Zinc-doped covalent organic frameworks as high-efficiency chemiresistors for acetylene gas detection

Abstract

This paper details the synthesis and characterization of zinc-doped covalent organic frameworks (Zn@DADE-Tp COF) for the highly sensitive and selective detection of acetylene (C₂H₂). The Schiff base condensation of 4,4′-diaminodiphenyl ether and 2,4,6-hydroxybenzene-1,3,5-tricarbaldehyde produced a porous framework, which was then functionalized with Zn²⁺ ions to improve gas-sensing efficacy. The synthesized MCOFs were synthesized by incorporating Zn²⁺ ions into COFs by a simple solution method. Structural characterization by XPS, PXRD, and SEM-EDAX validates the effective integration of Zn, whereas AFM indicates an elevated surface roughness of 137.32 nm in contrast to the pure COF, which measures 115.09 nm. The chemiresistive sensor demonstrated outstanding performance at ambient temperature, achieving a response of 1.41 at 150 ppm C₂H₂, swift response and recovery times (7.32 s/7.10 s), and a minimal detection limit of 10 ppm. The increased sensitivity is due to Zn²⁺ coordination, which promotes electron transfer and enhances C₂H₂ adsorption. In support of the enhanced sensing performance, DFT studies revealed a reduction in the HOMO–LUMO gap from 3.74 eV (pristine COF) to 2.64 eV after Zn-doped COF, and further to 2.59 eV upon C₂H₂ adsorption. This, along with increased orbital delocalization and stronger electrostatic interaction at the Zn site, confirms improved charge transfer and validates the observed chemiresistive response. This study highlights the potential of metal-doped COFs (MCOFs) as advanced sensors for industrial safety and environmental monitoring.