Haizhu Sun

In Situ Binding Sb Nanospheres on Graphene via Oxygen Bonds as Superior Anode for Ultrafast Sodium-Ion Batteries

Graphene incorporation should be one effective strategy to develop advanced electrode materials for a sodium-ion battery (SIB). Herein, the micro/nanostructural Sb/graphene composite (Sb-O-G) is successfully prepared with the uniform Sb nanospheres (∼100 nm) bound on the graphene via oxygen bonds. It is revealed that the in-situ-constructed oxygen bonds play a significant role on enhancing Na-storage properties, especially the ultrafast charge/discharge capability. The oxygen-bond-enhanced Sb-O-G composite can deliver a high capacity of 220 mAh/g at an ultrahigh current density of 12 A/g, which is obviously superior to the similar Sb/G composite (130 mAh/g at 10 A/g) just without Sb-O-C bonds. It also exhibits the highest Na-storage capacity compared to Sb/G and pure Sb nanoparticles as well as the best cycling performance. More importantly, this Sb-O-G anode achieves ultrafast (120 C) energy storage in SIB full cells, which have already been shown to power a 26-bulb array and calculator. All of these superior performances originate from the structural stability of Sb-O-C bonds during Na uptake/release, which has been verified by ex situ X-ray photoelectron spectroscopies and infrared spectroscopies.

Conducting the Temperature-Dependent Conformational Change of Macrocyclic Compounds to the Lattice Dilation of Quantum Dots for Achieving an Ultrasensitive Nanothermometer

We report a ligand decoration strategy to enlarge the lattice dilation of quantum dots (QDs), which greatly enhances the characteristic sensitivity of a QD-based thermometer. Upon a multiple covalent linkage of macrocyclic compounds with QDs, for example, thiolated cyclodextrin (CD) and CdTe, the conformation-related torsional force of CD is conducted to the inner lattice of CdTe under altered temperature. The combination of the lattice expansion/contraction of CdTe and the stress from CD conformation change greatly enhances the shifts of both UV-vis absorption and photoluminescence (PL) spectra, thus improving the temperature sensitivity. As an example, β-CD-decorated CdTe QDs exhibit the 0.28 nm shift of the spectra per degree centigrade (0.28 nm/°C), 2.4-fold higher than those of monothiol-ligand-decorated QDs.

Directing the Growth of Semiconductor Nanocrystals in Aqueous Solution : Role of Electrostatics

In this study, we demonstrate a new insight into the growth stage of aqueous semiconductor nanocrystals (NCs); namely, that the experimental variable-dependent growth rate and photoluminescence quantum yields (PLQYs) are understandable according to electrostatics. In this context, the aqueous NCs possess (from core outwards) an inorganic core, ligand layer, adsorbed layer, and a diffuse layer. The presence of an electric double-layer not only makes the NCs dispersible in the colloidal solution, but also governs the migration of monomers and monomer adsorption on the NC surface. To maintain NC growth, monomers need to migrate through the double-layer. Consequently, the nature of the diffuse layer influences the ability of monomer diffusion and hence the growth rate of NCs. Systematic studies reveal that the experimental variables, including precursor concentrations, pH of the solution, additional NaCl concentrations, ratio of Cd to ligand, and the nature of the ligands significantly govern the nature of the NC electric double-layer. The experimental variables, which reduce the thickness of the diffuse layer, benefit from monomer diffusion and a rapid growth of NCs. However, on the other hand, the diffuse layer also presents a charge-selective transfer of Cd monomers. The neutral monomers, such as the complex of Cd(2+) and 3-mercaptopropionic acid (MPA) with 1:1 molar ratio [Cd(MPA)], migrate through the diffuse layer more easily than the charged ones [Cd(MPA)(2) (2-) or Cd(MPA)(3) (4-)], thus facilitating the growth of NCs. The nature of the adsorbed layer inside the diffuse layer, defined as the assumed interface of solid NCs and the liquid environment, also affects the growth rate and especially the PLQYs of NCs through the adsorption and coalescence of monomers on this interface. Strong interaction between the adsorbed layer and Cd monomers provides the opportunity to accelerate NC growth and to obtain NCs with high PLQYs.

Enhanced Biocompatibility of PLGA Nanofibers with Gelatin/Nano-Hydroxyapatite Bone Biomimetics Incorporation

The biocompatibility of biomaterials is essentially for its application. The aim of current study was to evaluate the biocompatibility of poly(lactic-co-glycolic acid) (PLGA)/gelatin/nanohydroxyapatite (n-HA) (PGH) nanofibers systemically to provide further rationales for the application of the composite electrospun fibers as a favorable platform for bone tissue engineering. The PGH composite scaffold with diameter ranging from nano- to micrometers was fabricated by using electrospinning technique. Subsequently, we utilized confocal laser scanning microscopy (CLSM) and MTT assay to evaluate its cyto-compatibility in vitro. Besides, real-time quantitative polymerase chain reaction (qPCR) analysis and alizarin red staining (ARS) were performed to assess the osteoinductive activity. To further test in vivo, we implanted either PLGA or PGH composite scaffold in a rat subcutaneous model. The results demonstrated that PGH scaffold could better support osteoblasts adhesion, spreading, and proliferation and show better cyto-compatibility than pure PLGA scaffold. Besides, qPCR analysis and ARS showed that PGH composite scaffold exhibited higher osteoinductive activity owing to higher phenotypic expression of typical osteogenic genes and calcium deposition. The histology evaluation indicated that the incorporation of Gelatin/nanohydroxyapatite (GH) biomimetics could significantly reduce local inflammation. Our data indicated that PGH composite electrospun nanofibers possessed excellent cyto-compatibility, good osteogenic activity, as well as good performance of host tissue response, which could be versatile biocompatible scaffolds for bone tissue engineering.

Shale-like Co3O4 for high performance lithium/sodium ion batteries

In recent years, metal-organic compounds have been considered as ideal sacrificial templates to obtain transition metal oxides for electrochemical applications due to their diverse structures and tunable properties. In this work, a new kind of cobalt-based metal organic compound with a layered structure was designed and prepared, which was then transformed into ultrafine cobalt oxide (Co3O4) nanocrystallites via a facile annealing treatment. The obtained Co3O4 nanocrystallites further assembled into a hierarchical shale-like structure, donating extremely short ion diffusion pathway and rich porosity to the materials. The special structure largely alleviated the problems of Co3O4 such as inferior intrinsic electrical conductivity, poor ion transport kinetics and large volume changes during the redox reactions. When evaluated as anode materials for lithium-ion batteries, the shale-like Co3O4 (S-Co3O4) exhibited superior lithium storage properties with a high capacity of 1045.3 mA h g−1 after 100 cycles at 200 mA g−1 and good rate capabilities up to 10 A g−1. Moreover, the S-Co3O4 showed decent electrochemical performance in sodium-ion batteries due to the above-mentioned comprehensive merits (380 and 153.8 mA h g−1 at 50 and 5000 mA g−1, respectively).

The Effective Design of a Polysulfide-Trapped Separator at the Molecular Level for High Energy Density Li-S Batteries.

In this work, the lightweight and scalable organic macromolecule graphitic carbon nitride (g-C3N4) with enriched polysulfide adsorption sites of pyridinic-N was introduced to achieve the effective functionalization of separator at the molecular level. This simple method overcomes the difficulty of low doping content as well as the existence of an uncontrolled form of nitrogen heteroatom in the final product. Besides the conventional pyridinic-N-Li bond formed in the vacancies of g-C3N4, the C-S bond was interestingly observed between g-C3N4 and Li2S, which endowed g-C3N4 with an inherent adsorption capacity for polysulfides. In addition, the microsized g-C3N4 provided the coating layer with good mechanical strength to guarantee its restriction function for polysulfides during long cycling. As a result, an excellent reversible capacity of 840 mA h g(-1) was retained at 0.5 C after 400 cycles for a pure sulfur electrode, much better than that of the cell with an innocent carbon-coated separator. Even at a current density of 1 C, the cell still delivered a stable capacity of 732.7 mA h g(-1) after 500 cycles. Moreover, when further increasing the sulfur loading to 5 mg cm(-2), an excellent specific capacity of 1134.7 mA h g(-1) was acquired with the stable cycle stability, ensuring a high areal capacity of 5.11 mA h cm(-2). Besides the intrinsic adsorption ability for polysulfides, g-C3N4 is nontoxic and mass produced. Therefore, a scalable separator decorated with g-C3N4 and a commercial sulfur cathode promises high energy density for the practical application of Li-S batteries.

Self-Assembly of CdTe Nanoparticles into Dendrite Structure: A Microsensor to Hg2+

A novel microsensor to Hg(2+) was fabricated through self-assembly of aqueous CdTe nanoparticles (NPs). The morphologies of self-assembly mainly included classical dendrites, straight dendrites, and small islands. The formation process of these morphologies was systematically investigated by using the field emission scanning electron microscope, confocal laser scanning microscope, and atom force microscope instruments, etc. The proposed mechanism showed that the dendrite structure was formed via manipulating the short-range van der Waals interaction and long-range electrostatic interaction, which was realized through altering the ligand and concentration of the CdTe NPs. Furthermore, polymers with positive charges were used to effectively control the morphology of the self-assembly as well as improve the property of photoluminescence. These CdTe dendrites were used as microsensors to Hg(2+), which presented the advantages of low cost, quick detection time, high selectivity, and easy operation.

A vertical and cross-linked Ni(OH)2 network on cellulose-fiber covered with graphene as a binder-free electrode for advanced asymmetric supercapacitors

Nanostructured transition metal oxides are attractive pseudocapacitive materials with high theoretical specific capacitance, scale-up potential and environmental benignity. However, realizing high capacitance and excellent rate capability remains a critical challenge. Herein, a three-dimensional carbon support of cellulose-fiber covered with graphene (CFG) to induce the growth of a hierarchical nanostructured Ni(OH)2 (Ni(OH)2–CFG) is fabricated through a one-pot hydrothermal reaction without using any surfactants or hard templates. The resulting Ni(OH)2–CFG composite exhibits a special vertical and cross-linked network structure with a large surface area (425.9 m2 g−1, higher than that of unsupported Ni(OH)2, 366.9 m2 g−1) and appropriate pore size distribution of micro–mesopores, which offer fast electrolyte ion-transport and short ion-diffusion pathways. Electrochemical characterization demonstrates that the Ni(OH)2–CFG composite as a binder-free electrode reveals high mass capacitance (2276 F g−1, at 1 A g−1), good rate capability and excellent cycling stability (no capacitance decay after 1000 cycles at a high current density of 5 A g−1). In addition, an asymmetric Ni(OH)2–CFG//activated carbon supercapacitor exhibits a high cell-voltage of 1.6 V and a maximum specific capacitance of 191.3 F g−1 with an energy density up to 15.0 W h kg−1. The excellent performances of the Ni(OH)2–CFG composite demonstrate its promising potential for future capacitor based energy storage and conversion.

Nanoscale Polysulfides Reactors Achieved by Chemical Au–S Interaction: Improving the Performance of Li–S Batteries on the Electrode Level

In this work, the chemical interaction of cathode and lithium polysulfides (LiPSs), which is a more targeted approach for completely preventing the shuttle of LiPSs in lithium-sulfur (Li-S) batteries, has been established on the electrode level. Through simply posttreating the ordinary sulfur cathode in atmospheric environment just for several minutes, the Au nanoparticles (Au NPs) were well-decorated on/in the surface and pores of the electrode composed of commercial acetylene black (CB) and sulfur powder. The Au NPs can covalently stabilize the sulfur/LiPSs, which is advantageous for restricting the shuttle effect. Moreover, the LiPSs reservoirs of Au NPs with high conductivity can significantly control the deposition of the trapped LiPSs, contributing to the uniform distribution of sulfur species upon charging/discharging. The slight modification of the cathode with <3 wt % Au NPs has favorably prospered the cycle capacity and stability of Li-S batteries. Moreover, this cathode exhibited an excellent anti-self-discharge ability. The slight decoration for the ordinary electrode, which can be easily accessed in the industrial process, provides a facile strategy for improving the performance of commercial carbon-based Li-S batteries toward practical application.

A novel approach to prepare Si/C nanocomposites with yolk-shell structures for lithium ion batteries

A novel method was developed to successfully prepare mesoporous Si/C nanocomposites with yolk–shell structures (MSi@C). Different from the reported methods, this approach was unique, straightforward and easily scaled up. A plausible mechanism for the formation of MSi@C nanocomposites was proposed, which was in accordance with the results of transmission electron microscopy (TEM). When the mixture of mesoporous Si (M-Si) and citric acid was heated up, the volume of air adsorbed by the M-Si expanded, and the viscoelastic citric acid layers inflated just like balloons, directly leading to the formation of the yolk–shell structured MSi@C nanocomposites during the carbonization. The MSi@C nanocomposites possessed an M-Si core with diameter ∼150 nm and a carbon shell with diameter ∼230 nm. Such nano and mesoporous structure combined with voids between the M-Si core and carbon shell not only provides enough space for the volume expansion of M-Si during lithiation, but also accommodates the mechanical stresses/strains caused by the volume inflation and contraction. Moreover, partial graphitization of the carbon contributed to the improved electrical conductivity and rate performance of MSi@C. As a result, the prepared MSi@C exhibited an initial reversible capacity of 2599.1 mA h g−1 and maintained 1264.7 mA h g−1 even after 150 cycles at 100 mA g−1, with high coulombic efficiency (CE) above 99% (based on the weight of M-Si in the electrode). Therefore, this work provided an alternative method to fabricate yolk–shell nanostructured materials with great potential as anode materials for lithium ion batteries.