Template-Free Synthesis of Hollow CaO/Ca₂SiO₄ Nanoparticle as a Cyclically Stable High-Capacity CO₂ Sorbent

Abstract

Cyclically stable and highly effective CaO-based CO2 sorbents are crucial to calcium looping, which is a CO2-capture technique that offers an effective and feasible way to achieve the goal of carbon neutrality. With the goal of enhancing CO2-capture performance, a template-free synthetic route was reported in this work on the basis of the Kirkendall effect that yields hollow, Ca2SiO4-stabilized CaO nanoparticles. The hollow CaO/Ca2SiO4 nanoparticle features thin, nanometer-scale shells, large surface area, and a homogeneous elemental distribution, which are essential characteristics for high-performance CO2 sorbents. The synthetic sorbent with 10 mol % SiO2 offers superior and durable CO2 uptake during calcium looping. The capacity of CO2 capture of the synthetic sorbents still maintains 0.573 gCO2/gsorbent after the 20th cycle, exceeding that of other substances such as CaO/SiO2 synthesized via mechanical blending and CaCO3-derived sorbents by 195% and 290%, respectively. Detailed X-ray diffraction, N2 adsorption/desorption, transmission electron microscopy, and scanning electron microscopy analyses confirm that the unique hollow structure and thin shell of CaO/Ca2SiO4 nanoparticles are retained after the adsorption-desorption cycles. These results thus present an approach to obtain hollow nanostructured sorbents with better CO2 uptake performance, all without using templates or a high-temperature, long-term hydrothermal approach.