Development of cement/rice husk ash-derived nano-silica for CO2 regeneration capture

Abstract

Several recent studies have proved the ability of cement-based materials to capture carbon dioxide (CO2) through carbonation. Yet, the capture capacity may decline over multiple cycles, reflecting the poor regeneration performance inherent in other calcium-based sorbent materials. Partial replacement of nano-sized silica (SiO2) could potentially enhance both CO2 capture capacity and regeneration performance of cement. While previous research has extensively proven the significant improvement in cement properties with nano-silica, limited studies have examined its impact on CO2 capture and regeneration performance. Therefore, this study investigates how partial replacement of nano-silica in cement paste samples affects CO2 capture capacity and regeneration performance. Nano-silica was synthesized from rice husk ash (RHA) through the precipitation method, aiming to utilize agricultural waste. Before synthesizing, the RHA was acid-leached and thermally treated. Cement samples were partially replaced with nano-silica in various percentages (0.00% to 3.00%) and cured for 7, 14, and 28 days. Using the one-factor design from response surface method (RSM), the cement/nano-silica samples’ composition was determined. Characterization and analysis confirmed successful synthesis of high-purity, amorphous silica nanoparticles with diameters below 50 nm via the precipitation method. Nano-silica significantly improved the properties of hardened cement samples, with a notable 34.77% increase in compressive strength achieved with 3.00% nano-silica replacement compared to other samples across curing durations. XRD patterns indicated that nano-silica promoted hydration reactions, resulting in increased peak intensity of the C-S-H phase. Moreover, SEM-EDX analysis revealed the morphological characteristics of C-S-H phase throughout the observed morphology, along with a decrease in the Ca/Si ratio with increasing percentage of nano-silica replacement. The study findings suggest that inclusion of nano-silica significantly enhanced CO2 capture and regeneration performance of cement at room temperature conditions, with maximal improvement observed at 3.00% nano-silica partial replacement and 28 days of curing, displaying approximately 493.76% increment over the reference sample during a 150-minute experimental test. However, at 800℃ experimental temperatures, the presence of nano-silica did not effectively enhance CO2 capture capacity but rather led to its deterioration, potentially due to structural modification of the C-S-H phase during thermal cycles.