathers as sorbents. Chem Eng J 2011; 167: 67–76.

46.

Cui

. Development and characterizations of super-fine wool powder. Powder Technol 2004; 140: 136–140.

47.

Chowdhury

Saha

. Biosorption of methylene blue from aqueous solutions by a waste biomaterial: hen feathers. Appl Water Sci 2012; 2: 209–219.

48.

Akar

Ozcan

Akar

. Biosorption of a reactive textile dye from aqueous solutions utilizing an agro-waste. Desalination 2009; 249: 757–761.

49.

Aksu

Dönmez

. A comparative study on the biosorption characteristics of some yeasts for removal blue reactive dye. Chemosphere 2003; 50: 1075–1083.

50.

Han

Zhang

Han

. Study of equilibrium, kinetic and thermodynamic parameters about methylene blue adsorption onto natural zeolite. Chem Eng J 2009; 145: 496–504.

51.

Langmuir

. The constitution and fundamental properties of solids and liquids. J Am Chem Soc 1916; 38: 2221–2295.

52.

Dubinin

. The potential theory of adsorption of gases and vapors for adsorbents with energetically non-uniform surface. Chem Rev 1960; 60: 235–266.

53.

Radushkevich

. Potential theory of sorption and structure of carbons. Zh Fiz Khim 1949; 23: 1410–1420.

54.

Hobson

. Physical adsorption isotherms extending from ultrahigh vacuum to vapor pressure. J Phys Chem 1969; 73: 2720–2727.

55.

Wang

Boyjoo

Choueib

. Removal of dyes from aqueous solution using fly ash and red mud. Water Res 2005; 39: 129–138.

56.

Kumar

. Optimum sorption isotherm by linear and non-linear methods for malachite green on lemon peel. Dyes Pigm 2006; 74: 595–597.

57.

Leng

Yuan

Huang

. Bio-char derived from sewage sludge by liquefaction: Characterization and application for dye adsorption. Appl Surf Sci 2015; 346: 223–231.

58.

Gong

Yang

. Removal of cationic dyes from aqueous solution by adsorption on peanut hull. J Hazard Mater 2005; 121: 247–250.

59.

Saha

Chowdhury

Gupta

. Insight into adsorption equilibrium, kinetics and thermodynamics of malachite green onto clayey soil of Indian origin. Chem Eng J 2010; 165: 874–882.

60.

Chakraborty

Chowdhury

Papita

. Biosorption of hazardous textile dyes from aqueous solutions by hen feathers: batch and column studies. Korean J Chem Eng 2012; 29: 1567–1576.

61.

Oladoja

Asia

Aboluwoye

. Studies on the sorption of basic dye by rubber (Hevea brasiliensis) seed shell. Turk J Eng Environ Sci 2008; 32: 143–152.

62.

Hameed

Krishni

Sata

. A novel agricultural waste adsorbent for the removal of cationic dye from aqueous solutions. J Hazard Mater 2009; 162: 305–311.

63.

Ahmad

Rafatullah

Sulaiman

. Scavenging behaviour of meranti sawdust in the removal of methylene blue from aqueous solution. J Hazard Mater 2009; 170: 357–365.

64.

Bhattacharyya

Sarma

. Adsorption characteristics of the dye, Brilliant Green, on Neem leaf powder. Dyes Pigm 2003; 57: 211–222.

65.

Wang

Zhan

Ding

. Bioadsorption of lead(II) from aqueous solution by fungal biomass of Aspergilus niger. J Biotechnol 2001; 87: 273–277.

66.

McKay

. Pseudo-second order model for sorption processes. Process Biochem 1999; 34: 451–465.

67.

Zhang

Wang

Zhou

. Removal of Cd(II) from aqueous solution using cross-linked chitosan–zeolite composite. Desalin Water Treat 2015; 54: 2546–2556.