Engineering defects and ion pathways in MOF membranes for advanced low-concentration CO2 capture and photocatalytic conversion

Abstract

Efficient capture and conversion of low-concentration CO 2 (10–15 vol% in industrial flue gas, ∼420 ppm in ambient air) remains a critical bottleneck for carbon capture, utilization and storage (CCUS) toward global carbon neutrality. Conventional stepwise "capture-then-conversion" processes incur prohibitive energy penalties and low overall carbon conversion efficiency. Pristine metal-organic framework (MOF) membranes exhibit drastically diminished performance under low CO 2 partial pressure, fundamentally limited by insufficient adsorption driving force, hindered ion transport, and sluggish interfacial kinetics. This critical review systematically surveys defect-engineered MOF membranes for low-concentration CO 2 photocatalytic utilization. We first categorize multi-scale mass transfer pathways into three hierarchical levels: intrinsic crystalline pores, defect-derived functional channels, and mixed matrix membrane interfacial pathways. We then dissect ion transport kinetics and energy barrier regulation within confined nanochannels. Central to this review, we propose a conceptual "adsorption–conduction–conversion" coupling framework with positive feedback potential as a working hypothesis to interpret the defect-ion synergy. This qualitative model offers a unified mechanistic perspective for breaking the inherent permeance-selectivity trade-off and bridging CO 2 enrichment with in-situ photocatalytic reduction, though its quantitative validation and boundary conditions remain to be established through further in situ characterization and multiscale simulation. Distinct from conventional mass transfer-reaction coupling theories, this proposed conceptual framework takes ion transport as the core intermediate coupling bridge to theoretically enable dynamic mutual regulation between adsorption and conversion, representing a mechanistic advance beyond the traditional adsorption-catalysis synergy paradigm. Concurrently, we highlight unresolved academic controversies, particularly the steady-state assumptions and spatiotemporal mismatch in prevailing theoretical models, which constrain the rational design of high-performance membrane systems. Beyond conventional mechanistic summaries, this review further addresses practical industrial bottlenecks—long-term operational stability and scalable fabrication—and outlines frontier directions such as AI-driven high-throughput screening. Overall, this review proposes a unified conceptual framework for defective MOF membrane systems, offering a rational design roadmap to guide the industrial deployment of next-generation integrated CO 2 capture-conversion membrane reactors.