Selective Removal of Iron, Lead, and Copper Metal Ions from Industrial Wastewater by a Novel Cross-Linked Carbazole-Piperazine Copolymer

A novel cross-linked Copolymer (MXM) was synthesized by the polycondensation reaction of 3,6-Diaminocarbazole and piperazine with p-formaldehyde as a cross-linker. The Copolymer was fully characterized by solid 13C-NMR and FT-IR. The thermal stability of MXM was investigated by TGA and showed that the Copolymer was stable up to 300 °C. The synthesized polyamine was tested for the removal of iron (Fe2+), lead (Pb2+), and copper (Cu2+) ions from aqueous and industrial wastewater solutions. The effect of pH, concentration and time on the adsorption of iron (Fe2+), lead (Pb2+), and copper (Cu2+) ions was investigated. The adsorption of the studied ions from aqueous solutions onto the MXM polymer occurs following the Freundlich isotherm and pseudo-second-order kinetic models. The intraparticle diffusion model showed that the adsorption mechanism is controlled by film diffusion. The regeneration of MXM showed practical reusability with a loss in capacity of 2–5% in the case of Fe2+ and Cu2+ ions. The molecular simulation investigations revealed similarities between experimental and theoretical calculations. Industrial wastewater treatment revealed the excellent capabilities and design of MXM to be a potential adsorbent for the removal of heavy metal ions.


Introduction
The growth of population and industrialization has resulted in a massive quantity of hazardous chemicals being released into the environment, posing a warning to human life and the quality of the urban environment [1]. Due to their apparent cytotoxicity, even at low quantity levels, heavy metal pollution has been a major and serious problem globally in the last several decades. As a result, it is critical to continually monitor heavy metal pollution and health risks in cities, particularly mining and industrial areas [2].
Although iron is not harmful to one's health, it is regarded as a secondary or cosmetic contaminant. An increase in iron concentration in the human body could cause health issues, although it is necessary for health at a certain level since it aids in transferring oxygen in the blood [3]. However, iron contamination in the oil industry can be devastating as iron poisoning affects fluid catalytic-cracking catalysts. After iron contamination, a thick coating can build on the catalyst's surface, which prevents reactants from diffusing into the catalyst's inner structures. This poisoning has a significant detrimental impact on the catalyst's capacity to convert heavy oils, and it might significantly reduce gasoline output while significantly boosting dry gas, coke, and slurry yields [4,5].
On the other hand, copper becomes poisonous in high quantities and can damage the brain, heart, and kidneys of human beings [6]. Moreover, it can disrupt the metabolic 3,6-Diaminocarbazole, piperazine, p-formaldehyde, glacial acetic acid, methanol, and DMF were purchased from Sigma Aldrich and were used without further purification. Metal adsorption analysis was performed using ICP-OES Optima 8000 Perkin Elmer. Polymer structure was determined by 13 C-NMR spectra using solid-state type and was recorded by Bruker Avance III-400 WB. FTIR spectra were produced on iTR Nicolet is 10 spectrometer. pH measurements were performed using HACH HQ411D. Thermal stability was measured using (TGA) Q600 TA instruments at a heating rate of 20 • C/min under a nitrogen atmosphere.

Polymer Synthesis (MXM)
In a typical reaction [20], 3,6-Diaminocarbazole (0.01 mmol, 1.97 g), piperazine (0.04 mmol, 3.44 g), and p-formaldehyde (0.04 mmol, 1.201 g) in DMF (25 mL) were stirred for 10 min and in a 100 mL PTFE liner hydrothermal autoclave vessel. The vessel was purged with nitrogen and sealed. The reaction vessel was transferred into a stainless-steel reaction vessel and heated in an oven at 100 • C for 24 h. Once completed, the reaction Polymers 2022, 14, 2486 3 of 14 mixture was filtered and washed with methanol. The dark black solid powder was then dried under vacuum at 70 • C for 24 h (Yield: 5.1 g, 77%).

Adsorption Experiments
Batch adsorption studies were performed on the capability of MXM to remove three metal ions Fe 2+ , Cu 2+ , and Pb 2+ . In a typical experiment [21], 30 mg of the polymer was added to a 20 mL metal solution at a certain pH, initial concentration, and temperature and stirred for a specific amount of time. Once the adsorption experiment was completed, the reaction mixture was filtered, and the concentration of the metal ions after adsorption was measured. The capability of MXM was found by calculating the adsorption capacity as described in the following equation: where Q e is the adsorption capacity (mg/g), and C o and C f are the initial and final concentrations of metal ions (mg/L) in the solution, respectively. W is the mass of MXM (mg), and V is the volume of the metal ion solution (L).

Molecular Simulation
Molecular simulations were conducted using the COMPASS II forcefield [22] on Materials Studio 8.0 suite to determine the density and the fractional free volume (FFV) of the material, MXM. An amorphous cell comprising 20 units of MXM was constructed and minimized using the Forcite module, followed by dynamics simulations on the NPT and the NVT ensembles each for 1000 ps at a time step of 1.0 fs. The Nose-Hoover thermostat and the Berendsen barostat were used to control the temperature (at 298 K) and pressure (at 8 bar), respectively. The Ewald summation method was used for long-range Coulombic interactions, while Lennard-Jones interactions were estimated with a cut-off range of 12.5 Å. The interaction of MXM and metal ions were simulated by conducting quantum mechanical DFT simulations on Gaussian 09 [23], at the B3LYP exchange-correlation functional, in combination with the Pople's split valence basis set, 6-311G*, and the SDD pseudopotential basis set, for the non-metal and metal atoms, respectively [24,25]. The polarized continuum model-self-consistent reaction field (PCM-SCRF) model was used to simulate the aqueous media, with the solvent depicted as water [26]. After full geometry optimization, the adsorption energies of MXM and the metal ions were computed using the following equation: where E M-MXM represents the total energies of the metal ion-MXM complexes, while E M and E MXM represent the isolated energies of the metal ions and MXM, respectively. The nature of the interactions was explored using the reduced density gradient (RDG) isosurfaces plots as implemented on the multi-wavefunction analysis code [27].

Results and Discussion
A novel cross-linked Copolymer has been synthesized by the polycondensation reaction of 3,6-Diaminocarbazole and piperazine with p-formaldehyde to produce the MXM Copolymer (Scheme 1). The monomeric moieties of diaminocarbazole and piperazine were chosen to be typical for an adsorbent of heavy metal ions as they provide the rigidity of aromatic moieties in diaminocarbazole and the flexibility of piperazine units. The high amount of nitrogen atoms present in these monomers provides a high concentration of attractive adsorption sites for metal ions to be attached and removed.

MXM Copolymer Structure Characterization
Copolymer MXM was characterized by solid 13 C-NMR and FT-IR, as shown in Figure  1a Figure 1a shows an absorption band at ~3400 cm −1 , which represents the -N-H stretching frequency of MXM, and an absorption band at ~2980 cm −1 , which represents the -CH2-stretching vibration of the methylene units in piperazine moiety, and the methylene bridge that links the diaminocarbazole with the piperazine monomers. An absorption band at ~1600 cm −1 represents the -C=C-stretching vibrations of the benzene rings found in the diaminocarbazole monomer. An absorption band at ~1440 cm −1 represents the -C-N-stretching vibration in both monomeric units [28,29]. Figure 1b represents the solid 13 C-NMR spectrum for MXM; the spectrum shows multiple peaks ~30-50 ppm, referred to as the methylene units in the piperazine monomer and the methylene bridge between the diaminocarbazole and piperazine monomer. The peaks of ~100-150 ppm are characteristic of the aromatic carbons found in diaminocarbazole [30][31][32]. The peak present ~165 ppm is due to the formation of imine linkage between terminal amines with pformaldehyde. Figure 1c shows the thermogravimetric analysis of the MXM Copolymer. The thermogram shows two degradation steps; the first thermal degradation step at ~300 °C corresponds to the thermal degradation of aliphatic chains in the piperazine units and methylene bridges between monomeric units, followed by a sharp thermal degradation at ~500 °C due to the carbonization of diaminocarbazole aromatic units [33,34].

MXM Copolymer Structure Characterization
Copolymer MXM was characterized by solid 13 C-NMR and FT-IR, as shown in Figure 1a Figure 1a shows an absorption band at~3400 cm −1 , which represents the -N-H stretching frequency of MXM, and an absorption band at~2980 cm −1 , which represents the -CH 2 -stretching vibration of the methylene units in piperazine moiety, and the methylene bridge that links the diaminocarbazole with the piperazine monomers. An absorption band at~1600 cm −1 represents the -C=C-stretching vibrations of the benzene rings found in the diaminocarbazole monomer. An absorption band at~1440 cm −1 represents the -C-N-stretching vibration in both monomeric units [28,29]. Figure 1b represents the solid 13 C-NMR spectrum for MXM; the spectrum shows multiple peaks~30-50 ppm, referred to as the methylene units in the piperazine monomer and the methylene bridge between the diaminocarbazole and piperazine monomer. The peaks of~100-150 ppm are characteristic of the aromatic carbons found in diaminocarbazole [30][31][32]. The peak present~165 ppm is due to the formation of imine linkage between terminal amines with p-formaldehyde. Figure 1c shows the thermogravimetric analysis of the MXM Copolymer. The thermogram shows two degradation steps; the first thermal degradation step at~300 • C corresponds to the thermal degradation of aliphatic chains in the piperazine units and methylene bridges between monomeric units, followed by a sharp thermal degradation at~500 • C due to the carbonization of diaminocarbazole aromatic units [33,34].

MXM Copolymer Adsorption Properties
To fully comprehend the capability of the MXM Copolymer to adsorb heavy metal ions, the Copolymer was studied under different adsorption conditions experimentally. Moreover, the Copolymer was studied under molecular simulation to study the affinity of the MXM Copolymer toward the adsorption of lead, iron, and copper metal ions.

Effect of pH on the Adsorption Capacity of MXM
The synthesized Copolymer MXM was tested at different pHs (2.34, 3.57, 5.73, and 6.67) to find out the adsorption efficiency of MXM on a 1 ppm solution of iron (Fe 2+ ), copper (Cu 2+ ), and lead (Pb 2+ ) ions. In a typical experiment, 30 mg of MXM was added to a 20 mL metal ion and stirred for 1 h. Once completed, the solution was filtered, and the concentration of metal ions was measured. Figure 2 depicts the influence of pH on the adsorption capacity of MXM. As shown in the figure, the adsorption capacity of MXM increases as pH increases. In high acidic conditions, the increased protonation of the adsorbent surface results in lower metal ion adsorption, as shown in Scheme 2. The pH also has an impact on the speciation of heavy metal ions. The adsorption experiments were performed in the pH range of 2-6; after pH = 6, the metal ions start precipitating, which is expected due to the formation of metal hydroxides M(OH) 2 . As a result, pH = 5.73 was utilized for the rest of the adsorption studies.

MXM Copolymer Adsorption Properties
To fully comprehend the capability of the MXM Copolymer to adsorb heavy metal ions, the Copolymer was studied under different adsorption conditions experimentally. Moreover, the Copolymer was studied under molecular simulation to study the affinity of the MXM Copolymer toward the adsorption of lead, iron, and copper metal ions.

Effect of pH on the Adsorption Capacity of MXM
The synthesized Copolymer MXM was tested at different pHs (2.34, 3.57, 5.73, and 6.67) to find out the adsorption efficiency of MXM on a 1 ppm solution of iron (Fe 2+ ), copper (Cu 2+ ), and lead (Pb 2+ ) ions. In a typical experiment, 30 mg of MXM was added to a 20 mL metal ion and stirred for 1 h. Once completed, the solution was filtered, and the concentration of metal ions was measured. Figure 2 depicts the influence of pH on the adsorption capacity of MXM. As shown in the figure, the adsorption capacity of MXM increases as pH increases. In high acidic conditions, the increased protonation of the adsorbent surface results in lower metal ion adsorption, as shown in Scheme 2. The pH also has an impact on the speciation of heavy metal ions. The adsorption experiments were performed in the pH range of 2-6; after pH = 6, the metal ions start precipitating, which is expected due to the formation of metal hydroxides M(OH)2. As a result, pH = 5.73 was utilized for the rest of the adsorption studies.  demonstrates the influence of the initial metal ion concentration (mg/L) on the adsorption capacity of MXM. The adsorption investigation was carried out on three metal ion solutions (Cu 2+ , Fe 2+ , and Pb 2+ ) with a concentration ranging from 0.2 to 1 (mg/L) at pH = 5.73 and a specific time of 1 h. The figure shows that the adsorption capacity increases with increases in the initial concentration of the metal ion. Three adsorption isotherm models were used to analyze the experimental data acquired by the batch adsorption studies; Langmuir, Freundlich, and the Dubinin-Kaganer-Radushkevich (DKR) isotherm model. The Langmuir isotherm model describes adsorption as a single-layer adsorption where one metal is attached to one adsorption site (Figure 3b). It depicts the uniform adsorption of metal ions on the surface of the adsorbent [35]. The negative values shown in Table 1 reveal that the adsorption process of the three metal ions does not follow the Langmuir isotherm model. In contrast to the Langmuir isotherm, the Freundlich isotherm model explains the adsorption behavior when the surface is heterogeneous, where one active site can accommodate more than one metal ion [36,37]. The heterogeneity of the surface can be determined from the slope (1/n). High heterogeneity is described when the value of 1/n is ~0. When the value of 1/n < 1, adsorption is considered favorable. If the slope (1/n) has a value above one, this indicates cooperative adsorption. As shown in Table  1 (Figure 3c), the values of 1/n are higher than 1, indicating that the adsorption process is cooperative in nature [38]. The DKR model [39], which is applied to single solute systems, describes the adsorption mechanism as physical or chemical in nature [40]. The results shown in Table 1 (Figure 3d) show that adsorption energy E is exothermic, indicating favorable adsorption [40].  (Figure 3b). It depicts the uniform adsorption of metal ions on the surface of the adsorbent [35]. The negative values shown in Table 1 reveal that the adsorption process of the three metal ions does not follow the Langmuir isotherm model. In contrast to the Langmuir isotherm, the Freundlich isotherm model explains the adsorption behavior when the surface is heterogeneous, where one active site can accommodate more than one metal ion [36,37]. The heterogeneity of the surface can be determined from the slope (1/n). High heterogeneity is described when the value of 1/n is~0. When the value of 1/n < 1, adsorption is considered favorable. If the slope (1/n) has a value above one, this indicates cooperative adsorption. As shown in Table 1 (Figure 3c), the values of 1/n are higher than 1, indicating that the adsorption process is cooperative in nature [38]. The DKR model [39], which is applied to single solute systems, describes the adsorption mechanism as physical or chemical in nature [40]. The results shown in Table 1 (Figure 3d) show that adsorption energy E is exothermic, indicating favorable adsorption [40].

The Effect of Time on the Adsorption Capacity of MXM
The adsorption rate, which determines how long it takes for the adsorption process to reach equilibrium, is also influenced by adsorption kinetics and is shown in Figure 4. This information is critical for the process of innovation and adsorption system design. In this work, three kinetic models were used to analyze experimental data: pseudo first-order (PFO), pseudo second-order (PSO), and intraparticle diffusion (IPD), which were used to define the adsorption kinetics of Fe 2+ , Cu 2+ , and Pb 2+ by the MXM Copolymer.
PFO kinetic model posits that the rate of change of adsorbed solute by time is precisely comparative to the change in saturation concentration and the quantity of solid adsorption with time, and it may be applied to any adsorption process in the first stage [41,42] from the data shown in Table 2 (Figure 4b). The Q e(exp) values are not close to the values of Q e found by PFO, which implies that the experimental data does not fit the PFO kinetic model. PSO's premise is that the rate-limiting phase is chemisorption, and it predicts the behavior over the entire adsorption range [43,44]. In this situation, the adsorption rate is governed by the adsorption capacity rather than the adsorbate concentration. The model can determine the equilibrium adsorption, which is a key advantage of PSO over PFO; hence, no requirement is needed to assess the adsorption equilibrium capacity from the experiment.

The Effect of Time on the Adsorption Capacity of MXM
The adsorption rate, which determines how long it takes for the adsorption process to reach equilibrium, is also influenced by adsorption kinetics and is shown in Figure 4.   Figure 4c), Q e(exp) is close to the Q e values calculated in the PSO model with good regression values, implying that the adsorption process is chemisorption [45,46].
Weber and Morris devised an intraparticle diffusion model to determine the adsorption diffusion process. Nonlinearity, on the other hand, is occasionally found. When the data show several linear plots, it implies that adsorption was caused by more than one mechanism. As a result, these rate-determining processes may be split into multiple linear curve segments throughout time, each having control over the entire process [47,48]. The discovery of the rate-limiting step provides new insights into the mechanism of the adsorption process. According to the intraparticle diffusion model, first, metal ions move interfacially (i.e., film diffusion) between the absorbent and solution. Second, a rate-limiting intraparticle diffusion phase carries the ions into the adsorbent sites, and then adsorption reaches equilibrium [49]. From Figure 4d, the adsorption of Fe 2+ , Cu 2+ , and Pb 2+ metal ions by Copolymer MXM proceeds through two steps, with film diffusion followed by equilibrium.

Reusability of MXM
The reusability of MXM is a vital factor for its use in industrial wastewater treatment; for that, MXM was subjected to two cycles of adsorption, as shown in Figure 5. In a typical experiment, 100 mg of MXM was placed in a 20 mL 1 ppm solution of Pb 2+ , Fe 2+ , and Cu 2+ for 1 h under stirring. Once the experiment was completed, the adsorption capacity was measured. The polymer was soaked in a 1M solution of nitric acid for 15 min, followed by washing with water and 1M sodium hydroxide; then, it was thoroughly washed with water. The experiment was repeated, and the adsorption capacity of MXM was measured again. The adsorption experiments reveal the usability of MXM with small loss of activity in the adsorption of Fe 2+ and Cu 2+ , which proves the suitability of MXM to be used as an adsorbent.

Molecular Simulation
The results of MD simulations on 20 units of MXM are shown in Figure 6. The grey and blue isosurfaces represent the accessible free volume on MXM at a probe radius of 1.09 Å. The system was stabilized mainly by intermolecular hydrogen bonds and possible π-π stacking between the aromatic rings. The estimated FFV of MXM (0.15) indicates moderate hydrogen bonding within the system and suggests higher water permeance and greater mobility of the metal ions in good correlation with fully reported aromatic systems [50].

Reusability of MXM
The reusability of MXM is a vital factor for its use in industrial wastewater treatment; for that, MXM was subjected to two cycles of adsorption, as shown in Figure 5. In a typical experiment, 100 mg of MXM was placed in a 20 mL 1 ppm solution of Pb 2+ , Fe 2+ , and Cu 2+ for 1 h under stirring. Once the experiment was completed, the adsorption capacity was measured. The polymer was soaked in a 1M solution of nitric acid for 15 min, followed by washing with water and 1M sodium hydroxide; then, it was thoroughly washed with water. The experiment was repeated, and the adsorption capacity of MXM was measured again. The adsorption experiments reveal the usability of MXM with small loss of activity in the adsorption of Fe 2+ and Cu 2+ , which proves the suitability of MXM to be used as an adsorbent.

Molecular Simulation
The results of MD simulations on 20 units of MXM are shown in Figure 6. The grey and blue isosurfaces represent the accessible free volume on MXM at a probe radius of 1.09 Å . The system was stabilized mainly by intermolecular hydrogen bonds and possible π-π stacking between the aromatic rings. The estimated FFV of MXM (0.15) indicates moderate hydrogen bonding within the system and suggests higher water permeance and greater mobility of the metal ions in good correlation with fully reported aromatic systems [50]. The results of MD simulations on 20 units of MXM are shown in Figure 6. The grey and blue isosurfaces represent the accessible free volume on MXM at a probe radius of 1.09 Å . The system was stabilized mainly by intermolecular hydrogen bonds and possible π-π stacking between the aromatic rings. The estimated FFV of MXM (0.15) indicates moderate hydrogen bonding within the system and suggests higher water permeance and greater mobility of the metal ions in good correlation with fully reported aromatic systems [50].  Molecular level quantum simulations of the adsorption of Cu 2+ , Pb 2+ , and Fe 2+ ions on MXM molecules were conducted and presented in Figure 7. Three possible adsorption modes, the in-plane, the stack, and grip configurations, were identified and geometrically optimized. The adsorption energies, E ad , revealed that MXM exhibited higher adsorption capacity toward Cu 2+ ions with energies of −22.3, −7.55, and −7.99 eV for the in-plane, the stack, and the grip configurations, respectively. The order of E ad , Cu 2+ > Pb 2+ > Fe 2+ , was consistent with the change in the frontier molecular orbital (FMO) energy separation of MXM upon the adsorption of the metal ions ( Figure S1), which revealed the stabilization of the nucleophilic character of the Copolymer material by lowering the energy of the highest occupied molecular orbital. Consequently, a significant fraction of charges was transferred to the Copolymer materials when interacting with Cu 2+ ions, resulting in higher adsorption capacity that is consistent with the experimental data.
The RDG isosurface plots of the various optimized adsorption modes of the metal ions on the active sites of MXM are presented in Figure S2. It mainly depicts non-covalent interactions (NCIs) characterized by electron density ρ [51,52]. RDG isosurface plots revealed predominantly weak Van der Waals interactions between MXM and the metal ions. In-plane geometry exhibited higher ρ along the plane of interactions, suggesting stronger adsorption as revealed by E ad , and this is consistent with the change in FMO distribution. Meanwhile, partial repulsions were exhibited by Pb 2+ and Fe 2+ ions, resulting in slightly weaker adsorptions, in good correlation with the experimental adsorption data.

Wastewater Sample Treatment
The significant element in synthesizing an adsorbent polymer is to find out its ability to treat wastewater. The effectiveness of MXM in removing heavy metals was tested using two samples of wastewater (unspiked, spiked each by 1 mg/L iron, copper, and lead ions). The wastewater sample had a pH of 7.9, total dissolved solids of 1096.4 mg/L, total suspended solids of 11 mg/L, chlorides of 254 mg/L, and organic carbon of 9.8 mg/L. A 20 mL sample of unspiked and spiked samples containing the three metal ions was treated with MXM. The results in Table 3 reveal the efficiency of MXM as an adsorbent for removing Fe 2+ , Cu 2+ , and Pb 2+ from wastewater solutions. A comparison Table between MXM and other adsorbents reported in the literature shows the efficiency of MXM as an adsorbent for the removal of heavy metal ions (Table S1). modes, the in-plane, the stack, and grip configurations, were identified and geometrically optimized. The adsorption energies, Ead, revealed that MXM exhibited higher adsorption capacity toward Cu 2+ ions with energies of −22.3, −7.55, and −7.99 eV for the in-plane, the stack, and the grip configurations, respectively. The order of Ead, Cu 2+ > Pb 2+ > Fe 2+ , was consistent with the change in the frontier molecular orbital (FMO) energy separation of MXM upon the adsorption of the metal ions ( Figure S1), which revealed the stabilization of the nucleophilic character of the Copolymer material by lowering the energy of the highest occupied molecular orbital. Consequently, a significant fraction of charges was transferred to the Copolymer materials when interacting with Cu 2+ ions, resulting in higher adsorption capacity that is consistent with the experimental data. The RDG isosurface plots of the various optimized adsorption modes of the metal ions on the active sites of MXM are presented in Figure S2. It mainly depicts non-covalent interactions (NCIs) characterized by electron density ρ [51,52]. RDG isosurface plots revealed predominantly weak Van der Waals interactions between MXM and the metal ions. In-plane geometry exhibited higher ρ along the plane of interactions, suggesting stronger adsorption as revealed by Ead, and this is consistent with the change in FMO distribution. Meanwhile, partial repulsions were exhibited by Pb 2+ and Fe 2+ ions, resulting in slightly weaker adsorptions, in good correlation with the experimental adsorption data.

Wastewater Sample Treatment
The significant element in synthesizing an adsorbent polymer is to find out its ability to treat wastewater. The effectiveness of MXM in removing heavy metals was tested using  Table 3. Comparison of the metal ions concentrations before and after treatment of wastewater sample (unspiked and spiked) and spiked DI water.

Metal Ions
Unspiked Wastewater Sample

Conclusions
A novel cross-linked carbazole-piperazine Copolymer has been synthesized, and the adsorption properties were investigated under different conditions such as pH, initial metal ion concentration, and time. The adsorption results revealed that the MXM polymer followed the Freundlich isotherm model, where the adsorption process is heterogeneous, whereas the adsorption kinetics followed the pseudo-second-order kinetic model indicating chemisorption. The intraparticle diffusion model indicated that adsorption experiences film diffusion followed by equilibrium. The regeneration of MXM polymer showed its ability to be used again with little losses of 2-5% in capacity in the case of iron and copper, which makes it effective as an adsorbent. Interestingly, the performance of MXM was the most efficient in the case of industrial wastewater treatment, where MXM showed higher adsorption capacity toward iron and lead than copper, which could be due to the different environments, pH, and salinity of the industrial wastewater sample with a % removal of 55-100% removal capacity. The results indicate the strong potential of MXM to be an efficient adsorbent for the removal of heavy metal ions from wastewater solutions.