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Article

A New Generation of Porous Polymer Materials from Polystyrene Waste: Synthesis and Adsorption of Nitrate Anions in Aqueous Media

by
Mohamed Anannaz
,
Fatiha Tafraout
,
Charaf Laghlimi
,
Rachida Ouaabou
and
Jalal Isaad
*
ERCI2A, FSTH, Abdelmalek Essaadi University, Tetouan 93000, Morocco
*
Author to whom correspondence should be addressed.
Organics 2024, 5(4), 561-574; https://doi.org/10.3390/org5040029
Submission received: 2 October 2024 / Revised: 31 October 2024 / Accepted: 25 November 2024 / Published: 28 November 2024
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Abstract

:
A simple approach was developed to efficiently graft diethylene triamine onto polystyrene waste using succinic anhydride as a tracer to remove nitrate anions from aqueous solutions. Infrared spectroscopic data showed characteristic signs at 3395 cm−1 and 1695 cm−1 corresponding to N-H and C=O (ester and amide), confirming the grafting of DETA onto PS. The zeta potential study showed that the PS-Succ-DETA adsorbent had a pHiep of 8.2, and its charge was positive when the pH was lower than the pHiep. Parameters affecting nitrate adsorption, such as dosage, initial concentration, pH, and contact time, were studied. The adsorption data corresponded well to the Langmuir isotherm with an R2 correlation coefficient of 0.998, and the adsorption capacity was found to be 195.65 mg/g. The adsorption kinetics of NO3− ions by PS-Succ-DETA corresponded perfectly to the PS-II model, with an R2 coefficient of 0.999. The negative value of ΔG (−10.02 kJ/mol), ΔH (−18.76 kJ/mol), and ΔS (−28.83 J/K/mol) indicates that NO3- adsorption is spontaneous exothermic and suggests a decrease in randomness at the solid-liquid interface during the adsorption. The mechanism of adsorption of nitrate ions onto PS-Succ-DETA occurs via electrostatic interactions and hydrogen bonds between the NO3− ions and the -NH2 and NH functions of PS-Succ-DETA.

Graphical Abstract

1. Introduction

Nitrates are naturally present in certain food products, such as radishes, beetroot, spinach, lamb lettuce, celery, and turnips. They are also widely used as food additives, particularly in meat, charcuteries, and preserves [1]. Drinking water can also be a major source of nitrates, particularly in agricultural areas where fertilizers are used intensively and at the outlets of wastewater treatment stations [2,3]. The presence of nitrate ions in food and water sources can have serious effects on human health if they are consumed in excess. In organisms, nitrates are transformed into nitrites, which can interfere with oxygen transport by red blood cells, leading to a disease called methemoglobinemia or ‘blue baby syndrome’ [4,5]. This medical problem is particularly dangerous for infants, whose digestive systems are relatively susceptible to converting nitrates into nitrites [6]. In addition, high concentrations of nitrates in potable water have been linked to increased risks of certain cancers, such as those of the colon and stomach, due to the possible formation of carcinogenic compounds called nitrosamines [7,8]. In light of these environmental and health risks, nitrate levels in drinking water must be regulated such that they remain below 40 mg·L−1, as recommended by the WHO [9], and their concentration in food products is monitored to minimize any harmful effects on public health. Several methodologies have been developed to eliminate nitrate ions from aqueous solutions, such as biological denitrification [10], catalytic [11] and photocatalytic [12] transformation, electro-oxidation [13], coagulation-coprecipitation [14], and membrane filtration [15,16]. All these techniques are effective in removing nitrate ions, but they have several disadvantages, such as high financial costs and complicated processes and maintenance. To overcome these technical and economic limitations, adsorption is an ideal solution because of its simplicity of use, low financial cost, high efficiency, high pollutant adsorption rate, and environmental friendliness [17,18,19,20]. Several adsorbents based on activated carbons [10], clays [21], hybrid nanoparticles [22], zeolites [23], specific polymers [24], raw [25], and chemically modified agricultural waste [26] have been developed to eliminate nitrate ions. However, these adsorbents are characterized by low selectivity for nitrates, low adsorption capacity [20,21,22,23,24,25,26], and high economic cost. Consequently, developing low-cost, efficient adsorbents with high nitrate ion adsorption capacities remains a major challenge. In this context, the use of polystyrene waste as a starting material for developing adsorbents via chemical modification is a potentially promising alternative. Polystyrene (PS) is a polymer obtained by radical polymerization of styrene. It is an inert polymer that remains stable over time, which explains its use in food packaging and other applications, such as plates, disposable utensils, DVD covers, and foam cups.
From an environmental point of view, the lifetime of PS in nature before its complete degradation is one thousand years [27], and expanded polystyrene is classified as non-hazardous waste [27]. It is not directly toxic from a chemical point of view [27]. However, if subjected to high temperatures, PS releases styrene, which could be considered a weak carcinogen by inhalation or ingestion for humans and animals. In addition, recycling PS is often costly and underdeveloped, contributing to significant pollution known as ‘white’ pollution. Despite these environmental concerns, PS’s high surface area is an interesting feature. Consequently, using PS is a very promising way to develop adsorbents. To this end, this study used polystyrene waste to produce a low-cost adsorbent through simple chemical modification via diethylene triamine (DETA). The ability of DETA to adsorb nitrate ions has been well established [22]. To our knowledge, few studies have explored the modification of PS with DETA, which is a new and promising area of research. In the synthesis strategy, succinic anhydride was substituted into the aromatic nucleus of PS by Friedel–Crafts acylation. DETA was then grafted onto succinic anhydride-substituted PS (PS-Succ) via an acid-amine coupling reaction. The modification of PS with DETA (Figure 1) is a new and promising area of research. Adsorption studies were carried out using different parameters, revealing that the synthesized adsorbent (PS-Succ-DETA) effectively eliminated nitrate anions from the aqueous solution.

2. Materials and Methods

All chemical products were acquired from Sigma Aldrich (St. Louis, MO, USA) and used without prior purification. The polystyrene used in this synthesis was collected from packaging waste.

2.1. Preparation of PS-Succ

Succinic anhydride (2 g, 0.02 mol) and AlCl3 (2.66 g, 0.02 mol) were dissolved in DCM and agitated for 15 min. Then, polystyrene waste (3 g) was added, and the solution was stirred at R.T. for 6 h. The resulting product was precipitated by stirring on ice with a dilute hydrochloric acid solution. The solid precipitate was filtered, washed, and dried to obtain PS-Succ as a white powder.

2.2. Preparation of PS-Succ-DETA

PS-Succ (2 g) was dissolved in 35 mL of DCM. After that, DCC (2.00 g) and DETA (1.00 g) were added, and the mixture was agitated for 2 days at R.T. The mixture was then washed with DCM, filtered, and dried to obtain PS-Succ-DETA as a pale yellow solid.

3. Results

3.1. Synthesis of PS-Succ-DETA

The first step in the synthesis of PS-Succ-DETA involves electrophilic substitution of the aromatic nucleus in the para position of polystyrene by a carboxylic acid through Friedel–Crafts acylation of polystyrene waste with succinic anhydride in the presence of AlCl3 as a catalyst. Afterward, diethylene triamine and PS-Succi were condensed by an acid-amine coupling reaction in the presence of DCC as an activator to afford PS-Succ-DETA, as reported in Scheme 1.

3.2. Characterization of PS-Succ-DETA

3.2.1. Zeta Potential

The zeta potential plots of the PS and PS-Succ-DETA copolymers as a function of pH are presented in Figure 2. PS is negatively charged throughout the pH range studied (from 2–14). However, grafting DETA onto PS via succinic anhydride modifies the charge of PS-Succ-DETA. PS-Succ-DETA has a pHiep of 8.2. At pH values below 8.2, PS-Succ-DETA has a positive charge resulting from the protonation of the -NH2 and -NH groups, which is susceptible to increasing the electrostatic interactions between PS-Succ-DETA and NO3− anions. Above pHiep, the surface of PS-Succ-DETA becomes negatively charged due to the deprotonation of the amine functional groups, which favors electrostatic repulsion between this copolymer and the nitrate anions. These results also confirm the successful coupling between DETA and the PS-Succ copolymer.

3.2.2. TGA of PS and PS-Succ-DETA

TGA and DTG diagrams of PS and PS-Succ-DETA polymers are shown in Figure 3. Thermal degradation of PS begins at 370 °C when weight loss can be attributed to PS degradation. At temperatures above 450 °C, virtually no residue remains. Meanwhile, thermal degradation of PS-Succ-DETA occurs at 170 °C, with a mass loss of 9% due to the evaporation of water molecules physically captured by the amine functions. The second phase of weight loss occurs between 240 and 370 °C with a 59% weight reduction, which can be explained by the decomposition of the amide groups formed between succinic acid and DETA. The third degradation zone begins at 370 °C, with a weight loss of approximately 19% by weight. During this third degradation phase, the weight loss rate is lower than that during the second phase. At 600 °C, the weight of the residue is approximately 8% by weight. In summary, the difference in thermal behavior between PS and PS-Succ-DETA also demonstrated that amine groups were successfully incorporated into the waste of polystyrene.

3.2.3. Infrared Spectra of PS-Succ-DETA

The infrared spectra of PS, PS-Succ, and PS-Succ-DETA are presented in Figure 4 to determine the functional groups of these three copolymers and to confirm the coupling of DETA and PS via the use of succinic anhydride as a spacer. The infrared spectrum of PS shows characteristic bands at 3095 cm−1 (aromatic -C-H), 2915 cm−1 (-CH2 of the main chain), 1605 cm−1 (aromatic -C-C-), 1490–1445 cm−1 (-C6H5, in-plane), 1205–1112 cm−1 (-CH= aromatic, out-of-plane), and 915–608 cm−1 (-CH= aromatic, in-plane). In the spectrum of polymer PS-Succ, a new broad peak at 3250 cm−1 corresponds to the OH stretching of carboxylic acid, and the peaks at 1705 cm−1 correspond to the stretching of the carbonyl of the acid group, which confirms the substitution of succinic anhydride in the structure of PS. However, the infrared spectrum of PS-Succ-DETA shows the disappearance of the bands at 3250 cm−1 and 1705 cm−1 and the appearance of new bands at 3395 cm−1 and 1695 cm−1 corresponding to N-H and C=O (ester and amide), in addition to the characteristic PS bands, confirming the conversion of the acid group to an amide group between DETA and succinic acid.

3.2.4. BET-Specific Surface Area of PS and PS-Succ-DETA

Table 1 compares the properties of the two materials, PS and PS-Succ-DETA. The BET-specific surface area of PS-Succ-DETA is slightly greater than that of PS, suggesting an increase in the surface area available for reactions or ion exchange. The average pore diameter of PS-Succ-DETA is relatively large, indicating that the pores of this material are relatively large, which may facilitate the diffusion of nitrate anions. In terms of the TEC, PS-Succ-DETA has a total ion exchange capacity of 6.18 meq/g. However, this characteristic is not present in PS. In conclusion, the PS-Succ-DETA adsorbent significantly improved over PS, particularly in terms of the ion exchange capacity, which became stronger, and the pore diameter. These improvements suggest that PS-Succ-DETA is potentially more useful for applications that require ion exchange, particularly for the removal of nitrate anions.

3.3. Adsorption Studies

3.3.1. Effect of pH

The pH of a solution is a major parameter in the study of the adsorption process. Determining the optimum pH range in which PS-Succ-DETA achieves the maximum adsorption of NO3− anions is important. To this end, the influence of pH on NO3− adsorption was studied at 25 °C by mixing 200 mg of PS-Succ-DETA with 50 mL of nitrate solution (150 mg. L−1) for 60 min, with a pH ranging from 2 to 12. As shown in Figure 5, PS waste could not adsorb NO3− ions throughout the pH range studied. However, the qe of NO3− in the case of PS-Succ-DETA reached its maximum value of 195.65 mg.g−1 at pH 6 and decreased with increasing pH. This increased adsorption is due to the large specific surface area of PS-Succ-DETA, which increases the availability of DETA amine groups (NH and -NH2) that can be dispersed on the PS surface. These primary and secondary amine groups interact with NO3−, demonstrating the importance of DETA grafting on the surface of PS waste. The pH dependence of the zeta potential shows that PS-Succ-DETA has a pHpzc of 8.2. Below this pH, the surface of PS-Succ-DETA is positively charged, which facilitates the electrostatic capture of NO3−. However, at pH values below 6, the adsorption capacity decreases despite the positive charge, probably due to the chemical conversion of NO3− to N2O. Similarly, at pH values above 6, the low qe is attributed to the loss of NO3− into the solution when it decomposes into N2 and N2O [28]. At a pH below 3, NO3− is probably transformed into HNO3, which explains the low qe value in this pH range. At a pH above pHpzc, the PS-Succ-DETA surface becomes negatively charged and, therefore, electrostatically repels NO3− anions, which explains the decrease in qe values, in addition to the strong competition between NO3− and OH− ions, which are very abundant in the solution.

3.3.2. Effect of Adsorbent Dose

The influence of the adsorbent quantity on the removal efficiency was examined by maintaining the other parameters constant. A pH of 6 for the nitrate solution (50 mL, 150 mg. L−1) was maintained for all the adsorption experiments. The results in Figure 6 show that the adsorption capacity qe increased from 15 mg.g−1 to 195 mg.g−1 with increasing mass of PS-Succ-DETA up to a dose of 150 mg, and that this capacity reached a state of equilibrium despite the increase in the adsorbent dose. The saturation of the active sites of the PS-Succ-DETA adsorbent may explain this phenomenon, as reported in our previous studies [22].

3.3.3. Effect of Contact Time and Initial Anion Concentration

The adsorption capacity of nitrate ions by PS-Succ-DETA was calculated at different nitrate concentrations (50, 100, 150, 200, and 250 mg. L−1) as a function of time to study the influence of contact time and nitrate concentration on its adsorption by PS-Succ-DETA. Figure 7 shows that the adsorption capacity for nitrate ions increases significantly with increasing nitrate concentration. This can be explained by the greater concentration gradient as the concentration of NO3− increases, which then moves these ions to the active adsorption sites on PS-Succ-DETA [29].
On the other hand, the increase in qe as a function of time for all studied nitrate concentrations occurred over three time periods. During the first phase, between 0 and 40 min, qe increases quickly. During this stage, nitrate anions bind rapidly to the active sites available on the external surface of PS-Succ-DETA, which is rich in -NH2 and -NH groups. After 40 min, the increase in qs is maintained but at a slower rate until 60 min. During this phase, nitrate continues to adsorb at a reduced rate onto the internal surface of PS-Succ-DETA, which probably involves more complex interactions. Finally, after 60 min, qe stabilizes, probably because all the available binding sites on the external and internal surfaces are occupied, which allows the adsorption process to reach a state of equilibrium [22].

3.3.4. Effect of Temperature

The effect of temperature on the adsorption of NO3− by PS-Succ-DETA was evaluated by performing adsorption experiments at different temperatures (298 K, 303 K, 313 K, and 323 K) at pH 6 with 150 mg of adsorbent. Figure 8 shows that there was no change in qe as the temperature increased from 298 K to 323 K, except for a slight increase in qe at 323 K. This slight increase can be explained by the endothermic adsorption of NO3− by PS-Succ-DETA. Therefore, PS-Succ-DETA can potentially remove NO3− over a wide range of temperatures [30].

3.3.5. Bibliographic Comparison

Table 2 summarizes a literature comparison of the adsorption capacity of PS-Succ-DETA with those of other nitrate anion adsorbents. This comparison reveals that the qe of PS-Succ-DETA is comparable to, if not superior to, that of the adsorbents reported in the literature.

3.3.6. Adsorption Isotherms

The analysis of the adsorption mechanism of nitrate ions by PS-Succ-DETA, as well as the calculation of the maximum qe and the description of the nature of the interactions between PS-Succ-DETA and NO3−, requires the study of adsorption isotherms via various models, such as the Langmuir [36], Freundlich [37,38], Temkin [39], Sips [40,41], and Dubinin-Radushkevich [42] models. The calculated parameters are listed in Table 3.
Based on the correlation coefficients R2, the Langmuir model (R2 = 0.998) appears to be the best fit for the nitrate anion adsorption data on PS-Succ-DETA compared with the Freundlich (R2 = 0.905), Temkin (R2 = 0.885), Dubinin-Radushkevich (R2 = 0.892), and Sips (R2 = 0919) models. In addition, the low KL value of the Langmuir model indicates that NO3− adsorption is reversible, and the RL value also suggests that the adsorption of this ion is favorable. The E(D-R) value of the Dubinin-Radushkevich model, which remains below 20 kJ/mol [43,44], as well as the B value of the Temkin model, suggest that the adsorption of NO3− ions on PS-Succ-DETA can be considered physisorption caused mainly by electrostatic reactions between NO3− ions and the -NH3+ and -NH2+ functions of PS-Succ-DETA. The high values of KF and nF calculated via the Freundlich model suggest that PS-Succ-DETA has a high ability to adsorb NO3− ions [45].

3.3.7. Adsorption Kinetics

The pseudo-first-order (PS-I), pseudo-second-order (PS-II), and Elovich models were used to study the kinetics of nitrate ion adsorption on PS-Succ-DETA at three nitrate concentrations. The results in Table 4 clearly show that the pseudo-second-order model (PS-II) is the most suitable for describing the kinetics of nitrate ion adsorption on PS-Succ-DETA based on the R2 value. Compared with the other models, PS-II has the highest correlation coefficient (R2) values, exceeding 0.99. Furthermore, the qe(cal) values calculated according to the PS-II model closely agreed with the experimentally observed qe(exp) values, confirming the suitability of PS-II for describing NO3− adsorption on PS-Succ-DETA. These results suggest that NO3− adsorption on PS-Succ-DETA involves chemisorption and physisorption via physicochemical interactions between NO3− and the amine groups of the adsorbent [46].

3.3.8. Adsorption Thermodynamics

The thermodynamic parameters ΔG, ΔH, and ΔS of NO3− adsorption on PS-Succ-DETA were calculated at different temperatures (303 K, 313 K, and 323 K), and the obtained calculation results are presented in Table 5. The ΔG value of −10.02 kJ/mol calculated at 303 K indicates that NO3− adsorption is spontaneous; however, this adsorption becomes slightly less favorable with increasing temperature, resulting in decreasing ΔG values of −9.73 (calculated at 303 K) and −9.28 kJ/mol (calculated at 323 K). On the other hand, the negative value of ΔH (−18.76 kJ/mol) indicates that NO3− adsorption is exothermic. In addition, the negative value of ΔS (−28.83 J/K/mol) also suggests a decrease in randomness at the solid-liquid interface during adsorption [46].

3.4. Adsorption Mechanism

The adsorption of nitrate ions onto PS-Succ-DETA occurs through physicochemical interactions between NO3− and the -NH2 and NH functions of PS-Succ-DETA. The maximum adsorption capacity is observed at pH 6, which is lower than pHiep. Consequently, the surface of PS-Succ-DETA is positively charged, which increases the electrostatic interactions between NO3− and -NH3+ and between NO3− and NH2+ of the adsorbent. On the other hand, at pH values above pHiep, qe decreases considerably but remains between 20 and 40 mg.g−1, suggesting that there are other types of bonds between NO3− and the amine functions of PS-Succ-DETA, such as hydrogen bonds between the oxygen of NO3− and the free hydrogen of the amine functions (Figure 9).

3.5. Field Tests

To simulate the behavior of PS-Succ-DETA for NO3− adsorption under real conditions, adsorption experiments were carried out by adding 150 mg of PS-Succ-DETA to a nitrate solution (50 mL) in the presence of several ions, such as SO42−, Cl−, Br−, and CO32−, and the results obtained are presented in Table 6.
As reported in Table 5, the initial concentration of NO3− ions decreased significantly from 50.21 mg. L−1 to zero after adding 150 mg of PS-Succ-DETA within 60 min. In addition, the active sites of PS-Succ-DETA also reduced the concentrations of SO42−, Cl−, Br−, and CO32−, indicating that PS-Succ-DETA is an effective adsorbent for field applications.

3.6. Desorption Tests

The desorption capacity of PS-Succ-DETA for NO3− ions was determined using a NaOH solution (0.2 M), as reported in the literature [22,26]. Figure 10a shows that the NaOH solution (0.20 M) desorbed 90% of the NO3− ions within 60 min, stabilizing the desorption rate after this time. Figure 10b shows that after five adsorption/desorption cycles, NO3− qe decreased from 195.65 mg/g to 143.25 mg/g, then stabilized. This decrease in qe after the 5th cycle is mainly due to the competitive interaction between OH− ions and -amine groups on PS-Succ-DETA rather than with NO3− ions. However, PS-Succ-DETA remains effective in removing NO3− without any significant loss of efficiency.

4. Conclusions

A simple, innovative, and effective approach has been developed to reduce the concentration of nitrate ions in a contaminated aqueous solution. This approach involves recycling polystyrene waste by grafting diethylene triamine onto its surface using succinic anhydride, thereby increasing the number of amine-based active sites capable of capturing nitrate ions. The adsorbent developed PS-Succ-DETA has a pHiep of 8.2, and at pH values below 8.2, PS-Succ-DETA has a positive charge resulting from the protonation of the -NH2 and -NH groups, which is likely to increase the electrostatic interactions between PS-Succ-DETA and NO3− anions. The average pore diameter of PS-Succ-DETA is relatively large, around 51.64 nm, indicating that the pores of this material are relatively large and may facilitate the diffusion of nitrate anions. The adsorption data correspond well to the Langmuir isotherm, and the nitrate ion adsorption capacity is 195.65 mg/g at pH 6. The adsorption kinetics are in excellent agreement with the pseudo-second-order model, with a correlation coefficient value of 0.999. A thermodynamic study of the adsorption revealed that the adsorption of nitrate ions on PS-Succ-DETA can take place over a wide temperature range and that it is favorable, spontaneous, and exothermic based on the negative values of ΔG (−10.02 kJ/mol), ΔH (−18.76 kJ/mol), and ΔS (−28.83 J/K/mol. Mechanistic analysis revealed that nitrate ion adsorption on PS-Succ-DETA occurs via physicochemical interactions and hydrogen bonds between NO3− and the amine groups of PS-Succ-DETA. The desorption capacity of PS-Succ-DETA for NO3− ions showed that 90% of the nitrate ions were desorbed after 60 min in the presence of NaOH solution (0.20 M). Similarly, qe decreased from 195.65 mg/g to 143.25 mg/g after five adsorption/desorption cycles and stabilized due to competitive interactions between OH- ions and -amine groups on PS-Succ-DETA rather than with NO3− ions. Nevertheless, PS-Succ-DETA remains effective in removing NO3− without a significant loss of efficiency.

Author Contributions

M.A.: conceptualization, investigation, methodology, data curation, literature search; F.T.: conceptualization, investigation, methodology, data curation, literature search; C.L.: investigation, literature search, results analysis; R.O.: literature search, results analysis, and preparation of the original draft; J.I.: investigation, literature search, results analysis, and review—editing of the original draft. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Data Availability Statement

The raw data supporting the conclusions of this article will be made available by the authors on request.

Conflicts of Interest

The authors declare that they have no conflicts of interest.

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Organics 05 00029 g001
Figure 1. Structure of PS-Succ-DETA.
Figure 1. Structure of PS-Succ-DETA.
Organics 05 00029 g001
Organics 05 00029 sch001
Scheme 1. Synthesis scheme of PS-Succ-DETA. Reagents and conditions: (a) AlCl3, DCM, 6 h; RT; (b) DCC, DCM, 2 days; RT.
Scheme 1. Synthesis scheme of PS-Succ-DETA. Reagents and conditions: (a) AlCl3, DCM, 6 h; RT; (b) DCC, DCM, 2 days; RT.
Organics 05 00029 sch001
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Figure 2. Zeta potential plots of PS and PS-Succ-DETA copolymers in 5 wt% ethanol dispersions as a function of pH.
Figure 2. Zeta potential plots of PS and PS-Succ-DETA copolymers in 5 wt% ethanol dispersions as a function of pH.
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Organics 05 00029 g003
Figure 3. TGA thermograms of PS and PS-Succ-DETA.
Figure 3. TGA thermograms of PS and PS-Succ-DETA.
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Figure 4. Infrared spectra of PS and PS-Succ-DETA.
Figure 4. Infrared spectra of PS and PS-Succ-DETA.
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Organics 05 00029 g005
Figure 5. Effect of pH on NO3− adsorption onto PS waste and PS-Succ-DETA.
Figure 5. Effect of pH on NO3− adsorption onto PS waste and PS-Succ-DETA.
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Figure 6. Effect of the PS-Succ-DETA dose on NO3− adsorption.
Figure 6. Effect of the PS-Succ-DETA dose on NO3− adsorption.
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Figure 7. Effect of contact time and initial anion concentration on NO3− adsorption.
Figure 7. Effect of contact time and initial anion concentration on NO3− adsorption.
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Organics 05 00029 g008
Figure 8. Effect of temperature on NO3− adsorption.
Figure 8. Effect of temperature on NO3− adsorption.
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Figure 9. Proposed mechanism of NO3− adsorption onto PS-Succ-DETA.
Figure 9. Proposed mechanism of NO3− adsorption onto PS-Succ-DETA.
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Organics 05 00029 g010
Figure 10. (a) Desorption efficiency of NO3− adsorbed onto PS-Succ-DETA and (b) reusability of PS-Succ-DETA over multiple adsorption-desorption cycles of NO3−.
Figure 10. (a) Desorption efficiency of NO3− adsorbed onto PS-Succ-DETA and (b) reusability of PS-Succ-DETA over multiple adsorption-desorption cycles of NO3−.
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Table 1. The BET-specific surface areas of PS and PS-Succ-DETA.
Table 1. The BET-specific surface areas of PS and PS-Succ-DETA.
PSPS-Succ-DETA
BET surface area (m2/g)14.9415.88
Average pore diameter (nm)32.4551.64
Total ion exchange capacity (meq/g)n.d6.18
Table 2. Comparison of the adsorption capacity of PS-Succ-DETA with that of other nitrate anion adsorbents.
Table 2. Comparison of the adsorption capacity of PS-Succ-DETA with that of other nitrate anion adsorbents.
AdsorbentsConditionsqe (mg.g−1)Ref
Grafted tri-alkyl-amine onto polystyrenepH 744.92[31]
Biochar-Supported Aluminum-Substituted GoethitepH 4–896.14[32]
Magnetite-silica-chitosan-amine nanoparticlespH 6112.5[33]
Zinc ferrite on activated carbon supportAcidic pH75.58[34]
Magnetic amine-grafted chitosan compositespH 538.40[34]
Ethylenediamine grafted on hazelnut shellspH 4–725.79[35]
AEAPTES grafted on Pomegranate PeelspH 6124.57[26]
Grafted diethylene triamine onto polystyrenepH 6195.65This work
Table 3. The calculated adsorption isotherm parameters for NO3− onto PS-Succ-DETA.
Table 3. The calculated adsorption isotherm parameters for NO3− onto PS-Succ-DETA.
Isotherm ModelsParameterValue
(Nitrate)
Langmuirqmax (mg/g)195.34
KL (L/mg)0.036
R20.998
RL0.112
FreundlichKF (mg/g) (L/mg)1/n7.568
nF4.054
R20.905
Temkin KT (L/mg)2.994
B (J/mol)59.665
R20.885
Dubinin–Radushkevichqs (mg/g)128.74
KDR (mol2/J2)6.96 × 10–6
E(D-R) (kJ/mol)6.325
R20.892
Sipsqm (mg g−1)114.72
KS (L·mg−1)0.314
n4.113
R20.919
RMS12.975
Table 4. The calculated adsorption kinetic parameters for NO3− adsorption onto PS-Succ-DETA.
Table 4. The calculated adsorption kinetic parameters for NO3− adsorption onto PS-Succ-DETA.
Concentration (mg.L−1)50100150
qe (exp) mg.g−1108.21136.82195.65
Pseudofirst order
k1 (10−2)(min−1)0.04050.03560.0312
qe cal (mg.g−1)55.8574.1195.34
R20.9250.9320.938
Pseudosecond order
k2 (10−3) (g.mg−1. Min−1)0.02650.01950.0134
qe cal (mg. g−1)107.89136.94195.31
R20.9990.9980.999
Elovich
A (mg.g−1. Min−1)23.288521.054753.6566
β (g.mg−1)0.8250.6810.503
R20.9010.9050.914
Table 5. The calculated thermodynamic parameters of NO3− adsorption onto PS-Succ-DETA.
Table 5. The calculated thermodynamic parameters of NO3− adsorption onto PS-Succ-DETA.
ΔG°
(KJ/mol)		ΔH°
(KJ/mol)		ΔS°
(J/Kmol)
Anions303 K313 K323 K
NO3−−10.02.−9.73−9.44−18.76−28.83
Table 6. Field tests of PS-Succ-DETA.
Table 6. Field tests of PS-Succ-DETA.
Parameters of the Water QualityPS-Succ-DETA
BeforeAfter
pH6.116.45
NO3− (mg/L)50.21Nil
Cl− (mg/L)314.41168.23
SO42− (mg/L)224.6597.74
CO32−124.2458.14
Br−90.8451.42
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Anannaz, M.; Tafraout, F.; Laghlimi, C.; Ouaabou, R.; Isaad, J. A New Generation of Porous Polymer Materials from Polystyrene Waste: Synthesis and Adsorption of Nitrate Anions in Aqueous Media. Organics 2024, 5, 561-574. https://doi.org/10.3390/org5040029

AMA Style

Anannaz M, Tafraout F, Laghlimi C, Ouaabou R, Isaad J. A New Generation of Porous Polymer Materials from Polystyrene Waste: Synthesis and Adsorption of Nitrate Anions in Aqueous Media. Organics. 2024; 5(4):561-574. https://doi.org/10.3390/org5040029

Chicago/Turabian Style

Anannaz, Mohamed, Fatiha Tafraout, Charaf Laghlimi, Rachida Ouaabou, and Jalal Isaad. 2024. "A New Generation of Porous Polymer Materials from Polystyrene Waste: Synthesis and Adsorption of Nitrate Anions in Aqueous Media" Organics 5, no. 4: 561-574. https://doi.org/10.3390/org5040029

APA Style

Anannaz, M., Tafraout, F., Laghlimi, C., Ouaabou, R., & Isaad, J. (2024). A New Generation of Porous Polymer Materials from Polystyrene Waste: Synthesis and Adsorption of Nitrate Anions in Aqueous Media. Organics, 5(4), 561-574. https://doi.org/10.3390/org5040029

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