2 research outputs found
Graphene Oxide Membranes with Strong Stability in Aqueous Solutions and Controllable Lamellar Spacing
Graphene oxide (GO) membranes become
emerging efficient filters
for molecular or ionic separation due to their well-defined two-dimensional
nanochannels formed by closely spaced GO sheets and tunable physicochemical
properties. The stability of GO membranes in aqueous solutions is
a prerequisite for their applications. Here we show a novel and easy
strategy for fabricating GO membranes with strong stability in aqueous
solutions and controllable lamellar spacing by simply doping with
partially reduced graphene oxide (prGO) sheets. With our prGO-doping
strategy, the interlayer stabilizing force in GO membranes is enhanced
due to the weakened repulsive hydration and enhanced π–π
attraction between GO sheets; as a result, the fabricated GO membranes
are featured with controllable lamellar spacing and extraordinary
stability in water or even strong acid and base solutions as well
as strong mechanical properties, which will expand the application
scope of GO membranes and provide ever better performances in their
applications with aqueous solution environments
Insights into the Effects of 2:1 “Sandwich-Type” Crown-Ether/Metal-Ion Complexes in Responsive Host–Guest Systems
In-depth investigations of the specific
ion-responsive characteristics
based on 2:1 “sandwich” structures and effects of crown
ether cavity sizes on the metal-ion/crown-ether complexation are systematically
performed with a series of PNIPAM-based responsive copolymers containing
similar contents of crown ether units with different cavity dimensions
(12-crown-4 (12C4), 15-crown-5 (15C5), 18-crown-6 (18C6)). The lower
critical solution temperature (LCST) values of copolymers in deionized
water shift to lower temperatures gradually when the crown ether contents
increase or the ring sizes decrease from 18C6 to 12C4. With increasing
the concentrations of alkali metal ions (Na<sup>+</sup>, K<sup>+</sup>, Cs<sup>+</sup>) or the contents of pendent crown ether groups,
the copolymers with different crown ether cavity sizes exhibit higher
selectivity and sensitivity to corresponding cations. Importantly,
the ion sensitivities of the copolymers in response to corresponding
alkali metal ions increase dramatically with an increase in the crown
ether cavity size. Interestingly, a linear relationship between the
crown ether cavity size and the diameter of corresponding cation for
the formation of stable 2:1 “sandwich” complexes is
found for the first time, from which the size of metal ions or other
guests that able to form 2:1 “sandwich” complexes with
crown ethers can be deduced. The results in this work are valuable
and useful for further developments and practical applications of
various crown-ether-based smart materials