Amorphization of laser-fabricated ignoble high-entropy alloy nanoparticles and its impact on surface composition and electrochemistry.

High-entropy alloy nanoparticles (HEA NPs) represent a promising material class with significant potential in various applications, such as heterogeneous catalysis or magnetic devices. This is due to their exceptional compositional tunability arising from the synergistic interplay of multiple elements within a single particle. While laser-synthesized, surfactant-free colloidal HEA NPs have already been reported, the underlying formation mechanism remains unknown, particularly the underexplored preference of amorphous over crystalline structures warrants further investigation. Herein, we present a systematic study of laser-generated equimolar CrMnFeCoNi nanoparticles, focusing on structural differences, arising from varying pulse durations during synthesis in organic solvents (acetone, ethanol, acetonitrile). In a systematic experimental series using high-resolution transmission electron microscopy, scanning transmission electron microscopy with energy-dispersive X-ray spectroscopy, selected-area electron diffraction, X-ray diffraction, electron energy loss spectroscopy, in situ heating, post-irradiation experiments, and differential scanning calorimetry we demonstrate that a pulse-duration-driven structural difference occurs during laser ablation in liquid is observable to the three utilized solvents. While picosecond-pulsed laser ablation in liquid produces polycrystalline HEA NPs, nanosecond-pulsed laser ablation favors a metastable amorphous structure. Particle cores in all cases exhibit a homogeneous distribution of the metals Cr, Mn, Fe, Co, and Ni, while particle shells were found to vary between manganese-enriched oxide layers and thin graphitic carbon coatings. The discovery of the structure-directing mechanism allows one to select between crystalline or amorphous HEA NP products, simply by choice of the laser pulse duration in the same, well-scalable setup, giving access to colloidal particles that can be further downstream processed to heterogeneous catalysts or magnets. In that context, the outstanding temperature stability up to 375 °C (differential scanning calorimetry) or 500 °C (transmission electron microscopy) may motivate future application-relevant work.

Opportunities and Challenges for Laser Synthesis of Colloids.

We present a controlled fabrication of selective ultrathin metal–organic framework (MOF) nanosheets as preassembling platforms, yolk–shell structured with a few-layered N-doped carbon (NC) shell-en...

This study investigates the morphological evolution and enhanced crystallinity of FeMnNiAlSiC high-entropy alloy (HEA) nanoparticles (NPs) synthesized using a picosecond laser operating in burst mode and subsequently processed with a nanosecond laser in deionized water (DW). The initial synthesis via pulsed laser ablation in liquid (PLAL) revealed distinct phases, like B2, γ-brass, Fe5Si3, and body-centered cubic (BCC), as confirmed by high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), and X-ray diffraction (XRD) data. Elemental mapping indicated enrichment of B2-type phases (Al–Fe and Al–Ni) in the larger NPs, while smaller NPs exhibited γ-brass and Fe5Si3-type phases. Following nanosecond laser processing, the NPs displayed significant morphological transformations, including the emergence of hollow structures, as well as enhanced crystallinity. Post-processing analysis demonstrated the evolution of B2 and Fe5Si3-type phases, driven by a laser-induced annealing effect, which resembles the traditional furnace annealing. This dual-stage laser approach effectively combines the rapid synthesis of NPs with structural refinement, offering a versatile pathway for tailoring material properties. These findings underscore the potential of laser-based techniques in the controlled synthesis and structural modulation of HEA NPs, paving the way for applications in catalysis, energy conversion, and advanced functional materials.

Thin Films Fabricated by Pulsed Laser Deposition for Electrocatalysis

Developing active and stable bifunctional electrocatalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is essential for a wide range of applications of rechargeable air batteries, water electrolysers, and fuel cells. Here, we report that single-phase face-centred cubic structured PtPdFeCoNi high-entropy alloy (HEA) nanoparticles, synthesized via a facile colloidal synthesis approach, possess a good combination of activity and stability toward OER and ORR. Specifically, pristine PtPdFeCoNi HEA nanoparticles exhibit an overpotential of 306 mV at 10 mA cm-2 for OER and a half-wave potential of 0.82 V versus RHE for ORR, with a narrow overvoltage (ΔE) of 0.71 V in alkaline media, outperforming commercial Pt/C and RuO2 benchmark electrocatalysts. The OER and ORR activity of the HEA nanoparticles do not change significantly after prolonged electrochemical cycling (3000 cycles). Using X-ray photoelectron spectroscopy and transmission electron microscopy, we found no evident structural, morphological and compositional changes on the HEA nanoparticle surfaces after ORR cycling, explaining its high activity and stability. In contrast, after extended OER cycling, the PtPdFeCoNi nanoparticle surfaces transform into an amorphous layer embedded with Fe-, Co-, and Ni-rich oxyhydroxides, as well as Co-rich oxides, which likely promote activity. Additionally, the shell oxyhydroxide and oxide layer could prevent the continuous dissolution of Pt and Pd, providing long-term stability. Overall, this work underscores the importance of correlating morphological, structural, and compositional changes of HEA nanocatalysts with electrocatalytic performance, for understanding how individual elements behave toward bifunctional oxygen electrocatalysis.

Electrochemical water splitting presents an optimal approach for generating hydrogen (H2), a highly promising alternative energy source. Nevertheless, the slow kinetics of the electrochemical oxygen evolution reaction (OER) and the exorbitant cost, limited availability, and susceptibility to oxidation of noble metal-based electrocatalysts have compelled scientists to investigate cost-effective and efficient electrocatalysts. Bimetallic nanostructured materials have been demonstrated to exhibit improved catalytic performances for the oxygen evolution reaction (OER). Herein, we report carbon aerogel (CA) decorated with different molar ratios of Fe and Ni with enhanced OER activity. Microwave irradiation was involved as a novel strategy during the synthesis process. Inductively coupled plasma mass spectrometry (ICP-MS), X-ray diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS), Scanning Electron Microscope (SEM), Energy dispersive X-ray spectroscopy (EDAX spectra and EDAX mapping), Transmission Electron Microscope (TEM), High-Resolution Transmission Electron Microscope (HR-TEM), and Selected Area Electron Diffraction (SAED) were used for physical characterizations of as-prepared material. Electrochemical potential towards OER was examined through cyclic voltammetry (CV), chronoamperometry, and electrochemical impedance spectroscopy (EIS). The FeNi/CA with optimized molar ratios exhibits low overpotential 377 mV at 10 mAcm−2, smaller Tafel slope (94.5 mV dec−1), and high turnover frequency (1.09 s−1 at 300 mV). Other electrocatalytic parameters were also calculated and compared with previously reported OER catalysts. Additionally, chronoamperometric studies confirmed excellent electrochemical stability, as the OER activity shows minimal change even after a stability test lasting 3600 s. Moreover, the bimetallic (Fe and Ni) carbon aerogel exhibits faster catalytic kinetics and higher conductivity than the monometallic (Fe), which was observed through EIS investigation. This research opens up possibilities for utilizing bi- or multi-metallic anchored carbon aerogel with high conductivities and exceptional electrocatalytic performances in electrochemical energy conversion.

The purpose of this study is to identify the crystal structure of metastable phase in Ag added Al-Mg-Si alloy to compare the formation of β’-phases in Al-Mg-Si alloys without Ag, using images of high resolution transmission electron microscope (HRTEM), selected area electron diffraction (SAED) patterns and an energy dispersive X-ray spectroscopy (EDS). The result of SAED patterns and HRTEM images have been simulated and compared with images then SAED patterns obtained from actual precipitates. SAED patterns and HRTEM images obtained from metastable phase in the Ag added Al-Mg-Si alloy showed similar to those of β’-phase in Al-Mg-Si alloy without Ag and the lattice spacings changed because of the effect of Ag.

Occurrence, Structure and Mineral Phases of Nanoparticles in an Anthrosol

Compared with laser ablation in the gas phase, requiring a vacuum tight chamber and precise control of pressure and gas flow, the generation of nanoparticles via laser ablation in liquid (LAL) offers significant advantages. LAL facilitates the production of crystalline nanoparticles in a single-step procedure without subsequent heat-treatment. The entire product can be collected in solution, which simplifies handling. Up to now, most research activities have concentrated on the use of pulsed lasers, with pulse width in the range of ns to fs. In this work, we report on the generation of TiO2 spherical nanoparticles using continuous wave (CW) fiber laser by ablating pure Ti submerged both in water and in 0.01M sodium dodecyl sulphate (SDS) solution. The wavelength of the fiber laser used was 1070 nm with an irradiance of 20 MW/cm2, at a power level of 250 W using an exposure time of 1s. Characterization of the nanoparticles, in terms of morphology, chemical analysis and phase structure, was carried out by the means of transmission electron microscopy (TEM), high resolution TEM and X-ray diffractometry (XRD). Results showed the mean size of TiO2 nanoparticles generated in water to be 23 nm with only anatase being detected, while the mean size of the TiO2 nanoparticles generated in 0.01M SDS solution was 28 nm, consisting of both rutile and anatase phases.Compared with laser ablation in the gas phase, requiring a vacuum tight chamber and precise control of pressure and gas flow, the generation of nanoparticles via laser ablation in liquid (LAL) offers significant advantages. LAL facilitates the production of crystalline nanoparticles in a single-step procedure without subsequent heat-treatment. The entire product can be collected in solution, which simplifies handling. Up to now, most research activities have concentrated on the use of pulsed lasers, with pulse width in the range of ns to fs. In this work, we report on the generation of TiO2 spherical nanoparticles using continuous wave (CW) fiber laser by ablating pure Ti submerged both in water and in 0.01M sodium dodecyl sulphate (SDS) solution. The wavelength of the fiber laser used was 1070 nm with an irradiance of 20 MW/cm2, at a power level of 250 W using an exposure time of 1s. Characterization of the nanoparticles, in terms of morphology, chemical analysis and phase structure, was carried out by t...

Chromoionophoric molecular probe infused bimodal porous polymer rostrum as solid-state ocular sensor for the selective and expeditious optical sensing of ultra-trace toxic mercury ions

2H-MoS ₂ Modified Nitrogen-Doped Hollow Mesoporous Carbon Spheres as the Efficient Catalytic Cathode Catalyst for Aprotic Lithium-Oxygen Batteries

Laser ablation in liquid is one of the most widely investigated methods for generating various nanoparticles (NPs) that are difficult to produce using other means. In this paper, we report the generation of Al-oxide NPs by continuous-wave (CW) fibre laser ablation of corundum (α-Al2O3) target submerged in deionised water. The effects of CW fibre laser power and radiation time have been investigated. Characterisation of the NPs generated, in terms of size, size distribution, shape, chemical composition, and phase structure, was carried out by means of high-resolution transmission electron microscopy (HR-TEM), high angle annular dark field (HAADF) in scanning-transmission (STEM) mode, energy-dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD). The results show that the average size of Al-oxide NPs, in the range of 17 to 29 nm, increased with increasing the laser power and laser exposure time, and the NPs are dominated by stoichiometric γ-Al2O3 with a minor phase of α-Al2O3. The mechanism involved in the CWLAL is also discussed.

In recent years, laser ablation in liquid has become an increasingly important technique for the fabrication of nanoparticles (NPs). To date, only pulsed lasers have been used. This paper reports our recent studies on the generation of Ti-oxide and Ni-oxide NPs by the ablation of metal targets in aqueous environments using a high-power, high-brightness continuous-wave (cw) fibre laser at a wavelength of 1070 nm. Owing to the high and uniform irradiation, the fibre laser provides an alternative approach for NP generation with well-controlled phase, size and size distribution, along with high production rate. Characterization of the NPs, in terms of morphology, size and size distribution, chemical composition and phase structure, by means of high-resolution transmission electron microscopy (HRTEM), high-angle annular dark field (HAADF) in scanning-transmission (STEM) mode, energy-dispersive x-ray spectroscopy (EDS) and x-ray diffraction (XRD), has been presented. In addition, limitations of the cw fibre laser process have been discussed in comparison with pulsed laser process.

In this paper, 1D single-crystalline MnO2 nanowires have been synthesized using facile hydrothermal growth method using KMnO4 and Na2S2O8 as starting reaction reagents. The morphology, phase structure and composition of the as-prepared nanomaterial were characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM) with selected area electron diffraction (SAED), and energy dispersive X-ray spectroscopy (EDX). FESEM and TEM analysis shows that the as-prepared MnO2 nanowires have diameters of 25–35 nm. The structural features of as-synthesized MnO2 nanowires are studied to analyze the near-neighbor environment of oxygen coordination around manganese cations using Raman scattering (RS) spectroscopy. Photoluminescence Spectrophotometer was employed to study the optical properties of the synthesized material at room temperature which exhibits prominent emission bands located in green-violet spectral region.