Closed-loop upcycling of protein amyloid fibrils from food waste for atmospheric CO2 capture

Abstract Food waste contributes substantially to global CO2 emissions, yet it also offers underutilized opportunities for climate change mitigation within and beyond the food system. Direct air capture (DAC) technologies can help offset these emissions, but most current sorbents are synthetic, energy-intensive, and poorly aligned with circular-economy principles, while bio-based alternatives typically feature low CO2 capacity and poor stability. Here, we upcycle proteins recovered from dairy and tofu waste streams into functional amyloid fibril microbeads for ambient CO2 capture. Atomic-level design and templated moulding enable lysine and glutamine residues within the fibrils, along with hydroxyl groups introduced by mild KOH treatment, to form abundant active sites for CO2 capture, achieving up to 2.20 mmol g−1 under ambient air. The microbeads are regenerated within 10−12 min via alternating dilute acid–alkali mist without any thermal input and remain stable over 30 cycles. Life cycle assessment (LCA), ranking efficiency product (REP), and techno-economic analysis (TEA) reveal superior sustainability and cost efficiency compared with conventional sorbents, validating a circular economy approach that upcycles food waste into CO2 sorbents, which can, if needed, ultimately be reintegrated into the food system.