Gradually Fe-Doped Co₃O₄ Nanoparticles in 2-Propanol and Water Oxidation Catalysis with Single Laser Pulse Resolution

Abstract

Controlling the surface composition of colloidal nanoparticles is still a challenging yet mandatory prerequisite in catalytic studies to investigate composition-activity trends, active sites, and reaction mechanisms without superposition of particle size or morphology effects. Laser post-processing of colloidal nanoparticles has been employed previously to create defects in oxide nanoparticles, while the possibility of laser-based cation doping of colloidal nanoparticles without affecting their size remains mostly unaccounted for. Consequently, at the example of doping iron into colloidal Co 3 O 4 spinel nanoparticles, we developed a pulse-bypulse laser cation doping method to provide a catalyst series with a gradually modified surface composition but maintained extrinsic properties such as phase, size, and surface area for catalytic studies. Laser pulse number-resolved doping series were prepared at a laser intensity chosen to selectively heat the Co 3 O 4 -NPs to roughly 1000 K and enable cation diffusion of surface-adsorbed Fe 3+ into the Co 3 O 4 lattice. The combination of bulk-sensitive X-ray fluorescence and surface-sensitive X-ray photoelectron spectroscopy was used to confirm the surface enrichment of the Fe-dopant. X-ray diffraction, magnetometry, and Mossbauer spectroscopy revealed an increasing interaction between Fe and the antiferromagnetic Co 3 O 4 with arising number of applied laser pulses, in line with a herein proposed laser-induced surface doping of the colloidal Co 3 O 4 nanoparticles with Fe. Using Fick's second law, the thermal diffusionrelated doping depth was estimated to be roughly 2 nm after 4 laser pulses. At the example of gas-phase 2-propanol oxidation and liquid-phase oxygen evolution reaction, the activity of the laser-doped catalysts is in good agreement with previous activity observations on binary iron-cobalt oxides. The catalytic activity was found to linearly increase with the calculated doping depth in both reactions, while only catalysts processed with at least one laser pulse were catalytically stable, highlighting the presented method in providing comparable, active, and stable gradual catalyst doping series for future catalytic studies.

Laser-based ion doping is a suitable alternative to dope biologically active ions into colloidal bioglass nanoparticles

“…Hence, nanosecond-pulsed UV laser excitation of nanoparticles in the low fluence regime applied here is most likely linked to a particle-surface-heating process, causing pulsed-laser-induced diffusion enhancement. 17 Furthermore, ion uptake specificity (higher affinity of Fe than Cu as found in 18 ) seems to be less pronounced (not dominant) at lower doping levels or in case no size reduction occurs. Upon co-doping with Sr, the Fe doping levels drastically increased by a factor of 9, so the presence of Sr seemed to promote Fe doping.…”

“…16 Recently Zerebecki et al reported laser-induced doping of Fe ions into Co 3 O 4 by applying low fluence laser heating and precisely controlling the number of laser pulsed per colloid volume. 17 Laser-based doping of bioactive glass (BG) on the other hand has been rarely explored. In one study Li and Ramesh et al examined the reactive laser fragmentation of micrometer-sized 45S5 BG in the presence of Cu (EDTA) and Fe (EDTA) complex solutions.…”

Efficient Synthesis of Submicrometer‐Sized Active Pharmaceuticals by Laser Fragmentation in a Liquid‐Jet Passage Reactor with Minimum Degradation

“…In addition, we gained mechanistic insight into the LFL process of organic molecules, postulating a simultaneous contribution of multiple fragmentation mechanisms based on the stress confinement criterion, a degradation‐free ablation enabled by residual water, as well as the formation of an internal quasi‐stationary stress gradient within MP, prone to stimulate further fundamental research in this area. Here, particularly a newly developed flat‐jet passage reactor, which was demonstrated to enable a more homogeneous illumination and more precise pulse per volume control in metal [ 58 ] or oxide [ 59 ] nanoparticle pulsed laser excitation, could be a useful asset to further clarify the fragmentation mechanism.…”

Continuous and Scalable Laser Synthesis of Atom Clusters with Tunable Surface Oxidation for Electrocatalytic Water Splitting

“…Laser fragmentation in liquids fills this gap by providing monodisperse, surfactant-free, colloidal sub-5 nm particles . Additionally, particularly for transition metal oxide nanoparticles, changes in the oxidation state and cation occupancy of tetrahedral and octahedral sites with the number of laser pulses and even laser-induced cation doping have been shown in the past. Hereby, both oxidation and reduction , reactions, mostly located in surface-near particle layers, were observed to occur with ongoing laser irradiation, with the oxidation/reduction tendency appearing to correlate with the initial oxidation state and redox potential of the initial particles.…”