In situ growth of Zn-based metal–organic frameworks in ultra-high surface area nano-wood aerogel for efficient CO2 capture and separation

Abstract

Metal–organic frameworks (MOFs) combined with wood-based templates have drawn growing interest in the field of CO₂ capture and separation. However, the low MOFs loadings of these composites adversely limit their performance. In this study, a novel wood-based template with a nanocellulose aerogel network structure and natural wood anisotropy was prepared by dissolution-regeneration followed by 2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPO)-mediated oxidation. These TEMPO-nanocellulose networks have large numbers of polar groups in the TEMPO-oxidized regenerated wood (TRW) which can generate stronger interaction forces between the added metal ions (Zn²⁺). This improves the loading of MOFs into the composite. It also causes lower MOF aggregation in TRW. Three MOFs of different crystal size (Zn-MOF-74, ZIF-7-NH₂ and ZIF-8-NH₂) were synthesized in situ within TRW using different organic ligands, and designated as TRW/Z-74, TRW/Z-7N, and TRW/Z-8N. TRW/Z-74 exhibited a high CO₂ adsorption capacity (2.59 mmol g⁻¹) at 298 K, 106 kPa (1.06 bar). Even after 7 recycles, their CO₂ adsorption capacity still remained at 95% of its original value. A selectivity of TRW/Z-74 for CO₂ in a CO₂/N₂ (15%/85%) gas mixture up to 49 was calculated by ideal adsorption solution theory (IAST). In addition, TRW/Z-74 had good yield strengths in compression tests along the longitudinal axis. CO₂ uptake tests proved the scalability of TRW as a template for different metal based-MOFs. TRW/Mg-MOF-74 (4.97 mmol g⁻¹) and TRW/Co-MOF-74 (3.37 mmol g⁻¹) exceeded that of TRW/Zn-MOF-74 (2.59 mmol g⁻¹) at 298 K and 106 kPa. Thus, this study provides a novel strategy for the synthesis of wood-based MOF composites, also achieves a sustainable and efficient capture and separation of CO₂.