## 1 Introduction
(2019) evaluated the inhibitory properties of banana peel extract on mild steel in HCl solution [27]. They reported that the inhibition efficiency could be increased by increasing the extract concentration up to 87%. The authors noted from FTIR analyses that the adsorption of the extract occurs due to the presence of hydroxyl and carboxyl groups. [PERSON] et al. (2018) reported a maximum inhibition efficiency of 68% for banana peel extract in preventing iron corrosion in 3% NaCl solution [28]. They noted that, based on FTIR analysis, tannin compounds are present in banana peel extracts that reduce the corrosion rate. [PERSON] et al. (2021) used rice straw extract to inhibit Al corrosion in 2M HCl solution by conducting weight loss and electrochemical experiments [29]. They observed an inhibition efficiency of 96.8% at 25 \({}^{\circ}\)C after 3 h of immersion. The results showed that rice straw extract acted as a mixed-type green corrosion inhibitor. Both physical and chemical adsorptions occurred based on the use of the Langmuir isotherm model. In addition, the activation energy of the corrosion process in the presence of rice straw extract was higher than in its absence. [PERSON] et al. (2022) analyzed the corrosion protection of mild steel in 1.5 M sulfuric acid solution using rice straw extract at different temperatures, immersion times, and concentrations ([PERSON] et al., 2022). The authors optimized the corrosion inhibition process and determined the maximum efficiency of 86.4% at the optimal parameter values for rice straw extract. In addition, the authors noted that the formation of a double electrical layer on the surface of the metal sample by adsorption of extract molecules can inhibit the corrosion process. [PERSON] et al. (2019) used rice straw extract as a green corrosion inhibitor for mild steel samples in NaCl solution (3.5%) ([PERSON] et al., 2019). Based on LC-MS analysis, the authors noted the presence of 4-allysyringol and 4-ethyl guaiicol as the main compounds that act as corrosion inhibitors due to the presence of benzene rings and heteroatoms in their structures. In these compounds, the presence of lone electron pairs and relative positive charges caused both chemical and physical adsorptions. According to the above, the use of green corrosion inhibitors can solve the environmental problem compared with traditional ones. In addition, the increase in corrosion inhibition can be achieved by mixing different reagents. The inhibition results of a mixture of banana peel extract and rice straw extract have not been reported in the literature. For this purpose, in this study, a mixture of banana peel extract and rice straw extract is investigated for preventing corrosion damage of carbon steel in a one molar hydrochloric acid solution. The obtained extracts are used in a corrosive environment separately (100% banana peel and 100% rice straw), as well as in the form of mixtures in various mixing ratios. The inhibition efficiency of green corrosion inhibitors is evaluated by weight loss and electrochemical tests. Based on experimental analyses, the best mixing ratio and optimum inhibition concentration of the mixture of two extracts are determined. Moreover, the effect of immersion time on the inhibition efficiency of green inhibitors is examined. The formation of a protective film on the surface of metal samples in the presence of inhibitors is studied using scanning electron microscopy. Finally, the adsorption mechanism and Gibbs free energy are investigated to determine the type of adsorption of the extracts on the metal surface.