RESUMEN
Mercury (Hg) is a toxic element which impacts on biological systems and ecosystems. Because the toxicity of Hg species is highly dependent on their concentration levels and chemical forms, the sensitive identification of the chemical forms of Hg-i.e., Hg speciation-is of major significance in providing meaningful information about the sources of Hg exposure. In this study, a microfluidic-based device made of high-clarity poly(methyl methacrylate) (PMMA) was fabricated. Then, titanium dioxide nanoparticles (nano-TiO2s) were attached to the treated channel's interior with the aid of poly(diallyldimethylammonium chloride) (PDADMAC). After coupling the nano-TiO2-coated microfluidic-based photocatalyst-assisted reduction device (the nano-TiO2-coated microfluidic-based PCARD) with high-performance liquid chromatography (HPLC) and inductively coupled plasma mass spectrometry (ICP-MS), a selective and sensitive, hyphenated system for Hg speciation was established. Validation procedures demonstrated that the method could be satisfactorily applied to the determination of mercury ions (Hg2+) and methylmercury ions (CH3Hg+) in both human urine and water samples. Remarkably, the zeta potential measured clearly indicated that the PDADMAC-capped nano-TiO2s with a predominance of positive charges indeed provided a steady force for firm attachment to the negatively charged device channel. The cause of the durability of the nano-TiO2-coated microfluidic-based PCARD was clarified thus.
RESUMEN
This paper aims to characterize the stress intensity factor (SIF) of atomistic graphene sheet with central crack subjected to uniaxial loading. The equilibrium configuration of the defective graphene sheet with missing covalent bonds was generated through molecular dynamics (MD) simulation. Subsequently, the local stress distribution near the crack tip of atomistic structure was evaluated using the Hardy stress formulation as well as the non-local elasticity theory. Based on the local stress distributions, the SIF of the atomistic graphene sheet was determined through the projection process. In comparison, the graphene sheet was also treated as a continuum solid, and the stress distribution near the crack tip as well as the SIF were evaluated from the finite element method (FEM). In an attempt to understand the crack size effect, the crack length was assumed to vary from 3 lattice distance to around 80 lattice distance. Results revealed that the SIF calculated based on the nonlocal elasticity theory in conjunction with the projection process is quite sensitive to the selection of the projection point. However, for the Hardy stress distribution, when the projection position is 1 lattice distance away from the crack tip, the SIF is quite consistent and the result is compatible to that obtained from the FEM analysis. Moreover, the agreement is better as the crack size is increasing. Therefore, the SIF calculated based on the Hardy stress formulation together with the projection approach could be a physical quantity correlating the defective atomistic graphene sheet with its continuum counterpart.
RESUMEN
In this study, three municipal solid waste incinerator (MSWI) ash wastes-bottom ash, scrubber residue, and baghouse ash-were extracted using a toxicity characteristic leaching procedure (TCLP) extractant. These so-called final TCLP extracts were applied to African green monkey kidney cells (Vero), baby hamster kidney cells (BHK-21), and pig kidney cells (PK-15), multi-well absorption reader analysis was performed to test how the cytotoxicity of the incineration ashes would affect the digestive systems of animals. Ion-coupled plasma analyses indicated that the baghouse ash extract possessed the highest pH and heavy metal concentration, its cytotoxicity was also the highest. In contrast, the bottom ash and the scrubber residue exhibited very low cytotoxicities. The cytotoxicities of mixtures of baghouse ash and scrubber residue toward the three tested cell lines increased as the relative ratio of the baghouse ash increased, especially for the Vero cells. The slight cytotoxicity of the scrubber residue arose mainly from the presence of Cr species, whereas the high cytotoxicity of the baghouse ash resulted from its high content of heavy metals and alkali ions. In addition, it appears that the dissolved total organic carbon content of these ash wastes can reduce the cytotoxicity of ash wastes that collect in animal cells.