Abstract
The hazardous effects of current nanoparticle synthesis methods have steered researchers to focus on developing newer eco-friendly methods for synthesizing nanoparticles using non-toxic chemicals. Owing to the diverse applications of nanoparticles in various fields such as catalysis, medicine, diagnostics, and sensors, several novel green approaches have been explored for synthesizing nanoparticles using different natural sources such as plants, algae, bacteria, and fungi. Hence, in the present work, a green method for the synthesis of gold nanoparticles (AuNPs) under ambient conditions using aqueous extracts of marine brown algae is reported and the synthesized AuNPs were evaluated for their catalytic efficiency. The aqueous extracts of algae comprise reducing as well as capping agents required for the formation of AuNPs. The Fourier transform infrared spectra of the extracts revealed the presence of compounds having hydroxyl groups that are largely responsible for the reduction of auric chloride to AuNPs at room temperature. Results from high-resolution transmission electron microscopy and dynamic light scattering studies suggested that most of the biosynthesized AuNPs are nearly spherical in shape with an average size in the range of 27–35 nm. High negative values of zeta potential measurement confirmed the stability of AuNPs. Moreover, the reduction kinetics of AuNPs studied by UV–visible spectrophotometry showed that they have good catalytic efficiency in the degradation of dyes as well as reduction of nitro compounds in the presence of sodium borohydride as reducing agent. This simple process for the biosynthesis of gold nanoparticles is rapid, cost-effective and eco-friendly. The formation of AuNPs was observed with the change of pale yellow gold solution to ruby red color of gold nanoparticles and confirmed by surface plasmon spectra using UV–visible spectroscopy. Nanoparticles synthesized through such environmentally benign routes can be used for synthesizing many other metal nanoparticles as well as for a wide range of biomedical applications, for commercial production on a large scale and also can be used as efficient catalysts for different organic reactions.
Highlights
Nanoparticles are gaining enormous research attention in various fields such as chemistry, physics, materials science, life sciences and engineering
The color change from light yellow to ruby red or pinkish red is due to the excitation of surface plasmon resonance (SPR) in the gold nanoparticles induced by passing light and this observation was confirmed by UV– vis spectral analysis [11]
The spectral pattern in the near infrared (NIR) region shows a shoulder band around 750 nm which increased along with reaction time, thereby indicating that the biosynthesized Au(III) ions to gold nanoparticles (AuNPs) are anisotropic in nature which is confirmed by TEM images
Summary
Nanoparticles are gaining enormous research attention in various fields such as chemistry, physics, materials science, life sciences and engineering. Many of the existing physical and chemical methods suffer from few drawbacks such as high cost, use of environmentally hazardous chemicals and non-availability for medical applications due to presence of toxic capping agents [3, 4] These factors contributed towards exploration of new methods and materials for the production of nanoparticles based on the principles of ‘‘Green Chemistry’’. The emphasis in this approach is on the synthesis and application of the nanoparticles for a maximum societal benefit, with minimal impact on the ecosystem [5]. The compounds present in the extracts can act as reducing as well as stabilizing agents and render more biocompatibility to biosynthesized nanoparticles [10]
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