Abstract
The versatile one-pot green synthesis of a highly concentrated and stable colloidal dispersion of silver nanoparticles (Ag NPs) was carried out using the self-assembled tannic acid without using any other hazardous chemicals. Tannic acid (Plant-based polyphenol) was used as a reducing and stabilizing agent for silver nitrate in a mild alkaline condition. The synthesized Ag NPs were characterized for their concentration, capping, size distribution, and shape. The experimental results confirmed the successful synthesis of nearly spherical and highly concentrated (2281 ppm) Ag NPs, capped with poly-tannic acid (Ag NPs-PTA). The average particle size of Ag NPs-PTA was found to be 9.90 ± 1.60 nm. The colloidal dispersion of synthesized nanoparticles was observed to be stable for more than 15 months in the ambient environment (25 °C, 65% relative humidity). The synthesized AgNPs-PTA showed an effective antimicrobial activity against Staphylococcus Aureus (ZOI 3.0 mM) and Escherichia coli (ZOI 3.5 mM). Ag NPs-PTA also exhibited enhanced catalytic properties. It reduces 4-nitrophenol into 4-aminophenol in the presence of NaBH4 with a normalized rate constant (Knor = K/m) of 615.04 mL·s−1·mg−1. For comparison, bare Ag NPs show catalytic activity with a normalized rate constant of 139.78 mL·s−1·mg−1. Furthermore, AgNPs-PTA were stable for more than 15 months under ambient conditions. The ultra-high catalytic and good antimicrobial properties can be attributed to the fine size and good aqueous stability of Ag NPs-PTA. The unique core-shell structure and ease of synthesis render the synthesized nanoparticles superior to others, with potential for large-scale applications, especially in the field of catalysis and medical.
Highlights
The Antimicrobial activity of synthesized nanoparticles was analyzed against Gramnegative, Escherichia coli (E. coli, ATCC1129) and Gram-positive, Staphylococcus aureus (S. aureus, ATCC 6538)
The average particle size measured by the dynamic light scattering (DLS) was around 10.4 nm (Figure 4)
It was observed that the reference/control sample (C) shows no inhibition against the antimicrobe while the ACF sheets drop coated with Ag NPs-PTA and bare Ag NPs dispersions displayed remarkable antimicrobial performance and a clear Zone of Inhibition (ZOI) was noticed
Summary
There have been many attempts for the synthesis of highly concentrated AgNPs. low reaction efficiency, slow speed, high energy input, complex synthesis process, high cost, or use of toxic chemicals limits their applications at the industrial scale [4,21–23]. A two-step methodology was adopted to produce the core-shell nanoparticles, but the processes are long routed, require the addition of Fe3+ ions as crosslinkers [28,29], and they are often complex and require the use of toxic reagents, which may limit some practices applications. Tannic acid (TA) contains catechol and galloyl groups, which are well known for their metal chelation and material surface binding properties It plays a vital role in the green synthesis of nanoparticles at room temperature by acting as both reducing and capping agents [33,34]. Based on the unique performance properties, they can be used for a wide range of applications where antimicrobial and catalytic activities are desired
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