Shunli Liu

Hierarchical alginate biopolymer papers produced via lanthanide ion coordination

Inspired by the heterogeneous architectures of biological composites, mimicking the hierarchical structure of nacre is a powerful strategy to construct high-performance materials. This paper presents a lightweight and nacre-like hierarchical paper which was fabricated via lanthanide ion coordination. Sodium alginate (SA) biopolymers and lanthanide ions (Nd3+, Gd3+, Ce3+ and Yb3+) were used as ideal building blocks and connection points, respectively. SA biopolymers and lanthanide ions rapidly self-assembled into an aligned hydrogel. The synthesized hydrogel was subsequently dried to form layered alginate-based papers. The formation mechanism of the layered paper was investigated and demonstrated that lanthanide ion coordination can produce the hierarchical structure. The as-prepared layered SA–Nd(III) nanopaper exhibited a high strength of 124.2 ± 5.2 MPa, toughness of 8.2 ± 0.4 MJ m−3, and Youngs modulus of 5.2 ± 0.2 GPa, as well as excellent resistance to solvents. Owing to their outstanding mechanical properties and easy and fast fabrication, the layered SA–Nd(III) papers demonstrated a potential application in the fields of biomaterials. This new strategy based on lanthanide ion coordination, can also be used to construct integrated, high-performance, and biopolymer materials.

Green synthesis of oriented xanthan gum–graphene oxide hybrid aerogels for water purification

Three-dimensional xanthan gum (XG)/graphene oxide (GO) hybrid aerogels were fabricated by ice crystal templating without using chemical modifiers. The hybrid aerogels were prepared by the stirring of xanthan gum-graphene oxide hybrid solution, followed by freezing at low temperature and finally by freeze-drying. The whole preparation could be completed within 12h without producing any contamination and thus considered a fast, simple, economical, and green method for aerogel fabrication. XG/GO hybrid aerogels possessed different hierarchical pore structures because of various freezing temperatures. A network composed of co-aligned pore channels was obtained at a freezing temperature of -40°C. The as-prepared hybrid aerogels exhibited stability and excellent adsorption capacity for organic dyes and heavy metal ions. Therefore, these aerogels could be used as efficient adsorbents in water purification. This study provided a basis for the cost-effective and large-scale commercial production of high-performance graphene oxide-based aerogels for water purification.

Lanthanide ions-induced formation of hierarchical and transparent polysaccharide hybrid films

Nacre-like hybrid films based on N-succinyl chitosan (NSC), sodium alginate (SA) and lanthanide ions were fabricated via coordination interactions. In this work, the binary building blocks (NSC and SA) were self-assembled into aligned hydrogel films by coordination with lanthanide ions, and hierarchical NSC-SA hybrid films were obtained upon drying. Two species of lanthanide ions (Gd3+ and Yb3+) were used to fabricate the hierarchical NSC-SA hybrid films. The as-prepared NSC-SA hybrid films exhibit high tensile strength and stability. The tensile strength and toughness of as-prepared hybrid films reach 122.10MPa and 3.89MJm-3, respectively. Meanwhile, the well-aligned lamellar microstructures also exhibit a good light transmittance. The highest light transmittance reaches 92% for NSC-SA hybrid films at 760nm. This fabrication method for hierarchical NSC-SA hybrid films is innovative due to the utilization of rare earth coordination bonding, and can serve as the basic strategy for the construction of high-performance composites in the near future.

Glycogen-based self-healing hydrogels with ultra-stretchable, flexible, and enhanced mechanical properties via sacrificial bond interactions

The development of hydrogel materials with enhanced mechanical properties is the primary focus in designing autonomous self-healable hydrogel materials. Here, we present a facile and cost-effective method for the autonomous self-healing hydrogel based on Glycogen (Gly/PAA-Fe3+) with enhanced mechanical properties by simple insertion of ferric ions in the physically cross-linked network via metal-ligand interactions. This dual physically cross-linked hydrogel has an excellent elongation at break and self-healing properties due to the dynamic ionic cross-linking point. This work will encourage researchers to focus on this facile technique for the synthesis of self-healing hydrogel materials with enhanced mechanical properties.

Characterization of Xanthan Gum-based Hydrogel with Fe3+ Ions Coordination and Its Reversible Sol-gel Conversion

Since redox-responsive hydrogels have a wide range of applications especially in biochemistry, such as drug release and biosensors, a kind of redox-responsive hydrogel was fabricated based on iron which has two stable oxidation states, while xanthan gum (XG) was selected as a matrix. In this work, characterization of XG-based hydrogel with Fe3+ ions coordination and its reversible sol-gel conversion property were studied. Xanthan gum solutions with different concentrations were coordinated in situ with constant trivalent iron ions concentration to form hydrogels under ambient temperature. The chemical features of XG-based hydrogels were characterized by Fourier transform infrared spectroscopy (FT-IR) and ultraviolet visible light spectrum (UV-vis), while scanning electron microscope (SEM) was used to observed the morphologies of XG-based hydrogels cross-sections. In addition, the mechanical properties, thermal stability and swelling behavior of xanthan gum hydrogels were also investigated, respectively. The results showed that xanthan gum hydrogels possessed relatively uniform layered structure, in addition to possessing enhanced mechanical strength and excellent swelling behavior. Furthermore, the sol-gel conversion of XG-based hydrogel could be realized by UV light in the presence of sodium lactate. The process of changes in viscosity was studied. The result indicated that the XG-based hydrogel could be recycled and these characteristic studies may be of reference for future use of xanthan gum hydrogels in the field of biomedical materials or sensors.

Characterization and study of luminescence enhancement behaviour of alginate-based hydrogels

Lanthanide luminescence could be quenched by water or high frequency vibrations, which seriously limit the application of luminescent composites, especially hydrogels based on lanthanides. Here, luminescent hydrogels were fabricated by introducing 5-sulfosalicylic acid molecules into a hybrid system which stemmed from the self-assembly of sodium alginate with terbium ions (Tb3+). The shape of the enhanced luminescent hydrogels was not limited, as both layered and spherical hydrogels can be prepared. The morphology and luminescence properties of the hydrogels were thereafter studied. The results showed that the as-prepared alginate hydrogels exhibited clearly identified green emissions under ultraviolet radiation through the metal coordination interactions with the assembled alginate, while the luminescence intensity of the alginate hydrogels increased with increasing reaction time between the alginate and Tb3+ ions. Even, when dried, the hydrogels still exhibited enhanced luminescence, which might be used twice. The results demonstrated that 5-sulfosalicylic acid synergistic terbium–polymer self-assembly is an effective approach to fabricate luminescent composites containing terbium complexes.

A Conductive Self-Healing Double Network Hydrogel with Toughness and Force Sensitivity

Mechanically tough and electrically conductive self-healing hydrogels may have broad applications in wearable electronics, health-monitoring systems, and smart robotics in the following years. Herein, a new design strategy is proposed to synthesize a dual physical cross-linked polyethylene glycol/poly(acrylic acid) (PEG/PAA) double network hydrogel, consisting of ferric ion cross-linked linear chain extensions of PEG (2,6-pyridinedicarbonyl moieties incorporated into the PEG backbone, PEG-H2 pdca) as the first physical network and a PAA-Fe3+ gel as the second physical network. Metal-ion coordination and the double network structure enable the double network hydrogel to withstand up to 0.4 MPa tensile stress and 1560 % elongation at breakage; the healing efficiency reaches 96.8 % in 12 h. In addition, due to dynamic ion transfer in the network, the resulting hydrogels exhibit controllable conductivity (0.0026-0.0061 S cm-1 ) and stretching sensitivity. These functional self-healing hydrogels have potential applications in electronic skin. It is envisioned that this strategy can also be employed to prepare other high-performance, multifunctional polymers.