ABSTRACT
A series of porous carbon nitrides modified by different polyoxometalates (POMs) were prepared by the ultrasonic method. POMs were assembled on the surface of mpg-C3N4 via electrostatic attraction. The catalyst has visible light degradation activity for phenol (λ > 420 nm). mpg-C3N4 modified by H4SiW12O40 with a mass ratio of 1 : 5 showed the highest catalytic activity, which was 3.5 times higher than that of mpg-C3N4. As an electron acceptor, polyoxometalate can capture the photoelectron of C3N4, which can promote the separation of photocharge and improve the photocatalytic activity. ESR also confirmed that the superoxide radicals play a major role in degradation. The results show that the charge separation efficiency and catalytic activity can be enhanced by polyacids.
ABSTRACT
A novel label-free fluorescence assay for detection of Hg2+ was developed based on the Hg2+-binding single-stranded DNA (ssDNA) and SYBR Green I (SG I). Differences from other assays, the designed rich-thymine (T) ssDNA probe without fluorescent labelling can be rapidly formed a T-Hg2+-T complex and folded into a stable hairpin structure in the presence of Hg2+ in environmental drinking water samples by facilitating fluorescence increase through intercalating with SG I in one-step. In the assay, the fluorescence signal can be directly obtained without additional incubation within 1 min. The dynamic quantitative working ranges was 5-1000 nM, the determination coefficients were satisfied by optimization of the reaction conditions. The lowest detection limit of Hg2+ was 3 nM which is well below the standard of U.S. Environmental Protection Agency. This method was highly specific for detecting of Hg2+ without being affected by other possible interfering ions from different background compositions of water samples. The recoveries of Hg2+ spiked in these samples were 95.05-103.51%. The proposed method is more viable, low-costing and simple for operation in field detection than the other methods with great potentials, such as emergency disposal, environmental monitoring, surveillance and supporting of ecological risk assessment and management.
Subject(s)
Drinking Water/chemistry , Environmental Monitoring/methods , Mercury/analysis , Staining and Labeling , Fluorescence , Imaging, Three-Dimensional , Limit of Detection , Reference StandardsABSTRACT
In 2001-2002, 14 maize cultivars in Liaoning Province were used for the analysis of their entophytic bacteria population. The entophytic bacteria strains with a higher frequency in maize roots were Bacillus spp., Enterobacter spp., Serratia spp., Pseudomonas spp., Xanthomonas spp., Clavibacter spp., Bacillus spp., Enterobacter spp. and Serratia spp. Comparatively, Bacillus spp. was the most prevalent entophytic bacterium, including 8 species, B. subtilis, B. megaterium, B. cereus, B. licheniformis, B. anthracis, B. mycoides, B. pumilus and B. circulans, and with an average isolation frequency of 75.5% at seedling stage and 77.6% at adult stage. There existed significant differences in the population and dynamics of endophytic bacteria among maize cultivars and growth periods, and a significant correlation was found between maize genetic background and entophytic bacteria population.
