Specially Structured AgCuTi Foil Enables High-Strength and Defect-Free Brazing of Sapphire and Ti6Al4V Alloys: The Microstructure and Fracture Characteristics.

A novel AgCuTi brazing foil with a unique microstructure was developed, which could achieve strong vacuum brazing of Ti6Al4V (TC4) and sapphire. The brazing foil was composed of Ag solid solution (Ag(s,s)), Cu solid solution (Cu(s,s)), and layered Ti-rich phases, and had a low liquidus temperature of 790 °C and a narrow melting range of 16 °C, facilitating the defect-free joining of TC4 and sapphire. The sapphire/TC4 joint fabricated by using this novel AgCuTi brazing foil exhibited an outstanding average shear strength of up to 132.2 MPa, which was the highest value ever reported. The sapphire/TC4 joint had a characteristic structure, featuring a brazing seam reinforced by TiCu particles and a thin Ti3(Cu,Al)3O reaction layer of about 1.3 µm. The fracture mechanism of the sapphire/TC4 joint was revealed. The crack originated at the brazing seam with TiCu particles, then propagated through the Ti3(Cu,Al)3O reaction layer, detached the reaction layer from the sapphire, and finally penetrated into the sapphire. This study offers valuable insights into the design of active brazing alloys and reliable metal-ceramic bonding.

Selective adsorption of palladium and platinum from secondary wastewater using Escherichia coli BL21 and Providencia vermicola.

It is important to recover precious metals from secondary wastewater because of their low crustal abundance. The selective adsorption of palladium (Pd) and platinum (Pt) ions from secondary wastewater, which contains a large amount aluminium and sodium ions, was investigated using Escherichia coli BL21 (BL21), genetically modified E. coli BL21 (EC20) and Providencia vermicola (P. V.). The results demonstrated that P.V., BL21 and EC20 cells took 95.9%, 88.2% and 97.5% of Pd ions, and 64.8%, 93.2% and 100% of Pt ions form industrial wastewater, respectively. All three bacterial biomass could be reused for Pd adsorption with a second adsorption efficiency of > 85%, specifically, the EC20 cells could absorb 93.8% of Pd ions from wastewater. SEM-EDS and XPS analyses confirmed the occurrence of Pd and Pt on the surface of wastewater-absorbed biomass. The shift in FTIR spectrum implied that functional groups, such as hydroxyl, amino, carboxyl and phosphate groups, were involved in wastewater adsorption.

Microbial synthesis of Pd-Pt alloy nanoparticles using Shewanella oneidensis MR-1 with enhanced catalytic activity for nitrophenol and azo dyes reduction.

Bimetallic nanoparticles (NPs) often exhibit improved catalytic performance due to the electronic and spatial structure changes. Herein, a novel green biosynthesis method for Pd-Pt alloy NPs using Shewanella oneidensis MR-1 was proposed. The morphology, size and crystal structure of Pd-Pt alloy NPs were studied by a suite of characterization techniques. Results showed Pd-Pt alloy NPs were successfully synthesized inside and outside the cell. The biosynthesized Pd-Pt alloy NPs were polycrystalline and face-centered-cubic structure with the particle size ranged from 3-40 nm. Furthermore, the catalytic experiment demonstrated that the Pd-Pt alloy NPs exhibited the highest performance for the catalytic reduction of nitrophenol and azo dyes compared with the as-synthesized Pd and Pt monometallic NPs. This enlarged catalytic activity resulted from the synergistic effect of Pd and Pt element. Thereby, this paper provided a simple biosynthesis method for producing bimetallic alloy nanocatalyst with superior activity for contaminant degradation.

Enhancement of platinum biosorption by surface-displaying EC20 on Escherichia coli.

To increase the platinum adsorption capacity of Escherichia coli (E. coli) biomass, we fused EC20 protein to the E. coli cell surface using an InaKN-based display system, which is the N-terminal region of ice nucleation protein that can be employed as a cell surface display motif. The media and culture conditions were optimized for EC20 (a phytochelatin analogue with 20 repeating units of glutamate and cysteine) expression and Pt (IV) biosorption. Furthermore, the adsorption process was elucidated from aspect of adsorption kinetics and equilibrium, and the characterization of blank and Pt-loaded cells were analyzed using SEM, AFM, TEM, FT-IR and XPS. Our study demonstrated that E. coli strain, which had InaKN-EC20 protein expressed on the cell surface, showed a great enhancement in Pt (IV) adsorption under optimized condition when comparing with that of original E. coli strain. The SEM-EDX analysis revealed that the cellular morphology has been changed in Pt-loaded cells, and the weight percent of platinum in the surface of E.coli increased substantially after displaying EC20 protein. Furthermore, intracellular platinum accumulation was detected in Pt-loaded EC20 cells since a clear peak of platinum exhibited, implying that cytoplasmic EC20 protein might also contribute to platinum accumulation. FTIR analysis revealed that the predominant functional groups in platinum adsorption were amine, carboxyl and phosphate groups.