Article AL-QADISIYAH JOURNAL FOR ENGINEERING SCIENCES 14 (2021) 031–041 Contents lists available at http://qu.edu.iq Al-Qadisiyah Journal for Engineering Sciences Journal homepage: http://qu.edu.iq/journaleng/index.php/JQES * Corresponding author. E-mail address: orashussien1@gmail.com (Oras Abd Al Hussien Qatta) https://doi.org/10.30772/qjes.v14i1.692 2411-7773/© 2021 University of Al-Qadisiyah. All rights reserved. This work is licensed under a Creative Commons Attribution 4.0 International License. Coated material (Graphene oxide coated sand ) as a new approach in Wastewater treatment field :Equilibrium and thermodynamic studies Oras Abd Al Hussien Qatta a*, Abbas Khalaf Mohammad a a Chemical Engineering Department– College of Engineering −University of Al-Qadisiyah-Iraq. 1. Introduction Wastewater is one of the major environmental damages that seriously affect all aspects of life Albright et al. [1]. The effects of contaminants can differ depending on their form and source Inyinbor Adejumoke et al. [2]. Dyes in particular known as reactive basic . ,acidic Lellis et al. [3]. Textile effluent treatment is necessary to protect the environment Yaseen et al. [4]. A wide variety of methods for sorption synthetic dyes from water and wastewater have been developed to reduce their environmental effects Forgacs et al. [5]..Various promising techniques have been used to remove dyes from wastewater. Such treatment systems, such as chemical, physical, and biological approaches, have their drawbacks like high expense, radioactive sludge production, etc. The most inexpensive and efficient adsorption process has been the most favoured approach for dye removal Seow et al. [6]. Graphene oxide, especially as magnetic particles, has recently been used as a suitable adsorbent for A R T I C L E I N F O Article history: Received 20 September 2020 Received in revised form 19 October 2020 Accepted 19 October 2020 A B S T R A C T The present work describes a coating process that was carried out on the surface of graphene oxide powder. Coated material (GO−Sand composite) was prepared by soaking screened and washed sand particles (100 µm) with 3% graphene oxide aqueous solution. The coating process was done in two stages, first at a temperature of 105 ◦C for three hours then at 150 ◦C for two hours. FTIR spectroscopy was used to investigate the surface of graphite and graphene oxide . Adsorption of methylene blue and methyl orange dyes onto the prepared graphene oxide coated sand was done experimentally using batch apparatus with controlled conditions of temperature and stirring. Effects of temperature and initial dye concentration for the adsorption process were examined. The analysis of adsorption equilibrium isotherms shows that the experimental data follows Fruendlich isotherm model with coefficient of variance (R2) equals to (0.99). This indicates that the adsorption of both dyes onto the GO−sand was done on heterogeneous surface with multilayer of dyes molecules. Furthermore, basic thermodynamic parameters for the adsorption of both dyes on GO−sand were calculated using the most well known relationships. The results indicate that the process is spontaneous and exothermic as the values of Gibbs free energy changes lies between -37.078 and -24.231 kJ/mole and the values of enthalpy changes lies between -0.669 and -0.348 kJ/mole for methylene blue and methyl orange dyes. Finally, the activation energy for the adsorption process was determined using Arrhenius equation and found to be equals to 28.643 kJ/mol and 20.224 kJ/mol for methylene blue and methyl orange adsorption, respectively. This proves the physical nature of dyes adsorption on the surface of the adsorbent. © 2021 University of Al-Qadisiyah. All rights reserved. Keywords: Coating process Support material Sand Batch adsorption Nano material http://qu.edu.iq/ https://doi.org/10.30772/qjes.v14i http://creativecommons.org/licenses/by/4.0/ 32 ORAS ABD AL HUSSIEN QATTA , ABBAS KHALAF MOHAMMAD /AL-QADISIYAH JOURNAL FOR ENGINEERING SCIENCES 14 (2021) 031–041 wastewater treatment. It was successfully applied for heavy metals and organic materials (dyes, antibiotics, reactive black 5, etc.) treatments Kyzas et al. [7]. Coating has been used in many applications such as wear resistance, corrosion protection, anti-fouling, thermal barrier, self-cleaning, etc. for a long time ago. However, its used in the field of coating adsorbents to remove industrial dyes from wastewater was still silent.. It is a modern approach and advanced technology for treating industrial wastewater from organic pollutants such as dyes Azha et al. [8]. Adsorbent in the form of coated material has benefits over particulate adsorbents such as powders, pellets or beads The objective is to easily separate after the adsorption process (e.g. filtration or centrifugation) as well as to increase the surface area by weight ratio of the adsorbent used and to reduce the amount of solid adsorbent needed Azha et al. [9]. The selection of the appropriate support material that used for coating process was one of the important and critical decisions to be taken when preparing for the coating process. So as to use the supporting materials for the purpose of wastewater treatment, it must meet the following criteria: They are non-toxic, insoluble, non-biodegradable, lightweight and non- polluting; High mechanical and chemical stability, flexibility in general shape, high diffusivity, high proliferation, high biomass retention, low cost and minimal attachment to other organisms Martins et al. [10]. There are many types of supported materials which used in the filed of wastewater treatment, but inorganic supported material were the most important which included ceramic and sand polymer materials Singh et al. [11]. Sand one of the important natural supported materials that widely used in wastewater treatment processes, studies focused on the use of sand as a support material more than others materials such as clay or clay minerals due to its distinctive characteristics and its meets the effective adsorption requirements Jada et al. [12]. The study focuses on the use of sand as an inorganic support material in the field of wastewater treatment. Also, this work explains the stages of the coating process that was carried out on the surface of graphene oxide with specific conditions. studying of the equilibrium and thermodynamic characteristics for the adsorption process was one of the important analysis which applied in the present work. 2. Experimental work 2.1. Materials Sand was collected from AL-Najaf sand quarry. Also, chemicals that used in the practical aspect have high purities with analytical grades including, H2SO4 (Aldrich, Germany), H3PO4 (Aldrich, USA), original graphite powder (>150 µm), potassium permanganate (Alpha Chemika, Iso Co., India), ethanol (Aldrich, Germany), hydrogen peroxide (Panreac, Germany). 2.2. Coated material preparation (graphene oxide−sand composite) preparation of coated adsorbent (GO−sand) was included two main steps. Firstly, preparation of graphene oxide powder. Secondly, coating the surface of the sand grains with prepared graphene oxide. 2.2.1. apparatus used for coating process The apparatus shown photographically and schematically in Fig. (1) and (2) was used for coating of sand grains with graphene oxide. A coating container was used with 1000 ml Pyrex glass beaker (Simax, Germany). The beaker was fitted with a glass stir bar for mixing the coating mixture manually. A digitally operated drying oven (Memmert, Germany) was used to dry any excessive quantity of solvent . Figure 1. photographic picture of the apparatus used for coating sand with graphene oxide. Nomenclature Ea Activation energy (Kj/mol) qe Ce Adsorption capacity (mg/g) Concentration of adsorbate solution C2 Concentration of solution after dilution (mg/L) C1 Concentration of solution before dilution (mg/L). Kf Ke ΔH◦ ΔS◦ Constant of freundlich Dimensionless equilibrium constant Enthalpy energy change (Kj/mol) Entropy energy change (J/mol.K) A Frequency factor GO ΔG◦ C0 Gaphene oxide Gipps free energy (Kj/mol) Initial concentration N b Intensity of adsorption Langmuir isotherm constant (l/mg) qm MB MO Qm V1 V2 Maximum adsorption capacity (mg/g) Methylene blue Methyl orange Theoretical adsorption capacity (mg/g) Volume of solution before dilution (litre) Volume of the distilled water required for dilution in litre. ORAS ABD AL HUSSIEN QATTA , ABBAS KHALAF MOHAMMAD /AL-QADISIYAH JOURNAL FOR ENGINEERING SCIENCES 14 (2021) 031–041 33 Figure 2. Schematic diagram of the apparatus used for coating process. 2.2.2. Procedure modified Hummer method was used for preparation of graphene oxide powder Andrijanto et al. [13]. A 9:1 mixture of two concentrated sulphuric acids (H2SO4, 98%) and phosphoric acid (H3PO4, 70%) was added to the conical flask, then (3 gram) from the original graphite powder (>150 μm) was put in the flask. After that (18 gram) from the permanganate potassium (KMnO4) was slowly added to the mixture, after this addition, the temperature steadily rose to (35 ◦C) due to the occurrence of an oxidation reaction. Then the mixture heated up until the temperature reaches 50 ◦C with continuing to stir for 12 hours. After that, decreasing the solution temperature to room temperature. Finally, hydrogen peroxide added (3 ml) (30%, H2O2), Fig. (3) shows the schematic diagram for the apparatus used for preparing grapheme oxide powder. The finale product was washed and filtered by using filtration apparatus which show in Fig. (4).Finally. produced graphene oxide was dried in drying oven at 60 ◦C for three hours. Figure 3. Schematic diagram of apparatus used for preparation of grapheme oxide . Figure 4. Photographic picture for filtration apparatus. After preparing of graphene oxide powder the step followed that was coating process. The process was performed under certain conditions in the laboratory. Firstly, sand was prepared for coating, it was sieved by using laboratory sieving device which show in Fig. (5). The device consisted of six section each section has its own mesh number and the size of diameter in ( MIC). This test was important to select which section was appropriate in terms of quantity, mesh number and diameter, after sieving the second section was chosen (100 MIC). Figure 5. Photographic picture of laboratory sieving machine. Then sand was washed more than one time with tap water and soaked with 10 % HCl for 6 hours to remove impurities and salts, after that, drying oven was used to dry the clean sand. The preparation of sand grains for coating process shows in Fig. (6). 34 ORAS ABD AL HUSSIEN QATTA , ABBAS KHALAF MOHAMMAD /AL-QADISIYAH JOURNAL FOR ENGINEERING SCIENCES 14 (2021) 031–041 Figure 6. Photographic picture of the steps of preparation sand for coating process. After washing and drying the sand, 30 gram of dried sand were taken and submerged in (50 ml) from 3% suspended solution of distilled water and grapheme oxide. then heated the mixture for three hours at 105 ◦C for water evaporation. After that the mixture was heated at 150 ◦C for an additional 2 hours to stabilize the graphene oxide on the sand grain surface. The final product was resulted from the coating process was a black powder of sand coated by graphene oxide which represent the adsorbent material for waste water treatment process. Fig. (7) shows a photographic picture of prepared graphene oxide−sand. Figure 7 . Photographic picture for GO-sand composite after coating process. 2.3. Equilibrium experiment Several methylene blue and methyl orange dyes solutions were prepared According to the dilution law [14]: 𝐶1 ∗ 𝑉1 = 𝐶2 ∗ 𝑉2 ……………….(1) Fig. (8) shows the stocks solution. Figure 8 . Photographic picture of the stock solution. Adsorption equilibrium experiments were done in two steps. Firstly, the equilibrium time was determined at the highest dyes concentration and the lowest temperature to ensure obtaining enough time for mass transfer. Secondly, dyes concentration in aqueous solutions as a function of dyes concentration in the solid phase was obtained at different temperatures. A 500 ml three nick conical flask (Goel, Germany) was used as an adsorption chamber. A glass thermometer was immersed inside the flask for measuring and recording of adsorption temperature. The flask was equipped with Pyrex glass recycling condenser to ensure retarding of any vapors from adsorption mixture. An antifreeze chiller (HYSC, Korea) was used to supply condensing media at (-5 ◦C) for the recycling condenser. 1000 ml Pyrex glass beaker (Simax, Germany) covered via a layer of glass wool insulation material was used as a water bath for the adsorption mixture. A thermo couple connected to a digital recorder (Micro Max, Germany) was putted inside the beaker for continuous monitoring of water bath temperature. The hole adsorption equipment was putted over a hot plate magnetic stirrer (SH-2, Germany) for supplying necessary heat required for the water bath as well as providing the vigorous mixing of adsorption mixture. Fig. (9) and (10) show photographically and schematically batch adsorption device. Figure 9 . Photographic picture for batch adsorption system. ORAS ABD AL HUSSIEN QATTA , ABBAS KHALAF MOHAMMAD /AL-QADISIYAH JOURNAL FOR ENGINEERING SCIENCES 14 (2021) 031–041 35 Figure 10 .Schematic diagram for batch adsorption system. Then, a set of experiments were conducted to examine the effect of temperature and initial concentration on the adsorption of methylene blue and methyl orange from aqueous solution onto the prepared super sand. This was done by taking a range of concentrations (50, 100, 150, 160, 180, 200) ppm of basic dye (methylene blue) and acidic dye (methyl orange) at different temperatures (20, 25, 30, 35) ◦C with constant contact time 3 hours. Each experiment was done by putting 1 gram of the adsorbent material (super sand) in a Pyrex flask with (30 ml) of the dye solution. The colour of solutions for the two dyes before and after the adsorption process were shown in Fig. (11). Figure 11. Photographic picture for methylene blue and methyl orange before and after adsorption . 3. Result and discussion 3.1. Dyes concentration by Photometric method Ultraviolet/Visible Absorption Spectrometer (UV−Vis) analyzes the light beam reflected from the surface of the sample or after passing through it. Where there is a linear relationship between the concentration of material and absorption. This makes the UV spectroscopy very important in making quantitative measurements [15]. The wave length of the methylene blue and methyl orange dyes was checked firstly. This was done by putting a sample from the two dyes solutions in the sample cell of the machine. Distilled water was used as a comparative solution where it was putted in the solvent cell. After that, a scan for the whole wave length range was performed to analyze the peaks of the spectrum. Fig. (12 and 13) show the calibration curves of methylene blue and methyl orange dyes. Figure 12. Calibration curve of methyl orange dye . Figure 13. Calibration curve of methylene blue dye. 3.2. Characterization of prepared graphene oxide Fourier Transform Infrared (FTIR) spectroscopy was used to investigate the presence of functional groups on the surface of graphene oxide. Fig. (14) & (15) show the spectra of graphite and graphene oxide. From Fig. (15) , the characteristic peaks were appeared in different in different wavenumber. The peak falls at (3332) cm-1 refers to the presence of hydroxyl stretching vibration (-OH). Several researchers suggested that the peaks at the range (3000−3500) cm-1 refers to (C-OH) groups on the surface of GO [16, 17]. In addition [18] study showed that the hydrophilic 36 ORAS ABD AL HUSSIEN QATTA , ABBAS KHALAF MOHAMMAD /AL-QADISIYAH JOURNAL FOR ENGINEERING SCIENCES 14 (2021) 031–041 property of graphene oxide due to the presence of the hydroxyl functional group. Peak at (2973) cm-1 refers to sp3 (C-H) group which indicates that the prepared graphene oxide was produced in acidic media. This conclusion was based on the evidence recognized by Aziz et al. [19]. Peak at (1390) cm-1 indicates the presence of carboxyl stretching vibration (C=O) while the peaks at (1088) cm-1, (1045) cm-1 and (879) cm- 1 refer to (C-O) stretching vibration. The presence of all these functional groups (epoxy, hydroxyl, carboxyl) on the surface of prepared graphene oxide proves the successful preparation process which was used in our experimental work. This results were based on the observations that done by several researchers[17, 20]. Figure 14. Fourier Transform Infrared (FTIR) for graphite. Figure 15. Fourier Transform Infrared (FTIR) for graphene oxide. 3.3. Equilibrium study of adsorption Isothermal information analyzes with the application of characteristic isothermal modeling is a major development in determining the appropriate model that can be used for design purposes. As a result, the relationship of equilibrium data that uses either a theoretical or experimental formula to understand and predict the degree of adsorption, in choosing the most extreme adsorption limit for a given adsorbent Foo et al. [21]. Fig. (16 and 17) represent the equilibrium adsorption isotherms curves for the acidic dye (methyl orange) and the basic dye (methylene blue) on the surface of the prepared graphene oxide coated sand adsorbent. These curves were plotted for the range of concentration (50−200) ppm at different temperatures (20, 25, 30, 35 ◦C). Figure 16. adsorption equilibrium isotherms for methyl orange adsorbed on the GO−sand at different temperatures. Figure 17. adsorption equilibrium isotherms for methylene blue adsorbed on the GO−sand at different temperatures. It could be recognized from these figures that there is a proportional relationship between the concentration of dyes in the solution and its concentration in the adsorbed phase. This is clearly shown from the shape of isotherms curves that are of classical adsorption type. This means that any increasing of concentration of dye in the solution increases the concentration of dye on the surface of the adsorbent. But this proportionality becomes less notable at high concentrations of dyes in the solution because the adsorbent reaches its maximum capacity. The values of maximum capacities for the prepared GO−sand is shown in Table 1. Figure (14): Fourier Transform Infrared (FTIR) for graphite. ORAS ABD AL HUSSIEN QATTA , ABBAS KHALAF MOHAMMAD /AL-QADISIYAH JOURNAL FOR ENGINEERING SCIENCES 14 (2021) 031–041 37 Table (1) Maximum capacities of GO−sand for methylene blue and methyl orange dyes. 3.3.1. Langmuir and Freundlich Models Langmuir and freundlich adsorption isotherm models were used to correlate the experimental adsorption data of methylene blue and methyl orange onto GO−sand composite. These models were used in the present study because they are the most well known equations that could represent the adsorption of solute in aqueous solution onto a solid adsorbent [22]. Langmuir adsorption isotherm represents the adsorption of solute that limits to a single monolayer of solute molecules on the solid adsorbent. This is based on the Langmuir theory of adsorption which assume the surface of the solid adsorbent as a homogeneous surface. However, Langmuir adsorption isotherm equation could be represented mathematically as [23]: 𝑞𝑒 = 𝑄𝑚 𝑏 𝐶𝑒/(1 + 𝑏 𝐶𝑒) ……………………….. (2) Freundlich adsorption isotherm represents the adsorption of solute as a multilayer of molecules onto the heterogeneous surface of solid adsorbent. Freundlich adsorption isotherm equation could be represented mathematically as [22]: 𝑞𝑒 = 𝐾𝑓 𝐶𝑒 1 𝑛 …………………………..................(3) Langmuir and Freundlich adsorption isotherm equations were expressed in linear forms respectively as follow: 𝐶𝑒/𝑞𝑒 = 1/(𝑄𝑚 𝑏) + 1/𝑄𝑚 𝐶𝑒 ……………….(4) 𝐿𝑜𝑔 𝑞𝑒 = 𝐿𝑜𝑔 𝐾𝑓 + 1/𝑛 𝐿𝑜𝑔 𝐶𝑒 ………………...(5) The experimental data for adsorption of methylene blue and methyl orange on prepared GO−sand composite were correlated with the linearized form of Langmuir and Freundlich adsorption equations and shown in Fig. (18 and 21). It was clearly observed from these figures that the experimental data corresponding the Freundlich isotherm very well. This result indicates that the adsorption methylene blue and methyl orange onto the GO−sand was empirical and occurred on heterogeneous surface and also due to the high concentrations used in the present work. Figure 18. Linearized form of fruendlich isotherm model for methyl orange adsorbed at different temperatures. Figure 19. Linearized form of fruendlich isotherm model for methylene blue. Adsorbed at different temperatures. Figure 20. Linearized form of Langmuir isotherm model for methyl orange adsorbed at different temperatures. Figure 21. Linearized form of Langmuir isotherm model for methylene blue adsorbed at different temperatures. This congruence with freundlich isotherm could be clearly evident by recognizing the values of confidence level (R2). Tables (2 and 3) show the comparison between the Langmuir and freundlich isotherms for methylene blue and methyl orange dyes equilibrium adsorption data. Temp. ◦C Methylene blue Methyl orange Ce qe Ce qe 20 1.922 5.983 15.667 5.682 25 2.011 5.612 16.321 5.322 30 2.126 5.376 17.511 5.087 35 2.157 5.102 18.563 4.722 38 ORAS ABD AL HUSSIEN QATTA , ABBAS KHALAF MOHAMMAD /AL-QADISIYAH JOURNAL FOR ENGINEERING SCIENCES 14 (2021) 031–041 Table (2): Isotherm parameters for methyl orange at temperature range (20–35) ◦C. Table (3): Isotherm parameters for methylene blue at temperature range (20 – 35) ◦C. 3.3.2. Effect of initial concentration The initial concentration of the dyes is an important tool in the study of the adsorption capacity. And the removal percentage of dye Zhang et al. [24],which was calculated by the following equation Wang et al. [25]: % 𝑟𝑒𝑚𝑜𝑣𝑒𝑙 = 𝐶0−𝐶𝑒 𝐶0 ∗ 100 …………………………………(6) Fig. (22 and 25) show the initial concentration of methyl orange and methylene blue dyes in the solution as a function of removal percentage of them due to adsorption which on the surface of graphene oxide coated sand. Figure 22. Removal percentage of methylene blue and methyl orange dyes for different initial concentration at 20 ◦C. Figure 23. Removal percentage of methylene blue and methyl orange dyes for different initial concentration at 25 ◦C. Figure 24. Removal percentage of methylene blue and methyl orange dyes for different initial concentration at 30 ◦C. Figure 25. Removal percentage of methylene blue and methyl orange dyes for different initial concentration at 35 ◦C. It was clearly shown from these figures that an increasing of the initial concentration of the two dyes in the solution associated with a decreasing of the removal percentage. However, the increase in initial concentration enhances the adsorption capacity but diminishes the removal percentage of dye. This clearly observed from Fig. (16 & 17) and (22−25), where the removal percentage at 20 ◦C decreased from 99.55% to the 70.44% for methylene blue and decreased from 83.32% to 61.22% for methyl orange. This behavior is in agreement with study by Foo et al. [21]. This behavior may be explained as follows. In most cases of low concentrations of dyes in solution, the ratio of the initial number of dye molecules to the available Surface area is small Hence, the partial adsorption is independent on the Temp. ◦C Langmuir model Freundlich model Qm b R2 Kf n R2 20 25 30 35 5.682 5.322 5.087 4.722 0.066 0.05 0.049 0.048 0.5448 0.75 0.4601 0.603 0.448 0.293 0.176 0.091 1.019 0.949 1.115 0.848 0.9961 0.9971 0.9974 0.9999 Temp.◦C Langmuir model Freundlich model Qm b R2 kf n R2 20 25 30 35 5.983 5.612 5.376 5.102 0.702 0.638 0.574 0.537 0.2773 0.3134 0.2958 0.2142 0.265 0.325 0.405 0.505 0.975 0.963 0.917 0.874 0.9985 0.9988 0.9988 0.9986 ORAS ABD AL HUSSIEN QATTA , ABBAS KHALAF MOHAMMAD /AL-QADISIYAH JOURNAL FOR ENGINEERING SCIENCES 14 (2021) 031–041 39 initial concentrations. Although, in high concentrations of dyes in solution, the available adsorption sites become less as a result of reaching the adsorption sites to the saturation state. However, figures (22− 25) indicate that there is an optimal value for the initial concentration of both dyes in the solution. This optimal value is about 100 mg/l where the relationship between the removal percentage and the initial concentration up to this value is approximately a horizontal line. 3.3.3. Effect of temperature In the adsorption process it is very important to know the extent to which the temperature affects the efficiency of the adsorbents Corda et al. [26]. Fig. (16 and 17) show the effect of temperature on the adsorption capacity of GO−sand for methyl orange and methylene blue dyes. The temperature range using for the adsorption process is (20 – 35) ◦C, it was clearly observed from these figures that an increase in the temperature causes a decrease in the adsorption capacity of the two dyes. This behavior refers that the adsorption phenomena is an exothermic process, this result is in agreement with study by Yagub et al. [27]. They expressed that If the the adsorption capacity increases with increasing temperature, this means adsorption is an endothermic process. This is due to the increased susceptibility of the dye molecules and the expansion in the active sites upon increase in temperature. While the adsorption capacity decreases with increase in temperature, this means that the process is exothermic. This behavior may be due to the weakening of the attraction forces between the dye. molecules with the active sites on the surface of the adsorbent upon increased temperature. Fig. (22 & 25) show the effect of temperature on the removal percentage of dyes. The figures indicate that an increase in temperature leads to a decrease in the removal percentage of the two dyes. Where, the removal of methylene blue decreased from 99.55% to 87.12% with increasing the temperature from 20 ◦C to 35 ◦C. Also, the removal of methyl orange decreased from 83.32 % to 75.33% with the same increasing in temperature. This behavior is in agreement with the study by Gupta et al. [28]. They explained that the adsorption forces between the dye molecules and the active sites become weak when the temperature increases, which leads to a decrease in the removal percentage of dye. 3.3.4. Effect of adsorbate type Fig. (22 & 25) show that the GO−sand composite is more effective in removing methylene blue than the methyl orange. Where, the maximum percentage of removal methylene blue reached to 99.55% at 20 ◦C. While the maximum percentage of removal methyl orange reached to 83.32% at the same temperature. This result is due to the extent of attraction and repulsion between the active sites on the surface of the GO−sand and the different charges of the dye molecules. For this reason, the attraction is greater between the surface charges (acidic media) with methylene blue (basic dye) and less with methyl orange (acidic dye). This behavior is in agreement with the study by Santoso et al. [29]. The study showed that graphene oxide has a high efficiency in removing methylene blue from aqueous solutions due to the attraction between their different charges. In comparison this result with study by Shahabuddin et al. [30], they used poly aniline coated graphene oxide for removal methylene blue and methyl orange dyes from aqueous solution. The results showed that methylene blue removal percentage was 57% which it was higher than of methyl orange 36%. They concluded that the surface of the graphene oxide contain various functional groups such as (epoxy and hydroxyl), also the presence of sp3 hybrid framework that makes it effective in removing basic dyes such as MB more than MO. 3.4. Kinetics and thermodynamic studies The estimation of the thermodynamic parameters depend on the value of the thermodynamic equilibrium constant (Ke). The mathematical equations used in the thermodynamic calculations could be presented as [31]: ∆𝐺° = −𝑅𝑇 𝑙𝑛(𝐾𝑒) ……………………. (7) ∆𝐺° = ∆𝐻° − 𝑇∆𝑆° ………………………(8) 𝑙𝑛 (𝐾𝑒) = −(∆𝐻°)/𝑅𝑇 + (∆𝑆°)/𝑅 ……….(9) 𝐾𝑒 = 𝑞𝑒/𝑞𝑚/(1 − 𝑞𝑒/𝑞𝑚)(𝐶𝑒/(𝐶°))………(10) Fig. (26 and 27) represent the plot of (lnKe) as function of the inverse of the temperature (1/T) for adsorption of methyl orange and methylene blue dyes onto the GO− sand. The values enthalpy change (∆H◦) and entropy change (∆S◦) were computed from the slops and intercepts of these lines. Figure 26. Thermodynamic plot of (lnKe) versus (1/T) for adsorption of methyl orange at different concentrations. Figure 27. Thermodynamic plot of (lnKe) versus (1/T) for adsorption of methylene blue at different concentrations. It was clearly observed from the figures that the slopes and intercepts of all lines are positive. Therefore, the adsorption of methyl orange and methylene blue on the GO−sand is exothermic process since the enthalpy changes are always negative. Furthermore, the process was happened spontaneously because the values of entropy changes are always positive. In addition, the positive values of the entropy changes (∆S◦) refer to the randomness of the surface. This result is in agreement with study did by Alghamdi et al.[32]. They used graphene oxide composite for the removal of azo dyes from aqueous solution. They computed the values of (ΔH◦, ΔS◦ 40 ORAS ABD AL HUSSIEN QATTA , ABBAS KHALAF MOHAMMAD /AL-QADISIYAH JOURNAL FOR ENGINEERING SCIENCES 14 (2021) 031–041 and ΔG◦). Their results gave the same idea for the nature of the adsorption process. They concluded that the process was exothermic and spontaneous. Activation energy (Ea) for adsorption of methyl orange and methylene blue on the GO−sand was studied and computed by applying Arrhenius equation Saha et al. [33]: 𝑙𝑛𝑘 = 𝑙𝑛𝐴 − 𝐸𝑎/𝑅𝑇 ……………………..(11) Fig. (28 and 29) represent a plot of (lnk) versus (1/T) for methyl orange and methylene blue adsorption on GO−sand. The values of the activation energies were determined from the slops of the figures for the two dyes. Tables (4) & (5) show the values of ΔG◦ , ΔS◦ and ΔH energies for methylene blue and methyl orange dyes. Figure 28. Arrhenius plot for methyl orange adsorption at temperature range (20 − 35) ◦C. Figure 29. Arrhenius plot for methylene blue adsorption at temperature range (20 − 35) ◦C. Table (4): Thermodynamic parameter for the adsorption of methyl orange on the super sand at temperature range (20−35) ◦C. Table (5): Thermodynamic parameter for the adsorption of methylene blue on the super sand at temperature range (20−35) ◦C. 4. Conclusions This research demonstrates the use of coated materials as a new approach in wastewater treatment. Coating process gave a good result of graphene oxide–sand composite with high dyes removal efficiency from aqueous solution. This work will conclude on a variety of important points:  The product of the coating process was a homogeneous compound of sand and graphene oxide. The process was completed successfully and gave graphene oxide fixed well on the surface of sand grains after five hours without the need for reheating.  FTIR spectra was showed the chemical structure of graphene oxide, the result expresses different functional groups (epoxy, hydroxyl and carboxyl) distributed on the surface that indicate the success of the preparation process.  The equilibrium adsorption isotherm were applied on the experimental data showed that the freundlich isotherm fitted well the experimental adsorption data with confidence level 0.99.  GO−sand material has high efficiency in removing, where the maximum percentages removal of methylene blue and methyl orange equals to 99.55% and 83.22% , respectively.  Methylene blue has higher adsorption capacity than methyl orange, this may be due to the difference in the attracting forces between the surface of the adsorbent and the charges carried by the dyes.  Thermodynamic study showed that the adsorption process was spontaneous and exothermic process in nature, this due to the negative values of the Gibbs free energy change (ΔG◦) and enthalpy energy change (ΔH◦).  The values of Gibbs free energy changes lies between -37.078 and - 24.231 kJ/mole and the values of enthalpy changes lies between - 0.669 and -0.348 kJ/mole. This result indicates that the adsorption process of the present study could be suggested as physical adsorption In addition, the activation energy was studied for the two dyes and the result showed that the activation energy were equals to Ea=28.643 KJ/mol and Ea=20.224 Kj/mol for methylene blue and methyl orange, respectively. It was concluded from these results that the energy needed for interacting the adsorbate and the adsorbent are not high and this refers to the physical nature of the process. CO NC. PPM ∆H ◦ ∆S◦ ∆G◦ (kJ/mol) 293 K 298 K 303 K 308 K 50 100 150 160 180 200 - 0.6 69 - 0.6 29 - 0.5 77 - 0.6 54 - 0.6 89 - 0.5 1.043 0.837 0.569 0.756 0.793 0.416 - 25.358 -60.33 -26.537 -28.323 -29.902 -31.405 -31.962 - 25.1 89 - 26.2 77 - 28.0 26 - 29.0 32 - 30.2 53 - 32.3 - 24.2 31 - 26.2 02 - 28.0 23 - 28.7 64 - 29.7 23 - 30.6 - 24.9 57 - 26.2 42 - 27.8 71 - 25.4 13 - 29.1 65 - 29.4 CONC. PPM ∆H◦ ∆S◦ ∆G◦ (kJ/mol) 293 K 298 K 303 K 308 K 50 100 150 160 180 200 -0.402 -0.348 -0.427 -0.559 -0.479 -0.459 0.085 0.357 0.198 0.171 0.198 0.351 -30.053 - 60.33 -31.225 -33.877 -35.098 -36.540 -37.078 -30.236 -31.225 -33.877 -35.098 -36.540 -35.765 -30.332 -31.469 -33.376 -28.027 -33.827 -34.227 -30.337 -31.602 -33.674 -34.259 -34.385 -34.901 ORAS ABD AL HUSSIEN QATTA , ABBAS KHALAF MOHAMMAD /AL-QADISIYAH JOURNAL FOR ENGINEERING SCIENCES 14 (2021) 031–041 41 REFERENCES [1] R. Albright et al., "Ocean acidification: Linking science to management solutions using the Great Barrier Reef as a case study," Journal of Environmental Management, vol. 182, pp. 641-650, 2016. [2] A. Inyinbor Adejumoke, O. Adebesin Babatunde, P. Oluyori Abimbola, A. Adelani Akande Tabitha, O. Dada Adewumi, and A. Oreofe Toyin, "Water pollution: effects, prevention, and climatic impact," Water Challenges of an Urbanizing World, vol. 33, 2018. [3] B. Lellis, C. Z. Fávaro-Polonio, J. A. Pamphile, and J. C. Polonio, "Effects of textile dyes on health and the environment and bioremediation potential of living organisms," Biotechnology Research and Innovation, vol. 3, no. 2, pp. 275-290, 2019. [4] D. Yaseen and M. Scholz, "Textile dye wastewater characteristics and constituents of synthetic effluents: a critical review," International journal of environmental science and technology, vol. 16, no. 2, pp. 1193-1226, 2019. [5] E. Forgacs, T. Cserhati, and G. Oros, "Removal of synthetic dyes from wastewaters: a review," Environment international, vol. 30, no. 7, pp. 953-971, 2004. [6] T. W. Seow and C. K. Lim, "Removal of dye by adsorption: a review," International Journal of Applied Engineering Research, vol. 11, no. 4, pp. 2675-2679, 2016. [7] G. Z. Kyzas, E. A. Deliyanni, and K. A. Matis, "Graphene oxide and its application as an adsorbent for wastewater treatment," Journal of Chemical Technology & Biotechnology, vol. 89, no. 2, pp. 196-205, 2014. [8] S. Azha, A. Ahmad, and S. Ismail, "A new approach of thin coated adsorbent layer for batch adsorption using basic dye," ASEAN Journal of Chemical Engineering, vol. 15, no. 1, pp. 10-21, 2014. [9] S. F. Azha, S. Abd Hamid, and S. Ismail, "Development of composite adsorbent coating based acrylic polymer/bentonite for methylene blue removal," Journal of Engineering and Technological Sciences, vol. 49, no. 2, pp. 225-235, 2017. [10] S. C. S. Martins, C. M. Martins, L. M. C. G. Fiúza, and S. T. Santaella, "Immobilization of microbial cells: A promising tool for treatment of toxic pollutants in industrial wastewater," African journal of biotechnology, vol. 12, no. 28, 2013. [11] N. Singh, G. Nagpal, and S. Agrawal, "Water purification by using adsorbents: a review," Environmental technology & innovation, vol. 11, pp. 187-240, 2018. [12] A. Jada and R. A. Akbour, "Adsorption and removal of organic dye at quartz sand-water interface," Oil & Gas Science and Technology–Revue d’IFP Energies nouvelles, vol. 69, no. 3, pp. 405-413, 2014. [13] E. Andrijanto, G. Subiyanto, N. Marlina, H. Citra, and C. Lintang, "Preparation of Graphene Oxide Sand Composites as Super Adsorbent for Water Purification Application," in MATEC Web of Conferences, 2018, vol. 156: EDP Sciences, p. 05019. [14] B. Lacher, Pharmacy Technician Certification Review and Practice Exam. ASHP, 2016. [15] B. M. Tissue, "Ultraviolet and visible absorption spectroscopy," Characterization of Materials, pp. 1-13, 2002. [16] Y. Yao, S. Miao, S. Liu, L. P. Ma, H. Sun, and S. Wang, "Synthesis, characterization, and adsorption properties of magnetic Fe3O4@ graphene nanocomposite," Chemical engineering journal, vol. 184, pp. 326-332, 2012. [17] W. Zhang et al., "Fast and considerable adsorption of methylene blue dye onto graphene oxide," Bulletin of environmental contamination and toxicology, vol. 87, no. 1, p. 86, 2011. [18] A. M. Dimiev and S. Eigler, Graphene oxide: fundamentals and applications. John Wiley & Sons, 2016. [19] M. Aziz, F. S. A. Halim, and J. Jaafar, "Preparation and characterization of graphene membrane electrode assembly," Jurnal Teknologi, vol. 69, no. 9, 2014. [20] N. Hidayah et al., "Comparison on graphite, graphene oxide and reduced graphene oxide: Synthesis and characterization," in AIP Conference Proceedings, 2017, vol. 1892, no. 1: AIP Publishing LLC, p. 150002. [21] K. Foo and B. H. Hameed, "An overview of dye removal via activated carbon adsorption process," Desalination and Water Treatment, vol. 19, no. 1-3, pp. 255-274, 2010. [22] A. Dada, A. Olalekan, A. Olatunya, and O. Dada, "Langmuir, Freundlich, Temkin and Dubinin–Radushkevich isotherms studies of equilibrium sorption of Zn2+ unto phosphoric acid modified rice husk," IOSR Journal of Applied Chemistry, vol. 3, no. 1, pp. 38-45, 2012. [23] S. Wang and Y. Peng, "Natural zeolites as effective adsorbents in water and wastewater treatment," Chemical engineering journal, vol. 156, no. 1, pp. 11- 24, 2010. [24] J. Zhang, Q. Zhou, and L. Ou, "Kinetic, isotherm, and thermodynamic studies of the adsorption of methyl orange from aqueous solution by chitosan/alumina composite," Journal of Chemical & Engineering Data, vol. 57, no. 2, pp. 412- 419, 2012. [25] L. Wang, J. Zhang, R. Zhao, C. Li, Y. Li, and C. Zhang, "Adsorption of basic dyes on activated carbon prepared from Polygonum orientale Linn: equilibrium, kinetic and thermodynamic studies," Desalination, vol. 254, no. 1-3, pp. 68-74, 2010. [26] N. C. Corda and M. S. Kini, "A review on adsorption of cationic dyes using activated carbon," in MATEC Web of Conferences, 2018, vol. 144: EDP Sciences, p. 02022. [27] M. Yagub, T. Sen, S. Afroze, and H. Ang, "Dye and its removal from aqueous solution by adsorption: a review. Adv Colloid Interfac 209: 172–184," ed, 2014. [28] V. Gupta, A. Agarwal, M. Singh, and N. Singh, "Removal of Red RB dye from aqueous solution by belpatra bark charcoal (BBC) adsorbent," J. Mater. Environ. Sci, vol. 8, pp. 3654-3665, 2017. [29] E. Santoso, R. Ediati, Y. Kusumawati, H. Bahruji, D. Sulistiono, and D. Prasetyoko, "Review on recent advances of carbon based adsorbent for methylene blue removal from waste water," Materials Today Chemistry, vol. 16, p. 100233, 2020. [30] S. Shahabuddin, N. M. Sarih, M. Afzal Kamboh, H. Rashidi Nodeh, and S. Mohamad, "Synthesis of polyaniline-coated graphene oxide@ SrTiO3 nanocube nanocomposites for enhanced removal of carcinogenic dyes from aqueous solution," Polymers, vol. 8, no. 9, p. 305, 2016. [31] O. M. Bankole, O. E. Oyeneyin, S. E. Olaseni, O. K. Akeremale, and P. Adanigbo, "Kinetics and Thermodynamic Studies for Rhodamine B Dye Removal onto Graphene Oxide Nanosheets in Simulated Wastewater," American Journal of Applied Chemistry, vol. 7, no. 1, pp. 10-24, 2019. [32] A. A. Alghamdi et al., "Adsorption of Azo Dye Methyl Orange from Aqueous Solutions Using Alkali-Activated Polypyrrole-Based Graphene Oxide," Molecules, vol. 24, no. 20, p. 3685, 2019. [33] P. Saha and S. Chowdhury, "Insight into adsorption thermodynamics," Thermodynamics, vol. 16, pp. 349-364, 2011.