Concentration-dependent effect of photoluminescent carbon dots on the microbial activity of the soil studied by combination methods

A Review on the Catalytic Remediation of Dyes by Tailored Carbon Dots

Water polluted with dyes has become a serious global concern during the twenty-first century, especially for developing countries. Such types of environmental contaminant pose a severe threat to biodiversity, ecosystems, and human health globally; therefore, its treatment is an utmost requirement. Advanced technologies including the use of nanomaterials represent a promising water treatment technology with high efficiencies, low production costs, and green synthesis. Among the nanomaterials, carbon dots, as a new class of carbon-based nanoparticles, have attracted attention due to their unique features and advantages over other nanomaterials, which include high water solubility, easy fabrication and surface functionalisation, excellent electron-donating ability, and low toxicity. Such properties make carbon dots potential nanocatalysts for the Fenton-like degradation of environmental pollutants in water. Although recent studies show that carbon dots can successfully catalyse the degradation of dyes, there are still limited and controversial studies on the ecotoxicity and fate of these nanoparticles in the environment. In this review, the authors aim to summarise the recent research advances in water remediation by technologies using carbon dots, discuss important properties and factors for optimised catalytic remediation, and provide critical analysis of ecotoxicity issues and the environmental fate of these nanoparticles.

Combined effects of antimony and sodium diethyldithiocarbamate on soil microbial activity and speciation change of heavy metals. Implications for contaminated lands hazardous material pollution in nonferrous metal mining areas

The combined effects of antimony (Sb) and sodium diethyldithiocarbamate (DDTC), a common organic flotation reagent, on soil microbial activity and speciation changes of heavy metals were investigated for the first time. The results showed that the exchangeable fraction of Sb was transformed to a stable residual fraction during the incubation period, and the addition of DDTC promoted the transformation compared with single Sb pollution, probably because DDTC can react with heavy metals to form a complex. In addition, the presence of DDTC and Sb inhibited the soil microbial activity to varying degrees. The growth rate constant k of different interaction systems was in the following order on the 28th day: control group ≥ single DDTC pollution > combined pollution > single Sb pollution. A correlation analysis showed that the concentration of exchangeable Sb was the primary factor that affected the toxic reaction under combined pollution conditions, and it significantly affected the characteristics of the soil microorganisms. All the observations provide useful information for a better understanding of the toxic effects and potential risks of combined Sb and DDTC pollution in antimony mining areas.

Microbial Toxicity of a Type of Carbon Dots to Escherichia coli

Carbon dots (Cdots), as a class of novel photoluminescence nanoprobes, has attracted tremendous interest for its broad application in recent years. Thus, the toxicity and behavior of Cdots in biological systems become important fundamental problems that require significant attention. In this study, Cdots with diameters of 5 nm are produced using mixed-acid treatment. The Cdots exhibit strong yellow fluorescence under UV irradiation and shifted emission peaks as the excitation wavelength is changed. Gram-negative bacteria Escherichia coli (E. coli) are applied as testing model to study the biological effect of Cdots on the cell growth by microcalorimetric, spectroscopic, and microscopic investigation. The introducing of Cdots caused a gradual increase of the maximum heat power (P peak) and the total heat produced (Q total) at low concentrations (0.0-5.00 mg/L). The metabolism rate constant (k) and half inhibitory concentration (IC50) were calculated from the microcalorimetric data. The results indicated that Cdots had a concentration-dependent effect on the growth of E. coli. For confirmation, the growth curves and colony-forming units at different concentration of Cdots were studied. The morphology of E. coli in the absence and presence of Cdots was determined by scanning electron microscopy (SEM). The results of these studies were in agreement well with the analysis explored from microcalorimetry.