| Summary: | We show that the degree of oxidation of graphene oxide (GO) can be obtained by using a combination of state-of-the-art ab initio computational modeling and X-ray photoemission spectroscopy (XPS). We show that the shift of the XPS C1s peak relative to pristine graphene, <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mo>Δ</mo><msub><mi>E</mi><mrow><mi>C</mi><mn>1</mn><mi mathvariant="normal">s</mi></mrow></msub></mrow></semantics></math></inline-formula>, can be described with high accuracy by <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mo>Δ</mo><msub><mi>E</mi><mrow><mi>C</mi><mn>1</mn><mi mathvariant="normal">s</mi></mrow></msub><mo>=</mo><mi>A</mi><msup><mrow><mo>(</mo><msub><mi>c</mi><mi>O</mi></msub><mo>−</mo><msub><mi>c</mi><mi>l</mi></msub><mo>)</mo></mrow><mn>2</mn></msup><mo>+</mo><msub><mi>E</mi><mn>0</mn></msub></mrow></semantics></math></inline-formula>, where <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><msub><mi>c</mi><mn>0</mn></msub></semantics></math></inline-formula> is the oxygen concentration, <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>A</mi><mo>=</mo><mn>52.3</mn></mrow></semantics></math></inline-formula> eV, <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msub><mi>c</mi><mi>l</mi></msub><mo>=</mo><mn>0.122</mn></mrow></semantics></math></inline-formula>, and <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msub><mi>E</mi><mn>0</mn></msub><mo>=</mo><mn>1.22</mn></mrow></semantics></math></inline-formula> eV. Our results demonstrate a precise determination of the oxygen content of GO samples.
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