Materials chemists play a strategic role in achieving ambitious global climate goals, including removing legacy CO₂ via direct air capture (DAC). Innovating diverse DAC materials will enable their effective use in varying conditions and improve our understanding of CO₂ capture mechanisms. In our current contribution, we have synthesized a family of homoleptic alkali tetraperoxotitanate materials (generally formulated A₄Ti(O₂)₄, A = Li, Na, or K) and studied their DAC reactivity. Synthesis was achieved with inexpensive reagents and >90% yields. We present the first single-crystal X-ray structures (five total) of A₄Ti(O₂)₄ compounds along with supplemental bulk characterization and computation. We compare their DAC behavior in simple ambient benchtop experiments, determining CO₂ uptake by combustion analysis of postcapture materials. The K analogue exhibited the most rapid and high-capacity DAC, 8.17 mmol CO₂/g sorbent, translating to nearly 3 mol CO₂ per mole Ti and reaching near maximum capacity in under 10 days. The Li and Na analogues exhibit delayed reactivity along with high DAC capacity (6.66 and 8.18 mmol of CO₂/g sorbent, respectively). Characterization of the DAC products via scanning electron microscopy shows phase separation of alkali-rich and Ti-rich regions in core–shell morphologies for the Na and Li analogues; this is discussed with respect to the role of titanium vs alkali in DAC. On the other hand, no phase separation was observed for the K analogue. In situ monitoring detailed the early-stage CO₂ capture behavior of the K analogue, reaching ∼50% of maximum capacity within 1 h. The differentiating behavior of the K analogue is attributed to its unique composition, containing four H₂O₂ lattice molecules in addition to the four O₂^– peroxide anions bonded to Ti^IV. While H₂O₂ (aq) alone does not exhibit CO₂ chemisorption, the basic environment of the A₄Ti(O₂)₄ lattice activates its rapid DAC, inspiring the future exploration of peroxosolvate materials for DAC.

中文翻译：

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用于高容量空气直接捕获二氧化碳的四过氧乙酸酯


材料化学家在实现雄心勃勃的全球气候目标方面发挥着战略作用，包括通过直接空气捕获 （DAC） 去除遗留的 CO₂。创新不同的 DAC 材料将使它们能够在不同的条件下有效使用，并提高我们对 CO₂ 捕获机制的理解。在我们目前的贡献中，我们合成了一族同源碱四过氧酸酯材料（通常表示为 A₄Ti（O₂）_4，A = Li、Na 或 K）并研究了它们的 DAC 反应性。使用廉价的试剂和>90%的产量实现合成。我们提出了 A₄Ti（_{O） 2}）₄ 化合物的第一个单晶 X 射线结构（总共五个）以及补充的体表征和计算。我们在简单的环境台式实验中比较了它们的 DAC 行为，通过捕获后材料的燃烧分析来确定 CO₂ 吸收。K 类似物表现出最快速和高容量的 DAC，即 8.17 mmol CO₂/g 吸附剂，转化为近 3 mol CO₂/mol Ti，并在 10 天内达到接近最大容量。Li 和 Na 类似物表现出延迟反应性以及高 DAC 容量（分别为 6.66 和 8.18 mmol/g 吸附剂的 CO₂）。通过扫描电子显微镜对 DAC 产物的表征显示，Na 和 Li 类似物的核壳形态中富碱和富 Ti 区域的相分离;这是关于钛与碱在 DAC 中的作用讨论的。另一方面，没有观察到 K 类似物的相分离。原位监测详细描述了 K 类似物的早期 CO₂ 捕获行为，在 1 小时内达到最大容量的 ∼50%。 K 类似物的区分行为归因于其独特的组成，除了与 Ti^IV 键合的四个 O₂^– 过氧化物阴离子外，还包含四个 H₂O₂ 晶格分子。虽然单独的 H₂O₂ （aq） 不会表现出 CO₂ 化学吸附，但 A₄Ti（O₂）₄ 晶格的基本环境激活了其快速 DAC，激发了未来对 DAC 用过氧化物溶解物材料的探索。