Applications and synergistic degradation mechanisms of nZVI-modified biochar for the remediation of organic polluted soil and water: A review

Performance of nano zero-valent iron activated peroxydisulfates prepared by carbothermal reduction using various bagasse components

Biomass has been utilized in the carbothermal reduction method to reduce iron cations, thereby synthesizing nano zero-valent iron (nZVI). The effect of the biomass components on the regulation of the performance of prepared nZVI is not clear and the mechanism of action remains to be explored. Biomass components such as cellulose, hemicellulose, lignin, and amylum were used to prepare carbon-loaded nano zero-valent iron. It was demonstrated that increasing the cellulose content of the mixture led to higher Fe0 content by 2-6 times and a greater activation efficiency of peroxydisulfate (PDS) by 2-5 times. nZVI prepared by carbothermal reduction using bagasse (Fe0/CB) removed 99.8 % of metronidazole in 60 min. The bagasse's cellulose content was found to be 59.5 % and the results demonstrated that the composites prepared with the cellulose content exceeded 60 % had unusual properties. The pyrolysis process of the mixtures showed that cellulose promotes the production of nZVI by generating more reducing gases (e.g. CO, CH4). Furthermore, the efficiency of activated PDS in removing metronidazole was confirmed, with cellulose-prepared nZVI (c-Fe0/C) proving to be the most effective activator. Its removal rate was 1.3 times higher than that of Fe0/CB. Physical characterization and mechanistic investigations demonstrated that c-Fe0/C has the same active sites as Fe0/CB and produces the same type and amount of reactive oxygen species. These demonstrates that cellulose is a critical component in the preparation of nZVI during carbothermal reduction. This study provides guidelines for preparing carbothermal reduced nZVI and establishes a theoretical basis for its engineering application.

Nano zero-valent iron with a self-forming Co-catalytic surface for enhanced Fenton-like reactions

Fenton reactions, commonly employed in environmental remediation, decompose H₂O₂ using Fe2⁺ to generate free radicals. However, the efficiency is often limited by the slow conversion of Fe³⁺ to Fe2⁺. In this study, we synthesize zero-valent iron nanoparticles (nZVI) via a green, plant extract-mediated reduction method, resulting in nZVI coated with a reductive polyphenolic layer that enhances Fe³⁺/Fe2⁺ cycling. Supported on bamboo-derived biochar (BBC) via in situ reduction, the nZVI showe improved dispersibility and recovery during catalytic processes. Characterizations by SEM, TEM, FTIR, XRD, and XPS together confirm the successful synthesis of the nZVI/BBC composite. We evaluate the catalytic performance by degrading Eriochrome Black T (EBT) dye in the presence of H₂O₂. Under optimal conditions (35 °C, pH 3), the nZVI/BBC catalyst achieves over 90% degradation of EBT within 10 min. The dual function of the surface-functionalized nZVI as both iron source and co-catalyst significantly improves the reaction efficiency, offering a promising approach for environmental remediation.

Characteristic study of biological CaCO3-supported nanoscale zero-valent iron: stability and migration performance

nZVI has attracted much attention in the remediation of contaminated soil and groundwater, but the application is limited due to its aggregation, poor stability, and weak migration performance. The biological CaCO3 was used as the carrier material to support nZVI and solved the nZVI agglomeration, which had the advantages of biological carbon fixation and green environmental protection. Meanwhile, the distribution of nZVI was characterised by SEM-EDS and TEM carefully. Subsequently, the dispersion stability of bare nZVI and CaCO3@nZVI composite was studied by the settlement experiment and Zeta potential. Sand column and elution experiments were conducted to study the migration performance of different materials in porous media, and the adhesion coefficient and maximum migration distances of different materials in sand columns were explored. SEM-EDS and TEM results showed that nZVI could be uniformly distributed on the surface of biological CaCO3. Compared with bare nZVI, CaCO3@nZVI composite suspension had better stability and higher absolute value of Zeta potential. The migration performance of nZVI was poor, while CaCO3@nZVI composite could penetrate the sand column and have good migration performance. What's more, the elution rates of bare nZVI and CaCO3@nZVI composite in quartz sand columns were 5.8% and 51.6%, and the maximum migration distances were 0.193 and 0.885 m, respectively. In summary, this paper studies the stability and migration performance of bare nZVI and CaCO3@nZVI composite, providing the experimental and theoretical support for the application of CaCO3@nZVI composite, which is conducive to promoting the development of green remediation functional materials.

Enhanced remediation of organotin compounds and metal(loid)s in polluted sediments: Chemical stabilization with mining-wastes and nZVI versus physical soil washing

Here we describe two innovative approaches for remediating sediments contaminated with organotin compounds (OTCs, mainly TBT) and metal(loid)s. The first involves chemical stabilization through amendments with nanoscale zero-valent iron (nZVI), dunite mining waste, and coal tailings, materials that have not been previously studied for OTC remediation. The second focuses on physical soil washing, using grain-size separation and magnetic separation to isolate the most polluted fractions, thereby reducing the volume of contaminated material destined for landfills. The results for the first approach indicated that OTC degradation occurred mainly through nZVI application, with concurrent immobilization of As and mobilization of Cu. Furthermore, combining nZVI with coal tailings enhanced OTC degradation whereas dunite mining waste effectively immobilized Zn. In turn, in the second approach, grain-size separation efficiently removed coarse material (>500 μm) with low pollutant concentrations. Subsequent magnetic separation selectively concentrated less than 5% of the initial volume of sediment in a magnetic fraction that showed the highest contaminant content. Therefore, 95% of material revealed lower contaminant concentrations than the feed material. These findings highlight the potential of combining physical soil washing, which significantly reduces the volume of contaminated sediments, with chemical stabilization, which can effectively stabilize the polluted fractions isolated in the physical treatment.

Engineered biochar for in-situ and ex-situ remediation of contaminants from soil and water

Tailoring physical and chemical properties of biochar enhances its selectivity, treatability, and efficiency in contaminant remediation. Thus, engineered biochar has emerged as a promising remedy for both in-situ and ex-situ remediation of polluted soil and water. Several factors influence the effectiveness of engineered biochar, including feedstock sources, pyrolysis conditions, surface functionalization, mode of application, and site characteristics. The advantages and disadvantages of different modification approaches to engineered biochar and their specific treatability for in-situ and ex-situ remediation are obscure and must be adequately addressed. This review critically evaluates the application of engineered biochar for on/off-spot contamination management, taking into account the long-term stability and biocompatibility prospects. The properties of engineered biochar resulting from modification with clay minerals, nanoparticles, polymers, surfactants, and oxidants/reductants were critically reviewed. Recent progress and advances in remediation mechanisms and modes of application were elaborated for the effective removal of organic and inorganic contaminants, including heavy metals, pesticides, dyes, polycyclic aromatic hydrocarbons, per- and poly-fluoroalkyl substances, and agrochemicals. Several crucial parameters influence in-situ remediation, including the distribution of contaminants, background electrolytes, hydraulic conductivity, as well as dispersion and stability of adsorbents. Ex-situ remediation of pollutants relies heavily on adsorption or degradation kinetics, background electrolytes, adsorbent dose, and pollutant concentrations. In addition, factors restricting the application of engineered biochar were highlighted for long-term sustainable contaminant management and maintaining low environmental impact. Finally, the challenges and future perspectives of utilizing engineered biochar for field-scale demonstration of contaminated sites are proposed.

Progress on the removal of PFAS contamination in water by different forms of iron-modified biochar

Per- and polyfluoroalkyl substances (PFAS) contamination poses a significant threat to human health. Iron-modified biochar is an eco-friendly, cost-effective, and efficient adsorption material. There is a beneficial interaction between iron groups and biochar to remove PFAS from water through adsorption and degradation. The removal mechanism of the iron-modified biochar mainly includes advanced oxidation, iron group reduction, and adsorption. The adsorption mechanism shifted from being dominated by hydrophobic interactions to electrostatic interactions and ion exchange. Different forms of iron-modified biochar showed excellent removal of short-chain PFAS, which is not found in other modified biochar. Few existing studies have systematically investigated the role of various forms of iron-modified biochar in PFAS removal. Accordingly, this review explores the following areas, the synthesis methods of different forms of iron-modified biochar, the removal effect on long and short-chain PFAS, the key factors affecting removal capacity and the mechanisms of their interaction, the mechanism of PFAS removal, and the regeneration capacity of the composites. In this study, the potential of different forms of iron-modified biochar for PFAS remediation was explored in depth. To provide new ideas for subsequent studies of PFAS removal using iron-modified biochar.

Application of Biochar-Based Materials for Effective Pollutant Removal in Wastewater Treatment

With the growth of the global population and the acceleration of industrialization, the problem of water pollution has become increasingly serious, posing a major threat to the ecosystem and human health. Traditional water treatment technologies make it difficult to cope with complex pollution, so the scientific community is actively exploring new and efficient treatment methods. Biochar (BC), as a low-cost, green carbon-based material, exhibits good adsorption and catalytic properties in water treatment due to its porous structure and abundant active functional groups. However, BC's pure adsorption or catalytic capacity is limited, and researchers have dramatically enhanced its performance through modification means, such as loading metals or heteroatoms. In this paper, we systematically review the recent applications of BC and its modified materials for water treatment in adsorption, Fenton-like, electrocatalytic, photocatalytic, and sonocatalytic systems, and discuss their adsorption/catalytic mechanisms. However, most of the research in this field is at the laboratory simulation stage and still needs much improvement before it can be applied in large-scale wastewater treatment. This review improves the understanding of the pollutant adsorption/catalytic properties and mechanisms of BC-based materials, analyzes the limitations of the current studies, and investigates future directions.

N-doped lignin-based activated carbon aerogel derived from bamboo black pulp liquor for efficient removal of malachite green in wastewater

In this study, a lignin-based aerogel (LA) was prepared through acid precipitation of BPBL, followed by sol-gel method and freeze-drying. Additionally, a one-step activation-carbonization method was used to acquire nitrogen-doped lignin-based activated carbon aerogel (NLACA). The adsorption and catalytic degradation performance for malachite green (MG) were examined. The specific surface area of NLACA after N-doping was 2644.5 m2/g. The adsorption capacity for MG was increased to 3433 mg/g with the presence of nitrogenous functional groups on surface of NLACA compared without N-doping. Meanwhile, non-radical singlet oxygen is the primary active substance and degradation efficiency arrives at 91.8% after the catalytic degradation within 20 min and it has good stability and reuse. Three possible degradation pathways during degradation were analyzed by LC-MS technique. The adsorption isotherm and kinetic data demonstrated conformity with both the Langmuir model and the pseudo-second-order kinetic model. The primary mechanisms of the adsorption for MG dyes on NLACA include hydrogen bonding, π-π interactions, attraction of electrostatic and pore filling. Hence, NLACA derived from BPBL acts as a cost-effective and high-performance adsorbent and catalyst for removal of MG in dye wastewater. This concept introduces an innovative approach of "treatment of waste with waste" for developing a low-consumption, high-efficiency dye wastewater treatment and provides significant reference to treatment dye wastewater.

Combined exposure to decabromodiphenyl ether and nano zero-valent iron aggravated oxidative stress and interfered with metabolism in earthworms

Decabromodiphenyl ether (BDE-209) is a common brominated flame retardant in electronic waste, and nano zero-valent iron (nZVI) is a new material in the field of environmental remediation. Little is known about how BDE-209 and nZVI combined exposure influences soil organisms. During the 28 days study, we determined the effects of single and combined exposures to BDE-209 and nZVI on the oxidative stress and metabolic response of earthworms (Eisenia fetida). On day 7, compared to CK, malondialdehyde (MDA) content increased in most combined exposure groups. To remove MDA and reactive oxygen species (ROS), superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD) activities were induced in most combined exposure groups. On day 28, compared to CK, the activities of SOD and CAT were inhibited, while POD activity was significantly induced, indicating that POD plays an important role in scavenging ROS. Combined exposure to BDE-209 and nZVI significantly affected amino acid biosynthesis and metabolism, purine metabolism, and aminoacyl-tRNA biosynthesis pathways, interfered with energy metabolism, and aggravated oxidative stress in earthworms. These findings provide a basis for assessing the ecological impacts of using nZVI to remediate soils contaminated with BDE-209 from electronic waste.

Size Control of Carbon Xerogel Spheres as Key Factor Governing the H2O2 Selectivity in Metal-Free Bifunctional Electro-Fenton Catalysts for Tetracycline Degradation

Carbon xerogel spheres co-doped with nitrogen and eco-graphene were synthesized using a typical solvothermal method. The results indicate that the incorporation of eco-graphene enhances the electrochemical properties, such as the current density (JK) and the selectivity for the four transferred electrons (n). Additionally, nitrogen doping has a significant effect on the degradation efficiency, varying with the size of the carbon xerogel spheres, which could be attributed to the type of nitrogenous group doped in the carbon material. The degradation efficiency improved in the nanometric spheres (48.3% to 61.6%) but decreased in the micrometric-scale spheres (58.6% to 53.4%). This effect was attributed to the N-functional groups present in each sample, with N-CNS-5 exhibiting a higher percentage of graphitic nitrogen (35.7%) compared to N-CMS-5 (15.3%). These findings highlight the critical role of sphere size in determining the type of N-functional groups present in the sample. leading to enhanced degradation of pollutants as a result of the electro-Fenton process.

Synthesis of an innovative SF/NZVI catalyst and investigation of its effectiveness on bio-oil production in liquefaction process alongside other parameters

Today, new energy sources alternative to fossil fuels are needed to meet the increasing energy demand. It is becoming increasingly important to constitute new energy sources from waste biomass through the liquefaction process. In this study, walnut shells (WS) were liquefied catalytically and non-catalytically under different parameters using the liquefaction method. In this process, the effect of silica fume/nano zero-valent iron (SF/NZVI) catalysts on the conversion rates was investigated. The catalyst was synthesized by reducing NZVI using a liquid phase chemical reduction method on SF. The SF/NZVI catalyst was characterized by scanning electron microscopy- energy dispersive X-ray (SEM-EDX), transmission electron microscope (TEM), Brunauer-Emmett-Teller (BET), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) analysis. The effect of various process parameters on the liquefaction process was investigated. In this context, the reaction temperature ranged from 300 to 400 °C, the solid/solvent ratio ranged from 1/1 to 1/3, the reaction time ranged from 30 to 90 min, and the catalyst concentration ranged from 1 to 6%. According to the results obtained, the most suitable operating conditions for non-catalytic experiments in liquefaction of WS were found to be temperature of 400 °C, reaction time of 60 min, and solid/solvent of 1/3. In catalytic conditions, the optimum values were obtained as temperature of 375 °C, reaction time of 60 min, solid/solvent ratio of 1/3, and catalyst concentration of 6%. The highest total conversion and (oil + gas) % conversion were 90.4% and 46.7% under non-catalytic conditions and 90.7% and 62.3% under catalytic conditions, respectively. Gas chromatography/mass spectrometry (GC/MS) analysis revealed the bio-oil was mainly composed of aromatic compounds (benzene, butyl-, indane and their derivatives,) and polyaromatic compounds (naphthalene, decahydro-, cis-, naphthalene, 1-methyl-.). The aim of increasing the quantity and quality of the light liquid product in the study has been achieved.