Trace-amount phenolphthalein surface-modified Na₂CO₃ for enhanced low-temperature dry SO₂ capture via altered product...

Effective control of SO₂ emissions is crucial for air quality and environmental protection. Non-regenerable dry flue gas desulfurization remains attractive for small boilers, low-temperature flue gas treatment, and water-scarce regions. However, developing highly active sorbents remains a critical challenge for practical applications. Sodium carbonate (Na₂CO₃) offers a theoretical SO₂ uptake nearly 1.6 times that of sodium bicarbonate (NaHCO₃), but its low reactivity and rapid surface passivation limit its practical application. Here, we report a simple, low-energy surface modification in which a trace amount of phenolphthalein (0.1 mol%) markedly enhances the SO₂ uptake by ∼530 % and increases sorbent utilization from 9.8 % to 62.5 %. The phenolphthalein-modified Na₂CO₃ (PP-Na₂CO₃) exhibited optimal performance at 130-150 °C under 7.9-14.7 vol% water vapor, showing robust adaptability under high SO₂ concentrations. Moreover, the optimized PP-Na₂CO₃ achieved an SO₂ uptake 1.84 times higher than that of NaHCO₃. These enhancements overcome the long-standing limitations of Na₂CO₃, underscoring its potential for practical application in low-temperature dry flue gas treatment. Based on structural and compositional characterization, mechanistic analysis shows that this enhancement is derived from the rearrangement of phenolphthalein molecules on the Na₂CO₃ surface, which introduces polar oxygen-containing functional groups and thereby forms a temperature-responsive functional active interface that enhances SO₂ and H₂O adsorption. Meanwhile, the interface promotes the formation of a Na₂SO₃-dominated product layer with a reticulated-wrinkled morphology, which mitigates pore blockage, enhances accessibility of unreacted cores, and thereby substantially improves sulfur conversion efficiency and sorbent utilization. This work provides insights for designing high-performance sorbents with functional organic-inorganic interfaces.