Environmental Engineering Reference
In-Depth Information
than 180× reuse). Zou et al.
242
reported the use of a polypyrrole-graphene composite-
coated hybrid iber for the SPME of phenols.
Magnetic graphene composites are also used as SPMEs. A graphene-based magnetic
nanocomposite was also used for the preconcentration of the ive carbamate pesticides,
including metolcarb, carbofuran, pirimicarb, isoprocarb, and diethofencarb from water
samples before feeding this to HPLC-DAD for their detection.
243
Here, the high adsorp-
tion capacity of the composite and the magnetic properties of the NPs, which aid in
the phase separation of the adsorbent from the sample solution, were utilized, which
helped save extra time required in traditional SPE. In a similar method, graphene-Fe
3
O
4
magnetic NP hybrids (graphene-Fe
3
O
4
magnetic NPs) were used as the SPME for the
detection of triazine herbicides such as atrazine, prometon, propazine, and prometryn in
environmental water samples with the aid of HPLC-DAD.
244
Extraction of neonicotinoid
using magnetic graphene NPs as adsorbent was reported by Wang and coworkers.
245
In this study, graphene-Fe
3
O
4
NPs were used to extract thiamethoxam, imidacloprid,
acetamiprid, and thiacloprid from water samples. Using HPLC, accurate determina-
tion of analytes at spiking levels of 0.5 and 5 ng/mL was done. Graphene-based mag-
netic nanocomposite (graphene-Fe
3
O
4
) was recently used as an effective adsorbent for
the preconcentration of various triazole fungicides such as myclobutanil, tebuconazole,
and hexaconazole from environmental water samples before feeding it to HPLC for their
detection.
246
Shi et al.
247
used a graphene-magnetite composite for enrichment and detection of
small molecules where the composite was used as a novel matrix for matrix-assisted
laser desorption/ionization-time-of-light-MS. A cyclodextrin-functionalized GO-Fe
3
O
4
nanocomposite was used as a tunable stationary phase in open-tubular capillary electro-
chromatography by Liang et al.
248
The composite showed excellent wettability, enhanced
stability against high ionic strength, suppressed electro-osmotic mobility, and less non-
speciic adsorption toward analytes compared with the native polydimethylsiloxane
microchip. Graphene-coated stainless-steel ibers were also used for microwave-assisted
headspace SPME of organochlorine pesticides in water samples recently.
249
34.2.5 Surface-Enhanced Raman Spectroscopy-Based Sensors
Graphene-based sensors utilizing surface-enhanced Raman spectroscopy (SERS)-based
sensing/detection protocols are another category of highly explored sensors. The Raman
signal enhancement obtained by using the graphenic composite is used for detecting the
analyte. This can occur either by enhancing the signal intensity or by removing the lumi-
nescent background of the spectrum to give a better signal. An ultrasensitive detection
strategy based on the SERS property of graphene-based materials for the detection of aro-
matic molecules was devised by Liu et al.
250
recently. Graphene ilms having anchored
Ag NPs were fabricated. In the composite, GO acts as the matrix that catches the aro-
matic molecule, and Ag NPs aid in the localized surface plasmon resonance-based SERS
property. The utility of the above hybrid system was illustrated using positively charged
crystal violet, negatively charged amaranth (a cosmopolitan genus of herbs), and neutral
phosphorus triphenyl as model molecules. Ren et al.
251
used a similar graphene-Ag NP
composite for the detection of folic acid. Ag NPs were anchored onto GO sheets via a self-
assembly method with the aid of poly(diallyldimethyl ammonium chloride) (PDDA) as
the functional macromolecule (Figure 34.5f through h). The hybrid showed excellent SERS
