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Abstract

Pyrene is a polycyclic aromatic hydrocarbon, classified as a priority pollutant. Aiming to minimize the presence of this polycyclic aromatic hydrocarbon in aquatic ecosystems, it is important to develop and consider new alternatives that enable its partial or total removal by different mechanisms and/or processes. In this sense, several techniques have been used for this purpose. Among them, adsorption techniques employing natural adsorbents as peat represent an attractive alternative due to its low cost and high removal efficiency. In the present study, two samples (decomposed peat – DP, and fibrous peat – FP) were used to remove pyrene at concentrations of 1.0, 2.0, 3.0, 4.0, and 5.0 µg L⁻¹ for up to 72 h. The removal percentages with DP were between 75.5 and 91.0%, while for FP these values were in the range of 77.7 to 92.1%. The experimental data showed that the adsorption kinetics were better described using a pseudo-second-order model. Regarding the adsorption equilibrium, the experimental data were adequately fitted by the Freundlich equation for both peat samples. Finally, the adsorption capacity depended on thermodynamic parameters, indicating that the adsorption process was spontaneous and occurred by physisorption.

Keywords

Pyrene peat adsorption kinetics equilibrium thermodynamics

Introduction

Chemicals provide valuable benefits to humanity. Nonetheless, because of their intrinsic hazardous properties, some of them pose risks to the environment and human health. In this sense, organic contaminants stand out as being particularly dangerous. These substances can come from both diffuse and point sources, with contributions from urban drainage, agricultural activities, and domestic and industrial effluent discharges (Cheema et al., 2010).

Polycyclic aromatic hydrocarbons (PAHs), in particular, are a class of organic contaminants of environmental interest since a number of such compounds cause carcinogenic and mutagenic effects and are potent immunosuppressants (Rajendran et al., 2013). They are originated from various sources, including bacterial biosynthesis, incomplete combustion of fossil fuels, and petroleum or petrochemical materials. PAHs comprise more than 100 different chemicals (Rios et al., 2007), and the compounds with high molecular weight and more benzene rings (four or more rings) are the most important in the field of pollution due to their higher stability, hydrophobicity, and low biodegradability (Seo et al., 2009).

Pyrene is a member of the PAHs family and has four benzene rings. This compound is a major proportion of the PAH compounds found in both aquatic and terrestrial environments and its presence is linked to anthropogenic activities (Guo et al., 2007). Like other high-molecular weight PAHs, pyrene is classified by the US Environmental Protection Agency as a priority pollutant (US EPA, 1987) and can be accumulated in the body of aquatic organisms due to its lipophilic nature, exerting adverse health effects (Honkanen et al., 2008). A study carried out by Mäenpää et al. (2009), for example, found a narcotic effect of this PAH in oligochaetes, indicating a sublethal toxicity to these invertebrates. Other studies also have shown negative effects on fish after coming into contact with pyrene, where they were subjected to oxidative stress and damage resulting from exposure (Sun et al., 2008). With crustaceans, a decrease in egg hatching has been observed in females, demonstrating the consequences of exposure to pyrene (Jensen et al., 2008).

In order to minimize the presence of pyrene in aquatic ecosystems, it is important to develop and consider new alternatives that enable its partial or total removal by different mechanisms and/or processes. This thematic is a subject of great importance, garnering the attention not only of researchers, but also industries, governments, and the general public, who have felt the consequences of negligence in the generation and disposal of wastes (Rey-Salgueiro et al., 2009).

A wide range of technologies has been developed for the removal organic contaminants from waters and wastewaters to decrease their environmental impacts. In this context, there are different techniques that vary with regard to efficiency, cost, and process complexity, including precipitation, ion exchange, adsorption, coagulation, and reverse osmosis (Liu et al., 2008). Among these, adsorption involves the ability of a substance to be incorporated into another compound by physical and/or chemical interactions. This technique is considered superior to the others because of the possibility of reusing water in terms of initial cost, flexibility and simplicity of the process design, and ease of operation. Moreover, this process also has the advantage of not leading to the formation of hazardous substances (Rafatullah et al., 2010).

Due to the low cost of the material and the high efficiency of removing contaminants, the employment of natural adsorbents of biological origin in adsorption studies has become an alternative and promising method. In general, the most widely used adsorbent material in studies involving the adsorption of contaminants is activated carbon. However, this material has a high cost and, moreover, it cannot be regenerated. Therefore, there is growing interest in the search for alternative materials with a lower cost that can replace activated carbon, such as peat (Hemmati et al., 2016).

The adsorption capacity of peat has attracted the attention of researchers, since this is an alternative material of low cost, has high removal efficiency, and usually does not require activation to adsorb molecules in solution (Fernandes et al., 2007, 2010a, 2011). Peat is a complex material whose major constituents are lignin, cellulose, and humic substances. These materials have polar functional groups, apolar moieties, high reactivity and which are active in ion exchange reactions, thus increasing the potential for the adsorption of specific solids (Couillard, 1994). The use of peat as an adsorbent material is very promising, especially in countries like Brazil where there is excellent availability of the material.

In view of all these facts, the aim of this work was to evaluate the applicability of two different peat samples in the removal of pyrene from aqueous solutions. This compound was chosen as the model PAH in the present study because of its high detection frequency in environmental samples.

Materials and methods

Chemicals

The reagents and solvents used in this work were all of analytical grade. Ethanol was obtained from Vetec Química Fina. Pyrene (>99% purity) was purchased from Sigma-Aldrich. Stock solutions of pyrene at a concentration of 40 µg L⁻¹ were prepared by dissolving the compound in ethanol and were stored at 278 K. Working aqueous solutions of pyrene were prepared daily by diluting the stock solution in deionized water to attain the required concentrations for calibration measurements. The deionized water was obtained from a Milli-Q system from Millipore.

Sampling, preparation, and characterization of the peat samples

The peat samples used in this study were collected from a peatland situated in the municipality of Balneário Arroio do Silva (Santa Catarina State, Brazil). The two collected samples were classified according to the method proposed by Von Post as H3 (poorly decomposed) and H7 (highly decomposed), and by the International Peat Society as decomposed peat (DP) and fibrous peat (FP) (Girardello et al., 2013).

The two sampling points are situated in a region where the incidence of vegetation is dominated mainly by mosses and other bryophytes, sedges, grasses, shrubs, and small-sized trees. Samples were collected with an aluminum shovel by scraping approximately 10 cm below the soil surface. After collection, the samples were dried under ventilation in a fume hood and sieved to a particle size less than 63 µm. At the end of this procedure, the samples were stored in glass bottles and were used without any physical or chemical pretreatment.

The specific surface areas were determinate by nitrogen adsorption–desorption isotherms using a Nova 1000 surface analyzer and a Micrometrics Instrument TriStar II 3020. Before analysis, the samples were degassed for 10 h at 423 K under vacuum. The hydrophobicity of peat samples was evaluated by measuring water contact angle (WCA) using a Kruss brand Drop Shape Analyzer (DSA 30). The measurements were conducted in triplicate using room temperature water as the test liquid in drops of 2 µL. The complete characterization of these samples has been reported elsewhere (Fernandes et al., 2010b; Girardello et al., 2013; Rovani et al., 2014).

Adsorption studies

The adsorption studies were carried out using the batch contact method. For these experiments, 5.0 mg of peat sample (DP or FP) were placed in 100 mL glass flasks containing 50 mL of pyrene solution (at concentrations of 1.0, 2.0, 3.0, 4.0, and 5.0 µg L⁻¹), which were stirred for a suitable time (from 0.0833 to 72 h). The stirring speed was kept constant at 500 r/min with a mechanical shaker of a five-axis AM5E apparatus. The experiments were performed at the natural pH (∼5.0), which is the pH of the deionized water after adding pyrene, with a controlled temperature (298 K). Blanks were also collected in order to correct the emission fluorescence signal of the pyrene solutions due to the presence of dissolved organic matter. The method detection limit was 0.03 µg L⁻¹ with a measurement error of ± 2%.

The pyrene concentration range used in this work is in accordance with the data published in the HPA Dutch List of target and intervention values for soil remediation and groundwater and is indicative of serious contamination. The reference alert is 2.5 µg L⁻¹ for groundwater, while the intervention value is 5.0 µg L⁻¹. The first indicates that some change in the functional properties of the environmental compartment has occurred, while the second indicates the need for implementing actions to remediate waters, due to the possible risk to human health and the environment (Lista holandesa de valores de qualidade do solo e da água subterrânea – Valores STI 6530, 1999).

After 72 h, the solutions (including blanks) were centrifuged for 15 min at 300 r/min. The concentration of pyrene in the supernatant solution (after and before adsorption) was determined using a calibration curve. Emission fluorescence spectra were performed in a 1.0 cm quartz cell, using a scan rate of 500 nm min⁻¹ from 350 to 600 nm in a Perkin Elmer LS45 spectrofluorimeter. The excitation and emission slits were set at 10 nm and the excitation wavelength (λ_exc) used to monitor the fluorescence of pyrene was 334 nm. The emission intensity of the band at 375 nm was used for the construction of the calibration curve obtained from three replicates.

The amount of pyrene uptaken and the removal percentage of pyrene by the peat samples were calculated by applying equations (1) and (2), respectively

q_{t} = \frac{(C_{0} - C_{f}) . V}{m}

(1)

% Removal = 100 . \frac{(C_{o} - C_{f})}{C_{o}}

(2)where q_t is the amount of pyrene adsorbed by the peat sample (mg g⁻¹) at time t, C_o is the initial pyrene concentration (mg L⁻¹), C_f is the pyrene concentration (mg L⁻¹) after the batch adsorption procedure, m is the peat sample mass (g), and V is the volume of pyrene solution (L).

Kinetic parameters

The kinetic study of adsorption provides useful data on the adsorption efficiency and viability of operations. Several kinetic models are available to examine the control mechanism of the adsorption process and test the experimental data (Errais et al., 2011). The kinetic of the adsorption process for both peat samples (DP and FP) was evaluated by means of pseudo-first- (equation 3) (Lagergren, 1898) and pseudo-second-order (equation 4) (Weber and Morris, 1963) models, shown below

q_{t} {= q}_{e} [1 {- exp (- k}_{1} \cdot t)]

(3)

q_{t} {= q}_{e} - \frac{q_{e}}{[k_{2} {(q}_{e}) \cdot t + 1]}

(4)where q_t is the amount of pyrene adsorbed by the adsorbent (mg g⁻¹) at time t, q_e is the amount of pyrene adsorbed at the equilibrium time (mg g⁻¹), k₁ is the pseudo-first-order rate constant (h⁻¹), k₂ is the pseudo-second-order rate constant (h⁻¹), and t is the contact time between pyrene and the adsorbent (h).

Kinetic models were fitted using a non-linear method, with successive iterations calculated by the Levenberg-Marquardt and Simplex methods, based on the non-linear adjustment capacity of Origin Microcal software. Furthermore, the models were also assessed using the coefficient of determination (R²) (Lima et al., 2015). Equation (5) shows as R² was calculated

R^{2} = (\frac{\sum_{i}^{n} (q_{i, \exp} - {\bar{q}}_{i, \exp})^{2} - \sum_{i}^{n} (q_{i, \exp} - q_{i, model})^{2}}{\sum_{i}^{n} (q_{i, \exp} - {\bar{q}}_{i, \exp})^{2}})

(5)where q_i,model is each value of q predicted by the fitted model, q_i, exp is each value of q measured experimentally,

{\bar{q}}_{i, \exp}

is the average of q experimentally measured, n is the number of experiments performed, and p is the number of parameters of the adjusted model.

Isotherms

Adsorption isotherm models are extremely important to describe how the adsorbate molecules are distributed between the liquid phase and solid phase at equilibrium. The equilibrium of a given system is achieved when there is no change in the adsorbate concentrations in both phases of the system. Furthermore, the equilibrium condition reflects the capacity and/or affinity of an adsorbate by an adsorbent, under a given set of conditions to which the system is subjected. Thus, the correlation of equilibrium data through theoretical or empirical equations is essential for describing adsorption. In this study, equilibrium data were analyzed using the Langmuir (1916) and Freundlich (1906) isotherms.

The Langmuir model assumes that adsorption is homogeneous and occurs at specific sites of the adsorbent to form a monolayer. In addition, the molecules adsorbed at an adsorption site should not affect the adsorption of other molecules. The linear form of the Langmuir isotherm is given by equation (6)

\frac{C_{e}}{q_{e}} = \frac{1}{{QK}_{L}} + \frac{C_{e}}{Q}

(6)where C_e is the equilibrium concentration of the adsorbate (mg L⁻¹), q_e is the amount of adsorbate adsorbed at equilibrium (mg g⁻¹), and K_L (L mg⁻¹) and Q (mg g⁻¹) are the Langmuir parameters related to the affinity of adsorption sites and the maximum amount of adsorbate required for formation of the adsorbent monolayer, respectively.

The Freundlich model, on the other hand, considers that adsorption occurs at heterogeneous surfaces and is not limited to the formation of a monolayer, providing that the amount of solute adsorbed is a function of the solute concentration in the solution. This empirical model has been shown to be consistent with an exponential distribution of active sites, characteristic of heterogeneous surfaces. The linear form of the Freundlich isotherm is given by equation (7)

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

(7)where K_F (L mg⁻¹) is the Freundlich constant which is related to the adsorption capacity and n is a parameter that is related to the intensity of adsorption. Moreover, these two parameters may indicate if the nature of the adsorption process is favorable or unfavorable.

Thermodynamics

The adsorption capacity depends on thermodynamic parameters such as the Gibbs free energy change (ΔG^o), enthalpy change (ΔH^o), and entropy change (ΔS^o) (Soto et al., 2011). The ΔG^o (J mol⁻¹) values were calculated according to equations (8) and (9)

K_{d} = \frac{C_{ad, e}}{C_{e}}

(8)

Δ G^{o} = - RT \ln K_{d}

(9)where C_ad,e (mg L⁻¹) is the concentration of pyrene in peat samples at equilibrium, K_d is the apparent equilibrium constant, R is the universal gas constant (8.314 J K⁻¹mol⁻¹), and T (298 K) is the absolute temperature of the system.

If the ΔH^o contribution is disregarded, equation (10) can be reduced to equation (11) and, consequently, the ΔS^o values can be estimated

Δ G_{ads}^{o} = Δ H_{ads}^{o} - T Δ S_{ads}^{o}

(10)

- \frac{Δ G_{ads}^{o}}{T} = Δ S_{ads}^{o}

(11)

Results and discussion

Adsorption parameters

According to Figure 1, the adsorption for both samples was more intense in the first 2 h, at which point the maximum amount of pyrene had been adsorbed per gram of peat (q_t) found only after a few hours of contact time.

Figure 1.

Effects of the amount of pyrene adsorbed (q_t) by peat samples: (a) DP and (b) FP. Conditions: temperature = 298 K; pH = 5.0; mass of adsorbent = 5.0 mg.

At the beginning of the adsorption process, the majority of active sites present in the peat structure are available, allowing a large number of pyrene molecules interact with these sites. Thus, the amount of pyrene adsorbed by peat occurs quickly. Then, a slower adsorptive process takes place and finally there is greater difficulty in removing the last traces of pyrene from the solution. It is possible that the pyrene reached saturation in the first adsorption layer, followed by the formation of another adsorption layer.

The data set presented in Figure 2 shows that the increase in the contaminant concentration promotes a slight increase in the percentage of removal, especially with regard to the lowest concentrations studied. In the solution with a pyrene concentration of 5.0 µg L⁻¹, removal of more than 90% of the contaminant was achieved for both DP and FP. The small difference observed between the removal percentages of both samples seems to be related to their respective micropore areas. It is likely that the pyrene adsorption process occurs in a higher proportion in the micropores of the peat samples, being more favored in FP which has higher micropore area (Table 1). Overall, the removal percentage for DP was between 75.5 and 91.0%, while for the FP, these values were in the range of 77.7 to 92.1%.

Figure 2.

Removal percentage of pyrene by peat samples. Conditions: temperature = 298 K; pH = 5.0; mass of adsorbent = 5.0 mg.

Table 1.

Parameters of the porous structure and water contact angles for the peat samples.

Samples	Specific area BET (m² g⁻¹)	Micropore area BET (cm² g⁻¹)	Contact angle (°)	Hydrophilicity
DP	1.01	0.294	151.6 ± 6.6	Hydrophobic
FP	0.0952	1.17	139.2 ± 2.6	Hydrophobic

According to Girardello et al. (2013), peat presents in its composition a high content of humic substances, which are responsible for the various interactions with organic contaminants. Previous studies carried out by Jung et al. (2010) showed that pyrene can be incorporated into the structure of humic substances through hydrophobic sites, which are responsible for their capture. Another study performed by Sierra et al. (2005) revealed that, in the presence of apolar contaminants such as pyrene, humic substances might organize themselves and form hydrophobic microenvironments. Thus, the probable interactions existing in the adsorption process are of the hydrophobic–hydrophobic type due to the hydrophobic characteristic of peat (Table 1) and the hydrophobicity of pyrene (K_ow = 5.18). All these aspects contribute to the high percentage removal of pyrene by both peat samples.

Kinetic parameters

The choice of the kinetic model that best fits the experimental behavior should take into account the closest values of unit of R² (Xiong and Mahmood, 2010). The R² value measures the differences between each data point and the average value obtained from all curve points. The results summarized in Tables 2 and 3 suggest that the adsorption of the pyrene onto peat samples follows the pseudo-second-order kinetic model that showed the best fit to the experimental data due to the good values of this parameter. Furthermore, the calculated data (q_{e, cal}) are more consistent with the experimental data (q_{e, exp}).

Table 2.

Kinetic parameters for adsorption of pyrene onto the DP sample.

	Initial concentration of pyrene
	1.0 µg L⁻¹	2.0 µg L⁻¹	3.0 µg L⁻¹	4.0 µg L⁻¹	5.0 µg L⁻¹
q_e, exp (mg g⁻¹)	0.00675	0.0164	0.0261	0.0352	0.0466
Pseudo-first-order
k₁ (g mg⁻¹ h⁻¹)	3.43	2.78	3.81	1.79	3.52
q_e, calc (mg g⁻¹)	0.00655	0.0159	0.0254	0.0332	0.0443
R²	0.8917	0.9879	0.9720	0.9734	0.9904
Pseudo-second-order
k₂ (g mg⁻¹ h⁻¹)	916.8	253.9	238.0	74.03	124.1
q_e, calc (mg g⁻¹)	0.00679	0.0167	0.0265	0.0354	0.0464
R²	0.8923	0.9885	0.9918	0.9915	0.9988

Conditions: temperature = 298 K; pH = 5.0; mass of adsorbent = 5.0 mg.

Table 3.

Kinetic parameters for adsorption of pyrene onto the FP sample.

	Initial concentration of pyrene
	1.0 µg L⁻¹	2.0 µg L⁻¹	3.0 µg L⁻¹	4.0 µg L⁻¹	5.0 µg L⁻¹
q_e, exp (mg g⁻¹)	0.00752	0.0179	0.0256	0.0367	0.0471
Pseudo-first-order
k₁ (g mg⁻¹ h⁻¹)	6.40	4.10	3.64	1.82	3.02
q_e, calc (mg g⁻¹)	0.00714	0.0168	0.0246	0.0342	0.0443
R²	0.9196	0.9625	0.9590	0.9769	0.9788
Pseudo-second-order
k₂ (g mg⁻¹ h⁻¹)	1491	377.6	228.6	72.13	105.1
q_e, calc (mg g⁻¹)	0.00745	0.0176	0.0258	0.0365	0.0465
R²	0.9600	0.9855	0.9936	0.9968	0.9917

Conditions: temperature = 298 K; pH = 5.0; mass of adsorbent = 5.0 mg.

This observation can be confirmed by visual analysis of Figure 3. Pseudo-second-order model indicates that the process is dependent on both the amount of pyrene and the number of active sites present in the peat, i.e. an increase in the pyrene concentration resulted in an increase in the adsorbed mass for both peat samples. It is likely that the saturation of active sites induced the formation of new adsorbent layers, allowing the removal of more pyrene molecules present in the solution. The similar adsorption behavior between the two samples is a result of their structural similarity, as mentioned previously.

Figure 3.

Kinetics parameters of pyrene adsorption onto peat samples: (a) DP and (b) FP. Conditions: temperature = 298 K; pH = 5.0; mass of adsorbent = 5.0 mg.

Equilibrium parameters

The pyrene adsorption results for peat samples were not adequately described by the Langmuir model. The graphs of C_e/q_e versus C_e do not exhibit linear behavior and therefore the values of R² were not satisfactory. On the other hand, the Freundlich model showed good agreement with experimental data for both samples, with an R² value of 0.8865 for DP and 0.9172 for FP. It is assumed that the strongest binding sites are initially occupied, and that the binding potential is reduced with increasing local occupancy rate, suggesting that the pyrene adsorption process for the studied peat samples occurs in multiple layers, corroborating the previous results (Fernandes et al., 2011).

The K_F and n values, calculated by means of equation (7) for the Freundlich model, are shown in Table 4. The K_F values found for DP and FP were 0.314 and 0.210 L mg⁻¹, respectively.

Table 4.

Parameters of the Freundlich isotherm for the adsorption of pyrene onto peat samples.

DP			FP
K_F (L mg⁻¹)	n	R ²	K_F (L mg⁻¹)	n	R ²
0.314	0.312	0.8865	0.210	0.454	0.9172

Conditions: temperature = 298 K; pH = 5.0; mass of adsorbent = 5.0 mg.

The values of n, by other hand, were 0.312 for DP and 0.454 for FP. According to Xiong and Mahmood (2010), a high value of n indicates favorable adsorption; more specifically, it is stated that values of n between 1 and 10 represent good potential for adsorption (Errais et al., 2011). The n values found indicate that adsorption is an unfavorable action. However, values of n lower than 1 are also associated with efficient adsorption processes, such as in the removal of microcystin-LR by a peat sample which showed 90% removal (Sathishkumar et al., 2010), confirming the results presented here.

Thermodynamic parameters

A negative value for ΔG^o indicates spontaneous adsorption and that the process does not require high activation energy values (Almeida et al., 2010). Furthermore, ΔG° values between –20 and 0 kJ mol⁻¹ correspond to physisorption, while values between –400 and –80 kJ mol⁻¹ correspond to chemisorption. These features show that the adsorption of pyrene by both peat samples occurred through physisorption. The ΔG^o values shown in Table 5 decrease as the concentration of pyrene in solution increases, indicating greater spontaneity of adsorption due to the increased possibility that pyrene molecules will be accommodated at the active sites of both peat samples. All these issues are related to the ΔS^o of the process.

Table 5.

Thermodynamic parameters for the adsorption of pyrene onto peat samples.

Initial concentration of pyrene (µg L⁻¹)	DP			FP
Initial concentration of pyrene (µg L⁻¹)	K_d (L g⁻¹)	ΔG^o (kJ mol⁻¹)	ΔS^o (J K⁻¹mol⁻¹)	K_d (L g⁻¹)	ΔG^o (kJ mol⁻¹)	ΔS^o (J K⁻¹mol⁻¹)
1.0	1.97	−1.67	5.65	3.01	−2.70	9.16
2.0	4.16	−3.50	11.85	6.30	−4.52	15.31
3.0	6.48	−4.58	15.53	5.85	−4.33	14.69
4.0	6.17	−4.46	15.12	8.58	−5.27	17.87
5.0¹	8.76	−5.32	18.05	9.41	−5.50	18.64

Conditions: temperature = 298 K; pH = 5.0; mass of adsorbent = 5.0 mg.

Positive values of ΔS^o indicate the random organization of the adsorbate at solid/solution interface (Soto et al., 2011). Table 5 shows an increase in the entropy of adsorption with increasing concentrations of pyrene. A positive and increasing value for ΔS^o indicates an increase in the entropy of the system, which implies an increase in randomness at the solid/solution interface due to structural changes in the adsorbate and in the adsorbent as well as the affinity of the adsorbent for the adsorbate. All these aspects demonstrate that the peat samples studied here may be considered as an alternative material to remove pyrene from aqueous solutions.

Conclusion

Peat samples were found to be highly effective in the removal of pyrene from aqueous solutions with percentages exceeding 90% in some cases. The small difference observed between the removal percentages of the two peat samples is directly related to their respective areas of micropores and the probable hydrophobic–hydrophobic interactions in the adsorption process;

Based on the determination coefficients of the kinetic models, the pseudo-second-order model was more appropriate to describe the adsorption process, indicating that the overall process was dependent on the amount of pyrene and the sites available in the peat;

The overall results were described by the Freundlich isotherm equation, suggesting that the pyrene adsorption process on the studied peat samples occurred in multiple layers. Furthermore, the thermodynamic parameters showed that the nature of adsorption was spontaneous and occurred by physisorption;

All these aspects demonstrate the efficiency of pyrene adsorption onto peat.

Footnotes

Acknowledgements

The authors are grateful to the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) for the scholarship.

Declaration of Conflicting Interests

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

Funding

The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This work was supported by the Fundação de Amparo à Pesquisa do Estado do Rio do Sul (FAPERGS, Brazil).

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Removal of pyrene from aqueous solutions by adsorption onto Brazilian peat samples

Abstract

Keywords

Introduction

Materials and methods

Chemicals

Sampling, preparation, and characterization of the peat samples

Adsorption studies

Kinetic parameters

Isotherms

Thermodynamics

Results and discussion

Adsorption parameters

Kinetic parameters

Equilibrium parameters

Thermodynamic parameters

Conclusion

Footnotes

Acknowledgements

Declaration of Conflicting Interests

Funding

References