Nano

A green synthesis of gold nanoparticles (AuNPs) using aqueous solution of sodium alginate (SA) has been demonstrated in this work. The SA plays the roles of both reducing and stabilizing agent. The surface plasmon resonance (SPR) band of UV-Vis spectrum around 532nm confirmed the formation of AuNPs. The characterization through high resolution-transmission electron microscopic (HRTEM), energy dispersive X-ray (EDX) spectroscopy and X-ray diffraction (XRD) infer the as-synthesized AuNPs which were spherical in shape with a face cubic crystal (FCC) structure. The results obtained from zeta potential and dynamic light scattering (DLS) suggest the good stability and narrow size distribution of the AuNPs. The size-controlled AuNPs were obtained through adjusting the reaction parameters such as the concentration of SA, pH of the reaction mixture, temperature and the time of incubation. The as-synthesized AuNPs–SA conjugates were employed to prepare AuNPs–SA beads easily based on SA high affinity toward divalent metal ions. The resulting AuNPs–SA beads function as an efficient heterogeneous catalyst in reducing decoloration of azo-dye model compounds, acidic orange 7 (AO7) and reactive orange 5 (RO5), in the presence of sodium borohydride. The reaction rate constants, estimated based on the reduction reactions followed pseudo-first-order kinetics, suggest the high catalytic activity and stability of the AuNPs–SA beads.

Fluorinated SnO₂ hollow nanospheres (HS) were synthesized via a solvothermal treatment of stannous fluoride in the presence of hydrogen peroxide. These nanospheres with diameters from 60nm to 100nm were composed of small nanoparticles with rutile phase. A small amount of fluorine ions were observed to be adsorbed on the surface of SnO₂ physically. The introduction of polyethylene glycol 200 (PEG 200) in the reaction system could obviously improve the crystallinity and specific surface areas of the product while maintaining the hollow nanosphere structure. Furthermore, the as-prepared SnO₂ sample (HS-PEG) showed a much enhanced photocatalytic activity with 100% degradation of Rhodamine B (RhB) within only 40min under UV light irradiation.

Low-density Fe-doped ordered mesoporous carbon (CMK-3)-silica (SBA-15) nanocomposites with different Fe contents have been prepared by a catalytic carbonization procedure followed by high-temperature calcination in N₂. From field emission-scanning electron microscope (FE-SEM) and high resolution-transmission electron microscope (HR-TEM) images, it can be concluded that CMK-3 particles are dispersed homogeneously into a silica matrix and form a novel, special and interesting composite nanostructure. The metal species ($\sim$18nm) are dispersed on the surface of frameworks during the catalytic carbonization procedure and endow a magnetic property to the carbon–silica nanocomposites. The optimal reflection loss (RL) calculated from the measured permittivity and permeability is $-$19dB at 17.2GHz for an absorber thickness of 2.00mm. Moreover, the electromagnetic (EM) wave absorption less than $-$10dB is found to exceed 5.76GHz as the layer thickness is 2.37 mm. The permittivity dispersion behaviors have been explained based on the Cole–Cole model and the conductivity contribution model. A new simple empirical model was also supposed to find the fitted curves of the multi-resonance imaginary permeability spectra of the composites. The EM wave can hardly be reflected on the absorber surface because of a better match between dielectric loss and magnetic loss, which originates from the combination of dielectric carbon–silica and magnetic Fe species.

A novel electrochemical immunosensor for determination of carcinoembryonic antigen (CEA) in human serum was fabricated by depositing Mo–Mn₃O₄/MWCNTs/Chits nanocomposite onto an indium-tin oxide (ITO) electrode. Mo-doped Mn₃O₄ (MMO) was synthesized by sol–gel method and the presence of molybdenum improved its electrochemical properties. The MMO/MWCNTs/Chits nanocomposite could accelerate the electron transfer rate and enlarge the surface area to capture a large number of Carcinoembryonic Antigen (CEA). The factors influencing the performance of the immunosensor were investigated, such as incubation time, incubation temperature and pH. Under optimal conditions, the electrochemical immunosensor could detect CEA in a linear range from 0.1ng$\cdot$mL${}^{-1}$ to 125ng$\cdot$mL${}^{-1}$ with a detection limit of 4.9pg$\cdot$mL${}^{-1}$ ($S∕N=$$3$). In addition, it exhibited high sensitivity and acceptable stability on a promising immobilization platform for signal amplification, which could be extended to other labeled recognition systems. This electrochemical immunosensor may provide potential applications for the clinical diagnosis.

Multi-walled carbon nanotubes (MWCNTs) produced by chemical vapor deposition (CVD) are the most common commercial products at extremely low price in the market. However, due to the inherent drawbacks of CVD surroundings at temperature below $\sim$1000${}^{\circ }$C, CVD-grown nanotubes usually have very disordered structure, resulting in most of their properties being much below expectations. Herein, we present a simple and energy-efficient method for improving rapidly the structure of CVD-grown MWCNTs via a drastic thermite reaction process. Direct observations from scan electron microscope (SEM) and transmission electron microscope (TEM) images, decrease of $I_D∕I_G$ ratios in Raman spectra, increase of the starting oxidation temperatures observed in thermogravimetric analysis (TGA), decrease of the volumetric electrical resistivity and decrease of the turn-on electric fields from 3.64 to 2.88V/$\mu$m in field emission measurements suggest that the graphitization of MWCNTs can be effectively enhanced and the structure of nanotubes becomes more ordered after the drastic thermite reaction process.

Co-precipitated undoped and Fe-doped WO₃ nanomaterials have been investigated by X-ray diffraction, Raman spectroscopy and scanning electron microscopy in order to study the influence of Fe doping in their structural and morphological properties. The synthesized WO₃ nanomaterials have been found to possess monoclinic structure having average crystallite sizes 15–20nm. The diffuse reflectance spectroscopy shows the optical bandgap $\sim$2.85eV. The 1.8 at.% Fe-doped WO₃ exhibits selective high response to formaldehyde over methanol, ethanol, propan-2-ol and acetone. It exhibits the maximum response ($\sim$80%) to formaldehyde at the operating temperature of 225${}^{\circ }$C for 50ppm concentration in air.

Systems with nanoscale dimensions have attracted great attention for many decades since they manifest interesting size-dependent behavior and have many possible technological applications. While significant progress has been made toward the experimental and theoretical understanding of various phenomena at nanoscale, much is yet is to be explored in fully comprehending how the interplay of several parameters such as shape, size and dimensionality affects the resulting properties. In this work, we study the nature of the interaction in a nanosystem consisting of a charged nanoplate and a charged nanowire. The two constituent nanostructures of this nanosystem represent important building blocks for bottom-up assembly processes. We consider a specific orientation of the two nanostructures and calculate exactly their interaction energy as a function of shape, size and relative distance. With help from suitable though nontrivial mathematical transformations, we are able to derive a closed form exact expression for such an interaction energy. It is shown that the interaction energy of this configuration is very sensitive to shape and depends in a nontrivial way on size and separation distance.

Gold core-induced polypyrrole nanohybrids (Au–PPyNHs) were successfully synthesized via in situ chemical oxidation polymerization of pyrrole molecules, and their structure was directly confirmed and characterized by scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy and X-ray diffraction. Furthermore, gold nanoparticles (AuNPs) were assembled onto the as-prepared Au–PPyNHs by electrostatic interaction to fabricate the nanohybrids of Au–PPyNH–Au. The created Au–PPyNH–Au nanohybrids was immobilized onto glassy carbon electrode and applied to construct dopamine (DA) sensor. We found that the fabricated sensor with Au–PPyNH–Au nanohybrids is highly specific probe for sensing DA. The Au–PPyNH–Au based DA sensor has a linear detection range from 1$\mu$M to 0.321 mM and a detection limit of 0.32$\mu$M.

Functionalized carbon nanotubes (MWNT–COOH) was selected as conducting wrapping agent to prepare composites of MWNT–COOH and carbonized polyaniline (C–PANI), to improve the supercapacitive performance of C–PANI. The morphology was characterized by scanning electron microscope and transmission electron microscope which showed that C–PANI was trapped in the conductive network of MWNT–COOH. The electrochemical measurement results indicated the increased specific capacitance and enhanced cycling stability of C–PANI with the addition of MWNT–COOH. When the weight ratio of C–PANI and MWNT–COOH was 4:1, the specific capacitance of the composites was 149 Fg${}^{-1}$, and the capacitance retention was 93.7% after 1000 charge–discharge cycling.

Multilayered nanoshells have attracted much attention due to their unique optical, electronic and magnetic properties. In this work, numerical calculation using discrete dipole approximation (DDA) is conducted to investigate the quad-layered metal nanoshell consisting of a particle with a dielectric silica (SiO₂) core, inner cadium sulfide (CdS) shell, middle indium tin oxide (ITO) shell and outer metal silver (Ag) shell. The phenomenon is interpreted by plasmon hybridization theory and the Ag–ITO–CdS–SiO₂ multilayered nanoshells are studied by extinction spectra of localized surface plasmon resonance. The variation in the spectrum peak with nanoparticle thickness and refractive index of the surrounding medium is derived. The electric field enhancement contour around the nanoparticles under illumination is analyzed at the plasmon resonance wavelength. The $|{\omega }_{-}^{-}〉$, $|{\omega }_{-}^{+}〉$, and $|{\omega }_{+}^{-}〉$ modes red-shift with the refractive index of the surrounding medium and increase in the layer thickness causes either blue-shift or red-shift as shown by the extinction spectra. The mechanism of the red-shift or blue-shift is discussed. The $|{\omega }_{-}^{-}〉$ mode blue-shifts and furthermore, the $|{\omega }_{+}^{-}〉$ and $|{\omega }_{-}^{+}〉$ modes of the Ag coated multilayered nanostructure are noticeable by comparing the extinction efficiency spectra of the Au–ITO–CdS–SiO₂ and Ag–ITO–CdS–SiO₂ multilayered nanoshells.

Phase-change probe memory using Ge₂Sb₂Te₅ has been considered as one of the promising candidates as next-generation data storage device due to its ultra-high density, low energy consumption, short access time and long retention time. In order to utmostly mimic the practical setup, and thus fully explore the potential of phase-change probe memory for 10 Tbit/in² target, some advanced modeling techniques that include threshold-switching, electrical contact resistance, thermal boundary resistance and crystal nucleation-growth, are introduced into the already-established electrothermal model to simulate the write and read performance of phase-change probe memory using an optimal media stack design. The resulting predictions clearly demonstrate the capability of phase-change probe memory to record 10 Tbit/in² density under pico Joule energy within micro second period.

A facile one-step method was developed for the first time to fabricate BiOCl film on Cu substrate by simply dipping the Cu substrate in the mixed solution containing HCl, glycol, H₂O₂ and BiCl₃. This method shows the advantages of a simple technique, uniform and controllable morphology, as well as easy mass production. The absorption capacity of BiOCl film was investigated by adsorption of Rhodamine B and Congo red (CR) and their maximum adsorption capacities were 1667mgg${}^{-1}$ and 1429mgg${}^{-1}$, respectively. The negative values of free energy and the positive values of enthalpy suggested that the adsorption were spontaneous and endothermic, respectively. Moreover, both adsorptions were matched with the pseudo-second-order equation. This film could be reused and the recycle rates for Rhodamine B and CR were still about 95% and 75% after five cycles, respectively. The adsorption mechanism revealed that hydrogen bond mainly accounted for the adsorption of dyes.

In the hydrogen storage problem, if an attractive potential well is formed inside the void space of porous materials, the storage gas density is expected to increase significantly compared to the H₂ gas density outside the material. Actually, the overall H₂ density inside the material is enhanced basically by a Boltzmann factor of exp[$-U$/kT] where U ($<$0) is some averaged potential energy. Corresponding to this negative potential energy, latent heat is released in the H₂ gas confinement process. We theoretically investigate the energetics involved during the H₂ storage in the potential well and, from the equilibrium thermodynamic principles, we derive a formalism for the isosteric heat of potential confinement of the H₂ gas. Since the gas density inside the potential well increases tremendously, the van der Waals equation is adopted to describe the nonideal gas behavior of H₂. We compare our results to the well-known expression for the isosteric heat of adsorption where, unlike our case, the molecules are bound to specific adsorption sites in the material.

Graphene oxide nanosheet (NGO) was covalently functionalized with positively charged, branched polyethylenimine (bPEI) via an amide bond, coated with serum proteins by electrostatic interaction. Operating as a newly fashioned, multifunctional nanocarrier, the processed NGO showed promise for use in combined gene therapy, chemotherapy, photothermal therapy, bioimaging and as a biosensor of cancer cells. Our current research is focused on the systematic studies of mechanisms of cancer cellular uptake, subcellular location, cytotoxicity and the cellular exclusion of the NGO–bPEI nanocarriers. It was observed that NGO–bPEI accumulated in the mitochondria and that long-term retention of NGO–bPEI led to a decrease in mitochondrial membrane potential while levels of reactive oxygen species increased. The mitochondrial effects associated with long-term retention of NGO–bPEI have potential as a synergistic enhancer of the cytotoxic effects of anti-cancer drugs or genes in human lung carcinoma (A549) cells. This work demonstrated the utility of NGO–bPEI-based multifunctional nanocarriers while detailing the mechanism at the cellular level and providing guidance for further research in cancer therapy.

Allura red (AR) is a water-soluble synthetic colorant often used as an additive in the food industry, but excess AR can be harmful to human health. In this work, we report the development of a new removal method for AR by using amino-functionalized microspheres with Fe₃O₄ cores and twolayer shells composed of SiO₂ particles and perpendicularly aligned mesoporous SiO₂ (designated Fe₃O₄@nSiO₂@mSiO₂–NH₂). The material exhibits good dispersibility in aqueous solutions and a high saturation magnetization of 45.68emug${}^{-1}$, and can be magnetically separated efficiently with an external magnet. Importantly, the material has great adsorption capacity of 29.6mgg${}^{-1}$ for AR and the capacity for reuse with a simple treatment. The adsorption process is very fast and the kinetics data are consistent with a pseudo-second order model. Based on these, a rapid and efficient method for extraction and analysis of AR in water and soft drinks has been established.

A novel strategy toward one-pot hydrothermal synthesis of copper sulfide nanoplates-decorated reduced graphene oxide (RGO–CuS) composites was developed. CuS nanoplates were successfully loaded onto the surface of RGO in the hydrothermal procedure, which was confirmed by transmission electron microscopy, UV-Vis–NIR and Raman spectroscopy. The as-synthesized RGO–CuS composites showed pronounced enhanced optical absorbance in near infrared (NR) region and higher photothermal conversion efficiency than noncomposite GO and CuS nanoplates. The RGO–CuS materials were used in photothermal ablation of cancer cells with a 980nm laser irradiation and showed improved performance than CuS nanoplates.