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Development of sample preparation technique to characterize chemical structure of humin by synchrotron‐radiation–based X‐ray photoelectron spectroscopy
Author(s) -
Pham Duyen Minh,
Miyata Yasushi,
Awata Takanori,
Nakatake Masashi,
Zhang Chung Fang,
Kanda Keiji,
Ogawa Satoshi,
Ohta Shozo,
Yagi Shinya,
Katayama Arata
Publication year - 2019
Publication title -
surface and interface analysis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.52
H-Index - 90
eISSN - 1096-9918
pISSN - 0142-2421
DOI - 10.1002/sia.6574
Subject(s) - x ray photoelectron spectroscopy , analytical chemistry (journal) , chemistry , binding energy , synchrotron radiation , spectral line , carbon fibers , copper , materials science , nuclear magnetic resonance , atomic physics , composite number , physics , organic chemistry , chromatography , quantum mechanics , astronomy , composite material
Carbon‐binding state of humin (HM, a non‐conductive insoluble organo‐mineral humic substance) was successfully characterized for the first time by synchrotron‐radiation–based X‐ray photoelectron spectroscopy (XPS). Four sample preparation techniques—HM on double‐sided carbon tape, indium sheet, copper mesh, and in pellet formed from the mixture of HM and copper powder (Cu) at different mixing ratios (1:1, 1:2, and 1:6 v /v)—were compared. The results show that HM samples prepared using the first three methods had significant charge buildup, which made the interpretation of the XPS spectra impossible because of the shifts in the binding energy of C 1s XPS spectra. Pellets of HM:Cu mixture enhanced the electrical conductivity and reduced charge buildup on the sample surface. Pellets prepared with HM:Cu ratio of 1:1 ( v /v) provided the minimum charge buildup and high sensitivity with difference in C 1s spectra regardless of the observing position. The C 1s spectra, estimated by the subtraction of the carbon contamination in Cu, showed the resolution of CC (284.0 eV), CC/CH (285.1 eV), CO (286.3 eV), CO (287.3 eV), and OCO (288.3 eV) and three additional peaks of CF (289.3 eV), CF 2 (290.2 eV), and CF 3 (291.4 eV). Soft X‐ray absorption spectroscopic (XAS) analysis further proved the existence of fluoride (F 1s) in HM structure. The detection of fluorinated carbon in HM showed a great advancement of XPS compared with other conventional analyses. X‐ray with the incident angle of 0° provided the smallest (nearly negligible) energy shift in the C 1s spectra of HM and did not damage the surface of the sample.