If you are saying " few reported literature," you are supposed to provide references.

In general, the answer is yes if photochemistry is a rate limiting step.

The attached article reported zero order kinetics of RhB

" Is it right to follow zero order kinetics ?"

The attached paper confirms that the zero order is possible

"If it is possible in which circumstances it is true ? "

if photochemistry is a rate limiting step.

Hi,

I agree with Dr. Yurii Geletii,

Zero Order kinetic is possible.

With my best regards,

Dr. Adel OUESLATI

Thank you very much Dr. Geletti Sir.

I agree with Dr. Yurii Geletii, and this suggest that rate-determining step is the interaction of excited dye with oxygen(eqn.2) not dye excitation step(eqn.1).

Dye +hυ ---Dye*

Dye*+ O2---Dye+ +O2-

Thank you Dr. Alshamsi. But still I am little confused with this. Please explain me. I proposed these following equations for zero order kinetics. From scavenger test I found hydroxyl and superoxide radicals are active species. Are these equations correct ?

ZFO + hu → ZFO (e-) + ZFO (h+)

ZFO (e-) + O2 → •O2-

ZFO (e-) + •O2- +2H+ → H2O2

ZFO (e-) + H2O2 → •OH + OH-

Rh B + •OH → de-colorization

Rh B + •O2- → de-colorization

Hence the net reaction is

Rh B + •OH + •O2- → de-colorization

What is pH?

The first reaction is reversible. The net reaction is not balanced. What happens with ZFO(+)?

Irradiation of ZFO:

ZFO+ hν↔ -eCB+ +hBV

-eCB + O2 → •O2-

Production of the •OH radicals:

H2O ↔H++ OH-

(OH-)ads+ +hBV→ •OH

-eCB +•O2- +2H+ → H2O2

-eCB + H2O2 → •OH + OH-

Oxidation of dye via attacks by•OH and ˙O2− radicals:

Dye + •OH→ degradationproducts(CO2 + H2O + inorganic ions)

Dye+˙O2−→ degradationproducts(CO2 + H2O + inorganic ions)

Through oxidation of dye via •OH and ˙O2− ,R. species may formed (abstraction of H+ from dye produce R.) as intermediate and trnsform into peroxy radicals which then oxidized to CO2 H2O and inorganic ions:

R. + O2→ROO.

Oxidation of peroxyl radicals to CO2

ROO. + O2→CO2 + H2O +….

Thanks a lot Dr. Hassan Alshamsi.

Dear D. Kandi

As to your question ’Can the degradation of Rhodamine B follows zero order kinetics?’

Unfortunately, the very format of this page doesn’t allow to present equations and plots. So, send me your conventional e-mail, and you will be replied via e-mail.

My requisite you can see below.

Greetings, V. Dimitrov

Vasili DIMITROV, Ph.& Ch.D.

Emeritus Professor of Chemical Physics.

25 Fisherville Rd, #703, North York,

ON, M2R 3B7, Canada.

Tel. home (1)-416-546-8442, cell (1)-647-632-6355.

E-mail: [email protected]

Skype vasilidim

Thank a lot prof Vasili Ivanovich Dimitrov for your response.