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.摘要 纺织工业为全球污染最为严重的行业之一，其主要污染来源为合成染料残渣随废水排放。当前用于去除废水中染料的部分工艺存在经济可行性偏低、难以大规模推广的缺陷。与此同时，固体废物的处置与降解亦为严峻的环境问题，给回收利用与降解策略的研发带来挑战。 鉴于部分染料具备光敏特性，且部分废弃固体材料具有多孔结构，本研究提出一种可同时实现废水中染料去除与颗粒状固体废物协同降解的策略。该工艺的核心原理为利用固体颗粒残渣作为吸附剂，吸附水中溶解的染料，使负载染料的残渣与吸附剂自身均更易发生光降解。 本研究中：选用阴离子合成卟啉TPPS4（meso-四(4-磺苯基)卟啉，meso-tetrakis (4-sulfonatophenyl) porphyrin）作为待脱除的光敏染料模型物；固体废物模型分别为纯聚乳酸（poly(lactic acid), PLA）以及添加10%质量分数热塑性淀粉（thermoplastic starch, TPS）的共混物。游离态与吸附态的卟啉经单日日光照射后均可发生降解。TPPS4在PLA/TPS共混物中的吸附效率更高，而在纯PLA中的降解速度更快。卟啉的吸附可促进PLA与PLA/TPS两者的光降解。