Preparation of activated carbon from black wattle bark waste and its application for phenol adsorption

Journal of Environmental Chemical Engineering 7 (2019) 103396

Contents lists available at ScienceDirect

Journal of Environmental Chemical Engineering journal homepage: www.elsevier.com/locate/jece

Preparation of activated carbon from black wattle bark waste and its application for phenol adsorption

T

⁎

Sabrina F. Lütkea, Andrei V. Igansib, Luana Pegorarob, Guilherme L. Dottoa, , Luiz A.A. Pintob, Tito R.S. Cadaval Jrb a b

Chemical Engineering Department, Federal University of Santa Maria–UFMS, 1000 Roraima Avenue, 97105–900, Santa Maria, RS, Brazil School of Chemistry and Food, Federal University of Rio Grande–FURG, km 8 Italia Avenue, 96203–900, Rio Grande, RS, Brazil

A R T I C LE I N FO

A B S T R A C T

Keywords: Adsorption Activated carbon Black wattle bark waste Phenol

Black wattle bark waste is generated in large amounts by tannin extraction industries, which leads to an environmental problem. In literature there are few reports about reusing this waste, mainly in adsorption processes. An activated carbon from black wattle bark waste was produced, characterized and applied for phenol adsorption. Activated carbon was produced under different carbonization and activation conditions, being characterized and applied as an adsorbent for phenol removal from aqueous solution. The results showed that phenol adsorption capacity increased with the increase of carbonization temperature and of activating agent ratio and, decreased with the increase of carbonization time. Activated carbon presented a micro/mesoporous structure and the surface area was 414.97 m2 g−1. FTIR analysis showed that lactone and quinone groups compose the surface chemistry of the activated carbon. The adsorption kinetics followed the pseudo-second order model. The Weber-Morris model showed that the adsorption occurred by film and intra-particle diffusion, and the increase in stirring rate led to an increase in film diffusion. Temperature increase led to an increase in phenol adsorption capacity, and the highest value was around 98.57 mg g−1, obtained at 55 °C. The Freundlich isotherm model was the more suitable to represent the equilibrium data. Thermodynamic study indicated that phenol adsorption onto the developed activated carbon was a spontaneous, favorable, endothermic and entropycontrolled process. The activated carbon can be used in two cycles with a slight decrease in the equilibrium adsorption capacity and presented a good efficiency to remove phenolic compounds in a simulated industrial effluent.

1. Introduction Phenol is an organic compound found in wastewaters disposed from many industries, such as refineries, petrochemicals, cooking operations, coal processing pharmaceutical, pint, polymeric resin, pesticides industries, among others [1,2]. This contaminant, even at low concentrations, presents high toxicity, being considered one of the most hazardous. Phenol presents serious effects for humans, because the inhalation, ingestion or skin adsorption of phenol can to cause comas, convulsions, cyanosis, affect the liver, kidneys lungs and vascular system. The ingestion of 1 g of phenol is deadly for humans [2]. Thus, phenol must be removed from wastewaters before disposing in the environment. In this sense, several methods have been used for the wastewaters treatment containing phenol, such as membrane filtration [3], coagulation-flocculation [4] photocatalytic degradation [5,6],

advanced oxidation processes [7], biodegradation [8] and adsorption [9]. When compared to these other methods, adsorption has advantages such as ease of implementation and operation, high efficiency, low cost and regeneration capacity [10]. In adsorption process, activated carbon is the most used adsorbent [11]. This material presents good surface characteristics, such as high surface area and high pore volume. Besides that, activated carbon may contain functional groups, which interact with contaminant molecules. These features make it a good material to be used in adsorption operations, presenting high adsorption capacity [12]. In relation to activated carbon production, there is a great interest in researches focusing on alternatives and low-cost precursor materials and, in this field, the utilization of lignocellulosic wastes is a potentially viable alternative [10,13–16]. Residual woods from tannin extraction can be used for activated

⁎ Corresponding author at: Chemical Engineering Department, Federal University of Santa Maria–UFSM, 1000, Roraima Avenue, 97105–900 Santa Maria, RS, Brazil. E-mail address: [email protected] (G.L. Dotto).

https://doi.org/10.1016/j.jece.2019.103396 Received 27 June 2019; Received in revised form 30 August 2019; Accepted 30 August 2019 Available online 30 August 2019 2213-3437/ © 2019 Elsevier Ltd. All rights reserved.

Journal of Environmental Chemical Engineering 7 (2019) 103396

S.F. Lütke, et al.

carbon production. Usually, these residual woods are used in the production of pellets for heating and energy production [17]. However, other possibilities can be explored. In this sense, black wattle bark waste, generated in tannin extraction through steam explosion [18], is a material whose use has been little explored in literature. Black wattle bark waste can be used as precursor material for activated carbon production due to three main reasons: composition, availability and waste management. Black wattle bark waste consist of cellulose, hemicellulose, lignin, residual tannins and 2% of inorganics [19]. Due to the high carbon content and the low inorganic content, the black wattle bark waste is a good material to be used as precursor material for activated carbon production. Besides that, this waste is generated in large amounts by tannin extraction industries, which implies high availability. According to the Brazilian Institute of Geography and Statistics (IBGE) [20] more than 136.000 ton of black wattle bark were generated in 2017. This leads to an environmental problem since this waste is generally burned. Therefore, the utilization of black wattle bark waste for activated carbon production is a good way to manage this waste. Black wattle bark waste has already been investigated as adsorbent by Silva et al [19]. The authors submitted black wattle bark waste to acetosolv treatment, whit acetone and sulfuric acid, and applied the modified waste to remove crystal violet from aqueous solution. However, in the literature, there is no report of application of activated carbon derived from black wattle bark waste from tannin extraction, as an alternative adsorbent for contaminants removal. This application leads to a synergistic effect from the environmental viewpoint, since it contributes for the solid waste management and for the treatment of liquid effluents. The aim of this work was to evaluate the potential of the activated carbon from black wattle bark waste for the phenol removal from aqueous solution. For this, activated carbon was prepared under different conditions, characterized and phenol adsorption studies were carried out. For activated carbon production, the effect of carbonization temperature, carbonization time, activating agent ratio and immersion time using the factorial experimental design methodology were investigated. Kinetics, equilibrium and thermodynamic adsorption studies were performed under different experimental conditions.

Table 1 Matrix of fractional factorial experimental design for the activated carbon production, in coded values (actual values), and the results of phenol equilibrium adsorption capacity. Experiment

CT (°C)

Ct (h)

%AA (w/w)

It (h)

qe (mg g−1)*

1 2 3 4 5 6 7 8

−1 +1 −1 +1 −1 +1 −1 +1

−1 −1 +1 +1 −1 −1 +1 +1

−1 −1 −1 −1 +1 +1 +1 +1

−1 +1 +1 −1 −1 +1 +1 −1

38.37 57.49 13.20 44.66 41.54 76.19 29.95 72.76

(500) (700) (500) (700) (500) (700) (500) (700)

(2) (2) (4) (4) (2) (2) (4) (4)

(5) (5) (5) (5) (20) (20) (20) (20)

(12) (24) (24) (12) (12) (24) (24) (12)

± ± ± ± ± ± ± ±

0.47 0.65 0.99 0.91 0.89 1.02 0.97 1.19

* Mean ± standard deviation (n = 3). CT: carbonization temperature; Ct: carbonization time; %AA: activating agent ratio; IT: immersion time in the activation agent; qe: equilibrium phenol adsorption capacity.

agent in the precursor material, 10 g of BWBW were added into 200 mL of ZnCl2 solution, in ratios of 5 and 20% w/w (ZnCl2/precursor material), and stirred at room temperature for 12 and 24 h. After impregnation, the material was vacuum filtered and dried in an oven at 110 °C for 24 h. The carbonization was conducted in a furnace in the temperatures of 500 and 700 °C for 2 and 4 h [14,21]. The BWBW-AC obtained at the different conditions was washed with HCl 0.5 mol L−1 at 95 °C for 30 min to remove Zn2+ and, subsequently, washed several times with distilled warm water until the solution pH reached 6. After, the material was dried at 110 °C for 24 h [21]. 2.3. Fractional factorial experimental design In order to study the conditions of BWBW-AC production, a fractional factorial design 24−1 was employed [22]. The factors of study were: carbonization temperature (CT, 500 and 700 °C), carbonization time (Ct, 2 and 4 h), activating agent ratio (%AA, 5 and 20%w/w) and immersion time in activation agent (It, 12 and 24 h). The treatments (experimental assays) were according to the experimental design matrix shown in Table 1, in coded values -1 and +1 (actual values within the parentheses). As the response of the fractional factorial design was considered the phenol equilibrium adsorption capacity (qe). The results are analyzed using Statistic 7.0 software (StatSoft Inc., USA), and the significance level was 95% (p < 0.05).

2. Material and methods 2.1. Material

2.4. Characterization The black wattle bark waste (BWBC), used as precursor material for activated carbon production, was supplied by TANAC SA Company, located in Montenegro (Brazil). The black wattle bark is used to tannin extraction by steam explosion with water. Ethanol (P.A.-A.C.S, purity of 99.50%), used to wash the BWBW, was obtained from Synth (Brazil). ZnCl2, (136.30 g mol−1, purity of 97.00%), used as activation agent, was obtained from Dinamica (Brazil). Phenol (94.11 g mol−1, purity of 99.00%) was acquired from Synth (Brazil). Commercial activated carbon (CAC) (average particle diameter (Dp) of 68 ± 6 μm, specific surface area (As) of 650.00 ± 10.50 m2 g−1, pores diameter of 2.00 ± 0.05 nm, sphericity (ø) of 0.75 ± 0.05 and density (ρ) of 1100 ± 10 kg m-3) was purchased from Vetec (Brazil).

The BWBW-AC textural properties (specific surface area (As), average pore size and total pore volume) were determined based on nitrogen adsorption/desorption isotherms at 77 K, using an automated gas sorption analyzer (Quantachrome Instruments, Nova 4200e, USA). Before the analysis, samples were maintained at 573 K for 12 h. The specific surface area was obtained from the Brunauer, Emmett, Teller (BET) method and the pore size distribution was obtained from BarrettJoyner-Halenda (BJH) method. The mean particles diameter (Dp, μm) was determined by sieving, the sphericity (ø) by permeametry and density (ρ, kg m−3) by picnometry. The surface morphologies of the BWBW waste and BWBW-AC were obtained by scanning electron microscopy (SEM) (JEOL, JSM 6610 L V, Japan). The working voltage was 15 kV and the magnification of 1000 × . The information about the functional groups of the BWBW and BWBW-AC were investigated by Fourier transform infrared (FTIR) spectroscopy (Shimadzu 01722, IR Prestige, Japan). The analyses was realized by diffuse reflectance technique, with KBr. The spectra were obtained with a resolution of 4 cm−1 over the range of 400-4000 cm−1. The thermogravimetric (TGA) and derivative thermogravimetric (DTG) curves of the BWBW and BWBW-AC were obtained in a Thermogravimetric Analyzer (Shimadzu, TGA-50, Japan). The curves

2.2. Preparation of activated carbon BWBW was first ground in a mill (Willey model no. 3, Philadelphia, USA). Then, was washed with water (80 °C) and ethanol (60 °C) in order to remove residuals tannins, filtered and dried in an oven at 40 °C for 24 h. Afterward, the washed waste was sieved and the fraction with particle diameter between 300 μm and 425 μm was used in the preparation of activated carbon. The activated carbon from BWBW (BWBW-AC) was prepared by chemical activation with ZnCl2. For the impregnation of the activation 2

Journal of Environmental Chemical Engineering 7 (2019) 103396

S.F. Lütke, et al.

2.9. Regression analysis

were obtained in temperatures from 20 °C to 1000 °C with a heating rate of 10 °C min−1, at a synthetic air flow of 100 mL min−1 and with a solid mass of 20 mg.

The parameters were estimated by the fit of the models with the experimental data through nonlinear regression using the QuasiNewton estimation method. Statistica 7.0 software (Statsoft, USA) was used in the calculations. The fit quality was evaluated by coefficient of determination (R2) (Eq. (3)) and average relative error (ARE) (Eq. (4)):

2.5. Batch adsorption assays The adsorption experiments were carried out in three steps: fractional factorial design experiments, kinetic experiments and equilibrium experiments. All kinetics and equilibrium studies were realized with the BWBW-AC obtained in the most suitable condition of the fractional factorial design, with adsorbent dosage of 1 g L−1. The pH of the solution was 6.5, remaining constant throughout the adsorption process. This pH value is characteristic of the aqueous phenol solution. Besides that, since pH < pKa, the dissociation degree of the phenol molecules is negligible. In the factorial design adsorption study, the assays were conducted with initial phenol concentration of 500 mg L−1, at 25 °C and stirring rate of 150 rpm, using an orbital stirrer (Nova Ética, 109-1, Brazil), for a contact time of 24 h. In the same conditions, adsorption experiments were carried out using CAC, for comparison purpose. The kinetic studies were performed at 25 °C, with initial phenol concentration of 500 mg L−1. The stirring rates used were 100, 150 and 200 rpm (Nova Ética, 109-1, Brazil). Aliquots were removed at set time intervals (5–120 min). The equilibrium assays were carried out at 150 rpm using a thermostatic agitator (Fanem, 315 SE, Brazil) until the equilibrium. The temperatures were 25, 35, 45 and 55 °C, and the initial phenol concentrations were from 50 to 500 mg L−1. Afterward, the adsorbent was separated from the medium by filtration, and the remaining phenol concentration in the liquid phase was measured by UV–vis spectrometer (Shimadzu, UV240, Japan) at 270 nm. The assays were performed in replicate (n = 3) and blank tests were realized. The adsorption capacity at time t (qt) and equilibrium adsorption capacity (qe) were determined by Eqs. (1) and (2), respectively:

qt =

V (C0 − Ct ) m

(1)

qe =

V (C0 − Ce ) m

(2)

n

R2 =

n

2 2 ⎛ ∑i qi,exp − qi,exp − ∑i qi,exp − qi,mod el ⎞ n 2 ⎜ ⎟ ∑i qi,exp − qi,exp ⎝ ⎠

ARE =

100 n

n

∑1

(3)

qi,mod el − qi,exp qi, exp

(4)

where qi,model is each value of q predicted by the fitted model, qi,exp is each value of q measured experimentally, qi,exp is the average of q experimentally measured, and n is the number of experimental points. 2.10. Desorption and reuse assays To verify the possible reutilization of BWBW-AC, desorption tests are realized. The BWBW-AC was firstly loaded with phenol. These assays were conducted with initial phenol concentration of 500 mg L−1, adsorbent dosage of 1 g L-1 at 25 °C and stirring rate of 150 rpm, using an orbital stirrer (Nova Ética, 109-1, Brazil), for a contact time of 24 h. After, the adsorbent was separated from the medium by filtration and dried at 110 °C for 24 h. Then, desorption step was realized using a muffle furnace (Quimis, Q.318.24, Brazil) at temperature of 300 °C for 2 h. Thereafter, BWBW-AC was used again for phenol adsorption. This cycle was realized several times. 2.11. Test in a simulated effluent A simulated industrial effluent was used to investigate the efficiency of the BWBW-AC to remove a mixture of phenolic compounds in a medium with high concentrations of salts. The composition of the real effluent was as follows [13]: phenol (60 mg L−1), 2-Chloro-phenol (10 mg L−1), Bisphenol A (10 mg L−1), 2-Nitro phenol (10 mg L−1), 4Nitro phenol (10 mg L−1), 2-Naphthol (10 mg L−1), Hydroquinone (10 mg L−1), Resorcinol (10 mg L−1), Sodium sulphate (40 mg L−1), Sodium carbonate (40 mg L−1), Sodium chloride (50 mg L−1) and Potassium phosphate (40 mg L−1). The pH of the prepared simulated effluent was 8.4. The spectra before and after the adsorption were obtained in a UV–vis spectrometer (Shimadzu, UV240, Japan) from 200 to 800 nm and the areas under the absorption bands were used to obtain the removal percentage.

where C0 is the phenol initial concentration in liquid phase (mg L−1), Ct is the phenol concentration in liquid phase at time t (mg L−1), Ce is the phenol equilibrium concentration in liquid phase (mg L−1), m is amount of adsorbent (g) and V is the volume of solution (L). 2.6. Kinetic models The phenol adsorption kinetics behavior onto BWBW-AC was evaluated at different stirring rates (100, 150 and 200 rpm) by pseudo-first order (PFO), pseudo-second order (PSO) and Elovich models [23].

3. Results and discussion

2.7. Weber-Morris analysis

The experimental design conditions and the respective results of the equilibrium phenol adsorption capacities are shown in Table 1. It can be observed that the highest equilibrium phenol adsorption capacity (76.19 mg g−1) was obtained for experiment 6 (carbonization temperature of 700 °C, carbonization time of 2 h, activating agent ratio of 20% and immersion time in the activation agent of 12 h). Therefore, BWBW-AC obtained in these conditions (from now called BWBW-AC-6) was selected to carry out the kinetic and equilibrium experiments. In the same adsorption conditions, equilibrium phenol adsorption capacity onto CAC was 129.70 ± 1.09 mg g−1. This higher value can be explained since CAC presents greater surface area (650.00 m2 g−1) when compared to BWBW-AC-6 (305.51 m2 g−1). However, BWBW-AC-6 is a promising adsorbent to remove phenol in aqueous medium. In order to verify how the conditions of activated carbon production affected the response, the Pareto chart (Fig. 1) was used. Fig. 1 shows

3.1. Activated carbon production

In order to identify the mass transfer steps in phenol adsorption onto BWBW-AC in all stirring rates, the Weber-Morris model was used [24]. 2.8. Isotherm models and thermodynamic parameters The equilibrium isotherms of phenol adsorption onto BWBW-AC were obtained at 25, 35, 45 and 55 °C. In order to fit the equilibrium curves obtained, Langmuir [25] and Freundlich [26] isotherms models were used. The phenol adsorption onto BWBW-AC was also studied by estimation of the thermodynamic parameters, Gibbs free energy change (ΔG, kJ mol−1), enthalpy change (ΔH, kJ mol−1) and entropy change (ΔS, kJ mol−1 K−1) [27]. 3

Journal of Environmental Chemical Engineering 7 (2019) 103396

S.F. Lütke, et al.

Fig. 1. Pareto chart of the factors effects in activated carbon production.

Fig. 2. Nitrogen adsorption-desorption isotherms and the Barrette-JoynereHalenda desorption pore size distribution of BWBW-AC-6.

that the main effects of the carbonization temperature, carbonization time and activating agent ratio were significant at 95% (p < 0.05). The carbonization temperature was the factor that most influenced the equilibrium phenol adsorption capacity (Fig. 1). Besides, the increase in the carbonization temperature caused an increase in the response. This effect can be explained because higher temperatures can increase the decomposition of the precursor material, resulting in the formation of more pores and, consequently, in a higher adsorption capacity [28]. Sayğili and Güzel [29] observed same behavior in the production of activated carbon from tomato processing solid waste by zinc chloride activation. The authors found that the increase in carbonization temperature, from 400 °C to 600 °C, lead to an increase in the specific surface area and in the total pore volume. In relation to the carbonization time, it was observed a negative effect, that is, the increase in the carbonization time led to a decrease in equilibrium phenol adsorption capacity (Fig. 1). This behavior can be result of a sintering effect occurred in high carbonization times. The sintering effect causes reduction in the particle size of activated carbon and, consequently, reduction in total pore volume. This effect was also observed by Sayğili and Güzel [29] and Nasrullah et al. [30]. The increase in the activating agent ratio conducted to an increase in equilibrium phenol adsorption capacity (Fig. 1). Zn2+ impregnated in the precursor material promotes the dilation of cellulose structure, preventing the particles shrinkage. In the washes with acid and water, Zn2+ is removed and the spaces previously occupied by the activating agent becomes free, forming pores [31]. In this way, the use of a higher activating agent ratio can increase the pores formation. Miao et al. [14] produced activated carbon from soybean straw by chemical activation with zinc chloride, in different activating agent ratios, and applied in phenol adsorption. The authors verified that the increase of the activating agent ratio lead to an increased in the specific surface area and in the total pore volume of the activated carbon produced and, also, an increase in equilibrium phenol adsorption capacity. The immersion time in the activation agent was not significant (p > 0.05) (Fig. 1). This can be explained, probably, because the immersion time of 12 h was enough for the activation agent to impregnate in the material precursor, reaching equilibrium. Nasrullah et al. [30] found the same behavior in relation to the immersion time.

is a typical characteristic of mesoporous materials. Furthermore, an adsorption hysteresis is present in adsorption-desorption isotherms. The adsorption hysteresis also had a wide variety of shapes, and is classified according to IUPAC into four classes (H1-H4) [32]. Therefore, the adsorption hysteresis exhibited by BWBW-AC-6 can be classified as Type H4, which is characteristic of micro/mesoporous carbonaceous materials. From the pore size distribution, the presence of micropores and mesopores is observed. Table 2 shows the following characteristics of BWBW-AC-6: specific surface area, average pore size, total pore volume, mean particles diameter, sphericity and density. The specific surface area was 414.097 m2 g−1, which is similar to values reported in literature for activated carbon produced from lignocellulosic waste using zinc chloride [14]. The average pore size of BWBW-AC-6 was 4.7 nm. The average pore size defines the ability of the adsorbate molecules to penetrate inside the activated carbon [33]. Thus, for the adsorbate molecules to be able to penetrate the adsorbent, the pores must have a diameter larger than the effective molecular diameter of the adsorbate. Since phenol has effective molecule diameter of 0.75 nm, the average pore size presented by BWBW-AC-6 is suitable for phenol adsorption. Fig. 3 shows the SEM images of BWBW (Fig. 3a) and of BWBW-AC-6 (Fig. 3b). It was found that BWBW-AC-6 kept the cavities of precursor material. The presence of cavities in the BWBW-AC-6 structure is favorable for adsorption process because enable the penetration of phenol molecules into the adsorbent [34]. However, it was verified that BWBW-AC-6 presented a less rough surface than BWBW. This cleaning in the cavities is a result of the carbonization process. FTIR analysis was realized to verify the functional groups modifications occurred due to the carbonization process, and verified the functional groups present in BWBW-AC-6 surface that can establish interaction with the phenol molecules. Fig. 4 shows the FTIR spectrums of the BWBW and BWBW-AC-6. In the FTIR spectrum of BWBW, it is possible to observe the characteristic bands of hemicellulose, cellulose and lignin. The band at 3323 cm−1 is due to OeH stretching of Table 2 BWBW-AC-6 characteristics. Property

3.2. Characteristics of BWBW-AC-6

As (m2 g−1) Average pore size (nm) Total pore volume (cm3 g−1) Dp (μm)* Ø (dimensionless)* ρ (kg m−3)*

Fig. 2 shows the N2 adsorption-desorption isotherms and the BJH desorption pore size distribution of BWBW-AC-6. According to International Union of Pure and Applied Chemistry (IUPAC) classification of adsorption isotherms [32], the adsorption isotherm for BWBW-AC-6 showed a mixture of Type I and Type IV isotherms. Type I isotherm is a typical characteristic of microporous materials, while Type IV isotherm

414.097 4.7 0.064 180.5 ± 10.1 0.67 ± 0.07 1100 ± 20

* Mean ± standard deviation (n = 3). Dp: mean particles diameter; ø: sphericity; ρ: density. 4

Journal of Environmental Chemical Engineering 7 (2019) 103396

S.F. Lütke, et al.

aromatic CeH stretching [39]. Changes can be verified in FTIR spectrum of BWBW-AC-6. A decrease was observed in the band at 3319 cm−1, which is relative to OeH stretching [40]. The increase of the band at 3047 cm−1 and the − increase of the bands between 700 cm−1 and 900 cm 1 may indicate an increase in aromaticity, which is due to the carbonization process [41]. Besides that, the band related to sp3 CeH stretching, present at 2910 cm-1 in BWBW spectrum, cannot be observed in BWBW-AC-6, which indicates a decrease in aliphacity. The band at 1707 cm-1 is characteristic of C]O stretching of lactone groups and the band at 1575 cm-1 is characteristic of C]O stretching of quinone groups [41,42]. The presence of these oxygenated groups confers a negative charge density in BWBW-AC-6 surface. Mattson et al. [43] suggested that the phenol adsorption onto activated carbon occurs through the formation of a donor-acceptor complex between the phenol molecules and the carbonyl and carbonyl groups, in which these oxygenated groups act as an electron donor and the aromatic ring of phenol act as electron acceptor. In these way, the lactone and quinone groups present on the BWBW-AC-6 surface can favor the phenol adsorption [44,45]. In order to verify the thermal stability and decomposition profile of BWBW and BWBW-AC-6, TGA and DTG curves were obtained. Fig. 5 shows the thermogravimetric profiles of BWBW (Fig. 5a) and of BWBWAC-6 (Fig. 5b). The thermogravimetric curve for BWBW presents three decomposition stages. In the first stage is observed a small weight loss between 50 °C and 100 °C, which is due to the removal of adsorbed water [46]. The second stage occurs between 250 °C and 350 °C and is attributed to the decomposition of hemicellulose and cellulose. And, in the third stage, which occurs between 350 °C and 580 °C, the weight loss is due to the decomposition of both cellulose and lignin [47]. Above 600 °C no considerable weight loss is observed. The thermogravimetric curve for BWBW-AC-6 shows a first decomposition stage between 50 °C and 100 °C, which is due to the loss of adsorbed water [46,48]. The second decomposition stage, at about 450 °C, can be assigned to the decomposition of surface groups formed during the activation process [48]. According to the literature, groups like lactone and quinone decompose with evolution of carbon dioxide from 400 °C [49]. The third stage, from 700 °C, the observed weight loss is attributed to decomposition of the carbon skeleton [48].

Fig. 3. SEM images (×1.000): (a) BWBW, and (b) BWBW-AC-6.

3.3. Kinetic study The adsorption kinetic analysis was carried out using BWBW-AC-6. The stirring rate effect was studied (100–200 rpm). The curves of adsorption capacity as function of time are shown in Fig. 6. In all stirring rates, adsorption was fast, reaching about 75% of saturation in 30 min. Later, the adsorption rate gradually decreased. It can be also observed that the phenol adsorption capacity onto BWBW-AC-6 increased with the increase of stirring rate from 100 to 200 rpm. This behavior can be explained because the increase in the stirring rate led to an increase in the energy dissipation and, consequently, in the mobility system. This also decreased the external mass transfer effect, facilitating the adsorbate molecules migration to the adsorbent surface [50,51]. The kinetics experimental data were fitted to the pseudo-first order, pseudo-second order and Elovich models. The results are presented in Table 3. Based on the higher values of determination coefficient and the lower values of average relative error, it can be concluded that the pseudo-second order model was the more suitable to represent the phenol adsorption kinetic onto BWBW-AC-6. Several authors demonstrated that the pseudo-second order model was the more suitable to represent the kinetic data of phenol adsorption onto activated carbon [40,52–54]. The pseudo-second order model has the same equation for the external and internal mass transfer mechanisms. In this way, the best fit of the pseudo second order model suggests that phenol molecules adsorption onto BWBW-AC-6 occurs through both mass transfer mechanisms [55–57].

Fig. 4. FTIR spectrum of BWBW and BWBW-AC-6.

hydroxyl groups in lignin, cellulose and hemicellulose structures [35]. The bands at 3064 cm-1 and 2910 cm−1 are relative to sp2 CeH and sp3 CeH stretching, respectively, in cellulose and hemicellulose [36]. At 1734 cm−1 it is possible to observe the band relative to non-conjugated C]O stretching of the hemicellulose structure. At 1658 cm−1 it is possible to observe the band relative to conjugated C]O stretching of the lignin structure [37]. The band at 1595 cm−1 is relative to C]C stretching of aromatic ring in lignin structure [38]. The bands at −1 2 1454 cm−1and 1321 cm are due CeH stretching of eCH and eCH3 groups, respectively, that confirms the presence of cellulose and hemicellulose [39]. At 1200 cm−1, the band refers to CeO stretching of acetyl groups in lignin and, at 1100 cm−1, the band refers to CeO stretching of hydroxyls in cellulose and hemicellulose structures [36,37]. Between 700 cm−1 and 900 cm−1, the bands are due to 5

Journal of Environmental Chemical Engineering 7 (2019) 103396

S.F. Lütke, et al.

Fig. 5. TGA curves of BWBW and BWBW-AC-6.

Fig. 6. Kinetic curves for phenol adsorption onto BWBW-AC-6 in different stirring rates.

Fig. 7. Weber-Morris plot for phenol adsorption onto BWBW-AC-6 in different stirring rates.

Table 3 Kinetic parameters for phenol adsorption onto BWBW-AC-6.

process onto BWBW-AC-6 [51]. In all stirring rates studied, the adsorption occurred by film diffusion until 30 min. The diffusion rate constants obtained by fitting the Weber-Morris model with the first (kWB1) and the second portion (kWB2), in all stirring rates studied, are shown in Table 4. It is verified that the increase in stirring rate led to an increase in the values of the diffusion rate constant relative to the film region (kWB1). This behavior facilitates the phenol molecules diffusion to the adsorbent surface and, consequently, lead to an increase in the adsorption capacity [51]. The similarity in kWB2 values showed that the intraparticle diffusion was independent of stirring rate. The intraparticle diffusion depends mainly of the adsorbent surface properties, being independent of the stirring rate [51]. Comparing kWB1 e kWB2 values presented in Table 4, it is verified that, in all stirring rates studied, the adsorption was controlled by intraparticle diffusion (kWB1 > kWB2). Besides that, corroborating with this result, in Fig. 7 it is possible to observe that the first linear portion of the Weber-Morris plot goes through the origin [24,58]. The literature affirms that, usually, in adsorption onto activated carbon, the intraparticle diffusion is the limiting step [53]. These behavior can be explained due to the presence of micropores in the adsorbent [24,58].

Model

Stirring rate (rpm) 100

150

200

PFO q1 (mg g−1) k1 (min−1) R2 ARE (%)

63.69 0.056 0.985 5.60

65.39 0.063 0.990 5.52

78.48 0.052 0.994 3.89

PSO q2 (mg g−1) k2 (g mg−1 min−1) R2 ARE (%)

75.07 0.0009 0.998 2.05

76.74 0.0010 0.999 3.20

93.04 0.0006 0.992 2.96

Elovich a (g mg−1) b (mg g−1 min−1) R2 ARE (%)

0.060 9.14 0.995 3.05

0.058 10.53 0.994 3.39

0.050 11.81 0.990 6.36

3.4. Weber-Morris analysis Table 4 Diffusion rate constants of Weber-Morris model in different stirring rates.

The Weber-Morris equation was used to differentiate the film diffusion and intraparticle diffusion steps on adsorption kinetic and the effect of the different stirring rates studied (100–200 rpm). The WeberMorris plots are shown in Fig. 7. It can be observed that the plot has two different regimes, each one showing linear behavior. This shows that both film and intraparticle diffusion occurred in the phenol adsorption 6

Stirring rate (rpm)

kWB1 (mg g−1 t-1/2)

R2

kWB2 (mg g−1 t-1/2)

R2

100 150 200

9.51 10.09 10.72

0.996 0.995 0.988

2.92 2.66 2.87

0.998 0.958 0.966

Journal of Environmental Chemical Engineering 7 (2019) 103396

S.F. Lütke, et al.

Table 6 Comparison between BWBW-AC-6 and other activated carbons used for phenol adsorption. Precursor material

pH

T (°C)

qe (mg g−1)

Ref.

Black wattle bark waste Pyrolytic tyre Sewage sludge Waste tea Fox nutshell Rice husk Peanut shell Coconut shell Avocado kernel seed Tobacco residue Wood chip Soybean straw Rattan sawdust Coconut shells

6.5 6.7 6.8 7.0 7.0 – 6.0 – 6.0 7.0 7.0 – – 4.0

55 25 20 30 30 25 – 25 25 20 50 – 30 25

98.6 51.9 30.1 108 78.7 27.5 21.0 144.9 90.0 17.9 171.5 278.0 149.25 50.07

This work [61] [62] [44] [52] [63] [64] [54] [65] [66] [13] [14] [67] [68]

Fig. 8. Equilibrium curves for phenol adsorption onto BWBW-AC-6 in different temperatures.

black wattle bark waste, produced in this work, with reported values in literature. BWBW-AC-6 seems to be a promising adsorbent that can be used for phenol removal, since presents the sixth maximum adsorption capacity among the 14 activated carbons exposed in Table 6. Thermodynamics behavior of phenol adsorption onto BWBW-AC-6 was evaluated by values of Gibbs free energy change (ΔG), enthalpy change (ΔH), and entropy change (ΔS). These parameters are shown in Table 7. The R2 value of the linear fit was 0.996. The negative ΔG values indicate that the adsorption was a spontaneous and favorable process. Besides, the ΔG value was more negative at 55 °C, confirming that the adsorption was favored by the temperature increase. The negative ΔH value indicates an endothermic operation. This behavior is result of the water molecules desolvation from adsorbent surface, which occurs previously to the phenol molecules adsorption [69]. The magnitude of ΔH value suggested that physisorption occurs in the phenol adsorption onto BWBW-AC-6 [70]. The positive ΔS value indicate that disorder in solid-liquid interface increased after the adsorption [71]. Also, it was observed that only the entropy change contributed to obtain negative values of ΔG. This shows that the phenol adsorption onto BWBW-AC-6 was an entropy-controlled phenomenon. Similar thermodynamic behavior was found by Thue et al. [13] in phenol adsorption onto activated carbon obtained from wood chips.

3.5. Equilibrium and thermodynamic studies Phenol adsorption equilibrium curves onto BWBW-AC-6 were obtained in the range of 25–55 °C, with phenol initial concentrations from 50 to 500 mg L−1. The curves obtained are shown in Fig. 8. These curves are typical type L1 isotherms, that imply high affinity between adsorption sites of activated carbon and phenol molecules [59]. Similar curves were obtained for Din, Hameed and Ahmad [60], Zhang, Huo and Liu [54]. It can be also seen that the adsorption capacity was increased with the temperature increase, being the highest adsorption capacity value (around 98.57 mg g−1) found at 55 °C. This behavior suggests that phenol adsorption onto BWBW-AC-6 is an endothermic process, which will be confirmed by the thermodynamic study. Langmuir and Freundlich models were used to interpret the phenol adsorption equilibrium onto activated carbon. The equilibrium parameters are presented in Table 5. It was verified that the higher values of coefficient of determination and the lower values of average relative error were obtained using the Freundlich model. For this reason, this model was chosen as the most suitable to represent the equilibrium data. The best fit of the Freundlich model to the experimental data suggests the presence of heterogeneous adsorption sites in the activated carbon surface. This corroborates with the FTIR spectra obtained, which showed that BWBW-AC-6 contain different oxygenated functional groups, like lactone and quinone. Also, the kF values increased with the temperature increase, confirming that the adsorption was favored at 55 °C. To compare the effectiveness of BWBW-AC-6 to remove phenol in aqueous medium, a comparison with other activated carbons derived from wastes was realized. Table 6 shows the comparison of the maximum adsorption capacity (qm) of the activated carbon derived from

3.6. Reutilization study The possibility of reuse of an adsorbent is related to their regeneration ability and is an important aspect in the economic point of view, since possibilities an extended use of the material [72]. The desorption step of the BWBW-AC-6 was carried out at 300 °C for 2 h in a muffle furnace and, subsequently, the adsorbent was used over again in phenol removal to test their equilibrium adsorption capacity. Fig. 9 shows the equilibrium adsorption capacity of phenol for five utilization cycles of BWBW-AC-6. In the first two cycles of utilization the equilibrium adsorption capacity decreased from 73.95 mg g−1 to 70.73 mg g−1. Following uses exhibited a higher decrease, with a reduction of approximately 60% for the fifth use in relation to the first use. Thus, the use of BWBW-AC-6 is possible for two cycles with a slight decrease of approximately 4% in the equilibrium adsorption capacity.

Table 5 Equilibrium parameters for phenol adsorption onto BWBW-AC-6. Model

Temperature (°C) 25

35

45

55

Langmuir qm (mg g−1) kL (L mg−1) R2 ARE (%)

85.75 0.0083 0.994 3.98

91.48 0.0218 0.967 7.99

96.60 0.0244 0.976 7.32

98.57 0.0372 0.932 12.14

Frendlich kF ((mg g−1)(L mg−1)−1/n) 1/n R2 ARE (%)

5.66 2.25 0.995 3.20

13.45 3.20 0.968 8.31

13.87 3.12 0.998 1.42

20.14 3.71 0.993 3.87

Table 7 Thermodynamic parameters for phenol adsorption onto BWBW-AC-6.

7

Temperature (°C)

ΔG (kJ mol−1)a

25 35 45 55

−12.20 −13.72 −14.42 −15.17

± ± ± ±

0.09 0.08 0.05 0.03

ΔH (kJ mol−1)

ΔS (kJ mol−1

7.89

0.070

K-1)

Journal of Environmental Chemical Engineering 7 (2019) 103396

S.F. Lütke, et al.

endothermic. The entropy controlled the operation, and the magnitude of ΔH suggested that physisorption occurred. It was possible to use BWBA-AC-6 two times with a reduction in the equilibrium adsorption capacity of approximately 4%. In the simulated industrial effluent, BWBW-AC-6 presented an efficiency of 95.89% to remove phenolic compounds. In summary, the utilization of black wattle bark waste as an alternative precursor material for activated carbon production showed two important aspects. Firstly, the possibility to reuse an abundant industrial waste, aggregating value to this material, and second, the application of the low cost and promising adsorbent to remove phenol from aqueous solution. Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Fig. 9. Reutilization study of BWBW-AC-6.

References [1] M. Ahmaruzzaman, Adsorption of phenolic compounds on low-cost adsorbents: a review, Adv. Colloid Interface Sci. 143 (2008) 48–67. [2] G. Busca, S. Berardinelli, C. Resini, L. Arrighi, Technologies for the removal of phenol from fluid streams: a short review of recent developments, J. Hazard. Mater. 160 (2008) 265–288. [3] D.P. Zagklis, A.I. Vavouraki, M.E. Kornaros, C.A. Paraskeva, Purification of olive mill wastewater phenols through membrane filtration and resin adsorption/desorption, J. Hazard. Mater. 285 (2015) 69–76. [4] F. Sher, A. Malik, H. Liu, Industrial polymer effluent treatment by chemical coagulation and flocculation, J. Environ. Chem. Eng. 1 (2013) 684–689. [5] A. Turki, C. Guillard, F. Dappozze, Z. Ksibi, G. Berhault, H. Kochkar, Phenol photocatalytic degradation over anisotropic TiO2 nanomaterials: kinetic study, adsorption isotherms and formal mechanisms, Appl. Catal. B Environ. 163 (2015) 404–414. [6] F. Güleç, F. Sher, A. Karaduman, Catalytic performance of Cu- and Zr-modified beta zeolite catalysts in the methylation of 2-methylnaphthalene, Pet. Sci. 16 (2019) 161–172. [7] S.N. Hussain, E.P.L. Roberts, H.M.A. Asghar, A.K. Campen, N.W. Brown, Oxidation of phenol and the adsorption of breakdown products using a graphite adsorbent with electrochemical regeneration, Electrochim. Acta 92 (2013) 20–30. [8] N.V. Pradeep, S. Anupama, K. Navya, H.N. Shalini, M. Idris, U.S. Hampannavar, Biological removal of phenol from wastewaters: a mini review, Appl. Water Sci. 5 (2015) 105–112. [9] G.L. Dotto, J.O. Gonçalves, T.R.S. Cadaval Jr, L.A.A. Pinto, Biosorption of phenol by nanoparticles from Spirulina sp. LEB 18, J. Environ. Chem. Eng. 407 (2013) 450–456. [10] M.A. Zazycki, M. Godinho, D. Perondi, E.L. Foletto, G.C. Collazzo, G.L. Dotto, New biochar from pecan nutshells as an alternative adsorbent for removing reactive red 141 from aqueous solutions, J. Clean. Prod. 171 (2018) 57–65. [11] S.H. Lin, R.S. Juang, Adsorption of phenol and its derivatives from water using synthetic resins and low-cost natural adsorbents: a review, J. Environ. Manage. 90 (2009) 1336–1349. [12] A. Bhatnagar, W. Hogland, M. Marques, M. Sillanpää, An overview of the modification methods of activated carbon for its water treatment applications, Chem. Eng. J. 219 (2013) 499–511. [13] P.S. Thue, M.A. Adebayo, E.C. Lima, J.M. Sieliechi, F.M. Machado, G.L. Dotto, J.C.P. Vaghetti, S.L.P. Dias, Preparation, characterization and application of microwave-assisted activated carbons from wood chips for removal of phenol from aqueous solution, J. Mol. Liq. 223 (2016) 1067–1080. [14] Q. Miao, Y. Tang, J. Xu, X. Liu, L. Xiao, Q. Chen, Activated carbon prepared from soybean straw for phenol adsorption, J. Taiwan Inst. Chem. Eng. 44 (2013) 458–465. [15] M. Dizbay-Onat, U.K. Vaidya, C.T. Lungu, Preparation of industrial sisal fiber waste derived activated carbon by chemical activation and effects of carbonization parameters on surface characteristics, Ind. Crops Prod. 95 (2017) 583–590. [16] Z. Zou, Y. Tang, C. Jiang, J. Zhang, Efficient adsorption of Cr (VI) on sunflower seed hull derived porous carbon, J. Environ. Chem. Eng. 3 (2015) 898–905. [17] L. Panzella, F. Moccia, M. Toscanesi, M. Trifuoggi, S. Giovando, A. Napolitano, Exhausted woods from tannin extraction as an unexplored waste biomass: evaluation of the antioxidant and pollutant adsorption properties and activating effects of hydrolytic treatments, Antioxidants 8 (2019) 10–14. [18] A. Arbenz, L. Avérous, Chemical modification of tannins to elaborate aromatic biobased macromolecular architectures, Green Chem. 17 (2015) 2626–2646. [19] J.S. da Silva, M.P. da Rosa, P.H. Beck, E.C. Peres, G.L. Dotto, F. Kessler, F.S. Grasel, Preparation of an alternative adsorbent from Acacia mearnsii wastes through acetosolv method and its application for dye removal, J. Clean. Prod. 180 (2018) 386–394. [20] P. rodução da Extração Vegetal e da Silvicultura, (ISSN 0103-8435), Ministério Do Planejamento, Orçamento E Gestão. Instituto Brasileiro de Geografia E Estatística−IBGE, Rio de Janeiro, Brasil 32 (2017).

Fig. 10. Molecular absorption spectra of the simulated industrial effluent before and after adsorption using BWBW-AC-6.

3.7. Adsorption of phenolic compounds in a simulated effluent A simulated industrial effluent was prepared to evaluate the efficiency of BWBW-AC-6 to remove phenolic compounds in a medium with high concentration of salts. Fig. 10 shows the spectra of the simulated effluent before and after the adsorption process. BWBW-AC-06 was capable to remove 95.89%. These results indicate that BWBW-AC06 is a good adsorbent for removal of phenolic compounds from industrial effluents.

4. Conclusion In this work, the black wattle bark waste was used as precursor material to produce activated carbon. The most suitable conditions for activated carbon production was carbonization temperature of 700 °C, carbonization time of 2 h, activating agent ratio of 20% and immersion time in the activation agent of 12 h. BWBA-AC-6 presented micro/mesoporous structure, surface area of 414 m2 g−1 and total pore volume of 0.064 cm3 g−1. After carbonization, a cleaning in the cavities and the presence of lactone and quinone groups were observed in BWBA-AC-6 surface. Pseudo-second order model was the more suitable to represent the kinetic behavior. The Weber-Morris analysis showed that phenol adsorption occurred through film and intraparticle diffusion, and that the increase in stirring rate led to an increase in film diffusion. Freundlich model presented the best fit to the equilibrium data. The maximum adsorption capacity was 98.57 mg g−1, at 55 °C. The phenol adsorption onto BWBA-AC-6 was spontaneous, favorable and 8

Journal of Environmental Chemical Engineering 7 (2019) 103396

S.F. Lütke, et al.

[47] A.C. Lua, T. Yang, J. Guo, Effects of pyrolysis conditions on the properties of activated carbons prepared from pistachio-nut shells, J. Anal. Appl. Pyrolysis 72 (2004) 279–287. [48] G.F. de Oliveira, R.C. de Andrade, M.A.G. Trindade, H.M.C. Andrade, C.T. de Carvalho, Thermogravimetric and spectroscopy study (TG-DTA/FT-IR) of activated carbon from the renewable biomass source babassu, Quim. Nova 40 (2017) 284–292. [49] G.S. Szymański, Z. Karpiński, S. Biniak, A. Świa̧tkowski, The effect of the gradual thermal decomposition of surface oxygen species on the chemical and catalytic properties of oxidized activated carbon, Carbon N. Y. 40 (2002) 2627–2639. [50] G.L. Dotto, L.A.A. Pinto, Analysis of mass transfer kinetics in the biosorption of synthetic dyes onto Spirulina platensis nanoparticles, Biochem. Eng. J. 68 (2012) 85–90. [51] G.L. Dotto, L.A.A. Pinto, Adsorption of food dyes acid blue 9 and food yellow 3 onto chitosan: stirring rate effect in kinetics and mechanism, J. Hazard. Mater. 187 (2011) 164–170. [52] A. Kumar, H.M. Jena, Removal of methylene blue and phenol onto prepared activated carbon from Fox nutshell by chemical activation in batch and fixed-bed column, J. Clean. Prod. 137 (2016) 1246–1259. [53] E. Lorenc-Grabowska, G. Gryglewicz, M.A. Diez, Kinetics and equilibrium study of phenol adsorption on nitrogen-enriched activated carbons, Fuel 114 (2013) 235–243. [54] D. Zhang, P. Huo, W. Liu, Behavior of phenol adsorption on thermal modified activated carbon, Chin. J. Chem. Eng. 24 (2016) 446–452. [55] Y.S. Ho, G. Mckay, Kinetic models for the sorption of dye from aqueous solution by wood, Process Saf. Environ. Prot. 76 (1998) 183–191. [56] H. Qiu, L. Lv, B. Pan, Q. Zhang, W. Zhang, Q. Zhang, Critical review in adsorption kinetic models, J. Zhejiang Univ. Sci. A 10 (2009) 716–724. [57] X.Q. Liu, H. Ding, Y. Wang, W. Liu, H. Jiang, Pyrolytic temperature dependent and ash catalyzed formation of sludge char with ultra-high adsorption to 1-naphthol, Environ. Sci. Technol. 50 (2016) 2602–2609. [58] X.-R. Jing, Y.-Y. Wang, W.-J. Liu, Y.-K. Wang, H. Jiang, Enhanced adsorption performance of tetracycline in aqueous solutions by methanol-modified biochar, Chem. Eng. J. 248 (2014) 168–174. [59] C.H. Giles, D. Smith, A. Huitson, A General treatment and classification of the solute adsorption isotherm, J. Colloid Interface Sci. 47 (1974) 755–765. [60] A.T.M. Din, B.H. Hameed, A.L. Ahmad, Batch adsorption of phenol onto physiochemical-activated coconut shell, J. Hazard. Mater. 161 (2009) 1522–1529. [61] V. Makrigianni, A. Giannakas, Y. Deligiannakis, I. Konstantinou, Adsorption of phenol and methylene blue from aqueous solutions by pyrolytic tire char: equilibrium and kinetic studies, J. Environ. Chem. Eng. 3 (2015) 574–582. [62] I. Sierra, U. Iriarte-Velasco, E.A. Cepeda, M. Gamero, A.T. Aguayo, Preparation of carbon-based adsorbents from the pyrolysis of sewage sludge with CO2. Investigation of the acid washing procedure, Desalin. Water Treat. 57 (2016) 16053–16065. [63] Y. Shen, Y. Fu, KOH-activated rice husk char via CO2 pyrolysis for phenol adsorption, Mater. Today Energy 9 (2018) 397–405. [64] B.M.V. da Gama, G.E. do Nascimento, D.C.S. Sales, J.M. Rodríguez-Díaz, C.M.B. de, M. Barbosa, M.M.M.B. Dutra, Mono and binary component adsorption of phenol and cadmium using adsorbent derived from peanut shells, J. Clean. Prod. 201 (2018) 219–228. [65] L.A. Rodrigues, M.L.C.P. da Silva, M.O. Alvarez-Mendes, A. dos, R. Coutinho, G.P. Thim, Phenol removal from aqueous solution by activated carbon produced from avocado kernel seeds, Chem. Eng. J. 174 (2011) 49–57. [66] M. Kilic, E. Apaydin-varol, E. Pütün, Adsorptive removal of phenol from aqueous solutions on activated carbon prepared from tobacco residues: equilibrium, kinetics and thermodynamics, J. Hazard. Mater. 189 (2011) 397–403. [67] B.H. Hameed, A.A. Rahman, Removal of phenol from aqueous solutions by adsorption onto activated carbon prepared from biomass material, J. Hazard. Mater. 160 (2008) 576–581. [68] K.P. Singh, A. Malik, S. Sinha, P. Ojha, Liquid-phase adsorption of phenols using activated carbons derived from agricultural waste material, J. Hazard. Mater. 150 (2008) 626–641. [69] N.A. Travlou, G.Z. Kyzas, N.K. Lazaridis, E.A. Deliyanni, Graphite oxide/chitosan composite for reactive dye removal, Chem. Eng. J. 217 (2013) 256–265. [70] C.L. Sun, C.S. Wang, Estimation on the intramolecular hydrogen-bonding energies in proteins and peptides by the analytic potential energy function, J. Mol. Struct. Theochem. 956 (2010) 38–43. [71] G. Yang, L. Tang, G. Zeng, Y. Cai, J. Tang, Y. Pang, Y. Zhou, Y. Liu, J. Wang, S. Zhang, W. Xiong, Simultaneous removal of lead and phenol contamination from water by nitrogen-functionalized magnetic ordered mesoporous carbon, Chem. Eng. J. 259 (2015) 854–864. [72] R. Krishnamoorthy, B. Govindan, F. Banat, V. Sagadevan, M. Purushothaman, P.L. Show, Date pits activated carbon for divalent lead ions removal, J. Biosci. Bioeng. 128 (2019) 88–97.

[21] M.U. Dural, L. Cavas, S.K. Papageorgiou, F.K. Katsaros, Methylene blue adsorption on activated carbon prepared from Posidonia oceanica (L.) dead leaves: Kinetics and equilibrium studies, Chem. Eng. J. 168 (2011) 77–85. [22] G.E.P. Box, W.G. Hunter, J.S. Hunter, Statistics for Experimenters, An Introduction to Design, Data Analysis, and Model Building, John Wiley & Sons, New York, 1978. [23] Y.S. Ho, G. McKay, A comparison of chemisorption kinetic models applied to pollutant removal on various sorbents, Process Saf. Environ. Prot. 76 (1998) 332–340. [24] Q. Zhu, G.D. Moggridge, M. Ainte, M.D. Mantle, L.F. Gladden, C. D’Agostino, Adsorption of pyridine from aqueous solutions by polymeric adsorbents MN 200 and MN 500. Part 1: adsorption performance and PFG-NMR studies, Chem. Eng. J. 306 (2016) 67–76. [25] I. Langmuir, The adsorption of gases on plane surfaces of glass, mica and platinum, J. Am. Chem. Soc. 40 (1918) 1361–1403. [26] H. Freundlich, Über die Adsorption in Lösungen, Zeitschrift Für Phys, Chemie 57U (1907) 385–470. [27] Y. Liu, Is the free energy change of adsorption correctly calculated? J. Chem. Eng. 54 (2009) 1981–1985. [28] K. Mohanty, M. Jha, B.C. Meikap, M.N. Biswas, Preparation and characterization of activated carbons from Terminalia arjuna nut with zinc chloride activation for the removal of phenol from wastewater, Ind. Eng. Chem. Res. 44 (2005) 4128–4138. [29] H. Sayğılı, F. Güzel, High surface area mesoporous activated carbon from tomato processing solid waste by zinc chloride activation: process optimization, characterization and dyes adsorption, J. Clean. Prod. 113 (2016) 995–1004. [30] A. Nasrullah, B. Saad, A.H. Bhat, A.S. Khan, M. Danish, M.H. Isa, A. Naeem, Mangosteen peel waste as a sustainable precursor for high surface area mesoporous activated carbon: characterization and application for methylene blue removal, J. Clean. Prod. 20 (2019) 1190–1200. [31] H. Demiral, İ. Demiral, Surface properties of activated carbon prepared from wastes, Surf. Interface Anal. 40 (2008) 612–615. [32] M. Thommes, K. Kaneko, A.V. Neimark, J.P. Olivier, F. Rodriguez-Reinoso, J. Rouquerol, K.S.W. Sing, Physisorption of Gases, with Special Reference to the Evaluation of Surface Area and Pore Size Distribution (IUPAC Technical Report), (2015). [33] O. Oginni, K. Singh, G. Oporto, B. Dawson-Andoh, L. McDonald, E. Sabolsky, Influence of one-step and two-step KOH activation on activated carbon characteristics, Bioresour. Technol. Rep. 7 (2019) 100266. [34] N. Soltani, A. Bahrami, M.I. Pech-Canul, L.A. González, Review on the physicochemical treatments of rice husk for production of advanced materials, Chem. Eng. J. 264 (2015) 899–935. [35] B. Biswas, N. Pandey, Y. Bisht, R. Singh, J. Kumar, T. Bhaskar, Pyrolysis of agricultural biomass residues: comparative study of corn cob, wheat straw, rice straw and rice husk, Bioresour. Technol. (2017). [36] B. de Diego-Díaz, A. Duran, M.R. Álvarez-García, J. Fernández-Rodríguez, New trends in physicochemical characterization of solid lignocellulosic waste in anaerobic digestion, Fuel 245 (2019) 240–246. [37] K.B. Fontana, E.S. Chaves, J.D.S. Sanchez, E.R.L.R. Watanabe, J.M.T.A. Pietrobelli, G.G. Lenzi, Textile dye removal from aqueous solutions by malt bagasse: isotherm, kinetic and thermodynamic studies, Ecotoxicol. Environ. Saf. 124 (2016) 329–336. [38] E. Espinosa, R. Sánchez, Z. González, J. Domínguez-Robles, B. Ferrari, A. Rodríguez, Rapidly growing vegetables as new sources for lignocellulose nanofibre isolation: physicochemical, thermal and rheological characterisation, Carbohydr. Polym. 175 (2017) 27–37. [39] M. Kumar, S.N. Upadhyay, P.K. Mishra, A comparative study of thermochemical characteristics of lignocellulosic biomasses, Bioresour. Technol. Rep. (2019) 100186. [40] Y. Fu, Y. Shen, Z. Zhang, X. Ge, M. Chen, Activated bio-chars derived from rice husk via one- and two-step KOH-catalyzed pyrolysis for phenol adsorption, Sci. Total Environ. 646 (2019) 1567–1577. [41] M. Asadullah, M. Asaduzzaman, M.S. Kabir, M.G. Mostofa, T. Miyazawa, Chemical and structural evaluation of activated carbon prepared from jute sticks for Brilliant Green dye removal from aqueous solution, J. Hazard. Mater. 174 (2010) 437–443. [42] W.T. Tsai, C.Y. Chang, M.C. Lin, S.F. Chien, H.F. Sun, M.F. Hsieh, Adsorption of acid dye onto activated carbons prepared from agricultural waste bagasse by ZnCl2 activation, Chemosphere 45 (2001) 51–58. [43] J.A. Mattson, H.B. Mark, M.D. Malbin, W.J. Weber, J.C. Crittenden, Surface chemistry of active carbon: specific adsorption of phenols, J. Colloid Interface Sci. 31 (1969) 116–130. [44] Y. Gokce, Z. Aktas, Nitric acid modification of activated carbon produced from waste tea and adsorption of methylene blue and phenol, Appl. Surf. Sci. 313 (2014) 352–359. [45] A.P. Terzyk, Further insights into the role of carbon surface functionalities in the mechanism of phenol adsorption, J. Colloid Interface Sci. 268 (2003) 301–329. [46] Y. Cui, A. Masud, N. Aich, J.D. Atkinson, Phenol and Cr (VI) removal using materials derived from harmful algal bloom biomass: characterization and performance assessment for a biosorbent, a porous carbon, and Fe/C composites, J. Hazard. Mater. 368 (2019) 477–486.

9