“Stereoscopic” 2D super-microporous phosphazene-based covalent organic framework: Design, synthesis and selective sorption towards uranium at high acidic condition

• Published in: Journal of hazardous materials Vol. 314; pp. 95 - 104
• Main Authors: Zhang, Shuang, Zhao, Xiaosheng, Li, Bo, Bai, Chiyao, Li, Yang, Wang, Lei, Wen, Rui, Zhang, Meicheng, Ma, Lijian, Li, Shoujian
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 15.08.2016
• Subjects: Construction; Covalence; Covalent organic frameworks; Hexachlorocyclotriphosphazene; Monomers; Selectivity; Separation; Solvethermal synthesis; Sorption; Synthesis; Uranium; Covalent organic frameworks; Uranium; Separation; Hexachlorocyclotriphosphazene; Solvethermal synthesis
• ISSN: 0304-3894; 1873-3336
• DOI: 10.1016/j.jhazmat.2016.04.031

[Display omitted] •Phosphorus element was first introduced into covalent organic frameworks (COFs).•Monomer in C3-like spatial configuration was first used to construct COF materials.•A new 2D super-microporous phosphazene-based sorbent (MPCOF) was synthesized.•Separation of U (VI) by MPCOF at high acidic media (up to 1M HNO3) was achieved.•Selectivity for U (VI) separation from multi-ion solution can reach unreported 92%. So far, only five primary elements (C, H, O, N and B) and two types of spatial configuration (C2–C4, C6 and Td) are reported to build the monomers for synthesis of covalent organic frameworks (COFs), which have partially limited the route selection for accessing COFs with new topological structure and novel properties. Here, we reported the design and synthesis of a new “stereoscopic” 2D super-microporous phosphazene-based covalent organic framework (MPCOF) by using hexachorocyclotriphosphazene (a P-containing monomer in a C3-like spatial configuration) and p-phenylenediamine (a linker). The as-synthesized MPCOF shows high crystallinity, relatively high heat and acid stability and distinctive super-microporous structure with narrow pore-size distributions ranging from 1.0–2.1nm. The results of batch sorption experiments with a multi-ion solution containing 12 co-existing cations show that in the pH range of 1–2.5, MPCOF exhibits excellent separation efficiency for uranium with adsorption capacity more than 71mg/g and selectivity up to record-breaking 92%, and furthermore, an unreported sorption capacity (>50mg/g) and selectivity (>60%) were obtained under strong acidic condition (1M HNO3). Studies on sorption mechanism indicate that the uranium separation by MPCOF in acidic solution is realized mainly through both intra-particle diffusion and size-sieving effect.