Efforts to limit rising concentrations of CO₂ have motivated the development of negative emission technologies. Direct air capture (DAC) of CO₂ is one of the negative emissions technologies that has been proposed for the direct removal of CO₂ from the atmosphere. Phase-changing bis(iminonoguanidine) (BIG) sorbents have been developed for the direct air capture of CO₂. These phase changing sorbents, specifically glyoxal-bis(iminoguanidine) (GBIG), involve (1) CO₂ absorption with aqueous amino acid salts, such as K- or Na-glycinate to yield bicarbonate-rich solutions, (2) crystallization of the bicarbonate anions with a BIG solid, which regenerates the amino acid, and (3) solid-state CO₂ release from the carbonate crystals and BIG regeneration. Despite the promising potential of these materials, their structural evolution during the thermal regeneration of the BIG solids, chemical regeneration of the sodium or potassium glycinate solvents, and the crystallization behavior of CO₂-loaded BIG bicarbonate remain to be evaluated and understood in detail. The aim of this study is to probe these knowledge gaps. In situ wide-angle X-ray Scattering (WAXS) results show that CO₂ and water molecules in GBIG bicarbonate are simultaneously released in a single step during the thermal regeneration of the sorbent at 97 – 134 °C. In situ ATR-FTIR measurements showed that sodium glycinate and GBIG bicarbonate are simultaneously generated when GBIG, glycine, and sodium bicarbonate are reacted. The crystallization of GBIG bicarbonate from GBIG and CO₂-loaded monoethanolamine (MEA) occurs rapidly in the first 10 min of the reaction, as determined using in situ GI-SAXS measurements. The insights from these studies are essential for the scalable implementation of CO₂ capture technologies using these phase-changing sorbents.

中文翻译：

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利用相变胍碱直接捕获空气中的CO _2的混合吸收-结晶策略：Operando X射线散射和红外光谱测量的见解

限制CO ₂浓度上升的努力已经推动了负排放技术的发展。CO _2的直接空气捕获（DAC）是已提出的用于从大气中直接去除CO ₂的负排放技术之一。相变双（亚氨基胍）（BIG）吸附剂已被开发用于直接空气捕集CO ₂。这些相变吸附剂，特别是乙二醛-双（亚氨基胍）（GBIG），涉及（1）用氨基酸水溶液（例如K-甘氨酸或Na-甘氨酸盐）吸收CO ₂以产生富含碳酸氢盐的溶液，（2）含BIG固体的碳酸氢根阴离子可再生氨基酸，以及（3）固态CO ₂从碳酸盐晶体中释放出来并产生大的再生。尽管这些材料具有潜在的潜力，但是它们在BIG固体的热再生，甘氨酸钠或甘氨酸盐溶剂的化学再生以及装载CO _2的BIG碳酸氢盐的结晶行为期间的结构演变仍待评估和详细了解。这项研究的目的是探究这些知识差距。原位广角X射线散射（WAXS）结果表明，CO ₂在97 – 134°C的吸附剂热再生过程中，GBIG碳酸氢盐中的水和分子同时一步释放。原位ATR-FTIR测量表明，当GBIG，甘氨酸和碳酸氢钠反应时，会同时生成甘氨酸钠和GBIG碳酸氢盐。如使用原位GI-SAXS测量所确定的，在反应的前10分钟内，由GBIG和负载有CO _2的单乙醇胺（MEA）结晶出GBIG碳酸氢盐。这些研究的见解对于使用这些相变吸附剂的可扩展实施CO ₂捕集技术至关重要。