Determination of trace amounts of mercury using hierarchically nanostructured europium oxide

This work reports a highly sensitive procedure for the determination of trace amounts of mercury, based on fluorescence quenching of thenoyltrifluoroacetone (TTA) capped hierarchically nanostructured europium oxide (cHN-Eu2O3). The HN-Eu2O3 consisted of nanometer-thick Eu2O3 sheets self-organized into nano- and micro-sized monoliths with a hierarchical architecture while retaining its desirable fluorescence properties. The fluorescence intensity of the cHN-Eu2O3 was 1000 times higher than that of commercial Eu2O3 nanoparticles (equivalent weight) when it was capped with TTA, suggesting that a synergetic effect, confining the longtime Eu3+ excitation within the nanostructure and light-harvesting effect of the capping agent, is responsible for this fluorescence enhancement. Excellent interaction between the cHN-Eu2O3 and solution species is expected owing to its large surface area, high surface-to-bulk ratio, and ultrahigh fluorescence intensity. As an example, aqueous suspensions of the cHN-Eu2O3 were used as sensing agent for the determination of trace amounts of mercury. A linear relationship between the concentration of mercury and fluorescence quenching was observed from 10 ppb to 10 ppm with a correlation coefficient of 0.997 and a detection limit of 5.0 ppb. Mercury in various samples was analyzed using the cHN-Eu2O3 suspension.