A Hollow Microtubular Triazine- and Benzobisoxazole-Based Covalent Organic Framework Presenting Sponge-Like Shells...

In this paper we report the construction of a hollow microtubular triazine- and benzobisoxazole-based covalent organic framework (COF) presenting a sponge-like shell through a template-free [3+2] condensation of the planar molecules 2,4,6-tris(4-formylphenyl)triazine (TPT-3CHO) and 2,5-diaminohydroquinone dihydrochloride (DAHQ-2HCl). The synthesized COF exhibited extremely high crystallinity, a high surface area (ca. 1855 m²  g^-1 ), and ultrahigh thermal stability. Interestingly, a time-dependent study of the formation of the hollow microtubular COF having a sponge-like shell revealed a transformation from initial ribbon-like crystallites into a hollow tubular structure, and confirmed that the hollow nature of the synthesized COF was controlled by inside-out Ostwald ripening, while the non-interaction of the crystallites on the outer surface was responsible for the sponge-like surface of the tubules. This COF exhibited significant supercapacitor performance: a high specific capacitance of 256 F g^-1 at a current density of 0.5 A g^-1 , excellent cycling stability (98.8 % capacitance retention over 1850 cycles), and a high energy density of 43 Wh kg^-1 . Such hollow structural COFs with sponge-like shells appear to have great potential for use as high-performance supercapacitors in energy storage applications.