Fenton and Photo-Fenton Nanocatalysts Revisited from the Perspective of Life Cycle Assessment

Sara Feijoo,María Teresa Moreira,Carlos Vázquez-Vázquez,Lucía Fernández,Gumersindo Feijoo,Jorge González-Rodríguez

doi:10.3390/catal10010023

Sara Feijoo, María Teresa Moreira + Show 4 more

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https://doi.org/10.3390/catal10010023

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Abstract

This study provides an overview of the environmental impacts associated with the production of different magnetic nanoparticles (NPs) based on magnetite (Fe3O4), with a potential use as heterogeneous Fenton or photo-Fenton catalysts in wastewater treatment applications. The tendency of Fe3O4 NPs to form aggregates in water makes necessary their decoration with stabilizing agents, in order to increase their catalytic activity. Different stabilizing agents were considered in this study: poly(acrylic acid) (PAA), polyethylenimine (PEI) and silica (SiO2), as well as the immobilization of the magnetite-based catalysts in a mesoporous silica matrix, SBA-15. In the case of photo-Fenton catalysts, combinations of magnetite NPs with semiconductors were evaluated, so that magnetic recovery of the nanomaterials is possible, thus allowing a safe discharge free of NPs. The results of this study suggest that magnetic nanoparticles coated with PEI or PAA were the most suitable option for their applications in heterogeneous Fenton processes, while ZnO-Fe3O4 NPs provided an interesting approach in photo-Fenton. This work showed the importance of identifying the relevance of nanoparticle production strategy in the environmental impacts associated with their use.

Highlights

In the era of nanotechnology, there is a growing interest in the use of nanomaterials, which is largely attributed to their characteristic high specific surface and reactivity
The proposal of any process under development which aims at replacing more developed alternatives must clearly demonstrate the expected benefits, from the point of view of technological feasibility and cost, and of the environmental impacts associated with the process to be developed
What is the point if the global analysis shows that beyond the capability of certain NPs to degrade target chemicals with high performance, we are introducing higher environmental loads associated with the production of the nanocatalyst?

Summary

Introduction

In the era of nanotechnology, there is a growing interest in the use of nanomaterials, which is largely attributed to their characteristic high specific surface and reactivity In this regard, nanomaterials are emerging as an interesting alternative in multiple applications in substitution of bulk chemicals, from biomedical and clinical diagnosis to their use in the field of biochemical catalysis and environmental engineering. Advanced oxidation processes (AOPs) based on the use of NPs have shown great potential for the treatment of industrial wastewaters [1,2,3,4,5] These processes encompass the generation of highly reactive oxygen species (ROS), such as hydroxyl radicals (HO ), superoxide radicals (O2 − ) and singlet oxygen (1 O2 ), which are involved in the degradation of organic matter, generally leading to more biodegradable species with less environmental impact. While bulk Fe3 O4 is ferromagnetic, Fe3 O4 NPs are superparamagnetic, which provides them with a stronger magnetic response when exposed to Catalysts 2020, 10, 23; doi:10.3390/catal10010023 www.mdpi.com/journal/catalysts

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