We haven't used ZnO as photocatalyst in the presence of H2O2. As you know, commercial H2O2 is only 30% and since you are probably using a low concentration of the dye I suggest that you use a small amount of H2O2 as a test(about 5 mL) and check the degradation process.You can then increase the amount of H2O2 if degradation of the dye is not high.

thanks Mohammad Kooti  sir

It depends on the concentration of substrate and amount of catalyst and volume. I will suggest to perform a series of experiments stating from the lower concentration of 10 uL to 100 ul and optimize the rate of degradation required as the rate is expected to increase with the increase in concentartion  

You may use about 1 mL of H2O2 in the beginning and if the rats of degradation  are lower then you may increase its amount (Concentration) accordingly to achieve optimum conditions. It all depends on the nature and concentration of substrate.

The experiments were run with varying catalyst dosage from mg to

 mg/L in optimum mg/L solution of MO for different time interval under

sunlight and uv light. The percent removal of the dye reached their

maximum at mg/L of samples respectively and then decreased.