Peganum Harmala L. plant as green non-toxic adsorbent for iron removal from water

: The present work focuses on examining the batch removal of Fe (III) from water using powdered Peganum Harmala seeds, characterized as FT-IR. In this work, several parameters are measured, including contact time, pH, Fe (III) concentration, reaction temperature effect, and adsorbent dose effect. Fe (III) adsorption was assessed using a UV-vis spectrophotometer at a wavelength of 620 nm. The findings demonstrated a positive correlation between the dosage of adsorbent and Fe (III) ions removal, with an increase in the adsorbent


Introduction
Toxic metals are classified as non-biodegradable toxic pollutants.They can accumulate in the tissues of living organisms and pass through the food chain.For this reason, many studies have investigated the elimination of heavy metals from the food chain to protect public health.In small amounts, such heavy metals as zinc, iron, chromium, manganese, and copper are vital for human bodily functions.However, if accumulated in sufficient quantities to cause poisoning, high levels of heavy metals can result in significant damage.Metal ions such as Fe (III) are often discharged into the environment during various industrial processes, including electroplating, leather tanning, vehicle manufacturing, power plant construction, nuclear facility development, the manufacturing of paint pigments and dyes, and metal finishing (Ayaz et al. 2020).The release of heavy metals into marine ecosystems has become a significant concern in recent years.Iron toxicity in living organisms arises from Fenton and Haber-Weiss reactions, generating reactive oxygen species that cause substantial damage to proteins, lipids, DNA, and other cytoplasmic molecules (Hejna et al. 2020).It is imperative to remove Fe (III) from wastewater prior to disposal into oceans and seas to mitigate its harmful effects.Several physicochemical techniques, including chemical oxidation or reduction, chemical precipitation, membrane filtration, ion exchange, flotation, adsorption, coagulationflocculation, and electrochemical methods, can be used to address metal contamination (Kučić at al. 2017, Trus et al. 2021, Wu et al. 2019).However, these processes often require significant energy input, and the resulting residual sludge may lead to secondary environmental pollution (Mamba, Dlamini, and Mulaba-Bafubiandi 2009).
The elimination of industrial effluents using traditional methods is costly and sometimes ineffective.Therefore, there is a pressing need to identify new, effective, environmentally friendly, and cost-efficient techniques for treating integrated wastewater.To achieve this goal and ensure economical removal of Fe (III), readily available and inexpensive materials are essential.Surface adsorption is one effective method for purifying aqueous samples by removing heavy metals is.In such processes, various inexpensive and widely available natural resources, including mineral rocks, agricultural waste, and industrial byproducts, have been employed as adsorbents (Laghrib et al. 2021, Rasgele 2021).
Based on a literature scan conducted by the authors across peer-reviewed publications, the adsorption of Fe (III) using Peganum Harmala seed as an adsorbent has not been previously studied.Therefore, this research represents the first instigation of its kind conducted by the authors.The primary objective of this research is to use powdered seeds of Peganum Harmala for the removal of Fe (III) from water.Multiple parameters, including the pH level of the aqueous solution, the initial metal concentration, the effect of temperature, and the stirring effect will be assessed and analyzed for their impact on the adsorption process.

Preparation of adsorbent
The Peganum Harmala seeds and sheath were gathered from the nearby region during the arid period and thereafter subjected to gradual pounding.They were then strained through a sieve to purify and isolate them.The purified seeds were exposed to sunlight for 5 days to ensure thorough desiccation.To create the Peganum Harmala seed powder (PPH), granular seeds were ground, pulverized, and calcinated at 300 ⁰C, after which they were applied as an adsorbent.This investigation involved a series of batch adsorption studies, conducted 100 ml Erlenmeyer flasks placed inside an incubator.Magnetic stirrers were used to mix the contents of the Erlenmeyer flasks.

Preparation of Fe (III) as an Adsorbate
The stirrers were set at a predetermined setting to maintain a consistent pace.To prepare a stock solution with a concentration of 1000 mg/l of Fe (III), the required quantity of ammonium iron (III) sulfate dodecahydrate NH 4 Fe (SO 4 ) 2 .12H 2 O (Aldrich, purity 97%) was dissolved in 1000 ml of double-distilled water.Dilutions of the stock solution were made to achieve the desired concentrations of Fe (III) for the standard solution.
In each study, a 100 ml sample containing the determined concentration was placed in the Erlenmeyer flask.Throughout the investigation, HCl (Aldrich, purity 99%) or NaOH (Aldrich, purity 99%) 1N solution was used to regulate the pH level.The pH levels were adjusted using a Metrohm digital pH meter (model 780) equipped with a combination glass electrode.Once the determined adsorbent dose was added to the flask, it was shaken at a regulated speed using a magnetic stirrer.After the designated duration had elapsed, the samples were passed through filter paper, and the resulting filtrates were examined to determine the remaining concentration of Fe (III).

Adsorbent characteristics
FTIR spectra analysis was performed on the fresh Peganum Harmala sample, covering wavelengths ranging from 400 and 4000 cm -1 (see Figure 1).The analysis revealed the presence of many significant functional groups on the adsorbents' surface.The novel adsorbent exhibited a wide adsorption band spanning a wavelength range of 3000 to 3633 cm -1 , with a maximum at 3400 cm -1 .These findings align with prior studies (Gładysz-Płaska et al. 2012), indicating the formation of chemical bonds between both free and bound hydroxyl groups (OH) and the surface.Furthermore, the novel adsorbent materials exhibited a broad adsorption band spanning wavelengths from 2800 to 3000 cm -1 , with a peak at 2931 cm -1 , indicating the presence of C-H groups on the Peganum Harmala surfaces.Wide absorption bands at wavelengths 1300-1500 cm -1 could be attributed to the presence of phenolic groups.Peaks at wavelengths between 1550-1700cm - 1 suggest the presence of carbonyl groups (C-O) on the surface of the new adsorbents (Moussavi and Khosravi 2012) The Brunauer-Emmett-Teller (BET) surface area was determined by conducting nitrogen adsorption-desorption experiments at a temperature of 77.35 K. Prior to measurement, the samples were stored in a desiccator until testing.The samples were subjected to cooling using liquid nitrogen and were then examined by quantifying the volume of gas (N 2 ) adsorbed at designated pressures.The pore volume was determined by extracting data from the adsorption branch of the isotherm at a pressure ratio (P/Po) of 0.995, assuming complete pore saturation.The results revealed that the BET surface area of Peganum Harmala powder was 132.957 m²/g, with a pore diameter of 1.5711 nm and a pore volume of 0.10445 cm 3 /g.

The effect of pH
The pH values significantly impact the charges on adsorbent surfaces, influencing the ionization process.Therefore, the solution's pH level plays a crucial role in the adsorption process (Sud, Mahajan, and Kaur 2008).This parameter also affects the heavy metal solution, which, in turn, influences the biosorbents' capacity (Chakravarty, Sarma, and Sarma 2010).Combing 1 g of Peganum Harmala adsorbent with 100 mL of 40 mg/L of Fe (III) ion solution and allowing it to stand for 1 hour enabled researchers to test the removal efficiency of Fe (III) cations at various pH levels.The pH range for the solutions ranged from 1.3 to 6.2.As illustrated in Figure 2 (a, b), the removal of Fe (III) ions was significantly low at acidic pH levels and increased as the pH of the Fe (III) ion solution increased.Similar findings were observed in lead removal using pomegranate peel (El-Ashtoukhy, Amin, and Abdelwahab 2008), where iron removal increased from 47% to 80% at equilibrium.However, at pH levels higher than 6, retardation was observed, possibly due to the involvement of iron hydroxide in the process (Oo et al. 2013).Consequently, pH 6.2 was determined to be optimal for removing Fe (III).The pH value in these circumstances is often referred to as the "adsorption edge" because the metal's removal and adsorption efficiency increase from very low to very high (Skwarek et al. 2008).
Several factors contribute to the reduction in removal efficiency at low pH levels.Firstly, at low pH values, there is a competition between Fe (III) ions and H+ ions on the surface of Peganum Harmala (Kumar Meena, Rajagopal, and Mishra 2010).Secondly, high concentrations of H+ ions in the solution result in a positively charged Peganum Harmala surface, leading to electrostatic repulsion between the positively charged surface and Fe (III) ions in the solution, thereby causing poor adsorption (Veli and Alyüz 2007).Thirdly, an increase in Cl − ions in the solution leads to the development of chloro-complexes, reducing the number of available Fe (III) ions for adsorption.Additionally, the larger size of Fe (III) complex molecules compared to free Fe (III) ions minimizes Fe (III) adsorption, further reducing the effectiveness of the process (Zendelska et al. 2015).Higher pH values result in lower hydronium ion concentrations on the adsorbent's surface, thereby reducing proton presence and increasing Fe (III) adsorption (Pandey et al. 2009).

The effect of contact time and initial concentration on the adsorption equilibrium
Time is the only variable that impacts the processes of Fe (III) ion adsorption and removal process when left in contact with the adsorbent for varying periods.Figure 3 illustrates the investigation of the correlation between adsorption and contact time.This study involved using a consistent quantity (1 g) of Peganum Harmala placed in a set volume (100 ml) of Fe (III) solution.Initially, the iron concentration was established at 40 mg/L under a pH of 5.The reaction temperature was set at 323 K, and agitation occurring at 300 rpm.To visualize the impact of increasing contact time on adsorption, a plot was created.A rapid increase in adsorption was observed during the first ten minutes, followed by a slower phase that continued for 20 minutes until maximum adsorption was reached.It is evident that the Fe (III) uptake process occurred rapidly during the initial 15 minutes, followed by a gradual slowdown until the 60-minute mark, where maximum adsorption of Fe (III) ions onto Peganum Harmala q e at 40 min occurred.Furthermore, the findings indicate that there was no further increase in adsorption beyond this point, indicating equilibrium.The primary aim of increasing the duration throughout the process is to enhance the percentage uptake of the adsorbate metal ions.During the initial minutes of the rapid stage, there was a build-up of metal ions on the active centers of the adsorbent's surface.
A low adsorption rate persisted throughout the slow stage until saturation was reached, marking the stable stage where no further Fe (III) ions could be adsorbed on the Peganum Harmala surface.This phenomenon is elucidated in light of the following point: the reduction of the solution into the adsorbent in solute diffusion leads to the bonding of small quantities of metal ions on the active centers of the adsorbent (El-Araby et al. 2017).This occurs because the binding sites become fixed, resulting in significant resistance to the presence of metal ions at the center of the remaining surface.Furthermore, this process is influenced by the increasing repulsive force between metal ions on the solid surface and the remaining metal ions in the liquid phase (Belay and Hayelom 2014).After 40 minutes, 88 % of the iron ions were removed and remained on the Peganum Harmala surface.6 Raiedhah Alsaiari, Iman Shedaiwa, Fatima A. Al-Qadri, Esraa M. Musa, Huda Alqahtani, Faeza Alkorbi.Norah A. Alsaiari, Mervate M. Mohamed

Effect of the Adsorbent Dose
The impact of various concentrations of Peganum Harmala as an adsorbent for the elimination and adsorption of Fe (III) ions is illustrated in Figure 4.This study investigated various concentrations of Fe (III) in 100 mL: 0.2, 0.4, 0.6, 0.8, and 1.0 g/100 mL.The pH level was adjusted to 5, the temperature maintained at 323 K, and the revolutions per minute were set to 300.The experiment lasted for a total of sixty minutes.The results emphasized that the elimination of Fe (III) ions increased with the dosage of the adsorbent rising from 0.2 to 1g.As a result, the percentage of removal increased as follows: 60%, 72%, 78%, 84%, and finally 86% for 1 g.The increase in Fe (III) ion removal is sensible as the adsorbent's surface area facilitates more exchanges on the connecting areas of adsorbent pores, leading to an increase in the number of Fe (III) ions removed.This phenomenon is also observed in iron ions uptake (Hossain et al. 2012).However, there is a decrease in adsorption after the dose exceeds 0.6 g.This decrease is primarily because the adsorbent pores become saturated by the Fe (III) ions (Vijayaraghavan et al. 2009).
The adsorbent accumulates at the active centers alongside the adsorbate, leading to a significant reduction in available surface adsorption sites (Joseph et al. 2019).Interestingly, it appears that as the adsorbent dose increases, the adsorption of Fe (III) ions and the uptake ability decline.The poor adsorption capacity values, ranging between 4 mg/g to 12 mg/g, result from some adsorbent sites remaining vacant throughout the adsorption process due to incomplete absorption of adsorbate ions by the adsorbent surface pores.An increase in the adsorbent dose results in a greater number of unsaturated active sites because the solution contains fewer metal ions compared to the number of available binding sites (Annadurai, Juang, and Lee 2003).Moreover, elevated adsorbent concentrations and sorbent concentrations decrease the qe, whereas increases in adsorbent concentration and qe can elevate the qe.By reducing the adsorbate surface area, the binding sites become isolated from the iron ions, thereby prolonging the diffusion path of the adsorbent particles (Tumin et al. 2008).The effects of adsorbate concentration Figure 5 (a, b), shows that as the concentration of the initial Fe (III) ions increases from 50 to 150 mg/L, the uptake of Fe (III) ions also increases.This phenomenon occurs because the adsorbent provides a better surface area ready for adsorption.With a higher concentration of Fe (III) ions, the ratio of the initial number of moles of Fe (III) ions to available adsorption sites increases.As a result, the adsorption percentage will be reduced.Initially, the rate of removal was slow.However, as the concentration of the adsorbate increased, the percentage of removal also increased.The presence of non-adsorbed ions in the liquid phase and the efficiency of removing metal ions by reduction are influenced by the initial concentration.These observations are in agreement with previous studies conducted by (Bhatti et al. 2008).

Effect of temperature
The removal of Fe (III) ions by Peganum Harmala was investigated at temperatures of 303 K, 313 K, 333 K, and 343 K, with an initial concentration of 40 mg/L.The results indicate that as the temperature increased from 303 to 333 K, the removal of Fe (III) metal ions by Peganum Harmala increased from 78.0 % at 333 K to 84.1% but it decreased to 83.1% at 343 K. (see Figure 6).
The increase in temperature leads to enhanced effective adsorbate diffusion in the adsorbent's porous microstructure, as the adsorption process is notably influenced by temperaturedependent dispersion forces and electrostatic interactions.Consequently, significant changes occur to the surface chemistry of the adsorbent, potentially promoting desorption.At higher temperatures, the adsorption of heavy metals is reduced, and bonds between the adsorbent and adsorbate may break, facilitating desorption.Moreover, high temperatures result in a decrease in the thickness boundary, allowing Fe (III) ions to leave the surface and enter the liquid phase, thereby reducing the amount of available adsorbent surface area.

Effects of mixing speed
Table 1 outlines the effects of mixing speed on Fe (III) sorption.The findings reveal that as the mixing speed increases, there is a corresponding increase in the amount of F (III) adsorbed.For instance, at a mixing speed of 300 rpm, 9 mg/g of Fe (III) is absorbed into the PPH.This suggests that the removal of Fe (III) is more effective at higher mixing speeds.The efficiency of Fe (III) removal is enhanced with higher mixing speed because iron ions are distributed more efficiently onto the   surface of adsorbents.The increased agitation facilitates better contact between the Fe (III) ions and the adsorbent surface, leading to greater adsorption.

Isotherms of Adsorption
The result showed that as the initial concentration Fe (III) ions increases, there is an extension in the driving force for mass transfer, facilitating adsorption within the range of 50 to 150 mg/L.The highest adsorption of Fe (III) ions was observed at an initial concentration of 100 mg/L, reaching 65 mg/g, followed by a decrease to 59 mg/g at 150 mg/L.This trend suggests that the increased adsorption of Fe (III) ions can be attributed to the expansion of the mass transfer driving force with rising initial concentrations (Hema and Arivoli 2010).These findings are similar to those reported by Ang (Ang et al. 2013), who investigated the adsorption of Fe (III) using powdered neem leaf.In their study, they observed that the maximum adsorption capacity was reached when the active sites of the adsorbent became saturated, resulting in a subsequent decline in adsorption efficiency.This observation was further verified by the examination of the results, which indicated a proportional increase in adsorption capacity with rising initial concentrations of metal ions.Thus, the data suggest a direct correlation between the adsorption capacity and the initial concentration of Fe (III) ions.The Langmuir and Freundlich isotherm models were both used in this study to analyze the adsorption of Fe (III) ions.The observed increase in Fe (III) ion adsorption can be attributed to the growing mass transfer driving force as the initial concentration of metal ions increases (Hema and Arivoli 2010).These findings are similar to those revealed by Ang (Ang et al. 2013), who investigated the adsorption of Fe (III) using powdered neem leaf.In their study, they observed that the maximum adsorption occurred when the active sites of the adsorbent became saturated, resulting in the observed decrease in adsorption.This trend was confirmed by the analysis of the findings, which also showed that the adsorption capacity rose as the initial concentration of metal ions increased.Therefore, both the Langmuir and Freundlich isotherm models were employed in this work.

Langmuir Isotherm
The Langmuir Model is a widely utilized and essential tool used to examine the adsorption isotherm process.It involves plotting C e /q e against C e to obtain a linear relationship.This makes it possible to compute the correlation coefficient, R 2 value, and Langmuir constants b and q e .In this study, the correlation coefficient R 2 value was found to be 0.93.This is presented in Table 2 alongside the values for the Langmuir b and q e constants.The following equation represents the Langmuir (Langmuir 1916) model: The adsorbent's maximum capacity is represented as q max (mg/g), while q e (mg/g) denotes the equilibrium adsorption capacity for the ions present on the adsorbent.C e denotes the equilibrium ion concentration in the solution, and this refers to the coverage monolayer of the adsorbate on the adsorbent.
Both the adsorption efficiency and adsorption energy are affected by the Langmuir constants q max and b (Imran Ali and V. K. Gupta 2006).Figure 7 presents a straight line obtained from the linear plot of C e /q e versus C e .Analysis of the results suggests that adsorption appears to be adequate when using the Langmuir model.Furthermore, there is a dimensionless equilibrium parameter known as the existence of monolayer adsorption.(R L ) (Weber and Chakravorti 1974) which can be applied to describe the Langmuir isotherm.This can be written in the following way: R L represents favorable and unfavorable adsorption: Unfavorable: R L > 1; Linear: R L = 1; Favorable: 0 < R L < 1; Irreversible: R L = 0. C i denotes different Fe (III) ion concentrations.Moreover, Table 2 also presents the analysis results for the Langmuir isotherms, and the following R L values can be seen: 0.28, 0.14, 0.095, 0.071, and 0.0057.In this respect, the R L values, which ranged from 0 to 1, indicate that there was adequate adsorption of Fe (III) ions onto the active Peganum Harmala centers (Yao, Qi, and Wang 2010).

Freundlich isotherms
Equation 3 is derived from Freundlich's work (Freundlich 1906), and expresses the logarithmic form, with K F and n being Freundlich constants.When plotting log q e versus log C e , a straight line is identified in Figure 8 and Table 2.
The experimental parameter n, which is associated with the adsorption concentration of the adsorbent, serves as an indicator of the extent of favorable adsorption.This parameter is influenced by the solid variety and heterogeneity of the material, thereby quantifying the adsorption convenience represented by parameter n.When the value of n falls within  the range of 1 to 10 (with 1/n being less than 1), it indicates that adsorption occurred on the heterogeneous surface of the adsorbent (Ho and McKay 1998), indicating multilayer sorption as well (Aksu and Kutsal 1991).
As determined by both the linear and nonlinear Langmuir models, Table 3 displays the maximum adsorption capacities (mg/g) of Fe (III) using different adsorbents mentioned in the literature.

Adsorption kinetics
Pseudo-first-and pseudo-second-order kinetic models describe the kinetic mechanism of adsorption (Aksu and Işoǧlu 2005).Moreover, the first-order model adsorption rate constant from prior work (Tran, You, and Chao 2016) and the rate-limiting phase in the adsorption process (Aregawi and Mengistie 2013) are detailed.The following equation may be used to represent the first-order kinetic reaction: The linear form of the above equation is written as follows: (5) At equilibrium and time t, the quantities of Fe (III) ions adsorbed onto the surface of Peganum Harmala are represented by q e and q t , respectively, in mg/g.The rate constant of the pseudo-first-order kinetic model is denoted as K 1 (min−1).By plotting ln (q e -q t ) against t, a straight line can be created.This line also enables the derivation of the constant K 1 , correlation coefficient R 2 and theoretical q e .Figure 9 indicates discrepancies between the calculated (q e , calc.) and experimental values.The poor correlation coefficient R 2 of the pseudo-first-order kinetic model, compared to the pseudo-second-order kinetic model, suggests that its adsorption kinetics were not suitable.
The appropriate kinetic model for the adsorption mechanism is the pseudo-second-order model.This model is characterized by chemical reactions where electrons are shared    10 Raiedhah Alsaiari, Iman Shedaiwa, Fatima A. Al-Qadri, Esraa M. Musa, Huda Alqahtani, Faeza Alkorbi.Norah A. Alsaiari, Mervate M. Mohamed or exchanged between the adsorbate and adsorbent due to valence forces.The equilibrium adsorption can be determined using the following relationship: A linear relationship between the plot of t/q t versus t is observed (Figure 10).This relationship is used to determine the rate constant k 2 (g / (mg.min)) of the pseudo-secondorder kinetic model, as well as the calculated value of q e .The findings are summarized in Table 4, where the R 2 value approached 1.The calculated equilibrium adsorption capacity values, q e , calc., were either identical to or had a relative value to the experimental q e exp.The adsorption kinetics in this case conform to the pseudo-second-order model kinetics, regardless of the initial Fe (III) concentrations.

Thermodynamic Parameters
Figure 11 shows the calculation of thermodynamic parameters, including free energy (ΔG•), standard enthalpy (ΔH•), and standard entropy (ΔS•).The process may be described by the transport of the solute in the mole unit to the solid-liquid interface.The thermodynamic parameters may be computed using the following equation: (9) The thermodynamic parameters mentioned earlier, namely, ΔH•, ΔG°, and ΔS° were determined through the calculation of ln Kc versus 1/T.The corresponding outcomes are presented in Table 5.The negative values of the thermodynamic parameters indicated that the adsorption process was characterized by exothermic.According to Table 5, the negative value of ΔS° may be attributed to the association between ΔS° and the adsorption process.The binding of Fe (III) ions to the active sites of Peganum Harmala seeds did not follow a specific pattern during the formation of the activated complex between the substance being adsorbed and the substance doing the adsorbing (Tran et al. 2016).Furthermore, in these circumstances (ΔS° < 0), the negative value of ΔS indicated Peganum Harmala's affinity for Fe (III) ions as well as the growing unpredictability at the solidsolution interface throughout the adsorption process (Bulut and Tez 2007).
The process and spontaneous nature of the adsorption of Fe (III) ions onto the prepared Peganum Harmala were indicated by the negative value of ΔG•.It was observed that    as the temperature increased, the magnitude of ϔG• decreased, indicating a reduction in driving force and consequently a decline in adsorption capacity.

Conclusion
• The findings of the current study clearly indicate that the pseudo-first-order model is more suitable for describing the adsorption of Fe (III) ions on the active centers of the surface of Peganum Harmala compared to the pseudo-secondorder reaction model.Additionally, the Langmuir adsorption isotherm proves to be more appropriate than the Freundlich adsorption isotherm.The negative values of thermodynamic parameters suggest the exothermic nature of the adsorption process, while the negative values of entropy exposure indicate the absence of randomness and organized structure at the liquid-solid interface.
• In addition, it is noteworthy that associative adsorption took place; the adsorption of Fe (III) ions onto 1 g of Peganum Harmala was spontaneous, as indicated by the negative magnitude of free energy ΔG.This suggests that Peganum Harmala is a more effective natural adsorbent in comparison to synthetic adsorbents.
• Peganum Harmala is a convenient, easily accessible, and cost-effective plant for reducing the amount of pollutants and some heavy metals in water.

Fig. 2 .
Fig. 2. (a) Effect pH on the Fe (III) ions adsorption capacity at equilibrium on the surface of Peganum Harmala (b) Effect pH on the Fe (III) ions removal by Peganum Harmala

Fig. 5 .
Fig. 5. (a) Effect of initial concentrations on the adsorption capacity at equilibrium (b) The Effect of initial concentration on removal Fe (III).

FigFig. 4 .Fig 6 .
Fig. 5. (a) Effect of initial concentrations on the adsorption capacity at equilibrium (b)The Effect of initial concentration on removal Fe(III).

Fig. 11 .
Fig. 11.Effect of temperature on thermodynamic behavior of adsorption of Fe (III) onto Haramla plant.

Table 2 .
Parameters of Langmuir and Freundlich isotherms for adsorption of Fe (III) onto Peganum Harmala surface

Table 3 .
Maximum adsorption capacities q max of Fe (III) by different adsorbents

Table 5 .
Thermodynamic parameters for the adsorption of Fe (III) onto Peganum Harmala