MICHAEL MEISTELMAN¹, JAYDEEP ADHIKARY², ARIELA BURG³, DROR SHAMIR⁴, GREGORY GERSHINSKY⁵, DAN MEYERSTEIN^2,6, YAEL ALBO*^,1
*Corresponding author
1. Chemical Engineering, Biotechnology and Materials Department, Ariel University, Ariel, Israel
2. Chemical Sciences Department, Ariel University, Ariel, Israel
3. Chemical Engineering Department, Sami Shamoon College of Engineering, Beer-Sheva, Israel
4. Chemistry Department, Nuclear Research Centre Negev, Beer-Sheva, Israel
5. Chemistry Department, Bar-Ilan University, Ramat Gan, Israel
6. Chemistry Department, Ben-Gurion University, Beer-Sheva, Israel

Abstract

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.

INTRODUCTION

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),