Enas N. Mahmoud
| Rafea Naffa | Khalil M. Ibrahim | Sawsan Jaafreh* | Manal H. Al-Bzour | Abdallah Abuferweh
© 2025 The authors. This article is published by IIETA and is licensed under the CC BY 4.0 license (http://creativecommons.org/licenses/by/4.0/).
OPEN ACCESS
The widespread use of pesticides has led to significant contamination of both surface and groundwater, emerging as a critical environmental issue in recent years. One common method to remove pesticides from aqueous solutions is the adsorption process utilizing activated carbon. Here, the olive oil pomace (locally known as Jift) was used to prepare the activated carbon. The ability of the activated carbon prepared from Jift (ACJ) to remove several pesticides, including Metalaxyl, Imidacloprid, Methomyl, and Paraquat Dichloride, from aqueous solution was then investigated. The Jift was roasted and then activated by CO2 at 800℃. ACJ was characterized by Scanning Electron Microscope, which shows that the pores in ACJ are mostly micropores. The specific surface area of ACJ and clay Jordanian minerals (Zeolite and Bentonite) was calculated using Methylene Blue (MB). Among these adsorbents, ACJ has the highest specific surface area (561.1 m2/g), making it a promising adsorbent for pesticide removal. The uptake of pesticides using ACJ was compared with that of Zeolite and Bentonite. ACJ showed a high ability to remove all four pesticides, while Zeolite and Bentonite were only able to remove Paraquat Dichloride. The experimental data derived from the equilibrium adsorption isotherm were analyzed using the Langmuir and Freundlich models. The results indicated that the Langmuir model provided a superior fit to the data for the four pesticides, as evidenced by a high correlation coefficient (R2 > 0.95) compared to the Freundlich model. Langmuir maximum adsorption capacity (qm) were 277.30, 233.97, 119.71, and 74.94 mg/g for Methomyl, Imidacloprid, Metalaxyl, and Paraquat Dichloride, respectively. The Freundlich model was fitted only to the data for Methomyl and Imidacloprid (R2 > 0.96). The heterogeneity factor (1/n) values for the two pesticides are less than unity, indicating a favorable adsorption process, and an increase in adsorption capacity. That explains why qm of Methomyl and Imidacloprid were significantly higher than those of the other pesticides. The nature of the adsorption process was favorable for all four pesticides, as indicated by the estimated values of the Langmuir isotherm equilibrium parameter (RL), which fell within the range of 0 < RL < 1. Two kinetic models (pseudo-first-order and pseudo-second-order) were used to assess the adsorption kinetic data. The pseudo-second-order model provided a better representation of the adsorption kinetics (R2 > 0.97), which indicates that the adsorption process follows a chemisorption mechanism. These results demonstrate the potential of ACJ as an effective adsorbent for removing pesticides in water treatment applications.
environmental remediation, water treatment, Metalaxyl, imidacloprid, methomyl, paraquat dichloride, adsorption, olive oil pomace
Jordan, a country in the Middle East, confronts a significant water scarcity crisis. This country has one of the lowest levels of water resources in the world and is considered to be among the most arid countries. Jordan currently supplies 150 m3 of water per person annually, representing approximately one-third of the worldwide average. Water scarcity is attributable to the growing fluctuations in climate conditions, specifically concerning precipitation and rising temperatures. Furthermore, the issue has worsened due to the continuous large-scale refugee influx, exacerbating the population-water imbalance. Although there are some surface water resources available, Jordan's main supply of water is derived from harvested rainwater through various means such as rivers, dams, lakes, and groundwater. As a result, it is crucial to utilize treated wastewater in Jordan, particularly in the agriculture sector [1-3]. Consequently, approximately 95% of Jordan's wastewater is treated, with over 92% utilized in agricultural activities [4]. In Jordan, similar to many nations, the assessment of wastewater quality depends on the monitoring of standard parameters governed by the European Urban Wastewater Directive (91/271/EEC). These metrics encompass phosphates, nitrates, chemical and biochemical oxygen demand, and total suspended solids. Nevertheless, some compounds that may present a risk to human health are not covered by these restrictions [2]. Recently, there has been wide documentation of the presence of emerging contaminants, such as pesticides, X-ray contrast media, personal care items, medicines, and endocrine disruptors in wastewater, surface waters, and groundwater [5].
Regarding pesticide contaminants, pesticides are recognized as agents that safeguard crops from harmful pests and diseases affecting humans. Their beneficial effects render pesticides an essential tool for maintaining and improving the quality of life for individuals across the globe. Each year, an average of two million tons of pesticides are utilized worldwide to combat weeds and pests. Pesticides are traditionally categorized based on the specific species they target including insecticides, herbicides, fungicides, rodenticides, and so forth [6]. The methods employed for the application of pesticides, such as spraying and spreading, can lead to their infiltration into soil and water systems in both agricultural and urban environments. The leaching of pesticides into groundwater is especially significant, given that groundwater serves as a crucial source for drinking water production. Consequently, pesticides adversely impact the environment [7, 8]. Pesticides are highly detrimental to human health, due to their toxicity, and being mutagenic, carcinogenic, and allergenic [9]. Pesticides have led to the widespread presence of pollution worldwide [10]. Therefore, there is an urgent need to remove residual pesticides from water systems.
Among various water-soluble pesticides, we selected, in this work, Metalaxyl, Imidacloprid, Methomyl, and Paraquat Dichloride as model pesticide pollutants. The selection of these pesticides was based on their high solubility in water, their existence in the Jordanian market, and their use by Jordanian farmers. These pesticides were obtained from the Jordanian factory VAPCO (Veterinary and Agricultural Products Manufacturing Company, Jordan) which is considered one of the largest factories in Jordan. The properties of these pesticides are shown in Table 1.
Table 1. Pesticides used in this study and their properties
|
Pesticide |
Structure and Chemical Formula |
Molecular Weight (g/mole) |
Solubility in Water |
References |
|
Metalaxyl (97% Pure, Solid) |
C15H21NO4 |
279.3 |
7.9 g/L at 25℃ |
[11] |
|
Imidacloprid (97% Pure, Solid) |
C9H10ClN5O2 |
255.7 |
0.61 g/L at 20℃ |
[12] |
|
Methomyl (98% Pure, Solid) |
C5H10N2O2S |
162.2 |
57.9 g/L at 25℃ |
[13] |
|
Paraquat Dichloride (30.5% w/v, Solution) |
C12H14N2Cl2 |
257.2 |
620 g/L at 20℃ |
[14] |
Metalaxyl is a fungicide used to suppress plant diseases [15, 16]. However, the significant solubility of Metalaxyl in water facilitates its leaching to groundwater and flow into waterways through agricultural runoffs. Accordingly, owing to its high residual levels in agricultural crops, Metalaxyl might lead to environmental hazards under natural conditions [16]. On the other hand, Imidacloprid ranks among the best-selling insecticides globally, and it is considerably effective in crop protection from pests [17]. Recent research has demonstrated that imidacloprid poses a toxic threat to humans, with acute toxicity potentially resulting in loss of consciousness and significant respiratory failure [18]. Additionally, Methomyl is an insecticide utilized in agriculture for crop protection. Nevertheless, the extensive use of this insecticide has caused human health issues and environmental toxicity. Methomyl is highly toxic to humans, and severe poisoning or death can result if exposed to high concentrations [13]. Based on the European Union pesticide regulations, Methomyl has been revoked as a recognized active ingredient; it can only be used by specially trained and certified applicators or under their direct supervision [19]. Finally, Paraquat Dichloride is a commonly utilized herbicide in agriculture to manage grassy weeds and broadleaf. Its herbicidal and toxicological properties are attributed to the presence of a diquaternary bipyridyl unit, whereas the chloride anions have few toxic effects [20]. The fatality rate of paraquat poisoning far surpasses that of other pesticide poisonings owing to its severe toxicity [21]. Due to its profound toxicity to humans, Paraquat use is prohibited in the European Union and restricted in the United States of America [20].
Developing various removal strategies for pesticides has motivated a new research drive in environmental remediation. Consequently, numerous techniques have been examined for the breakdown of pesticides, including biodegradation [22], adsorption [23-25], photocatalytic [26], electrochemical [27] processes, as well as nano-based techniques [28]. However, activated carbon adsorption remains the most effective and common method for the removal of pesticides from water sources [29].
Activated carbon is widely recognized for its large surface area and significant adsorption capacity, high specific porosity, pore structure, customizable surface functionalization, and chemical and thermal stability. Furthermore, a variety of materials can be used to create activated carbon, including petroleum byproducts, biomass, coal, wood, polymers, and resins [30-33]. Additionally, activated carbon produced from biomass has received significant attention since it is considered to have an environmentally and economically friendly nature [30-32]. Moreover, activated carbon is notable for its low cost and simple operation [34]. Moreover, many researchers have studied adsorption of a wide range of pesticides from water using activated carbon as an adsorbent prepared from various biomass sources such as wheat straw [35], prickly pear seeds [9], peach stones [36], tea residue [37], pomegranate peels [38], cassava husks [39], strawberry seeds and pistachio shells [40], orange peels [41], and silkworm feces [42].
The present study focused on the investigation of pesticides adsorption on activated carbon prepared from Jift (the local name for olive oil pomace) [43]. With an approximate yearly production of 21.5 × 103 tons, olive oil is one of Jordan's most important agricultural products [44]. The olive oil extraction process produces olive oil (main product, 20%), moist solid waste (byproduct, 30%), and liquid waste (byproduct, 50%). Jift, which represents 65% of the moist solid waste, is a mixture of leftover pits and olive paste that is generated after the olives have been pressed [45]. Each year, Jordan produces around 50 - 60 thousand tons of olive Jift [45, 46].
Consequently, the primary aim of this research is to prepare and characterize activated carbon from Jordanian Jift (ACJ) and to investigate its efficiency for the removal of Metalaxyl, Imidacloprid, Methomyl, and Paraquat Dichloride pesticides from water. These pesticides were chosen to be investigated in this study because of their toxic nature and significant solubility in water. Additionally, the efficiency of ACJ was compared with that of some commercial adsorbents. These adsorbents include Bentonite and Zeolite. After the characterization of different adsorbents, a study was performed to assess the effectiveness of removing these pesticides from aqueous solutions. This research aimed to address two significant waste issues in Jordan: harmful pesticides and Jift.
2.1 Chemicals
Metalaxyl, Imidacloprid, Methomyl, and Paraquat Dichloride pesticides were used in this study. These pesticides were obtained in solid form from VAPCO industry with a purity ranging from 97% - 98% except for Paraquat Dichloride which was obtained in a solution form with a concentration of 30.5% w/v. All pesticides were used as received. The pesticides and chemicals utilized in this study are detailed in Table 2.
Table 2. Chemicals utilized in this work
|
Material |
Grade |
Source |
Note |
|
Distilled Water |
- |
The Hashemite University |
pH = 5.3 - 6.5 |
|
Methylene Blue Trihydrate |
Analytical |
Scharlau |
Hydrated water is lost on drying at 110℃ |
|
Metalaxyl |
Technical |
VAPCO |
97% pure |
|
Imidacloprid |
Technical |
VAPCO |
97% pure |
|
Methomyl |
Technical |
VAPCO |
98% pure |
|
Paraquat Dichloride |
Technical |
VAPCO |
30.5% w/v |
|
Sodium Dithionite |
Analytical |
VAPCO |
- |
|
Acetonitrile |
HPLC |
VAPCO |
- |
|
HPLC Water |
HPLC |
VAPCO |
- |
|
N2 gas |
Analytical |
Jordanian Gas Company |
98% - 99% |
|
CO2 gas |
Analytical |
Jordanian Gas Company |
92% - 96% |
2.2 Equipment
Thermostatic Shakers and Baths: A Julabo GLF 1083 thermostatic water bath shaker was used, and its temperature was controlled within ± 0.2℃ and kept at 25℃. pH-Meter: All pH measurements of samples were carried out using 420A Orion pH meter with a combination of glass electrode with an accuracy of ± 0.005 pH units. Ultrasonic Shaker: All solids were dissolved using 5510 Branson ultrasonic shaker with a constant frequency of 42 kHz. UV-Visible Spectrophotometer: Absorbance measurements were carried out using a Cary 100 Bio Spectrophotometer, and the wavelength accuracy was within ± 0.2 nm. Furnaces: Activated carbon was prepared by using a Thermolyne 47900 furnace, and the temperature accuracy was within ± 2℃. High Performance Liquid Chromatography (HPLC): The instrument was located in the VAPCO Factory, and the system includes a Merck and Hitachi series D-6200A. Centrifuge: Adsorbents were separated from solutions using Z 200A Hermel centrifuge, with rotational speed ranging from 100 rpm to 6000 rpm and with a timer range from 1 min up to 60 min. Scanning Electron Microscope (SEM): Adsorbents’ surface characterization was done using a SEM FEI Model Quanta 200, and the coating machine was a Polaron E 6100 using a Vacuum Coater with gold disk (sputtering method) at 1200 V and 20 mA.
2.3 Analysis of pesticides
The analysis of Metalaxyl, Imidacloprid and Methomyl was carried out using HPLC as illustrated in Table 3, whereas Paraquat Dichloride was converted to a complex with sodium dithionite to obtain an absorption curve in the visible region. The stock solution for the calibration curve of Paraquat Dichloride was prepared by mixing 100 mL of a 100 ppm Paraquat Dichloride solution with a freshly prepared 1% sodium dithionite solution in 1 M NaOH. The absorbance was measured using a UV spectrophotometer at the maximum wavelength (λmax) of 600 nm.
Table 3. HPLC conditions for pesticides analysis
|
Pesticide |
Mobile Phase (Acetonitrile: Water) |
λmax (nm) |
Concentration Working Range (ppm) |
Retention Time (min) |
|
Metalaxyl |
60 : 40 |
236 |
10 - 50 |
2.99 ± 0.20 |
|
Imidacloprid |
60 : 40 |
274 |
5 - 40 |
3.23 ± 0.20 |
|
Methomyl |
80 : 20 |
267 |
50 - 500 |
3.95 ± 0.20 |
2.4 Adsorbents preparation
2.4.1 Collection and preparation of Zeolite and Bentonite
Zeolite was collected from Jabal Hannoun which is approximately 180 km northeast of Amman. Whereas Bentonite was collected from Ein-Al Bayda and Qa’a Al-Azraq that are approximately 120 km northeast of Amman. Both clay samples were ground using an agate mortar, and particles larger than 147 μm were removed by sieving with a CISA sieve St. (ISO 3310.1). Only those that passed the 147 μm sieve were used in the present investigation.
2.4.2 Collection and preparation of Jift raw samples
Raw Jift samples were collected from an olive mill press company in Al-Zarqa city, Jordan. The samples were dried in a large open area for 15 days to ensure complete drying. The samples were subsequently processed through mechanical grinding, and particles larger than 1 mm were removed through sieving. Only those that passed the 1 mm sieve were used in the following experiment.
2.4.3 Preparation of roasted Jift
The ground Jift samples (≤ 1 mm) were roasted in an iron pan for approximately 30 min until all the Jift was converted to black ash. The black ash was sieved through a 147 μm, and only those passing the sieve were used in the following experiment.
2.4.4 Preparation of activated carbon from Jift (ACJ)
To hold the roasted Jift sample inside the furnace, a laboratory-scale iron box reactor was designed and manufactured by the engineering workshops of The Hashemite University. Figure 1 shows a schematic diagram of the experimental setup of the reactor-furnace systems used in this research.
Figure 1. Reactor-Furnace system setup
A 50 g sample of roasted Jift (≤ l47 μm) was placed in the reactor-furnace. To ensure an oxygen free atmosphere during temperature elevation, N2 gas was pumped into the reactor for 15 min before heating, then the temperature increased to 600℃, while the N2 gas flow kept continuous. Subsequently, the sample was kept under the N2 atmosphere for half an hour. After that, the temperature was raised to 800℃ and the N2 gas was replaced with a continuous flow of CO2 gas for one hour at the same temperature [47]. Then, the furnace was turned off while continuous CO2 gas kept flowing for another hour. Subsequently, the gas flow was turned off and the sample was left in the furnace to cool for 3 hours, and it was then transferred to a desiccator to cool overnight. Finally, the sample was ground gently in an agate mortar and sieved. Only particles that passed through the 147 μm sieve were utilized in the subsequent analyses.
2.5 Batch adsorption isotherm
Isotherm models are commonly employed to illustrate the equilibrium of the bio-sorption process, with experimental data being fitted to models such as Langmuir and Freundlich. In this work, we applied the Langmuir and Freundlich models which are represented in linear form as in Eq. (1) and Eq. (2), respectively [48, 49].
$\frac{C_e}{q_e}=\frac{C_e}{q_m}+\frac{1}{K_L q_m}$ (1)
$\log q_e=\frac{1}{n} \log C_e+\log K_F$ (2)
where, Ce is the equilibrium concentration of adsorbate in the solution (mg/L), qe is the adsorption capacity at equilibrium (mg/g), qm is the maximum adsorption capacity (mg/g), KL is the Langmuir constant (L/mg), KF is the Freundlich constants related to adsorption capacity ([mg/g] [L/mg]1/n), n is a constant which gives an idea of the grade of heterogeneity, and 1/n is the heterogeneity factor. The equilibrium concentration of adsorbate (qe), which appears in both Eq. (1) and Eq. (2), can be calculated using Eq. (3) [48]:
$q_e=\frac{\left(C_0-C_e\right) \times V}{m}$ (3)
where, C0 is the adsorbate initial concentration (mg/L), V is the sample volume (L), and m is the mass of the dry adsorbent (g).
Langmuir model posits that adsorption happens only at a limited number of specific localized locations, resulting in a monolayer adsorption, where the adsorbed layer is a single-molecule-thick of adsorbate [50]. Meanwhile, Freundlich isotherm describes the process of multilayer and heterogeneous adsorption on the surface of the adsorbent [51].
The fundamental properties of the Langmuir isotherm can be expressed through a dimensionless constant known as the equilibrium parameter (RL), which is calculated as indicated in Eq. (4) [52]:
$R_L=\frac{1}{\left(1+K_L C_0\right)}$ (4)
The values of RL indicate the nature of the adsorption process [52]. For instance, the adsorption process is unfavorable if RL > 1. While the adsorption process is linear if RL = 1. Whereas the adsorption process is favorable if the value lies between 0 and one (0 < RL < 1). On the other hand, the adsorption process is irreversible if RL = 0.
In this study we used the isotherm models to evaluate the specific surface area of roasted Jift, ACJ, Bentonite, and Zeolite adsorbents. Furthermore, the isotherm models were employed to assess the qm for the pesticides (Metalaxyl, Imidacloprid, Methomyl, and Paraquat Dichloride) on ACJ.
To guarantee the reliability of the data for the ensuing experiments, both blank and control samples were simultaneously prepared and processed for each adsorption test. A blank sample composed of the adsorbent and distilled water in a screw-cap flask devoid of any adsorbate. While the control sample consisted of adsorbate in a screw-cap flask without any adsorbent.
2.5.1 Specific surface area
The determination of specific surface area for activated carbon by the adsorption of Methylene Blue (MB) in liquid phase has been adopted widely [53]. In order to determine the specific surface area of adsorbents (Roasted Jift, ACJ, Bentonite, and Zeolite), we employed MB as adsorbate, and the data were analyzed using the Langmuir mode.
The subsequent formula was used to determine the specific surface area [53]:
$S_{M B}=\frac{q_m \times A_{M B} \times N_A \times 10^{-20}}{M}$ (5)
where, SMB is the specific surface area in m2/g, qm is the maximum number of molecules of MB adsorbed at the monolayer of adsorbent in mg/g (obtained from Eq. (1)), AMB is the occupied surface area of one molecule of MB = 120 Å2 [54], NA is Avogadro’s number = 6.02 × 1023 mol-1, and M is the molar weight of MB = 319.85 × 103 mg/mol.
SMB for four different adsorbents (Roasted Jift, ACJ, Bentonite, and Zeolite) were calculated based on the MB adsorption isotherm. Different weights of adsorbents ranging from (0.02 - 0.2 g) were mixed with 50 mL of MB (100 ppm with Roasted Jift, 500 ppm with ACJ, 250 ppm with Bentonite, and 100 ppm with Zeolite) in 100 mL screw-cap flasks. To achieve equilibrium, the flasks were shaken overnight at 25℃ [55]. Following this, the suspension was filtered and, when necessary, diluted to achieve the desired concentration. Subsequently, a UV-Visible spectrophotometer was employed to determine the concentration of MB at its peak wavelength of 664 nm [56].
2.5.2 Pesticides uptake
The pesticides uptake was measured using three adsorbents (ACJ, Bentonite, and Zeolite) by using certain weight from each adsorbent. The adsorbents were mixed with a 50 mL of Metalaxyl, Imidacloprid, Methomyl, and Paraquat Dichloride in 100 mL screw-cap flasks. The weight of adsorbents and pesticides concentration are summarized in Table 4. In order to attain equilibrium, the flasks were shaken overnight at 25℃. The suspension was subsequently filtered and diluted as required. Then, the analysis of Pesticides was carried out as mentioned before in section 2.3 (Analysis of Pesticides).
2.5.3 Maximum adsorption capacity (qm)
qm was calculated for ACJ by utilizing different weights of adsorbent ranging from (0.02 - 0.2 g). The ACJ was mixed with a 50 mL of Metalaxyl (500 ppm), Imidacloprid (500 ppm), Methomyl (500 ppm), and Paraquat Dichloride (200 ppm) in 100 mL screw-cap flasks. To establish equilibrium, the flasks were shaken overnight at 25℃. The suspension was subsequently filtered and diluted if deemed necessary. Then, the analysis of Pesticides was carried out as mentioned before in section 2.3 (Analysis of Pesticides).
Table 4. The adsorption capacity
|
Pesticide |
Pesticide Concertation (ppm) |
Adsorbent Weight (g) |
||||
|
ACJ |
Bentonite |
Zeolite |
ACJ |
Bentonite |
Zeolite |
|
|
Metalaxyl |
500 |
50 |
50 |
0.13 |
2.00 |
2.00 |
|
Imidacloprid |
500 |
50 |
50 |
0.13 |
2.00 |
2.00 |
|
Methomyl |
500 |
50 |
50 |
0.13 |
2.00 |
2.00 |
|
Paraquat Dichloride |
200 |
200 |
200 |
0.13 |
0.20 |
0.30 |
2.6 Batch kinetic study
Batch kinetic study was performed for Pesticides adsorption on ACJ. The concentration of Metalaxyl, Imidacloprid, and Methomyl was 500 ppm. Ultrasonication was used to dissolve the pesticides at room temperature. While Paraquat Dichloride pesticide solution had a concentration of 200 ppm. All solutions were freshly prepared for each run. Fourteen samples from each pesticide were prepared by adding 50 mL of the pesticide solution to a fixed mass of 0.1 g of ACJ in 100 mL screw-cap flask. Each sample was prepared in duplicate. All flasks were put in a thermostat shaker at 25℃. After appropriate time intervals (1, 5, 10, 15, 20, 30, 60, 120, 180, 240, 300, 360, 480, and 1440 min), the samples were centrifuged, filtered, and the clear solution was analyzed for pesticide concentration as mentioned before in section 2.3 (Analysis of Pesticides). Two additional samples from each pesticide were prepared using the previously mentioned procedure. These samples were put in a thermostat shaker for 1440 min (24 hours) to allow the adsorption process to reach equilibrium.
3.1 Characterization
The production of activated carbon can be achieved by two methods: physical activation with oxidizing agents such as steam or CO2, and chemical activation with mineral salts [57]. In this study, physical activation for Jift was selected. CO2 was chosen as the activation gas due to its cleanliness and ease of handling. Furthermore, CO2 is often selected as the activation gas on the laboratory scale, as it allows for enhanced control over the activation process owing to its low reaction rate at temperatures near 800℃ [58]. Before the activation process, the ground Jift samples (≤ 1 mm) were roasted. According to Zhao et al. [59], roasting of biomass increased its hydrophobicity, and can effectively reduce its moisture content. The features of roasted Jift and ACJ were characterized as follows:
3.1.1 Scanning Electron Microscopy (SEM)
SEM is extensively utilized to investigate the morphology and surface characteristics of the adsorbent materials. Figure 2 and Figure 3 present the SEM micrographs for the roasted Jift and ACJ, respectively.
Figure 2 shows that the roasted Jift has an almost smooth surface with very low micropores. This is probably due to the lack of the activation step responsible for pore growth at the surface. On the other hand, Figure 3 shows that the ACJ is mostly microporous with low mesopores. This is consistent with the findings of Wang et al. [60], who mentioned that activated carbon is mainly a microporous solid, but it also contains mesopores and macropores.
Figure 2. SEM for roasted Jift
Figure 3. SEM for the ACJ
3.1.2 Specific surface area by Methylene Blue (MB)
In addition to roasted Jift and ACJ, the specific surface area was measured for commercial adsorbents (Bentonite and Zeolite). This measure was implemented for comparison. The data obtained for the adsorption of MB by the adsorbents were analyzed using Langmuir adsorption isotherms model (Eq. (1)). The values of qm for MB and the correlation coefficient are listed in Table 5.
Using the calculated qm values listed in Table 5, the specific surface areas (SMB) were calculated using Eq. (5), and the results are shown in Figure 4.
Table 5. The maximum adsorption capacity of MB
|
Adsorbent |
qm (mg/g) |
R2 |
|
Roasted Jift |
130.6 |
0.9863 |
|
ACJ |
248.4 |
0.9913 |
|
Bentonite |
203.2 |
0.9984 |
|
Zeolite |
124.4 |
0.9967 |
Figure 4. Specific surface area (m2/g) for all adsorbents using MB adsorption methods, where RJ, ACJ, BE, and ZE refers to the roasted Jift, ACJ, Bentonite, and Zeolite, respectively
The findings indicate that the ACJ exhibits a greater specific surface area when compared to the roasted Jift, which aligns with the results obtained from the SEM analysis. The physical activation process of biomass (carbon surface) with CO2 proceeds via a certain reaction (Eq. (6)), which increases the porosity of the surface resulting in a larger surface area [31, 61].
$\mathrm{C}_{(\mathrm{S})}+\mathrm{CO}_{2(g)} \rightarrow 2 \mathrm{CO}_{(g)}$ (6)
Furthermore, the ACJ has the highest specific surface area (561 m2/g) compared with the used commercial adsorbents; such that ACJ > Bentonite > Zeolite. Compared to literature, the same arrangement was found [62, 63].
3.2 Pesticides uptake
The uptake of Metalaxyl, Imidacloprid, Methomyl, and Paraquat Dichloride by ACJ was evaluated using the adsorption capacity (qe), which was calculated using Eq. (3). Promising results were obtained for the removal of the pesticides from aqueous solutions demonstrating that the ACJ has a high ability to remove the pesticides. For each pesticide, one gram of ACJ was able to adsorb around 161 mg of Methomyl, 151 mg of Imidacloprid, 119 mg of for Metalaxyl, and 70 mg of Paraquat Dichloride (see Table 6).
The qe of ACJ was compared with that of clay Jordanian minerals (Zeolite and Bentonite), and the results are listed in Table 6. The results shows that the Zeolite and Bentonite are disabled to remove the Metalaxyl, Imidacloprid, and Methomyl. While for Paraquat Dichloride, the ACJ has the largest adsorption capacity followed by Bentonite, and the Zeolite has the lowest value. These results agreed with the measured specific surface area shown in Figure 4. ACJ shows promising results for removing all four pesticides from aqueous solutions, this may arise from the ability of the ACJ surface to form π-π associations with pesticides [64]. While Zeolite and Bentonite demonstrate predictable behavior attributable to their inorganic cation content, which becomes highly hydrated in aqueous solutions. This hydration confers a hydrophilic quality to their surfaces, facilitating the adsorption of polar or ionic compounds. Conversely, these materials are not suitable for the adsorption of hydrophobic or non-ionic organic substances [65, 66].
Table 6. The adsorption capacity at equilibrium
|
Pesticide |
qe (mg/g) |
||
|
ACJ |
Bentonite |
Zeolite |
|
|
Metalaxyl |
119.030 |
0.838 |
0.000 |
|
Imidacloprid |
151.220 |
0.450 |
0.100 |
|
Methomyl |
160.740 |
1.175 |
0.225 |
|
Paraquat Dichloride |
70.280 |
49.500 |
21.000 |
3.3 Adsorption isotherm of pesticide over ACJ
To investigate the relationship between the adsorbate (Metalaxyl, Imidacloprid, Methomyl, and Paraquat Dichloride) and ACJ at equilibrium, different adsorption isotherm models were employed to interpret the experimental data. The Langmuir and Freundlich models were investigated in this study. As seen in Figure 5 and Figure 6, Langmuir provides a better fitting than the Freundlich mode.
The calculated parameters for the adsorption isotherm models are listed in Table 7. The linear plotting of Ce/qe versus Ce in Langmuir model gives high correlation coefficient (R2 > 0.95) for all pesticides, which indicates monolayer adsorption. The highest Langmuir maximum adsorption capacity (qm) was for Methomyl (277.30 mg/g), due to its low molecular weight compared to the other pesticides investigated in this study. This finding aligns with Cougnaud et al. [67], who reported that a decrease in pesticide molecular weight generally results in an increase in qm. While the qm order for the other pesticides is Imidacloprid > Metalaxyl > Paraquat Dichloride. This order indicates that the qm of pesticides was inversely related to their water solubility. A similar behavior was also observed by Faur et al. [68]. It is also notable that the maximum adsorption capacity of Methomyl (277.30 mg/g) and Imidacloprid (233.97 mg/g) are considerably greater than those of Metalaxyl (119.71 mg/g) and Paraquat Dichloride (74.94 mg/g), which could be explained by the Freundlich model. This model was only fitted to the data for Methomyl and Imidacloprid. The linear correlation between Log qe and Log Ce (Figure 6) for these two pesticides exhibits a high correlation coefficient (R2 > 0.96). The parameters derived from the Freundlich model are detailed in Table 7. The calculated 1/n values for Methomyl and Imidacloprid are less than unity, which indicates that the adsorption process for these pesticides is favorable, with available new adsorption sites and an increase in adsorption capacity [69].
Figure 5. Adsorption Langmuir isotherm model, where Mt, Im, Me, and Pa refers to Metalaxyl, Imidacloprid, Methomyl, and Paraquat Dichloride, respectively
Figure 6. Adsorption Freundlich isotherm model, where Mt, Im, Me, and Pa refers to Metalaxyl, Imidacloprid, Methomyl, and Paraquat Dichloride, respectively
Table 7. Adsorption isotherm models parameter
|
Pesticide |
Langmuir Adsorption Isotherm |
Freundlich Adsorption Isotherm |
||||
|
qm (mg/g) |
KL (L/mg) |
R2 |
1/n |
KF ([mg/g] [L/mg]1/n) |
R2 |
|
|
Metalaxyl |
119.71 |
0.0625 |
0.9537 |
0.0444 |
87.86 |
0.0878 |
|
Imidacloprid |
233.97 |
0.0189 |
0.9935 |
0.2436 |
49.66 |
0.9937 |
|
Methomyl |
277.30 |
0.0213 |
0.9921 |
0.3157 |
41.27 |
0.9679 |
|
Paraquat Dichloride |
74.94 |
-1.6406 |
0.9910 |
0.0659 |
56.46 |
0.5469 |
To determine the nature of the adsorption process, the Langmuir isotherm equilibrium parameter (RL) for the adsorption of the pesticides was calculated from Equation 4. RL values for the uptake of Metalaxyl, Imidacloprid, Methomyl, and Paraquat Dichloride are 1.68×10-5, 8.62×10-6, 7.27×10-6 and 6.43×10-5, respectively, which reflect a favorable adsorption for the four pesticides.
3.4 Kinetic of pesticides removal
The adsorption Kinetic characteristics of pesticides by ACJ are shown in Figure 7. Metalaxyl, Methomyl, and Paraquat Dichloride have almost the same adsorption behavior, they show two distinct stages. The initial stage demonstrates a rapid surge in adsorption capacity (qt), ensued by a more modest rise. At the end of the first stage (~ 20 min) the adsorption capacity (in mg/g) for Metalaxyl, Methomyl, and Paraquat Dichloride increases up to 95.8, 185.9, and 40.9, respectively. After approximately 20 min, the second stage starts. The adsorption capacities for the three pesticides show a tiny increase with time until it reaches the equilibrium. The equilibrium adsorption capacity (in mg/g) for Metalaxyl, Methomyl, and Paraquat Dichloride are 132.40, 208.35, and 84.40, respectively. On the other hand, the adsorption process of Imidacloprid shows a different behavior. The adsorption capacity of Imidacloprid gradually increases over time, reaching 184.2 mg/g at approximately 360 minutes, which is a relatively long time compared to the other pesticides. While at equilibrium the adsorption capacity of Imidacloprid was 189.35 mg/g. The equilibrium stage for all pesticides is explained by the decline in the number of active adsorption sites on ACJ with time [70].
Figure 7. Adsorption capacity of pesticides versus time, where Mt, Im, Me, and Pa refer to Metalaxyl, Imidacloprid, Methomyl, and Paraquat Dichloride, respectively
In the present investigation, the Lagergren kinetic models (pseudo-first-order and pseudo-second-order) were utilized to elucidate the mechanism governing the adsorption process. The pseudo-first-order kinetic model of Lagergren is represented by Eq. (7) [71]:
$\log \left(q_e-q_t\right)=\log q_{1 e}-2.303 K_1 t$ (7)
where, qe and qt are the amounts of pesticide adsorbed on ACJ (mg/g) at equilibrium and at time t (min), respectively, while q1e is the calculated amounts of pesticide adsorbed on ACJ (mg/g) at equilibrium, and K1 is the rate constant of pseudo-first-order adsorption (min−1). The slope and intercept of the plot of Log (qe−qt) versus t were used to determine K1 and q1e. On the other hand, the pseudo-second-order kinetic model of Lagergren is expressed by Eq. (8) [70]:
$\frac{t}{q_t}=\frac{1}{K_2 q_{2 e}^2}+\frac{1}{q_{2 e}} t$ (8)
where, q2e is the calculated amounts of pesticide adsorbed on ACJ (mg/g) at equilibrium, and K2 is the rate constant of pseudo-second-order adsorption (g.mg-1.min-1). The slope and intercept of the plot of t/qt versus t are used to calculate q2e and K2. The adsorption rate constant and the calculated amounts of pesticide adsorbed on ACJ (K1, K2, q1e and q2e) along with correlation coefficients for the pseudo-first-order and pseudo-second-order Lagergren model are shown in Table 8.
Comparing the results shown in Table 8, the pseudo-second-order adsorption mechanism demonstrates the most favorable alignment with the data, as indicated by high correlation coefficient values (R2 > 0.97). Additionally, a pseudo-second-order kinetic model is found to have a greater agreement between the computed (q2e) and experimental (qe) values than the pseudo-first-order kinetic model. This result indicates that the adsorption process is a chemisorption mechanism [72]. Similar kinetic results were reported for the adsorption of various pesticides by activated carbon prepared from orange peel [41] and silkworm feces [42].
Table 8. The parameter of kinetic model and the experimental qe
|
Pesticide |
qe (mg/g) |
Pseudo-First-Order |
Pseudo-Second-Order |
||||
|
K1 (min−1) |
q1e (mg/g) |
R2 |
K2 (g.mg-1.min-1) |
q2e (mg/g) |
R2 |
||
|
Metalaxyl |
132.40 |
9.84 × 10-8 |
48.33 |
0.8696 |
9.81 × 10-4 |
125.29 |
0.9992 |
|
Imidacloprid |
189.35 |
1.65 × 10-7 |
147.58 |
0.9676 |
1.35 × 10-4 |
194.61 |
0.9757 |
|
Methomyl |
208.35 |
1.03 × 10-7 |
25.97 |
0.9374 |
1.30 × 10-7 |
204.90 |
0.9999 |
|
Paraquat Dichloride |
84.40 |
6.79 × 10-8 |
45.54 |
0.9748 |
7.41 × 10-4 |
72.83 |
0.9898 |
In the present work adsorption of pesticides on ACJ was studied. ACJ was characterized by SEM and Specific Surface Area. Compared with Zeolite and Bentonite (their surface has a hydrophilic character), ACJ has the highest Specific Surface Area making it a promising candidate for pesticide adsorption, this may be due to the possibility to form π-π associations between the ACJ surface and pesticides. Furthermore, pesticides uptake using ACJ were compared with that of Zeolite and Bentonite, with ACJ showing a much higher ability to remove for all four pesticides. The Langmuir model provided a more accurate representation of the adsorption isotherm for all pesticides examined. Langmuir maximum adsorption capacity (qm) were 277.30, 233.97, 119.71, and 74.94 mg/g for Methomyl, Imidacloprid, Metalaxyl, and Paraquat Dichloride, respectively. While Freundlich isotherm model was only fit to the data for Methomyl and Imidacloprid with heterogeneity factor values less than unity, indicating a favorable adsorption process, an increase in adsorption capacity for these pesticides. The nature of the adsorption process was favorable for the four pesticides, as indicated by Langmuir isotherm equilibrium parameter (RL). Kinetics and equilibrium studies were also performed and they demonstrated that the pseudo-second-order model fits all four pesticides better, suggesting that the adsorption mechanism is chemisorption. The ACJ, being both cost-effective and simple to prepare, demonstrates a significant capacity to adsorb four different pesticides from aqueous solutions, which may increase its applicability in wastewater treatment processes. Nevertheless, to confirm the results and implement this technique on an industrial scale; more research using different kinds of pesticides, actual wastewater samples, and the reuse of the ACJ bio-sorbent are needed.
The authors express their gratitude to The Jordanian Factory VAPCO (Veterinary and Agricultural Products Manufacturing Company, Jordan) for all their support. The authors also acknowledge the management of The Hashemite University (THU) for their administrative, technical, and financial assistance, which significantly contributed to the success of this research project titled "Removal of Pesticides from Aqueous Solutions Using Activated Carbon Derived from Jordanian Jift".
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