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(1) BiNbO4(U-BiNbO4) was produced with oxygen vacancies that were controlled by carbon. (2) More effective degradations of the cationic dyes methylene blue (MB, 75.7 3.5%) and brilliant green (BG, 86.3 3.5%) than the pristine BiNbO4 were attained.

Here, we report a simple sono-chemical method to fabricate Pd-loaded α/β-Bi2O3 nanorods with exceptional methylene blue (MB), brilliant green (BG) and acid red 1 (AR) dye degradation properties. The unique nanorods morphology was accomplished by treating of bismuth complexes with sodium hydroxide at room temperature. Palladium was introduced by UV-photo-deposition method from palladium (II) chloride source. The successful substitution of Bi3+ by Pd2+ in bulk of Pd-loaded α/β-Bi2O3 was confirmed by X-ray diffraction (XRD) and Fourier-transform infrared spectroscopy (FTIR). The surface presence of α-, β-Bi2O3, PdO and metallic Pd0 was confirmed by X-ray photoelectron spectroscopy (XPS). The rational design and fabrication approach is based on matching of (1) valence band (VB) and conduction band (CB) of as-prepared catalyst with redox potentials of dyes, (2) VB and CB with reactive oxygen species (ROS), and (3) redox potentials of dyes with ROS. By using the approach of rational design the material is able to degrade cationic MB (90.8%), BG (83.3%) and anionic AR (83.2%) dyes within 20 min under LED light irradiation (100 mW/cm2), as well as to degrade mixtures of cationic/anionic MB-AR and BG-AR dyes. Further optimization of dye degradation parameters, such as initial concentration of dye, amount of catalyst, and solution pH was carried out. A mechanism of dye degradation was proposed based on ROS scavenging experiments and mapping out of semiconductor band structures with redox potentials of dyes and ROS. Pd-loaded α/β-Bi2O3 catalyst has potential applications in wastewater treatment, water splitting and healthcare industries.

In principle, n-type and p-type semiconductors are respectively responsible for photo-catalytic degradation of cationic dyes (e.g., methylene blue) and anionic dyes (e.g., acid red 1), governed by photoelectrons in the former and photo-holes in the later system. Hence, we present a new strategy: design and fabrication of photocatalytic structures to match the redox potentials of mixed basic/acidic dyes as well as the reactive oxygen species (ROS). For the first time Ag/Ag2O/BiNbO4 structure is (1) designed to match the redox potentials of basic/acidic dyes as well as ROS, (2) fabricated using photoreduction to control the Ag/Ag2O/BiNbO4 interfaces, and (3) able to simultaneously degrade 84% methylene blue dye (MB) in 240 min and 88% acid red 1 (AR) in 25 min under LED light irradiation, corresponding to 7 wt% Ag loading. To the best of our knowledge, this is the first photocatalytic degradation study on mixed basic and acidic dyes using a single catalyst. We also tested the new redox potential matching strategy in mixed basic dyes (MB and rhodamine B (RhB)). As expected our experimental results reproduced well our model predictions: in particular, results support our proposed hydroxyl radical ( OH) mechanism, which is initiated by photo-holes. Therefore, this new design strategy, which consists of matching band structures of the photocatalyst with redox potentials of dyes and ROS, has immediate implications to general photocatalytic applications beyond dye degradation and water-splitting.

In a search for Pb-free photovoltaic materials, a double perovskite Cs2AgSbBr6 with an indirect optical bandgap of 1.64 eV has been synthesized. Single crystal X-ray diffraction determined the space group as Fm3[combining macron]m with a = 11.1583(7) Å. The black, as-synthesised compound turned brown after heat treatment at 480 K while the symmetry and crystallinity were preserved. X-ray photoelectron spectroscopy indicated the existence of Sb5+ in the black crystals, suggesting that the dark colour arises from the Sb3+-Sb5+ charge transfer. Furthermore, UV visible spectroscopy and density functional theory calculations have been applied to probe the optical properties and electronic structure.

Fatigue performance of Inconel 718 (IN718) parts built using laser powder bed fusion (L-PBF) is often poorer than that of the cast and wrought alloy parts. This is because of detrimental effects arising from the microstructures such as brittle phases and anisotropy as well as porosities. To improve fatigue performance of L-PBF IN718, two types of post processes namely hot isostatic pressing (HIP) (performed at 980 °C, 100 MPa and 4 h) and shot peening (performed at 0.45 mmA intensity and 200 % coverage) were employed individually as well as sequentially on different specimens in addition to a standard processing route consisting of L-PBF build followed by solution annealing and double aging heat treatment. Porosities were considerably reduced by HIP-ing (from 0.39 % to 0.08 % porosity volume ratio) but this did not translate to improvements in fatigue performance. This can be attributed to the presence of inclusions and yield strength reduction resulting from γ” solutionisation. High compressive residual stresses of close to 1 GPa were recorded following shot peening regardless of whether HIP-ing was carried out prior to the shot peening. Improvement in fatigue lives particularly at high stress levels was observed on shot peened specimens without HIP-ing (H + SP) which can be explained by the compressive residual stresses that delay the onset of fatigue crack initiation. Shot peening applied on the HIP-ed specimens (H + HIP + SP) however, resulted in fatigue performance deterioration. This is related to the harmful tensile stresses that must exist alongside the compressive residual stresses in a shot peened surface, as evident from the location of the sub-surface crack initiations near the residual stress transition region approximately 300 μm from the free surface. In this case, detrimental effects arising from tensile stresses appear to have outweighed the benefits from compressive stresses on fatigue performance.

Laser surface melting is one of the most important processes in laser material processing. Selective vaporization of alloying elements in laser melting offers fundamental understanding of laser processing on metallic alloys. This work provides linkage between laser melting and material properties using secondary ion mass spectrometry (SIMS) for tiny vaporized species in laser-generated plume and energy dispersive spectroscopy (EDS) for solid solution range in molten pool, both qualitatively and quantitatively (up to hundreds of micron). Silicon wafer was used to collect the generated plume. Chemical analysis was carried out on top surface and sub-surface of the deposited plume. Transport behavior as well as distribution of the vaporized species inside the plume was further proposed. ASTAR (Agency for Sci., Tech. and Research, S’pore)