CICECO - Aveiro Institute of Materials, Department of Chemistry , University of Aveiro, Campus Universitário de Santiago , 3810-193 Aveiro , Portugal.
Environ Sci Technol. 2019 Mar 5;53(5):2758-2767. doi: 10.1021/acs.est.8b05978. Epub 2019 Feb 20.
Chemisorbent materials, based on porous aminosilicas, are among the most promising adsorbents for direct air capture applications, one of the key technologies to mitigate carbon emissions. Herein, a critical survey of all reported chemisorbed CO species, which may form in aminosilica surfaces, is performed by revisiting and providing new experimental proofs of assignment of the distinct CO species reported thus far in the literature, highlighting controversial assignments regarding the existence of chemisorbed CO species still under debate. Models of carbamic acid, alkylammonium carbamate with different conformations and hydrogen bonding arrangements were ascertained using density functional theory (DFT) methods, mainly through the comparison of the experimental C and N NMR chemical shifts with those obtained computationally. CO models with variable number of amines and silanol groups were also evaluated to explain the effect of amine aggregation in CO speciation under confinement. In addition, other less commonly studied chemisorbed CO species (e.g., alkylammonium bicarbonate, ditethered carbamic acid and silylpropylcarbamate), largely due to the difficulty in obtaining spectroscopic identification for those, have also been investigated in great detail. The existence of either neutral or charged (alkylammonium siloxides) amine groups, prior to CO adsorption, is also addressed. This work extends the molecular-level understanding of chemisorbed CO species in amine-oxide hybrid surfaces showing the benefit of integrating spectroscopy and theoretical approaches.
基于多孔氨基硅的化学吸附材料是最有前途的直接空气捕集应用吸附剂之一，也是减少碳排放的关键技术之一。在此，通过重新审视和提供迄今为止文献中报道的不同 CO 物种的实验新证据，对所有报道的化学吸附 CO 物种进行了批判性调查，突出了关于化学吸附 CO 物种存在的有争议的分配，这些物种仍然存在争议。使用密度泛函理论 (DFT) 方法确定了氨基甲酸、不同构象和氢键排列的烷基铵氨基甲酸酯的模型，主要通过比较实验 C 和 N NMR 化学位移与计算得到的化学位移。还评估了具有可变数量的胺和硅醇基团的 CO 模型，以解释在受限条件下胺聚集对 CO 形态的影响。此外，还详细研究了其他不太常见的化学吸附 CO 物种（例如，烷基铵碳酸氢盐、双键合氨基甲酸和丙基硅基氨基甲酸酯），这主要是由于难以获得这些物种的光谱鉴定。在 CO 吸附之前，还存在中性或带电（烷基铵硅氧化物）胺基团。这项工作扩展了对胺-氧化物混合表面中化学吸附 CO 物种的分子水平理解，展示了整合光谱和理论方法的好处。
