1 Introduction

Water is vital source for energy and all living organisms, although many of people global are suffering from the deficiency of fresh water and clean drinking. Industrial effluents management is one of the international environmental challenges and the water contamination by different contaminants as well currently a main environmental issue as it would result in a damage of biodiversity (Moneer et al., 2023). Also, several kinds of pollutants can pose a risk to environmental water as a result for growing industrial development worldwide especially drinking water resulting hazardous human health risks (Tepe & Çebi, 2019) Dyes are synthetic aromatic water or solvent soluble organic compounds, these chemical compounds with colored pigments (organo mettalic complexes or inorganic) which have been used in potential application in several textile industries (Alprol et al., 2023a, 2023b; Elzain et al., 2019). Textile wastewater from the industry comprise highly colored constituents that can led to cause abnormal coloration of surface waters and it can block the light penetration in aquatic system which is very necessary for aquatic plants and photosynthetic organism (Alprol et al., 2023a, 2023b). Methylene blue is a cationic organic dye complex, which is used in textile industries as coloring material for dyeing wool, cotton and silk (AL-Aoh et al., 2014). MB is frequently utilized in the printing and dyeing steps of the textile manufacturing process (Abrouki et al., 2021). MB when existing in water, occur alterations in chemical oxygen demand, transparency, pH and color (Berenjian et al., 2018). Various treatment techniques Viz., coagulation, flocculation, ozonation, membrane filtration, adsorption and reverse osmosis have been studied conventionally for removal of dye wastewater (Venkataraghavan et al., 2020). Adsorption is physio-chemical technique, which is economically feasible, effective and realistic methods for the elimination of textile dyes from industrial effluents (Alardhi et al., 2020). The best vital factors of any adsorbent are the chemical nature, structure, polarity of the surface and the surface area of adsorbents, in addition to structure which can affect the attractive forces among the adsorbate and adsorbent (Lee et al., 2018). Adsorbents such as zeolite, activated carbon, clay minerals, agricultural biomass and silica gel have all been developed to remove dyes. However, a number of disadvantages of these adsorbents include oxidation, aggregation, low selectivity, restricted adsorption capacity, and high cost (Abdelwahab & Thabet, 2023; Jioui et al., 2023; Loukili et al., 2021) The nanofibers that can be processed using the electrospinning approach offer unique qualities such as high porosity with delicate pores, cheap cost, and a high specific surface area. These properties lead to application of electrospun nanofiber for the dye ions removal from industrial sources (Lee et al., 2018). The electrospinning method is simple, requiring only a high-voltage power supply, a nozzle, and an aluminum foil-covered collector (Liu et al., 2011). The solution stretches as a result of the potential difference between the nozzle and the collector, producing a thin jet of polymeric solution that travels in the direction of the collector (El-Aassar, et al., 2015). Solvent evaporates as the solution is stretched to the collector, resulting in the collection of ultrafine nanofibers (Lee et al., 2016). In the collecting plate below, non-woven membranes with nanoscale fiber diameter are finally gathered (Elkady et al., 2016). Under the same volumetric settings as standard fibers (diameter 50 microns), these fibers showed a higher porosity, more closely connected pores, and a smaller diameter pore aperture. Furthermore, nanofibers have a particular surface area that is around 100 times larger than that of ordinary fibers. Nanofiber membrane filters have numerous surface functionalization options, a high surface area to volume ratio, lower energy consumption, small inter-fibrous pore size, shorter transmission distance, higher adsorption of pollutants, faster reaction, high porosity, and other benefits when compared to conventional filters (El-aassar et al., 2016).

Hydrophilic polyacrylonitrile (PAN) was lately electrospun to make nanofiber for water treatment due to the PAN material is relatively easy to work with and the porosity and pore size of the resultant membranes can be easily controlled by altering the electrospinning conditions (Lee et al., 2018). As a result, it has piqued the interest of many scholars over the last decade. It is frequently utilized in the manufacture of ultrafiltration, microfiltration, and hollow fiber membranes. Furthermore, a cyano group that can be altered is present in PAN molecular chains. If a portion of the hydrolysis process could be carried out using carboxyl functional groups (-COOH) in a solution, metal ions, lysozymes, and other molecules would quickly adsorb. Large capacity for absorption, rapid rate of absorption, and strong dynamic performance are some of its distinguishing characteristics. It is a great substance to employ in the lysozyme and heavy metal wastewater purification processes (El-aassar et al., 2016; Wang et al., 2007;Yazdi et al., 2018).

This research demonstrates the reliable synthesis of a nanofiber composite consisting of melamine-maleic acid polymer adduct and polyacrylonitrile (ME-MA/PAN) using the electrospinning process. The primary focus of this study is on utilizing the ME-MA/PAN composite for the removal of MB dye from aqueous solutions, encompassing several objectives such as synthesizing a novel nanofiber composite of melamine-maleic acid polymer adduct and polyacrylonitrile (ME-MA/PAN) through the electrospinning process. Furthermore, characterization of ME-MA PAN nanofibers composite using FTIR and SEM for surface morphology. Moreover, the thermal properties of these nanofibers composite were examined by Thermogravimetric analyzer (TGA). The investigation for influence of MB concentrations, contact time, pH, temperature, and adsorbent dose on the performance ME-MA PAN nanofibers for MB removal. Subsequently, further analyzed the adsorption capacities and efficiencies, and data of equilibrium used to determine adsorption isotherms, kinetics and thermodynamics. The novelty of this research is multifaceted. Firstly, it introduces a novel adsorbent material, the Melamine-maleic acid polyamide adduct/polyacrylonitrile (ME-MA amide polymer/PAN) nanofiber composite, fabricated via the electrospinning technique. This composite presents a fresh approach to tackling dye removal from aqueous solutions. Additionally, the study aligns with the increasing focus on sustainability in material science and environmental cleanup by employing green compounds and environmentally acceptable nanofiber composites. Furthermore, it underscores the practical utility of the ME-MA amide polymer/PAN nanofiber composite as an eco-friendly and efficient material for wastewater dye removal. This emphasis highlights its potential benefits in terms of ease of regeneration, cost-effectiveness, stability, and rapid synthesis, thereby paving the way for future advancements in dye adsorption applications.

2 Material and Methods

2.1 Materials

Maleic acid, Melamine, acrylonitrite monomer chemically pure grade products of Sigma Aldrich and other solvents are products of some international and local companies.

2.2 Methods of Preparation

2.2.1 2.2.1. Synthesis of Melamine-Maleic Acid Polyamide Adduct (ME-MA Polyamide Adduct) by Condensation Reaction According to our Previously Reported Articles (Abd El-Ghaffar et al., 2003; El‐Adly et al. 2004)

In a similar procedure, the amide polymer of melamine and maleic acid was prepared by the condensation reaction as follow: Melamine (0.68 mol, 8.58g) and maleic acid (0.1 mol, 11.61g) were mixed and charged together with 100 mL of O-Xylene as isotropic solvent in a 250 ml flask. Reflux was applied to the reaction mixture for roughly 4 h, or until the reaction medium was cleared of the theoretical volume of water (3.6 ml). The formed polymeric adduct was filtered, left for evaporation of xylene and drying, washed several times using methanol and purified with hot water, ethanol and finally with acetone and left for drying in an electric oven at 50° C under vacuum. The produced polymer structure is brownish yellow with melting point more than 300°C (Fig. S1).

2.2.2 Preparations of (Melamine—Maleic Acid Amide Polymer Condensation Adduct)/Poly Acrylonitrile Nanofiber Composite via Electrospinning Technique

Melamine—maleic acid amide polymer/ Poly acrylonitrile nanofiber composite was prepared via electrospinning. The electrospun nanofibers of ME-MA/PAN composite were obtained by introducing the polymer solution into a syringe pump, and electrospinning was applied to create nanofiber mats using an electrospinning system (Model; ESR100D -South Korea), with the aforementioned criteria: voltage 18 kV, flow rate of of 0.1 mL/ h, at a distance of 15 cm, and room temp (25°C). The formed nano-fibrous mats were subjected to drying in a vacuum oven at 60 °C for 6h (Khalil & Al-deyab, 2019).

2.2.3 Preparation of Dye Solutions

Methylene Blue obtained in solid form Sigma-Aldrich (Milano, Italy), which is a cationic dye with chemical formula C16H18N3SCl, λ max = 665 nm and molecular weight of 319.85 (g. mol−1). MB dye at 293 K leads to high water solubility and presents positive charge on S atom (Mansour et al., 2022a, 2022b). By combining one gram of powder dye with one liter of distilled water, the stock solutions of MB were prepared.

2.3 Characterization of ME-MA PAN Nanofibers

2.3.1 Scanning Electron Microscopy (SEM)

SEM of ME-MA PAN was investigated by SEM (JEOLGSM-6610LV) at raising voltage of 25 kV. The surface of adsorbent was vacuum-coated by using gold for determination.

2.3.2 Thermogravimetric Analysis (TGA)

Thermogravimetric analyzer (TA Instruments, Q500TGA, United States) was used to study the thermal degradation behaviors of PAN and MEPAN in the range of temperature from 23 °C to 800 °C under N2 gas atmosphere at a flow average of 40 mL.min−1.

2.3.3 FTIR Spectral Analysis

The chemical composition of the synthesized PAN and MEPAN nanofibers were recorded by using FTIR (TENSOR Series FT-IR Spectrophotometer, Germany) in the scope 500–4000 cm−1 using KBr pellet method.

2.4 Experimental Procedure

2.4.1 Batch Adsorption Experiments

Batch adsorption tests were applied under various parameters, different initial dye concentrations (5- 40 mgL−1) with contact times (10, 20, 30, 40, 60, 90, 120, 180 and 1440 min), initial pH of dye (2.3, 4.2, 6.4, 8.5 10, and 12), different dosages of MEPAN (0.005, 0.01, 0.02, 0.03 and 0.04 g), effect of temperatures (20, 25, 30, 40 and 50 ºC). For each run, 100 mL of dye solution was introduced to 250 ml screw caped flask and was shaken in a platform shaker at 220 rpm for appropriate time. After which, the mixture in each flask was centrifuged to separate MEPAN and the residual concentration of MB within the solution was determined using (Perkin Elmer Lambda 35 UV/vis Spectrophotometer, USA) at wavelength 665 nm.

2.4.2 Dyes Removal Efficiency

Adsorption capacity (qe), the amount of dyes adsorbed per gram of ME-MA/PAN, can be calculated at equilibrium in mg g−1by the following equation:

$$\text{qe }=\frac{C\text{i }-Ce}{m}\times V$$
(1)

Dyes uptake can also be displayed by the percentage of dyes adsorbed (efficiency) given by

$$\text{Adsorption }(\%) =\frac{\text{Ci }-\text{Ce}}{\text{Ci}}\times 100$$
(2)

where: Ci is the initial and Ce is equilibrium concentration of MB dye, respectively (mgL−1), m (g) mass of MEPAN and V (L) volume of the MB solution.

2.4.3 Kinetics and Isotherm Studies

In order to analyze the experimental data, the adsorption kinetics of MB dye were represented using a pseudo first order kinetic equation, a pseudo second order kinetic model, as well as an intra particle diffusion model, as shown in Table S1 (Abdelwahab et al., 2017). Parameters of the adsorption were evaluated using Langmuir (Langmuir, 1917), Freundlich (Freundlich, 1906), Tempkin (Tempkin & Pyzhev, 1940), in addition to Dubinin–Radushkevich (D–R) isotherm models (Dubinin, 1969).

Where: Qm is the maximum adsorption capacity of the solute per gram of MEPAN (mg g−1) and Ka is adsorption equilibrium constant (L mg−1) that is related to the apparent energy of adsorption for Langmuir. KF (mg g−1) adsorption coefficients for Freundlich and (n) is the Freundlich constant related to the surface site heterogeneity. KT (L g−1) is the Tempkin constant. KD is a constant appertain the adsorption energy, bT (J. mol−1) is a constant representing heat of sorption, R indicate the gas constant (8.314 J. mol K−1), T is the absolute temperature (K) and ε is the Polanyi potential for Dubinin–Radushkevich. The important characteristics of the Langmuir isotherm could be described by RL (a dimensionless constant) referred to as equilibrium parameter (Abualnaja et al., 2021).

3 Results and Discussion

3.1 Surface Characterization of ME-MA PAN Nanofiber

3.1.1 Scanning Electron Microscopy

The microstructure of ME-MA PAN was examined by using SEM as showed in Fig. 1. The SEM images can the direct monitoring of the variations in the external surface, texture and porosity of microstructures. The size of the cylinders ranged from about 1 to 3 μm. However, there were some changes between the detailed structures before and after removal of dyes by ME-MA PAN composite. SEM micrograph indicates that the structure of material like fiber or bundle cylinder. The arrangement of cylinders or fibers of untreated martial appear that surface of fibres were randomly, smooth and homogeneous. Nevertheless, after treatment the arrangement of fibers appear adherent with some mass.

Fig. 1
figure 1

SEM micrographs of ME-MA/PAN electrospun before (A) and after MB removal (B)

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3.1.2 Thermo Gravimetric Analysis (TGA)

The quantity of moisture and volatile substances present in composites and nanocomposite fibres, weight loss, and heat breakdown can all be quantitatively analysed using thermal gravimetric analysis. In this study the samples of melamine maleic acid amide polymer/poly acrylonitrile electrospun fibers composite [ME-MA/PAN] was analyzed to examine its thermal stability compared with pure poly acrylonitrile fibers. The mass loss of the fibers composite was checked as a function of temperature by heating under N2 gas from room temperature (20ºC) to (800ºC) in 5 given main stages. The results are illustrated in Fig. 2A and 2B. One can see from Fig. 2A and B) that, the mass loss of the first heating stage 20- 199 °C of ME-MA/PAN fiber composite and pure PAN fiber are nearly around 2.5 & 2.6% for ME-MA/PAN and pure PAN respectively which, relates to the release of bound water and volatile maters from the fiber composite and that of the pure PAN fiber.

Fig. 2
figure 2

TGA thermographs with Mass (mg) versus temp of ME-MA PAN (A) and TGA thermographs with Mass (%) of (ME-MA/PAN) and pure PAN fiber (B)

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The second heating stage from 200–300 oC indicates total mass loss of 3.0% for ME-MA/ PAN composite and also PAN fiber which indicates stat of slight decomposition near 5% and. The 3rd heating stage from 310–350 °C shows total mass loss of 15% for ME-MA/PAN and 30% for PAN fiber which may be attributed to starting degradation in the back bone of both the composite fiber, and the PAN fiber, that indicating better thermal stability of the composite fiber than that of PAN. With respect to the fourth stage of heating from 350 to 600 °C, which an increase in the degradation of the PAN fibers more than that of the ME-MA/PAN fiber indicating total mass loss of 40% for neat PAN compared with 30% for ME-MA/PAN retaining 70% of its mass. In addition, the properties of thermal degradation can be shown in terms of the T50, which is referring to the temperature required for a material to lose fifty percentages from its original mass. It is clear from the results (Fig. 2B) that T50 for ME-MA/PAN fiber composite is 757 °C, while in case of PAN nanofiber; the value of T50 is 730 °C, which indicates that ME-MA/PAN electrospun nanofiber composite is highly thermal stable more than that of PAN. In addition, these results are nearly in accordance with the data reported by Charles Edward Blackwell (Blackwell, 2019).

3.1.3 Fourier Transform Infrared Spectroscopic (FTIR)

The thiol groups presence on the nanoparticles surface and their covalent attachment to the nanofibers surface were confirmed using FTIR (Yazdi et al., 2018). The samples were dried and characterized in the extent 4000–500 cm−1 using KBr pellet method. Strong similarities among the FTIR spectra of PAN and MEPAN can be seen in Fig. 3 (curve A and B). Because of intra- and intermolecular hydrogen bonding in polymeric complexes like phenols and alcohols, the area between 3200 and 3500 cm−1 displays the stretching vibration of O–H stretching H-bonded. Another peak with a shoulder at 2937 cm−1 and 2939 cm−1 assigning the C-H stretching in ˃CH2 and CH3 functional groups. The presence of an amide group may be the cause of the peaks at 2349.38 and 2353.23 cm−1. Moreover, the absorption peaks between 2260–2190 cm−1, probably assigned to (R–C≡C-R). New peaks created at 1950 cm−1 was caused by the existence of (> C = C = C <). The absorbance peak at 1651 cm−1 is because of the presence of N–H group bending types of bonds of amide. In addition to the peaks at region 1660 to 1500 cm−1reveal the presence of C = N and C = C stretching due to the existence of olefinic and aromatic compounds. The absorbance peaks at 1356–1460 cm−1 reveal to sp3 C-H bend stretching of COOH. While, the he absorption peaks at 1074 and 1076 cm−1 confirm the presence of sulfoxides in structure. The shift in the wavenumber of functional groups, moreover there are two peaks in the PAN at 3961 and 3502 cm−1 disappeared, while there are five new absorption bands created in the ME-MA PAN and PAN at 3736, 3439, 2247, 1932 and 881 cm−1, these changes in peak intensity may be affecting the removal of dyes.

Fig. 3
figure 3

FTIR of (a) PAN and (b) MEPAN nanofiber composite

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3.2 Effect of Process Variables on Adsorption

3.2.1 Effect of the pH

The effect of pH on the adsorption process, particularly in the context of dye adsorption, is a critical parameter because of its influence on the electrostatic interactions between the adsorbent and the adsorbate. This study investigated the influence of initial pH on the adsorption process of Methylene Blue (MB) using ME-MA PAN (Methyl Ethyl Methacrylate Polyacrylonitrile) nanofibers. The pH of the dye solution was varied from 2 to 12 while keeping the initial MB concentration constant at 20 mg/L and utilizing 0.01 g of nanofibers in a 50 mL solution. The mixture was shaken at a constant temperature of 30 °C for a duration of 90 min to allow for equilibrium to be reached. The choice of pH ranges from 2 to 12 encompasses a wide spectrum of acidic, neutral, and alkaline conditions, reflecting the potential environmental scenarios where such adsorption processes might occur (Abdallah & Alprol, 2024). By systematically varying the pH, the study ensures a comprehensive understanding of the pH dependence of the adsorption process. The data collected were analyzed and represented in Fig. 4, providing a visual insight into the relationship between pH and the adsorption capacity of ME-MA PAN nanofibers for MB. Interestingly, the results indicated an optimum and maximum adsorption capacity at pH 12. This finding suggests that alkaline conditions favor the adsorption of MB onto ME-MA PAN nanofibers. The observed trend of lower adsorption capacities at lower pH values (acidic solutions) can be attributed to the surface charge characteristics of the adsorbent (ALDEGS et al., 2008). As the pH of the solution decreases, the surface of ME-MA PAN tends to become positively charged. This phenomenon reduces the electrostatic attraction between the positively charged MB dye molecules and the adsorbent, leading to decreased adsorption capacities (Pathania et al., 2017). Conversely, at higher pH values, the surface of ME-MA PAN gains a negative charge due to the deprotonation of surface functional groups. This enhances the electrostatic attraction between the negatively charged adsorbent and the positively charged MB dye molecules, resulting in higher adsorption capacities.

Fig. 4
figure 4

Influence of pH on adsorption capacity of MEPAN nanofibers

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3.2.2 Influence of Contact Time and Initial MB Concentration

The study investigated the influence of contact time and initial Methylene Blue (MB) concentration on the adsorption efficiency of ME-MA PAN (Methyl Ethyl Methacrylate-Grafted Polyacrylonitrile) as illustrated in Fig. 5. The contact time was varied over a range of concentrations including 5, 10, 20, 30, and 40 mg L−1. Initially, rapid adsorption of MB was observed, indicating the high affinity of ME-MA PAN for the dye molecules. This rapid adsorption phase can be attributed to the availability of numerous active adsorption sites on the surface of the adsorbent material. Subsequently, the rate of adsorption slowed down, reaching equilibrium after 1440 min (24 h). This equilibrium time indicates the point at which the adsorption process reaches its maximum capacity, suggesting saturation of available adsorption sites (Thabet et al., 2020). The equilibrium time is consistent with the behavior expected for a porous adsorbent material like ME-MA PAN, where the process gradually slows down as the surface becomes saturated with dye molecules. The results also revealed that the removal capacity of MB dye increased with the rise in initial dye concentration until reaching a peak at 30 mg/L. This trend can be attributed to the increased driving force for adsorption at higher initial concentrations, leading to more dye molecules being adsorbed onto the available active sites of the adsorbent (Rápó & Tonk, 2021). Also, this observation aligns with the Langmuir adsorption model, where higher initial concentrations enhance adsorption until a saturation point is reached. However, beyond 30 mg/L, the removal capacity of the dye began to decrease. This decline can be attributed to the phenomenon of overcrowding at higher concentrations, where the number of dye molecules exceeds the available active sites for adsorption. This saturation of active sites leads to a decrease in adsorption capacity per unit mass of adsorbent (Gupta et al., 2017).

Fig. 5
figure 5

Influence of contact time on adsorption capacity at different MB concentrations

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3.2.3 Effect of Adsorbent Dosage

The influence of ME-MA PAN dosage on MB dye removal from the aqueous solution was examined by using various dosages of ME-MA PAN from 0.005 to 0.04 g in 50 mL of the prepared dye solution. The effect of adsorbent dose has been showed in Fig. 6. As the dosage of ME-MA PAN increased, a noticeable enhancement in both the rate and capacity of MB dye removal was observed. This phenomenon can be attributed to the increase in available adsorption sites due to the higher dosage of the adsorbent (Elzahar & Bassyouni, 2023). With more active sites accessible for interaction with the dye molecules, the adsorption capacity naturally improves. This is consistent with the Langmuir adsorption isotherm, which suggests a direct relationship between adsorbent dosage and adsorption capacity under ideal conditions. However, beyond a certain point (0.02 g in this study), the increase in adsorbent dosage did not result in a significant improvement in MB adsorption. This saturation phenomenon can be attributed to the aggregation and overlapping of unoccupied surface areas of ME-MA PAN with MB dye molecules (Nayeri & Mousavi, 2020). Such aggregation leads to an enlargement of the diffusion path length, hindering the efficient adsorption of dye molecules onto the adsorbent surface. This observation aligns with the notion of surface saturation, wherein all available active sites on the adsorbent surface become occupied, limiting further adsorption despite an increase in adsorbent dosage (Rout et al., 2023).

Fig. 6
figure 6

Influence of MEPAN dose on MB dye removal efficiency

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3.2.4 Effect of Temperature

The influence of temperature on the elimination percentage of MB dyes was determined within range from 20–50 °C as presented in Fig. 7. It can be clear up that the efficiency of MB removal was raised with augmentation temperature value up to 40°C. The modest temperature advantage in the adsorption of MB proves that the adsorption process is almost endothermic. This might be due to the fact that as temperature rises, dye ions become more mobile and there are more active sites available for the adsorption process (Yagub et al., 2014). The weakening of the adsorptive interactions between functional groups and active sites on the adsorbent and the dyes ions may be the reason of the decrease in the removal % of MB dyes by adsorbent with increasing temperature values over 40 °C (Ofomaja & Ho, 2007).

Fig. 7
figure 7

Adsorption capacity of MEPAN on MB removal at different temperatures

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3.3 Adsorption Kinetics

Three models such as pseudo first order, pseudo second order kinetic and intra-particle diffusion models were performed for methylene blue dye adsorption onto ME-MA PAN. The adsorption kinetic parameters at various MB concentrations are presented in Table 1 and Fig. 8a and b. It was observed that the pseudo-second-order model parameters agreed very well with the experimental data.

Table 1 Model kinetic parameters for the removal of MB dye by MEPAN nanofibers
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Fig. 8
figure 8

(a) Pseudo–second-order kinetics; (b) Intra-particle diffusion, over different concentrations for the removal of methylene blue

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These data indicate that rate-limiting step is chemisorption process, include exchange of electrons or valence forces through sharing (Ahmadi et al., 2020). The discrepancy in mass transfer between the main and final stages of the adsorption process is what causes the results to deviate from the original. This approves that the MB removal on ME-MA PAN was a multi-step process including adsorption through the diffusion into the interior and outer surface of adsorbent (Zhang et al., 2017).

3.4 Adsorption Isotherm

An adsorption isotherm describes the relationships among the residual concentration of the adsorbate and adsorption capacity at constant dosage, pH, temperature and contact time. The Langmuir, Freundlich, Tempkin, and Dubinin-Radushkevich (D-R) isotherm models were used to analyze the adsorption parameters. Adsorption isotherm determines the relationships among the residual concentration of the adsorption capacity and adsorbate at fixed temperature.

The adsorption capacity of ME-MA PAN was depicted in Fig. 9 as a function of the equilibrium dye solution concentration. Table (S2) contains the results of the evaluation of isotherm parameters and linear correlation coefficients. Two isotherm models Langmuir and Freundlich were found to be more fit for the experimental results on the adsorption of MB dye onto ME-MA PAN after investigation of the correlation coefficients. This verifies the participation of both physical and chemical processes in the adsorption process because of the complex characteristics of ME-MA PAN. However, the batch operation most closely followed the Freundlich adsorption isotherm model, as these values were closer to unit. This indicates the greater interfering of physical phenomenon. Consequently, one hypothesis was that the mechanism of the adsorption process was electrostatic attraction (Mashkoor et al., 2020). The maximum adsorption capacity (qm) was calculated to be 111.1 mg g−1. RL value (the separation factor) was 0.297 (0 < RL < 1) indicating that the equilibrium adsorption of MB onto ME-MA PAN was favorable.

Fig. 9
figure 9

Linear equilibrium isotherms for the adsorption of MB onto MEPAN

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3.5 Adsorption thermodynamic

By conducting the experiments at different temperatures: 20, 25, 30, 40, and 50 °C, it was possible to determine the thermodynamic parameters for the adsorption of MB dye on ME-MA PAN, such as Gibbs free energy change (ΔG°), entropy change (ΔS°) and enthalpy change (ΔH°), and these parameters can be calculated from the next equations.

In,

$$RT$$
(3)
$${\text{K}}_{\text{d}} = {\text{q}}_{\text{e}} / {\text{C}}_{\text{e}}$$
(4)
$$RT$$
(5)
$$\Delta G^\circ =\Delta H^\circ -T \Delta S^\circ$$
(6)

where: R (8.314 J.mol−1. K−1) is the universal gas constant, while T (Kelvin) is the absolute temperature. The values of ΔS° and ΔH° parameters were calculated from the intercept and slope of the plot of lnKd versus 1/T, then the value of ΔG° was calculated using the Eq. (6). Table 2 provides the values of these thermodynamic parameters. The negative values of ΔHo (-53,524.7 J. mol−1) for methylene blue dye using the ME-MA PAN nanofiber material indicated the exothermic nature of adsorption process. While, the negative ΔGo value at the five temperatures proves the thermodynamic feasibility and spontaneous nature of the adsorption process, however, the increase in ΔGo value with rising temperature indicates the increase in reaction spontaneity (Mansour et al., 2022a, 2022b). According to Table 3's findings, the adsorption process onto the ME-MA PAN caused the positive ΔS° (190.265 J.mol−1. K1) to indicate that the randomness rises at the liquid/solid boundary. Ushakumary (2013) mentioned that this take place as a result of redistribution of energy between the adsorbent and adsorbate. Prior to adsorption, the dye ions close to the ME-MA PAN's external surface will be more controlled than when the dye is later adsorbed, and the ratio of free dye ions to interacting ions by the ME-MA PAN will be higher than when the dye is in the adsorbent state (Surchi, 2011). As a result, augmentation adsorption produces a positive value of the ΔS° parameter, which enhances randomness at the solid solution interface as a result of the adsorption process. This increases the distribution of translational and rotational energy across a small number of particles.

Table 2 Parameters of thermodynamics for MB dye removal by MEPAN
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Table 3 Comparison of MB adsorption capacity with different adsorbents
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3.6 Comparison of MB adsorption capacity with different adsorbents

The results presented in Table S2 highlight the adsorption performance of various adsorbents and bio-adsorbents compared to a nanofiber composite of melamine maleic acid polyamide adduct/poly acrylonitrile (ME-MA amide polymer/PAN) for the removal of Methylene Blue (MB) dye. The nanofiber composite exhibited a remarkable MB adsorption capacity of 111.10 mg/g. This exceptional performance surpasses that of many other adsorbents and bio-adsorbents listed in the Table (3). When compared to natural adsorbents such as peanut husk, rice straw, fruit peels, and walnut shell, the synthetic ME-MA amide polymer/PAN composite demonstrates significantly higher MB adsorption capacity. This indicates the advantages of tailored materials over naturally occurring adsorbents. The most significant findings and discussions are as follows:

  1. i.

    Comparison with Modified Adsorbents: The ME-MA amide polymer/PAN composite also outperforms modified adsorbents, such as sodium dodecyl sulfate-treated salacca skin and sodium dodecyl sulfate-modified activated carbon. This suggests that the engineered composite possesses superior adsorption properties, possibly due to its specific surface chemistry and structural characteristics.

  2. ii.

    Comparison with Surfactant-Modified Adsorbents: Surfactant-untreated and modified Macadamia nutshell, with an adsorption capacity ranging from 125.06 to 195.95 mg/g, show competitive performance with the ME-MA amide polymer/PAN composite. However, the synthetic composite still demonstrates notable efficacy in MB removal.

  3. iii.

    Comparison with Nanoparticles and Biomass: The ME-MA amide polymer/PAN composite's performance is comparable to or even surpasses that of hydroxyapatite nanoparticles and waste cinnamon bark biomass. This underscores the potential of engineered nanomaterials in achieving high adsorption capacities for dye removal.

  4. iv.

    Comparison with Previous Studies: The study's findings suggest that the ME-MA amide polymer/PAN composite outperforms a wide range of natural and modified materials previously investigated for MB removal. This highlights the potential of engineered materials in improving adsorption efficiency.

Overall, the results underscore the effectiveness of the ME-MA amide polymer/PAN composite as an adsorbent for MB removal. Its superior adsorption capacity compared to various natural and modified materials suggests its promising application in wastewater treatment and environmental remediation processes. However, further research could delve into the scalability, cost-effectiveness, and long-term stability of this composite material.

4 Conclusions and Limitations

This study explores the potential of Melamine-maleic acid polyamide adduct/polyacrylonitrile (ME-MA amide polymer/PAN) nanofibers as a novel adsorbent for MB dye removal. Synthesized via electrospinning, ME-MA/PAN composites exhibit promising capabilities for efficient dye removal. High adsorption of MB dye was exhibited at pH 12 and a ME-MA PAN dose of 0.02 g, 30 mg/L, and higher temperatures up to 40°C. Besides, characterization techniques including scanning electron microscopy (SEM), thermogravimetric analysis (TGA), and Fourier transform infrared (FT-IR) confirm the composite's structural integrity and adsorption-friendly functional groups. Nevertheless, adsorption isotherm models reveal a Langmuir adsorption capacity (Qm) of 111.10 mg g−1, indicative of favorable adsorption behavior. Kinetic studies support the suitability of the Laguerre pseudo-second-order model, while isotherm studies are in alignment with the Freundlich model. Thermodynamic analysis suggests spontaneous, exothermic MB removal by ME-MA/PAN nanofibers, feasible at laboratory scale. The kinetics study is favored by Laguerre pseudo–second-order and the experimental results display that; isotherm study was adequately fitted with the Freundlich model. The numerical values of thermodynamic factors (ΔG°, ΔH° and ΔS°) were determined and showed that the removal of MB by ME-MA/PAN nanofiber was a spontaneous, exothermic process and feasible at laboratory scale. The ME-MA/PAN composite emerges as a promising solution for MB dye removal, offering eco-friendly and effective performance.

However, further research is warranted to explore regeneration methods and scale-up processes for practical implementation in real-world scenarios. This study underscores the significance of sustainable materials in environmental remediation efforts, emphasizing the continued exploration and utilization of novel adsorbents for wastewater treatment to ensure long-term environmental sustainability.

5 Limitations of this study:

  1. A.

    Laboratory Scale Feasibility: The findings suggest that the removal of MB by ME-MA/PAN nanofibers is feasible at the laboratory scale. However, translating these results to larger-scale applications, such as industrial wastewater treatment, may pose challenges. Factors like scalability, cost-effectiveness, and practical implementation in real-world scenarios need further investigation.

  2. B.

    Limited Regeneration Studies: The study lacks in-depth exploration of regeneration methods for the ME-MA/PAN nanofiber composite after dye adsorption. Understanding the regeneration efficiency and potential loss of adsorption capacity over multiple cycles is crucial for assessing the long-term sustainability and practicality of the adsorbent material.

  3. C.

    Lack of Real Wastewater Testing: The research primarily focuses on synthetic dye solutions, specifically methylene blue. Real wastewater samples from textile industries, which are complex mixtures containing various dyes and contaminants, were not tested. Evaluating the performance of ME-MA/PAN nanofibers in real wastewater scenarios is essential to validate its effectiveness under practical conditions.

  4. D.

    Limited Exploration of Environmental Impact: While the study highlights the potential of ME-MA/PAN nanofibers as environmentally friendly adsorbents, a comprehensive assessment of their overall environmental impact, including energy consumption during synthesis, disposal of used adsorbents, and potential leaching of contaminants, is necessary for a holistic understanding of their sustainability.

Addressing these limitations through further research and experimentation will enhance the applicability and reliability of ME-MA/PAN nanofibers as a viable solution for dye pollution in aqueous systems, advancing towards more sustainable environmental management practices.

6 Authorship Contribution

Ahmed. E. Alprol Conceptualization, Methodology, Investigation, Formal analysis, Writing – review & editing., M. Abu-Saied Conceptualization, Methodology, W.M. Thabet Conceptualization, Methodology, Investigation, Formal analysis, review & editing., O. Abdelwahab Conceptualization– review, editing and revising manuscript, M.A.Abd El-Ghaffar Methodology– revising.