Nano

The lithium titanium spinel Li₄Ti₅O${}_{12}$ has attracted more and more attention as anode materials applied in lithium ion batteries. Li₄Ti₅O${}_{12}$ material has been found to be able to intercalate lithium ions without deformation of the lattice. However, compared with graphite and other anode materials, the low conductivity of Li₄Ti₅O${}_{12}$ restricts its charging and discharging rate. Doping is deemed to be a businesslike method to enhance ionic and electronic conductivity of Li₄Ti₅O${}_{12}$. This paper reviews the effects of Li₄Ti₅O${}_{12}$ with different doping ions on different crystal lattice states. And it has been found by a summary that the doping objective of doping ions at Li₄Ti₅O${}_{12}$ is also different. Moreover, the applications of ion doping in different fields of Li₄Ti₅O${}_{12}$ are prospected.

Graphene nanosheets have attracted immense research interest among the materials science community from electronics to the biomedical field. Being the first member of two-dimensional nanomaterials family, discovered in 2004 followed by the Nobel Prize winning in 2010, it is now readily witnessing global industrial revolutions. The nanomaterial is bestowed with such unprecedented features that can be tangible to a wide spectrum of applications ranging from energy storage devices to sensor application. Enormous flattened surfaces, superior mechanical strength and flexibility, ballistic intrinsic carrier mobility, nearly transparent nature, high thermal conductivity and room-temperature ferromagnetic behavior are few of the extraordinary attributes of the monolayer of carbon nanosheets. In this comprehensive review, an attempt has been put forward to precisely revisit and represent the literature available on the fundamental properties of graphene nanomaterials. Also, the usage of its characteristic features in various applications as well as synthesis process has been briefly discussed.

Development of a neutral Zn–air battery is of much significance due to the high stability of zinc in a neutral electrolyte. Here, Ni/Co-doped C–N nanotube composites (C–N, Ni/C–N, Co/C–N, and Ni–Co/C–N) as efficient oxygen reduction reaction (ORR) electrocatalysts in a neutral medium have been prepared by direct pyrolysis of Ni/Co salt, dicyandiamide (DCD) and glucose. Among the synthesized catalysts, Ni–Co/C–N presents a high ORR current density of 8.5mA$\cdot$cm${}^{-2}$ in a 0.5mol$\cdot$L${}^{-1}$ KNO₃ solution. The ORR electron transfer number of the catalyst Ni–Co/C–N is 3.8, indicating that O₂ is almost completely reduced to H₂O. A neutral zinc–air battery utilizing a 0.5mol$\cdot$L${}^{-1}$ KNO₃ solution has been assembled by using the prepared composite catalyst coated on carbon paper as an air cathode, and Zn plate as an anode. The battery with the cathode catalyst Ni–Co/C–N delivers the open-circuit voltage of 1.13V and the maximum power density of 65mW$\cdot$cm${}^{-2}$. The constant discharge current density of 50mA$\cdot$cm${}^{-2}$, 100mA$\cdot$cm${}^{-2}$ and 150mA$\cdot$cm${}^{-2}$ can last 202h, 93h and 11h, respectively. A stable voltage plateau appears at various discharge current densities. The neutral zinc–air battery can be repeatedly discharged after replacing the zinc anode. Results indicate that the synthesized Ni–Co/C–N catalyst is an excellent cathode material applied to a neutral zinc–air battery, showing broad application prospects as a mobile power source.

Multifunctional photoluminescent (PL) nanomaterials have attracted considerable interest in terms of their potential applications in the field of clinical medicine. Carbon dots (CDs), as emerging optical nanomaterials, are promising in various fields including biological imaging, drug transport and nerve tracing. However, little research has investigated on bone tissue engineering as of now. In this study, a new kind of bifunctional Zn${}^{2+}$-doped carbon dots (Zn-CDs) has been synthesized by a one-step hydrothermal method, Zn-CDs show effective fluorescent imaging and induce osteoblastic differentiation abilities in vitro. Moreover, compared with the raw material, Zn-CDs exhibited more effective osteoblastic differentiation promoting capability. Overall, the biocompatible nanomaterial Zn-CDs show potential to be used as a promising novel nanodrug for bone loss therapy and also a monitor of cell variation by fluorescence imaging.

A nanoflower structure of Zn${}_{0.76}$Co${}_{0.24}$S directly grown on carbon fiber papers (CFP) was successfully designed by a mild two-step hydrothermal method. Benefiting from their fascinating structural features, Zn${}_{0.76}$Co${}_{0.24}$S/CFP electrode exhibits a maximum specific capacitance of 300Fg${}^{-1}$ at current density of 1Ag${}^{-1}$ and 84% capacitance retention after 5,000 cycles at current density of 5Ag${}^{-1}$. Subsequently, Zn${}_{0.76}$Co${}_{0.24}$S/CFP//AC all-solid-state asymmetric supercapacitor (ASC) device is assembled and able to illuminate the red LEDs. ASC devices deliver a maximum energy density of 9.59Whkg${}^{-1}$ at a power density of 750Wkg${}^{-1}$. Therefore, this impressive result demonstrates that the nanoflower Zn${}_{0.76}$Co${}_{0.24}$S have promising applications in the development of high-performance supercapacitors.

A hollow silicon oxide coated with cuprous oxide and polyaniline (hSiO_x/Cu₂O/PANI) was prepared via Stober method, magnesium reduction and chemical oxidative polymerization. The hSiO_x/Cu₂O/PANI (SiO_x 62wt.%, PANI 33wt.%, Cu₂O 5wt.%) presented charge/discharge capacities of up to 2000mAhg${}^{-1}$ after 60 cycles at 0.2Ag${}^{-1}$ current density and higher than 880mAhg${}^{-1}$ at 8Ag${}^{-1}$ current density. Microstructural analysis demonstrated that the improvement was due to the nanostructure of hollow SiO_x sphere coated with Cu₂O and PANI, which could release high stress caused by volume expansion during the lithiation/delithiation process and had little damage to electrode materials. Cycle voltammetry (CV) and electrochemical impedance spectroscopy (EIS) results further confirmed that Cu₂O and PANI dual-coating improved reversibility and conductivity of hSiO_x and prevented it to drop from the electrode surface.

A series of nickel sulfides derived from the hexagonal Ni-MOF are vulcanized through adjusting the hydrothermal time and the thiourea concentration. Among all the obtained nickel sulfides, one sample Ni-S2-3, which inherits the Ni-MOF’s morphology, shows the best electrochemical performance with a remarkable specific capacitance of 1128Fg${}^{-1}$ at 1Ag${}^{-1}$, a rate capacitance of 50% and a long cycle life of 74% retention after 5000 cycles. Furthermore, the asymmetrical supercapacitors (SCs) based on Ni-S2-3//AC exhibit a good supercapacitive performance with a maximum power density of 16.3Wh kg${}^{-1}$ at a power density of 800Wkg${}^{-1}$. All these results indicate that vulcanizing Ni-MOF is an effective way to fabricate a superior electrode material with excellent electrochemical performance for SCs.

In this paper, we report a facile strategy to design and prepare reduced graphene oxide (rGO) supported MoS₂ nanoplatelet (MoS₂/rGO) via a solvothermal co-assembly process. It is found that in the as-obtained MoS₂/rGO nanocomposite, MoS₂ possesses unique platelet structure and rGO is exfoliated due to the in situ growth of MoS₂ nanoplatelet, leading to a large specific surface area, facilitating rapid diffusion of lithium ions. The nanocomposite is used as a promising anode material for lithium-ion batteries and displays a high initial charge capacity (1382mAhg${}^{-1}$), excellent rate capability and cycling stability. The remarkable lithium storage performance of MoS₂/rGO nanocomposite is mainly ascribed to the inherent nanostructure of the MoS₂, and the synergistic effect between rGO nanosheets and MoS₂ nanoplatelets.

Density functional theory (DFT) calculations have been carried out to study the capacity of the B${}_{12}$N${}_{12}$ nanocage encapsulated with alkali metals (Li, Na, K) for the CO₂ adsorption and activation. It is found that after encapsulating alkali metals, the alkali metal atoms are closer to one side of clusters instead of exactly lying at the center, and a considerable charge transfers from the inner alkali metal atoms to the B${}_{12}$N${}_{12}$ cage. Besides, the HOMO–LUMO gap (HLG) values of Li@B${}_{12}$N${}_{12}$, Na@B${}_{12}$N${}_{12}$ and K@B${}_{12}$N${}_{12}$ are decreased to about 6eV, being much smaller than that of the pristine B${}_{12}$N${}_{12}$. Although the geometry structure parameters and the energy differences of M06-2X are slightly different from the ones of $\omega$B97X-D, some identical results of two kinds of functional can be obtained. CO₂ can be adsorbed chemically and physically on majority bonds of all the clusters, except for some bonds with large change in bond length and bond indices. The encapsulation of alkali-metal atoms may enhance the physical and chemical adsorption of CO₂ on the surface of the clusters, in which Na@B${}_{12}$N${}_{12}$ and K@B${}_{12}$N${}_{12}$ are the most powerful physical and chemical adsorbent for CO₂, respectively.

A series of new organic–inorganic nanohybrids were successfully prepared by using Congo red and heat-treated halloysite clays. The results show that an increase in calcination temperature leads to the reduction of lightness ($L$*) and color hue ($a$*, $b$*). The hybrids prepared, respectively, with 400^∘C treated and 500^∘C treated halloysites have the same order of HNO${}_3>\mathrm{\text{HCl}}>{\mathrm{\text{H}}}_2{\mathrm{\text{SO}}}_4$ with respect to the acid resistance. The hybrid with a light red hue can be obtained by alkali treatment when halloysite calcined at higher temperature was used as a host. There exists a strong host–guest interaction between nanotubes and Congo red anions. The leaching of aluminum in the clay has a decisive influence on the acid/alkali resistance of the hybrid.

Water pollution caused by intensive use of organic dyes has become an increasingly serious problem recently. Green and efficient processes are desperately needed to remove persistent organic pollutants from waste waters. Herein, Ag nanoparticles loaded ZnO hollow microspheres were synthesized through a simple solvothermal method and used as a photocatalyst for dye degradation. The calculated band gap of Ag/ZnO — 5% (2.97eV) is much narrower than that of pure ZnO (3.37eV). The obtained Ag/ZnO samples show a remarkable photocatalytic activity in photodegradation of Rhodamine B (RhB) under simulated sunlight irradiation. The degradation efficiency of RhB for Ag/ZnO — 5% is 98.8% after 100min irradiation while only 52.8% degradation rate is obtained over pure ZnO. The enhancement is attributed to the exposed active ZnO (001) plane and the surface plasmon resonance (SPR) effect of Ag nanoparticles that promote the separation of photogeneated electrons and holes.

Three-dimensional reduced graphene oxide (RGO) matrix decorated with nanoflowers of layered MoS₂ (denoted as 3D MoS₂/RGO) have been synthesized via a facile one-pot stepwise hydrothermal method. Graphene oxide (GO) is used as precursor of RGO and a 3D GO network is formed in the first-step of hydrothermal treatment. At the second stage of hydrothermal treatment, nanoflowers of layered MoS₂ form and anchor on the surface of previously formed 3D RGO network. In this preparation, thiourea not only induces the formation of the 3D architecture at a relatively low temperature, but also works as sulfur precursor of MoS₂. The synthesized composites have been investigated with XRD, SEM, TEM, Raman spectra, TGA, N₂ sorption technique and electrochemical measurements. In comparison with normal MoS₂/RGO composites, the 3D MoS₂/RGO composite shows improved electrochemical performance as anode material for lithium-ion batteries. A high reversible capacity of 930mAh$\cdot$g${}^{-1}$ after 130 cycles under a current density of 200mA$\cdot$g${}^{-1}$ as well as good rate capability and superior cyclic stability have been observed. The superior electrochemical performance of the 3D MoS₂/RGO composite as anode active material for lithium-ion battery is ascribed to its robust 3D structures, enhanced surface area and the synergistic effect between graphene matrix and the MoS₂ nanoflowers subunit.

Reduced graphene oxide (rGO) aqueous dispersions were synthesized from GO suspensions with hydrazine as reducing agent via a microwave-hydrothermal process in ammonia solution. The rGO films were fabricated by vacuum filtration of above dispersions. When the weight ratio of hydrazine to GO (R${}_{{\mathrm{\text{N}}}_2{\mathrm{\text{H}}}_4∕\mathrm{\text{GO}}}$) increases from 0.125 to 9, the dispersion stability of rGO nanosheets in hydrazine/ammonia solution degrades gradually, the surfaces of resultant films become rough from smooth and large interspaces turn up in the transverse section. With the increasing of R${}_{{\mathrm{\text{N}}}_2{\mathrm{\text{H}}}_4∕\mathrm{\text{GO}}}$, the C/O atomic ratio and orientation degree of (002) plane of rGO films increase, and the in-plane thermal conductivity also increases, achieving a maximum value of 1056W/m K when R${}_{{\mathrm{\text{N}}}_2{\mathrm{\text{H}}}_4∕\mathrm{\text{GO}}}$ is 3.375, then decreases because large interspaces in the rGO film with higher reduction degree greatly limit the thermal transport due to the severe phonon scatterings at the sheets boundaries.

In₂O₃ and metal-doped (Ni or Ce) In₂O₃ mesoporous three-dimensional (3D) nanospheres arrays were synthesized via nanocasting using mesoporous silica as hard templates. Effects of Ni or Ce doping on the structure, optical and gas-sensing properties of the In₂O₃ nanospheres were investigated. Both the undoped and the doped In₂O₃ nanospheres showed single-phase structure without any impurity. The nanospheres were about 20nm in size and they stacked closely to form rigid 3D mesoporous structure. A change in the value of optical band gap was observed upon metal doping. The room temperature photo luminescence behavior also showed some differences between pure and doped In₂O₃. Compared with pure In₂O₃ nanospheres, the metal-doped In₂O₃ exhibited superior response, fast recovery and good selectivity to ethanol. The enhanced gas-sensing properties might be related to the doping of metal ion and its effective contribution towards the oxygen vacancies, conductivity and crystallite size of the grains.