Yeru Liang

Solid‐State Carbon Dots with Red Fluorescence and Efficient Construction of Dual‐Fluorescence Morphologies

Stable solid-state red fluorescence from organosilane-functionalized carbon dots (CDs) with sizes around 3 nm is reported for the first time. Meanwhile, a novel method is also first reported for the efficient construction of dual-fluorescence morphologies. The quantum yield of these solid-state CDs and their aqueous solution is 9.60 and 50.7%, respectively. The fluorescence lifetime is 4.82 ns for solid-state CDs, and 15.57 ns for their aqueous solution. These CDs are detailedly studied how they can exhibit obvious photoluminescence overcoming the self-quenching in solid state. Luminescent materials are constructed with dual fluorescence based on as-prepared single emissive CDs (red emission) and nonfluorescence media (starch, Al2 O3 , and RnOCH3 COONa), with the characteristic peaks located at nearly 440 and 600 nm. Tunable photoluminescence can be successfully achieved by tuning the mass ratio of CDs to solid matrix (such as starch). These constructed dual-fluorescence CDs/starch composites can also be applied in white light-emitting diodes with UV chips (395 nm), and oxygen sensing.

Hierarchical NiO mesocrystals with tuneable high-energy facets for pseudocapacitive charge storage

Mesocrystals are advantageous in providing a large specific surface and favorable transport properties, and have been extensively studied for energy-related applications including supercapacitors, solar cells, lithium-ion batteries, and catalysis. However, the practical applications of mesocrystals are hindered by many obstacles, such as high cost, complicated synthesis processes, and utilization of deleterious additives. Herein, we report a facile one-step and additive-free route for the controllable synthesis of NiO mesocrystals (NOMs) with a cuboctahedral morphology and layered hierarchical structures consisting of self-assembled NiO nanosheets. When employed as an electrode material for supercapacitors, the as-prepared NOMs exhibited an exceptional electrochemical performance such as an ultrahigh reversible specific capacity of ca. 1039 F g−1 at a current density of 1.0 A g−1 and excellent cycling stability (ca. 93% capacitance retention after 10 000 charge/discharge cycles). Moreover, an all-solid-state hybrid supercapacitor based on hierarchical NOMs and three-dimensional nitrogen-doped graphene manifested a high energy density of 34.4 W h kg−1 at a power density of 150 W kg−1 in 2.0 M KOH aqueous electrolyte. These results further demonstrate the potential of NiO mesocrystals as a promising electrode material by constructing a hierarchical mesostructure, which can improve the electrochemical performance for energy storage. The outstanding electrochemical performance may be attributed to their hierarchical mesostructure that can effectively enhance the electrical conductivity and avoid the aggregation of NiO nanosheets, and the exposed {100} facets with a high electrochemical activity.

Interconnected 3 D Network of Graphene-Oxide Nanosheets Decorated with Carbon Dots for High-Performance Supercapacitors

Interconnected 3 D nanosheet networks of reduced graphene oxide decorated with carbon dots (rGO/CDs) are successfully fabricated through a simple one-pot hydrothermal process. The as-prepared rGO/CDs present appropriate 3 D interconnectivity and abundant stable oxygen-containing functional groups, to which we can attribute the excellent electrochemical performance such as high specific capacitance, good rate capability, and great cycling stability. Employed as binder-free electrodes for supercapacitors, the resulting rGO/CDs exhibit excellent long-term cycling stability (ca. 92 % capacitance retention after 20 000 charge/discharge cycles at current density of 10 A g-1 ) as well as a maximum specific capacitance of about 308 F g-1 at current density of 0.5 A g-1 , which is much higher than that of rGO (200 F g-1 ) and CDs (2.2 F g-1 ). This work provides a promising strategy to fabricate graphene-based nanomaterials with greatly boosted electrochemical performances by decoration of with CDs.

Ultrahigh-surface-area hierarchical porous carbon from chitosan: acetic acid mediated efficient synthesis and its application in superior supercapacitors

The development of an effective route to high-performance carbonaceous electrode materials derived from low-cost biomass is critical but remains challenging for supercapacitors. Here we propose a new and cost-effective way to produce chitosan-based hierarchical porous carbons by the union of hydrothermal carbonization and chemical activation. The key to this preparation strategy is the utilization of acetic acid as an additive for hydrothermal carbonization, which not only favors the construction of a conducive environment for accessibility of activator KOH, but also leads to the formation of a rigid semi-carbonized framework substrate for generating an ultrahighly porous structure. Thus, our synthetic approach allows for a lower amount of activation agent and lower heating temperature when compared with normal chemical activation techniques, providing a more efficient way to produce ultrahigh-surface-area carbon materials. The as-prepared hierarchical porous carbon possesses a unique honeycomb-like framework and the highest BET surface area of 3532 m2 g−1 among all the carbon materials derived from chitosan. The combination of the hierarchical pore structure for rapid ion diffusion and the ultrahigh surface area for sufficient electrochemically active sites significantly improves the materials capacitive behaviors. An unusually high capacitance of 455 F g−1, an excellent cycling stability with 99% capacity retention over 20 000 cycles in KOH aqueous electrolyte, and a high energy density of 20.6 W h kg−1 at a power density of 226.8 W kg−1 in 1.8 V Na2SO4 aqueous supercapacitors have been obtained, demonstrating that the chitosan-based hierarchical porous carbons developed here are very attractive for application in supercapacitors.

Facile one-step and high-yield synthesis of few-layered and hierarchically porous boron nitride nanosheets

Few-layered boron nitride nanosheets (BNNSs) have attracted increasing research interest in the past few years due to their unique material properties. However, the lack of a reliable scale-up production method is an inhibiting issue for their practical applications. In this work, we report a facile one-step and high-yield method for the synthesis of few-layered and hierarchically porous BNNSs through simultaneous etching and in situ nitridation of calcium hexaboride (CaB6) by ammonium chloride under moderate conditions. The output of the few-layered BNNSs is as high as 1.4 g with respect to 1.06 g of starting CaB6 crystals. Transmission electron microscopy and atomic force microscopy characterizations confirm the successful synthesis of few-layered BNNSs, most of which are layered with a thickness less than 3 nm (layer number < 10). The as-prepared BNNSs exhibit a high specific surface area (492–795 m2 g−1) and a high pore volume (0.34–0.50 cm3 g−1). In addition, the as-resulted BNNSs exhibit high and tuneable H2 uptakes from 1.48 to 2.18 wt% at 77 K and at a relatively low pressure of 1.0 MPa, thus guiding the further search of materials for H2 storage. Our results suggest that the simultaneous etching and in situ nitridation of metallic borides is a facile and effective method for reliable production of few-layered BNNSs with hierarchical porosity for potential applications such as gas storage and functional composites.

Large-scale synthesis of porous carbon via one-step CuCl2 activation of rape pollen for high-performance supercapacitors

Sustainable synthesis methods for the production of porous carbon with appropriate structural properties for use as supercapacitor electrodes are in high demand. Generally, activation is the most convenient and effective method to increase the surface area of carbon materials. However, the existing activation methods usually suffer from a low yield and low specific surface area; so the search for a new activation agent capable of preparing porous carbon with both a high yield and large surface area remains a great challenge. Here, a new and efficient activation agent copper chloride (CuCl2) is proposed for the production of porous carbon using rape pollen biomass as the carbon precursor. The advantages of using CuCl2 to fulfil synchronous carbonization and activation can be ascribed to the following features: (i) excellent ability to generate micropores in biomass; (ii) a high yield of porous carbon; (iii) low-destruction of the natural structure of the precursor; (iv) high retention of heteroatoms. The as-prepared rape pollen carbon (RPC) exhibits a porous structure with a large specific surface area (2488 m2 g−1), sphere-like structure and high heteroatom content. More importantly, the RPC exhibits a high yield of porous carbon of up to 37.6 wt% based on the raw rape pollen. Furthermore, the RPC electrode exhibits extremely high specific capacitance (390 F g−1 at 0.5 A g−1) and long cycling stability (retaining 92.9% after 10 000 cycles at 20 A g−1) in 6.0 M KOH aqueous electrolyte, and a high energy density of 26.8 W h kg−1 at a power density of 181.4 W kg−1 in 1.0 M Na2SO4 aqueous electrolyte. This method has universal significance in producing highly porous and high-performance carbons from biomass for various energy storage/conversion energy storage applications.