To quote the article:

"The reactions break the carbon dioxide into oxygen gas, as well as carbonaceous sheets which ‘float’ to the surface of the container due to differences in density and can therefore be easily extracted."

and

"According to the research team, the process showed 92% efficiency in converting a tonne of CO2, using just 230kWh of energy."

Exactly. Carbonaceous.

Which is Carbon, because that's what left when you take away the O2 from CO2.

No it’s still oxidized carbon (graphene oxide) just less oxidized than CO2.

Otherwise, if it was unoxidized you could just burn that carbon again and regain 10x the energy you spent!