Graphene oxide was synthesized by Hummers method Graphite flakes (2 g) and NaNO₃ (2 g) were mixed in 50 mL of H₂SO₄ (98%) in a 1000 mL volumetric flask kept under at ice bath (0˚C - 5˚C) with continuous stirring. The mixture was stirred for 2 hrs at this temperature and potassium permanganate (6 g) was added to the suspension very slowly. The rate of addition was carefully controlled to keep the reaction temperature lower than 15˚C. The ice bath was then removed, and the mixture was stirred at 35˚C until it became pasty brownish and kept under stirring for one days. It is then diluted with slow addition of 100 ml water. The reaction temperature was rapidly increased to 98˚C with effervescence, and the color changed to brown color, Further this solution was diluted by adding additional 200 ml of water stirred continuously for purification. The solution is finally treated with 10 ml H₂O₂ to terminate the reaction by appearance of yellow color, the mixture was washed by rinsing and centrifugation with 10% HCl and then deionized (DI) water several times After filtration and drying under vacuum at room temperature (Scheme (1-1)) [11] [12] [13] .

Scheme (1-1). Chemical equation of preparation of GO.

The functionalize GO, (0.5 g) was placed in a (250 mL) dried beaker with (100 mL) DMF and amino ethanol 6.17 mL, 10 mmole) sonicated for 1 h to form homogeneous solution, then added DCC (2.06 g, 10 mmole), DMAP (1.22 g, 10 mmole) into mixture with stir 24 h at room temperature, after the reaction finish, the product was filter, then black powder was dried [14] the preparation process of (GON) is shown in Scheme (2-2).

Scheme (2-2). Chemical equation of preparation (GON).

The functionalize GO, (0.5 g) was placed in a (250 mL) dried beaker with (100 mL) DMF and amino ethanol (0.86 mL, 10 mmole) sonicated for 1 h to form homogeneous solution, then added DCC (2.06 g, 10 mmole), DMAP (1.22 g, 10 mmole) into mixture with stir 24 h at room temperature, after the reaction finish, the product was filter, then black powder was dried [14] . The preparation process of (GOS) is shown in Scheme (2-3).

Scheme (2-3). Chemical equation of preparation (GOS).

The electrochemical measurements were performed using a potentiostat/galvanostat (ACM) connected to a computer. A three electrode cell assembly, consisting of a C-steel rod embedded in araldite as the working electrode (WE), and a saturated calomel electrode as the reference electrode (RE), aplatinum sheet as the counter electrode (CE), was used for the electrochemical measurements. The temperature of the electrolyte was maintained at the required temperature using a water bath. Before immersion in the test solutions, the WE was polished with a polishing machine using emery paper from 600 to 1200 grade until a mirror image was obtained. Then, the WE was washed with distilled water thenimmersed in acetone for 1Minute in an ultrasonic cleaner. The WE electrode was prepared directly before electrochemical measurements then immersed in the test solution at open circuit potential for one hour until a steady state potential was obtained polarization measurements were performed. All experiments were performed in aerated solutions. From the polarization data, were calculated like the degree of surface coverage (θ), the percent tage inhibition efficiency (% IE), corrosion rate and charge transfer resistance [15] .

Typical potentiodynamic polarization curves for the C-steel in 1M HCl in the presence and absence of different concentrations of GO, GON, GOS are shown in (Figures 5-16). The respective Tafel parameters, inhibition efficiency (% IE), I_corr corrosion current, corrosion rate and charge transfer resistance are provided in Tables 1-3. It is clear that the shapes of the Tafel plots for the inhibited electrodes are different from those of uninhibited electrodes. The presence of the inhibitor decreases the current density but does not change other aspects of the behavior.

It is evident from Tables 1-3 from E_corr at constant temperature compared with E_corr to blank at 298 K for graphene oxide (GO) the E_corr decrease at all concentration compared with E_corr to blank that value (−474 mv) but this decreasing less to (89 mv) so inhibitor behavior it mix inhibitor, as observed from previous studies [22] [23] [24] , if the difference E_corr between blank and inhibitor (89 mv) decreasing less the inhibitor is mix, also E_corr other organic inhibitors GON, GOSdecreasing less (89 mv) compared with E_corr blank that mean It behavesmix inhibitor at all concentration (1 - 6 ppm) and temperature (298 - 328 K). In this study used very small concentration organic inhibitors it gives high efficiency inhibitor, show graphene oxide have less efficiency inhibitor (20.13%) at (1 ppm) and (80.92%) at (6 ppm) in spite of containing carboxylic group in graphene oxide layer GON, GOS have efficiency inhibitor (67.68%, 64.39%), respectively at (1 ppm) and (96.96%, 95.79%) respectively at (6 ppm) at different temperature.

The R_ct values of the inhibited are increase as the concentration of the inhibitors increases on the other hand increase in efficiency inhibitors due to productive carbon steel surface to resist polarization, and the anodic reaction the dissolution of Iron in carbon steel alloy to reduce in present inhibitors the signification that increase of Tafel (β_a) [25] .

The study of effect of temperature on the corrosion rate to the organic inhibtors on carbon steel alloylwere immersed in 1 M hydrochloric acid with different concentration (1 - 6 ppm) of inhibitor at temperature ranging from 298 K, 308 K, 318 K, and 328 K, the activation energy value was calculated from Arrhenius equation [26]

ln CR = ln A − − Ea RT (3)

where: CR = corrosion rate (mpy), Ea = activation energy (KJ/mol);

A = frequency factor, R= molar gas constant (8.3143 J・K⁻¹・mol⁻¹);

T = temperature (K).

Figure 17, Figure 18, Figure 19 show good relationship between (ln CR) vs (1/T K⁻¹) for without and with inhibitors organic compound in 1M HCl solution, straight lines were obtained with slope of (-Ea/R), the activation energy was calculated from slope of Arrhenius plot. the activation energy as the concentration of inhibitor increase which indicates physical adsorption [27] and it due to be corrosion reaction in which charge transfer has been blocked by the adsorption of inhibitor molecular on the carbon steel surface. The activation energy (Ea) value in the presence of corrosion inhibitors is higher than in absence of inhibitor also Ea increase with increasing concentration in inhibitors.

Enthalpy (∆H) and entropy (∆S) of activation have been calculated from the following equation

CR = RT Nh L n ( Δ S ∗ R ) L n ( − Δ H ∗ RT ) (4)

CR = corrosion rate (mpy), Δ H = Enthalpy (KJ/mol), Δ S = entropy (J/mol, K), R= molar gas constant (8.3143 J・K⁻¹・mol⁻¹), T= temperature (K), N = Avogadro number (6.022 × 10²³ mol⁻¹); h = plank, constant (6.62 × 10⁻³⁴ J・s).

Figure 20, Figure 21, Figure 22 are the plots of (ln CR/T) vs (1/T K⁻¹) for carbon steel in with and without inhibitors organic compound in 1N HCl solution. Curves showed straight lines with slope ( Δ H ∗ /R) and intercept ( Δ S ∗ /R). The positive value of Δ H ∗ reflect that the process of desorption of the inhibitors on the surface is an endothermic process (chemical adsorption) and it has been clearly observed that the value of Δ H ∗ increasing as the concentration inhibitor increase. The entropy of activation in mentioned table clear that these values increased positively in the presence of inhibitor than in its absence. The increase of reveals that an increase in disordering takes place from reactant to the activated complex [28] (Tables 4-6).

The adsorption isotherms provide basic information about the interaction between the inhibitor and the Carbon steel surface. In this study fit with Langmuir isotherm and the Langmuir isotherm best model to gives of value of (R²) correlation coefficient equal one or approaching one, through R² to found Langmuir isotherm was calculated using the equation below [29]

θ 1 − θ = K . C (5)

where surface coverage (θ) for various inhibitor concentrations, K_ads the adsorptive equilibrium constant, C is the concentration of the inhibitor, the isotherms at different temperatures for different concentration of organic compound in 1M HCl, show date in Tables 7-9 and Figures 23-25.

The equilibrium constant for the adsorption process was related to the standardfree energy of adsorption by the expression [30] .

Δ G ∘ a d s = − RT L n ( 55.5 K a d s ) (6)

where R is the gas constant, T is the experiment absolute temperature, and theconstant value of 55.5 is the concentration of water in a solution in mol・L⁻¹. The following equation can be used to calculate a thermodynamic functions [31]

Δ G ∘ a d s T = Δ H ∘ a d s T + K (7)

The variation of Δ G ∘ a d s /T with 1/T gives a straight line with a slope that equals Δ H ∘ a d s (Figures 26-28). The Δ G ∘ a d s /T decreases with 1/T in a linear manner. The calculated values are shown in Tables 10-12. The adsorption heat could be approximately regarded as the standard adsorption heat under experimental conditions. The negative sign of Δ H ∘ a d s in 1M HCl solution indicates that the adsorption of inhibitormolecule is an exothermic process [32] . Then the standard adsorption entropy Δ S ∘ a d s was obtained using the thermodynamic basic equation:

Δ G a d s = Δ H a d s − Δ S a d s (8)