A comparison of different nanoscopic silver species with respect to their capacity to bind mercury from the gas-phase using total reflection X-ray fluorescence

Abstract

Mercury compounds like mercury chloride (HgCl2) were often used to protect cultural heritage specimens, e.g., herbaria and paintings from damage. Over time, Hg0 is formed by bacterial activity and released into the air.Here we present our study on the performance of different nanoscopic Ag species to collect airborne Hg, which is subsequently analyzed by total reflection X-ray fluorescence (TXRF). We studied silver nanoparticles (AgNPs) of different size, i.e., 10 nm and 100 nm AgNPs(Citrate) and particles with presumably weaker stabilizers, i.e., 10 nm AgNPs(borohydride(BH4−)) as well as species from light-exposed (LE) pure aqueous (LE-AgNO3(H2O)) and ammoniacal silver nitrate solutions (LE-AgNO3(NH3)). Hg capture was highest for the LE-AgNO3(NH3) species with a ratio of Hg/Ag of 0.78 in the amalgam. The performance to capture Hg decreased from LE-AgNO3(NH3) to AgNPs(Citrate) in the following order LE-AgNO3(NH3) > LE-AgNO3(H2O) > 10 nm AgNPs(BH4−) > 10 nm AgNPs(Citrate) > 100 nm AgNPs(Citrate), the latter collected airborne Hg with a ratio of Hg/Ag of 0.0006. The relative standard deviation of the TXRF measurements of Hg collected from a saturated atmosphere (n = 3 and n = 5) was lowest with 9% for LE-AgNO3(H2O) and highest for the AgNPs(Citrate) with 38%. The AgNPs(BH4−) and AgNPs(Citrate) species were also used to study Hg capture from the gas-phase in concentrations between 0.0012 mg/m3 and 0.024 mg/m3 (European Union regulated threshold: 0.02 mg/m3; saturated Hg atmosphere: 13.6 mg/m3 at 20 °C). Detection limits were found to be 0.018 μg/m3 for AgNPs(BH4−) and AgNPs(Citrate).