Effect of 2,4-dichlorophenol on the production of methane from anaerobic granular sludge during anaerobic digestion through spectroscopy analysis

Chlorophenols in urban high organic wastewater increases, which plays an inhibitory role in the process of anaerobic fermentation and methanogenesis. The release rules of extracellular polymers (EPS) and soluble microbial products (SMP) and the production of methane from anaerobic granular sludge were evaluated by spectroscopic analysis. The methane production was reduced by 21.6%, 41.4% and 50.5% respectively by adding 2,4-DCP of different concentrations (25 mg/L, 50mg/L and 100 mg/L). Activity tests of methanogenic functional enzymes indicated that F420 was more susceptible to the toxic of 2, 4-DCP than Acetyl-CoA and NADH. The decrease in methane production was due to the reduction in the activity of conversion enzymes rather than the loss of crucial precursors for methanogenesis. 2,4-DCP disintegrated the protein ‘shell’ of anaerobic granular sludge by destroying α-helix and β-sheet structures. After the protein ‘shell’ in EPS was destroyed, 2, 4-DCP entered the interior of granular, which inhibited the activity of functional enzymes and affected the process of acidogenesis and methanogenesis. At the same time, due to the partial rupture of the cells after being affected by the toxicity of 2,4-DCP, the protein material could be dissolved into the aqueous phase and complexed with 2,4-DCP to reduce the toxic effect of 2,4-DCP.</p

Iodine Ions Mediated Formation of Monomorphic Single-Crystalline Platinum Nanoflowers

Well-defined and strikingly monomorphic single-crystalline Pt nanoflowers were successfully synthesized through the addition of a large amount of iodine ions into polyol process (5 mM H₂PtCl₆, 30 mM KI, and 50 mM PVP in ethylene glycol solution at 160 °C). The detailed structures of the Pt nanoflowers were studied with high-resolution TEM, indicating that high-quality production of the Pt nanoflowers could be obtained when the KI concentration was increased to six times of H₂PtCl₆. The size of Pt nanoflowers could be tuned by changing the concentration of H₂PtCl₆ with the constant Pt/I ratio (1:6). The formation process of the nanoflowers was investigated by the UV–vis and EXAFS spectroscopic studies, demonstrating that the iodine ions played a key role in inducing the formation of the single-crystalline Pt nanoflowers. After the addition of iodine ions into the polyol synthesis, the Pt–I complex was formed and reduced by different kinetics compared with that of H₂PtCl₆ to induce the overgrowth of Pt nanocrystals. Additionally, a small portion of iodine element was found to be strongly adsorbed on the surfaces of Pt nanoflowers, which probably also favored the anisotropic overgrowth of Pt nanocrystals resulting in the single-crystalline Pt nanoflowers. A comprehensive set of systematic studies on the synthesis factors (the concentrations of Pt precursor, iodine ions and PVP, reaction temperature, different kinds of Pt precursors and reaction atmosphere) was also reported

Facile Synthesis of Carbon Supported Pd₃Au@Super-Thin Pt Core/Shell Electrocatalyst with a Remarkable Activity for Oxygen Reduction

Aiming at developing a highly active electrocatalyst with high platinum utilization efficiency, we report a facile synthesis of carbon supported Pd₃Au@Pt electrocatalyst by chemical reduction of K₂PtCl₄, K₂PdCl₄, and aq NaAuCl₄ with ascorbic acid (AA) under ambient conditions in the absence of surfactants. The resultant Pd₃Au@Pt/C electrocatalyst comprises of a thin platinum layer less than 1 nm in thickness deposited on the outer surface of Pd₃Au alloy core with an average diameter of 3.4 nm. Remarkably, Pd₃Au@Pt/C exhibited a high mass activity (MA, 939 mAmg^–1_Pt) toward oxygen reduction reaction (ORR), which is 4.6 times that of commercial Pt/C (203 mAmg^–1_Pt). The durability of Pd₃Au@Pt/C is close to that of commercial Pt/C. According to X-ray diffraction (XRD) patterns, the lattice constant of the Pd₃Au alloy supported on carbon is determined to be 3.950 Å close to yet slightly larger than that of Pt/C (3.920 Å), inducing a lateral tensile strain of the platinum shell. Meanwhile, electrons from the Pd₃Au core appear transferred to the platinum shell as evidenced by X-ray photoelectron spectroscopy (XPS). We propose that the lateral tensile strain (geometric effect) and the electron transfer (electronic effect) as well as the high platinum utilization efficiency have contributed to the significantly improved electrocatalytic activity of Pd₃Au@Pt/C. The coexistence of the lateral tensile strain and the electron transfer in the electrocatalyst with a high ORR activity has not been reported prior to this study

Nanoparticles at Grain Boundaries Inhibit the Phase Transformation of Perovskite Membrane

The high-energy nature of grain boundaries makes them a common source of undesirable phase transformations in polycrystalline materials. In both metals and ceramics, such grain-boundary-induced phase transformation can be a frequent cause of performance degradation. Here, we identify a new stabilization mechanism that involves inhibiting phase transformations of perovskite materials by deliberately introducing nanoparticles at the grain boundaries. The nanoparticles act as “roadblocks” that limit the diffusion of metal ions along the grain boundaries and inhibit heterogeneous nucleation and new phase formation. Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ, a high-performance oxygen permeation and fuel cell cathode material whose commercial application has so far been impeded by phase instability, is used as an example to illustrate the inhibition action of nanoparticles toward the phase transformation. We obtain stable oxygen permeation flux at 600 °C with an unprecedented 10–1000 times increase in performance compared to previous investigations. This grain boundary stabilization method could potentially be extended to other systems that suffer from performance degradation due to a grain-boundary-initiated heterogeneous nucleation phase transformations

Self-Assembly of Atomically Thin and Unusual Face-Centered Cubic Re Nanowires within Carbon Nanotubes

Rhenium (Re), a high-performance engineering material with a hexagonal close-packed (hcp) structure, remains stable even under pressures of up to 250 GPa and at temperatures up to its melting point (3453 K). We observed here that Re atoms self-assembled, within the confined space of carbon nanotubes (CNTs) with a diameter of <1.5 nm, into ultrathin nanowires stacking with an unusual face-centered cubic (fcc) structure along the CNTs. In contrast, only Re nanoparticles of hcp structure formed on an open surface of graphite and carbon black. Aberration-corrected electron microscopy unambiguously showed the atomic arrangements of the Re nanowires and their confinement within the CNTs, ∼80% exhibiting a four-atom and 15% a nine-atom configuration. Density functional theory calculations confirmed that the formation of unusual fcc-stacking Re nanowires is largely facilitated by the strong interaction between Re atoms and CNTs and the spatial restriction within the CNTs. The use of CNTs as nanoscale reactors to create novel structures not only is fundamentally interesting but also may find unique applications in catalysis, sensing, and nanoelectronics

Facilitated Diffusion of Methane in Pores with a Higher Aromaticity

Shale gas, which was recently discovered with a large reserve, has invoked wide interest as an alternative energy resource of natural gas. However, little is known about the molecular properties of shale gas (mainly methane) confined in the nanopores of shale, such as their diffusivity, which is essential for its exploitation and utilization. We study here the diffusivity of methane using ¹H pulsed field gradient (PFG) NMR and theoretical modeling. Following analysis of the physicochemical properties of shale, a well-ordered mesoporous silica material (SBA-15) modified with organic functional groups is employed to model the mesopores observed in the shale and to study the fundamental behavior of shale gas. The results demonstrate that methane moves faster in the pores modified with the aromatic phenyl groups than those with nonaromatic cyclohexyl groups, suggesting a higher diffusivity of methane with increasing maturity of shale

Thin Porous Alumina Sheets as Supports for Stabilizing Gold Nanoparticles

Thin porous alumina sheets have been synthesized using a lysine-assisted hydrothermal approach resulting in an extraordinary catalyst support that can stabilize Au nanoparticles at annealing temperatures up to 900 °C. Remarkably, the unique architecture of such an alumina with thin sheets (average thickness ∼15 nm and length 680 nm) and rough surface is beneficial to prevent gold nanoparticles from sintering. HRTEM observations clearly showed that the epitaxial growth between Au nanoparticles and alumina support was due to strong interfacial interactions, further explaining the high sinter-stability of the obtained Au/Al₂O₃ catalyst. Consequently, despite calcination at 700 °C, the catalyst maintains its gold nanoparticles of size predominantly 2 ± 0.8 nm. Surprisingly, catalyst annealed at 900 °C retained the highly dispersed small gold nanoparticles. It was also observed that a few gold particles (6–25 nm) were encapsulated by an alumina layer (thickness less than 1 nm) to minimize the surface energy, revealing a surface restructuring of the gold/support interface. As a typical and size-dependent reaction, CO oxidation is used to evaluate the performance of Au/Al₂O₃ catalysts. The results obtained demonstrated Au/Al₂O₃ catalyst calcined at 700 °C exhibited excellent activity with a complete CO conversion at ∼30 °C (<i>T</i>_100% = 30 °C), and even after calcination at 900 °C, the catalyst still achieved its <i>T</i>_50% at 158 °C. In sharp contrast, Au catalyst prepared using conventional alumina support shows almost no activity under the same preparation and catalytic test conditions

Conversion of Isobutene and Formaldehyde to Diol using Praseodymium-Doped CeO₂ Catalyst

Conversion of low-carbon olefins to higher alcohols or olefins via the formation of C–C bonds is an increasingly important topic. We herein report an example of converting isobutene and formaldehyde (38 wt % aqueous solution) to 3-methyl-1,3-butanediol (MBD), a precursor for isoprene. The reaction occurs through a Prins condensation–hydrolysis reaction over a praseodymium (Pr)-doped CeO₂ catalyst. The best MBD yield (70%) is achieved over the Pr-doped CeO₂ catalyst. Catalyst characterizations with high-angle annular dark field transmission electron microscopy (HAADF-TEM), pyridine adsorption infrared (IR) and Raman spectroscopy, and density functional theory (DFT) calculations show that the doped Pr is uniformly and highly dispersed in the CeO₂ crystalline phase. In addition, the Pr doping creates more oxygen vacancy sites on CeO₂ and thus enhances the Lewis acidity of the catalyst, which is responsible for the catalytic performance of the Pr-CeO₂ catalyst

Hydrogenation of Nitroarenes by Onsite-Generated Surface Hydroxyl from Water

Directly using water as a hydrogen source for hydrogenation of nitroarenes to anilines (HNA) without using H2 is an ideal reduction reaction route but is limited by unfavorable thermodynamics. Herein, we report a high-efficiency and durable H2O-based HNA process achieved by using in situ-generated hydroxyl species from water as a hydrogen donor and low-cost CO as an oxygen acceptor over a molybdenum carbide-supported gold catalyst (Au/α-MoC1–x). It affords nitroarene conversion of over 99% with aniline selectivity of over 99% and excellent functional group tolerance at 25 °C and remains stable after 10 cycles, outperforming the traditional H2-involved route. Spectroscopic and theoretical studies reveal the key role of Au/α-MoC1–x boundaries, at which not only hydroxyl species are generated as a soft reductant on α-MoC1–x but also the nitro group is selectively hydrogenated to anilines with other unsaturated groups intact, and residual O* is removed by adsorbed CO on the atomically thin Au layer. This process provides a durable H2O-based route for aniline production at room temperature

Ferrous Centers Confined on Core–Shell Nanostructures for Low-Temperature CO Oxidation

A noble metal (NM) can stabilize monolayer-dispersed surface oxide phases with metastable nature. The formed “oxide-on-metal” inverse catalyst presents better catalytic performance than the NM because of the introduction of coordinatively unsaturated cations at the oxide–metal boundaries. Here we demonstrate that an ultrathin NM layer grown on a non-NM core can impose the same constraint on the supported oxide as the bulk NM. Cu@Pt core–shell nanoparticles (NPs) decorated with FeO patches use much less Pt but exhibit performance similar to that of Pt NPs covered with surface FeO patches in the catalytic oxidation of CO. The “oxide-on-core@shell” inverse catalyst system may open a new avenue for the design of advanced nanocatalysts with decreased usage of noble metals