18 research outputs found
Fabrication of Anion-Exchange Polymer Layered Graphene–Melamine Electrodes for Membrane Capacitive Deionization
A novel
nitrogen-doped reduced graphene sponge composite (NRGS)
is fabricated by using melamine sponge to restrain the aggregation
of graphene sheets during reduction. The anion-exchange polymer layered
graphene composites (A-NRGS) are prepared by coating the surface of
the NRGS electrode with cross-linked polyÂ(vinyl alcohol) with quaternization
modification (C-qPVA). With the help of a melamine sponge to suppress
the agglomerate of graphene sheets, the NRGS exhibits a unique three-dimensional
(3D) interconnected porous structure with abundant nitrogen doping
of 5.2%. Its specific surface area is up to 241 m<sup>2</sup>/g. In
addition, the enhanced wettability of A-NRGS composites favors the
diffusion of ion from the electrolyte to electrode. Therefore, A-NRGS
composites have excellent electrochemical capacity (184 F/g). The
membrane capacitive deionization (MCDI) performance for A-NRGS electrode
(11.3 mg/g) is higher than that of pristine reduced graphene oxide
(RGO) (6.2 mg/g) and NRGS (8.6 mg/g) electrodes. All the results demonstrate
that A-NRGS composites can be a promising candidate for CDI and other
electrochemical applications
A Triblock Copolymer Design Leads to Robust Hybrid Hydrogels for High-Performance Flexible Supercapacitors
We
report here an intriguing hybrid conductive hydrogel as electrode
for high-performance flexible supercapacitor. The key is using a rationally
designed water-soluble ABA triblock copolymer (termed as IAOAI) containing
a central polyÂ(ethylene oxide) block (A) and terminal polyÂ(acrylamide)
(PAAm) block with aniline moieties randomly incorporated (B), which
was synthesized by reversible additional fragment transfer polymerization.
The subsequent copolymerization of aniline monomers with the terminated
aniline moieties on the IAOAI polymer generates a three-dimensional
cross-linking hybrid network. The hybrid hydrogel electrode demonstrates
robust mechanical flexibility, remarkable electrochemical capacitance
(919 F/g), and cyclic stability (90% capacitance retention after 1000
cycles). Moreover, the flexible supercapacitor based on this hybrid
hydrogel electrode presents a large specific capacitance (187 F/g),
superior to most reported conductive hydrogel-based supercapacitors.
With the demonstrated additional favorable cyclic stability and excellent
capacitive and rate performance, this hybrid hydrogel-based supercapacitor
holds great promise for flexible energy-storage device
A Triblock Copolymer Design Leads to Robust Hybrid Hydrogels for High-Performance Flexible Supercapacitors
We
report here an intriguing hybrid conductive hydrogel as electrode
for high-performance flexible supercapacitor. The key is using a rationally
designed water-soluble ABA triblock copolymer (termed as IAOAI) containing
a central polyÂ(ethylene oxide) block (A) and terminal polyÂ(acrylamide)
(PAAm) block with aniline moieties randomly incorporated (B), which
was synthesized by reversible additional fragment transfer polymerization.
The subsequent copolymerization of aniline monomers with the terminated
aniline moieties on the IAOAI polymer generates a three-dimensional
cross-linking hybrid network. The hybrid hydrogel electrode demonstrates
robust mechanical flexibility, remarkable electrochemical capacitance
(919 F/g), and cyclic stability (90% capacitance retention after 1000
cycles). Moreover, the flexible supercapacitor based on this hybrid
hydrogel electrode presents a large specific capacitance (187 F/g),
superior to most reported conductive hydrogel-based supercapacitors.
With the demonstrated additional favorable cyclic stability and excellent
capacitive and rate performance, this hybrid hydrogel-based supercapacitor
holds great promise for flexible energy-storage device
Thermoresponsive Melamine Sponges with Switchable Wettability by Interface-Initiated Atom Transfer Radical Polymerization for Oil/Water Separation
Here we have obtained a
temperature responsive melamine sponge with a controllable wettability
between superhydrophilicity and superhydrophobicity by grafting the
octadecyltrichlorosilane and thermoresponsive polyÂ(<i>N</i>-isopropylacrylamide) (PNIPAAm) onto the surface of melamine sponge
skeletons. The whole process included the silanization in which step
the rough surface with low surface energy and the NH<sub>2</sub> were
provided, and the atom transfer radical polymerization which ensured
the successful grafting of PNIPAAm onto the skeleton’s surface.
The product exhibits a good reversible switch between superhydrophilicity
and superhydrophobicity by changing the temperature below or above
the lower critical solution temperature (LCST, about 32 °C) of
PNIPAAm, and the modified sponge still retains a good responsiveness
after undergoing two temperature switches for 20 cycles. Simultaneously,
the functionalized sponges could be used to absorb the oil under water
at 37 °C, and they released the absorbed oil in various ways
under water at 20 °C, showing wide potential applications including
oil/water separation
Renewable Lignin-Based Xerogels with Self-Cleaning Properties and Superhydrophobicity
A novel dissocyanate-modified lignin xerogel is facilely prepared
using renewable lignin as precursors via a sol–gel process
and ambient pressure drying method. The xerogel possesses high performance
in self-cleaning and superhydrophobicity with no need for further
hydrophobic modification. Furthermore, the xerogel obtained can find
potential applications in absorbents, coatings, and scaffolds
H- and J‑Aggregation of Fluorene-Based Chromophores
Understanding
of H- and J-aggregation behaviors in fluorene-based polymers is significant
both for determining the origin of various red-shifted emissions occurring
in blue-emitting polyfluorenes and for developing polyfluorene-based
device performance. In this contribution, we demonstrate a new theory
of the H- and J-aggregation of polyfluorenes and oligofluorenes, and
understand the influence of chromosphere aggregation on their photoluminescent
properties. H- and J-aggregates are induced by a continuous increasing
concentration of the oligofluorene or polyfluorene solution. A relaxed
molecular configuration is simulated to illustrate the spatial arrangement
of the bonding of fluorenes. It is indicated that the relaxed state
adopts a 2<sub>1</sub> helical backbone conformation with a torsion
angle of 18° between two connected repeat units. This configuration
makes the formation of H- and J-aggregates through the strong π–π
interaction between the backbone rings. A critical aggregation concentration
is observed to form H- and J-aggregates for both polyfluorenes and
oligofluorenes. These aggregates show large spectral shifts and distinct
shape changes in photoluminescent excitation (PLE) and emission (PL)
spectroscopy. Compared with “isolated” chromophores,
H-aggregates induce absorption spectral blue-shift and fluorescence
spectral red-shift but largely reduce fluorescence efficiency. “Isolated”
chromophores not only refer to “isolated molecules”
but also include those associated molecules if their conjugated backbones
are not compact enough to exhibit perturbed absorption and emission.
J-aggregates induce absorption spectral red-shift and fluorescence
spectral red-shift but largely enhance fluorescence efficiency. The
PLE and PL spectra also show that J-aggregates dominate in concentrated
solutions. Different from the excimers, the H- and J-aggregate formation
changes the ground-state absorption of fluorene-based chromophores.
H- and J-aggregates show changeable absorption and emission derived
from various interchain interactions, unlike the β phase, which
has relatively fixed absorption and emission derived from an intrachain
interaction
Preparation of Photoresponsive Azo Polymers Based on Lignin, a Renewable Biomass Resource
Lignin-based
azo polymers are prepared from alkali lignin, a byproduct in spent
liquor from the pulping and papermaking industry, and their
structures and photochromic effects are characterized by elemental
analysis, Fourier transform infrared, <sup>1</sup>H nuclear magnetic
resonance, and ultraviolet–visible spectroscopy. Results show
that only the 2-(4-nitrophenyl azo)
phenol lignin-modified polymer (AL-azo-NO<sub>2</sub>) shows a significant
photochromic effect, and its photoresponsive behavior is evidently
slower than that
of the synthetic polymer with a similar azo chromophore. For the 2-(4-methoxyphenyl
azo) phenol lignin-modified polymer, its photoisomerization behavior
was expected to be similar
to that of azobenzene-type molecules, but its photoresponse is not
obvious. The abnormal photochromic effect of AL-azo polymers is related
to strong steric hindrance of lignin backbones. With addition of water
(poor solvent), AL-azo-NO<sub>2</sub> shrinks gradually, which prevents
azobenzene groups from isomerizing and results in a lower isomerization
efficiency at higher water contents. Preparation of lignin-based azo
polymers offers a novel source of azo polymers and provides a green
and sustainable pathway for value-added utilization of lignin biomass
recovered from the pulping industry
Fabrication of Lignosulfonate Vesicular Reverse Micelles to Immobilize Horseradish Peroxidase
Sodium lignosulfonate reverse micelles
(SLRMs) with vesicular structure
were prepared by self-assembling in ethanol–water media and
applied to encapsulate horseradish peroxidase (HRP). Results showed
that sodium lignosulfonate (SL) could not form SLRMs until the ethanol
content reached 63% when its initial concentration was 7.5 g L<sup>–1</sup>. Owing to strong electrostatic repulsion, solid spherical
SLRMs gradually swelled to stable vesicular structures with an average
size of 240 nm. The shell of the SLRM thickened when NaCl was added
to screen the electrostatic interaction. HRP can be effectively encapsulated
while retaining its activity in the hydrophilic core of a SLRM. When
hydrogen peroxide was added to initiate the catalytic activity of
HRP, SL molecules would be polymerized and the structure of SLRMs
would be fixed. Furthermore, HRP immobilized in polymerized SLRMs
showed high activity at a more acidic pH of 4 and at a lower optimal
temperature decrease of 35 °C compared to free HRP. SLRM allows
enzymes such as HRP to work at more acidic and lower temperature conditions
Conductivity Enhancement of Poly(3,4-ethylenedioxythiophene)/Lignosulfonate Acid Complexes via Pickering Emulsion Polymerization
PolyÂ(3,4-ethylenedioxythiophene)/lignosulfonate
acid (PEDOT/LS)
submicron particles are doped into a 3,4-ethylenedioxythiophene (EDOT)/water
mixture as a solid stabilizer to form a Pickering emulsion. The conductivity
of the new PEDOT/LS complexes prepared by Pickering emulsion polymerization
(PEDOT/LS-PEP) is improved by 2 orders of magnitude. The structure
and properties of PEDOT/LS-PEP are investigated by UV, FTIR, XRD,
XPS, DLS, optical microscope, four point probe meter, and surface
resistance tester. The results show that the average particle size
increases from 550 nm to 2.4 ÎĽm, and the PEDOT content in PEDOT/LS-PEP
is 3.5 times that in the original PEDOT/LS submicron particles, while
the structure of PEDOT/LS-PEP remains amorphous. Due to the enhancement
in conductivity, the coating film made by PEDOT/LS-PEP decreases the
surface resistance of glass from 10<sup>12</sup> to 10<sup>6</sup> Ω sq<sup>–1</sup>. These new PEDOT/LS-PEP complexes
meet the requirement of industrial antistatic materials well
Biobased Self-Growing Approach toward Tailored, Integrated High-Performance Flexible Lithium-Ion Battery
Here
we present an innovative, universal, scalable, and straightforward
strategy for cultivating a resilient, flexible lithium-ion battery
(LIB) based on the bacterial-based self-growing approach. The electrodes
and separator layers are integrated intrinsically into one unity of
sandwich bacterial cellulose integrated film (SBCIF), with various
active material combinations and tailored mechanical properties. The
flexible LIB thereof showcases prominent deformation tolerance and
multistage foldability due to the unique self-generated wavy-like
structure. The LTO|LFP (Li4Ti5O12 and LiFePO4) SBCIF-based flexible LIB demonstrates reliable
long-term electrochemical stability with high flexibility, by exhibiting
a high capacity retention (>95%) after 500 cycles at 1C/1C after
experiencing
a 10 000 bending/flattening treatment. The LTO|LFP SBCIF battery
subjected to a simultaneous bending/flattening and cycling experiment
shows an extraordinary capacity retention rate (>68%) after 200
cycles
at 1C/1C. The biobased self-growing approach offers an exciting and
promising pathway toward the tailored, integrated high-performance
flexible LIBs