A Study Aimed at Understanding the Use of Nanomaterial-Treated Filters …
105
Depending on the type and/or concentration of the metal ions, different degree of
aggregation is generated. It is surmised that the heavy metal ions are bound to the
nanoparticle through some combination of complexation to the carboxyl groups in
the citrate anion and nonspecific electrostatic interactions with the negatively charged
particle surface [16, 22, 23].
Incubating citrate-capped gold nanoparticles solutions with copper (II) ions can
be used efficiently as a colorimetric sensor. For example, concentration of 0.1 mM
copper (II) causes a very small redshift of the plasmon band of only 5 nm, from 524
to 529 nm, that continues to increase steadily as the concentration increases (Fig. 6).
The intermediate and final aggregate size responds steadily, linearly, and predictably
to the increased concentration of copper (II). This demonstrates that citrate-capped
gold nanoparticles are a suitable sensor for copper (II) ions.
On the other side, a concentration of 0.2 mM or lower zinc (II) has limited impact
on the gold nanoparticles plasmon band position (Fig. 7). Only when the concentration zinc (II) increases to 0.3 mM or higher, a significant plasmon band redshift was
recorded from 524 to 676 nm. This suggests that other factors influence the process
and will be reported at a later time.
Typically, citrate binds with the metal through a chelation bond, in which electrondonating from citrate to metal makes the central metal ion more electron rich [22].
The negatively charged oxygen atom of citrate’s carboxylate groups establishes a
coordination interaction with the metal ion [22, 23]. Citrate-capped gold nanoparticles had a greater sensitivity toward the copper (II) than zinc (II) as the colorimetric
sensor demonstrated an incremental visible color change (Fig. 7). These results are
in agreement with previous studies [24].
Heavy Metal Uptake on Gold Nanoparticle-Treated
Stainless-Steel Wool Filters
L-cysteine-capped gold nanoparticles-modified stainless-steel wool filters were incubated with heavy metal ions and evaluated for their sequestration and uptake capability. A visual comparison of the stainless-steel wool filters control and stainlesssteel wool filters decorated with L-cysteine-capped gold nanoparticles before and
after heavy metal ions sequestration is shown in Fig. 8. The color differences are
suggestive of an interaction between gold nanoparticles and heavy metal occurring.
Scanning electron microscopy and energy-dispersive X-Ray spectroscopy were
used to evaluate the heavy metal uptake (Fig. 9). Scanning electron microscopy
studies did not show any morphological changes of the stainless-steel wool treated
with gold nanoparticles.
Energy-dispersive X-Ray spectroscopy analysis was performed to evaluate chemical composition of the modified stainless-steel wool filters before and after zinc
(II) capture. A closer energy-dispersive X-Ray spectroscopy investigation of the
L-cysteine gold nanoparticle-treated stainless-steel wool incubated with zinc (II)
105
Depending on the type and/or concentration of the metal ions, different degree of
aggregation is generated. It is surmised that the heavy metal ions are bound to the
nanoparticle through some combination of complexation to the carboxyl groups in
the citrate anion and nonspecific electrostatic interactions with the negatively charged
particle surface [16, 22, 23].
Incubating citrate-capped gold nanoparticles solutions with copper (II) ions can
be used efficiently as a colorimetric sensor. For example, concentration of 0.1 mM
copper (II) causes a very small redshift of the plasmon band of only 5 nm, from 524
to 529 nm, that continues to increase steadily as the concentration increases (Fig. 6).
The intermediate and final aggregate size responds steadily, linearly, and predictably
to the increased concentration of copper (II). This demonstrates that citrate-capped
gold nanoparticles are a suitable sensor for copper (II) ions.
On the other side, a concentration of 0.2 mM or lower zinc (II) has limited impact
on the gold nanoparticles plasmon band position (Fig. 7). Only when the concentration zinc (II) increases to 0.3 mM or higher, a significant plasmon band redshift was
recorded from 524 to 676 nm. This suggests that other factors influence the process
and will be reported at a later time.
Typically, citrate binds with the metal through a chelation bond, in which electrondonating from citrate to metal makes the central metal ion more electron rich [22].
The negatively charged oxygen atom of citrate’s carboxylate groups establishes a
coordination interaction with the metal ion [22, 23]. Citrate-capped gold nanoparticles had a greater sensitivity toward the copper (II) than zinc (II) as the colorimetric
sensor demonstrated an incremental visible color change (Fig. 7). These results are
in agreement with previous studies [24].
Heavy Metal Uptake on Gold Nanoparticle-Treated
Stainless-Steel Wool Filters
L-cysteine-capped gold nanoparticles-modified stainless-steel wool filters were incubated with heavy metal ions and evaluated for their sequestration and uptake capability. A visual comparison of the stainless-steel wool filters control and stainlesssteel wool filters decorated with L-cysteine-capped gold nanoparticles before and
after heavy metal ions sequestration is shown in Fig. 8. The color differences are
suggestive of an interaction between gold nanoparticles and heavy metal occurring.
Scanning electron microscopy and energy-dispersive X-Ray spectroscopy were
used to evaluate the heavy metal uptake (Fig. 9). Scanning electron microscopy
studies did not show any morphological changes of the stainless-steel wool treated
with gold nanoparticles.
Energy-dispersive X-Ray spectroscopy analysis was performed to evaluate chemical composition of the modified stainless-steel wool filters before and after zinc
(II) capture. A closer energy-dispersive X-Ray spectroscopy investigation of the
L-cysteine gold nanoparticle-treated stainless-steel wool incubated with zinc (II)