Hen feather: a bio-waste material for adsorptive removal of methyl red dye from aqueous solutions

Water is necessary for every survival but nowadays water pollution by discharging different toxic chemicals from the industrial and urban area is a matter of global concern (Shakoor & Nasar 2016). Among the numerous toxic chemicals, dyes in industrial effluents are highly familiar (Subbaiah & Kim 2016). Dyes are commonly used for coloring purpose in different industries such as food, textiles, cosmetics, leather, printing, paper, rubber, plastics and cosmetics (Sharma et al. 2011). Discharge from these industries of colored wastewater in water bodies can create inescapable difficulties because it limits the photosynthesis rate by reducing sunlight infiltration rate into the receiving water and gradually makes the unstable condition in aquatic ecosystem (Mubarak et al. 2017). Dyes and their degraded byproducts are considered as mutagenic, toxic and carcinogenic nature, so it is comparatively risky for the environment as well as living beings if they are exposed to these substances even at low levels (Huang et al. 2017). Dyes may also create severe human health problems such as skin irritation, dermatitis, cancer, abdominal discomfort, damage of liver, kidneys and reproductive system, jaundice and tumors (León et al. 2016). Methyl red (MR) is an anionic azo dye used in scientific tests, textile and other business purposes; this causes skin, eye and digestive tract discomfort, pharyngeal or digestive tract irritation if swallowed or inhaled (Muthuraman & Teng 2009) and other health hazards. The removal of MR dye is difficult due to its aromatic ring structure, oxidation reaction and highly light stability (León et al. 2016). From an ecological point of view, dyes from polluted water must be removed before being released into the environment, so the selection of applicable and relevant treatment method is most significant for the elimination of dyes from the wastewater. Diverse methods (e.g. adsorption, flocculation, electrolysis, oxidation, ion-exchange, biodegradation, Fenton chemical oxidation, photocatalysis, etc.) for removing MR dye from wastewater have been applied (Bhatnagar & Sillanpää 2010). Among these methods, adsorption has been considered as most popular in the aspect of cost-effectiveness, operational simplicity and low energy requirements (Ghosh et al. 2018). Various types of biomaterials (e.g. natural, agricultural and industrial wastes/byproducts) for dyes removal from wastewater have been investigated, including sawdust, pine leaves, sugarcane bagasse, fly ash, residue sludge, peanut husk, tea waste, orange peel, jute fiber, chitosan, activated carbon (Yagub et al. 2014), jute stick (Chakraborty et al. 2020) and bark (Ghosh et al. 2020). Globally, poultry processing companies create 8.5 billion tons of trash annually (Sarita & Neeraj 2010) and it is a big problem for managing these wastes. The scientific use of feathers as a removable material offers considerable environmental and economic benefits (Gupta et al. 2006). Hen feather (HF) exhibits tremendous adsorption capacity for removing several harmful metal ions (Al-Asheh & Banat 2003; Teixeira & Ciminelli 2005) from the wastewater as well as it is available, non-soluble and non-toxic. Therefore, it is a distinct idea to use HF to remove MR from wastewater. The objectives of this research are to examine the effectiveness of HF in aqueous solution for removing MR, by the influencing of different experimental parameters, including contact time, pH, adsorbents dose and initial MR concentration, and finally evaluate the adsorption behavior of HF by adsorption kinetics and adsorption isotherms.

HF was collected from a local poultry farm in Jashore, Bangladesh. After collection, it was rinsed with tap water numerous times and then distilled water for dirt removal, dried at 80 °C for 24 h in an oven (Labtech LDO-150F, Korea). After that, the soft barbs were cut into very fine pieces of about 0.1 mm length with the help of scissors and hard stems are discarded, then kept in a hydrogen peroxide (30% w/v) solution for 24 h to remove organic materials. Finally, the adsorbent was rinsed with distilled water and heated for 2 h in the oven at 100 °C. Then, this adsorbent was ready to use and it was stored in airtight borosilicate glass bottles. Table 1 presents the chemical properties of HF.

By the use of a field emission scanning electron microscope (FE-SEM, Zeiss Sigma, Carl Zeiss, Germany), HF surface morphology has been observed (before MR adsorption). FTIR spectra of HF (before adsorption of MR) were recorded by using an FTIR-4600, spectrophotometer (JASCO Corporation Ltd, Japan).

MR dye was purchased from Sigma-Aldrich, USA. Chemical formula C₁₅H₁₅N₃O₂; Molecular weight of MR is 269.30 g/mol. Figure 1 shows MR's molecular structure. Analytical grade chemicals were used in this work. The stock solution of MR was made by dissolving the necessary amount of MR powder in double-distilled water. The desired working solution was produced from the stock solution. pH was adjusted by using 0.1M HCl and 0.1M NaOH solution and measured with a digital pH meter (EZdo 6011, Taiwan).

The linear plot of t/q_t vs t shows 1/q_e as the slope and 1/K₂q_e² as the intercept and the parameter can be calculated from here.

The FTIR analysis was utilized to detect adsorbent surface chemistry. Figure 2 shows the FTIR of HF. The adsorption peak at 2,875.86 cm⁻¹ (C–H stretching vibration) and 3,606.89 cm⁻¹ (O–H stretching vibration of hydroxyl group) was the primal peak of HF. The C = O stretching vibration of ketones, carboxylic anhydrides and lactones was found at 1,739.79 and 1,627.92 cm⁻¹. The amide II of the peak was at 1,521.84 cm⁻¹. The other peaks at 1,041.56 cm⁻¹ (C–C skeleton vibration); 985.62 cm⁻¹ (C–H out-of-plane deformation vibration) and 804.32 cm⁻¹ (C–O–C stretching vibration, =CH₂ twisting vibration) was observed in HF.

Scanning electron microscopy (SEM) has been utilized to characterization the surface morphology of adsorbents. The feather's side branches are called barbs and are joined by a group of barbs. Barbs have their own side branches named barbules. The SEM image of HF is shown in Figure 3. The surface of HF showed uneven, irregular spaces of various shapes and sizes which can be used for adsorption of MR. Sun et al. (2009) have noticed a similar finding.

The experiment was conducted at equilibrium condition: initial 20 mg/L MR dye concentration, HF dose (7 g/L), pH (4) and temperature of (25 ± 2 °C) to evaluate the effect of contact time for removal of MR, as presented in Figure 4(a). MR dye removal efficiency and adsorption capacity by HF increased when the adsorption time increased and rise dramatically in the initial 20 min, and after that time it increased slowly and equilibrium reached at 90 min (Figure 4(a)). A higher adsorption rate was found at the primary stage due to the availability of vacant sites on the adsorbent source. Additionally, MR dye removal and adsorption rates were decreased due to the occupied of HF external adsorption sites by MR dye molecules with time progress. However, no significant change was observed after 90 min. So, further batch experiments were conducted at 90 min equilibrium contact time.

On the other hand, experiments were carried out at the initial MR concentration of 20 mg/L, 7 g/L HF dose, starring speed of 200 rpm, at 25 ± 2 °C temperature and 90 min equilibrium contact time with different pH ranges (4–8) in order to determine the effects of pH on MR adsorption by HF, as presented in Figure 4(b). The efficacy of MR removal dropped by 89 to 57% with increasing studied pH (4–8) (Figure 4(b)). pH not only affects the adsorbent's surface load but also the degree of color ionization in solution during the adsorption process. A maximum MR dye removal (89%) was found at pH 4 (Figure 4(b)), because at acidic pH, the adsorbent surface is positively charged due to protonation, which increased the electrostatic attraction between adsorbent and adsorbate, this might be leads to the maximum MR removal (Saad et al. 2007). Conversely, the removal efficiency decreased at higher pH due to the increase of competition for adsorption sites between excess OH⁻ ions and anionic MR dye molecules.

The adsorption of MR onto HF was examined by the variation of HF dose (3–25 g/L) in solution while keeping the other operation parameters constant; equilibrium contact time of 90 min, initial MR dye concentration of 20 mg/L, starring speed of 200 rpm, pH 4 and temperature of 25 ± 2 °C. The removal of MR increased from 87 to 92% when the HF dose increased from 3 to 25 g/L, due to the increasing surface area and more binding adsorption sites. On the other hand, the adsorption rate was gradually reduced (5.80–0.74 mg/g) with the same dose shown in Figure 5(a). On the other hand, the adsorption capacity was decreased with increase HF dose because of the particle interaction, for example aggregation, resulting from reduced the total adsorbent surface area (Aksakal & Ucun 2010). Ghosh et al. (2020) found a similar trend for removing anionic dye from aqueous solution by biosorbent.

Adsorption experiments with the variation of initial MR dye concentrations (5–50 mg/L) were carried out at a fixed HF dose of 7 g/L, pH of 4, starring speed of 200 rpm, temperature of 25 ± 2 °C for 90 min equilibrium contact time. The findings indicated that the HF adsorption capacity increased (0.66–5.01 mg/g) with increasing initial MR concentration (5–50 mg/L) due to the mass transfer resistance of the dye between the solid and aqueous phases, which improved the interaction of MR molecules and HF surface. On the other hand, the removal of MR gradually reduced from 92 to 70% shown in Figure 5(b), because at the constant dose, the adsorbent external surface is saturated as well as dye molecules block the pores of the adsorbent (Chowdhury & Saha 2010). So, the removal efficiency significantly depends on the initial MR concentration and contact time.

The adsorption isotherm is significant for describing the common behavior among the adsorbent and the solutes, and it is also important for the adsorption system design (Dadfarnia et al. 2015). In this study, the isothermal models of Langmuir and Freundlich were used to explore the MR adsorption behaviors onto HF. The linearized form of the isotherm and calculated parameters are presented in Figure 6 and Table 2, respectively. On the basis of correlation coefficient (R²) value, the Langmuir isotherm model (R² = 0.98) fitted better as compared with the Freundlich model (R² = 0.96), indicating that MR molecules create monolayer coverage with homogenous nature onto HF surface and the maximum adsorption capacity was 6.02 mg/g (Table 2). The separation factor (R_L) value (0.41–0.065) was less than 1 but greater than 0, suggesting that the MR adsorption onto HF is suitable. Moreover, the Freundlich constant value (n = 1.83) was greater than 1 and higher K_f value (1.288) indicating a favorable behavior toward MR adsorption.

HF absorption capacity is compared with other adsorbents, as presented in Table 3. From the table, it shows that HF is a suitable and alternative adsorbent for the removal of MR from aqueous solution, for its low cost and easy availability.

In this study, four kinetic models (Lagergren pseudo-first-order, Ho's pseudo-second-order, intraparticle diffusion and liquid film) were applied to determine the adsorption behavior of MR onto HF, as presented in Figure 7, and the model's parameters values are given in Table 4. The higher R² and calculated (q_e,cal) value was found for the pseudo-second-order kinetic model than the pseudo-first-order kinetic model (Table 4), confirming that the adsorption process follows the pseudo-second-order kinetic model. So, the whole adsorption processes seem to be controlled by chemisorption, i.e. the electrostatic interactions between the surface of the positively charged HF and negatively charged MR molecules. The experimental data were further analyzed by intraparticle diffusion in order to investigate the diffusion mechanisms. The intraparticle diffusion plot did not pass through the origin (Figure 7(c)) and higher intercept value (C = 1.19) (Table 3), indicating that multi-diffusion was involved during MR adsorption onto HF such as external diffusion (i.e. agglomerate of MR molecules on the adsorbent surface) and internal diffusion (i.e. transport of MR molecules inside the adsorbent particle), that may occur simultaneously. Moreover, the liquid film plot showed that film diffusion was the rate-limiting step for adsorption of MR onto HF because the plot was linear and did not pass through the origin (Figure 7(d)).

The usability of HF to remove MR dye from aqueous solution was investigated under different experimental conditions, such as pH, contact time, initial MR dye concentration and adsorbent dosage. A maximum MR dye removal was detected at pH 4. The HF efficiency for MR dye removal was 92%, from solutions containing 5 mg/L of dye at adsorbent dose of 7 g/L. The Langmuir isotherm fit better with the experimental data as well as the maximum adsorption capacity was 6.02 mg/g. Kinetic studies show that the adsorption process followed the pseudo-second-order kinetic model with multi-steps diffusion process, and film diffusion was the potential rate-limiting step. The study of the FTIR and SEM showed that the HF surface has distinct function groups and more porous active sites for MR dye adsorption. Finally, it concluded that, for the removal of MR from aqueous solutions, HF is an available, effective and low cost/no cost adsorbent.

We would like to thank the Department of Environmental Science and Technology, Jashore University of Science and Technology, Bangladesh, for providing the necessary support. We also thank the Ministry of Science and Technology, Bangladesh, for the research grant (R&D) award.

The authors declare that they have no competing interests.

The authors would like to thank the Ministry of Science and Technology, Bangladesh, for the research grant (R&D) award.

All relevant data are included in the paper or its Supplementary Information.