Growth Process Of Nanoparticles Research Articles

Fuel Cell Catalyst Layers with Platinum Nanoparticles Synthesized by Sputtering onto Liquid Substrates.

Platinum (Pt) nanoparticles are widely used as catalysts in proton exchange membrane fuel cells. In recent decades, sputter deposition onto liquid substrates has emerged as a potential alternative for nanoparticle synthesis, offering a synthesis process free of contaminant oxygen, capping agents, and chemical precursors. Here, we present a method for the synthesis of supported nanoparticles based on magnetron sputtering onto liquid poly(ethylene glycol) (PEG) combined with a heat-treatment step for attachment of nanoparticles to a carbon support. Transmission electron microscopy imaging reveals Pt nanoparticle growth during the heat-treatment process, facilitated by the carbon support and the reducing properties of PEG. Following the heat treatment, a bimodal size distribution of Pt nanoparticles is observed, with sizes of 2.5 ± 0.8 and 6.7 ± 1.8 nm, compared to 1.8 ± 0.4 nm after sputtering. Synthesized Pt nanoparticles display excellent specific and mass activities for the oxygen reduction reaction, with 1.75 mA/cm2 Pt and 0.27 A/mgPt respectively, measured at 0.9 V vs the reversible hydrogen electrode. The specific activities reported herein outperform literature values of commercial Pt/C catalysts with similar loading and are on par with values of bulk Pt and mass-selected nanoparticles of comparable size. Also, the mass activities agree well with the literature values. The results provide new insights into the growth processes of SoL-synthesized carbon-supported Pt catalyst nanoparticles, and most crucially, the high performance of the synthesized catalyst layers, along with the possibility of nanoparticle growth through a straightforward heat-treatment step at relatively low temperatures, offer a scalable new approach for producing fuel cell catalysts with more efficient material utilization and new material combinations.

Multi-diagnostic of dust growth in a capacitive Ar/C2H2 plasma

Abstract The interest in the production of nanoparticles (NPs) within Ar/C2H2 reactive plasmas is increasing, driven by their potential applications in functional materials or for their analogy to cosmic dust. The growth process of NPs has been thoroughly examined using a broad array of diagnostic tools. Significant among these tools are those that determine two-dimensional distributions of NP sizes and densities. The inherent complexity of these techniques has resulted in a limited number of works that integrate these measurements with a multitude of other diagnostic tools. Here, we show a multi-diagnostic exploration of the growing process of NPs in Ar/C2H2 plasmas. The combination of in-situ techniques, such as scattered light images, optical emission spectroscopy, light extinction, quadrupole mass signals, or self-bias voltage, with ex-situ scanning electron microscopy images and FTIR spectra of the deposited dust, provides a detailed picture of the growth process. The temporal evolution of plasma parameters, coupled with chemical composition measurements, provides a comprehensive description of the dust growth phases, and the FTIR measurements reveal an appreciable difference in chemical composition between the core and shell of the NPs. Furthermore, employing a method based on the terminal falling velocity of NPs in the afterglow, the intrinsic mass density of NPs is estimated. The asymmetries observed in the spatial distributions of NP size and density are qualitatively discussed in terms of neutral drag, ion drag, and electrostatic forces.

Deep learning-assisted characterization of nanoparticle growth processes: unveiling SAXS structure evolution

Deep learning-assisted characterization of nanoparticle growth processes: unveiling SAXS structure evolution

Construction of core-triple shell upconversion nanostructures NaNdF4:Yb,Gd@NaGdF4:Yb@NaGdF4:Yb,Er@NaGdF4 with high FRET efficiency for the biochemical sensor

Upconversion nanoparticles (UCNPs) are excellent energy donors for Föster resonance energy transfer (FRET) systems. However, the lower FRET efficiency to some extend limits its application. To improve the efficiency of FRET, NaNdF4:Yb,Gd@NaGdF4:Yb@NaGdF4:Yb,Er@NaGdF4 core-triple shell (CTS) UCNPs with sensitizers in the core region and activators doped in the outer shell region were successfully prepared by changing the traditional core-shell structure design sequence. By introducing a certain amount of Gd3+ into the core nanoparticles, the crystal growth process of core nanoparticles was regulated, solving the problem of excessive and uneven size caused by high concentration of sensitizers. The insertion of Yb3+ doped transition layer weakens the negative effect between Nd3+ and activator ions, and enhances the luminescence intensity. In addition, comparing CTS UCNPs with UCNPs prepared in the traditional core-shell structure design sequence proves that CTS UCNPs have higher FRET efficiency. A biochemical sensing system was designed using this novel core-shell structure UCNPs, achieving simultaneous detection of GSH and Cd2+ with detection limits of 4.2 nM and 15.2 nM, respectively. The new core-shell structure UCNPs have broader application prospects in the field of biochemical sensing design.

In situ tuning and investigating the growth process of size controllable gold nanoparticles and statistical size prediction analysis

A critical understanding of the formation and growth process of gold nanoparticles (GNPs) is crucial, in order to synthesize monodisperse gold nanocrystals of controllable size and shape in a predictable way. GNPs of different shapes and sizes can be produced by altering different physicochemical reaction conditions, such as pH, temperature, and the ratio of reactants. The significant variations in the morphological features of GNPs can be monitored in situ in a time-dependent manner by using UV–visible spectroscopy. In this study, we have synthesized seedless GNPs by reduction of HAuCl4 by using various molar ratios of HEPES and Na2HPO4. The shape and the geometry of the gold nanostructures were optimized by varying the pH (5, 7, and 9) of the HEPES, molar concentrations of disodium phosphate to HAuCl4, and reaction temperatures (20 °C, 40 °C, and 60 °C). The changes in the color of the reaction mixtures over time were recorded in situ in terms of the absorbance of the UV–visible light to tune and investigate the growth process of gold nanostructures. Transmission electron microscopic (TEM) images indicated that the gold nanostructures are anisotropic, stable, and exist in the size range of < 1–100 nm. The present study also confirms that the change in the color of nanostructure reaction mixtures is a function of the surface plasmon resonance bands under the influence of physicochemical reaction conditions and corroborates with the size and shape of nano-gold. Physicochemical parameters such as temperature, pH, and the molar concentration of the reactants act synergistically to influence the growth, molecular mechanics, and reaction thermodynamics that aid to affect the particle size, shape, and surface corona of the GNPs. By tracking the growth process, we can confirm that the nucleation, growth process, size, and shape of the gold nanostructures depend on the HEPES free radicals and phosphate ions which cluster to form polymeric chains on the gold nanocore. The present study's findings explain the growth process of the GNPs of various colors that can be observed by the naked eye and have promising applications, for example in the development of the biosensing rapid lateral flow immunoassays (LFIA) for the detection of mycotoxins in food samples.

One-step annealing synthesis of Co core-PdZn intermetallic shell composite as a bifunctional oxygen electrocatalyst for zinc-air batteries

PdZn intermetallic has excellent electrocatalytic properties due to the strong synergistic effects caused by the ordered arrangement of atoms. It is often synthesized by annealing Pd/ZnO in a hydrogen atmosphere. However, the low conductivity of ZnO crystals limits electron conduction, which is not conducive to electrocatalytic reactions. To avoid conductivity degradation, we annealed Zn2+-doped ZIF-67 adsorbed with Pd precursors in a nitrogen atmosphere. The key component, “ghost ZnO,” produced by the decomposition of ZIF during pyrolysis, was used to form intermetallic with Pd by reactive metal-support interaction. The remaining ZnO crystals were converted to amorphous ZnO or removed by sublimation. A composite structure of metal core-intermetallic shell was formed with the surface energy as the driving force. Co@o-PdZn/NC (Pdweight = 2.47 %) exhibited strong oxygen reduction reaction (ORR)/oxygen evolution reaction (OER) electrocatalytic activity (reversible oxygen overpotential of 0.771 V). Moreover, it provided great performance in rechargeable zinc-air batteries (ZABs). In this study, the reactive metal-support interaction (RMSI) between the key component “ghost ZnO” and Pd was used by a one-step annealing method, and the growth process of nanoparticles was precisely controlled using the difference in surface energy between the metals to properly design the catalyst surface structure. The synthesized metal core-PdZn intermetallic shell composite is a promising bifunctional oxygen electrocatalyst. These findings provide a new strategy for designing composites with a metal core-intermetallic shell structure.

Non-Oxidized Bare Metal Nanoparticles in Air: A Rational Approach for Large-Scale Synthesis via Wet Chemical Process.

Metal nanoparticles (MeNPs) have been used in various industrial applications, owing to their unique physical and chemical properties different from the bulk counterparts. However, the natural oxidation of MeNPs is an imminent hindrance to their widespread applications despite much research efforts to prevent it. Here, a rational approach for non‐oxidized bare MeNPs in air, which requires no additional surface passivation treatment is reported. The direct synthetic route uses the [Gd2C]2+ · 2e− electride as an exceptional electron‐donating agent to reduce diverse metal precursors in alcoholic solvents. All synthesized bare Cu, Ag, and Sn nanoparticles are ultra‐stable in ambient air, exhibiting no trace of metal oxides even on their outermost atomic layer. This unique resistance to oxidation is ascribed to the accumulation of excess electrons on the surface of bare MeNPs, which originates from the spontaneous transfer of anionic electrons from the electride during the nanoparticle growth process. This approach provides not only a revolutionary scheme to obtain MeNPs with non‐passivated and non‐oxidized surfaces, but also fundamental knowledge about metal oxidation.

Hollow nanoparticles synthesized via Ostwald ripening and their upconversion luminescence-mediated Boltzmann thermometry over a wide temperature range

Upconversion nanoparticles (UCNPs) with hollow structures exhibit many fascinating optical properties due to their special morphology. However, there are few reports on the exploration of hollow UCNPs and their optical applications, mainly because of the difficulty in constructing hollow structures by conventional methods. Here, we report a one-step template-free method to synthesize NaBiF4:Yb,Er (NBFYE) hollow UCNPs via Ostwald ripening under solvothermal conditions. Moreover, we also elucidate the possible formation mechanism of hollow nanoparticles (HNPs) by studying the growth process of nanoparticles in detail. By changing the contents of polyacrylic acid and H2O in the reaction system, the central cavity size of NBFYE nanoparticles can be adjusted. Benefiting from the structural characteristics of large internal surface area and high surface permeability, NBFYE HNPs exhibit excellent luminescence properties under 980 nm near-infrared irradiation. Importantly, NBFYE hollow UCNPs can act as self-referenced ratiometric luminescent thermometers under 980 nm laser irradiation, which are effective over a wide temperature range from 223 K to 548 K and have a maximum sensitivity value of 0.0065 K−1 at 514 K. Our work clearly demonstrates a novel method for synthesizing HNPs and develops their applications, which provides a new idea for constructing hollow structure UCNPs and will also encourage researchers to further explore the optical applications of hollow UCNPs.

Platinum-Based Nanoparticle Fuel Cell Catalysts Synthesized By Sputtering Onto Liquid Substrates

The quest of finding cheaper and better fuel cell catalyst materials has been long ongoing and remains a crucial step in making fuel cells a commercially viable technology. Platinum (Pt) is still the conventional catalyst used in proton exchange membrane (PEM) fuel cells, however, with slow cathode kinetics and high material cost. Platinum-rare earth (RE) and lanthanide alloys have been found to greatly enhance the catalytic activity towards the oxygen reduction reaction (ORR).1 Increases in ORR activity of up to one order of magnitude compared to pure platinum has been observed for these alloys, but high oxygen affinity of the RE alloying agents considerably complicates their synthesis. Sputter deposition into low vapor pressure liquid substrates, such as ionic liquids and certain polymers enables fabrication of clean nanoparticles, without the presence of air and other contaminates, making it a potential technique for Pt-RE nanoparticle synthesis.Here, we will present our recent work on magnetron sputtering of Pt 2 and Pt-alloys into different liquid substrates, including polyethylene glycol and three imidazolium-based ionic liquids. We have investigated the influence of substrate temperature on Pt nanoparticle growth during sputtering, and in post-sputtering heat treatment.2 We show that whilst substrate temperature influences the Pt nanoparticle size, the effect is not as great as for other materials. Better understanding the growth processes of Pt nanoparticles sputtered into liquids is an important step towards tunable sizes and catalytic activities of Pt-RE nanocatalysts. Escudero-Escribano, María, et al. "Tuning the activity of Pt alloy electrocatalysts by means of the lanthanide contraction." Science 352.6281 (2016): 73-76.Brown, Rosemary, et al. "Plasma-Induced Heating Effects on Platinum Nanoparticle Size During Sputter Deposition Synthesis in Polymer and Ionic Liquid Substrates." Langmuir 37.29 (2021): 8821-8828.

Retrieval of Size Distribution and Concentration of Au-Ag Alloy Nanospheroids by Spectral Extinction Method.

In order to monitor the synthesis processes or characterize nanoparticles for application, a new method that allows in situ determination of the two-dimensional size distribution and concentration of Au-Ag alloy nanospheroids, based on their extinction spectrum, is developed. Non-negative Tikhonov regularization and T-matrix method were used to solve the inverse problem. The effects of the two-dimensional size steps, wavelength range, and measurement errors of extinction spectrum on the retrieval results were analyzed to verify the feasibility and accuracy of the retrieval algorithm. Through comparative analysis, the size steps and wavelength range that make the retrieval error smaller are found. After adding 0.1% random noise to the extinction spectrum, a small variation in the retrieval error of the mean size is observed. The results showed that the error of the mean size is smaller than 2% and the error of the concentration is smaller than 3%. This method is simple, fast, cheap, nondestructive, and can be done in situ during the growth process of nanoparticles.

Mathematical Analysis of Cyclic and Sampled Current Voltammetries for the Description of Nucleation and Growth Processes of Metallic Nanoparticles

The electrodeposition of metallic nanoparticles was studied using numerical methods under progressive and instantaneous nucleation regimes to calculate cyclic and sampled current voltammetries. The cyclic voltammograms (CV) for both types of nucleation were calculated using diffusion and kinetics limited growth conditions. The sampled current voltammograms (SCV) were built from numerically generated chronoamperometric curves. Comparison of the SCV and CV curves shows that the current response corresponding to the progressive nucleation was similar under both growth regimes, although the nuclei density was considerably different. Under instantaneous nucleation, the CV and SCV showed similar current responses only under kinetic control due to similar cluster growth, and the diffusion-controlled growth showed a similar cluster growth, but a different current response. The comparison made in this work provides a guideline to understand experimental electrodeposition results and makes a good argument for using SCV to complement the CV curves.

Comparative Study of Bulk and Nanoengineered Doped ZnSe

Chromium- and cobalt-doped zinc selenide nanoparticles were synthesized using a low-temperature reactive solution growth method. The morphological and optical characteristics were compared to those of doped zinc selenide (ZnSe) bulk crystals grown by the physical vapor transport (PVT) method. We observed agglomeration of particles; however, the thioglycerol capping agent has been shown to limit particle grain growth and agglomeration. This process enables doping by addition of chromium and cobalt salts in the solution. A slightly longer refluxing time was required to achieve cobalt doping as compared with chromium doping due to lower refluxing temperature. The nanoparticle growth process showed an average particle size of approximately 300 nm for both Cr- and Co-doped zinc selenide. The optical characterization of Co:ZnSe is ongoing; however, preliminary results showed a very high bandgap compared to that of pure ZnSe bulk crystal. Additionally, Co:ZnSe has an order of magnitude higher fluorescence intensity compared to bulk Cr:ZnSe samples.

Enhanced electromechanical conversion via in situ grown CsPbBr3 nanoparticles/poly(vinylidene fluoride) fibers for physiological signal monitoring

Mechanical energy conversion based on piezoelectric principle has received much attention due to its promising applications in sustainable power supply systems and sensor technology. Ferroelectric poly(vinylidene fluoride) (PVDF) combines the advantages of both good electromechanical coupling and easy processability, yet the low piezoelectric coefficient limits its output performances thus cannot meet the increasing requirements for power generation and sensing. Here, inorganic metal halide perovskite CsPbBr3 (CPB) nanoparticles have been incorporated into the PVDF fibers via electrospinning technique, where an in situ crystallization and growth process of CPB nanoparticles have been established. Meanwhile, both the CPB nanoparticles and PVDF fibers are poled by the electric field during electrospinning process, which promotes the formation of polar phase of PVDF and the distortion of CPB lattice, resulting in greatly enhanced piezoelectric performances of CPB/PVDF composites. The output performances under external force of the flexible generator developed from electrospun CPB/PVDF films are significantly enhanced compared with neat PVDF film, with the maximum Voc value 8.4 times higher; while the measurements on the microscopic piezoelectric responses unambiguously reveal that the increased polar phase mainly contributes to the enhanced electromechanical coupling. The functions of CPB/PVDF film as physiological signals monitoring sensor have been performed, demonstrating its potential applications as flexible piezoelectric generator and wearable health monitoring electronics.

Structural and magnetic properties of a BaFe12O19/NiFe2O4 nanostructured composite depending on different particle size ratios

A nanostructured magnetic composite based on hexagonal ferrite BaFe12O19 (magnetically hard) and cubic ferrite NiFe2O4 (magnetically soft) is synthesized. The hexagonal ferrite precursor is obtained by the Sol-Gel method using citric acid as a coordinating agent. The precursor obtained is heated at different temperatures to get nanoparticles with different sizes. Cubic ferrite is obtained by chemical co-precipitation, method and the nanoparticle growth process is controlled with different heat treatments. The hexagonal and cubic ferrite nanoparticles are mixed providing low energy. Three samples of this kind of composite are obtained with a different ratio of particle size. The composites are a mixture where there are clusters of the minority phase NiFe2O4 distributed in a matrix of the main phase BaFe12O19. Both ferrite phases are composed of nanoparticles with an average size less than 50 nm without tensions in the crystal lattice. These structural parameters were compared between the composites and their precursor ferrites. The relationship between the composite microstructures and their magnetic properties is analyzed. A weak exchange coupling was detected between the component magnetic phases of the composites. Depending on the synthesis conditions, some samples exhibit monodomain or a multidomain regime. The higher BH product appears for composites from ferrites with a nanoparticle size ratio approximately equal to one. The structural characterization is carried out by X-ray diffraction. The homogeneity of the composition in the volume of the nanostructured composites is analyzed with a field emission scanning electron microscope equipped with energy dispersive spectroscopy for the analysis of the element mapping. The magnetic study is carried out through measurements of magnetization as a function of the applied field (M vs. H) at 300 K.

PtPd‐decorated Multibranched Au@Ag Nanocrystal Heterostructures for Enhanced Hydrogen Evolution Reaction Performance in Visible to Near Infrared Light

AbstractPtPd‐decorated multibranched Au@Ag nanocrystals (NCs) were synthesized to form heterostructures with enhanced electrochemical performance for water splitting in the visible/near infrared (vis‐NIR) light region. Three kinds of heterostructures including PtPd‐covered, PtPd‐edged, and PtPd‐tipped Multi‐branched Au@Ag NCs were fabricated by controlling the growth process of PtPd alloy nanoparticles on Au@Ag NCs. PtPd‐covered Multi‐branched Au@Ag nanocrystal exhibited the best photo‐assisted electrocatalytic activity. The initial overpotential under vis‐NIR light is 33 mV with a Tatel slope of 101 mV/dec while the overpotential is 150 mV at 10 mA cm−2. The enhanced catalyst activity is ascribed to samples with heterogeneous structures and changed morphology and composition. In addition, localized surface Plasmon resonance (LSPR) effect from the surface of samples resulted in the effective separation of electron‐hole pairs (photoelectric effect). Finally the photothermal effect generated from the absorbance of Au nanostructures in near‐infrared light increased the temperature of the catalyst. The synergy of structure, photoelectricity, and photothermal effect endows the catalyst with excellent photo‐assisted electrocatalytic activity.

(Invited) Chemical Modulation of Precursor Reactivity for Systematic Synthesis of High-Quality Quantum Dots

With their size-dependent electronic properties, solution processability, and synthetic tunability, quantum dots (QDs) have been heavily studied for fundamental research and commercial applications. The performance of QD-based devices and QD probes are greatly affected by their size distribution and structural quality. To date, extensive studies have investigated size control, allowing us to grow QDs with less than a single monolayer difference in their size variation. In contrast, high quality QD growth is achieved mostly by trial-and-error and a reaction condition optimized for a specific QD system cannot be adapted to QDs of different sizes or materials. To address this critical gap in QD synthesis, we first identified the key parameters contributing to the structural quality of QDs and examined how they affect QD growth. Our study shows that the reaction temperature governs the instability of the QD surface and the level of lattice relaxation, while precursor reactivity impacts the reaction kinetics at the surface as well as satellite particle formation. Systematic optimization of growth conditions requires independent tuning of these two parameters. Unfortunately, conventional precursors do not allow temperature-independent modulation of their reactivity, requiring new precursors to be synthesized for different reaction conditions. This approach is inherently low throughput and labor-intensive.To enable temperature-independent modulation of precursor reactivity, we designed a new sulfur precursor that has a reactivity that can be chemically tuned in a predictable manner. The additives used for this reaction are commercially available, making the new chemistry highly accessible. The new precursor chemistry represents a new paradigm for QD growth: chemically-induced precursor conversion. We show that the new precursor allows systematic growth of high quality QDs of various sizes and materials for both core-only and core-shell QDs. Moreover, a close examination of the growth results provided invaluable insight into the nanoparticle growth process, enabling logical tuning of the reaction condition. We also show that this new precursor chemistry employs completely different reaction mechanisms for nucleation and growth. By effectively separating growth and nucleation even at a high concentration of precursors, the new precursor allows heat-up-based growth of high quality shells that are comparable to those created by the injection method. Our study inspires the design of other precursors to systematically grow high quality nanocrystals and achieve the heat-up-based growth of high quality shells, a highly economical and scalable approach for large-scale synthesis.

Computational Study of Quenching Effects on Growth Processes and Size Distributions of Silicon Nanoparticles at a Thermal Plasma Tail.

In this paper, quenching effects on silicon nanoparticle growth processes and size distributions at a typical range of cooling rates in a thermal plasma tail are investigated computationally. We used a nodal-type model that expresses a size distribution evolving temporally with simultaneous homogeneous nucleation, heterogeneous condensation, interparticle coagulation, and melting point depression. The numerically obtained size distributions exhibit similar size ranges and tendencies to those of experiment results obtained with and without quenching. In a highly supersaturated state, 40–50% of the vapor atoms are converted rapidly to nanoparticles. After most vapor atoms are consumed, the nanoparticles grow by coagulation, which occurs much more slowly than condensation. At higher cooling rates, one obtains greater total number density, smaller size, and smaller standard deviation. Quenching in thermal plasma fabrication is effectual, but it presents limitations for controlling nanoparticle characteristics.

Preparation and optical properties of Au nanoparticle “Sandwich” structure (AuNPs/ZNNs/AuNPs) substrate based on ZnO nanosheets template

Surface enhancement Raman scatting (SERS) substrate was synthesized by two-step electrodeposition method based on ZnO nanosheets (ZNNs) template. ZNNs membrane was prepared via first-electrodeposition by using zinc nitrate hexahydrate (ZnNO3•6H2O) as the precursor. Subsequently, an Au seed layer was coated on the ZNNs membrane substrate using ion sputtering apparatus. Finally, Au nanoparticles composite membrane was obtained by the second-electrodeposition growth process of Au nanoparticles in chlorogenic acid (HAuCl4•4H2O) solution. The Au nanoparticles composite membrane could be served as an activity SERS substrate, and it showed that ZNNs are mutually hinged and grow vertically ITO substrate and Au nanoparticles grew along the (111) crystalline orientation. Results demonstrate that Au nanoparticles with an average diameter of 50 nm are uniformly deposited on the surface of ZNNs template, and the as-prepared AuNPs/ZNNs/AuNPs “sandwich” structures membrane was a high activity and sensetivity SERS substrate, it showed a rather low detection limitation of 10−12 mol/L for R6G solution.

Enhancement of nanoparticle formation and growth during the COVID-19 lockdown period in urban Beijing

Abstract. Influenced by the spread of the global 2019 novel coronavirus (COVID-19) pandemic, primary emissions of particles and precursors associated with anthropogenic activities decreased significantly in China during the Chinese New Year of 2020 and the lockdown period (24 January–16 February 2020). The 2-month measurements of the number size distribution of neutral particles and charged ions showed that during the lockdown (LCD) period, the number concentration of particles smaller than 100 nm decreased by approximately 40 % compared to the pre-LCD period in January. However, the accumulation mode particles increased by approximately 20 % as several polluted episodes contributed to secondary aerosol formation. In this study, new particle formation (NPF) events were found to be enhanced in the nucleation and growth processes during the LCD period, as indicated by the higher formation rate of 2 nm particles (J2) and the subsequent growth rate (GR). The relevant precursors, e.g., SO2 and NO2, showed a clear reduction, and O3 increased by 80 % during LCD period, as compared with pre-LCD. The volatile organic vapors showed different trends due to their sources. The proxy sulfuric acid during the LCD period increased by approximately 26 %, as compared with pre-LCD. The major oxidants (O3, OH, and NO3) of VOCs were also found to be elevated during LCD. That indicated higher J2 and GR (especially below 5 nm) during the LCD period were favored by the increased concentration level of condensing vapors and decreased condensation sink. Several heavy haze episodes have been reported by other studies during the LCD period; however, the increase in nanoparticle number concentration should also be considered. Some typical NPF events produced a high number concentration of nanoparticles that intensified in the following days to create severe aerosol pollution under unfavorable meteorological conditions. Our study confirms a significant enhancement of the nucleation and growth process of nanoparticles during the COVID-19 LCD in Beijing and highlights the necessity of controlling nanoparticles in current and future air quality management.

Increase the rate of plasma-assisted synthesis of silver nanoparticles through additives

The plasma-assisted method was used to synthesize silver nanoparticles, and the growth process of silver nanoparticles (Ag-NPs) was monitored in real time by localized surface plasmon resonance (LSPR) absorption spectroscopy. The effect of additives on the synthesis of Ag-NPs was verified. It is found that the addition of isopropanol and glucose can increase the plasmon resonance absorption intensity of the reaction solution, and promote the synthesis of Ag-NPs. In the plasma-assisted method, the additives can effectively improve the synthesis efficiency of Ag-NPs, which has great inspiration for the synthesis of other metal nanoparticles.