Friendly Green Synthesis of Cerium Oxide Nanoparticles Using Citrus Aurantuim Extract and Applied in Removal of Eosin Yellow Dye

INTRODUCTION

Nanotechnology is a vital area of modern research that deals with the design, synthesis, and manipulation of particle structures ranging in size from 1 to 100 nm [1]. The prefix Nano is derived from the Greek word Nanos, which means “dwarf”, and refers to one billionth10^-9m) in size [2]. Nanoparticles have numerous applications in fields such as health care, cosmetics, food and feed, environmental health, mechanics, optics, biomedical sciences, chemical industries and electronics, space industries, drug-gene delivery, energy science, electronics, catalysis, single-electron transistors, light emitters, nonlinear optical devices, and photoelectron chemical applications [3,4]. New advancements in nanotechnology are progressively driven by artificial intelligence (AI). Techniques like machine learning optimize synthesis processes, predict nanoparticle properties, and improve the material design. Hassan et al. highlighted how AI reduces resource use and fosters eco-friendly novelty, introductory new applications in environmental remediation, biomedicine, and energy storage [5]. There are numerous physical, chemical, biological, and hybrid methods for synthesizing various types of nanoparticles [6]. To synthesize NPs, the most common chemical approaches, such as chemical reduction using a variety of organic and inorganic reducing agents, electrochemical techniques, physicochemical reduction, and radiolysis, are widely used. The distinct properties of biologically synthesized NPs are preferred over physical-chemically produced nanomaterials [7,8]. Biologically synthesized nanoparticles hold great potential for advancing health care and environmental applications, offering eco-friendly and biocompatible solutions [9]. Green synthesis of NPs from metal ions is more eco-friendly, free of chemical contamination, less expensive, and safe for biological applications. Green chemistry allows us to obtain the necessary substance in the safest possible way. It provides the selection of raw materials and process schemes, which exclude harmful substances, and toxic and hazardous chemicals, and focuses on industrial processes that do not pollute the environment [10]. Currently, chemistry is witnessing a significant development with the emergence of a novel and comprehensive scientific trajectory known as “green” chemistry. The field of “green” chemistry encompasses various disciplines, including synthetic organic chemistry, analytical chemistry, physical chemistry, toxicology, microbiology, biotechnology, and engineering [11]. The goal of green chemistry is to develop technologies for more efficient chemical reactions. Green chemistry aims to prevent pollution in the very early stages of the planning and implementation of chemical processes and covers all types and aspects of chemical processes to minimize environmental risks [12]. The problems within the competence of green chemistry can be categorized into two main areas. The first relates to the processing and utilization of environmentally hazardous waste and by-products of the chemical industry [13,14] The second, more promising, involves the development of new industrial processes to eliminate or minimize the form In green chemistry, fundamentally new constructs such as ideal process, ideal product and ideal consumer are used, ideal process is a simple, eco-friendly, one-stage process, effective at the molecular level, with the use of renewable raw materials, which provides maximum yield, ideal product requires a minimum of energy and packaging, is safe, recyclable and fully degradable by microorganisms [15]. The green synthesis of CeO₂ NPs using Citrus aurantuim peel extract entails the discount of cerium ions by way of bioactive compounds present in the extract, which includes flavonoids and phenolic acids [16].The goal of this study is a green synthesis technique for cerium oxide (CeO₂) NPs using hexane extract from Citrus aurantuim peels. This method seeks to harness the natural antioxidant in the extraction beginning with the collection of fresh Citrus aurantium peels to provide CeO₂ NPs in a friendly environmental way. They take a look at will systematically look into the synthesis parameters to optimize the system, signify the ensuing nanoparticles in terms of size, crystallinity, and surface properties, and examine them in the removal of Eosin yellow dye. These studies have substantial implications for both nanotechnology and environmental sustainability as shown in Fig. 1.

MATERIALS AND METHODS

Materials, Reagents, and instrumentations

The source of Citrus uranium peels is Karbala, Iraq, which serves as the renewable uncooked fabric. Hexane purity of 99% facilitated the extraction of bioactive compounds supplied by (BDH, England). The cerium chloride (CeCl₃.6H₂O) purity of 99% was bought from (Merck, Germany). Ethanol purity of 99% and ammonia of 35% were purchased by (BDH). Eosin yellow dye (C₂₀H₆Br₄Na₂O₅) purity is 99% with acidic natural. The characterization of the nanoparticles was analyzed using a UV-visible spectrophotometer (UV-1900i, Shimadzu, Japan), Fourier Transform Infrared spectrophotometer (FT-IR) (IR Spirit, Shimadzu, Japan) using a KBr pellet with a scan rate of approximately 4 cm s⁻¹ at 25 °C, field emission Scanning Electron Microscopy (Fe-SEM), Energy Dispersive X-ray spectroscopy (EDX) analysis (SU-8000, Hitachi, Japan) at accelerating voltages of 10 and 15 kV, and X-ray diffraction (XRD) (Rigaku Smart Lab spectrometer, Japan) with Cu-Kα radiation. A pH ION/EC/DO METER (MM-43X) was used to measure the pH of the solution.

Extraction of Citrus aurantuim peels

The extraction technique was started with the gathering of fresh Citrus aurantuim peels. Thorough washing the removal of impurities, and subsequent drying at room temperature for 48 hours were done to eliminate moisture. The dried peels (800g) were powdered using a mechanical grinder. Consequently, Soxhlet extraction was used to extract the bioactive compounds. Specifically, 370 g of the floor peel powder underwent extraction with 200 mL of hexane for 6 hours. Whatman No. 1 filter paper was used to filter the hexane extract to remove solid residues, and the extract was then concentrated, yielding an effective source of bioactive compounds. The steps of the bioactive compound extraction are displayed in Fig. 2.

Synthesis of CeO₂ Nanoparticles

The synthesis technique commenced with the dissolution of 4 g of cerium chloride (CeCl₃.6H₂O) in 100 mL of ethanol, making sure of complete dissolution via 10 min of stirring. Subsequently, 1g of the Citrus aurantuim peel extract was added, allowing the bioactive compounds to interact with the cerium ions as a template, capping agent, and stabilizer for 10 min beneath non-stop agitation. To facilitate oxide nanoparticle formation, the pH must be between 9 and 10, observed by adding drops of ammonia with stirring for 20 min. The heating process at 80°C for 3 hours with continuous stirring triggered was useful to grow the CeO₂ NP as a brown precipitate. The produced precipitate was washed with deionized water to cast off chloride ion residues. In this manner, to remove all chloride ions from the precipitate, must add drops of AgNO₃ solution to the filter. The produced CeO₂ was washed with ethanol to eliminate water and then dried at 60°C for 2h. Finally, the calcination of CeO₂ NPs yielded was performed at 600 °C for 3h to remove all organic compounds.

Removal of Eosin yellow dye using CeO₂ nanoparticles

Kinetic studies were done by taking different volumetric flasks and placing them in each of the 25 mL with a concentration range of (5,10,15 and 20) ppm of each of the adsorbed solutions of Eosin yellow dye. These solutions were contacted with (0.010, 0.015, 0,020, and 0.025) g of adsorbent surface (CeO₂ NPs), and then these flasks were placed in a water bath equipped with a vibrator at a different temperature within the range (283-298) K. The acid function for the removal process was adjusted within pH (3,4,5,6,7and 8). The flasks were then withdrawn at contact times between 15 min and 120 min, and the amount of adsorption was measured. The residue of Eosin yellow dye in solution after the adsorption process was measured at the maximum wavelength (λ_max) equal to 516 nm [17,18]. The adsorption capacity at various times qt in (mg/g) can be calculated using [19, 20]:

Where: C_o is the actual dye concentration in the solution, C_t is the concentration (mg/L) of dye at different times, V is the volume of the dye solution (L), and m is the mass of the adsorbent (CeO₂ NPs) used in (g).

The adsorption efficiency E % can be calculated by following the equation [21, 22]:

The kinetic study of the adsorption of eosin yellow dye is evaluated by using the following equations depending on the adsorption capacity at equilibrium (q_e) as a maximum value in (mg/g)and adsorption capacity at various times qt in (mg/g).

Pseudo –first-order kinetic: [23, 24]

Here: k₁: is the rate constant in (sec^-1) of pseudo-first order.

Pseudo-second order kinetic: [25,26].

Where: k₂:is the rate constant in (L.M^-1.sec^-1) of pseudo-second order.

RESULTS AND DISCUSSION

Characterization of extract Citrus aurantuim peels

Gas Chromatography-Mass Spectrometry (GC-MS) analysis was used to identify and quantify the bioactive compounds extracted from Citrus aurantuim peels. These compounds are essential oils as they facilitate the reduction and stabilization of CeO₂NPs during synthesis, as shown in Table 1 and Fig. 3.

The GC-MS analysis identified several key bioactive compounds in the Citrus aurantuim peel extract, GC/MS Analytical Condition, Injection: amount = 1µL Split ratio = 1:10 Heat of injection = 250 ℃, Column oven: initial temperature is 50 ℃ increase by 5 ℃ / min to 180 ℃ increase by 10 ℃ / min to 250 ℃ hold 1 min, Sample Preparation: 100 µL of the sample is diluted with 5 mL of N-Hexane (HPLC-Grade) before injection, and Gas flow ratio: 1 mL/min Pressure: 10 psi m/z Range:1 – 2000.

Limonene (35.72%) was the most abundant compound, followed by β-Pinene (25.43%), Myrcene (15.87%), and Linalool (12.34%). These compounds are known for their reducing and capping properties, which are essential in the green synthesis of nanoparticles. The presence of these compounds suggests their significant role in reducing cerium ions to CeO₂ NPs and stabilizing them against aggregation.

Characterization of CeO₂ nanoparticles

To comprehensively understand the properties and potential applications of the synthesized CeO₂ nanoparticles, a series of advanced characterization techniques were employed. These analyses included (FT-IR) spectroscopy, X-ray Diffraction (XRD), field emission Scanning Electron Microscopy (FE-SEM), Energy dispersive X-ray spectroscopy (EDX), Bruner–Emmett–Teller (BET) surface area analysis and Zeta potential analysis. Each technique provided valuable insights into the composition, structure, morphology, and surface characteristics of the nanoparticles, further elucidating their functional capabilities.

X-ray Diffraction (XRD)Analysis

XRD was performed to determine the crystalline structure of the synthesized CeO₂ NPs. The diffraction pattern provides information about the phase and purity of the nanoparticles, as shown in Fig. 4. The XRD evaluation confirmed the crystalline nature of the nanoparticles, showing peaks corresponding to the cubic fluorite structure of CeO₂ NPs [27]. This crystalline shape is essential for the catalytic and biological activities of the nanoparticles because it enables the redox biking between Ce³⁺ and Ce⁴⁺ states [28, 29].

The characteristic peaks of the CeO₂ NPs correspond to the (111), (200), (220), (311), (222), and (400) planes. The strong peak at 28.6° for the (111) plane indicates a high degree of crystallinity and purity. The presence of these peaks confirms the formation of the cubic fluorite structure of CeO₂ NPs. The relative intensities of the peaks provide insights into the crystallographic orientation and crystal size [30]. The mean crystal size was calculated using the Scherer equation [30- 33].

Where D is the crystal size, k is the shape aspect (typically 0.9), λ is the X-ray wavelength (1.5406 Å for Cu Kα), β is the total width at half maximum (FWHM) of the height, and θ is the Bragg attitude, the calculated mean crystal size changed was found to be 12 nm.

FT-IR Analysis

The FTIR spectrum of the hexane extract was found to contain alcohols, phenols, aromatics, carboxylic acids, nitro compounds, and alkanes, as validated by the spectrum, as illustrated in Fig. 5A. A large peek at 3400-3600 cm⁻¹ that attributed to O-H stretching vibrations, while another peak at 3051 cm^-1 assignments to the N-H bending. The wide peak at 1408 cm^-1 was observed, which was due to the bending of the O-H of carboxylic acid [34,35]. The peak demonstrated at 1627cm^-1 is an attitude to the presence of C=O. The peak at 2850 cm^-1 was assigned to C-H stretching, and the band at 1750 cm⁻¹ corresponds to the bending of H–O–H which partly overlaps the O–C–O stretching band. The prominent absorption bands at 2927 and 1452 cm^-1 are responsible for CH and CH₂ groups, respectively [36].

FTIR spectrum of CeO₂ NPs in Fig. 5B showed characteristic peaks. The new sharp peaks  at 401 and 588 cm⁻¹ indicative of Ce-O and O-Ce-O stretching vibrations, respectively [37,38].

FE-SEM Analysis

FE-SEM was used to observe the surface morphology and find the particle size of the synthesized CeO₂ NPs. This technique provides a high-resolution image that reveals detailed surface structure. FE-SEM images at different magnifications revealed that the CeO₂ NPs are predominantly spherical agglomerates like truffles, as shown in Fig. 6 A. At 10,000x magnification, the nanoparticles appeared well-dispersed with minimal aggregation.

At higher magnifications (20,000x) more detailed structures including clusters and surface textures were observed. The uniformity in shape and size suggests a controlled synthesis process, which is beneficial for applications requiring consistent nanoparticle characteristics. The particle size was determined to range between  29.3 nm  and  45 nm. Based on Fig. 6B, the EDX spectrum demonstrated that the presence of cerium in the sample is found to be 62.6%, as well as the presence of oxygen observed at 25.5% and carbon at 12% resulting in the substrate material.

N₂ Adsorption - desorption isotherm (BET) Analysis

BET analysis was conducted to determine the specific surface area, total pore volume, and average pore diameter of CeO₂ nanoparticles. These parameters are critical for understanding the surface properties and potential catalytic activity of the nanoparticles. Based on Fig. 7A and B, the BET analysis revealed a specific surface area of 85.6 m²/g, indicating a high surface area that is beneficial in catalytic applications. The total pore volume is found to be 0.35 cm³/g and an average pore diameter is equal to 8.2 nm, these results suggest that the nanoparticles have a mesoporous structure [39]. This porosity enhances the accessibility of reactants to the active sites on the nanoparticle surface, making them suitable for various applications such as catalysis adsorption.

The adsorption isotherms classification is important in the theoretical modeling of adsorption phenomena and practical reasons. That considers the surface area measurements depending on the BET method [40]. The international standards use this method in different applications depending on the first IUPAC manual [39,40], which divides the isotherms into five types. Fig. 7A is in agreement with Adsorption isotherms type IV, and the hysteresis loop was demonstrated in the relative pressure (P/P₀) range of 0.3~1.0, belonging to type H3 [39]. The expected pore is open with the shape may be as a cylinder [41].

Zeta Potential Analysis

Zeta potential analysis provides significant insights into the surface charge and colloidal stability of synthesized CeO₂ nanoparticles. The zeta potential is an important parameter affecting the diffusion and aggregation behavior of nanoparticles in solution [42]. The results of the zeta potential analysis are presented in Table 2.

At pH 3, CeO₂ NPs exhibited a zeta potential of +15.2 mV, indicating a moderate colloidal state. This positive charge indicates the presence of protonated surface groups, contributing to the electrostatic repulsion between the particles. At pH 6, the zeta potential increased sharply to +32.8 mV, indicating high stability[43]. This pH value is optimal for dispersion and prevention of aggregation of nanoparticles, which is useful for applications that require stable suspensions. At pH 8 the zeta potential is decreased and shifted to -21.4 mV, indicating good stability due to negative surface charge. The negative charge is apparently due to the de-protonation of the surface hydroxyl groups, resulting in explosive forces that prevent aggregation.

Adsorption of Eosin Yellow Dye

The synthesized CeO₂ NPs using Citrus aurantuim peel extract were evaluated to remove the Eosin yellow dye. The adsorption efficiency and kinetic adsorption constant (kd) were calculated at various time intervals, pH levels, temperatures, and initial dye concentrations. The mechanism of dye removal is shown in Fig. 8.

Effect of Removal Time

The data in Fig. 9 elucidates the temporal evolution of Eosin yellow dye adsorption by the synthesized CeO₂ nanoparticles. A substantial increase in the efficiency of dye removal and the adsorption constant values over time signifies the effective adsorption of the dye, this behavior is due to an increase in the kinetic energy for dye particles that enhances the diffusion and adsorption on active sites of the CeO₂NP surface until saturated[44]. The adsorption efficiency increased significantly from 26.18% at the initial 15 min to 70.66% after 120 min. Simultaneously, the adsorption constant (kd) increased, peaking at 2.4270 min⁻¹ at 90 min and staying similar with continuous time.

The kinetic results as shown in Fig. 10 and Table 3. The values ​​of the correlation coefficients for the pseudo-second-order model are relatively high, and the amount of adsorbed material calculated by this model is close to the value determined by experiments. The value of the correlation coefficient for the pseudo-first-order model of the adsorption system is not convincing. Therefore, the pseudo-second-order model is more accepter for describing the adsorption kinetic, so the rate-limited step depends on the Eosin yellow dye molecule and the CeO₂ nanoparticles surface.

Effect of Initial Dye Concentration on the Removal Process

The influence of varying initial dye concentrations on the adsorption process is encapsulated in Fig. 11 a discernible inverse relationship emerges between the initial dye concentration and the adsorption efficiency after increasing the dye concentration by more than 10 ppm. Specifically, the maximum efficiency was found at a concentration of 10 mg/L yielded an impressive 70.82%, while efficiencies decreased by using high concentrations, which reached 20 mg/L, resulting in a substantial to 26.58%. This observation can be attributed to the limited availability of active sites on the nanoparticle surface at higher dye concentrations, thereby hindering the adsorption and subsequent adsorption process [45,46]. Consequently, optimizing the initial dye concentration is crucial to maximize the potential of CeO₂ nanoparticles.

Effect of CeO₂ NP Dose

Fig. 12 encapsulates the effect of various dosages of CeO₂ NPs at the adsorption method. A clear positive correlation emerges between the nanoparticle dose and the adsorption performance, with the best efficiency of 70.82% achieved at a dose of 0.025 g. This trend may be attributed to the improved availability of energetic sites at the nanoparticle surface, which helps greater efficient adsorption and next adsorption of the dye molecules. However, it is crucial to strike a balance between the nanoparticle dosage and the associated costs, as an immoderate dose might not yield commensurate enhancements in efficiency. The results show that increasing the dosage of CeO₂ NPs led to higher adsorption efficiencies, with the best result observed at a dose of 0.025 g. The increase in the removal of dyes with adsorbent dose is due to the introduction of more binding sites for adsorption [47, 48].

Thermodynamic Parameters

Thermodynamic characteristics are essential for determining the kind of adsorption process that occurs on any solid surface. The thermodynamics parameters such as activation energy, Gibb’s free energy change, entropy, and isotherm heat of adsorption are vitally required. These parameters are critical design variables in estimating the performance and predicting the mechanism of an adsorption separation process First, using equation 7, the sorption distribution coefficient (kd) [49,50] was determined.

where C_ads is the amount of adsorbate (dye) on the solid surface equilibrium (mg/L) and Ce is the amount of leftover dye (mg/L) in an equilibrium solution.

The Van’t Hoff formula was used to estimate the changes in the standard entropy ΔS^⁰ and the standard enthalpy ΔH^⁰ [51, 52], as shown in Fig. 13A.

Here, R stands for the universal gas constant (J/mol. K) and T is the absolute temperature in Kelvin.

Using the Nernst equation (equation 9), the standard Gibbs free energy (ΔG^⁰) was determined [53,54], and the relation between ΔG^⁰ and temperature is plotted in Fig. 13B.

However, equation) 10(was used to get the activation energy (Ea) [55].

Based on Figs. 13A and B, Table 3 elucidates the thermodynamic parameters predominated on the adsorption manner. The Gibbs free energy (ΔG^⁰) values are positive indicating the adsorption of Eosin yellow dye by green synthesized CeO₂ NP is a non-spontaneous reaction. The positive ΔH^⁰ of this reaction was found to be 13.430 kJ/mol, this value suggests that the adsorption type of the adsorption is physical (∆H^₀ less than 20-40 kJ/mol) and the system is endothermic [56]. Furthermore, the small value of ΔS⁰ (0.0423 kJ/mol. K) ensures the decline in the randomness of the solid-solution interface in the course of the adsorption system [57].

Effect of pH of Eosin dye on the Adsorption Process

This parameter shall describe via many phenomena that can be happened, which caused the change in surface charge properties of the nanoparticles and the solubility or ionization state of dye. Fig. 14 encapsulates the pivotal role of pH in modulating the adsorption of Eosin yellow dye. The efficiency increases from pH 3 to pH 6 and gives a maximum adsorption efficiency 97.48%. The results indicate the maximum adsorption efficiency at pH 6 was accepted with the result of zeta potential at maximum value at pH 6. The protonation of surface enhances the anionic dye adsorption owing to the electrostatic attraction [58]. Conversely, the adsorption efficiency diminished from pH 7 to 8 that attitude to excess the hydroxyl ions in surface that increases the repulsive force with this negative dye [59].

Adsorption Isotherms

In this study, we used Freundlich, Langmuir, and Temkin’s isotherm equations to match the experimental data for eliminating eosin dye at different concentrations. The adsorption isotherm describes the relationship between the amount of removed dye and the remaining concentration at equilibrium. This work used non-linear Langmuir and Freundlich models to analyze adsorption isotherm data and characterize the process. The monolayer adsorption of the adsorbate on homogeneous sites within the adsorbent is characterized as:

Isotherm Langmuir

Definition of Langmuir isotherm (Equation10) states the adsorption process takes place across homogeneous sites of the adsorbent [ 60].

Where; Q𝑒 = defined as the quantity of eosin yellow adsorption at the time of equilibrium(mg/g). (a, b) are the constants of Langmuir.

Where: 𝑅𝐿 = meaning refer to adsorption kinds is Irreversible (R_L=0), Likely (0< R_L< 1) linear (R_L=1) [56]. The (a) and (b) values are calculated from the slopes (1/a) and intercepts (1/ab) of linear plots of Ce /Qe versus Ce are shown in Fig. 15A.

Isotherm Freundlich

Multi-layered adsorption over heterogeneous active sites is indicated by the Freundlich isotherm pattern of adsorption. Freundlich isothermal. [ 57].

Where: k_F, n =Freundlich’s constants. Fig. 15B shows the applicability of the Freundlich equation well when plotting Log Qe against the values of Log Ce

Temkin Isotherm

The following is how it is frequently used [57]:

Where: A_T is the equilibrium binding constant. β = associated with the heat of adsorption. where the eosin yellow dye adsorption Temkin isotherm curves are shown in Fig. 15C.

The (a, b, RL) for Langmuir constants, (n, KF) for the Freundlich pattern and the Temkin pattern constants (β, AT) with linear correlation coefficients are shown in Table 5.

From the results the (R²) values in Table 5 for Langmuir, Freundlich and Temkin it turns out that the best results are in the Freundlich and Temkin values [60,61]. The Freundlich constant n is found to equal 3.198 that agreement with the actual this reaction is a multilayer (physical adsorption) and this process is favorable for the studied dye because the n value ranges between 1 and 10 [62]. The RL value is obtained less than 1, hence this reaction is Likely [60]. The R² is low which indicates the adsorption of dye on the surface of CeO₂ NP is heterogeneous.

Effect of Addition the Oxidation Agents on Eosin yellow dye removal process

Fig. 16 encapsulates have an impact on supplementary oxidizing dealers, specifically hydrogen peroxide (H₂O₂) and ferrous ions (Fe²⁺), at the adsorption of eosin yellow dye. The records show that the addition of these oxidizing agents enhanced the adsorption performance, with the Fenton response (related to both H₂O₂ and Fe²⁺) yielding an outstanding efficiency of 96.37%. This synergistic effect may be ascribed to the era of especially reactive hydroxyl radicals (•OH) through the Fenton technique, which augments the oxidative adsorption of the dye molecules. Consequently, the judicious incorporation of such oxidizing agents presents a viable strategy to further optimize the adsorption performance of the CeO₂ nanoparticles. The results indicate that the addition of hydrogen peroxide alone and ferrous ions alone depress the adsorption efficiency. This behavior due to the Fe²⁺ may be compared to the dye on occupies active sites in the cerium oxide nanoparticles via the adsorption process. Moreover, the H₂O₂ shall oxide the semiconductor surface to give a positive charge with hydroxyl ion and hydroxyl radical, and the last species will adsorption on the surface and decrease the negative dye adsorption (eosin yellow dye) this result is in agreement with result that reported in reference [63,64].   Whereas, using the Fenton reaction, which involves both H₂O₂ and Fe²⁺ resulted in an adsorption efficiency of 96.37%, very close to the efficiency observed without any additional oxidizing agents to generate equivalent positive and negative charges at the same time. As in the following equations [63-65].

Reusability of CeO₂ nanoparticles

The statistics provided in Fig. 17 shed mild on the reusability of the synthesized CeO₂ NPs for packages. While the nanoparticles exhibited an impressive 97.48 % removal efficiency performance in the preliminary cycle, a gradual decline in performance was found with subsequent reuse cycles. This phenomenon can be ascribed to the capacity deactivation by saturated or blocking the active sites of surface by dye molecules, or fouling of the nanoparticle surface, which may restrict the adsorption and adsorption strategies [66]. Nevertheless, the nanoparticle’s proven ability to perform well during the first three rounds pastime more than one cycle underscores their potential for sustainable and fee-effective applications. The results indicate a decline in adsorption efficiency with a continuous reuse cycle when used five times. it maintained its warranty until the third time because the dye molecules are gradually accumulating and preventing interaction with the surface [67,68]. However, the nanoparticles still exhibited significant adsorption activity after multiple cycles. The results observed good reusability, which is the acceptable loss in the sorption ability after five circulations.

CONCLUSION

Green synthesis of CeO₂ NPs using Citrus aurantuim peel extract was successfully prepared and it provided a sustainable and environmentally friendly method. The synthesized CeO₂ NP was characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), Energy dispersive X-ray spectroscopy (EDX), Bruner–Emmett–Teller (BET) surface area analysis and Zeta potential analysis. Based on the XRD data, the CeO₂ NP structure was estimated as a cubic fluorite with a crystal size of 12 nm. The nanoparticles demonstrated good adsorption and antioxidant properties, making them suitable for a wide range of applications and emphasizing the need for further research to fully exploit their advantages. Based on kinetic studies and isothermal fitting, the second-order model was investigated as an appropriate model to express the adsorption behavior of dye on synthesized CeO₂ NP. The thermodynamic study indicated that the adsorption mechanism between synthesized CeO₂ NP and Eosin yellow dye was non- spontaneous and endothermic process. The Adsorption activity was studied by way of the preliminary dye concentration, pH, and temperature. Higher adsorption efficiencies were located at 10ppm dye concentrations, with a finest pH of 6, and multiplied interest at 25˚C temperature. Additionally, the green synthesis technique by leveraging agricultural –products, this observation aims to contribute to sustainable improvement and pollutant reduction, at the same time as exploring the practical packages of green–synthesized CeO₂ NPs in various fields such as environmental remediation. Research into the future Environmentally friendly and non-toxic preparation of Cerium oxide nanoparticles, including green synthesis. Characterize produced surfaces with TEM, TGA, and XPS to determine surface properties and bending energy. Investigating the impact of several parameters on adsorption, including ionic strength, and shaking speed. Examined the biological activity of produced materials.

ACKNOWLEDGMENTS

The authors would like to thank all supported people at the University of Karbala and Al-Zahraa Center for Medical and Pharmaceutical Research Sciences (ZCMRS), Al-Zahraa University for Women.

CONFLICT OF INTEREST

The authors declare that there is no conflict of interests regarding the publication of this manuscript.