Effects of Na/K-Cl Salts on Hydrolysis of Aluminosilicate Glass Using Ab Initio Molecular Dynamics.

The structural and chemical modifications on the surface of pure and alkali-doped aluminosilicate (AS) glasses due to hydrolysis are investigated using ab initio molecular dynamics. The effects of water on the glass network are fully elucidated by analyzing the short- and intermediate-range structural orders embedded in the pair distribution function, bond length and angle distribution, coordination number, and interatomic bonding. A novel concept of total bond order is used to quantify and compare the strength of bonds in hydrated and unhydrated glasses. We show that AS glass is hydrolyzed by water diffusion near the surface and by proton (H+) transfers into the bulk, which increases with time. Hence, a dissolved glass-water interface becomes rich in Si-OH and Al-OH. The alkali ions associated with the nonbridging oxygen accelerate the hydrolysis by facilitating water and H+ diffusion. Al is more impacted by hydrolysis than Si, resulting in greater variation in the Al-O bond order than Si-O. Doping of NaCl and KCl enhances the ionization of water and the hydrolysis of ASs with increased salt concentration. The KCl doping ionizes more water molecules and causes more degradation of the glass network than NaCl. Co-doping of Na and K results in a mixed alkali effect due to complex interatomic bonding from different-sized ions. These exceptionally detailed findings in highly complex glasses with varying salt compositions provide new and unprecedented atomistic insights that can help to understand the hydrolysis and dissolution mechanisms of ASs and other silicate glasses.

The effect of biochar and acid activated biochar on ammonia emissions during manure storage.

Animal manure contains valuable plant nutrients which need to be stored until field application. A significant proportion of slurry nitrogen is volatilized in the form of ammonia (NH3) during storage. This impacts human health, biodiversity, air and water quality and thus urgent action is needed to reduce NH3 emissions. In this experiment, we evaluated the NH3 emission mitigation potential of biochars derived from miscanthus (MB) and solid separated anaerobic digestate (DB), and orthophosphoric acid activated MB (AMB) and DB (ADB) as well as lightweight expanded clay aggregate (LECA) during four months of liquid manure storage. A slurry without amendment was included as a control (Ctrl). Acid activated and non-activated biochars were applied on top of the slurry maintaining a 7 mm thick surface layer, while LECA was applied in a 2 cm thick layer. NH3 emissions were measured by photoacoustic analyzer. In comparison to Ctrl, acid activated biochar decreased (p < 0.05) NH3 emissions during the slurry storage. Activated biochar reduced the emissions by 37-51% within the first month of slurry storage and achieved a 25-28% emissions reduction efficiency throughout the four month period due to the reduction in emission mitigation efficiency as the storage period progressed. LECA reduced NH3 emissions by 21% during storage. Losses of NH3 as a percentage of total ammoniacal N were 29-31% for activated biochars, 35-39% for non-activated biochars and 33% for LECA. In conclusion, acid activated biochars and LECA could be good floating-covers to mitigate NH3 emissions during manure storage, but activated biochars may have better mitigation potential than LECA.

First-Principles Calculations of Thermoelectric Transport Properties of Quaternary and Ternary Bulk Chalcogenide Crystals.

Chalcogenide crystals have a wide range of applications, especially as thermoelectric materials for energy conversion. Thermoelectric materials can be used to generate an electric current from a temperature gradient based on the Seebeck effect and based on the Peltier effect, and they can be used in cooling applications. Using first-principles calculations and semiclassical Boltzmann theory, we have computed the Seebeck coefficient, electrical conductivity, electronic thermal conductivity, power factor, and figure of merit of 30 chalcogenide crystals. A Quantum Espresso package is used to calculate the electronic properties and locate the Fermi level. The transport properties are then calculated using the BoltzTraP code. The 30 crystals are divided into two groups. The first group has four crystals with quaternary composition (A2BCQ4) (A = Tl; B = Cd, Hg; C = Si, Ge, Sn; Q = S, Se, Te). The second group contains 26 crystals with the ternary composition (A'B'Q2) (A' = Ag, Cu, Au, Na; B' = B, Al, Ga, In; Q = S, Se, Te). Among these 30 chalcogenide crystals, the results for 11 crystals: Tl2CdGeSe4, Tl2CdSnSe4, Tl2HgSiSe4, Tl2HgSnS4, AuBSe2, AuBTe2, AuAlTe2, AuGaTe2, AuInTe2, AgAlSe2, and AgAlTe2 are revealed for the first time. In addition, temperature-dependent transport properties of pure and doped AgSbSe2 and AgSbTe2 crystals with dopant compositions of AgSb0.94Cd0.06Te2 and AgSbTe1.85Se0.15 were explored. These results provide an excellent database for bulk chalcogenides crucial for a wide range of potential applications in renewable energy fields.

Interactive effects of straw management, tillage, and a cover crop on nitrous oxide emissions and nitrate leaching from a sandy loam soil.

Minimum tillage, residue recycling and the use of cover crops are key elements of conservation agriculture that play important roles in soil carbon (C) and nitrogen (N) dynamics. This study determined the long-term effects of tillage practice (conventional ploughing vs. direct seeding), straw management (retained vs. removed), and the presence of a cover crop (CC; fodder radish in this study) on nitrous oxide (N2O) emissions, nitrate (NO3-) leaching, and soil mineral N dynamics between October 2019 and June 2020. In the factorial experiment with eight treatment combinations, cumulative N2O emissions ranged from 0.04 to 0.8 kg N ha-1, whereas NO3- leaching varied between 4 and 28 kg N ha-1. The study did not find effects of straw retention on NO3- leaching or N2O emissions. No-till reduced N2O emissions by on average 46% compared to ploughing. Fodder radish reduced NO3- leaching by 80-84%, and there was little N2O emission in the presence of the cover crop; however, after termination in spring there was a flush of N2O, cumulative N2O-N averaged 0.1 and 0.5 kg N ha-1 without and with a cover crop. With information about long-term soil C retention from straw and fodder radish, an overall greenhouse (GHG) balance was calculated for each system. Without straw retention after harvest, there was always a positive net GHG emission, and the indirect N2O emission from NO3- leaching was similar to, or greater than direct N2O emissions. However, in the presence of fodder radish, the direct N2O emissions after termination were much more important than indirect emissions, and negated the C input from fodder radish. Direct seeding, straw retention and the use of a cover crop showed positive effects on N retention and/or GHG balance and could substantially improve the carbon footprint of agroecosystems on sandy soil in a wet temperate climate.

Long-term variability in N2O emissions and emission factors for corn and soybeans induced by weather and management at a cold climate site.

Nitrous oxide (N2O) emissions are highly variable in space and time due to the complex interplay between soil, management practices and weather conditions. Micrometeorological techniques integrate emissions over large areas at high temporal resolution. This allows identification of causes of intra- and inter-annual variability of N2O emissions and development of robust emission factors (EF). Here, we investigated factors responsible for variability in N2O emissions during growing and non-growing seasons of corn and soybeans grown in an imperfectly drained silt loam soil, in Ontario, Canada. We used quasi-continuously (at half-hourly to hourly intervals) N2O fluxes measured via the flux-gradient technique over 11 years for corn and 5 years for soybeans and evaluated the uncertainty of default IPCC and Canada-specific EFs. In the growing season, emissions were controlled by soil nitrate content, soil moisture and temperature in the fertilized corn, while moisture and temperature regulated N2O emissions in the unfertilized soybeans. In the non-growing season, nitrogen (N) input from the crop residue did not affect the emissions, pointing to freeze-thaw cycles as mechanisms for enhanced N2O emissions. The non-growing season contribution to annual emissions was 38% in corn and 43% in soybeans. On average, annual emissions were 2.6-fold higher in corn than soybeans. Observed mean N2O EFs were 0.84% (0.12-2.02%) for growing season and 1.69% (0.29-7.32%) for yearly emissions. The growing season EF derived from long-term N2O emissions was 0.9 ± 0.14%. The interannual variability in N2O emissions and EFs can be attributed to management practices and annual weather variability. The default IPCC approach based on overall N input had poorer performance in predicting annual N2O emissions compared to the current Canadian methodology, which includes management and environmental factor in addition to N inputs. The observed emissions were further evaluated with a newly developed growing season N2O emission prediction approach for Canada. However, performance of the approach was poorer than IPCC or the current national Canadian approach. Additional tests of the new national methodology are recommended as well as consideration of non-growing season emissions.

Solvent Effect on the Structure and Properties of RGD Peptide (1FUV) at Body Temperature (310 K) Using Ab Initio Molecular Dynamics.

The structure and properties of the arginine-glycine-aspartate (RGD) sequence of the 1FUV peptide at 0 K and body temperature (310 K) are systematically investigated in a dry and aqueous environment using more accurate ab initio molecular dynamics and density functional theory calculations. The fundamental properties, such as electronic structure, interatomic bonding, partial charge distribution, and dielectric response function at 0 and 310 K are analyzed, comparing them in dry and solvated models. These accurate microscopic parameters determined from highly reliable quantum mechanical calculations are useful to define the range and strength of complex molecular interactions occurring between the RGD peptide and the integrin receptor. The in-depth bonding picture analyzed using a novel quantum mechanical metric, the total bond order (TBO), quantifies the role played by hydrogen bonds in the internal cohesion of the simulated structures. The TBO at 310 K decreases in the dry model but increases in the solvated model. These differences are small but extremely important in the context of conditions prevalent in the human body and relevant for health issues. Our results provide a new level of understanding of the structure and properties of the 1FUV peptide and help in advancing the study of RGD containing other peptides.

Temperature-Dependent Properties of Molten Li2BeF4 Salt Using Ab Initio Molecular Dynamics.

Molten lithium tetrafluoroberyllate (Li2BeF4) salt, also known as FLiBe, with a 2:1 mixture of LiF and BeF2 is being proposed as a coolant and solvent in advanced nuclear reactor designs, such as the molten salt reactor or the fluoride salt cooled high-temperature reactor. We present the results on the structure and properties of FLiBe over a wide range of temperatures, 0-2000 K, from high-throughput ab initio molecular dynamics simulation using a supercell model of 504 atoms. The variations in the local structures of solid and liquid FLiBe with temperature are discussed in terms of a pair distribution function, coordination number, and bond angle distribution. The temperature-dependent electronic structure and optical and mechanical properties of FLiBe are calculated. The optical and mechanical property results are reported for the first time. The results above and below the melting temperature (∼732 K) are compared with the experimental data and with data for crystalline FLiBe. The electronic structure and interatomic bonding results are discussed in correlation with the mechanical strength. A novel concept of total bond order density (TBOD), an important quantum mechanical parameter, is used to characterize the internal cohesion and strength in the simulated models. The results show a variation in the rate of change in properties in solid and liquid phases with anomalous behavior across the melting region. The observed trend is the decrease in mechanical strength, band gap, and TBOD in a nonlinear fashion as a function of temperature. The refractive index shows a surprising minimum at 850 K, among the tested temperatures, which lies above the melting point. These findings provide a new platform to understand the interplay between the temperature-dependent structures and properties of FLiBe salt.

Structural and physical properties of 99 complex bulk chalcogenides crystals using first-principles calculations.

Chalcogenide semiconductors and glasses have many applications in the civil and military fields, especially in relation to their electronic, optical and mechanical properties for energy conversion and in enviormental materials. However, they are much less systemically studied and their fundamental physical properties for a large class chalcogenide semiconductors are rather scattered and incomplete. Here, we present a detailed study using well defined first-principles calculations on the electronic structure, interatomic bonding, optical, and mechanical properties for 99 bulk chalcogenides including thirteen of these crytals which have never been calculated. Due to their unique composition and structures, these 99 bulk chalcogenides are divided into two main groups. The first group contains 54 quaternary crystals with the structure composition (A2BCQ4) (A = Ag, Cu; B = Zn, Cd, Hg, Mg, Sr, Ba; C = Si, Ge, Sn; Q = S, Se, Te), while the second group contains scattered ternary and quaternary chalcogenide crystals with a more diverse composition (AxByCzQn) (A = Ag, Cu, Ba, Cs, Li, Tl, K, Lu, Sr; B = Zn, Cd, Hg, Al, Ga, In, P, As, La, Lu, Pb, Cu, Ag; C = Si, Ge, Sn, As, Sb, Bi, Zr, Hf, Ga, In; Q = S, Se, Te; [Formula: see text], 2, 3; [Formula: see text], 1, 2, 5; [Formula: see text], 1, 2 and [Formula: see text], 4, 5, 6, 9). Moreover, the total bond order density (TBOD) is used as a single quantum mechanical metric to characterize the internal cohesion of these crystals enabling us to correlate them with the calculated properties, especially their mechanical properties. This work provides a very large database for bulk chalcogenides crucial for the future theoretical and experimental studies, opening opportunities for study the properties and potential application of a wide variety of chalcogenides.

Ab Initio Study of Hydrolysis Effects in Single and Ion-Exchanged Alkali Aluminosilicate Glasses.

Hydrolysis in alkali-doped aluminosilicate glasses is one of the most complicated mechanisms in glass science. There remain many fundamental and unresolved issues with implications on their potential applications. Herein, we address this challenge by carrying out detailed calculations on the structure and properties of both anhydrate (dry) and hydrated alkali aluminosilicate glasses on carefully constructed models. Specifically, the Na-, (Na + K)-, and K-doped aluminosilicate glasses with compositions (SiO2)0.6(Al2O3)0.2(Na2O)0.2 - x(K2O)x (x = 0, 0.10, and 0.20) are simulated using ab initio molecular dynamics (AIMD). The local short- and intermediate-range order in these glasses is analyzed in terms of atomic pair distribution, coordination number, bond length, and bond angle distributions to delineate the subtle variations due to different alkali sizes and hydrolysis. The electronic structure, interatomic bonding, mechanical, and optical properties for these models are calculated and validated with available experimental data. We use the novel concept of total bond order density (TBOD), the quantum mechanically derived metric, to characterize the internal cohesion and strength in the simulated glasses. Detailed analysis of the hydrolysis mechanism enables us to provide information on the complex interplay of various participating elements and their interactions at the atomic level. Such detailed information provides a new platform of knowledge, which is crucial for understanding the issues related to glass corrosion and durability, and ways and means for their special applications in commercial glass products. Both undissociated molecular water and dissociated water in the form of hydroxyl groups exist in the hydrated models in the presence of alkali ions. For the first time, we observed the opposite mixed alkali effect in the Poisson's ratio for anhydrate and hydrated glasses.

Nitrate leaching and nitrous oxide emissions from maize after grass-clover on a coarse sandy soil: Mitigation potentials of 3,4-dimethylpyrazole phosphate (DMPP).

Cropping of maize (Zea mays L.) on sandy soil in wet climates involves a significant risk for nitrogen (N) losses, since nitrate added in fertilizers or produced from residues and manure may be lost outside the period with active crop N uptake. This one-year lysimeter experiment investigated the potential of Vizura®, a formulation for liquid manure (slurry) with the nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP), to mitigate nitrous oxide (N2O) emissions and nitrate (NO3-) leaching from a coarse sandy soil cropped with maize. Maize followed grass-clover (Lolium perenne L.-Trifolium pratense L.) with spring incorporation and was fertilised with cattle slurry. A total of 12 treatments in triplicate were included in a factorial experiment with 1 m2 large and 1.4 m deep lysimeters: 1) with or without spraying the above-ground biomass of grass-clover with DMPP before incorporation; 2) application of cattle manure with or without DMPP, or no fertilization; and 3) natural rainfall or extra rain events to represent wet spring conditions, which were simulated with an automated and programmable irrigation system. Around 20 kg N ha-1 was returned to the soil in grass-clover above-ground biomass, and 145 kg N ha-1 in cattle manure. Cumulative annual N2O emissions ranged from 0.4 to 1.3 kg N ha-1, with between 49 and 86% of emissions occurring during spring. Manure application increased N2O emissions, while extra rainfall had no effect. The mitigation of N2O emissions by DMPP ranged from 46 to 67% under natural, and from 44 to 48% under high rainfall conditions. Total annual NO3- leaching ranged from 65 to 162 kg N ha-1. The extent of NO3- leaching to 1.4 m depth during spring was low, and instead most (72-83%) of total annual NO3--N leaching was recorded during autumn before harvest. The extra rainfall during spring increased NO3--N leaching in the pre-harvest period, but it is not clear to what extent this was associated with the N in grass-clover residues or manure applied in spring, or from N mineralisation below the root zone. Despite evidence for a reduction of NO3- leaching in three of four scenarios, overall this effect was not significant. No DMPP was detected in leachates. In conclusion, DMPP significantly reduced N2O emissions from cattle manure on this sandy loam soil independent of rainfall, while there was no significant effect on NO3- leaching. The results indicate that N2O emissions and NO3--N leaching were partly derived from below-ground sources of N not affected by DMPP, which should be further investigated to better predict the mitigation potential of nitrification inhibitors.

Interfacial Interaction between Suolunite Crystal and Silica Binding Peptide for Novel Bioinspired Cement.

Cement and concrete have been important construction materials throughout human history. There is an urgent need to explore novel and untraditional cementitious materials to enhance the durability of building materials and structures in response to increased infrastructure demand worldwide. We report an exploratory study on a biocomposite cement based on a large-scale computational study using density functional theory. An explicitly solvated mixture of a mineral calcium silicate hydrate (C-S-H) crystal suolunite (Ca2Si2O5(OH)2·H2O) and a silicon binding peptide with amino acid sequence PRO-PRO-PRO-TRP-LEU-PRO-TYR-MET-PRO-PRO-TRP-SER is constructed using ab initio molecular dynamics (AIMD). Detailed analysis on the interface structure, interatomic bonding, mechanical properties, and solvent effect of this model reveals a complex interplay of different types of covalent and ionic bonding, including ubiquitous hydrogen bonding which plays a crucial role in their properties. The use of the total bond order density (TBOD), a single quantum mechanical metric, for assessing the interfacial cohesion for this composite biocement is proposed. We find that the solvated model has a slightly larger TBOD than the dried one. These results could lead to a systematic search and rational design for different types of bioinspired and hybrid functional materials with other inorganic minerals and organic peptides.

Ab Initio Modeling of Structure and Properties of Single and Mixed Alkali Silicate Glasses.

A density functional theory (DFT)-based ab initio molecular dynamics (AIMD) has been applied to simulate models of single and mixed alkali silicate glasses with two different molar concentrations of alkali oxides. The structural environments and spatial distributions of alkali ions in the 10 simulated models with 20% and 30% of Li, Na, K and equal proportions of Li-Na and Na-K are studied in detail for subtle variations among the models. Quantum mechanical calculations of electronic structures, interatomic bonding, and mechanical and optical properties are carried out for each of the models, and the results are compared with available experimental observation and other simulations. The calculated results are in good agreement with the experimental data. We have used the novel concept of using the total bond order density (TBOD), a quantum mechanical metric, to characterize internal cohesion in these glass models. The mixed alkali effect (MAE) is visible in the bulk mechanical properties but not obvious in other physical properties studied in this paper. We show that Li doping deviates from expected trend due to the much stronger Li-O bonding than those of Na and K doping. The approach used in this study is in contrast with current studies in alkali-doped silicate glasses based only on geometric characterizations.

Dietary Nitrate for Methane Mitigation Leads to Nitrous Oxide Emissions from Dairy Cows.

Nitrate supplements to cattle diets can reduce enteric CH emissions. However, if NO metabolism stimulates NO emissions, the effectiveness of dietary NO for CH mitigation will be reduced. We quantified NO emissions as part of a dairy cow feeding experiment in which urea was substituted in nearly iso-N diets with 0, 5, 14 or 21 g NO kg dry matter (DM). The feeding experiment was a Latin square with repetition of Period 1. Each period lasted 4 wk, with CH emission measurements in Week 4 using respiration chambers. During Period 3, NO concentrations in chamber outlet air were monitored semicontinuously during 48 h. High, but fluctuating, NO concentrations were seen at the two highest NO levels (up to between 2 and 5 µL L), and dynamics were linked with recent feed intake. In Periods 4 and 5, NO concentrations and feed intake were determined from all four respiration chambers during two 7-h periods. Emissions of NO coincided with feed intake, again with NO concentrations in the microliter per liter range at the two highest NO intake levels. Neither feed nor excretion of NO via urine were significant sources of NO, indicating that emissions came from the animals. Leakages due to rumen fistulation could also not account for NO emissions. The possibility that NO is produced in the oral cavity is discussed. Nitrous oxide emission factors ranged between 0.7 and 1.0% except in one case at 21 g NO kg DM, where it was 3.4%. When accounting for NO emissions at the highest NO intake level, the overall GHG mitigation effect in two different animal-diet combinations changed from -47 to -40%, and from -19 to -17%, respectively, due to NO emissions.