Sustainable hierarchical porous silica supports from coal gasification slag for enhanced CO2 capture: Effects of weak acid modulation and mixed amine strategies

Efficient CO 2 capture is critical for mitigating climate change, and solid amine adsorbents have emerged as a promising solution. This study reports a sustainable strategy for developing high-performance solid amine adsorbents by valorizing coal gasification slag (CGS), an industrial waste byproduct, into hierarchical porous silica supports (X-SiO 2 ). A key innovation of this work lies in the use of weak-acid modulation (formic, acetic, and citric acids) to precisely tailor pore architecture. Among the resulting materials, the citric acid–modulated silica (CA-SiO 2 ) exhibits an exceptionally high specific surface area (447 m 2 /g) and pore volume (0.8 cm 3 /g), providing an optimal framework for uniform amine dispersion. To further enhance adsorption performance and overcome the stability limitations of conventional mono-amine systems, a mixed-amine strategy combining diethanolamine (DEA) and tetraethylenepentamine (TEPA) was introduced. Mechanistic investigations reveal that DEA suppresses TEPA aggregation through hydrogen-bonding interactions, thereby improving amine accessibility and CO 2 diffusion pathways. As a result, the optimized adsorbent (CA-30TEPA-30DEA) achieves a high CO 2 uptake of 5.07 mmol/g at 70 °C and retained 4.51 mmol/g after 20 adsorption–desorption cycles, representing a ∼ 10% enhancement in cyclic stability relative to the mono-amine counterpart. This work demonstrates the synergistic benefits of industrial waste valorization, pore structure engineering, and mixed-amine chemistry, offering a scalable and sustainable route toward next-generation solid adsorbents for carbon capture.