RESUMO
To further improve carbonization efficiency of epoxy resin (EP) composites to form compact protective layers during combustion process, alkyl glycoside modified CuAl layered double hydroxide (CuAl-(APG)LDH) was designed and synthesized via one-step coprecipitation method, which was incorporated into EP matrix for preparing EP/CuAl-(APG)LDH nanocomposites. The results of XRD and TEM confirmed that EP nanocomposites with low incorporation of CuAl-(APG)LDH were exfoliated structures. The TGA results showed that the incorporation of CuAl-(APG)LDH remarkably increased the residues at 700 °C. The improved flame retardancy of EP/CuAl-(APG)LDH nanocomposites was proved by cone calorimeter test. The peak heat release rate, total heat release, peak smoke production rate and total smoke production value of EP/4 wt%CuAl-(APG)LDH nanocomposites dramatically decreased, which were attributed to the formation of hard and condensed residual layers on the surface of EP/CuAl-(APG)LDH nanocomposites.
RESUMO
Introduction: Understanding the impact of deep groundwater depth on vegetation communities and soil in sand dunes with different underground water tables is essential for ecological restoration and the conservation of groundwater. Furthermore, this understanding is critical for determining the threshold value of groundwater depth that ensures the survival of vegetation. Method: This paper was conducted in a semi-arid region in eastern China, and the effects of deep groundwater depth (6.25 m, 10.61 m, and 15.26 m) on vegetation communities and soil properties (0-200 cm) across three dune types (mobile, semi-fixed, and fixed dunes) were evaluated in a sand ecosystem in the Horqin Sandy Land. Results: For vegetation community, variations in the same species are more significant at different groundwater depths. For soil properties, groundwater depth negatively influences soil moisture, total carbon, total nitrogen, available nitrogen, available phosphorus concentrations, and soil pH. Besides, groundwater depth also significantly affected organic carbon and available potassium concentrations. In addition, herb species were mainly distributed in areas with lower groundwater depth, yet arbor and shrub species were sparsely distributed in places with deeper groundwater depth. Discussion: As arbor and shrub species are key drivers of ecosystem sustainability, the adaptation of these dominant species to increasing groundwater depth may alleviate the negative effects of increasing groundwater depth; however, restrictions on this adaptation were exceeded at deeper groundwater depth.
RESUMO
Understanding the effects of groundwater depth on soil microbiota and multiple soil functions is essential for ecological restoration and the implementation of groundwater conservation. The current impact of increased groundwater levels induced by drought on soil microbiota and multifunctionality remains ambiguous, which impedes our understanding of the sustainability of water-scarce ecosystems that heavily rely on groundwater resources. This study investigated the impacts of altered groundwater depths on soil microbiota and multifunctionality in a semi-arid region. Three groundwater depth levels were studied, with different soil quality and soil moisture at each level. The deep groundwater treatment had negative impacts on diversity, network complexity of microbiota, and the relationships among microbial phylum unites. Increasing groundwater depth also changed composition of soil microbiota, reducing the relative abundance of dominant phyla including Proteobacteria and Ascomycota. Increasing groundwater depth led to changes in microbial community characteristics, which are strongly related to alterations in soil multifunctionality. Overall, our results suggest that groundwater depth had a strongly effect on soil microbiota and functionality.
RESUMO
Heavy metals are considered as hazardous substances to human because of their toxicity, persistence and bioaccumulation, and the level in serum is an important factor to evaluate the caused health risk, which depends on efficient and sensitive analytical methods. Here, a triple signal-amplified electrochemical sensing platform based on metal-dependent DNAzymes was fabricated for sensitive determination of heavy metals in serum (copper as a model target). Under the optimized conditions, the proposed method showed good sensitivity (limit of detection, 0.33 fM for Cu2+) with excellent selectivity and stability, which is ascribed to: (i) tetrahedral DNA nanostructures (TDNs) that was used as a promising scaffold to adjust the selective transformation between heterogeneous and homogeneous reactions, preventing the nonspecific binding of electrodes surface and DNA probes; (ii) the magnetic beads (MBs) used which led to signal amplification and decreased background owing to its excellent properties of extracting equivalent targets from the complex samples; (iii) two signal amplification strategy of catalytic hairpin assembly (CHA) and hybridization chain reaction (HCR). In addition, the proposed sensing platform displayed satisfactory accuracy through the validation with inductively coupled plasma-mass spectrometry (ICP-MS) and a spike-recovery analysis (recoveries, 87.92-111.61%; RSD, 4.89-8.85%), indicating the great potential for rapid and sensitive detection of Cu2+ or other metal ions.