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

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.