Document Type : Original Research Article


1 Dept. of Pharmaceutical Chemistry, College of Pharmacy, University of Babylon, Babylon, Iraq

2 Department of Chemistry, College of Science for Women, University of Babylon, Hillah, Iraq


In this study, a microwave assisted hydrothermal technique was employed for the synthesis of CNT/ZnO nanocomposite. Carbon nanotubes were obtained from incineration stacks in furnaces. They were treated with concentrated (0.1 N) H3PO4. The structures of nano-composites were characterized via utilizing powder (FE-SEM), and (TEM). Specific surface area (BET), total pore volume, and mean pore size were too studied through utilizing Bruneuer Emmatt Teller (BET) technique to refer to the properties surface of the nano-composites. Several operational factors like initial concentration of GRL dye, amount of CNT/ZnO nanocomposite, solution of pH, and temperature solution by utilize of CNT/ZnO nanocomposite in the adsorption of GRL dye. It was found that removal percentage E % rises with increase weight of the nanocomposite until all the active sites of the nanocomposite are saturated. The percentage removal of GRL dye rises from 45.42% to 90.853% for solution pH increase about 3.2-10.5. The result of the kinetic was studied by means of several model kinetic like first model, the second  model,  and Elcovich model was found to be the maximum kinetic model second-order (R2=0.9986) for our adsorption investigation. The thermodynamic factor having change Gibbs energy (ΔG), change entropy (ΔS), and change enthalpy (ΔH). The negative value of ∆H (-9.043 kJ.mol-1) was estimated for the adsorption method and the adsorption is a physical and exothermic, positive value ∆S (13.8469 J.mol-1 K-1), and the values negative of (∆G) in the range temperature of 10-30 oC, confirming that the dye adsorption on to Nano composite was spontaneous.

Graphical Abstract

Microwave-assisted hydrothermal synthesis as a nanocomposite with superior adsorption capacity for efficient removal of toxic Maxillon blue(GRL) dye from aqueous solutions



In recent years, the aquatic environment has been polluted with human pollutants like heavy metals, dyes, pesticides, organic and inorganic pollutants, and others. Organic dyes are commonly found in wastewater produced by industries such as textiles, paper, leather, pharmaceuticals, printing, etc.[1-8]. Maxillon blue dye is a basic dye that causes many health problems such as skin and eye irritation, diarrhea, shortness of breath, cough, and nausea. Therefore, the treatment of industrial wastewater loaded with these dyes is a major concern for the researcher. Therefore, several techniques have been used such as membrane separation, adsorption, photocatalysis, advanced oxidation process, ozone, and others. Among these technologies, adsorption is preferred for the treatment of industrial wastewater loaded with dyes [9-11]. This technique makes the absorbent materials highly efficient. The most important of these surfaces is carbon nanotube, which has a good internal porous interface and a high surface area. It is considered as one of the better and utmost usually utilized absorbent material in water treatment. Zinc oxide is characterized by its environmentally friendly nature and is widely used in the photocatalytic process, but there are few studies on its use in the adsorption method. In this research, ZnO was loaded on to CNT to make the surface with high efficiency in relation to removal dyes.

Adsorption experiments

Preparation of CNT decorated (zinc oxide /nanocomposite)

Carbon nanotubes were obtained from incineration stacks in furnaces, they were treated with concentrated (0.1 N) H3PO4 with continuous stirring for two hours, and then washed by distilled water in several times, filtered and dried at (65 oC). Zinc oxide nanoparticles were prepared in the laboratory by taking 5 g of oxalic acid, and 5 g of zinc acetate dissolved in distilled water and mixing for 30 minute, and then addition 0.1 g of CNT to it and mixing it well in ultrasound for 30 minute. Before preparing the mixture, it was placed in a hydrothermal solution at 160 °C for about 24 h, and the surface was washed different times by distilled water and dry at 60 °C for 12 h to obtain the powder used in the experiment.

Batch adsorption

Stock solution of Maxillon blue (GRL) dye 500 mg/L was prepared via dissolving 0.5 g dye in 500 mL of distilled water. A 0.05 g ZnO/CNT nanocomposite in 100 mL a suitable concentration of dye was shaken in shaker at 130 rpm at 20 oC. After removal of the nanocomposite filtration by centrifuge of 3000 rpm, the GRL concentrations in the supernatant were estimation via a UV-Vis spectrophotometer. The (E%) and (Qe, mg/g) were estimated by Equations 1 and 2. 

Where, Co primary concentration of GRL and Ce equilibrium concentration of GRL in the solution (mg/L), V volume (mL) of GRL, and m is the quantity of nanocomposite (g).

Results and discussion

Characterization of CNT/ZnO nanocomposites

 The surface area and structure pore of CNT/ZnO nanocomposite are estimated using the nitrogen adsorption isothermal system. The nitrogen isotherms adsorption-desorption and distributions pore size of CNT/ZnO nanocomposite is represented. The isotherm profile of CNT/ZnO demonstrates a small hysteresis loop that can be categorized as kind IV. The surface area, total pore volume, and average pore diameter were improved after the incorporation of carbone on to the grafted ZnO as shown in Figure 1. The interfacial interactions among carbone and ZnO have a great impact on the pore structure of material as evident from this study [12-17].

The FE-SEM method was utilized to clarify the morphology of the prepared CNT/ZnO nanocomposite. Figure 2a shows an image of carbon nanotubes, where the appearance of clusters similar to tubes spread on the nanotubes surface, and through Figure 2b, zinc oxide was loaded on nanotubes carbon. We notice the spread of zinc on the surface in the form of small spherical clusters, but after the adsorption process. The emergence of many irregular spherical assemblies and the surface CNT/ZnO nanocomposite became more swollen clear evidence of the GRL loading inside the surface and occurrence of the adsorption method, as appeared in Figure 2c.

The TEM technique was utilized to estimate the characteristics of prepared surface before and after adsorption, as it was observed that some dark spots seemed on the surface, evidence of loading GRL on the prepared surface and the occurrence of adsorption method [18], as depicted in Figure 3.

Effect of different parameter

Effect of weight of nanocomposite

The quantity of nanocomposite utilized in adsorption is for the most part because it limits the equilibrium sorbent-sorbate in the way and can too be utilized to predict the treatment cost of adsorbent per unit of solution GRL [19]. The influence of mass adsorbent on E% of GRL was studied and the results are demonstrated in Figure 4. The percentage removal E% of dye rise through rise in mass adsorbent. For instance, E% of dye at equilibrium increased about 15.14%-97.82% when the mass adsorbent increased about 0.003-0.15 g. The increased percentage% of GRL via nanocomposite was as a data of raised surface area and increased adsorption site occasioned through greater than before mass adsorbent. Similar data have been previously reported [20-22]. Furthermore, above 0.1 g, there is hardly any improvement in removal capacity of dye.

Effect of solution pH

One of the utmost important parameter that affects the adsorption behavior of nanocomposite is the solution pH. The adsorption of dye on to nanocomposite as a function of pH was studied for pH values rang about 3.2-10.5 by a primary concentration CRL of 100 mg.L-1 (Figure 5).

The percentage removal of GRL dye a rises from 90.42%- 95.853% for a solution pH increase about 3.2 to 6.8. Therefore, it is clear from the result that the adsorption process is the dependent pH, the adsorption capacity and the removal E% of GRL adsorbed increasing through solution pH and being at best at pH 6.8. Several reasons may be attributed to the adsorption of GRL dye via the nanocomposite relative to pH [23-25].

Effect of solution temperature and thermodynamic parameter

To observe the influence of solution temperature, the adsorption studies were carried out for the concentration of GRL 100 mg L-1 at different temperatures 10, 20, and 30 oC, at pH 6.6.

Figure 6 illustrates the adsorption efficiency against the adsorption time at different temperatures. It was observed that equilibrium adsorption of GRL raised from 58.1 -239.5 mg g-1 by temperature solution rise 10 to 30 oC, indicating the nature ex-othermic of the reaction adsorption. To study the  adsorption thermo-dynamics of GRL on nanocomposite, basic three thermos-dynamic factor, (∆H), (∆S), and (∆G) were estimated using equations [18,26].

Where, T temperature solution (K), Ka adsorption equilibrium constant, and R gas constant. (Change enthalpy) and (change entropy) were estimated from the slope and intercept from the plot of ln(Xm) vs. 1000/T(K) (figure not shown).

The value of (∆G) was estimated using Equation 5. The result is presented in Table 1. The negative value of ∆H (-9.043 kJ.mol-1) indicates that adsorption of GRL on to nanocomposite is an exothermic. The negative values of (∆G) in the range temperature of 10-30 oC, confirming that the adsorption of GRL on to Nano composite was spontaneous and favorable thermodynamically. The positive value ∆S (13.8469 J mol-1 K-1) indicates a decrease in the degree of freedom of adsorption GRL on to ZnO/ CNT [27,28].


Adsorption kinetics

Equilibrium time is another key factor affect the impurity uptake via the sorbent. The influence of agitation duration and the GRL dye (10-100 mgL-1) on the dye uptake was carefully studied at 20 oC. Figure 7 illustrates the improvement efficiency by time and primary conc. The uptake rate is initially fast until an value equilibrium constant at 1 h [29]. The rapid uptake rate at the first sorption was caused via the utmost the reactive groups and avail-ability of the outer surface of the sorbent.

It is evident that the adsorption efficiency (qe) rises from 83.71 to 231.84 mg/g as the GRL concentration is greater about 10-100 mg/L. Because greater primary concentration leads to larger mass transfer driving force, thus leading to higher dye sorption, we fixed the equilibrium time to 1 h for our batch investigational [30] .

Adsorption kinetic result was analyzed using the kinetic adsorption Lagergren first model calculated by Equation 6.

Ln(qe-qt)= Lnqe-K1t                                                  (6)

Where, K1 (min-1) is the first-model constant rate adsorption and time t (min). Values of K1 and equilibrium adsorption density qe at 20 oC were determine from the plots of ln(qe–qt) vs. t for several primary concentration of GRL (Figure 7). The kinetic second-order can be expressed as Equation 7:

The nonlinear model of the Chemisorption (Elovich kinetic model) [30] was calculated by Equation 8.

Intercept of the linear plot of t/qt vs. t, as appeared in Figure 5.

The kinetic model data for the first-order, the second-order kinetic, and Elcovch models adsorption appear in Table 2. The nonlinear plots of qt vs. time (kinetic adsorption second-order) indicated the best agreement among the investigational and estimation values qe for several primary concentrations of GRL. Likewise, the correlation coefficients of the kinetic second model (R2 > 0.9986) were greater than kinetic first model. It can be said that the adsorption second kinetic model better than the First model [31,32].


Through the results that were reached, after the process of loading zinc oxide onto multi carbon nanotube, the surface became highly efficient and the surface area increased. A low-cost, environmentally friendly surface with a very high capacity in removing industrial dyes. With an increase weight of nanocomposite, the removal percentage E% increases, as the percentage of removal reach (95%) at the weight of (0.05 g) and any increase in weight did not notice any significant increase because of saturation of most active sites of the surface. The percentage removal of GRL dye a rises from 90.42%-95.853% for a solution pH increase about 3.2 to 6.8. The percentage removal increases with increasing temperature and the best result at 25 oC, Gibbs energy (∆G) the values negative in the range temperature of 10-30 oC, confirming that GRL adsorption on to nanocomposite was spontaneous and the positive value (∆S 13.8469 J.mol-1 K-1).


The financial support for this research was provided by Ministry of Higher Education Malaysia under FRGS Grant no. 2019-0147-103-02.

Conflict of Interest

The authors declare that there is no conflict of interest.


Rana S. Al-Shemary:

Aseel M. Aljeboree:

Ayad F. Alkaim:




Copyright © 2023 by SPC (Sami Publishing Company) + is an open access article distributed under the Creative Commons Attribution License(CC BY)  license  (, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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