Dear Tanvir Ahamed, the C/O ratio or the oxidation degree of the as-synthesized GO nanosheets highly depends on the drying temperature and the lower temperatures ensure higher oxidation degrees for the final product. Accordingly, since freeze-dried GO has a high oxidation degree, it undergoes thermal reduction even by small heat produced by friction in grinding. As you might know, the friction between the mortar and the pastel locally increases the temperature and triggers the thermal reduction process in which GO loses its oxygen content in the form of CO and CO2, and the explosion occurs. In such cases, it is better to use "cold grinding" or "cryogenic grinding" to prevent thermal reduction. So, I suggest you cool down the mortar and the pastel in advance and do the grinding in a cooling bath like an ice bath or dry ice. Despite all this, If freeze-drying is not indispensable in your research, try to dry GO using a vacuum desiccator at room temperature which not only preserves GO oxidation degree but also yields a more stable product that can be ground easily.

Best,

Dear Tanvir Ahamed ,

The explosion is mainly due to the high oxygen content present in the graphene oxide. Any friction produced by the pestle and mortar will induce heat which could lead to an explosion of which size depends on the amount of GO present.

Dear Tanvir Ahamed

During grinding (using mortar and pastel) of GO, it's mechanical energy is converted into sufficient heat and transferred to GO. After getting this heat (thermal), GO was exfoliated and slightly reduced. This explosion (burst) occurs by getting heat due to grinding and releasing the CO2/CO gases (also other gases).

I suggest you that

1. First wash your sample with DI water several times to complete removal of H2SO4, KMnO4/ Na2NO3 which has been used in the Hummers method for graphite oxide poreparation.

2. Do not grind hard as well as for long time.