8 research outputs found
The Primarily Undergraduate Nanomaterials Cooperative: A New Model for Supporting Collaborative Research at Small Institutions on a National Scale
The Primarily Undergraduate Nanomaterials Cooperative (PUNC) is an organization for research-active faculty studying nanomaterials at Primarily Undergraduate Institutions (PUIs), where undergraduate teaching and research go hand-in-hand. In this perspective, we outline the differences in maintaining an active research group at a PUI compared to an R1 institution. We also discuss the work of PUNC, which focuses on community building, instrument sharing, and facilitating new collaborations. Currently consisting of 37 members from across the United States, PUNC has created an online community consisting of its Web site (nanocooperative.org), a weekly online summer group meeting program for faculty and students, and a Discord server for informal conversations. Additionally, in-person symposia at ACS conferences and PUNC-specific conferences are planned for the future. It is our hope that in the years to come PUNC will be seen as a model organization for community building and research support at primarily undergraduate institutions
Interactive Forces between Sodium Dodecyl Sulfate-Suspended Single-Walled Carbon Nanotubes and Agarose Gels
Selective
adsorption onto agarose gels has become a powerful method
to separate single-walled carbon nanotubes (SWCNTs). A better understanding
of the nature of the interactive forces and specific sites responsible
for adsorption should lead to significant improvements in the selectivity
and yield of these separations. A combination of nonequilibrium and
equilibrium studies are conducted to explore the potential role that
van der Waals, ionic, hydrophobic, π–π, and ion–dipole
interactions have on the selective adsorption between agarose and
SWCNTs suspended with sodium dodecyl sulfate (SDS). The results demonstrate
that any modification to the agarose gel surface and, consequently,
the permanent dipole moments of agarose drastically reduces the retention
of SWCNTs. Because these permanent dipoles are critical to retention
and the fact that SDS–SWCNTs function as macro-ions, it is
proposed that ion–dipole forces are the primary interaction
responsible for adsorption. The selectivity of adsorption may be attributed
to variations in polarizability between nanotube types, which create
differences in both the structure and mobility of surfactant. These
differences affect the enthalpy and entropy of adsorption, and both
play an integral part in the selectivity of adsorption. The overall
adsorption process shows a complex behavior that is not well represented
by the Langmuir model; therefore, calorimetric data should be used
to extract thermodynamic information
Unique Toxicological Behavior from Single-Wall Carbon Nanotubes Separated via Selective Adsorption on Hydrogels
Over
the past decade, extensive research has been completed on
the potential threats of single-wall carbon nanotubes (SWCNTs) to
living organisms upon release to aquatic systems. However, these studies
have focused primarily on the link between adverse biological effects
in exposed test organisms on the length, diameter, and metallic impurity
content of SWCNTs. In contrast, few studies have focused on the bioeffects
of the different SWCNTs in the as-produced mixture, which contain
both metallic (m-SWCNT) and semiconducting (s-SWCNT) species. Using
selective adsorption onto hydrogels, high purity m-SWCNT and s-SWCNT
fractions were produced and their biological impacts determined in
dose–response studies with <i>Pseudokirchneriella subcapitata</i> as test organism. The results show significant differences in the
biological responses of <i>P. subcapitata</i> exposed to
high purity m- and s-SWCNT fractions. Contrary to the biological response
observed using SWCNTs separated by density gradient ultracentrifugation,
it is found that the high-pressure CO conversion (HiPco) s-SWCNT fraction
separated by selective adsorption causes increased biological impact.
These findings suggest that s-SWCNTs are the primary factor driving
the adverse biological responses observed from <i>P. subcapitata</i> cells exposed to our as-produced suspensions. Finally, the toxicity
of the s-SWCNT fraction is mitigated by increasing the concentration
of biocompatible surfactant in the suspensions, likely altering the
nature of surfactant coverage along SWCNT sidewalls, thereby reducing
potential physical interaction with algal cells. These findings highlight
the need to couple sample processing and toxicity response studies
Strongly Bound Sodium Dodecyl Sulfate Surrounding Single-Wall Carbon Nanotubes
NMR
techniques have been widely used to infer molecular structure,
including surfactant aggregation. A combination of optical spectroscopy,
proton NMR spectroscopy, and pulsed field gradient NMR (PFG NMR) is
used to study the adsorption number for sodium dodecyl sulfate (SDS)
with single-wall carbon nanotubes (SWCNTs). Distinct transitions in
the NMR chemical shift of SDS are observed in the presence of SWCNTs.
These transitions demonstrate that micelle formation is delayed by
SWCNTs due to the adsorption of SDS on the nanotube surface. Once
the nanotube surface is saturated, the free SDS concentration increases
until micelle formation is observed. Therefore, the adsorption number
of SDS on SWCNTs can be determined by the changes to the apparent
critical micelle concentration (CMC). PFG NMR found that SDS remains
strongly bound onto the nanotube. Quantitative analysis of the diffusivity
of SDS allowed calculation of the adsorption number of strongly bound
SDS on SWCNTs. The adsorption numbers from these techniques give the
same values within experimental error, indicating that a significant
fraction of the SDS interacting with nanotubes remains strongly bound
for as long as 0.5 s, which is the maximum diffusion time used in
the PFG NMR measurements