Green, efficient and controllable synthesis of high-quality MOF-74 with high gravity technology

Abstract

MOF-74 or M₂(dhtp) (M = metal ions, dhtp = 2,5-dihydroxyterephthalic acid), as a typical class of metal–organic frameworks (MOF), have garnered considerable interest due to their abundant unsaturated metal sites. However, environmental and economic limitations caused by the extensive use of organic solvents in traditional syntheses hinder their industrial applications. Although water as a green solvent is considered to be the best candidate solvent, water-based MOFs often have poor crystallinity and long synthesis time, and controlling the particle size is difficult. Herein, a water-based strategy is proposed to synthesize high-quality MOF-74–Co with controllable particle sizes in a rotating packed bed (RPB) reactor using high-gravity technology. MOF-74–Co could be rapidly prepared in the RPB, and shows a smaller and more uniform particle size, higher crystallinity, and larger specific surface area, as compared to the counterpart prepared in a traditional stirred tank reactor. Further adopting acetic acid as a modulator, the as-prepared MOF-74–Co has the highest BET surface area (1599 m² g⁻¹) in the reported literature so far and simultaneously possesses a high space–time yield (293 kg m⁻³ day⁻¹). High-quality MOF-74–Zn and MOF-74–Ni can also be prepared, proving the generality of this strategy. Furthermore, the small-sized MOF-74–Co-78 nm exhibits a faster adsorption rate and a larger saturation adsorption capacity (298 mg g⁻¹) for CO₂ compared with large-sized samples. This study not only advances the field of green synthesis of MOFs but also paves the way for efficient manufacturing processes in MOF-74 synthesis for CO₂ adsorption.