Systematic Review Synthesis of Iron-Based and Aluminum-Based Bimetals: A Systematic Review

metals Systematic Review Synthesis of Iron-Based and Aluminum-Based Bimetals: A Systematic Review

Abstract: Bimetals-materials composed of two metal components with dissimilar standard reduction-oxidation potentials-offer unique electronic, optical, and catalytic properties, surpassing monometallic systems. These materials exhibit not only the combined attributes of their constituent metals but also new and novel properties arising from their synergy. Although many reviews have explored the synthesis, properties, and applications of bimetallic systems, none have focused exclusively on iron- and aluminum-based bimetals. This systematic review addresses this gap by providing a comprehensive overview of conventional and emerging techniques for iron-based and aluminum-based bimetal synthesis. Specifically, this work systematically reviewed recent studies from twenty fourteen to twenty twenty-three using the Scopus, Web of Science, and Google Scholar databases, following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines, and was registered under INPLASY with the registration number INPLASY twenty twenty forty-two six. Articles were excluded if they were inaccessible, non-English, review articles, conference papers, book chapters, or not directly related to the synthesis of iron- or aluminum-based bimetals. Additionally, a bibliometric analysis was performed to evaluate the research trends on the synthesis of iron-based and aluminum-based bimetals. Based on the one hundred twenty-two articles analyzed, iron-based and aluminum-based bimetal synthesis methods were classified into three types: (i) physical, (ii) chemical, and (iii) biological techniques. Physical methods include mechanical alloying, radiolysis, sonochemical methods, the electrical explosion of metal wires, and magnetic field-assisted laser ablation in liquid. In comparison, chemical protocols covered reduction, dealloying, supported particle methods, thermogravimetric methods, seed-mediated growth, galvanic replacement, and electrochemical synthesis. Meanwhile, biological techniques utilized plant extracts, chitosan, alginate, and cellulose-based materials as reducing agents and stabilizers during bimetal synthesis. Research works on the synthesis of iron-based and aluminum-based bimetals initially declined but increased in twenty eighteen, followed by a stable trend, with fifty percent of the total studies conducted in the last five years. China led in the number of publications, followed by Russia, Australia, and India, while Saudi Arabia had the highest number of citations per document. RSC Advances was the most active journal, publishing eight papers from twenty fourteen to twenty twenty-three, while Applied Catalysis B: Environmental had the highest number of citations per document at two hundred three. Among the three synthesis methods, chemical techniques dominated, particularly supported particles, galvanic replacement, and chemical reduction, while biological and physical methods have started gaining interest. Iron-copper, iron-aluminum, and iron-nickel were the most commonly synthesized bimetals in the last ten years. Finally, this work was funded by DOST-PCIEERD and DOST-ERDT.

One. Introduction

The efficacy of monometallic materials or zero-valent metals in treating polluted surface water, wastewater, groundwater, and soils, including municipal, industrial, and mining wastes, is well known. Metallic iron and zero-valent iron, for example, have been effectively used to degrade halogenated organic compounds like trichloroethylene, tetrabromobisphenol A, pentachlorophenol, and two, four-dichlorophenol, trichlorophenol, as well as residual medicine and antibiotics such as florfenicol and diclofenac. Similarly, zero-valent iron and aluminum or zero-valent aluminum have been applied for decontaminating lead-contaminated soil and lead- and zinc-bearing hydrometallurgical residues from legacy mining and mineral processing operations. Zero-valent metals have also been used in the industrial-scale recovery of gold from pregnant robbing solutions as well as in the recovery of valuable metals like copper and cobalt from electronic wastes. Another emerging application of zero-valent metals is their potential to passivate pyrite, the primary source of acid mine drainage, via galvanic encapsulation.

Despite their widespread use, the efficacy of zero-valent metals is often hampered by issues like excessive corrosion, rapid passivation, and suboptimal utilization. For example, zero-valent iron and zero-valent aluminum exhibit slow removal rates and low efficiency at high pollutant concentrations and neutral-to-alkaline pH conditions because of the formation of a metal oxide or carbonate passivation layer, reducing their reactivity, so these materials work best under highly acidic conditions near pH three. Zero-valent metals are also prone to agglomerate, reducing their effective surface area, and are challenging to recover and regenerate when used in contaminated solutions and wastewater. Finally, zero-valent metals exhibit low selectivity for target contaminants, posing limitations to their application. One possible solution to address these drawbacks of zero-valent metals is by combining two metals into bimetals, a configuration that enhances efficiency by taking advantage of the individual monometallic properties and the synergistic effects of the paired metals.

In general, bimetals (also referred to as bimetallic materials and bimetallic particles) are materials composed of two metal components with different standard reduction-oxidation potentials, which are highly attractive for their unique electronic, optical, and catalytic properties, surpassing their monometallic counterparts. Bimetals have been shown to form galvanic cells and promote either reduction or oxidation reactions depending on the geochemical properties of the system. For example, pairing zero-valent iron with more noble metals, such as copper, cobalt, nickel, or silver,

has been shown to enhance its reactivity and performance in wastewater treatment by inhibiting surface passivation. For these bimetal systems, the contaminant removal primarily occurred through galvanic couple formation, which influenced iron corrosion and facilitated electron transfer to contaminants. However, the relatively high cost of these noble metals poses challenges for scaling this technology up economically. Aluminum is a promising alternative due to its abundance, lower cost, and significantly lower standard reduction-oxidation potential, enabling a strong thermodynamic force for metal removal when coupled with zero-valent iron. Adding zero-valent aluminum to other zero-valent metals, such as zero-valent iron in aluminum-iron bimetallic systems, enhances their reactivity by preventing passive layer formation on zero-valent iron and maintaining its reactivity throughout the reaction. In many studies, bimetallic catalysts have improved performance when applied to polluted water and wastewater treatment and are better than their monometallic counterparts. In an aluminum-iron bimetal system, aluminum acts as the primary reactive metal or anode, while iron serves as the more noble secondary metal or cathode that ferries electrons to surface reactive compounds.

Because of their unique properties and huge potential as sustainable catalysts and adsorbents for circular economy applications, bimetals are gaining a lot of attention in the research community. To date, a number of review papers have been published discussing synthesis protocols, electrochemical properties of products, and applications of bimetal systems. For instance, Scaria et al. and Quiton et al. reported physical, chemical, and biological synthesis methods of bimetallic particles and their applications to water and wastewater treatment. Consequently, none of these review articles delved comprehensively and exclusively into iron- and aluminum-based bimetals. Hence, this systematic review aims to provide a thorough overview of conventional and emerging synthesis methods for synthesizing iron-based and aluminum-based bimetals. A bibliometric analysis was also performed to evaluate research activity related to the syntheses of iron- and aluminum-based bimetals.

This review is structured as follows: Section Two outlines the review methodology; Section Three discusses the production of iron- and aluminum-based bimetals by physical techniques; Section Four explores the chemical methods for aluminum- and iron-based bimetal synthesis; Section Five examines the use of plant extracts, chitosan, and cellulose-based materials as green reducing agents and stabilizers for bimetallic nanoparticle synthesis; and Section Six provides a summary and future directions of bimetal material synthesis.