Very Green Photosynthesis of Gold Nanoparticles by a Living Aquatic Plant: Photoreduction of Au^III by the Seaweed Ulva armoricana

Abstract

Light-assisted in vivo synthesis of gold nanoparticles (NPs) from aqueous solutions of dilute Au salts by a living green marine seaweed (Ulva armoricana) is reported for the first time. NPs synthesised using typical procedures have many associated environmental hazards. The reported methods involve green, nontoxic, eco-friendly synthetic procedures. The formation of AuNPs was extremely rapid (≈15 min) following illumination of the living U. armoricana, while the rate of NP formation in the dark was very slow (over 2 weeks). The properties of the AuNPs formed were confirmed using a battery of spectroscopic techniques. U. armoricana were found to be very efficient in Au uptake, and this, together with the rapid formation of AuNPs under illumination, indicated that the seaweed remained living during NP formation. The TEM images supported this, revealing that the thylakoid membranes and cell structure remained intact. The AuNPs formed on the surface of U. armoricana thallus, along the cell walls and in the chloroplasts. Without further workup, the dried, U. armoricana-supported AuNPs were efficient in the catalytic reduction of 4-nitrophenol, demonstrating the completely green cycle of AuNP formation and catalytic activity. The results mean that an aquatic plant growing in water rich in gold salts could bio-accumulate AuNPs from its aquatic environment, simply with the activation of sunlight.

Nanoscience teaching and research program in South Africa

“…An overview and appraisal of the research activities of the DSI/ Mintek NIC (Biolabels Unit) and its contribution towards capacity development within Africa was recently published (Sibuyi et al, 2022). Several researchers also work in the field of green nanotechnology, which involves the use of plants to produce nanoparticles that are not only biocompatible but also demonstrate a range of bioactivities that can be exploited in medicine (Mukhoro et al, 2018).…”

Marine organisms: Pioneer natural sources of polysaccharides/proteins for green synthesis of nanoparticles and their potential applications

“…Through another study, Ramakrishna et al discussed the role of AgNPs mediated by two marine algae; T. conoides and S. tenerrimum in biocatalysis and degradation of nitro compounds (4-NP and p-nitroaniline), and organic dye molecules (Rhodamine B and Sulforhodamine) in the presence of NaBH 4 (Table 2) [49]. The 4-NP dye could also be biodegraded using a marine aquatic plant; Ulva armoricana mediated AuNPs, whereas the biosynthesized AuNPs have the potential to reduce 4-NP to 4-AP with the help of NaBH 4 at a constant degradation rate of 1.49 × 10 − 4 s − 1 [84]. Taken together , during the reduction process, NaBH 4 acts as electrons donors (BH 4− ) while the dyes serve as electron receptors and the NPs used as an adsorption surface for the reactant (dyes plus NaBH 4 ).…”

Methods of green synthesis of Au NCs with emphasis on their morphology: A mini-review

“…Commiphora wightii [106], Crinum macowanii [107], Hibiscus sabdariffa [108], Flammulina velutipes [109], Dracocephalum Kotschyi [110], Solidago Canadensis [111], Pseudomonas monteilii [112], Justicia adhatoda [113] Hamelia patens [114], Pongamia pinnata [115], Cucurbita pepo L [116], Aconitum violaceum [117], Ulva armoricana [118], Solanum lycopersicon [119], Annona squamosal [120], Sasa borealis [121], Prosopis farcta [122] etc.…”