Search Results (312)

To address the ecological risks associated with highly mobile hexavalent chromium [Cr(VI)], woody biochar was functionalized with hydrogen peroxide (H₂O₂) to develop a dual-phase remediation material (H-BC) for aqueous and soil environments. Batch post-contact isotherm fitting yielded a Langmuir-fitted/extrapolated apparent retention capacity q_m of 77.44 mg/g at 328 K. This value reflects enhanced overall Cr(VI)-derived retention within the tested concentration range, rather than increased electrostatic affinity for chromate oxyanions. Empirical kinetic diagnostics and FTIR/XPS results were consistent with adsorption-coupled interfacial reduction, while DFT analysis provided qualitative support for the enhanced electronic responsiveness of H-BC. The OFG-enriched interface may facilitate short-range, non-electrostatic interfacial interactions and stabilize surface-associated Cr(III). Temperature-dependent apparent isotherm fitting suggested that elevated temperature favored the overall Cr(VI)-derived retention process under the tested conditions, and should not be interpreted as rigorous standard-state adsorption thermodynamics. Continuous-flow column leaching and accelerated wet–dry (W–D) aging experiments demonstrated that H-BC substantially suppressed the mobility of operationally filtered Cr(VI), achieving a maximum filtered-Cr(VI)-based retention efficiency of 99.98% under cyclic drying–rewetting conditions. Spatial configuration analysis indicated that homogeneous incorporation of H-BC improved soil–biochar contact and was more effective than stratified placement in limiting vertical filtered-Cr(VI) migration. Overall, oxidatively functionalized H-BC shows promise as a biomass-derived amendment for reducing Cr(VI) mobility in complex environmental matrices, although complete chromium mass redistribution will require future total-Cr and Cr(III)-resolved analyses. 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

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 problem of chromium contamination, especially Cr(VI), in acidic wastewater has drawn significant attention, requiring effective and sustainable remediation measures. In this study, tannic-acid/Fe₃O₄-modified corn straw biochar (Fe-TA-CSB) is prepared by a grinding-calcination method to remove Cr(VI). The factors influencing the removal effect of Fe-TA-CSB are investigated through static adsorption experiments. The removal mechanism is explored by combining adsorption kinetics, isothermal adsorption, and thermodynamics, as well as characterization methods. The results show that the removal efficiency of Cr(VI) increases with the increase in pH, contact time (t), and solid–liquid ratio (m/v), but decreases with the increase in initial concentration (C₀). Under optimal conditions of TA/Fe₃O₄ mass ratio = 12.5%, pH = 3.0, m/v = 1.0 g/L, and C₀ = 10 mg/L, the removal efficiency value is 94.02%, which is approximately 81.44% after four adsorption–desorption cycles. The adsorption behavior is fitted well by the Sips isotherm model and Elovich kinetics model, suggesting the adsorption process of heterogeneous monolayer chemisorption. The removal mechanism of Cr(VI) by Fe-TA-CSB involves electrostatic interaction with Cr(VI), reduction in Cr(VI) to Cr(III) through C–O and Fe(II), and complexation of reduced Cr(III) with the introduced Fe–O and phenolic hydroxyl groups. Fe-TA-CSB is an environmentally friendly and renewable adsorbent with good potential for the treatment of acidic wastewater. Full article

In this investigation, optical emission spectrometers, a Brinell hardness tester, optical light and scanning microscopes, and X-ray diffraction were used for general metallurgical characterization of the experimental irons in as-cast states. The hole-drilling method was used to assess residual stress distributions under gross and net casting weight conditions. To create experimental irons using the casting process, raw materials were transformed from a solid to a liquid state using an industrial furnace and ladle to melt and cast, respectively. The casting shakeout temperatures for samples A and B were recorded at 60 °C and 180 °C, respectively, after a characteristic stress lattice casting component was allowed to cool for about 1645 min and 1295 min. Chemical analysis verified the experimental hypoeutectic irons of ASTM A532, Type A, Class III, 25%Cr, i.e., high chromium white cast iron alloys. Additionally, it was discovered that micrographs were made of an austenitic-martensitic matrix that contained eutectic M₇C₃ and secondary M₂₃C₆-type carbides. The residual stress distributions were found to be influenced by various carbide and metallic volume fraction proportions, casting section thickness, and casting shakeout duration and temperature. Optimal hardness values, however, were shown to be associated with higher residual stress distributions and an increase in major alloying elements in experimental irons. Consequently, different residual stress distributions are produced by casting shakeout temperatures at lower and higher values under gross and net casting weight conditions. Full article

Candida albicans remains one of the leading causes of invasive fungal infections and is recognized as a critical-priority pathogen by the World Health Organization. The increasing emergence of resistance to azole antifungals such as fluconazole highlights the need for alternative therapeutic strategies. In this study, we evaluated the antifungal potential of a chromium(III)–triazole coordination complex (CrL1) against C. albicans. In vitro susceptibility testing showed that CrL1 exhibited notable antifungal activity against the fluconazole-resistant strain with low cytotoxicity in murine macrophages. To facilitate aqueous dispersion and enable in vivo administration, CrL1 was incorporated into an oil-in-water nanoemulsion (NE-CrL1). The antifungal activity of NE-CrL1 was evaluated in a murine model of invasive candidiasis. In mice infected with a fluconazole-resistant C. albicans strain, treatment with NE-CrL1 reduced renal fungal burden and was associated with attenuation of histopathological alterations and changes in local inflammatory responses. Although the present study has limitations, including the absence of mechanistic assays and additional physicochemical characterization, these results suggest in vivo antifungal activity of NE-CrL1 and warrant further preclinical evaluation against drug-resistant Candida infections. Full article

Plasma polymerization offers a solvent-free route to functional polymer materials, but the structural integrity and accessibility of functional groups in plasma-derived networks remain insufficiently validated. Herein, N-vinylimidazole (NVI) was polymerized using atmospheric-pressure dielectric barrier discharge (DBD) plasma in a liquid-film configuration to generate a chemically heterogeneous poly(N-vinylimidazole)-like material that could be recovered and evaluated in aqueous solution. ATR–FTIR and ¹H NMR spectroscopy indicate substantial vinyl-group consumption with retention of imidazole functionality. Functional behavior was probed using chromium(III) (Cr³⁺) as a model metal ion. UV–Vis spectroscopy revealed systematic changes in the Cr³⁺ d–d transition region (~580–600 nm) with increasing polymer concentration, consistent with ligand-field perturbation arising from interactions with imidazole donor sites. A monotonic increase in absorbance with an increasing ligand-to-metal ratio was observed, followed by plateau behavior at higher ratios, indicating saturation of accessible coordination environments. These results demonstrate that plasma-polymerized material retains chemically accessible imidazole functionalities capable of coordinating transition-metal ions in solution, establishing atmospheric-pressure plasma polymerization as a viable route to functional imidazole-containing materials. Full article

Coagulation-based technologies are increasingly recognized as key for controlling fluoride and hexavalent chromium in urban water and wastewater. Combined geogenic and industrial sources often drive chronic exposure and create an underrecognized public health burden. This review synthesizes current knowledge on the occurrence, speciation, and toxicology of F⁻ and Cr(VI) in urban systems, links regulatory targets to health outcomes, and critically examines conventional, advanced, and electrochemical coagulation processes for their removal under realistic water-quality conditions. Mechanistic sections describe how aluminum-, iron-, magnesium- and zirconium-based coagulants, including pre-polymerized and composite formulations (e.g., IPC-type coagulants, PSiFAC-Mg, ZrCl₄), remove fluoride via Al–F complexation, Al–F–OH co-precipitation, ion exchange, and sweep flocculation, while Cr(VI) control relies on Fe(II)-mediated reduction to Cr(III), followed by adsorption and co-precipitation with metal hydroxides. The review assesses how water chemistry and operating conditions affect single- and multi-contaminant removal, highlighting competition among fluoride, Cr(VI), nutrients, and other oxyanions. Performance data from bench-, pilot-, and selected full-scale studies show that optimized coagulation and electrocoagulation can substantially reduce fluoride and Cr(VI) (to drinking-water-relevant levels) in diverse urban waters, but also reveal persistent issues of sludge generation and stability, residual metals, process robustness, and cost. The review identifies priorities, including long-term urban-scale assessments, low-toxicity green coagulants, life-cycle and health impact assessments, and real-time coagulation control for fluoride and Cr(VI). Full article

Soil contamination by heavy metals is a significant sustainability and ecological issue, impacting on the health of ecosystems and groundwater. This study assessed the efficacy of malic acid as a biodegradable and environmentally benign agent for the remediation of soils contaminated with cadmium, chromium, copper, and zinc. Two soils with contrasting textures were treated with a 10% malic acid solution at solid/liquid ratios of 1:5 and 1:10 for contact times of 2, 4, 6, and 8 h. The extraction efficiency varied depending on metal type, soil texture, and washing conditions. Cadmium removal ranged from 26% to 55%, zinc removal ranged from 10% to 25%, while copper showed variable extraction (5–45%) depending on initial soil concentration. Chromium exhibited the highest removal efficiency (30–90%), quantified as total chromium; however, the absence of speciation analysis (Cr(III)/Cr(VI)) represents a key limitation and may affect the interpretation of the removal performance. FTIR and UV–Vis analyses confirmed the formation of metal–carboxylate complexes and changes in soil functional groups during the washing process. In addition, significant mobilization of nitrogen and potassium was observed, whereas phosphorus remained relatively stable. The results highlight the influence of soil texture and multi-metal interactions on malic acid washing efficiency and provide a laboratory-scale environmental assessment of malic acid as a sustainable remediation alternative for soil remediation, while emphasizing the need for further evaluation regarding chromium speciation and post-treatment soil quality and sustainability impacts. Full article

Hexavalent chromium (Cr(VI)) contamination in agricultural soils poses a significant risk to environmental and food safety owing to its high mobility and acute toxicity. To investigate possible mitigation strategies, a greenhouse pot experiment was conducted using sandy loam and silty loam soils spiked with Cr(VI) at 30 mg kg⁻¹ and amended with natural clinoptilolite and modified HDTMA-Br (hexadecyl-trimethyl-ammonium-bromide) zeolite, while celery (Apium graveolens) was cultivated to assess chromium bioavailability and plant accumulation. Hexavalent chromium concentrations declined in all treatments (up to 88.2% in sandy loam and 73.5% in silty loam), indicating progressive reduction to Cr(III), although amendment effectiveness varied by soil type. In addition, celery accumulated extremely high chromium concentrations, particularly in sandy loam soil, where root Cr(VI) reached 1776 mg kg⁻¹, indicating substantial safety concerns. Translocation factor values were below 1 across treatments, indicating limited relocation of Cr from roots to shoots. In the zeolite treatments, Cr(VI) concentrations in aboveground biomass decreased; however, plant uptake was not completely inhibited. Nonetheless, the high bioaccumulation factor (Cr in plant over available Cr in soil) of as high as 34 in the Cr(VI)-amended treatment indicated an uptake potential under Cr load. We conclude that modified zeolite was successful in mitigating Cr(VI) uptake in plants. Further investigation on the effectiveness of the materials in open-field conditions is required to establish a remediation framework for Cr species. Full article

Aligned CS/Rx aerogels were fabricated by inducing non-directional ice growth (freeze-molding) followed by low-temperature curing, resulting in monoliths with interconnected channels, a high void fraction, and moldability. The swelling index (S%) was calculated to be 1029, the apparent density 0.496 g·cm⁻³, and the estimated porosity 90% based on micrographic analysis. Aerogels have mechanical behavior Shore A hardness greater than 25. Batch metal removal tests were performed (10 mL, 100 mg·L⁻¹ Cr(VI), 0.19 g adsorbent, 24 h, and pH 5–5.5), and the material achieved 95% metal removal. Additional kinetic and isothermal results were obtained using CS85R15 on a packed column (20 to 140 mg·L⁻¹, 1000 mL Cr(VI), 0.80 g adsorbent, 24 h, and pH 5–5.5). Equilibrium data were consistent with a heterogeneous surface hosting a specific site, as reflected in the joint Freundlich/Langmuir fit (q_max 100.8 mg·g⁻¹ for Langmuir). This confirmed the preservation of chitosan functionalities (–OH/–NH) after processing, while XPS detected chromium on the surface with signals consistent with the partial reduction of Cr(VI) to Cr(III) on the aerogel surface. This highlights the relevance of adsorption-based technologies for water remediation, where high-porosity and low-density materials allow for short diffusion pathways and capture electrostatics by protonated amines and redox conversion of hazardous substances. The soft-cure freeze-molding technique is simple, scalable, and compatible with packed-bed/column operation, providing a material platform for tailoring the microstructure (sheets and channels) and surface chemistry to regenerable sorbents for industrial wastewater treatment. Full article

Ion-imprinting technology based on biosorbents via sorption demonstrates potential for the selective removal of metal ions from water and wastewater. This offers both high sorption capacity and selectivity for specific metals. Current research trends are toward the development of sorbents with minimal environmental impact. Among the most rapidly evolving classes of sorbents are those derived from biopolymers, such as chitosan—a natural derivative of chitin that can be readily functionalized. Due to the growing interest in this topic, it is necessary to summarize the current knowledge. In this article, we provide a comprehensive overview of the latest advances in ion-imprinted chitosan-based materials designed for the purification of metal-contaminated aqueous systems. We conduct a bibliographic analysis and describe a variety of chitosan-based materials exhibiting selectivity toward heavy metals, including chromium Cr(III/VI), cobalt Co(II), nickel Ni(II), copper Cu(II), zinc Zn(II), arsenic As(III/V), cadmium Cd(II), mercury Hg(II), and lead Pb(II). Finally, we discuss future prospects and highlight current research gaps, aiming to guide further scientific exploration and innovation in this promising field. Full article

Acidic mine drainage (AMD) poses a severe global environmental threat due to its high acidity and elevated levels of toxic hexavalent chromium (Cr(VI)), for which biogenic iron sulfide (FeS) nanoparticles have emerged as a promising remediation agent; however, their practical application is hindered by aggregation and oxidative deactivation. This research synthesized biogenic FeS nanoparticles via sulfate-reducing bacteria (SRB) and employed humic acid (HA) as a stabilizing agent to enhance Cr(VI) removal performance in simulated AMD conditions. Single-factor experiments combined with response surface methodology identified the optimal biosynthetic conditions for FeS: yeast extract powder dosage of 2.2 g/L, Fe/S molar ratio of 0.8, and NH₄Cl dosage of 3.1 g/L. Under these conditions, the material achieved 84.25% Cr(VI) removal, with the Fe/S molar ratio identified as the most influential parameter governing synthesis and performance. Introducing HA at an optimal dosage of 2 mg/L drove marked improvements in both nanoparticle yield and reactivity: FeS yield increased to 1096.26 mg/L, Cr(VI) removal efficiency reached 99.62%, and residual Cr(VI) dropped from 15.75 mg/L to just 0.38 mg/L. Kinetic and isotherm analyses, paired with SEM/TEM imaging and zeta potential measurements, revealed that HA stabilization improved particle dispersion and reduced lamellar stacking, resulting in a surface-controlled Cr(VI) removal process. FTIR and 2D-COS analyses demonstrated that HA-derived oxygen-containing functional groups, including O–H/N–H, C=O, and C–O moieties, played a central role in interfacial interactions during Cr(VI) sequestration. XRD results confirmed that Cr(VI) was reduced to Cr(III) and primarily immobilized as low-solubility CrOOH and Cr₂S₃, while the formation of Fe–Cr spinel-like phases remains tentative without X-ray Photoelectron Spectroscopy (XPS) validation. Further investigation via surface-sensitive spectroscopy and dynamic leaching tests is needed to fully assess the long-term stability of the reaction products. Full article

This study investigates the potential of Quercus robur leaves as a bio-coagulant for the removal of heavy metal ions, including zinc (II), iron (III), copper (II), and chromium (VI), from water. The Quercus robur leaves were used in two forms: Quercus robur powder (QRP) and Quercus robur extract (QRE). The extract was prepared using distilled water to extract the active compounds responsible for coagulation, such as proteins, polysaccharides, and total phenolics. The QRP was characterized by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), X-ray diffraction (XRD), and zeta potential analysis to identify the active functional groups, surface morphology, crystallinity, and surface charge, all of which are key factors influencing its performance in the coagulation–flocculation process. In this work, the Response Surface Methodology (RSM)-based Central Composite Design (CCD), with two factors (bio-coagulant dosage and initial metal concentration), was used examine the effects of each factor and their interaction, while the responses were zinc (II) removal, iron (III) removal, copper (II) removal, and chromium (VI). The results revealed high removal efficiency for these metal ions, reaching up to 100% for all metal ions treated with QRP and QRE. The quality of the model predictions was evaluated using analysis of variance (ANOVA). For all metal ions, the R² (≥97%), R² adjusted (≥95%), and p-values (<0.05), indicating an excellent model accuracy. These results show that bio-coagulants (QRP and QRE) based a Quercus robur leaves are a promising, effective, and reliable option for removing heavy metal ions from water, and that the models developed can be used to optimize the coagulation-flocculation process. Full article