Jie He

Interfacial mechanisms of heterogeneous Fenton reactions catalyzed by iron-based materials: A review.

The heterogeneous Fenton reaction can generate highly reactive hydroxyl radicals (OH) from reactions between recyclable solid catalysts and H2O2 at acidic or even circumneutral pH. Hence, it can effectively oxidize refractory organics in water or soils and has become a promising environmentally friendly treatment technology. Due to the complex reaction system, the mechanism behind heterogeneous Fenton reactions remains unresolved but fascinating, and is crucial for understanding Fenton chemistry and the development and application of efficient heterogeneous Fenton technologies. Iron-based materials usually possess high catalytic activity, low cost, negligible toxicity and easy recovery, and are a superior type of heterogeneous Fenton catalysts. Therefore, this article reviews the fundamental but important interfacial mechanisms of heterogeneous Fenton reactions catalyzed by iron-based materials. OH, hydroperoxyl radicals/superoxide anions (HO2/O2(-)) and high-valent iron are the three main types of reactive oxygen species (ROS), with different oxidation reactivity and selectivity. Based on the mechanisms of ROS generation, the interfacial mechanisms of heterogeneous Fenton systems can be classified as the homogeneous Fenton mechanism induced by surface-leached iron, the heterogeneous catalysis mechanism, and the heterogeneous reaction-induced homogeneous mechanism. Different heterogeneous Fenton systems catalyzed by characteristic iron-based materials are comprehensively reviewed. Finally, related future research directions are also suggested.

Understanding the evolution of stratified extracellular polymeric substances in full-scale activated sludges in relation to dewaterability

Activated sludge is a highly changeable colloidal system. In this study, the dynamic variation in physicochemical characteristics, especially distribution and abundance of extracellular polymeric substances (EPS) of activated sludges from different WWTPs was investigated in order to establish the relationships between floc properties and the sludge dewatering property. Firstly, it was observed that the total EPS content of the activated sludge was significantly decreased with the rise in temperature. Three-dimensional fluorescence excitation–emission matrix (3D-EEM) spectroscopy analysis indicated that each sludge fraction (soluble EPS, loosely-bound EPS (LB-EPS), tightly bound EPS (TB-EPS) and pellet) from different WWTPs had a similar fluorescence fingerprint in the same time period. In addition, protein-like substances were found to be the dominant components in TB-EPS and pellets regardless of operating time for each WWTP sludge. At low temperatures, soluble EPS and LB-EPS also mainly contained protein-like compounds, while the amount of humic acids of them was increased significantly in the summer. According to Pearsons correlation analysis, normalized CST correlated well with the composition and content of soluble EPS, indicating that the change in soluble EPS properties caused fluctuation of sludge dewatering behavior. Finally, we proposed some operating strategies for improving the dewatering performance of activated sludge in full-scale WWTPs by regulating the soluble EPS properties.

Solidification of Immiscible Alloys: A Review

Immiscible alloys gained a considerable interest in last decades due to their valuable properties and potential applications. Many experimental and theoretical researches were carried out worldwide to investigate the solidification of immiscible alloys under the normal gravity and microgravity condition. The objective of this article is to review the research work in this field during the last few decades.

Effect of phosphate on heterogeneous Fenton oxidation of catechol by nano-Fe3O4： Inhibitor or stabilizer？

The effect of phosphate on adsorption and oxidation of catechol, 1,2-dihydroxybenzene, in a heterogeneous Fenton system was investigated. In situ attenuated total reflectance infrared spectroscopy (ATR-FTIR) was used to monitor the surface speciation at the nano-Fe3O4 catalyst surface. The presence of phosphate decreased the removal rate of catechol and the abatement of dissolved organic compounds, as well as the decomposition of H2O2. This effect of phosphate was mainly due to its strong reaction with surface sites on the iron oxide catalyst. At neutral and acid pH, phosphate could displace the adsorbed catechol from the surface of catalyst and also could compete for surface sites with H2O2. In situ IR spectra indicated the formation of iron phosphate precipitation at the catalyst surface. The iron phosphate surface species may affect the amount of iron atoms taking part in the catalytic decomposition of H2O2 and formation of hydroxyl radicals, and inhibit the catalytic ability of Fe3O4 catalyst. Therefore, phosphate ions worked as stabilizer and inhibitor in a heterogeneous Fenton reaction at the same time, in effect leading to an increase in oxidation efficiency in this study. However, before use of phosphate as pH buffer or H2O2 stabilizer in a heterogeneous Fenton system, the possible inhibitory effect of phosphate on the actual removal of organic pollutants should be fully considered.

Enhancement of Fenton oxidation for removing organic matter from hypersaline solution by accelerating ferric system with hydroxylamine hydrochloride and benzoquinone.

Fenton oxidation is generally inhibited in the presence of a high concentration of chloride ions. This study investigated the feasibility of using benzoquinone (BQ) and hydroxylamine hydrochloride (HA) as Fenton enhancers for the removal of glycerin from saline water under ambient temperature by accelerating the ferric system. It was found that organics removal was not obviously affected by chloride ions of low concentration (less than 0.1mol/L), while the mineralization rate was strongly inhibited in the presence of a large amount of chloride ions. In addition, ferric hydrolysis-precipitation was significantly alleviated in the presence of HA and BQ, and HA was more effective in reducing ferric ions into ferrous ions than HA, while the H2O2 decomposition rate was higher in the BQ-Fenton system. Electron spin resonance analysis revealed that OH production was reduced in high salinity conditions, while it was enhanced after the addition of HA and BQ (especially HA). This study provided a possible solution to control and alleviate the inhibitory effect of chloride ions on the Fenton process for organics removal.

Vickers-indentation-induced crystallization in a metallic glass

Crystallization preferentially occurs on the compressive sides of some metallic glasses due to bending, implying that stress state is a critical factor affecting the mechanically induced crystallization. However, the role of stress state in mechanically induced crystallization in metallic glasses is poorly understood. Here, we report on the crystallization kinetics in different deformed regions during Vickers indentation of Zr65Al7.5Ni10Cu12.5Ag5 metallic glass. Our results indicate that the nucleation rate beneath the indenter tip is much higher than that under an indenter edge. It is revealed that the nucleation rate I (m−3u2009s−1) and the effective compressive stress P (MPa) follow an expression Iu2009=u2009exp(3.81u2009+u20090.044 P), which agrees well with our experimental results. Our findings reduce the role of stress state in mechanically induced crystallization in metallic glasses, which is helpful in understanding the mechanism of mechanically induced crystallization.

Microstructure evolution during a liquid-liquid decomposition under the common action of the nucleation, growth and Ostwald ripening of droplets

Abstract The kinetic details of the microstructure evolution during a liquid – liquid phase transformation under the common action of the nucleation, diffusional growth and Ostwald ripening of the minority phase droplets are investigated numerically. The results demonstrate that the cooling rate during the nucleation period of the minority phase droplets has an overwhelmingly strong effect on the microstructure formation compared with the cooling rate after the nucleation period. Generally, the effect of the Ostwald ripening of the minority phase droplets is weak in an alloy cooled continuously all through the miscibility gap and the average radius of the minority phase particles shows an inverse square root dependence on cooling rate. An obvious coarsening of the minority phase droplets occurs and the exponential varies towards – 1/3 only when the cooling rate decreases by more than two orders of magnitude after the nucleation of the precipitated droplets.

Liquid-liquid hierarchical separation and metal recycling of waste printed circuit boards

Waste electrical and electronic equipment is rapidly increasing worldwide, resulting in a large quantity of waste printed circuit boards (WPCBs). There is a great challenge on how to efficiently separate mixed metals in WPCBs, which consists of more than 10 elements including hazardous Cr, Pb and Cd. In this work, based on atomic interactions, a method of liquid-liquid hierarchical separation is developed to separate the mixed metals dissociated from the pyrolyzed WPCBs of mobile phones. The hierarchical separation of L→LFe-rich + LCu,Pb-rich, LCu,Pb-rich→LCu-rich + LPb-rich and LPb-rich→SCu-dendritical + LPb-rich produces four immiscible Fe-rich, Cu-rich, Cu-dendritical and Pb-rich substances. The separation rate between these substances can reach more than 96% in a super-gravity field of G = 1000g. Other metals selectively distribute in the four substances. The Fe-rich substance collects Cr, Co, Ni and Si. Almost all of Au and Ag are trapped in the Cu-rich and Cu-dendritical substances. The low-melting-point metals, i.e. Bi, Cd, In and Sn, are located in the Pb-rich substance. This work provides a green shortcut for efficiently separating and recycling overall metals in WPCBs.

Ni-Based Metallic Glass Composites Containing Cu-Rich Crystalline Nanospheres

In this work, a quaternary Ni–Cu–Nb–Ta system has been designed to obtain composite microstructure with spherical crystalline Cu-rich particles embedded in amorphous Ni-rich matrix. The alloy samples were prepared by using single-roller melting-spinning method. The microstructure and thermal properties of the as-quenched alloy samples were characterized by X-ray diffraction, scanning electron microscopy, high-resolution transmission electron microscopy, and differential scanning calorimetry. It shows that the spherical crystalline Cu-rich particles are embedded in the amorphous Ni-rich matrix. The average size of the Cu-rich particles is strongly dependent upon the Cu content. The effect of the alloy composition on the behavior of liquid–liquid phase separation and microstructure evolution was discussed. The phase formation in the Ni-based metallic glass matrix composite was analyzed.

Effect of addition of elements on two-glass-forming ability of Zr–Ce–Co–Cu immiscible alloys

ABSTRACT The effects of Al element addition and partial substitution of Ce with La, Pr, and Nd on the two-glass-forming ability of the phase-separating Zr–Ce–Co–Cu alloy system have been studied. The distribution of the additions in the two coexistent immiscible liquids was analysed thermodynamically. The results indicate that Al almost equally distributes in the two liquids, whereas the elements La, Pr, and Nd are predominantly found in the Ce–Cu-rich liquid. X-ray diffraction analysis reveals that these additions obviously enhance the two-glass-forming ability of the coexisting liquids. This work presents a strategy for improving the two-glass-forming ability of immiscible alloys to obtain phase-separated bulk metallic glasses.