10 research outputs found
Portable Visible-Light Photocatalysts Constructed from Cu<sub>2</sub>O Nanoparticles and Graphene Oxide in Cellulose Matrix
For
the first time, portable visible-light photocatalysts were
fabricated by in situ synthesizing Cu<sub>2</sub>O in the micropores
of regenerated cellulose (RC)/graphene oxide (GO) composite films,
in which the porous matrix was used as a microreactor for the formation
of Cu<sub>2</sub>O nanoparticles. Cu<sub>2</sub>O nanoparticles were
immobilized and evenly distributed in the RC matrix to excite and
generate free photoelectrons and electron holes, leading to the high
photodegradation efficiency against methyl orange dye under visible-light
irradiation. Moreover, the introduction of GO has dramatically improved
the photocatalytic activities of Cu<sub>2</sub>O nanoparticles in
the Cu<sub>2</sub>O/GO/RC nanocomposite films, leading to a significant
enhancement of the photodegradation rate from 2.0 to 6.5 mg h<sup>–1</sup> g<sub>cat</sub><sup>–1</sup>. In the Cu<sub>2</sub>O/GO/RC photocatalysts, Cu<sub>2</sub>O nanoparticles inside
the matrix tended to generate on the GO sheets, which transferred
the yielded photoelectrons to prevent local high potential zone generation
and to induce the chain degradation reaction at more points, leading
to the improvement of the photocatalyst activity. Moreover, the portable
photocatalysts could be easily recycled and reused, showing great
potential applications for wastewater purification by utilizing solar
energy
High-Strength Films Consisted of Oriented Chitosan Nanofibers for Guiding Cell Growth
Chitosan
has biocompatibility and biodegradability; however, the
practical use of the bulk chitosan materials is hampered by its poor
strength, which can not satisfy the mechanical property requirement
of organs. Thus, the construction of highly strong chitosan-based
materials has attracted much attention. Herein, the high strength
nanofibrous hydrogels and films (CS-E) were fabricated from the chitosan
solution in LiOH/KOH/urea aqueous system via a mild regenerating process.
Under the mild condition (ethanol at low temperature) without the
severe fluctuation in the system, the alkaline-urea shell around the
chitosan chains was destroyed, and the naked chitosan molecules had
sufficient time for the orderly arrangement in parallel manner to
form relatively perfect nanofibers. The nanofibers physically cross-linked
to form CS-E hydrogels, which could be easily oriented by drawing
to achieve a maximum orientation index of 84%, supported by the scanning
electron microscopy and two-dimensional wide-angle X-ray diffraction.
The dried CS-E films could be bent and folded arbitrarily to various
complex patterns and shapes. The oriented CS-E films displayed even
ultrahigh tensile strength (282 MPa), which was 5.6× higher than
the chitosan films prepared by the traditional acid dissolving method.
The CS-E hydrogels possessed hierarchically porous structure, beneficial
to the cell adhesion, transportation of nutrients, and removal of
metabolic byproducts. The cell assay results demonstrated that the
CS-E hydrogels were no cytotoxicity, and osteoblastic cells could
adhere, spread, and proliferate well on their surface. Furthermore,
the oriented CS-E hydrogels could regulate the directional growth
of osteoblastic cells along the orientation direction, on the basis
of the filopodia of the cells to extend and adhere on the nanofibers.
This work provided a novel approach to construct the oriented high
strength chitosan hydrogels and films
Translational Entropy and Dispersion Energy Jointly Drive the Adsorption of Urea to Cellulose
The
adsorption of urea on cellulose at room temperature has been
studied using adsorption isotherm experiments and molecular dynamics
(MD) simulations. The immersion of cotton cellulose into bulk urea
solutions with concentrations between 0.01 and 0.30 g/mL led to a
decrease in urea concentration in all solutions, allowing the adsorption
of urea on the cellulose surface to be measured quantitatively. MD
simulations suggest that urea molecules form sorption layers on both
hydrophobic and hydrophilic surfaces. Although electrostatic interactions
accounted for the majority of the calculated interaction energy between
urea and cellulose, dispersion interactions were revealed to be the
key driving force for the accumulation of urea around cellulose. The
preferred orientation of urea and water molecules in the first solvation
shell varied depending on the nature of the cellulose surface, but
urea molecules were systematically oriented parallel to the hydrophobic
plane of cellulose. The translational entropies of urea and water
molecules, calculated from the velocity spectrum of the trajectory,
are lower near the cellulose surface than in bulk. As urea molecules
adsorb on cellulose and expel surface water into the bulk, the increase
in the translational entropy of the water compensated for the decrease
in the entropy of urea, resulting in a total entropy gain of the solvent
system. Therefore, the cellulose–urea dispersion energy and
the translational entropy gain of water are the main factors that
drive the adsorption of urea on cellulose
MXene-Mediated Cellulose Conductive Hydrogel with Ultrastretchability and Self-Healing Ability
Constructing natural polymers such as cellulose, chitin,
and chitosan
into hydrogels with excellent stretchability and self-healing properties
can greatly expand their applications but remains very challenging.
Generally, the polysaccharide-based hydrogels have suffered from the
trade-off between stiffness of the polysaccharide and stretchability
due to the inherent nature. Thus, polysaccharide-based hydrogels (polysaccharides
act as the matrix) with self-healing properties and excellent stretchability
are scarcely reported. Here, a solvent-assisted strategy was developed
to construct MXene-mediated cellulose conductive hydrogels with excellent
stretchability (∼5300%) and self-healability. MXene (an emerging
two-dimensional nanomaterial) was introduced as emerging noncovalent
cross-linking sites between the solvated cellulose chains in a benzyltrimethylammonium
hydroxide aqueous solution. The electrostatic interaction between
the cellulose chains and terminal functional groups (O, OH, F) of
MXene led to cross-linking of the cellulose chains by MXene to form
a hydrogel. Due to the excellent properties of the cellulose–MXene
conductive hydrogel, the work not only enabled their strong potential
in both fields of electronic skins and energy storage but provided
fresh ideas for some other stubborn polymers such as chitin to prepare
hydrogels with excellent properties
Rubbery Chitosan/Carrageenan Hydrogels Constructed through an Electroneutrality System and Their Potential Application as Cartilage Scaffolds
In
the present work, the bulk and homogeneous composite hydrogels
were successfully constructed from positively charged chitosan (CS)
and negatively charged carrageenan (CG) in alkali/urea aqueous solution
via a simple one-step approach for the first time. An electroneutral
CS solution was achieved in alkali/urea, leading to a homogeneous
solution blended by CS and CG, which could not be realized in acidic
medium because of the agglomeration caused by polycation and polyanion.
Subsequently, the CS/CG composite hydrogels with multiple cross-linked
networks were prepared from blend solution by using epichlorohydrin
(ECH) as the cross-linking agent. The composite hydrogels exhibited
hierarchically porous architecture, excellent mechanical properties
as well as pH- and salt-responsiveness. Importantly, the composite
hydrogels were successfully applied for spreading ATDC5 cells, showing
high attachment and proliferation of cells. The results of fluorescent
micrographs and scanning electronic microscope images revealed that
the CS/CG composite hydrogels enhanced the adhesion and viability
of ATDC5 cells. The alcian blue staining, glycosaminoglycan quantification,
and real-time PCR analysis proved that the CS/CG composite hydrogels
could induce chondrogenic differentiation of ATDC5 cells in vitro,
exhibiting great potential for application in cartilage repair. This
work provides a facile and fast fabrication pathway for the construction
of ampholytic hydrogel from polycation and polyanion in an electroneutrality
system
Intermolecular Interaction and the Extended Wormlike Chain Conformation of Chitin in NaOH/Urea Aqueous Solution
The
intra- and intermolecular interactions of chitin in NaOH/urea
aqueous system were studied by a combination of NMR measurements (including <sup>13</sup>C NMR, <sup>23</sup>Na NMR, and <sup>15</sup>N NMR) and differential
scanning calorimetry. The results revealed that the NaOH and chitin
formed a hydrogen-bonded complex that was surrounded by the urea hydrates
to form a sheath-like structure, leading to the good dissolution.
The optimal concentration range, in which chitin was molecularly dispersed
in NaOH/urea aqueous, was found to investigate the chain conformation
in the dilute solution with a combination of static and dynamic light
scattering. The weight-average molecular weight (<i>M</i><sub>w</sub>), radii of gyration (⟨<i>R</i><sub>g</sub>⟩<sub><i>z</i></sub>), and hydrodynamic radii
(⟨<i>R</i><sub>h</sub>⟩<sub><i>z</i></sub>) values of chitin were determined, and the structure-sensitive
parameter (ρ) and persistent length (<i>L</i><sub>p</sub>) were calculated to be >2.0 and ∼30 nm, respectively,
suggesting an extended wormlike chain conformation. The visualized
images from TEM, cryo-TEM, and AFM indicated that, chitin nanofibers
were fabricated from the parallel aggregation of chitin chains in
NaOH/urea system. This work would provide a theoretical guidance for
constructing novel chitin-based nanomaterials via “bottom-up”
method at the molecular level
Dissolution and Metastable Solution of Cellulose in NaOH/Thiourea at 8 °C for Construction of Nanofibers
To
develop a facile approach for the dissolution of cellulose,
a novel solvent (9.3 wt % NaOH/7.4 wt % thiourea aqueous solution)
was used, for the first time, to dissolve cellulose within 5 min at
8 °C. The results of NMR and Raman spectra demonstrated that
stable thiourea···OH<sup>–</sup> complexes were
formed through strong hydrogen bonds in NaOH/thiourea at room temperature.
Moreover, the strength of the hydrogen bonds in thiourea···OH<sup>–</sup> complexes was much higher than that in urea···OH<sup>–</sup> complexes, and the number of thiourea···OH<sup>–</sup> complexes increased significantly in 9.3 wt % NaOH/7.4
wt % thiourea compared to that in 9.5 wt % NaOH/4.5 wt % thiourea,
which dissolved cellulose at −5 °C, leading to the dissolution
of cellulose at a relatively high temperature (8 °C). The cellulose
that dissolved at such a high temperature was metastable. The results
of dynamic light scattering and transmission electron microscope experiments
confirmed that the extended cellulose chains and their aggregates
coexisted in the dilute cellulose solution. Interestingly, stiff cellulose
chains could be self-assembled in parallel to form nanofibers in the
metastable cellulose solution, from which cellulose microspheres consisting
of nanofibers could be easily produced by inducing heating. This work
not only proposed a novel method for the dissolution of cellulose
in aqueous system at temperatures over 0 °C but also opened up
a new pathway for the construction of nanofibrous cellulose materials
Effects of Chitin Whiskers on Physical Properties and Osteoblast Culture of Alginate Based Nanocomposite Hydrogels
Novel nanocomposite hydrogels composed
of polyelectrolytes alginate
and chitin whiskers with biocompatibility were successfully fabricated
based on the pH-induced charge shifting behavior of chitin whiskers.
The chitin whiskers with mean length and width of 300 and 20 nm were
uniformly dispersed in negatively charged sodium alginate aqueous
solution, leading to the formation of the homogeneous nanocomposite
hydrogels. The experimental results indicated that their mechanical
properties were significantly improved compared to alginate hydrogel
and the swelling trends were inhibited as a result of the strong electrostatic
interactions between the chitin whiskers and alginate. The nanocomposite
hydrogels exhibited certain crystallinity and hierarchical structure
with nanoscale chitin whiskers, similar to the structure of the native
extracellular matrix. Moreover, the nanocomposite hydrogels were successfully
applied as bone scaffolds for MC3T3-E1 osteoblast cells, showing their
excellent biocompatibility and low cytotoxicity. The results of fluorescent
micrographs and scanning electronic microscope (SEM) images revealed
that the addition of chitin whiskers into the nanocomposite hydrogels
markedly promoted the cell adhesion and proliferation of the osteoblast
cells. The biocompatible nanocomposite hydrogels have potential application
in bone tissue engineering
Intermolecular Interactions and 3D Structure in Cellulose–NaOH–Urea Aqueous System
The dissolution of cellulose in NaOH/urea
aqueous solution at low
temperature is a key finding in cellulose science and technology.
In this paper, <sup>15</sup>N and <sup>23</sup>Na NMR experiments
were carried out to clarify the intermolecular interactions in cellulose/NaOH/urea
aqueous solution. It was found that there are direct interactions
between OH<sup>–</sup> anions and amino groups of urea through
hydrogen bonds and no direct interaction between urea and cellulose.
Moreover, Na<sup>+</sup> ions can interact with both cellulose and
urea in an aqueous system. These interactions lead to the formation
of cellulose–NaOH–urea–H<sub>2</sub>O inclusion
complexes (ICs). <sup>23</sup>Na relaxation results confirmed that
the formation of urea–OH<sup>–</sup> clusters can effectively
enhance the stability of Na<sup>+</sup> ions that attracted to cellulose
chains. Low temperature can enhance the hydrogen bonding interaction
between OH<sup>–</sup> ions and urea and improve the binding
ability of the NaOH/urea/H<sub>2</sub>O clusters that attached to
cellulose chains. Cryo-TEM observation confirmed the formation of
cellulose–NaOH–urea–H<sub>2</sub>O ICs, which
is in extended conformation with mean diameter of about 3.6 nm and
mean length of about 300 nm. Possible 3D structure of the ICs was
proposed by the M06-2X/6-31+G(d) theoretical calculation, revealing
the O3H···O5 intramolecular hydrogen bonds could remain
in the ICs. This work clarified the interactions in cellulose/NaOH/urea
aqueous solution and the 3D structure of the cellulose chain in dilute
cellulose/NaOH/urea aqueous solution
Mechanically Strong Multifilament Fibers Spun from Cellulose Solution via Inducing Formation of Nanofibers
Mechanically strong
cellulose fibers spun with environmentally
friendly technology have been under tremendous consideration in the
textile industry. Here, by inducing the nanofibrous structure formation,
a novel cellulose fiber with high strength has been designed and spun
successfully on a lab-scale spinning machine. The cellulose–NaOH–urea
solution containing 0.5 wt % LiOH was regenerated in 15 wt % phytic
acid/5 wt % Na<sub>2</sub>SO<sub>4</sub> aqueous solution at 5 °C,
in which the alkali–urea complex as shell on the cellulose
chain was destroyed, so the naked stiff macromolecules aggregated
sufficiently in a parallel manner to form nanofibers with apparent
average diameter of 25 nm. The cellulose fibers consisting of the
nanofibers exhibited high degree of orientation with Herman’s
parameter of 0.9 and excellent mechanical properties with tensile
strength of 3.5 cN/dtex in the dry state and 2.5 cN/dtex in the wet
state, as well as low fibrillation. This work provided a novel approach
to produce high-quality cellulose multifilament with nanofibrous structure,
showing a great potential in the material processing