Effective removal of heavy metal ions by attapulgite supported sulfidized nanoscale zerovalent iron from aqueous solution

Removal mechanism of Pb(ii) from soil by biochar-supported nanoscale zero-valent iron composite materials

As an adsorbent, biochar has a highly porous structure and strong adsorption capacity, and can effectively purify the environment. In response to the increasingly serious problem of heavy metal pollution in water, this study used nano zero valent iron and rice husk biochar to prepare a new type of magnetic sheet-like biochar loaded nano zero valent iron (BC-nZVI) composite material through rheological phase reaction, showing remarkable advantages such as low cost, easy preparation, and superior environmental remediation effect. The physical and chemical properties and structure of the material were extensively characterized using various methods such as HRTEM, XPS, FESEM, EDS, XRD, FTIR, and RAMAN. Concurrently, batch experiments were undertaken to assess the removal efficiency of Pb(ii) by BC-nZVI, with investigations into the influence of pH value, temperature, soil water ratio, and initial concentration of heavy metal ion solution on its removal efficiency. The results indicate that the removal of Pb(ii) by BC-nZVI reaches an equilibrium state after around 120 minutes. Under the conditions of pH 6, temperature 20 °C, soil water ratio 1 : 5, and BC-nZVI dosage of 1 g L-1, BC-nZVI can reduce the Pb(ii) content in wastewater with an initial concentration of 30 mg L-1 to trace levels, and the treatment time is about 120 minutes. The analysis of adsorption kinetics and isotherms indicates that the adsorption process of Pb(ii) by BC-nZVI adheres to the quasi-second-order kinetic model and Langmuir model, suggesting a chemical adsorption process. Thermodynamic findings reveal that the adsorption of Pb(ii) by BC-nZVI is spontaneous. Furthermore, BC-nZVI primarily accumulates Pb(ii) through adsorption co-precipitation. BC-nZVI serves as an eco-friendly, cost-effective, and highly efficient adsorbent, showing promising capabilities in mitigating Pb(ii) heavy metal pollution. Its recoverability and reusability facilitated by an external magnetic field make it advantageous for remediating and treating lead-contaminated sites.

Enhancement of norfloxacin degradation by citrate in S-nZVI@Ps system: Chelation and FeS layer

The degradation of organic pollution by sulfur-modified nano zero-valent iron(S-nZVI) combined with advanced oxidation systems has been extensively studied. However, the low utilization of nZVI and low reactive oxygen species (ROS) yield in the system have limited its wide application. Herein, a natural organic acid commonly found in citrus fruits, citric acid (CA), was combined with the conventional S-nZVI@Ps system to enhance the degradation of norfloxacin (NOR). The addition of CA increased the NOR removal by about 31% compared with the conventional S-nZVI@Ps system under the same experimental conditions. Among them, the enhanced effect of CA is mainly reflected in its ability to promote the release of Fe2+ and accelerate the cycling of Fe2+ and Fe3+ to further improve the utilization of nZVI and the generation of ROS; it also promotes the dissolution of the active substance (FeS) on the surface of S-nZVI to further improve the degradation rate of NOR. More importantly, the chelate of CA and Fe2+ (CA-Fe2+) had higher reactivity than alone Fe2+. Free radical quenching and electron spin resonance (ESR) experiments indicated that the main ROS for the degradation of NOR in the CA/S-nZVI@Ps system were SO4•- and OH•. CA-bound sulfur-modifying effects on NOR degradation was systematically investigated, and the degradation mechanism of NOR in CA/S-nZVI@Ps system was explored by various techniques. Additionally, the effect of common anions in water matrix on the degradation of NOR in CA/S-nZVI@Ps system and its degradation of various pollutants were also studied. This study provides a new perspective to enhance the degradation of pollutants by S-nZVI combined with advanced oxidation system, which can help to solve the application boundary problem of S-nZVI.

Performance evaluation of sulfidated nanoscale iron for hexavalent chromium removal from groundwater in sequential batch study

Chromium [Cr] contamination in groundwater is one of the serious environmental concerns due to the carcinogenicity of its water-soluble and mobile hexavalent [Cr(VI)] form. In spite of the existence of multiple precipitation and adsorption-based Cr(VI) remediation technologies, the usage of sulfidated nano zerovalent iron (S-nZVI) has recently attracted researchers due to its high selectivity. Although S-nZVI effectively immobilized Cr(VI), its long-term performance in multiple shifted equilibrium has not been explored. In this contribution, influences of S-nZVI dosage, initial concentration of Cr(VI), pH, ionic strength, total hardness, sulfate, carbonate, and silicate were probed in ultrapure water. Further experiments were performed in synthetic groundwater to investigate the effects of initial concentration of Cr(VI) in the pH range of 4-8 for 1 g L-1 S-nZVI dosage. Cr(VI) removal rate was quantified in groundwater without pH fixation. Finally, a comparative study between conventional nano zerovalent iron (nZVI) and S-nZVI was conducted in sequential batch reactors to investigate their respective efficiencies during repeated usage. Mechanistic interpretation of the processes governing the immobilization of Cr(VI) was done by integrating the results of these experiments with the metadata. While aggregation due to magnetic properties and rapid oxidation of Fe decreased the efficiency of nZVI with repeated usage, sulfidation minimized the passivation and favored an extended reducing environment because of continuous electron transfer from iron and sulfur components.

Recent advances in sulfidized nanoscale zero-valent iron materials for environmental remediation and challenges

Over the past decade, sulfidized nanoscale zero-valent iron (S-nZVI) has been developed as a promising tool for the remediation of contaminated soil, sediment, and water. Although most studies have focused on applying S-nZVI for clean-up purposes, there is still a lack of systematic summary and discussion from its synthesis, application, to toxicity assessment. This review firstly summarized and compared the properties of S-nZVI synthesized from one-step and two-step synthesis methods, and the modification protocols for obtaining better stability and reactivity. In the context of environmental remediation, this review outlined an update on the latest development of S-nZVI for removal of heavy metals, organic pollutants, antibiotic resistance genes (ARGs), and antibiotic resistant bacteria (ARB) and also discussed the underlying removal mechanisms. Environmental factors affecting the remediation performance of S-nZVI (e.g., humic acid, coexisting ions, S/Fe molar ratio, pH, and oxygen condition) were highlighted. Besides, the application potential of S-nZVI in advanced oxidation processes (AOP), especially in activating persulfate, was also evaluated. The toxicity impacts of S-nZVI on the environmental microorganism were described. Finally, the future challenges and remaining restrains to be resolved for better applicability of S-nZVI are also proposed. This review could provide guidance for the environmental remediation with S-nZVI-based technology from theoretical basis and practical perspectives.

Synergistic effect of sulfidated nano zerovalent iron and proton-buffering montmorillonite in reductive immobilization of alkaline Cr(VI)-contaminated soil

Effective remediation of Cr(VI)-contaminated soil with strong alkalinity and high Cr(VI) concentration is a severe challenge. Herein, a proton-buffering montmorillonite-supported sulfidated nano zerovalent iron (nFeS/Fe⁰@H-Mt) was developed for remediation of alkaline Cr(VI)-contaminated soil. The reductive efficiencies of water-soluble Cr(VI) reached 99.7%, 99.3% and 99.8% in three tested soils with initial concentrations of 439.6, 3307.5 and 4626.7 mg kg^-1, respectively, after 15 d of nFeS/Fe⁰@H-Mt treatment. Further speciation analyses demonstrated most available Cr species (exchangeable and carbonate-bound Cr) were transformed into more stable Cr species. The leachable Cr(VI) and total Cr obtained by toxicity leaching procedures decreased to extremely low levels and maintained long-term stability for 120 d. Such superior reductive immobilization performance of FeS/Fe⁰@H-Mt was attributed to the synergistic effect of sulfidated nano zerovalent iron and proton-buffering montmorillonite, which induced the coordination of proton donation and electron transfer. The proton-buffering montmorillonite (H-Mt) could prevent the aggregation of nanoparticles and provide protons to accelerate the corrosion of Fe⁰. In addition, the FeS component improved electron selectivity and facilitated electron transfer of Fe⁰ to Cr(VI). Our study demonstrated that the coordination of proton donation and electron transfer significantly enhanced the Cr(VI) reduction under the alkaline condition thus leading to effective remediation of alkaline Cr(VI)-contaminated soil.

Recent Advances in Adsorptive Nanocomposite Membranes for Heavy Metals Ion Removal from Contaminated Water: A Comprehensive Review

Water contamination is one of the most urgent concerns confronting the world today. Heavy metal poisoning of aquatic systems has piqued the interest of various researchers due to the high toxicity and carcinogenic consequences it has on living organisms. Due to their exceptional attributes such as strong reactivity, huge surface area, and outstanding mechanical properties, nanomaterials are being produced and employed in water treatment. In this review, recent advances in the use of nanomaterials in nanoadsorptive membrane systems for wastewater treatment and heavy metal removal are extensively discussed. These materials include carbon-based nanostructures, metal nanoparticles, metal oxide nanoparticles, nanocomposites, and layered double hydroxide-based compounds. Furthermore, the relevant properties of the nanostructures and the implications on their performance for water treatment and contamination removal are highlighted. The hydrophilicity, pore size, skin thickness, porosity, and surface roughness of these nanostructures can help the water permeability of the nanoadsorptive membrane. Other properties such as surface charge modification and mechanical strength can improve the metal adsorption effectiveness of nanoadsorptive membranes during wastewater treatment. Various nanocomposite membrane fabrication techniques are also reviewed. This study is important because it gives important information on the roles of nanomaterials and nanostructures in heavy metal removal and wastewater treatment.