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The microstructures and micro-mechanical properties of the melt-spun ribbons of U-5.4 wt%Nb alloy were characterized using optical microscopy, scanning electron microscopy, X-ray diffraction and nanoindentation. Observed variations in microstructures and properties are related to the changes in ribbon thicknesses and cooling rates. The microstructures of the melt-spun ribbon consist of fine-scale columnar grains (∼1 μm) adjacent to the chill surface and coarse cellular grains in the remainder of the ribbon. In addition, the formation of inclusions in the ribbon is suppressed kinetically due to the high cooling rate during melt spinning. Compared with the water-quenched specimen prepared by traditional gravity casting and solution heat treatment, the elastic modulus values of the U-5.4 wt%Nb alloy were examined to vary with grain size and exhibited diverse energy dissipation capacities.

Nano zero-valent iron (NZVI) with high chemical reactivity and environmental friendliness had recently become one of the most efficient technologies for wastewater restoration. However, the unitary NZVI system had not met practical requirements for wastewater treatments. Expectantly, the development of NZVI would prefer multifunctional NZVI-based composites, which could be prepared and optimized by the combined methods and technologies. Consequently, a systematic and comprehensive summary from the perspective of multifunctional NZVI-composite had been conducted. The results demonstrated that the advantages of various systems were integrated by multifunctional NZVI-composite systems with a more significant performance of pollutant removal than those of the bare NZVI and its composites. Simultaneously, characteristics of the product prepared by the incorporation of numerous methods were superior to those by a simple method, resulting in the increase of the entirety efficiency. By comparison with other preparation methods, the ball milling method with higher production and field application potential was worthy of attention. After combining multiple technologies, the effect of NZVI and its composite systems could be dramatically strengthened. Preparation technology parameters and treatment effect of contaminants could be further optimized using more comprehensive experimental designs and mathematical models. The mechanism of the multifunctional NZVI system for contaminants treatment was primarily focused on adsorption, oxidation, reduction and co-precipitation. Multiple techniques were combined to enhance the dispersion, alleviating passivation, accelerating electron transfer efficiency or mass transfer action for optimizing the effect of NZVI composites.

The removal of arsenic(III), one of the most poisonous wastewater pollutants, was investigated using nanoscale zero-valent iron supported onto pumice and modified by chitosan (CS-P-NZVI). Scanning electron microscopy (SEM) analysis revealed that NZVI was distributed dispersedly on CS-P-NZVI without being oxidized. As(III) could be removed by adsorption on CS-P-NZVI in a very short time (minute scale) with high removal rates (more than 99.5%) over a wide range of pH (2.01–12.54) and concentration (20–100 mg/L). The removal of As(III) by CS-P-NZVI agreed well with the pseudo-first-order reaction kinetics and pseudo-second-order reaction kinetics. Reaction rate constants (Kobs) ranged from 0.27 to 0.96 min−1 at varied NZVI dosage. Freundlich isotherm provided a good model of the sorption system, indicating that CS-P-NZVI was heterogeneous in the surface properties. The thermodynamic parameters suggested that As(III) adsorption by CS-P-NZVI was a spontaneous and exothermic process. X-ray photoelectron spectroscopy (XPS) and atomic fluorescence spectrophotometer (AFS) analyses indicated that As(III) was only physically adsorbed on the surface of CS-P-NZVI within 60 min. Our results indicated that CS-P-NZVI might be an effective material for both in situ and ex situ remediation.

As-cast microstructural features of a U-5.4Nb alloy, including average grain size, dendrite structure, inclusion evolution behavior, solute (Nb) distribution and micromechanical properties were investigated with respect to a diverse number of calculated cooling rates in this paper. Various solidification techniques, including suction casting, arc remelting and induction melting followed by argon cooling, were employed to obtain wide ranges of cooling rates between 90 K/s and 9.9 × 105 K/s. Average grain sizes of suction cast samples decreased from 16.8 μm to 4.35 μm with increasing cooling rates. Similarly, inclusion evolution behavior was shown to refine in size with the increase of cooling rates. Fully developed dendrites inside the argon-cooled sample at a low cooling rate consisted of primary dendrite arms, secondary dendrite arms and tertiary dendrite arms that exhibited a fascinating dendrite structure with hexagonal symmetry. In addition, the segregation ratios of niobium decreased with decreasing cooling rates. Furthermore, the nanoindentation test indicated that the segregation of niobium had a significant influence on the mechanical properties of the dendrite arms and interdendritic regions. The elastic modulus and hardness for the primary dendrite arm, the secondary dendrite arm, and the interdendritic region were 61 GPa and 3.6 GPa, 62 GPa and 3.3 GPa, and 113 GPa and 6.5 GPa, respectively.

Persulfate could be activated by zero-valent iron (ZVI) leading to the rapid removal of various contaminants. However, quick consumption of Fe2+ largely constrained the removal (%) of target pollutants. Here it was reported that Na2S2O8 (SP) combined with ZVI, as an external source of Fe2+, was activated by Fe2+ to quickly (minutes scale) and efficiently (more than 90%) remove As (III) from aqueous solution at an initial pH value from 1.0 to 9.0. As (III) removal was obviously improved by an increase of Fe2+ rather than Na2S2O8 dosage. The removal of As (III) using Fe2+-SP-ZVI system followed the pseudo-second-order kinetic and pseudo-first-order kinetic expression. Fe2+ from ZVI oxidization could improve the efficient generation of , which obviously boosted ZVI corrosion. The production of could be manipulated by oxalic acid, ethylenediaminetetraacetic acid (EDTA), citric acid and phosphates through controlling the concentration of dissociative Fe2+, leading to an obvious repression on As (III) removal. The fitting of X-ray absorption fine structure (XAFS) spectra illustrated that the interatomic distance of As–O shell was located between As(III)–O and As(V)–O shell and external Fe2+ could promote the oxidation of As (III) to As (V) from 35.6% in 1.0 min–44.5% in 10.0 min. Goethite as the main component of iron oxyhydroxides might play a significant role of As (III) adsorption in Fe2+-SP-ZVI system. These findings are crucial for knowing the fate and transport of arsenic under permeable reactive barriers.

The removal of heavy metals from wastewater is one of the most important issues for the world, especially from industrial effluents. Pumice-nanoscale zero-valent iron (P-NZVI) was successfully prepared in different experimental conditions. Meanwhile, the shape, size and distribution of NZVI on P-NZVI were evaluated using a scanning electron microscope (SEM). At the optimum condition, NZVI with a mean diameter of 20.2 nm was distributed uniformly and consistently on the surface of pumice. Freundlich isotherm analysis suggested that the surface property of P-NZVI were heterogeneous. The removal of Hg (II) and Cr (VI) by P-NZVI could be well described by pseudo-first-order kinetic model. At equilibrium qmax of Hg (II) and Cr (VI) was 107.1 and 106.9 mg/g, respectively. Thermodynamic investigation suggested that the removal of Hg (II) and Cr (VI) by P-NZVI was an endothermic and spontaneous process. The less values of ΔH0 for Hg (II) than those for Cr (VI) demonstrated that more thermal energy was needed to remove Cr (VI) than Hg (II) at the same reaction rate.

Nanoscale zero-valent iron successfully supported on pumice (P-NZVI) was used to remove heavy metals from wastewater with a higher removal capacity and efficiency. NZVI particles with a mean diameter of 30.6 nm are distributed uniformly on the surface of P-NZVI. The thermal stability and mechanical strength of P-NZVI were also obviously enhanced. P-NZVI with a 7.7% NZVI mass fraction had a specific surface area (SBET) of 32.2 m2/g. The removal capacity of Hg (II) and Cr (VI) by P-NZVI was 332.4 mg Hg/g Fe and 306.6 mg Cr/g Fe, respectively. As an increase of pH, the removal rates of Hg (II) increased but those of Cr (VI) decreased gradually. P-NZVI is a regenerated material. The X-ray photoelectron spectroscope analysis (XPS) results indicated that Hg (II) and Cr (VI) were removed by a rapid physical adsorption in the first 0.5 min and predominantly by reduction. In terms of the efficiency and speed, P-NZVI was a promising candidate for applications to in situ environmental remediation, especially to the heavy metals pollution incidents with an extremely high concentration of heavy metals.

The synergistic effect of two different advanced oxidation technologies, heterogeneous sulfate radical based Fenton and TiO2 photocatalysis, was observed through a drastic enhancement of Rhodamine B removal in Co–TiO2/Oxone/Photo process. Our catalysts were obtained by a citric acid-assisted sol–gel method and Rhodmine B was used as model organic pollutant. The cobalt species in Co–TiO2 play a crucial role of integration Fenton with TiO2 photocatalysis in one heterogeneous hybrid system that not only active Oxone to produce SO4-, but also enhance the photocatalytic activity of TiO2 as well as extend its absorption spectrum to visible region, thus it can be defined as a type of bifunctional catalyst. The influence of the pH, [Oxone]/[RhB] molar ratio and catalyst concentration of the catalytic performance were investigated. The Rhodamine B can be eliminated 100% and TOC removal of solution can reach 68% at the optimum conditions by Photo/Co–TiO2/Oxone process. Moreover, the catalyst was demonstrated to have good stability and reusability.

Fe0 nanoparticles (NZVI) were successfully immobilized on epichlorohydrin/chitosan beads (ECH–CS–NZVI beads) for reduction of Cr(VI) from wastewater. Characterization with scanning electron microscope (SEM) showed that ECH–CS–NZVI beads with an average aperture size of 23.2 μm mainly consisted of Fe, O, C and N. Fourier transform infrared (FTIR) spectrum suggested that ECH could be grafted to CS–NZVI beads. A marked decrease in crumpling ratios indicated that the mechanical strength of Fe0-nanoparticles–chitosan (CS–NZVI) beads was obviously enhanced by cross-linking of epichlorohydrin (ECH). The thermal stability of ECH–CS–NZVI beads was also enhanced. Cr(VI) concentration, NZVI dosage, pH values and reaction temperature played an important role in the lifetime and using efficiency of ECH–CS–NZVI beads. Under all experimental conditions, the removal of Cr(VI) using ECH–CS–NZVI beads was consistent with pseudo first-order reaction kinetics. A removal rate could be maintained as high as 76.6% and 48.2% on the second and third runs, respectively, which hinted that ECH–CS–NZVI beads could be regenerated. The study demonstrates that ECH–CS–NZVI beads could become an effective and promising technology for in situ remediation of Cr(VI).