Low-angle-dependent CdS@SiO2 photonic crystal hydrogel material for visual detection and removal of uranyl ions.

Abstract

A low-angle-dependent photonic crystal hydrogel (LAD-PCH) material was developed to simultaneously detect and remove uranyl ions (UO22+). Different from traditional SiO2 photonic crystal hydrogel with the problem of angle dependency, the LAD-PCH material overcomes the restriction of observation direction. The LAD-PCH is a composite material with the photonic crystal array of 180-nm monodisperse CdS@SiO2 particles embedded into the functional hydrogel. As one UO22+ can bind to multiple carboxyl groups and amide groups, the functional hydrogel fabricated by acrylic acid and acrylamide will shrink after chelating. These changes in the hydrogel volume alter the array spacing and trigger a blue shift of diffraction wavelength and naked-eye visual color changes of LAD-PCH. The color can vary from orange-red to orange, yellow, green, and cyan, corresponding to the determination range of 100pM-100μM. The LAD-PCH material detects UO22+ sensitively as the lowest detectable concentration is about 100pM, and removes UO22+ high-efficiently as the maximum adsorption capacity of U(VI) is about 1010mgg-1 at 298K. This LAD-PCH material is convenient and has potential to simultaneously monitor and remove UO22+ from uranium-polluted water. Schematic representation of the low-angle-dependent photonic crystal hydrogel (LAD-PCH) material for UO22+ detection and removal: The structural colors of LAD-PCH material overcome the restriction of observation angles. After the ligands complex with UO22+, the networks of LAD-PCH show different degrees of shrinkage; these volume changes of hydrogel trigger obvious naked-eye visual color changes of LAD-PCH.