Nano

Because the motion of charge carriers in nanowires and quantum dots is restricted within nanoscale in two and three dimensions, respectively, both nanowires and quantum dots exhibit many excellent optoelectronic properties. Particularly, with the advantage of being compatible with Si integrated circuits, Silicon nanowires (SiNWs) and germanium quantum dots (GeQDs) have been extensively studied in the past few decades. In order to explore novel physical properties, the integration of SiNWs and GeQDs has attracted great attention recently. In this paper, recent researches on the preparation methods and structures of SiNWs, GeQDs and their composites are reviewed, respectively. The synthesis of SiNWs with random distribution and ordered arrays by using vapor–liquid–solid growth mechanism and metal-assisted chemical etching technique is firstly summarized. Some special structures of SiNWs are also discussed. Furthermore, the development of some novel structures of GeQDs for further improving their optical properties is reviewed. Finally, the growth mechanism and structure evolution of SiNWs/GeQDs composites are illustrated from the view of theory and experiment. The strain in Ge shell layers and SiNWs, the relationship between Ge growth mode and SiNW diameter, and the distribution of GeQDs on the radial and axial directions of SiNWs are discussed in detail. The research about the growth of SiNWs/GeQDs composite structures is in its early stage, so there are many questions that need to be resolved in future.

Transparent conducting films based on solution-synthesized copper nanowires (Cu NWs) are considered to be an attractive alternative to indium tin oxide (ITO) due to the relative abundance of Cu and the low cost of solution-phase NW coating processes. Moreover, transparent electrodes tend to be flexible. This makes Cu NWs more attractive because ITO is brittle and can not meet the requirements of flexibility. For Cu NWs, aspect ratio is an important property. Cu NWs can be directly prepared by chemical reduction with various reducing agents and suitable capping agents. In general, the selectivity of the capping agent is very important for the formation of one-dimensional nanostructures because it plays a major role in the thermodynamic regulations and growth kinetics that influence the geometry and morphology of the crystal facets. Therefore, different aspect ratios are formed. Conductivity is the most important property for transparent electrodes. Organic pickling, annealing and glare pulses have a certain improvement in conductivity. Meanwhile, it is also essential to increase the oxidation resistance of the transparent electrode. The reduction of graphene oxide (r-GO), the coating of metal and polymer improve the oxidation resistance of the transparent electrode to varying degrees. This paper reviews the effect of different capping agents on the aspect ratio of NWs, and the effects of different post-treatments on oxidation resistance and conductivity of transparent electrodes.

The nanoparticle (NP) is one of the most used nanostructures in biomedicine. The Np–biomembrane interface plays an important role in delivering NPs into a living biological cell. While most researchers focus on the interaction between a single Np and a cell membrane, we pay attention to the NP–biomembrane interaction when a cluster of NPs are put into a biological cell together, and analyze the cooperative effect of these NPs. We find that the NPs would not enter the cell individually, but have a trend to form an aggregation to reduce the repel force from the cell membrane. The dissipative particle dynamics simulation shows that the NP aggregation may have three interactive states with the membrane: adhere on the surface of the cell, uptaken by the membrane and enter the cell. We propose to use catalytic (CA) particles which are not sensitive to the membrane to reduce the driving force required in NP delivery. Energy analysis demonstrates that the introduced (CA) particles can decrease the free energy gap between the inside and the outside of the membrane, and increase the success rate of NPs entering the cell.

Amorphous FeCo nanowires (NWs) with the average diameter of 120nm were successfully prepared with a magnetic-field-assisted (MFA) hydrothermal method. Rapid reaction time was adopted to obtain amorphous FeCo NWs, being checked by XRD and TEM. Tuning the stoichiometric ratio of Fe/Co content meets the optimal impedance matching under different absorption frequency, making both improved intensities and frequency ranges of microwave absorption. For example, under 3mm coating thickness, the reflection loss (RL) peaks of Fe₃Co₇, Fe₅Co₅ and Fe₇Co₃ NWs are $-$25.88dB at 4GHz, $-$19.06dB at 4.24GHz and $-$21.98dB at 5.44GHz. The related efficient absorption bandwidths ($f_E<-$10 dB) of Fe₃Co₇ NWs, Fe₅Co₅ NWs and Fe₇Co₃ NWs are 5.40GHz, 3.52GHz and 4.91GHz, respectively. It is ascribed to integrating enhanced dielectric/conductive losses, negligible damages from eddy current effect and good impedance matching for high-performance FeCo NWs absorbers. This work paves a new path on synthesizing bimetallic wire-like nanostructures for microwave absorption demands.

Doping carbon materials with heteroatoms such as N, F is an effective approach to elevating the capacitive performance of supercapacitors. In this paper, nitrogen and fluorine dual-doped two-dimensional (2D) porous carbon nanosheets (PCNSs) have been fabricated by a straightforward template carbonization method, using trisodium citrate as carbon source and self-template, and ammonium fluoride as N/F dopants. The N/F-doped carbon samples are well characterized by a series of techniques and measured in a three-electrode system and two-electrode system, respectively. As a result, N/F-doped carbon has delivered large capacitance of 110Fg${}^{-1}$ at 1Ag${}^{-1}$ and high-energy density of 3.82W h kg${}^{-1}$ at the power density of 0.5kWkg${}^{-1}$. It is also revealed that semi-ionic C–F bonds in PCNSs have enhanced electrical conductivity, hence, facilitating electron transport in the electrode. For comparison, ammonium chloride is used as sole dopant for producing N-doped carbon materials, whose capacitive performances are much lower than the N/F-codoped one, indicating the synergistic effect of N/F for capacitive improvement.

The representative spinel-type materials AB₂O₄ (both A and B are transition metals) electrocatalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) have been investigated and significant improvements have been achieved in the activity and durability for ORR and OER in the alkaline solution. But CoFeCoO₄ was not explored widely like ZnCo₂O₄ (or NiCo₂O${}_4)$ as the ORR electrocatalyst for its relatively complicated atomic site occupation. CoFeCoO₄ has a typical cubic spinel structure with Co${}^{2+}$ in the tetrahedron and Co${}^{3+}$ and Fe${}^{3+}$ in the octahedron. A mixture of Co${}^{3+}$ and Fe${}^{3+}$ in the B site makes the oxide have a wider overlap between transition metal 3d orbit and O 2p orbit, which can lead to an effective charge transfer in the rate-determining steps of ORR process and then enhance the ORR activity. The high electronic conductivity and specific surface area of rGO can accelerate charger transfer and provide more catalytic sites, which would contribute to a faster ORR process. In this work, the porous spindle CoFeCoO₄ microparticles which were synthesized by hydrothermal technology, were assembled on the rGO surface to obtain the CoFeCoO₄/rGO composite, which exhibited enhanced ORR activity and catalytic stability comparable to that of Pt/C. On the other hand, the OER catalytic activity of the prepared samples was also studied to explore the potential of CoFeCoO₄/rGO as a bifunctional oxygen catalyst.

3D structure composite made of tiny basic nickel carbonate arrays on the surface of reduced graphene oxide nanosheets (G-NiCH) are prepared by the hydrothermal method. The specific surface area of the G-NiCH composites is twice that of single basic nickel carbonate, which is due to the tiny basic nickel carbonate arrays structure wherein each individual nanoneedle is about 20nm in length and 2nm in width. The G-NiCH electrodes display high-efficiency electrochemical performance with good specific capacitance (1230Fg${}^{-1}$) and excellent stability (100% capacitance retention after 2000 cycles). This is attributed to the synergistic effect that reduced graphene oxide offer fast electron transmission path and basic nickel carbonate act as high effective active material.

In this study, CuO films with hollow cubic cages were prepared by a facile two-step procedure consisting of electrodeposition synthesis and subsequent direct calcination. First, Cu₂O nanocubes were fabricated on ITO substrate through a simple electrodeposition procedure. Then, Cu₂O nanocubes were converted to CuO hollow cubic cages without obvious morphological change through direct calcination. The obtained CuO cubic cages serving as active materials illustrated a favorable performance for nonenzymatic glucose sensing with high sensitivity of $2117.44\mu$AmM${}^{-1}$cm${}^{-2}$ at a low applied potential of 0.50V, fast-response time (less than 3s), low detection limit of 1.0$\mu$M and wide linear range up from 2.0$\mu$M to 1.0mM ($R^2=0.9983$). Moreover, the good selectivity of the CuO cubic cages-based nonenzymatic glucose sensor against electroactive compounds such as ascorbic acid, uric acid and dopamine were also demonstrated. These good features indicate that the as-prepared CuO cubic cages can be used as promising electrode materials, which have a great potential in the development of sensitive and selective nonenzymatic glucose sensors.

In this work, flower-like $\gamma$-AlOOH and $\gamma$-Al₂O₃ nanoarchitectures with excellent surface and mesoporous properties were successfully synthesized in ionic liquid-assisted hydrothermal reaction system. The as-prepared suprastructures were characterized by several techniques, such as X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and nitrogen adsorption/desorption measurement. The formation mechanism of flower-like $\gamma$-AlOOH mesoporous crystallites by ionic liquid-assisted hydrothermal process was proposed and discussed. Flower-like $\gamma$-Al₂O₃ nanostructures were obtained by calcining the as-prepared $\gamma$-AlOOH at 600^∘C for 2h, preserving the same morphology.

Cellulose nanofibers, detached from natural plants, are very promising for applications in the energy storage devices. The swelling of cellulose nanofibers provides abundant paths in the hybrid hydrogels for ion diffusion towards the active material. There is an optimal composition of 50wt.% for cellulose nanofibers in the hybrid hydrogels due to the balance between ion diffusion and electron transport, that is, facilitated by conductive graphite nanoplatelets. The aqueous Zn-ion batteries, assembled from the optimized hybrid hydrogels, have a high-specific capacity of 149.4mAh/g and energy density of 113.2mWh/g, respectively. Moreover, high flexibility of the aqueous Zn-ion batteries is guaranteed by the hybrid hydrogels. There is only a little decay in the electrochemical performance under mechanical bending.

Novel hierarchical porous NiMoS₄ microspheres with high electrochemical performance was successfully prepared using a facile one-step hydrothermal method. The dual application of porous NiMoS₄ microspheres in energy harvesting and storage (i.e., dye-sensitized solar cells (DSSCs) and supercapacitors (SCs), respectively) is explored. In contrast to NiS₂ nanosheets, MoS₂ nanosheets and Pt counter electrodes (CEs), the NiMoS₄ microspheres CE demonstrated the lowest charge transfer resistance and highest electrocatalytic activity for the I${}_3^{-}$/I⁻ redox couple reaction. The NiMoS₄-based DSSC showed a higher power conversion efficiency (8.9%) even than that of Pt-based DSSC (8.7%) under simulated standard global AM 1.5G sunlight (100mWcm${}^{-2}$). As an electroactive material for SCs, the assembled NiMoS₄//AC asymmetric supercapacitor showed excellent specific capacitance (118.7Fg${}^{-1}$ at 1A${\mathrm{\text{g}}}^{-1})$, high energy density of 42.2Whkg${}^{-1}$ (with a power density of 799.2Wkg${}^{-1})$, and superior cycling durability with a specific capacitance retention of 79.5% after 9000 cycles at 3Ag${}^{-1}$.

Holey Fe-Anderson-type polyoxometalate/polyaniline/graphene (PPG) hybrid materials were first prepared by anchoring Anderson-type polyoxometalates [FeMo₆O${}_{24}$H₆]${}^{3-}$ (FeMo${}_6)$ onto graphene modified with polyaniline via a facile hydrothermal treatment. The as-prepared materials exhibited an excellent electrochemical performance with a high specific capacitance of 1366 F g${}^{-1}$ at 1 A g${}^{-1}$ and outstanding cycling stability (97.6% capacitance retention after 5000 cycle times). The uptake of polyaniline/FeMo₆ nanoparticles on graphene not only provided the pseudocapacitance but also weakened the aggregation between the graphene layers, resulting in a higher surface area compared with pure graphene. In addition, the AC//PPG-15 asymmetric supercapacitor device showed a high energy density of 24.65W h kg${}^{-1}$ at a low power density of 326.25W kg${}^{-1}$ and good cycling stability (94.82% capacitance retention after 5000 cycles). Hence, the as-prepared PPG hybrid materials in this work possess tremendous potential as electrodes for high-performance supercapacitors.

Bi₅O₇I microflowers were synthesized through a simple liquid coprecipitation under alkaline condition at 75^∘C in an open system without using autoclave or other complex equipment. The addition of NaBr was a key factor for controlling the morphology of Bi₅O₇I. The assembled Bi₅O₇I samples are constructed by elementary nanowires, which were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and UV-Vis diffuse reflection spectroscopy (UV-Vis DRS) methods. The photocatalytic performance of Bi₅O₇I samples on rhodamine B (RhB), methylene blue (MB) and ciprofloxacin (CIP) was evaluated under 350 W xenon lamp irradiation. On comparison with the blank Bi₅O₇I microflowers, Bi₅O₇I microflowers with NaBr addition exhibited better photocatalytic performance, and the photocatalytic activity enhanced with the increase of NaBr amount. The photocatalytic efficiency reached 81.1% in 150min for RhB, 42.5% in 210min for MB and 56.3% in 210min for CIP in the degradation system at $\mathrm{\text{pH}}=7$ without any assistant agent. Trapping experiments were performed to reveal the degradation mechanism of Bi₅O₇I samples. It was proposed that valid separation of photogenerated electrons and holes in Bi₅O₇I microflowers led to good catalytic properties.

Lithium-ion batteries have received considerable attention as energy storage tool for modern-life equipments. However, drawbacks like low electric conductivity and volume expansion are the obstacles that hinder its application. To solve these problems, we developed a facile method using waste eggshell as hard template to reduce its particle size and change its morphology by simple hydrothermal process. Then, by utilizing waste paper, conductive paper (CP) current collector with graphene and multiwalled carbon nanotube implanted was prepared and combined with MnO₂ anode material. The composite anode shows extraordinary electrochemical performances like much smaller impedance, high reversible capacity of 1767/1762mAh/g even after 200 cycles at 100mA/g, superior rate performance, etc. Compared with anode using metal current collectors, this composite anode will reduce weight and can be generalized to other high energy storage applications. Our environment-friendly method has far-reaching referential significance to other active materials and battery systems.