X-ray Absorption Near Edge Structure Spectroscopy Analysis Research Articles

A highly efficient pathway to recover gold from acid aqueous solution by using an amidoxime-functionalized UHMWPE fiber

A new amidoxime-functionalized ultrahigh molecular weight polyethylene fibrous adsorbent (UHMWPE-g-PAO) was used for the recovery of Au(III) from acid aqueous solution. The maximum experimental absorption capacity of UHMWPE-g-PAO fiber was found to be approximately 220.0 mg·g−1. Au adsorption on UHMWPE-g-PAO was characterized by synchrotron radiation-based microcomputed tomography (SR-μ-CT), transmission electron microscopy (TEM), X-ray absorption near-edge structure spectroscopy (XANES) and synchrotron radiation-based Fourier transform infrared microspectroscopy (SR-FTIR). The SR-μ-CT and TEM results showed the distribution features of gold particles on the fiber. The mechanism of Au(III) recovery from aqueous solutions by UHMWPE-g-PAO was based on the adsorbed Au(III) ions, which were reduced to metallic zero-valent gold (Au(0)) by amino groups (–NH2) in the amidoxime (AO) groups during the adsorption process, as confirmed by high-resolution TEM (HRTEM) and XANES analyses. X-ray diffraction (XRD) results indicated that the incineration ashes contained metallic zero-valent gold. In conclusion, this amidoxime-functionalized fibrous adsorbent is a promising material for recovering gold from aqueous solution.

The contribution of XANES spectroscopy to tribology

X-ray absorption near edge structure spectroscopy (XANES) analysis has been routinely used to study the complex chemical interactions between additives in engine oil and metallic surfaces during high-temperature and pressure reciprocating wear conditions. XANES analysis provides detailed chemical and structural information on the resultant antiwear and tribo films formed on metallic surfaces. The following review will illustrate how XANES analysis on the macro scale can provide the information required to elucidate complex film formation mechanisms, then describes the use of emerging XANES spectromicroscopy to such systems, and concludes by showing the complementary nature of the macro and micro scale spatially resolved XANES analysis; Professor Bancroft has utilized the combination of these to stay at the forefront of XANES research in the field of tribology and in spectroscopy science in general.Key words: tribology, XANES, X-ray absorption near edge structure spectroscopy, metals, thiophosphates, spectromicroscopy, tribochemistry.

Time-Dependent Film Formation from ZnDTPs and Nonphosphorus Antiwear Agents

Electrical contact resistance (ECR) studies, X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), and X-ray absorption near-edge structure spectroscopy (XANES) were carried out on specimens run with oils containing 0.05% phosphorus as either primary zinc dialkyldithio-phosphate (ZnDTP) or secondary ZnDTP in Group II base oil. A series of progressively longer ECR experiments were run on each ZnDTP. At the end of each run in the series, the ball was removed and preserved for surface analysis. The surface analyses were designed to observe chemical species deposited on the surface and within the deposited films. The observation of surface phenomena at different intervening times during the ECR experiment, allowing for characterization of the maturing antiwear film, was the distinct feature of these experiments. In general, short ECR experiments gave poorer films than long ECR experiments. Atomic concentrations versus depth were determined from AES. Quite strikingly, the antiwear films formed after only 10 min of the ECR experiment showed that both primary and secondary ZnDTPs form a thin film (∼70 Å) very rapidly. Those films are rich in Zn, P, and S. Auger and XANES analyses of the same specimens were not as revealing, most likely due to the small wear scar on the balls and the unfortunately relatively large beam cross section. ECR, XPS, and AES were then performed on oils containing nonphosphorus antiwear agents in American Petroleum Institute Group II base oil. Several nonphosphorus supplemental antiwear inhibitors were evaluated. These experiments showed separation in apparent performance among the various components.