Deep Eutectic Solvent-Mediated Synthesis of Bullet-Shaped Cerium Zinc Oxide and Sheet-Like Cerium Zinc Hydroxide Nitrate: Colorimetric and Fluorometric Detection of Pyrophosphate Ions

This work demonstrates a simple and versatile deep eutectic solvent (DES)-assisted synthesis of bullet-shaped cerium–zinc oxide (Ce–ZnO) and sheet-like cerium–zinc hydroxide nitrate (Ce–Zn5(OH)8(NO3)2·2H2O). DES could serve not only as a green solvent but also as a superior template to produce these two different hierarchically shaped materials. Interestingly, Ce–ZnO shows catalytic activity toward polymerization of dopamine to initially pink color quinone derivatives with the visible light absorption at 475 nm and finally to blue-emitting polydopamine with highest fluorescence intensity at 480 nm. The catalytic activity of Ce–ZnO can be selectively inhibited by pyrophosphate ions (PPi), which leads to a decrease in the absorbance intensity or fluorescence emission. PPi detection strategies were established, and the linearity was achieved from 0.5 to 100 μM with a low detection limit of 0.05 μM for the fluorometric detection, while the linear detection was 0.5–150 μM and the low detection limit was 0.19 μM for colorimetric detection. This work offers a new opportunity to produce Ce–ZnO and Ce–Zn5(OH)8(NO3)2·2H2O using an inexpensive and eco-friendly solvent, and provides a useful way of detecting PPi. Hence, from these findings, the proposed synthesis strategy is expected to serve as a novel green strategy for preparing hierarchically shaped materials.