Laser Fragmentation of Colloidal Gold Nanoparticles with High-Intensity Nanosecond Pulses is Driven by a Single-Step Fragmentation Mechanism with a Defined Educt Particle-Size Threshold

Abstract

Laser-inducd fragmentation is a promising tool for controlling the particle size of ligand-free colloidal nanoparticles and to synthesize ligand-free gold nanoclusters. However, because the underlying mechanisms are not fully understood, increasing the yield of this process remains challenging. In this work, we examine the pulsed laser fragmentation of gold nanoparticles in liquid under statistical single-pulse conditions with high-fluence nanosecond pulses and correlate them with the educt particle size, number of pulses, and laser fluence. We conclusively prove that the fragmentation process of gold nanoparticles is a one-pulse and one-step event, which yields monomodal particles of ≪10 nm down to 2.8 +/- 0.1 nm when exceeding a pulse peak power of 1.6 × 1012 W/m2 and when all educt particles are larger than 13.4 nm. This size threshold for quantitative fragmentation fits well with the size limit of 13.1 nm calculated with respect to the evaporation–heat–energy balance. Furthermore, we found strong evidence that the number of irradiation cycles, varied within the regime of one to four laser pulses/colloid volume, can be used to tune the surface chemistry and surface charge of the resulting nanoparticles in an aqueous medium.

Perspective of Surfactant‐Free Colloidal Nanoparticles in Heterogeneous Catalysis

“…Yet up until now, broad nanoparticle size distributions are often observed during LAL in water requiring post‐treatment like continuous centrifugation or laser fragmentation . The origin of the different nanoparticle sizes is mainly thought to be linked to (sub)nanosecond‐scale molecular dynamics as well as liquid‐particle jetting, cavitation bubble dynamics, non‐uniform laser intensity profiles or post‐irradiation …”

“…A well‐established post‐treatment method for broad size distributions is provided by LFL and depicted in Figure c. This technique is often applied to control the nanoparticle size and gain very narrow size distributions in scalable quantities and without further additives . In accordance to LAL, these fragmentation processes can be realized by re‐irradiation of nanoparticle colloids using short laser pulses (femtosecond to nanosecond pulses) with sufficient laser pulse energy and wavelength .…”

“…In accordance to LAL, these fragmentation processes can be realized by re‐irradiation of nanoparticle colloids using short laser pulses (femtosecond to nanosecond pulses) with sufficient laser pulse energy and wavelength . Depending on the applied laser pulse duration, wavelength and hence the absorption cross‐section of the irradiated nanoparticles, a size‐selective fragmentation of nanoparticles is achieved by choosing a suiting laser (pulse) intensity . In this way nanoparticle sizes down to≤2 nm can be generated under surfactant‐free conditions and subsequently deposited on support materials making them useful in many catalytic applications …”

“…Yet, further experimental and theoretical basic research is required to improve the current models that describe the nanoparticle formation mechanisms . A prime example is the lack of comprehensive studies to understand how the resulting nanoparticle size depends on the oxidation potential of different materials and oxides in water (and other dielectric liquids).…”

In situstructural kinetics of picosecond laser-induced heating and fragmentation of colloidal gold spheres

“…Gold nanoparticles have been produced by pulsed laser ablation in liquids (LAL) by ablating a gold target in ultra-pure water (MilliQ, Millipore) in a batch chamber with a Nd:YAG laser (Ekspla, Atlantic Series, 10 ps, 1064 nm, 9.6 mJ, 100 kHz, 10 min), containing typically a multimodal size distribution. [39][40][41] To get a well size-separated sample for the study, a centrifugal step (Hettich, 67.1 g, 70 min) had been added. The obtained pellet is left for one week to force coalescence processes 42 and is subsequently diluted to 100 mg L À1 either in ultra-pure water or in an aqueous solution containing 0.3 mM NaOH and 0.3 mM NaCl each.…”