Magnetic nanocomposites decorated on multiwalled carbon nanotube for removal of Maxilon Blue 5G using the sono-Fenton method

Herein, multiwalled carbon nanotube-based Fe3O4 nano-adsorbents (Fe3O4@MWCNT) were synthesized by ultrasonic reduction method. The synthesized nano-adsorbent (Fe3O4@MWCNT) exhibited efficient sonocatalytic activity to remove Maxilon Blue 5G, a textile dye, and present in a cationic form, in aqueous solution under ultrasonic irradiation. The magnetic nano-adsorbent particles were characterized by high-resolution transmission electron microscopy (HR-TEM), transmission electron microscopy (TEM), Raman spectroscopy and X-ray diffraction (XRD). Some important parameters such as nano-adsorbent dosage, solution pH, initial dye and H2O2 concentration, reaction time, ultrasonic power and temperature were tested to determine the optimum conditions for the elimination of Maxilon Blue 5G dye. The reusability results showed that Fe3O4@MWCNT nano-adsorbent has a decrease of about 32.15% in the removal efficiency of Maxilon Blue 5G under ultrasonic irradiation after six times reuse. Additionally, in order to reveal the sufficient kinetic explanation, various experiments were performed at different temperatures and testing three kinetic models like the pseudo-first-order, pseudo-second-order and intraparticle diffusion for removal adsorption process of Maxilon Blue 5G using Fe3O4@MWCNT nano-adsorbent. The experimental kinetic results revealed that the adsorption process of Maxilon Blue 5G in the aquatic mediums using sono-Fenton method was found to be compatible with the intraparticle diffusion. Using kinetic models and studies, some activation parameters like enthalpy, entropy and Gibbs free energy for the adsorption process were calculated. The activation parameters indicated that Fe3O4@MWCNT nano-adsorbent could be used as an effective adsorbent for the removal of Maxilon Blue 5G as a textile dye and the adsorption process of Maxilon Blue 5G with Fe3O4@MWCNT nano-adsorbent is spontaneous.

www.nature.com/scientificreports www.nature.com/scientificreports/ intensively on suitable and efficient technological techniques for the removal of pollutants. One of these methods is the ultrasonic and the Fenton process, which contains an oxidation process 15 . In heterogeneous Fenton-like processes, OH − radicals are formed as Fe 3+ ions and are converted into Fe 2+ ions (Reactions 1, 2). Another way to obtain OH − radicals is a fracturing water molecule by sending ultrasound waves (eq. (3)) through cavitation phenomena processes 15 . Hydrogen peroxide could be released by OH − radicals under the influence of ultrasonic radiation in a solution medium (eq. (4)) [13][14][15][16][17] .
(1) (2) (3) (4) There are some cavitation phenomena such as microbubble formation, precipitation, as well as pressure due to the temperature factor under the ultrasonic wave in the solution environment 18,19 . Furthermore, removal of organic materials by ultrasonic wave method is limited; because a long reaction process is required 20 . Generally, iron-containing nano-adsorbent can be exceeded by integrating the Fenton-like application process to eliminate this obstacle 15 . There are also some disadvantages due to the problems such as the removal of the nano-adsorbent from the wastewater and the accumulation of Fe +3 ions in the environment. To overcome this problem, the Fenton processes can be addressed by resorting to heterogeneous catalytic applications 21,22 . Recently, researchers have been interested in the use of particles as catalysts [23][24][25][26][27][28][29][30][31][32] . Especially, magnetic nanoparticles provides an opportunity to remove dyes from water sources using nano-adsorbents which have an external magnetic field in heterogeneous Fenton systems 33,34 . This will allow for quick, efficient and easy separation of the magnetic nanoparticles from the water sources 33 . For this purpose, in this study, Fe 3 O 4 @MWCNT were synthesized and used as a nano-adsorbent and not only exhibited a high sonocatalytic activity but also high stability, reusability, and easy application for the removal of Maxilon Blue 5G in aquatic mediums. Fe 3 O 4 @MWCNT nano-adsorbent combined with sono Fenton technique is a non-toxic, cheap and effective solution for the removal of Maxilon Blue 5G from the solution medium. Fe 3 O 4 @MWCNT is an effective example of a new magnetic nano-adsorbent in the sonocatalytic removal of the dye material by the Fenton-like process method. In this study, various parameters such as initial dye concentration, efficient of absorbent, pH, H 2 O 2 concentration and ultrasonic power (US) were investigated under specific standard parameters. Moreover, the reaction mechanism and the parameters of the thermodynamic function were also studied. Experimental adsorption procedure of Maxilon Blue 5G using Fe 3 o 4 @MWCNt nano-adsorbents under sono-Fenton waves. The samples for the characterization process were prepared by taking a 5 mL solution containing Fe 3 O 4 and MWCNT. This solution was divided into 8 tubes with 5 × 100 volumes and then centrifuged. The formed precipitates were filtered and dried under inert medium, and then stored for further analysis. The X-ray diffraction (XRD) analysis of Fe 3 O 4 @MWCNT nano-adsorbent was performed using an analytical Empyrean diffractometer capable of X-ray diffraction (Cu K, λ = 1.54056 Å, at 45 kV and 40 Ma). Transmission electron microscopy (TEM) analysis was conducted with a JEOL 200 kV instrument. To take TEM analysis various sample was taken to prepare colloidal slurry and the resulting mixtures were dropped on Cu-TEM grid comprised of carbon. The mean particles size of Fe 3 O 4 @MWCNT nano-adsorbent were calculated counting diameter of regions present in TEM patterns. The resulting solution was mixed using Maxilon Blue 5G and Fe 3 O 4 @MWCNT in the dark condition to ensure adsorption-desorption balance for 15 min. The desired temperature, pH, Maxilon Blue 5G concentration at a given initial concentration of H 2 O 2 (2 mM) and ultrasonic power were adjusted. 4 ml samples were also taken at regular intervals from the reaction solution medium. Then the wastewater is separated by centrifugation (Sigma 3-30 KS) at 15000 rpm and 10 minutes. The measurements were taken by a UV-Vis spectrometer (Perkin Elmer Lambda 750) to determine the concentration of the Maxilon Blue 5G at 410 nm wavelength. The removal efficiency of the dye material was determined from the equation given below.
www.nature.com/scientificreports www.nature.com/scientificreports/ where, C 0 and C t (mg/L) are the dye concentration for the initial and specific times at equilibrium, respectively. The reusability tests also conducted for the Fe 3 O 4 @MWCNT nano-adsorbents.

Results and Discussion
The chemical and morphological analysis of Fe 3 o 4 @MWCNT nano-adsorbent. In order to reveal the crystalline structure of the prepared Fe 3 O 4 @MWCNT nano-adsorbent, XRD analysis has been conducted. The XRD results for Fe 3 O 4 @MWCNT nano-adsorbent are given in Fig. 1  TEM and HR-TEM analysis were performed to determine the structural properties of the Fe 3 O 4 @MWCNT catalyst. As can be seen from Fig. 2, the mean particle size of the monodisperse Fe 3 O 4 @MWCNT nanoparticle was 3.24 ± 0.61 nm which is in good agreement with XRD results. In addition, Fig. 2 shows a uniform distribution of Fe 3 O 4 over the MWCNT without any agglomeration. HR-TEM image also shows that the atomic lattice fringe of Fe 3 O 4 @MWCNT nanoparticle is consistent with the literature data (0.21 nm) 4 . TEM image of Fe 3 O 4 is also given in Fig. S1.  www.nature.com/scientificreports www.nature.com/scientificreports/ For further structural analysis of synthesized Fe 3 O 4 @MWCNT nano-adsorbent, Raman 35 spectroscopic analyses were carried out. Raman spectroscopic analysis (given in Fig. 3) of Fe 3 O 4 @MWCNT nano-adsorbent, further details of the structure of Fe 3 O 4 @MWCNT nano-adsorbent were revealed in Fig. 3. The modification and structural disorders were controlled by comparing the density ratios of G and D bands. ID/IG ratios for MWCNT and Fe 3 O 4 @MWCNT were found to be 0.77 and 0.98, respectively. The findings of Raman spectroscopy showed that MWCNT were functionalized with Fe 3 O 4 [36][37][38] . D band in 1340 cm −1 region and G band in 1600cm −1 region were observed in Raman spectra of the prepared materials. The vibrations created by carbon on the basal plane and the E 2g mode form the G band. D and G bands are formed due to the Raman mechanism in double resonance structure. These bands are directly related to lattice structure and particle size [26,27]. The ratio obtained from the bands D and G (I D /I G ) is inversely proportional to the size of the crystalline structure of carbon. The I D /I G ratios of the

The effects of Fe 3 O 4 @MWCNT nano-adsorbent concentrations on the removal efficiency.
One of the most effective parameters for removing of Maxilon Blue 5G is the amount of nano-adsorbent concentrations. The nano-adsorbent effects were analyzed at pH of 9 for 120 minutes in solutions containing 2 mM H 2 O 2 . As shown in Fig. 4(a), the increase in the dosage of Fe 3 O 4 @MWCNT magnetic nano-adsorbent was found to be effective for removing Maxilon Blue 5G. As shown in Fig. 4(a), the extraction yield of Maxilon Blue 5G was found to be the highest for the 0.0024 g L −1 Fe 3 O 4 @MWCNT magnetic nano-adsorbent dose (about with %98 yield). It can be related to an increase in the number of active catalytic sites due to the increase in the amount of magnetic nano-adsorbent Fe 3 O 4 @MWCNT, and therefore, more reactive radicals can be produced. Furthermore, a larger increase in the amount of magnetic nano-adsorbent particles results in a decrease in the efficiency of Maxilon Blue 5G removals in sono adsorption systems. In this case, the addition of the nano-adsorbent may have a cleaning effect on the %OH − radicals, resulting in a reduction of the Maxilon Blue 5G removal efficiency in the solution medium 15 . Another reason is that in sonocatalytic heterogeneous systems, excessive screening quantification of ultrasonic waves by the magnetic nano-adsorbent particle prevents the same amount of ultrasonic energy from being absorbed 39 . The highest removing amount of the Maxilon Blue 5G by the using of Fe 3 O 4 @MWCNT was also detected, as seen in Fig. 4(a).
The effects of Maxilon Blue 5G concentrations on the removal efficiency. To investigate the effect of Maxilon Blue 5G dye concentration, some experiments were conducted at different initial concentrations of Maxilon Blue 5G at constant parameters such as 2 mM of H 2 O 2 concentration, 303 K temperature, and pH of 9. By increasing the dye concentration of Maxilon Blue 5G from 0.0012 to 0.0024 g. L −1 in the sono adsorption process, the efficiency of the Maxilon Blue 5G removals increased from 50.2% to 82.1% within 120 min ( Fig. 4(b)). The amount of adsorbed dye on the surface of the magnetic nano-adsorbent material is increased when the amount of dye in the solution medium increased, and this prevents absorption of energy produced due to acoustic cavitation by nano-adsorbent particles 40 . Hence, the percentage of OH − radicals and removing dye capacity will result in a decrease. It can be explained that the removal efficiency of intermediates, which is particularly evident as a result of the interaction of OH − molecules with dye molecules, can be reduced 39 . Also, it blocks active areas on the surface of Fe 3 O 4 @MWCNT as a result of high dye concentration in the solution medium. In this case, it causes the minimal growth of the OH radicals and thus, results in lower Maxilon Blue 5G removal efficiency. Besides, the nitrogen adsorption and desorption isotherms of Fe 3 O 4 @MWCNT nano-adsorbents are also given in Fig. S3  www.nature.com/scientificreports www.nature.com/scientificreports/ in order to explain the higher efficiency of prepared nano-adsorbents. The analysis was performed by evaluating the hysteresis curve of nitrogen adsorption and desorption at isothermal conditions. According to the analysis, it is known that the Fe 3 O 4 /MWCNT nanocomposites have a large surface area, namely 335 m 2 /g. Such large area would improve the performance of the adsorption property of the nanocomposites and very appropriate for removal of maxilon 5G.

The effects of H 2 O 2 concentrations, ultrasonic wavelength, temperatures, and solution pH on the removal of Maxilon
Blue 5G from aqueous medium. Figure 4 also shows the effects of H 2 O 2 concentrations (Fig. 4c), ultrasonic wavelength (Fig. 4d), temperatures (Fig. 4e), and solution pH (Fig. 4f) on the removal Maxilon Blue 5G from aqueous medium. In this study, the effect of H 2 O 2 concentration on the elimination of the dye in the solution www.nature.com/scientificreports www.nature.com/scientificreports/ medium was checked. In heterogeneous Fenton-like systems, the concentration of H 2 O 2 has a positive effect on the increase of active radicals 41 . To investigate the effect of H 2 O 2 at different concentrations, experiments were conducted at the constant parameters such as 0.02 g L −1 Fe 3 O 4 @MWCNT, pH of 9 in aqueous solution and 120 minutes of reaction time. The experimental results showed that the removal efficiency of Maxilon Blue 5G was highest at 2 M concentration of H 2 O 2 as shown in Fig. 4c. This situation is considered due to the increase in OH − released to the solution environment. The efficiency of dye elimination decreased at higher hydrogen peroxide (H 2 O 2 ) concentrations. This is because the hydrogen peroxide (H 2 O 2 ) added after a certain point in the sonocatalytic heterogeneous processes was found to interfere with the interaction between the surface of the nano-adsorbent material and the dye material. As stated in eqs (5) and (6), excessive concentration of hydrogen peroxide in the solution medium can induce OH − radical scavenging effect 42 and cause reduction of radicals required for oxidation 43,44 .
One of the essential parameters for the removal of Maxilon Blue 5G dye is the amount of ultrasonic power.
To determine the effect of the ultrasonic power, the same constant parameter conditions were prepared with 20 mg L −1 of Fe 3 O 4 @MWCNT, pH of 9 and 2 mM H 2 O 2 concentration. As indicated in Fig. 4(d), the ultrasonic power effect was seen to be more effective in removal efficiency from 350 W to 450 W. It can be explained this situation on two different mechanisms. Firstly, the increase in ultrasound power increased dissolution turbulence. This leading to the higher release of reactive radicals and an increase in the mass transfer rate of Maxilon Blue 5G, which positively contributed to the reduction in the number of by-products present throughout the nano-adsorbent surface 13 . Secondly, the cleaning of the ultrasonic beam responded positively to the increase in power. It is thought that the increase of ultrasonic irradiation causes further expands of active fields on the surface of the magnetic nano-adsorbent 13,45 . In can be concluded that the increase in ultrasonic power results in a further increase of reactive radicals. In order to determine the optimum temperature for the adsorption of Maxilon Blue 5G on Fe 3 O 4 @MWCNT, a set of experiments at different temperatures ranging 296-323 K was performed. The results of the experiments conducted at different temperatures are given in Fig. 4e. The optimum temperature on the adsorption process was found to be 323 K. Increasing temperature effects the interaction of particle, and that increasing interactions increased the adsorption of Maxilon Blue 5G. additionally, the volumes of pores on the adsorbent is increased with increasing temperature 12 . These results affected positively the adsorption amount of Maxilon Blue 5G. The effect of pH solution is also a very crucial parameter in the adsorption process to gain the properties of materials investigated under ultrasonic wave iridations 41,42 . The results for pH effects of the solution containing 0.002 g.L −1 Fe 3 O 4 @MWCNT magnetic nanomaterials and 20 mg L −1 Maxilon Blue 5G in 120 minutes to remove the Maxilon Blue 5G are given in Fig. 4(f). The highest yield was obtained at a pH of 11. These might be explained by two reasons. The situation of the surface of nano-adsorbent affects the values of pH, and it can be explained according to the zero-load point of Fe 3 O 4 @MWCNT. The zero-load point of the Fe 3 O 4 @ MWCNT magnetic nano-adsorbent was determined to be 6.8 by the method specified in the literature 46 . When the pH of the solution lower than the zero-load point of the Fe 3 O 4 @MWCNT magnetic nano-adsorbent, the surface of the nano-adsorbent material is protonated. Similarly, the surface of the nano-adsorbent is deprotonated when a higher pH value applied 47 . For this reason, the cationic dye can be adsorbed onto the Fe 3 O 4 @MWCNT nano-adsorbent, and the surface binding domains of the nano-adsorbent material are affected. Therefore, the ionic state of the Maxilon Blue 5G molecule has great importance. At low pH, the nano-adsorbent surface charge is positively charged and H + the ions encounter an impulsive force effectively with the Maxilon Blue 5G cations, thus causing a reduction in the amount of adsorbed dye. At higher pH values, the magnetic nano-adsorbent particle increases the negatively charged density. By this way, the electrostatic attraction forces between the support material and the cationic dye can be increased 48,49 . Besides, as shown in Table S1, the iron ion concentration in the solution medium increased at high pH. This relates to both the absolute concentration of dissolved iron and the increased dissociation of OH − radicals of H 2 O 2 molecules in the heterogeneous sono-Fenton process 50 . As a result, the presence of % OH − radicals also significantly affected the electrostatic attraction between the nano-adsorbent and the dye. The most efficient removal was achieved at an optimum pH value of 11 ( Fig. 4(f)).

The comparisons of some parameters studied for Maxilon Blue 5G removal using Fe 3 O 4 @MWCNT nano-adsorbent
and their reusability efficiency. The experiments of removal of Maxilon Blue 5G conducted at different parameters were carried out at pH of 9 with 10 mgL −1 of Fe 3 O 4 @MWCNT nano-adsorbent; the results of these experiments are given in Fig. 5a. As indicated in Fig. 5a, the efficiency of Maxilon Blue 5G removal was determined to be approximately 3.75% and 5.72% after operating the system for 120 minutes using ultrasonic wave and H 2 O 2, respectively. The data obtained under these experimental conditions show how stable Maxilon Blue 5G is. The efficiency of Fe 3 O 4 @MWCNT magnetic nano-adsorbent in removing the Maxilon Blue 5G dye was not nearly at the desired level. Among the different compositions of the prepared nano-adsorbents as shown in Fig. 5a, Fe 3 O 4 @ MWCNT/H 2 O 2 nano-adsorbent exhibited a best efficiency for the removal of Maxilon Blue 5G compared to the others. As seen in Fig. 5a, the conversion of H 2 O 2 to free OH radicals in the Fe 3 O 4 @MWCNT/H 2 O 2 system positively increased the oxidation process in experimental studies (6). As stated in the eq. (1) the interaction between active sites of the Fe 3 O 4 @MWCNT surface and H 2 O 2 supplied a positive increase in the percentage of OH − radicals. In the US/Fe 3 O 4 @MWCNT/H 2 O 2 working process, the magnetic nano-adsorbents interacted with ultrasonic waves and produced a higher contact area of magnetic nano-adsorbent as a support material 50 . The heterogeneous catalytic efficiency has been enhanced because of the formation of cavitation microbubbles and their www.nature.com/scientificreports www.nature.com/scientificreports/ collapse on the surface of the magnetic nano-adsorbent 51,52 . The amount of iron and OH − radicals present on the surface of the nanoparticles increased the efficiency of the Fenton-like process depend on eqs ((1) and (2)) 9 .
Another most critical parameters of nano-adsorbents in the removal of dye studies is the reusability tests conducted to investigate the stability of the synthesized materials 10 . The stability of Fe 3 O 4 @MWCNT magnetic nano-adsorbents was investigated reusability in 6 sequential reuse at fixed parameters with 0.020 g L −1 nano-adsorbent, 20 mg L −1 Maxilon Blue 5G dye, 2 mM H 2 O 2 , pH of 9, 120 minutes. The magnetic nano-adsorbents were magnetically separated from the treated solution after each treatment and washed using ultrapure water, dried and reused for subsequent work (Fig. 5b). As shown in Fig. 5b, six successive dye-extraction yields were obtained in % 88.51, 80.72, 75.56, 73.09, 70.16, and %67.85 respectively. The obtained data in Fig. 5b demonstrate the reusability of Fe 3 O 4 @MWCNT magnetic nano-adsorbents for treatment of wastewater. TEM image of used nano-adsorbents was obtained as shown in Fig. S4 and it was seen that some of the particles was agglomerated which results in the decrease of the reusability efficiency. We have also checked the content of the catalyst with the help of ICP (Inductively Coupled Plasma spectroscopy) in order to see whether there is any leaching in nanocomposite or not and we have seen that there was no leaching in nanocomposite.
Also, the recycling of the Fe 3 O 4 @MWCNT nano-adsorbent film from water is crucial to prevent further contamination during wastewater treatment in industrial applications because the nanoadsorbent can be easily removed from the water using magnetic force. The absorbance changes of Maxilon Blue 5G containing Fe 3 O 4 @ MWCNT adsorbent at 300-500 nm (Maxilon Blue 5G of 20 mg L −1 , Fe 3 O 4 @MWCNT of 0.020 g L −1 , H 2 O 2 of 2 mM, UP of 350 W, pH of 9) for 120 min are shown in Fig. 5c. The maximum absorbance value was obtained as >90%. Figure 5c shows the initial and latest solution color and absorbance values for Maxilon Blue 5G aqueous solution containing Fe 3 O 4 @MWCNT adsorbent. As shown in this figure, Maxilon Blue 5G lost its color during the adsorption process after interaction with Fe 3 O 4 @MWCNT adsorbent. Fig. 6a,b shows adsorption capacity of Fe 3 O 4 nano-adsorbent and its adsorption amount from aqueous mediums. As seen in Fig. 6a the initial concentration of Maxilon Blue 5G was investigated in concentrations ranging 5-40 mg/L for 120 min. The highest adsorption value of Maxilon Blue 5G on Fe 3 O 4 @MWCNT nano-adsorbents was obtained as 25 mg/L. Figure 6b shows that the maximum adsorption capacity of Maxilon Blue 5G on Fe 3 O 4 @MWCNT nano-adsorbent was reached in almost 60 min. and after this time the adsorption process has reached the equilibrium. According to www.nature.com/scientificreports www.nature.com/scientificreports/ obtained data, the Fe 3 O 4 @MWCNT magnetic nano-adsorbents proved to be a very effective nano-adsorbent to remove Maxilon Blue 5G under different parameters.

Kinetic parameters and their calculation for sono -Fenton-like method.
Three models were used to find the sufficient kinetic model for the adsorption of Maxilon Blue 5G using Fe 3 O 4 @MWCNT magnetic nano-adsorbent through heterogeneous under the ultrasonic irradiations. The equations used in the calculation to determine the sufficient model are given formulas 53 , where the t is time (min.), k i is adsorption rate constant, q e , and q t are the initial and final concentration (mol. g −1 ) of Maxilon Blue 5G dye, respectively. The calculation results obtained from the models are seen in Table S1. Equations of 7, 8 are the first order and second-order models, respectively 54 . In eq. (8); time is t, k 2 is a constant rate at the adsorption equilibrium, the Maxilon Blue 5G amount is q e (mol. min −1 ). Equation (9) was used to calculate halftime of adsorption process for Maxilon Blue 5G with Fe 3 O 4 @MWCNT nano-adsorbent under ultrasonic wave irradiations. The eq. (10) is used to calculate the initial adsorption rate, h (mol/(g min) and in the values of t 1/2 , k 2 and q e were calculated and given in Table S1. The initial rate of the intraparticle diffusion is calculated using eq. (11) 55 .  Table S2 shows k int values (mg (g min −1/2 ) −1 calculated from the intra-particle diffusion model. The studies in the literature revealed that the slopes between q t and t 1/2 are multilinear; the graph of q t with t 1/2 is multilinear 52 . In the adsorption process of Maxilon Blue 5G containing Fe 3 O 4 @MWCNT nano-adsorbent, the first stage of the adsorption process is compatible with the intraparticle. In Fig. 6 the first portion curve exhibited the boundary layer effect in the adsorption process and the second curve shows the effect of the intraparticle and diffusion in pores. Table S2 shows the k int1,2 values. The first plot values are so high, and these values are not sufficient for the first stage. k int2 is used in the intraparticle diffusion and is compatible with the second linear plot (mol.g.mol −1/2 ) 56 . The ln [(C t .Co −1 ) −1 (1 + mK)] is used for obtaining R 12 and R 2 2 calculated values 57 and its values are seen in Table S2. The model of mass transfer equations values with particle distribution equations is not appropriates for the adsorption of Maxilon Blue 5G on Fe 3 O 4 @MWCNT nano-adsorbent.
The calculation of thermodynamic parameters. To calculate the activation parameters for the adsorption of Maxilon Blue 5G using Fe 3 O 4 @MWCNT nano-adsorbent from the aqueous medium, Arrhenius Equation (eq. 12) and k 2 values were used as shown in Fig. S5. In eq. (12), R is gas constant (J.K −1 .mol −1 ), and T is temperature (K). The activation energy of Maxilon Blue 5G using Fe 3 O 4 nano-adsorbent was found to be 27 k J.mol −1 . Generally, the adsorption process having enthalpies less than 40 k J.mol −1 was considered as physical interactions. www.nature.com/scientificreports www.nature.com/scientificreports/ Vice versa the adsorption processes which having enthalpies higher than 40 k J.mol −1 was considered as chemical processes 58 . The following eqs (12 and 13)  The results for these activation parameters and kinetic data are given in Table S3. Fig. S5a,b shows Arrhenius plots for calculations the adsorption parameters for removal Maxilon Blue 5B dye. The value of ∆S (entropy change) was founded to be −94 J.K.mol −1 . This value indicates that the Maxilon Blue 5G dye was distributed regularly on the Fe 3 O 4 @MWCNT magnetic nano-adsorbent. The results also revealed that the adsorption mechanism for Maxilon Blue 5G dye containing Fe 3 O 4 @MWCNT magnetic nano-adsorbent occurs spontaneously. It was determined that the sonocatalytic removal of the magnetic nano-adsorbent particle was suitable for Langmuir-Hinshelwood kinetic expression by looking at the obtained regression coefficient (R 2 = 0.9930). The calculation activation parameters were performed using eq. (14) as given below; The calculated values of the adsorption of Maxilon Blue 5G dye on the Fe 3 O 4 @MWCNT surface were given in Table S3.

Conclusion
In this work, Fe 3 O 4 @MWCNT magnetic nano-adsorbent particles were synthesized by ultrasonic reduction method. The nano-adsorbent particles from the data obtained in experimental studies were found to have extreme sonocatalytic efficiency in eliminating dyes from aqueous medium under ultrasonic condition. It has been proved that Maxilon Blue 5G dye is successfully removed from the aqueous solution by using Fe 3 O 4 @MWCNT as the adsorbent material and with the help of ultrasonication, separately. The experimental process reached a disposal efficiency of %92 at pH of 9 after a 120-minute reaction period. The obtained data showed that OH. radicals play a significant role in the removal of Maxilon Blue 5G dye by the sonocatalytic method in the presence of Fe 3 O 4 @ MWCNT magnetic nano-adsorbent. Moreover, the reusability test has shown the stability of Fe 3 O 4 @MWCNT magnetic nano-adsorbents with very high sonocatalytic removal efficiency under optimum conditions. The thermodynamic parameters such as Gibbs free energy (ΔG * ), Ea, ΔH*, and ΔS* were calculated as −61.465, 27.01, 32.325 kJ mol −1 and 94.00 J mol −1 K −1 for removal of Maxilon Blue 5G dye, respectively. According to the calculated values of free Gibbs Energy also shows that the adsorption process occurs spontaneously. It was also determined that the most suitable kinetic model for the adsorption mechanism was intra-particle diffusion models. As a result, the prepared Fe 3 O 4 @MWCNT nano-adsorbent is very effective for the removal of the dyes from industrial wastewater.