All the plots seemed to have the type of adsorption as stepwise isotherm which our experimental data could
cover only the first monolayer and fairly rapid rise to form the second monolayer. The first monolayers
from all of those plots could be fitted by Langmuir adsorption isotherm which is expressed as the following
equation: C / X = C / Xmax + 1 / Xmax b where C is the equilibrium amount of carbon dioxide after adsorption
(mmol), X is the amount of adsorbed carbon dioxide per gram of activated carbon (mmol/g), Xmax is the
maximum adsorption at monolayer coverage (mmol/g) and b is the adsorption equilibrium constant (mmol).
It was found that activated carbon from activation with the weight ratio of zinc chloride and activated carbon
of 2:1 and 3:1 at 600 °C and 800 °C gave the maximum adsorption of carbon dioxide in first monolayer
approximately 4.735 mmol g-1, 5.616 mmol g-1, 4.743 mmol g-1, and 5.774 mmol g-1, respectively. One
example of Langmuir plots is shown in Figure 3.