Two-dimensional porous porphyrin materials composed of robust tin(<scp>iv</scp>)-porphyrin linkages for photocatalytic wastewater remediation

Porphyrin-based two-dimensional porous materials (SnP-H2TCPP, SnP-ZnTCPP) composed of robust Sn(IV)-porphyrin linkages have been synthesized by reacting <i>trans</i>-dihydroxo[5,10,15,20-tetraphenylporphyrinato]tin(IV) (SnP) with [5,10,15,20-tetrakis(4-carboxyphenyl)porphyrin] (H₂TCPP) and [5,10,15,20-tetrakis(4-carboxyphenyl)porphyrinato]zinc(II) (ZnTCPP), respectively. The strength of the interaction between the carboxylic acid group of the monomeric porphyrins (H₂TCPP and ZnTCPP) and the axial hydroxyl moiety of SnP enables the construction of highly stable framework materials, which were characterized by FT-IR, UV-vis, and emmission spectroscopy, powder XRD, elemental analysis, and thermogravimetric analysis (TGA). SnP-H2TCPP and SnP-ZnTCPP absorb visible light strongly over a wide range, demonstrating weak perturbation in the electronic ground state structures of the π-conjugated aromatic moieties compared to the starting monomeric units. TGA indicated that SnP-H2TCPP and SnP-ZnTCPP exhibited greater thermal stability than SnP. The permanent porosity of SnP-H2TCPP and SnP-ZnTCPP resulted in large specific surface areas (BET) of 210.0 m² g^-1 and 185.0 m² g^-1, respectively. Uniform spherical nanoplates with an average diameter in the range of 900-1000 nm were observed for SnP-H2TCPP, whereas a nanocomposite morphology was observed for SnP-ZnTCPP, whose shape and size could not be specifically defined. Finally, the photodegradation performance of SnP-H2TCPP and SnP-ZnTCPP was found to be 89% (<i>K</i> = 0.0179 min^-1) and 97% (<i>K</i> = 0.0246 min^-1) within 120 min, respectively, for the degradation of methylene blue (MB), and 50% (<i>K</i> = 0.0091 min^-1) and 60% (<i>K</i> = 0.0120 min^-1) within 75 min, respectively, for the tetracycline (TC) antibiotic. The enhanced catalytic photodegradation activity of SnP-H2TCPP or SnP-ZnTCPP is attributed to the cooperation between the carboxylate-bearing porphyrin units and SnP.