Impact of Thermochemical Treatments on Electrical Conductivity of Donor-Doped Strontium Titanate Sr(Ln)TiO3 Ceramics.

The remarkable stability, suitable thermomechanical characteristics, and acceptable electrical properties of donor-doped strontium titanates make them attractive materials for fuel electrodes, interconnects, and supports of solid oxide fuel and electrolysis cells (SOFC/SOEC). The present study addresses the impact of processing and thermochemical treatment conditions on the electrical conductivity of SrTiO3-derived ceramics with moderate acceptor-type substitution in a strontium sublattice. A-site-deficient Sr0.85La0.10TiO3-δ and cation-stoichiometric Sr0.85Pr0.15TiO3+δ ceramics with varying microstructures and levels of reduction have been prepared and characterized by XRD, SEM, TGA, and electrical conductivity measurements under reducing conditions. The analysis of the collected data suggested that the reduction process of dense donor-doped SrTiO3 ceramics is limited by sluggish oxygen diffusion in the crystal lattice even at temperatures as high as 1300 °C. A higher degree of reduction and higher electrical conductivity can be obtained for porous structures under similar thermochemical treatment conditions. Metallic-like conductivity in dense reduced Sr0.85La0.10TiO3-δ corresponds to the state quenched from the processing temperature and is proportional to the concentration of Ti3+ in the lattice. Due to poor oxygen diffusivity in the bulk, dense Sr0.85La0.10TiO3-δ ceramics remain redox inactive and maintain a high level of conductivity under reducing conditions at temperatures below 1000 °C. While the behavior and properties of dense reduced Sr0.85Pr0.15TiO3+δ ceramics with a large grain size (10-40 µm) were found to be similar, decreasing grain size down to 1-3 µm results in an increasing role of resistive grain boundaries which, regardless of the degree of reduction, determine the semiconducting behavior and lower total electrical conductivity of fine-grained Sr0.85Pr0.15TiO3+δ ceramics. Oxidized porous Sr0.85Pr0.15TiO3+δ ceramics exhibit faster kinetics of reduction compared to the Sr0.85La0.10TiO3-δ counterpart at temperatures below 1000 °C, whereas equilibration kinetics of porous Sr0.85La0.10TiO3-δ structures can be facilitated by reductive pre-treatments at elevated temperatures.

Ecological and human health impact assessments based on long-term monitoring of soil PAHs near a coal-fired power plant.

The combustion of coal in power plants releases significant amounts of polycyclic aromatic hydrocarbons (PAHs), which are highly toxic and carcinogenic. This study assesses the ecological and human health impacts of PAHs contamination from a coal-fired power plant over 8 years. The monitoring site selection considered the distance from the power plant and the prevailing wind direction in the investigated area. The results reveal that, during the monitoring period, PAH levels increased on average by 43%, 61%, and 37% in the zone of the prevailing wind direction, in the area proximate to the power plant, and the zone distant from it, respectively. The site, which has a radius of 4.5 km in the prevailing wind direction, exhibited the highest ecological and human health impacts. Additionally, a strong correlation was observed between environmental and human health impacts, depending on the distance from the power plant, particularly in areas with the prevailing wind direction. These insights contribute to a comprehensive understanding of the intricate dynamics linking power plant emissions, PAHs contamination, and their far-reaching consequences on the environment and human health.

Ecological consequences of biochar and hydrochar amendments in soil: assessing environmental impacts and influences.

Anthropogenic activities have caused irreversible consequences on our planet, including climate change and environmental pollution. Nevertheless, reducing greenhouse gas (GHG) emissions and capturing carbon can mitigate global warming. Biochar and hydrochar are increasingly used for soil remediation due to their stable adsorption qualities. As soil amendments, these materials improve soil quality and reduce water loss, prevent cracking and shrinkage, and interact with microbial communities, resulting in a promising treatment method for reducing gas emissions from the top layer of soil. However, during long-term studies, contradictory results were found, suggesting that higher biochar application rates led to higher soil CO2 effluxes, biodiversity loss, an increase in invasive species, and changes in nutrient cycling. Hydrochar, generated through hydrothermal carbonization, might be less stable when introduced into the soil, which could lead to heightened GHG emissions due to quicker carbon breakdown and increased microbial activity. On the other hand, biochar, created via pyrolysis, demonstrates stability and can beneficially impact GHG emissions. Biochar could be the preferred red option for carbon sequestration purposes, while hydrochar might be more advantageous for use as a gas adsorbent. This review paper highlights the ecological impact of long-term applications of biochar and hydrochar in soil. In general, using these materials as soil amendments helps establish a sustainable pool of organic carbon, decreasing atmospheric GHG concentration and mitigating the impacts of climate change.

Effect of wood and peanut shell hydrochars on the desiccation cracking characteristics of clayey soils.

Soil cracking can significantly alter the water and nutrient migration pathways in the soil, influencing plant growth and development. While biochar usage has effectively addressed soil cracking, the feasibility of using less energy-intensive hydrochars in desiccating soils remains unexplored. This study investigates the impact of wood and peanut shell hydrochars on the desiccation cracking characteristics of clayey soil. A series of controlled environmental laboratory incubations with regular imaging was conducted to determine crack development's dynamic in unamended and hydrochar-amended soils. The results reveal that the addition of wood hydrochar at 2% and 4% dosage reduced the crack intensity factor (CIF) by 22% and 43%, respectively, compared to the unamended control soil. Similarly, the inclusion of peanut shell hydrochar at 2% and 4% lowered the CIF by 22% and 51%, respectively. The presence of hydrophilic groups on the surface of hydrochars, such as O-H, CH, and C-O-C, enhanced the water retention capacity, as confirmed by Fourier-transform infrared analysis. The CIF decrease is attributed to mitigated water evaporation rates, enabled by enhanced water retention within the hydrochar pore spaces. These findings are supported by scanning electron microscopy analyses of the hydrochar morphology. Despite CIF reduction with hydrochar incorporation, the crack length density (CLD) increased across all hydrochar-amended series. In contrast to unamended soil which exhibited pronounced widening of large cracks and extensive inter-pore voids, the incorporation of hydrochar resulted in higher CLD due to the formation of finer interconnecting crack meshes. Consequently, the unamended control soil suffered greater water loss due to heightened evaporation rates. This study sheds new light on the potential of hydrochars in addressing desiccation-induced soil cracking and its implications for water conservation.

A comparative life cycle assessment of recycling waste concrete powder into CO2-Capture products.

Waste concrete powder (WCP), a byproduct of construction and demolition (C&D), currently has a low degree of recycling despite its potential for environmentally friendly applications. WCP can serve as a valuable substitute for cement, offering advantages for resource conservation and carbon sequestration. However, there are very few studies that quantitatively assess the environmental impact of incorporating WCP into the circular economy as a secondary material instead of disposing of it. The energy-intensive processing of WCP raises questions about the optimal carbonation time using available equipment. This study aims to fill this knowledge gap by employing carbon footprint and life cycle assessments (LCA) to optimize WCP recycling. Three recycling WCP scenarios are analyzed. The first scenario involved the conversion of WCP into compacts that absorb CO2 during the carbonation process. The results of the first scenario revealed that the optimal carbonation time for WCP compacts was 8 h, during which 42.7 kg CO2-e per tonne of WCP compacts was sequestered. The total global warming potential (GWP) was -4.22 kgCO2-e, indicating a carbon-negative recycling process. In the second and third scenarios, LCA was conducted to compare the use of carbonated and uncarbonated WCP as a partial replacement for cement in concrete. In these scenarios, it was found that uncarbonated WCP is a more effective solution for reducing the carbon footprint of traditional concrete mixes, achieving a significant 16% reduction of GWP when 20% of cement is replaced. Conversely, using carbonated WCP as a partial cement replacement in concrete mixtures shows limited potential for CO2 uptake. The sensitivity analysis reveals that the carbon footprint of the WCP compacts production process is strongly influenced by the electricity supplier used.

Influences of phosphorus-modified biochar on bacterial community and diversity in rhizosphere soil.

Root-associated bacteria play a vital role in the soil ecosystem and plant productivity. Previous studies have reported the decline of bacterial community and rhizosphere soil quality in the cultivation of some medicinal plants (i.e., Pseudostellaria heterophylla). Phosphorus (P)-modified biochar has the potential to improve soil health and quality. However, its influence on the bacterial community and diversity in the rhizosphere of medicinal plants is not well understood. Therefore, this study aims to investigate the effects of P-modified biochar on the bacterial community and diversity in the rhizosphere of P. heterophylla. Soil samples were collected from the rhizosphere of 4-month P. heterophylla under control (no biochar), 3% unmodified and 3% P-modified biochar treatments, respectively. Compared with control and unmodified biochar treatment, P-modified biochar significantly increased the relative abundance of plant-beneficial bacteria (P < 0.05), particularly Firmicutes, Nitrospirae and Acidobacteria. The relative abundance of Bacillus, belonging to Firmicutes, was dramatically raised from 0.032% in control group to 1.723% in P-modified biochar-treated group (P < 0.05). These results indicate the potential enhancement of soil quality for the growth of medicinal plants. The application of biochar significantly increased bacterial richness and bacterial diversity (P < 0.05). P modification of biochar did not have significant effects on soil bacterial richness (P > 0.05), while it reduced Shannon and increased Simpson diversity index of soil bacterial communities significantly (P < 0.05). It indicates a decrease in bacterial diversity. This research provides a new perspective for understanding the role of P-modified biochar in the rhizosphere ecosystem.

Effects of phase change material inclusion on reducing greenhouse gas emissions from soil in cold region.

Increased gas emissions from soil into the atmosphere are one form of ecosystem feedback in response to climate change. Soil temperature plays a critical role in the soil emission of carbon dioxide (CO2) and nitrous oxide (N2O) suggesting that the release of gases can be reduced by regulating soil temperature. This study proposes a green microencapsulated phase-change material (mPCM) as a soil temperature regulator due to its ability to absorb and release heat during temperature phase transition. The objective is to test how mPCM in soil mixtures influences CO2 and N2O fluxes under laboratory-controlled conditions. For this purpose, a series of soil incubations were carried out with different temperature regimes and soil moisture. The test results revealed that at 20% soil moisture mPCM reduced cumulative CO2 emissions from the soil by 16.4% during the thawing stage and by 20.5% during the freezing stage. At 25% soil moisture, mPCM showed a greater effect reducing cumulative CO2 emissions by 23.9% during the thawing stage and by 24.2% during the freezing stage. At below-zero temperatures, mPCM reduced the total N2O flux by 11.6% at 20% soil moisture and by 26.0% at 25% soil moisture, compared to soil without mPCM. As soil moisture increased, the effects of mPCM on CO2 and N2O fluxes became more pronounced. Cyclic freezing and thawing of soil led to an increase in gas flux. This variation was reduced by the mPCM due to its ability to mitigate the change of soil temperature. Inhibition of the rise in soil temperature due to the inclusion of mPCM reduced the rate of activation of soil mineralization, which reduced gas fluxes. This study demonstrates the potential of mPCM application to reduce greenhouse gas emissions from soil through thermoregulation.

Dynamics of carbon dioxide emission during cracking in peanut shell biochar-amended soil.

As a primary source of greenhouse gas emissions and a carbon sink, soil plays a key role in climate regulation. The development of cracks in soil strongly influences CO2 emissions, and soil amendment with biochar has been shown to reduce cracking. However, the impact of biochar on CO2 emissions during soil cracking is not well understood. This study investigates the release of CO2 flux during the cracking of peanut shell biochar-amended soil. The biochar-amended soil was incubated at a constant temperature of 35 °C for 160 h with periodic photography and analysis of CO2 concentration and soil moisture. To achieve continuous monitoring of incubation soil, a new coupled sensor was specially designed to measure CO2 concentration and soil moisture, based on the Arduino microcontroller. Measured results reveal that peanut shell biochar reduced the evaporation rate by 29 % compared to unamended soil, resulting in slower soil cracking caused by water loss. The biochar also decreased the shrinkage crack length by 20 % compared to unamended soil. In addition, the crack volume fraction was reduced by 16 % after the peanut shell biochar amendment. Due to the reduction of the soil crack channel openings during drying shrinkage when biochar was applied to the soil, cumulative CO2 fluxes were also reduced by 5 % compared to unamended soil. The presence of biochar induced more stable and larger compounds with the soil particles, which blocked the crack propagation path and inhibited further development of the crack.

Impact of Oxygen Deficiency on the Electrochemical Performance of K2 NiF4 -Type (La1-x Srx )2 NiO4-δ Oxygen Electrodes.

Perovskite-related (La1-x Srx )2 NiO4-δ (x=0.5-0.8) phases were explored for possible use as oxygen electrodes in solid electrolyte cells with a main focus on the effect of oxygen deficiency on the electrocatalytic activity. (La1-x Srx )2 NiO4-δ solid solutions were demonstrated to preserve the K2 NiF4 -type tetragonal structure under oxidizing conditions. Acceptor-type substitution by Sr is compensated by the formation of oxygen vacancies and electron holes and progressively increases high-temperature oxygen nonstoichiometry, which reaches as high as δ=0.40 for x=0.8 at 950 °C in air. The electrical conductivity of (La1-x Srx )2 NiO4-δ ceramics at 500-1000 °C and p(O2 )≥10-3  atm is p-type metallic-like. The highest conductivity, 300 S cm-1 at 800 °C in air, is observed for x=0.6. The average thermal expansion coefficients, (14.0-15.4)×10-6  K-1 at 25-900 °C in air, are sufficiently low to ensure the thermomechanical compatibility with common solid electrolytes. The polarization resistance of porous (La1-x Srx )2 NiO4-δ electrodes applied on a Ce0.9 Gd0.1 O2-δ solid electrolyte decreases with increasing Sr concentration in correlation with the concentration of oxygen vacancies in the nickelate lattice and the anticipated level of mixed ionic-electronic conduction. However, this is accompanied by increasing reactivity between the cell components and necessitates the microstructural optimization of the electrode materials to reduce the electrode fabrication temperature.