EPR spectroscopy: not to be sniffed out in deodorization

Odour vie

Electron paramagnetic resonance spectroscopy has allowed researchers to study how nanoparticles can eliminate offensive household odours by removing the odour molecules at source rather than simply masking the bad smells.

Amit Singh, Vijay Krishna, Alexander Angerhofer and Brij Moudgil of the University of Florida, Gainesville, and Bao Do and Gavin MacDonald of Kimberly-Clark Corporation, Roswell, Georgia, explain how odour plays an important role in our lives. Some odours, such as perfumes are perhaps desirable, although not in all circumstances, others are most certainly undesirable, often arising from bacterial or fungal action on the skin, bodily and domestic waste, and other sources. Surprisingly, majority of malodorous compounds can be classified into one of three categories: sulfur-containing compounds (including thiols), nitrogen-containing compounds (specifically amines), and oxygen containing compounds (oxo-acids, aldehydes, alcohols, and ketones).

Smell destruction

Controlling odours usually involves simply masking these various compounds, particularly in the home environment. Although there are techniques for absorbing and filtering gases that can extract the malodorous from industrial installations and public places there are no simple and inexpensive ways to do so in the home. Some industrial methods involve catalytic degradation using transition metals, silica, zeolites and activated charcoal. The researchers hoped to evaluate copper nanoparticles supported on silica as a possible solution to domestic odours that would destroy the chemicals responsible at source.

The team used ethyl mercaptan as a typical odour compound to test their nanoparticles. They used electron paramagnetic resonance spectroscopy as well as measurements of surface area and pore size distribution to evaluate the effect of lower copper concentration on activity. Copper species preferentially adsorbed in the 20 angstrom pores of the silica support which are catalytically active in removing ethyl mercaptan as diethyl disulfide. They found that best performance was possible with 3% by weight of copper in which all the nanopores of that size are filled with isolated copper species. Higher loading led to cluster formation, which reduced efficacy.

Odour elimination

"The present study suggests that the nature of the copper species and their site of adsorption, as well as state of dispersion, are important parameters to be considered for catalytic removal of sulfur-containing compounds," the team explains. "These parameters are critical for designing high-performance catalytic copper-coated silica nanoparticles for applications such as deodorization, removal of sulfur compounds from crude oil, hydrogenation, and antimicrobial activity."

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