Surface or pure adsorption controlled process is a phenomenon occurring due to the migration of molecules or particles from the bulk aqueous phase to the interface. On the contrary, in a diffusion controlled process, the molecules are transported from bulk phase to the subsurface (just below the interface). The molecules then move from subsurface to interface.  

Therefore, a surface controlled process is characterized by the rate of molecule transport from the bulk to the interface, whereas a diffusion controlled process is explained by the rate of molecules diffuse initially into the subsurface and then finally onto the interface.

For better understanding, please refer to the following paper.

1. Nilanjan Pal, Neha Saxena, Ajay Mandal, Equilibrium and dynamic adsorption of gemini surfactants with different spacer lengths at oil/aqueous interfaces, Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2017, ISSN 0927-7757, http://dx.doi.org/10.1016/j.colsurfa.2017.08.020.

Article Dynamic adsorption of a gemini surfactant at the air/water interface

Article Equilibrium and dynamic adsorption of gemini surfactants wit...

Hi there,

Firstly, which scan rate range you studied. Ok, follow attached file to check more details about your question.

Regards,

Want to fit the kinetic model to what kind of kinetic data? And what's the kinetic model for you? For me, a kinetic model is a kinetic equation (in form of monomial, hyperbolic function ect.), and I usually fit it to the data: concentration / conversion vs. time for different temperatures and initial concentrations (integral method), or reaction / process rate as a function of concentration for different temperatures and concentration ratios (differential method). Is that so in your case?

It is also worth remembering that the rate of chemical reaction and the different transport phenomena depend, to a various extent, on the temperature, flow rate (tubular type reactor), number of stirrer rotations (tank type reactor), the size of particle, the average pore size of the particle (solid particles) etc. Therefore, under certain conditions, the same reaction can take place in the kinetic region and in others in the diffusion region. There are also different types of diffusion.

Regards,

Thank you all

In chemical processes usually one can resume the entire phenomenon to be governed by different types of reaction mechanisms  (e.g. diffusion,  adsorption, convection, etc). Diffusion controlled mechanisms are normally observed in systems in which the kinetics is fast. A good approach is to evaluate different mechanisms under the same normalised conditions so the governing mechanism can be evaluated. Please have a look at the attached article.  There you can find examples of different mechanisms for solid-state reactions. 

Kind regards 

Article The applicability of isoconversional models in estimating th...

Of course, the most important is the relation of reaction rate to the rate of inter and intraparticle mass transfer.

Regards,

Thank you for this discussion , I have learned quite a lot from the literature suggested.

when driving force is dissipated in diffusion, the interface is said to move at a rate controlled by diffusion. Interface–controlled growth occurs when most of the available free energy is dissipated in the process of transferring atoms across the interface