Figure 3

(a) XPS spectra of GO films after different treatments; (b) C1s spectra of unreduced GO films; (c) C1s spectra of GO films reduced twice by SnCl₂ for 10 min; (d) C1s spectra of GO films reduced twice by SnCl₂ for 10 min and treated by acid; (e) Sn₃d spectra of GO films before and after acid treatment.