Amorphous iron sulfide nanowires as an efficient adsorbent for toxic dye effluents remediation

FeS-based nanocomposites: A promising approach for sustainable environmental remediation - Focus on adsorption and photocatalysis - A review

Population expansion, industrialization, urban development, and climate changes increased the water crisis in terms of drinking water availability. Among the various nanomaterials for nanoremediation towards water treatment, FeS-based nanocomposites have emerged as promising candidates in the adsorptive and photocatalytic removal of contaminants. This paper, therefore, evaluates the potential of FeS-based nanocomposites for environmental applications, more specifically the combined use of adsorption and photocatalysis. Pyrite and mackinawite structures outcompeted the other FeS configurations due to their large surface areas, numerous active sites, and enhanced conductivity, factors that enhance the adsorption and photovoltaic processes. To improve photocatalytic performance FeS requires modification with additional materials. Various fabrication strategies (including hydrothermal method, co-precipitation, electrochemical anodization, electrospinning, impregnation, green synthesis, mechanochemical approach/ball milling) of FeS-based composites and their efficacy and the mechanisms for removing organic and inorganic pollutants are reviewed in this paper. The structural characteristics of FeS scaffolds play a crucial role in the effective removal of heavy metals, such as Hg and Cr ions, primarily through ion exchange and surface complexation. Organic pollutants such as methylene blue and tetracycline were effectively degraded by advanced oxidation processes (AOPs). A large scale applications of FeS include industrial wastewater treatment, groundwater remediation towards trichloroethylene and other organic solvents removal, municipal wastewater, oil spills cleanup, pre-treatment for seawater desalination. Current challenges relate to catalysts stability, their removal after treatment stage, recycling, metals leaching and up-scaling as well as high effectiveness in real case-scenario and costs optimization. In summary, this review will help to advance research in the field of environmental remediation using FeS-based nanocomposites.

Perfluorooctanoic acid transport and fate difference driven by iron-sulfide minerals transformation interacting with different types of groundwater

Perfluorooctanoic acid (PFOA) is an emerging persistent organic pollutant that threatens human health and ecosystems. However, the intricate mechanism of the change in PFOA transport behavior that interacts with FexSy minerals under groundwater-type differences is not clear. To address this knowledge gap, multi-scale experiments and multi-process reaction models were constructed to investigate the underlying mechanisms. The results showed that different groundwater (NO3-, Cl--Na+, SO42-, and HCO3- types) had significant effects on PFOA transport. NO3-, Cl--Na+, SO42-, and HCO3- decreased the retardation effect of PFOA in the FexSy media. Compared to other groundwater types, the adsorption sites of FexSy were the least occupied in the NO3- groundwater. This observation was supported by the least inhabition of λ in FexSy-NO3- interaction system, which demonstrated that more PFOA was in a high reaction zone and electrostatic repulsion was weakest. The surface tension of different ion types in groundwater provided evidence explaining the lowest inhibition in the FexSy-NO3- system. The 2D spatiotemporal evolution results showed that in FexSy with NO3- system, the pollutant flux (6.00 ×10-5 mg·(m2·s)-1) was minimal. The pollutant flux in the SO42- groundwater system was 9.95-fold that in FexSy with the NO3- groundwater. These findings provide theoretical support for understanding the transport and fate of PFOA in FexSy transformations that interact with different types of groundwater.

Removal of toxic metals using iron sulfide particles: A brief overview of modifications and mechanisms

Growing mechanization has released higher concentrations of toxic metals in water and sediment, which is a critical concern for the environment and human health. Recent studies show that naturally occurring and synthetic iron sulfide particles are efficient at removing these hazardous pollutants. This review seeks to provide a concise summary of the evolution in the production of iron sulfide particles, specifically nanoparticles, through the years. This review presents an outline of the synthesis process for the most dominant forms of iron sulfide: mackinawite (FeS), pyrite (FeS2), pyrrhotite (Fe1-x S), and greigite (Fe3S4). The review confirms that both natural forms of iron sulfide and modified forms of iron sulfide are highly effective at removing different heavy metals and metalloids from water. Concurrently, this review reveals the interaction mechanism between toxic metals and iron sulfide, along with the impact of conditions for remedy and rectification. None the less, modifications and future investigations into the synthesis of novel iron sulfides, their use to adsorb diverse environmental pollutants, and their fate after injection into polluted aquifers, remain crucial to maximizing pollution control.

Synthesis of Sb2S3 nanosphere layer by chemical bath deposition for the photocatalytic degradation of methylene blue dye

An antimony tri-sulfide Sb₂S₃ nanosphere photocatalyst was effectively deposited utilizing sodium thiosulfate and antimony chloride as the starting precursors in a chemical bath deposition process. This approach is appropriate for the large-area depositions of Sb₂S₃ at low deposition temperatures without the sulfurization process since it is based on the hydrolytic decomposition of starting compounds in aqueous solution. X-ray diffraction patterns and Raman spectroscopy analysis revealed the formation of amorphous Sb₂S₃ layers. The scanning electron microscopy images revealed that the deposited Sb₂S₃ has integrated small nanospheres into sub-microspheres with a significant surface area, resulting in increased photocatalytic activity. The optical direct bandgap of the Sb₂S₃ layer was estimated to be about 2.53 eV, making amorphous Sb₂S₃ appropriate for the photodegradation of organic pollutants in the presence of solar light. The possibility of using the prepared Sb₂S₃ layer in the photodegradation of methylene blue aqueous solutions was investigated. The degradation of methylene blue dye was performed to evaluate the photocatalytic property of Sb₂S₃ under visible light. The amorphous Sb₂S₃ exhibited photocatalytic activity for the decolorization of methylene blue solution under visible light. The mechanism for the photocatalytic degradation of methylene blue has been proposed. Our results suggest that the amorphous Sb₂S₃ nanospheres are valuable material for addressing environmental remediation issues.

Synthesis and characterization of nanoparticles of cobalt and nickel ferrites for elimination of hazardous organic dyes from industrial wastewater

This study presents the results of synthesis and characterization of nanoparticles of cobalt ferrite (CoFe₂O₄) and nickel ferrite (NiFe₂O₄) using co-precipitation method followed by application for removal of hazardous organic textile dyes of thiazole yellow G (TYG) and alizarin yellow R (AYR). XRD analysis confirmed formation of cubic spinel structure with average crystallite sizes at 16.07 nm and 13.84 nm for CoFe₂O₄ and NiFe₂O₄, respectively. Field emission scanning electron microscopy (FESEM) analysis showed agglomeration of spherical shape morphology with uniformly distributed Co, Ni, Fe, and O elements. The surface area calculated from Brunauer-Emmett-Teller (BET) analysis was 64 m²/g and 62 m²/g for CoFe₂O₄ and NiFe₂O₄, respectively. Vibrating sample magnetometer (VSM) showed super-paramagnetic behavior for all samples with magnetic saturation (M_s) at 7.269 and 6.61 emu/g for CoFe₂O₄ and NiFe₂O₄, respectively. The adsorption influencing parameters such as pH of solution, quantity of adsorbent, and contact time on dye removal efficiency were thoroughly investigated. Overall, acidic condition of samples with pH at 4 favored the maximum removal efficiency by CoFe₂O₄ as 98, 97, and 93%, and by NiFe₂O₄ as 96, 93, and 92%, respectively, for TYG, AYR, and mixture sample. The Langmuir adsorption isotherm model describes the equilibrium of all samples with the best fit of coefficient of determination (R²). The adsorption results fitted well with a pseudo-second-order kinetic model for all samples. The regeneration-reuse ability of adsorbents and cost estimation analysis of the dye removal process suggested that the economic suitability of nano-adsorbents for remediation of textile effluents was favored. The estimated thermodynamic parameters inferred that the removal of organic dyes onto the surface of CoFe₂O₄ and NiFe₂O₄ is a spontaneous, favorable, and exothermic physical adsorption process.

Multi-catalysis of glow discharge plasma coupled with FeS2 for synergistic removal of antibiotic

Fe-based composites improved the energy utilization efficiency of plasma for removing contaminants through multi-catalysis have received much attention. However, the energy efficiency and catalytic activity are compromised by the slow transformation from Fe (Ⅲ) to Fe (Ⅱ). Here, given the electron-donating ability of reducing sulfur species, as well as the acidic environment generated by FeS₂, single FeS₂ was introduced into the glow discharge plasma (GDP) reactor for the removal of tylosin (TYL). The results showed that a significant synergistic effect between FeS₂ and GDP improved the energy efficiency of plasma and the removal efficiency of TYL (99.7%). FeS₂ boosted the generation of radicals (·OH, ·O₂^-) and nonradicals (h⁺, e^-) rather than H₂O₂ and O₃, which played an important role in TYL abatement. Moreover, the electrons donating sulfur and iron species from FeS₂ can accelerate the conversion of Fe(III) to Fe(II), which was conducive to the generation of radicals. Besides, acid solution self-adjustment resulted from the oxidation of FeS₂ improved heterogeneous Fenton reaction, the oxidation potential of ·OH and adsorption of positive charged TYL. The plausible degradation pathways of TYL were proposed in GDP/FeS₂ system. In summary, enhanced removal of TYL was mainly attributed to the catalytic pathway altered by FeS₂ through high-energy electrons, photocatalysis, heterogeneous Fenton and O₃ catalysis in the GDP system simultaneously. The strategy of integrating GDP with FeS₂ proposed in this work is expected to offer a feasible and potential technique for organic wastewater treatment.

A facile chemical synthesis of nanoflake NiS2 layers and their photocatalytic activity

A single-phase and crystalline NiS2 nanoflake layer was produced by a facile and novel approach consisting of a two-step growth process. First, a Ni(OH)2 layer was synthesized by a chemical bath deposition approach using a nickel precursor and ammonia as the starting solution. In a second step, the obtained Ni(OH)2 layer was transformed into a NiS2 layer by a sulfurization process at 450 °C for 1 h. The XRD analysis showed a single-phase NiS2 layer with no additional peaks related to any secondary phases. Raman and X-ray photoelectron spectroscopy further confirmed the formation of a single-phase NiS2 layer. SEM revealed that the NiS2 layer consisted of overlapping nanoflakes. The optical bandgap of the NiS2 layer was evaluated with the Kubelka-Munk function from the diffuse reflectance spectrum (DRS) and was estimated to be around 1.19 eV, making NiS2 suitable for the photodegradation of organic pollutants under solar light. The NiS2 nanoflake layer showed photocatalytic activity for the degradation of phenol under solar irradiation at natural pH 6. The NiS2 nanoflake layer exhibited good solar light photocatalytic activity in the photodegradation of phenol as a model organic pollutant.

Trichloroethylene degradation by PVA-coated calcium peroxide nanoparticles in Fe(II)-based catalytic systems: enhanced performance by citric acid and nanoscale iron sulfide

In this study, the enhanced trichloroethylene (TCE) degradation performance was investigated by polyvinyl alcohol coated calcium peroxide nanoparticles (PVA@nCP) as an oxidant in Fe(II)-based catalytic systems. The nanoscale iron sulfide (nFeS), having an average particle size of 115.4 nm, was synthesized in the laboratory and characterized by SEM, TEM, HR-TEM along with EDS elemental mapping, XRD, FTIR, ICP-OES, and XPS techniques. In only ferrous iron catalyzed system (PVA@nCP/Fe(II)), TCE degradation was recorded at 58.9% in 6 h. In comparison, this value was increased to 97.5% or 99.7% with the addition of citric acid (CA) or nFeS in PVA@nCP/Fe(II) system, respectively. A comparative study was performed with optimum usages of chemical reagents in both PVA@nCP/Fe(II)/CA and PVA@nCP/Fe(II)/nFeS systems. Further, the probe compounds tests and electron paramagnetic resonance (EPR) analysis confirmed the generation of reactive oxygen species. The scavenging experiments elucidated the dominant role of HO• to TCE degradation, particularly in PVA@nCP/Fe(II)/nFeS system. Both CA and nFeS strengthened PVA@nCP/Fe(II) system, but displayed completely different mechanisms in the enhancement of active radicals generation; hence, their different contribution to TCE degradation. The acidic environment was favorable for TCE degradation, and a high concentration of HCO₃^- inhibited TCE removal in both systems. Conclusively, compared to PVA@nCP/Fe(II)/nFeS system, PVA@nCP/Fe(II)/CA system resulted in encouraging TCE degradation outcomes in actual groundwater, showing great potential for prolonged benefits in the remediation of TCE polluted groundwater. Graphical abstract.

Elimination performance of methylene blue, methyl violet, and Nile blue from aqueous media using AC/CoFe2O4 as a recyclable magnetic composite

The present paper describes the sono-assisted adsorption (sono-adsorption) of methylene blue (MB), methyl violet (MV), and Nile blue (NB) from aqueous solution by AC/CoFe₂O₄ magnetic composite. FT-IR, TGA-DTG, VSM, XRD, TEM, SEM, EDX, Map, and Raman analysis were used to characterize the magnetic composite. The magnetization saturation value of AC/CoFe₂O₄ magnetic composite was determined to be 53.06 emu/g. Dye sono-adsorption efficiency was increased by increasing adsorbent dose, pH value, and contact time, but not dye concentration. Pseudo-first-order, pseudo-second-order, and intra-particle diffusion models were used to study the kinetic behavior of the cationic dye sono-adsorption. The sono-adsorption kinetics was reasonably followed by pseudo-second-order model (R² > 0.998). The results showed that the Freundlich model (R² > 0.976) was more able to describe the sono-adsorption equilibrium behavior than Langmuir, D-R, and Scatchard models. The maximum sono-adsorption capacity of NB, MV, and MB was determined as 86.24, 83.90, and 87.48 mg/g, respectively. Based on the parameters derived from isotherm modeling (R_L, n, and E), the sono-adsorption process of cationic dyes is desirable and physical. An increase in NaCl concentration reduced the sono-adsorption efficiency for all dyes. Also, the adsorption-desorption of AC/CoFe₂O₄ magnetic was studied up to 10 stages, and it was confirmed that the sono-adsorption efficiency is acceptable up to the eight stage. AC/CoFe₂O₄ magnetic composite is, therefore, an affordable and recyclable adsorbent to remove the molecule of NB, MV, and MB dyes from aqueous media.