Nano scale zero valent iron production methods applied to contaminated sites remediation: An overview of production and environmental aspects

Ball-milled sulfide iron-copper bimetals based composite permeable materials for Cr (VI) removal: Effects of preparation parameters and kinetics study

Zero-valent iron (ZVI) and modified ZVI have been investigated extensively for groundwater remediation. However, ZVI based powder was difficult to be applied directly as permeable reactive barrier (PRB) materials due to their low water permeability and usage rate. In this study, sulfide iron-copper bimetal was prepared by ball milling, which is environment-friendly without second contamination. The optimal preparation parameters of sulfide iron-copper bimetal for Cr(VI) removal were determined (Cu/Fe ratio (w/w), 0.018; FeS/Fe ratio (w/w), 0.1213; ball milling speed, 450 rpm; ball milling time, 5 h). A composite permeable material was prepared by sintering a mixture of sulfide iron-copper bimetal, sludge, and kaolin. The parameters for composite permeable material preparation including sludge content and particle size, and sintering time were optimized, which were 60%, 60-75 mesh, and 4 h, respectively. The optimal composite permeable material was characterized by SEM-EDS, XRD, and FTIR. The results demonstrated preparation parameters can affect the hydraulic conductivity and hardness of composite permeable material. High sludge content, small particles size, and moderate sintering time resulted in high permeability of composite permeable material and were beneficial for Cr(VI) removal. The dominant Cr(VI) removal mechanism was reduction, and the reaction followed pseudo-first order kinetics. Conversely, low sludge content and large particle size, and long sintering time lead to low permeability of composite permeable material. Chromate removal was mainly by chemisorption following pseudo-second order kinetics. The hydraulic conductivity and hardness of the optimal composite permeable material achieved 1.732 cm/s and 50, respectively. The results of column experiments indicated that its Cr(VI) removal capacity was 0.54 mg/g, 0.39 mg/g and 0.29 mg/g at pH 5, 7 and 9, respectively. The ratio of Cr(VI) to Cr(III) on composite permeable material surface was similar under acidic and alkaline conditions. This study will provide an effective reactive material of PRB for field application.

Environmental safety of nanotechnologies: The eco-design of manufactured nanomaterials for environmental remediation

Nanosafety is paramount considering the risks associated with manufactured nanomaterials (MNMs) whose implications could outweigh their advantages for environmental applications. Although nanotechnology-based solutions to implement pollution control, remediation and prevention are incremental with clear benefits for public health and Earth' natural ecosystems, nanoremediation is having a setback due to the risks associated with the safety of MNMs for humans and the environment. MNMs are diverse, work differently and bionano-interactions occurring upon environmental exposure will guide their fate and hazardous outcomes. Here we propose a new ecologically-based design strategy (eco-design) having its roots in green nanoscience and LCA that will ground on an Ecological Risk Assessment approach, which introduces the evaluation of MNMs' ecotoxicity along with their performances and efficacies at the design stage. As such, the proposed eco-design strategy will allow recognition and design-out since the very beginning of material synthesis, those hazardous peculiar features that can be hazardous to living beings and the natural environment. A more ecologically sound eco-design strategy in which nanosafety is conceptually included in MNMs design will sustain safer nanotechnologies including those for the environment as remediation by leveraging any risks for humans and natural ecosystems.

Conversion and reducing agent effect on zero valent iron into Fe3O4 for photocatalytic degradation under UV light irradiation

Conversion and reducing agent (NaBH₄) effect on zero valent iron into Fe₃O₄ nanoparticles with diverse molar ratios of reducing agent was produced through chemical reduction technique. The structural, optical, vibrational analyses were executed via XRD, UV-Vis, Raman, and FT-IR analysis. The crystallite size obtained were 35 nm, 27 nm, and 18 nm for Fe:NaBH₄ (1:1), Fe:NaBH₄ (1:2) and Fe:NaBH₄ (1:3). The morphology of the Fe:NaBH₄ (1:1) was not in good orientation with higher dimensions. As explored in Fe:NaBH₄ (1:2) and (1:3) samples, there is a proper growth of nanoneedles and nanosheets formation. This was due to the addition of reducing agent which greatly helped in enhancement of morphology. The prepared photocatalysts were tested to reduce Malachite Green (MG) under UV illumination. The pure dye solution obtained 57% efficiency after irradiation. Fe:NaBH₄ (1:3) photocatalyst achieved 97% efficiency on reducing pollutants. The rate constant values calculated was 0.007, 0.013, 0.02 and 0.03 min^-1 for pure, Fe: NaBH₄ (1:1), Fe: NaBH₄ (1:2) and Fe: NaBH₄ (1:3) assisted MG samples. The as prepared photocatalyst is more potential one on removal of toxic pollutants from wastewater which is due to the better enhancement of nanoneedles and nanosheets oriented by the effect of reducing agent. The advantage of Fe₃O₄ nanoparticles for wastewater is that the removal of these nanoparticles can be ease with magnetic separation methods. On considering the advantage of removing of photocatalyst and efficiency, this prepared product is suitable one for wastewater remediation process in future days.

Biosynthesis and chemical composition of nanomaterials in agricultural soil bioremediation: a review

Nanomaterials (NMs) are currently being used in agricultural soils as part of a new bioremediation (BR) process. In this study, we reviewed the biosynthesis of NMs, as well as their chemical composition and prospective strategies for helpful and sustainable agricultural soil bioremediation (BR). Different types of NMs, such as nanoparticles, nanocomposites, nanocrystals, nano-powders, and nanotubes, are used in agricultural soil reclamation, and they reflect the toxicity of NMs to microorganisms. Plants (Sargassum muticum, Dodonaea viscose, Aloe Vera, Rosemarinus officinalis, Azadirachta indica, Green tea, and so on) and microorganisms (Escherichia coli, Shewanella oneidensis, Pleurotus sp., Klebsiella oxytoca, Aspergillus clavatus, and so on) are the primary sources for the biosynthesis of NMs. By using the BR process, microorganisms, such as bacteria and plants, can immobilize metals and change both inorganic and organic contaminants in the soil. Combining NMs with bioremediation techniques for agricultural soil remediation will be a valuable long-term solution.

Molecular Structure and Sulfur Content Affect Reductive Dechlorination of Chlorinated Ethenes by Sulfidized Nanoscale Zerovalent Iron

Sulfidized nanoscale zerovalent iron (SNZVI) with desirable properties and reactivity has recently emerged as a promising groundwater remediation agent. However, little information is available on how the molecular structure of chlorinated ethenes (CEs) affects their dechlorination by SNZVI or whether the sulfur content of SNZVI can alter their dechlorination pathway and reactivity. Here, we show that the reactivity (up to 30-fold) and selectivity (up to 70-fold) improvements of SNZVI (compared to NZVI) toward CEs depended on the chlorine number, chlorine position, and sulfur content. Low CEs (i.e., vinyl chloride and cis-1,2-dichloroethene) and high CEs (perchloroethene) tended to be dechlorinated by SNZVI primarily via atomic H and direct electron transfer, respectively, while SNZVI could efficiently and selectively dechlorinate trichloroethene and trans-1,2-dichloroethene via both pathways. Increasing the sulfidation degree of SNZVI suppressed its ability to produce atomic H but promoted electron transfer and thus altered the relative contributions of atomic H and electron transfer to the CE dechlorination, resulting in different reactivities and selectivities. These were indicated by the correlations of CE dechlorination rates and improvements with CE molecular descriptors, H₂ evolution rates, and electron transfer indicators of SNZVI. These mechanistic insights indicate the importance of determining the structure-specific properties and reactivity of both SNZVI materials and their target contaminants and can lead to a more rational design of SNZVI for in situ groundwater remediation of various CEs.

Green synthesis of Fe0 nanoparticles using Eucalyptus grandis leaf extract: Characterization and application for dye degradation by a (Photo)Fenton-like process

Zero-valent iron nanoparticles (EGnZVI) were synthesized using Eucalyptus grandis (EG) leaf extract as a reducing/stabilizing agent. The studied materials (EG leaves, extract and EGnZVI) were characterized using the XRD, FTIR, Raman spectroscopy, SEM, TEM/EDS techniques. The results indicate that several organic compounds, including phenolics, present in the EG leaves were successfully extracted and incorporated into the structure of the material, possibly promoting the capping and stabilization of the formed zero-valent iron particles. The EGnZVI presented low crystallinity, varied size (50-500 nm), approximately spherical shape, and formed aggregates. The EGnZVI were utilized in the removal of the Direct Red 80 (DR80), an azo dye. The effects of the temperature (15-35 °C), initial DR80 concentration (10-250 mg L-1), initial pH (2.5-8.5), the doses of H2O2 (0.5-5 mmol L-1) and EGnZVI (0.2-10 mg L-1), and the incidence of UV-light were evaluated. The EGnZVI did not present reactivity towards the DR80 in the absence of H2O2. However, in the presence of H2O2, the EGnZVI was highly efficient at removing the DR80 at slightly acidic pH0 values (4 and 5.5). Under these pH0 conditions, the EGnZVI/Fenton process proved to be more effective than the classic homogenous Fenton. Finally, in the presence of the UV-light, the process was highly efficient throughout the studied pH0 interval, with increased removal rates. Therefore, the nZVI/Fenton process, using the synthesized material, presents itself as a promising alternative for the degradation of organic pollutants, and the incidence of UV light can considerably improve its efficiency.

Nano-biotechnology, an applicable approach for sustainable future

Nanotechnology is one of the most emerging fields of research within recent decades and is based upon the exploitation of nano-sized materials (e.g., nanoparticles, nanotubes, nanomembranes, nanowires, nanofibers and so on) in various operational fields. Nanomaterials have multiple advantages, including high stability, target selectivity, and plasticity. Diverse biotic (e.g., Capsid of viruses and algae) and abiotic (e.g., Carbon, silver, gold and etc.) materials can be utilized in the synthesis process of nanomaterials. "Nanobiotechnology" is the combination of nanotechnology and biotechnology disciplines. Nano-based approaches are developed to improve the traditional biotechnological methods and overcome their limitations, such as the side effects caused by conventional therapies. Several studies have reported that nanobiotechnology has remarkably enhanced the efficiency of various techniques, including drug delivery, water and soil remediation, and enzymatic processes. In this review, techniques that benefit the most from nano-biotechnological approaches, are categorized into four major fields: medical, industrial, agricultural, and environmental.

Social life cycle assessment of the nanoscale zero-valent iron synthesis process for application in contaminated site remediation

Nanoscale zero-valent iron (nZVI) is the main nanomaterial used in environmental remediation processes. However, as with any remediation technique, the production and the use of nanomaterials can also cause environmental, economic, and social impacts. Thus, the present study investigated the social life cycle analysis (S-LCA) of nZVI production methods applied in environmental remediation. Three production methods of nZVI were selected for analysis: milling, reduction with sodium borohydride, and reduction with hydrogen gas. The social life cycle analysis was developed based on the ISO 14040 standard steps. Limits of the S-LCA system involve the stages of raw material extraction and manufacturing when not considering the use of nZVI postproduction. The analysis of social impact was conducted considering the involved stakeholders, through the application and improvement of an existing methodology and through the following procedures: characterization of social indicators according to a normalized scale, identification of the normalization factor for the indicators, employment of a social questionnaire, calculation of the total points in each impact subcategory (midpoint), calculation of the total points in the impact categories (endpoint), and calculation of the Social Index. The three production methods of nZVI result in significantly equal Social Indices. All methods were classified as socially sustainable according to the implemented methodology. The sensitivity analysis demonstrates the results dependent with the geographic location of the inventory data, while changes in the weighting can affect the Social Index results. Overall, this study significantly contributed to the state-of-the-art application of S-LCA in studies using nanomaterials; however, several limitations were also observed, and thus, steps for future development were suggested to future researches. In addition, this study improved the S-LCA methodology which can be used to assess the social impact of any product.

A Content Review of Life Cycle Assessment of Nanomaterials: Current Practices, Challenges, and Future Prospects

This paper provides a comprehensive review of 71 previous studies on the life cycle assessment (LCA) of nanomaterials (NMs) from 2001 to 2020 (19 years). Although various studies have been carried out to assess the efficiency and potential of wastes for nanotechnology, little attention has been paid to conducting a comprehensive analysis related to the environmental performance and hotspot of NMs, based on LCA methodology. Therefore, this paper highlights and discusses LCA methodology’s basis (goal and scope definition, system boundary, life cycle inventory, life cycle impact assessment, and interpretation) to insights into current practices, limitations, progress, and challenges of LCA application NMs. We found that there is still a lack of comprehensive LCA study on the environmental impacts of NMs until end-of-life stages, thereby potentially supporting misleading conclusions, in most of the previous studies reviewed. For a comprehensive evaluation of LCA of NMs, we recommend that future studies should: (1) report more detailed and transparent LCI data within NMs LCA studies; (2) consider the environmental impacts and potential risks of NMs within their whole life cycle; (3) adopt a transparent and prudent characterization model; and (4) include toxicity, uncertainty, and sensitivity assessments to analyze the exposure pathways of NMs further. Future recommendations towards improvement and harmonization of methodological for future research directions were discussed and provided. This study’s findings redound to future research in the field of LCA NMs specifically, considering that the release of NMs into the environment is yet to be explored due to limited understanding of the mechanisms and pathways involved.

A review of the new multifunctional nano zero-valent iron composites for wastewater treatment: Emergence, preparation, optimization and mechanism

Nano zero-valent iron (NZVI) with high chemical reactivity and environmental friendliness had recently become one of the most efficient technologies for wastewater restoration. However, the unitary NZVI system had not met practical requirements for wastewater treatments. Expectantly, the development of NZVI would prefer multifunctional NZVI-based composites, which could be prepared and optimized by the combined methods and technologies. Consequently, a systematic and comprehensive summary from the perspective of multifunctional NZVI-composite had been conducted. The results demonstrated that the advantages of various systems were integrated by multifunctional NZVI-composite systems with a more significant performance of pollutant removal than those of the bare NZVI and its composites. Simultaneously, characteristics of the product prepared by the incorporation of numerous methods were superior to those by a simple method, resulting in the increase of the entirety efficiency. By comparison with other preparation methods, the ball milling method with higher production and field application potential was worthy of attention. After combining multiple technologies, the effect of NZVI and its composite systems could be dramatically strengthened. Preparation technology parameters and treatment effect of contaminants could be further optimized using more comprehensive experimental designs and mathematical models. The mechanism of the multifunctional NZVI system for contaminants treatment was primarily focused on adsorption, oxidation, reduction and co-precipitation. Multiple techniques were combined to enhance the dispersion, alleviating passivation, accelerating electron transfer efficiency or mass transfer action for optimizing the effect of NZVI composites.