Microwave-Assisted Rapid Substitution of Ti for Zr to Produce Bimetallic (Zr/Ti)UiO-66-NH2 with Congenetic "Shell-Core" Structure for Enhancing Photocatalytic Removal of Nitric Oxide

Abstract

Efficient nitric oxide (NO) removal without nitrogen dioxide (NO₂ ) emission is desired for the control of air pollution. Herein, a series of (Zr/Ti)UiO-66-NH₂ with congenetic shell-core structure, denoted as Ti-UION, are rapidly synthesized by microwave-assisted post-synthetic modification for NO removal. The optimal Ti-UION (i.e., 2.5Ti-UION) exhibits the highest activity of 80.74% without NO₂ emission with moisture, which is 21.65% greater than that of the UiO-66-NH₂ . The NO removal efficiency of 2.5Ti-UION further increases to 95.92% without photocatalyst deactivation under an anhydrous condition. This is because selectively produced NO₂ in photocatalysis is completely adsorbed into micropores, refreshing active sites for subsequent reaction. In addition, the enhanced photocatalytic activity after Ti substitution is due to the presence of Ti electron acceptor, the potential difference between the shell and core of Ti-UION crystal, and the high conductivity of TiO units. Additionally, the improved adsorption of gas molecules not only favors NO oxidation, but also avoids the emission of NO₂ . This work provides a feasible strategy for rapid metal substitution in metal-organic frameworks and insights into enhanced NO photodegradation.

Keywords: Ti-substitution; bimetallic (Zr/Ti)UiO-66-NH 2; microwave-assisted synthesis; nitric oxide photodegradation; shell-core structures.