Exploring Chicken Feathers as a Cost-Effective Adsorbent for Aqueous Dye Removal

Abstract

This study explored the use of chicken feathers, a low-cost and abundant agricultural byproduct, as a sorbent for the removal of reactive yellow dye from aqueous solutions. The dual potential of feathers as both adsorbents and sorbents, attributed to their keratin-rich structure, was utilized to investigate their effectiveness in dye removal. Feathers, activated with 1.0 mol/L HCl, exhibited a maximum adsorption capacity at 70 °C and pH 5.5, as determined from Langmuir isotherm modeling. A 2² central composite rotatable design revealed that temperature and pH significantly influence the adsorption efficiency, with higher temperatures favoring the process. Kinetic studies demonstrated pseudo-first-order behavior, with rapid initial adsorption reaching equilibrium within 120 min. Thermodynamic analysis confirmed the endothermic nature of the process (ΔH° = 28.04 kJ mol⁻¹), a positive entropy change (ΔS° = 66.62 J/mol·K), and a reduction in Gibbs free energy (ΔG°) with increasing temperature, suggesting enhanced feasibility at elevated temperatures. This research highlights the potential of utilizing poultry industry residues as sustainable and efficient sorbents for environmental remediation, contributing to waste valorization and eco-friendly wastewater treatment solutions.

1. Introduction

Human activities and industrial processes have led to an increase in emerging contaminants in the environment. This growing issue is a public health concern and is studied worldwide, although effective solutions have yet to be found. Among the most concerning emerging contaminants are pharmaceuticals (such as hormones, antibiotics, and others), cosmetics, synthetic dyes, and pesticides, which are prevalent in many regions. Among these pollutants, dyes and pigments are particularly notable, as their presence can result either from their production processes or from their use in a wide range of industries, including textiles, printing, paper, plastics, leather, cosmetics, and food processing [1,2].

Dyes and pigments are often characterized by complex aromatic molecular structures, which make them more stable and less susceptible to biodegradation. Additionally, they can reduce sunlight penetration in aquatic environments, potentially affecting the aquatic ecosystem. In some cases, they may also be toxic to certain microorganisms, interfering with their catalytic functions [3,4,5]. Synthetic dyes are extensively used in industries such as textiles, printing, cosmetics, and food production, generating effluents that pose significant environmental challenges. These dyes not only impart undesirable coloration to water bodies but can also produce hazardous by-products through chemical reactions like oxidation or hydrolysis, threatening aquatic ecosystems. Their complex aromatic structures make them highly stable and resistant to biodegradation [6,7,8].

Among treatment technologies for dye removal, sorption methods are particularly notable for their efficiency and for preserving the active principle, which in some cases allows for its recovery. However, to be economically feasible, these methods require low-cost adsorbents, ideally ones that are also environmentally friendly. A promising alternative is the use of by-products or waste materials from various industrial processes, known as Low-Cost Alternative Adsorbents (LCAs), such as residual wet blue leather [9], seawater-based geopolymers [10], citrus limetta peel [11], and clays [12], among others. In this sense, biosorbents have emerged as a promising solution due to their affordability and accessibility. Biosorption is the process by which biological materials accumulate contaminants on their surface through metabolic or physicochemical mechanisms [6].

In this context, the reuse of residual feathers generated by poultry processing industries as dye adsorbents could serve as a sustainable alternative for the poultry sector. The poultry industry has become one of the largest food industries worldwide, producing significant amounts of feather waste—ranging from 5 to 10% of a chicken’s total weight. This material is generated as an unavoidable by-product in poultry processing plants, with approximately 5 million tons of feathers produced globally each year. Managing these protein-rich materials presents considerable challenges for the poultry industry [13,14]. Traditional disposal methods, such as landfilling, require large areas and create environmental liabilities. Furthermore, the uncontrolled anaerobic decomposition of these materials in landfills can release ammonia and hydrogen sulfide. Incineration, while reducing large quantities of feathers rapidly, is an expensive process that can also have negative health and environmental impacts due to the emission of toxic gases. Given the environmental risks, high costs, and limited profitability of these traditional methods, innovative approaches have been explored for managing keratinous materials. Feathers and keratins can be effectively transformed into composites, absorbents, films for food packaging, textiles, and even electronic devices. This versatility offers benefits across various industries, including automotive, construction, and plastics [15].

Furthermore, feathers can be considered sorbents because they have the potential to both adsorb and absorb substances, depending on the process and conditions. Feathers are often classified as adsorbents when they are used for adsorption processes, where substances like dyes or pollutants adhere to their surface. The structure of feathers, particularly their keratin content, provides surface area for adsorption, making them effective for removing various compounds from solutions. Feathers are also sorbents in the broader sense because they can take up substances through adsorption and possibly absorption. Thus, while the term adsorbent is more commonly used to describe the role feathers play in removing contaminants like dyes from water, they are technically also sorbents, as they may involve both adsorption and absorption depending on the application [16].

In sorption and adsorption processes, several factors, such as solution pH, temperature, initial dye concentration, and adsorbent activation, can influence the efficiency of the process. Each of these factors plays a crucial role in determining how effectively the process removes contaminants. This study aimed to assess the potential of residual feathers, which are generated by a poultry processing industry, as a sorbent for the removal of reactive yellow dye from aqueous solutions.

2. Materials and Methods

2.1. Dye

The dye used as a model molecule was reactive yellow (Molecular Weight: 551.3 g), as shown in Figure 1. The dye was provided by NEWCO Comércio e Representações Ltda., located in Diadema, SP, Brazil.

2.2. Adsorbent

The material evaluated in this study consisted of poultry feathers obtained from a local poultry processing facility. Upon collection, the feathers were thoroughly washed with water to remove any coarse residues. They were then left to air-dry at room temperature (25–28 °C) for five days. For the experiments, only the plumage portion of these feathers was used. The plumage was carefully separated by manually trimming it with scissors.

2.3. Kinetic Experiments

Kinetic experiments were performed in batch mode using 0.2 g of natural feathers and 20.0 mL of a reactive yellow dye solution with a concentration of 100 mg L⁻¹. Tests were conducted at room temperature and pH 5.5, under constant mechanical agitation. Samples were allowed to interact for predefined time intervals of 10, 30, 60, 90, 180, and 360 min, with each time interval corresponding to an independent test. The amount of dye adsorbed was determined by UV-Vis spectrophotometry (Agilent, model 8453, Santa Clara, CA, USA), monitoring the absorbance at a wavelength of 417 nm.

2.4. Influence of Activation

Before conducting adsorption tests, feathers were subjected to an activation process in both acidic and alkaline media. Activation was carried out using a mass–solution ratio of 3.0 g of feathers per 250 mL of activating solution. The solutions used for activation were HCl or NaOH at concentrations of 0.1 and 1.0 mol L⁻¹. Feathers were immersed in the activating solution for 3.5 h at room temperature under constant mechanical agitation. After activation, the feathers were filtered, thoroughly rinsed with 100 mL of distilled water, and dried under sunlight.

Subsequent adsorption tests were performed using 0.2 g of the activated feathers with 20 mL of a dye solution containing 100 mg L⁻¹. For comparison, parallel tests were conducted with untreated feathers. Based on results from the kinetic studies, all adsorption tests were standardized to 90 min of contact time and conducted at room temperature, pH 5.5, and under constant agitation.

2.5. Adsorption Experiments

Adsorption experiments were performed in batch mode to evaluate the removal of reactive yellow dye by poultry feathers. A 2² Central Composite Design (CCD) with three central points was used to investigate the influence of two variables: temperature and pH. The contact time (90 min), adsorbent mass (0.2 g), solution volume (20 mL), and dye concentration (100 mg L⁻¹) were maintained constant throughout these tests. The pH range studied varied from 2.2 to 7.8, while the temperature ranged from 26 °C to 54 °C. The response variable measured was the amount of dye adsorbed, calculated using Equation (1).

$$q={\displaystyle \frac{\left[Vx\left(C_i-C_f\right)\right]}{m}}$$

(1)

where q is the amount of dye adsorbed per gram of adsorbent (mg g⁻¹); V is the volume of the solution (L); C_i is the initial dye concentration (mg L⁻¹); C_f is the equilibrium dye concentration (mg L⁻¹); and m is the mass of the adsorbent (g).

The initial (C_i) and equilibrium (C_f) dye concentrations were determined via UV-Vis spectrophotometry (Agilent 8453), monitoring absorption at 417 nm. Statistical analyses to evaluate the effects of the studied variables on the adsorption response were performed using StatSoft Software, version 5.0.

2.6. Adsorption Isotherms

Adsorption isotherms were determined at three temperatures: 27 °C, 50 °C, and 70 °C, using the batch method. For each test, 0.2 g of the adsorbent material (feathers) were mixed with 20 mL of dye solution at a concentration of 100 mg L⁻¹. Tests were conducted for 90 min under constant agitation at a natural pH of 5.5.

The suitability of adsorption data to the Langmuir theoretical model was assessed by applying a linearization procedure using Equations (2) and (3).

$${\displaystyle \frac{C_{eq}}{q_{eq}}}={\displaystyle \frac{1}{k_{1}N}}+{\displaystyle \frac{C_{eq}}{N}}$$

(2)

$$\ln q_{eq}=\ln k_2+{\displaystyle \frac{1}{\ln C_{eq}}}$$

(3)

where C_eq is the equilibrium concentration of the adsorbate (mg L⁻¹); q_eq is the amount of dye adsorbed per gram of adsorbent (mg g⁻¹); k₁ is the equilibrium constant (L mg⁻¹); N is the maximum adsorption capacity, or the mass of solute needed to saturate the adsorbent (mg g⁻¹); n is the affinity constant of the adsorbent–adsorbate system (L mg⁻¹); and k₂ is the adsorption capacity (mg g⁻¹).

Thermodynamic parameters, including ΔH°, ΔG°, and ΔS°, were determined by plotting lnK_L versus 1/T and applying Equations (4) and (5) [17].

lnK_L = ΔS°/R − ΔH°/(RT)

(4)

ΔG° = −RT lnK_L

(5)

where R is the universal gas constant (8.314 J mol⁻¹ K⁻¹); T is the absolute temperature in Kelvin (K), and K_L (L mg⁻¹) is the Langmuir adsorption constant derived from the isotherms at 27, 50, and 70 °C.

3. Results and Discussion

3.1. Kinetic Studies

Understanding the kinetic and equilibrium properties of an adsorbate–adsorbent system is essential for determining the saturation time (the time required for the system to reach equilibrium) and the adsorption rate. The progression of the adsorption process of reactive yellow dye by natural chicken feathers, monitored over time, is shown in Figure 2.

An increase in the amount of dye adsorbed (reflected by a decrease in absorbance) was observed with contact time, reaching a plateau at approximately 90 min. At this point, the adsorbed amount remained relatively constant, indicating that the system had achieved equilibrium. At equilibrium, the rate of solute adsorption onto the surface equaled the rate of solute desorption from the surface. The adsorption kinetics (Figure 3) suggest a first-order dependency on the concentration of active sites on the adsorbent surface.

The observed adsorption rate constant for reactive yellow dye was 5.0 × 10⁻³ min⁻¹. Mittal [18] showed the use of hen feathers as a potential adsorbent for removing the hazardous triphenylmethane dye, malachite green, from wastewater. The rate constants at different temperatures were calculated, yielding values of 1.34 × 10⁻², 1.36 × 10⁻², and 1.43 × 10⁻² min⁻¹ at 30, 40, and 50 °C, respectively, at a malachite green concentration of 5 × 10⁻⁵ M. These results further confirm the increase in dye uptake with rising temperature.

3.2. Influence of Activation

The influence of both the acidic (HCl) and basic (NaOH) activating solutions and their concentrations (0.1 and 1.0 mol/L) was evaluated. The effects were assessed based on the adsorption capacity of the treated feathers compared to the natural feathers for the reactive yellow dye (

Table 1. Adsorbed amount of reactive yellow dye for natural and treated feathers.

Treatment	Adsorption Capacity (mg g−1)
Natural feather	3.18 ± 0.12
Feather treated with HCl 0.1 mol L−1	5.00 ± 0.15
Feather treated with HCl 1.0 mol L−1	5.79 ± 0.10
Feather treated with NaOH 0.1 mol L−1	1.35 ± 0.08
Feather treated with NaOH 1.0 mol L−1	0.86 ± 0.06

).

The adsorption capacities of the treated samples demonstrated distinct behaviors compared to that of the natural feathers (Table 1), depending on the activating solution used. Feathers treated with NaOH exhibited a decrease in adsorption capacity, indicating an adverse effect of alkaline activation. In particular, the sample treated with 1.0 mol L⁻¹ NaOH experienced noticeable discoloration during the activation process, attributed to dye leaching into the solution. Additionally, partial degradation of the feathers was observed, likely due to alkaline hydrolysis [19,20,21,22].

In contrast, feathers treated with HCl showed a notable enhancement in adsorption capacity for reactive yellow dye compared to the untreated sample. The highest adsorption capacity was achieved with feathers activated using 1.0 mol L⁻¹ HCl, highlighting the positive influence of higher HCl concentrations. Based on these results, subsequent experiments were carried out using feathers activated in 1.0 mol L⁻¹ HCl.

These differences in adsorption performance are linked to changes in the surface charge of the adsorbent induced by the activation process. Acidic activation generates positive surface sites, whereas alkaline activation results in the formation of negative sites. The presence of positive surface sites facilitated electrostatic interaction with the reactive yellow dye, which has anionic characteristics due to sulfonic groups (-SO₃⁻) in its structure at pH 5.5.

3.3. Adsorption Tests: Evaluation of Temperature and pH

The optimization of the adsorption process was performed using a 2² Central Composite Design (CCD) to assess the effects of pH and temperature on the adsorption capacity of reactive yellow dye. The adsorption capacity was expressed as the amount of dye adsorbed (mg) per gram of feathers activated with 1.0 mol L⁻¹ HCl.

Table 2. The 2² CCD matrix with axial points (real and coded values) and adsorption responses in mg_dye g⁻¹_feathers.

Run	pH	T (°C)	mgdye g−1feather
1	−1 (3.0)	−1 (30)	4.72 ± 0.10
2	1 (7.0)	−1 (30)	5.90 ± 0.03
3	−1 (3.0)	1 (50)	8.43 ± 0.00
4	1 (7.0)	1 (50)	9.53 ± 0.21
5	0 (5.0)	1.41 (54)	8.15 ± 0.18
6	0 (5.0)	−1.41 (26)	4.96 ± 0.05
7	1.41 (7.8)	0 (40)	5.62 ± 0.02
8	−1.41 (2.2)	0 (40)	6.65 ± 0.12
9	0 (5.0)	0 (40)	4.80 ± 0.05
10	0 (5.0)	0 (40)	4.94 ± 0.00
11	0 (5.0)	0 (40)	4.82 ± 0.02

presents the 2² CCD matrix, which includes both real and coded values, as well as the corresponding adsorption responses.

These results indicate that all evaluated factors, including both first- and second-order effects, were statistically significant (p < 0.1) and positively influenced the adsorption capacity. Based on these findings, a second-order empirical model describing dye removal by feathers was proposed, as shown in Equation (6).

mg_dye g_feathers⁻¹ = 4.852 + 0.102 pH + 0.843 pH² + 1.483 T + 1.055 T²

(6)

The optimized coded model was validated through analysis of variance (ANOVA) with 95% confidence (F_calculated (9.63) > F_tabulated (4.6)), achieving an explained variance of 93%. As at pH 5.0, sufficient uptake of the dye took place, all further studies were carried out using the natural pH value of 5.5. Mittal [18] observed that in highly acidic solutions, low dye adsorption suggests the development of a positive charge on the adsorbent, which inhibits dye uptake. However, as the pH moved toward the basic range, dye adsorption increased, likely due to a change in the dye’s polarity and the formation of an electric double layer around the adsorbent.

Mittal et al. [23] studied the adsorption of Congo red dye using hen feathers as an adsorbent, and also found these to be highly efficient and dependent on several factors such as pH, contact time, adsorbent quantity, adsorbate concentration, and temperature. The process was optimized at a dye concentration of 6 × 10⁻⁵ M, pH 7.0 and 0.070 g of hen feathers. Kinetic studies revealed that the adsorption followed pseudo-second-order kinetics, suggesting that the rate-determining step involves film diffusion.

3.4. Adsorption Isotherms

The adsorption capacity of reactive yellow dye onto feathers activated with 1.0 mol L⁻¹ HCl was evaluated through adsorption isotherms at three different temperatures (27, 50, and 70 °C) while maintaining a free pH of 5.5. The isotherms obtained for these temperatures are presented in Figure 4. An increase in adsorption capacity with temperature was observed, aligning with findings from the experimental design. This behavior indicates that the adsorption process was endothermic.

The adsorption isotherms suggest adherence to the Langmuir model. Accordingly, experimental data were fitted to the Langmuir Equation, as shown in Figure 5 and

Table 3. Parameters of Langmuir isotherms.

T (°C)	N (mg g−1)	KL (L mg−1)	R2
27	14.12	0.0347	0.9982
50	19.68	0.122	0.9993
70	50.76	0.136	0.9949

.

The correlation coefficients (R²) indicate that the adsorption isotherms fit well to the Langmuir Equation. The values of ΔH° and ΔS° were obtained, as shown in Figure 6. The thermodynamic parameters for the adsorption of the reactive yellow dye onto feathers activated with 1.0 mol L⁻¹ HCl are shown in

Table 4. Thermodynamic parameters for the adsorption of reactive yellow dye onto feathers activated with 1.0 mol L⁻¹ HCl.

T (°C)	ΔG° (kJ mol−1)	ΔH° (kJ mol−1)	ΔS° (J Kmol−1)
27	8.01	28.04	66.62
50	6.46
70	5.15

.

The calculated activation energy (Ea) for the adsorption process in this study was 28.03 kJ/mol (Figure 6), consistent with a chemisorption mechanism. This value aligns with criteria proposed in the literature, where sorption energies above 8 kJ/mol typically indicate chemisorption, distinguishing it from physical sorption processes occurring below this threshold [24,25]. The higher activation energy observed here underscores the chemical nature of the dye–adsorbent interaction, further supporting the proposed adsorption mechanism. The activation energy for the adsorption of ARV (basic violet 16) onto montmorillonite was reported as 35.474 kJ/mol, indicating the significant energy requirement for dye interaction with the adsorbent surface [26].

These positive ΔG° values indicate that the adsorption process is non-spontaneous. However, the decrease in ΔG° with increasing temperature suggests that the process becomes more favorable at higher temperatures. The endothermic nature of the process was confirmed by the positive ΔH° value, while the affinity of the dye for the adsorbent was reflected in the positive ΔS° value. The endothermic nature of the dye adsorption process observed in this study aligns with findings from previous research [6], where chicken feathers were utilized as biosorbents for the removal of synthetic dyes. In that study, up to 80% of the dye (CI Acid Blue 80) was adsorbed at 50 °C, with thermodynamic parameters, including enthalpy and entropy, indicating a spontaneous and endothermic process. The increase in dye uptake from 53% to 76% with rising temperature further supports this conclusion, demonstrating that the adsorption process benefits from higher thermal energy [6].

The endothermic nature of the dye adsorption process observed in this study is also consistent with findings from research on the removal of “Aniline Blue” dye using hen feathers (HFs) as an adsorbent [16]. The authors reported positive enthalpy (ΔH°) values, confirming the endothermic nature of the process, and the adsorption of aniline blue was found to follow pseudo-second-order kinetics and was well described by multiple isotherm models, including the Langmuir isotherm. These findings underscore the potential of hen feathers as a highly efficient biosorbent for the removal of toxic dyes from aqueous solutions.

Although no regeneration tests were conducted as part of this research, it is worth noting that the regeneration of adsorbent materials like chicken feathers is feasible for up to three recycles. The regeneration of the feathers could involve several methods depending on the nature of the adsorbed dye and the adsorption process. Common approaches include chemical desorption, using solutions of acids (e.g., HCl) or bases (e.g., NaOH), thermal treatment, water leaching or solvent washing, and oxidative treatments [27].

4. Conclusions

This study demonstrated that poultry feathers, an abundant agro-industrial byproduct, can serve as an effective and low-cost adsorbent for the removal of reactive yellow dye from aqueous solutions. Acidic activation with 1.0 mol L⁻¹ HCl significantly enhanced their adsorption capacity by generating positive surface charges that facilitated electrostatic interactions with anionic dye molecules. The adsorption process was characterized by pseudo-first-order kinetics, adherence to the Langmuir isotherm, and an endothermic nature, with higher temperatures favoring dye uptake. Overall, these findings show the potential of poultry feathers as a sustainable and efficient adsorbent for dye removal, contributing to the valorization of agricultural residues and providing an eco-friendly solution for wastewater treatment. Future research could explore the scalability of this approach and evaluate its effectiveness for other industrial dyes or pollutants.