Nano

The Quantum Dots/Graphene (QDs/GR) composites have attracted numerous interests caused by its unique physical and chemical properties in past few decades. The shortages of the single QD and graphene materials could be remedied by the synergistic effects from QDs/GR composite materials; meanwhile, some unique phenomena and superior physical properties were also produced. The QDs/GR composites processed better photocatalytic activities, higher photon capture abilities and excellent optical responsibilities. Therefore, they were widely applied in various techniques. Here, we reviewed and discussed recent research progresses about the QDs/GR composites and focused on their industrial preparation and commercial applications. Among these synthetic methods, ion beam sputtering deposition (IBSD) and molecular beam epitaxy (MBE) were discussed in detail because they could be directly applied in commercial industry for preparing size-tunable quantum dots. In another part, the applications of the QDs/GR composites were also discussed, the advanced physical and chemical properties promoted these composites to have numerous potential for being applied in photodetectors, lithium ion batteries, solar cells, supercapacitors and other devices. The appropriate synthetic method for QDs/GR materials is highly dependent on the requirements of its applications. We firmly believe that the direct synthesis technique of ideal QDs/GR composite for specific applications is a challenge and research emphasis for scientist and engineers in future.

Cobalt phosphide (CoP) has aroused extensive research interest in a field of electrochemical application due to its excellent catalytic activities. CoP and its compounds have been widely reported using in hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). However, few reports about CoP as electrocatalysts for oxygen reduction reaction (ORR) were presented. In this work, we prepare reduced graphene-oxide(rGO)-loaded CoP (rGO@CoP) as an electrocatalyst for ORR through in situ hydrothermal treatment. The rGO@CoP as ORR catalyst exhibits excellent activities where its onset potential has a positive increase of 129mV, and the ORR potential achieves an increase of 330mV at a current density of 1.0mAcm${}^{-2}$ compared with that of pure CoP. The current density is also significantly improved with an increase of 0.51mAcm${}^{-2}$ at $-$350mV, and the Tafel slope has a decrease of 19mV dec${}^{-1}$. Further tests show that the electron transfer number of rGO@CoP is 3.66, which is larger than 2.19 of pure CoP, indicating that it is dominated by a four-electron transfer pathway. Moreover, its stability (remained 98.6% current after working 6000s) and methanol tolerance are outstanding. These results show that rGO@CoP may be considered to replace traditional Pt-based ORR catalysts for fuel cells, and rGO loading has been proven to be an effective strategy to enhance the ORR performance of CoP, which may provide a new idea to synthesize transition metal phosphides as ORR catalysts.

In the present study, a controlled release electrochemical (CRE) technique based on the controlled release of Cu${}^{2+}$ ion from Cu anode in the presence of decanoic acid (HDe) has been used to synthesize Cu(II) decanoate (CuDe₂) complex. The effect of applied voltages (1–10V) and electrolyte concentrations (0.1–2.0M CH₃COONH₄) during the electrolysis on the nanoparticles obtained was studied using TEM. The results reveal that small-sized nanoparticles ($2\pm 1$nm) were obtained by using lowest applied voltage and CH₃COONH₄ concentration (1V and 0.1M, respectively). The smallest nanoparticle obtained was then used in the cytotoxicity study against A549 and HeLa cells. The synthesized complex gives moderate cytotoxic effect on the selected cells (IC${}_{50}=15.85\mu$M and 20.89$\mu$M, respectively) and low cytotoxic effect on normal cells (IMR90). Apoptosis is the mode of cell death based on the apoptosis assay that has been conducted.

In this work, we designed a simple substrate-immersed solvothermal route for the one-step synthesis of novel ordered SiO₂/Ag arrays, employing SiO₂ colloidal crystals as templates and alcohol as reducing agent. The Ag nanoparticles were uniformly deposited in situ onto SiO₂ colloidal crystals, which exhibited high surface enhanced Raman spectroscopy (SERS) activity and uniform SERS intensity. It was found that ordered SiO₂/Ag arrays could rapidly scavenge the absorbed-Nile blue A (NBA) molecules from the surfaces with the assistance of H₂O₂, while the SERS signals of NBA decreased sharply and almost completely disappeared within four minutes. This can be attributed to the superior catalytic activity of Ag nanoparticles. After five times of re-immersion and re-absorbing process of NBA, the substrates could still keep $\sim$ 74.8% SERS intensity versus the original. The high activity and durability of the as-prepared SiO₂/Ag SERS substrate endow them as a promising candidate for trace detection.

Transition metal oxides as Li-ion batteries (LIBs) anodes have attracted much attention because of their high theoretical capacity. However, the large volume change and low electrical conductivity still hinder their application in LIBs. In this work, a new strategy is proposed to enhance the electrochemical performance by anchoring ultrafine MnFe₂O₄ and MnCO₃ ($\sim 5$nm) on amorphous carbon-coated carbon nanotubes. Benefiting from the unique structure, the electrode displays excellent cyclability with a reversible specific capacity of 1012mAh g${}^{-1}$ at 0.1A g${}^{-1}$ after 100 cycles and outstanding rate performance accompanied by a high specific capacity of 568mAh g${}^{-1}$ at 5A g${}^{-1}$ as anode for lithium batteries. When evaluated as supercapacitors, the electrode delivers the specific capacitance of 588.9F g${}^{-1}$ at a current density of 1A g${}^{-1}$ and maintains the capacitance retention 94.7% after 4000 cycles at 5A g${}^{-1}$.

The Bi₂S₃-TiO₂-RGO composites were synthesized by a facile one-step hydrothermal method and applied for the photocatalytic degradation of Rhodamine B (Rh B) under the visible light. The Bi₂S₃-TiO₂-RGO composites were characterized by transmission electron microscopy, X-ray diffraction, Raman and Fourier transform infrared spectrometer. The results indicated that the Bi₂S₃-TiO₂-RGO composites were successfully prepared, and Ti-O-C and S-C bonds were existing among Bi₂S₃, TiO₂ as well as RGO. Furthermore, the photocatalytic ability of Bi₂S₃-TiO₂-RGO composites was excellent under visible light due to its responding to the whole visible light region, low recombination rate of photogenerated electron–hole pairs and relatively negative conduction band. Rh B photocatalytic degradation rate was 99.5% after 50min and still could reach 98.4% after five cycles. Finally, a formation mechanism as well as a photocatalytic mechanism of Bi₂S₃-TiO₂-RGO composites were proposed based on the experimental results.

Core–shell Cu@Ni chains were successfully synthesized through a mild hydrothermal reaction. The morphology, structure and microwave electromagnetic properties of the composite were then characterized by X-ray diffraction, energy-dispersive spectroscopy, scanning electron microscopy and vector network analysis. The formation mechanisms of the core–shell structure and one-dimensional chains were ascribed to the varying redox potentials of Cu and Ni ions and the magnetic dipole–dipole attraction. Furthermore, a minimal reflection loss (RL) of $-$20.7dB was observed at 9.6GHz with a thickness of 2.0mm and the effective absorption ($\le$10dB, 90% microwave attenuation) bandwidth can be adjusted between 5.2GHz and 16.6GHz for the thin absorber thickness of 2.0–4.0mm. The novel core–shell chain-like Cu@Ni alloy can be used as a promising absorbing material because it shows numerous features such as thin thickness, strong absorption, low cost and lightweight.

Novel surface-enhanced Raman scattering (SERS) substrates with stable and recyclable properties have been prepared by assembling gold nanoparticles-loaded PET (AuNPs/PET) nanocomposite superhydrophobic surfaces. After a physical vapor deposition process, the AuNPs/PET surfaces with vast plasmonic “hot spots” showed superhydrophobic properties, and it can hold target molecules droplets for rapid SERS detection. From blown off droplets and rinsed substrates with water after detection, we found that no probe molecules remained on the surfaces from Raman spectra. The prepared substrates were not contaminated in the detection process. Furthermore, the new SERS substrates were used for rapidly detecting droplets of crystal violet (CV) and the lowest detection concentration was about $1\times 10^{-9}$ M. The as-prepared AuNPs/PET substrates also have good performance in terms of reproducibility and recyclability.

A photoelectrochemical (PEC) sensor for the determination of organophosphate pesticides (OPs) was developed based on rGO/TiO₂/CdS photoactive nanomaterials. The rGO/TiO₂/CdS nanocomposites were prepared by solvothermal method and electrochemical deposition technique successively. The morphologies and structures of the as-prepared nanocomposites were extensively investigated by SEM and XRD. In alkaline condition, p-nitrophenol as the hydrolysate of parathion-methyl (PM) could be obtained by a simple hydrolyzation process. Under optimal conditions, the rGO/TiO₂/CdS NPs modified ITO electrode exhibited a good PEC performance toward the hydrolysate of PM. The photocurrent intensity was enhanced with the increase of the concentration of the hydrolysate of PM. The proposed PEC method could detect PM in the range from 0.05nmol L${}^{-1}$ to 10nmol L${}^{-1}$ with a detection limit of 0.02nmol L${}^{-1}$ ($S∕N=3$). Thus, the excellent performance of the rGO/TiO₂/CdS nanocomposites serve as the matrix of the sensor, which provides a new way for the fabrication of high-sensitivity PEC sensing system.

The biaxial and planar characteristics of surface stress produce a parabolic differential stress distribution inside the sensing zone of microcantilever biosensors, which can be used to design novel biosensors. The present work studies and compares the effect of parabolic and conventional rectangular-shaped piezoresistor placed inside this sensing zone on sensitivity of the biosensors. Two different cantilevers made of silicon and silicon dioxide with doped silicon as piezoresistor are used in five design variations. The cantilevers are characterized for their deflections, von Mises stresses, resonant frequencies and self-heating temperatures produced using ANSYS. Analytical models for predicting deflections in the cantilevers is presented and compared with numerical results obtained. Results show good compatibility between analytical and numerical values for deflection with a 4–5% average deviation and that parabolic designs have higher sensitivity.

A TiO₂ photocatalyst with peony-like microstructures and a large percentage of exposed {001} facets was synthesized using a facile solvethermal method. The peony-like TiO₂ was obtained using HF as a capping agent, TiCl₄ as the precursor and ethanol as the solvothermal agent. The parameters which influence the mophology and formation mechanism of the products including the HF concentration, the reaction time and temperature and the solvothermal solvent, were investigated. The samples were characterized using field emission scanning electron microscopy, transmission electron microscopy, X-ray diffraction and N₂ adsorption and desorption analysis. As the reaction time or reaction temperature increased, the morphology TiO₂ changed from hexagonally assembled microspheres to peony-like microflowers which were composed of stacks of ultrathin nanosheets. The other reaction parameters also play a crucial role in the formation of the TiO₂ microstuctures. Photocatalytic experiments showed that the synthesized TiO₂ outperformed Degussa P25 in the photodegradation of methelene blue under a very weak UV light irradiation (power: 8W, light intensity: 0.4mWcm${}^{-1}$).

The incorporation of dopant atoms alters the structure of MoS₂, resulting in unique properties and practical applications. Herein, a facile and low-cost approach for producing N-doped molybdenum disulfide (N-MoS${}_2)$ was carried out using melamine and MoS₂ in a laboratory tube furnace at 400${}^{\circ }$C for 2h. The N-MoS₂ fluorescent probe showed sensitive response to Hg${}^{2+}$ in a wide concentration range of 0.4–10$\mu$M with a low limit of 28nM. The practical applicability of detecting Hg${}^{2+}$ in lake water samples may open a new way to evaluate Hg${}^{2+}$ in wastewater.

Nanoporous copper (NPC) and nanoporous copper-nickel (NPC-Ni) can be prepared by free corrosion dealloying Mn${}_{72}$Cu${}_{28-x}$Ni_x ($x=0$, 1, 3at.% Ni) precursor alloys. Microscopic morphology characterization by scanning electron microscopy exhibited a three-dimensional bicontinuous porous structure with nanoscale ligaments and pores. NPC with a pore size of 48.7nm was obtained in 0.1M hydrochloric acid solution for 3.5h dealloyed at 25${}^{\circ }$C. Under the same free corrosion dealloying condition, NPC-Ni₁ and NPC-Ni₃ were obtained with the pore size of 36.6nm and 28.1nm, respectively. The results indicate that minor Ni atoms addition to the precursor greatly refined the dealloyed nanoporous structure. This effect could be attributed to the lower Ni surface diffusivity than that of Cu and resulted in slow down of the diffusion and rearrangement of Cu atoms during dealloying process. Post-dealloying heat treatment at 300${}^{\circ }$C, 450${}^{\circ }$C and 600${}^{\circ }$C made the ligaments coarsen in NPC and NPC-Ni.