Preparation and characterization of highly conductive lignin aerogel based on tunicate nanocellulose framework.

The highly conductive and elastic three-dimensional mesh porous material is an ideal platform for the fabrication of high electrical conductivity conductive aerogels. Herein, a multifunctional aerogel that is lightweight, highly conductive and stable sensing properties is reported. Tunicate nanocellulose (TCNCs) with a high aspect ratio, high Young's modulus, high crystallinity, good biocompatibility and biodegradability was used as the basic skeleton to prepare aerogel by freeze-drying technique. Alkali lignin (AL) was used as the raw material, polyethylene glycol diglycidyl ether (PEGDGE) was used as the cross-linking agent, and polyaniline (PANI) was used as the conductive polymer. Preparation of aerogels by freeze-drying technique, in situ synthesis of PANI, and construction of highly conductive aerogel from lignin/TCNCs. The structure, morphology and crystallinity of the aerogel were characterized by FT-IR, SEM, and XRD. The results show that the aerogel has good conductivity (as high as 5.41 S/m) and excellent sensing performance. When the aerogel was assembled as a supercapacitor, the maximum specific capacitance can reach 772 mF/cm2 at 1 mA/cm2 current density, and maximum power and energy density can reach 59.4 µWh/cm2 and 3600 µW/cm2, respectively. It is expected the aerogel can be applied in the field of wearable devices and electronic skin.

Lignin-containing hydrogels with anti-freezing, excellent water retention and super-flexibility for sensor and supercapacitor applications.

We developed a highly conductive and flexible, anti-freezing sulfonated lignin (SL)-containing polyacrylic acid (PAA) (SL-g-PAA-Ni) hydrogel, with a high concentration of NiCl2. Ni2+ contributes multi-functions to the preparation of the hydrogel and its final properties, such as fast polymerization reaction as a result of the presence of redox pairs of Ni3+/Ni2+ and hydroquinone/quinone, and anti-freezing properties of the hydrogel due to the salt effects of NiCl2 so that at -20 °C the hydrogel shows similar properties to those at the room temperature. Thanks to the effective coordinations of Ni2+ with catecholic groups and carboxylic groups, as well as the rich hydrogen bonding capacity, the resultant hydrogel possesses excellent mechanical properties. High ionic conductivity (6.85 S·m-1) of the hydrogel is obtained due to the supply of high concentration of Ni2+. Moreover, the ionic solvation effect of NiCl2 in the hydrogel imparts excellent water retention ability, with water retention of ~93 % after 21-day storage. The SL-g-PAA-Ni hydrogel can accurately detect various human motions at -20 °C. The supercapacitor assembled from SL-g-PAA-Al hydrogel at -20 °C manifests a high specific capacitance of 252 F·g-1, with maximum energy density of 26.97 Wh·kg-1, power density of 2667 W·kg-1, and capacitance retention of 96.7 % after 3000 consecutive charge-discharge cycles.

High lignin containing hydrogels with excellent conducting, self-healing, antibacterial, dye adsorbing, sensing, moist-induced power generating and supercapacitance properties.

Herein, we design a dynamic redox system of using high contents of lignosulfonate (LS) and Al3+ to prepare poly acrylic acid (PAA) (LS-g-PAA-Al) hydrogels. The presence of high LS and Al3+ contents, in combination with the effective Al3+ complexes formed, renders the resultant hydrogel with some unique attributes, including excellent ionic conductivity (as high as 7.38 S·m-1) and antibacterial activity; furthermore, a very fast gelation (in 1 min) was obtained. As a flexible strain sensor, the LS-g-PAA-Al hydrogel with high conductivity demonstrates superior sensitivity in human movement detection. In addition, the rich anionic hydrophilic groups, such as sulfonic groups, phenolic hydroxyl groups, in the hydrogels impart the resultant hydrogels with excellent adsorption capacity for cationic dyes: when using Rhodamine B (RB) as a model cationic dye, the adsorption capacity of the resultant hydrogel reaches 334.64 mg·g-1; as a moist-induced power generator, it generates maximum 150.5 mV open circuit voltage with moist air flow. When the hydrogel electrolyte is assembled into a supercapacitor assembly, it shows high specific capacitance of 245.4 F·g-1, with the maximum energy density of 21.8 Wh·kg-1, power density of 2.37 kW·kg-1, and capacitance retention of 95.1% after 5000 consecutive charge-discharge cycles.

Design of Fe3+-Rich, High-Conductivity Lignin Hydrogels for Supercapacitor and Sensor Applications.

Preparation of natural polymer-based highly conductive hydrogels with tunable mechanical properties for applications in flexible electronics is still challenging. Herein, we report a facile method to prepare lignin-based Fe3+-rich, high-conductivity hydrogels via the following two-step process: (1) lignin hydrogels are prepared by cross-linking sulfonated lignin with poly(ethylene glycol) diglycidyl ether (PEGDGE) and (2) Fe3+ ions are impregnated into the lignin hydrogel by simply soaking in FeCl3. Benefiting from Fe3+ ion complexation with catechol groups and other functional groups in lignin, the resultant hydrogels exhibit unique properties, such as high conductivity (as high as 6.69 S·m-1) and excellent mechanical and hydrophobic properties. As a strain sensor, the as-prepared lignin hydrogel shows high sensitivity when detecting various human motions. With the flow of moist air, the Fe3+-rich lignin hydrogel generates an output voltage of 162.8 mV. The assembled supercapacitor of the hydrogel electrolyte demonstrates a high specific capacitance of 301.8 F·g-1, with a maximum energy density of 26.73 Wh·kg-1, a power density of 2.38 kW·kg-1, and a capacitance retention of 94.1% after 10 000 consecutive charge-discharge cycles. These results support the conclusion that lignin-based Fe3+-rich, high-conductivity hydrogels have promising applications in different fields, including sensors and supercapacitors, rendering a new platform for the value-added utilization of lignin.

Preparation and characterization of super hydrophobic aerogels derived from tunicate cellulose nanocrystals.

First time aerogels composite with super hydrophobic properties were developed by using tunicate cellulose nanocrystals (TCNC), which expanded the application scope of animal cellulose resources. In this study, the TCNC was firstly cross-linked with silica and methyltrimethylsilane (MTMS), further coated with fluorodopa to form an aerogel with super hydrophobic properties. The aerogel was characterized by scanning electron microscope (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectra (FT-IR), and X-ray photoelectron spectroscopy (XPS). Results indicated that the contact angle of aerogel was 158.7°, which showed good hydrophobicity. The composite aerogel has superior stability in wide pH range, after 72 h immersion in pH = 0 and 12 solutions, the contact angle was still greater than 150°. The aerogel shows excellent oil-water separation ability and it can be repeatedly used more than 10 times. The separation efficiency can all reach more than 90% for different water-oil mixtures. This synthesized super hydrophobic aerogels derived from tunicate cellulose has greatly extended the application of marine animal celluloses.

Preparation of lignosulfonate ionic hydrogels for supercapacitors, sensors and dye adsorbent applications.

Lignin, an abundant natural polymer but presently under-utilized, has received much attention for its green/sustainable advantages. Herein, we report a facile method to fabricate lignosulfonate (LS) ionic hydrogels by simple crosslinking with poly (ethylene glycol) diglycidyl ether (PEGDGE). The as-obtained LS-PEGDGE hydrogels were comprehensively characterized by mechanical measurements, FT-IR, and SEM. The rich sulfonic and phenolic hydroxyl groups in LS hydrogels play key roles in imparting multifunctional smart properties, such as adhesiveness, conducting, sensing and dye adsorption, as well as superconductive behavior when increasing the moisture content. The hydrogels have a high adsorption capacity for cationic dyes, using methylene blue as a model, reaching 211 mg·g-1. As a moist-induced power generator, the maximum output voltage is 181 mV. The LS-PEGDGE hydrogel-based flexible strain sensors exhibit high sensitivity when detecting human movements. As the hydrogel electrolyte, the assembled supercapacitor shows high specific capacitance of 236.9 F·g-1, with the maximum energy density of 20.61 Wh·kg-1, power density of 2306.4 W·kg-1, and capacitance retention of 92.9% after 10,000 consecutive charge-discharge cycles. Therefore, this multifunctional LS hydrogels may have promising applications in various fields, providing a new platform for the value-added utilization of lignin from industrial waste.