Bulk-scale production of individual graphene sheets is still challenging although several methodologies have been developed. We report here a rapid and cost-effective approach to reduction of graphene oxide (GO) using hydroxylamine as a reductant. We demonstrated that the reduction of GO with hydroxylamine could take place quickly under a mild condition, and the as-produced graphene sheet showed high electrical conductivity, fair crystalline state, and admirable aqueous dispersibility without using any stabilizing reagents. A mechanism for removal of epoxide and hydroxyl groups from GO by hydroxylamine has been proposed. Comparing with other reported methods, the reduction of GO with hydroxylamine should be a preferable route to bulk-scale production of the graphene because it is simple, efficient, and cost-effective.
Individual nanocomposite sheets of chemically reduced graphene oxide (CRG) and poly(N-vinyl pyrrolidone) (PVP), namely CRG/PVP, have been fabricated through a simple one-pot procedure. The structure and composition of the as-prepared CRG/PVP sheets were complementarily characterized using solid-state 13 C NMR, atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and other spectroscopic measurements, demonstrating that the PVP molecules were chemically grafted on the CRG surfaces. The electrical conductivity of the individual CRG/PVP sheets was measured at different levels of relative humidity (RH) using a conductive atomic force microscopy (CAFM) system, revealing that the electrical conductivity of a CRG/PVP sheet is sensitive to RH variation with a response time of a few seconds. Given the easy mass scale production and improved electrical conductivity, we envisage that the CRG/PVP nanocomposite sheets should have a broad spectrum of applications in electrical conductivity based sensors.
Assembly
from ultrasmall solution droplets follows a different
dynamic from that of larger scales. Using an independently controlled
microfluidic probe in an atomic force microscope, subfemtoliter aqueous
droplets containing polymers produce well-defined features with dimensions
as small as tens of nanometers. The initial shape of the droplet and
the concentration of solute within the droplet play significant roles
in the final assembly of polymers due to the ultrafast evaporation
rate and spatial confinement by the small droplets. These effects
are used to control the final molecular assembly in terms of feature
geometry and distribution and packing of individual molecules within
the features. This work introduces new means of control over molecular
assembly, bringing us closer to programmable synthesis for chemistry
and materials science. The outcomes pave the way for three-dimensional
(3D) nanoprinting in additive manufacturing.
Adsorbents
that are capable of controllable pollutants adsorption
and release without secondary pollution are attractive in water treatment.
Here, we propose eco-friendly CO2 as a trigger to switch
the charge states and collapse–expansion transition of giant
microgels consisting of hydrophilic acrylamide and hydrophobic 2-(diethylamino)ethyl
methacrylate and demonstrated the on–off, selective, and recyclable
adsorption of anionic dyes on microgels under CO2 stimulation.
Apart from easy-handling separation from the water by a simple filtration
process, the maximum adsorption capacity is as high as 821 mg g–1, and the adsorption isotherms and kinetics obeyed
Langmuir isotherm and the pseudo-second-order kinetics models, respectively.
The anionic dye can also be separated from the mixture solution using
CO2-treated microgels. Moreover, a wastewater treatment
prototype with microgel-packed column was fabricated. Under continuous
flow condition, the dye was removed and recovered by alternative bubbling
CO2 and flushing with aqueous alkali (pH 12). Thus, this
type of microgels with CO2-induced protonation–deprotonation
transition can serve as a cost-effective, environmentally friendly,
and efficient adsorbent for water purification applications.
Tunneling
nanotubes (TNTs) play an important role in cell–cell
communication. TNTs have been predominantly reported among cells in
monolayer culture. Using various imaging modalities, including scanning
electron microscopy (SEM) and laser scanning confocal microscopy (LSCM),
this work reports the finding of TNTs between cells within human mesenchymal
stem cell (MSC) spheroids. TNTs visualized by SEM are consistent in
size and geometry with those observed in cellular monolayer culture.
LSCM imaging of living spheroids confirms the presence of F-actin
filaments within the TNTs, which are known to maintain nanotube integrity.
In addition, LSCM revealed the distribution of F-actin fibers across
the entire spheroid body instead of being confined within individual
cells. Intracellular material transport by TNTs was tested in MSC
spheroids treated with cytochalasin D (CytoD), a known actin polymerization
inhibitor for disrupting TNT formation. CytoD treatment decreased
the transport of cytosolic material by at least four-fold compared
to untreated spheroids. To the best of our knowledge, this work represents
the first direct observation of TNTs within MSC spheroids. These findings
offer new physical insight into cellular interactions within spheroids,
providing structural information for increasing interests in spheroid-based
cell therapy.
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