In this X-ray photoelectron spectroscopies B and G illustrate before and after adsorption, respectively. After Cu2+ adsorption, the binding energies of 3 peaks including CO/OCO, CO, and CN/C

OC groups appeared to shift to higher values. Please explain in detailed why this indicated that the electrostatic attraction existed between Cu2+ and COO? What is the working principle of X-ray photoelectron spectroscopy? thank you, your answer means a lot to me.

(G) as