Ultrahigh adsorption capacity of a new metal sieve-like structure nanocomposite-based chitosan-graphene oxide nanosheet coated with poly-o-toluidine for the removal of Acid Red dye from the aquatic environment

Abstract This article describes an easy and simple method to remove a toxic Acid Red dye from aqueous solution. Ternary poly(O-toluidine)/graphene oxide/chitosan P(OT)/GO/CS nanocomposites (NCs) were fabricated by an oxidative polymerization technique to remove Acid Red (A.R.) dye from aqueous solutions using solid-phase extraction. The P(OT)/GO/CS NCs exhibit a metal sieve-like structure consisting of GO nanosheets and a core shell-shell porous structure, which provides several adsorption sites and channels for the transport of dye molecules. FTIR, XRD, RAMAN, TEM, SEM, BET, and TGA-DTG investigations were carried out on NCs. To investigate the removal effectiveness of the NCs using adsorbent dose, pH and solution temperature, shaking time, and ionic strength. Experimental adsorption findings, utilizing 15 mg of solid-phase NCs, can remove the majority of the A.R. dye in 75 min at pH 2.0 with an adsorption efficiency and an adsorption capacity of 99.6% and 169.5 mg/g, respectively. The pseudo-second-order kinetic model best captures the adsorption process of A.R. dye on the NC solid phase, according to experimental data. Thermodynamically, the removal process was endothermic, spontaneous, and associated with increasing randomness. Finally, NCs were tested by removing A.R. dye from real samples. NCs removed A.R. dye from aqueous solutions for four cycles. Graphical Abstract


Introduction
Water contamination is increasingly a priority, and industrialization and wastewater generation have caused several aquatic concerns [1].Paper, leather, textile, plastic, medicines, food, and cosmetics industries employ synthetic dyes, which create highly colored wastewater [2][3][4].Synthetic dyes with an azo group (N ¼ N) can cause cancer, mutagenesis, and aesthetic issues [5][6][7].Toxic, nondegradable dyes harm humans, animals, and the environment [8].It is visible in water at concentrations as low as 1 ppm [2].Moreover, azo dyes can create issues with oxygen solubility in water sources and can disrupt photosynthesis even at low concentrations [9,10].Approximately 10-15% of the colors produced during the dying process are discharged into the sewage [11][12][13].Untreated colored wastewater pollutes water sources, making its removal from solutions crucial.Traditional wastewater dye removal methods are less effective [14].Treatment of colored wastewater has included the use of physical and chemical processes such as coagulation and flocculation, adsorption, photocatalytic processes, advanced oxidation precipitation, electrochemical techniques, and biological treatments [14][15][16].In comparison to the other methods, adsorption is widely adopted because of its efficiency, operational method, and simple and costeffective preparation processes [5,[17][18][19][20].
Many different polymer NC adsorbents have been tested for this purpose, resulting in enhanced surface area, processability, tunable properties, costeffectiveness, and stability [AQ].Fast decontamination capabilities along with high selectivity for removing different contaminants were both shown by the polymer NCs [21].
GO nanoparticles (NPs) have a stronger aptitude for adsorbing a variety of dye molecules owing to (p-p) stacking interactions.This is because the twodimensional structure of GO NPs is conjugated, which gives them a two-dimensional structure [22][23][24][25][26][27].Recently, owing to their eco-friendliness, ease of modification, nontoxicity, biodegradability, and broad range of applications, natural polymer adsorbents such as chitosan (CS), cellulose (CE), starch (ST), and lignin have garnered more attention [28][29][30][31].Functional groups can be easily added to the skeleton to improve the adsorption of target pollutants such as metal ions and dyes through chelating effects, hydrogen bonding, and electrostatic interactions [32][33][34].Modern hybrids of materials containing conducting polymers (poly-aniline, poly o-toluidine, polypyrrole, poly thiophene, and poly oanisidine) are of enormous practical significance because they may be used to create composite materials by adding organic moieties to inorganic NPs of different shapes and sizes.For adsorption and ion exchange, numerous nanocomposite materials with conducting polymer coatings have been reported [35].
Alqarni synthesized two different types of ternary NCs by combining polythiophene (PTh), multiwalled carbon nanotubes (MWCNTs), zinc oxide (ZnO), and oxidized multiwalled carbon nanotubes (OXMWCNTs) using in situ chemical polymerization.Using both (PTh-ZnO-MWCNTs) and (PTh-ZnO-OXMWCNTs) NCs to remove brilliant green (B.G.) dye from water shows excellent results.For PTh-ZnO-OXMWCNTs, 9.1 mg g À1 had the greatest adsorption capacity, whereas for PTh-ZnO-MWCNTs, it was 8.3 mg g À1 .This finding demonstrates that oxidation of MWCNTs improves the adsorption capacity of the NCs by the addition of more carboxylic (-COOH) groups to the surface of the MWCNTs [36].Beads of ZnO NPs impregnated with chitosan (CS@ZnO) NCs have been prepared by Raval and colleagues by mechanical stirring as well as microwave-assisted techniques and used for Eriochrome Black-T dye removal [37].Adsorption capabilities for dye removal from a solution with a multipollutant were highest for the CS@ZnO beads synthesized by microwave-assisted techniques, reaching up to 71%.This work depends on the simple synthesis and incorporation of NPs of metaloxide in biopolymers to provide the CS with a high capacity for adsorption, a specific surface area, and a mechanical strength to remove dye molecules from textile effluent.In the current study, natural polymer adsorbents have required functional groups (cellulose with abundant hydroxyl groups, chitosan with abundant amino and hydroxyl groups [38] and a hydroxyl group in starch [39] are used as functional entities for the generation of NCs to remove targeted dyes through electrostatic interaction.The GO sheet used to enhance the adsorption capacity of NCs via negative charges from different functional groupings with plenty of oxygen, such as hydroxyl, carbonyl, epoxy, and carboxyl groups, permits additional vigorous electrostatic interactions with cationic dye molecules [27,40,41].In addition, when GO is incorporated with polymers, it helps to improve the properties of NCs, which include a large surface area, efficient electron transport, a two-dimensional structure, chemical stability, and the capacity to encourage negative charge accumulation on surfaces [42].OT is used here as the matrix phase.These polymers have a large surface area, are ductile, malleable, and have good mechanical strength [43], in addition to peculiar functional groups (-NH) and remarkable electrical characteristics [44] that improve their organic pollutant removal.Thus, this study describes the modification of NCs with OT by its ease of synthesis, low cost, excellent environmental stability, and ability to avoid aggregation of components [45].
An oxidative polymerization technique was applied for the fabrication of ternary P(OT)/GO/CS, P(OT)/GO/SE, and P(OT)/GO/ST NCs.The biggest advantage was that the NCs exhibit a metal sievelike structure consisting of GO nanosheets and a core-shell-shell porous structure, which provides several adsorption sites and channels for transport of dye molecules.They are predicted to make surface groups on NCs readily available as adsorption sites for pollutants and allow functional NCs to interact with contaminants in water.It was used to adsorb Acid Red dye from water.On the basis of many factors, including pH, adsorbent dose, dye concentration, and time, we assessed the dye's adsorptive ability.Additionally, the findings were compared to previously published literature and connected with kinetic and isotherm models.

Instrumentation
High-resolution transmission electron microscopy (HR-TEM; JEM-2100; 25Â magnification and 200 kV) and field emission scanning electron microscopy (SEM Model Quanta 250 FEG; 30 kV accelerating voltage at 14Â magnification and up to 1,000,000 resolution for Gun.1n) were used to assess the morphologies of the materials under study.To obtain essential structural and crystallographic information about the NCs, X-ray diffraction (XRD) of the NC crystallinity was also examined.The analysis was carried out with a Bruker Model D8 [including reflectometry, highresolution diffraction, in-plane grazing incidence diffraction (IP-GID), small-angle X-ray scattering (SAXS), and residual stress and texture investigations] with CuKa radiation (1.5418 Å, Madison, WI, USA) working at a current of 30 mA, voltage of 40 kV and step scan of 0.02 .However, the samples must be prepared before measurement, and sample milling using a simple planetary ball mill (LZQM0.4L,Shicheng Oasis Mineral Equipment Manufacturing Co., Ltd.) in which a ball mill of stainless steel with a 0.1 cm diameter was placed in a milling dram with samples for 30 min at 2500 rpm.To establish the thermal stability of the NC materials and to specify their degradation temperature, thermogravimetric analysis (TGA) and DTG tests were utilized.The analysis was performed on TGA-50 systems at a heating rate of 10 C/min in air.Fourier transform infrared (FTIR) spectra were recorded and analyzed to determine the sample's functional groupings, and a Shimadzu spectrometer was utilized in the range of 4000-400 cm À1 .The materials were analyzed using a Raman spectrometer to acquire Raman readings.(Lab.RAM-HR Evolution Horiba Co.) with a single visible spectrometer equipped with an aircooled open electrode 1024 Â 256 pixel CCD detector, a 532 nm He-Cd laser with an 1800 grating (450-850 nm) and a 10% ND filter using an acquisition time of 5 s, 5 accumulations without spike filter and delay time, and a 100Â objective.The specific surface area (S BET ) of Quantachrome's NOVA touch LX2 model, NT2LX-2, USA, was calculated using the BET technique.The statistics on absorption.The pore volumes and pore-size distributions were obtained from nitrogen sorption isotherms using the Dubinin-Astakhov (DA) method.The samples were degassed in a vacuum for at least three h at 150 C before measurement.The Stokes-Einstein equation uses the angular intensity distribution to calculate the particle size.This study used a Perkin-Elmer UV-visible (190-1100 nm) spectrophotometer (model Lambda 25, USA) with a 10 mm (path width) quartz cell to capture all spectrophotometric readings.A digital micropipette (Volac) was used to prepare standard Brilliant Green dye, and an Orion pH meter (model EA 940) was used to measure the pH of the test solutions.Milli-Q Plus system (Millipore, Bedford, MA, USA) deionized water was utilized for solution preparation.

Synthesis of GO
GO was created using a modified version of Hummers' method following the procedure described in [46].

Synthesis of P(OT)/GO/CS NCs
In situ polymerization was utilized to prepare the NCs of P(OT)/GO/CS.GO NPs were introduced into hydrochloric acid (100 mL, 1 M).The solution [designated solution A] was sonicated for one h.APS (5 g) was added to HCl (100 mL, 1 M) [designated solution B].A dispersion (solution designated C) was obtained by dissolving CS (0.5 g) in acetic acid (4%) in a 250 mL (three-neck flask) for 1 h while constantly stirring.
The temperatures of solutions A, B, and C were lowered to 0-4 C in an ice bath.Dropwise additions of solution A were added into solution (C) over the course of approximately 30 min while stirring continuously between 0 and 4 C in a nitrogen atmosphere.The procedure for polymerization included adding OT (doubly distilled, 1.07 mL) and stirring continuously for 30 min, followed by adding solution B dropwise into the aforementioned mixture for approximately 30 min while stirring continuously between 0 and 4 C in a nitrogen atmosphere.For 24 h, the polymerization process was stirred continuously at 0-4 C in a nitrogen environment.The resulting black precipitate was extracted using ultracentrifugation, and the filtrate was washed in deionized water until it was clear.The obtained black fine powder was dried for 24 h at 60 C.
The ternary P(OT)/GO/SE NCs and P(OT)/ GO/ST NCs were synthesized in the same procedure as the ternary P(OT)/GO/CS NCs, except solution C in the ternary P(OT)/GO/SE NCs was prepared by adding 0.5 g of SE to a three-neck flask (250 mL) and swirling vigorously for 1 h to adequately dissolve it in 83% phosphoric acid to create a dispersion.For P(OT)/GO/ST NCs, 0.5 g of ST was poured into a 250-mL (three-neck flask), adequately dissolved in distilled water and vigorously mixed for an hour to obtain an even distribution.The rest of the steps are the same as those described for the synthesis of P(OT)/GO/CS NCs.The method used to synthesize the three ternary NCs is presented in Scheme 1.For comparison purposes, pure P(OT) and P(OT)/GO NCs without GO/natural polymers and without natural polymers, respectively, were prepared using the same in situ polymerization process that was used to prepare the ternary P(OT)/GO/CS NCs.

Step of batch extraction
Dissolving 0.05 g of A.R. dye into 100 ml of deionized water yielded a stock solution (500 mg L À1 ) for later use.To create more dilute standard solutions, deionized water was used to dilute the stock solution (10-50 mg L À1 ).As an extraction medium, a variety of buffers of Bitton-Robinson (BR) with HCl concentration (0.1 mol L À1 ) at pH (2)(3)(4)(5)(6)(7)(8)(9)(10)(11) were used in an A.R. dye sorption experiment by solid phase P(OT) ternary and P(OT)/GO/CS NCs.Accurately measured amounts (0.005 ± 0.0005 g) of P(OT) and P(OT)/GO/CS NCs as the solid phase were equilibrated in 50 mL of an aqueous solution including 20 mg L À1 A.R. dye at pH ¼ 2. The sample solution was mechanically shaken for 120 min.Separating, the aqueous phase allowed us to determine the quantity of A.R. dye remaining in the aqueous phase spectrophotometrically by using a calibration curve and measuring the absorbance of the A.R. dye in aqueous solution at 530 nm before and after adsorption [47] in the P(OT) and P(OT)/GO/CS NC solid phases.Finally, the following Eq.( 1) for the dye adsorption percentage (%E) and dye adsorption quantity (q t ) per unit mass of P(OT) and P(OT)/GO/CS NCs were calculated using these relationships: Scheme 1. Illustration of the fabrication route of the ternary P(OT)/GO/CS, P(OT)/GO/SE, and P(OT)/GO/ST NCs.
where (C o ) is the initial concentration of dye, (C t ) is the final concentration of dye in the solution (mg L À1 ), the aqueous solution volume is (V, L), and the solid phase mass utilized is (m, g).

Environmental applications and sample collection
The effectiveness of the solid phases P(OT) and P(OT)/GO/CS NCs sorbent in the extraction and recovery of A.R. dye from the water of the Red Sea, waste, and tap was studied.The samples were taken from the Red Sea and the Membrane Bioreactor Technology Wastewater at King Abdulaziz University and the lab in the Department of Chemistry, King Abdulaziz University, at Jeddah City (KSA), respectively.After being filtered via a 0.45 m membrane, the samples were stored in Teflon bottles in a refrigerator at 5 C. A 100 mL sample was modified to pH equal to 2 by using 0.1 mol L À1 HCl before being processed across the solid phases P(OT) and P(OT)/GO/CS NCs.Then, the recovered A.R. dye was measured spectrophotometrically.

Characterization
Incorporating GO into branching reticular structures provides properties for depositing nanoscale layers of conducting polymers, for example, a relatively large area that increases NC adsorption.The adsorption of NCs is enhanced by the presence of natural polymers such as chitosan, cellulose, and starch, which provide a number of effective adsorption sites in the NCs.Scheme 1 shows the synthesis route of the P(OT)/GO/CS, P(OT)/GO/SE, and P(OT)/GO/ST ternary NCs.

XRD measurement
The XRD diffraction patterns for pure P(OT) and its NCs are shown in Figure 1A.The amorphous character of P(OT) is shown by the presence of a large peak between 2h ¼ 19 and 33 , resulting from component interactions.The literature suggests that periodicities running parallel and perpendicular to the polymer account for the primary diffraction peaks at 20 and 25 [43,44].Binary P(OT)/GO NCs exhibit the wide diffraction peak of P(OT) in their diffraction patterns.Moreover, the peak at approximately 2h ¼ 17.75 confirms the presence of GO in the matrix of P(OT) [48].On the other hand, the patterns created by XRD for the P(OT)/GO/CS, P(OT)/GO/SE, and P(OT)/GO/ST ternary NCs had recognizable peaks in both P(OT) and GO in addition to the characteristic peaks of CS at 2h ¼ 20.00 and 12.20 corresponding to the CS characteristic peaks [49], at 2h ¼ 16.75 and 22.20 [50] of cellulose, and the starch exhibits diffraction peaks of 2h ¼ 12.00 , 14.30 , 16.50 , 18.40 , 19.60 , and 22.30 [51].The appearance of these peaks proved that all ternary compounds were produced.Moreover, it is noted that the greatest intensity peak has shifted, demonstrating that the grafted polymer differs from its parent polymer in terms of its physical and chemical characteristics.

FTIR spectra
The FTIR spectra of P(OT) and its NCs are shown in Figure 1B, which are consistent with earlier findings [35] The N-H stretching vibration was responsible for the band at 3434 cm À1 seen in the spectra of P(OT), while the 1585 and 1490 cm À1 bands were assigned to stretching of C¼C in a quinoid ring and C¼N stretching in a benzenoid ring, respectively.The 1220 cm À1 band was produced by stretching vibrations of C-N in the benzenoid ring.Benzene ring C-H out-of-plane bending vibrations were responsible for the 797 cm À1 band seen in P. (OT).In a doped structure, the conductivity is enhanced by the high doping level, which causes the strongest peak to appear at approximately 1114 cm À1 [52,53].
The decreased peak intensities in the spectra of binary P(OT)/GO NCs show that the P(OT) chains interact with the GO surfaces [54].Doped P(OT) is responsible for the 1114 cm À1 peak, which is used to quantify electron delocalization [55].Thus, it is the electrical conductivity peak seen in P(OT).The presence of significant interactions between the conjugated structure of P(OT) and the p-bonded structure of GO is supported by the fact that the strength of the 1114 cm À1 peak increases and the peak is slightly shifted with the addition of GO [56][57][58], The FTIR spectra of the P(OT)/GO/CS, P(OT)/GO/SE, and P(OT)/GO/ST ternary NCs had characteristic peaks of both P(OT) and GO in addition to the characteristic peaks of CS at 1654 cm À1 corresponding to the -NH bands in CS characteristic peaks [59].Bands of -NH 2 spanning 3435-3500 cm À1 for P(OT) and the range of free -OH at 3500 cm À1 to SE have quite different characteristic bands [60].The starch exhibits (3432 cm À1 ) diffraction peaks, which are part of the O-H group's (in the presence of H-band) characteristic broad band [61].The appearance of these peaks proved that all ternary compounds were produced.Moreover, the peaks of certain FTIR absorptions have moved to lower wavenumbers, whereas the peaks of other bands have moved to higher wavenumbers.These FTIR data indicated that the effective creation of NCs was the consequence of a combination of electrostatic forces and hydrogen bonding interactions.

Raman spectra
The existence of GO as well as P(OT) in the NCs was verified by Raman spectroscopy.Figure 1C shows the Raman spectra of P(OT) with its NCs.The NC Raman spectra show the distinctive peaks of both D and G of GO.The E 2g mode of in-plane stretching is represented by the G band.Sp 3 -hybridized carbon atoms and other disorder-inducing factors are responsible for the D band [62].Peaks at 1346 and 1590 cm À1 in the P(OT) polymer are attributed to the (C-N þ ) stretching vibrations in the semiquinone radical state and quinoid ring C ¼ C ring stretching vibration, respectively [63].At 1454 cm À1 , the stretching vibration of C ¼ N in a ring of quinoid [64] was observed.The bending mode of N-H is located at 1400 cm À1 [65].The bands of both D and G in the Raman spectra are indicative of GO NPs, which are at approximately 1344 and 1591 cm À1 , respectively.The P(OT)/GO NCs have a Raman spectrum with the same D and G peaks seen in GO NPs.When compared to GO NPs, the P(OT)/GO NC bands of D and G emerge at 1346 and 1587 cm À1 , respectively, which is a minor shift.The ternary NCs of P(OT)/GO/CS, P(OT)/GO/SE and P(OT)/GO/ST Raman spectra showed both the G band and the D band.There is a noticeable shift in the G and D bands when compared to GO.This minor change can be the result of the polymer and GO interacting strongly [66].
Additionally, the ternary NC curves showed an increase in the D bands, and the ratios of I D /I G of all ternary NCs (I D /I G ¼ 0.85, 0.84, and 0.84 for P(OT)/GO/CS, P(OT)/GO/SE, and P(OT)/GO/ST NCs, respectively) are identical to the I D /I G ratio of GO (I D /I G ¼ 0.84), demonstrating that the level of disorder in GO remains stable through chemical treatment [67].These findings proved the existence of the polymers P(OT), GO, and CS, SE, and ST in the ternary NCs.

BET
Pure P(OT) and its NCs have their BET surface area as well as volume determined, along with an isotherm.In Figure 1D, the isotherm curves are displayed.All samples showed (IV) isotherms which means they were all mesoporous adsorbents with unrestricted monolayer-multilayer adsorption.The results of BET analysis of all samples are shown in Table 1.According to the study results, adding GO to P(OT) caused a decrease in the P(OT) total surface area due to the GO NPs filling the pores of P(OT).On the other hand, the effect of the addition of natural polymers (CS, ES, and ST) on the BET surface area of P(OT)/GO was demonstrated.The BET surface area of ternary NCs of P(OT)/GO/CS, (OT)/GO/SE, and P(OT)/GO/ST showed total surface area decreases.The lower S BET and average total pore volume of ternary NCs with various natural polymers may be attributable to filler instability, which causes agglomeration of fillers inside the adsorbent pores and hence reduces the adsorbent's adsorption capacity.In comparison to the other ternary NCs, P(OT)/GO/CS was shown to have the largest surface area and the largest average pore volume, measuring 44.2405 m 2 /g and 0.180873 cc/g, respectively.
3.1.5.Morphological study Figure 2 displays SEM and TEM images of the samples.Figure 2A shows that P(OT) is similar to a lump structure with some smaller granular sizes, which reveals the irregular clustered morphology of the polymer.Figure 2B shows that the lump structure of P(OT) is evidently reduced due to conduction with GO, and the GO is covered by P(OT) to form a more compact composite with a micro/nanostructure.When CS is added to the binary polymer matrix (Figure 2C), the lump structure of P(OT) increases owing to P(OT) and CS electrostatic interactions first, which increases the lump structure after both polymer P(OT) and CS cover the GO to form a core-shell-shell structure.Due to their structure, ternary NCs have a larger surface area and can distribute nanomaterials more effectively.The ternary P(OT)/GO/SE NCs in Figure 2D show the same morphology as the ternary P(OT)/ GO/CS NCs. Figure 2E displays the SEM image of P(OT)/GO/ST NCs as stronger aggregation, which may be caused by chains that form stronger interactions.
Figure 2F portrays the production of P(OT) with twisting and clustering of fibers into a weblike structure as opposed to a simple bundle.The dark areas show the multilayer P(OT), whereas the transparent regions, which are caused by nanostructure exfoliation, show low-density layers.However, the dark parts are more evident, showing that most layers of P(OT) are exfoliated.After adding GO (Figure 2G), the morphology of the binary P(OT)/GO NC particles primarily consisted of sheet-like structures.After the incorporation of CS, SE, and ST with GO in the P(OT) matrix in P(OT)/GO/CS NCs (Figure 2H), P(OT)/GO/SE NCs (Figure 2I), and P(OT)/GO/ST NCs (Figure 2J), the structure of ternary NCs was determined to be a hollow polymer, and GO was contacted in the center of the hollow polymer to produce a strainer-like structure.The hollow structure of the NCs is clearly visible with the thickness of the shell with a relatively uniform shape.This thickness may be attributed to a homogeneous layer of P(OT) coated on the surface of CS, SE, and ST.

Thermal stability
Thermogravimetric analysis was used to characterize the P(OT) and its NC samples, which allowed for the study of thermal stability in addition to weight loss of the manufactured materials (TGA-DTG).In Figure 3A, the TGA curves are shown.There are three major levels of disintegration visible in the   TGA thermogram generated for P(OT).First, at lower temperatures (85 C), H 2 O molecules are lost, and HCl is desorbed, resulting in a weight loss of approximately 15%.At 256 C, a further 25% mass loss occurs, which may be attributable to the dissolution of lighter-weight P(OT).The thermal degradation of the chains of P(OT) is responsible for the ultimate loss of mass of 40% seen at greater temperatures (more than 444 C).At 533 C, we observed that P(OT) completely decomposed.Ternary P(OT)/GO/SE and P(OT)/GO/ST NCs have been observed to exhibit comparable behavior; however, with the addition of GO/SE and GO/ST, respectively, the temperature of thermal degradation changed.The curves moved to higher temperatures, as shown in Figure 3A.There is a slight difference in the behavior of binary P(OT)/GO NCs and ternary P(OT)/GO/CS NCs, and there are primarily three levels of deterioration in the binary P(OT)/GO NCs.In the first level, desorption of HCl as well as loss of H 2 O molecules at lower temperatures (100 C) results in a 10% weight loss.At 260 C, there is a second mass loss of approximately 15%, probably as a result of the degradation of P(OT) at a lower temperature.The P(OT) chain thermal degradation is responsible for the ultimate mass loss of 25% seen at higher temperatures (above 465 C).At 530 C, it was shown to completely decompose.For ternary P(OT)/GO/CS NCs, a similar behavior was described, but with the curves shifting to lower temperatures.
The temperatures at which 10 and 25% of a substance's mass is lost due to combustion are shown in Table 2 as T 10 and T 25 , respectively.The P(OT)/GO/CS ternary NCs have T 10 and T 25 values of 50 and 478 C, respectively.P(OT)/GO/CS NCs had the highest residual mass retentions and thermal stabilities at high temperatures among the three ternary NCs.P(OT), GO, and CS may interact to provide increased stability.
The final composite degradation temperature [CDT final ], is where temperature is considered the temperature at which the decomposition ends [49,68,69].Table 2 displays the results of the TGA curves, elucidating the similarity between the CDT final of all ternary NCs.Moreover, based on the DTG curves seen in Figure 3B, the PDT max values, which are the maximum temperatures at which polymers degrade [49,70,71] proven for samples in Table 2, confirm that the ternary P(OT)/GO/CS NCs are more thermally stable due to their interplaying constituents.In comparison between the ternary NCs, the values of PDT max and CDT final of ternary P(OT)/GO/CS NCs are higher than the values of both ternary P(OT)/GO/SE and P(OT)/GO/ St NCs.
The previous analysis forms the basis for the proposed mechanism for the formation of ternary P(OT)/GO/CS NCs.The ternary P(OT)/GO/CS NCs were synthesized in an acidic medium using the facile chemical oxidative polymerization method, and their network core-shell-shell structures are shown in Scheme 2a.Acidic conditions cause the -COOH groups on the surface of GO to become protonated, gaining H þ from the surrounding medium [70].Protonated amine groups in the CS biopolymer structure provide active sites, along with hydroxyl and carboxylate groups [49,69,72].As a result, the cationic properties of the polymer are due to the protonation of amine groups in acidic conditions [73].As a result, the surface positive charges of CS as well as GO might be neutralized by the adsorption of several Cl À anions.In addition, in this charge compensation system, throughout the process of P(OT)/GO/CS NC creation, additional Cl À adsorption on the CS and GO surface may act as a charge compensator for P(OT) chains that are positively charged.On the other hand, in acidic environments, the OT monomers transform into O-toluidinium cations.Anions absorbed by the surfaces of CS and GO interact in electrostatic interactions with one another, as well as cationic O-toluidinium.Furthermore, it is possible that there will be two types of hydrogen bonding.First, oxygen and nitrogen atoms on the CS and GO surfaces form hydrogen bonds with P(OT) chains.Second, hydrogen bonding between P(OT) chains occurs in ternary P(OT)/GO/CS NCs.Finally, GO (bonds) stacking with the P(OT) aromatic rings in the p-p configuration assists in stabilizing the ternary P(OT)/GO/CS NC-bound structure [49].The interactions can confirm that the CS contacted the GO first to form the CS/GO core-shell structure, then the P(OT) was coated with CS to form the P(OT)/CS/GO coreshell-shell structure that produces ternary NCs which show a hollow polymer connected with GO sheets inside the hollow polymer circle and form the NCs as a metal sieve-like structure.As a result, uniform and continuous high interconnection networks are generated.This network provides active centers that are ideal for increasing dye adsorption, so the P(OT)/GO/CS NCs provide a framework for the removal of dye materials.P(OT)/GO/CS NCs were better than other correspondents in dye extraction, so it was selected as the most appropriate NC for all experimental studies.One absorption peak at 530 nm was visible in the electronic spectrum of A.R. dye when it was recorded in the aqueous phase, as shown in Figure 4B.Meanwhile, after shaking with solid phases P(OT) and P(OT)/GO/CS, this peak substantially diminished (Figure 4B curves b and c, respectively).This result supports the solid phases' effectiveness in the removal of A.R. dye from the aqueous phase.

Comparison with other adsorbents
Table 3 compares the P(OT)/GO/CS NC adsorption capacity and adsorption time to those of other literature-reported adsorbents.From the data in Table 3, it is evident that P(OT)/GO/CS NCs have a remarkable uptake capacity and are potentially an effective, competitive, and promising replacement for other solid adsorbents when used to remove A.R. dyes from solutions.

Influence of pH
A solution's adsorption for recovery of dyes depends on several factors, one of which is pH.The features of sorption in aqueous solutions containing A.R. dye at various pH values by solid phases P(OT) and P(OT)/GO/CS NCs was studied after being shaken at room temperature for 120 min.After reaching equilibrium, the amount of A.R. dye in the aqueous phase was determined photometrically [47].The percentage %E of adsorption of A.R. dye onto solid phases P(OT) and P(OT)/GO/CS NCs have the maximum value in (pH ¼ 2) then the percentage decrease with pH increase.Figure 5A displays sample data.There is a very large concentration of H þ ions in both acidic and slightly alkaline dye solutions [77,78].This causes the P(OT)/GO/CS NCs to become highly protonated, which facilitates the rapid adsorption of the anionic dye molecules.Dye solution decolorization happens owing to strong electrostatic interaction among positively charged P(OT)/GO/CS NCs and negatively charged dye molecules [79].When exposed to a very alkaline dye solution with a pH ¼ 10, however, due to the high concentration of OH ions, the P(OT)/GO/CS NC surface attracted hydroxyl ions, neutralizing their charges and limiting dye adsorption.This caused poor dye removal [80,81].As a result, the researchers decided that a pH value of 2 was ideal for moving forward.The proposed mechanism of dye removal is suggested in Scheme 2b.

Influence of mass
At an A.R. dye (20 mg/L), the impact of the adsorbent mass on the A.R. dye removal from aqueous solution was analyzed (Figure 5B).Dye removal is found to increase in tandem with the mass of NCs because there are more free sites for the dye to occupy.The plot demonstrated an increase in the percentage of removed A.R. dye from the aqueous solution from 41.6 to 99.6% as the P(OT)/GO/CS NC solid phase mass increased from 2.5 to 15 mg and from 12.2 to 64.4% as the P(OT) solid phase mass increased from 2.5 to 15 mg.In this work, we used 5 mg of P(OT)/GO/CS NCs solid phase mass, which corresponds to 68.2%, to investigate how changing other variables impacts the adsorption procedure.

Influence of contact time
One of the most crucial variables in dye adsorption studies is contact time.The results are displayed in Figure 5C, which shows how the contact time affected the A.R. dye removal by the P(OT) and P(OT)/GO/CS NCs solid phases.The percentage of A.R. dye removal increased over time.Within the first 75 min, when the majority of the A.R. dye was adsorbed, this effect was particularly noticeable.Within 135 min, the percentage of A.R. dye removal reached equilibrium.This demonstrates that A.R. dye adsorption on solid phases P(OT) and P(OT)/GO/CS NCs took place in two stages in succession, first in which A.R. dye was transferred from the aqueous phase to the exterior surface of solid phases, was the fastest.The diffusion of A.R. dye between the solid phase bundles was the second step, which was the slower one.

Influence of temperature
The effect of solution temperature on the adsorption process was studied.Experiments at a constant time were conducted at four temperatures: 10, 20, 35, and 50 C. Solid phase removal of A.R. dye P(OT) and P(OT)/GO/CS NCs was found to increase dramatically with increasing solution temperature (from 10 to 20 to 35 to 50 C; see Figure 5D).These data point to the adsorption process being endothermic in nature.

Influence of ionic strength
In the dyeing industry, a number of additives are used, including surfactants and salts (sodium chloride).The presence of salts may reduce dye uptake by reducing the attractive forces between dye molecules and an adsorbent with opposing charges.In contrast, the presence of foreign ions may promote dye dissociation, leading to a general improvement in dye adsorption [82].Thus, large-scale industrial wastewater cleanup must carefully examine this aspect.Adsorption studies of A.R. dye onto solid phases P(OT) and P(OT)/GO/CS NCs were performed, and the effect of ionic strength on adsorption was also studied.By varying the ionic strength during the adsorption experiments, KNO 3 concentrations of 0.025, 0.05, 0.075, and 0.1 mol/L were used (Figure 5E).Increasing the ionic strength of the aqueous solution was shown to decrease the proportion of dye species that were adsorbed.Due to charge accumulation near the adsorbent surface, cations such as K þ reduce the dye species' contact with it [83].[84].Therefore, film and intraparticle diffusion are necessary for the kinetics of a dye's adsorption on solid phase sorbents.The kinetics of A.R. sorption onto solid phase P(OT) and P(OT)/GO/CS NCs were studied using the following models.

Weber-Morris model
The Weber-Morris model was applied based on the following equation [85]: in which q t and R d are the sorbed A.R. dye concentration at time t and the rate constant of intraparticle transport, respectively.Figure 6A displays the plot of q t as a function of time, and the numerical values of R d are determined by the distinct slope of the Weber-Morris plots, as shown in Table 4.

Fractional power function model
To determine the kinetic model of the fractional power function, the following equations were used [86]: where at any time t, q t (mg/g) represents the amount of A.R. dye adsorbed per unit of mass of solid phases P(OT) and P(OT)/GO/CS NCs, while a and b are coefficients with b < 1.The experimental data of the adsorption route are applied to the fractional power function equation displayed in Figure 6B, and the values of (R 2 ) are shown in Table 4.This information could suggest that the fractional power function kinetic model suitability for the description of A.R. dye adsorption by the solid phases P(OT) and P(OT)/GO/CS NCs.

Lagergren pseudo-first-order model
The Lagergren equation is one of the most often used equations for characterizing rates of adsorption in liquid-phase approaches.We use the following equation [87]: log ðq e À q t Þ ¼ log q e À K lager t=2:303 where q e is the A.R. dye amount absorbed per unit of mass of sorbent at equilibrium.For the retention process, K Lager is the first-order overall rate constant, and the time is t.From the slope and intercept of the plot log (q eÀ q t ) against t (Figure 6C), which gives the starting line, we calculated both K Lager and q e , and the values are presented in Table 4.
The first-order kinetics of the sorption of the A.R. dye species onto the employed solid phase sorbent is not supported by all of these data [88,89].

Pseudo-second-order model
In this kinetics model, the following must be considered [90,91]: (i) the total number of binding sites at equilibrium is determined by the quantity of adsorbate adsorbed, and (ii) the concentration of the adsorbate is constant over time.To express the pseudo-second order rate in its linearized form, the following equation was used.
where h ¼ k 2 q e2 represents the initial sorption rate, and q e and q t are the amounts of adsorbate that are absorbed per unit of mass at equilibrium and at any time.As demonstrated, the t/q t plots versus t were linear under these conditions (Figure 6D).The values of both the second-order rate constant (k 2 ) and the equilibrium capacity (q e ) for A.R. dye removed by solid phases, are listed in Table 4.
The values of k 2 , which are generally dependent on experimental factors such as the initial dye concentration, pH, and temperature of the solution, are shown to be in excellent agreement with all of the experimental data [92].

Elovich model
The Elovich model is often used to describe the rate equation mainly depending on their capacity for absorption [93,94].In most cases, for situations where the absorbing surface is not uniform, this model is valid, and it is most useful for calculating chemisorption kinetics.The following equation provides an expression for this model: where a and b are the initial adsorption rate (g mg À1 min À1 ) and the desorption coefficient (mg g À1 min À1 ), respectively.The Elovich parameters a and b were computed from the intercepts and the slopes of the plot of q t against lnt, which was linear (Figure 6E).The data is listed in Table 4.
The results of the above various models depend on the correlation coefficient values (see Table 4).The pseudo-second-order adsorption model with good regression coefficients can simulate A.R. dye adsorption on nanocomposites.

Thermodynamic studies
The retention of A.R. dyes on solid phases is calculated, its sorption was studied at a range of temperatures (293-323 K) using solid phase P(OT) and P(OT)/GO/CS NCs.To calculate the values of the thermodynamic parameters [DH, DS, and DG], we used the following formulas [95]: DG ¼ DH À TDS (9) DG ¼ ÀRTlnK c (10) where changes in enthalpy, entropy, and Gibbs free energy are denoted by DH, DS, and DG, respectively.The temperature, denoted by T in Kelvin, and the constant for gases are denoted by R (%8.314 J K À1 mol À1 ) and the equilibrium constant constant, denoted by K C .To determine the K C values for A.R. dye equilibrium retention from the aqueous solution under test onto the sorbent in the solid phase, we can use the following equation: where C e is the A.R. dye concentration at equilibrium in aqueous solution (mg L À1 ), C a is the amount of A.R. dye adsorbed onto the solid phase per liter at equilibrium (mg L À1 ).For A.R. dye retention onto solid phases P(OT) and P(OT)/GO/CS NCs, a linear relationship between ln K C versus 1000/T was observed, as proven in Figure 6F, over a wide temperature range (293-323 K).The retention of A.R. dye on the utilized sorbents is an endothermic process, as evidenced by the increase in the constant of equilibrium for solids with increasing temperature.
From the linear plot slope and intercept of ln K C versus 1000/T, we were able to derive the DH, DS, and DG numerical values for A.R. dye retention (Figure 6F).The results are listed in Table 5.
The solid phases have values of DH that are proportional to the bond energy difference between the sorbent and the analyte, indicating that the uptake process is endothermic.The positive value of DS for solid phases suggests that A.R. dye binding increases the degree of freedom at the solid-liquid interface owing to the release of water molecules from the hydration sphere through adsorption.The negative value of DG at 293 K for solid phases suggests spontaneous along with physical retention of A.R. dye onto solid phases.

Environmental applications
Real samples from the environment must be examined to determine whether solid phases P(OT) and P(OT)/GO/CS NCs are appropriate for the removal of compounds.Water from three different sources was taken for testing: Red Sea water, waste water, and tap water (described in Section 2.6).Three of the samples had their A.R. dye concentration measured, and it was discovered that this concentration was below the (UV-vis) measurement's detection limit.The results are displayed in Table 6 and Figure 7.
For the purpose of removing A.R. dye from solution, the solid phases used were cleaned with acetone, dried, and reused.Adsorption percentages were nearly constant across all four cycles.This demonstrates that solid phases P(OT) and P(OT)/GO/CS NCs can be recycled without losing efficiency.

Conclusion
The current investigation shows the fabrication of ternary P(OT)/GO/CS, P(OT)/GO/SE, and P(OT)/ GO/ST NCs by the oxidation polymerization method.The properties of these NCs were characterized.Among the ternary NCs, the P(OT)/GO/CS NCs exhibit the greatest A.R. dye removal efficiency compared to other ternary NCs.NCs were tested by removing A.R. dye from real water samples.The removal procedure was efficient for four consecutive cycles.The simple method of production and good reusability of this material demonstrate that natural polymer/GO functionalized poly o-toluidine-based adsorbents may be useful in the treatment of industrial wastewater.

Figure 3 .
Figure 3. (A) TGA curves and (B) DTG curves for pure P(OT) and its NCs.

Figure
Figure 4A displays a comparison of the polymers' performance in removing A.R. dye from aqueous solution, the rustle demonstrations that the ternary

Scheme 2 .
Scheme 2. Illustration of the fabrication procedure of ternary P(OT)/GO/CS NCs (a) and proposed mechanism of dye removal (b).

Figure 4 .
Figure 4. (A) Comparison of the efficiency of the five samples in removing the A.R. dye from an aqueous phase.(B) The electronic spectra of 20 ppm concentration of A.R. dye in aqueous phase (a), and after shaking with 5 mg of P(OT) solid phase (b), and after shaking with 5 mg of P(OT)/GO/CS solid phase (c).

Figure 5 .
Figure 5. Optimization of parameters for the adsorbent solid phases of A.R. dye from the solution samples.Effect of the solution pH with contact time 120 min (a), mass of material with shaking time 90 min (B), contact time (C), temperature at 10, 20, 35, and 50 C (D) and Influence of concentration of KNO 3 (E).(experimental conditions: A.R. dye (20 ppm), pH ¼ 2, 20 ± 0.1 C temperature, 5 mg of P(OT) (a) and P(OT)/GO/CS NCs (b) solid phases.

Figure 6 .
Figure 6.Kinetic models for the adsorption removal of A.R. by P(OT) and P(OT)/GO/CS NCs (A) Weber-Morris plot, (B) Fractional power model, (C) Lagergren plot, (D) Pseudo-second order plot, (E) Elovich model plot and (F) The plot of ln K c vs. 1000/T for calculating thermodynamic parameters.

Table 2 .
Thermal behaviour of P(OT), binary P(OT)/GO NCs, ternary P(OT)/GO/CS NCs, ternary P(OT)/GO/SE NCs and ternary P(OT)/GO/ST NCs.The values were determined by TGA at a heating rate of 10 C min À1 .

Table 3 .
Adsorption capacity of various adsorbents on Acid Red dye.
Sorption kinetics of pollutants such as A.R. dye from aqueous solution via solid sorbent are important because they reveal important information about reaction pathways and sorption mechanisms.

Table 4 .
Different kinetic models parameters for the adsorption of A.R. dye on the solid phases at 293 K.

Table 6 .
The percentages of A.R. dye removed from the real samples by P(OT) and P(OT)/GO/CS NCs solid phase.