I have done adsorption studies of brilliant blue dye using graphene as adsorbent for different temperatures. for 20 and 30 C, the R2 value of freundlich fitted well whereas for 40 C, R2 value of langmuir best fitted. What can be the reason behind this phenomena?
Bogeshwaran Karunanithi, Presumably, for lower temperatures, the initial concentration of the dye you used is too low to come close to saturation. For T = 293 K and 303 K, additional equilibrium tests must be performed for larger Co. Apart from R2 value, also determine the value of ARE.
I suggest you to repeat the experiment under the same conditions. Replication lets you see patterns and trends in your results. This is affirmative for your work, making it stronger and better able to support your claims. This helps maintain the integrity of data.
First of all I suggest to repeat each experiments thrice to confirm the data trend. Moreover the initial concentration of dye solutions needs to be same for all different temperatures. In addition to R2 values, also go for other error analysis like chi square test, etc. That may help you to conclude.