Abstract

The past decade has observed a significant surge in efforts to discover biological systems for the fabrication of metal nanoparticles. Among these methods, plant-mediated synthesis has garnered sizeable attention due to its rapid, cost-effective, environmentally benign single-step procedure. This study explores a step-wise, room-temperature protocol for the synthesis of gold nanoparticles (AuNPs) using Carallia brachiata, a mangrove species from the west coast of Peninsular Malaysia. The effects of various reaction parameters, such as incubation time, metal ion concentration, amount of extract and pH, on the formation of stable colloids were monitored using UV-visible (UV-Vis) absorption spectrophotometry. Our findings revealed that the physicochemical properties of the AuNPs were significantly dependent on the pH. Changing the pH of the plant extract from acidic to basic appears to have resulted in a blue-shift in the main characteristic feature of the surface plasmon resonance (SPR) band, from 535 to 511 nm. The high-resolution-transmission electron microscopy (HR-TEM) and field emission scanning electron microscopy (FESEM) images revealed the morphologies of the AuNPs synthesized at the inherent pH, varying from isodiametric spheres to exotic polygons and prisms, with sizes ranging from 10 to 120 nm. Contrarily, an optimum pH of 10 generated primarily spherical-shaped AuNPs with narrower size distribution (8–13 nm). The X-ray diffraction (XRD) analysis verified the formation of AuNPs as the diffraction patterns matched well with the standard value of a face-centered cubic (FCC) Au lattice structure. The Fourier-transform infrared (FTIR) spectra suggested that different functional groups are involved in the biosynthetic process, while the phytochemical test revealed a clear role of the phenolic compounds. The reduction of 4-nitrophenol (4-NP) was selected as the model reaction for evaluating the catalytic performance of the green-synthesized AuNPs. The catalytic activity of the small, isotropic AuNPs prepared using basic aqueous extract was more effective than the nanoanisotrops, with more than 90% of 4-NP conversion achieved in under an hour with just 3 mg of the nanocatalyst.

Highlights

  • Metal nanoparticles (NPs) have been adopted in various scholarly fields, medical and environmental research included

  • Gold nanoparticles (AuNPs), in particular, have caught the attention among various noble metals present and are among the nanometals commonly incorporated in biomedical science (Hu et al, 2020), such as for catalysis (Hutchings and Edwards, 2012) and sensors (Saha et al, 2012; Zhang, 2013)

  • The nucleation and growth conditions of NPs are primarily impacted by parameters such as incubation time, metal ion concentration, pH, nature of reducing and stabilizing agents, seeds, and more

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Summary

INTRODUCTION

Metal nanoparticles (NPs) have been adopted in various scholarly fields, medical and environmental research included. AuNPs boast of embedded physical and chemical attributes resulting in critical applications, which are tunable via size and shape modifications Such processes are a key function for bigscale advanced material manufacturing, rendering an excellently regulated synthesis of the particles a necessity. Conventional AuNP synthesis denotes the incorporation of chemical reducing agents This practice emerges as significant over time due to its general toxicity yielding a multitude of biological side effects, thereby sparking doubts pertaining to the development of environmentally-friendly nanosynthesis routes (Mohanpuria et al, 2008; Sardar et al, 2009). The conversion of simple or complex 4-NP to its non-hazardous intermediate, 4-aminophenol (4-AP), is deemed critical for eradicating environmental contamination generated due to the chemical In this case, the abundance and diversity offered by nanocatalytic systems via reducing agent utilization have resulted in the evolution of substrates possibly equipped for industrially-useful reduction of 4-NP (Mehmood et al, 2016; Rodríguez Molina et al, 2019). The present work describes the catalytic potential of the enhanced AuNPs for the purpose of 4-NP degradation using hydrazine hydrate, paving the way for new possibilities in future bioremediation programs

Materials
Synthesis of AuNPs
Characterization of the Synthesized
Catalytic Activities of the Biosynthesized AuNPs in the Reduction of 4-NP
Phytochemical Screening Tests
UV-Visible Analyses
Morphological Studies
Elemental Analysis
Crystallographic Analysis
Functional Group Analysis
Catalytic Reduction of 4-NP
DATA AVAILABILITY STATEMENT
CONCLUSION

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