Attractive solution: Magnetic graphene nanoparticles for triazole extraction

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  • Published: Aug 16, 2012
  • Author: Steve Down
  • Channels: Sample Preparation
thumbnail image: Attractive solution: Magnetic graphene nanoparticles for triazole extraction

Magnetic solid-phase extraction

A recently developed magnetic nanocomposite material comprising graphene and iron oxide has been used for the solid-phase extraction of triazole fungicides from water.

One of the extraction techniques derived from solid-phase extraction (SPE) involves the use of magnetic particles which are mixed with the adsorbent to aid the separation process. Magnetic SPE eliminates any filtration and centrifugation steps that might be required when conventional SPE is carried out with loose extractant as opposed to a packed SPE cartridge. The technique has been applied successfully to the removal of a range of hazardous pollutants from environmental samples.

Adsorbents based on carbon, like activated carbon and carbon nanotubes, have been used extensively to date as adsorbents and the heavily exploited form of carbon known as graphene is also finding favour. Its hexagonal structure and pi-electron system are believed to be especially useful for trapping benzenoid compounds.

In the last few years, several research groups have succeeded in preparing magnetic nanocomposites based on graphene and one group has now used their own composition for the separation of triazole pesticides from various types of environmental water. Zhi Wang and colleagues from the Agricultural University of Hebei, China, described their process in the Journal of Separation Science.

Graphene grabs herbicides

Earlier this year, the group reported the synthesis of a nanocomposite material consisting of graphene and ferriferous oxide (Fe3O4) by a chemical precipitation method, before applying the material to the extraction of four neonicotinoid insecticides from water. They achieved recoveries of 96-110%. Now, they have used the same material for the removal of myclobutanil, tebuconazole and hexaconazole from water.

The process is simple. The magnetic nanoparticles are shaken in the aqueous sample in a glass vessel, then the dispersion is transferred to a centrifuge tube and a magnet is applied to the side of the glass to trap the particles. The remaining liquid is removed by pipette and the particles are extracted with acetone, then reconstituted in methanol for analysis of the triazoles by HPLC with UV detection.

The power of the graphene-iron oxide nanocomposite was illustrated by comparing its recovery with those of two other systems containing Fe3O4. For composites containing graphene oxide and multiwalled carbon nanotubes, the recoveries were 14.1-15.6% and 44.2-46.9%, respectively, but those of the graphene-Fe3O4 nanocomposite were 59.0-92.1% for the three herbicides.

In tests on standard solutions of the herbicides, the extraction conditions were optimised to find the best amount of sorbent, extraction time, solution pH and ionic strength. When these were established, they led to detection limits of 0.005-0.01 ng/mL and enrichment factors of 3600-5824.

The nanocomposite material was used to analyse water collected from a reservoir, river and the sea, after spiking with known amounts of the three herbicides. None of them were found in the seawater and the Fuping river water contained a low level of tebuconazole at 0.25 ng/mL. The reservoir water was contaminated with two of the herbicides, but at lower concentrations, with 0.05 and 0.08 ng/mL of myclobutanil and tebuconazole, respectively.

Recovery studies on these real samples, as opposed to standard solutions, confirmed the good performance of the graphene nanocomposite with values in the range 86-102%. The adsorbent was also recovered after desorption of the herbicides by a simple acetone wash, enabling it to be reused at least 20 times "without significant loss of the sorption capacity."

The simple, fast procedure and the high sensitivity of magnetic SPE using the graphene-Fe3O4 nanocomposite have demonstrated its effectiveness for the removal of triazole herbicides from water and it might also be extended to other environmental pollutants.

Related Links

Journal of Separation Science 2012, 46 (Article in Press): "The use of graphene-based magnetic nanoparticles as adsorbent for the extraction of triazole fungicides from environmental water"

Article by Steve Down

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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