Surface studies of a chalcogenide glass ferric ion‐selective electrode Part 2: The effects of inorganic ions, organic ligands and seawater on sensor response

Abstract

X-ray photoelectron spectroscopy (XPS), secondary ion mass spectrometry (SIMS) and electrochemical impedance spectroscopy (EIS) have been used to investigate the effect of inorganic ions, organic ligands and seawater on the response of the Fe III ion-selective electrode (ISE). X-ray photoelectron spectroscopy has shown that the formation of antimony(V) oxide/hydroxide on the chalcogenide glass membrane soaked in seawater is dictated by electrode kinetics. It has been found that selenide atoms in the chalcogenide glass are replaced by oxygen in the presence of seawater. Furthermore, EIS aging studies demonstrated that the chalcogenide glass membrane experiences a sluggish charge transfer reaction in seawater. By contrast, SIMS imaging and depth profiling on various regions of a seawater-exposed membrane identified a phase comprising iron oxide-hydroxide-carbonate-carboxylate. Furthermore, SIMS revealed a uniform chemisorption of oxygen on the membrane surface, and adsorption does not appear to be related to specific coordination sites. X-ray photoelectron spectroscopy failed to detect any chloride chemisorption on the membrane surface, whereas in situ EIS showed that chloride along with hydroxide ions facilitate the charge transfer process of the Fe III ISE. Moreover, the effect of humic acid on the Fe III ISE was studied using EIS. The results of this XPS, SIMS and EIS study have enabled the derivation of a response mechanism for the Fe III ISE in seawater.

Ion‐Selective Electrode Potentiometry in Environmental Analysis

“…A further mechanistic study of the iron(III) chalcogenide glass ISE using secondary ion mass spectrometry (SIMS), EIS and XPS in various media [108,109] suggested that chloride, hydroxide, nitrate, etc. in seawater together with ubiquitous organic ligands do not pose a serious problem for the electroanalysis of Fe 3þ in seawater, but it is necessary to condition the electrode in seawater prior to analysis, while regular recalibration, reconditioning (preferably overnight) and frequent polishing is required, if the ISEs response in seawater is to remain internally consistent with its response in iron(III) calibration standards.…”

In situ synchrotron radiation grazing incidence X-ray diffraction—A powerful technique for the characterization of solid-state ion-selective electrode surfaces

“…These studies revealed the formation of various oxidation products on the chalcogenide surface after exposure to seawater electrolyte [29,30]. It was shown that the physical and chemical condition of the membrane surface has a profound influence on the reactivity of the Fe 3+ ISE [28,29]. The long-term aging of the Fe 2.5 (Se 60 Ge 28 Sb 12 ) 97.5 membrane in saline and alkaline electrolytes has a tendency to destroy the surface structure of the sensor [31].…”

“…These studies revealed the formation of various oxidation products on the chalcogenide surface after exposure to seawater electrolyte [29,30]. It was shown that the physical and chemical condition of the membrane surface has a profound influence on the reactivity of the Fe 3+ ISE [28,29].…”

“…De Marco and co-workers [28][29][30] used various surface analytical tools to explain the response mechanism of the chalcogenide membrane Fe III ISE. These studies revealed the formation of various oxidation products on the chalcogenide surface after exposure to seawater electrolyte [29,30].…”

“…Furthermore, we have compromised the surface sensitivity of the in situ SR-GIXRD measurements to tens of nanometres by using a high beam energy (12.41 keV or 1.000Å) in order to enhance the penetration of the X-ray beam through the liquid in the cell. In this context, we have used a model electrochemical system of the iron chalcogenide glass ion sensor [29][30], which previous ex situ X-ray photoelectron spectroscopy (XPS) and secondary ion mass spectrometry (SIMS) surface studies have shown forms a 200 nm thick modified surface layer (MSL), which is of adequate thickness and suitability for examination by the in situ SR-GIXRD technique. Furthermore, electrochemical impedance spectroscopy (EIS) research [31] has demonstrated that the iron sensor undergoes a severe chemical ageing effect in artificial and real seawater media rendering the electrode unusable after a prolonged period of exposure, and it is anticipated that in situ SR-GIXRD will shed new insights into the dynamic electrochemical reactivity of the MSL of the iron chalcogenide glass ion sensor.…”