Hasil untuk "physics.comp-ph"

Jie Zheng, Wenchao Sheng, Z. Zhuang et al.

A universal correlation is established between HOR/HER activity and hydrogen binding energy on platinum-group metals. Understanding how pH affects the activity of hydrogen oxidation reaction (HOR) and hydrogen evolution reaction (HER) is key to developing active, stable, and affordable HOR/HER catalysts for hydroxide exchange membrane fuel cells and electrolyzers. A common linear correlation between hydrogen binding energy (HBE) and pH is observed for four supported platinum-group metal catalysts (Pt/C, Ir/C, Pd/C, and Rh/C) over a broad pH range (0 to 13), suggesting that the pH dependence of HBE is metal-independent. A universal correlation between exchange current density and HBE is also observed on the four metals, indicating that they may share the same elementary steps and rate-determining steps and that the HBE is the dominant descriptor for HOR/HER activities. The onset potential of CO stripping on the four metals decreases with pH, indicating a stronger OH adsorption, which provides evidence against the promoting effect of adsorbed OH on HOR/HER.

H. Nyein, W. Gao, Ziba Shahpar et al.

N. Ninan, Aurélien Forget, V. P. Shastri et al.

Jin Qu, Xin Zhao, P. Ma et al.

Shanshan Jiang, Junzhou Ding, J. Andrade et al.

Christoph Ratzke, J. Gore

Microbes usually exist in communities consisting of myriad different but interacting species. These interactions are typically mediated through environmental modifications; microbes change the environment by taking up resources and excreting metabolites, which affects the growth of both themselves and also other microbes. We show here that the way microbes modify their environment and react to it sets the interactions within single-species populations and also between different species. A very common environmental modification is a change of the environmental pH. We find experimentally that these pH changes create feedback loops that can determine the fate of bacterial populations; they can either facilitate or inhibit growth, and in extreme cases will cause extinction of the bacterial population. Understanding how single species change the pH and react to these changes allowed us to estimate their pairwise interaction outcomes. Those interactions lead to a set of generic interaction motifs—bistability, successive growth, extended suicide, and stabilization—that may be independent of which environmental parameter is modified and thus may reoccur in different microbial systems.

Simin Pourjavaher, H. Almasi, S. Meshkini et al.

Seung Yun Oh, Soo Yeong Hong, Y. Jeong et al.

David G. Kwabi, Kaixiang Lin, Yunlong Ji et al.

Summary We demonstrate a long-lifetime, aqueous redox-flow battery that can operate at a pH as low as 12 while maintaining an open-circuit voltage of over 1 V. We functionalized 2,6-dihydroxyanthraquinone (2,6-DHAQ) with highly alkali-soluble carboxylate terminal groups. The resulting negative electrolyte material 4,4′-((9,10-anthraquinone-2,6-diyl)dioxy)dibutyrate (2,6-DBEAQ) was six times more soluble than 2,6-DHAQ at pH 12. Symmetric cell cycling with 2,6-DBEAQ on both sides of the cell demonstrates a capacity fade rate of

Erez Persi, Miquel Duran-Frigola, Mehdi Damaghi et al.

A reverse pH gradient is a hallmark of cancer metabolism, manifested by extracellular acidosis and intracellular alkalization. While consequences of extracellular acidosis are known, the roles of intracellular alkalization are incompletely understood. By reconstructing and integrating enzymatic pH-dependent activity profiles into cell-specific genome-scale metabolic models, we develop a computational methodology that explores how intracellular pH (pHi) can modulate metabolism. We show that in silico, alkaline pHi maximizes cancer cell proliferation coupled to increased glycolysis and adaptation to hypoxia (i.e., the Warburg effect), whereas acidic pHi disables these adaptations and compromises tumor cell growth. We then systematically identify metabolic targets (GAPDH and GPI) with predicted amplified anti-cancer effects at acidic pHi, forming a novel therapeutic strategy. Experimental testing of this strategy in breast cancer cells reveals that it is particularly effective against aggressive phenotypes. Hence, this study suggests essential roles of pHi in cancer metabolism and provides a conceptual and computational framework for exploring pHi roles in other biomedical domains. Tumors often exhibit a pH gradient, with an acidic extracellular space and alkaline cytoplasm. Here the authors develop a computational model to show how alkaline pHi supports changes inherent to cancer cell metabolism and acidification disables these adaptations, and demonstrate the effect of acidic pHi on breast cancer cell survival.

N. Jain, K. Roberts, E. Jabbour et al.

M. Ghoneim, A. Nguyen, N. Dereje et al.

pH-sensing materials and configurations are rapidly evolving toward exciting new applications, especially those in biomedical applications. In this review, we highlight rapid progress in electrochemical pH sensors over the past decade (2008-2018) with an emphasis on key considerations, such as materials selection, system configurations, and testing protocols. In addition to recent progress in optical pH sensors, our main focus in this review is on electromechanical pH sensors due to their significant advances, especially in biomedical applications. We summarize developments of electrochemical pH sensors that by virtue of their optimized material chemistries (from metal oxides to polymers) and geometrical features (from thin films to quantum dots) enable their adoption in biomedical applications. We further present an overview of necessary sensing standards and protocols. Standards ensure the establishment of consistent protocols, facilitating collective understanding of results and building on the current state. Furthermore, they enable objective benchmarking of various pH-sensing reports, materials, and systems, which is critical for the overall progression and development of the field. Additionally, we list critical issues in recent literary reporting and suggest various methods for objective benchmarking. pH regulation in the human body and state-of-the-art pH sensors (from ex vivo to in vivo) are compared for suitability in biomedical applications. We conclude our review by (i) identifying challenges that need to be overcome in electrochemical pH sensing and (ii) providing an outlook on future research along with insights, in which the integration of various pH sensors with advanced electronics can provide a new platform for the development of novel technologies for disease diagnostics and prevention.

Shikai Chang, Dingyanyan Zhou, Yujin Ji et al.

Two-dimensional (2D) materials have emerged as promising candidates as photocatalytic materials due to their large surface areas and tunable electronic properties. In this work, we systematically design and screen a series of octuple-atomic-layer M2A2Z4 monolayers (M = Al, Ga, In; A = Si, Ge, Sn; Z = N, P, As) using first-principles calculations. 108 structures are constructed by intercalation approach, followed by a comprehensive evaluation of their thermodynamic and dynamic stability, band gaps, and band edge alignments to assess their potential for photocatalytic overall water splitting. Eight candidates meet the criteria for overall water splitting, among which Al2Si2N4 and Al2Ge2N4 exhibit suitable band edge positions, pronounced visible-light absorption, high electron mobility and high solar-to-hydrogen (STH) efficiencies for photocatalysis under both acidic and neutral environments (pH = 0 and 7). Importantly, the introduction of N vacancies on the surfaces of Al2Si2N4 and Al2Ge2N4 significantly enhances their catalytic activity for both hydrogen reduction and water oxidation reactions, further supporting their potential as photocatalysts for overall water splitting. Both materials also display robust structural stability in aqueous environments. Our study provides theoretical insights for the rational design of efficient and stable 2D photocatalysts for overall water splitting.

G. Thamizharasan, R. D. Eithiraj

The development of industrial growth raises global energy demand. Novel materials with promising unorthodox features satiate and demand for sustainable, non-toxic, and cost-effective energy. A first-principles investigation were carried out to ground state and transport properties of CaV$_2$TeO$_8$ towards energy harvesting and photocatalytic applications was carried out. In groundstate the CaV$_2$TeO$_8$ showed good mechanically stable with a volume of (1138.235 \textÅ^3) and a high elastic modulus of (215.73 GPa). Further, the electronic properties of CaV$_2$TeO$_8$, PBE-GGA exchange-correlation was utilized, demonstrates direct and indirect transitions with a wide bandgap of 2.7 and 2.8 eV, indicating its semiconducting nature. Photoinduced charge carriers were investigated through Deformation Potential Theory (DPT) to estimate the mobility of charge carriers, excitonic radius, and effective mass. Axial anisotropic strain in band degeneracy and shifts in the S-Y and Y-Γtransitions offer a (3.17 \textÅ^3) Frenkel-type strongly bound exciton with a high carrier mobility of (2409.91 \, \text{cm}^2 \, \text{V}^{-1} \, \text{s}^{-1}) electrons and (316.46 \, \text{cm}^2 \, \text{V}^{-1} \, \text{s}^{-1}) holes respectively. To estimate the feasibility of CaV$_2$TeO$_8$ in photocatalysis, we examined the conduction and valence band edges under harsh pH conditions within PBE-GGA exchange-correlation functionals. The band edges of CaV$_2$TeO$_8$ show the halfway reaction for hydrogen evolution with reference to the Normal Hydrogen Electrode (NHE). Moreover, the Boltzmann equation interface was used to investigate the transport and thermoelectric properties. A high Seebeck coefficient in CaV$_2$TeO$_8$ at 300 K directs a thermoelectric figure of merit of 0.94.

Stefano Americo, Ivano E. Castelli, Kristian S. Thygesen

A key challenge for computational discovery of electrocatalytic materials is the reliable prediction of thermodynamic stability in aqueous environment and under different electrochemical conditions. In this work, we first evaluate the electrochemical stability of more than 3000 two-dimensional (2D) materials using conventional Pourbaix diagrams (CPDs). Due to the complete neglect of thermodynamic barriers along the (often complex) reaction pathways, the vast majority of the materials are predicted to be unstable even though some are known to be stable in practice. We then introduce an analysis based on the surface Pourbaix diagram (SPD) including 'early intermediate states' that represent the first steps of the key surface passivation and dissolution reactions. The SPD framework is applied to the 2D materials MoS$_2$, phosphorene, and the MXene Ti$_2$C, all of which are predicted to be unstable by the CPD. For MoS$_2$, our approach reproduces the experimental pH-U stability window as well as the experimental desulphurization potential. For phosphorene and Ti2$_C$, the SPD approach is used to investigate the spontaneous degradation mechanism and the potential-dependent surface termination, respectively, again yielding good agreement with experiments. The SPD-based stability analysis emerges as a versatile and quantitative method for prediction of stability and investigation of surface structures in electrochemical environments.

Wenting Qian, Bin Ma, Xiyao Li et al.

Partial-denitrification (nitrate to nitrite) can supply nitrite for anammox which can reduce organic matter consumption in wastewater treatment plants (WWTPs). In order to achieve stable partial-denitrification, the effect of pH on denitrification were investigated for 420 days in three reactors with influent pH of 5.0, 7.0 and 9.0. The results indicate that the nitrite accumulation rate (NAR) increased with pH, with average effluent NARs being 21%, 38% and 57% in the above reactors, respectively. The sludge cultivated at a high pH of 9.0 was resistant to pH shock, with a high NAR being maintained at 83% when it was exposed to a low pH of 5.0. Metagenomic analysis showed that the higher NAR at pH 9.0 was correlated with an enrichment of Thauera, which harbored more nitrate reductase (8098 hits) than nitrite reductase (2950 hits). Based on these findings, a novel process was proposed for achieving partial-denitrification/anammox in mainstream WWTPs.

J. Carstensen, C. Duarte

A synthesis of long-term changes in pH of coastal ecosystems shows that, in contrast to the uniform trends of open-ocean acidification (-0.0004 to -0.0026 pH units yr-1) driven by increased atmospheric CO2, coastal ecosystems display a much broader range of trends (-0.023 to 0.023 pH units yr-1) and are as likely to show long-term increase as decline in pH. The majority of the 83 investigated coastal ecosystems displayed nonlinear trends, with seasonal and interannual variations exceeding 1 pH unit for some sites. The high pH variability of coastal ecosystems is primarily driven by inputs from land. These include freshwater inputs that typically dilute the alkalinity of seawater thereby resulting in reduced buffering, nutrients enhancing productivity and pH, as well as organic matter supporting excess respiration driving acidification. For some coastal ecosystems, upwelling of nutrient-rich and corrosive water may also contribute to variability in pH. Metabolic control of pH was the main factor governing variability for the majority of coastal sites, displaying larger variations in coastal ecosystems with low alkalinity buffering. pH variability was particularly pronounced in coastal ecosystems with strong decoupling of production and respiration processes, seasonally or through stratification. Our analysis demonstrate that coastal pH can be managed by controlling inputs of nutrients, organic matter, and alkalinity. In well-mixed coastal waters, increasing productivity can improve resistance to ocean acidification, whereas increasing productivity enhances acidification in bottom waters of stratified coastal ecosystems. Environmental management should consider the balance between the negative consequences of eutrophication versus those of acidification, to maintain biodiversity and ecosystem services of our coastal ecosystems.

Jiaqi Wu, Bo Peng

The assembly of molecules to form covalent networks can create varied lattice structures with distinct physical and chemical properties from conventional atomic lattices. Using the smallest stable [5,6]fullerene units as building blocks, various 2D C$_{24}$ networks can be formed with superior stability and strength compared to the recently synthesised monolayer polymeric C$_{60}$. Monolayer C$_{24}$ harnesses the properties of both carbon crystals and fullerene molecules, such as stable chemical bonds, suitable band gaps and large surface area, facilitating photocatalytic water splitting. The electronic band gaps of C$_{24}$ are comparable to TiO$_2$, providing appropriate band edges with sufficient external potential for overall water splitting over the acidic and neutral pH range. Upon photoexcitation, strong solar absorption enabled by strongly bound bright excitons can generate carriers effectively, while the type-II band alignment between C$_{24}$ and other 2D monolayers can separate electrons and holes in individual layers simultaneously. Additionally, the number of surface active sites of C$_{24}$ monolayers are three times more than that of their C$_{60}$ counterparts in a much wider pH range, providing spontaneous reaction pathways for hydrogen evolution reaction. Our work provides insights into materials design using tunable building blocks of fullerene units with tailored functions for energy generation, conversion and storage.

Evellin Balbinot-Alfaro, Débora Vieira Craveiro, Karina Oliveira Lima et al.

Laura A Wallace, Lauren Gwynne, T. Jenkins

Regarded as a silent epidemic, chronic wounds are a global public health issue. Wound healing is a complex, synchronized cascade of physiological processes restoring the anatomic and functional integrity of the skin; however, chronic wounds fail to proceed through the wound healing cascade. Wound pH oscillates during wound healing, usually traversing from a neutral pH to an acidic pH, while chronic wounds perpetuate in an elevated alkaline milieu. Although a neglected clinical parameter, pH has implications for relatively all pathologies of wound healing affecting oxygen release, angiogenesis, protease activity, bacterial toxicity and antimicrobial activity. Despite the array of wound healing products currently marketed, understanding the implications of pH on arresting wound healing can stimulate innovation within this vast market.