With the rapid development of nanotechnology, molybdenum (Mo)-based nanomaterials have been widely used in various fields, and the ensuing environmental behavior has also raised widespread concern. Here, we report the nanotoxic effects and mechanism of nano-Mo treatment on the soybean–rhizobia symbiotic system in the sterilized mixture of sand and vermiculite environment. Exposure to different concentrations and types of Mo-based nanomaterials was shown to have significant physiological and biochemical toxicity to soybean. The accumulation of Mo in plant tissues increased with the concentration of nano-Mo in the sand and vermiculite media. The Mo-based nanomaterials that enter plant tissues were found to affect not only the growth and development of plants, but also the microstructure of the roots and the activity of rhizobium in the symbiotic system, thereby weakening the nitrogen fixation capacity of the soybean–rhizobia symbiotic system. Meanwhile, the activity of superoxide dismutase (SOD) and peroxidase (POD) showed a significant increase, indicating that these enzymes were activated after exposure to nano-Mo, which helps to remove the reactive oxygen species. Furthermore, the treatment of high-concentration Mo nanoparticles was shown to have obvious epigenetic toxicity to plants. These results demonstrate that high concentrations of Mo nanoparticles can affect the agronomical and physiological parameters in soybean, which may impact human nutrition and health.
The highly efficient electrochemical hydrogen evolution reaction (HER) provides a promising way to solve energy and environment problems. In this work, various transition metals (Fe, Co, Ni, Cu, Ag, and Pt) were selected to support on molybdenum carbides by a simple organic-inorganic precursor carburization process. X-ray diffraction (XRD) analysis results indicated that the β-Mo2C phase was formed in all metal-doped samples. X-ray photoelectron spectroscopy analysis indicated that the binding energy of Mo2+species (Mo2C) shifted to a lower value after metal was doped on the molybdenum carbide surface. Comparing with pure β-Mo2C, the electrocatalytic activity for HER was improved by transition metal doping on the surface. Remarkably, the catalytic activity improvement was more obvious when Pt was doped on molybdenum carbide (2% Pt-Mo2C). The 2% Pt-Mo2C required a η10of 79 mV, and outperformed that of pure β-Mo2C (η10= 410 mV) and other transition metal doped molybdenum carbides, with a small Tafel slope (55 mV/dec) and a low onset overpotential (32 mV) in 0.5 M H2SO4. Also, the 2% Pt-Mo2C catalyst demonstrated a high stability for the HER in 0.5 M H2SO4. This work highlights a feasible strategy to explore efficient electrocatalysts with low cost via engineering on the composition and nanostructure.Keywords:hydrogen evolution reaction;nano-molybdenum-carbide;electro-catalysis;transition metal
Chuanhao Yan,Xuefeng Yu,Jinlong Zhang,Jinglei He,Wenyi Jia,Jianlong Wang,Fuqiang Liu,Junfeng Liu,Xilong Wang
To significantly enhance the unsatisfactory Au(III) sorption performance (2280 mg g−1) by a material designed in our previous work, we ingeniously fabricated a nano-sized and uniform molybdenum composite (MoCOM) using a household microwave oven; it was embedded in a nanofiber mat by electrospinning technique to synthesize a novel material (CS-MoCOM-Th) for effective Au(III) sorption. After embedding MoCOM, an ultrahigh maximum sorption capacity (4090 mg g−1) of Au(III) at high concentrations and a sorption efficiency at low concentrations by CS-MoCOM-Th (99.59%) were achieved at pH 4.0. Mechanistically, the excellent Au(III) sorption performance was mainly driven by electrostatic attraction by protonated C–N+ groups and coordination interaction with N- or S-containing moieties: C–N, CN, C–N+, CS, S(−II), and Sn(−II). During sorption, 69.42% of Au(III) was directly reduced to elemental gold on CS-MoCOM-Th, and gold foils precipitated on the nanofiber mat. Notably, excellent sorption selectivity of Au(III) on CS-MoCOM-Th was achieved when heavy metals, including Cu(II), Ni(II), Pb(II), and Zn(II), and noble metal Pt(IV) were co-present at 2 × 10−3 mg mL−1. CS-MoCOM-Th could still sorb 82.15% of Au(III) at 0.01 mg mL−1 after four cycles. Overall, this study highlights that CS-MoCOM-Th is one of the most competitive candidates for Au(III) recovery from the aqueous phase.
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