You can see the following links:

1. Article Aqueous chemical route synthesis and the effect of calcinati...

2. Article Effect of Calcination on Properties of ZnO Nanoparticles

Dear researcher

I do not know exactly what method you used, but usually the methods used by plants to synthesize zinc oxide nanoparticles do not require calcination.

not require calcination

Dear Hanan Ahmad

Yes, you have to do the calcination step in ZnO NPs synthesis from a plant extract. The following references support this trend, and anyone who says otherwise should provide the supportive references.

In [1] "The obtained powders were subjected to an additional heat treatment in air at 500 °C for 1 h."

In [2] "ZnO nanoparticles have been prepared using the aqueous extract of broccoli, followed by calcination process at 450°C for 2 h under normal air condition given ZnO nanoparticles."

In [3] as cited by [4] ""Karnan and Selvakumar26 studied the mechanism of formation of ZnO NPs using extracts of the extract peel of Nephelium lappaceum L. They found that polyphenolic ellagic acid in Nephelium lappaceum L. containing aromatic hydroxyl groups could form a stable Zinc-ellagate complex with Zn2+ at pH 5–7, from which ZnO NPs could be prepared by calcination at 450℃."

In [4] "As can be observed from a survey of the literature presented here, the morphology of ZnO NPs is dependent on plant species, plant extract concentration, precursor concentration, reaction time, pH value, and calcination temperature."

In [5] as cited by [4] "Mayedwa et al.27 also established that aromatic hydroxyl groups could complex stably with metal ions, from which metal oxide NPs could be prepared by calcination."

Best regards

[1]Article ZnO nanoparticles via Moringa oleifera green synthesis: Phys...

[2]Article Green synthesis of ZnO nanoparticles using aqueous Brassica ...

[3]https://www.sciencedirect.com/science/article/abs/pii/S0022286016307001?via%3Dihub

[4]Article A review of the green synthesis of ZnO nanoparticles using p...

[5]Article Green Synthesis of Nickel Oxide, Palladium and Palladium Oxi...

What synthesis method have you employed?

I think si better 450 degrades for 2 hours under normal condition, is possible in oven or furnace. Is better if You use quartz material or maybe Pyrex.