Complexation-Based Super Crystalline Assembly of Zinc Oxide Quantum Dots for Sensitive Carbon Dioxide Gas Sensing

Abstract

Herein, we report a facile method to assemble ZnO quantum dots (Qdots) into three-dimensional superstructures via surface complexation between zinc ions and phosphate. Results suggest that such programmed assembly was initiated by control growth of triclinic zinc phosphate tetrahydrate (Zn3(PO4)2·4H2O) structures over the Qdot surface. Addition of phosphate to the ZnO Qdot dispersion not only led to growth of such parahopeite structures but also resulted in crystalline assembly of the Qdots in the colloidal medium. The crystalline nature of the assembly was investigated by using spectroscopic and microscopic characterization techniques. The inter-Qdot distance was found to be 0.53 nm in the assembled superstructure. In general, the method described here has the potential to generate new ideas in the structural engineering of nanoscale assemblies, key to fabricating devices with rich functionalities. Finally, the so-generated ZnO Qdot–phosphate crystalline assembly was successfully applied to devise a gas sensor, which showed great sensitivity and selectivity toward CO2 gas at room temperature.