pH-dependent size and structural transition in P123 micelle induced gold nanoparticles

Abstract

The influence of the pH-value of the aqueous solution of P123-micelles on the growth and formation of gold nanoparticles (AuNPs), which is of immense importance for their controlled growth in a simple single-step synthesis process, was investigated using time-evolution optical absorption spectroscopy, dynamic light scattering and transmission electron microscopy techniques. The size and structures of the AuNPs are found pH-dependent, even within basic region, with transition near pH ≈ 9.5, though the free P123-micelles remain almost unchanged. Below this pH-value, the slow reduction rate of gold ions creates less number of nucleation centers, which through autocatalytic thermodynamically controlled reduction (ATCR), initially formed chain-like aggregated small AuNPs (of different chain length) and subsequently through further diffusion and coalescence, formed well-faceted near symmetrical large AuNPs of size ≫ 19 nm, the size of the free P123miclles. Above this pH-value, the fast reduction rate of the gold ions creates large number of nucleation centers. The growth of which is well restricted by the limited amount of available gold ions for the ATCR and also due to the metal-polymer hydrophobic and polymer-water hydrophilic interactions. Accordingly, controlled growth of the majority of the centers takes place through ATCR, diffusion and early capping through near individual micelles to form isolated symmetric small AuNPs of size < 19 nm, with narrow size distribution, which are really intended for the different applications and fundamental studies. However, minority (but not insignificant amount) of the centers still remain in very small sizes and trapped inside the large micellar assemblies or even in the near atomic states, which create hindrance in the yield of the isolated small AuNPs.

Effect of Pluronic P103 Concentration on the Simple Synthesis of Ag and Au Nanoparticles and Their Application in Anatase-TiO2 Decoration for Its Use in Photocatalysis

“…The increase in volume size distribution is evident when the polymer concentration is augmented (0.01, 0.1, and 0.5 wt%), as observed in Figure 4 a. The presence of a single peak may indicate large AgNPs or AgNPs agglomeration [ 49 ]. This behavior correlates with UV-Vis spectroscopy ( Figure 2 b), in that an increase in polymer concentration promotes a redshift, indicating an increase in particle size [ 38 , 42 ].…”

“…Surprisingly, an excess of polymer (10 wt%) shifts the plasmon position to a lower wavelength (530 nm), suggesting the presence of smaller NPs ( Figure 5 c). The SPR band becomes less broad and more symmetric, indicating a narrow size distribution or less aggregation [ 49 ].…”

“…As can be observed in Figure 7 a,c, both have similar behaviors; however, when analyzing the UV-Vis spectra, λ max is different (see Figure 6 b), which highlights that the polymer concentration determines the size of the NPs [ 7 ]. As a reference, other researchers, such as Chatterjee and Hazra [ 49 ], synthesized 4-nm AuNPs entrapped in Pluronic P123 polymeric templates. Also, Antonisamy et al [ 53 ] incorporated tiny AuNPs on the surface of polymeric templates formed with the Pluronic F127 copolymer.…”

Solution-Phase Synthesis of KCl Nanocrystals Templated by PEO-PPO-PEO Triblock Copolymers Micelles

“…Through the EI technique [11], nanocrystals with cubic shapes and 32 nm edges were successfully grown from ultra-dilute NaCl solution (1 μg.mL −1 ) on a millisecond timescale. In the current work, the concentration of sodium ions is 44 μg.mL −1 , and the mean diameter is 32 nm, which is on the same scale with that produced The effect of pH value on this reaction was investigated in our previous work [19] and by another researcher [37]. Synthesis of gold nanoparticles is typically determined by competition between nucleation (step 1) and growth (step 2 and 3) processes.…”

“…Based on all results, the formation of inorganic crystals and gold nanoparticles needs the involvement of both the polymer ether group and the hydroxyl group. The effect of pH value on this reaction was investigated in our previous work [19] and by another researcher [37]. Synthesis of gold nanoparticles is typically determined by competition between nucleation (step 1) and growth (step 2 and 3) processes.…”