Iterative Bragg peak removal on X-ray absorption spectra with automatic intensity correction.

This study introduces a novel iterative Bragg peak removal with automatic intensity correction (IBR-AIC) methodology for X-ray absorption spectroscopy (XAS), specifically addressing the challenge of Bragg peak interference in the analysis of crystalline materials. The approach integrates experimental adjustments and sophisticated post-processing, including an iterative algorithm for robust calculation of the scaling factor of the absorption coefficients and efficient elimination of the Bragg peaks, a common obstacle in accurately interpreting XAS data, particularly in crystalline samples. The method was thoroughly evaluated on dilute catalysts and thin films, with fluorescence mode and large-angle rotation. The results underscore the technique's effectiveness, adaptability and substantial potential in improving the precision of XAS data analysis. While demonstrating significant promise, the method does have limitations related to signal-to-noise ratio sensitivity and the necessity for meticulous angle selection during experimentation. Overall, IBR-AIC represents a significant advancement in XAS, offering a pragmatic solution to Bragg peak contamination challenges, thereby expanding the applications of XAS in understanding complex materials under diverse experimental conditions.

Interrogating site dependent kinetics over SiO2-supported Pt nanoparticles.

A detailed knowledge of reaction kinetics is key to the development of new more efficient heterogeneous catalytic processes. However, the ability to resolve site dependent kinetics has been largely limited to surface science experiments on model systems. Herein, we can bypass the pressure, materials, and temperature gaps, resolving and quantifying two distinct pathways for CO oxidation over SiO2-supported 2 nm Pt nanoparticles using transient pressure pulse experiments. We find that the pathway distribution directly correlates with the distribution of well-coordinated (e.g., terrace) and under-coordinated (e.g., edge, vertex) CO adsorption sites on the 2 nm Pt nanoparticles as measured by in situ DRIFTS. We conclude that well-coordinated sites follow classic Langmuir-Hinshelwood kinetics, but under-coordinated sites follow non-standard kinetics with CO oxidation being barrierless but conversely also slow. This fundamental method of kinetic site deconvolution is broadly applicable to other catalytic systems, affording bridging of the complexity gap in heterogeneous catalysis.

Enhanced Hot Electron Flow and Catalytic Synergy by Engineering Core-Shell Structures on Au-Pd Nanocatalysts.

The synergistic catalytic performances of bimetallic catalysts are often attributed to the reaction mechanism associated with the alloying process of the catalytic metals. Chemically induced hot electron flux is strongly correlated with catalytic activity, and the interference between two metals at the atomic level can have a huge impact on the hot electron generation on the bimetallic catalysts. In this study, we investigate the correlation between catalytic synergy and hot electron chemistry driven by the electron coupling effect using a model system of Au-Pd bimetallic nanoparticles. We show that the bimetallic nanocatalysts exhibit enhanced catalytic activity under the hydrogen oxidation reaction compared with that of monometallic Pd nanocatalysts. Analysis of the hot electron flux generated in each system revealed the formation of Au/PdOx interfaces, resulting in high reactivity on the bimetallic catalyst. In further experiments with engineering the Au@Pd core-shell structures, we reveal that the hot electron flux, when the topmost surface Pd atoms were less affected by inner Au, due to the concrete shell, was smaller than the alloyed one. The alloyed bimetallic catalyst forming the metal-oxide interfaces has a more direct effect on the hot electron chemistry, as well as on the catalytic reactivity. The great significance of this study is in the confirmation that the change in the hot electron formation rate with the metal-oxide interfaces can be observed by shell engineering of nanocatalysts.

Transient-rare Bacterial Taxa Are Assembled Neutrally across Temporal Scales.

Despite the importance of microbial communities in ecosystem functions, the mechanisms underlying the assembly of rare taxa over time are poorly understood. It remains largely unknown whether rare taxa exhibit similar assembly processes to common taxa in local communities. We herein retrieved the 16S rRNA sequences of bacteria collected bimonthly for 2 years from the Pohang wastewater treatment plant. The transient-rare taxa showed different abundance distributions from the common taxa. Transient-rare taxon assemblages also exhibited higher temporal variations than common taxon assemblages, suggesting the distinct ecological patterns of the two assemblages. A multivariate analysis revealed that environmental parameters accounted for 25.3 and 61.6% of temporal variations in the transient-rare and common taxon assemblages, respectively. The fitting of all observed taxa to a neutral community model revealed that 96.4% of the transient-rare taxa (relative abundance, 71.4%) and 73.3% of the common taxa (relative abundance, 45.6%) followed the model, suggesting that stochastic mechanisms were more important than deterministic ones in the assembly of the transient-rare taxa. Collectively, the present results indicate that the transient-rare bacterial taxa at the Pohang wastewater treatment plant differed from the common taxa in ecological patterns, suggesting that dispersal is a key process in their assembly.

Operando Surface Characterization on Catalytic and Energy Materials from Single Crystals to Nanoparticles.

Modern surface science faces two major challenges, a materials gap and a pressure gap. While studies on single crystal surface in ultrahigh vacuum have uncovered the atomic and electronic structures of the surface, the materials and environmental conditions of commercial catalysis are much more complicated, both in the structure of the materials and in the accessible pressure range of analysis instruments. Model systems and operando surface techniques have been developed to bridge these gaps. In this Review, we highlight the current trends in the development of the surface characterization techniques and methodologies in more realistic environments, with emphasis on recent research efforts at the Korea Advanced Institute of Science and Technology. We show principles and applications of the microscopic and spectroscopic surface techniques at ambient pressure that were used for the characterization of atomic structure, electronic structure, charge transport, and the mechanical properties of catalytic and energy materials. Ambient pressure scanning tunneling microscopy and X-ray photoelectron spectroscopy allow us to observe the surface restructuring that occurs during oxidation, reduction, and catalytic processes. In addition, we introduce the ambient pressure atomic force microscopy that revealed the morphological, mechanical, and charge transport properties that occur during the catalytic and energy conversion processes. Hot electron detection enables the monitoring of catalytic reactions and electronic excitations on the surface. Overall, the information on the nature of catalytic reactions obtained with operando spectroscopic and microscopic techniques may bring breakthroughs in some of the global energy and environmental problems the world is facing.

Impact of fouling on the decline of aeration efficiency under different operational conditions at WRRFs.

Biofilm formation influences the most energy-demanding process in the waste water treatment cycle. Biofilm growth on the surface of wastewater aeration diffusers in water resource recovery facilities (WRRFs) can increase the energy requirements up to 50% in less than 2 years. The impact of biofilms in aeration diffusers was quantified and assessed for first time using molecular tools (i.e., Energy-dispersive X-ray, Ra and RMS and Pyrosequencing) and state-of-the-art techniques (i.e., EPS quantification, Hydrophobicity and DNA quantification). To provide a better understanding and quantitative connections between biological activity and aeration energy efficiency, two replicates of the most common diffusers were installed and tested in two different operational conditions (higher and lower organic loading rate processes) during 15 months. Different scenarios and conditions provided for first time comprehensive understanding of the major factors contributing to diffuser fouling. The array of analysis suggested that higher loading conditions can promote specialized microbial populations to halve aeration efficiency parameters (i.e., αF) in comparison to lower loading conditions. Biofilms adapted to certain operational conditions can trigger changes in diffuser membrane properties (i.e., biological enhanced roughness and hydrophobicity) and enhance EPS growth rates. Improved understanding of the effects of scaling, biofouling, aging and microbial population shifts on the decrease in aeration efficiency is provided.

3D Architectures of Cox P Using Silk Fibroin Scaffolds: An Active and Stable Electrocatalyst for Hydrogen Generation in Acidic and Alkaline Media.

Developing nonprecious, highly active, and stable catalysts is essential for efficient electrocatalytic hydrogen evolution reaction in water splitting. In this study, the facile synthesis of a 3D flower-like Cox P/carbon architecture is proposed composed of an assembly of nanosheets interconnected by silk fibroin that acts as 3D scaffolds and a carbon source. This unique 3D architecture coupled with a carbon matrix enhances catalytic activity by exposing more active sites and increasing charge transport. The flower-like Cox P/carbon can facilitate a lower overpotential, Tafel slope, charge transfer resistance, and a higher electrochemically active surface than carbon-free and silk-free Cox P. The nanostructured architecture exhibits excellent catalytic performance with low overpotentials of 109 and 121 mV at 10 mA cm-2 and Tafel slopes of 55 and 62 mV dec-1 in acidic and alkaline media, respectively. Furthermore, it minimally degrades the overpotential and current density after long-term stability tests 10 000 cyclic voltammetry cycles and a chronoamperometric test over 40 h, respectively, in acidic media, which confirms the high durability and stability of the flower-like Cox P/carbon.

Lauroyl Arginate Ethyl Blocks the Iron Signals Necessary for Pseudomonas aeruginosa Biofilm Development.

Pseudomonas aeruginosa is a ubiquitous gram-negative bacterium capable of forming a biofilm on living and non-living surfaces, which frequently leads to undesirable consequences. We found that lauroyl arginate ethyl (LAE), a synthetic non-oxidizing biocide, inhibited biofilm formation by P. aeruginosa at a sub-growth inhibitory concentration under both static and flow conditions. A global transcriptome analysis was conducted using a gene chip microarray to identify the genes targeted by LAE. In response to LAE treatment, P. aeruginosa cells up-regulated iron acquisition and signaling genes and down-regulated iron storage genes. LAE demonstrated the capacity to chelate iron in an experiment in which free LAE molecules were measured by increasing the ratio of iron to LAE. Furthermore, compared to untreated cells, P. aeruginosa cells treated with LAE exhibited enhanced twitching motility, a phenotype that is usually evident when the cells are starved for iron. Taken together, these results imply that LAE generated iron-limiting conditions, and in turn, blocked iron signals necessary for P. aeruginosa biofilm development. As destroying or blocking signals leading to biofilm development would be an efficient way to mitigate problematic biofilms, our findings suggest that LAE can aid in reducing P. aeruginosa biofilms for therapeutic and industrial purposes.

Polyvinylidene Fluoride Alters Inflammatory Responses by Activation-induced Cell Death in Macrophages.

Carbon nanotubes (CNTs) are nanomaterials that have been employed in generating diverse materials. We previously reported that CNTs induce cell death in macrophages, possibly via asbestosis. Therefore, we generated CNT-attached polyvinylidene fluoride (PVDF), which is an established polymer in membrane technology, and then examined whether CNT-attached PVDF is immunologically safe for medical purposes compared to CNT alone. To test this, we treated RAW 264.7 murine macrophages (RAW cells) with CNT-attached PVDF and analyzed the production of nitric oxide (NO), a potent proinflammatory mediator, in these cells. RAW cells treated with CNT-attached PVDF showed reduced NO production in response to lipopolysaccharide. However, the same treatment also decreased the cell number suggesting that this treatment can alter the homeostasis of RAW cells. Although cell cycle of RAW cells was increased by PVDF treatment with or without CNTs, apoptosis was enhanced in these cells. Taken together, these results indicate that PVDF with or without CNTs modulates inflammatory responses possibly due to activation-induced cell death in macrophages.

General and rare bacterial taxa demonstrating different temporal dynamic patterns in an activated sludge bioreactor.

Temporal variation of general and rare bacterial taxa was investigated using pyrosequencing of 16S rRNA gene from activated sludge samples collected bimonthly for a two-year period. Most of operational taxonomic units (OTUs) were allocated to rare taxa (89.6%), but the rare taxa comprised a small portion of the community in terms of abundance of sequences analyzed (28.6%). Temporal variations in OTUs richness significantly differed between the two taxa groups in which the rare taxa showed a higher diversity and a more fluctuating pattern than the general taxa. Furthermore, the two taxa groups were constrained by different explanatory variables: influent BOD, effluent BOD, and DO were the significant (P < 0.05) parameters affecting the pattern of the general taxa, while temperature was the factor for the rare taxa. Over the test period, the general taxa persisted for a longer time (i.e., lower turnover rate) in the bioreactor than the rare taxa. In conclusion, this study demonstrated clear differences in temporal dynamic patterns for the general and rare bacterial taxa in an activated sludge bioreactor, which would be a foundation for better understanding the bacterial ecology of activated sludge.

Analysis of the time dependency of ammonia-oxidizing bacterial community dynamics in an activated sludge bioreactor.

An autoregressive error term model was applied to examine the dynamic oscillation of ammonia-oxidizing bacterial (AOB) lineages found in an activated sludge bioreactor. The current abundance of AOB lineages was affected by the past abundance of AOB lineages and past environmental and operational factors as well as current influencing factors.

Pyrosequencing demonstrated complex microbial communities in a membrane filtration system for a drinking water treatment plant.

Microbial community composition in a pilot-scale microfiltration plant for drinking water treatment was investigated using high-throughput pyrosequencing technology. Sequences of 16S rRNA gene fragments were recovered from raw water, membrane tank particulate matter, and membrane biofilm, and used for taxonomic assignments, estimations of diversity, and the identification of potential pathogens. Greater bacterial diversity was observed in each sample (1,133-1,731 operational taxonomic units) than studies using conventional methods, primarily due to the large number (8,164-22,275) of sequences available for analysis and the identification of rare species. Betaproteobacteria predominated in the raw water (61.1%), while Alphaproteobacteria were predominant in the membrane tank particulate matter (42.4%) and membrane biofilm (32.8%). The bacterial community structure clearly differed for each sample at both the genus and species levels, suggesting that different environmental and growth conditions were generated during membrane filtration. Moreover, signatures of potential pathogens including Legionella, Pseudomonas, Aeromonas, and Chromobacterium were identified, and the proportions of Legionella and Chromobacterium were elevated in the membrane tank particulate matter, suggesting a potential threat to drinking water treated by membrane filtration.

Nitrifying bacterial community structure of a full-scale integrated fixed-film activated sludge process as investigated by pyrosequencing.

Nitrifying bacterial community structures of suspended and attached biomasses in a full-scale integrated fixed-film activated sludge process were investigated by analyzing 16S rRNA gene sequences obtained from pyrosequencing. The suspended biomass had a higher number of ammoniaoxidizing bacterial sequences (0.8% of total sequences) than the attached biomass (0.07%), although most of the sequences were within the Nitrosomonas oligotropha lineage in both biomasses. Nitrospira-like nitrite-oxidizing bacterial sequences were retrieved in the suspended biomass (0.06%), not in the attached biomass, whereas the existence of Nitrobacter-like sequences was not evident. The suspended biomass had higher nitrification activity (1.13 mg N/TSS/h) than the attached biomass (0.07 mg N/TSS/h). Overall, the results made it possible to conclude the importance of the suspended biomass, rather than the attached biomass, in nitrification in the wastewater treatment process studied.

Bacterial community composition and diversity of a full-scale integrated fixed-film activated sludge system as investigated by pyrosequencing.

The integrated fixed-film activated sludge (IFAS) system is a variation of the activated sludge wastewater treatment process, in which hybrid suspended and attached biomass is used to treat wastewater. Although the function and performance of the IFAS system are well studied, little is known about its microbial community structure. In this study, the composition and diversity of the bacterial community of suspended and attached biomass samples were investigated in a full-scale IFAS system using a highthroughput pyrosequencing technology. Distinct bacterial community compositions were examined for each sample and appeared to be important for its features different from conventional activated sludge processes. The abundant bacterial groups were Betaproteobacteria (59.3%), Gammaproteobacteria (8.1%), Bacteroidetes (5.2%), Alphaproteobacteria (3.9%), and Actinobacteria (3.2%) in the suspended sample, whereas Actinobacteria (14.6%), Firmicutes (13.6%), Bacteroidetes (11.6%), Betaproteobacteria (9.9%), Gammaproteobacteria (9.25%), and Alphaproteobacteria (7.4%) were major bacterial groups in the attached sample. Regarding the diversity, totals of 3,034 and 1,451 operational taxonomic units were identified at the 3% cutoff for the suspended and attached samples, respectively. Rank abundance and community analyses demonstrated that most of the diversity was originated from rare species in the samples. Taken together, the information obtained in this study will be a base for further studies relating to the microbial community structure and function of the IFAS system.