Methylated Biochemical Fulvic Acid-Derived Hydrogels with Improved Swelling Behavior and Water Retention Capacity.

Although humic acids (HAs) have been used to prepare absorbent hydrogels, their applications in many areas, such as agriculture, wastewater treatment and hygienic products, are not satisfactory due to their low solubility in organic solvents. In this work, biochemical fulvic acid (BFA), as a kind of HA, was initially methylated for preparation of the methylated BFA (M-BFA), which contributed to enhancing the solubility in organic solvents. Then, M-BFA reacted with N,N'-methylene diacrylamide (MBA) in the N,N-Dimethylacrylamide (DMAA) solution, and the expected hydrogel (M-BFA/DMAA) was successfully obtained. XPS confirmed that there were more C=O and C-N groups in M-BFA/DMAA than in DMAA; thus, M-BFA/DMAA was able to offer more reactive sites for the water adsorption process than DMAA. The combined results of BET and SEM further demonstrated that M-BFA/DMAA possessed a larger BET surface area, a larger pore volume and a more porous structure, which were favorable for the transfer of water and accessibility of water to active sites, facilitating water adsorption and storage. In addition, the swelling ratio and water retention were investigated in deionized (DI) water at different conditions, including test times, temperatures and pHs. Amazingly, the swelling ratio of M-BFA/DMAA was 10% higher than that of DMAA with the water retention time from 100 to 1500 min. Although M-BFA/DMAA and DMAA had similar temperature sensitivities, the pH sensitivity of M-BFA/DMAA was 0.9 higher than that of DMAA. The results proved that M-BFA/DMAA delivered superior water retention when compared to the pristine DMAA. Therefore, the resultant materials are expected to be efficient absorbent materials that can be widely used in water-deficient regions.

Two-dimensional porous (Co, Ni)-based monometallic hydroxides and bimetallic layered double hydroxides thin sheets with honeycomb-like nanostructure as positive electrode for high-performance hybrid supercapacitors.

CoNi layered double hydroxides (LDH) and related monometallic hydroxides (Ni(OH)2 and Co(OH)2) were synthesized by a facile, simple and inexpensive method under mild condition (50 °C). The resulting products displayed a unique honeycomb-like nanoflakes array assembled two-dimensional (2D) thin sheets structure. Among them, CoNi-LDH thin sheets delivered higher specific capacity (394.5 C g-1 at 1 A g-1) with superior cyclic performance (92.3% capacity retention over 10,000 cycles) than Co/Ni monometallic hydroxides owing to the synergistic effect of cobalt and nickel. Afterward, hybrid supercapacitors (HSC) devices were fabricated using the as-obtained products (CoNi-LDH, Co(OH)2 and Ni(OH)2 thin sheets) and activated carbon (AC) as the positive and negative electrode, respectively. The operating voltage of the devices can be extended to 1.6 V. What's more, the assembled CoNi-LDH HSC device exhibited a maximum energy density of 20.38 Wh kg-1 at the power density of 800 W kg-1. Consequently, these outstanding electrochemical performances of the CoNi-LDH thin sheet endow it with great potential to be implemented in HSCs or other energy storage systems.

Freestanding two-dimensional Ni(OH)2 thin sheets assembled by 3D nanoflake array as basic building units for supercapacitor electrode materials.

Freestanding two dimensional (2D) porous nanostructures have great potential in electrical energy storage. In the present work, we reported the first synthesis of two-dimensional (2D) ß-Ni(OH)2 thin sheets (CQU-Chen-Ni-O-H-1) assembled by 3D nanoflake array as basic building units under acid condition by direct hydrothermal decomposition of the mixed solution of nickel nitrate (Ni(NO3)2) and acetic acid (CH3COOH, AA). The unique 3D nanoflake array assembled mesoporous 2D structures endow the thin sheets with a high specific capacitance of 1.78Fcm-2 (1747.5Fg-1) at the current density of 1.02mAcm-2 and good rate capability of 67.4% retain from 1.02 to 10.2mAcm-2. The corresponding assembled asymmetric supercapacitor (ASC) achieves (CQU-Chen-Ni-O-H-1//active carbon (AC)) a high voltage of 1.8V and an energy density of 23.45Whkg-1 with a maximum power density of 9kWkg-1, as well as cycability with 93.6% capacitance retention after 10,000 cycles. These results show the mesoporous thin sheets have great potential for SCs and other energy storage devices.

Single-crystal Cr2O3 nanoplates with differing crystalinities, derived from trinuclear complexes and embedded in a carbon matrix, as an electrode material for supercapacitors.

As one kind of important p-type semiconductors, Cr2O3 has been widely used for optical and electronic devices due to its high electrical conductivity and special optoelectronic characteristics, as well as high chemical and thermal stability. In this paper, single-crystalline Cr2O3 nanoplates embedded in carbon matrix were successfully synthesized through direct thermal decomposition of a trinuclear cluster complex of [Cr3O(CH3CO2)6(H2O)3]NO3·CH3COOH ([Cr3O]) in Ar atmosphere. The synergetic effect of the plate-like structure and embedding in carbon matrix contributes to the enhanced electrochemical performance of the Cr2O3-C nanoplates. Owing to different crystallinity and composition, the obtained products at 400, 500, 600, and 700°C with different carbon content of 12.52, 8.26, 5.35 and 3.27% exhibited enhanced battery-type electrode materials in three-electrode system with high specific capacitance (823.11, 781.65, 720.72, and 696.73Fg-1 at 1Ag-1) and remarkable cycling stability (about 0.3, 2.7, 4.5 and 5.6% loss of its initial capacitance after 5000 charge-discharge cycles at a current density of 5Ag-1). Furthermore, an assembled asymmetric device (Cr2O3-C nanoplates (positive electrode)//activated carbon (AC, negative one)) with an extended operating voltage window of 1.8V achieves a specific capacitance of 58.06Fg-1 at the current density of 1Ag-1 and an energy density of 26.125Whkg-1 at power density of 0.9kWkg-1, as well as superior cycling stability with 91.4% capacitance retention after 10,000 cycles. The results indicate that the Cr2O3 nanoplates embedded in carbon matrix show promising potential to construct high-performance energy storage devices.