Nano

Modification by electronic excitation of semiconductor surfaces and carbon-related quasi-two-dimensional (2D) nanostructured materials, namely graphene, carbon nanotubes is reviewed. Defect creation in these materials takes place not by low-intensity photoirradiation, but by laser or electron irradiation. The defect creation processes are different from ordinary photochemical processes in molecules or in some solids like alkali halides, which can be modified by a localized exciton. It is pointed out that there are common features in defect creation by electronic excitation in semiconductor surfaces and carbon-related quasi-2D nanomaterials: the yield-intensity relation shows strong superlinearity for laser irradiation near the bandgap energies and linearity or weak superlinearity for higher energy electron or photon irradiation. These results are explained in terms of multi-hole localization, in which bonds are weakened more strongly and more energy is available upon recombination with trapped electrons in comparison with excitons. The multi-hole localized state is considered to be realized by the creation of dense excitons or by cascade excitation for laser irradiation and by multiple excitations or multiple exciton generation by single impacts for electron irradiation. The review includes also polymerization of C${}_{60}$ films by electronic excitation, which is induced by low-intensity photoirradiation as well as by laser or electron irradiation. The experimental observation that laser or electron irradiation polymerize C${}_{60}$ films differently from low-intensity photoirradiation is explained in terms of multi-hole localization similar to the defect formation mechanism. Although fragmentation of C${}_{60}$ is due to electronic excitation of the molecule, it is included in the review because its yield is strongly superlinear for laser irradiation near bandgap energies and weakly superlinear for high-energy electron or photon irradiation as for other cases.

To reveal the wear mechanism of hyperbranched polysilane (HBPSi) grafted multi-walled carbon nanotubes (HBPSi–MWCNTs) modified benzoxazine–bismaleimide (BOZ–BMI) resin (HBPSi–MWCNTs/BOZ–BMI), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and thermogravimetric analysis (TGA) were employed. The results indicated that the suitable addition of HBPSi–MWCNTs could largely enhance the tribological properties of BOZ–BMI composites. The worn surface of the composites showed that the severe wear of the BOZ–BMI resin was converted from adhesive wear to abrasive wear with the addition of HBPSi–MWCNTs. The excellent tribological properties can be attributed to the improved interfacial adhesion between HBPSi–MWCNTs and the BOZ–BMI resin matrix. The TGA demonstrated that the composite with 0.8wt.% HBPSi–MWCNTs exhibits better thermal resistance; thus, it can inhibit adhesive wear during the friction process. The XPS spectra and the surface energy showed that the HBPSi–MWCNTs could be exposed on the worn surface of the composite to improve the anti-wear capacity of the composites further.

Using KOH and WO₃ as raw materials, K₁₀[H₂W₁₂O₄₂]$\cdot$10H₂O nanorod was successfully synthesized via controlling the pH value and the K/W mole ratio of hydrothermal system. The structure and morphology of the samples were characterized by XRD, SEM, TEM, HRTEM and selected area electron diffraction (SAED). The size of K₁₀[H₂W₁₂O₄₂]$\cdot$10H₂O nanorod was about 300nm in width and 3–10$\mu$m in length. The nanorod consisted of self-assembly nanowires with about 10nm in width. Moreover, the electrochemical performance of K₁₀[H₂W₁₂O₄₂]$\cdot$10H₂O as anode material was investigated, indicating that the as-prepared sample electrode possessed a certain ability of lithium ion insertion/extraction, and exhibited a high initial discharge capacity of 310mAh g${}^{-1}$.

Here, we present a simple and novel method based on using insulin amyloid fibrils (INSAFs) as sacrificial templates for the construction of Pt–Pd nanoparticle chains (Pt–PdNPCs) under mild conditions. By incubating INSAFs in metal salt solution and then reduction, Pt–Pd nanoparticles with an uniform particle size of around 2.5nm nucleated and grew along the axial direction of INSAFs, and thus formed a long chain structure with length up to several micrometers. The as-prepared Pt–PdNPCs exhibit an improved catalytic activity for low-temperature CO and methanol oxidation and possess greater CO tolerance compared with the commercial Pt/C catalyst, which makes them promising for a variety of possible catalytic applications.

The development of palladium nanoparticles (PdNPs) with a narrow size distribution is an important aspect of nanotechnology. Methanobactin (Mb) is a copper-binding small peptide that appears to function as an agent for copper sequestration and uptake in methanotrophs. Here, Mb was shown to bind and catalytically reduce Pd (II) to Pd (0). The one-step synthesis of monodisperse PdNPs using Mb as both coordination agent and reduction agent is reported. Fluorescence spectra, UV-visible spectra, X-ray photoelectron spectroscopy (XPS) and Fourier transform-infrared spectroscopy (FT-IR) suggested that the Mb molecules catalytically reduce Pd (II) to Pd (0) with the concomitant production of PdNPs. The Mb is then adsorbed onto the surface of the PdNPs to form an Mb–PdNPs coordination compound. This avoids secondary nucleation. The PdNPs are small with high monodispersity and are easily synthesized in Mb solution. The PdNPs were extremely stable and resisted aggregation even after several months.

The Pd–P selective catalyst for liquid-phase hydrogenation of o-chloronitrobenzene (o-CNB) was obtained by the reduction of Pd(acac)₂ with hydrogen at 80^∘C in the presence of white phosphorus (P/Pd = 1) in N,N-dimethylformamide (DMF). It has been shown [(high-resolution transmission electron microscopy (HRTEM), energy dispersive X-ray spectroscopy (EDX), X-ray powder diffraction (XRD)] that such low-temperature synthesis of the Pd–P catalyst affords nanoparticles of palladium phosphides (Pd₅P₂, PdP₂), the Pd₅P₂ phosphide being prevailing. On the nanoparticle surface, palladium is present as a phosphide (BE (Pd3d_5∕2) = 336.2 eV; BE (P2p_3∕2) = 130 eV) and as palladium clusters of ≈ 1 nm in diameter. The formation of the Pd–P catalyst proceeds through a number of stages: a redox process between Pd(acac)₂ and white phosphorus affording mainly PdP₂ nanoparticles, H₃PO₃ and acacH; next follows the reduction of unreacted Pd(acac)₂ with hydrogen at 80^∘C and the reaction of Pd(0) atoms with each other and with PdP₂. It is assumed that formation of small palladium clusters on the surface of the Pd₅P₂ nanoparticles ensures the high selectivity of the Pd–P catalyst in the o-CNB hydrogenation.

An anatase TiO₂ photoanode with a novel three-dimensional nest-like structure was prepared directly on a transparent conductive glass substrate through hydrothermal cycles by three times. First, an unidirectional banded structure film was prepared by a facile hydrothermal method. And then, with the time of hydrothermal cycle increased, part of nanobelts were ruptured into a lot of small polyhedrons, but they still maintained a trend of the previous connection, and some fine nanobelts were interweaved in small polyhedrons. Finally, we successfully prepared a film with a novel 3D nest-like structure, and it had all the characteristics of the hierarchitectures. It had better photoelectric properties than the film with fewer times of hydrothermal cycle. Its photoelectric conversion efficiency reached 3.81%, which is due to a large dye adsorption amount, rapid electronic transmission, and superior light scattering and more electrons transmission paths.

Uniform rare-earth ytterbium oxide (Yb₂O₃) hollow microspheres have been successfully prepared via a urea-based homogenous precipitation method using carbon spheres as template, followed by a heat treatment. The main synthesis process was carried out in aqueous conditions without any organic solvents, surfactants or etching agents. X-ray diffraction, Fourier transform infrared spectroscopy, thermogravimetry, X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy, Brunauer–Emmett–Teller surface area measurement were employed to characterize the samples. The results show that the final products can be indexed to cubic Yb₂O₃ phase with high purity. The as-obtained Yb₂O₃ microspheres with spherical shape and hollow structure are uniform in size and distribution of about 450nm and wall thickness of approximately 15nm.

Black Porous Zr-doped TiO₂ monoliths were successfully synthesized by a combined route including sol–gel method with polystyrene spheres as template followed by calcination at high temperature in the presence of oxygen. As-synthesized samples were then treated in hydrogen atmosphere at 500${}^{\circ }$C for 6h to obtain black Porous Zr-doped TiO₂ monoliths. This as-synthesized black porous Zr-doped TiO₂ composite showed relatively narrow bandgap compared to the pure anatase phase of TiO₂, which may have its origin from the contributions from the Zr impurity and oxygen vacancies. The photocatalytic activity of the black porous Zr-doped TiO₂ monolith was examined by carrying out the dye degradation on Rhodamine B under visible irradiation. Our experimental results indicate that black porous 0.9% Zr-doped TiO₂ sample exhibits high photocatalytic activity with the photodecomposition of 95.25% under visible irradiation for 120min.

The equilibrium structure and electronic properties of four ultrathin free-standing pentagonal and hexagonal noble metal nanowires, that is, copper nanowires (CuNWs), silver nanowires (AgNWs), gold nanowires (AuNWs) and platinum nanowires (PtNWs), have been studied comprehensively by adopting a first-principles simulation based on the density-functional theory. The staggered topologies are more stable than the eclipsed ones by analyzing the bonding energy. The staggered ones with a linear atom chain in the center of the pentagonal or hexagons topologies are the preferred structures for CuNWs and AgNWs, but the staggered ones without a linear atom chain in the center of the pentagon or hexagon are the preferred structures for AuNWs and PtNWs due to the increasing core–core repulsions. The calculated electronic band structures and density of states present that all the noble metal nanowires are metallic. The projected densities of states (PDOS) of dominant d-states and the charge density show that the narrower d-state moved to the Fermi energy and metallic bonding character for all the noble metal nanowires.

A new photocatalyst of sodium humate (HA–Na)/Nano-TiO₂ coating on the glass spheres for flue gas denitrification (DeNO_x) was prepared using the impregnation method. The HA–Na/TiO₂ is characterized by Brunauer–Emmett–Teller (BET), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and scanning electron microscope (SEM). The photocatalytic activity of HA–Na/TiO₂ on removing NO_x was investigated in a self-designed photocatalytic reactor. The synergistic mechanism of HA–Na and TiO₂ on DeNO_x is also proposed and demonstrated. The experimental results indicate that specific surface area and average pore size of HA–Na are improved owing to the mixed TiO₂ nanoparticles. The crystal structure of TiO₂ has little change after mixing with HA–Na. Due to high photocatalytic performance of TiO₂, NO was oxidized to NO₂ and HNO₃ eventually. On the other hand, HA–Na support can absorb and react with HNO₃, which accelerates 10% of the catalytic reaction of TiO₂ and the utilization of light source. The chemical and physiological activity of oxidized HA–Na are improved than the original humate. The HA–Na/TiO₂ photocatalysts show great property on eliminating NO_x because of the promoting effect between HA–Na and TiO₂, and the NO removal efficiency can reach to 80% at the optimum condition.

The composite $\alpha$-FeOOH nanorods/Ag₃PO₄ photocatalyst has been successfully fabricated through a facile hydrothermal process combined with a successive in situ precipitation technique. The SEM and TEM images show that Ag₃PO₄ particles have been successfully loaded on the surface of FeOOH nanorods. The photocatalytic activities of the $\alpha$-FeOOH/Ag₃PO₄ composite were investigated for their efficiency on the degradation of Rhodamine B (RhB) under ultra-violet light and visible light irradiation, and the results showed that the $\alpha$-FeOOH/Ag₃PO₄ composite possessed remarkable photocatalytic activities. The enhanced photocatalytic activity can be attributed to the strong absorption in visible light and the effective separation of photogenerated hole–electron pairs between Ag₃PO₄ and $\alpha$-FeOOH.