Porphyrin@Lignin nanoparticles: Reusable photocatalysts for effective aqueous degradation of antibiotics

The aqueous photocatalyzed degradation of trimethoprim (TMP) and sulfamethoxazole (SMX), highly prescribed antibiotics, often found in hospital wastewaters and/or surface/ground waters in high concentrations, is described, using a 400 W medium pressure mercury lamp as irradiation source, air as oxidant and a porphyrin based photocatalyst. The new photocatalyst was prepared by encapsulation of stable meso-tetra(2,6-dichlorophenyl)porphyrin photosensitizer into acetylated lignin nanoparticles, which are derived from a bio-based cellulose industry byproduct. This is a reusable stable catalyst (after at least 7 cycles, no loss of activity or degradation/leaching, was observed) capable of promoting the nearly complete degradation of TMP and SMX antibiotics, with unprecedented total organic carbon (TOC) removal, namely 75 % and 85 %, respectively. Mechanistic studies of these reactions, using singlet oxygen and radical scavengers, followed by HPLC-MS analysis allowed the identification of only two residual TMP photoproducts.