Volcano-Type Pore-Size Dependence of HMF Adsorption in Aluminum-Based Metal–Organic Frameworks: A Transport–Affinity Tradeoff for Sugar Purification

Abstract Furfural derivatives like 5-hydroxymethylfurfural (HMF) are potent fermentation inhibitors whose selective removal remains a bottleneck in biorefining due to limited pore-level mechanistic understanding. Here, we deploy five metal–organic frameworks with graded pore apertures to elucidate pore-size effects on HMF adsorption. Integrated kinetic, thermodynamic, and dynamic breakthrough studies reveal a volcano-type trend governed by a dual trade-off between steric accessibility and spatial confinement. MIL-53(Al)-TDC, with an optimally matched 8.1 Å pore balancing rapid intracrystalline diffusion with strong host–guest affinity, synergizes π–π stacking and hydrophobic microenvironments to deliver an HMF capacity of 579.58 mg·g–1 and mass transfer coefficient of 22.36 L·g–1·h–1. Breakthrough experiments demonstrate its potential for continuous purification of simulated hydrolysate. A technoeconomic assessment confirms 33–50% lower equipment investment and 47–51% lower annualized cost vs conventional distillation. This work establishes a predictive framework coupling pore commensurability with interfacial interactions, guiding rational design of adsorbents for biorefinery separations.