Peganum Harmala seeds extract: A green synthesis route for Mn-doped ZnO nanoparticles as an adsorbent for crystal violet dye removal

: The employment of green synthesized nanomaterials for water pollution prevention is increasing nowadays. Herein, Mn-doped ZnO nanoparticles were synthesized using Peganum Harmala seed extract and subsequently used for crystal violet (CV) dye removal from aqueous solutions. The first part of the study describes the preparation of the adsorbent (Mn-ZnO NPs) using a simple coprecipitation method. The surface properties of the material were characterized by Fourier transform infrared spectra (FTIR), scanning electron microscopy (SEM), and X-ray diffraction (XRD). The second part investigates the adsorption of CV dye onto the surface of the prepared Mn-ZnO NPs. Additionally, the isotherm, kinetics, and thermodynamics of the adsorption process were studied in detail. Batch adsorption analysis was carried out by evaluating different parameters, such as the amount of the adsorbent (0.01g to 0.04 g), CV concentration (20 to 80 mg/L), adsorption time (30 to 120 min), and temperature (35 to 65 ⁰C). The maximum CV dye adsorption capacity of the Mn-ZnO NPs was 45.60 mg/g. The thermodynamic study revealed the spontaneous, exothermic, and feasible nature of the adsorption process, primarily driven


Introduction
Heavy metal ions and synthetic organic dyes harm human health and living organisms, causing environmental pollution.Synthetic organic dyes are widely used in various industries and have become indispensable.Crystal violet (CV), a cationic triphenylmethane dye, is frequently used in various industrial applications.This harmful and toxic material does not break down and causes many serious diseases in humans, including cancer.Long-term exposure to this dye, even in minimal proportions, leads to serious health complications for humans (Homagai et al. 2022).In recent years, growing concerns about water pollution, climate change, limited natural resources, and public health have increased the importance of developing environmentally friendly products and procedures.Adsorption is one of the viable methods to remove dyes from wastewater.It is proven to be an effective strategy because it is simple, inexpensive, and sustainable, allowing the adsorbent to be reused.Adsorption has been widely applied in research to remove organic dyes and heavy metals.The efficiency of the dye removal through adsorption greatly relies on the adsorbent used.
Elimination of dyes from wastewater can be achieved using various adsorbents in adsorption techniques, one of which is nanostructured metal oxides.Metal oxide nanoparticles have proven to be effective adsorbents due to their easy and cost-effective synthesis, requiring minimal quantities for the successful removal of pollutants.Additionally, they are favored for their strength, high surface reactivity, and high adsorption capacity (Kasbaji et al. 2023).
Zinc oxide nanoparticles are among the metal oxides extensively employed as adsorbents due to their distinct chemical, physical, and photocatalytic properties.Additionally, ZnO nanoparticles exhibit extraordinary efficacy in the removal of heavy metal ions and dyes from water-based solutions.The physicochemical characteristics of ZnO nanoparticles can be significantly modified by doping them with a secondary metal element to improve adsorption efficiency and selectivity (Jadoun et al. 2024).Nanobiotechnology, an emerging and rapidly growing field, involves the synthesis of nanoscale materials.Plant extracts are commonly used for this synthesis due to their safety, ready availability, lack of toxicity, and the presence of diverse active phytochemicals, which facilitate the reduction of metallic ions (Aigbe and Osibote, 2024).
Peganum Harmala L., a plant from the Zygophyllaceae family, thrives naturally in North Africa and the Middle East.Its seeds are rich in therapeutic alkaloids, known as harmala alkaloids, as well as anthraquinones, flavonoids, and polysaccharides, Additionally, Peganum Harmala possesses a wide array of biological components with antioxidant, antimicrobial, and anticancer activities (Zhu et al. 2022).Peganum Harmala L. seed powder has been reported as a green absorbent for heavy metals such as Ni (Ghasemi et al. 2014), Co (Alsaiari, 2022), Fe (Alsaiari et al. 2024), and Cu (Alsaiari et al. 2021).Moreover, the seed extract has been used to synthesize various metals and metal oxides for different applications.Biogenic synthesis of Au, Ag (Ullah et al. 2024), Pt, Pd (Fahmy et al. 2021), CuO (Fekri et al. 2022), and ZnO (Mehar et al. 2019) has been reported using Peganum Harmala seeds.The active components, such as harmala alkaloids, anthraquinones, and flavonoids, are responsible for the bioreduction of various metal ions (Fekri et al. 2022;Mehar et al. 2019).
In this work, Peganum Harmala seed extract was used as a green agent in the synthesis of Zinc oxide which doped with 10% Mn ions.The resulting material was applied as an adsorbent to eliminate CV dye from aqueous systems.To derive the adsorption isotherm models and kinetics, the impact of various factors on the adsorption process of CV dye was considered, including adsorbent quantity, contact duration, initial dye concentration, and temperature.The thermodynamic parameters were also determined to assess the viability of CV adsorption onto Mn-doped ZnO.

Materials
Peganum Harmala seeds were purchased from a local store.The chemicals, which were of analytical grade and used without any additional treatment, were obtained from Sigma-Aldrich (Germany).These chemicals included crystal violate dye (CV), zinc sulfate heptahydrate (ZnSO 4 .7H 2 O), manganese sulfate monohydrate (MnSO 4 .H 2 O), ethanol, and sodium hydroxide (NaOH).Deionized milli-Q water, obtained from the Millipore-Milli-Q CLX 7080 system (MillporeSigma, USA) was used in the preparation of all aqueous solutions.

Preparing the Peganum Harmala Seeds extract.
Peganum Harmala seeds were thoroughly rinsed with deionized water to eliminate any contaminants and then left to dry in the open air.Ten grams of the dried seeds were weighed and transferred into a round-bottom flask fitted with a condenser, followed by the addition of 100 mL of deionized water.The mixture was heated for 45 minutes at 80 °C.After heating, the mixture was left to cool at room temperature.The Peganum Harmala seeds were then removed by filtration, and the aqueous extract was collected and stored at 4 ⁰C (Fekri et al. 2022).

Synthesis of 10% Mn-doped ZnO
A green method was adopted to prepare the Mn-doped ZnO adsorbent using the alkaline co-precipitation technique with Peganum Harmala seed extract.To synthesize the 10% Mn-ZnO catalyst, 7.030 g (24.45 mmoles) of Zn SO 4 .7H 2 O and 0.4141 g (2.45 mmoles) of MnSO 4 .H 2 O were added to 100 mL of the Peganum Harmala seed aqueous extract.The mixture was stirred with a magnetic stirrer for 2 hours at ambient temperature.Then, 2M NaOH was added gradually until the pH was adjusted to 11, monitored using a digital pH meter (model 744, Metrohm AG, Switzerland) equipped with a combined glass electrode.The resultant precipitate was subjected to centrifugation, followed by two washes with deionized water and ethanol.Subsequently, it was dried at 80°C in an oven for 24 hours.The powdered sample was then calcined at 300°C for 3 hours (Lemecho et al. 2022).

Characterization of Mn-Doped ZnO Nanostructures
The surface morphology and elemental composition of Mn-ZnO nanoparticles (NPs) were investigated using a JEOL JSM-7600F Field Emission Scanning Electron Microscope (JEOL, Japan).Fourier transform infrared (FT-IR) spectroscopy was performed using a 100 FT-IR Spectrometer (Perkin Elmer, USA) to determine the functional groups within the wavenumber range of 400 to 4000 cm -1 .The crystallographic arrangement of Mn-doped ZnO was examined using an X'Pert Pro powder X-ray Diffractometer (Malvern PANalytical, UK).Optical absorption was measured at room temperature using a GENESYS 10S UV-Vis Spectrophotometer (Thermo Fisher Scientific, USA) in the wavelength range of 200-800 nm.

Dye adsorption experiments
The following batch adsorption tests were performed: In a conical flask, 25 mL of a stock solution containing 40 mg/ L of the crystal violet (CV) dye was added.The solution and a set quantity of adsorbent (0.02 g) were then stirred at room temperature for 60 minutes.The supernatant underwent centrifugation at 2000 rpm.The quantity of crystal violet dye adsorbed onto the sorbent and the removal percentage were determined using the equations provided below (Ahmadi & Ganjidoust, 2021;Kumar & Kirthika, 2010;Paksamut & Boonsong, 2018).
4 was added gradually until the pH was adjusted to 11, monitored using a digital pH r (model 744, Metrohm AG, Switzerland) equipped with a combined glass electrode.The tant precipitate was subjected to centrifugation, followed by two washes with deionized and ethanol.Subsequently, it was dried at 80°C in an oven for 24 hours.The powdered le was then calcined at 300°C for 3 hours (Lemecho et al. 2022).

acterization of Mn-Doped ZnO Nanostructures
surface morphology and elemental composition of Mn-ZnO nanoparticles (NPs) were tigated using a JEOL JSM-7600F Field Emission Scanning Electron Microscope (JEOL, ).Fourier transform infrared (FT-IR) spectroscopy was performed using a 100 FT-IR trometer (Perkin Elmer, USA) to determine the functional groups within the wavenumber of 400 to 4000 cm -1 .The crystallographic arrangement of Mn-doped ZnO was ined using an X'Pert Pro powder X-ray Diffractometer (Malvern PANalytical, UK). the sorbent and the removal percentage were determined using the equations provided (Ahmadi & Ganjidoust, 2021;Kumar & Kirthika, 2010;Paksamut & Boonsong, 2018).
e, q e is the adsorption capacity measured in mg/g, while C o and C e represent the initial quilibrium concentrations of crystal violate dye in water post the removal process (mg/ spectively.V stands for the solution volume (L), and W corresponds to the amount of oped ZnO adsorbent used (g).The adsorption efficiency (%R) was used as the analytical nse.To achieve optimal results, the study explored the influence of Mn-doped ZnO Where, q e is the adsorption capacity measured in mg/g, while C o and C e represent the initial and equilibrium concentrations of crystal violate dye in water post the removal process (mg/ L), respectively.V stands for the solution volume (L), and W corresponds to the amount of Mn-doped ZnO adsorbent used (g).The adsorption efficiency (%R) was used as the analytical response.To achieve optimal results, the study explored the influence of Mn-doped ZnO dosages (0.01, 0.02, 0.03, and 0.04 g), initial CV concentration (20, 40, 60, and 80 mg/L), exposure time (30, 60, 90, and 120 min), and temperature (35, 45, 55, and 65 ⁰C).

Characterization of Mn-ZnO
Figure 1(a) shows the X-ray diffraction pattern of Mn-doped ZnO nanoparticles.The figure illustrates several diffraction peaks, indicating the polycrystalline nature of the synthesized powder.The primary diffraction peak was recorded at 36.34 o corresponding to the reflection peak of (101) according to ICDD card number 79-2205 for the hexagonal ZnO phase.ZnO exists in three phases: cubic Zinc blende, hexagonal Wurtzite, and rock salt phases (Shaba et al. 2021).The hexagonal Wurtzite phase is recognized as the thermodynamically most stable phase among these three, and it is usually obtained as reported by many authors (Al-Kahlout, 2012;Darroudi et al. 2013;Liu et al. 2002;Sriram et al. 2017;Theyvaraju & Muthukumaran, 2015;Yildirimcan et al. 2016).The other two phases are considered metal-stable phases which need special conditions for preparation.
The deposited powder shows a preferred orientation in ( 101) direction as recorded.The other diffraction peaks are indexed to different planes, as shown in Figure 1.The three strongest diffraction peaks belong to the ( 002), (100), and (101) planes.These high intensities of these planes are attributed to the low surface free energy of formation.Andrade et al. (Paraguay et al. 1999) revealed that the surface free energy densities of these three planes are 9.9, 12.3, and 20.9 eV/nm 2 for (002), ( 110), and (100), respectively.No additional peaks related to any other phases, such as copper oxide or manganese oxide, were recorded, confirming the singularity of the ZnO phase and the good solubility of Mn into ZnO.This could be due to the low concentration of Mn, which is below the recorded solubility limit of Mn (30% (Mandal et al. 2006)) in ZnO.Additionally, the similar ionic radii of Mn and Zn facilitate the substitution of Zn by Mn, preventing the segregation of Mn into separate grains (Mn 2+ (0.8Å (Castañeda et al. 2005)), Mn 3+ (0.65Å (Trari et al. 2005)) and Zn 2+ (0.74Å (Aboud et al. 2019)).
Scherer's equation is applied to estimate the crystallite size of the deposited powder (Aboud et al. 2023);

Characterization of Mn-ZnO
Figure 1(a) shows the X-ray diffraction pattern of Mn-doped ZnO nanoparticles.
illustrates several diffraction peaks, indicating the polycrystalline nature of the s powder.The primary diffraction peak was recorded at 36.34 o corresponding to the peak of (101) according to ICDD card number 79-2205 for the hexagonal ZnO p exists in three phases: cubic Zinc blende, hexagonal Wurtzite, and rock salt phases al. 2021).The hexagonal Wurtzite phase is recognized as the thermodynamically m phase among these three, and it is usually obtained as reported by many authors (A 2012; Darroudi et al. 2013;Liu et al. 2002;Sriram et al. 2017;Theyvaraju & Muth 2015;Yildirimcan et al. 2016).The other two phases are considered metal-sta which need special conditions for preparation.
The deposited powder shows a preferred orientation in ( 101) direction as The other diffraction peaks are indexed to different planes, as shown in Figure 1.
strongest diffraction peaks belong to the ( 002), (100), and ( 101) planes.These high of these planes are attributed to the low surface free energy of formation.And (Paraguay et al. 1999) revealed that the surface free energy densities of these three 9.9, 12.3, and 20.9 eV/nm 2 for (002), ( 110), and (100), respectively.No additio related to any other phases, such as copper oxide or manganese oxide, were confirming the singularity of the ZnO phase and the good solubility of Mn into could be due to the low concentration of Mn, which is below the recorded solubili Mn (30% (Mandal et al. 2006)) in ZnO.Additionally, the similar ionic radii of M facilitate the substitution of Zn by Mn, preventing the segregation of Mn into sepa (Mn 2+ (0.8Å (Castañeda et al. 2005)), Mn 3+ (0.65Å (Trari et al. 2005)  Where denotes the incident X-ray wavelength, represents the full wid maximum, and is the center of the diffraction peak, the average crystallite size wa Where λ denotes the incident X-ray wavelength, β represents the full width at half maximum, and is the center of the diffraction peak, the average crystallite size was found to be 36.5 nm.This value has been documented by Bououdina et al (Bououdina et al. 2014) for Mn-doped ZnO nanoparticles synthesized through the Sol-Gel method.Also, in the work of Mote et al (D. Mote et al. 2013) the crystallite size was found to range from 42.5 to 33.64 nm as Mn content increases.
The lattice parameters (a and c), lattice volume (V), and the Zn-O bond length can be estimated using the following equations (Aboud et al. 2023), (Seetawan et al. 2011); be 36.5 nm.This value has been documented by Bououdina et al (Bououdina et al. 2014) Mn-doped ZnO nanoparticles synthesized through the Sol-Gel method.Also, in the work  The lattice parameters of the prepared powder were found to be a=3.245Å and c=5.196Å.These values are slightly smaller than the recorded values in the ICDD card, which are a=3.25 and c=5.2Å.Consequently, the volume is recorded to be 47.398Å 3 , which is smaller than the ICDD value of 47.63Å 3 .This reduction in lattice volume can be explained by the replacement of Zn 2+ with Mn 2+ , which has a smaller ionic radius.The bond length was found to be 2.01 Å, matching the value of the Zn-O bond in bulk ZnO (Chen et al. 2019).
Figure 1(b) shows the FT-IR spectrum of the deposited Mn-doped ZnO nanoparticles, revealing several absorption peaks.The IR spectrum depends not only on the nature of the material but also on its morphology (Yang et al. 2009).The broad peak between 2970 to 3660 cm −1 is assigned to water molecules present in the nanoparticles or adsorbed on the surface (Khan et al. 2011).Weak peaks at 1408 cm −1 and 1596 cm −1 correspond to the vibrations of symmetric and asymmetric C=O bonds, respectively.Additional bands were detected at below 1400 cm −1 associated with Zn-O bond vibrations (Zafar et al. 2019).
The surface morphology, grain size, and chemical composition of the prepared powder have been investigated using SEM and EDX techniques.Figure 2 displays the SEM image of the prepared powder along with the statistical distribution of the recorded grains.The figure shows particles of various shapes with irregular size distribution.The average particle size was measured to be 209.6 nm, significantly larger than the calculated crystallite size obtained from Scherer's equation.This discrepancy could be attributed to the agglomeration phenomena.Figure 3 shows the EDX spectrum, where Zn, Mn, and O peaks are recorded at their regular positions.The elemental ratios of the recorded elements are found to be O:Mn: Zn = 54.62:0.2:45.18.
The UV-Vis spectrometer was employed to examine the optical characteristics of ZnO doped with Mn at room temperature.The analysis revealed a decrease in absorbance with an increase in wavelength, as illustrated in Figure 4. Tauc's relation was then applied to the UV-Vis absorbance data to construct plots for calculating the energy band gap (Eg): Where α is the absorption coefficient, h is Planck's constant, Eg is the optical band gap of a semiconductor, ν is the photon frequency, and A is the proportionality constant.The band gap can be determined by extending the linear portion of the (αhν)² versus hν plot to the X-axis.The point of intersection on the X-axis provides the band gap value.The estimated Eg value of the Mn-doped ZnO is 2.9 eV, as shown in Figure 4, exhibiting a slight decrease compared to the generally acknowledged value.This agrees with the reported values by Ahmed (Ahmed, 2017).It is reported that a higher concentration of Mn in ZnO (Mn>4%) causes a decrease in the optical band (Singh et al. 2016).

Absorption study Effect of Adsorbent dose
The influence of the dosage of Mn-ZnO on CV removal was studied by varying the dosage from 0.01, 0.02, 0.03, and 0.04 g at an initial CV concentration of 40 mg/L.As shown in Figure 5, Mn-doped ZnO nanoparticles exhibited a rise in removal percentage, achieving 91% removal at a dosage of 0.01 g.There was no additional increase in the amount of Crystal   Violet dye adsorbed when the adsorbent dose was increased beyond 0.01g.The adsorption potential of an adsorbent at a particular starting concentration is largely dependent on the adsorbent dosage.One primary explanation for the variance in adsorption capabilities at different adsorbent doses is the number of accessible adsorption sites.As the dosage increased, the adsorbent's surface area and active sites became more accessible for adsorption.However, once adsorption reached equilibrium, the additional adsorbent dosage induced unavailable sites that did not contribute to further adsorbate uptake (Elsayed et al. 2020).Moreover, the equilibrium concentration of Mn-doped ZnO nanoparticles was lower despite the increased adsorbent dosage, which increased the interference of the adsorbent surface among the active groups.This occurred because there was insufficient driving force for the adsorbate to spread and bind to the adsorbent surface.These results align with earlier investigations (Park et al. 2008).

Effect of contact time
The time needed to achieve equilibrium is a crucial element in the wastewater treatment process.The impact of contact time on CV adsorption on Mn-doped ZnO was investigated at varying times (30, 60, 90, 120 min).Figure 6 displays the results of this effect on CV removal efficiency and adsorption capacity.The findings indicate that the adsorption efficacy for CV and the percentage elimination of CV increased as the contact time increased, reaching equilibrium after 30 min.The abundant pores in the Mn ZnO structure led to a faster transfer of CV mass from the solution onto the material, resulting in faster adsorption at the initial contact.This demonstrates the strong accessibility of adsorbent's CV binding sites, which is favorable for efficient adsorption.Mn-ZnO can bind CV in two different ways.CV can be readily adsorbed by the mesoporous Mn-ZnO material due to the abundant active sites and strong mass transfer driving force in the initial phase of adsorption.However, over time, a significant layer of CV builds up on the surface of Mn-ZnO, limiting the available active sites and obstructing the mobility of CV, leading to nonlinear adsorption.After suitable contact times of 30 and 60 minutes, the highest percentage of CV removal was achieved, reaching 91.20%.

Effect of initial CV concentration
The influence of initial CV concentration (20, 40, 60, 80 mg/L) on the removal efficiency of CV by Mn-ZnO is shown  in Figure 7.The graph indicates that the adsorbed amount increases very marginally with increasing concentrations, exhibiting an upward incline at low concentrations and a steady, flat plateau at higher values.At equilibrium, the adsorption capacity (q e ) rose from 22.24 mg/g to 44.70 mg/g when the initial CV concentration increased from 20 mg/L to 40 mg/L respectively.At a concentration of 80 mg/L, the highest adsorption capacity recorded was 95.14 mg/g.The increase in the initial concentration enhanced the driving power of mass transfer, leading to increased CV adsorption.
At an initial concentration of 20 mg/L, the efficiency of CV removal was 94%.

Effect of Temperature
To investigate the impact of the temperature on the adsorption process of CV, experiments were conducted at various temperatures: 35, 45, 55, and 65°C, while maintaining the CV concentration at 40 mg/L.Figure 8 shows that as the temperature increased from 35°C to 45°C, both the percentage removal of CV and the adsorption capacity increased.The amount of CV adsorbed onto Mn-ZnO increased from 45.18 mg/g to 45.53 mg/g.As temperature increased, adsorbent degradation altered the sorbent's surface chemistry, enhancing the accessibility of active functional groups and decreasing CV adsorption.In addition, the increased temperature facilitated the desorption process by altering bond structures (Sharaf & Hassan, 2014).This effect was due to the diminished boundary layer thickness with increasing temperature, which caused metal ions to escape from the surface into the solution phase, limiting the adsorption capacity.Similar findings have been reported by Sharaf and Hassan (2014).

Adsorption Isotherms
The isotherms of the adsorption are produced using the wellknown Langmuir and Freundlich isotherm models to identify the appropriate model for optimizing the adsorption processes.The Langmuir isotherm presumes homogenous adsorption, whereas the Freundlich isotherm is an empirical equation  Where C e represents the initial CV concentration, q max (mg/g) is the maximum capacity of the monolayer, and b represents a Langmuir adsorption constant.The Langmuir constants b and q max were derived from the slope and intercept (Figure 9).Langmuir isotherm asserts that while undergoing the adsorption process, there is no interaction between adsorbate molecules after the formation of a monolayer (Langmuir, 1916).A dimensionless equilibrium parameter (R L ) can be employed to characterize the fundamental features of the Langmuir isotherm.This parameter's definition is as follows: the adsorption is considered unfavorable when R L is greater than 1; linear when R L is equal to 1, favorable when R L is within the range of 0 to 1, or irreversible when R L is at 0 (Owoeye et al. 2019).Here, R L fell within the range of 0-1, signifying the favorable adsorption of CV onto the Mn-ZnO.The monolayer adsorption capacity of CV, as determined by Langmuir isotherm, was 94.3 mg/g.e 9: Langmuir isotherm model for adsorption of CV dye on Mn-doped ZnO Where C e represents the initial CV concentration, q max (mg/g) is the maximum capacity of the monolayer, and b represents a Langmuir adsorption constant.The Langmuir constants b and q max were derived from the slope and intercept (Figure 9).Langmuir isotherm asserts that while undergoing the adsorption process, there is no interaction between adsorbate molecules after the formation of a monolayer (Langmuir, 1916).A dimensionless equilibrium parameter (R L ) can be employed to characterize the fundamental features of the Langmuir isotherm.This parameter's definition is as follows: the adsorption is considered unfavorable when R L is greater than 1; linear when R L is equal to 1, favorable when R L is within the range of 0 to 1, or irreversible when R L is at 0 (Owoeye et al. 2019).Here, R L fell within the range of 0-1, signifying the favorable adsorption of CV onto the Mn-ZnO.The monolayer adsorption capacity of CV, as determined by Langmuir isotherm, was 94.3 mg/g.The Freundlich isotherm is an experimental model that can be represented by the following equation: he Freundlich isotherm is an experimental model that can be represented by the equation: f and n are the Freundlich constants, denote the adsorbent's capacity and the intensity tion, respectively, q e stands for the amount adsorbed per unit of adsorbent at m (mg/g), and C e is the concentration of dye at the equilibrium (mg/L).Figure 10 a linear regression plot log q e against log C e , the Freundlich constants K f and n are rived from that plot (Freundlich, 1906).From the Freundlich isotherm, the value of fies the favorability of the isotherm type: it is favorable when 1/n is smaller than 1 orable when 1/n is greater than 1.That accounts for the arrangement of active sites urface as well as any element that causes the adsorbent-adsorbate interaction to ith increasing surface density.
able 1 provides the parameters of the Langmuir and Freundlich isotherm models, K f and n are the Freundlich constants, denote the adsorbent's capacity and the intensity of adsorption, respectively, q e stands for the amount adsorbed per unit of adsorbent at equilibrium (mg/g), and C e is the concentration of dye at the equilibrium (mg/L).Figure 10 illustrates a linear regression plot log q e against log C e , the Freundlich constants K f and n are easily derived from that plot (Freundlich, 1906).From the Freundlich isotherm, the value of 1/n signifies the favorability of the isotherm type: it is favorable when 1/n is smaller than 1 and unfavorable when 1/n is greater than 1.That accounts for the arrangement of active sites on the surface as well as any element that causes the adsorbent-adsorbate interaction to weaken with increasing surface density.
Table 1 provides the parameters of the Langmuir and Freundlich isotherm models, along with correlation coefficients, for the adsorption of CV on Mn-ZnO.Based on the correlation coefficient R 2 values from the isotherm models, the adsorption data demonstrated better conformity with the Freundlich isotherm (R 2 = 0.99) compared to the Langmuir model (R 2 = 0.92) (Solmaz et al. 2024).Both K f and n values of the present investigation indicate that CV adsorption on Mn-ZnO is favorable.

Adsorption kinetics studies
The two kinetic models, namely the pseudo-first-order and pseudo-second-order models, were employed to fit the adsorption mechanisms and identify potential rate-determining phases.The solid capacitance is a key factor in the pseudo-firstorder model, while the pseudo-second-order model effectively replicates the sorption of analytes from aqueous solutions when chemisorption involves the integration of valence forces.This encompasses the sharing or exchange of electrons between adsorbents and forces (Taha et al. 2017).

Langmuir
Freundlich   The following equation can be applied to the pseudo-firstorder kinetic model: 10 nifies the favorability of the isotherm type: it is favorable when 1/n is smaller than 1 favorable when 1/n is greater than 1.That accounts for the arrangement of active sites surface as well as any element that causes the adsorbent-adsorbate interaction to with increasing surface density.
Table 1 provides the parameters of the Langmuir and Freundlich isotherm models, ith correlation coefficients, for the adsorption of CV on Mn-ZnO.Based on the tion coefficient R 2 values from the isotherm models, the adsorption data demonstrated onformity with the Freundlich isotherm (R 2 = 0.99) compared to the Langmuir model .92)(Solmaz et al. 2024).Both K f and n values of the present investigation indicate adsorption on Mn-ZnO is favorable.ich isotherm model for adsorption of CV dye on Mn-doped ZnO isotherms parameters for CV dye adsorption Mn-doped ZnO.

tion kinetics studies
o kinetic models, namely the pseudo-first-order and pseudo-second-order models, were ed to fit the adsorption mechanisms and identify potential rate-determining phases.lid capacitance is a key factor in the pseudo-first-order model, while the pseudo--order model effectively replicates the sorption of analytes from aqueous solutions hemisorption involves the integration of valence forces.This encompasses the sharing ange of electrons between adsorbents and forces (Taha et al. 2017).
lowing equation can be applied to the pseudo-first-order kinetic model: Here q i and q t (mg/g) denote the quantities of CV adsorbed onto Mn ZnO surface at rium and time t, respectively; the rate constant for the pseudo-first-order kinetic model Here q i and q t (mg/g) denote the quantities of CV adsorbed onto Mn ZnO surface at equilibrium and time t, respectively; the rate constant for the pseudo-first-order kinetic model is represented by k 1 (min⁻¹).A linear relationship was achieved by plotting ln(q e -q t ) against time 't' (refer to Figure 11), and from this linear trend, the rate constant k 1 was determined.
The pseudo-second-order kinetic model is described as follows: ted by k 1 (min⁻¹).A linear relationship was achieved by plotting ln(q e -q t ) against er to Figure 11), and from this linear trend, the rate constant k 1 was determined.irst-order plot of CV adsorption on Mn-doped ZnO e pseudo-second-order kinetic model is described as follows: displays the standard graph for the fictitious second-order problem.cond-order plot of CV adsorption on Mn-doped ZnO le 2 displays the kinetic parameters for the pseudo-first order and pseudo-second els.The correlation factor R 2 for both models was 0.99.The q e theoretical value from the pseudo-first-order model varies significantly from the actual observed gesting that this model does not represent the adsorption kinetics.In contrast, the ond-degree model shows great compatibility with the experimental data for CV (Gul et al. 2023).The outcomes show that the adsorption of CV by the Mn-ZnO is governed by a chemisorption process, with the pseudo-second-order binding predominating.This process involves valence forces through the exchange of etween the dye and adsorbent.A significant affinity exists between CV and the as demonstrated by the short half-adsorption time and the high removal efficiency rameters and correlation coefficients for CV adsorption on Mn-doped ZnO.rption capacity q e(exp) = 45.60 mg/g] namic Parameters odynamic analysis provides important insights into the adsorption mechanism.Table 2 displays the kinetic parameters for the pseudo-first order and pseudo-second order models.The correlation factor R 2 for both models was 0.99.The q e theoretical value calculated from the pseudo-first-order model varies significantly from the actual observed value, suggesting that this model does not represent the adsorption kinetics.In contrast, the pseudo-seconddegree model shows great compatibility with the experimental data for CV adsorption (Gul et al. 2023).The outcomes show that the adsorption of CV by the Mn-ZnO adsorbent is governed by a chemisorption process, with the pseudo-second-order binding mechanism predominating.This process involves valence forces through the exchange of electrons between the dye and adsorbent.A significant affinity exists between CV and the adsorbent, as demonstrated by the short half-adsorption time and the high removal efficiency of CV.

Thermodynamic Parameters
The thermodynamic analysis provides important insights into the adsorption mechanism.Various thermodynamic parameters are obtained to comprehend the adsorption process, such as the changes in the entropy (ΔS°), enthalpy (∆H°), and free energy (ΔG°).These parameters were determined using the equations below: 11 is represented by k 1 (min⁻¹).A linear relationship was achieved by plotting ln(q e -q t ) a time 't' (refer to Figure 11), and from this linear trend, the rate constant k 1 was determine Figure 11: Pseudo-first-order plot of CV adsorption on Mn-doped ZnO The pseudo-second-order kinetic model is described as follows: Figure 12 displays the standard graph for the fictitious second-order problem.
Figure 12: Pseudo-second-order plot of CV adsorption on Mn-doped ZnO Table 2 displays the kinetic parameters for the pseudo-first order and pseudo-s order models.The correlation factor R 2 for both models was 0.99.The q e theoretical calculated from the pseudo-first-order model varies significantly from the actual obs value, suggesting that this model does not represent the adsorption kinetics.In contra pseudo-second-degree model shows great compatibility with the experimental data fo adsorption (Gul et al. 2023).The outcomes show that the adsorption of CV by the Mn adsorbent is governed by a chemisorption process, with the pseudo-second-order bi mechanism predominating.This process involves valence forces through the exchan electrons between the dye and adsorbent.A significant affinity exists between CV an adsorbent, as demonstrated by the short half-adsorption time and the high removal effic of CV.
Table 2. Kinetic parameters and correlation coefficients for CV adsorption on Mn-doped ZnO.

Thermodynamic Parameters
The thermodynamic analysis provides important insights into the adsorption mecha Various thermodynamic parameters are obtained to comprehend the adsorption process as the changes in the entropy (ΔS°), enthalpy (∆H°), and free energy (ΔG°).These param were determined using the equations below: Based on the slope and y-intercept of the log k d against temperature (measu Kelvin) plot in Figure 13, the values of ∆H° and ∆S° are depicted.Table 3 summariz information regarding the thermodynamic characteristics associated with the adsorption CV process on Mn-doped ZnO.The adsorption is identified as exothermic due to the ne ΔG = -RTlnK Based on the slope and y-intercept of the log k d against temperature (measured in Kelvin) plot in Figure 13, the values of ∆H° and ∆S° are depicted.Table 3 summarizes the information regarding the thermodynamic characteristics associated with the adsorption of the CV process on Mndoped ZnO.The adsorption is identified as exothermic due to the negative ∆H° value.The ΔS° value was positive, which confirms that the adsorption process occurs randomly at the solid solution interface between Mn-ZnO and CV solution.
al absorption was measured at room temperature using a GENESYS 10S UV-Vis trophotometer (Thermo Fisher Scientific, USA) in the wavelength range of 200-800 nm.dsorption experiments following batch adsorption tests were performed: In a conical flask, 25 mL of a stock ion containing 40 mg/ L of the crystal violet (CV) dye was added.The solution and a set tity of adsorbent (0.02 g) were then stirred at room temperature for 60 minutes.The natant underwent centrifugation at 2000 rpm.The quantity of crystal violet dye adsorbed ) and Zn 2+ (0.74 et al. 2019)).

Figure 1 :
Figure 1: XRD pattern and FT-IR spectra for Mn-doped ZnO nanoparticles Scherer's equation is applied to estimate the crystallite size of the deposit (Aboud et al. 2023); Mote et al (D.Mote et al. 2013)  the crystallite size was found to range from 42.5 to 33.64 as Mn content increases.The lattice parameters (a and c), lattice volume (V), and the Zn-O bond length can estimated using the following equations(Aboud et al. 2023),(Seetawan et al. 2011); , where The lattice parameters of the prepared powder were found to be a=3.245Å a c=5.196Å.These values are slightly smaller than the recorded values in the ICDD ca where be 36.5 nm.This value has been documented by Bououdina et al (Bououdina Mn-doped ZnO nanoparticles synthesized through the Sol-Gel method.Also, Mote et al (D.Mote et al. 2013) the crystallite size was found to range from 42 as Mn content increases.The lattice parameters (a and c), lattice volume (V), and the Zn-O bon estimated using the following equations (Aboud et al. 2023), (Seetawan et al. 2 , where The lattice parameters of the prepared powder were found to be a c=5.196Å.These values are slightly smaller than the recorded values in t

Figure 2 .
Figure 2. SEM image for Mn-doped ZnO nanoparticle and the statistical distribution of the grain size.

Figure 4 .
Figure 4. UV spectrum and Energy band gap of Mn-doped ZnO.

Figure 5 .
Figure 5.Effect of adsorbent dose on a) adsorption capacity and b) removal efficiency of CV.

Figure 6 .
Figure 6.Effect of contact time on a) adsorption capacity and b) removal efficiency of CV.

Figure 8 .
Figure 8.Effect of temperature on a) adsorption capacity and b) removal efficiency of CV.

Figure 7 .
Figure 7. Effect of initial CV dye concentration on a) adsorption capacity and b) removal efficiency of CV.

Figure 9 .
Figure 9. Langmuir isotherm model for adsorption of CV dye on Mn-doped ZnO.

Figure 10 .
Figure 10.Freundlich isotherm model for adsorption of CV dye on Mn-doped ZnO.

Figure 12
Figure12displays the standard graph for the fictitious second-order problem.Table2displays the kinetic parameters for the pseudo-first order and pseudo-second order models.The correlation factor R 2 for both models was 0.99.The q e theoretical value calculated from the pseudo-first-order model varies significantly from the actual observed value, suggesting that this model does not represent the adsorption kinetics.In contrast, the pseudo-seconddegree model shows great compatibility with the experimental data for CV adsorption(Gul et al. 2023).The outcomes show that the adsorption of CV by the Mn-ZnO adsorbent is governed

Figure 13 .
Figure 13.Thermodynamic behavior during the adsorption of CV.

Table 2 .
Kinetic parameters and correlation coefficients for CV adsorption on Mn-doped ZnO.[Experimental adsorption capacity q e(exp) = 45.60 mg/g].

Table 3 .
Thermodynamic parameters for CV adsorption on Mn-doped ZnO.