Device-Free Colorimetric Sensing of Lead in Water by Kinetically Trapping Lead(II) Rhodizonate into a Solid-solution of Cellulose Paper

Anthropogenic lead pollution remains a serious environmental concern due to the high incidence of human exposure worldwide and its severe health impact, particularly to children. We report a device-free colorimetric sensor for lead(II) ions in water based on the microdrop detection of the lead(II) rhodizonate complex trapped into a solid-solution of cellulose paper. This allows for the selective colorimetric detection of Pb 2+ with a qualitative and quantitative detection limit of ~ 1 ppm. Comparative studies with Li + , Na + , K + , Ca 2+ , Mg 2+ , Sr 2+ , Ba 2+ , Cd 2+ , Ni 2+ , Cu 2+ , Zn 2+ , Fe 2+ , Hg 2+ , Co 2+ , Ce 2+ , Mn 2+ , Cr 2+ , Cr 2+ , and Au 3+ show high detectability for Pb 2+ due to the unique charge transfer band present in the kinetically trapped Pb-RA complex. We demonstrated that without the solid-solution matrix, the lead(II) rhodizonate complex polymerizes into an extended solid. The mechanism and kinetics of Pb 2+ detection were studied by UV-visible spectroscopy, XRD, transmission electron microscope (TEM), and dynamic light scattering analysis (DLS). This device-free sensing method for Pb 2+ is highly portable and suitable for applications on the field. Graphical Abstract