It would be easier the help of the mechanisms that the degradation products were presented. It is difficult to evaluate a degradation mechanism without the specific data of the dye molecule and in particular its products formed after the photocatalytic process.
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Thank you for your replies Ravi, Ailton and Prof Grezes. Apologies for not giving proper details. My catalyst system consist of metal nanoparticles immobilized over graphene polymer composite, which i used for degradation of Rhodamine B, and methyl orange in presence of NaBH4. I got some good results but not very much sure of mechanism. I am following the same mechanism as Mr. Ravi has suggested in his answer. It would be very greatful of you if you can help me further in this regard.
Regarding reactivity catalyst is not reactive to NaBH4 (as i have used NaBH4 for catalyst synthesis already) but yes dyes are reactive to NaBH4.