Abstract In this paper, ultrafine platinum nanoparticles (Pt/Co-N-C) were prepared by irradiating the mixture of Co-N-C and K2[PtCl4] with near-ultraviolet (UV) light at a wavelength of 395 nm and visible light at 450 and 550 nm without adding any reducing and stabilizing agents using MOFs-modified carbon materials (Co-N-C) as the carrier. The composition and morphology of the Pt/Co-N-C catalysts were investigated using characterization tools such as X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), and high-resolution transmission electron microscopy (HR-TEM), etc. The results showed that the Pt nanoparticles were well dispersed on the surface of the Co-N-C, with average particle sizes of about 2.39, 2.86, and 3.53 nm, respectively. In the catalytic 4-NP reduction experiments, the catalyst (Pt/Co-N-C-1) prepared under near-ultraviolet light (395 nm) irradiation showed the highest catalytic activity with a rate constant k=0.64 min-1. After five cycles, the conversion rate was still maintained at about 90%, which was highly reusable. It was demonstrated that 395 nm near-ultraviolet light was more favorable for the modulation of the distribution of the species during the hydrolysis and reduction of platinum in this reaction to form smaller-sized platinum nanocrystals, which was conducive to the catalyst to exhibit higher activity.
Cadmium toxicity to 23 kinds of commonly cultivated crops of 9 families was studied by solution culture with different cadmium concentrations. Most of the studied crop seedlings showed cadmium toxicity symptoms with 0.1-0.25 mg x L(-1). The toxic effects of cadmium on the crops were quite different. The effect of Cd on shoot biomass was more obvious and stable than the other parameters at low Cd concentrations (0.1-0.5 mg x L(-1)), Therefore, shoot fresh weight was selected to be the indicator of plant sensitivity to Cd. The EC20 (effective concentration causing a 20% inhibition of shoot biomass) values of Cd for the studied crops ranged from 0.03 to 24.67 mg x L(-1). The Cd sensitivity of the crops is classified according to the response endpoint of apparent symptoms and the EC20 values. Chinese cabbage, brassica napus, youmai lettuce, mustard and pakchoi are sensitive species to Cd toxicity that can be used as ecological receptors to determine the critical value of the toxicity of soil Cd to crops or as monitoring crop species of soil Cd pollution. Cucumber is most tolerant to Cd toxicity among the studies crops.
Laboratory incubation experiment was conducted to study the kinetics of N mineralization and to investigate the effect of two factors(sludge rate and incubation temperature) on N mineralization during a 16-week incubation period.The results showed that N mineralization followed a one pool kinetic model(Nm=N0[1-exp(1-k×t)]).The value of N0 increased with temperature and sludge amount while value of k increased with temperature and decreased with sludge amount.The results also indicated that the effect of sludge amount on N mineralization could be separated into two ranges: when sludge was amended at the rate between 3 % to 6 %,the rate of N mineralization decreased obviously with sludge amount;when sludge was amended at the rate of ≥6 %,N mineralization changed little among treatments.It was also found that the rate of N mineralization increased with temperature.
Saltwater is detrimental to biological wastewater treatment processes. Anaerobic reduction is a promising technology for treating complex organic wastewater but is limited by relatively long reaction times and high demand for electron donors. In microbial fuel cells (MFCs), the salinity contained in saltwater promotes the redox reaction between the electrodes to accelerate the removal of chemical oxygen demand (COD) and generate electricity. In this study, a system combining an anaerobic fluidized bed (AFB) with an MFC was constructed to treat high-salinity wastewater. As a result, the anode attained good removal efficiency of 98.6% for COD and 52.1% for -N when the Cl− concentration was <6500 mg/L. Electricity generation was maintained when the Cl− concentration was ∼12,000 mg/L; a maximum output of 841.3 mV and 35.4 mW/m2 was achieved. Investigation of the biological characteristics confirmed that the high biomass in the AFB ensured good contaminant removal efficiency. Furthermore, the ratio of proteins to polysaccharides in extracellular polymeric substances decreased sharply at a Cl− concentration of 6500 mg/L. Genomic sequencing analysis of anode bioparticles showed that Halanaerobiaceae bacterium sp. and Methanolinea tarda sp. were predominant in the bacterial and archaeal communities, respectively. This study suggested that the AFB-MFC system has good potential for contaminants removal and electricity generation in treatment of high-salinity wastewater.
Arsenic (As) toxicity threshold value (TTV) for plants is fundamental to both establishing regional As reference values in soil and performing risk assessment. However, TTV varies among different plant species and soil properties, which influences the application of reference values. In this study, hydroponic experiments with the seedlings of 23 plant species belonging to nine families were conducted to screen the most As-sensitive plant species. The results revealed that the EC20 (effective As concentration at which shoot biomass or height is inhibited by 20%) values were 1.38–104.4 mg L-1 for shoot height and 0.24–42.87 mg L-1 for above-ground fresh biomass, with 75.7 and 179 times of difference, respectively. As rice was observed to be more sensitive to As toxicity than the other crops, it was chosen as the ecological receptor in the pot experiment on As phytotoxicity in nine types of soils collected from Fujian Province in South China. The EC10 and EC20 with respect to rice shoot height were 3.72–29.11 mg kg-1 and 7.12–45.60 mg kg-1, respectively. Stepwise regression analysis indicated that free iron oxide concentration was the major factor that affects As bioavailability in soil. The regression analysis also showed that EC x (x = 10, 20, and 50) of soil available As for shoot height was positively related to free iron oxide concentration in soil. In addition, soil cation exchange capacity, clay (< 0.002 mm) content, and exchangeable magnesium content are also important factors influencing As phytotoxicity in acidic soils. The regression models have potential application in the prediction of As phytotoxicity in acidic soils.
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