Development of sample preparation technique to characterize chemical structure of humin by synchrotron‐radiation–based X‐ray photoelectron spectroscopy

Abstract

Carbon-binding state of humin (HM, a non-conductive insoluble organo-mineral humic substance) was successfully characterized for the first time by synchrotronradiation-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 C¼C (284.0 eV), C-C/C-H (285.1 eV), C-O (286.3 eV), C¼O (287.3 eV), and O¼C-O (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 conventionalanalyses. 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.

Hierarchical porous NiFe-P@NC as an efficient electrocatalyst for alkaline hydrogen production and seawater electrolysis at high current density

“…S6 †) had three main peaks, at 284.8 eV, 286.3 eV and 288.07 eV, which corresponded to the binding energies of C-C, C-O and N-CvN, respectively. [72][73][74] In addition, the surface properties of the NIF substrate changed after the corrosion process and following phosphorization. As shown in Fig.…”

Effect of Humin and Chemical Factors on CO2-Fixing Acetogenesis and Methanogenesis

“…Soil was collected from a paddy field in Kamajima, Aichi Prefecture, Japan, and utilized for humin extraction. Humin was prepared as described previously [ 28 ]. Humin contained 1.3% carbon, 0.4% hydrogen, 0.2% nitrogen, 4.3% of oxygen, and 93.9% of ash ( Table S1 ).…”

Humin as an External Electron Mediator for Microbial Pentachlorophenol Dechlorination: Exploration of Redox Active Structures Influenced by Isolation Methods

“…The sample preparation technique for HM characterized by synchrotron based-XPS had been developed successfully recently by Pham et al [32]. Briefly, HM was first mixed thoroughly with copper powder (size 75 µm, purity 99.95%) at a HM:Cu ratio of 1:1 v / v in a ceramic mortar.…”