An extension of the characteristic curve model of plant species behavior in heavy metal soils.

This article proposes a mathematical model to characterize phytoremediation processes in soils contaminated with heavy metals. In particular, the proposed model constructs characteristic curves for the concentrations of several metals (As, Cd, Cu, Fe, Pb, Sb, and Zn) in soils and plants based on the experimental data retrieved from several bibliographical sources comprising 305 vegetal species. The proposed model is an extension of previous models of characteristic curves in phytoremediation processes developed by Lam et al. for root measurements using the bioconcentration factor. However, the proposed model extends this approach to consider roots, as well as aerial parts and shoots of the plant, while at the same time providing a less complex mathematical formula compared to the original. The final model shows an adjusted R2 of 0.712, and all its parameters are considered statistically significant. The model may be used to assess samples from a given plant species to identify its potential as an accumulator in the context of soil phytoremediation processes. Furthermore, a simplified version of the model was constructed using an approximation to provide an easy-to-compute alternative that is valid for concentrations below 37,000 mg/kg. This simplified model shows results similar to the original model for concentrations below this threshold and it uses an adjusted factor defined as [Formula: see text] that must be compared with a threshold depending on the metal, type of measurement, and target (e.g., accumulator or hyperaccumulator). The full model construction shows that 90 out of the 305 species assessed have a potential behavior as accumulators and 10 of them as hyperaccumulators. Finally, out of the 1405 experimental measurements, 1177 were shown to be accumulators or hyperaccumulators. In particular, 85% of the results coincide with the reported values, thus validating the proposed model.

Evaluation of copper tailing amendments through poultry waste and ammonium nitrate.

In this study, two amendments, poultry waste and ammonium nitrate, were evaluated to condition and stabilize a mine tailing and thus help the vegetation cover settle. Individually, ammonium nitrate was tested as a nitrogen source and chicken bone ash as a phosphate source. For this, laboratory tests were made on soil columns from the area to be remediated. The mobility and availability of metals and nutrients were determined by analyzing their leachates chemically. The results showed that the use of chicken bone ash decreases soluble metal concentrations, particularly in Fe and soluble Mn. On the other hand, experimental conditions proved that the acidification produced by ammonium nitrate nitrification does not significantly increase the lechate metal content. Therefore, its use for fertilization does not involve phytotoxicity risks. Regarding the availability of macronutrients as well as trace elements, the results showed that the concentrations lie within the ranges suitable for plant nutrition. So, the treatments are effective both for fertilization and phytoremediation.

N-Doped Carbon Xerogels as Pt Support for the Electro-Reduction of Oxygen.

Durability and limited catalytic activity are key impediments to the commercialization of polymer electrolyte fuel cells. Carbon materials employed as catalyst support can be doped with different heteroatoms, like nitrogen, to improve both catalytic activity and durability. Carbon xerogels are nanoporous carbons that can be easily synthesized in order to obtain N-doped materials. In the present work, we introduced melamine as a carbon xerogel precursor together with resorcinol for an effective in-situ N doping (3-4 wt % N). Pt nanoparticles were supported on nitrogen-doped carbon xerogels and their activity for the oxygen reduction reaction (ORR) was evaluated in acid media along with their stability. Results provide new evidences of the type of N groups aiding the activity of Pt for the ORR and of a remarkable stability for N-doped carbon-supported Pt catalysts, providing appropriate physico-chemical features.

Design Principles of Perovskites for Thermochemical Oxygen Separation.

Separation and concentration of O2 from gas mixtures is central to several sustainable energy technologies, such as solar-driven synthesis of liquid hydrocarbon fuels from CO2 , H2 O, and concentrated sunlight. We introduce a rationale for designing metal oxide redox materials for oxygen separation through "thermochemical pumping" of O2 against a pO2 gradient with low-grade process heat. Electronic structure calculations show that the activity of O vacancies in metal oxides pinpoints the ideal oxygen exchange capacity of perovskites. Thermogravimetric analysis and high-temperature X-ray diffraction for SrCoO3-δ , BaCoO3-δ and BaMnO3-δ perovskites and Ag2 O and Cu2 O references confirm the predicted performance of SrCoO3-δ , which surpasses the performance of state-of-the-art Cu2 O at these conditions with an oxygen exchange capacity of 44 mmol O 2 mol SrCoO 3-δ(-1) exchanged at 12.1 µmol O 2 min(-1) g(-1) at 600-900 K. The redox trends are understood due to lattice expansion and electronic charge transfer.