Iron oxide-supported gold nanoparticle electrode for simultaneous detection of arsenic and sulfide on-site

The environmental behavior of arsenic (As) has garnered significant attention due to its hazardous nature. The fate of As often couples with sulfide, thus co-detecting arsenic and sulfide on-site is crucial for comprehending their geochemical interactions. While electrochemical methods are suitable for on-site chemical analysis, there currently exists no electrode capable of simultaneously detecting both arsenic and sulfide. To address this, we developed a dual-metal electrode consisting of iron oxide-encased carbon cloth loaded with gold nanoparticles (Au/FeO_x/CC) using the electrochemical deposition method. This electrode enables square wave stripping voltammetry (SWASV) binary detection of As and sulfide. Comparison experiments reveal that the reaction sites for sulfide primarily reside on FeO_x, while the interface synergy of iron oxide and gold nanoparticles enhances the response to arsenite (As^III). Arsenate (As^V) is directly reduced to As⁰ on Fe⁰, obviating the need for an external reducing agent. The electrode achieves detection limits of 1.5 μg/L for As^V, 0.25 μg/L for As^III, and 11.6 μg/L for sulfide at mild conditions (pH 7.8). Field validation was conducted in the Tengchong geothermal hot spring region, where the electrochemical method exhibited good correlation with the standard methods: Total As (r = 0.978 vs. ICP-MS), As^III (r = 0.895 vs. HPLC-ICP-MS), and sulfide (r = 0.983 vs. colorimetric method). Principal component analysis and correlation analysis suggest that thioarsenic, could potentially be positive interferents for As^III. However, this interference can be anticipated and mitigated by monitoring the abundance of sulfide. The study provides new insights and problems for the electrochemical detection of coexisted As and sulfide.