Understanding the Degradation
Pathway of the Pesticide,
Chlorpyrifos by Noble Metal Nanoparticles
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Abstract
Application of nanoparticles (NPs) in environmental remediation
such as water purification requires a detailed understanding of the
mechanistic aspects of the interaction between the species involved.
Here, an attempt was made to understand the chemistry of noble metal
nanoparticle–pesticide interaction, as these nanosystems are
being used extensively for water purification. Our model pesticide,
chlorpyrifos (CP), belonging to the organophosphorothioate group,
is shown to decompose to 3,5,6-trichloro-2-pyridinol (TCP) and diethyl
thiophosphate at room temperature over Ag and Au NPs, in supported
and unsupported forms. The degradation products were characterized
by absorption spectroscopy and electrospray ionization mass spectrometry
(ESI MS). These were further confirmed by ESI tandem mass spectrometry.
The interaction of CP with NP surfaces was investigated using transmission
electron microscopy, energy dispersive analysis of X-rays, Raman spectroscopy,
and X-ray photoelectron spectroscopy (XPS). XPS reveals no change
in the oxidation state of silver after the degradation of CP. It is
proposed that the degradation of CP proceeds through the formation
of AgNP–S surface complex, which is confirmed by Raman spectroscopy.
In this complex, the P–O bond cleaves to yield a stable aromatic
species, TCP. The rate of degradation of CP increases with increase
of temperature and pH. Complete degradation of 10 mL of 2 ppm CP solution
is achieved in 3 h using 100 mg of supported Ag@citrate NPs on neutral
alumina at room temperature at a loading of ∼0.5 wt %. The
effect of alumina and monolayer protection of NPs on the degradation
of CP is also investigated. The rate of degradation of CP by Ag NPs
is greater than that of Au NPs. The results have implications to the
application of noble metal NPs for drinking water purification, as
pesticide contamination is prevalent in many parts of the world. Study
shows that supported Ag and Au NPs may be employed in sustainable
environmental remediation, as they can be used at room temperature
in aqueous solutions without the use of additional stimulus such as
UV light