I am using CTAB as a surfactant onto a ZnCl2 treated biochar made from oil tea shells. Nitrates in aqueous solution are being adsorbed onto this CTAB-biosorbent. with R^2 = 0.999 pseudo-2nd order fitting suggests chemisorption but when isotherm models are applied Dubinin-Raduskovich (DR) models parameter (E=1/√2β) gives a value of 2.67 kJ/mol and suggests physical adsorption. How this is justified?
Regards
For further validation I think it will be better if you can calculate thier error analysis using thier respective qexp and qcal to check which one is more closer to the qexp. My view
Hey,
an isotherm or a kinetic analysis is not the solution for your question. If you want to understand your mechanism you have to look to the surface chemistry.
Your systems seem to be charged posititv on the surface?
For the adsorption you got different step which controls the kinetic Diffusion and a chemical kinetic. But you just measure the slowest reaction step, which is often the diffuison. Exspecially in a case like a highly porous system you got intrapraticle diffuision, which should be the rate limiting step and only this controls your speed of adsorption.
With the langmuir isotherm you got an isotherm which is derived by the law of mass action and depending on the equilibrium constant you can calculate the thermodynamik data.
Article On the use of the Dubinin-Radushkevich equation to distingui...
The abstract tell you something more about it.
Dear Dr. Mehmood;
DR is the isotherm model. In other words, it deals with the adsorption that has come to equilibrium. Therefore, you work with Ce (Equilibrium concentration). PSO is the kinetic model. You use the qt (not qe) values you get from the Ct concentration, which changes against time. Also, I could not find what DR meant by E in any publication. dG cannot be positive. If dH is physical, it is negative (as much as the state change energy). However, there is no negative value in the DR model. If Langmuire fits (because it's monolayer), we can say it's chemical.
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