Nafion offers microporous channels of typically 1–4-nm diameter for cation exchange. Recently, it has been shown that these cation exchanger properties can be inverted to allow anion binding by pre-filling the hydrophilic channel structure. Here, pre-filling is performed with hydrous iron oxide and sensitivity towards anionic phosphate and arsenate analytes is investigated. After a period of phosphate/arsenate accumulation, the voltammetric response in aqueous 1 M NaNO 3 is obtained based on the Fe(III/II) redox process. The position of the peak at distinct potentials clearly reveals the presence of either phosphate or arsenate, presumably present in the form of FePO 4 and FeAsO 4. In the presence of mixtures of phosphate and arsenate, a competition of FePO 4 versus FeAsO 4 nucleation (within the Nafion microporous host) is suggested to result in a switch of phosphate detection at higher concentrations (ca. > 500 μM, solubility controlled) towards arsenate detection at lower concentrations (ca. < 500 μM, nucleation controlled). This phenomenon is suggested to be linked to the Ostwald step rule. [Figure not available: see fulltext.].
ASJC Scopus subject areas
- Materials Science(all)
- Condensed Matter Physics
- Electrical and Electronic Engineering