Triazene-Linked Porous Organic Polymers for Heterogeneous Catalysis and Pollutant Adsorption

Porous organic polymers (POPs) are highly promising materials for heterogeneous catalysis and pollutant adsorption from aqueous medium due to their high surface area, permanent porosity, monomer diversity, and synthetic versatility. In this work, two triazene-linked POPs were synthesized under mild reaction conditions, via the diazo-coupling reaction, between 1,3,5-tris(4-aminophenyl) triazine and benzidine (TAPT-Bd-POP) or 4,4′-diamino-[1,1′-biphenyl]-2,2′-disulfonic acid (TAPT-Bd(SO3H)2-POP), the latter containing intrapore sulfonic groups. These POPs, containing triazene (−N═N–NH−) linkages with interesting properties, have been overlooked as a method for organic polymer synthesis. The polymers exhibited BET average pore diameters of around 10 nm, BET surface areas of up to 133 ± 2.0 m2 g–1, and thermal stability of up to 333 °C. TAPT-Bd-POP and TAPT-Bd(SO3H)2-POP were evaluated as catalysts for the metal-free Henry, Knoevenagel, and multicomponent one-pot Biginelli reactions, between aromatic aldehydes and nitromethane, ethyl cyanoacetate, and urea/ethyl acetoacetate, respectively, with moderate to almost full conversions. Both POPs were further used as adsorbents for the removal of methylene blue, crystal violet, phenol red, phenol, Cu(II), and Cr(VI), with maximum adsorption capacities up to 953 ± 71 mg g–1 for the adsorption of methylene blue. These results show the versatility of these polymers for heterogeneous catalysis and environmental remediation.