Performance of graphene Oxide/SiO₂ Nanocomposite-based: Antibacterial Activity, dye and heavy metal removal

1 Introduction

Contaminants from various industrial engineering processes, like fine chemical production, metal smelting, gas and oil production, and mining, are a potential threat to valuable and scarce drinking water resources, especially in developing areas (Omer et al., 2022; Elsayed et al., 2022; Yusop et al., 2022). Wastewater treatment methods to eliminate multiple contaminants from water resources, are vital for the sustainable water supply in addition to socio-economic development, human well-being, and sustaining livelihoods (Zhang et al., 2022; Zhang et al., 2022; Bagheri et al., 2021). Dyes are chemical substances that can attach themselves to fabrics or surfaces to impart color. Dyes are considered one of the primary contaminants that may be found in the water and have an injurious influence on the environment and human life. The discharge of dyes into waters has a negative impact on the environment because of contaminants even, at low concentration values, coupled with producing the color of the receiving water (Lai and Wong, 2021; Bagheri et al., 2021; Halim and Yong, 2018). Many dyes are mutagenic, carcinogenic and, toxic for human life, and they are the primary reason for cancer diseases in the liver, urinary bladder and, kidney. Moreover, dyes may cause skin irritation and respiratory disease. Therefore, the removal of them from water is a too important aim (Mohammadzadeh et al., 2022; Wang et al., 2022). Dyes can be classified in terms of color, structure and application techniques. But, because of the color nomenclature complexities of the chemical structure system, classification according to application and their solubility is often favorable. Reactive, basic, acidic, direct, and acid dyes are instances of soluble ones, while vat, Sulphur, disperse, and azo dyes are instances of insoluble ones (Chen et al., 2022; Jiang et al., 2021; Banivaheb et al., 2021). Methylene blue (MB) is a heterocyclic compound applied as a medication and as a dye and it was first synthesized in 1876 with the chemical formula C₁₆H₁₈N₃SCl. After that, MB was used as inactivated and stained microbial species and antidote to cyanide and carbon monoxide poisoning (Liu and Ying, 2022). MB appears as dark green powder at room temperature but is a blue color in water, and can absorb light at around 665 nm. MB inharmonious influences on human health and the environment. Some of the mentioned problems are irritation of the esophagus, throat, stomach, and mouth, nausea, diarrhea, dizziness, gastrointestinal pain, and headache (Dan et al., 2021; Bagheri et al., 2021; Mo et al., 2022). Therefore, controlling water contamination caused based on the MB dye is vital.

Pollution of aquatic systems with heavy and toxic metals has become a primary, issue universally because of their damaging and persistence influence on human health and marine life. (Wan et al., 2022). Waste streams from power generation facilities and electroplating, mining operations, and tanneries may include heavy and toxic metals at amounts above the discharge limits. The wastewater streams include heavy and toxic metals like copper, nickel, mercury, lead, cadmium, and chromium (Cr) (Anastopoulos et al., 2017). Cr is a hard metal, a steel-grey and lustrous metallic element extensively distributed in the crust of Earth. Cr is a leading industrial metal applied in processes and diverse products (e.g., Cr is an anticorrosive and anti-biofouling) (Liu et al., 2008). At lots of locations, Cr, as the most toxic trace element has been released in the environment or to ground/surface waters because of leakage, poor storage, and unfair removal practices or its widespread use in industrial uses. Groundwater is the primary drinkable water source throughout the world. Cr is present in remarkable concentrations in many natural groundwater sources applied for public water supply (Almeida et al., 2019; Wang et al., 2022; Tan et al., 2022). Due to Cr's carcinogenic influence on human health, is unwanted in natural water supplies. Cr (VI), Cr (III) and Cr⁰ are the most common forms of Cr that is present in the background. Cr (III) occurs obviously in the environment, and is a vital nutrient, while Cr⁰ and Cr (VI) are usually produced using chemical processes (Prabu et al., 2022). The total concentration of Cr (VI) in drinkable water must be less than 5 × 10^-5 g/L, due to Cr (III) can be easily oxidized to Cr (VI) using free chlorine. Many tries have been made to treat wastewaters using traditional techniques like adsorption onto active carbon, membrane separation, reverse osmosis, ion exchange, lime coagulation, and chemical precipitation (Herath et al., 2022). Nonetheless, the mentioned physicochemical methods show serious disadvantages like toxic metallic sludge generation, high operational cost, and low performance in low concentrations. Several techniques like membrane separation, advanced oxidation, coagulation and adsorption are applied to remove the dyes and heavy metals from wastewater (Tan et al., 2022; Dovi et al., 2022; Sheth et al., 2022; Chen et al., 2022).

Graphite is the most popular carbon allotropic, and it is a natural mineral. Graphite contains sp² hybridized carbon element layers that are stacked with van der Waals forces. The carbon atoms' single layers firmly packed in a two-dimensional honeycomb crystal framework is called graphene (Li et al., 2020; Ge et al., 2019; Pei and Cheng, 2012). Graphene is a type of promising and novel carbon material, and it has attracted remarkable attention as a special adsorbent because for its high capacity of adsorption. Graphene shows a unique anisotropic treatment with regarding electrical and thermal conductivity properties. It is very conductive into direction parallel to graphene layers due to its in-plane character, but graphite indicates weak conductivity in a direction vertical to layers due to the weak van der Waals forces interactions among them (Thakur and Kandasubramanian, 2019; Almoisheer et al., 2019; Cao et al., 2021). Graphene and Graphene oxide and their composites have good chemical stability, significant pore volume, exceedingly flexibility and large theoretical specific surface area that makes it an appropriate promise to adsorb the material. Graphene and composite-based graphene can be used to absorb several pollutants from water, like heavy metals, pesticides, antibiotics and dyes (Gupta et al., 2022; Radwan et al., 2022). Functionalization of graphene oxide and graphene lead to their surface modification and can be adjusted to be reactant specific for several organic entities. Silicon dioxide (SiO₂) nanoparticles with graphene oxide have enhanced physical and chemical properties compared with graphene oxide-like surface area. Many methods are applied for dye removals like membrane separation, chemical oxidation, media filtration, electro-sorption, photocatalytic methods, microbial degradation, distillation, ion exchange, precipitation and adsorption methods. Based on the low cost, highly effective and simplicity factors, adsorption is considered one of the most impressive and eco-friendly methods for water treatment (Liu et al., 2020; Kumar et al., 2016; Dan et al., 2022).

Many researches have been performed to remove MB from wastewater using composite based on graphene and graphene oxide. The more details of obtained results are given by Thakur and Kandasubramanian (Thakur and Kandasubramanian, 2019). Liu et al. (Liu et al., 2020) designed a porous SiO₂-graphene oxide membrane to remove MB dye. They investigated the capability of SiO₂-graphene oxide with various SiO₂ loadings (SiO₂-graphene oxide mass ratio was 0, 0.5, 1, 2, 3, and 5) and different volumes of MB. The obtained results show increasing MB solution volume leads to improve dye removal capability of SiO₂-graphene oxide membrane with SiO₂-graphene oxide mass ratio equal to 1 and 2. Moreover, through various MB concentrations (10–40 ppm), the dye removal efficiency of SiO₂-graphene oxide membrane with SiO₂-graphene oxide mass ratio equal to 2 was better. Wu et al., (Wu et al., 2016) used Fe₃O₄-graphene@mesoporous SiO₂ to remove MB dye. At the first step, they decorated Fe₃O₄ nanoparticles onto graphene after that, mesoporous SiO₂ was deposited on the surface of the Fe₃O₄-graphene composite. The obtained results indicate the increasing of pH solution leads to improvement in MB adsorption, and high values of pH are advantageous to adsorption of MB. Indeed, there is competition adsorption between hydrogen ions and positive MB ion. At high pH values, the number of H⁺ decreases and MB ions are adsorbed on active sites. Furthermore, the influence of dosage of Fe₃O₄-graphene@mesoporous SiO₂ on adsorption of MB shows increasing behavior. To better understand MB adsorption mechanisms, Moreover, Wu et al., (Wu et al., 2016) studied adsorption isotherms and kinetics. The adsorption isotherms and kinetics were considered with Langmuir correlation and pseudo-second-order equation, respectively. Almoisheer et al. (Almoisheer et al., 2019) prepared GO/SiO₂/single-wall carbon nanotubes (SWCNTs) composite to adsorb of Congo red dye synthetic wastewater. The obtained results indicate using SWCNT and SiO₂ gives a lower capacity Congo red dye adsorption at all pH ranges. Initial concentration of Congo red dye had an enormous influence on the adsorption and increasing the initial concentration of dye leads to an increase in Congo red dye adsorption. Also, the uptake of Congo red dye increases by contact time because active sites are considerably available. Almoisheer et al. (Almoisheer et al., 2019) used the Langmuir equation and pseudo-second-order and first-order to describe kinetics and adsorption process.

Many methods are presented in the literature for the synthesis of a nanocomposite based on a graphene oxide/SiO₂. In this communication, we reported a new and simple process to synthesize the GO/SiO₂ and employed three ways to investigate the performance of the new nanocomposite. Firstly, the graphene oxide was prepared based on the modified Hummer method, and afterward, the GO/SiO₂ nanocomposite was synthesized. The characterization of synthesized graphene oxide and graphene oxide/SiO₂ nanocomposite was investigated by various analyses i.e., X-ray diffraction (XRD), scanning electron microscope (SEM) and Fourier transforms infrared spectroscopy (FTIR). To examine the performance of the obtained GO/SiO₂ nanocomposite, it was used of removing the MB dye and Cr ion from the aqueous environment. The effecting adsorption parameters like contact time, adsorbent dosage, solution pH, and initial MB dye concentration, were considered. Furthermore, the adsorption kinetics of MB dye and Cr ion were studied, using four isotherms i.e., Temkin, Flory-Huggins, Freundlich, and Langmuir isotherm. In addition, in the other method of investigation of the obtained nanocomposite, an antibacterial test was carried out.

2 Material method

Graphite powder (purity over 99.5 % and mean particle size less than 50 µm), sulfuric acid (H₂SO₄), phosphoric acid (H₃PO₄), and Hydrochloric acid (HCl) these chemicals were purchased at analytical grade from Merck Company and used without any further purification. Hydrogen peroxide (H₂O₂), potassium permanganate (KMnO₄), Silica Nanoparticles (purity over 99.5 % and mean particles size less than 20 nm), sodium hydroxide (NaOH), MB (C₁₆H₁₈ClN₃S) and Potassium Dichromate (K₂Cr₂O₇) analytical grade were obtained from Sigma Aldrich company and applied as received. Furthermore, deionized water was consumed in all of the experiments and all other chemicals and solvents were at analytical stage.

3 Results and discussion

3.1

3.1 Structural characterization

Structural information of synthesized nanocomposite can be obtained by XRD. The XRD spectra of the GO and GO/SiO₂ are represented or presented in Fig. 1. The X-ray crystallography pattern of GO indicated prominent diffraction peaks at 2θ (i.e. 10.57°) that correspond to the graphite layer structure of the graphene. Which indicates a sharp diffraction height at about 10.57° and a broad one in the region of 15-25°. The peak at 10.7° should be assigned for the stacked GO Nano sheets (Arabpour et al., 2021), the other one should be given for amorphous SiO₂ (Banivaheb et al., 20211), which indicates that the synthesis reaction of nanocomposite has been successfully done.

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Fig. 1

The XRD spectral of GO and synthesized GO/SiO₂ nanocomposite.

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To investigate the morphological features of the synthesized nanocomposite and proves that the synthesized reaction was successfully carried out, the SEM analysis was performed on both raw Graphene oxide and synthesized GO/SiO₂ nanocomposite. Fig. 2 represents the SEM analysis at different magnifications for both graphene oxide and nanocomposite.

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Fig. 2

The SEM images of synthesized (A-C) GO and (D-F) GO/SiO₂ nanocomposite at different magnifications of the synthesized nanocomposite.

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As can be seen, graphene oxide indicates a raging structure which is due to the Nano graphite layers’ formation over each other in the structure of graphene oxide. As shown in Fig. 2 D-F, the SiO₂ nanoparticles are evenly distributed at the surface of the graphene determining the coating and synthesis of the nanocomposite has been successfully done. Comparing the structure of raw graphene oxide and synthesized composite determines that the addition of SiO₂ nanoparticles between the graphene oxide layer structure changes the internal structure of the graphene oxide into a more porous structure. Nano particles create a hollow space between the graphene oxide planes. To prove the existence of SiO₂ nanoparticles on graphene sheets, Energy Dispersive X-ray (EDX) analysis can be applied. Fig. 3 represents the EDX analysis of synthesized GO/SiO₂ nanocomposite, in which the existence of SiO₂ nanoparticles and their distribution among the graphene Nano sheets can be proved.

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Fig. 3

The EDX analysis of the synthesized GO/SiO₂ nanocomposite.

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Another analysis that is used to characterize the synthesized GO/SiO₂ nanocomposite is thermal gravimetric analysis (TGA), which considers the thermal stability of the compound. According to Fig. 4, TGA chart for GO indicates the degradation trend as the temperature increases, in which the GO exhibits a slow weight loss reduction due to the water evaporation in temperatures lower than T = 150 °C, as the temperature increases to T = 200 °C the surface functional groups of graphene sheets decompose (Arabpour et al., 2021 Mar 1). At higher temperatures over T = 600 °C, the carbonyl and phenol functional groups that exist in the structure of graphene destroy and result in a massive weight loss. The total weight loss of graphene is equal to 82.61 %, as for nanocomposite, the whole weight loss is highly reduced to 23 % proves the existence of SiO₂ nanoparticles in the structures increased the thermal stability of the composite.

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Fig. 4

The thermal gravimetric analysis of graphene and synthesized nanocomposite.

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3.2

3.2 Adsorption study

The concentration of pollutants, MB dye, and Cr (VI) ion in the waste waters are varied and depends on the source of the pollution. For this reason, the effect of the initial concentration of the adsorption process is one of the main factors of study the structure of the adsorbent. In this work, initial concentration of MB and Cr (VI) ion varied from 25 to 300 and 10 to 150, respectively. As can be seen in Fig. 5A, as the initial concertation increases, the adsorption capacity of the adsorbent increase until it reaches a plateau.

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Fig. 5

The effect of A) initial concentration, B) pH on removal of MB and Cr by GO/SiO₂ nanocomposite.

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3.2.1

3.2.1 pH dependency

MB and Cr (VI) solution form strongly depends on the pH of the solution; therefore, the first step is to obtain the value of optimum pH for the pollutant removal. The effects of pH (varying from 2 to 8) of the MB and Cr (VI) solution on the adsorption process are shown in Fig. 5 B. The capacity of adsorption of nanocomposites for removal of the MB from solution increased remarkably from 250.13 to 325.45 mg/g as the pH increased from 2 to 6; beyond the pH = 6, the adsorption capacity reached a plateau and remained fixed until pH = 8. The maximum dye removal, nearly to 100 % dye removal, was obtained at pH > 6, in which most of the carboxylic groups in the nanocomposite structure are activated and ionized interact with the dye structure in the solution and therefore improve the MB adsorption capacity of the GO/SiO₂ nanocomposite. As for the Cr (VI) removal, it can be seen that the adsorption capacity decreases from 123 to 66 as the pH increases from 2 to 8. Cr (VI) form in the solution varies as the pH of the solution changes from acidic to basic. Different forms of Cr (VI) exist in the solutions are H₂Cr₂O₇, HCr₂O₇^-, Cr₂O₇^2-, and CrO₄^2-. Therefore, the adsorption process capacity changes at different pHs due to the variation of Cr (VI) form (Lv et al., 2012).

The adsorption process on GO/SiO₂ can be described by two proposed mechanisms: 1) graphene oxide Nano sheets experience a negative electrostatic charge due to the existence of carboxylic functional groups (–COO^-) that can create an electrostatic link with positively charged molecules of MB and Cr (VI) ions and 2) the second adsorption purposed mechanism for the MB removal, rely on the role of SiO₂ and its structural OH functional groups. MB is a dye that have several active functional groups, these functional groups can interact with hydroxyl functional group of SiO₂. This interaction results in a hydrogen bond between SiO₂ and MB which increases the adsorption of MB. As for Cr (VI) ion, as the form of the Cr (VI) varies in different pHs, surface interaction and complexation are the mechanism that controls the adsorption process.

3.2.2

3.2.2 Kinetics studies

The adsorption time is one of the essential parameters that affect the adsorption process. Consequently, to consider the influence of contact time on the MB dye and Cr (VI) ion adsorption on the GO/SiO₂ nanocomposite and to investigate the adsorption mechanism, two kinetic models, including a pseudo-first-order kinetic model as well as a pseudo-second-order kinetic model, were applied at different initial concentrations. The equations related to these two kinetic models are given as following (Lin and Wang, 2009; Simonin, 2016):

(3)

$$\ln \left({\mathrm{q}}_{\mathrm{e}}-{\mathrm{q}}_{\mathrm{t}}\right)=\mathrm{l}\mathrm{n}{\mathrm{q}}_{\mathrm{e}}-\frac{{\mathrm{k}}_1\mathrm{t}}{2.303}$$

(4)

$$\frac{\mathrm{t}}{{\mathrm{q}}_{\mathrm{t}}}=\frac{1}{{\mathrm{k}}_2{{\mathrm{q}}_{\mathrm{e}}}^2}+\frac{\mathrm{t}}{{\mathrm{q}}_{\mathrm{e}}}$$

Eq. (3) is pseudo-first-order and Eq. (4) is pseudo-second-order model. Also, ${\mathrm{q}}_{\mathrm{t}}$ and ${\mathrm{q}}_{\mathrm{e}}$ (mg/g) express the quantity of pollutant absorbed on the surface of GO/SiO₂ adsorbent and equilibrium condition, respectively. The values of k₁ (min⁻¹) and k₂ (g.mg⁻¹.min⁻¹) as constants of pseudo-first/second-order models for the adsorption of MB and Cr (VI) on the synthesized nanocomposite are given in Table 1. Correspondingly, the behavior of Pseudo-first/second-order model for adsorption of MB dye and Cr (VI) ion on the synthesized nanocomposite are shown in Fig. 6. As can be seen, the pseudo-second-order kinetic model is the desired model for the adsorption of both MB and Cr (VI) because of the higher correlation regression coefficient (given in Table 1). Thus, the adsorption of MB dye and Cr (VI) ion on the surface of GO/SiO₂ is based on chemisorption or chemical adsorption.

Table 1 The kinetic parameters of a pseudo-first order and a pseudo-second order adsorption constants.

Kinetic model	Parameter	MB (50 ppm)	MB (75 ppm)	MB (100 ppm)	Cr (VI) (20 ppm)	Cr (VI) (40 ppm)	Cr (VI) (100 ppm)
Pseudo-first-order	K1	−0.108	−0.120	−0.083	−0.052	−0.109	−0.077
	qe (Exp.)	166.210	249.470	332.580	63.856	107.683	173.846
	qe (Calc.)	162.960	341.970	365.090	39.47	98.129	109.395
	R2	0.9600	0.8720	0.9420	0.9942	0.9360	0.94620
Pseudo-second-order	K2	0.0018	0.0009	0.0004	0.0028	0.0032	0.0017
	qe (Exp.)	166.210	249.470	332.580	63.856	107.683	173.846
	qe (Calc.)	172.410	263.150	357.140	67.110	111.110	181.810
	R2	0.9985	0.9983	0.9970	0.9991	0.9991	0.9989

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Fig. 6

Pseudo-first-order model for A) MB and B) Cr (VI) and Pseudo-second-order kinetics model for C) MB dye and D) Cr ion adsorption.

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Fig. 6

Pseudo-first-order model for A) MB and B) Cr (VI) and Pseudo-second-order kinetics model for C) MB dye and D) Cr ion adsorption.

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3.2.3

3.2.3 Isotherm study

Adsorption isotherms are one the most valuable and common ways to apply the GO/SiO₂ nanocomposite as an absorbent. This mathematical modeling describes how the adsorption process carries out, and adsorbate (MB dye and Cr (VI) ions) interacts with absorbents (GO/SiO₂). The maximum adsorption capacity of GO/SiO₂ for MB can be obtained using equilibrium isotherms at different initial concentrations. Isotherm studies for MB and Cr (VI) adsorption was carried out using four isotherm models i.e., Temkin, Flory-Huggins, Freundlich, and Langmuir models.

The Langmuir model studies the layer interaction of adsorption, determining the monolayer coverage of adsorbate over a homogenous adsorbent surface (Banivaheb et al., 2021). The linear form of the Langmuir isotherm equation can be given as follows (Banivaheb et al., 2021; Mazzotti, 2006):

(5)

$$\frac{C_e}{q_e}=\frac{1}{q_{m}b}+\frac{1}{q_m}{C}_e$$ where $q_e$ (mg/g) and $C_e$ (mg/L) are amount adsorbed at equilibrium and the equilibrium concentration, respectively. Furthermore, $b$ (L/mg) is the heat of adsorption and $q_m$ (mg/g) relates to monolayer adsorption capacity. Langmuir plot is shown in Fig. 7 indicates a good between experimental data and the Langmuir model results. The Langmuir model results are given in Table 2 separation factor constant, $R_L$ , is a dimensionless constant that is calculated using the following formula (Banivaheb et al., 2021 Aug 1; Arabpour et al., 2021 Mar 1):

(6)

$$R_L=\frac{1}{b{C}_0+1}$$

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Fig. 7

The various isotherm model for MB and Cr (VI) adsorption: A) Langmuir, B) Freundlich, C) Flory-Huggins, and D) Temkin.

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Fig. 7

The various isotherm model for MB and Cr (VI) adsorption: A) Langmuir, B) Freundlich, C) Flory-Huggins, and D) Temkin.

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Table 2 The adsorption isotherm study of MB and Cr on GO/SiO₂ nanocomposite.

Isotherm model	Isotherm constants	MB	Cr (VI)
Langmuir	qm (mg/g)	555.500	181.810
	b	0.290	0.364
	R2	0.996	0.998
	RL	0.007–0.700	0.010–0.670
Freundlich	1/n	0.255	0.257
	Kf	180.314	63.030
	R2	0.935	0.967
Flory-Huggins	Ka	−2.843	−2.552
	n	−0.609	−0.907
	R2	0.961	0.908
Temkin	AT	21.786	20.582
	B	69.286	23.903
	bT	34.967	101.357
	R2	0.984	0.954

If the separation factor constant is equal to 1, the isotherm is linear, if 0 < $R_L$  < 1 the adsorption process exhibits desirable adsorption, if $R_L$  > 1, it represents an undesirable adsorption conditions, and $R_L$  = 0 indicates an irreversible adsorption process (Arabpour et al., 2021; Mazzotti, 2006). The $R_L$ values results calculated in the this communication were found out in the range of 0.003–1.00, determining that MB dye adsorption and Cr (VI) ion by the GO/SiO₂ nanocomposite is favorable (0 < R_L < 1).

The interaction between the molecules of adsorbed dyes and representation of the multilayer adsorption is explained and determines using the Freundlich isotherm at the equilibrium state. General form and linear form of the Freundlich isotherm is presented as follows (Yang, 1998):

(7)

$$q_e=K_f{C_e}^{1/n}$$

(8)

$$\mathit{ln}{q}_e=\mathit{ln}{q}_e+\frac{1}{n}\mathit{ln}{C}_e$$

To calculate the constant, $K_f$ and 1/n, ln $q_e$ against $\mathit{ln}{C}_e$ as to be plotted. The estimated data are shown in Table 2.

Table 2.

Another important note in the adsorption process is how much of the adsorbent surface is covered by the adsorbate molecules. This parameter is studied and determined using the Flory-Huggins adsorption isotherm. The Flory-Huggins adsorption isotherm formula is as follows (Shikuku and Mishra, 2021 Jun):

(9)

$$\mathit{log}\left(\frac{\theta }{C_0}\right)=\mathit{log}\left(K_a\right)+n\mathit{log}\left(1-\theta \right)$$

In which the degree of surface coverage is represented by θ = (1- C_e/C_o), the number of dye molecules settled in adsorption sites on the adsorbents surface is shown by the n parameter, and the equilibrium adsorption coefficient is described by $K_a$ . To calculate the constants, first, we have to plot $log\left(\frac{\theta }{C_0}\right)$ vs $\mathit{log}\left(1-\theta \right)$ , then $K_a$ and n can be calculated from the slope and intercept of the plot. Fig. 7 shows the behavior of Flory-Higgins isotherm vs experimental data. The values of R² are quite low hence, Flory-Higgins equation is not suitable for the MB dye adsorption and Cr (VI) ion on the GO/SiO₂ nanocomposite.

One of the most accurate and precise isotherms that express adsorbent-adsorbate interaction is Temkin isotherm (Gowda et al., 2022). The Temkin isotherm equation is represented as follows (Gowda et al., 2022):

(10)

$$q_e=\frac{RT\mathit{ln}{A}_T}{b_T}+\frac{\mathit{RT}}{b_T}\mathit{ln}{C}_e$$

(11)

$$B=\frac{\mathit{RT}}{b_T}$$

(12)

$$q_e=B\ln A_T+B\ln C_e$$

In the Temkin isotherm equilibrium binding constant is shown by $A_T$ (L/g), the Temkin isotherm constant represented by $b_T$ and R is the universal gas constant, and temperature is indicated by T, and B means the constant associated heat of sorption (J/mol). To determine and calculate the Temkin constants values $A_T$ and $b_T$ , $q_e$ versus $\ln C_e$ must be plotted, and the constants are extracted from the slope and intercept of the plot (see Fig. 7). The results are tabulated in Table 2.

To determine the governing isotherm on the adsorption, process, isotherms have to be compared and judged by their applicability. One of the factors that determine the accuracy of the isotherm is the correlation between mathematical data and experimental data; for this purpose, is correlation coefficients i.e., R². The higher values of R² determine the higher correlation between the mathematical and experimental data. The R² values are in the range of 0.999–1.000 show that the adsorption experimental data of MB dye and Cr (VI) ions on the GO/SiO₂ nanocomposite were well fitted in the Langmuir model.

A comparison between raw materials adsorption, the synthesized Nanocomposite and other adsorbents' maximum capacity is shown in Table 3. As shown in the table addition of Nano silica to graphene oxide structure with 2:1 ratio of GO-SiO₂ decreased the adsorption capacity of MB due to the lowering the free space between the GO planes. As for Cr (VI) removal existence of SiO₂ increased the adsorption capacity of the adsorbent. Silica Nano particles also shown a low adsorption capacity, due to the agglomeration of the Nano particle in the adsorption process, while in the nanocomposite structure they are fixed on the Graphene oxide planes and show removal activity. As can be seen, the synthesized Nano composite achieved a higher adsorption capacity than to other adsorbents. It is proved that the nanocomposite structure synthesized using a novel method using ultrasonic resulted in a homogenous nanocomposite that interacts and adsorb pollutants better and more efficient compared to other adsorbents.

Table 3 The comparison between maximum adsorption capacity of various adsorbents.

Adsorbent	Pollutant	Q max (mg/g)	Reference
Carbon from the banana stem	MB	101.01	(Misran et al., 2022)
activated magnesium silicate	MB	99.92	(Kaya-Özkiper et al., 2022)
PPy-Fe3O4-SW	MB	666.66	(Sarojini et al., 2022)
PPy-Fe3O4-SW	Cr (VI)	0.44	(Sarojini et al., 2022)
Fe3O4-Bone Activated Carbon	Cr (VI)	27.86	(Sánchez-Ponce et al., 2022)
Biochar	Cr (VI)	58.54	(Thangagiri et al., 2022)
GO	MB	1474	This study
GO	Cr (VI)	38.97	This study
SiO2	MB	26.72	This study
SiO2	Cr (VI)	17.59	This study
GO/SiO2	MB	555.50	This study
GO/SiO2	Cr (VI)	181.81	This study

4 Conclusions

The synthesized nanocomposite graphene oxide/SiO₂ adsorbent was found as a well-organized adsorbent for MB and Cr (VI) ion and with excellent the antibacterial activity. The graphene oxide was synthesized based on a novel method, and its properties, and characterization of it were studied using SEM, and TGA analyses. After that, graphene oxide/SiO₂ nanocomposite was synthesized based on a simple and new producer and SEM, EDX, and XRD analyses were performed to investigate the structure of the nanocomposite. The performance of graphene oxide/SiO₂ nanocomposite was studied using two methods: removal of dye and heavy metal ion from polluted water and an antibacterial activity test. The overall investigation indicates the high capacity of graphene oxide/SiO₂-based nanocomposite adsorbent in industrial conditions of treatment of wastewater polluted by MB and Cr (VI) ion. The adsorptive performance of graphene oxide/SiO₂ nanocomposite was found more effective in the removal of MB in comparison to Cr (VI) ion. Antibacterial activity of synthesized nanocomposite increases its application in water treatment plants as a suitable and efficient adsorbent. In addition, using four isotherm models i.e., the Temkin, Flory-Huggins, Freundlich, and Langmuir models, the kinetic of adsorption was investigated and the obtained results indicated the Langmuir model had acceptable conformity with experimental data of dye and ion removal.