Environmental Fate of the Next Generation Refrigerant 2,3,3,3-Tetrafluoropropene (HFO-1234yf)

The hydrofluoroolefin 2,3,3,3-tetrafluoropropene (HFO-1234yf) has been introduced to replace 1,1,1,2-tetrafluoroethane (HFC-134a) as refrigerant in mobile, including vehicle, air conditioning systems because of its lower global warming potential. HFO-1234yf is volatile at ambient temperatures; however, high production volumes and widespread handling are expected to release this fluorocarbon into terrestrial and aquatic environments, including groundwater. Laboratory experiments explored HFO-1234yf degradation by (i) microbial processes under oxic and anoxic conditions, (ii) abiotic processes mediated by reactive mineral phases and zerovalent iron (Fe⁰, ZVI), and (iii) cobalamin-catalyzed biomimetic transformation. These investigations demonstrated that HFO-1234yf was recalcitrant to microbial (co)­metabolism and no transformation was observed in incubations with ZVI, makinawite (FeS), sulfate green rust (GR_SO4), magnetite (Fe₃O₄), and manganese oxide (MnO₂). Sequential reductive defluorination of HFO-1234yf to 3,3,3-trifluoropropene and 3,3-dichloropropene with concomitant stoichiometric release of fluoride occurred in incubations with reduced cobalamins (e.g., vitamin B₁₂) indicating that biomolecules can transform HFO-1234yf at circumneutral pH and at ambient temperature. Taken together, these findings suggest that HFO-1234yf recalcitrance in aquifers should be expected; however, HFO-1234yf is not inert and a biomolecule may mediate reductive transformation in low redox environments, albeit at low rates

Rapid Removal of Hg(II) from Aqueous Solutions Using Thiol-Functionalized Zn-Doped Biomagnetite Particles

The surfaces of Zn-doped biomagnetite nanostructured particles were functionalized with (3-mercaptopropyl)­trimethoxysilane (MPTMS) and used as a high-capacity and collectable adsorbent for the removal of Hg­(II) from water. Fourier transform infrared spectroscopy (FTIR) confirmed the attachment of MPTMS on the particle surface. The crystallite size of the Zn-doped biomagnetite was ∼17 nm, and the thickness of the MPTMS coating was ∼5 nm. Scanning transmission electron microscopy and dynamic light scattering analyses revealed that the particles formed aggregates in aqueous solution with an average hydrodynamic size of 826 ± 32 nm. Elemental analyses indicate that the chemical composition of the biomagnetite is Zn_0.46Fe_2.54O₄, and the loading of sulfur is 3.6 mmol/g. The MPTMS-modified biomagnetite has a calculated saturation magnetization of 37.9 emu/g and can be separated from water within a minute using a magnet. Sorption of Hg­(II) to the nanostructured particles was much faster than other commercial sorbents, and the Hg­(II) sorption isotherm in an industrial wastewater follows the Langmuir model with a maximum capacity of ∼416 mg/g, indicating two −SH groups bonded to one Hg. This new Hg­(II) sorbent was stable in a range of solutions, from contaminated water to 0.5 M acid solutions, with low leaching of Fe, Zn, Si, and S (<10%)

Influence of Structural Defects on Biomineralized ZnS Nanoparticle Dissolution: An in-Situ Electron Microscopy Study

The dissolution of metal sulfides, such as ZnS, is an important biogeochemical process affecting fate and transport of trace metals in the environment. However, current studies of in situ dissolution of metal sulfides and the effects of structural defects on dissolution are lacking. Here we have examined the dissolution behavior of ZnS nanoparticles synthesized via several abiotic and biological pathways. Specifically, we have examined biogenic ZnS nanoparticles produced by an anaerobic, metal-reducing bacterium <i>Thermoanaerobacter</i> sp. X513 in a Zn-amended, thiosulfate-containing growth medium in the presence or absence of silver (Ag), and abiogenic ZnS nanoparticles were produced by mixing an aqueous Zn solution with either H₂S-rich gas or Na₂S solution. The size distribution, crystal structure, aggregation behavior, and internal defects of the synthesized ZnS nanoparticles were examined using high-resolution transmission electron microscopy (TEM) coupled with X-ray energy dispersive spectroscopy. The characterization results show that both the biogenic and abiogenic samples were dominantly composed of sphalerite. In the absence of Ag, the biogenic ZnS nanoparticles were significantly larger (i.e., ∼10 nm) than the abiogenic ones (i.e., ∼3–5 nm) and contained structural defects (e.g., twins and stacking faults). The presence of trace Ag showed a restraining effect on the particle size of the biogenic ZnS, resulting in quantum-dot-sized nanoparticles (i.e., ∼3 nm). In situ dissolution experiments for the synthesized ZnS were conducted with a liquid-cell TEM (LCTEM), and the primary factors (i.e., the presence or absence structural defects) were evaluated for their effects on the dissolution behavior using the biogenic and abiogenic ZnS nanoparticle samples with the largest average particle size. Analysis of the dissolution results (i.e., change in particle radius with time) using the Kelvin equation shows that the defect-bearing biogenic ZnS nanoparticles (γ = 0.799 J/m²) have a significantly higher surface energy than the abiogenic ZnS nanoparticles (γ = 0.277 J/m²). Larger defect-bearing biogenic ZnS nanoparticles were thus more reactive than the smaller quantum-dot-sized ZnS nanoparticles. These findings provide new insight into the factors that affect the dissolution of metal sulfide nanoparticles in relevant natural and engineered scenarios, and have important implications for tracking the fate and transport of sulfide nanoparticles and associated metal ions in the environment. Moreover, our study exemplified the use of an in situ method (i.e., LCTEM) to investigate nanoparticle behavior (e.g., dissolution) in aqueous solutions

MOESM1 of Clostridium thermocellum LL1210 pH homeostasis mechanisms informed by transcriptomics and metabolomics

Additional file 1. Data logs, substrate and product concentrations, internal and external pH readings, and media formulation for chemostat reactor cultures of C. thermocellum LL1210

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Additional file 2. Raw and processed read counts, alignment statistics, log2-fold changes in the gene expression, and K-means clusters and GO enrichment of differentially expressed genes from samples taken from C. thermocellum LL1210 cultured in chemostats at pH values 6.98, 6.48, pH 6.24, and pH 6.12 (washout conditions). Gene expression at pH 6.98 was used as a reference for differential expression at lower pH values

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Additional file 6: Table S3. Fold changes of intercellular metabolite there were significantly higher or lower in concentration at growth-limiting pHs

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Additional file 8: Table S4. Strains and primers used in this study

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Additional file 7. Extracellular amino acid concentrations in media from C. thermocellum LL1210 chemostats that were sampled when pH values were pH 6.48, pH 6.24, pH 6.12, and below. Demonstrations of data homoscedasticity for T tests

MOESM4 of Clostridium thermocellum LL1210 pH homeostasis mechanisms informed by transcriptomics and metabolomics

Additional file 4: Figure S2. Average growth (A), terminal pH (B), and remaining substrates and products at the end of C. thermocellum-mutant strain fermentations of cellobiose in MOPS-free carbon-replete medium (C). Averages were computed with data from four biological replicates. Error bars in each graph indicate standard deviation. Some error bars are too small to see. Deletion mutants are designated as LL1210 (hydrogenase maturation protein, lactate dehydrogenase, pyruvate formate lyase, phosphotransacetylase and acetate kinase), GLDH (glutamate dehydrogenase), GS (glutamine synthetase), GOGAT (glutamate synthase), GS-GOGAT (both), and NifH (nitrogenase iron protein). The parental strain designated DSM1313 has a deletion in the hypoxanthine phosphoribosyltransferase

MOESM5 of Clostridium thermocellum LL1210 pH homeostasis mechanisms informed by transcriptomics and metabolomics

Additional file 5: Figure S3. Differential expression of genes found in Clostridia sporulation cascades. pro-σE processing protease is a stage III sporulation factor. BofA is an inhibitor of the stage IV pro-σK processing protease SpoIVFB. Table S2. Percentage of spherical morphologies 144 and 216 h after inoculation. Figure S4. Substrates and products (A) and the pH (B) after 144 and 216 h of C. thermocellum-mutant fermentations on MOPS-free carbon-replete medium starting with an initial pH of 6.75. Significant differences at α = 0.001 for comparisons with DSM1313 (∆hpt) are indicated with a “*” and comparisons with DSM1313 (∆hpt) and LL1210 are indicated with “**”. Averages were calculated with six biological replicates. Error bars indicate standard deviation