Facile preparation of coprecipitates between iron oxides and dissolved organic matter for efficient Fenton-like degradation of norfloxacin.

As two important components of dissolved organic matter (DOM), dissolved black carbon (DBC) and humic acid (HA) possess different chemical and structural properties, which might influence their activities like metal complexation and mediating electron transfer. In this study, a series of coprecipitates of iron oxides (FeOx) and DOM (HA or DBC) having different C/Fe molar ratios (0.2-3.0) was prepared under ambient conditions, which exhibited excellent catalytic efficiencies upon Fenton-like degradation of norfloxacin (NOR). Pseudo-first-order rate constant of NOR oxidation catalyzed by DBC-FeOx (C/Fe=3.0, 1.13 h-1) was 30.5, 4.3-14.2, and 1.3-15.7 folds higher than those mediated by FeOx alone, HA-FeOx and DBC-FeOx coprecipitates having C/Fe molar ratios of 0.2 and 1.6, respectively. Due to the higher concentrations of surface-bound Fe(III)/Fe(II) in the DBC-FeOx mediated systems, improved Fe(III)/Fe(II) cycling rates, •OH accumulation and NOR degradation were observed as compared with those of counterpart systems mediated by HA-FeOx. Besides functioning in Fe-C complexation to accelerate FeOOH cleavage, carbonyl/carboxyl groups of the coprecipitates also serve as electron shuttles, both of which improved Fe(III)/Fe(II) cycling and •OH production. Our findings emphasized the influence of DOM source and compositions on Fe(III)/Fe(II) cycling and provided a facile approach of preparing Fe-C catalyst for contaminants elimination.

The Utility of Electrochemical Systems in Microbial Degradation of Polycyclic Aromatic Hydrocarbons: Discourse, Diversity and Design.

Polycyclic aromatic hydrocarbons (PAHs), especially high molecular weight PAHs, are carcinogenic and mutagenic organic compounds that are difficult to degrade. Microbial remediation is a popular method for the PAH removal in diverse environments and yet it is limited by the lack of electron acceptors. An emerging solution is to use the microbial electrochemical system, in which the solid anode is used as an inexhaustible electron acceptor and the microbial activity is stimulated by biocurrent in situ to ensure the PAH removal and avoid the defects of bioremediation. Based on the extensive investigation of recent literatures, this paper summarizes and comments on the research progress of PAH removal by the microbial electrochemical system of diversified design, enhanced measures and functional microorganisms. First, the bioelectrochemical degradation of PAHs is reviewed in separate and mixed PAH degradation, and the removal performance of PAHs in different system configurations is compared with the anode modification, the enhancement of substrate and electron transfer, the addition of chemical reagents, and the combination with phytoremediation. Second, the key functional microbiota including PAH degrading microbes and exoelectrogens are overviewed as well as the reduced microbes without competitive advantage. Finally, the typical representations of electrochemical activity especially the internal resistance, power density and current density of systems and influence factors are reviewed with the correlation analysis between PAH removal and energy generation. Presently, most studies focused on the anode modification in the bioelectrochemical degradation of PAHs and actually more attentions need to be paid to enhance the mass transfer and thus larger remediation radius, and other smart designs are also proposed, especially that the combined use of phytoremediation could be an eco-friendly and sustainable approach. Additionally, exoelectrogens and PAH degraders are partially overlapping, but the exact functional mechanisms of interaction network are still elusive, which could be revealed with the aid of advanced bioinformatics technology. In order to optimize the efficacy of functional community, more advanced techniques such as omics technology, photoelectrocatalysis and nanotechnology should be considered in the future research to improve the energy generation and PAH biodegradation rate simultaneously.

Effects of T2 Heat Treatment on Microstructure and Properties of the Selective Laser Melted Aluminum Alloy Samples.

In this paper, aluminum alloy samples were fabricated by selective laser melting (SLM) and subsequently T2 heat treatment was undertaken. In order to obtain comprehensive results, various experiments on densification, hardness, tensile strength, bending strength and microstructure characterization were carried out. The results show that densification of samples after T2 heat treatment does not vary very much from the SLMed ones, while the Brinell hardness and strength decreases to about 50%. Moreover, the plasticity and fracture deflection increases about 3 fold. The effects on the microstructure and the mechanical properties of the SLMed aluminum alloy samples and subsequent T2 heat treatment were studied.

Microstructure and mechanical properties of stainless steel/calcium silicate composites manufactured by selective laser melting.

Selective laser melting (SLM) is raised as one kind of additive manufacturing (AM) which is based on the discrete-stacking concept. This technique can fabricate advanced composites with desirable properties directly from 3D CAD data. In this research, 316L stainless steel (316L SS) and different fractions of calcium silicate (CaSiO3) composites (weight fractions of calcium silicate are 0%, 5%,10% and 15%, respectively) were prepared by SLM technique with a purpose to develop biomedical metallic materials. The relative density, tensile, microhardness and elastic modulus of the composites were tested, their microstructures and fracture morphologies were observed using optical microscope (OM), scanning electron microscopy (SEM) and X-ray diffraction (XRD). It was found that the addition of CaSiO3 particles influenced the microstructure and mechanical properties of specimens significantly. The CaSiO3 precipitates from the overlap of adjacent tracks and became the origin of the defects. The tensile strength of specimens range 320-722MPa. The microhardness and elastic modulus are around 250HV and 215GPa respectively. These composites were ductile materials and the fracture mode of the composites was mixed mode of ductile and brittle fracture. The 316L SS/CaSiO3 composites can be a potential biomedical metallic materials in the medical field.

[Dissolved aluminum and organic carbon in soil solution under six tree stands in Lushan forest ecosystems].

Different depths of soils under 6 tree stands in Lushan Botany Garden were sampled and water-digested at room temperature. The dissolved aluminum and organic carbon were then determined by colorimetry, using 8-hydroxylquilin and TOC Analyzer, respectively. The results indicated that even derived from a naturally identical soil type, the test soils exhibited a diverse solution chemistry, regarding with the Al speciation. The soil solutions under Japanese cedar, giant arborvitae and tea had lower pH values and higher contents of soluble aluminum than those under Giant dogwood, azalea and bamboo. Under giant arborvitae, the lowest pH and the highest content of total soluble aluminum and monomeric aluminum were found in soil solution. There was a significant correlation between soluble aluminum and DOC, which tended to depress the accumulation of toxic monomeric aluminum. The 6 tree stands could be grouped into 2 categories of solution chemistry, according to aluminum mobilization.