Hydrazine-Hydrazide-Linked Covalent Organic Frameworks for Water Harvesting

We report a postsynthetic
strategy and its implementation to make
covalent organic frameworks (COFs) with irreversible hydrazide linkages.
This involved the synthesis of three 2D and 3D hydrazine-linked frameworks
and their partial oxidation. The linkage synthesis and functional
group transformationhydrazine and hydrazidewere evidenced
by 15N multi-CP-MAS NMR. In addition, the isothermal water
uptake profiles of these frameworks were studied, leading to the discovery
of one hydrazine-hydrazide-linked COF suitable for water harvesting
from air in arid conditions. This COF displayed characteristic S-shaped
water sorption profiles, a steep pore-filling step below 18% relative
humidity at 25 °C, and a total uptake capacity of 0.45 g g–1. We found that even small changes made on the molecular
level can lead to major differences in the water isotherm profiles,
therefore pointing to the utility of water sorption analysis as a
complementary analytical tool to study linkage transformations.

我们报道了一种可制备具有不可逆酰肼键共价有机框架（covalent organic frameworks, COFs）的后合成策略及其实施方法。该策略包含三种二维、三维肼键连接框架的合成，以及它们的部分氧化过程。通过15N多交叉极化魔角旋转核磁共振（15N multi-CP-MAS NMR）验证了键合合成与官能团转化——即肼基与酰肼基的转化。此外，我们对这些框架的等温吸水率曲线展开了研究，最终发现一款兼具肼键与酰肼键的COF，适用于干旱环境下从空气中集水。该COF呈现出典型的S型水吸附曲线：在25℃、相对湿度低于18%时存在陡峭的孔填充阶段，总吸附容量可达0.45 g·g⁻¹。我们发现，分子层面的微小改动即可导致水吸附等温曲线产生显著差异，这也证明了水吸附分析可作为研究键合转化的补充分析工具。