Ultralight, High Capacitance, Mechanically Strong Graphene-Cellulose Aerogels.

With increasing energy demand driving the need for eco-friendly and efficient energy storage technology, supercapacitors are becoming increasingly prevalent in wearable devices because of their portability and stability. The performance of these supercapacitors is highly dependent on the choice of electrode material. The high capacitance and mechanical properties needed for these materials can be achieved by combining graphene's stable electrical properties with renewable cellulose's excellent mechanical properties into porous aerogels. In this study, graphene-cellulose hydrogels were prepared by a one-step hydrothermal method, with porous, ultra-light, and mechanically strong graphene-cellulose aerogels then prepared by freeze-drying. These composite aerogels possess excellent mechanical strength and high specific capacitance, capable of bearing about 1095 times the pressure of their own weight. Electrochemical tests show the specific capacitance of these composite aerogels can reach 202 F/g at a scanning rate of 5 mA/cm2. In view of their high surface area and fast charge transport provided by their 3D porous structure, graphene-cellulose aerogels have great potential as sustainable supercapacitor electrodes.

Ultralight, Mechanically Enhanced, and Thermally Improved Graphene-Cellulose-Polyethyleneimine Aerogels for the Adsorption of Anionic and Cationic Dyes.

Graphene-cellulose-polyethyleneimine aerogels (GA-MCC-PEI) were prepared using a simple, environmentally friendly method to remove anionic and cationic dyes in water. Graphene-cellulose hydrogels were prepared using a hydrothermal method and then immersed in a polyethyleneimine aqueous solution for 48 h to obtain graphene-cellulose-polyethyleneimine hydrogels, which were then freeze-dried. The light and porous composite aerogels had a good compression resistance, and the maximum allowable pressure of the graphene-cellulose-polyethyleneimine aerogel with a cellulose content of 43% was 21.76 kPa, which was 827 times its weight. Adsorption of the anionic dye amaranth and the cationic dye methylene blue by the graphene-cellulose-polyethyleneimine aerogel was satisfactorily modeled using the Langmuir isothermal equation, indicating monolayer adsorption. When the cellulose content was 39%, the equilibrium adsorption capacities of the composite aerogel for amaranth and methylene blue were 369.37 mg/g and 237.33 mg/g, respectively. This graphene-cellulose-polyethyleneimine aerogel can be used to remove dye pollutants in water to maintain ecological balance, thus broadening the application space of aerogel materials, that is, as adsorbents in different environments.

A novel graphene-based micro/nano architecture with high strength and conductivity inspired by multiple creatures.

In the long history of development and elimination, the creatures have derived a variety of exquisite structures and unique properties, typically natural nacre, marine mussel and Glycera to adapt to the environment and resist the predation of the enemy. Hence, inspired by the combination of special structures and properties of multiple creatures, a novel type of graphene-based micro/nano architecture was proposed, and the related bioinspired nanocomposites were fabricated, Polydopamine coated Graphene oxide/Nanocellulose/Polydopamine (P-GCP). Apart from replicating the layered structure of natural nacre, P-GCP also introduced copper ions and polydopamine to simulate the hardening mechanism of the Glycera's jaw and the composition of adhesive proteins in mussels to further improve the tensile strength and conductivity of nanocomposites, respectively. The test results showed that the tensile strength of P-GCP reached 712.9 MPa, which was 5.3 times that of natural nacre. The conductivity of artificial nacre was as high as 207.6 S/cm, which was equivalent to that of reduced graphene oxide (rGO). Furthermore, the material exhibited outstanding electrical conductivity when it connected as wires in a circuit, demonstrating the practical application prospects in aerospace, supercapacitors, biomaterials, artificial bones and tissue engineering.

Preparation of Graphene Oxide/Cellulose Composites with Microcrystalline Cellulose Acid Hydrolysis Using the Waste Acids Generated by the Hummers Method of Graphene Oxide Synthesis.

The Hummers method is the most commonly used method to prepare graphene oxide (GO). However, many waste acids remain in the raw reaction mixture after the completion of this reaction. The aim of this study was to reuse these waste acids efficiently. In this study, microcrystalline cellulose (MCC) was directly dissolved in the mixture after the high-temperature reaction of the Hummers method. The residual acid was used to hydrolyze MCC, and the graphene oxide/microcrystalline cellulose (GO/MCC) composites were prepared, while the acid was reused. The effects of MCC addition (0.5 g, 1.0 g, and 1.5 g in 20 mL) on the properties of the composites were discussed. The structure, composition, thermal stability, and hydrophobicity of GO/MCC composites were characterized and tested by SEM, XRD, FTIR, TG, and contact angle tests. The results showed that MCC could be acid hydrolyzed into micron and nano-scale cellulose by using the strong acidity of waste liquid after GO preparation, and it interacted with the prepared GO to form GO/MCC composites. When the addition amount of MCC was 1 g, the thermal stability of the composite was the highest due to the interaction between acid-hydrolyzed MCC and GO sheets. At the same time, the hydrophobic property of the GO/MCC composite is better than that of the GO film. The freeze-dried GO/MCC composites are more easily dispersed in water and have stronger stability.

Mechanically Strong, Low Thermal Conductivity and Improved Thermal Stability Polyvinyl Alcohol-Graphene-Nanocellulose Aerogel.

Porous aerogel materials have advantages of a low density, low thermal conductivity and high porosity, and they have broad application prospects in heat insulation and building energy conservation. However, aerogel materials usually exhibit poor mechanical properties. Single-component aerogels are less likely to possess a good thermal stability and mechanical properties. It is necessary to prepare multiple-composite aerogels by reinforcement to meet practical application needs. In this experiment, a simple preparation method for polyvinyl alcohol (PVA)-graphene (GA)-nanocellulose (CNF) ternary composite aerogels was proposed. This is also the first time to prepare ternary composite aerogels by mixing graphene, nanocellulose and polyvinyl alcohol. A GA-CNF hydrogel was prepared by a one-step hydrothermal method, and soaked in PVA solution for 48 h to obtain a PVA-GA-CNF hydrogel. PVA-GA-CNF aerogels were prepared by freeze drying. The ternary composite aerogel has advantages of excellent mechanical properties, a low thermal conductivity and an improved thermal stability, because strong hydrogen bonds form between the PVA, GA and CNF. The composite aerogels were characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray diffractometry, Brunauer-Emmett-Teller analysis, dynamic thermal analysis, thermogravimetry and thermal constant analysis to characterize the properties of the ternary composite aerogels. The lightweight, low-density and porous PVA-GA-CNF composite aerogels withstood 628 times their mass. The thermal conductivity of the composite aerogels was 0.044 ± 0.005 W/mK at room temperature and 0.045 ± 0.005 W/mK at 70 °C. This solid, low thermal conductivity and good thermal stability PVA-GA-CNF ternary composite aerogel has potential application in thermal insulation.