Introduction to subpressure-driven soft deformation method for removing inherent voids in green components manufactured by material extrusion.

This study introduces a post-treatment process, the subpressure-driven soft deformation method, to reduce inherent voids in Material Extrusion (MEX) components. By subjecting printed green components to heat treatment under subpressure, the process enhances viscosity, effectively filling voids formed between deposited tracks. The average porosities of the samples sintered from the green components without and with soft deformation are calculated to be 3.55% and 2.36%, respectively. A comparison of the tensile strengths and fracture surfaces of the sintered samples with and without soft deformation treatment indicated that the sintered samples with soft deformation treatment exhibited narrower standard deviation for the various mechanical properties. Capillary rheometer calculations indicate feedstock viscosity to be between 450.34 and 1018.31 Pa s under subpressure, diminishing inter-track voids without sizeable dimensional changes. Molecular dynamics simulation demonstrates a 3.7-fold increase in bond strength, indicating intertrack voids effectively eliminated. Reduced inter-particle distances facilitate necking, grain growth, and improved sintered density.

Current trends on dry photocatalytic oxidation technology for BTX removal: Viable light sources and highly efficient photocatalysts.

One of the main gaseous pollutants released by chemical production industries are benzene, toluene and xylene (BTX). These dangerous gases require immediate technology to combat them, as they put the health of living organisms at risk. The development of heterogeneous photocatalytic oxidation technology offers several viewpoints, particularly in gaseous-phase decontamination without an additional supply of oxidants in air at atmospheric pressure. However, difficulties such as low quantum efficiency, ability to absorb visible light, affinity towards CO2 and H2O synthesis, and low stability continue to limit its practical use. This review presents recent advances in dry-phase heterogeneous photodegradation as an advanced technology for the practical removal of BTX molecules. This review also examines the impact of low-cost light sources, the roles of the active sites of photocatalysts, and the feasible concentration range of BTX molecules. Numerous studies have demonstrated a significant improvement in the efficiency of the photodegradation of volatile organic compounds by enhancing the photocatalytic reactor system and other factors, such as humidity, temperature, and flow rate. The mechanism for BTX photodegradation based on density functional theory (DFT), electron paramagnetic resonance (EPR) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) investigations is also discussed. Finally, the present research complications and anticipated future developments in the field of heterogeneous photocatalytic oxidation technology are discussed.

Study of solid loading of feedstock using trimodal iron powders for extrusion based additive manufacturing.

Volume loading of feedstock using trimodal iron (Fe) powders was investigated for the application of extrusion-based additive manufacturing (AM). Fe trimodal powder composed of nano, sub-nano, and micro particles was manufactured via the powder metallurgy process where small particles behave as rolling bearings among large particles, and thereby improving the flow characteristics of feedstock by minimizing friction among the particles. The flow behavior and microstructures of the monomodal feedstock were compared with those of the trimodal feedstock. We have confirmed that the critical powder loading of monomodal powder was measured to be 70 vol.% while trimodal powder showed up to 74 vol.%. Furthermore, trimodal feedstocks of 60, 65, 70, 75, and 80 vol.% Fe powder were prepared to determine the optimal powder content for sintering. As a result, the feedstock with powder content of 70 vol.% gave the highest sintered density of 92.32%, the highest Vickers hardness of 80.67 HV, with the smallest dimensional variation in shrinkage, proposing 70 vol.% of trimodal feedstock to be the suitable powder content for AM. Finally, its microstructural and mechanical comparison with 70 vol.% sintered part using monomodal Fe powder, showed that the sintered part using trimodal feedstock displayed higher hardness, uniform shrinkage as well as smaller grain size, confirming trimodal feedstock to be favorable for the application of extrusion-based AM.

High Optical Contrast of Quartet Dual-Band Electrochromic Device for Energy-Efficient Smart Window.

A quartet dual-band electrochromic device (ECD) was developed to selectively control the transmittance from the visible to near-infrared wavelengths for the application of an energy-efficient smart window. The new AgNO3+TBABr+LiClO4 (ATL)-based electrolyte was developed to independently control the redox reaction of lithium and silver ions to demonstrate the quartet mode of an ECD. A dual-band ECD with a sandwich structure was assembled using an ATL-based electrolyte, WO3 electrochromic layer, and antimony-doped tin oxide (ATO) ion storage layer. The employed WO3 and ATO films were fabricated using a nanoparticle deposition system (NPDS), a novel ecofriendly dry deposition method. Four modes, namely, transparent, warm, cool, and all-block modes, were demonstrated via an independent redox reaction of both lithium and silver ions through the simple control of the applied voltage. In the warm mode, the localized surface plasmon resonance effect was exploited by producing silver nanoparticles upon two-step voltage application. Furthermore, since the high surface roughness of the WO3 thin film fabricated by NPDS maximized the light scattering effect, 0% transmittance at all wavelengths was observed in the all-block mode. Dual-band ECD showed high optical contrasts of 73% and long-term durability over 1000 cycles with no degradation. Therefore, the possibility of controlling transmittance at the target wavelength was confirmed using a simple device with a simple process, suggesting a new strategy for the design of dual-band smart windows to reduce the energy consumption of buildings.

Epitaxial Growth of Flower-Like MoS2 on One-Dimensional Nickel Titanate Nanofibers: A "Sweet Spot" for Efficient Photoreduction of Carbon Dioxide.

Herein, a full spectrum-induced hybrid structure consisting of one-dimensional nickel titanate (NiTiO3) nanofibers (NFs) decorated by petal-like molybdenum disulfide (MoS2) particles was designed through a facile hydrothermal method. The key parameters for tailoring the morphology and chemical, surface, and interfacial properties of the heterostructure were identified for efficient and selective conversion of CO2 into valuable chemicals. Introducing MoS2 layers onto NiTiO3 NFs provided superior CO2 conversion with significantly higher yields. The optimized hybrid structure produced CO and CH4 yields of 130 and 55 µmol g-1 h-1, respectively, which are 3.8- and 3.6-times higher than those from pristine NiTiO3 nanofibers (34 and 15 µmol g-1 h-1, respectively) and 3.6- and 5.5-times higher than those from pristine MoS2 (37 and 10 µmol g-1 h-1, respectively). This improved performance was attributed to efficient absorption of a wider spectrum of light and efficient transfer of electrons across the heterojunction. Effective charge separation and reduced charge carrier recombination were confirmed by photoluminescence and impedance measurements. The performance may also be partly due to enhanced hydrophobicity of the hierarchical surfaces due to MoS2 growth. This strategy contributes to the rational design of perovskite-based photocatalysts for CO2 reduction.

Quantum scale biomimicry of low dimensional growth: An unusual complex amorphous precursor route to TiO2 band confinement by shape adaptive biopolymer-like flexibility for energy applications.

Crystallization via an amorphous pathway is often preferred by biologically driven processes enabling living species to better regulate activation energies to crystal formation that are intrinsically linked to shape and size of dynamically evolving morphologies. Templated ordering of 3-dimensional space around amorphous embedded non-equilibrium phases at heterogeneous polymer─metal interfaces signify important routes for the genesis of low-dimensional materials under stress-induced polymer confinement. We report the surface induced catalytic loss of P=O ligands to bond activated aromatization of C-C C=C and Ti=N resulting in confinement of porphyrin-TiO2 within polymer nanocages via particle attachment. Restricted growth nucleation of TiO2 to the quantum scale (≤2 nm) is synthetically assisted by nitrogen, phosphine and hydrocarbon polymer chemistry via self-assembly. Here, the amorphous arrest phase of TiO2 is reminiscent of biogenic amorphous crystal growth patterns and polymer coordination has both a chemical and biomimetic significance arising from quantum scale confinement which is atomically challenging. The relative ease in adaptability of non-equilibrium phases renders host structures more shape compliant to congruent guests increasing the possibility of geometrical confinement. Here, we provide evidence for synthetic biomimicry akin to bio-polymerization mechanisms to steer disorder-to-order transitions via solvent plasticization-like behaviour. This challenges the rationale of quantum driven confinement processes by conventional processes. Further, we show the change in optoelectronic properties under quantum confinement is intrinsically related to size that affects their optical absorption band energy range in DSSC.

Novel design of hollow g-C3N4 nanofibers decorated with MoS2 and S, N-doped graphene for ternary heterostructures.

Herein, we newly design a ternary structure of 1-dimensional hollow g-C3N4 nanofibers (HGCNF) decorated with molybdenum disulfide (MoS2) and sulfur/nitrogen-doped graphene (SNG) via a one-pot hydrothermal treatment at relatively low temperature. The firstly presented HGCNF are fabricated using electrospinning followed by the thermal sintering method. After that, MoS2 is grown onto HGCNF, while SNG covered the structures during the hydrothermal method. We observed the morphological structures, chemical composition and optical absorbance of this ternary HGCNF/SNG/MoS2 structure. Of the as-prepared catalysts, HGCNF/SNG/MoS2 exhibited a good possibility to produce hydrogen as an electrocatalyst. Furthermore, we evaluated its stability performance using chronoamperometry for 48 hours, as well as by 3000 cycles of cyclic voltammetry. From the double-layer capacitance measurement, HGCNF/SNG/MoS2 proved itself as an electrocatalyst due to the higher value of electrocatalytically active sites to be 6.97 × 10-3 F cm-2 than that of only HGCNF (0.18 × 10-5 F cm-2) and the binary structure of HGCNF/MoS2 (2.54 × 10-3 F cm-2). We believe that our novel 1-dimensional ternary HGCNF/SNG/MoS2 structure has expedited the electron pathways by reducing the resistance at interfaces among HGCNF, SNG and MoS2, to be potentially useful for the hydrogen evolution reaction.

Evaluation of dual layered photoanode for enhancement of visible-light-driven applications.

Ternary structures consisting of hollow g-C3N4 nanofibers/MoS2/sulfur, nitrogen-doped graphene and bulk g-C3N4 (TCN) were designed as a dual layered film and fabricated using a spin-coating method. The first ternary structures were spin-coated on fluorine-doped tin oxide (FTO) glass, followed by spin-coating of g-C3N4 film to form dual layers. We characterized the microstructural morphologies, chemical composition/bonding and optical properties of the dual layered film and observed significantly reduced recombination rates of photo-induced electron-hole pairs due to effective separation of the charge carriers. We tested methylene blue (MB) photodegradation and observed remarkable MB degradation by the dual layered film over 5 hours, with a kinetic rate constant of 1.24 × 10-3 min-1, which is about four times faster than that of bare TCN film. Furthermore, we estimated the H2 evolution of the dual layered film to be 44.9 µmol over 5 hours, and carried out stable recycling over 45 hours under visible irradiation. Due to the lower electrochemical impedance spectroscopy (EIS) resistance value of the dual layered film (∼50 ohm cm2) compared to the TCN film, the ternary structures and bulk g-C3N4 film were well-connected as a heterojunction, reducing the resistance at the interface between the film and the electrolyte. These results indicate that the effective separation of the photo-induced electron-hole pairs using the dual layered film dramatically improved its photo-response ability under visible light irradiation.

Direct coating of a g-C3N4 layer onto one-dimensional TiO2 nanocluster/nanorod films for photoactive applications.

We report the coating of metal-free graphitic carbon nitride (g-C3N4) onto titanium dioxide (TiO2) nanorods via a thermal evaporation method. Prior to g-C3N4 coating, TiO2 nanoclusters were grown on TiO2 nanorods to enhance the surface area by dipping in a TiCl3 solution for 12, 24 and 36 h. The prepared films were analyzed to assess the improvement in absorbance and reduction in recombination losses. Nanoclustered TiO2 grown for 24 h and then coated with a g-C3N4 film (i.e., TC_24h_CN) had the highest photocurrent of 235 and 290 µA, respectively, when measured by transient photocurrent and linear sweep voltammetry techniques. The enhanced performance resulted from a reduced recombination of electron-hole pairs. The TC_24h_CN film displayed an excellent photoresponse over 15 h of exposure to visible light and hence could potentially be used in water purification device technology.

Low temperature fabrication of Fe2O3 nanorod film coated with ultra-thin g-C3N4 for a direct z-scheme exerting photocatalytic activities.

We engineered high aspect ratio Fe2O3 nanorods (with an aspect ratio of 17 : 1) coated with g-C3N4 using a sequential solvothermal method at very low temperature followed by a thermal evaporation method. Here, the high aspect ratio Fe2O3 nanorods were directly grown onto the FTO substrate under relatively low pressure conditions. The g-C3N4 was coated onto a uniform Fe2O3 nanorod film as the heterostructure, exhibiting rational band conduction and a valence band that engaged in surface photoredox reactions by a direct z-scheme mechanism. The heterostructures, particularly 0.75g-C3N4@Fe2O3 nanorods, exhibited outstanding photocatalytic activities compared to those of bare Fe2O3 nanorods. In terms of 4-nitrophenol degradation, 0.75g-C3N4@Fe2O3 nanorods degraded all of the organic pollutant within 6 h under visible irradiation at a kinetic constant of 12.71 × 10-3 min-1, about 15-fold more rapidly than bare Fe2O3. Further, the hydrogen evolution rate was 37.06 µmol h-1 g-1, 39-fold higher than that of bare Fe2O3. We suggest that electron and hole pairs are efficiently separated in g-C3N4@Fe2O3 nanorods, thus accelerating surface photoreaction via a direct z-scheme under visible illumination.

Hybrid photocatalysts using graphitic carbon nitride/cadmium sulfide/reduced graphene oxide (g-C3N4/CdS/RGO) for superior photodegradation of organic pollutants under UV and visible light.

Graphitic carbon nitride (g-C3N4) was hybridized with CdS nanoparticles and reduced graphene oxide (RGO) sheets using a facile chemical method, for the application of catalytic photodegradation of Rhodamine B and Congo red dyes under irradiation with UV and visible light. Fourier-transform infrared (FTIR) spectroscopy and X-ray photoemission spectroscopy (XPS) analyses confirmed the formation of pure g-C3N4, as well as g-C3N4/CdS, g-C3N4/RGO, and g-C3N4/CdS/RGO composites. The large surface area of the g-C3N4/CdS/RGO composite (70.42 m(2) g(-1)) resulted in rapid dye adsorption onto the surface of the photocatalyst, leading to effective photodegradation of organic pollutants. The addition of CdS and RGO increased the photocatalytic activity of g-C3N4 by a factor of approximately twenty compared with that of the commercially available TiO2 catalyst under visible light, and the g-C3N4/CdS/RGO composite was found to significantly enhance the catalytic effect compared with pure g-C3N4 and with the g-C3N4/CdS and g-C3N4/RGO composites. The superior photocatalytic activity of the g-C3N4/CdS/RGO composite is attributed to enhanced separation of the photogenerated electron-hole pairs, as well as increased visible-light absorption. The improved transport of photoelectrons was consistent with the results of transient photocurrent measurements. Therefore, g-C3N4/CdS/RGO composites using a facile method are applicable to the development of high-efficiency photocatalytic devices for industrial applications.

Improvement of the tool life of a micro-end mill using nano-sized SiC/Ni electroplating method.

High mechanical properties of a tungsten carbide micro-end-mill tool was achieved by extending its tool life by electroplating nano-sized SiC particles (< 100 nm) that had a hardness similar to diamond in a nickel-based material. The co-electroplating method on the surface of the micro-end-mill tool was applied using SiC particles and Ni particles. Organic additives (saccharin and ammonium chloride) were added in a Watts bath to improve the nickel matrix density in the electroplating bath and to smooth the surface of the co-electroplating. The morphology of the coated nano-sized SiC particles and the composition were measured using Scanning Electron Microscope and Energy Dispersive Spectrometer. As the Ni/SiC co-electroplating layer was applied, the hardness and friction coefficient improved by 50%. Nano-sized SiC particles with 7 wt% were deposited on the surface of the micro-end mill while the Ni matrix was smoothed by adding organic additives. The tool life of the Ni/SiC co-electroplating coating on the micro-end mill was at least 25% longer than that of the existing micro-end mills without Ni/SiC co-electroplating. Thus, nano-sized SiC/Ni coating by electroplating significantly improves the mechanical properties of tungsten carbide micro-end mills.

Dry-spray deposition of TiO2 for a flexible dye-sensitized solar cell (DSSC) using a nanoparticle deposition system (NPDS).

TiO2 powders were deposited on indium tin oxide (ITO) coated polyethylene terephthalate (PET) substrates for application to the photoelectrode of a dye-sensitized solar cell (DSSC). In the conventional DSSC manufacturing process, a semiconductor oxide such as TiO2 powder requires a sintering process at higher temperature than the glass transition temperature (T(g)) of polymers, and thus utilization of flexible polymer substrates in DSSC research has been constrained. To overcome this restriction related to sintering, we used a nanoparticle deposition system (NPDS) that could produce a thin coating layer through a dry-spray method under atmospheric pressure at room temperature. The powder was sprayed through a slit-type nozzle having a 0.4 x 10 mm2 rectangular outlet. In order to determine the deposited TiO2 thickness, five kinds of TiO2 layered specimens were prepared, where the specimens have single and double layer structures. Deposited powders on the ITO coated PET substrates were observed using FE-SEM and a scan profiler The thicker TiO2 photoelectrode with a DSSC having a double layer structure showed higher energy efficiency than the single layer case. The highest fabricated flexible DSSC displayed a short circuit current density J(sc) = 1.99 mA cm(-2), open circuit voltage V(oc) = 0.71 V, and energy efficiency eta = 0.94%. These results demonstrate the possibility of utilizing the dry-spray method to fabricate a TiO2 layer on flexible polymer substrates at room temperature under atmospheric pressure.

Study of sintering behavior of vapor forms of 1-octanethiol coated copper nanoparticles for application to ink-jet printing technology.

Sub-50 nm copper nanoparticles coated with sub-5 nm 1-octanethiol layer for oxidation inhibition were examined to confirm the 1-octanethiol removal temperature as the sub-50 nm copper nanoparticles are sintered. As a result, 1-octanethiol Self-Assembled Multi-layers (SAMs) on sub-50 nm copper nanoparticles were successfully removed before sintering of copper nanoparticles so that a high density of copper line could be obtained. Finally, the line resistivity was measured and compared to verify the effect of sintering in different atmospheres. As a result, electrical resistivity of the copper pattern sintered in hydrogen atmosphere was measured at 6.96 x 10(-6) ohm-cm whereas that of the copper pattern sintered in mixed gas atmosphere was measured at 2.62 x 10(-5) ohm-cm. Thus, sintering of copper patterns was successfully done to show low electrical resistivity values. Moreover, removal of 1-octanethiol coating after sintering process was confirmed using X-ray photoelectron spectroscopy (XPS) analysis. By showing no sulfur content, XPS results indicate that 1-octanethiol is completely removed. Therefore, the vapor form of 1-octanethiol coating layers can be safely used as an oxidation inhibition layer for low temperature sintering processes and ink-jet applications.

Fabrication of dye-sensitized solar cell (DSSC) using different particle sizes of TiO2 deposited via nano-particle deposition system (NPDS).

TiO2 layers were fabricated using a nano-particle deposition system (NPDS) on transparent conductive oxide (TCO) glass for dye sensitized solar cells (DSSCs). Conventionally, TiO2 paste for working electrodes has been fabricated using paste type methods. The fabricated paste composed of a mixture of nano-sized TiO2 powders, binders and solutions is then painted on TCO glass. After drying, the TiO2 layer on TCO glass is sintered to make a path for electron transfer. TiO2 layers formed by this paste type method require numerous steps, which can be time consuming. In this study, TiO2 powders were sprayed directly on TCO glass using NPDS in order to simplify the fabrication steps. To improve porosity and produce scattering layers, commercial nanocrystalline TiO, powders with different sizes were alternately deposited. Moreover, powders with different sizes were mixed and deposited on the TCO glass. The results indicate that the DSSCs with a TiO2 layer composed of different particle sizes had better cell performance than the cells assembled with single-sized TiO2 particles. Therefore, this study shows that a dry TiO2 coating process is possible for DSSC fabrication to improve its cell efficiencies, and this method can easily be applied on flexible substrates since NPDS is a room-temperature deposition process.

Controlled thicknesses of vaporized self-assembled multilayers on copper nanopowders under ultra-high vacuum (UHV).

Copper nanoparticles were coated with 1-octanethiol self-assembled monolayers (SAMs) using the dry-coating method for oxidation prevention. In this study, thicknesses of 1-octanethiol SAMs were successfully controlled, and the stability of SAMs as a passivation layer on copper nanoparticles was examined. Thicknesses of 1-octanethiol SAMs varied with vacuum levels and coating cycles. Under low-vacuum conditions, the thickness was 10 nm, regardless of the coating conditions. In contrast, various thicknesses resulted under ultra-high vacuum (UHV) and ranged from 4 nm to 10 nm. SAMs that were nearly a monolayer thick (4 nm) resulted from two coating cycles of 1.5 min, and the oxidation inhibition period was 15 days. Thus, the dry-coating method successfully controlled the thicknesses of SAMs with satisfactory oxidation inhibition properties under ultra-high vacuum.

Transmission electron microscopy analysis of octanethiol-coated Cu powders.

In this study, microstructures of Cu powders coated with octanethiol were analyzed using (scanning) transmission electron microscopy. Moreover, aging process of the octanethiol-coated layer as time passes by was analyzed using the electron energy loss spectroscopy technique. The octanethiol layer coated on the surface of Cu powders was kept until it was exposed to air for around 30 days. As days passes by, the coating layer had been decomposed and then a Cu(2)O layer was formed on the surface of powders.