Ultrafine Particle Size Research Articles

NiO nanocrystals encapsulated into a nitrogen-doped porous carbon matrix as highly stable Li-ion battery anodes

Though the carbon matrix is extensively investigated to enhance the electrochemical performances of metal oxides for lithium-ion batteries (LIBs), it is still difficult to expose the whole active sites in the electrode material to participate in electrochemical reactions. Herein, we report a facile MOF-derived strategy for the controlled synthesis of a hybrid structure with NiO nanocrystals uniformly distributed into nitrogen-doped porous carbon matrix (NiO@N–C). In this strategy, the simultaneously generated nitrogen-doped porous carbon matrix can confine the further growth of the resulting NiO nanocrystals during the carbonization process, in which the ultrafine particle sizes of NiO can shorten ion diffusion length and provide abundant exposed active sites for lithium-storage, while the carbon matrix can function as a buffer layer to alleviate the volume expansion. Benefiting from the advantages of the structural features and porous carbon matrix, NiO@N–C delivers a large reversible capacity of 1373 mAh g−1 at 100 mA g−1 after 200 cycles and a remarkable cycling stability up to 1000 cycles at 1 A g−1 with a capacity of 877 mAh g−1, suggesting its potential as an anode material for lithium-ion batteries.

Rubber Dam Isolation and High-Volume Suction Reduce Ultrafine Dental Aerosol Particles: An Experiment in a Simulated Patient

The ongoing Coronavirus Disease 2019 (COVID-19) pandemic has triggered the paralysis of dental services ascribed to the potential spread of severe acute respiratory syndrome (SARS)-CoV-2. Aerosol-generating procedures (AGPs) are common in dentistry, which in turn increase the risk of infection of the dental personnel due to the salivary presence of SARS-CoV-2 in COVID-19 patients. The use of rubber dam isolation (RDI) and high-volume evacuators (HVE) during AGPs is recommended to control dental aerosols, but the evidence about their effectiveness is scarce. This first study aimed to compare, in a simulated patient, the effectiveness of the following strategies: standard suction (SS), RDI and RDI + HVE. Using the laser diffraction technique, the effect of each condition on the volume distribution, average size and concentration of coarse (PM10), fine (PM2.5) and ultrafine (PM0.1) particles were evaluated. During the teeth drilling, the highest volume fraction of dental aerosol particles with SS was below 1 μm of aerodynamic diameter. Additionally, the RDI + HVE significantly reduced both the ultrafine dental aerosol particles and the concentration of total particulate matter. AGPs represent a potential risk for airborne infections in dentistry. Taken together, these preliminary results suggest that isolation and high-volume suction are effective to reduce ultrafine dental aerosol particles.

Predicting outdoor ultrafine particle number concentrations, particle size, and noise using street-level images and audio data

Outdoor ultrafine particles (UFPs) (<0.1 µm) may have an important impact on public health but exposure assessment remains a challenge in epidemiological studies. We developed a novel method of estimating spatiotemporal variations in outdoor UFP number concentrations and particle diameters using street-level images and audio data in Montreal, Canada. As a secondary aim, we also developed models for noise. Convolutional neural networks were first trained to predict 10-second average UFP/noise parameters using a large database of images and audio spectrogram data paired with measurements collected between April 2019 and February 2020. Final multivariable linear regression and generalized additive models were developed to predict 5-minute average UFP/noise parameters including covariates from deep learning models based on image and audio data along with outdoor temperature and wind speed. The best performing final models had mean cross-validation R2 values of 0.677 and 0.523 for UFP number concentrations and 0.825 and 0.735 for UFP size using two different test sets. Audio predictions from deep learning models were stronger predictors of spatiotemporal variations in UFP parameters than predictions based on street-level images; this was not explained only by noise levels captured in the audio signal. All final noise models had R2 values above 0.90. Collectively, our findings suggest that street-level images and audio data can be used to estimate spatiotemporal variations in outdoor UFPs and noise. This approach may be useful in developing exposure models over broad spatial scales and such models can be regularly updated to expand generalizability as more measurements become available.

Surgical Smoke and Airborne Microbial Contamination in Operating Theatres: Influence of Ventilation and Surgical Phases.

Air cleanliness is a crucial factor in operating theatres (OTs), where the health of patients and staff must be preserved by controlling air contamination. Particular attention must be paid to ultrafine particles (UFPs) size range, generated for instance by electrosurgical instruments (ESTs). OT contamination is also affected by ventilation systems, medical staff and their gowning system, staff routines, instruments, etc. This comparative study is based on experimental measurements of airborne microbial contamination and UFPs carried out during real ongoing surgeries in two OTs equipped with upward displacement ventilation (UWD) and hybrid ventilation, with unidirectional airflow on the operating table and peripheral mixing (UDAF+Mixing) ventilation systems. Airborne contamination concentration at the exit grilles has been analyzed as function of four different surgical phases normally performed during an operation. Results highlight that airborne contamination is influenced by the activities carried out during the surgical phases. EST usage affects the contamination level more than staff size during operation observed. Colony forming unit (CFU) values in the protected area close to the patient’s wound are influenced more by the type of ventilation system than by surgical phases. CFU values decrease by 18 to 50 times from the UWD system to the hybrid one. The large airflow volumes supply together with high air velocities in OTs equipped with UDAF+Mixing systems guarantee a better and a safer airborne contamination control for patients and medical team in comparison with UWD systems.

Particle size distributions and hygroscopic restructuring of ultrafine particles emitted during thermal spraying

We report measurements of the size, concentration, and hygroscopicity of ultrafine particles (UFPs) emitted during thermal spraying of ceramic coatings in an industrial setting. High concentrations...

Integrated evanescent field detector for ultrafine particles-theory and concept.

Recent studies on ultrafine particles (UFP), which are smaller than 100 nm, emphasized their hazardous potential to the human organism. They are comparable in size to typical nano-organisms such as viruses and can penetrate physiological barriers in a similar way. Currently, there are no low-cost and miniaturized detectors for UFP available. In our first experiments with an integrated evanescent field particle detector, we could already successfully detect single 200 nm polystyrene latex (PSL) spheres, although the implemented waveguide geometry was only rudimentary optimized with costly 3D simulations. We developed a fast and structured optimization model for waveguide geometry and operation wavelength of an integrated evanescent field particle detector in order to exploit its full potential for the detection of discrete analytes in the UFP size range. The optimization model is based on a modified formulation of Mie theory and its computational effort is reduced by a factor of 100 compared to 3D simulations. The optimization potential of the sensor response signal is demonstrated for several waveguide geometries that can be produced with established semiconductor fabrication technology at high production volumes and low costs. An optimized silicon nitride waveguide features sensor response signals that are about one order of magnitude higher compared to previous experiments, which pushes the limit of detection even further down to particle sizes below 100 nm. A small integrated evanescent field particle detector based on this optimized waveguide will be used for the first low-cost and miniaturized devices that can monitor the personal exposure to UFP.

In situpreparation of ultrafine Ru nanocatalyst supported on nitrogen‐doped layered double hydroxide by nitrogen glow discharge plasma for catalytic hydrogenation ofN‐ethylcarbazole

Ultrafine Ru nanoparticles (RuNPs) supported on nitrogen‐doped layered double hydroxide (Ru/LDH) werein situprepared by nitrogen glow discharge plasma (nGDP) without adding any chemical reducing agents or stabilizers. The as‐synthesized Ru/LDH catalysts were characterized by X‐ray diffraction, X‐ray photoelectron spectroscopy, transmission electron microscopy, and Fourier transform infrared spectroscopy. During treatment with nGDP, the reduction of Ru3+and nitrogen doping were carried out simultaneously. The resulting RuNPs has a narrow particle size distribution of 1.41–2.61 nm, an ultrafine average particle size of 1.86 nm, and were uniformly dispersed on nitrogen‐doped LDH. The complexation of RuNPs and O/N‐containing functional groups on LDH improve the catalytic activity and stability of Ru/LDH. The catalyst exhibited excellent properties for the hydrogenation reaction ofN‐ethylcarbazole (NEC). The conversion of NEC and the selectivity of 12H‐NEC were 100% and 99.06% for 1 hr at 120°C and 6 MPa H2, respectively. The mass hydrogen storage capacity was 5.78 wt%. The apparent activation energy was 35.78 kJ/mol.

Functionalization of silk by silver nanoparticles synthesized using the aqueous extract from tea stem waste

Silk has poor antibacterial and UV protection properties which limit its application fields. Silver nanoparticles (AgNPs) have attracted great attention due to their excellent antibacterial activity. This work proposed a green and efficient way to prepare AgNPs from silver nitrate using the aqueous extract from tea stem waste, and a functional finishing of silk material with the resulting AgNPs by an immersion technique. AgNPs prepared at pH 9 and 40℃ exhibited ultra-fine particle size (<20nm), good dispersibility and good storage stability. When silk was treated with AgNPs at pH 3 and 80℃ for 40min, it displayed high silver content and color depth. The antibacterial and UV protection ability of AgNPs treated silk fabric of crepe de chine (52g/m2) increased as the silver content of silk increased. At a silver content of 3.64mg/g, the antibacterial rate of treated silk against Escherichia coli and Staphylococcus aureus was as high as 99%, and it was above 92% even after 20 cycles of washing under a neutral condition. At the same silver content, the UV protection factor of treated silk reached 21.3, being classified as “good protection”. The present study not only presents a novel approach for the functionalization of silk material using biosynthesized AgNPs, but also implements the reuse of tea stem waste.

Improved densification and hardness of high-entropy diboride ceramics from fine powders synthesized via borothermal reduction process

High-entropy boride ceramics of (Zr0.2Ta0.2Ti0.2Nb0.2Hf0.2)B2 and (Zr0.2W0.2Ti0.2Mo0.2Hf0.2)B2 were prepared by combining powder synthesis via borothermal reduction process at 1600 °C and subsequent ceramic densification by spark plasma sintering at 2000 °C in argon. High-entropy diboride powdered products exhibited ultra-fine particle size (<0.5 μm) after borothermal reduction. (Zr0.2Ta0.2Ti0.2Nb0.2Hf0.2)B2 ceramic with the single phase was obtained after sintering. However, the minor phase with the nominal WB composition was detected in (Zr0.2W0.2Ti0.2Mo0.2Hf0.2)B2 ceramic. (Zr0.2W0.2Ti0.2Mo0.2Hf0.2)B2 ceramic exhibited a high relative density associated with the high hardness of 27.7 GPa, which were higher than those measured for (Zr0.2Ta0.2Ti0.2Nb0.2Hf0.2)B2 ceramics (94.0% in relative density and 16.4 GPa in hardness) or the reported values (~92% in relative densities and 17.5–23.7 GPa in hardness) of other high-entropy boride ceramics.

Selective and efficient adsorption of Au (III) in aqueous solution by Zr-based metal-organic frameworks (MOFs): An unconventional way for gold recycling

Recycling precious metals from secondary resources is of great environmental and economic significance. In this study, the Zr-based MOFs UiO-66-NH2 was synthesized and used to adsorb Au (III) in aqueous solution. The ultrafine particle size (∼50 nm), excellent crystallinity and huge specific surface area (1039.2 m2 ·g−1) were verified by transmission electron microscope (TEM), powder X-ray diffraction (PXRD) and surface area analysis. About 50 % Au (III) was adsorbed within 6 min and the maximum adsorption capacity at 298 K reached up to 650 mg·g−1, showing superiority to traditional adsorbents. The general order kinetics model and Liu equation were suitable to describe the adsorption process, which was spontaneous, endothermic and driven by the increasing system entropy. Electrostatic attraction between -NH3+ and Au (III) anions and inner complexation to Zr-OH played a vital role in adsorption. Au (Ⅲ) was reduced to Au° by amino groups via redox reaction certified by X-ray photoelectron spectroscopy (XPS), PXRD and high-resolution transmission electron microscopy (HRTEM) analysis. Moreover, UiO-66-NH2 displayed high selectivity, robust stability and excellent reusability, making it an ideal candidate for gold recycling in industrial practice.

Fine and ultrafine particle number and size measurements from industrial combustion processes: Primary emissions field data

This study is to our knowledge the first to present the results of on-line measurements of residual nanoparticle numbers downstream of the flue gas treatment systems of a wide variety of medium- and large-scale industrial installations. Where available, a semi-quantitative elemental composition of the sampled particles is carried out using a Scanning Electron Microscope coupled with an Energy Dispersive Spectrometer (SEM-EDS). The semi-quantitative elemental composition as a function of the particle size is presented. EU's Best Available Technology documents (BAT) show removal efficiencies of Electrostatic Precipitator (ESP) and bag filter dedusting systems exceeding 99% when expressed in terms of weight. Their efficiency decreases slightly for particles smaller than 1 μm but when expressed in terms of weight, still exceeds 99% for bag filters and 96% for ESP. This study reveals that in terms of particle numbers, residual nanoparticles (NP) leaving the dedusting systems dominate by several orders of magnitude. In terms of weight, all installations respect their emission limit values and the contribution of NP to weight concentrations is negligible, despite their dominance in terms of numbers. Current World Health Organisation regulations are expressed in terms of PM2.5 wt concentrations and therefore do not reflect the presence or absence of a high number of NP. This study suggests that research is needed on possible additional guidelines related to NP given their possible toxicity and high potential to easily enter the blood stream when inhaled by humans.

Basil Essential Oil and Its Nanoemulsion Mitigate Non Alcoholic Steatohepatitis in Rat Model with Special Reference to Gut Microbiota.

The present research evaluated the protective effect of basil essential oil nanoemulsion (BNO) and its parent basil essential oil (BO) towards steatohepatitis. Chemical composition of BO was assessed followed by formulation into different BNOs using the low energy spontaneous emulsification technique. An ideal formula of BNO was selected among the others based on its ultra-fine particle size (15.42 nm) and physical stability at 25-37°C, which was then tested in steatohepatitis rat model along with BO. Rats were divided into four groups, the first was fed on balanced diet (C), and the other groups were maintained on high fructose saturated fat diet deficient in choline to induce steatohepatitis, one of such groups served as control steatohepatitis (SC), the other groups received daily oral dose of BO and BNO, respectively. Microbiota (Firmicutes and Bacteroidetes) were counted in colon content and their ratio (F/B) was calculated. Liver fat, plasma lipid profile, plama interlukin-6, plasma lipopolysaccharides and plasma and colon content of lipocaline were assessed with histopathological examination of liver and colon. Results showed that the major volatile components of BO were linalool (60.9 %), eugenol (5.1 %) and eucalyptol (9.5%). SC group exhibited significant increase in liver lipids, plasma triglycerides, total cholesterol (TC), low density lipoprotein cholesterol and significant reduction in high density lipoprotein-cholesterol (HDL-C) compared to C group. Significant increase in plasma TC/HDL-C, interlukin-6, and lipocaline and F/B ratio and lipocaline in colon content were demonstrated in SC group without changes in plasma lipopolysaccharides compared to C. Histopathology of SC group showed liver fatty degeneration and fibroblasts activation while the colon demonstrated erosion and mucosal epithelium detachment. Treatment with either BNO or BO showed improvement compared to SC group. BNO was superior in reducing F/B ratio, liver lipids and histopathological changes. BO was more efficient in reducing TC, triglycerides and low density lipoprotein cholesterol. It is concluded that BO and BNO reduced the progression of nonalcoholic steatohepatitis in rat model. Gut microbiota in relation to steatohepatitis and related new therapies needs further investigations.

A Cost-effective, Miniature Electrical Ultrafine Particle Sizer (mini-eUPS) for Ultrafine Particle (UFP) Monitoring Network

ABSTRACT A cost-effective, miniature electrical ultrafine particle sizer (mini-eUPS) has been developed for future UFP (ultrafine particle) monitoring networks in cities with high traffic density and in communities close to freeways, airports or stationary combustion sources. The mini-eUPS mainly consists of a mini-plate unipolar particle charger, a mini-plate differential mobility classifier and a mini-particle Faraday cage with a sensitive electrometer. A custom-made circuit board was designed for operating the mini-eUPS. In addition to the primary function of measuring the UFP size distribution, the mini-eUPS records the temperature, relative humidity, pressure, altitude, timing and location for each measured data set. The operational status of the mini-eUPS is also registered for data quality assurance. Due to the built-in features of self-diagnosis, malfunction reporting and wireless networking, this particle sizer is suitable for UFP monitoring network. The prototype, which possesses overall dimensions of 6.5′′ (L) × 5.0′′ (W) × 4′′ (H) and a total weight of ~1.0 kg, measures particles ranging in size from 5 to 200 nm. To evaluate the performance of the mini-eUPS, size distribution measurements of lab-generated particles in both unimodal and bimodal distributions and of UFPs emitted from a low-cost 3D printer and diesel engine were compared with those taken by a Scanning Mobility Particle Sizer (SMPS; TSI Inc.). A reasonably good agreement between the mini-eUPS and SMPS data was found.

Evaluation of Second-Hand Exposure to Electronic Cigarette Vaping under a Real Scenario: Measurements of Ultrafine Particle Number Concentration and Size Distribution and Comparison with Traditional Tobacco Smoke.

The present study aims to evaluate the impact of e-cig second-hand aerosol on indoor air quality in terms of ultrafine particles (UFPs) and potential inhalation exposure levels of passive bystanders. E-cig second-hand aerosol characteristics in terms of UFPs number concentration and size distribution exhaled by two volunteers vaping 15 different e-liquids inside a 49 m3 room and comparison with tobacco smoke are discussed. High temporal resolution measurements were performed under natural ventilation conditions to simulate a realistic exposure scenario. Results showed a systematic increase in UFPs number concentration (part cm−3) related to a 20-min vaping session (from 6.56 × 103 to 4.01 × 104 part cm−3), although this was one up to two order of magnitude lower than that produced by one tobacco cigarette consumption (from 1.12 × 105 to 1.46 × 105 part cm−3). E-cig second-hand aerosol size distribution exhibits a bimodal behavior with modes at 10.8 and 29.4 nm in contrast with the unimodal typical size distribution of tobacco smoke with peak mode at 100 nm. In the size range 6–26 nm, particles concentration in e-cig second-hand aerosol were from 2- (Dp = 25.5 nm) to 3800-fold (Dp = 9.31 nm) higher than in tobacco smoke highlighting that particles exhaled by users and potentially inhaled by bystanders are nano-sized with high penetration capacity into human airways.

Evaluation of ultrafine particle concentrations and size distributions at London Heathrow Airport

A study to monitor UFP at Heathrow Airport was undertaken in the autumn of 2016. The objective was to assess the context of measurements at the airport compared to measurements at “typical” traffic, background and rural locations in the south east of England. Measurements were made at two airport locations (called LHR2 and Oaks Road) at opposite ends of the airfield, to further understand the contribution of the airport to local air quality. Average concentrations showed that total particle number concentrations at the airport are typically lower than a traffic location and higher than an urban background location in London, matching the trends seen for NOx, PM10, PM2.5 and BC pollutants. However, the size distribution of the submicrometre particles at the airport is completely different to the London monitoring stations, with the airport PSD dominated by particles with a mode of 20 nm. In contrast, measurements of PN in London have a significantly larger mode of 30 nm. This study demonstrated that measurements of particle number from within the airport perimeter are dominated by the smallest particles and are closely associated with aircraft. Analysis of the operating modes at the airport showed that aircraft departing from the airport emit particles in much higher numbers than those arriving. Nucleation mode particles are commonly associated with emissions from combustion processes. However, measurement of these particles at the airport are not strongly correlated with Black Carbon. There does appear to be some correlation of nucleation mode particles with UV active BC particles (brown carbon, typically associated with biomass combustion or wood smoke) at the Heathrow airside monitoring station, LHR2. There is also modest association between nucleation mode particles and NO2. The study showed that the classical air pollutants measured at Heathrow are very similar in concentration to typical urban environments in London and south east England, but particle numbers in the sub 30 nm size range are markedly different to those measured in London.

MICRO-EMULSION METHOD FOR THE SYNTHESIS AND CHARACTERIZATION OF La, Mn-DOPED Ba3Co2 Fe24O41 Z-TYPE HEXA-NANOFERRITES

In this report, micro-emulsion method was used to obtain La, Mn-doped Ba3Co2 [Formula: see text][Formula: see text] single-phase Z-type hexa-nanoferrites by maintaining annealing temperature at 1200∘C. X-ray diffraction (XRD) analysis shows lattice parameters, crystallite size, and volume are significantly enhanced by introducing La and Mn ions instead of Ba and Fe, respectively. Moreover, La and Mn ion doping improved the preferred orientation of atoms through the basal plane of Z-type hexaferrite. Field emission scanning electron microscopy (FESEM) study reveals that the surface morphology of La- and Mn-doped Ba3Co2 [Formula: see text][Formula: see text], Z-type ferrites show ultrafine and small particle size. The analysis of X-Ray absorption near edge spectroscopy (XANES) suggests that transition in [Formula: see text] has occurred from 3d core level to empty electronic state above the Fermi level. Furthermore, it is observed that in the Z-type ferrites Co exist as divalent ion and Fe as trivalent ion by analyzing XANES. Vibrating samples magnetometer (VSM) indicated that the samples are ferromagnetic as they have narrow hysteresis loops. The decrease in coercivity is due to paramagnetic dopant element Manganese (Mn).

Immobilizing palladium nanoparticles on boron-oxygen-functionalized carbon nanospheres towards efficient hydrogen generation from formic acid

Carbon nanospheres (XC-72R) were functionalized by boron-oxygen (B-O) through coannealing with boric acid, to which highly dispersed palladium nanoparticles (Pd NPs) (~ 1.7 nm) were immobilized by a wet chemical reduction for the first time. The resultant Pd/OB-C catalyst exhibits significantly improved activity for the dehydrogenation from formic acid (FA) compared to pristine XC-72R supported Pd NPs (Pd/C). Impressively, by adding melamine precursor, the B-O and nitrogen (N)-functionalized product OB-C-N displays an extremely high B content, ca. 34 times higher than OB-C. The Pd/OB-C-N catalyst with an ultrafine Pd particle size of ~ 1.4 nm shows a superb activity, with a turnover frequency (TOF) as high as 5,354 h−1 at 323 K, owing to the uniform ultrafine Pd NPs and the effect from B-O and N functionalities.

Size Distributions of Different Carbonaceous Components in Ambient Aerosols

It is important to obtain the size distribution of carbonaceous components in aerosols for studying the formation and transformation mechanisms and radiation characteristics of regional aerosols. However, only a few studies on the size distribution of aerosol carbonaceous fractions have been conducted in Beijing. In this study, a Micro-Orifice Uniform Deposit Impactor (MOUDI)-120 sampler was used to collect size-resolved aerosol samples in three seasons in Beijing, and the concentrations of different types of carbonaceous fractions were analyzed. Furthermore, the size distribution, characteristics, sources, and interrelationship of each carbonaceous component in different seasons and under different pollution levels were systematically studied. The results show that the carbonaceous components were concentrated mainly in fine particles, and the proportion of carbonaceous components in fine particles in autumn and winter was higher than that in summer. The carbonaceous components are distributed in two main modes:accumulation mode and coarse mode. Organic carbon fraction 1 (OC1) and OC2 were distributed mainly in the accumulated mode, with a higher proportion in the range of 0.056-0.56 μm, and OC3+OC4 was more abundant in the coarse mode. The concentration of Soot-elemental carbon (EC) was low but was highest in the 0.10-0.18 μm size range, which indicates that the EC emitted by high temperature combustion was distributed mainly in the ultra-fine particle size range. The Char-EC concentration was much higher, accounting for the majority of EC. The distribution appearances of the main carbonaceous components were essentially the same in the daytime and at night. Summer and winter were more conducive to the formation of SOC, and the OC/EC ratio was significantly higher than that in autumn. The OC/EC values varied greatly in different particle sizes because the water-soluble organic compounds (WSOC) were distributed mainly in the range of 0.056-0.10 μm, with significantly higher OC/EC values than other particle sizes. Sunlight and high temperature were beneficial to the oxidation of gaseous organic matter to SOC, resulting in the OC/EC ratio in summer in daytime to be significantly higher than that at night. Among the carbonaceous components, EC1 and OC1 had the strongest interrelation. In addition, EC1 also had stronger interrelation with potassium.

Biotemplate-Assisted Synthesis of Layered Double Oxides Confining Ultrafine Ni Nanoparticles as a Stable Catalyst for Phenol Hydrogenation

A confined Ni(0) nanocatalyst derived from NiAl-layered double hydroxide (NiAl-LDH), with ultrafine Ni nanoparticles implanted in the NixAlyO support, was first fabricated by the urea coprecipitation method using pine pollen as a biotemplate, together with subsequent calcination/reduction process. This hollow biotemplate-assisted catalyst displayed high phenol-hydrogenation activity and stability, which can be ascribed to its higher surface area, better dispersibility, and ultrafine Ni particle size. The hollow morphology and confinement effect of lamellar NiAl-LDH can not only lead to better dispersion of the active Ni(0) species, but also strengthen the interaction between Ni(0) species and NixAlyO support. This protocol can overcome the shortcomings of conventional LDH-derived catalysts that lack specifically shaped morphology and hierarchical structure, inhibiting the aggregation of the Ni nanoparticles, hence resulting in its good activity and stability.

Surface modification-assisted solvent annealing to prepare high quality M-phase VO2 nanocrystals for flexible thermochromic films

Well-crystalline and stoichiometric M-phase vanadium dioxide (VO2 (M)) ultrafine nanoparticles are desired in fabricating high-efficient VO2-based flexible thermochromic films. In this study, a novel solvent annealing technique is developed to avoid growth and agglomeration of VO2 (M) nanoparticles in the post-annealing process. Oxygen-deficient VO2 (D) nanoparticles (~36 nm) are firstly prepared by a facial hydrothermal method. A double-layered reactor is designed to separate the surfactant-modified VO2 (D) nanoparticles physically from H2O2 which serves as the oxidant. The unique reactor enables the formation of a moderate oxygenation environment in the solvent annealing process, making the transformation of oxygen-deficient VO2 to VO2 (M) more controllable. The growth and agglomeration of VO2 nanoparticles are effectively suppressed due to the surface modification by polyvinyl pyrrolidone, liquid environment and low temperature. The obtained VO2 (M) nanoparticles have an average particle size of ~41 nm. The flexible film prepared with the VO2 (M) nanoparticles exhibit excellent thermochromic properties with ΔTsol reaching 18.03% and Tlum up to 58.33%. This amazing performance is attributed to the high quality of VO2 (M) nanoparticles and ultrafine particle size that makes the surface plasmon absorption take effect in the solar light region. This work demonstrates the proposed solvent annealing technique is an effective approach to prepare high-quality ultrafine VO2 (M) nanoparticles for achieving efficient thermochromic performance of the flexible smart windows.