Perfluorooctanesulfonate (PFOS) is a persistent organic pollutant that is bioaccumulative and toxic. While its use in most countries has been restricted to certain industrial applications due to environmental and health concerns, chrome plating and semiconductor manufacturing facilities are industrial point sources of PFOS-containing wastewater. Current remediation technologies are ineffective at treating these highly concentrated industrial effluents. In this work, UiO-66 metal–organic frameworks (MOFs) of several defect concentrations were studied as sorbents for the removal of PFOS from concentrated aqueous solutions. PFOS sorption isotherms indicated that defective UiO-66, prepared with HCl as a modulator, had a maximum Langmuir sorption capacity of 1.24 mmol/g, which was ∼2× greater than powdered activated carbon (PAC), but ∼2× less than that of a commercial ion-exchange resin. Defective UiO-66 adsorbed PFOS 2 orders of magnitude faster than the ion-exchange resin. Large pore defects (∼16 and ∼20 Å) within the framework were critical to the increased adsorption capacity due to higher internal surface area and an increased number of coordinatively unsaturated Zr sites to bind the PFOS head groups. Of the common co-contaminants in chrome plating wastewaters, chloride ions have a negligible effect on PFOS sorption, while sulfate and hexavalent chromium anions compete for cationically charged adsorption sites. These materials were also effective adsorbents for the shorter-chain homologue, perfluorobutanesulfonate (PFBS). The enhanced PFOS and PFBS adsorptive properties of UiO-66 highlight the advantage of structurally defective MOFs as a water treatment approach toward environmental sustainability.
Concern over water contamination by per/polyfluoroalkyl substances (PFAS) has highlighted the lack of effective treatment approaches. Photocatalysis offers advantages of using ambient conditions for reaction, air as the oxidant, and light as the energy source, but identifying photoactive materials is challenging. Herein, we report that boron nitride (BN) degrades PFOA upon irradiation with 254 nm light. The ability of BN to degrade PFOA photocatalytically has previously been unreported and is unexpected, because its band gap is too large for light absorption. On the basis of scavenger results, we suggest that PFOA degrades in the presence of BN via a hole-initiated reaction pathway similar to the TiO 2 case and involves superoxide/hydroperoxyl and hydroxyl radicals. We surmised that defects allow BN to absorb in the UVC range and to photogenerate reactive oxygen species. Sealed batch studies indicated BN was ∼2 and ∼4 times more active than TiO 2 , before and after ball milling the material, respectively. BN can be reused, showing no decrease in activity over three cycles. BN was active for the photocatalytic degradation of GenX, another PFAS of concern. These findings present fresh opportunities for materials design and for the re-evaluation of other wide band gap semiconductors for PFAS photocatalytic degradation.
An unintended consequence of industrial nitrogen fixation through the Haber–Bosch process is nitrate (NO3 –) and nitrite (NO2 –) contamination of ocean, ground, and surface waters from fertilizer runoff. Transition-metal catalysts, particularly those based on Pd, are effective in removing NO3 –/NO2 – through reduction to N2 or NH4 +. Pd is regarded as the most effective metal for NO3 –/NO2 – reduction, and as such, few studies have thoroughly explored the performance of other transition metals as a function of varying reaction conditions. In this work, we investigated the NO2 – reduction properties of alumina-supported Rh using Pd as a benchmark, where we varied the bulk solution pH to probe the effect of reaction conditions on the catalytic chemistry. Pd expectedly showed a high reduction activity (289 L/g-surface-metal/min) and a high N2 selectivity (>99% at 20% conversion) at low pH and near inactivity at high pH. Surprisingly, the Rh catalyst, while inactive at low pH, showed moderate activity (22 L/g-surface-metal/min) and high NH4 + selectivity (>90% at 20% conversion) at high pH. Hydrazine (N2H4) was also detected as a reaction intermediate when NH4 + was formed. Microkinetic models built with energetics from density functional theory reveal that Rh catalysts are poisoned by NO* at low pH because of the rapid dissociative adsorption of protonated nitrite (HNO2) under acidic conditions, which was confirmed by in aqua surface-enhanced Raman spectroscopy. NO* poisoning of the Rh surface lessens at increased solution pH because NO2 – does not dissociate as readily compared to HNO2, which explains why Rh exhibits higher activity in basic solutions. The microkinetic models further elucidate the competition between N2H4 and NH3/NH4 + formation as a function of pH, where we find that hydrogen surface coverage dictates product selectivity. These results update the common view that only Pd-based catalysts are effective for NO2 – reduction and suggest unexplored avenues for nitrogen chemistry.
Consideration of the water-energy-food nexus is critical to sustainable development, as 18 demand continues to grow along with global population growth. Cost-effective, 19 sustainable technologies to clean water of toxic contaminants are needed. Oxyanions 20 comprise one common class of water contaminants, with many species carrying 21 significant human health risks. The United States Environmental Protection Agency (US 22 EPA) regulates the concentration of oxyanion contaminants in drinking water via the 23 National Primary Drinking Water Regulations (NPDWR). Degrading oxyanions into 24 innocuous compounds through catalytic chemistry is a well-studied approach that does 25 not generate additional waste, which is a significant advantage over adsorption and 26 separation methods. Noble metal nanostructures, e.g., Au, Pd and Pt, are particularly 27 opportunities for metal nanostructures to contribute to improved quality and sustainability 33 of water resources.
While RNA structures have been extensively characterized in vitro, very few techniques exist to probe RNA structures inside cells. Here, we have exploited mechanisms of post-transcriptional regulation to synthesize fluorescence-based probes that assay RNA structures in vivo. Our probing system involves the co-expression of two constructs: (i) a target RNA and (ii) a reporter containing a probe complementary to a region in the target RNA attached to an RBS-sequestering hairpin and fused to a sequence encoding the green fluorescent protein (GFP). When a region of the target RNA is accessible, the area can interact with its complementary probe, resulting in fluorescence. By using this system, we observed varied patterns of structural accessibility along the length of the Tetrahymena group I intron. We performed in vivo DMS footprinting which, along with previous footprinting studies, helped to explain our probing results. Additionally, this novel approach represents a valuable tool to differentiate between RNA variants and to detect structural changes caused by subtle mutations. Our results capture some differences from traditional footprinting assays that could suggest that probing in vivo via oligonucleotide hybridization facilitates the detection of folding intermediates. Importantly, our data indicate that intracellular oligonucleotide probing can be a powerful complement to existing RNA structural probing methods.
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