Predicting pyrolysis decomposition of PFOA using computational nanoreactors: a thermodynamic study.

Per- and polyfluoroalkyl substances (PFAS) are a large, complex, environmentally persistent, and ever-expanding group of manufactured chemicals. Disposal of these compounds could produce potentially dangerous products necessitating the need to quickly predict their decomposition products. This study focuses on the thermal decomposition of perfluorooctanoic acid (PFOA) using nanoreactor simulations to find the decomposition products and their respective energies. Applying the nanoreactor method, which is novel for this system, allows for rapid prediction of thermal decomposition pathways with minimal researcher bias and it predicted PFOA to decompose at ∼650 °C, consistent with previously reported experimental studies.

Single crystal neutron and magnetic measurements of Rb2Mn3(VO4)2CO3 and K2Co3(VO4)2CO3 with mixed honeycomb and triangular magnetic lattices.

Two new alkali vanadate carbonates with divalent transition metals have been synthesized as large single crystals via a high-temperature (600 °C) hydrothermal technique. Compound I, Rb2Mn3(VO4)2CO3, crystallizes in the trigonal crystal system in the space group P3[combining macron]1c, and compound II, K2Co3(VO4)2CO3, crystallizes in the hexagonal space group P63/m. Both structures contain honeycomb layers and triangular lattices made from edge-sharing MO6 octahedra and MO5 trigonal bipyramids, respectively. The honeycomb and triangular layers are connected along the c-axis through tetrahedral [VO4] groups. The MO5 units are connected with each other by carbonate groups in the ab-plane by forming a triangular magnetic lattice. The difference in space groups between I and II was also investigated with Density Functional Theory (DFT) calculations. Single crystal magnetic characterization of I indicates three magnetic transitions at 77 K, 2.3 K, and 1.5 K. The corresponding magnetic structures for each magnetic transition of I were determined using single crystal neutron diffraction. At 77 K the compound orders in the MnO6-honeycomb layer in a Néel-type antiferromagnetic orientation while the MnO5 triangular lattice ordered below 2.3 K in a colinear 'up-up-down' fashion, followed by a planar 'Y' type magnetic structure. K2Co3(VO4)2CO3 (II) exhibits a canted antiferromagnetic ordering below TN = 8 K. The Curie-Weiss fit (200-350 K) gives a Curie-Weiss temperature of -42 K suggesting a dominant antiferromagnetic coupling in the Co2+ magnetic sublattices.

Cationic polymer for selective removal of GenX and short-chain PFAS from surface waters and wastewaters at ng/L levels.

The emerging classes of perfluorinated alkyl substances (PFAS) (e.g., Perfluorobutanoic acid (PFBA), perfluorobutane sulfonic acid (PFBS), GenX, ADONA, and F-53B) are persistent and recalcitrant to removal by conventional treatment techniques. Herein, we report on poly (N-[3-(dimethylamino)propyl]acrylamide, methyl chloride quaternary, DMAPAA-Q) hydrogel matrix as an effective sorbent for sequestering PFAS from different water matrices. The selective removal of 16 PFAS from different classes using DMAPAA-Q polymer was confirmed in surface waters and treated wastewater at environmentally relevant concentration (i.e., <1000 ng/L). The results showed fast removal kinetics with equilibrium time of 60-120 min and a higher removal of sulfonated than carboxylic PFAS, regardless of their chain lengths. These observations were in agreement with adsorption energy calculations of short- and long-chain PFAS on poly DMAPAA-Q hydrogel using density functional theory (DFT). No desorption was observed when the experimental time was extended to 24 h, which gives an added advantage of poly DMAPAA-Q hydrogel over previously reported adsorbents in the literature. In addition, the removal efficiency was not affected under a varying pH range of 4-10. The impact of background anions on PFAS removal by poly DMAPAA-Q hydrogel was tested and found to follow an order of SO42- > Cl- > NO3-. The performance of poly DMAPAA-Q hydrogel was maintained in six consecutive adsorption/regeneration cycles to remove PFAS. The unique fast kinetics and high adsorption activity of poly DMAPAA-Q hydrogel towards PFAS exhibits a great potential for being a promising material for PFAS control.

Sinter-Resistant Platinum Catalyst Supported by Metal-Organic Framework.

Single atoms and few-atom clusters of platinum are uniformly installed on the zirconia nodes of a metal-organic framework (MOF) NU-1000 via targeted vapor-phase synthesis. The catalytic Pt clusters, site-isolated by organic linkers, are shown to exhibit high catalytic activity for ethylene hydrogenation while exhibiting resistance to sintering up to 200 °C. In situ IR spectroscopy reveals the presence of both single atoms and few-atom clusters that depend upon synthesis conditions. Operando X-ray absorption spectroscopy and X-ray pair distribution analyses reveal unique changes in chemical bonding environment and cluster size stability while on stream. Density functional theory calculations elucidate a favorable reaction pathway for ethylene hydrogenation with the novel catalyst. These results provide evidence that atomic layer deposition (ALD) in MOFs is a versatile approach to the rational synthesis of size-selected clusters, including noble metals, on a high surface area support.

Using terahertz spectroscopy and solid-state density functional theory to characterize a new polymorph of 5-(4-pyridyl)tetrazole.

A new high-temperature polymorph of 5-(4-pyridyl)tetrazole has been discovered and characterized using X-ray crystallography and terahertz (THz) spectroscopy. The THz spectrum of the new polymorph was compared to the previously published form and was replicated by means of solid-state density functional theory. Terahertz spectroscopy was used to determine the influence of the different packing motifs on the molecular and low energy lattice vibrations displayed in the region from 10 to 100 cm(-1). It was found that there is only a ∼2 cm(-1) difference in the primary peak location, caused by a whole molecule rotation along the principal a axis, between the two polymorphic forms. In addition, the energy of formation was determined, and it was found that the previously known polymorphic form is more stable by ∼0.25 kJ/mol, compared to the newly discovered form.

A new model for quantifying the extent of interaction between soluble polyphenylene-vinylenes and single-walled carbon nanotubes in solvent dispersions.

The ability to disperse and, hence, manipulate single-walled carbon nanotubes is critical for their use in organic photovoltaic devices, either as a transparent electrode or as an electron acceptor material. We present data to quantify the physical interaction of single wall carbon nanotubes (SWCNTs) with two soluble phenylene vinylene conjugated polymers, poly[2'-methoxy-5-(2'-ethylhexyloxy)-1,4-phenylenevinylene] and poly(2,5-di(hexyloxy)cyanoterephthalylidene). We provide static quenching constants, associated with polymer-SWCNT complexation, as a weight percent ratio of polymer to nanotubes for different solvent and polymer concentration conditions. Optimization of conditions for nanotube dispersion using a given polymer can now be predicted, and furthermore, we can describe a technique allowing for enhanced relative comparisons of polymer materials for nanotube dispersion.

Spectroscopic evidence for interaction of poly[2-methoxy-5-(2'-ethylhexyloxy)-1,4-phenylenevinylene] conformers and single-walled carbon nanotubes in solvent dispersions.

Organic photovoltaic devices promise low-cost, flexible options for future renewable energy that will reduce reliance on oil. Single-wall carbon nanotubes (SWCNTs) provide possibilities for increasing the efficiency of organic solar cells through increasing conductivity of composites used in such devices or through use as a charge acceptor in a bulk heterojunction device. We present data to indicate the physical interaction of SWCNTs with a conjugated polymer, poly[2'-methoxy-5-(2'-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV), on the basis of the spectroscopic assignments of various conformational species of different optical signature in N,N-dimethylacetamide (DMA) dispersions. We go on to show that energy transfer from nonaggregated MEH-PPV leads to enhanced SWCNT fluorescence in solutions of poorer solvent quality. Energy transfer from polymer chain lengths that are torsionally restricted is not observed. This would suggest that any electron transfer taking place is occurring through a concerted Dexter mechanism and that use of SWCNTs as an electron acceptor will likely have associated drawbacks.