Facile synthesis of electrocatalytically active bismuth oxide nanosheets for detection of palladium traces in pharmaceutical wastewater

Current synthesis routes of bismuth oxide nanosheets (BiONS) are relatively complicated, requiring the use of halogens or metalloids. Herein, a facile method to synthesize BiONS without the addition of halogens or other metalloids was developed. The synthesized BiONS were identified to have flake-shaped structures (300-1000 nm in width) with the thickness of 6-10 nm, which were predominantly made of β-Bi₂O₃. Such BiONS were applied to modify the surface of screen-printed carbon electrodes (BiONS-SPCEs) for the development of a robust palladium (Pd²⁺) sensor. After optimizing the electrochemical parameters of the sensor, it was found that the linear sensor response range and limit of detection for Pd²⁺ were 40-400 and 1.4 ppb, respectively. The electrocatalytic activity of the Pd²⁺-sensor was validated in the competing environment of other metal and metalloid ions. Real samples collected during a Pd recovery process from pharmaceutical wastewater were used to verify the application of BiONS-SPCEs in control of palladium recovery process. The quantitative results of post recovery palladium concentrations obtained using BiONS-SPCEs in treated pharmaceutical wastewater samples were in good agreement with those obtained by inductively coupled plasma-optical emission spectrometry (ICP-OES). Thus, such Pd²⁺-sensor provided the possibility of on-site process control of complex industrial samples for obtaining near-instant information that would lead to better management of resources used in the process, and same time assure environmental standards for both recovered products and processed discharge.

Solvent-particles interactions during composite particles formation by pulsed laser melting of α-Fe2O3

This work thoroughly investigates chemical solvent-particles interactions during the formation of composite particles by pulsed laser melting of α-Fe₂O₃. Two solvents, with different dielectric constants, such as ethyl acetate (ε_r = 6) and ethanol (ε_r = 24.6), were examined in terms of their effect on the morphology, size, and phase composition of iron oxide composites. We calculated the laser fluence curves using the heating-melting-evaporation approach to identify the critical particle size that undergoes the phase changes first. We assessed the temperature of the particles irradiated with 390 mJ/pulse^.cm² in both solvents, including the heat dissipation between the particles and the liquid. The phase diagram of the Fe-O-C-H system was calculated to determine the temperature-pressure relationship of the system in equilibrium. We also employed an in situ GC-MS analysis to identify the volatile products during irradiation. Based on our experimental results, we concluded that the final diameter of the composites increases from 400 to 600 nm, along with the decreasing dielectric constant of the solvent, which is related to the different polarization of the organic liquid and the degree of particle agglomeration. The reduction of hematite in ethanol proceeded much faster, ending up with Fe/FeC_x, while in ethyl acetate, it ended up with Fe₃O₄. Among all the particles, those with a diameter of 200 nm have the highest temperature and undergo the phase transition first. The temperature of a 200 nm composite particle in ethanol is slightly lower than in ethyl acetate, i.e. 1870 K as compared to 1902 K. Phase equilibrium diagrams proved the existence of Fe, FeO, and Fe₃O₄ as the preferred phases at about 1900 K. Our research provides a new insight into the process of submicron particle formation during pulsed laser irradiation and allows proposing a mechanism for the growth of particles of different size and phase composition depending on the solvent.

Pulsed Laser in Liquids Made Nanomaterials for Catalysis

Catalysis is essential to modern life and has a huge economic impact. The development of new catalysts critically depends on synthetic methods that enable the preparation of tailored nanomaterials. Pulsed laser in liquids synthesis can produce uniform, multicomponent, nonequilibrium nanomaterials with independently and precisely controlled properties, such as size, composition, morphology, defect density, and atomistic structure within the nanoparticle and at its surface. We cover the fundamentals, unique advantages, challenges, and experimental solutions of this powerful technique and review the state-of-the-art of laser-made electrocatalysts for water oxidation, oxygen reduction, hydrogen evolution, nitrogen reduction, carbon dioxide reduction, and organic oxidations, followed by laser-made nanomaterials for light-driven catalytic processes and heterogeneous catalysis of thermochemical processes. We also highlight laser-synthesized nanomaterials for which proposed catalytic applications exist. This review provides a practical guide to how the catalysis community can capitalize on pulsed laser in liquids synthesis to advance catalyst development, by leveraging the synergies of two fields of intensive research.

Reduction Mechanism of Transition Metal Oxide Particles in Thermally Induced Nanobubbles during Pulsed Laser Melting in Ethanol

Pulsed laser melting in liquid (PLML) is a technique to fabricate spherical submicrometer particles (SMPs) wherein nanosecond pulsed laser (several tens to several hundreds of mJ pulse^-1 cm^-2 ) irradiates raw particles dispersed in liquid. Raw particles are transiently heated above the melting point to form spherical particles, which enables pulsed heating of surrounding liquid to form thermally induced bubbles by liquid vaporization. These transient bubbles play an important role as a thermal barrier to rapidly heat the particle. Reduced SMPs are generated from raw metal-oxide nanoparticles by PLML process in ethanol. This reduction cannot be explained by high-temperature thermal decomposition, but by mediation of molecules decomposed from ethanol. Computational simulations of ethanol decomposition by pulsed heating for 100 ns at the temperature 1000-4000 K revealed that ethylene is generated as the main product. Gibbs free energies of oxide reduction reactions mediated by ethylene greatly decreased compared to those without ethylene mediation. This explanation can be applied to reductive SMP formation from various transition metal oxides by PLML.

Phase transformation and room temperature stabilization of various Bi2O3 nano-polymorphs: effect of oxygen-vacancy defects and reduced surface energy due to adsorbed carbon species

We report the grain growth from the nanoscale to microscale and a transformation sequence from Bi →β-Bi₂O₃→γ-Bi₂O₃→α-Bi₂O₃ with the increase of annealing temperature. The room temperature (RT) stabilization of β-Bi₂O₃ nanoparticles (NPs) was attributed to the effect of reduced surface energy due to adsorbed carbon species, and oxygen vacancy defects may have played a significant role in the RT stabilization of γ-Bi₂O₃ NPs. An enhanced red emission band was evident from all the samples attributed to oxygen-vacancy defects formed during the growth process in contrast with the observed white emission band from the air annealed Bi ingots. Based on our experimental findings, the air annealing induced oxidation of Bi NPs and transformation mechanism within various Bi₂O₃ nano-polymorphs are presented. The outcome of this study suggests that oxygen vacancy defects at the nanoscale play a significant role in both structural stabilization and phase transformation within various Bi₂O₃ nano-polymorphs, which is significant from theoretical consideration.

Room-Temperature Laser Synthesis in Liquid of Oxide, Metal-Oxide Core-Shells, and Doped Oxide Nanoparticles

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.

Laser Fragmentation Synthesis of Colloidal Bismuth Ferrite Particles

Laser fragmentation of colloidal submicron-sized bismuth ferrite particles was performed by irradiating a liquid jet to synthesize bismuth ferrite nanoparticles. This treatment achieved a size reduction from 450 nm to below 10 nm. A circular and an elliptical fluid jet were compared to control the energy distribution within the fluid jet and thereby the product size distribution and educt decomposition. The resulting colloids were analysed via UV-VIS, XRD and TEM. All methods were used to gain information on size distribution, material morphology and composition. It was found that using an elliptical liquid jet during the laser fragmentation leads to a slightly smaller and narrower size distribution of the resulting product compared to the circular jet.