Two-dimensional porous porphyrin materials composed of robust tin(IV)-porphyrin linkages for photocatalytic wastewater remediation

Abstract

Porphyrin-based two-dimensional porous materials (SnP-H₂TCPP (1), SnP-ZnTCPP (2)) composed of robust Sn(IV)-porphyrin linkages have been synthesized by reacting trans-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). 1 and 2 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 1 and 2 exhibited greater thermal stability than SnP. The permanent porosity of 1 and 2 resulted in large specific surface areas (BET) of 210.0 m²g⁻¹ and 185.0 m²g⁻¹, respectively. Uniform spherical nanoplates with an average diameter in the range of 900−1000 nm were observed for 1, whereas a nanocomposite morphology was observed for 2, whose shape and size could not be specifically defined. Finally, the photodegradation performance of 1 and 2 was found to be 89% (K = 0.0179 min⁻¹) and 97% (K = 0.0246 min⁻¹) within 120 min, respectively, for the degradation of methylene blue (MB), and 50% (K = 0.0091 min⁻¹) and 60% (K = 0.0120 min⁻¹) within 75 min, respectively, for the tetracycline (TC) antibiotic. The enhanced catalytic photodegradation activity of 1 or 2 is attributed to the cooperation between the carboxylate-bearing porphyrin units and SnP.