Upcycling Polystyrene into Hydrophobic-Shielded Adsorbents for Efficient Direct Air Capture

Developing strategies that address both the plastic pollution crisis and climate change is increasingly urgent yet technically challenging. Porous materials are promising candidates for direct air capture (DAC) of CO₂, but their efficiency is severely impeded by coadsorption of atmospheric water, which incurs substantial energy penalties during regeneration. In this work, we demonstrate an effective and low-cost method for upcycling polystyrene (PS) into a robust hydrophobic shield on the surface of metal-organic framework (MOF) nanoparticles, thereby creating core-shell adsorbents (MOF@PS). This strategy dramatically enhances surface hydrophobicity, yielding water contact angles exceeding 125° (compared to 0° before encapsulation), and reduces water uptake by around 70% compared to pristine MOF. Notably, this hydrophobic gating does not impede CO₂ penetration and allows limited access of water vapor to the amine-functionalized core that facilitates amine-mediated chemisorption. The resulting material with amine loading exhibits an exceptional DAC breakthrough capacity of approximately 3.06 mmol g^-1 under ambient air and maintains excellent stability over 10 cycles. This work provides innovative insights into the interconnection between PS upcycling, hydrophobic engineering, and DAC.