Your peak is large and has a lower wave-length that you are waiting. In your case, The wave-length depends on the conjugation of alkene bonds. So, if your product is not presenting the similar structure, particularly if you have less conjugating bonds in your product than is in your graphene reference, the peak that you observe shifts to a lower wave-length. I don't know which process you used to obtain graphene, but if you employed a thermic treatment of a precursor, I think the conversion is not finished at the end of the process.

Thank u very much sir, you are right i did thermal treatment but i used an organic compound as the reducing agent .what is the good instrumental tool to confirm the formation and quality of the product ( graphene) except XPS.

I think in you case, an elemental analysis (C,N,O,H) of your product is enough to bring out impurity, and you can adjust process according to elemental impurity. Finaly, UV is an interesting way to caracterise graphene because your aim is to reach a wave-lenght of 270nm to obtain a pure product (Be careful of other species that absorb at the same wave lengh C=O conjugated....).

Thank you sir ,anyway now my products uv absorption is better than previous one, somebody reported at 260 - 270 nm for reduced graphene but you said good product must absorbs at 270 nm,, so the remaining products may be have high oxygen content right , ok sir i will try to get absorption at 270nm