Exfoliating silica bilayers via intercalation at the silica/transition metal interface

The growth of the silica (SiO2) bilayer (BL) films on transition metal (TM) surfaces creates a new class of two-dimensional (2D) crystalline, self-contained materials that interact weakly with the TM substrate. The BL-silica/TM heterojunction has shown unique physical and chemical properties that can lead to new chemical reaction mechanisms under the sub-nm confinement and broad potential applications ranging from surface protection, nano transistors, molecular sieves to nuclear waste removal. Novel applications of BL-silica can be further explored as a constituent of van der Waals assembly of 2D materials. Key to these applications is an unmet technical challenge to exfoliate and transfer BL-silica films in a large area from one substrate to another without material damage. In this study, we propose a new exfoliation mechanism based on gas molecule intercalation from density functional theory studies of the BL-silica/TM heterojunction. We found that the intercalation of O atoms and CO molecules at the BL-silica/TM interface weakens the BL-silica – TM hybridization, which results in an exponential decrease of the exfoliation energy against the interface distance, as the coverage of interfacial species increases. This new intercalation mechanism opens up the opportunity for non-damaging exfoliation and transfer of large area silica bilayers.

Acidity and the multiphase chemistry of atmospheric aqueous particles and clouds

The acidity of aqueous atmospheric solutions is a key parameter driving both the partitioning of semi-volatile acidic and basic trace gases and their aqueous-phase chemistry. In addition, the acidity of atmospheric aqueous phases, e.g., deliquesced aerosol particles, cloud, and fog droplets, is also dictated by aqueous-phase chemistry. These feedbacks between acidity and chemistry have crucial implications for the tropospheric lifetime of air pollutants, atmospheric composition, deposition to terrestrial and oceanic ecosystems, visibility, climate, and human health. Atmospheric research has made substantial progress in understanding feedbacks between acidity and multiphase chemistry during recent decades. This paper reviews the current state of knowledge on these feedbacks with a focus on aerosol and cloud systems, which involve both inorganic and organic aqueous-phase chemistry. Here, we describe the impacts of acidity on the phase partitioning of acidic and basic gases and buffering phenomena. Next, we review feedbacks of different acidity regimes on key chemical reaction mechanisms and kinetics, as well as uncertainties and chemical subsystems with incomplete information. Finally, we discuss atmospheric implications and highlight the need for future investigations, particularly with respect to reducing emissions of key acid precursors in a changing world, and the need for advancements in field and laboratory measurements and model tools.

Acidity and the multiphase chemistry of atmospheric aqueous particles and clouds

The acidity of aqueous atmospheric solutions is a key parameter driving both the partitioning of semi-volatile acidic and basic trace gases and their aqueous-phase chemistry. In addition, the acidity of atmospheric aqueous phases, e.g. deliquesced aerosol particles, cloud and fog droplets, is also dictated by aqueous-phase chemistry. These feedbacks between acidity and chemistry have crucial implications for the tropospheric lifetime of air pollutants, atmospheric composition, deposition to terrestrial and oceanic ecosystems, visibility, climate, and human health. Atmospheric research has made substantial progress in understanding feedbacks between acidity and multiphase chemistry during recent decades. This paper reviews the current state of knowledge on these feedbacks with a focus on aerosol and cloud systems, involving both inorganic and organic aqueous-phase chemistry. Here, we describe the impacts of acidity on the phase partitioning of acidic and basic gases and buffering phenomena. Next, we review feedbacks of different acidity regimes on key chemical reaction mechanisms and kinetics, as well as uncertainties and chemical subsystems with incomplete information. Finally, we discuss atmospheric implications and highlight needs for future investigations, particularly with respect to reducing emissions of key acid precursors in a changing world, and needs for advancements of field and laboratory measurements and model tools.

LaMer's 1950 model of particle formation: a review and critical analysis of its classical nucleation and fluctuation theory basis, of competing models and mechanisms for phase-changes and particle formation, and then of its application to silver halide, semiconductor, metal, and metal-oxide nanoparticles

Are classical nucleation theory and the 1950 LaMer model of particle formation supported for a wide range of particle formations, or do competing models in the form of chemical reaction mechanisms have better experimental support? Read on to find out.

Deep Reinforcement Learning of Transition States

Combining reinforcement learning (RL) and molecular dynamics (MD) simulations, we propose a machine-learning approach, called RL‡, to automatically unravel chemical reaction mechanisms. In RL‡, locating the transition state of a...

Visualization of reaction route map and dynamical trajectory in reduced dimension

In the quantum chemical approach, chemical reaction mechanisms are investigated based on a potential energy surface (PES). Automated reaction path search methods enable us to construct a global reaction route...

Revealing the sulfur dioxide emission reductions in China by assimilating surface observations in WRF-Chem

The anthropogenic emission of the sulfur dioxide (SO2) over China has significantly declined as the consequence of clean air actions. In this study, we have developed a new emission inversion system based on a Four-Dimensional Local Ensemble Transform Kalman Filter (4D-LETKF) and the Weather Research and Forecasting model coupled with Chemistry (WRF-Chem) to dynamically update the SO2 emission grid by grid over China by assimilating the ground-based hourly SO2 observations. Sensitivity tests for the assimilation system have been conducted firstly to tune four system parameters: ensemble size, horizontal and temporal localization lengths, and perturbation size. Our results reveal that the same random perturbation factors used throughout the whole model grids with assimilating observations within about 180 km can efficiently optimize the SO2 emission, whereas the ensemble size has only little effect. The temporal localization by assimilating only the subsequent hourly observations can reveal the diurnal variation of the SO2 emission, which is better than that to update the the magnitude of SO2 emission every 12 hours by assimilating all the observations within the 12-hour window. The inverted SO2 emission over China in November 2016 has declined by an average of 49.4 % since 2010, which is well in agreement with the bottom-up estimation of 48.0 %. Larger reductions of SO2 emission are found over the priori higher source regions such as the Yangtze River Delta (YRD). The simulated SO2 surface mass concentrations using two distinguished chemical reaction mechanisms are both much more comparable to the observations with the newly inverted SO2 emission than those with the priori emission. These indicate that the newly developed emission inversion system can efficiently update the SO2 emissions based on the routine surface SO2 observations. The reduced SO2 emission induces the sulfate and PM2.5 surface concentrations to decrease up to 10 μg m−3 over the center China.

Carbonation and Chloride Ions’ Penetration of Alkali-Activated Materials: A Review

Alkali-activated materials (AAMs) are widely recognized as potential alternatives to ordinary Portland cement (OPC) due to their lower carbon footprint. However, like OPC, AAMs can also generate some durable problems when exposed to aggressive environments and the mechanisms and possible improvements are still not fully clear in existing investigations. Furthermore, the corrosion mechanisms of AAMs are different from OPC due to the discrepant reaction products and pore structures. Thus, this study’s aim is to review the chemical reaction mechanisms, factors, and mitigation methods when AAMs are attacked by carbonation and chloride ions, along with a summative discussion regarding instructive insights to durable problems of AAMs.