Ag0 and Au0 nanoparticles encapsulated in sol-gel matrices as catalysts in reductive de-halogenation reactions
Halogenated pollutants have low solubility, are toxic, tend to accumulate in food chains and are the contaminates most often found in the subsurface environment. Various approaches to achieve their degradation have been applied, including bioremediation, chemical methods based on zero valent iron and bimetallic particles, and electro-catalysis. In this review we discuss our recent results concerning Ag0 and Au0 nanoparticles incorporated within SiO2 matrices via the sol-gel synthesis route as heterogeneous catalysts for the reductive de-halogenation of halogenated organic compounds by NaBH4. Matrices with different compositions were prepared in order to optimize the preparation procedure.
The reduction percentage and the product distribution are affected by the matrix composition and the reduction conditions; pH, substrate concentration and NaBH4 rate of addition. The role of the encapsulated metal nanoparticles on the reductive de-halogenation of halo-acetic acids is discussed.
An enormous number of halogenated organic compounds are routinely found in water, and are of great concern due to their bioaccumulation, toxicity and persistence (1).
They make up a large part of the emerging persistent organic pollutants and toxic compounds (2). These include polychlorinated biphenyls, polybrominated diphenyl ethers extensively used as brominated flame-retardants and disinfection by-products usually generated during the chlorine disinfection process (3). Various technologies have been developed to degrade these kinds of halogenated organic compounds to environmentally safe products, such as biodegradation (4), electrochemical methods (5),
zero-valent metal (6), iron-based bimetallic catalysts and UV irradiation (7). Even though, they are efficient catalysts for a variety of important processes, noble metal nanoparticles have not been used for the removal of halo-organic compounds found in waste-water. In recent years, noble metal nanoparticles have attracted tremendous attention due to their potential applications in various fields such as catalysis (8), sensors (9-13), optics (13) and fuel cells (14),