以複合金屬有機骨架薄膜提昇二氧化碳分離效能

Abstract

有機金屬框架(Metal-Organic Frameworks, MOFs)由有機配體與金屬節點構成，形成高度多孔的晶體結構，具備優異的氣體分離潛力。相較於傳統的蒸餾與吸附等氣體分離技術，由MOF構成的薄膜材料具備更優異的通量和選擇性，為具有潛力的氣體分離材料。本研究採用多孔α-氧化鋁(α-Al₂O₃)為基材，並採用MOF-on-MOF策略合成複合MOF薄膜。此薄膜由MIL-160和MOF-303兩種MOF共同構成，於 MIL-160薄膜表面生長MOF-303，製備出複合結構MOF-303@MIL-160。兩種材料具有相似的配位方式與化學結構，故具良好的配體相容性與表面接合能力，有助於降低界面缺陷、提升膜層結晶性與結構穩定性，藉此複合兩種材料達到良好的氣體分離效能。本研究測試MOF-303@MIL-160膜對CO₂/N₂與 CO₂/CH₄的分離能力，並與單一MOF薄膜(MIL-160與 MOF-303)進行比較。結果顯示，MOF-on-MOF結構雖略降低通量，但顯著提升選擇性。具體而言，MOF-303@MIL-160對CO₂/N₂的選擇率為114.49，對CO₂/CH₄為154.54，均高於MIL-160(71.86與85.46)與MOF-303(62.00與132.98)。為驗證 MOF-303成功生長於MIL-160上，本研究結合多項量測手段。X光繞射(XRD) 圖譜與CCDC模擬對照證實兩相訊號共存；13C核磁共振光譜(NMR)進一步支持此結構。此外，共軛焦顯微鏡則揭示MOF-303薄層主要生長於 MIL-160晶粒邊界。本研究成功開發出具高CO₂分離效能的MOF-on-MOF複合薄膜，提供了一種以複合材料達到良好薄膜氣體分離效能的具體策略。

Metal–Organic Frameworks (MOFs), composed of organic linkers and metal nodes, form highly porous crystalline structures with excellent potential for gas separation. Compared to conventional gas separation technologies such as distillation and adsorption, MOF-based membranes exhibit superior permeability and selectivity, making them promising candidates for gas separation applications. In this study, porous α-alumina (α-Al₂O₃) was used as the substrate, and a MOF-on-MOF strategy was adopted to fabricate composite MOF membranes. The resulting membrane, composed of MIL-160 and MOF-303, features a layered structure where MOF-303 is grown on the surface of a MIL-160 membrane, forming a MOF-303@MIL-160 composite. Due to their similar coordination environments and chemical structures, the two MOFs exhibit good ligand compatibility and interfacial adhesion. It helps reduce interfacial defects, enhance membrane crystallinity, and improve structural stability. By integrating the properties of both materials, the composite membrane achieves excellent gas separation performance. The gas separation ability of the MOF-303@MIL-160 membrane was evaluated for CO₂/N₂ and CO₂/CH₄ systems and compared to single-component MOF membranes (MIL-160 and MOF-303). Results show that although the MOF-on-MOF structure slightly reduces the gas flux, it significantly improves selectivity. Specifically, the MOF-303@MIL-160 membrane exhibited a CO₂/N₂ selectivity of 114.49 and a CO₂/CH₄ selectivity of 154.54, both higher than those of MIL-160 (71.86 and 85.46) and MOF-303 (62.00 and 132.98), respectively. To confirm the successful growth of MOF-303 on MIL-160, multiple characterization techniques were employed. X-ray diffraction (XRD) patterns, in comparison with CCDC simulations, verified the coexistence of both MOF phases. Solid-state ¹³C nuclear magnetic resonance (NMR) further supported the composite structure. In addition, confocal microscopy revealed that the MOF-303 layer primarily grew along the grain boundaries of MIL-160. This study successfully demonstrates a high-performance MOF-on-MOF composite membrane for CO₂ separation and provides a concrete strategy for enhancing membrane separation performance through MOF hybridization.