Nano

High-performance permanent magnets (PMs) have gained high and growing interest due to their excessive demand in energy conversion systems and electric vehicles. PM-based electric machines exhibit great advantages over traditional motors due to their high efficiency of energy conversion. Nd–Fe–B magnet is the best available magnet in terms of energy-product at room temperature. Replacement of Nd by heavy rare earth (HRE) and of Fe by Co results in an enhanced anisotropy field and an improved thermal stability, but also increases the production costs. Developing a strong PM with minimum use of HRE elements is required due to their high cost, low availability and issues associated with international politics. Grain boundary diffusion (GBD) process allows the HRE to diffuse around the grain boundaries, unlike adding expensive HRE to the middle of a grain. Here, we review the recent progress in PMs, especially the novel development of grain boundary-diffused magnets and nanostructured magnets. GBD processes using RE, fluorides or hydrides of RE and eutectic alloys are discussed. Development of nanostructured PMs using physical and chemical methods such as melt spinning, high-energy ball milling, surfactant-assisted ball milling, mechanochemical method, etc. is elucidated. The current and future trends in the area of high performance permanent magnets are outlined.

Electrochemical energy storage and conversion have been in a significant position for meeting the increasing demand for the development of the society. The design and preparation of high-performance functional semiconductor materials have played a critical role in the development of electrochemical energy storage and conversion. In this context, the nanostructures in functional semiconductor materials provide an alternative route by virtue of their unique and promising nanoscale. Controlling the geometrical parameters of nanostructures and thus forming expected nanomaterials is very important to the investigation and applications of functional semiconductor materials. In this review, we summarized the preparation and applications of the nanostructures for electrochemical energy storage and conversion. It demonstrates simple and controllable design methods for functional materials with ideal nanostructures.

In recent years, many researchers have developed the triboelectric nanogenerators (TENGs) technology to harvest mechanical energy. Here, we proposed a spring-like supporting structure triboelectric nanogenerator (S-TENG) to gain mechanical energy and translate them into electrical energy. From the results, the open-circuit voltage ($V_{\mathrm{\text{oc}}}$) of S-TENG can arrive at 390V, and the short-circuit current ($I_{\mathrm{\text{sc}}}$) of S-TENG can reach 13.13$\mu$A. Also, the transferred charge of S-TENG can get to 130nC, and as for the maximum output power of S-TENG with the size of $2\mathrm{\text{cm}}\times 3$cm, it can reach 1.44mW. Besides, the electrical output signal of S-TENG can reflect the human motion state such as walking, running and jumping. This design not only greatly promoted the TENGs in mechanical energy harvesting but also the development of self-powered human motion sensor.

It is profound to obtain simply carbon nanodots (CDots)-based solid-state fluorescent in photoelectric field. However, synthesizing such material is still faced with a challenge due to the serious quenching effect. Here, a microwave pyrolytic route is reported to rapidly synthesize sulfur (S) and nitrogen (N) co-doping CDots wrapped by the crystalline phthalate (CDots/PA). The results show that CDots/PA presents needle-like crystal to coat abundant cluster of CDots inside, after fully optimizing the preparation conditions. The solid state CDots/PA emits a dazzling fluorescence with the fluorescence quantum yield (FLQY) $=17$%, which is attributed to the formation of barrier from the crystal to avoid the aggregation of CDots. In addition, due to the co-doping of S and N elements, it also presents an orange–red light with a multipeak feature. The excellent photoluminescence (PL) property of CDots/PA gives it an advantage to fabricate light emitting diode (LED)/white light emitting diode (WLED) devices, which achieves an orange light with the correlated color temperature $(\mathrm{\text{CCT}})=1810$K, color rendering index $(\mathrm{\text{CRI}})=59$ and a warm-white light with the CCT $\approx$ 3700K, CRI $\approx$ 82 at the Commission Internationale de L’Eclairage $(\mathrm{\text{CIE}})=(0.43$, 0.40) combined with the commercial phosphors. Moreover, CDots/PA also shows an excellent recognition capacity in the application of detecting latent fingerprints, endowing such fluorescent nanomaterials broad prospect in the photoelectric industry.

Hexavalent chromium (Cr${}^{6+}$), a heavy metal ion, is widely used in a variety of industries, but it is an environmental pollutant and a recognized human carcinogen. Highly selective quantitative detection of Cr${}^{6+}$ is important for environmental pollution monitoring and early disease prevention in humans. In this study, nitrogen-containing carbon quantum dots (N-CQDs) were synthesized by hydrothermal carbonization of Pseudomonas aeruginosa and were found to be efficient detectors of Cr${}^{6+}$, with a detection limit (LOD) of 0.23 nmol L${}^{-1}$(nM). N-CQDs were detectable in plant leaves and onion cells and successfully stained cell membranes and nuclei. Multi-colored images revealed that in Caenorhabditis elegans, N-CQDs entered the digestive tract through ingestion, spared rapidly throughout the body, and were excreted though the anus within 40 min. Synthesis of fluorescent N-CQDs can be exploited to increase the use and a range of applications of bacterial resources. The study methods and results also provide theoretical guidance for future research into the development of bacterial resources.

The research aimed to synthesize the polyethylene glycolylated silver–gold core–shell nanoparticles (Ag@Au NPs), and to evaluate their in vitro and in vivo computed tomography (CT) contrast properties. A range of Ag@Au NPs with varying molar ratios of Ag–Au were prepared and characterized by transmission electron microscopy (TEM), Ultraviolet-Visible (UV-Vis) spectroscopy, dynamic light scattering and inductively coupled plasma mass spectrometry. Micro CT was used to evaluate the X-ray attenuation capabilities of Ag@Au NPs with different compositions. The CT imaging effects of Ag@Au NPs with high X-ray attenuation were detected in U87 glioma cells and a mouse subcutaneous glioma model. The characterization results showed that Ag@Au NPs synthesized with different molar percentages of Ag (75%, 50% and 25%) were spherical, and their mean diameters were between 12–16 nm. Ag@Au NPs with an Ag molar percentage of 50% were selected for subsequent research, because of their excellent X-ray attenuation capability, morphology and dispersibility. The attenuation coefficient of glioma cells treated with Ag@Au NPs increased in a concentration-dependent manner. The contrast of the tumor area of the mice was significantly enhanced in CT images after intratumoral injection of Ag@Au NPs. Our results suggested that Ag@Au NPs could be an excellent CT contrast agent, which provided a new thought for the development of highly efficient contrast agents for tumor CT imaging.

Cow milk is an important source of protein, but it is also a food that can cause allergies. In this research, a novel photoelectrochemical immunosensor based on CdWO₄–CdS type-II heterojunction was constructed for the detection of allergen $\alpha$-lactalbumin ($\alpha$-Lac) in milk. CdWO₄–CdS heterojunction was synthesized by one-step hydrothermal method. Compared with pure CdWO₄, the CdWO₄–CdS heterojunction significantly improved the photocurrent intensity. The polydopamine (PDA) was used as a crosslinking agent to couple basis materials and biomolecules. Ascorbic acid was used as an efficient electron donor to eliminate the photo-generated holes and inhibit the recombination of photo-generated electrons and holes. Under the optimum experimental conditions, the photocurrent intensity reduced linearly with the logarithm of $\alpha$-Lac concentration ranging from 0.001 ng$\cdot$mL${}^{-1}$ to 10 ng$\cdot$mL${}^{-1}$ and the limit of detection was 0.17pg$\cdot$mL${}^{-1}$. The constructed photoelectrochemical immunosensor exhibited excellent stability, selectivity and reproducibility, which provided a novel ideal for sensitive detection of $\alpha$-Lac and shed light on monitoring of other allergenic proteins in foods.

Bismuth has a great potential as the anode for sodium-ion batteries (SIBs) because of the layered structure with large interlayer space, long mean free path, and high volumetric capacity. In this paper, carbon-coated bismuth (Bi@C) core-shell nanostructure has been in situ synthesized by one-step direct current (DC) arc discharge method for the first time. The Bi@C nanocomposite without further decoration or any other treatment exhibits superior electrochemical performance as anode for SIBs and delivers stable capacities of 356, 342, 334, 327, 325, 323, and 318mAhg${}^{-1}$ at the current densities of 0.2, 0.5, 1, 3, 5, 7 and 10Ag${}^{-1}$, respectively. There is no obvious decay after 630 cycles with a capacity of 291mAhg${}^{-1}$ at 10Ag${}^{-1}$, showing the excellent rate capability and long cycle stability in SIBs. Electrochemical tests proved that the ultra-fast charge–discharge performance is related to the fast redox kinetics of Na${}^{+}$ in layered structure of bismuth crystal. The Na${}^{+}$ storage mechanism of Bi@C nanocomposite anode was also investigated by cyclic voltammetry and in situ XRD. Based on experimental data, this paper proves that the arc discharge method is a simple and efficient method for preparing nanoscale electrode materials.

g–C₃N₄ nanosheets were first synthesized by calcining the mixture of hydrochloric acid-pretreated melamine and ammonium chloride. Then, by the aiding of solvothermal method and hydrofluoric acid as morphology modifier, 001-TiO₂/g–C₃N₄ (TCN-X, $X=5$, 3, 2, 1) nanocomposites were synthesized using g–C₃N₄ nanosheets and tetrabutyl titanate, with the mass ratio of g–C₃N₄ to TiO₂ was 5:1, 3:1, 2:1 and 1:1, respectively. The as-synthesized samples were characterized by X-ray diffraction, scanning electron microscope, transmission electron microscopy, Fourier transform infrared spectroscopy, nitrogen adsorption–desorption method, ultraviolet–visible diffuse reflectance spectrum, photoluminescence spectrum, etc. Their photocatalytic properties were evaluated under visible light irradiation with rhodamine B (RhB) as the target pollutant. The results reveal that the TCN-3 composites had a large specific surface area of 67.38m²/g and consisted of g–C₃N₄ nanosheets and anatase TiO₂ crystals about 10–20nm in size. The (001) crystal planes of TiO₂ can be easily observed in TCN-X composites. All TiO₂/g–C₃N₄ composites exhibited excellent photocatalytic activity compared with the pure g–C₃N₄ did. The photocatalytic property of TCN-X samples varied with the mass ratio of g–C₃N₄to TiO₂, and TCN-3 presented the optimum photocatalytic performance. In total, 50mg of TCN-3 completely degraded 50mL and 100mL of RhB solution (10mg/L) in 15min and 40min, respectively. The reaction rate constant of TCN-3 was 6.7 times as large as that of pure g–C₃N₄. TCN-3 also presented outstanding activity for the photocatalytic degradation of the colorless tetracycline solution. The significant improvement in photocatalytic activity of TCN-3 was attributed to the evenly distribution of TiO₂ on g–C₃N₄, the enhanced specific surface area and the construction of 001-TiO₂/g–C₃N₄ heterojunction between the g–C₃N₄ nanosheets and the (001) crystal planes of anatase TiO₂, which greatly reduced the recombination rate of the photo-generated electron and hole.

Semiconductor materials used in the field of photocatalysis have been attracting much attention. Due to the advantages of green, pollution-free and sustainable development of solar energy, it is an ideal strategy to explore excellent semiconductor materials as high light photocatalysts for energy conversion. Herein, Bi₄Ti₃O${}_{12}$/CdS composites were synthetized by coprecipitation method, which CdS particles selectively deposited on Bi₄Ti₃O${}_{12}$ nanosheets. The phase structure and optical properties of the samples were characterized by XRD, SEM, N₂ adsorption–desorption and UV-visible diffuse spectra (UV-DRS). The results showed that the Bi₄Ti₃O${}_{12}$/CdS composites had the highest photocatalytic activity against RhB under visible light, and the degradation rate of RhB was 98.8% after 120min of simulated light, 2.14 times that of pure Bi₄Ti₃O${}_{12}$, and the Bi₄Ti₃O${}_{12}$/CdS-10wt.% composites also showed good stability. UV-DRS demonstrated that the optical absorption range of the composite extends to visible regions, and photocurrent tests also showed that the composite enhances the separation and migration of photoogenic electron–hole pairs, mainly due to the formation of 2D nanosheets/0D particles heterojunctions between the bronzn CdS of the perovskite BTO and hexagonal fibers. Furthermore, free radical assays confirmed that both $\cdot$O${}_2^{-}$, h${}^{+}$ and $\cdot$OH have effects in the degradation of RhB, and thus suggested a possible mechanism for the photodegradation process of the Bi₄Ti₃O${}_{12}$/CdS-10wt.% composite photocatalyst.