You can find CIF files for graphene oxide on various online databases such as the Cambridge Crystallographic Data Centre (CCDC), the American Mineralogist Crystal Structure Database (AMCSD), and the Inorganic Crystal Structure Database (ICSD).
Here's a step-by-step guide to finding a CIF file for graphene oxide on the CCDC:
Go to the CCDC website at https://www.ccdc.cam.ac.uk/
Click on "Search Structures" in the top menu.
In the "Search Structures" page, select "Quick Search" and type "graphene oxide" in the search box.
Click on "Search" to view the results.
Select a result that matches the graphene oxide structure you are looking for.
Click on "View & Download" to view the details of the structure.
Under "Files Available", select "CIF" to download the CIF file for the structure.
Note that the CIF file for graphene oxide may be available on other databases as well, so you may want to check those as well.