C/O ratio from high-resolution XPS results and carbon–oxygen content from survey.

Sample	Time (min)	C/O ratio	Carbon (atomic%)	Oxygen (atomic%)
GO-0	0	1.95	67.76	32.24
GO-30	30	1.96	68.4	31.6
GO-60	60	1.89	67.54	32.46
GO-90	90	1.89	66.45	33.55
GO-120	120	1.95	67.88	32.12
GO-240	240	2.01	68.36	31.64