Ecofriendly Reduction of Methylene Blue with Polyurethane Catalyst

Abstract

A number of physical, chemical, and biological technologies have been developed to address the issue of synthetic dyes in wastewater. One of the important chemical methods involves reduction of these stringent pollutants into less hazardous products. In this study, a cross-linked polyurethane foam (CPUF) was prepared from toluene diisocyanate (TDI), tetraethylenepentamine (TEPA), and polycaprolactone diol (PCL; Mw: 1000 g/mole). To avoid harmful reducing agents, ecofriendly reduction of methylene blue (MB) was executed with CPUF as catalyst where ascorbic acid and fresh juice extracts were applied as reducing agents. The FTIR and SEM analysis confirmed the chemical composition and porous morphology of CPUF, respectively. The 100% reduction of MB was recorded in just 15 minutes with ascorbic acid and CPUF, while similar result was obtained in 37 minutes in blank experiment composed of only MB and ascorbic acid. Thus, catalytic role of CPUF in reduction process was proved. Fresh fruit extracts also participated in the reduction process, but rate of reaction was accelerated in the presence of CPUF. The reusability study of the catalyst supported its stability and efficiency. All the successful reduction processes followed 1st-order kinetics with highest apparent rate constant for ascorbic acid. Furthermore, phytotoxicity evaluation proved safe reduction of MB with 60% germination index. Hence, it can be concluded that catalytic role of CPUF has been established with safe and biodegradable reducing agents which can be extended to other redox processes.