Search Results (768)

This work aims to perform a detailed mineralogical, crystal-chemical, and geochemical characterization of bentonites from the Benavila outcrop, the largest known deposit of bentonites in continental Portugal. Bulk samples and different size fractions were characterized through X-Ray Diffraction (XRD). Structural formulae of the smectites were fitted from point analyses acquired by analytical electron microscopy (AEM) with transmission electron microscopy (TEM). Smectites are the major component with variable amounts of calcite and minor amounts of quartz, feldspar, illite, and chlorite. Occasionally, amphiboles and dolomite have also been identified. The high content of carbonates in different parts of the sampling area is related to the circulation of carbonate-rich fluids. The smectites present high-layer charge, are intermediate terms of the montmorillonite–beidellite series, and also show an intermediate cisvacant–transvacant configuration. Major and trace elements concentrations were determined by ICP-MS. The geochemical analysis of the samples indicates an enrichment in SiO₂ and Al₂O₃ and a depletion of the more clayey materials in REE, HFSE, and Y, among others. The calculation of the PIA and CIA alteration indices, along with other parameters observed, shows the possible alteration pathways of the Benavila deposit. Research to evaluate the ability of these bentonites to be used as engineering barrier systems (EBS) and sealing materials for radioactive waste repositories is ongoing. Full article

Carbon fiber-reinforced plastics (CFRPs) offer excellent in-plane mechanical performance, but their relatively low interlaminar fracture toughness makes them vulnerable to delamination, particularly around intralaminar discontinuities such as resin-rich regions or fiber gaps. This study investigates the effectiveness of polyamide (PA) mesh inserts in improving interlaminar toughness and suppressing delamination in CFRP laminates with such features. Two PA mesh configurations were evaluated: a fully embedded continuous layer and a 20 mm cut mesh strip placed between continuous and discontinuous plies near critical regions. Fracture toughness tests showed that PA mesh insertion improved interlaminar toughness approximately 2.4-fold compared to neat CFRP, primarily due to a mechanical interlocking mechanism that disrupts crack propagation and enhances energy dissipation. Uniaxial tensile tests with digital image correlation revealed that while initial matrix cracking occurred at similar stress levels, the stress at which complete delamination occurred was approximately 60% higher in specimens with a 20 mm mesh and up to 92% higher in specimens with fully embedded mesh. The fully embedded mesh provided consistent delamination resistance across the laminate, while the 20 mm insert localized strain redistribution and preserved global mechanical performance. These findings demonstrate that PA mesh is an effective interleaving material for enhancing damage tolerance in CFRP laminates with internal discontinuities. Full article

The increasing demand for rapid, sensitive, and eco-friendly methods for the detection of trace heavy metals in environmental samples, attributed to their serious threats to health and the environment, has spurred considerable interest in the development of sustainable sensor materials. Toxic metal ions, namely, lead (Pb²⁺), cadmium (Cd²⁺), mercury (Hg²⁺), arsenic (As³⁺), and chromium, are potential hazards due to their non-biodegradable nature with high toxicity, even at trace levels. Acute health complications, including neurological, renal, and developmental disorders, arise upon exposure to such metal ions. To monitor and mitigate these toxic exposures, sensitive detection techniques are essential. Pre-existing conventional detection methods, such as atomic absorption spectroscopy (AAS) and inductively coupled plasma-mass spectrometry (ICP-MS), involve expensive instrumentation, skilled operators, and complex sample preparation. Electrochemical sensing, which is simple, portable, and eco-friendly, is foreseen as a potential alternative to the above conventional methods. Carbon-based nanomaterials play a crucial role in electrochemical sensors due to their high conductivity, stability, and the presence of surface functional groups. Biochar (BC), a carbon-rich product, has emerged as a promising electrode material for electrochemical sensing due to its high surface area, sustainability, tunable porosity, surface rich in functional groups, eco-friendliness, and negligible environmental footprint. Nevertheless, broad-spectrum studies on the use of biochar in electrochemical sensors remain narrow. This review focuses on the recent advancements in the development of biochar-based electrochemical sensors for the detection of toxic heavy metals such as Pb²⁺, Cd²⁺, and Hg²⁺ and the simultaneous detection of multiple ions, with special emphasis on BC synthesis routes, surface modification methodologies, electrode fabrication techniques, and electroanalytical performance. Finally, current challenges and future perspectives for integrating BC into next-generation sensor platforms are outlined. Full article

Biochar, a carbon-rich material derived from biomass, presents a sustainable solution to several pressing challenges in U.S. agriculture, including soil degradation, carbon emissions, and waste management. Despite global advancements, the U.S. biochar market remains underexplored in terms of economic viability, adoption potential, and sector-specific applications. This narrative review synthesizes two decades of literature to examine biochar’s applications, production methods, and market dynamics, with a focus on its economic and environmental role within the United States. The review identifies biochar’s multifunctional benefits: enhancing soil fertility and crop productivity, sequestering carbon, reducing greenhouse gas emissions, and improving water quality. Recent empirical studies also highlight biochar’s economic feasibility across global contexts, with yield increases of up to 294% and net returns exceeding USD 5000 per hectare in optimized systems. Economically, the global biochar market grew from USD 156.4 million in 2021 to USD 610.3 million in 2023, with U.S. production reaching ~50,000 metric tons annually and a market value of USD 203.4 million in 2022. Forecasts project U.S. market growth at a CAGR of 11.3%, reaching USD 478.5 million by 2030. California leads domestic adoption due to favorable policy and biomass availability. However, barriers such as inconsistent quality standards, limited awareness, high costs, and policy gaps constrain growth. This study goes beyond the existing literature by integrating market analysis, SWOT assessment, cost–benefit findings, and production technologies to highlight strategies for scaling biochar adoption. It concludes that with supportive legislation, investment in research, and enhanced supply chain transparency, biochar could become a pivotal tool for sustainable development in the U.S. agricultural and environmental sectors. Full article

The widespread adoption of sodium-ion batteries (SIBs) remains constrained by the inherent limitations of conventional anode materials, particularly their inadequate electronic conductivity, limited active sites, and pronounced structural degradation during cycling. To overcome these limitations, we propose a novel redox engineering approach to fabricate oxygen-vacancy-rich SnO₂ dots anchored on reduced graphene oxide (rGO), which are encapsulated within N-doped carbon nanofibers (denoted as ov-SnO₂/rGO@N-CNFs) through electrospinning and subsequent carbonization. The introduction of rich oxygen vacancies establishes additional sodium intercalation sites and enhances Na⁺ diffusion kinetics, while the conductive N-doped carbon network effectively facilitates charge transport and mitigates SnO₂ aggregation. Benefiting from the well-designed architecture, the hierarchical ov-SnO₂/rGO@N-CNFs electrode achieves remarkable reversible specific capacities of 351 mAh g⁻¹ after 100 cycles at 0.1 A g⁻¹ and 257.3 mAh g⁻¹ after 2000 cycles at 1.0 A g⁻¹ and maintains 177 mAh g⁻¹ even after 8000 cycles at 5.0 A g⁻¹, demonstrating exceptional long-term cycling stability and rate capability. This work offers a versatile design strategy for developing high-performance anode materials through synergistic interface engineering for SIBs. Full article

Benzoxazine resins are gaining attention for their impressive thermal stability, low water uptake, and strong mechanical properties. In this work, two new bio-based benzoxazine monomers were developed using renewable arbutin: one combined with 3-(2-aminoethylamino) propyltrimethoxysilane (AB), and the other with furfurylamine (AF). Both were synthesized using a simple Mannich-type reaction and verified through FT-IR and ¹H-NMR spectroscopy. By blending these monomers in different ratios, copolymers with adjustable thermal, dielectric, and surface characteristics were produced. Thermal analysis showed that the materials had broad processing windows and cured effectively, while thermogravimetric testing confirmed excellent heat resistance—especially in AF-rich blends, which left behind more char. The structural changes obtained during curing process were monitored using FT-IR, and XPS verified the presence of key elements like carbon, oxygen, nitrogen, and silicon. SEM imaging revealed that AB-based materials had smoother surfaces, while AF-based ones were rougher; the copolymers fell in between. Dielectric testing showed that increasing AF content raised both permittivity and loss, and contact angle measurements confirmed that surfaces ranged from water-repellent (AB) to water-attracting (AF). Overall, these biopolymers (AB/AF copolymers) synthesized from arbutin combine environmental sustainability with customizability, making them strong candidates for use in electronics, protective coatings, and flame-resistant composite materials. Full article

The increasing need for sustainable valorization of fossil-based and waste-derived materials has gained interest in converting complex organic matrices such as kerogen into valuable chemicals. This study explores a two-step oxidative strategy to decompose and valorize kerogen-rich oil shale, aiming to develop a locally based source of aliphatic dicarboxylic acids (DCAs). The method combines air oxidation with subsequent nitric acid treatment to enable selective breakdown of the organic structure under milder conditions. Air oxidation was conducted at 165–175 °C using 1% KOH as an alkaline promoter and 40 bar oxygen pressure (or alternatively 185 °C at 30 bar), targeting 30–40% carbon conversion. The resulting material was then subjected to nitric acid oxidation using an 8% HNO₃ solution. This approach yielded up to 23% DCAs, with pre-oxidation allowing a twofold reduction in acid dosage while maintaining efficiency. However, two-step oxidation was still accompanied by substantial degradation of the structure, resulting in elevated CO₂ formation, highlighting the need to balance conversion and carbon retention. The process offers a possible route for transforming solid fossil residues into useful chemical precursors and supports the advancement of regionally sourced, sustainable DCA production from unconventional raw materials. Full article

Depending on the feedstock type and the pyrolysis conditions, biochars exhibit different physical, chemical, and structural properties, which highly influence their performance in various applications. This study presents a comprehensive characterization of biochar materials derived from the waste wood of pine (Pinus sylvestris L.) and beech (Fagus sylvatica) after low-temperature pyrolysis at 270 °C, followed by chemical activation using zinc chloride. The resulting materials were thoroughly analyzed in terms of their chemical composition (FTIR), thermal behavior (TGA/DTG), structural morphology (SEM and XRD), elemental analysis, and particle size distribution. The successful modification of raw biomass into carbon-rich structures of increased aromaticity and thermal stability was confirmed. Particle size analysis revealed that the activated carbon of Fagus sylvatica (FSAC) exhibited a monomodal distribution, indicating high homogeneity, whereas Pinus sylvestris-activated carbon showed a distinct bimodal distribution. This heterogeneity was supported by elemental analysis, revealing a higher inorganic content in pine-activated carbon, likely contributing to its dimensional instability during activation. These findings suggest that the uniform morphology of beech-activated carbon may be advantageous in filtration and adsorption applications, while pine-activated carbon’s heterogeneous structure could be beneficial for multifunctional systems requiring variable pore architectures. Overall, this study underscored the potential of chemically activated biochar from lignocellulosic residues for customized applications in environmental and material science domains. Full article

As a carbon-rich material with sufficient inorganic nutrients, biochar is potentially an inexpensive and suitable additive to improve the quality of soil and achieve sustainable agriculture. However, the addition of biochar generally increases pesticide adsorption in soil because of the well-maintained porous structure, and the specific effects of the properties of biochar, soil, and pesticides on the adsorption capacity of pesticides remain unknown. In this study, a meta-analysis was conducted to investigate the effects of biochar addition on pesticide adsorption in soils, focusing on characteristics such as the biochar addition dosage, biochar properties (pH, specific surface area (SSA), pore diameter, (O+N)/C, H/C), and soil properties (texture, initial pH, cation exchange capacity). Overall, wood-derived biochar that was treated at ≥700 °C for 2–4 h, with a pH of 9–10 and a 2–4% addition rate led to the greatest enhancement in the pesticide adsorption capacity of soil. Additionally, the pyrolysis temperature of the biochar, the biochar’s pore diameter, and the soil’s pH significantly influenced the adsorption capacity. Based on this meta-analysis, we conclude that the (O+N)/C ratio of biochar is the most influential predictor of soil’s pesticide adsorption capacity. Full article

Oyster shells, though rich in calcium, are mostly discarded and contribute to environmental issues. Developing calcium-based materials with antimicrobial functionality offers a promising solution. However, their low bioavailability limits their direct use, requiring processing to enhance their applicability. Therefore, this study aims to evaluate the physicochemical properties and antimicrobial activity of thermally processed pulverized oyster shells (TPOS) and citric acid-treated TPOS (TPOSc) compared with those of fibrous calcium carbonate (FCC) and coral-derived calcium product (CCP), which are used as reference materials. The solubility values were 0.7 mg/g for FCC, 0.5 mg/g for TPOS, 0.4 mg/g for TPOSc, and 0.05 mg/g for CCP. The average particle sizes were 476 (FCC), 1000 (TPOS and TPOSc), and 1981 nm (CCP). Scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD) analyses revealed calcium ion release and structural changes in TPOS and TPOSc. Antibacterial testing further confirmed that these samples exhibited significant antimicrobial activity. Furthermore, to assess their practical applicability, TPOS and TPOSc samples with antimicrobial properties were incorporated into rice cakes. All samples retained antimicrobial activity at 0.3 wt%, while higher concentrations led to deterioration in their textural properties. These findings support the potential of thermally processed oyster shell powders for food applications that require microbial control with minimal impact on product quality. Full article

Calcium–magnesium (Ca–Mg) carbonates are among the most widely distributed carbonates in the Earth’s surface environment, and their formation mechanisms are of great significance for revealing geological environmental changes and carbon sequestration processes. In this study, the gas diffusion method was employed with L-glutamic acid, L-glycine, and L-lysine as nucleation templates for carbonate minerals to systematically investigate their regulatory effects on the mineralization of Ca–Mg carbonates. The results demonstrated that L-glycine, with the shortest length, was more conducive to forming aragonite, whereas acidic L-glutamic acid, which contains more carboxyl groups, was more beneficial for the structural stability of aragonite. The morphology of the Ca-Mg carbonate minerals became more diverse and promoted the formation of spherical and massive mineral aggregates under the action of amino acids. Moreover, the amino acids significantly increased the MgCO₃ content in Mg calcite (L-glutamic acid: 10.86% > L-glycine: 7.91% > L-lysine: 6.63%). The acidic L-glutamic acid likely promotes the dehydration and incorporation of Mg²⁺ into the Mg calcite lattice through the preferential adsorption of Mg²⁺ via its side-chain carboxyl groups. This study shows how amino acid functional groups influence Ca–Mg carbonate mineralization and provides insights into biogenic Mg-rich mineral origins and advanced mineral material synthesis. Full article

Automated fiber placement (AFP) composites exhibit complex mechanical behaviors due to manufacturing-induced mesostructural variations, including resin-rich regions and tow gaps that significantly influence both local stress distributions and global material responses. This study presents a hierarchically nested modeling framework based on the Parametric High-Fidelity Generalized Method of Cells (PHFGMC) to predict the effective elastic properties and nonlinear mechanical response of AFP composites. The PHFGMC model integrates micro- and meso-scale analyses using representative volume elements (RVEs) derived from micrographs of AFP composite laminates to capture these manufacturing-induced characteristics. Multiple RVE configurations with varied gap patterns are analyzed to quantify the influence of mesostructural features on global stress–strain response. Predictions for linear and nonlinear elastic behaviors are validated against experimental results from carbon fiber/epoxy AFP specimens, demonstrating good quantitative agreement with measured responses. A cohesive extension of the PHFGMC framework further captures damage initiation and crack propagation under transverse tensile loading, revealing failure mechanisms specifically associated with tow gaps and resin-rich areas. By systematically accounting for manufacturing-induced variability through detailed RVE modeling, the nested PHFGMC framework enables the accurate prediction of global mechanical performance and localized behavior, providing a robust computational tool for optimizing AFP composite design in aerospace and other high-performance applications. Full article

The construction sector makes a major contribution to global greenhouse gas emissions, in which cement alone produces approximately 7–8% of global CO₂ emissions. To abate environmental impact and promote sustainable construction, alternative low-carbon cementitious materials are gaining attention. Biochar (BC), a carbon-rich material obtained from biomass sources through the process of pyrolysis, has surfaced as a capable supplementary cementitious material due to its carbon capture capabilities and positive impact on the characteristics of cement composites. This review investigates the role of BC in cement composites, including its effects on hydration kinetics, microstructural development, fresh-state properties, and its optimal utilisation. The study also highlights the internal curing capabilities of BC when used in cement composites, its role in promoting hydration product formation, and its dual function in enhancing mechanical performance while facilitating carbon capture. Despite the benefits, there are some challenges such as variable BC properties, optimal dosage, and scalability. The review highlights the need for standardisation and further research to fully harness BC’s potential as a sustainable component in low-carbon construction technologies. Full article

The Erentaolegai silver deposit is located within the Derbugan metallogenic belt in the eastern segment of the Central Asia–Mongolia giant orogenic belt. The ore bodies are primarily hosted in the volcanic rocks of the Middle Jurassic Tamulangou Formation of the Mesozoic. The mineralization process of the deposit is divided into three stages: Stage I: Pyrite–Quartz Stage; Stage II: Sulfide–Quartz Stage; Stage III: Quartz–Manganese Carbonate Stage. This paper discusses the ore-forming fluids, ore-forming materials, and deposit genesis of the Erentaolegai silver deposits using fluid inclusions microthermometry, laser Raman spectroscopy, and H-O-S isotope analyses. Fluid inclusion microthermometry and laser Raman spectroscopy analyses indicate that the Erentaolegai silver deposit contains exclusively fluid-rich two-phase fluid inclusions, all of which belong to the H₂O-NaCl system. Homogenization temperatures of fluid inclusions in the three stages (from early to late) ranged from 257 to 311 °C, 228 to 280 °C, and 194 to 238 °C, corresponding to salinities of 1.91 to 7.86 wt%, 2.07 to 5.41 wt%, and 0.70–3.55 wt% NaCl equivalent, densities of 0.75 to 0.83 g/cm⁻³, 0.80 to 0.86 g/cm⁻³ and 0.85 to 0.89 g/cm⁻³. The mineralization pressure ranged from 12.2 to 29.5 MPa, and the mineralization depth was 0.41 to 0.98 km, indicating low-pressure and shallow-depth mineralization conditions. H-O isotope results indicate that the ore-forming fluid is a mixture of magmatic fluids and meteoric water, with meteoric contribution dominating in the late stage. The δ³⁴S values of metallic sulfides ranged from −1.8 to +4.0‰, indicating that the metallogenic material of the Erentaolegai silver deposit was dominated by a deep magmatic source. This study concludes that meteoric water mixing and subsequent fluid cooling served as the primary mechanism for silver mineral precipitation. The Erentaolegai silver deposit is classified as a low-sulfidation epithermal silver deposit. Full article

The pursuit of sustainable alternatives to portland cement has become a global imperative within the construction sector, driven by the need to reduce carbon dioxide emissions and energy consumption. Among the promising alternatives, agricultural ashes have garnered attention for their potential as alternative supplementary cementitious materials (ASCMs), owing to their inherent pozzolanic properties when appropriately processed. However, the availability and utilization of these ashes have predominantly been concentrated in tropical and subtropical regions, where such biomass is more abundant. This review offers a comprehensive bibliometric analysis to identify and assess agricultural ashes (specifically switchgrass, barley, sunflower, and oat husks) that are cultivated in temperate and cold climates and exhibit potential for SCM application. The analysis aims to bridge the knowledge gap by systematically mapping the existing research landscape and highlighting underexplored resources suitable for cold-region implementation. Key processing parameters, including incineration temperature, retention duration, and post-combustion grinding techniques, are critically examined for their influence on the resulting ash’s physicochemical characteristics and pozzolanic reactivity. In addition, the effect on fresh, hardened, and durability properties was evaluated. Findings reveal that several crops grown in colder regions may produce ashes rich in reactive silica, thereby qualifying them as viable ASCM candidates and bioenergy sources. Notably, the ashes derived from switchgrass, barley, oats, and sunflowers demonstrate significant reactive silica content, reinforcing their potential in sustainable construction practices. Hence, this study underscores the multifaceted benefits of contributing to the decarbonization of the cement industry and circular economy, while addressing environmental challenges associated with biomass waste disposal and uncontrolled open-air combustion. Full article