Luminescent Triazene-Based Covalent Organic Frameworks Functionalized with Imine and Azine: N2 and H2 Sorption and Efficient Removal of Organic Dye Pollutants

Design of adsorbents with high stability and efficiency to achieve rapid uptake and high capacity for dye pollutants is a key challenge in environmental remedies. Herein, we have design and synthesized three triazene-based imine and azine functionalized covalent organic frameworks (COFs 1-3) via the formation of imine bonds by the condensation of a flexible tripodal tri aldehyde (TFPT) with linear diamines. The COFs are characterized by elemental analysis, FTIR, solid-state NMR, TGA, FESEM, TEM, and DRS. They exhibit permanent porosity with high surface areas and N-2 uptake capacities of 540, 1600, and 2235 cc/g by COFs 1-3, respectively. They are found to be chemically and thermally stable and exhibit moderate hydrogen storage capacities. Photophysical studies reveal that COFs 1-3 exhibited low band gap values of 3.0, 2.5, and 2.25 eV, respectively, indicating their semiconducting nature. All three materials are highly luminescent, and their emission maxima are found to depend on the nature of the diamine linker. Further, COFs 1-3 are highly stable in water and function as robust adsorbents, as evidenced by their high rapid uptake capacity (>96%) toward anionic (MO, CR) and cationic (MB, CV) organic dye pollutants from their respective aqueous solutions (2.5 x 10(-5) M).