Defective hierarchical porous copper-based metal-organic frameworks synthesised via facile acid etching strategy

TL;DR

This paper presents a scalable method to create hierarchical porosity in water-unstable HKUST-1 MOFs using phosphoric acid etching, enhancing molecular diffusion for catalytic applications.

Contribution

It introduces a novel acid etching technique with phosphoric acid to generate hierarchical pores in water-sensitive MOFs without losing crystallinity.

Findings

Hierarchical macropores formed in HKUST-1 via acid etching.

Etching process is time- and acidity-dependent.

Enhanced molecular accessibility demonstrated.

Abstract

Introducing hierarchical pore structure to microporous materials such as metal-organic frameworks (MOFs) can be beneficial for reactions where the rate of reaction is limited by low rates of diffusion or high pressure drop. This advantageous pore structure can be obtained by defect formation, mostly via post-synthetic acid etching, which has been studied extensively on water-stable MOFs. Here we show that a water-unstable HKUST-1 MOF can also be modified in a corresponding manner by using phosphoric acid as a size-selective etching agent and a mixture of dimethyl sulfoxide and methanol as a dilute solvent. Interestingly, we demonstrate that the etching process which is time- and acidity- dependent, can result in formation of defective HKUST-1 with extra interconnected hexagonal macropores without compromising on the bulk crystallinity. These findings suggest an intelligent scalable synthetic method for formation of hierarchical porosity in MOFs that are prone to hydrolysis, for improved molecular accessibility and diffusion for catalysis.