Bimetallic catalyst system for the degradation of PCBs in sediments.

In this paper, we report the successful application of a patent-pending reduced bimetallic nanoparticle catalytic system developed for the remediation of polychlorinated biphenyl (PCB)-contaminated sediment and aquatic media. The formation of bimetallic nanoparticles associated with the granular activated carbon (GAC) were confirmed by high-resolution transmission electron microscopy. X-ray photoelectron spectroscopy showed the presence of the bimetallic matrix in reduced, albeit mixed, states. In the degradation studies, the bimetallic nanoparticles were deposited on a GAC substrate and utilized to treat both a surrogate PCB, 2-Chlorobiphenyl (2-CBP) in water and contaminated bottom-river sediments collected from a site with mixed-congener PCB contamination. The degradation studies on non-degassed water contaminated with 2-CBP at room temperature showed a high yield of 2-CBP degradation to biphenyl and phenol. Results from the bottom-river sediments contaminated with PCBs (tested in laboratory environment at ambient temperature and atmospheric conditions, not degassed) have indicated the bimetallic catalyst has great promise for remedial application in sediment and aquatic media. Results illustrate that this newly-developed and patent-pending catalytic system degrades PCBs through stepwise dichlorination, with expected byproducts such as biphenyl and phenol leading to mineralization of the PCBs.

Phytosampling-a supplementary tool for particulate matter (PM) speciation characterization.

Ambient air particulate matter (PM) and PM-associated environmentally persistent free radicals (EPFRs) have been documented to contribute to pollution-related health effects. Studies of ambient air PM potentially bear artifacts stemming from the collection methods. We have investigated the applicability of PM phytosampling (PHS) as a supplementary tool to a classic PM sampler in respect of achieving better PM chemical composition assessment (primarily organic fraction). Phytosampling is a static PM collection method relying on the particle entrapment by the plant's leaf through electrostatic forces and surface trichomes. We have investigated the differences in the EPFR and polycyclic aromatic hydrocarbon (PAH) speciation and concentration on ambient air PM for PHS and high-volume PM sampler (HVS). The advantages of PHS are easy particle recovery from the matrix, collection under natural environmental conditions, and the ability to apply a dense collection network to accurately represent spatial pollutant distribution. The experimental results show that the PHS can provide valuable speciation information, sometimes different from that observed for HVS. For PM collected by PHS, we detected the larger contribution of oxygen-centered EPFRs, different decay behavior, and more consistent PAH distribution between different PM sizes compared to the PM from HVS. These results indicate that the isolation of samples from the ambient during HVS sampling and exposure to high-volume airflow may alter the chemical composition of the samples, while the PHS method could provide details on the original speciation and concentration and be more representative of the PM surface. However, PHS cannot evaluate an absolute air concentration of PM, so it serves as an excellent supplementary tool to work in conjunction with the standard PM collection method.

VOC Emissions and Formation Mechanisms from Carbon Nanotube Composites during 3D Printing.

A commercially available, 3D printer nanocomposite filament of carbon nanotubes (CNTs) and acrylonitrile-butadiene-styrene (ABS) was analyzed with respect to its VOC emissions during simulated fused deposition modeling (FDM) and compared with a regular ABS filament. VOC emissions were quantified and characterized under a variety of conditions to simulate the thermal degradation that takes place during FDM. Increasing the residence time and temperature resulted in significant increases in VOC emissions, and the oxygen content of the reaction gas influenced the VOC profile. In agreement with other studies, the primary emitted VOC was styrene. Multiple compounds are reported in this work for the first time as having formed during FDM, including 4-vinylcyclohexene and 2-phenyl-2-propanol. Our results show that printing 222.0 g of filament is enough to surpass the reference concentration for inhalation exposure of 1 mg/m3 according to the EPA's Integrated Risk Information System (IRIS). The presence of CNTs in the filament influenced VOC yields and product ratios through three types of surface interactions: (1) adsorption of O2 on CNTs lowers the available O2 for oxidation of primary backbone cleavage intermediates, (2) adsorption of styrene and other VOCs to CNTs leads to surface-catalyzed degradation, and (3) CNTs act as a trap for certain VOCs and prevent them from entering vapor emissions. While the presence of CNTs in the filament lowered the total VOC emission under most experimental conditions, they increased the emission of the most hazardous VOCs, such as α-methylstyrene and benzaldehyde. The present study has identified an increased risk associated with the use of CNT nanocomposites in 3D printing.