Synthesis of metal nanoparticles using plant extracts is one of the most simple, convenient, economical, and environmentally friendly methods that mitigate the involvement of toxic chemicals. Hence, in recent years, several eco-friendly processes for the rapid synthesis of silver nanoparticles have been reported using aqueous extracts of plant parts such as the leaf, bark, roots, etc. This review summarizes and elaborates the new findings in this research domain of the green synthesis of silver nanoparticles (AgNPs) using different plant extracts and their potential applications as antimicrobial agents covering the literature since 2015. While highlighting the recently used different plants for the synthesis of highly efficient antimicrobial green AgNPs, we aim to provide a systematic in-depth discussion on the possible influence of the phytochemicals and their concentrations in the plants extracts, extraction solvent, and extraction temperature, as well as reaction temperature, pH, reaction time, and concentration of precursor on the size, shape and stability of the produced AgNPs. Exhaustive details of the plausible mechanism of the interaction of AgNPs with the cell wall of microbes, leading to cell death, and high antimicrobial activities have also been elaborated. The shape and size-dependent antimicrobial activities of the biogenic AgNPs and the enhanced antimicrobial activities by synergetic interaction of AgNPs with known commercial antibiotic drugs have also been comprehensively detailed.

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Green synthesis of silver nanoparticles using plant extracts and their antimicrobial activities: a review of recent literature

Phyto-synthesis of silver nanoparticles (AgNPs) was achieved using aqueous garlic, green tea and turmeric extracts, and characterized by different spectroscopic techniques. Phytochemical analysis revealed the presence of rich amount of biochemicals in these extracts, which serve as reducing and capping agents for converting silver nitrate into AgNPs. FT IR spectroscopy confirmed the role of biomolecules in the bioreduction and efficient stabilization of AgNPs. UV–Vis DRS spectra showed a band around 450 nm characteristics of AgNPs. XRD patterns revealed the crystalline nature of the synthesized AgNPs with fcc structure. SEM and TEM analysis revealed the spherical shape of the synthesized AgNPs with an average particle size of 8 nm. EDX analysis confirmed the purity of the synthesized AgNPs with a strong signal at 3.2 keV. The antioxidant activity was assessed by ABTS, DPPH, p-NDA, H2O2 and DMSO scavenging assays, in which the AgNPs synthesized using green method showed remarkable activity with respect to the standard antioxidants ascorbic acid and rutin. In vitro cytotoxicity activity was tested on four cancer cell lines such as human breast adenocarcinoma (MCF-7), cervical (HeLa), epithelioma (Hep-2) and lung (A549) along with one normal human dermal fibroblasts (NHDF) cell line. The AgNPs synthesized using turmeric extract exhibits excellent antioxidant and cytotoxicity activity compared to that synthesized using other extracts.

Garlic, green tea and turmeric extracts-mediated green synthesis of silver nanoparticles: Phytochemical, antioxidant and in vitro cytotoxicity studies.

In the field of nanotechnology, the development of reliable and eco-friendly methods for the synthesis of NPs is crucial. The conventional methods for the synthesis of NPs are costly, toxic, and not ecofriendly. To overcome these issues, natural sources such as plant, bacteria, fungi, and biopolymers have been used to synthesize AgNPs. These natural sources act as reducing and capping agents. The shape, size, and applications of AgNPs are prominently affected by the reaction parameters under which they are synthesized. Accessible distributed data on the synthesis of AgNPs include the impact of different parameters (temperature and pH), characterization techniques (DLS, UV-vis, FTIR, XRD, SEM, TEM and EDX), properties and their applications. This review paper discusses all the natural sources such as plants, bacteria, fungi, and biopolymers that have been used for the synthesis of AgNPs in the last ten years. AgNPs synthesized by green methods have found potential applications in a wide spectrum of areas including drug delivery, DNA analysis and gene therapy, cancer treatment, antimicrobial agents, biosensors, catalysis, SERS and magnetic resonance imaging (MRI). The current limitations and future prospects for the synthesis of inorganic nanoparticles by green methods are also discussed herein.

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Facile green synthesis and applications of silver nanoparticles: a state-of-the-art review

Catalytic reduction of nitrophenols and dyes using silver nanoparticles @ cellulose polymer paper for the resolution of waste water treatment challenges

Silver-iron bimetallic nanoparticles (BMNPs) were synthesized by using AgNO3 and Fe(NO3)3 as an Ag/Fe source in presence of Palm dates fruit. Upon addition of extract to a solution of Ag+ and Fe3+, a prefect transparent stable dark brown color appears with in a few minuets at room temperature. In order to conform the nature of resulting color, UV-visible spectroscopy, transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDX) techniques were used. The absence of surface plasmon resonance (SPR) peaks in the entire UV-visible region suggests the formation of silvercore-ironshell BMNPs. The obtained nanoparticles were used as a catalyst for the degradation of bromothymol blue (BTB) in absence and presence of sunlight. The degradation kinetics was studied in presence of electron acceptors and scavengers, such as hydrogen peroxide, ammonium oxalate, ammonium per sulphate, benzoquinone, isopropyl alcohol, n-butanol, potassium bromate and potassium iodide. Radical trapping experiments demonstrates that active holes (h+) and generated hydroxy radical are primary species involved in H2O2 assisted catalytic degradation process. The free-radical scavenging, antioxidant and antimicrobial activities were determined for extract and BMNPs. The 1,1-diphenyl-2-picrylhydrazyl (DPPH) scavenging activities were found to increase with increasing the amounts of extract. The silver-iron showed good invitro antibacterial activities against human pathogens.

Eco-friendly green synthesis of Ag@Fe bimetallic nanoparticles: Antioxidant, antimicrobial and photocatalytic degradation of bromothymol blue.

CTAB capped synthesis of bio-conjugated silver nanoparticles and their enhanced catalytic activities

The present study explores the reducing and capping potentials of aqueous Raphanus sativus root extract for the synthesis of silver nanomaterials for the first time in the absence and presence of two stabilizers, namely, water-soluble starch and cetyltrimethylammonium bromide (CTAB). The surface properties of silver nanoparticles (AgNPs) were determined by dynamic light scattering (DLS), transmission electron microscopy (TEM), energy dispersion X-ray spectroscopy (EDX), scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier transform infrared (FT-IR) techniques. The mean size of AgNPs, ranging from 3.2 to 6.0 nm, could be facilely controlled by merely varying the initial [extract], [CTAB], [starch], and [Ag+] ions. The agglomeration number, average number of silver atoms per nanoparticle, and changes in the fermi potentials were calculated and discussed. The AgNPs were evaluated for their antimicrobial activities against different pathogenic organisms. The inhibition action was due to the structural changes in the protein cell wall.

Green synthesis of biogenic silver nanomaterials using Raphanus sativus extract, effects of stabilizers on the morphology, and their antimicrobial activities

Cationic surfactant assisted morphology of Ag@Cu, and their catalytic reductive degradation of Rhodamine B

Catalytic Activity of Cobalt Nanoparticles for Dye and 4‐Nitro Phenol Degradation: A Kinetic and Mechanistic Study

Removal of Congo red is a serious environmental problem. Metal nanoparticles are emerging as a efficient catalysts and/or adsorbents to the degradation of dyes due to the large surface area. UV–visible absorption spectroscopy was used to quantify the decolorization of Congo red by Co-nanoparticles with and with out sun light at different time intervals. The experimental results show that the 100% Congo red ( 2 . 1 × 1 0 − 4 mol dm − 3 ) can be mineralized after ca. 1 min with Co-nanoparticles ( 3 . 2 × 1 0 − 3 mol dm − 3 ) in presence of sun light irradiation. The degradation pathway of Congo red under the optimal experimental conditions is also proposed and discussed. In this paper, a simple and nonexpensive method was used to the synthesis of Co-nanoparticles in absence and presence of stabilizers. The morphology, stability and color of cobalt sols strongly depends on the nature and/or presence of stabilizers. Transmission electron microscopic data revealed that the Co-nanoparticles possesses multi-layered aggregated sheet, and dumbly shaped morphology with different stabilizers.

Mohammad Naved Khan

Papers

CTAB capped synthesis of bio-conjugated silver nanoparticles and their enhanced catalytic activities

Green synthesis of biogenic silver nanomaterials using Raphanus sativus extract, effects of stabilizers on the morphology, and their antimicrobial activities

Cationic surfactant assisted morphology of Ag@Cu, and their catalytic reductive degradation of Rhodamine B

Catalytic Activity of Cobalt Nanoparticles for Dye and 4‐Nitro Phenol Degradation: A Kinetic and Mechanistic Study

Influence of stabilizing agents on the microstructure of Co-nanoparticles for removal of Congo red