Strategies to enhance the stability of nanoscale zero-valent iron (NZVI) in continuous BrO3- reduction

Comparative investigation on the adsorption behavior of bromate in aqueous solutions using Zn/Ni/Al-LDH and Ni/Al-LDH: optimization, equilibrium analysis, and mechanistic insights

The presence of bromate in water poses a significant health risk. In order to effectively eliminate bromate from water, this study synthesized a series of ternary Zn-Ni-Al layered double hydroxides with varying Zn/Ni/Al atomic ratios using a co-precipitation method. The adsorbents were characterized using various techniques including XRD, Fourier transform infrared spectroscopy, and N2 adsorption-desorption isotherms. Among them, ZnNiAl-2 exhibited the highest crystallinity and largest specific surface area (316.1 m2 g-1), which was compared to the binary hydrotalcite NiAl-LDH for its ability to adsorb bromate from water. Results demonstrated that the adsorption isotherm of bromate on ZnNiAl-2 followed the Langmuir model, with a maximum adsorption capacity of 120.5 mg g-1, significantly higher than that of NiAl at 75.5 mg g-1, indicating strong adsorption capability and reusability performance. The adsorption kinetics were also found to be in accordance with the pseudo-second-order kinetic model. The mechanism involved both surface adsorption and anion exchange.

Supplementary Information

The online version contains supplementary material available at 10.1007/s40201-025-00932-6.

Recent advances in bimetallic nanoscale zero-valent iron composite for water decontamination: Synthesis, modification and mechanisms

The environmental pollution of water is one of the problems that have plagued human society. The bimetallic nanoscale zero-valent iron (BnZVI) technology has increased wide attention owing to its high performance for water treatment and soil remediation. In recent years, the BnZVI technology based on the development of nZVI has been further developed. The material chemistry, synthesis methods, and immobilization or surface stabilization of bimetals are discussed. Further, the data of BnZVI (Fe/Ni, Fe/Cu, Fe/Pd) articles that have been studied more frequently in the last decade are summarized in terms of the types of contaminants and the number of research literatures on the same contaminants. Five contaminants including trichloroethylene (TCE), Decabromodi-phenyl Ether (BDE209), chromium (Cr(VI)), nitrate and 2,4-dichlorophenol (2,4-DCP) were selected for in-depth discussion on their influencing factors and removal or degradation mechanisms. Herein, comprehensive views towards mechanisms of BnZVI applications including adsorption, hydrodehalogenation and reduction are provided. Particularly, some ambiguous concepts about formation of micro progenitor cell, production of hydrogen radicals (H·) and H2 and the electron transfer are highlighted. Besides, in-depth discussion of selectivity for N2 from nitrates and co-precipitation of chromium are emphasized. The difference of BnZVI is also discussed.

Nitrate pollution and its solutions with special emphasis on electrochemical reduction removal

Nitrate pollution has become a serious environmental concern all over the world including in China due to the mismanagement of water resources and human activities. Agricultural runoff and industrial and nuclear waste are among the major sources of nitrate pollution. Consuming nitrate-rich water can cause many chronic diseases including digestive problems, which can lead to many types of cancer and other serious health issues. Denitrification is the natural process for nitrate reduction under aerobic conditions, but it cannot handle an excess of nitrate, so several methods have been adopted for nitrate removal, i.e., biological, chemical, physicochemical, and electrochemical reduction removal. Among all, electrochemical reduction removal is a cost-effective and environmental-friendly process. To obtain the maximal elimination efficiency ideal conditions of current intensity, pH, plate distance, initial nitrate concentration, and type of electrolyte solution should be studied for effective nitrate removal. Electrochemical reduction removal of nitrate involves the transfer of electrons and hydrogenation. Besides an efficient nitrate removal process, electrochemical reduction removal has some drawbacks like sludge formation, low selectivity for nitrogen, and production of brine that limit its long-term implementation. This review focused on nitrate pollution, previous nitrate removal strategies, and essential principles for understanding the mechanism of electrochemical reduction removal and controlling the products of the reaction.

The Use of H2 in Catalytic Bromate Reduction by Nanoscale Heterogeneous Catalysts

The formation of bromate (BrO₃^-)in groundwater treatment is still a severe environmental problem. Catalytic hydrogenation by nanoscale heterogeneous catalysts with gaseous H₂ or solid-state H₂ has emerged as a promising approach, which relies on reducing BrO₃^- to innocuous Br^- via the process of direct electron transfer or reduction with atomic hydrogen. Several nanocatalysts have demonstrated high efficiency with a 100% effective BrO₃^- reduction with greater than 95% of Br^- generation in the batch and continuous reactors. However, this technology has not been widely adopted in water treatment systems. Indeed, this research article summarizes the advantages and disadvantages of these technologies by highlighting the factors of nanomaterials reduction efficiency, long-term durability, and stability, as well as addressing the essential challenges limiting the implementation of the use of H₂ for BrO₃^- reduction. In this work, we provide an economic evaluation of catalytic BrO₃^- removal, safe hydrogen supply, storage, and transportation.

Competitive inhibition of catalytic nitrate reduction over Cu-Pd-hematite by groundwater oxyanions

The presence of various oxyanions in the groundwater could be the main challenge for the successive application of Cu-Pd-hematite bimetallic catalyst to aqueous NO₃^- reduction due to the inhibition of its catalytic reactivity and alteration of product selectivity. The batch experiments showed that the reduction kinetics of NO₃^- was strongly suppressed by ClO₄^-, PO₄^3-, BrO₃^- and SO₃^2- at low concentrations (>5 mg/L) and HCO₃^-, CO₃^2-, SO₄^2- and Cl^- at high concentrations (20-500 mg/L). The presence of anions significantly changing the end-product selectivities influenced high N₂ selectivity. The selectivity toward N₂ increased from 55% to 60%, 60%, and 70% as the concentrations of PO₄^3-, SO₃^2-, and SO₄^2- increased, respectively. It decreased from 55% to 35% in the presence of HCO₃^- and CO₃^2- in their concentration range of 0-500 mg/L. The production of NO₂^- was generally not detected, while the formation of NH₄⁺ was observed as the second by-product. It was found that the presence of oxyanions in the NO₃^- reduction influenced the reactivity and selectivity of bimetallic catalysts by i) competing for active sites (PO₄^3-, SO₃^2-, and BrO₃^- cases) due to their similar structure, ii) blockage of the promoter and/or noble metal (HCO₃^-, CO₃^2-, SO₄^2-, Cl^- and ClO₄^- cases), and iii) interaction with the support surface (PO₄^3- case). The results can provide a new insight for the successful application of catalytic NO₃^- reduction technology with high N₂ selectivity to the contaminated groundwater system.

Modified nanoscale zero-valent iron in persulfate activation for organic pollution remediation: a review

Under the action of different activators, persulfate can produce sulfate radicals (SO₄·^-) with strong oxidizing ability, which can destruct many organic compounds. Meanwhile, persulfate is widely used in groundwater and soil remediation because of its fast reaction and wide application. With the high specific surface area and reactivity of nanoscale zero-valent iron (nZVI), it can enhance the degradation efficiency of the persulfate system on organic pollutants in soil and water as a persulfate activator. However, nZVI is easy to get oxidized and has a tendency to aggregation. To solve these problems, a variety of nZVI modification methods have been put forward and put into to applications in the activation of persulfate. This article will give a systematic introduction of the background and problems of nZVI-activated persulfate in the remediation of organic pollution. In addition, the modification methods and mechanisms of nZVI are summarized, and the applications and progress of modified nZVI-activated persulfate are reviewed. The factors that affect the removal of organic compounds by the activation system are discussed as well. Worldwide, the field studies and full-scale remediation using modified nZVI in persulfate activation are yet limited. However, the already known cases reveal the good prospect of applying modified nZVI in persulfate activation to organic pollution remediation.

A Review on the Catalytic Hydrogenation of Bromate in Water Phase

The presence of bromate in water sources generates environmental concern due to its toxicity for humans. Diverse technologies, like membranes, ion exchange, chemical reduction, etc., can be employed to treat bromate-polluted water but they produce waste that must be treated. An alternative to these technologies can be the catalytic reduction of bromate to bromide using hydrogen as a reducing agent. In this review, we analyze the research published about this catalytic technology. Specifically, we summarize and discuss about the state of knowledge related to (1) the different metals used as catalysts for the reaction; (2) the influence of the support on the catalytic activity; (3) the characterization of the catalysts; (4) the reaction mechanisms; and (5) the influence of the water composition in the catalytic activity and in the catalyst stability. Based on published papers, we analyze the strength and weaknesses of this technique and the possibilities of using this reaction for the treatment of bromate-polluted water as a sustainable process.

Synthesis of illite/iron nanoparticles and their application as an adsorbent of lead ions

Illite/iron nanoparticles (I-nZVI) with different iron contents were synthesized using a liquid-phase reduction method to remove Pb(II) from aqueous solution. The adsorbents were characterized by Lorentz transmission electron microscopy (L-TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and the BET-N₂ technique. The composite adsorbents and illite removed Pb(II) from aqueous solution to explore the effect of different reaction conditions, including contact time, concentration, pH, and temperature. The results of batch experiments demonstrated that the removal efficiency mainly depends on the amount of nanoscale zerovalent iron. Under different conditions, the order of the removal efficiency was 30% I-nZVI > 20% I-nZVI > 10% I-nZVI > illite. Reactions between Fe(0) and Pb(II) took place on the surface of the absorbents, and the removal of Pb(II) was based on adsorption and reductive reactions. The adsorption of lead ions by I-nZVI and pure illite conformed to the pseudo-second-order reaction kinetic model, and intraparticle diffusion may not play a remarkable role in removing Pb(II). The adsorption of Pb(II) by 30% I-nZVI, 20% I-nZVI, 10% I-nZVI, and illite was more in line with the Langmuir adsorption model. Thermodynamic studies indicated that the Pb(II) removal process is endothermic in nature, which is in agreement with the experimental results. The high removal efficiency helps to achieve the goal of remediation.