Removal of Basic Blue 41 dyes using Persea americana-activated carbon prepared by phosphoric acid action
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Adsorption study of Basic Blue 41 dye onto activated carbon from Persea americana nuts with phosphoric acid activation was achieved. The effect of operating parameters, the effect of pH (2–12), adsorbent amount (5–30 mg/50 mL), dye concentration (25–125 mg/L), contact time (0–200 min) and temperature (298–323 K), on the adsorption capacity was examined. The experimental isotherm data were analyzed using Langmuir and Freundlich models, which showed that the best fit was achieved by the Langmuir model with the maximum monolayer adsorption capacity at 625 mg/g. The adsorption kinetic process followed pseudo-second-order kinetics. Thermodynamic evaluation showed that the process was endothermic (ΔH0 = 144.60 kJ/mol) and spontaneous (ΔG0 varied from to −11.64 to −19.50 kJ/mol), while the positive value of entropy (ΔS0 = 524.3 J/mol K) revealed increased randomness at the adsorbent–adsorbate interface. It was found to be a very efficient adsorbent and a promising alternative for dye removal from aqueous solutions.
KeywordsRemoval of dye Persea americana-activated carbon Surface area Adsorption Kinetics and thermodynamic studies
The textile industry plays a part in the economy of several countries around the world. However, effluents from textile and dyeing have a low biological oxygen demand and strong chemical oxygen demand. Disposal of this colored water into receiving water can be toxic to aquatic life and cause food chain contamination, resulting in deleterious health effect even in very low concentrations. Moreover, most of these dyes can cause allergy, dermatitis, skin irritation and also provoke cancer and mutation in humans [1, 2]. Dyes are usually highly visible, very difficult to biodegrade, and extremely difficult to eliminate in natural aquatic environments [3, 4].
To improve the effluent quality, the addition of physical and/or chemical treatments comprising adsorption [5, 6, 7, 8, 9], photocatalytic [10, 11] or electrochemical methods  and reverse osmosis  are necessary. Adsorption is the most simple and known for the treatment of effluents containing dyes using the new low-cost and environmentally friendly adsorbents in the carbon-based or not activated means [13, 14, 15, 16, 17, 18].
The potential properties of activated carbon as adsorbents are due to their highly developed porosity, favorable pore size distribution, large surface area, and high degree of surface reactivity . Chemical activation and physical activation are two methods for the preparation of activated carbon. Chemical activation uses chemical agents for the preparation of activated carbon in a single step method, while physical activation involves carbonization of carbonaceous materials followed by activation of the resulting substrate in the presence of dioxide carbon or steam as activating agents . It is recognized that the carbon yields of chemical activation are higher than the physical one. The most common precursors used for the production of activated carbon are organic materials that are rich in carbon.
Several studies to find low-cost carbonaceous materials have been reported. These materials include Jerusalem artichoke , waste rice hulls , homemade cocoa shell , waste tea , coir pith , orange peels , jute sticks , walnut , palm oil shell , Acacia mangium wood  and waste tires .
In the present study, we examine the feasibility of using activated carbon prepared using Persea americana as adsorbent for the removal of Basic Blue 41 dyes from aqueous solutions. The effect of different parameters including solution pH, adsorbent dosage, dye concentration, temperature and contact time were studied to optimize the adsorption process. The isotherm and kinetic and thermodynamic parameters were examined to analyze the experimental data.
Materials and methods
The Persea americana nuts were collected, washed with distilled water and dried at ambient temperature for several days. The unmodified Persea americana nuts were abbreviated as PAN. The carbonization of PAN was carried out using an appropriate weight of PAN and 25 mL concentrated phosphoric acid with a mass ratio (1:4). A glass beaker of 100 mL was heated to 500 °C for 1 h producing a black carbonaceous residue. The solid material was neutralized with KOH solution until a neutral pH was obtained. The resulting carbonized Persea americana nut (C-PAN) was filtered and washed intensively with water. The C-PAN was then dried at 100 °C for 2 h and kept in desiccators for further use.
The characterization of C-PAN was achieved by FT-IR spectroscopy and X-ray powder diffraction measurements. FT-IR spectra (4000–450 cm−1 range) were recorded with a Nicolet 5700 FT-IR spectrometer on samples prepared as KBr pellets. The polycrystalline sample of each adsorbent was lightly ground in an agate mortar and pestle and filled into 0.5 mm borosilicate capillary prior to being mounted and aligned on an Empyrean PANalytical powder diffractometer using Cu Kα radiation (λ = 1.54056 Å). Three repeated measurements were obtained at room temperature in the 10° < 2θ < 60° range with a step size of 0.01°. Scanning electronic microscopy (SEM) images were obtained with HITACHI-S4100 equipment operated at 20 kV.
Adsorption–desorption isotherms of nitrogen at −196 °C were measure with an automatic adsorption instrument (NOVA-1000 Gas Sorption analyzer) to determine the surface areas and total pore volumes. The BET surface area and the total pore volumes of the obtained Persea americana-activated carbon were found to be 1593 and 1.053 cm3/g, respectively.
For the adsorption experiments, fixed amounts of adsorbents (5–30 mg) were placed in a 100 mL glass Erlenmeyer flask containing 50 mL of dye solution at various concentrations (25–125 mg/L), which were stirred for a suitable time (5–200 min) from 293 to 313 K. The pH of the dye solutions ranging from 2 to 10 was adjusted by 0.1 M HCl or 0.1 M NaOH to investigate the effect of pH on the adsorption processes. Subsequently, to separate the adsorbents from the aqueous solutions, the samples were centrifuged at 3600 rpm for 10 min, and aliquots of 1–10 mL of the supernatant were taken. At a predetermined time, the residual dye concentration in the reaction mixture was analyzed by centrifuging the reaction mixture and then measuring the absorbance by UV–visible spectroscopy of the supernatant at the maximum absorbance wavelength of the sample at 606 nm.
Results and discussion
Characterization of C-PAN adsorbent
Effect of pH
The effect of C-PAN adsorbent dosage
Effect of BB41 concentration
To study the sorption process of BB41 onto C-PAN adsorbent, the data obtained from kinetic adsorption experiments were simulated with pseudo-first-order and pseudo-second-order models.
The pseudo-first-order and pseudo-second-order kinetic parameters for BB41 removal using C-PAN
Concentration of BB41 (mg/L)
k2 × 10−4 (g/mg min)
Adsorption isotherms are basic requirements for the design of adsorption systems. It can express the relationship between the amounts of adsorbate by unit mass of adsorbent at a constant temperature. Herein, we analyzed our experimental data by Langmuir and Freundlich isotherms models. The best-fitting model was evaluated using the correlation coefficient.
Adsorption isotherm constants for removal of BB41 onto the C-PAN adsorbent
KF (mg/g) (L/g)
The Freundlich constants n and Kf were obtained from the plot of log (qe) versus log (Ce) that should give a straight line with a slope of (1/n) and intercept of log (Kf) (as shown in Table 2). In this study, the values found for n were superior to 1, which indicates that the adsorption of BB41 onto C-PAN is favorable.
Thermodynamic data for the adsorption of BB41 onto C-PAN
ΔS0 (J/mol K)
In the study, ΔG0 values were determined at different temperatures and decrease from −11.64 to −19.50 kJ/mol when the temperature increases from 298 to 323 K. The negative values of ΔG0 suggest that the adsorption of BB41 onto C-PAN is a highly favorable process. The values of ΔH0 and ΔS0 were obtained as 144.6 and 524.3 J/mol K, respectively. The positive value of ΔH0 shows that the adsorption is an endothermic process, while a positive value of ΔS0 reflects the increase of randomness state at the solid/solution interface during the adsorption.
Comparison of adsorption capacities of C-PAN with those of various AC adsorbents
Comparison of the maximum monolayer adsorption capacities of C-PAN with those of various AC adsorbents
Homemade cocoa shell
Reactive violet 5
Acid yellow 17
Stricta algae based
Basic Blue 41
The percent (%) removal of BB41 was observed to increase with increasing initial dye concentration and increasing adsorbent dose.
The Langmuir isotherm best described the equilibrium data with acceptable R2, which signifies that a homogeneous adsorption takes place between the BB41 dye and C-PAN.
The pseudo-second-order equation best describes the kinetics of the C-PAN adsorption system due to its high R2. In addition, the theoretical qe generated by the pseudo-second-order equation is in good agreement with the experimental qe value. This implies that the rate-limiting step is a chemisorption process.
Thermodynamic studies indicated that the adsorption process is endothermic and spontaneous.
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