Template- and etching-free fabrication of two-dimensional hollow bimetallic metal-organic framework hexagonal nanoplates for ammonia sensing

This work reports the template- and etching-free fabrication of hollow bimetallic nickel-cobalt benzenetricarboxylic acid (Ni Co BTC) hexagonal nanoplates by a polyvinylpyrrolidone (PVP)-assisted approach. The incorporation of PVP can reduce the stacking of these nanoplates along the vertical direction and generate depletion forces between them to reduce aggregation. When employed for the quartz crystal micmbalance (QCM) sensing of ammonia (NH3), the hollow Ni Co BTC hexagonal nanoplates exhibit 1.6, 3.8, and 7.5 times higher sensitivity to 69.5 ppm of NH(3 )than non-hollow Ni Co BTC nanoplates, Ni-BTC nanobelts, and Co-BTC microrods, respectively, and a low limit of detection (LOD) of 1.53 ppm. Additionally, they show good selectivity to NH3 in the presence of other interfering compounds and excellent stability with only a very small decrease of 2.86 % in sensitivity after 6 months. The NH3 adsorption on the hollow Ni Co BTC hexagonal nanoplates follows a pseudo first-order kinetic model with the adsorption rate being 6.1 and 7.1 times faster than Ni-BTC nanobelts and Co-BTC microrods, respectively. The good sensing performance of the hollow Ni-Co BTC hexagonal nanoplates to NH3 is attributed to the existence of carboxyl and hydroxyl groups which can provide energetic sites for the chemisorption of NH(3 )molecules and the increased adsorption sites provided by the hollow two-dimensional structure and the bimetallic composition of this MOF.

Automated summary

This work presents a template- and etching-free approach to fabricate hollow bimetallic nickel-cobalt benzenetricarboxylic acid hexagonal nanoplates. These nanoplates exhibit high sensitivity and stability in the sensing of ammonia, and have faster adsorption rates compared to other nano materials. The hollow two-dimensional structure and bimetallic composition present in these nanoplates contribute to their excellent sensing performance.