《Table 2–Binding energies and relative contents of Cr, C and O in CNF950and Cr-adsorbed CNF950.》

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《"Preparation,characterization and performance of an electrospun carbon nanofiber mat applied in hexavalent chromium removal from aqueous solution"》

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In order to probe the possible mechanism of Cr（VI）adsorption on CNF950，the binding energy shifts of chromium，oxygen and carbon were examined using XPS.The XPS spectra of CNF950and Cr-adsorbed CNF950are shown in Fig.10.Fig.10a gives the wide survey scan of XPS spectra of CNF950with binding energy in the range from 0 to 1200 eV.It was observed that two new distinct peaks appeared at binding energies ranging from 575 to590 eV after the adsorption of Cr（VI），which confirmed the adsorption of Cr（VI）onto the CNF950.High-resolution Cr 2p XPS spectra of the Cr（VI）-loaded CNF950displayed a typical pattern consisting of two broad peaks positioned at 586.7 and 577.1 eV，which were assigned to Cr 2p1/2and Cr 2p3/2，respectively（Fig.10b）.The broad peak of the Cr 2p1/2XPS spectrum could be deconvoluted into 2 peaks with the binding energies of 586.3and 587.7 e V，which were attributed to Cr（III）and Cr（VI），respectively（Cheng et al.，2016）.Similarly，the Cr 2p3/2XPS spectrum could be deconvoluted into 3 peaks at binding energies of 576.4，577.3 and 578.5 eV，which represented Cr（Ш），Cr（Ш）and Cr（VI）species，respectively（Cheng et al.，2016；Sannino et al.，2009）.Furthermore，the relative contents of Cr atoms on the chromium-adsorbed CNF950were also calculated and summarized in Table 2.It was found that the chromium consisted of 52.2%（atomic concentration）Cr（III）and 47.8%Cr（VI）on the surface of CNF950.The XPS analysis results revealed that part of the Cr（VI）had been reduced to Cr（III）after its adsorption onto CNF950.The same phenomenon was also reported by researchers that used other materials to adsorb Cr（VI）（Cheng et al.，2016；Mu et al.，2015） .