Dear Navneet Singh ,

Generally in adsorption papers many authors used the variation in standard enthalpy DH° to determine the nature of adsorption. The chimisorption energy is high 30-70 kJ/mol for molecules and 100-400 kJ/mol for atomes. physisorption energy is low generally less than 40 kJ/mol but the barrier is not very clear because some authors considered that adsorption processes including hydrogen bends (less than 40 kJ/mol) are chimisorption processes.

Thanks Salim, 

You are right..Actually.. have taken 20 KJ/mol as limit to decide for sorption type in my few papers. Can we use kinetics data for the same purpose?

Dear Navneet Singh,

yes we can use kietics data for calculating the enrgy of adsorption "Ea" with

k=k0.Exp(-Ea/RT)   k and K0 are kinetics constants obtained from PFO or PSO model at two differents temperatures.

Good luck

That's fine! Ea comes later. What about PFO/PSO model itself ? What information can be inferred from these models to determine chemical  interaction at adsorbent-adsorbate interface. If you find pls communicate.

many authors like Ho and McKay (2001) suggests taht if the correlation coefficient R2 of pseudo second order model PSO is high and approach 1, this is an indication of chemisorption mechanism.

but personally in my PhD work i found a high correlation coefficient R2 with PSO, despite the standard enthalpy change is 20kJ/mol.

Ho, Y. S., Ng, J. C. Y., & McKay, G. (2001). Removal of lead (II) from effluents by sorption on peat using second-order kinetics. Separation Science and Technology, 36(2), 241-261.

So what is your say on this contradiction? Quite confusing...

I believe that we need to develop a theoretical relation between adsorption kinetic and thermodynamic parameters.

Dear Dr. Navneet

you can refer to Dr. Saied Azizian papers who is expert in adsorption process

Thanks Mansor for the suggestion.

do you have working on adsorption process?

Dear Mansor,

Apart from nonferrous extractive metallurgy, I have been working on adsorptive remediation of  ground water and industrial effluents contaminated with heavy metals. Please check contribution tab in my researchgate profile.

regards,

Dear friend

 During last 100 years there is one criteria for distinguish chemical and physical adsorptions. physical adsorption doesn't requires activation energy and  for chemisorption E is required

Best regards

You might look at the related question

What is physical sorption (physisorption) and what does it "include"?

https://www.researchgate.net/post/What_is_physical_sorption_physisorption_and_what_does_it_include

• i think its better to conduct isotherm studies and kinetic studies .from it you can confirm it ,

Temperature programmed desorption helps on distinguish between physical adsorption and chemisorption. In this context, a physisorbed molecule would desorb as it is while a chemisorbed intermediate species will react and desorb as a product.

Thanks  to all for the answers. Analysing the species desorbed as function of temperature is good idea, will do some work on that line.

I will support the idea of Laura Esterfania Briand i.e. TPD(Temperature programmed desorption) help to distinguish between physical adsorption and chemical adsorption. Also we can roughly calculate the number of that sites.

Thanks Muhammad Bilal,

While working on Ni(II) adsorption (mentioned below) by sea nodule residue, I have observed decreased adsorption when temperature raised above the ambient. It was attributed to the physisorption of Ni(II) onto adsorbent, also supported by activation energy.

Application of manganese nodules leaching residue for adsorption of nickel(II) ions from aqueous solution, International Journal of Environmental Science and Technology , http://dx.doi.org/10.1007/s13762-013-0460-4

Please be aware that adsorption is always between two partners. Temperature may also change surface properties of the nodules, which maybe part of the story.

Your should consider spectroscopy. As a rule, physical adsorption has negligible effect on the absorption spectrum  (such as low-scale shift) whereas chemical adsorption affects the shape of the absorption band.

Irina! Please suggest some literature referring spectroscopic method for differentiating the type of adsorption.

Please, choose proper citations from the paper:

Electronic spectra and photochemistry of adsorbed organic molecules. VI. Binding effects of silica as a mechanistic probe in systems of photochemical interest

Lawrence D. Weis, Ted R. Evans, and Peter A. Leermakers

Journal of the American Chemical Society 1968,  90 (22), 6109-6118

As well as

Robin M., Trueblood K.N. The ultraviolet absorption spectra of aromatic compounds adsorbed on silica acid // J. Am. Chem. Soc. 1957. V. 79, N 5. P. 5138 – 5139.

Berlman I.B. On an empirical correlation between nuclear conformation and certain fluorescence and absorption characteristics of aromatic compounds  J. Phys. Chem. - 1970. V. 74, №16. P. 3085-3093.

Thanks Irina for suggesting the papers. 

Reversibility. That is the easiest.

All the amount of gas you can desorb without changing the temperature, occurred due to physisorption, the rest that remained in the sample was chemisorption.

Dear Navneet

Identifying adsorbate-adsorbent interactions is most difficult issue in sorption field. Depend on the type of adsorbent and adsorbate complex mechanisms will influence the sorbate-sorbent interactions. Although above suggestions are good but it is better to use instrumental techniques to identify accurate mechanism.

Please refer the following publications for more information.

Article Influence of Adsorbate Interaction on Transport in Confined Spaces

Article Highlighting inconsistencies regarding metal biosorption

Thanks, Dr. Harikishore for the comments.

The sample technique to determine the type of interactions, just heat the system, if amount of adsorption decreases it meas it is physical adsorption. However,  effect of ionic strength, pH,  urea, etc. will provide the true picture. 

In my previous paper, I used XPS to differentiate electrostatic attraction and pi–pi

stacking in adsorption, and their relative contributions were also calculated according to XPS. In brief, chemical adsorption is characterized by large chemical shifts in XPS spectra of the elements at the active sites, while physisorption shows constant binding energies.

Article Wrapping carbon nanotubes with poly (sodium 4-styrenesulfona...

chemosorption you can know it from the delta H of R-D isotherm model and from the temkin adsorption isotherm also from activation energy value more than 30 kj/mol and delta H more than 30kj/mol

lower that will be physical sorption process

[email protected], for contact

Please refer the following publications for more information.

Article Influence of Adsorbate Interaction on Transport in Confined Spaces

Article Highlighting inconsistencies regarding metal biosorption

Robin M., Trueblood K.N. The ultraviolet absorption spectra of aromatic compounds adsorbed on silica acid // J. Am. Chem. Soc. 1957. V. 79, N 5. P. 5138 – 5139.

• DOI: 10.1016/j.cej.2014.06.020

Mahmoud Fathy Moubark

Dear Mahmoud,

do you have a reference for your answer?

your answer will be highly appreciated

Noor Aljammal you may wish to consider this reference,

Worch, E. (2012). Adsorption Technology in Water Treatment: Fundamentals, Processes, and Modeling. Walter de Gruyter GmbH & Co. KG, Berlin/Boston, Germany, 345 pp.

Rejoice Solomon Ibrahim Thank you, dear, so much

In the case of the adsorption mechanism, it is much better to rely on physicochemical studies on the adsorbent surface than on kinetic or equilibrium data. Relying on activation energy will not help much, because it makes sense for an elementary process, and adsorption is not such a process.