Search Results (2,188)

Wastewater containing heavy metals and dyes poses serious environmental risks. This study developed a multifunctional composite by coating polyurethane foam (PUF) with milled activated carbon (mAC) and a zirconium-based metal–organic framework (Zr-MOF) for the simultaneous removal of hexavalent chromium (Cr(VI)) and Congo red (CR). The composite was synthesized using a hydrothermal method to grow Zr-MOF on the surface. The SEM analysis confirmed the successful incorporation of mAC and surface modification with Zr-MOF, which resulted in increased surface roughness and porous morphology. XRD and FTIR confirmed the presence of organic ligands connected to the metal structure and the functional groups of each component in composite materials. The optimum conditions for Zr-MOF/mAC/PUF adsorption (nearly 100% removal) in the binary Cr(VI)/CR solution (50 mg/L each) were 25 °C, pH 9, and 150 rpm for 24 h. The Zr-MOF/mAC/PUF was hydrophilic with a swelling ratio of 2.64 g/g. The thermodynamic investigation of Zr-MOF/mAC/PUF resulted in 141.6218 kJ/mol for Cr(VI) and 166.111 kJ/mol for CR of ΔH° (rapid adsorption), negative ΔG° (spontaneous adsorption), a high positive value of ΔS° (disorder structure) and low activation energy (approximately 2.5 to 2.8 kJ/mol). After analyzing the isotherm and reaction kinetics, the possible mechanism could be endothermic physicochemical adsorption and pseudo-second-order kinetic behavior, with electrostatic attraction and diffusion control. The study of 6-times-reused Zr-MOF/mAC/PUF adsorption identified as a decrease of 7.55 percentage point without changing notable morphology and functional groups, based on SEM and FTIR. Full article

This study investigates the influence of barrel filling ratio on the microstructure, phase composition, and tribological performance of detonation-sprayed Cr₃C₂–NiCr coatings. Coatings were deposited at barrel filling ratios of 43% and 53% under identical spraying conditions. Microstructural characterization revealed the formation of dense lamellar coatings with low porosity and uniform distribution of Cr₃C₂ carbide particles within the NiCr metallic matrix. Compared with the coating deposited at a barrel filling ratio of 43%, the coating deposited at 53% exhibited a denser microstructure. X-ray diffraction analysis confirmed that Cr₃C₂ and NiCr remained the dominant phases after spraying, while a minor amount of Cr₇C₃ formed due to partial decarburization of chromium carbide during thermal exposure. Tribological performance was evaluated under dry sliding conditions using a ball-on-disc configuration at normal loads of 10 and 15 N and sliding speeds of 5 and 10 cm/s. Wear volume was determined from the geometry of the wear track after testing, and wear rate was calculated accordingly. The coating produced at a barrel filling ratio of 53% demonstrated improved wear resistance under elevated loads despite exhibiting a higher coefficient of friction. The minimum wear rate reached 1.23 × 10⁻⁴ mm³/(m·N), which was associated with reduced porosity and enhanced structural integrity of the coating. The obtained results demonstrate that optimization of detonation spraying parameters significantly affects coating structure and tribological behavior. The developed Cr₃C₂–NiCr coatings are promising protective materials for components operating under severe friction and wear conditions, including industrial and high-temperature engineering applications. Full article

Chromate-free conversion coatings are increasingly investigated as environmentally acceptable alternatives to conventional chromate conversion coatings for corrosion protection of aluminum alloys. In the present study, the electrochemical behaviour and long-term corrosion stability of several commercial conversion coating systems based on trivalent chromium (TCP), zirconium (ZrCC) and zirconium/titanium (Zr/TiCC) were systematically evaluated on AA3003 aluminum alloy and compared to chromate conversion coating (CCC) CR614. Three TCP coatings (ST650, MC1300 and B30002), two ZrCC (MC1700 and MC160/161), and one Zr/TiCC (B2040) were investigated. Coatings were prepared at pre-selected pH and concentration, but at varying conversion times. The protective performance of the coating was then tested across various exposure conditions using potentiodynamic polarization measurements: (i) after 24 h of exposure to air, (ii) after 24 h of immersion in 3.5 wt.% NaCl solution and (iii) simulated acid rain solution, and (iv) after exposure in a salt spray chamber for 500 h. The protective performance strongly depended on both the conversion conditions and the exposure environment. The optimal conversion times ranged between 40 s and 18 min, depending on the coating type. Differences between the investigated systems remained relatively limited when investigated after exposure to air and immersion in the simulated acid rain solution. However, in chloride-containing environments, substantially greater differentiation between the coatings was observed. Among the investigated systems, TCP coatings exhibited the most favourable overall corrosion performance, particularly after prolonged salt spray exposure, where ST650 and B30002 polarization resistance values were approximately 8800 and 5300 kΩ cm², respectively, together with corrosion current densities as low as 0.0004 and 0.001 μA cm⁻². ZrCC systems MC1700 and MC160/161 also provided significant corrosion protection, achieving polarization resistance values around 2700 and 2400 kΩ cm² after 500 h of salt spray exposure, whereas the Zr/TiCC coating B2040 exhibited poorer long-term performance. The results further demonstrated that prolonged salt spray exposure provides considerably more realistic evaluation of long-term coating protectiveness than short-term electrochemical measurements alone. Overall, optimized TCP and ZrCC systems provided corrosion protection under chloride-containing conditions comparable to or superior to the investigated conventional chromate conversion coating CR614 deposited on AA3003 alloy. Full article

Background: Degenerative joint diseases are a major cause of disability and drive the increasing demand for joint arthroplasty. Long-term prosthesis success depends on rapid and stable bone–implant integration, which is influenced by the osteo-inductive and osteo-conductive properties of implant materials. Chromium–cobalt (CrCo) and titanium (Ti) alloys are widely used in reconstructive orthopedics, but direct comparative data on their biological performance, particularly for trabecular titanium (T-Ti), remain limited. This study aimed to directly compare the biocompatibility and osteogenic potential of CrCo and T-Ti using human mesenchymal stromal cells (MSCs). Methods: Human MSCs were characterized by immunophenotyping and cultured on CrCo and T-Ti scaffolds under control and osteogenic conditions for up to 28 days. Cell adhesion and morphology were assessed by scanning electron microscopy. Proliferation and viability were quantified, and osteogenic differentiation was evaluated using alkaline phosphatase activity, calcium deposition assays, and gene expression profiling of osteogenic markers. Results: Both materials supported MSC adhesion and proliferation, confirming cytocompatibility. Under control conditions, T-Ti significantly increased alkaline phosphatase activity and osteogenic gene expression. Under osteogenic stimulation, T-Ti accelerated differentiation and mineralized matrix deposition. CrCo exhibited limited stimulation of the osteogenic-supportive microenvironment and delayed differentiation responses. Conclusions: Trabecular titanium, in terms of morphology and topology, provides a biologically active scaffold that both induces and conducts osteogenic differentiation of human MSCs, whereas CrCo acts primarily as a mechanically optimized but biologically passive material. These findings support the use of trabecular titanium at bone-contact interfaces in joint prostheses to enhance osteointegration and potentially improve long-term implant stability. Full article

Freshwater ecosystems are increasingly exposed to metal contamination arising from natural and anthropogenic activities, potentially affecting fish physiology and ecosystem health. However, limited information is available regarding metal accumulation and associated biological responses in fish populations from Dukan Lake, northern Iraq. Therefore, this study investigated metal concentrations in water and tissues of common carp (Cyprinus carpio) and evaluated their relationships with selected fish health indicators. Water and fish samples were collected monthly from Dukan Lake, and a total of 60 fish were classified into three length groups (20–29 cm, 30–39 cm, and 40–49 cm). Metal concentrations in water, liver, and gonad tissues were analyzed using ICP-OES, while condition factor (CF), gonadosomatic index (GSI), and hepatosomatic index (HSI) were used to assess fish physiological condition. Sodium (Na), magnesium (Mg), potassium (K), iron (Fe), zinc (Zn), and barium (Ba) were detected in both water and fish tissues, with concentrations in water ranging from 50 to 7069 μg/L. In contrast, chromium (Cr), manganese (Mn), nickel (Ni), selenium (Se), silver (Ag), cadmium (Cd), antimony (Sb), lead (Pb), copper (Cu), and arsenic (As) were below detection limits. Biometric analysis revealed significant differences (p < 0.05) in the gonadosomatic index (GSI) among fish length groups, indicating size-dependent reproductive development. However, no significant relationship was observed between fish length and either the CF or HSI, suggesting relatively stable somatic condition or liver status across size classes. Correlation analysis showed no significant associations between water metal concentrations and CF or GSI. A significant positive correlation was identified between Zn concentration and HSI in the 30–39 cm length group, indicating a possible link between Zn exposure and hepatic physiological response. The findings indicate that essential elements dominate the metal profile in Dukan Lake, with limited evidence of toxic metal contamination. No major adverse effects on the general condition of the fish were observed. These results contribute to understanding metal bioaccumulation patterns and their implications for fish health in freshwater ecosystems. Full article

Hexavalent chromium (Cr (VI)) contamination of water resources constitutes a major environmental and public health issue due to its high toxicity, mobility, and carcinogenic properties. This review examines recent advances in Cr (VI) removal technologies from water and wastewater, with emphasis on membrane-based separation processes and adsorption approaches. Conventional treatment methods, including chemical precipitation, ion exchange (IX), electrocoagulation (EC), electrodeionization (EDΙ), bioremediation, and photocatalysis, are comparatively discussed in terms of removal efficiency, operational limitations, and applicability. In parallel, sustainable adsorbent materials derived from biomass and agricultural waste are evaluated as environmentally friendly and cost-effective alternatives for chromium removal. The role of functional groups, adsorption mechanisms, and redox interactions involved in Cr (VI) reduction and immobilization is also analyzed. Attention is given to membrane technologies, such as reverse osmosis (RO), nanofiltration (NF), electrodialysis (ED), and ultrafiltration (UF) after surface modification with the incorporation of nanomaterials and/or the application of Layer-by-Layer (LBL) assembly techniques, which enhance selectivity, permeability, and antifouling behavior. The reviewed studies demonstrate that advanced membrane systems and bio-based adsorbents can achieve high chromium removal efficiencies while supporting sustainable water treatment practices. Overall, the combination of membrane technologies with functionalized materials represents a promising direction for the development of efficient and environmentally sustainable Cr (VI) remediation systems capable of meeting increasingly strict regulatory limits. Full article

This study investigates the degradation and failure mechanisms of AISI 310S stainless steel conveyor belt wires operating under cyclic conditions up to 900 °C in a continuous carburizing furnace. Microstructural evolution and mechanical responses after service exposure were evaluated using optical microscopy, scanning electron microscopy (SEM) equipped with energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), and Vickers microhardness testing. Results indicate that initial exposure led to σ-phase nucleation and the formation of a protective Cr₂O₃-SiO₂ oxide scale. However, prolonged service led to scale degradation driven by Na-containing residues from pre-cleaning agents, which reacted to form Na₂SiO₃ and NaAlSiO₄ phases. This degradation accelerated the growth of non-protective iron oxides (Fe₂O₃, Fe₃O₄). Simultaneously, the σ-phase decomposed into massive, continuous M₂₃C₆ and M₇C₃ carbide networks along grain boundaries, inducing severe chromium sensitization. Consequently, the matrix embrittled significantly, with Vickers hardness increasing from 150 HV to 290–340 HV. Fracture analysis confirmed that brittle intergranular cracking initiated at these carbide networks, oxide inclusions, and matrix pores. Ultimately, the synergistic effects of oxide scale degradation, extensive carbide precipitation, and grain boundary depletion caused the premature catastrophic failure of the conveyor mesh under cyclic operational stress. Full article

This study investigates the effects of post-processing on the surface roughness, wettability, and frictional behavior of selective laser-melted (SLM) cobalt–chromium–tungsten (CoCrW) alloys for orthodontic use. The SLM-CoCrW specimens were tested in as-manufactured, mechanically polished, and electropolished states. Surface characterization via stylus profilometry and atomic force microscopy (AFM) showed that both polishing methods reduced macro- and micro-scale roughness, with electropolishing producing the smoothest, most uniform topography. Static water contact angle (WCA) measurements revealed that mechanical polishing provided an optimal balance of roughness and hydrophilicity, resulting in the lowest friction, while ultrasmooth electropolished surfaces exhibited slightly higher friction due to increased hydrophobicity and a uniform Cr-rich oxide layer confirmed by X-ray photoelectron spectroscopy (XPS). XPS also indicated that electropolishing generated a homogenous chromium oxide passive film, whereas mechanical polishing left a chemically heterogeneous surface with exposed metallic sites. Importantly, performance is not governed solely by surface roughness; surface chemistry is equally critical, and both must be considered together—along with wettability and tribological behavior—to achieve optimal functional outcomes. From a clinical perspective, optimization of surface roughness and surface chemistry may result in decreased frictional resistance, improved sliding mechanics, and enhanced long-term performance of additively manufactured orthodontic components; however, the present study was restricted to in vitro characterization under simplified laboratory conditions, and further investigations involving artificial saliva, long-term aging, wear and clinical simulations are necessary to validate the translational relevance of these findings. Full article

Background/Objectives: Chromium contamination represents a major environmental challenge due to its detrimental effects on plant growth and agricultural productivity. Since dichromate uptake in plants occurs mainly through sulfate and phosphate transporters, identifying natural compounds capable of competitively inhibiting these transport pathways may provide an eco-friendly strategy for reducing chromium accumulation. This study aimed to investigate the inhibitory potential of phytochemicals from Djiboutian medicinal plants against sulfate and phosphate transporters using an integrated computational approach. Methods: 49 phytochemicals identified by GC–MS from ten Djiboutian medicinal plants were screened against the sulfate transporter (7LHV) and phosphate transporter (7SP5) using molecular docking. Binding interactions were compared with sulfate, phosphate, and dichromate ions to evaluate potential competitive inhibition. The most promising compounds were further assessed through ADMET prediction and 100 ns molecular dynamics simulations to evaluate their pharmacokinetic properties and complex stability. Results: Molecular docking revealed binding energies ranging from −7.04 to −2.91 kcal/mol for 7LHV and from −6.50 to −0.62 kcal/mol for 7SP5, indicating variable binding affinities among the screened phytochemicals. Several compounds exhibited favorable interactions with key amino acid residues involved in anion transport, suggesting their potential to compete with dichromate uptake. ADMET analysis identified multiple compounds with favorable toxicity and drug-likeness profiles. Among them, cyclohexanepropanoic acid from Aloe djiboutiensis demonstrated the strongest binding affinity toward both transporters. Molecular dynamics simulations confirmed the structural stability of the protein–ligand complexes throughout the 100 ns simulation. Conclusions: This study identifies naturally occurring phytochemicals, particularly cyclohexanepropanoic acid, as promising competitive inhibitors of dichromate transport in plants. These findings provide a theoretical foundation for developing sustainable phytochemical-based strategies to mitigate chromium accumulation in crops and support future experimental validation. Full article

This study determined the etiological distribution of naturally occurring bovine dermatophytosis and evaluated associated serum macro- and trace-element and redox alterations. Seventy-five calves and young cattle aged 2–12 months, of both sexes and mixed local, Simmental, Brown Swiss/Montofon, and crossbred types, were included: 50 clinically and mycologically confirmed dermatophytosis cases and 25 clinically healthy controls. Skin scrapings and hair samples from affected cattle were examined by direct microscopy and culture. Single jugular blood samples were collected from all animals during the same seasonal period (February–May 2026), and serum mineral and redox markers were analyzed. Copper, zinc, cobalt, selenium, molybdenum, manganese, magnesium, calcium, sodium, iron, and chromium concentrations, catalase (CAT), reduced glutathione (GSH), and malondialdehyde (MDA) were measured. Data were analyzed using a general linear model including group and sex as fixed effects and age in months as a covariate. Model-adjusted results were expressed as least-squares means ± standard error (LSM ± SE). Trichophyton verrucosum and T. mentagrophytes were identified in 90% and 10% of affected cattle, respectively. Affected cattle had lower Cu, Zn, Se, Na, Fe (p < 0.01), Mg (p = 0.009), Ca (p < 0.001), CAT, and GSH (p < 0.001), but higher Co, Cr (p < 0.01) and MDA (p < 0.001). These findings suggest field associations between bovine dermatophytosis, mineral imbalance, and redox disturbance. Full article

Titanium alloys are among the most important biomaterials due to their good biocompatibility, high corrosion resistance and favourable mechanical properties. Particular interest is directed towards β-Ti alloys, whose properties can be tailored by adding β-stabilisers such as molybdenum and chromium, with the aim of developing materials suitable for biomedical applications. This paper investigates the influence of chemical composition on the phase composition, microstructure, microhardness and corrosion properties of experimental Ti-Mo-Cr alloys produced by casting. Phase composition was determined by X-ray diffraction analysis (XRD), while microstructural characteristics were analysed by scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS). The results showed that increasing the molybdenum and chromium content contributes to the stabilisation of the β-phase and reduces the proportion of α and α″ martensite. Complete stabilisation of the β-phase was achieved in the Ti-10Mo-30Cr alloy, while the Ti-10Mo-10Cr alloy showed a dominant presence of α″ martensite. EDS analysis confirmed the segregation of alloying elements during solidification. Microhardness measurements showed an increase in hardness with increasing total alloying element content, with the highest hardness measured in the Ti-20Mo-20Cr alloy. Corrosion properties were tested using open circuit potential (OCP), electrochemical impedance spectroscopy (EIS) and Tafel polarisation methods in 0.9% NaCl (sodium chloride) medium. Among the alloys investigated, Ti-20Mo-20Cr showed a favourable overall balance of electrochemical properties, while Ti-10Mo-30Cr exhibited the lowest corrosion rate. The results suggest that a balanced ratio of molybdenum and chromium plays a key role in optimising the microstructure, mechanical properties, and corrosion performance of Ti-Mo-Cr alloys. Full article

The discharge of metal-containing effluents into aquatic systems remains a major environmental concern because metal ions can persist in water bodies and accumulate in biological systems, potentially affecting ecosystem and human health. Among these contaminants, Cr(III) is frequently encountered in waste streams generated by industrial activities, making its removal an important objective in water quality management. This study investigated the adsorption behavior of Cr(III) using lignocellulosic biosorbents obtained from tamarind shell (Tamarindus indica) after water, H₂O₂, and HCl pretreatments, with particular emphasis on equilibrium behavior, thermodynamic characteristics, and pretreatment-induced physicochemical modifications. Batch adsorption experiments were conducted to evaluate equilibrium behavior. The highest adsorption capacity (41.6 mg g⁻¹) was obtained with the water-treated biosorbent at 60 °C. The equilibrium data were best represented by the Sips model, suggesting that Cr(III) adsorption occurred on surfaces containing adsorption sites with different energetic characteristics. Thermodynamic analysis revealed that the adsorption process was spontaneous, while the enthalpy changes indicated predominantly endothermic behavior for the pretreated biosorbents. ATR-FTIR, SEM, EDS, and XRD analyses were performed to characterize the biosorbents before and after adsorption. The characterization results indicated that oxygen-containing functional groups, particularly hydroxyl and carbonyl functionalities, were associated with the adsorption process. SEM images showed morphological changes associated with pore occupation, while EDS confirmed chromium adsorption and suggested possible ion-exchange mechanisms. XRD patterns indicated a mainly amorphous structure. The results demonstrated that pretreatment-induced modifications strongly influenced the adsorption performance of tamarind shell. Water pretreatment produced the most favorable adsorption behavior, yielding the highest adsorption capacity among the evaluated biosorbents. The combined interpretation of equilibrium, thermodynamic, and characterization results revealed a close relationship between surface properties and Cr(III) uptake. Full article

The slag from electric arc furnace (EAF) steelmaking has potential for various applications, but its safe use requires the assessment of heavy metals, such as chromium leaching, to meet environmental standards. This study investigates the microstructure of EAF slag cooled in a slag pot and its effect on Cr immobilization. Slag samples were collected at full scale using a representative sampling method, dividing the slag pot into six zones (internal and external, top to bottom). Microstructural analysis was performed using scanning electron microscopy coupled with energy dispersive spectroscopy and X-ray diffraction, followed by leaching tests on the milled samples. Thermodynamic calculations were performed using FactSage 8.4 to evaluate phase stability and composition. The results indicate that cooling conditions inferred from slag-pot location, spinel size, and spinel zoning are correlated with variations in Cr leaching under neutral conditions. Slower cooling is associated with the formation of large, reverse-zoned spinel phases that may contribute to Cr stabilization, whereas rapid cooling is associated with smaller, homogeneous spinel phases that may increase leaching risk. These findings provide insights for the environmentally safe utilization of EAF slags and inform strategies to minimize Cr release during slag valorization. Full article

Slaughterhouse wastewater introduces potentially toxic elements into aquatic ecosystems, yet bioaccumulation patterns in commercial fish species and associated human health risks remain underexplored in West Africa. This study quantified zinc (Zn), lead (Pb), iron (Fe), magnesium (Mg), chromium (Cr), and cadmium (Cd) in three ecologically distinct fish species—Oreochromis niloticus (Nile tilapia), Clarias gariepinus (African sharptooth catfish), and Mugil cephalus (Flathead grey mullet)—from two slaughterhouse-impacted rivers (Transamadi and Mgbuosimini) and a control site (Iwofe) in Rivers State, Nigeria. Metal concentrations were measured using atomic absorption spectrophotometry. Two-way ANOVA assessed species and location effects. Principal component analysis (PCA) was performed, with Mg used as a potential geogenic tracer, as its loading pattern was independent of Pb and Cd and consistent with the natural background. A Water Quality Index (WQI) classified Mgboshimini and Iwofe as having poor water quality (WQI > 75), while Transamadi had medium quality. Health risks were evaluated using estimated daily intake (EDI), target hazard quotients (THQ), and hazard indices (HI) following USEPA guidelines. Metal levels varied significantly by species and location (p < 0.001). Flathead grey mullet from Mgbuosimini had the highest Pb (1.50 ± 0.05 mg/kg) and Cd (0.41 ± 0.02 mg/kg), exceeding EU maximum levels for fish muscle (Pb 0.30 mg/kg, Cd 0.05 mg/kg) by 500% and 800%, respectively. PCA explained 77.5% of the variance, with Pb and Cd clustering as anthropogenic sources, while Mg loaded independently. THQ for Pb approached unity in Flathead grey mullet (0.88), and THQ for Cd reached 0.97. HI exceeded 1.0 in all species from Mgbuosimini, peaking at 2.07 in Flathead grey mullet. Uncertainty analysis (using ±SD) gave a HI range of 1.89–2.25 for this species, all above the safety threshold. Carcinogenic risk for Flathead grey mullet (3.97 × 10⁻⁴) approached the upper acceptable limit. Slaughterhouse effluent appears to elevate Pb and Cd burdens in fish, with detritivorous Flathead grey mullet posing the highest health risk. Exceedance of safety thresholds and HI > 1.0 indicate potential non-carcinogenic and carcinogenic risks. We recommend improved wastewater treatment and species-specific consumption advisories. Full article

To reveal the varieties and color genesis of emerald-green tourmaline crystals from Tanzania, a systematic study was conducted using conventional gemological tests, X-ray diffraction, Fourier-transform infrared spectroscopy, polarized ultraviolet–visible spectroscopy (UV–vis), X-ray photoelectron spectroscopy (XPS), low-temperature photoluminescence (PL) spectroscopy, and electron probe microanalysis (EPMA). The results indicate that the tourmaline is dravite. Its UV–vis absorption spectrum shows strong broad absorption bands at approximately 436 and 600 nm, with a pronounced transmission at 520 nm, which directly accounts for its emerald green color. Obvious polarized absorption was observed along and perpendicular to the c-axis. XPS and PL results confirm that chromium is present in the samples in the form of Cr³⁺. EPMA compositional analysis indicated a low Cr₂O₃ content of 0.804 wt.%; combined with crystal structural properties and spectral responses, these results suggest that Cr³⁺ preferentially occupies the Y site in the crystal structure and that d–d electronic transitions represent the underlying mechanism of its color formation. This study comprehensively illustrated the mineralogical and spectral properties of Cr-bearing dravite, providing fundamental data for further research on its genesis and gemological application. Full article