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.

Due to material gaps and synthesis‐related cross‐correlations in heterogeneous catalysis, chemists and physicists are constantly motivated to develop novel catalyst preparation methods for independent control of morphology, size, and composition. Within this article, advances, opportunities, and the current limits of laser‐based catalyst preparation technique, as well as synergies with conventional methods will be reviewed in terms of purity, particle size, morphology, composition, and nanoparticle‐support interaction. It will be shown, that the surfactant‐free particles represent ideal model materials to validate kinetic models and conduct parametric activity studies by independent adjustment of functional properties like nanoparticle size, composition, and load. Consequently, the importance of transient plasma dynamics tailoring nanoparticle formation will be pointed out, comparing experimental studies with own calculations and novel simulations taken from literature. Finally, perspectives of surfactant‐free colloidal nanoparticles for unrevealing active sites in heterogeneous catalysts are presented.

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.

The structural and energetic pathway of picosecond laser fragmentation of gold colloids has been clarified by time-resolved X-ray scattering.

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Laser processing of neat and gold-nanoparticle-functionalized ZnO and TiO2 nanoparticles by nanosecond-355-nm or picosecond-532-nm light enabled control of photocurrent generation under simulated sunlight irradiation in neutral aqueous electrolytes. We obtained more than twofold enhanced photoelectrochemical performance of TiO2 nanoparticles upon irradiation by picosecond-532-nm pulses that healed defects. Laser processing and gold nanoparticle functionalization of ZnO and TiO2 nanomaterials resulted in color changes that did not originate from optical bandgaps or crystal structures. Two-dimensional photoluminescence data allowed us to differentiate and quantify surface and bulk defects that play a critical yet oft-underappreciated role for photoelectrochemical performance as sites for detrimental carrier recombination. We developed a detailed mechanistic model of how surface and bulk defects were generated as a function of laser processing parameters and obtained key insights on how these defects affected photocurrent production. The controlled healing of defects by pulsed-laser processing may be useful in the design of solar fuels materials. Pulsed lasers are powerful tools for the time-efficient preparation and/or modification of functional materials. 14-21 Recent investigations have shown that laser-modified TiO2 particles can be used to improve the light-driven water splitting to form hydrogen 22 or

Herein, we report nanosecond, single-pulse laser post-processing (PLPP) in a liquid flat jet with precise control of the applied laser intensity to tune structure, defect sites, and the oxygen evolution reaction (OER) activity of mesostructured Co 3 O 4 . High-resolution X-ray diffraction (XRD), Raman, and Xray photoelectron spectroscopy (XPS) are consistent with the formation of cobalt vacancies at tetrahedral sites and an increase in the lattice parameter of Co 3 O 4 after the laser treatment. X-ray absorption spectroscopy (XAS) and X-ray emission spectroscopy (XES) further reveal increased disorder in the structure and a slight decrease in the average oxidation state of the cobalt oxide. Molecular dynamics simulation confirms the surface restructuring upon laser post-treatment on Co 3 O 4 . Importantly, the defectinduced PLPP was shown to lower the charge transfer resistance and boost the oxygen evolution activity of Co 3 O 4 . For the optimized sample, a 2-fold increment of current density at 1.7 V vs RHE is obtained and the overpotential at 10 mA/cm 2 decreases remarkably from 405 to 357 mV compared to pristine Co 3 O 4 . Post-mortem characterization reveals that the material retains its activity, morphology, and phase structure after a prolonged stability test.

Noble metal aerogels (NMAs) are an emerging class of porous materials. Embracing nano‐sized highly‐active noble metals and porous structures, they display unprecedented performance in diverse electrocatalytic processes. However, various impurities, particularly organic ligands, are often involved in the synthesis and remain in the corresponding products, hindering the investigation of the intrinsic electrocatalytic properties of NMAs. Here, starting from laser‐generated inorganic‐salt‐stabilized metal nanoparticles, various impurity‐free NMAs (Au, Pd, and Au‐Pd aerogels) were fabricated. In this light, we demonstrate not only the intrinsic electrocatalytic properties of NMAs, but also the prominent roles played by ligands in tuning electrocatalysis through modulating the electron density of catalysts. These findings may offer a new dimension to engineer and optimize the electrocatalytic performance for various NMAs and beyond.