In situ growth of CeO2 on g-C3N4 nanosheets toward a spherical g-C3N4/CeO2 nanozyme with enhanced peroxidase-like catalysis: a selective colorimetric analysis strategy for mercury(II)

Cerium dioxide (CeO2) nanocatalysts were initially grown in situ on 2D graphitic carbon nitride (g-C3N4) nanosheets to yield the nanocomposites g-C3N4/CeO2 with a spherical structure for the catalysis-based colorimetric analysis of Hg2+ ions in blood and wastewater. As the synergetic introduction of g-C3N4 nanosheets might promote the electron transfer in CeO2, the resulting g-C3N4/CeO2 nanozyme was found to present greatly enhanced catalytic activity, as demonstrated by the steady-state kinetic studies, which is nearly 4-fold higher than that of pure CeO2. Moreover, the g-C3N4/CeO2 nanozymes would aggregate in the presence of Hg2+ ions due to the strong interaction between Hg2+ and the nitrogen of g-C3N4, leading to a decrease of catalysis rationally depending on the Hg2+ ion concentration. A colorimetric analysis strategy is therefore developed for the selective detection of Hg2+ ions separately in the complex samples of blood and wastewater, showing a linear concentration range from 0.50 nM to 800 nM with the LOD of 0.23 nM as exemplified for Hg2+ ions in blood. Also, the recovery tests indicated that the developed colorimetric method can allow for the accurate analysis of Hg2+ ions in wastewater and blood. Such a route for the fabrication of composite nanozymes by growing catalytic nanomaterials on conductive 2D substrates may be extended to the design of other kinds of nanozymes with enhanced catalytic performances for developing catalysis-based detection platforms.