scholarly journals Active sites in heterogeneous ice nucleation—the example of K-rich feldspars

Science ◽  
2016 ◽  
Vol 355 (6323) ◽  
pp. 367-371 ◽  
Author(s):  
Alexei Kiselev ◽  
Felix Bachmann ◽  
Philipp Pedevilla ◽  
Stephen J. Cox ◽  
Angelos Michaelides ◽  
...  
Keyword(s):  
Active Sites ◽  
Surface Defects ◽  
Molecular Level ◽  
High Energy ◽  
Ice Nucleation ◽  
Ice Formation ◽  
Electron Microscopic ◽  
Prismatic Crystal ◽  
Preferential Nucleation ◽  
Earth’S Climate

Ice formation on aerosol particles is a process of crucial importance to Earth’s climate and the environmental sciences, but it is not understood at the molecular level. This is partly because the nature of active sites, local surface features where ice growth commences, is still unclear. Here we report direct electron-microscopic observations of deposition growth of aligned ice crystals on feldspar, an atmospherically important component of mineral dust. Our molecular-scale computer simulations indicate that this alignment arises from the preferential nucleation of prismatic crystal planes of ice on high-energy (100) surface planes of feldspar. The microscopic patches of (100) surface, exposed at surface defects such as steps, cracks, and cavities, are thought to be responsible for the high ice nucleation efficacy of potassium (K)–feldspar particles.

Molecular dynamics approach to assess aqueous alteration of potassium-rich feldspar surfaces

2021 ◽  
Author(s):  
Anand Kumar ◽  
Allan K. Bertram ◽  
Grenfell N. Patey
Keyword(s):  
Molecular Dynamics ◽  
Ion Exchange ◽  
Active Sites ◽  
Water Structure ◽  
High Energy ◽  
Ice Nucleation ◽  
Ice Formation ◽  
Major Pathway ◽  
Near Surface ◽  
Spatial And Temporal Scales

<p>Ice clouds play an important role in the Earth’s radiative budget and hence climate. Heterogeneous ice nucleation, a major pathway for ice formation in cirrus and mixed-phase clouds, is induced by active sites present on atmospheric aerosol particles termed as ice-nucleating particles. Feldspars have been shown to be highly ice nucleation active. Despite the importance of mineral dusts for ice nucleation, the role of atmospheric aging (e.g. surface alteration due to interactions with chemical species) on their ice nucleation efficiency is largely unknown. This is primarily due to the lack of microscopic level insight into nucleation from laboratory/field-based experiments, due to the inability to experimentally access the small spatial and temporal scales at which nucleation process occurs – a problem that can be potentially tackled with computer simulations. We utilize direct Molecular Dynamics simulations (GROMACS 5.1.4) to investigate the interactions of solutes with different surfaces of potassium feldspar mineral (microcline) and the corresponding interfacial water structure at a microscopic scale. We investigated the interactions of monovalent cations (H<sub>3</sub>O<sup>+</sup>, (NH<sub>4</sub>)<sup>+</sup>, Li<sup>+</sup>, K<sup>+</sup>, Cs<sup>+</sup>) with various surfaces of microcline, and subsequent effects on the near-surface water structure at 300 K. The investigated surfaces include the perfect cleavage planes, (001) and (010), as well as the high energy plane (100) of microcline. Feldspar is modeled as semi-rigid (lattice atoms fixed expect K<sup>+</sup> and H of surface OH) and as fully flexible (all lattice atoms free to move) with the CLAYFF force field, and the TIP4P/Ice model is employed for water. Results show that on simulation timescales, lattice vibration is necessary for ion exchange between added cation and lattice K<sup>+</sup>, albeit at different exchange rates for the 3 planes. None of the 3 flexible surfaces show any preference for  over K<sup>+</sup> in terms of ion exchange within the simulation timescale. Both the semi-rigid and flexible surfaces show higher adsorption of molecular cations ((NH<sub>4</sub>)<sup>+</sup> and H<sub>3</sub>O<sup>+</sup>) compared with the simple spherical cations. In addition, we do not observe ice nucleation on modified microcline surfaces (both semi-rigid and flexible) at a supercooled temperature of 230 K within the simulation timescale. To conclude, the presented work provides an improved understanding of the processes modifying the feldspar surfaces in water and aqueous solutions and its possible relevance for ice formation.</p>

scholarly journals Comparison of Modeled and Measured Ice Nucleating Particle Composition in a Cirrus Cloud

2019 ◽  
Vol 76 (4) ◽  
pp. 1015-1029 ◽  
Author(s):  
Romy Ullrich ◽  
Corinna Hoose ◽  
Daniel J. Cziczo ◽  
Karl D. Froyd ◽  
Joshua P. Schwarz ◽  
...  
Keyword(s):  
Mineral Dust ◽  
Model Simulation ◽  
Ice Nucleation ◽  
Ice Formation ◽  
Cirrus Cloud ◽  
Reactive Trace Gases ◽  
Earth’S Climate ◽  
Activation Conditions ◽  
Cloud Ice ◽  
Heterogeneous Ice Nucleation

Abstract The contribution of heterogeneous ice nucleation to the formation of cirrus cloud ice crystals is still not well quantified. This results in large uncertainties when predicting cirrus radiative effects and their role in Earth’s climate system. The goal of this case study is to simulate the composition, and thus activation conditions, of ice nucleating particles (INPs) to evaluate their contribution to heterogeneous cirrus ice formation in relation to homogeneous ice nucleation. For this, the regional model COSMO—Aerosols and Reactive Trace Gases (COSMO-ART) was used to simulate a synoptic cirrus cloud over Texas on 13 April 2011. The simulated INP composition was then compared to measured ice residual particle (IRP) composition from the actual event obtained during the NASA Midlatitude Airborne Cirrus Properties Experiment (MACPEX) aircraft campaign. These IRP measurements indicated that the dominance of heterogeneous ice nucleation was mainly driven by mineral dust with contributions from a variety of other particle types. Applying realistic activation thresholds and concentrations of airborne transported mineral dust and biomass-burning particles, the model implementing the heterogeneous ice nucleation parameterization scheme of Ullrich et al. is able to reproduce the overall dominating ice formation mechanism in contrast to the model simulation with the scheme of Phillips et al. However, the model showed flaws in reproducing the IRP composition.

scholarly journals Size-dependent ice nucleation by airborne particles during dust events in the eastern Mediterranean

2019 ◽  
Vol 19 (17) ◽  
pp. 11143-11158 ◽  
Author(s):  
Naama Reicher ◽  
Carsten Budke ◽  
Lukas Eickhoff ◽  
Shira Raveh-Rubin ◽  
Ifat Kaplan-Ashiri ◽  
...  
Keyword(s):  
Particle Size ◽  
Active Sites ◽  
Mineral Dust ◽  
Eastern Mediterranean ◽  
Sampling Site ◽  
Ice Nucleation ◽  
Airborne Particles ◽  
Ice Formation ◽  
Airborne Dust ◽  
Dust Events

Abstract. The prediction of cloud ice formation in climate models remains a challenge, partly due to the complexity of ice-related processes. Mineral dust is a prominent aerosol in the troposphere and is an important contributor to ice nucleation in mixed-phase clouds, as dust can initiate ice heterogeneously at relatively low supercooling conditions. We characterized the ice nucleation properties of size-segregated mineral dust sampled during dust events in the eastern Mediterranean. The sampling site allowed us to compare the properties of airborne dust from several sources with diverse mineralogy that passed over different atmospheric paths. We focused on particles with six size classes determined by the Micro-Orifice Uniform Deposit Impactor (MOUDI) cutoff sizes: 5.6, 3.2, 1.8, 1.0, 0.6 and 0.3 µm. Ice nucleation experiments were conducted in the Weizmann Supercooled Droplets Observation on a Microarray (WISDOM) setup, whereby the particles are immersed in nanoliter droplets using a microfluidics technique. We observed that the activity of airborne particles depended on their size class; supermicron and submicron particles had different activities, possibly due to different composition. The concentrations of ice-nucleating particles and the density of active sites (ns) increased with the particle size and particle concentration. The supermicron particles in different dust events showed similar activity, which may indicate that freezing was dominated by common mineralogical components. Combining recent data of airborne mineral dust, we show that current predictions, which are based on surface-sampled natural dust or standard mineral dust, overestimate the activity of airborne dust, especially for the submicron class. Therefore, we suggest including information on particle size in order to increase the accuracy of ice formation modeling and thus weather and climate predictions.

scholarly journals Motion of water monomers reveals a kinetic barrier to ice nucleation on graphene

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Anton Tamtögl ◽  
Emanuel Bahn ◽  
Marco Sacchi ◽  
Jianding Zhu ◽  
David J. Ward ◽  
...  
Keyword(s):  
Molecular Level ◽  
Ice Nucleation ◽  
Atomic Scale ◽  
Ice Formation ◽  
Central Question ◽  
Interfacial Behaviour ◽  
Level Information ◽  
Repulsive Forces ◽  
And Control ◽  
Insight Into

AbstractThe interfacial behaviour of water remains a central question to fields as diverse as protein folding, friction and ice formation. While the properties of water at interfaces differ from those in the bulk, major gaps in our knowledge limit our understanding at the molecular level. Information concerning the microscopic motion of water comes mostly from computation and, on an atomic scale, is largely unexplored by experiment. Here, we provide a detailed insight into the behaviour of water monomers on a graphene surface. The motion displays remarkably strong signatures of cooperative behaviour due to repulsive forces between the monomers, enhancing the monomer lifetime ( ≈ 3 s at 125 K) in a free-gas phase that precedes the nucleation of ice islands and, in turn, provides the opportunity for our experiments to be performed. Our results give a molecular perspective on a kinetic barrier to ice nucleation, providing routes to understand and control the processes involved in ice formation.

scholarly journals Size-dependent ice nucleation by airborne particles during dust events in the Eastern Mediterranean

2019 ◽  
Author(s):  
Naama Reicher ◽  
Carsten Budke ◽  
Lukas Eickhoff ◽  
Shira Raveh-Rubin ◽  
Ifat Kaplan-Ashiri ◽  
...  
Keyword(s):  
Particle Size ◽  
Active Sites ◽  
Mineral Dust ◽  
Eastern Mediterranean ◽  
Sampling Site ◽  
Ice Nucleation ◽  
Airborne Particles ◽  
Ice Formation ◽  
Airborne Dust ◽  
Dust Events

Abstract. Predictions of cloud ice formation in climate models remain a challenge, partly due to the complexity of ice-related processes. Mineral dust is a prominent aerosol in the troposphere and is known to be an important contributor to ice nucleation in mixed phase clouds, as dust can initiate ice heterogeneously at relatively low supercooling conditions. We characterized the ice nucleation properties of size-segregated mineral dust sampled during dust events in the Eastern Mediterranean. The sampling site allowed us to compare between the properties of airborne dust from several sources with diverse mineralogy that passed over different atmospheric paths. We focused on particles with six size-classes, determined by the Micro-Orifice Uniform Deposit Impactor (MOUDI) cut-off sizes: 5.6, 3.2, 1.8, 1.0, 0.6 and 0.3 µm. Ice nucleation experiments were conducted in the WeIzmann Supercooled Droplets Observation on Microarray (WISDOM) setup, where the particles are immersed in nanoliter droplets using a microfluidics technique. We observed that the activity of airborne particles depended on their size-class, where supermicron and submicron particles had different activities, possibly due to different composition. The concentrations of ice nucleating particles and the density of active sites (ns) increased with the particle size and particle concentration. The supermicron particles in different dust events showed similar activity, which may indicate that freezing was dominated by common mineralogical components. Combining recent data of airborne mineral dust, we show that current predictions, which are based on natural dust or standard mineral dust, overestimate the activity of airborne dust, especially for the submicron class, and therefore we suggest to include information of particle size in order to increase the accuracy of ice formation and, thus, weather and climate predictions.

Preparatory Procedures for Electron Microscopic Analysis at the Molecular Level of Resolution

1978 ◽  
Vol 36 (3) ◽  
pp. 516-520
Author(s):  
F.J. Sjostrand
Keyword(s):  
Electron Microscope ◽  
Molecular Level ◽  
Microscopic Analysis ◽  
Resolving Power ◽  
Cellular Structures ◽  
Electron Microscopic ◽  
Systematic Analysis ◽  
Technical Developments ◽  
Thin Sectioning ◽  
Obvious Reason

In the 1940's and 1950's electron microscopy conferences were attended with everybody interested in learning about the latest technical developments for one very obvious reason. There was the electron microscope with its outstanding performance but nobody could make very much use of it because we were lacking proper techniques to prepare biological specimens. The development of the thin sectioning technique with its perfectioning in 1952 changed the situation and systematic analysis of the structure of cells could now be pursued. Since then electron microscopists have in general become satisfied with the level of resolution at which cellular structures can be analyzed when applying this technique. There has been little interest in trying to push the limit of resolution closer to that determined by the resolving power of the electron microscope.

scholarly journals Efficient Catalytic Conversion of Polysulfides by Biomimetic Design of “Branch-Leaf” Electrode for High-Energy Sodium–Sulfur Batteries

2021 ◽  
Vol 13 (1) ◽  
Author(s):  
Wenyan Du ◽  
Kangqi Shen ◽  
Yuruo Qi ◽  
Wei Gao ◽  
Mengli Tao ◽  
...  
Keyword(s):  
Active Sites ◽  
High Performance ◽  
Electrochemical Reaction ◽  
Molecular Layer ◽  
Specific Capacity ◽  
High Energy ◽  
Reduction Reaction ◽  
Biomimetic Design ◽  
Co Nanoparticles ◽  
Sodium Sulfur

AbstractRechargeable room temperature sodium–sulfur (RT Na–S) batteries are seriously limited by low sulfur utilization and sluggish electrochemical reaction activity of polysulfide intermediates. Herein, a 3D “branch-leaf” biomimetic design proposed for high performance Na–S batteries, where the leaves constructed from Co nanoparticles on carbon nanofibers (CNF) are fully to expose the active sites of Co. The CNF network acts as conductive “branches” to ensure adequate electron and electrolyte supply for the Co leaves. As an effective electrocatalytic battery system, the 3D “branch-leaf” conductive network with abundant active sites and voids can effectively trap polysulfides and provide plentiful electron/ions pathways for electrochemical reaction. DFT calculation reveals that the Co nanoparticles can induce the formation of a unique Co–S–Na molecular layer on the Co surface, which can enable a fast reduction reaction of the polysulfides. Therefore, the prepared “branch-leaf” CNF-L@Co/S electrode exhibits a high initial specific capacity of 1201 mAh g−1 at 0.1 C and superior rate performance.

scholarly journals Insights on forming N,O-coordinated Cu single-atom catalysts for electrochemical reduction CO2 to methane

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Yanming Cai ◽  
Jiaju Fu ◽  
Yang Zhou ◽  
Yu-Chung Chang ◽  
Qianhao Min ◽  
...  
Keyword(s):  
Energy Barrier ◽  
Active Sites ◽  
Theoretical Calculations ◽  
High Energy ◽  
Single Atom ◽  
Faradaic Efficiency ◽  
High Energy Barrier ◽  
Catalytic Sites ◽  
Electron Reduction ◽  
First Time

AbstractSingle-atom catalysts (SACs) are promising candidates to catalyze electrochemical CO2 reduction (ECR) due to maximized atomic utilization. However, products are usually limited to CO instead of hydrocarbons or oxygenates due to unfavorable high energy barrier for further electron transfer on synthesized single atom catalytic sites. Here we report a novel partial-carbonization strategy to modify the electronic structures of center atoms on SACs for lowering the overall endothermic energy of key intermediates. A carbon-dots-based SAC margined with unique CuN2O2 sites was synthesized for the first time. The introduction of oxygen ligands brings remarkably high Faradaic efficiency (78%) and selectivity (99% of ECR products) for electrochemical converting CO2 to CH4 with current density of 40 mA·cm-2 in aqueous electrolytes, surpassing most reported SACs which stop at two-electron reduction. Theoretical calculations further revealed that the high selectivity and activity on CuN2O2 active sites are due to the proper elevated CH4 and H2 energy barrier and fine-tuned electronic structure of Cu active sites.

scholarly journals Brief Overview of Ice Nucleation

Molecules ◽  
2021 ◽  
Vol 26 (2) ◽  
pp. 392
Author(s):  
Nobuo Maeda
Keyword(s):  
Molecular Level ◽  
Ice Nucleation ◽  
Nucleation Theory ◽  
Classical Nucleation Theory ◽  
Radiation Balance ◽  
Feature Article ◽  
Aircraft Wings ◽  
Food Engineering ◽  
Research Activities ◽  
Important Field

The nucleation of ice is vital in cloud physics and impacts on a broad range of matters from the cryopreservation of food, tissues, organs, and stem cells to the prevention of icing on aircraft wings, bridge cables, wind turbines, and other structures. Ice nucleation thus has broad implications in medicine, food engineering, mineralogy, biology, and other fields. Nowadays, the growing threat of global warming has led to intense research activities on the feasibility of artificially modifying clouds to shift the Earth’s radiation balance. For these reasons, nucleation of ice has been extensively studied over many decades and rightfully so. It is thus not quite possible to cover the whole subject of ice nucleation in a single review. Rather, this feature article provides a brief overview of ice nucleation that focuses on several major outstanding fundamental issues. The author’s wish is to aid early researchers in ice nucleation and those who wish to get into the field of ice nucleation from other disciplines by concisely summarizing the outstanding issues in this important field. Two unresolved challenges stood out from the review, namely the lack of a molecular-level picture of ice nucleation at an interface and the limitations of classical nucleation theory.

scholarly journals Efficiency of immersion mode ice nucleation on surrogates of mineral dust

2007 ◽  
Vol 7 (19) ◽  
pp. 5081-5091 ◽  
Author(s):  
C. Marcolli ◽  
S. Gedamke ◽  
T. Peter ◽  
B. Zobrist
Keyword(s):  
Contact Angle ◽  
Active Sites ◽  
Quantitative Agreement ◽  
Ice Nucleation ◽  
Nucleation Theory ◽  
Classical Nucleation Theory ◽  
Aqueous Suspensions ◽  
Freezing Temperatures ◽  
Good Agreement ◽  
Heterogeneous Ice Nucleation

Abstract. A differential scanning calorimeter (DSC) was used to explore heterogeneous ice nucleation of emulsified aqueous suspensions of two Arizona test dust (ATD) samples with particle diameters of nominally 0–3 and 0–7 μm, respectively. Aqueous suspensions with ATD concentrations of 0.01–20 wt% have been investigated. The DSC thermograms exhibit a homogeneous and a heterogeneous freezing peak whose intensity ratios vary with the ATD concentration in the aqueous suspensions. Homogeneous freezing temperatures are in good agreement with recent measurements by other techniques. Depending on ATD concentration, heterogeneous ice nucleation occurred at temperatures as high as 256 K or down to the onset of homogeneous ice nucleation (237 K). For ATD-induced ice formation Classical Nucleation Theory (CNT) offers a suitable framework to parameterize nucleation rates as a function of temperature, experimentally determined ATD size, and emulsion droplet volume distributions. The latter two quantities serve to estimate the total heterogeneous surface area present in a droplet, whereas the suitability of an individual heterogeneous site to trigger nucleation is described by the compatibility function (or contact angle) in CNT. The intensity ratio of homogeneous to heterogeneous freezing peaks is in good agreement with the assumption that the ATD particles are randomly distributed amongst the emulsion droplets. The observed dependence of the heterogeneous freezing temperatures on ATD concentrations cannot be described by assuming a constant contact angle for all ATD particles, but requires the ice nucleation efficiency of ATD particles to be (log)normally distributed amongst the particles. Best quantitative agreement is reached when explicitly assuming that high-compatibility sites are rare and that therefore larger particles have on average more and better active sites than smaller ones. This analysis suggests that a particle has to have a diameter of at least 0.1 μm to exhibit on average one active site.

Sign in / Sign up

Export Citation Format

Share Document