Wu Di, Xing Zhiwei, Guo Qing, Lai Zhuozhi, Yi Jiaming, Meng Qing-Wei, Wang Sai, Dai Zhifeng, Ma Shengqian, Sun Qi
Zhejiang Provincial Key Laboratory of Advanced Chemical Engineering Manufacture Technology, College of Chemical and Biological Engineering, Zhejiang University, Hangzhou, 310058, China.
Hangzhou Institute of Advanced Studies, Zhejiang Normal University, Hangzhou, 310015, China.
Angew Chem Int Ed Engl. 2025 Jul;64(27):e202503945. doi: 10.1002/anie.202503945. Epub 2025 May 5.
Nitric acid (HNO) is a vital industrial chemical, and its recovery from complex waste streams is essential for sustainability and resource optimization. This study demonstrates the effectiveness of bipolar covalent organic framework (COF) membranes with tunable ionic site distributions as a solution for this challenge. The membranes are fabricated by layering anionic COF nanosheets on cationic COF layers, supported by a porous substrate. The resulting membranes exhibit significant rectifying behavior, driven by the asymmetric charge polarity and the intrinsic electric field, which enhances HNO transport. The transmembrane diffusion coefficient of 2.74 × 10 cm s exceeds the self-diffusion rate of NO , leading to increased HNO flux and selectivity compared to the individual anionic and cationic COF membranes. The optimized bipolar membrane configuration achieves remarkable separation factors, ranging from 22 to 242,000 for HNO₃, in comparison to other solutes such as HCl, HSO, HPO, and various metal salts in an eight-component mixed waste stream. This results in a substantial increase in HNO₃ purity, from 12.5% to 94.1% after a single membrane separation. With the broad range of COF materials and the versatility of the proposed membrane design, this work represents a significant advancement in chemical separation technologies.
硝酸（HNO₃）是一种重要的工业化学品，从复杂废物流中回收硝酸对于可持续发展和资源优化至关重要。本研究证明了具有可调离子位点分布的双极共价有机框架（COF）膜可有效应对这一挑战。这些膜是通过在阳离子COF层上堆叠阴离子COF纳米片制备而成，并由多孔基材支撑。所得膜表现出显著的整流行为，由不对称电荷极性和固有电场驱动，这增强了HNO₃的传输。2.74×10⁻⁵ cm² s⁻¹的跨膜扩散系数超过了NO₃⁻的自扩散速率，与单独的阴离子和阳离子COF膜相比，导致HNO₃通量和选择性增加。与八组分混合废物流中的其他溶质（如HCl、H₂SO₄、H₃PO₄和各种金属盐）相比，优化后的双极膜配置实现了显著的分离因子，HNO₃的分离因子范围为22至242,000。这使得HNO₃纯度大幅提高，单次膜分离后从12.5%提高到94.1%。鉴于COF材料种类繁多以及所提出的膜设计的多功能性，这项工作代表了化学分离技术的重大进展。
