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

Integrated One-Step Fabrication of Protonic Sensing Devices for Respiratory Monitoring

The development of direct fabrication routes with seamless integration of both the macro/micropatterning process and nanostructure synthesis is crucial for the commercial realization of cost-effective nanoscale sensor devices. This, if realized, can liberate us from the conventional limitations inherent in nanoscale device manufacturing. Specifically, such fabrication routes can, in principle, address the challenges such as the complexity, multistep nature, and substantial costs associated with existing technologies, which are not suitable for widespread market adoption in everyday-use devices. Herein, we propose a novel yet facile one-step fabrication approach that simultaneously accomplishes both patterning and nanostructure synthesis by employing low-power, cost-effective laser technology with a minimal environmental footprint. Versatile in nature, this approach can enable the incorporation of diverse functionalities spanning a broad spectrum of technologies, encompassing fields such as sensors, catalysts, photonics, energy storage, and biomedical monitoring devices. As a proof of concept, using our approach, we fabricated an ultra responsive, high-speed protonic sensing device for real-time respiratory monitoring. The enhanced temporal characteristics of our as-fabricated device, particularly in the relative humidity levels of interest in breath monitoring (typically over 55%), exhibited a superior response/recovery time in rapid humidity fluctuations. We envisage that the advantages brought by the presented fabrication approach can pave the way to establish a new method for inexpensive large-scale functional-material-based device fabrication.

Thermally Stable Oxide-Capsulated Metal Nanoparticles Structure for Strong Metal-Support Interaction via Ultrafast Laser Plasmonic Nanowelding

Strong metal-support interaction (SMSI) has drawn much attention in heterogeneous catalysts due to its stable and excellent catalytic efficiency. However, construction of high-performance oxide-capsulated metal nanostructures meets great challenge in materials thermodynamic compatibility. In this work, dynamically controlled formation of oxide-capsulated metal nanoparticles (NPs) structures is demonstrated by ultrafast laser plasmonic nanowelding. Under the strong localized electromagnetic field interaction, metal (Au) NPs are dragged by an optical force toward oxide NPs (TiO2). Intense energy is simultaneously injected into this heterojunction area, where TiO2 is precisely ablated. With the embedding of metal into oxide, optical force on Au gradually turned from attractive to repulsive due to the varied metal-dielectric environment. Meanwhile, local ablated oxides are redeposited on Au NP. Upon the whole coverage of metal NP, the implantation behavior of metal NP is stopped, resulting in a controlled metal-oxide eccentric structure with capsulated oxide layer thickness ≈0.72-1.30 nm. These oxide-capsulated metal NPs structures can preserve their configurations even after thermal annealing in air at 600 °C for 10 min. This ultrafast laser plasmonic nanowelding can also extend to oxide-capsulated metal nanostructure fabrication with broad materials combinations (e.g., Au/ZnO, Au/MgO, etc.), which shows great potential in designing/constructing nanoscale high-performance catalysts.

Fabrication of Silicon Carbide Nanoparticles Using Pulsed Laser Ablation in Liquid and Viscosity Optimization via Solvent Tuning

In this study, silicon carbide nanoparticles (NPs) were produced via pulsed laser ablation in liquid, aiming to investigate the influence of processing parameters on the properties of the resultant NPs and their applicability for inkjet printing. The results revealed an increase in NP concentration with increasing laser power, but the maximal absorbance in the case of 0.743 and 1.505 W is lower than that for 1.282 W laser. Dynamic light scattering was employed to determine the size distribution of the NPs, demonstrating a range of 89 to 155 nm in diameter. Notably, an inverse relationship was established between increasing laser scanning speed and pulse repetition rate (PRR) and the mean size of the NPs. Higher PRR and laser power exhibited an augmentation in the concentration of NPs. Conversely, an increase in scanning speed resulted in a reduction in NP concentration. Based on FTIR, data formation of SiC NPs based on the target material is the most dominant behavior observed followed by an amount of oxidation of the NPs. Examination of the resulting NPs through field emission scanning electron microscopy equipped with energy-dispersive X-ray analysis (EDX) unveiled a predominantly spherical morphology, accompanied by particle agglomeration in some cases, and the elemental composition showed silicon, carbon, and some oxygen present in the resulting NPs. Furthermore, the modulation of colloidal solution viscosity was explored by incorporating glycerol, yielding a maximal viscosity of 10.95 mPa·s.

Rational Design and Facile Preparation of Palladium-Based Electrocatalysts for Small Molecules Oxidation

Direct liquid fuel cells (DLFCs) can convert the chemical energy of small organic molecules directly into electrical energy, which is a promising technique and always calls for electrocatalysts with high activity, stability and selectivity. Palladium (Pd)-based catalysts for DLFCs have been widely studied with the pursuit of ultra-high performance, however, most of the preparation routes require complex agents, multi-operation steps, even extreme experimental conditions, which are high-cost, energy-consuming, and not conducive to the scalable and sustainable production of catalysts. In this review, the recent progresses on not only the rational design strategies, but also the facile preparation methods of Pd-based electrocatalysts for small molecules oxidation reaction (SMOR) are comprehensively summarized. Based on the principles of green chemistry in material synthesis, the basic rules of "facile method" have been restricted, and the fabrication processes, perks and drawbacks, as well as practical applications of the "real" facile methods have been highlighted. The landscape of this review is to facilitate the mild preparation of efficient Pd-based electrocatalysts for SMOR, that is, to achieve a balance between "facile preparation" and "outstanding performance", thereby to stimulate the huge potential of sustainable nano-electrocatalysts in various research and industrial fields.

Synthesis and characterization of MoSe2 nanoscrolls via pulsed laser ablation in deep eutectic solvents

There is ongoing interest in the rapid, reproducible production of 2-dimensional (2-D) transition metal dichalcogenides (TMD), such as molybdenum-based TMD (MoX2), where X is a chalcogen atom such as sulphur (S), selenium (Se) or tellurium (Te), driven by their unique optical and electronic properties. Once fabricated into an atomically thin layer structure, these materials have a direct-indirect bandgap transition, strong spin-orbit coupling, and favourable electronic and mechanical strain-dependent properties which are attractive for electronics. Pulsed laser ablation in liquid (PLAL) is an economic, green alternative for synthesis of TMD. It has been shown that in the case of MoX2, the chemical processes during the plasma phase of the ablation can yield the formation of multispecies, including MoOx quantum dots when oxygen-containing solvents are used. Here, we introduce the formation of MoSe2 nanoscrolls with low oxygen content synthesized via pulsed laser ablation in deep eutectic solvents (PLADES). Our results suggest that the synthesis produces a stable colloidal solution of large 2-D structures with tuneable surface charge by replacing the deep eutectic solvent (DES) with DI water. Nuclear Magnetic Resonance (NMR) results suggest that irradiating the solvent at near infrared NIR energy does not affect its chemical composition. NMR also proves that serial washing can completely remove solvent from the nanostructures. Raman shifts suggest the formation of large, thin MoSe2 nanosheets aided by the solvent confinement resulting from van der Waal forces and hydrogen bonds interactions between MoSe2 and urea. Binding energies measured by X-ray photoelectron spectroscopy (XPS) confirm MoSe2-DES preference to form 1T-MoSe2versus molybdenum oxides and 2H MoSe2 in DI-water. Raman and XPS findings were validated by transmission electron microscopy (TEM) and selected area electron diffraction (SAED). Results of this work validate the use of PLADES for the synthesis of stable, crystalline, low-surface-oxygen-content colloidal MoSe2 nanoscrolls in scalable quantities.

Effect of wavelength and liquid on formation of Ag, Au, Ag/Au nanoparticles via picosecond laser ablation and SERS-based detection of DMMP

The present study investigates the effects of input wavelength (1064, 532, and 355 nm) and surrounding liquid environment (distilled water and aqueous NaCl solution) on the picosecond laser ablation on silver (Ag), gold (Au), and Ag/Au alloy targets. The efficacy of the laser ablation technique was meticulously evaluated by analyzing the ablation rates, surface plasmon resonance peak positions, and particle size distributions of the obtained colloids. The nanoparticles (NPs) were characterized using the techniques of UV-visible absorption, transmission electron microscopy, and energy-dispersive X-ray spectroscopy. Furthermore, NPs of various sizes ranging from 6 to 35 nm were loaded onto a filter paper by a simple and effective drop-casting approach to achieve flexible surface-enhanced Raman spectroscopy (SERS) substrates/sensors. These substrates were tested using a simple, portable Raman device to identify various hazardous chemicals (malachite green, methyl salicylate, and thiram). The stability of the substrates was also systematically investigated by determining the decay percentages in the SERS signals over 60 days. The optimized SERS substrate was subsequently employed to detect chemical warfare agent (CWA) simulants such as methyl salicylate (a CWA simulant for sulfur mustard) and dimethyl methyl phosphonate (has some structural similarities to the G-series nerve agents) at different laser excitations (325, 532, and 633 nm). A notably higher SERS efficiency for CWA simulants was observed at a 325 nm Raman excitation. Our findings reveal that a higher ablation yield was observed at IR irradiation than those obtained at the other wavelengths. A size decrease of the NPs was noticed by changing the liquid environment to an electrolyte. These findings have significant implications for developing more efficient and stable SERS substrates for chemical detection applications.

Synthesis of Ultrawide Band Gap TeO2 Nanoparticles by Pulsed Laser Ablation in Liquids: Top Ablation versus Bottom Ablation

Ultrawide band gap (UWBG) semiconductors are the future components of electronic devices due to their large energy band gap (>3.2 eV). In this article, spherical TeO2 nanoparticles, with sizes around ∼39 ± 12 and ∼29 ± 6 nm, were successfully synthesized by irradiating a pure tellurium target, totally submerged in ethanol, using a "Top-ablation" or "Bottom-ablation" synthesis protocol, respectively. Mostly, α-TeO2 nanoparticles were created (>95%) with only a small amount of γ-TeO2 nanoparticles being produced (<5%). Both colloids exhibited a ζ-potential larger than |30 mV|, indicating a stable colloidal solution. The energy band gaps of the TeO2 nanoparticles synthesized by the Top-ablation and Bottom-ablation synthesis protocols were determined to be around 5.3 and 5.8 eV, respectively. Finally, TeO2 UWBG nanoparticles were successfully synthesized using either a Top-ablation or Bottom-ablation synthesis protocol. The main advantage of the Bottom-ablation synthesis protocol is its ability to obtain smaller nanoparticles compared to that of the Top-ablation synthesis protocol.

Laser synthesis of nanoparticles in organic solvents - products, reactions, and perspectives

Laser synthesis and processing of colloids (LSPC) is an established method for producing functional and durable nanomaterials and catalysts in virtually any liquid of choice. While the redox reactions during laser synthesis in water are fairly well understood, the corresponding reactions in organic liquids remain elusive, particularly because of the much greater complexity of carbon chemistry. To this end, this article first reviews the knowledge base of chemical reactions during LSPC and then deduces identifiable reaction pathways and mechanisms. This review also includes findings that are specific to the LSPC method variants laser ablation (LAL), fragmentation (LFL), melting (LML), and reduction (LRL) in organic liquids. A particular focus will be set on permanent gases, liquid hydrocarbons, and solid, carbonaceous species generated, including the formation of doped, compounded, and encapsulated nanoparticles. It will be shown how the choice of solvent, synthesis method, and laser parameters influence the nanostructure formation as well as the amount and chain length of the generated polyyne by-products. Finally, theoretical approaches to address the mechanisms of organic liquid decomposition and carbon shell formation are highlighted and discussed regarding current challenges and future perspectives of LSPC using organic liquids instead of water.

High-performance Ag-TiO2 nanoparticle composite catalyst synthesized by pulsed laser ablation in liquid: properties, mechanism and preparation studies

Precious metal doping can effectively improves the catalytic performance of TiO2. In this study, pulsed laser ablation in liquid (PLAL) is employed to integrate preparation with doping and control composite nanoparticle products by adjusting the laser action time to synthesise Ag-TiO2 composite nanoparticles with high catalytic performance. The generation and evolution of Ag-TiO2 nanoparticles are investigated by analysing particle size, microscopic morphology, crystalline phase, and other characteristics. The generation and doped-morphology evolution of composite nanoparticles are simulated based on thermodynamics, and the optimisation of Ag-doped structure on the composite nanomaterials is investigated based on density functional theory. The effect of Ag-TiO2 structural properties on its performance is examined under different catalytic conditions to determine optimal degradation conditions. In this study, the effect of laser ablation time on the doped structure during PLAL is analysed, which is of further research significance in exploring the structural evolution law of laser and composite nanoparticles, multi-variate catalytic performance testing, reduction of photogenerated carrier complexation rate, and expansion of its spectral absorption range, thereby providing the basis for practical production.

Physical Regimes and Mechanisms of Picosecond Laser Fragmentation of Gold Nanoparticles in Water from X-ray Probing and Atomistic Simulations

Laser fragmentation in liquids has emerged as a promising green chemistry technique for changing the size, shape, structure, and phase composition of colloidal nanoparticles, thus tuning their properties to the needs of practical applications. The advancement of this technique requires a solid understanding of the mechanisms of laser-nanoparticle interactions that lead to the fragmentation. While theoretical studies have made impressive practical and mechanistic predictions, their experimental validation is required. Hence, using the picosecond laser fragmentation of Au nanoparticles in water as a model system, the transient melting and fragmentation processes are investigated with a combination of time-resolved X-ray probing and atomistic simulations. The direct comparison of the diffraction profiles predicted in the simulations and measured in experiments has revealed a sequence of several nonequilibrium processes triggered by the laser irradiation. At low laser fluences, in the regime of nanoparticle melting and resolidification, the results provide evidence of a transient superheating of crystalline nanoparticles above the melting temperature. At fluences about three times the melting threshold, the fragmentation starts with evaporation of Au atoms and their condensation into small satellite nanoparticles. As fluence increases above five times the melting threshold, a transition to a rapid (explosive) phase decomposition of superheated nanoparticles into small liquid droplets and vapor phase atoms is observed. The transition to the phase explosion fragmentation regime is signified by prominent changes in the small-angle X-ray scattering profiles measured in experiments and calculated in simulations. The good match between the experimental and computational diffraction profiles gives credence to the physical picture of the cascade of thermal fragmentation regimes revealed in the simulations and demonstrates the high promise of the joint tightly integrated computational and experimental efforts.

Physical and chemical parameters determining the formation of gold-sp metal (Al, Ga, In, and Pb) nanoalloys

Alloying is a key step towards the fabrication of advanced and unique nanomaterials demanded by the next generation of nanotechnology solutions. In particular, the alloys of Au with the sp-metals are expected to have several appealing plasmonic and electronic properties for a wide range of applications in optics, catalysis, nanomedicine, sensing and quantum devices. However, little is known about the thermodynamic and synthetic factors leading to the successful alloying of Au and sp-metals at the nanoscale. In this work, Au-M nanoalloys, with M = Al, Ga, In, or Pb, have been synthesized by a green and single step laser ablation in liquid (LAL) approach in two environments (pure ethanol and anhydrous acetone). To delve deeper into the key parameters leading to successful alloying under the typical operating conditions of LAL, a multiparametric analysis was performed considering the mixing enthalpy from DFT calculations and other alloying descriptors such as the Hume-Rothery parameters. The results showed that the dominant factors for alloying change dramatically with the oxidative ability of the synthesis environment. In this way, the tendency of the four sp metals to alloy with gold was accurately predicted (R2 > 0.99) using only two and three parameters in anhydrous and non-anhydrous environments, respectively. These results are important to produce nanoalloys using LAL and other physical methods because they contribute to the understanding of factors leading to element mixing at the nanoscale under real synthetic conditions, which is crucial for guiding the realization of next-generation multifunctional metallic nanostructures.

Photoacoustic detection of transient phase transformation of nanoparticles

The controllable preparation of spherical micro/nano particles of various materials has been achieved via the technology of the laser synthesis and processing of colloids (LSPC) recently. However, there is limited in situ research on the evolution processes of nanoparticles in photothermal transient environments, such as solid-state crystal transformations and changes of state, which limits the understanding and application of LSPC. Photoacoustic (PA) signals are sensitive to the optical, thermal and elastic properties of the medium, and can be used to measure the thermal and spectroscopic properties of matter. In this paper, the PA signals generated by the interaction of the laser with the surrounding liquid medium (ethanol, water, glycerin, etc.) and nanoparticles (Ag, TiO2, CeO2, ZrO2, etc.) are studied when the tunable LSPC technique provides different photothermal conditions (such as thermal expansion, solid crystal transformation and evaporation). It is found that semiconductors with different bandgaps, as light absorbers, have the ability to selectively absorb laser beams of different wavelengths. By changing the wavelength, the PA intensity can be adjusted accordingly. In addition, based on the fast laser heating and tunable fluence characteristics of non-focused laser beams in LSPC technology, transient processes such as material phase transitions and changes of state can be excited separately by adjusting the laser fluence. Taking titanium dioxide as an example, the PA signals generated by laser selective excitation of A-R (anatase into rutile) phase transitions and rutile vaporization can be detected.

Unveiling Fundamentals of Multi-Beam Pulsed Laser Ablation in Liquids toward Scaling up Nanoparticle Production

Pulsed laser ablation in liquids (PLAL) is a versatile technique to produce high-purity colloidal nanoparticles. Despite considerable recent progress in increasing the productivity of the technique, there is still significant demand for a practical, cost-effective method for upscaling PLAL synthesis. Here we employ and unveil the fundamentals of multi-beam (MB) PLAL. The MB-PLAL upscaling approach can bypass the cavitation bubble, the main limiting factor of PLAL efficiency, by splitting the laser beam into several beams using static diffractive optical elements (DOEs). A multimetallic high-entropy alloy CrFeCoNiMn was used as a model material and the productivity of its nanoparticles in the MB-PLAL setup was investigated and compared with that in the standard single-beam PLAL. We demonstrate that the proposed multi-beam method helps to bypass the cavitation bubble both temporally (lower pulse repetition rates can be used while keeping the optimum processing fluence) and spatially (lower beam scanning speeds are needed) and thus dramatically increases the nanoparticle yield. Time-resolved imaging of the cavitation bubble was performed to correlate the observed production efficiencies with the bubble bypassing. The results suggest that nanoparticle PLAL productivity at the level of g/h can be achieved by the proposed multi-beam strategy using compact kW-class lasers and simple inexpensive scanning systems.

Editorial: Special Issue "Laser Synthesis and Processing of Nanostructured Materials"

The fabrication of functional nanomaterials and nanotextured surfaces assisted by spatially and temporally confined laser radiation has matured from laboratory-scale methods to application-ready technology during recent decades [...].

The multivariate interaction between Au and TiO2 colloids: the role of surface potential, concentration, and defects

The established DLVO theory explains colloidal stability by the electrostatic repulsion between electrical double layers. While the routinely measured zeta potential can estimate the charges of double layers, it is only an average surface property which might deviate from the local environment. Moreover, other factors such as the ionic strength and the presence of defects should also be considered. To investigate this multivariate problem, here we model the interaction between a negatively charged Au particle and a negatively charged TiO2 surface containing positive/neutral defects (e.g. surface hydroxyls) based on the finite element method, over 6000 conditions of these 6 parameters: VPart (particle potential), VSurf (surface potential), VDef (defect potential), DD (defect density), Conc (salt concentration), and R (particle radius). Using logistic regression, the relative importance of these factors is determined: VSurf > VPart > DD > Conc > R > VDef, which agrees with the conventional wisdom that the surface (and zeta) potential is indeed the most decisive descriptor for colloidal interactions, and the salt concentration is also important for charge screening. However, when defects are present, it appears that their density is more influential than their potential. To predict the fate of interactions more confidently with all the factors, we train a support vector machine (SVM) with the simulation data, which achieves 97% accuracy in determining whether adsorption is favorable on the support. The trained SVM including a graphical user interface for querying the prediction is freely available online for comparing with other materials and models. We anticipate that our model can stimulate further colloidal studies examining the importance of the local environment, while simultaneously considering multiple factors.

Plasmonic Nanocomposites of ZnO-Ag Produced by Laser Ablation and Their Photocatalytic Destruction of Rhodamine, Tetracycline and Phenol

Hydrosphere pollution by organic pollutants of different nature (persistent dyes, phenols, herbicides, antibiotics, etc.) is one of the urgent ecological problems facing humankind these days. The task of water purification from such pollutants can be effectively solved with the help of modern photocatalytic technologies. This article is devoted to the study of photocatalytic properties of composite catalysts based on ZnO modified with plasmonic Ag nanoparticles. All materials were obtained by laser synthesis in liquid and differed by their silver content and preparation conditions, such as additional laser irradiation and/or annealing of produced powders. The prepared ZnO-Ag powders were investigated by electron microscopy, X-ray diffraction and UV-Vis spectroscopy. Photocatalytic tests were carried out with well- known test molecules in water (persistent dye rhodamine B, phenol and common antibiotic tetracycline) using LED light sources with wavelengths of 375 and 410 nm. The introduction of small concentrations (up to 1%) of plasmonic Ag nanoparticles is shown to increase the efficiency of the ZnO photocatalyst by expanding its spectral range. Both the preparation conditions and material composition were optimized to obtain composite photocatalysts with the highest efficiency. Finally, the operation mechanisms of the material with different distribution of silver are discussed.

Morphological analysis and grain size distribution of SnO2 nanoparticles via digital image processing across diverse calcination temperatures

This study presents a comprehensive image analysis of the SnO2 nanoparticles synthesised through calcination at diverse temperatures, which enables an estimation of grain size distribution (GSD) from field-emission scanning electron microscopy (FE-SEM) images. Even though FE-SEM images could provide us with a lot of information about sample differences, we can learn more and perform a more accurate analysis of them by using quantitative data obtained by our image processing application. The digital image processing techniques used in this research provide a detailed analysis of the nanoparticles' size and shape, enabling a deeper understanding of their unique characteristics. The results reveal the significant impact of calcination temperature on the morphology of the nanoparticles, with changes in grain size and grain size distribution observed at varying temperatures.

Data-Driven Predetermination of Cu Oxidation State in Copper Nanoparticles: Application to the Synthesis by Laser Ablation in Liquid

Copper-based nanocrystals are reference nanomaterials for integration into emerging green technologies, with laser ablation in liquid (LAL) being a remarkable technique for their synthesis. However, the achievement of a specific type of nanocrystal, among the whole library of nanomaterials available using LAL, has been until now an empirical endeavor based on changing synthesis parameters and characterizing the products. Here, we started from the bibliographic analysis of LAL synthesis of Cu-based nanocrystals to identify the relevant physical and chemical features for the predetermination of copper oxidation state. First, single features and their combinations were screened by linear regression analysis, also using a genetic algorithm, to find the best correlation with experimental output and identify the equation giving the best prediction of the LAL results. Then, machine learning (ML) models were exploited to unravel cross-correlations between features that are hidden in the linear regression analysis. Although the LAL-generated Cu nanocrystals may be present in a range of oxidation states, from metallic copper to cuprous oxide (Cu2O) and cupric oxide (CuO), in addition to the formation of other materials such as Cu2S and CuCN, ML was able to guide the experiments toward the maximization of the compounds in the greatest demand for integration in sustainable processes. This approach is of general applicability to other nanomaterials and can help understand the origin of the chemical pathways of nanocrystals generated by LAL, providing a rational guideline for the conscious predetermination of laser-synthesis parameters toward the desired compounds.

A review of physical, chemical and biological synthesis methods of bimetallic nanoparticles and applications in sensing, water treatment, biomedicine, catalysis and hydrogen storage

This article provides an in-depth analysis of various fabrication methods of bimetallic nanoparticles (BNP), including chemical, biological, and physical techniques. The review explores BNP's diverse uses, from well-known applications such as sensing water treatment and biomedical uses to less-studied areas like breath sensing for diabetes monitoring and hydrogen storage. It cites results from over 1000 researchers worldwide and >300 peer-reviewed articles. Additionally, the article discusses current trends, actionable recommendations, and the importance of synthetic analysis for industry players looking to optimize manufacturing techniques for specific applications. The article also evaluates the pros and cons of various fabrication methods, highlighting the potential of plant extract synthesis for mass production of capped BNPs. However, it warns that this method may not be suitable for certain applications requiring ligand-free surfaces. In contrast, physical methods like laser ablation offer better control and reactivity, especially for applications where ligand-free surfaces are critical. The report underscores the environmental benefits of plant extract synthesis compared to chemical methods that use hazardous chemicals and pose risks to extraction, production, and disposal. The article emphasizes the need for life cycle assessment (LCA) articles in the literature, given the growing volume of research on nanotechnology materials. This article caters to researchers at all stages and applies to various fields applying nanomaterials.

A Review on Pulsed Laser Fabrication of Nanomaterials in Liquids for (Photo)catalytic Degradation of Organic Pollutants in the Water System

The water pollution caused by the release of organic pollutants has attracted remarkable attention, and solutions for wastewater treatment are being developed. In particular, the photocatalytic removal of organic pollutants in water systems is a promising strategy to realize the self-cleaning of ecosystems under solar light irradiation. However, at present the semiconductor-based nanocatalysts can barely satisfy the industrial requirements because their wide bandgaps restrict the effective absorption of solar light, which needs an energy band modification to boost the visible light harvesting via surface engineering. As an innovative approach, pulsed laser heating in liquids has been utilized to fabricate the nanomaterials in catalysis; it demonstrates multi-controllable features, such as size, morphology, crystal structure, and even optical or electrical properties, with which photocatalytic performances can be precisely optimized. In this review, focusing on the powerful heating effect of pulsed laser irradiation in liquids, the functional nanomaterials fabricated by laser technology and their applications in the catalytic degradation of various organic pollutants are summarized. This review not only highlights the innovative works of pulsed laser-prepared nanomaterials for organic pollutant removal in water systems, such as the photocatalytic degradation of organic dyes and the catalytic reduction of toxic nitrophenol and nitrobenzene, it also critically discusses the specific challenges and outlooks of this field, including the weakness of the produced yields and the relevant automatic strategies for massive production.

Surface Chemistry and Specific Surface Area Rule the Efficiency of Gold Nanoparticle Sensitizers in Proton Therapy

Gold nanoparticles (AuNPs) are currently the most studied radiosensitizers in proton therapy (PT) applicable for the treatment of solid tumors, where they amplify production of reactive oxygen species (ROS). However, it is underexplored how this amplification is correlated with the AuNPs' surface chemistry. To clarify this issue, we fabricated ligand-free AuNPs of different mean diameters by laser ablation in liquids (LAL) and laser fragmentation in liquids (LFL) and irradiated them with clinically relevant proton fields by using water phantoms. ROS generation was monitored by the fluorescent dye 7-OH-coumarin. Our findings reveal an enhancement of ROS production driven by I) increased total particle surface area, II) utilization of ligand-free AuNPs avoiding sodium citrate as a radical quencher ligands, and III) a higher density of structural defects generated by LFL synthesis, indicated by surface charge density. Based on these findings it may be concluded that the surface chemistry is a major and underexplored contributor to ROS generation and sensitizing effects of AuNPs in PT. We further highlight the applicability of AuNPs in vitro in human medulloblastoma cells.

Recent Advances in DNA Nanomaterials

Applications of DNA-containing nanomaterials (DNA-NMs) in science and technology are currently attracting increasing attention in the fields of medicine, environment, engineering, etc. Such objects have become important for various branches of science and industries due to their outstanding characteristics such as small size, high controllability, clustering actions, and strong permeability. For these reasons, DNA-NMs deserve a review with respect to their recent advancements. On the other hand, precise cluster control, targeted drug distribution in vivo, and cellular micro-nano operation remain as problems. This review summarizes the recent progress in DNA-NMs and their crossover and integration into multiple disciplines (including in vivo/in vitro, microcircles excisions, and plasmid oligomers). We hope that this review will motivate relevant practitioners to generate new research perspectives and boost the advancement of nanomanipulation.

Effect of Sonication and Ceria Doping on Nanoparticles Fabricated by Laser Marker Ablation of Ti in Water

By employing the laser marker fast ablation technique in water, combined with the innovative inclusion of sonication, we successfully developed Ti-based nanoparticles with improved characteristics. sonication increased the nanoparticle concentration in the colloid, reduced nanoparticle size, and also narrowed size distribution. Our findings also provide valuable insights into the influence of laser parameters, such as wavelength and fluence, on nanoparticle properties. UV laser led to small nanoparticles compared with 1064 nm laser. Additionally, high laser fluence appeared to increase the ablated particle size until a plateau fluence at 28.5 J/cm2; at 38 J/cm2, the particle size decreased. Notably, all synthesized particles exhibited a regular spherical shape, as confirmed by energy dispersive X-ray spectroscopy (EDS) mapping, which also indicated that the majority of Ti-based particles were in an oxidized state. Additionally, the presence of rutile TiO2 in the particles was further confirmed by X-ray diffraction (XRD) analysis. Ceria doping Titania nanoparticles was also attempted.

Differentiating between Acidic and Basic Surface Hydroxyls on Metal Oxides by Fluoride Substitution: A Case Study on Blue TiO2 from Laser Defect Engineering

Both oxygen vacancies and surface hydroxyls play a crucial role in catalysis. Yet, their relationship is not often explored. Herein, we prepare two series of TiO₂ (rutile and P25) with increasing oxygen deficiency and Ti³⁺ concentration by pulsed laser defect engineering in liquid (PUDEL), and selectively quantify the acidic and basic surface OH by fluoride substitution. As indicated by EPR spectroscopy, the laser-generated Ti³⁺ exist near the surface of rutile, but appear to be deeper in the bulk for P25. Fluoride substitution shows that extra acidic bridging OH are selectively created on rutile, while the surface OH density remains constant for P25. These observations suggest near-surface Ti³⁺ are highly related to surface bridging OH, presumably the former increasing the electron density of the bridging oxygen to form more of the latter. We anticipate that fluoride substitution will enable better characterization of surface OH and its correlation with defects in metal oxides.

Photomechanical Laser Fragmentation of IrO2 Microparticles for the Synthesis of Active and Redox-Sensitive Colloidal Nanoclusters

Pulsed laser fragmentation of microparticles (MPs) in liquid is a synthesis method for producing high-purity nanoparticles (NPs) from virtually any material. Compared with laser ablation in liquids (LAL), the use of MPs enables a fully continuous, single-step synthesis of colloidal NPs. Although having been employed in several studies, neither the fragmentation mechanism nor the efficiency or scalability have been described. Starting from time-resolved investigations of the single-pulse fragmentation of single IrO₂ MPs in water, the contribution of stress-mediated processes to the fragmentation mechanism is highlighted. Single-pulse, multiparticle fragmentation is then performed in a continuously operated liquid jet. Here, 2 nm-sized nanoclusters (NCs) accompanied by larger fragments with sizes ranging between several ten nm and several µm are generated. For the nanosized product, an unprecedented efficiency of up to 18 µg J^-1 is reached, which exceeds comparable values reported for high-power LAL by one order of magnitude. The generated NCs exhibit high catalytic activity and stability in oxygen evolution reactions while simultaneously expressing a redox-sensitive fluorescence, thus rendering them promising candidates in electrocatalytic sensing. The provided insights will pave the way for laser fragmentation of MPs to become a versatile, scalable yet simple technique for nanomaterial design and development.

Targeted delivery of paclitaxel drug using polymer-coated magnetic nanoparticles for fibrosarcoma therapy: in vitro and in vivo studies

Fibrosarcoma is a rare type of cancer that affects cells known as fibroblasts that are malignant, locally recurring, and spreading tumor in fibrous tissue. In this work, an iron plate immersed in an aqueous solution of double added deionized water, supplemented with potassium permanganate solution (KMnO₄) was carried out by the pulsed laser ablation in liquid method (PLAIL). Superparamagnetic iron oxide nanoparticles (SPIONs) were synthesized using different laser wavelengths (1064, 532, and 266 nm) at a fluence of 28 J/cm² with 100 shots of the iron plate to control the concentration, shape and size of the prepared high-stability SPIONs. The drug nanocarrier was synthesized by coating SPION with paclitaxel (PTX)-loaded chitosan (Cs) and polyethylene glycol (PEG). This nanosystem was functionalized by receptors that target folate (FA). The physiochemical characteristics of SPION@Cs-PTX-PEG-FA nanoparticles were evaluated and confirmed by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-Ray diffraction (XRD), atomic force microscopy (AFM), and dynamic light scattering (DLS) methods. Cell internalization, cytotoxicity assay (MTT), apoptosis induction, and gene expression of SPION@Cs-PTX-PEG-FA were estimated in fibrosarcoma cell lines, respectively. In vivo studies used BALB/c tumor-bearing mice. The results showed that SPION@Cs-PTX-PEG-FA exhibited suitable physical stability, spherical shape, desirable size, and charge. SPION@Cs-PTX-PEG-FA inhibited proliferation and induced apoptosis of cancer cells (P < 0.01). The results of the in vivo study showed that SPION@Cs-PTX-PEG-FA significantly decreased tumor size compared to free PTX and control samples (P < 0.05), leading to longer survival, significantly increased splenocyte proliferation and IFN-γ level, and significantly decreased the level of IL-4. All of these findings indicated the potential of SPION@Cs-PTX-PEG-FA as an antitumor therapeutic agent.

Disproportional surface segregation in ligand-free gold-silver alloy solid solution nanoparticles, and its implication for catalysis and biomedicine

Catalytic activity and toxicity of mixed-metal nanoparticles have been shown to correlate and are known to be dependent on surface composition. The surface chemistry of the fully inorganic, ligand-free silver-gold alloy nanoparticle molar fraction series, is highly interesting for applications in heterogeneous catalysis, which is determined by active surface sites which are also relevant for understanding their dissolution behavior in biomedically-relevant ion-release scenarios. However, such information has never been systematically obtained for colloidal nanoparticles without organic surface ligands and has to date, not been analyzed in a surface-normalized manner to exclude density effects. For this, we used detailed electrochemical measurements based on cyclic voltammetry to systematically analyze the redox chemistry of particle-surface-normalized gold-silver alloy nanoparticles with varying gold molar fractions. The study addressed a broad range of gold molar fractions (Ag₉₀Au₁₀, Ag₈₀Au₂₀, Ag₇₀Au₃₀, Ag₅₀Au₅₀, Ag₄₀Au₆₀, and Ag₂₀Au₈₀) as well as monometallic Ag and Au nanoparticle controls. Oxygen reduction reaction (ORR) measurements in O₂ saturated 0.1 M KOH revealed a linear reduction of the overpotential with increasing gold content on the surface, probably attributed to the higher ORR activity of gold over silver, verified by monometallic Ag and Au controls. These findings were complemented by detailed XPS studies revealing an accumulation of the minor constituent of the alloy on the surface, e.g., silver surface enrichment in gold-rich particles. Furthermore, highly oxidized Ag surface site enrichment was detected after the ORR reaction, most pronounced in gold-rich alloys. Further, detailed CV studies at acidic pH, analyzing the position, onset potential, and peak integrals of silver oxidation and silver reduction peaks revealed particularly low reactivity and high chemical stability of the equimolar Au₅₀Ag₅₀ composition, a phenomenon attributed to the outstanding thermodynamic, entropically driven, stabilization arising at this composition.

Structural evolution under physical and chemical stimuli of metastable Au-Fe nanoalloys obtained by laser ablation in liquid

Metastable alloy nanoparticles are investigated for their variety of appealing properties exploitable for photonics, magnetism, catalysis and nanobiotechnology. Notably, nanophases out of thermodynamic equilibrium feature a complex "ultrastructure" leading to a dynamic evolution of composition and atomic arrangement in response to physical-chemical stimuli. In this manuscript, metastable Au-Fe alloy nanoparticles were produced by laser ablation in liquid, an emerging versatile synthetic approach for freezing multielement nanosystems in non-equilibrium conditions. The Au-Fe nanoalloys were characterized through electron microscopy, elemental analysis, X-ray diffraction and Mössbauer spectroscopy. The dynamics of the structure of the Au-Fe system was tracked at high temperature under vacuum and atmospheric conditions, evidencing the intrinsic transformative nature of the metastable nanoalloy produced by laser ablation in liquid. This dynamic structure is relevant to possible application in several fields, from photocatalysis to nanomedicine, as demonstrated through an experiment of magnetic resonance imaging in biological fluids.

Multigram-Scale Production of Hybrid Au-Si Nanomaterial by Laser Ablation in Liquid (LAL) for Temperature-Feedback Optical Nanosensing, Light-to-Heat Conversion, and Anticounterfeit Labeling

Recent progress in hybrid optical nanomaterials composed of dissimilar constituents permitted an improvement in the performance and functionality of novel devices developed for optoelectronics, catalysis, medical diagnostics, and sensing. However, the rational combination of contrasting materials such as noble metals and semiconductors within individual hybrid nanostructures via a ready-to-use and lithography-free fabrication approach is still a challenge. Here, we report on a two-step synthesis of hybrid Au-Si microspheres generated by laser ablation of silicon in isopropanol followed by laser irradiation of the produced Si nanoparticles in the presence of HAuCl₄. Thermal reduction of [AuCl₄]^- species to a metallic gold phase, along with its subsequent mixing with silicon under laser irradiation, creates a nanostructured material with a unique composition and morphology, as revealed by electron microscopy, tomography, and elemental analysis. A combination of basic plasmonic and nanophotonic materials such as gold and silicon within a single microsphere allows for efficient light-to-heat conversion, as well as single-particle SERS sensing with temperature-feedback modality and expanded functionality. Moreover, the characteristic Raman signal and hot-electron-induced nonlinear photoluminescence coexisting within the novel Au-Si hybrids, as well as the commonly criticized randomness of the nanomaterials prepared by laser ablation in liquid, were proved to be useful for the realization of anticounterfeiting labels based on a physically unclonable function approach.

In situ laser-assisted synthesis and patterning of graphene foam composites as a flexible gas sensing platform

Gas-sensitive semiconducting nanomaterials (e.g., metal oxides, graphene oxides, and transition metal dichalcogenides) and their heterojunctions hold great promise in chemiresistive gas sensors. However, they often require a separate synthesis method (e.g., hydrothermal, so-gel, and co-precipitation) and their integration on interdigitated electrodes (IDE) via casting is also associated with weak interfacial properties. This work demonstrates in situ laser-assisted synthesis and patterning of various sensing nanomaterials and their heterojunctions on laser-induced graphene (LIG) foam to form LIG composites as a flexible and stretchable gas sensing platform. The porous LIG line or pattern with nanomaterial precursors dispensed on top is scribed by laser to allow for in situ growth of corresponding nanomaterials. The versatility of the proposed method is highlighted through the creation of different types of gas-sensitive materials, including transition metal dichalcogenide (e.g., MoS2), metal oxide (e.g., CuO), noble metal-doped metal oxide (e.g., Ag/ZnO) and composite metal oxides (e.g., In2O3/Cr2O3). By eliminating the IDE and separate heaters, the LIG gas sensing platform with self-heating also decreases the device complexity. The limit of detection (LOD) of the LIG gas sensor with in situ synthesized MoS2, CuO, and Ag/ZnO to NO2, H2S, and trimethylamine (TMA) is 2.7, 9.8, and 5.6 ppb, respectively. Taken together with the high sensitivity, good selectivity, rapid response/recovery, and tunable operating temperature, the integrated LIG gas sensor array can identify multiple gas species in the environment or exhaled breath.

Solvent Influence on the Magnetization and Phase of Fe-Ni Alloy Nanoparticles Generated by Laser Ablation in Liquids

The synthesis of bimetallic iron-nickel nanoparticles with control over the synthesized phases, particle size, surface chemistry, and oxidation level remains a challenge that limits the application of these nanoparticles. Pulsed laser ablation in liquid allows the properties tuning of the generated nanoparticles by changing the ablation solvent. Organic solvents such as acetone can minimize nanoparticle oxidation. Yet, economical laboratory and technical grade solvents that allow cost-effective production of FeNi nanoparticles contain water impurities, which are a potential source of oxidation. Here, we investigated the influence of water impurities in acetone on the properties of FeNi nanoparticles generated by pulsed laser ablation in liquids. To remove water impurities and produce "dried acetone", cost-effective and reusable molecular sieves (3 Å) are employed. The results show that the Fe₅₀Ni₅₀ nanoparticles' properties are influenced by the water content of the solvent. The metastable HCP FeNi phase is found in NPs prepared in acetone, while only the FCC phase is observed in NPs formed in water. Mössbauer spectroscopy revealed that the FeNi nanoparticles oxidation in dried acetone is reduced by 8% compared to acetone. The high-field magnetization of Fe₅₀Ni₅₀ nanoparticles in water is the highest, 68 Am²/kg, followed by the nanoparticles obtained after ablation in acetone without water impurities, 59 Am²/kg, and acetone, 52 Am²/kg. The core-shell structures formed in these three liquids are also distinctive, demonstrating that a core-shell structure with an outer oxide layer is formed in water, while carbon external layers are obtained in acetone without water impurity. The results confirm that the size, structure, phase, and oxidation of FeNi nanoparticles produced by pulsed laser ablation in liquids can be modified by changing the solvent or just reducing the water impurities in the organic solvent.

Growth suppression of bacteria by biofilm deterioration using silver nanoparticles with magnetic doping

Decades of antibiotic use and misuse have generated selective pressure toward the rise of antibiotic-resistant bacteria, which now contaminate our environment and pose a major threat to humanity. According to the evolutionary "Red queen theory", developing new antimicrobial technologies is both urgent and mandatory. While new antibiotics and antibacterial technologies have been developed, most fail to penetrate the biofilm that protects bacteria against external antimicrobial attacks. Hence, new antimicrobial formulations should combine toxicity for bacteria, biofilm permeation ability, biofilm deterioration capability, and tolerability by the organism without renouncing compatibility with a sustainable, low-cost, and scalable production route as well as an acceptable ecological impact after the ineluctable release of the antibacterial compound in the environment. Here, we report on the use of silver nanoparticles (NPs) doped with magnetic elements (Co and Fe) that allow standard silver antibacterial agents to perforate bacterial biofilms through magnetophoretic migration upon the application of an external magnetic field. The method has been proved to be effective in opening micrometric channels and reducing the thicknesses of models of biofilms containing bacteria such as Enterococcus faecalis, Enterobacter cloacae, and Bacillus subtilis. Besides, the NPs increase the membrane lipid peroxidation biomarkers through the formation of reactive oxygen species in E. faecalis, E. cloacae, B. subtilis, and Pseudomonas putida colonies. The NPs are produced using a one-step, scalable, and environmentally low-cost procedure based on laser ablation in a liquid, allowing easy transfer to real-world applications. The antibacterial effectiveness of these magnetic silver NPs may be further optimized by engineering the external magnetic fields and surface conjugation with specific functionalities for biofilm disruption or bactericidal effectiveness.

A Review on Pulsed Laser Preparation of Nanocomposites in Liquids and Their Applications in Photocatalysis

The purpose of photocatalysis is to realize the conversion between solar energy and chemical energy, and it is essential to develop a high-performance photocatalyst under visible-light irradiation. The conventional methods for photocatalyst preparation are mainly wet chemical routes, and abundant yields can be obtained. However, the products are not neat and accompanied by chemical groups and impurities, which are not beneficial for the enhancement of photocatalytic performance. In recent years, as a powerful tool for nanomaterial fabrication, pulsed laser heating in a liquid medium has been utilized to prepare a variety of nanocomposites. Products with synergistic effects and high crystallinity can be rapidly prepared under pulsed laser selective heating, which is beneficial for obtaining more effective photocatalytic performance. In this review, the typical characteristics of pulsed laser heating in liquids and their prepared nanocomposites for photocatalytic applications are summarized. This review not only highlights the innovative works of pulsed-laser-prepared nanocomposites in liquids for photocatalysis but also briefly introduces the specific challenges and prospects of this field.

Progress in Laser Ablation and Biological Synthesis Processes: "Top-Down" and "Bottom-Up" Approaches for the Green Synthesis of Au/Ag Nanoparticles

Because of their small size and large specific surface area, nanoparticles (NPs) have special properties that are different from bulk materials. In particular, Au/Ag NPs have been intensively studied for a long time, especially for biomedical applications. Thereafter, they played a significant role in the fields of biology, medical testing, optical imaging, energy and catalysis, MRI contrast agents, tumor diagnosis and treatment, environmental protection, and so on. When synthesizing Au/Ag NPs, the laser ablation and biosynthesis methods are very promising green processes. Therefore, this review focuses on the progress in the laser ablation and biological synthesis processes for Au/Ag NP generation, especially in their fabrication fundamentals and potential applications. First, the fundamentals of the laser ablation method are critically reviewed, including the laser ablation mechanism for Au/Ag NPs and the controlling of their size and shape during fabrication using laser ablation. Second, the fundamentals of the biological method are comprehensively discussed, involving the synthesis principle and the process of controlling the size and shape and preparing Au/Ag NPs using biological methods. Third, the applications in biology, tumor diagnosis and treatment, and other fields are reviewed to demonstrate the potential value of Au/Ag NPs. Finally, a discussion surrounding three aspects (similarity, individuality, and complementarity) of the two green synthesis processes is presented, and the necessary outlook, including the current limitations and challenges, is suggested, which provides a reference for the low-cost and sustainable production of Au/Ag NPs in the future.

Pulsed-Laser Induced Photolysis of Synthesizing Magnetic Fe3O4 Nanoparticles for Visible-Light Photocatalysis

Our report is the first example describing the successful synthesis of magnetic Fe3O4 nanoparticles (NPs), for which we used pulsed-laser induced photolysis (PLIP). Compared with the previous method of using pulsed-laser ablation of a target, or strong energy of pulsed-laser light to decompose precursors in generating a solvated-ion reaction, the PLIP method used here is dependent on hydrogen peroxide (H2O2) to generate a hydrolysis reaction. Energy-dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD) were used to demonstrate the Fe3O4 crystalline structure of the synthesized NPs. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images revealed that the average size of the NPs was about 20–50 nm. Regarding their magnetic characteristics, the synthesized NPs exhibited a saturation magnetization of 5.62 emu/g, remanence of 3.82 emu/g, and coercive force of 49.8 Oe. The photocatalytic experiments confirmed that the synthesized magnetic Fe3O4 NPs have visible light-degradation effects based on their ability to photocatalytically degrade methylene blue (MB). The MB degradation efficiency was 60–80% under white-light exposure for 180 min. This study presents a new route for synthesizing magnetic Fe3O4 NPs for their potential use in photocatalysis.

Ag-Decorated Si Microspheres Produced by Laser Ablation in Liquid: All-in-One Temperature-Feedback SERS-Based Platform for Nanosensing

Combination of dissimilar materials such as noble metals and common semiconductors within unified nanomaterials holds promise for optoelectronics, catalysis and optical sensing. Meanwhile, difficulty of obtaining such hybrid nanomaterials using common lithography-based techniques stimulates an active search for advanced, inexpensive, and straightforward fabrication methods. Here, we report one-pot one-step synthesis of Ag-decorated Si microspheres via nanosecond laser ablation of monocrystalline silicon in isopropanol containing AgNO3. Laser ablation of bulk silicon creates the suspension of the Si microspheres that host further preferential growth of Ag nanoclusters on their surface upon thermal-induced decomposition of AgNO3 species by subsequently incident laser pulses. The amount of the AgNO3 in the working solution controls the density, morphology, and arrangement of the Ag nanoclusters allowing them to achieve strong and uniform decoration of the Si microsphere surface. Such unique morphology makes Ag-decorated Si microspheres promising for molecular identification based on the surface-enhanced Raman scattering (SERS) effect. In particular, the designed single-particles sensing platform was shown to offer temperature-feedback modality as well as SERS signal enhancement up to 106, allowing reliable detection of the adsorbed molecules and tracing their plasmon-driven catalytic transformations. Considering the ability to control the decoration degree of Si microspheres by Ag nanoclusters via amount of the AgNO3, the developed one-pot easy-to-implement PLAL synthesis holds promise for gram-scale production of high-quality hybrid nanomaterial for various nanophotonics and sensing applications.

Novel Approach for Synthesis of Graphene-like Phases by Pulsed Laser Ablation in a Flow-Mode Suspension

The present study investigates the possibility of obtaining graphene-like phases (defected graphene, graphene oxide, and reduced graphene oxide) as fine suspensions by applying a novel pulsed laser ablation (PLA) approach in flow mode. Two types of suspensions of microcrystalline graphite in aqueous suspensions and two types of microcrystalline graphite in suspensions of 6% hydrogen peroxide solution were irradiated in a quartz tube through which they flow. The third (λ = 355 nm) and fourth harmonics (λ = 266 nm) of an Nd:YAG laser system (15 ns pulse duration and 10 Hz pulse repetition rate) were used. The morphology of the obtained particles was studied by transmission electron microscopy (TEM). Their phase composition and structure were explored by X-ray photoelectron spectroscopy, X-ray diffractometry, and Raman spectroscopy.

Recent Developments in Plasmonic Alloy Nanoparticles: Synthesis, Modelling, Properties and Applications

Despite the traditional plasmonic materials are counted on one hand, there are a lot of possible combinations leading to alloys with other elements of the periodic table, in particular those renowned for magnetic or catalytic properties. It is not a surprise, therefore, that nanoalloys are considered for their ability to open new perspectives in the panorama of plasmonics, representing a leading research sector nowadays. This is demonstrated by a long list of studies describing multiple applications of nanoalloys in photonics, photocatalysis, sensing and magneto-optics, where plasmons are combined with other physical and chemical phenomena. In some remarkable cases, the amplification of the conventional properties and even new effects emerged. However, this field is still in its infancy and several challenges must be overcome, starting with the synthesis (control of composition, crystalline order, size, processability, achievement of metastable phases and disordered compounds) as well as the modelling of the structure and properties (accuracy of results, reliability of structural predictions, description of disordered phases, evolution over time) of nanoalloys. To foster the research on plasmonic nanoalloys, here we provide an overview of the most recent results and developments in the field, organized according to synthetic strategies, modelling approaches, dominant properties and reported applications. Considering the several plasmonic nanoalloys under development as well as the large number of those still awaiting synthesis, modelling, properties assessment and technological exploitation, we expect a great impact on the forthcoming solutions for sustainability, ultrasensitive and accurate detection, information processing and many other fields.

Impact of Sterilization on the Colloidal Stability of Ligand-Free Gold Nanoparticles for Biomedical Applications

Sterilization is a major prerequisite for the utilization of nanoparticle colloids in biomedicine, a process well examined for particles derived from chemical synthesis although highly underexplored for electrostatically stabilized ligand-free gold nanoparticles (AuNPs). Hence, in this work, we comprehensively examined and compared the physicochemical characteristics of laser-generated ligand-free colloidal AuNPs exposed to steam sterilization and sterile filtration as a function of particle size and mass concentration and obtained physicochemical insight into particle growth processes. These particles exhibit long-term colloidal stability (up to 3 months) derived from electrostatic stabilization without using any ligands or surfactants. We show that particle growth attributed to cluster-based ripening occurs in smaller AuNPs (∼5 nm) following autoclaving, while larger particles (∼10 and ∼30 nm) remain stable. Sterile filtration, as an alternative effective sterilizing approach, has no substantial impact on the colloidal stability of AuNPs, regardless of particle size, although a mass loss of 5-10% is observed. Finally, we evaluated the impact of the sterilization procedures on potential particle functionality in proton therapy, using the formation of reactive oxygen species (ROS) as a readout. In particular, 5 nm AuNPs exhibit a significant loss in activity upon autoclaving, probably dedicated to specific surface area reduction and surface restructuring during particle growth. The filtered analog enhanced the ROS release by up to a factor of ∼2.0, at 30 ppm gold concentration. Our findings highlight the need for carefully adapting the sterilization procedure of ligand-free NPs to the desired biomedical application with special emphasis on particle size and concentration.

Antibacterial and Photocatalytic Coatings Based on Cu-Doped ZnO Nanoparticles into Microcellulose Matrix

The paper presents a successful, simple method for the preparation and deposition of new hybrid Cu-doped ZnO/microcellulose coatings on textile fibers, directly from cellulose aqueous solution. The morphological, compositional, and structural properties of the obtained materials were investigated using different characterization methods, such as SEM-EDX, XRD, Raman and FTIR, as well as BET surface area measurements. The successful doping of ZnO NPs with Cu was confirmed by the EDX and Raman analysis. As a result of Cu doping, the hybrid NPs experienced a phase change from ZnO to (Zn0.9Cu0.1)O, as shown by the XRD results. All the hybrid NPs exhibited a high degree of crystallinity, as revealed by the very sharp reflections in XRD patterns and suggested also by the Raman results. The evaluation of the very low copper-doping (0.1-1 at.%) effect has shown different behavior trends of the hybrid coatings compared with the starting oxide NPs, for MB and MO photodegradation. Continuous increases up to 92% and 60% for MB and MO degradation, respectively, were obtained at maximum 1 at.%-Cu doping coatings. Strong antibacterial activity against S. aureus and E. coli were observed.

A comprehensive review and outlook on the experimental techniques to investigate the complex dynamics of pulsed laser ablation in liquid for nanoparticle synthesis

Pulsed laser ablation in liquid (PLAL) has been established as one of the most efficient and impactful methods for producing pure and ligand-free nanoparticles (NPs). PLAL has successfully been utilized for the synthesis of metal NPs, semiconductor NPs, ceramic NPs, and even nanocomposites. A variety of NPs, including core-shell, nanocubes, nanorods, and many other complex structures, can be synthesized using PLAL. The versatility associated with PLAL has led to the synthesis of NPs that have found applications in the field of biomedicine, sensing technology, energy harvesting, and various industries. Despite all the aforementioned advantages, there has been an ambiguity in terms of conditions/parameters for the nanoparticle synthesis as reported by various research groups. This has led to a perception that PLAL provides little or no control over the properties of the synthesized NPs. The properties of the NPs are reliant on transient dynamics caused due to a high-intensity laser's interaction with the target material. To understand the process of nanoparticle synthesis and to control the properties of NPs, it is critical to understand the various processes that occur during PLAL. The investigation of PLAL is essential for understanding the dynamical processes involved. However, the investigation techniques employed to probe PLAL present their own set of difficulties, as high temporal as well as spatial resolution is a prerequisite to probe PLAL. Hence, the purpose of this Review is to understand the dynamical processes of PLAL and gain an insight into the various investigation techniques and their data interpretation. In addition to the current challenges, some ways of overcoming these challenges are also presented. The benefits of concurrent investigations with special emphasis on the simultaneous investigation by multiple techniques are summarized, and furthermore, a few examples are also provided to help the readers understand how the simultaneous investigation works.

A Study of Zn-Ca Nanocomposites and Their Antibacterial Properties

This study aimed to develop Ca²⁺ doped ZnO nanoparticles (NPs) and investigate their antibacterial properties against microorganisms of dental interest. Zn-Ca NPs were synthesized by the sol-gel method with different concentrations of Ca²⁺ (1, 3, and 5 wt. %) and subsequently characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), UV-vis spectroscopy and Fourier transform infrared spectroscopy (FT-IR). The Kirby–Bauer method was used to measure antibacterial effects. NPs showed the wurzite phase of ZnO and bandgap energies (Eg) from 2.99 to 3.04 eV. SEM analysis showed an average particle size of 80 to 160 nm. The treatments that presented the best antibacterial activity were Zn-Ca 3% and Zn-Ca 5%. ZnO NPs represent an alternative to generate and improve materials with antibacterial capacity for dental applications.

Au-Ag Alloy Nanocorals with Optimal Broadband Absorption for Sunlight-Driven Thermoplasmonic Applications

Noble metal nanoparticles are efficient converters of light into heat but typically cover a limited spectral range or have intense light scattering, resulting in unsuited for broadband thermoplasmonic applications and sunlight-driven heat generation. Here, Au-Ag alloy nanoparticles were deliberately molded with an irregular nanocoral (NC) shape to obtain broadband plasmon absorption from the visible to the near-infrared yet at a lower cost compared to pure Au nanostructures. The Au-Ag NCs are produced through a green and scalable methodology that relies on pulsed laser fragmentation in a liquid, without chemicals or capping molecules, leaving the particles surface free for conjugation with thiolated molecules and enabling full processability and easy inclusion in various matrixes. Numerical calculations showed that panchromism, i.e., the occurrence of a broadband absorption from the visible to the near-infrared region, is due to the special morphology of Au-Ag alloy NCs and consists of a purely absorptive behavior superior to monometallic Au or Ag NCs. The thermoplasmonic properties were assessed by multiwavelength light-to-heat conversion experiments and exploited for the realization of a cellulose-based solar-steam generation device with low-cost, simple design but competitive performances. Overall, here it is shown how laser light can be used to harvest solar light. Besides, the optimized broadband plasmon absorption, the green synthetic procedure, and the other set of positive features for thermoplasmonic applications of Au-Ag NCs will contribute to the development of environmentally friendly devices of practical utility in a sustainable world.

Transient Solid-State Laser Activation of Indium for High-Performance Reduction of CO2 to Formate

Deficiencies in understanding the local environment of active sites and limited synthetic skills challenge the delivery of industrially-relevant current densities with low overpotentials and high selectivity for CO₂ reduction. Here, a transient laser induction of metal salts can stimulate extreme conditions and rapid kinetics to produce defect-rich indium nanoparticles (L-In) is reported. Atomic-resolution microscopy and X-ray absorption disclose the highly defective and undercoordinated local environment in L-In. In a flow cell, L-In shows a very small onset overpotential of ≈92 mV and delivers a current density of ≈360 mA cm^-2 with a formate Faradaic efficiency of 98% at a low potential of -0.62 V versus RHE. The formation rate of formate reaches up to 6364.4 µmol h^-1mgIn-1$mg_{{\rm{In}}}^{--1}$ , which is nearly 39 folds higher than that of commercial In (160.7 µmol h^-1mgIn-1$mg_{{\rm{In}}}^{--1}$ ), outperforming most of the previous results that have been reported under KHCO₃ environments. Density function theory calculations suggest that the defects facilitate the formation of *OCHO intermediate and stabilize the *HCOOH while inhibiting hydrogen adsorption. This study suggests that transient solid-state laser induction provides a facile and cost-effective approach to form ligand-free and defect-rich materials with tailored activities.

Inactivation of SARS-CoV-2 by a chitosan/α-Ag2WO4 composite generated by femtosecond laser irradiation

In the current COVID-19 pandemic, the next generation of innovative materials with enhanced anti-SARS-CoV-2 activity is urgently needed to prevent the spread of this virus within the community. Herein, we report the synthesis of chitosan/α-Ag₂WO₄ composites synthetized by femtosecond laser irradiation. The antimicrobial activity against Escherichia coli, Methicilin-susceptible Staphylococcus aureus (MSSA), and Candida albicans was determined by estimating the minimum inhibitory concentration (MIC) and minimal bactericidal/fungicidal concentration (MBC/MFC). To assess the biocompatibility of chitosan/α-Ag₂WO₄ composites in a range involving MIC and MBC/MFC on keratinocytes cells (NOK-si), an alamarBlue™ assay and an MTT assay were carried out. The SARS-CoV-2 virucidal effects was analyzed in Vero E6 cells through viral titer quantified in cell culture supernatant by PFU/mL assay. Our results showed a very similar antimicrobial activity of chitosan/α-Ag₂WO₄ 3.3 and 6.6, with the last one demonstrating a slightly better action against MSSA. The chitosan/α-Ag₂WO₄ 9.9 showed a wide range of antimicrobial activity (0.49-31.25 µg/mL). The cytotoxicity outcomes by alamarBlue™ revealed that the concentrations of interest (MIC and MBC/MFC) were considered non-cytotoxic to all composites after 72 h of exposure. The Chitosan/α-Ag₂WO₄ (CS6.6/α-Ag₂WO₄) composite reduced the SARS-CoV-2 viral titer quantification up to 80% of the controls. Then, our results suggest that these composites are highly efficient materials to kill bacteria (Escherichia coli, Methicillin-susceptible Staphylococcus aureus, and the yeast strain Candida albicans), in addition to inactivating SARS-CoV-2 by contact, through ROS production.

Co-doping of iron and copper ions in nanosized bioactive glass by reactive laser fragmentation in liquids

Bioactive glass (BG) is a frequently used biomaterial applicable in bone tissue engineering and known to be particularly effective when applied in nanoscopic dimensions. In this work, we employed the scalable reactive laser fragmentation in liquids method to produce nanosized 45S5 BG in the presence of light-absorbing Fe and Cu ions. Here, the function of the ions was twofold: (i) increasing the light absorption and thus causing a significant increase in laser fragmentation efficiency by a factor of 100 and (ii) doping the BG with bioactive metal ions up to 4 wt%. Our findings reveal an effective downsizing of the BG from micrometer-sized educts into nanoparticles having average diameters of <50 nm. This goes along with successful element-specific incorporation of the metal ions into the BG, inducing co-doping of Fe and Cu ions as verified by energy-dispersive X-ray spectroscopy (EDX). In this context, the overall amorphous structure is retained, as evidenced by X-ray powder diffraction (XRD). We further demonstrate that the level of doping for both elements can be adjusted by changing the BG/ion concentration ratio during laser fragmentation. Consecutive ion release experiments using inductively-coupled plasma mass spectrometry (ICP-MS) were conducted to assess the potential bioactivity of the doped nanoscopic BG samples, and cell culture experiments using MG-63 osteoblast-like cells demonstrated their cytocompatibility. The elegant method of in situ co-doping of Fe and Cu ions during BG nanosizing may provide functionality-advanced biomaterials for future studies on angiogenesis or bone regeneration, particularly as the level of doping may be adjusted by ion concentrations and ion type in solution.

Underfocus Laser Induced Ni Nanoparticles Embedded Metallic MoN Microrods as Patterned Electrode for Efficient Overall Water Splitting

Transition metal nitrides have shown large potential in industrial application for realization of the high active and large current density toward overall water splitting, a strategy to synthesize an inexpensive electrocatalyst consisting of Ni nanoparticles embedded metallic MoN microrods cultured on roughened nickel sheet (Ni/MoN/rNS) through underfocus laser heating on NiMoO₄ ·xH₂ O under NH₃ atmosphere is posited. The proposed laser preparation mechanism of infocus and underfocus modes confirms that the laser induced stress and local high temperature controllably and rapidly prepared the patterned Ni/MoN/rNS electrodes in large size. The designed Ni/MoN/rNS presents outstanding catalytic performance for hydrogen evolution reaction (HER) with a low overpotential of 67 mV to deliver a current density of 10 mA cm^-2 and for the oxygen evolution reaction (OER) with a small overpotential of 533 mV to deliver 200 mA cm^-2 . Density functional theory (DFT) calculations and Kelvin probe force microscopy (KPFM) further verify that the constructed interface of Ni/MoN with small hydrogen absorption Gibbs free energy (ΔG_H* ) (-0.19 eV) and similar electrical conductivity between Ni and metallic MoN, which can explain the high intrinsic catalytic activity of Ni/MoN. Further, the constructed two-electrode system (-) Ni/MoN/rNS||Ni/MoN/rNS (+) is employed in an industrial water-splitting electrolyzer (460 mA cm^-2 for 120 h), being superior to the performance of commercial nickel electrode.