Whereas noble metal compounds have long been central in catalysis, Earth-abundant metal-based catalysts have in the same time remained undeveloped. Yet the efficacy of Earth-abundant metal catalysts was already shown at the very beginning of the 20th century with the Fe-catalyzed Haber–Bosch process of ammonia synthesis and later in the Fischer–Tropsch reaction. Nanoscience has revolutionized the world of catalysis since it was observed that very small Au nanoparticles (NPs) and other noble metal NPs are extraordinarily efficient. Therefore the development of Earth-abundant metals NPs is more recent, but it has appeared necessary due to their “greenness”. This review highlights catalysis by NPs of Earth-abundant transition metals that include Mn, Fe, Co, Ni, Cu, early transition metals (Ti, V, Cr, Zr, Nb and W) and their nanocomposites with emphasis on basic principles and literature reported during the last 5 years. A very large spectrum of catalytic reactions has been successfully disclosed, and catalysis has been examined for each metal starting with zero-valent metal NPs followed by oxides and other nanocomposites. The last section highlights the catalytic activities of bi- and trimetallic NPs. Indeed this later family is very promising and simultaneously benefits from increased stability, efficiency and selectivity, compared to monometallic NPs, due to synergistic substrate activation.

The recent development of efficient Earth-abundant transition-metal nanocatalysts

Nanocatalysts and other nanomaterials for water remediation from organic pollutants

Green synthesis of metallic nanoparticles as effective alternatives to treat antibiotics resistant bacterial infections: A review.

Green-synthesized nanocatalysts and nanomaterials for water treatment: Current challenges and future perspectives.

One of the promising ways to overcome microbial antibiotic resistance is the use of nanoparticles of metal oxides. As you know, a wide range of metals has antimicrobial action: Ag, Al, Cu, Fe, Mo, Mn, etc. The mechanisms of the antimicrobial action of metals are impaired functioning of microbial enzymes, generation of reactive oxygen species, damage to the cell membrane, and genotoxic action. ZnO nanoparticles have bacteriostatic and bactericidal action against gram-positive and gram-negative bacteria, as well as fungicidal activity. The mechanism of action is based on the release of Zn2+, generation of reactive oxygen species, damage to the cell membrane, binding to microbial proteins and nucleic acids. NPs based on ZnO have a number of advantages: high antibacterial efficiency at low concentrations (0.16-5.00 mM/l), action on a wide range of microbial strains, and relatively low production costs. Methods have now been found to improve the antimicrobial properties of nanoparticles. The use of several methods at the same time in some cases gives a synergistic effect. All of the above allows us to predict the use of ZnO nanoparticles as a new generation of antimicrobial agents in the near future.

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A Mini Review of Antibacterial Properties of ZnO Nanoparticles

The use of biological products such as microorganisms, plant extracts or plant biomass is a better alternative to chemical and physical methods for the engineering of metal oxide nanoparticles through an environmentally benign route. Hematite (α-Fe2O3) nanoparticles have acquired significant attention from researchers for being the most stable iron oxide in air under ambient conditions. Further, they are also known for their extensive applications in diverse fields. In the present work, hematite (α-Fe2O3) nanoparticles have been synthesized by the sole use of the extract of guava (Psidium guajava) leaves. The synthesized material has been studied by X-ray diffraction (XRD), UV-visible spectroscopy, Fourier transform infrared (FTIR) spectroscopy, Vibrating Sample Magnetometry (VSM), Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) techniques. The average diameter of α-Fe2O3 nanoparticles is observed to be about 34 nm. Absorption studies of the sample from UV to near IR regions show four absorption bands at 347 nm, 543 nm, 652 nm and 849 nm. The photoluminescence (PL) spectrum shows band edge emission at 688 nm. The FTIR spectrum reveals the role of biomolecules present in the extract in capping the nanoparticles. The VSM study shows the weak ferromagnetic nature of the synthesized nanoparticles. The antibacterial activities of the synthesized nanoparticles against Gram-positive and Gram-negative bacteria have been ascertained through an agar-well diffusion method. Further, the nanoparticles show enhancement in thermal conductivity for the base fluids water and ethylene glycol. The bioefficacy and thermal conductivity enhancement exhibited by the as synthesized nanoparticles may lead to their possible applications in environmental and industrial fields.

N. Sreeju

Papers

Synthesis of biogenic hematite (α-Fe2O3) nanoparticles for antibacterial and nanofluid applications

Microwave-assisted rapid synthesis of copper nanoparticles with exceptional stability and their multifaceted applications

Biosynthesis of hematite (α-Fe2O3) nanostructures: Size effects on applications in thermal conductivity, catalysis, and antibacterial activity

Studies on catalytic degradation of organic pollutants and anti-bacterial property using biosynthesized CuO nanostructures

Size tunable biosynthesis and luminescence quenching of nanostructured hematite (α-Fe2O3) for catalytic degradation of organic pollutants