Researchers have used the Langmuir isotherm to predict the adsorption of different heavy metal ions, dyes, and organic pollutants onto AC (Gedam et al. 2019; Wong et al. 2019). The maximum adsorption capacity of an adsorbent can be calculated using the Langmuir isotherm model. This model assumes that the adsorbent has perfect monolayer coverage (Balarak et al. 2015). The isotherms can be studied by plotting the respective graphs based on the equilibrium. The Langmuir model was utilized in order to analyze the equilibrium data pertaining to the adsorption of MR onto AC made from orange peels. Figure 10 shows a linear relationship between the specific adsorption capacity (C_e/q_e) and the equilibrium concentration (C_e), with a coefficient of correlation (R²) of greater than 0.96, confirming the viability of the Langmuir model and evidencing the homogeneous nature of the AC from orange peels. The slope in Figure 10 was found to achieve the value of 1/(q_maxK_L). The value of 1/q_max came from the y-axis intercept. The results also showed that a monolayer of MR molecules formed on the adsorbent's surface. At a temperature of 60 °C, the Langmuir model predicted that the MR would have a maximum monolayer capacity of 111.11 mg/g when adsorbed onto AC from orange peels. Table 2 shows the Langmuir isotherm constants.