Retention of a nanostructure in thermoelectric materials through rapid sintering (e.g., field-assisted sintering) is generally associated with leaving certain amounts of porosity due to short sintering times. In this study, the influence of porosity on the thermoelectric transport properties in Bi2Te3-based alloys was studied by changing the sintering pressure during spark plasma sintering. N-type Bi2Te3 and p-type (Bi0.2Sb0.8)2Te3 were sintered at 673 K using pressures from 50 to 300 MPa to obtain different levels of porosity. Electrical resistivity, thermal conductivity, Seebeck coefficient, carrier concentrations, and Hall mobility were measured and characterized. The results show that increasing sintering pressure is effective in reducing porosity, which lowers electrical resistivity and increases the carrier concentrations. The transport properties were fitted to general effective medium equations and demonstrate that in p-type (Bi0.2Sb0.8)2Te3 sintered at high pressures, decreases in electrical resistivity and lattice thermal conductivity exceeded the Seebeck coefficient reduction, improving the thermoelectric figure of merit.

This work presents the preparation and characterization of N-doped TiO2 nanocrystals obtained by a solid-state reaction in vacuum with urea as the nitrogen source. The particle sizes of the products are smaller than 20 nm from the x-ray powder diffraction patterns and the transmission electron microscopy images. Different from the reported samples obtained in air or under dry N2 or NH3 gas flow, the doped nitrogen exists mainly as absorbed NOx groups but as smaller incorporated species in the nanocrystals, which is supported by the results from x-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and ultraviolet–visible diffuse reflectance spectroscopy. Dependent on the nitrogen amount, the surface photovoltage (SPV) response reaches the maximum at the mediate molar ratio of 5:4 (urea to TiO2), which can be explained that proper nitrogen concentration can enhance the separation of the photogenerated carriers to improve the SPV intensity, but excess nitrogen can spread the impurity energy levels to narrow energy gaps, which reinforces the combination of the photogenerated electrons and holes and then decreases the SPV signal. The corresponding detailed discussion is also reported.

Some hydrides that could replace TiH2 as the hitherto most suitable blowing agent for foaming aluminum alloys were investigated. Hydrides taken from the group MBH4 (M = Li, Na, K) and LiAlH4 were selected since these have not been studied in the past although their decomposition characteristics appear to be suitable. Foamable precursors of alloy AlSi8Mg4 were manufactured by pressing blends of metal and blowing agent powders. Powders, precursors and precursor filings were studied by mass spectrometry to obtain the hydrogen desorption profile. Foaming experiments were conducted with simultaneous x-ray radiographic monitoring. Two Li-containing blowing agents were found to perform well and can be considered alternatives to TiH2.

Nanosized anatase TiO2 nanosheets with highly exposed reactive {001} facets (∼80%) were prepared via hydrothermal reaction with the addition of hydrofluoric acid and characterized by various techniques including transmission electron microscopy, x-ray diffraction, x-ray photoelectron spectroscopy, and Brunauer–Emmett–Teller. High-quality TiO2 nanosheets films with different thicknesses (∼5–20 μm) were fabricated by doctor blading, and the effect of film thickness on the performance of dye-sensitized solar cells (DSSCs) was investigated by I-V characterization and dark current potential scan. The results show that each parameter of DSSCs performance depends strongly on the thickness of the TiO2 nanosheets films. An optimized DSSCs performance of 8.39% was obtained by the TiO2nanosheets film with a thickness of ∼15 μm.

The present work reports a soft-chemical pathway for preparing SnO–TiO2 composite nanocrystallites as photocatalyst through co-hydrolysis of tetrabutyl titanate and tin (II) chloride followed by acidic peptization of the hydrolysate under mild conditions. The procedure is simple and straightforward, from which a well-dispersed semitransparent hydrosol sample is obtained. The freestanding nanocrystallites observed in the as-prepared composite show diameters of 3–5 nm. TiO2 nanoparticles have almost entirely transformed into anatase phase, and the trace amounts of Sn in existence are mainly found in SnO crystals with tetragonal structure. The photocatalytic activity of the SnO–TiO2 composites is confirmed through the photodegradation of methyl blue dye under visible light irradiation (λ > 420 nm). As a p-type semiconductor, the incorporated SnO effectively improves the photocatalytic activity of TiO2 through promoting the separation of photo-generated charge carriers, inhibiting their recombination, and facilitating the reduction of O2 by the photo-generated electrons.

The 3D morphological evolution of titanium foams as they undergo a two-step fabrication process is quantitatively characterized through x-ray micro- and nano-tomography. In the first process step, a Cu–Ti–Cr–Zr prealloy is immersed in liquid Mg, where Cu is alloyed with Mg while a skeleton of crystalline Ti–Cr–Zr is created. In the second step, the Mg–Cu phase is etched in acid, leaving a Ti–Cr–Zr foam with submicron struts. 3D images of these solidified Ti–Cr–Zr/Mg–Cu composites and leached Ti–Cr–Zr foams are acquired after 5, 10, and 30 min exposure to liquid Mg. As the Mg exposure time increases, the Ti–Cr–Zr ligaments grow in size. The tortuosity loosely follows the Bruggeman relation. The interfacial surface distribution of these Ti-foams is qualitatively similar to other nano-porous metal prepared by one-step dealloying. The characteristic length of the Mg–Cu phase and pores are also reported.

High-performance and continuous zeolite MFI membranes have been successfully fabricated, using in situ hydrothermal synthetic method, on α-Al2O3 hollow ceramic fifibers (HCFs). The CO2 separation properties of the as-prepared MFI membrane are studied by single gas permeation and binary gas permeation of CO2/N2 and CO2/CH4. The separation results show that the membrane exhibits high CO2 selectivity with separation factors of 9.2 and 6.0 for CO2/N2 and CO2/CH4, respectively. A preferred permeance for CO2 in the binary gas mixtures is about 3 × 10−7mol/(m2 s Pa). Furthermore, the supported MFI membrane possesses high mechanical strength, strong thermal stability, and high reproducibility, which are expected to have potential applications in industrial CO2 recycling.

A novel hybrid titania paste comprising aqueous-synthesized anatase (A) nanocrystalites and submicrometer-sized “sea urchin”-like rutile (R) particles that enables the construction of thin (5–6 μm) single-layer photoanodes with competitive power conversion efficiency is described. Owing to the high surface area of the dye (N719)-coated anatase film, the scattering properties of the unique rutile particulates, and the incorporation of P25 particles, the constructed bifunctional electrode films exhibit excellent electron transport properties (long electron lifetime) and no electrolyte diffusion resistance. Dye-sensitized solar cell devices built with the thin (5–6 μm) hybrid electrodes showed greatly improved power conversion efficiency (PCE), namely 7.04%, when compared to devices based on single anatase (4.20%), double-layer (A + R), or double thickness commercial benchmark paste (6.74%). This is an impressive result as less than 1/2 material was used in a single printed layer. Thinner films as the ones built here may prove particularly advantageous in using new noniodide electrolytes associated with slow diffusion rates.

This paper presents the effect of oxygen, nitrogen, and carbon concentration on the microstructure and properties of titanium foams produced with a powder metallurgy process. Oxygen and nitrogen reduce the ductility and increase the compression yield strength of CpTi foams. The effect of nitrogen appears to be similar to the effect of oxygen, a trend different from the ones reported in the literature for dense titanium in tension, where the effect of nitrogen is recognized to be significantly more important than the effect of oxygen. For carbon, the levels investigated were above the room temperature solubility limit of carbon in α-Ti and titanium carbides were observed in the microstructure. The volume fraction of carbides observed in the microstructure increased with carbon content. The effect of the carbides on the compression properties and ductility of the titanium foams is, however, small compared to the effect of oxygen and nitrogen.

A binder-free titania paste was prepared by chemical modification of an acidic TiO2 sol with ammonia. By varying the ammonia concentration, the viscosity of the acidic TiO2 suspension increased, thereby allowing uniform films to be cast. The photoelectrochemical performance of TiO2 electrodes, cast as single layers, was dependent on the thermal treatment cycle. Fourier transform infrared spectroscopy was used to characterize the extent of residual organics and found that acetates from the TiO2precursor preparation were retained within the electrode structure after thermal treatment at 150 °C. Electrodes of nominal thickness 4 μm produced an energy conversion efficiency as high as 5.4% using this simple thermal treatment.

Recent advances in multiscale manufacturing enable fabrication of hollow-truss based lattices with dimensional control spanning seven orders of magnitude in length scale (from ∼50 nm to ∼10 cm), thus enabling the exploitation of nano-scale strengthening mechanisms in a macroscale cellular material. This article develops mechanical models for the compressive strength of hollow microlattices and validates them with a selection of experimental measurements on nickel microlattices over a wide relative density range (0.01–10%). The limitations of beam-theory-based analytical approaches for ultralight designs are emphasized, and suitable numerical (finite elements) models are presented. Subsequently, a novel computational platform is utilized to efficiently scan the entire design space and produce maps for optimally strong designs. The results indicate that a strong compressive response can be obtained by stubby lattice designs at relatively high densities (∼10%) or by selectively thickening the nodes at ultra-low densities.

Open pore metal foams may be of interest as regenerators because of their large specific surface area and their high porosity. In this experiment, three aluminum foam samples (pore size 2–2.36 mm and around 65% porosity) were manufactured by the replication process. The volumetric heat transfer coefficient and number of transfer units (NTU) of the foams and a packed bed of steel ball bearings (2 mm diameter) were determined using a single-blow transient technique over the range 500 < Rem < 1400. The NTU values of the foams and ball bearings both reduced with increasing Reynolds number (flow velocity). The pressure drop across the matrices increased with the velocity, though the values for the metal foams were much lower than that of the ball bearings, indicating that they may have potential for this type of application.

Hydrothermally grown TiO2 nanorod (NR) photoelectrodes were prepared by sensitizing CdS quantum dots to improve visible light activity of the TiO2. The CdS-sensitized photoelectrodes were heat-treated to obtain enhanced performance of the photoelectrode under visible light. Furthermore, performance of the TiO2 NR-based photoanodes was compared with those made of TiO2 nanotubes (NTs). Photocurrent measurement and overall cell efficiency of the NR-based solar cells showed higher efficiency compared to NT-based solar cell.

Nanocasting into silica templates for preparation of mesoporous materials has up to now been limited to those metal oxides and metals that can withstand the harsh silica etching processes currently used. Two new methods of removing the silica template are reported, either by dissolving the silica in methanolic base or by dissolution in aqueous base under an external potential. The utility of these methods is demonstrated in the synthesis of hierarchically porous zinc oxide, nickel oxide, and copper monoliths that would dissolve or react using other template removal methods. The successful etching of monolithic zinc oxide using methanolic base etching can be explained by the reduced solubility of zinc oxide in methanol compared with an aqueous base, while it also reduces the formation of hydroxides when etching the nickel oxide and copper monoliths. Alternatively, the formation of highly soluble copper oxide/hydroxide can be avoided by holding the copper monolith at a sufficiently negative potential while etching with an aqueous base.

Ink-jet printing technique is used to prepare porous (ZnO)1−x(TiO2)x composite films on indium tin oxide-coated glass substrates. Dye-sensitized solar cells were fabricated using well-characterized printed films of thickness ∼20 and 30 μm, respectively. It is found that the photovoltaic performance of the cells is dependent on the film thickness and the concentrations of ZnO. The obtained results are compared with those of pure ZnO- and TiO2-based cells prepared by the same route to optimize the device efficiency. This study suggests that ink-jet printers promise an inexpensive and simple technology for manufacturing solar cell composite films.

Among the different porous materials, bulk metallic glass (BMG) foams are of special interest due to their high strength combined with large elastic limit. Large surface areas and, therefore, high reactivity in chemical applications can be achieved by properly adjusting the pore characteristics. Pore size and pore size distribution are the key factors for determining the overall performance of open-cell porous materials used for functional applications, such as filtration or catalysis. As a result, the control of these factors is a necessary requirement for material design and application. In this work, BMG foams are produced by powder metallurgy through the selective dissolution of a fugitive phase. The work is focused on the manufacturing processes needed to properly control pore size and pore size distribution. The results reveal that customized hybrid BMG porous structures can be produced through the controlled milling of the BMG-composite powders.

ZnO/TiO2 heterojunction composite fibers were prepared via a physical route, i.e., first electrospinning titanium dioxide (TiO2) fibers, then pulse plating zinc (Zn) on the fibers, and at last thermal treating the fibers. The morphologies, phase structures, and photocatalytic property of the composite fibers were characterized by using field-emission gun scanning electron microscope, x-ray diffractometer, high-resolution transmission electron microscope, and ultraviolet–visible spectrophotometer. It was found that a full or partial lattice coherent heterojunction was formed between the TiO2 fibers and zinc oxide (ZnO) particles, due to thermal treatment at 400 °C, which simultaneously resulted in the phase transformations including Zn to ZnO and amorphous TiO2 to anatase TiO2. The experimental results demonstrated that the photocatalytic activity of the composite fibers was improved and exhibited a value more than two times higher than that of TiO2 fibers.

Simulations of TiO2(both rutile and anatase) nanoparticles with water, methanol, and formic acid were conducted using a ReaxFF reactive force field to investigate the characteristic behavior of reactivity to these organic solvents. The force field was validated by comparing water dissociative adsorption percentage and bond length between Na and O with density functional theory (DFT) and experimental results. In the simulations, 1-nm rutile and anatase nanoparticles with water, methanol, and formic acid were used, respectively. The numbers of attached hydroxyl with time and nanoparticles distortion levels are presented. We found that the rutile nanoparticle is more reactive than the anatase nanoparticle and that formic acid distorts nanoparticles more than water and methanol.