Influence of lithium precursors for Li4SiO4 based carbon capture

“Kim et al. [29] synthesized Li4SiO4 material from LiOH and fumed silicate by the solid-state reaction method. They reported that the synthesis temperature could be reduced to 600 °C due to the use of LiOH, and the obtained Li4SiO4 showed higher CO2 absorption capacity compared with those synthesized at 700 °C and 800 °C, which achieved 298 mg/g after 10 cycles. Wang et al. [55] synthesized Li4SiO4 with LiOH by the sol-gel technique and they found that LiOH-synthesized Li4SiO4 particles were primarily composed of porous grains, and the average grain size of Li4SiO4 prepared by the sol-gel method was much smaller than that synthesized by the solid-state reaction method.

Weng et al. [56] synthesized Li4SiO4 from LiNO3 as lithium precursor and tetraethyl orthosilicate (TEOS) as a silicon precursor by the sol-gel method. The CO2 absorption capacity of the obtained Li4SiO4 material increased with increasing temperature from 400 to 500 °C in 2% CO2. Bretado et al. [14] reported that the solid-state reaction method was more appropriate than the sol-gel method for the preparation of Li4SiO4 material when LiNO3 was used as the lithium precursor. However, Subha et al. [25] reported that the sol-gel method was superior to the solid-state reaction method for Li4SiO4 material prepared from LiNO3 and colloidal silica. This indicates that the most appropriate synthesis method depends on the lithium and silicon precursors simultaneously.

Compared with inorganic lithium precursors, organic lithium-containing materials seems more appropriate as the lithium precursor for the preparation of Li4SiO4 material. Yang et al. [19] used lithium acetate and lithium lactate to prepare novel Li4SiO4 materials by the impregnated suspension method. As shown in Figure 10, the two novel Li4SiO4 materials showed a bulgier morphology and more porous structure, compared with Li4SiO4 synthesized by the solid-state reaction method. Absorption capacities of Li4SiO4 material prepared from lithium acetate or lithium lactate as the lithium precursors were almost six times higher than that of a conventional Li4SiO4 material. Additionally, the CO2 absorption capacities and conversions of Li4SiO4 material prepared from lithium acetate or lithium lactate showed an incremental tendency over 40 cycles, and the conversion of Li4SiO4 prepared from lithium acetate was approximately 70% even in the last cycle, which was calculated according to Equation (8):


where XN is the conversion of Li4SiO4 during the Nth cycle, %; and m0 is the theoretical CO2 absorption capacity of Li4SiO4 material, which is 367 mg/g. Lee et al. [57] used Li and a Si-containing metal-organic framework (MOF) as the silicon precursor, and the prepared Li4SiO4 material was able to convert into Li4SiO4 thermally. The as-prepared material had a coral-like morphology, so the contact area between CO2 and Li4SiO4 material was enhanced, and the Li4SiO4 material showed higher CO2 absorption capacity than that prepared by the conventional solid-state reaction method.”

Figure 10. SEM images of three kinds of Li4SiO4 materials prepared with Li2CO3 (RS), lithium acetate (ORC) and lithium lactate (ORL) [19].”

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