Synthesis of Silver Nanowires Using a Polyvinylpyrrolidone-Free Method with an Alpinia zerumbet Leaf Based on the Oriented Attachment Mechanism

Abstract

In this study, silver nanowires (AgNWs) were successfully synthesized by using a polyvinylpyrrolidone (PVP)-free hydrothermal method with an Alpinia zerumbet leaf chunk as a reducing agent and template. Meanwhile, the mechanism of biomass synthesis of AgNWs is also explored. The AgNWs have a diameter of ∼77 nm and a length of ∼10 μm. During the hydrothermal process, the biomass initially serves as a reducing agent to reduce silver ions. As the reaction proceeds, the biomass will form a pipe-shaped soft template by hydrothermal carbonization. Silver ions are adsorbed and reduced along the pipe-shaped soft templates to form silver nanorods, and adjacent nanorods are merged to AgNWs. Thus, AgNWs are grown along the pipeline soft template based on the oriented attachment mechanism. Inspired by this, the mechanism of the polyol method was further investigated. In the initial growth stage, AgNWs synthesized by the polyol method have a V-shaped notch. Therefore, AgNWs synthesized by the polyol method may also grow on the basis of the oriented attachment mechanism with PVP as a template.

Phytochemical-Mediated Green Synthesis of Ag Nanowires and Fabrication of Highly Flexible, Biocompatible, and Antibiofouling Conductive Films

“…At the initial 30 min (associated with the induction period), Ag nanostructures or nanorods with a pea-like morphology were observed in the aliquots removed from the reaction mixture. This finding indicates that free Ag + ions are initially adsorbed and then reduced to AgNPs (pointed by blue arrows) by the biomolecules, thereby aggregating into Ag nanoclusters wrapped in a biomass layer (pointed by red arrows) . Afterward, the Ag nanoclusters exhibited spontaneous growth and free assembly along the longitudinal axis (oriented attachment).…”

“…This finding indicates that free Ag + ions are initially adsorbed and then reduced to AgNPs (pointed by blue arrows) by the biomolecules, thereby aggregating into Ag nanoclusters wrapped in a biomass layer (pointed by red arrows). 14 Afterward, the Ag nanoclusters exhibited spontaneous growth and free assembly along the longitudinal axis (oriented attachment). Prolonging the reaction to 1 h, the number of Ag clusters increases, and an irregular mixture of both pea-like short nanorods and micrometer-length fibers starts to appear.…”

“…Similar oriented attachment phenomena have been reported on the growth of AgNWs synthesized by plant extract of Alpinia zerumbet leaves as well as by the polyol method, where nanoparticles with common crystallographic orientations directly combine to form a fibrous morphology. 14,34 A closer inspection of the crystallization of AgNWs by HRTEM revealed a penta-twinned crystallographic structure (diameter of ∼40 nm) with five well-defined facets synthesized at the initial 10 min (Figure 2a), which is suggested to act as the Ag crystal seed. The resultant AgNW after 5 h of crystal growth is multitwinned with a pointed tip (Figure 2b).…”

“…Lin et al reported the first plant-mediated biosynthesis of AgNWs using broth of Cassia fistula leaf and found that the nanowires evolved from spherical nanoparticles via a linear aggregation rather than point-initiated vectoral growth . Similarly, in a study using an Alpinia zerumbet leaf chunk as a reducing agent and template, AgNWs were grown along the pipeline soft template based on an oriented attachment mechanism . It is clear that the growth of AgNWs by plants might involve several active components playing different roles (i.e., a reducing agent, a capping agent, or a shape-directing agent) .…”

“…13 Similarly, in a study using an Alpinia zerumbet leaf chunk as a reducing agent and template, AgNWs were grown along the pipeline soft template based on an oriented attachment mechanism. 14 It is clear that the growth of AgNWs by plants might involve several active components playing different roles (i.e., a reducing agent, a capping agent, or a shape-directing agent). 15 Nevertheless, due to the complicated nature of plants, mechanistic investigations into the plant components for AgNW formation are quite limited, except for tannin, a highly abundant plant polyphenolic compound.…”