Facile synthesis of molten-salt promoted and hetero-element doped Li4SiO4 particles for efficient and stable CO2 capture

Abstract

The growing demand for efficient high-temperature CO₂ capture technologies is accelerating the search for durable and regenerable solid sorbents. Lithium orthosilicate (Li₄SiO₄) is a promising candidate due to its moderate regeneration temperature (<700 °C). However, traditional solid-state synthesis often results in severe particle sintering and poor cycling stability, while advanced wet-chemical approaches remain complex and costly. In this work, we propose a facile and scalable solid-state synthesis strategy that combines molten-salt promotion with hetero-element doping (Ti, Al, Fe, and Ce) to enhance the performance of Li₄SiO₄-based sorbents. Through systematic screening, Ti-doped Li₄SiO₄ (K-Li₄Si_0.95Ti_0.05O₄) emerged as the optimal composition, achieving a high CO₂ uptake of 0.3 g_CO2 g_sorbent⁻¹ and stable performance over 50 cycles. The selected sorbent was further processed into mechanically strong particles using a direct physical doping approach. The resulting K-Li₄Si_0.95Ti_0.05O₄ particles exhibited excellent CO₂ sorption capacity (0.29 g_CO2 g_sorbent⁻¹), rapid kinetics (0.2 g_CO2 (g_sorbent min)⁻¹, long-term cycling stability over 100 cycles (0.28 g_CO2 g_sorbent⁻¹) and sufficient mechanical strength (17 N). Mechanistic investigations using various in situ and ex situ characterization experiments revealed that Ti doping enhances performance through a synergistic mechanism by inducing lattice distortions to facilitate ionic migration and optimizing textural properties to promote CO₂ diffusion. This work demonstrates that the facile, physically-doped solid-state route can deliver sorbents with performance on par with those made by wet-chemical methods, while retaining key advantages in simplicity, cost, and scalability, making them highly attractive for industrial-scale carbon capture applications.