Sorption Mechanisms of Organic Compounds by Carbonaceous Materials: Site Energy Distribution Consideration

Sorption of naphthalene, lindane, and atrazine on 10 kinds of carbonaceous materials which included four kinds of graphene, three kinds of graphite, two kinds of carbon nanotubes and one kind of mesoporous carbon was investigated. The approximate sorption site energy distributions were calculated based on Dubinin-Ashtakhov (DA) model. The average sorption site energy and standard deviation of the site energy distribution were deduced and applied to analyze the interaction between sorbents and sorbates, and the sorption site heterogeneity. The introduction of oxygen-containing functional groups to the sorbents caused a decrease in their average sorption energy for the studied compounds. However, relative to the decrease in average site energy, the reduction in number of sorption sites as indicated by surface area more strongly reduced their sorption capacity to the tested carbonaceous materials based on the result of the linear regression analysis. Sorption site heterogeneity of the sorbents decreased as their oxygen contents increased, which is attributed to the better dispersion of the oxygen-containing materials as indicated by their TEM images. The method proposed in this study to quantify the average sorption site energy and heterogeneity is helpful for a better understanding of the sorption mechanisms of organic pollutants to carbonaceous materials

Sorption of Four Hydrophobic Organic Compounds by Three Chemically Distinct Polymers: Role of Chemical and Physical Composition

The sorption behavior of four hydrophobic organic contaminants (HOCs) (i.e., phenanthrene, naphthalene, lindane, and 1-naphthol) by three types of polymers namely polyethylene (PE), polystyrene (PS), and polyphenyleneoxide (PPO) was examined in this work. The organic carbon content-normalized sorption coefficients (<i>K</i>_oc) of phenanthrene, lindane, and naphthalene by PEs of same composition but distinct physical makeup of domains increased with their crystallinity reduction (from 58.7 to 25.5%), suggesting that mobility and abundance of rubbery domains in polymers regulated HOC sorption. Cross-linking in styrene–divinylbenzene copolymer (PS2) created substantial surface area and porosity, thus, <i>K</i>_oc values of phenanthrene, lindane, naphthalene, and 1-naphthol by PS2 were as high as 274.8, 212.3, 27.4, and 1.5 times of those by the linear polystyrene (PS1). The <i>K</i>_oc values of lindane, naphthalene, and 1-naphthol by polar PPO were approximately 1–3 orders of magnitude higher than those by PS1, and PPO had comparable sorption for phenanthrene but higher sorption for naphthalene and 1-naphthol than PS2. This can be a result that a portion of O-containing moieties in PPO were masked in the interior part, while leaving the hydrophobic domains exposed outside, therefore demonstrating the great influence of the spatial arrangement of domains in polymers on HOC sorption

Mechanisms of Enhanced Optical Absorption for Ultrathin Silicon Solar Microcells with an Integrated Nanostructured Backside Reflector

This paper investigates mechanisms of enhanced light absorption exhibited by ultrathin Si solar microcells integrated with a periodically nanostructured, semitransparent metallic reflector. This backside reflector comprises periodic nanoscale relief features formed by soft-imprint lithography with a thin (∼35 nm) coating of Au. The work shows that microcells placed in direct contact above the nanostructured reflector’s surface creates Fabry–Pérot cavities, which traps impinging light inside the Si slab via the excitation of cavity modes. Experimental measurements show that the short-circuit current and efficiency values for devices incorporating this thin, semitransparent backside reflector outperform similar Si microcells integrated with a planar thick (∼300 nm) opaque mirror by ∼10–15% because of enhanced absorption. Computational modeling that is supported by experimental measurements reveal that the dominant methods of enhancement stem from a complex interplay between backside diffraction/scattering and Fabry–Pérot resonances. These same data demonstrate that plasmonic interactions contribute minimally to the optical enhancements seen

Suspending Multi-Walled Carbon Nanotubes by Humic Acids from a Peat Soil

Suspension of the pristine and COOH-substituted multi-walled carbon nanotubes (P- and C-MWCNTs) with different outer diameters (ODs) by humic acids (HAs) from a peat soil was examined. Under shaking condition, MWCNTs were not suspended within 5 d. Without HAs, C-MWCNTs were slightly suspended by sonication within 16 h, but no suspension was observed for the pristine ones (P-MWCNTs). HAs greatly enhanced suspension of both P- and C-MWCNTs. The suspension enhancement was attributed to HA sorption, which increased electrostatic repulsion and steric hindrance between individual MWCNTs. Introduction of O-containing hydrophilic moieties to MWCNTs via HA sorption enhanced the interactions of their surfaces with water through H-bonding. Suspending capability of various MWCNTs on suspended mass concentration basis by four HAs showed inconsistent orders with the increasing or decreasing trend of their ODs. However, the suspended surface area concentrations of both P- and C-MWCNTs by individual HAs consistently followed an order of P8 > P30 > P50, and C8 > C30 > C50 (P and C, respectively, refer to P- and C-MWCNTs, and the numbers represent their ODs). These data implied that MWCNTs with smaller OD could be more strongly suspended by a given HA relative to those with larger OD under sonication condition

Synergistic Effects Induced by a Low Dose of Diesel Particulate Extract and Ultraviolet‑A in <i>Caenorhabditis elegans</i>: DNA Damage-Triggered Germ Cell Apoptosis

Diesel exhaust has been classified as a potential carcinogen and is associated with various health effects. A previous study showed that the doses for manifesting the mutagenetic effects of diesel exhaust could be reduced when coexposed with ultraviolet-A (UVA) in a cellular system. However, the mechanisms underlying synergistic effects remain to be clarified, especially in an <i>in vivo</i> system. In the present study, using <i>Caenorhabditis elegans</i> (<i>C. elegans</i>) as an <i>in vivo</i> system we studied the synergistic effects of diesel particulate extract (DPE) plus UVA, and the underlying mechanisms were dissected genetically using related mutants. Our results demonstrated that though coexposure of wild type worms at young adult stage to low doses of DPE (20 μg/mL) plus UVA (0.2, 0.5, and 1.0 J/cm²) did not affect worm development (mitotic germ cells and brood size), it resulted in a significant induction of germ cell death. Using the strain of <i>hus-1::gfp</i>, distinct foci of HUS-1::GFP was observed in proliferating germ cells, indicating the DNA damage after worms were treated with DPE plus UVA. Moreover, the induction of germ cell death by DPE plus UVA was alleviated in single-gene loss-of-function mutations of core apoptotic, checkpoint HUS-1, CEP-1/p53, and MAPK dependent signaling pathways. Using a reactive oxygen species (ROS) probe, it was found that the production of ROS in worms coexposed to DPE plus UVA increased in a time-dependent manner. In addition, employing a singlet oxygen (¹O₂) trapping probe, 2,2,6,6-tetramethyl-4-piperidone, coupled with electron spin resonance analysis, we demonstrated the increased ¹O₂ production in worms coexposed to DPE plus UVA. These results indicated that UVA could enhance the apoptotic induction of DPE at low doses through a DNA damage-triggered pathway and that the production of ROS, especially ¹O₂, played a pivotal role in initiating the synergistic process