Green Synthesis of Transition-Metal Nanoparticles and Their Oxides: A Review

Abstract

In recent years, many researchers have begun to shift their focus onto the synthesis of nanomaterials as this field possesses immense potential that may provide incredible technological advances in the near future. The downside of conventional synthesis techniques, such as co-precipitation, sol-gel and hydrothermal methods, is that they necessitate the use of toxic chemicals, produce harmful by-products and require a considerable amount of energy; therefore, more sustainable fabrication routes are sought-after. Biological molecules have been previously utilized as precursors for nanoparticle synthesis, thus eliminating the negative factors involved in traditional methods. In addition, transition-metal nanoparticles possess a wide scope of applications due to their multiple oxidation states and large surface areas, thereby allowing for a higher reactivity when compared to their bulk counterpart and rendering them an interesting research topic. However, this field is still relatively unknown and unpredictable as the biosynthesis of these nanostructures from fungi, bacteria and plants yield undesired diameters and morphologies, rendering them as redundant when compared to their chemically synthesized counterparts. Therefore, this review aims to obtain a better understanding on the plant-mediated synthesis process of the major transition-metal and transition-metal oxide nanoparticles, and how process parameters—concentration, temperature, contact time, pH level, and calcination temperature affect their unique properties such as particle size, morphologies, and crystallinity.

Biosynthesis and Cytotoxic Properties of Ag, Au, and Bimetallic Nanoparticles Synthesized Using Lithospermum erythrorhizon Callus Culture Extract

“…It has been shown that photons of blue light have the strongest photocatalytic action compared to other spectral regions [81]. Boiling of the extract is also a commonly used practice for eco-friendly metal nanoparticle biosynthesis [82]. It is generally accepted that this procedure promotes the enrichment of extracts with biological reducing agents, thus enhancing their capacity for the formation of nanocrystals.…”

Biogenic Synthesis of CuO, ZnO, and CuO–ZnO Nanoparticles Using Leaf Extracts of Dovyalis caffra and Their Biological Properties

“…Therefore, several metal-based nanoparticles designed to function in biological cells were prepared from diverse arrays of plant materials, including stems, leaves, fruits, and roots [ 10 , 11 , 12 , 13 ]. These nanoparticles do not only offer medicinal benefits but were reported to possess multiple oxidation states and large surface areas, thereby allowing for high reactivity [ 14 ]. These metal-based nanoparticles prepared using the biomimetic routes offer better chemotherapeutic advantages than the conventional ones by improved efficacy, increasing half-life, and slowly releasing drugs into the biological system [ 15 ].…”

ZnO Semiconductor Nanoparticles and Their Application in Photocatalytic Degradation of Various Organic Dyes

“…S. Rajendrachari et.al., also in 2021, used cauliflower to biosynthesize ZnO NPs, managing to degrade 75% RhB within 2 h [32]. As has been disclosed in the literature, various natural stabilizing agents have been used, such as roots, leaves, fruits, and vegetables [33]; however, what has been seldom studied is the use of chili peppers in the green synthesis of ZnO NPs. Specifically, the use of Anaheim Chili (Capsicum annuum var.…”