What is a kinetic model? This is a sequence of elementary reaction, which quantitatively describes the kinetics of overall process. None of your reaction is elementary, Cr(VI) -> Cr(III) is three electron process. What is the source of electrons?

Dear Giang Luong ,

I discussed such reactions in my paper:

Djellabi, R., Ghorab, M. F., & Sehili, T. (2017). Simultaneous removal of methylene blue and hexavalent chromium from water using TiO2/Fe(III)/H2O2/sunlight. CLEAN–Soil, Air, Water, 45(6), 1500379.

Best regards

RD

Yurii V Geletii from UV light on TiO2 photocatalyst

Ridha Djellabi my data is not follow the 1st order as in your research so I try to find the model for my reaction

Is this a source of electrons? "from UV light on TiO2 photocatalyst" , If so, I give up to discuss further.

Giang Luong, What you are presenting is a kind of stoichiometric scheme and additionally wrong, because to obtain Cr (III) from a hexavalent chromium ion, three electrons are needed. The left side is also not equal to the right side. On the other hand, if you really think about kinetics, think about determining the ion concentration versus time for various initial ion concentrations, catalyst concentrations, and UV intensities.

Ridha Djellabi, Since you've linked your work, here's a quick comment. The most important thing is, of course, the possibility of complete removal of pollutants and the interpretation of the observed phenomena. The mathematical description of the kinetic data is of secondary importance. However, if you choose to do so, do not mislead the reader. There is no evidence in this paper that the processes under investigation are of the first-order. The mere compliance of the empirical exponential function with separate kinetic curves is not enough, and the results presented in Figs. 2 and 4 and in Table 1 even contradict it.

Mirosław Grzesik I totally agree with you, in most of these papers concerning adsorption be it dyes or ions , No one has explicitly explained the physical process, what I see is just empirical mathematical fitting mostly of Pseudo-second-order...this to me will fit most experiments and a few Pseudo-first order...

Dennis Gitau Njuguna, You are absolutely correct in having doubts about the use of PSO to describe kinetic data. Unfortunately, hundreds of scientists have no such doubts. PSO is, in fact, an empirical hyperbolic function, very flexible to different data. Data approximation with this function has a scientific value similar to storing data in a database, that is, neither. But various ignorant reviewers may ask you for such a description. And then what?

Thank you guys for taking the time to discuss this with me. I have already found the kinetics.