Abstract
Although oxide nanoparticles are ubiquitous in science and technology, a multitude of compositions, phases, structures, and doping levels exist, each one requiring a variety of conditions for their synthesis and modification. Besides, experimental procedures are frequently dominated by high temperatures or pressures and by chemical contaminants or waste. In recent years, laser synthesis of colloids emerged as a versatile approach to access a library of clean oxide nanoparticles relying on only four main strategies running at room temperature and ambient pressure: laser ablation in liquid, laser fragmentation in liquid, laser melting in liquid and laser defect‐engineering in liquid. Here, established laser‐based methodologies are reviewed through the presentation of a panorama of oxide nanoparticles which include pure oxidic phases, as well as unconventional structures like defective or doped oxides, non‐equilibrium compounds, metal‐oxide core–shells and other anisotropic morphologies. So far, these materials showed several useful properties that are discussed with special emphasis on catalytic, biomedical and optical application. Yet, given the endless number of mixed compounds accessible by the laser‐assisted methodologies, there is still a lot of room to expand the library of nano‐crystals and to refine the control over products as well as to improve the understanding of the whole process of nanoparticle formation. To that end, this review aims to identify the perspectives and unique opportunities of laser‐based synthesis and processing of colloids for future studies of oxide nanomaterial‐oriented sciences.
Highlights
Oxide nanoparticles (NPs) are largely exploited for a variety of purposes, which embraces fields as different as, for instance, heterogeneous catalysis, biotechnology, medicine, photonics, solar energy conversion, microelectronics, automotive industry, pharmaceutics, and food additives.[1,2] This variety of applications comes with a vast number of distinct compounds belonging to the class of oxide nanomaterials
It is of utmost importance to realize the synthesis of oxide NPs by environmentally friendly, energy-saving, simple and effective routes
We showed that laser-assisted synthesis in liquid environment is a versatile approach running at room temperature and pressure, with highly encouraging results in terms of purity of products and absence of undesired chemical compounds or pollutant wastes
Summary
Excited oxygen species have been observed in real-time inside the plasma plume in aqueous environment, up to hundreds of nanoseconds after pulse absorption,[116] and in ambient air during ablation of oxide targets.[117] oxygen coming from the molecules of liquid (e.g., H2O) or additives (e.g., H2O2 or atmospheric O2) will react with the ablated target species, and the extent of the oxidation reaction will depend on the type and concentration of reactive oxygen species and on the redox potential of the metal.[81] This is the source of persistent microbubbles affecting the ablation rate.[27] For the ablation of 7 different metals, Kalus et al observed that the developed gas volume is directly correlated with the respective redox potential of the metal.[81] A possible correlation of (temperature-dependent) redox potential and oxidation state during LAL has been discussed recently in literature.[19]. The rising of additive manufacturing has benefited from depositing laser-generated Y2O3 NPs on iron-chromium powders to obtain oxide dispersed strengthened alloy parts by laser powder bed fusion (often called selective laser melting SLM) (Figure 16 F).[361]
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