Characterizing the Chemical Structure of Ti(3)C(2)T(x) MXene by Angle-Resolved XPS Combined with Argon Ion Etching

Angle-resolved XPS combined with argon ion etching was used to characterize the surface functional groups and the chemical structure of Ti(3)C(2)T(x) MXene. Survey scanning obtained on the sample surface showed that the sample mainly contains C, O, Ti and F elements, and a little Al element. Analyzing the angle-resolved narrow scanning of these elements indicated that a layer of C and O atoms was adsorbed on the top surface of the sample, and there were many O or F related Ti bonds except Ti–C bond. XPS results obtained after argon ion etching indicated staggered distribution between C–Ti–C bond and O–Ti–C, F–Ti bond. It is confirmed that Ti atoms and C atoms were at the center layer of Ti(3)C(2)T(x) MXene, while O atoms and F atoms were located at both the upper and lower surface of Ti(3)C(2) layer acting as surface functional groups. The surface functional groups on the Ti(3)C(2) layer were determined to include O(2−), OH(−), F(−) and O(−)–F(−), among which F atoms could also desorb from Ti(3)C(2)T(x) MXene easily. The schematic atomic structure of Ti(3)C(2)T(x) MXene was derived from the analysis of XPS results, being consistent with theoretical chemical structure and other experimental reports. The results showed that angle-resolved XPS combing with argon ion etching is a good way to analysis 2D thin layer materials.