Fabrication of nanocrystalline Mg2Si via ball milling process: Structural studies

Solvent-Directed Construction of a Nanoporous Metal-Organic Framework with Potential in Selective Adsorption and Separation of Gas Mixtures Studied by Grand Canonical Monte Carlo Simulations

In this report, a microporous metal-organic framework of [Ca(TDC)(DMA)]n (1) and a two-dimensional coordination polymer of [Ca(TDC)(DMF)2 ]n (2), (TDC2- =Thiophene-2,5-dicarboxylate, DMA=N, N'-dimethylacetamide and DMF=N, N'-dimethylformamide) based on Ca(II) were designed by the effect of solvent, and X-ray analysis was performed for the single crystals of 1 and 2. Then, compound 1 was synthesized in three different methods and identified with a set of analyses. Compared to other adsorbents, MOFs are widely used in the field of adsorption and separation of various gases due to a series of distinctive features such as diverse and adjustable structures pores with different dimensions, high porosity and surface area with regular distribution of active sites. Therefore, the ability of 1 to uptake single gases (CH4 , CO2 , C2 H2 , H2, and N2 ) and separation of several binary mixtures of gases (CO2 /CH4 , CO2 /N2 , CO2 /H2 and CO2 /C2 H2 ), were investigated using Grand Canonical Monte Carlo simulations. Volumetric and gravimetric adsorption isotherms in various operating conditions, the isosteric heat of adsorption (qst ), the chemical potential for each thermodynamic state, and snapshots during the simulation process were reported in all cases. The results obtained from the adsorption simulation indicate that compound 1 has a high capacity for uptake of H2 (16 mmol g-1 ) and N2 (12.5 mmol g-1 ), CO2 (6.6 mmol g-1 ), C2 H2 (5 mmol g-1 ) and CH4 (1.5 mmol g-1 ) gases at 1 bar. It also performs well in separating CO2 in binary mixtures, which can be attributed to the presence of open metal sites in nodes of 1 and their electrostatic tendency to interact with CO2 containing the higher quadrupole dipole moment compared to other components of the mixture.

Nano scale zero valent iron production methods applied to contaminated sites remediation: An overview of production and environmental aspects

The nano scale zero valent iron (nZVI) is the most used material in the remediation process. The inclusion of sustainability in the remediation process has also been gaining prominence. Sustainable remediation seeks to consider the environmental, economic and social impacts of remediation. Thus, this article aims to: (i) identify and describe nZVI production methods and (ii) evaluate their environmental aspects. Thus, this research was carried out in two stages. The first consisted of systematic bibliographical research to identify and describe nZVI production methods. In the second stage, an environmental analysis of the methods was performed considering the methodology of life cycle inventory assessment. Based on the inventory analysis, a classification of environmental aspects was performed, which included criteria, icons and a color scale. Nine nZVI production methods were identified, which comprised different technologies and processes. All methods had negative environmental aspects, such as high energy consumption, waste, wastewater generation and atmospheric emissions. In the classification of methods with regard to environmental aspects, the milling method had the best score, and the ultrasonic wave method the worst. Overall, this study contributes significantly to the detailed knowledge of nZVI synthesis methods in relation to production processes and their environmental aspects.

Synthesis of thermoelectric magnesium-silicide pastes for 3D printing, electrospinning and low-pressure spray

In this work, eco-friendly magnesium-silicide (Mg₂Si) semiconducting (n-type) thermoelectric pastes for building components concerning energy-harvesting devices through 3D printing, spray and electrospinning were synthetized and tested for the first time. The Mg₂Si fine powders were obtained through the combination of ball milling and thermal annealing under Ar atmosphere. While the latter process was crucial for obtaining the desired Mg₂Si phase, the ball milling was indispensable for homogenizing and reducing the grain size of the powders. The synthetized Mg₂Si powders exhibited a large Seebeck coefficient of ~ 487 µV/K and were blended with a polymeric solution in different mass ratios to adjust the paste viscosity to the different requirements of 3D printing, electrospinning and low-pressure spray. The materials produced in every single stage of the paste synthesis were characterized by a variety of techniques that unequivocally prove their viability for producing thermoelectric parts and components. These can certainly trigger further research and development in green thermoelectric generators (TEGs) capable of adopting any form or shape with enhanced thermoelectric properties. These green TEGs are meant to compete with common toxic materials such as Bi₂Te₃, PbTe and CoSb that have Seebeck coefficients in the range of ~ 290-700 μV/K, similar to that of the produced Mg₂Si powders and lower than that of 3D printed bulk Mg₂Si pieces, measured to be ~ 4866 μV/K. Also, their measured thermal conductivities proved to be significantly lower (~ 0.2 W/mK) than that reported for Mg₂Si (≥ 4 W/mK). However, it is herein demonstrated that such thermoelectric properties are not stable over time. Pressureless sintering proved to be indispensable, but difficultly achievable by long thermal annealing (even above 32 h) in inert atmosphere at 400 °C, at least for bulk Mg₂Si pieces constituted by a mean grain size of 2-3 μm. Hence, for overcoming this sintering challenge and become the silicide's extrusion viable in the production of bulk thermoelectric parts, alternative pressureless sintering methods will have to be further explored.