Search Results (293)

This study analyzed the heavy metal tolerance and chromium reduction and the potential of plant growth to promote Rhizobium sp. OS-1. By genetic makeup, the Rhizobium strain is nitrogen-fixing and phosphate-solubilizing in metal-contaminated agricultural soil. Among the Rhizobium group, bacterial strain OS-1 showed a significant tolerance to heavy metals, particularly chromium (900 µg/mL), zinc (700 µg/mL), and copper. In the initial investigation, the bacteria strains were morphologically short-rod, Gram-negative, appeared as light pink colonies on media plates, and were biochemically positive for catalase reaction and the ability to ferment glucose, sucrose, and mannitol. Further, bacterial genomic DNA was isolated and amplified with the 16SrRNA gene and sequencing; the obtained 16S rRNA sequence achieved accession no. HE663761.1 from the NCBI GenBank, and it was confirmed that the strain belongs to the Rhizobium genus by phylogenetic analysis. The strain’s performance was best for high hexavalent chromium [Cr(VI)] reduction at 7–8 pH and a temperature of 30 °C, resulting in a total decrease in 96 h. Additionally, the adsorption isotherm Freundlich and Langmuir models fit best for this study, revealing a large biosorption capacity, with Cr(VI) having the highest affinity. Further bacterial chromium reduction was confirmed by an enzymatic test of nitro reductase and chromate reductase activity in bacterial extract. Further, from the metal biosorption study, an Artificial Neural Network (ANN) model was built to assess the metal reduction capability, considering the variables of pH, temperature, incubation duration, and initial metal concentration. The model attained an excellent expected accuracy (R² > 0.90). With these features, this bacterial strain is excellent for bioremediation and use for industrial purposes and agricultural sustainability in metal-contaminated agricultural fields. Full article

Hexavalent chromium (Cr(VI)), a common contaminant in industrial wastewater, poses severe health risks due to its carcinogenic and mutagenic properties. Consequently, the development of efficient and environmentally friendly methods to reduce Cr(VI) to the less toxic trivalent chromium (Cr(III)) is of great importance. In this study, we present a cost-effective photocatalytic approach using graphitic carbon nitride (g-C₃N₄) modified with 1,3,5-trihydroxybenzene via one-step thermal condensation. The modified photo-catalyst exhibited improved surface area, porosity, visible-light absorption, and a narrowed band gap, all of which contributed to enhanced charge separation. As a result, nearly complete reduction in Cr(VI) was achieved within 90 min under visible-light irradiation. Further optimization of catalyst dosage and EDTA concentration gave even higher reduction efficiency. This work offers a promising strategy for the design of high-performance photocatalysts for environmental remediation. Full article

Chromium slag sites pose severe environmental risks due to hexavalent chromium (Cr(VI)) contamination, characterized by high mobility and toxicity. This study focused on chromium-contaminated soil from a historical chromium slag site in North China, where long-term accumulation of chromate production residues has led to serious Cr(VI) pollution, with Cr(VI) accounting for 13–22% of total chromium and far exceeding national soil risk control standards. To elucidate Cr(VI) transformation mechanisms and elemental linkages, a combined approach of macro-scale condition experiments and micro-scale analysis was employed. Results showed that acidic conditions (pH < 7) significantly enhanced Cr(VI) reduction efficiency by promoting the conversion of CrO₄²⁻ to HCrO₄⁻/Cr₂O₇²⁻. Among reducing agents, FeSO₄ exhibited the strongest effect (reduction efficiency >30%), followed by citric acid and fulvic acid. Temperature variations (−20 °C to 30 °C) had minimal impact on Cr(VI) transformation in the 45-day experiment, while soil moisture (20–25%) indirectly facilitated Cr(VI) reduction by enhancing the reduction of agent diffusion and microbial activity, though its effect was weaker than chemical interventions. Soil grain-size composition influenced Cr(VI) distribution unevenly: larger particles (>0.2 mm) in BC-35 and BC-36-4 acted as main Cr(VI) reservoirs due to accumulated Fe-Mn oxides, whereas BC-36-3 showed increased Cr(VI) in smaller particles (<0.074 mm). μ-XRF and correlation analysis revealed strong positive correlations between Cr and Ca, Fe, Mn, Ni (Pearson coefficient > 0.7, p < 0.01), attributed to adsorption–reduction coupling on iron-manganese oxide surfaces. In contrast, Cr showed weak correlations with Mg, Al, Si, and K. This study clarifies the complex factors governing Cr(VI) behavior in chromium slag soils, providing a scientific basis for remediation strategies such as pH adjustment (4–6) combined with FeSO₄ addition to enhance Cr(VI) reduction efficiency. Full article

In this study, activated carbon, iron-based waterwork sludge, and polyethyleneimine (PEI) were employed as the primary raw materials to synthesize the composite PEI@MMI(800) under the optimized conditions identified through experimental investigations. The resulting composite was employed as an adsorbent for static Cr(VI) adsorption tests. The results demonstrated that increasing the pH from 2 to 9 significantly decreased the Cr(VI) adsorption capacity from 41.09 mg/g to 15.75 mg/g. The adsorption process was well described by both the pseudo-second-order kinetic model and the Langmuir isotherm model. Thermodynamic analysis revealed that the adsorption process was spontaneous and endothermic in nature. The presence of anions (Cl⁻, SO₄²⁻, and PO₄³⁻) negatively impacted Cr(VI) adsorption, with their inhibitory effects following the order Cl⁻ < SO₄²⁻ < PO₄³⁻. Moreover, higher concentrations of these anions led to reduced Cr(VI) adsorption efficiency. After six cycles of use, PEI@MMI(800) retained 79.80% of its initial Cr(VI) adsorption capacity, indicating a loss of 20.20%. Based on the comprehensive characterization of the adsorbent and the results of the Cr(VI) adsorption tests, it was concluded that the removal of Cr(VI) by PEI@MMI(800) involved a combination of electrostatic adsorption, chelation of Cr(VI) by PEI, and reduction of Cr(VI) to Cr(III). Full article

In order to develop an efficient, environmentally friendly heavy metal ions adsorbent, the amino-modified expanded vermiculite-supported nano zero-valent iron (nZVI@PEI/EVMT) was prepared by using polyethyleneimine (PEI) as the functional reagent and expanded vermiculite (EVMT) as the carrier. The characterization results of nZVI@PEI/EVMT confirm that the PEI modification did not destroy the crystal configuration of EVMT, and when nano zero-valent iron (nZVI) was successfully loaded onto the PEI/EVMT surface, the value of saturation magnetic field was 41.5 emu/g, which could be separated from solution with magnet. The performance of Cr(VI) adsorption onto nZVI@PEI/EVMT was studied, showing that the ideal mass ratio for nZVI@PEI/EVMT was 1:1, and the removal capacity was largest when solution pH was 2. After four adsorption–desorption cycles, the adsorption amounts remained 40.1 mg/g. The Cr(VI) adsorption onto nZVI@PEI/EVMT was more consistent with a pseudo-second-order kinetics equation. Isotherm adsorption data accord with the Langmuir model, which suggests that the adsorption was the monolayer, the maximum adsorption amount was 116.2 mg/g at 30 °C and pH 2, and the adsorption was spontaneous and endothermic. It was inferred that the adsorption mechanisms included electrostatic attraction, reduction, chemical complexation, and co-precipitation. Full article

Chromium (III) ions are essential for biological functions, whereas chromium (VI) ions (Cr (VI)) pose toxicity risks to both humans and animals. Therefore, it is crucial to remove these ions from industrial sources. In this work, to remove hazardous Cr (VI) from wastewater or convert it to Cr (III), catechol-modified alkali lignin (CAL) was prepared using catechol, acetone, and alkali lignin, which is a byproduct in the paper-pulping process. The sample was characterized using a combination of techniques, including scanning electron microscopy, thermogravimetric analysis, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. Various factors influencing the adsorption behavior of CAL were investigated. The adsorption behavior aligns with the pseudo-second-order kinetic model and adheres to the Langmuir isotherm model. CAL simultaneously achieves Cr (VI) adsorption (498.4 mg/g) and reduction (54.6% to Cr (III)), surpassing single-function lignin adsorbents by integrating catechol’s redox capacity with lignin’s structural stability, which is another way to efficiently utilize Cr (VI) solutions. The mechanism of adsorption and reduction is discussed, which is influenced by its functional groups. In brief, this method paves a new path for the utilization of alkali lignin and provides novel opportunities for the removal of Cr (VI) contamination. Full article

Significant heavy metals contamination is often caused by rapid industrialization, which is devastating to both public health and the environment. Conventional processes of metal removal also result in the accumulation of secondary waste. This work proposes the use of a novel fungal biomass (microwave heat dried) from Arthrinium malaysianum for the biosorption of toxic chromium. We have meticulously explored and investigated the interactions of hexavalent chromium with dried biomass using several cutting-edge techniques like FTIR for studying the involvement of functional groups on the biomass surface, XRD for the surface architecture changes after metal binding, XPS to unravel the reduction of hexavalent chromium into its non-toxic form, and FESEM-EDX for the visualization of the ultra-structure of fungal cell surface. The Langmuir isotherm demonstrates that the maximum removal capacity Q_max of Cr(VI) is 102.310 mgg⁻¹, at a pH of 3.5 with 100% removal of Cr(VI). There were substantial changes in the surface architecture during adsorption, confirmed by FESEM and AFM studies. FTIR and XPS data analysis indicated that carbonyl, hydroxyl, phosphate, and amine groups were responsible for the conversion of Cr(VI) (toxic) to Cr(III) (non-toxic). The IR spectra of biomass treated with Cr showed a decreased C-O stretching intensity and slight shriveling of the -OH band, and the bands in the FTIR spectra at 1642 cm⁻¹ to 1635 cm⁻¹ and at 1549 cm⁻¹ to 1547 cm⁻¹ shifted and appeared quite distinct. XRD revealed that the chromium-treated biomass had greater crystalline features and also the appearance of a wide peak where 2θ = 20°, approximately, indicating an amorphous nature at 576.0 eV and in highly loaded chromium (500 mg/L) biomass, with the Cr2p level displaying a slight shift, eventually terminating in a (576.0 eV) Cr₂O₃ to Cr(III) peak. Since the FTIR and XPS data obtained revealed that Cr(VI) reduces to Cr(III), this fungal biomass can also be used for generating metallic nanoparticles during biosorption. Thus, we suggest that the above-mentioned fungal biomass could be a very useful biomaterial for future translational research. We are in the process of fabricating beads with powdered biomass for further studies. Full article

Hexavalent chromium [Cr(VI)] is a hazardous environmental contaminant, and palladium nanoparticles (PdNPs) have shown promise as catalysts for its reduction. This study explores the primary factor influencing the catalytic performance of PdNPs in Cr(VI) reduction by investigating the crystal structure and composition of PdNPs in fungal-based catalysts. Five Pd-loaded catalysts were synthesized by treating fungal biomass with different chemical reagents, resulting in varying Pd(0) contents. The nanoparticle morphology, chemical states, and functional group interactions during Pd adsorption and reduction were investigated using multiple analytical techniques. The results showed that fungal hyphae remained structurally intact throughout the treatment process. PdNPs smaller than 2 nm were observed, with both Pd(0) and PdO present. The proportion of Pd(0) ranged from 6.4% to 37.2%, depending on the chemical reagent used. In addition, functional groups such as phosphate, amine, hydroxyl, and carboxyl were found to play key roles in palladium binding, underscoring the importance of surface chemistry in the adsorption and reduction process. A strong positive correlation was observed between the Pd(0) content and catalytic activity. Notably, the NCPdSF sample (palladium-loaded biomass treated with sodium formate) exhibited the highest Pd(0) content of 59.2% and achieved the most effective Cr(VI) reduction. These results suggest that Pd(0) content is a key determinant of catalytic efficiency in Cr(VI) reduction and that optimizing chemical treatments to enhance Pd(0) levels can substantially improve catalyst performance. Full article

Sulfidation has gained increasing attention due to its merits to improve the structural-activity of nanoscale zerovalent iron (nZVI) and thus enhance its reactivity toward contaminants. Few studies have been conducted to elucidate the correlation between the structural-activity and reactivity of nZVI, which is important for up-scaling such a decontamination strategy. Taking chromate (Cr(VI)) as the targeted contaminant, this study found that sulfidation enhanced the reactivity of nZVI toward Cr(VI) to varying extents, which was closely related to the degree and order of sulfidation. Particularly, the optimal rate constants of S-nZVI for Cr(VI) removal were 9.79 and 1.48 times higher than that of nZVI in the batch and column systems, respectively. In addition, this study suggested that sulfidation enhanced the electrical conductivity of nZVI by forming conductive iron sulfides (FeSx), while simultaneously reducing the particle aggregation and thus attenuating the settling rate of nZVI in water. More importantly, the reactivity of S-nZVI toward Cr(VI) exhibited negative correlations with its sedimentation activity and electrical conductivity. These relationships can be potentially used to predict the decontamination reactivity of S-nZVI if its sedimentation or conductivity activity was known in advance. Finally, this study clarified the sulfidation-induced improvement in reactivity of nZVI toward Cr(VI), which should be primarily associated with the improved reactive site of S-nZVI due to excellent dispersion and excellent conductivity due to FeSx introduction, ultimately facilitating the reduction of Cr(VI) by nZVI. Full article

Microbial remediation of Cr(VI)-polluted wastewater offers an effective and sustainable green method. In this study, a novel strain Priestia megaterium strain BM.1 that was capable of reducing Cr(VI) was domesticated. In order to improve its Cr(VI) reduction and adsorption performance, calcium-modified hydrochar (HC-Ca) was utilized to immobilize the strain to obtain the composite material BM.1-Ca. The BM.1-Ca composite achieved a Cr(VI) removal efficiency of 97% at an initial concentration of 60 mg/L within 60 h, representing a 1.96-fold enhancement compared to BM.1 alone and demonstrating significantly improved microbial Cr(VI) removal capacity. The addition of HC-Ca was instrumental in maintaining the stable Cr(VI) removal efficiency of BM.1 in the presence of altered incubation environments and interference from co-existing ions. The reduction in Cr(VI) by BM.1 and the immobilization of Cr(III) on the surface of BM.1-Ca are the main removal mechanisms of Cr(VI). Analysis of microbial oxidative stress and extracellular polymers showed that HC-Ca was able to attenuate the oxidative stress of BM.1 as well as promote the secretion of extracellular polymers. This study reveals the intrinsic mechanism of the novel material BM.1-Ca for remediation of Cr(VI) pollution in water bodies and provides an effective method for bioremediation of Cr(VI). Full article

Hexavalent chromium (Cr(VI)) is of significant interest in the environmental field due to its high toxicity. Biochar is commonly used as an adsorbent for Cr(VI) removal from wastewater. However, its lower removal efficiency remains a persistent challenge. This study develops an iron-modified rice straw biochar through a simple precipitation and pyrolysis method and applies it for Cr(VI) removal in wastewater, which could convert waste into treasure and improve the adsorption performance of adsorbent. In the adsorption experiments, the results revealed that the adsorption efficiency of Cr(VI) reached 95.54% within 480 min (conditions: adsorbent dosage 2.67 g/L, pH 2.5, temperature 25 ± 2 °C). The Langmuir isotherm model was more suitable to describe the adsorption behavior of Cr(VI) by Fe-BC, and the fitted adsorption capacity achieved 10.03 mg/g. The experimental process was better described by the pseudo-second-order kinetic model, indicating that the adsorption process chemical adsorption was the rate-limiting step. The thermodynamic experiments revealed that the adsorption process of Cr(VI) by Fe-BC was spontaneous and endothermic. Column experiments demonstrated that a lower flow speed was beneficial to adsorption performance. Mechanistic studies highlighted the synergistic roles of electrostatic attraction, ion exchange, and reduction in Cr(VI) removal. These findings provide novel perspectives and innovative approaches for the development and application of adsorbents. Full article

The widespread industrial use of chromium has exacerbated water contamination issues globally. In this study, a nitrogen-doped wheat straw biochar loaded with nanoscale zero-valent iron composite (nZVI/N-KBC) was synthesized via a liquid-phase reduction method, and its adsorption properties for hexavalent chromium (Cr(VI)) in aqueous solutions were systematically investigated. The material was characterized using SEM, XRD, Raman spectroscopy, FTIR, and XPS. Experimental results demonstrated that under optimal conditions (pH 2, 0.05 g adsorbent dosage, and 50 mg/L initial Cr(VI) concentration), the adsorption capacity reached 41.29 mg/g. Isothermal adsorption analysis revealed that the process followed the Langmuir model, indicating monolayer adsorption with a maximum capacity of 100.9 mg/g. Kinetic studies show that the adsorption conforms to the pseudo-second-order kinetic model, and thermodynamic and XPS analyses jointly prove that chemical adsorption is dominant. Thermodynamic analyses confirmed the endothermic and entropy-driven nature of adsorption. Mechanistic studies via XPS and FTIR revealed a dual mechanism: (1) partial adsorption of Cr(VI) onto the nZVI/N-KBC surface, and (2) predominant reduction in Cr(VI) to Cr(III) mediated by Fe⁰ and Fe²⁺. This study highlights the synergistic role of nitrogen doping and nZVI loading in enhancing Cr(VI) removal, offering a promising approach for remediating chromium-contaminated water. Full article

Extracting Cr(VI), a heavy metal known for its carcinogenic properties, from water poses a significant challenge. This research involved synthesizing nitrogen-infused starch-derived hydrothermal carbon (NS-HCS) from starch using a dual-phase hydrothermal method, aimed at removing Cr(VI) from industrial wastewater. N-doping increased the N content from 0.27% to 3.64%, providing active sites for enhanced Cr(VI) adsorption and reduction. Experimental data demonstrated 149.21 mg/g contaminant uptake capacity with 49.74% removal efficiency under specified conditions. Analysis of the kinetic and isotherm models revealed that the adsorption mechanism was characterized primarily by multilayer adsorption. Furthermore, after six cycles of use, NS-HCS demonstrated good reusability, with its Cr(VI) adsorption capacity remaining at approximately 79.05%. Additionally, NS-HCS exhibited strong resistance to interference in complex aqueous environments. This study provides new insights into the use of green and sustainable adsorbents, offering an economical and efficient solution for treating Cr(VI)-contaminated wastewater. Full article

Zero-valent iron (ZVI), particularly in its nanoscale form (nZVI), is now considered a highly promising material for the remediation of toxic metal ions from polluted groundwater owing to its strong reductive potential, significant surface area, and reactive behavior. This review systematically explores the application of pristine and modified ZVI systems—including doped ZVI, bio-stabilized composites, and ZVI supported on advanced materials like MXene and nanocellulose—for effective treatment of water containing metal species like As(III/V), Hg(II), Cr(VI), and Ni(II). Emphasis is placed on understanding the underlying mechanisms, including redox reactions, surface complexation, and synergistic adsorption–reduction pathways. Key factors affecting adsorption efficiency—such as pH, temperature, ZVI dosage, and competing ions—are thoroughly analyzed, alongside adsorption kinetics and isotherm models. Modified ZVI composites exhibit enhanced stability, selectivity, and reusability, demonstrating promising performance even in complex aqueous environments. Despite significant progress, challenges such as nanoparticle passivation, limited field-scale data, and potential toxicity of byproducts remain. The review concludes by highlighting future research directions focused on improving material longevity, regeneration efficiency, selective adsorption, and integration with other advanced remediation technologies for sustainable and scalable groundwater treatment. Full article

A polyoxometalate-based metal–organic complex with the ability to treat pollutants in water was obtained under hydrothermal conditions, namely [Ni(H₂L)(HL)₂](PMo₁₂O₄₀)·3H₃O·4H₂O (1) (H₂L = 4,4′-(1H,1′H-[2,2′-biimidazole]-1,1′-diyl)dibenzoicacid). Structural analysis reveals that the [Ni(H₂L)(HL)₂] units are interconnected into a 2D layer via hydrogen bonds between adjacent carboxyl groups and water molecules of crystallization. [PMo₁₂O₄₀]³⁻ anions are embedded within the larger pores of the layer and are connected to the adjacent layers through hydrogen bonds, ultimately expanding the structure into a 3D supramolecular architecture. The intermolecular interactions were studied via Hirshfeld surface (HS) analysis. Electrochemical performance tests reveal that 1 exhibits electrocatalytic activity toward the oxidation and reduction of diverse pollutants in water, including NO₂⁻, Cr(VI), BrO₃⁻, Fe(III), and ascorbic acid (AA). Additionally, it can also serve as an amperometric sensor for the detection of BrO₃⁻ and Cr(VI). Photocatalytic studies reveal that compound 1 functions as a bifunctional photocatalyst, which not only achieves efficient degradation of organic dyes but also demonstrates remarkable reduction efficiency for toxic Cr(VI). Compound 1 demonstrates significant potential for practical water remediation applications. Full article