In situ measurement of thallium in acid mine drainage-impacted waters using the diffusive gradients in thin-films technique embedded with a copper(II) ferrocyanide functionalized mesoporous silica gel layer

CFC-SBA was used as novel binding agent in the DGT configuration. • In situ monitoring Tl in AMD-impacted environments with CFC-SBA-DGT. • CFC-SBA-DGT analysis was independent of pH (2–12) and ionic strength (1–500 mmol L −1 ). • The proposed DGT is a robust tool for measuring Tl in groundwater and surface water. Thallium (Tl) contamination in groundwater and surface water poses serious ecological and human health risks. This study developed a diffusive gradients in thin-films (DGT) technique using a copper(II) ferrocyanide-functionalized mesoporous silica (CFC-SBA) binding gel for in situ measurement of DGT-labile Tl in acid mine drainage (AMD)-impacted waters. The CFC-SBA gel achieved near-quantitative elution with 5 mol L −1 HNO 3 and had a binding capacity of 48.2 μg cm −2 . Diffusion coefficients in agarose gel at 25 °C were 15.30 × 10 −6 cm 2 s −1 for Tl(I) and 8.01 × 10 −6 cm 2 s −1 for Tl(III). Laboratory tests supported Tl(I) measurement across pH 2–12 and Tl(III) measurement across pH 2–7. Performance was independent of ionic strength (1.0–500 mmol L −1 NaNO 3 ), and dissolved organic matter (0–30 mg L −1 humic acid). Method detection limits were 2.2 ng L −1 for Tl(I) and 3.2 ng L −1 for Tl(III), and the gel remained stable after 240 days of controlled storage. The method was further validated in quiescent solutions mimicking groundwater conditions. Field deployments at five AMD-impacted sites (24–72 h) demonstrated the feasibility of measuring DGT-labile Tl. Relative to TP-DGT, CFC-SBA-DGT showed an advantage under the strongly acidic and high-ionic-strength conditions tested, but the comparison does not demonstrate universal analytical superiority. Download: Download high-res image (225KB) Download: Download full-size image