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Cs-doped α-Bi2O3 was synthesized via a facile hydrothermal reaction. The phase formations of the samples were investigated via X-ray powder diffraction (XRD) patterns and structural refinements. The samples present well-crystalized microplates with smooth surfaces and a thickness about 300 nm. The experiments revealed that the undoped and Cs-doped α-Bi2O3 microplates could crystallized in a pure monoclinic phase. The band gap of α-Bi2O3 could be reduced via the Cs-doping in the lattices. The photocatalytic activity on photo-degradation of methylene blue (MB) was significantly improved with the Cs-doping. The effective photocatalysis was discussed on the improved visible-light response, the enhanced dispersion in the valence band composed of hybrid orbitals of Bi6s, O2p and Cs3d, and the lowered electron–hole recombination.

In the present study, BiNb5O14 and BiNb5O14/Nb2O5 heterojunction were prepared with co-precipitation synthesis. The crystal structure was studied via XRD patterns and Rietveld refinements, which has a typical tetragonal tungsten bronze (TTB)-type structure. The samples crystallized in micorods with a length of 1–4 µm and a diameter about 1 µm. As an indirect transition semiconductor, BiNb5O14 has a band energy of 2.81 eV with the valence-band formed by hybridized O-2p and Bi-6s, and the conduction band formed by Nb(6d) orbitals. The photocatalysis abilities of BiNb5O14 and BiNb5O14/Nb2O5 heterojunctions were evaluated via the photo-degradation of dye solutions. The photocatalytic activities were significantly improved via coupling BiNb5O14 with Nb2O5. In the photocatalysis reactions, •OH was the main reactive species, and the immigration rate of light-created charge-carriers was greatly improved via the heterojunction structure. The luminescence and decay lifetime were measured to discuss the photocatalysis mechanism.

In 4 FeTi 3 O 13.5 (InTi 0.75 Fe 0.25 O 3.375 ) semiconductor was prepared via sol-gel citrate-complexation synthesis. This ferrotitanate derives from a solid-solution with InFeO 3 :In 2 Ti 2 O 7 = 2:3. Phase formation and crystal structure of the sample were confirmed via XRD Rietveld refinement. Structural analyses indicated that there were two dimensional layers in the structure. The mutual repulsion in the layers induces great displacements of oxygen ions. The optical properties of In 4 FeTi 3 O 13.5 nanoparticles were investigated. The direct allowed band gap (2.56 eV) shows a characteristic charge-transfer (CT) transitions of (O2p + Fe3d) → (Ti/Fe)3d in visible-light region. The band structure and energy positions were discussed. In 4 FeTi 3 O 13.5 nanoparticles are demonstrated to be efficient for the photodegradation of Rhodamine B (RhB) under visible light irradiation (λ > 420 nm). The photocatalytic activities were attributed to the special layer structure and the catalytic mediators of multivalent Ti 4+/3+ and Fe 3+/2+ confirmed by XPS measurements.

Silver-containing niobate AgNb7O18 nanoparticles were prepared via sol-gel polymerized complex synthesis. The sample was given a good XRD Rietveld refinement in a typical perovskite-like structure. The detailed surface properties of AgNb7O18 nanoparticles were tested by SEM, EDS, TEM, nitrogen adsorption-desorption isotherms and XPS measurements. AgNb7O18 is characterized via a direct transition and the band energy is 2.76 eV. The hybridization between O 2p and Ag 3d states in valence band contributes to the narrowed band gap. The first principles electronic structure elucidation supports the narrow band gap of AgNb7O18. The sample shows an efficient degradation of methylene blue dye (MB) solutions. The trapping tests were performed to elucidate the real active species in the photocatalytic reactions. The results indicate that the superoxide radical is the main active species in the photocatalytic system, and the photocatalyst also shows a good stability and durability.

This work improved the optical absorption and photocatalytic ability of four-layered Aurivillius Bi5Ti3FeO15 through microstructural modification via partial substitution of Ti4+ with Fe3+. Bi5Ti3−xFe1+xO15 (x = 0–0.6) photocatalysts were prepared through sol-gel citrate-complexation synthesis. The sample crystallized into plate-like nanoparticles with [001] facets. Phase formation and crystal structure were confirmed via X-ray powder diffraction (XRD) Rietveld refinements. Bi5Ti3−xFe1+xO15 (x = 0–0.6) maintained its structural characteristic, i.e., a perovskite unit of (Bi3Ti3−xFe1+xO13)2– sandwiched by two (Bi2O2)2+ layers along c axis. The samples were investigated via scanning electron microscope (SEM), transmission electron microscope (TEM), energy-dispersive X-ray spectroscopy (EDX), and specific surface area analyses. The band gap showed characteristic transitions from the valence band (VB) of (O2p+Fet2 g+Bi6s) to the conduction band (CB) of (Ti-3d+Fe-eg). With increasing substitution of Ti4+ with Fe3+, the sample greatly red shifted its absorption edges. The d–d transitions in FeO6 greatly contribute to the narrow band-gap. Aurivillius is a potential photocatalyst and demonstrated photodegradation of Rhodamine B (RhB) under visible light irradiation (λ > 420 nm). Such photocatalytic activities were attributed to the special structural layer and the catalytic mediators of multivalent Ti4+/3+ and Fe3+/2+ ions in the perovskite slabs as confirmed by XPS measurements. Results suggested that substitution of Ti4+ with Fe3+ in an Aurivillius phase was an efficient method to modify the bandwidth and structure of Aurivillius phase. This phenomenon can be used as a strategy to improve the photochemical properties of Ti/Fe-containing Aurivillius phases.

Ag-containing niobate AgNb13O33 has been prepared by the sol–gel polymerized complex method. The structure was investigated via a good XRD Rietveld refinement in a typical perovskite-like framework. The morphological properties of the AgNb13O33 nanoparticles were tested via transmission electron microscopy (TEM), scanning electron microscope (SEM), and energy dispersive spectra (EDS) measurements. AgNb13O33 is a typical direct allowed semiconductor with band energy of 2.81 eV, which is much narrower than 3.4 eV of Nb2O5. This silver niobate can harvest both UV and near UV light, which is benefited from the (O-2p/Ag-4d) hybridization in the valence band. The photocatalytic abilities of AgNb13O33 nanoparticles were reported. The sample presents more efficient photocatalytic effects on photo-degradation of methylene blue (MB) dye solutions than that of Nb2O5. The photocatalytic mechanism was discussed on band energy levels, trapping experiments, photoluminescence and the decay lifetime.

A new ferrotitanate semiconductor NaFeTi 3 O 8 was developed by sol−gel citrate complexation synthesis. The sample preferentially developed into nanorods. The nanorods showed good XRD Rietveld refinements in the isostructure with Na 0.2 TiO 2 . The structure retains the two-dimensional layers of (Fe/Ti)O 6 octahedra and one-dimension channels in the structure. SEM, TEM, EDS, and specific surface area analysis were employed to characterize the samples. Results showed that the optical absorption of NaFeTi 3 O 8 nanorods is in the visible wavelength region. The direct allowed bandgap (2.12 eV) shows the characteristic charge-transfer transitions of O 2p/Fe 3d→(Ti/Fe) 3d. The d–d allowed transitions in the FeO 6 octahedron presented considerable contributions to the narrow bandgap. NaFeTi 3 O 8 exhibited potential as a photocatalyst for RhB photodegradation under visible light excitation ( λ > 420 nm). Photocatalytic activities are discussed in relation to the structural properties.

Ni-doped Cu2(OH)3Cl microcrystals were prepared by a facile hydrothermal synthesis without the help of any additive inorganic or organic reagent. The micro-particles were investigated by X-ray powder diffraction (XRD) with Rietveld refinement, scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV–vis optical absorption, and X-ray photoelectron spectroscopy (XPS) etc. Ni-doping could well stabilize the Cu2(OH)3Cl paratacamite phase at ambient temperature. The band structure and energy positions of Ni-doped Cu2(OH)3Cl microparticles were investigated. The band gap of Cu2(OH)3Cl could be greatly decreased by Ni-doping. The conduction band bottom of Ni-doped Cu2(OH)3Cl is lower and possesses greater dispersion than that of pure Cu2(OH)3Cl. The photocatalytic activity of Ni-doped Cu2(OH)3Cl micro-particles was evaluated by the photodegradation of Rhodamine B (RhB) dye under visible-light irradiation. The Ni-doping increases the photocatalytic activity of Cu2(OH)3Cl. The photocatalytic activity was discussed on the base of the structural and electronic characteristics. Keywords: Photocatalyst, Optical properties, Semiconductors, Band structure, Copper oxide

In this research, instrumented spherical micro-indentation/scratch tests were conducted to investigate microscopic mechanical properties of multilayer graphene (MLG) reinforced titanium based metal matrix composites (TiMMCs) synthesized using spark plasma sintering (SPS). Raman spectra and microstructure observation illustrated that MLGs survive the harsh SPS processing conditions and homogeneously distribute in Ti matrix. Instrumented indentation and scratch tests showed that mechanical properties in microscopic scale of MLG reinforced TiMMCs such as indentation yield strength and scratch resistance are significantly improved. The computed results corroborated that the critical length of most of the added MLGs satisfies the criterion of critical length of the reinforcement, and the strengthening mechanisms including enhanced dislocation density and Orowan mechanism play significant roles in the improved mechanical properties. This research is expected to facilitate a better understanding of mechanical behavior in microscopic scale of MLG reinforced metal matrix composites. Keywords: Graphene, Metal-matrix composites, Micro-mechanics, Mechanical testing, Sintering

The growth of Ag-nanofilaments in the solid electrolyte films of memristors based on Ag30S2P14O42 is investigated. After the formation of the Ag-nanofilaments in the solid electrolyte, the memory cells are switched to the high conductive state. With a positive voltage applied on the Ag electrode of the cells, the Ag-nanofilaments gradually become thicker due to the reduction and diffusion of Ag+ cations in the solid electrolyte. The relationship between the thickening rate of the Ag-nanofilaments and the concentration of the Ag+ cations surrounding them is analyzed, and the results show that the thickening of the Ag-nanofilaments is determined by the reduction and diffusion of Ag+ cations in the solid electrolyte.