Shape-Controlled CdS/ZnS Core/Shell Heterostructured Nanocrystals: Synthesis, Characterization, and Periodic DFT Calculations

CdS/ZnS core/shell heterostructured nanocrystals (NCs) with six monolayers (MLs) of ZnS shell on a zinc-blende CdS core were synthesized via successive ionic layer adsorption and reaction. By adjusting the growth temperature of the ZnS shell from 220 to 280 °C, the shape of CdS/ZnS NCs can be tuned to tetrapods, tetrahedra, and dots. Shell growth was confirmed to be uniform by X-ray diffraction, transmission electron microscopy, UV–vis absorption, and photoluminescence spectroscopy. Periodic density functional theory calculations were used to further study the growth mechanism of the differently shaped CdS/ZnS core/shell NCs. Our calculations revealed that the binding energy of model CH₃CH₂NH₂ molecules on the (110), (111), and (001) facets of the CdS core can determine which crystallographic facets are favored during the growth of the ZnS shell. The calculations provided insights into the effect of the interaction between the organic ligand and the facets of the CdS core on the shape engineering of CdS/ZnS core/shell NCs

Emission characteristics of harmful air pollutants from cremators in Beijing, China

<div><p>The process of corpse cremation generates numerous harmful air pollutants, including particulate matter (PM), sulfur dioxide (SO₂), nitrogen oxides (NO_x), volatile organic compounds (VOCs), and heavy metals. These pollutants could have severe effects on the surrounding environment and human health. Currently, the awareness of the emission levels of harmful air pollutants from cremators and their emission characteristics is insufficient. In this study, we obtained the emission characteristics of flue gas from cremators in Beijing and determined the localized emission factors and emission levels of harmful air pollutants based on actual monitoring data from nine typical cremators. The results show that the emissions of air pollutants from the cremators that directly discharge flue gas exceed the emission standards of China and Beijing. The installation of a flue gas post-treatment system could effectively reduce gaseous pollutants and the emission levels of PM. After being equipped with a flue gas post-treatment system, the emission concentrations of PM₁₀, PM_2.5, CO, SO₂ and VOCs from the cremators are reduced by 97.6, 99.2, 19.6, 85.2 and 70.7%, respectively. Moreover, the emission factors of TSP, PM₁₀, PM_2.5, CO, SO₂ and VOCs are also reduced to 12.5, 9.3, 3.0, 164.1, 8.8 and 19.8 g/body. Although the emission concentration of VOCs from the cremators is not high, they are one of major sources of “odor” in the crematories and demand more attention. Benzene, a chemical that can seriously harm human health, constitutes the largest proportion (~50%) of the chemical components of VOCs in the flue gas from the cremators.</p></div

Emission concentration of harmful air pollutants from cremators.

<p>Emission concentration of harmful air pollutants from cremators.</p

Comparison of harmful air pollutants in China and abroad (g/body).

<p>Comparison of harmful air pollutants in China and abroad (g/body).</p

Comparison of EFs of harmful air pollutants between gas-fired and oil-fired cremators.

<p>Comparison of EFs of harmful air pollutants between gas-fired and oil-fired cremators.</p

EFs of harmful air pollutants for the studied cremators.

<p>EFs of harmful air pollutants for the studied cremators.</p

Typical flue gas post-treatment system of a cremator.

<p>Typical flue gas post-treatment system of a cremator.</p