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
纺织工业是全球污染最为严重的行业之一，其主要污染成因为合成染料残余物随废水排放。当前用于去除废水中染料的部分工艺存在经济可行性低、难以大规模复现的缺陷。与此同时，固体废物的处置与降解同样构成严峻的环境问题，为其回收利用与降解策略带来了挑战。
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，本研究提出了一种可同时去除废水中染料并降解颗粒状固体废物的策略。该工艺的核心原理为利用固体颗粒残余物吸附水中溶解的染料，使吸附了染料的残余物与吸附剂本身均更易发生光降解。
本研究中，选用阴离子合成卟啉TPPS4（中位-四(4-磺酸苯基)卟啉，meso-tetrakis (4-sulfonatophenyl) porphyrin）作为模拟从水体中去除的光敏染料模型。本次研究的固体废物模型分别为纯聚乳酸（PLA），以及添加10 wt%热塑性酸（TPS）的聚乳酸复合材料。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复合材料中的吸附效率更高，而在纯PLA中的降解速度更快。卟啉的吸附可促进PLA与PLA/TPS复合材料的光降解。