Double Environmental Benefit by the Removal of Photosensitizing Dyes from the Water Using Particulate Solid Waste

ABSTRACT Textile industries are among the most pollutant sectors in the world, mainly by the discard of synthetic dye residues in effluents. Some processes currently used for the removal of dyes from the effluents have the disadvantages of low economic viability and difficulty for reproducing on a large scale. In parallel, the disposal and the degradation of solid waste also constitute serious environmental problems that pose challenges for recycling and degradation strategies. Considering that some dyes have photosensitizing properties and some discarded solid materials are porous, the present study proposes a strategy for removal and concomitant degradation of effluent dyes and particulate solid wastes. The rationale of this process is the use of solid particulate residue to adsorb dyes dissolved in water making both the adsorbed residue and adsorbents more susceptible to photodegradation. In the present study: an anionic synthetic porphyrin TPPS4 (meso-tetrakis (4-sulfonatophenyl) porphyrin) was used as a model of photosensitizing dye to be removed from the water. The solid waste models were neat poly(lactic acid) (PLA) and mixed with 10 wt% of thermoplastic acid (TPS). The free and adsorbed porphyrins degraded by one-day exposure to sunlight. TPPS4 adsorbed more efficiently in PLA/TPS and degraded faster in neat PLA. Adsorption of the porphyrin promoted photodegradation of both PLA and PLA/TPS.