High Performance of Multifunctional Cotton Fabrics Modified with TiO 2 , Fe, Ag-doped TiO 2 and Graphene Oxide Nanomaterials towards Antimicrobial and Adsorption Removal of Methylene Blue Dye

Multifunctional cotton textile nanocomposites are well developed by the functionalization of cotton with pure TiO 2 , Ag-, Fe-doped TiO 2 , and graphene oxide nanoparticles via sol-gel and modified Hummer methods. The treated fabrics materials are investigated by XRD, FT-IR, and SEM. The obtained treated fabrics have been used as an adsorbent for the methylene blue dye removal from aqueous solution. The functionalized cotton fabrics are tested for antimicrobial capability towards Escherichia coli, Bacillus cereus, and Candida albicans. All functionalized fabrics have higher antimicrobial activity compared to untreated cotton especially the fabrics containing silver and Fe doped TiO 2 . The optimum conditions of the adsorption process are determined via the study of the effect of the initial concentration of dye, pH, and contact time on the removal efficiency. Langmuir, Freundlich, and Tempkin isotherms are applied for the equilibrium adsorption data. GO-Cot and Ag-Ti@GO-Cot samples showed the highest adsorption removal activity. The linear correlation coefficient (R 2 ) showed that the Temkin model well fitted the data of adsorption on the GO-Cot sample. The analysis of experimental data with different kinetic models showed that the pseudo-second-order kinetic model well fitted the adsorption data better than the other kinetic models of pseudo-first-order, Elovich, and the intra-particle diffusion.


Introduction
As a result of dealing with dyes and using them for many purposes, it is necessary to remove the dyes effectively as a result of their harm to living organisms and the environments owing to its toxicity and stability [1][2][3]. In the present time, there are quite a lot of water treatment processes used to remove the dyes, such as adsorption on different sorbents, microbiological decolorating, chemical breakdown by oxidation, and so on [4]. One of the most popular and effective processes is adsorption [5,6]. Therefore, many adsorbent materials were used [6][7][8], such as activated carbon, which is one of the most important materials for adsorption due to its high surface area. But there is a problem with the inability to use it more than once. [5] Therefore, it is necessary to find other materials that are cheaper and can be used many times with high efficiency.
For woven natural fibers and fabrics, their surface can be treated during the manufacturing process to obtain many special characteristics such as antibacterial, adsorption, photocatalytic, ultraviolet protection, and flame retardant, etc [9][10][11][12][13][14][15]. Therefore, it is necessary to investigate the effect of adding nanoparticles and ultrastructure on their mechanical properties and other properties [16].
Nano-sized TiO2 [15], SiO2 [17], and ZnO [18], are a group of materials utilized for functionalization of fabrics. Amongst them, nanostructured TiO2 and its composites, which possess excellent adsorptive and photocatalytic properties, consider as the most important materials used to remove the dyes from water. This is because of their non-toxicity, huge domain of implementation, chemical and photostability, lower price, higher efficiency, etc. [19].
Recently, several methods for synthesizing TiO2 nanoparticles at low temperatures were developed [20]. Bozzi et al. have modified the surfaces of synthetic textile by TiO2 at temperatures lower than 100 °C [21]. Daoud et al. have treated various textile fibers with a TiO2 thin layer by a dip-pad-dry-cure process [22,23]. TiO2 coating on cotton is a gifted procedure in forming heat-sensitive materials with self-cleaning and anti-microbial properties, which can also be used to clean the environment.
The spread of microbes causes extremely hazardous diseases to humans, directly or indirectly. At present, nanomaterial-based antibacterial agents are the emerging agent against bacterial resistance owing to low to moderate cytotoxicity, realistic cost, and effective inhibition mechanism of antimicrobial. So, treating the textile fabrics with nanomaterials as antimicrobial agents were needed to improve the quality of the fabric to resist infections associated with some bacteria that cause many diseases. Therefore, one of the most popular materials that can be used as anti-bacterial is a metal oxide and is used as an additive to obtain anti-bacterial textiles fabrics such as the TiO2 nanomaterials which have been commonly tested for superiority in several applications [24]. The use of these compounds, such as titanium dioxide and doped TiO2, as additives are very suitable due to photocatalytic activity and high anti-microbial efficiency (90%) [25]. The use of these materials instead of silver nanoparticles has apportioned us to appreciably lessen the cost of the antibacterial textile. However, since the antibacterial properties of titanium TiO2 have a photo-induced nature; they are frequently unsteady in the dark [26]. Several literary foundations note the lack of pure titanium dioxide as a photocatalyst, involving the ineffective use of solar energy, as well as the e --h + pairs rapid recombination [27]. Because of these inadequacies, titanium dioxide modification has been required, such as doping with metals and nonmetals. Such modification should also assist to build the TiO2 based nanocoatings antimicrobial in the dark, i.e. cause the antimicrobial properties of the coatings independent from the existence of UV-radiation, which cannot always be confirmed in hospital conditions.
In this work, textile fabrics of cotton were modified with graphene oxide, pure TiO2, and doped TiO2 with Ag + and Fe 3+ ions. All fabrics were characterized by different tools such as XRD, FTIR, and SEM. The removal of methylene blue dye (MB), as a model of organic dyes, from wastewater by adsorption on fabrics was studied. The antimicrobial activity of these fabrics toward Escherichia coli (E. coli), Bacillus cereus (B. cereus), and Candida albicans (C. Albicans) was also tested.

Preparation of graphene oxide (GO)
Graphene oxide was prepared by modified Hummers-Offerman's method [28]. Five gm of graphite powder was added to 120 ml of 98% of H2SO4 in an ice bath with continuous stirring and the temperature didn't exceed 20 °C. Then 2.5 gm NaNO3, followed by 20 gm of KMnO4 was added gradually to avoid a sudden increase in temperature. The obtained solution was stirred in the ice bath for 2 h and at 35 °C for 1 h. Then 250 ml of distilled H2O was added gradually to the ice bath, which causes effervescence and temperature suddenly increased to 98 °C then cooled to room temperature after 10 min. Next, 50 ml of (H2O2) was added, leading to converting samples into oily color. The mixture was heated at 90°C for 30 min. The obtained mixture was centrifuged and washed by boiling distilled water until the mixture became neutral.
The resulting powder was dried at 65 °C for 24 h to get graphene oxide (GO).

Preparation of TiO2 nanoparticles
TiO2 was prepared using the sol-gel method as the following: 2 ml of 10% acetic acid was added to 6 ml of titanium isopropoxide under vigorous stirring. Then 56 ml of ethanol was added dropwise after 5 min with vigorous stirring. The pH of the solution was adjusted to 1-2 by adding 2 ml of (36%) HCl. Then the obtained solution was strongly stirred for 45 min. The produced gel TiO2 was used for functionalized the cotton fabrics.

Preparation of cotton fabric functionalized with GO
First, the cotton fabric was treated with a solution of sodium hydroxide 2% (w/v) under stirring at 80 o C for 5 min. A dispersion of an aqueous solution of GO nanosheet (5 mg/mL) into the cotton fabric surface was carried out by a vacuum filtration method to manufacture GO-Cotton fabric [29] . The treated fabric afterward dried at 60 o C for 10 min, and the produced cotton showed black color after the deposition of graphene oxide and symbolized as GO-Cot.

Preparation of cotton fabric functionalized with TiO2
The Pad-dry-curve method was used for treating the surface of cotton fabrics with the obtained nanomaterials [30]. 10 cm × 5 cm of untreated cotton fabrics were washed with a nonionic surfactant (tween 80). These wetted fabrics were dipped in colloidal solutions of the prepared nanomaterials separately. Then, two bowl padding mangle was used to pad these fabric samples for 15 min continuously. After completion of padding (then using a glass stem, distribute the material to the surface of the fabric and remove the excess) these fabrics were cured at 120 ○ C for 3 min. This step is repeated three times. Then the produced treated fabrics were washed with sodium lauryl sulfate solution to eliminate the excess nanoparticles. Finally, these fabrics were wholly washed 10 times with water and then dried. The fabric produced was denoted as Ti-Cot.

Preparation of cotton fabric functionalized with silver or Ferric doped TiO2
Cotton fabrics were coated with TiO2 doped with Ag + using the above-mentioned method for coating the fabrics with pure TiO2. Where, 0.12 g AgNO3 was added to the mixture of fabrics and TiO2 before adding ethanol. The fabric produced was designed as Ag-Ti-Cot.
The same procedures were carried out to prepare the functionalized cotton fabrics with ferric but with using 0.578 g 0.578 g Fe(NO3)3.9H2O. The fabric produced was denoted as Fe-Ti-Cot.

Preparation of GO-Cotton fabric functionalized with TiO2
GO-Cotton fabrics were coated with TiO2 using the above-mentioned method used for coating the fabrics with pure TiO2. The fabric produced was denoted as Ti@ GO-Cot.

Preparation of GO-Cotton fabric functionalized with Ag or Fe doped TiO2
GO/Cotton fabric was also coated with Ag-doped TiO2 using the above-mentioned method used for coating the fabrics with pure TiO2. Where, 0.12 g AgNO3 was added to the mixture of fabrics and TiO2 before adding ethanol. The fabric produced was symbolized as Ag- The same procedures were carried out to prepare the functionalized cotton fabrics with ferric but with using 0.578 g 0.578 g Fe(NO3)3.9H2O. The fabric produced was denoted as a Fe-Ti@GO-Cot.

Physico-chemical characterization
Before making the characterization of the prepared coated cotton, the samples were washed several times by distilled water and dried at 60 o C for 24 h. The fabric samples were weighed before and after the treatment process. For comparing the physical properties of the coated cotton samples, a constant weight of the covering materials on the cotton surface was used.

X-ray diffraction (XRD)
The crystallinity and types of phases present in the samples were determined by X-ray diffraction (XRD) analysis. XRD measurements were done in the range of 2 = 5 o -80 o on a Diano (made by Diano Corporation, U.S.A.), using Cu Kα radiation (λ = 1.5406 Å).

FTIR)
The Fourier transform infrared (FTIR) spectra were monitored via a double beam Perkin Elmer Spectrometer coupled with an ATR unit. The spectra were recorded in the 4000-400 cm −1 region.

Scanning Electron Microscope (SEM)
Determination of morphologies of untreated and treated fabrics and the effect of functionalization of cotton with different materials was carried out by a JSM-5200 Scanning Electron Microscope (JEOL) using conductive carbon paint.

Adsorption of methylene blue (MB) experiments
The capability of the treated and untreated fabrics for removal of methylene blue dye (MB) by adsorption from aqueous solution was tested at 25 ºC using an equilibrium technique. The adsorption isotherm was determined as the following, a piece of fabrics of 2 × 3 cm was added to 50 ml of the known initial concentration of MB dye solution with strong stirring at 25 ºC and pH = 9. Initial dye concentrations were changed in the range of 5 ppm to 20 ppm. At different time intervals, samples were withdrawn. Using UV-vis spectrophotometer (Jasco V-550, Japan) the remaining dye concentration was measured at the suitable wavelength (400 -800 nm) relating to the maximum absorption of MB dye (λmax = 664 nm). The adsorption capacity of the adsorbent was evaluated via obtained data. The impact of different initial dye concentrations on the adsorption capacity was tested. The percentage of removal (%R) of dye in the supernatant solution is calculated using the following relation: Where Co (mg/L) is the initial concentration of the dye solution and Ct (mg/L) is the concentration of the dye solution at time t.
The equilibrium adsorption capacities (qe) were then obtained by using the following equation.
Where qe is the adsorption capability (adsorption of the dye per unit mass of the sample, mg/g), Co is the initial concentration and Ce is the equilibrium concentration of the dye in the solution (mg/L) respectively, W is the amount of adsorbent (g), and V is the solution volume (L). The pH was adjusted with dilute NaOH and HCl solutions. The adsorption isotherms were examined by Langmuir, Freundlich, and Tempkin models. The kinetics of the adsorption process were tested with pseudo-first-order, pseudo-second-order, second, Elovich, and intra-particle diffusion kinetic models.

XRD study of cotton and coated cotton fabrics
The to cellulose I structure [31][32][33]. The XRD of all the treated samples exhibit similar peaks to that of uncoated cotton but with different intensities. As shown in figure 1, the peaks intensities for uncoated cotton and cotton coated graphene oxide are higher than those of other coated pieces of cotton [34]. It might be attributed to that the titanium dioxide coating on cotton screen the ray beam from spread through the surface of cotton directly [35,36]. It is also noted the absence of any diffraction peaks characterizing for the brookite, rutile, and/or anatase TiO2 structures on the TiO2-coated cotton fabrics, which could be attributed to the low content of TiO2 on the fabrics.

ATR-FTIR study of cotton and functionalized cotton fabrics
FTIR spectra were used to investigate the various functional groups present in cotton and functionalized cotton fabrics. FT-IR spectrum of cotton (Fig. 2) showed peaks attributed to cellulose structure around 1020-1200 cm -1 [37]. Other distinctive bands attributed to the cellulose chemical structure were the hydrogen-bonded OH stretching at 3328 cm -1 , the CH stretching at 2920 cm -1 , the asymmetrical COO-stretching at 1645 cm -1 , and the CH wagging at 1316 cm -1 [38][39][40][41]. The figure showed also a slightly weak absorbance band for cotton at ~ 1735 cm -1 , which could be attributed to the existence of the carboxylic ester in waxes and pectins [42].
On coating, the cotton fabrics with pure or doped TiO2, the intensities of the peaks related to OH groups decreased compared with those of undoped fabric. Commonly, titanium oxide shows significant bonding to hydroxyl groups [43]. Thus, the hydroxyl groups are involved in the coating process. Accordingly, it enters into the coating procedures. The incorporation process can be more verified through the reduction in the intensity observed for the bands at 1101 cm −1 and 1154 cm -1 , which can be ascribed to the C-O stretching vibration of the -CH2OH group and C-O stretching bond. Furthermore, the appearance of one additional peak at 1427 cm −1 , may be attributed to the symmetric stretching vibration of a bidentate carboxylic group with titanium atoms [44], and another noted at 1576 cm −1 due to asymmetric stretching vibration. The disappearing of the slight peak at 1714 cm −1 recommended that several carbonyl groups occurred in the blank cotton fabric providing favorable coordination sites with Ti-atoms [45]. The FT-IR spectrum of the cotton coated with GO showed that the peaks characterizing of GO merge in the same region of titanium and cotton.

SEM study
The surface morphologies of the control cotton fabric and coated cotton fabrics were investigated by using a scanning electron microscope and the images obtained are shown in

Antimicrobial activity
To study the antimicrobial activity of the treated and untreated cotton fabrics, Grampositive (Bacillus cereus), Gram-negative bacteria (Escherichia coli), and Fungi Candida (Candida Albicans) were used. The coated and untreated fabrics exhibited variable degrees of antimicrobial activity against the tested microorganisms by measuring the inhibition zone as illustrated in Table 1. It can be seen that pure cotton has antimicrobial activity toward only B.
cereus. On the other hand, all coated cotton samples exhibit excellent antimicrobial activity against all tested microorganisms (C. Albicans, E. coli, and B. cereus). It was also noted that the antimicrobial activity of the samples containing silver (Ag-Ti-Cot, Ag-Ti@GO-Cot,) toward B.
cereus exhibits higher activity compared to other treated samples. While the Fe-Ti@GO-Cot sample shows higher activity toward E. Coli compared to other samples. The cotton textiles coated with only titanium dioxide did not exhibit any antimicrobial effect against B.cereus.
The enhanced antibacterial ability of silver containing fabrics, as shown in the obtained results, can be attributed to the existence of the silver nanoparticles. The process of killing microorganisms can take place through the silver ions that come out from the silver particles then spread into the medium neighboring the samples [46], which appear as the inhibition zone rates across cell membranes into the cytosol to disrupt intra-cellular protein thiol groups [48][49][50].
In the case of Ag-Ti@GO-Cot (23 mm), the obtained high antimicrobial effect against B.
cerust can be ascribed to the synergistic effect of Ag-nanoparticles and the GO-nanosheets. The GO-nanosheets on the cotton fabrics occupied high specific surface area and hydrophobic character, resulting in increased barrier properties to diminish the adhesion and propagation of microorganisms from attaining the surface of fabrics [51]. Furthermore, the existence of GOnanosheets onto cotton fibers is greatly useful to the nucleation and creation of Ag-nanoparticles since they can work as the active surface to raise their distribution as well as their stability. This restricted the aggregation of nanoparticles and assisted the continuous liberation of Ag + and strong binding to the microbial cells.

Adsorption studies
The adsorptive elimination of methylene blue, as a model of organic dyes from aqueous solutions, on cotton fabrics coated with pure and doped titanium dioxide as well as its composite with graphene oxide, was studied. The adsorption of a dye can be influenced by significant factors, such as initial dye concentration, adsorbent dose, contact time, pH, and temperature. The concentration gradients tend to grow in MB sorption at the early stages. Fig. 4 demonstrates that the adsorption capacity of all fabrics has the following order:

Contact time effect
The removal efficiency after 10 min of adsorption were found to be 72.

Effect of PH
The effect of pH on the adsorptive removal of methylene blue dye was tested in the acidic which leads to an increase in the rate of adsorption [52][53][54][55].

Effect of the initial concentration of dye
The impact of the initial concentration of MB (5-20 mg/L) on the dye removal was studied on Cot-GO fabric (highest adsorption capacity of the studied fabrics) and the results obtained are illustrated in Fig. 6. All other parameters are kept constant. It can be noted from Fig.   7 that the adsorption capability enhances as the initial dye concentrations increases. This may be attributed to the rise in the number of adsorbate molecules opposing the accessible binding sites on the surface of the adsorbent. Also, the rise in the initial MB dye concentration amplifies the number of collisions between adsorbent and dye cations, which improves the process of sorption.
The obtained results showed that the dye was completely removed at a dye concentration of 5 mg/L in 11 min for GO-Cot fabric. While as the concentration increases above 5 mg/L the dye was not completely removed. This can be explained on the basis that at high dye concentrations, adsorption sites are saturated, which leads to a decrease in the adsorption capacity. Whereas at low concentrations there are many adsorption sites available for all the dye molecules present in the solution.

Equilibrium adsorption isotherm
Adsorption equilibrium is an important physical and chemical aspect to evaluate the adsorption process as an operating unit. The diffusion of a solute between the liquid and solid phases can be detected by Langmuir, Freundlich, and Temkin models [56,57]. Assuming that the adsorbate molecules adsorbed on at definite homogeneous sites in the absorbent material and as soon as a site occupied with the dye molecule, no additional adsorption occurs at that site according to the Langmuir model [58]. Moreover, the Langmuir model of adsorption assuming a formation of a monolayer of adsorbate molecules on an adsorbent surface of the homogeneous structure, with actively equivalent adsorption sites. The intermolecular forces rapidly diminish with distance and can be managed to predict the presence of a monolayer covering the adsorbent on the outside of the absorbent.
The Langmuir equation is given by Eq. 3: Where qmax is the theoretical maximum monolayer sorption capacity (mg/g), Ce is the equilibrium concentration of dye in solution (mg/L) and KL are empirical constants. KL is the Langmuir adsorption constant and evaluates the affinity of the sorbent for the solute.
In the Langmuir-sort adsorption process, the dimensionless partition component RL indicates the impact of the isotherm shape on whether adsorption is favorable or unfavorable, which is reflected as a more dependable indicator of the capacity of adsorption. RL is given by the following Eq. 4 [59]: Where Co is the initial dye concentration. The values of RL show the states of isotherms to be either irreversible (RL= 0), unfavorable (RL> 1), or favorable (0 ˂ RL˂ 1). The Freundlich isotherm model is an empirical equation through which adsorption is treated on heterogeneous surfaces and is not limited to forming a single layer [60]. Also, this model takes into account the different tendencies of the binding sites on the surfaces of the adsorbent with the molecules of the adsorbent material. This model assumes that highly attractive sites are firstly the occupied. The Freundlich equation is given by Eq. 5: Where qe is the equilibrium sorption capacity (mg/g), and Ce is the equilibrium concentration of dye in solution (mg/L), KF, and n are empirical constants. The values of 1/n reveal the type of isotherm to be favorable (0 ˂1/n ˂ 1), irreversible (1/n = 0), and unfavorable (1/n >1) [61].
Temkin isotherm model was also utilized to analyze the adsorption data and it can be given by the following equation: [62] q e = RT b T ⁄ lnA T + RT b T ⁄ lnC e (6) where ( / ) = (J/mol) is the Temkin constant related to the heat of adsorption, AT is the equilibrium binding constant related to the maximum binding energy (L/g), bT is the Temkin constant related to the heat of adsorption (kJ/mol), R is the universal gas constant (8.314 J/mol/K) and T is the absolute temperature (K).
Freundlich, Langmuir, and Temkin models were applied to analyze the obtained experimental adsorption data on GO-Cot fabric. Fig. 7 show the fitting data of these three models: Freundlich (log qe vs. log Ce) plots, the Temkin (qe vs. ln Ce) plots, and Langmuir (Ce/qe vs. Ce) plot for adsorption of MB.
The acceptance of any model to the practical results is usually evaluated through linear regression analysis, where the R 2 is calculated, and through its value, a judgment is made on how well the model fits the results. The parameters obtained from the fitting data are given in Table 2, which shows that the most suitable model fitted the data of adsorption on the Cot-GO sample is the Temkin model due to its highest correlation coefficient value (R 2 ). These results are indicating the chemical adsorption process.
The adsorption mechanism can be detected from the adsorption kinetics. The adsorption process is generally organized by three diffusion stages: (1) solute transportation from the bulk solution to the adsorbent film, (2) from the adsorbent film to the surface of the adsorbent, (3) from the surface of adsorbent to the inside of materials. The overall rate of the process of adsorption is evaluated by the slowest step [62].
Usually, the step is either the second or third step, which is produced by adsorption on the surface or that leads to intra-particle diffusion during adsorption, respectively [63].
Numerous kinetic models can be employed to know the mechanism of the sorption of solute molecules onto a sorbent. In the present work, pseudo-first-order [64], pseudo-secondorder [65], intraparticle diffusion [66], second-order, and Elovich models were examined to assess the kinetic mechanism which controls the adsorption process of MB dye on pure and coated cotton, fabrics. The weight of the models was confirmed by the linear equation analyses ln(qeqt) vs. t, (t/qt) vs. t, qt vs. t1/2, (1/qe-qt) vs t, and ln t vs qt, separately.
Pseudo-first order can be represented by the following form [64]: ln(q e − q t ) = lnq e − k 1 t (7) Where qt and qe are the adsorbed amounts of dye (mg/g) at time t (min) and equilibrium, individually, and k1 (min −1 ) is the rate constant of pseudo-first-order. The plots of ln(qe-qt) versus t which are presented in Fig. 8a are used to determine the values of k1 for all samples.
When the rate of reaction depends on the quantity of solute adsorbed on the surface of the adsorbent and the quantity adsorbed at equilibrium, the pseudo-second-order reaction can be used and given by Eq. 8 [62]: t q t ⁄ = 1 k 2 q e 2 ⁄ + t q e ⁄ (8)  Table 3.
The second-order model can be represented by the following form: 1/(qe-qt)=1/qe+k2t (9) Where qt and qe are the adsorbed amounts of dye (mg/g) at time t (min) and equilibrium, individually, and k2 (min −1 ) is the rate constant of second order. Fig. 9a reveals the fitting plots of Eq. 9 ((1/(qe-qt) vs. t). The values of qe, k2, and R 2 were estimated and listed in Table 3.
For numerous adsorption systems, Elovich's empirical adsorption model has extensive applicability. This model was constructed based on the heterogeneity energy of sites of adsorption in the form of a rectangular distribution [67]. The mathematical equation of the kinetic model of Elovich can be expressed as follows: where β is the rate of initial adsorption of the Elovich equation (mg·g −1 min −1 ) and α is the Elovich adsorption constant (g·mg −1 ) [68]; it is interrelated to the energy of adsorption [69].
The linear relation of the Elovich equation was obtained if αβt >> t and that q = qt for a time t = tt and q = 0 at t = 0 [70]. If plot qt against ln(t) (Fig. 9b) displays a straight line with a slope of (1/β) and an intercept of (1/β) ln (αβ) and given in Table 3 [68].
This model has been utilized by several researchers to elucidate the kinetics of adsorption of pollutants on different adsorbents. Different mechanisms such as activation of surface, its deactivation; interface phase, and diffusion in solution were explored using this model. It suffices to explain the process with greater changes in the energy of activation [71].
Through comparing the correlation coefficients (R 2 ) of the Pseudo-first-order, Pseudosecond-order, second-order, and the Elovich models, it was found that the Pseudo-second-order kinetic model matches the process of adsorption of all the studied materials superior to the other three. Additionally, the departure between experimental qe,exp, and calculated qe, cal values of the Pseudo-second-order kinetic model is very low. The good fitting line of Pseudo-second-order is shown in Fig. 8b, indicating that the adsorption-determining factor of the MB elimination may be involved in the chemisorption [72].
The kinetic results of the adsorption processes of the solutions are very important in defining the rate-determining step. The rate-determining step may be either the intra-particle (pore) diffusion or the boundary layer (film) in the adsorption process. The intra-particle diffusion process is studied by the modified Weber and Morries equation as following [66]: q t = k dif √t + C (11) related to the thickness of the boundary layer.
If the plot of qt versus t 0.5 according to Eq. 11, gives a straight line, then the intraparticle diffusion controls the adsorption process and if the plots give more than one straight line, then two or more steps controlled the adsorption process. As shown in Fig. 8c, the plots have one linear relationship, and C as well as kdif values gained from these plots were recorded in Table 3.
This reveals that the intra-particle diffusion controls the adsorption process [73].

Conclusion
The functionalized cotton fabrics with titanium dioxide, doped titanium dioxide with (ferric, silver), and its composite with graphene oxide well successful obtained via a simple method. All that the most suitable model fitted the data of adsorption on the GO-Cot sample is the Temkin model due to its highest correlation coefficient value (R 2 ). On comparing the correlation coefficients fitting (R 2 ) obtained by applying five different kinetic models, it was found that the Pseudo-second-order kinetic model fits the adsorption process of all samples. The intraparticle diffusion model exhibited one straight line, which reveals that the adsorption process was controlled by intraparticle diffusion.