Ultrafine Size Research Articles

Sustainable solid-state synthesis of uniformly distributed PdAg alloy nanoparticles for electrocatalytic hydrogen oxidation and evolution

New sustainable syntheses based on solid-state strategies have sparked enormous attention and provided novel routes for the synthesis of supported metallic alloy nanocatalysts (SMACs). Despite considerable recent progress in this field, most of the developed methods suffer from either complex operations or poorly controlled morphology, which seriously limits their practical applications. Here, we have developed a sustainable strategy for the synthesis of PdAg alloy nanoparticles (NPs) with an ultrafine size and good dispersion on various carbon matrices by directly grinding the precursors in an agate mortar at room temperature. Interestingly, no solvents or organic reagents are used in the synthesis procedure. This simple and green synthesis procedure provides alloy NPs with clean surfaces and thus an abundance of accessible active sites. Based on the combination of this property and the synergistic and alloy effects between Pd and Ag atoms, which endow the NPs with high intrinsic activity, the PdAg/C samples exhibit excellent activities as electrocatalysts for both the hydrogen oxidation and evolution reactions (HOR and HER) in a basic medium. Pd9Ag1/C showed the highest activity in the HOR with the largest j0,m value of 26.5 A g Pd−1 and j0,s value of 0.033 mA cmPd−2, as well as in the HER, with the lowest overpotential of 68 mV at 10 mA cm−2. As this synthetic method can be easily adapted to other systems, the present scalable solid-state strategy may open opportunity for the general synthesis of a wide range of well-defined SMACs for diverse applications.

Review: Effect on physical, mechanical, and wear performance of ZrB2‐based composites processed with or without additives

AbstractBecause of unique combination of properties, ultra high temperature ceramics (UHTCs) are considered the most suitable material for applications in extreme environments as in hypersonic flights, atmospheric reentry, and rocket propulsion system. Processing of UHTCs especially ZrB2‐based ceramic composites with additives offer advantages in terms of simple processing methodology and excellent properties. Processing route highly controls the ceramic properties. Present review share out systematically and explain the processing strategies of ZrB2‐based ceramic composites––conventional, hot press or spark plasma sintering and their effect on microstructure features, physical, and mechanical properties and tribological performance. Present review suggests that it is possible to process full dense ZrB2–SiC ceramic composite with ultrafine or nano size particles via fast sintering technique like spark plasma sintering and gives better mechanical and wear resistant properties.

Facile preparation of fluorescent carbon quantum dots from denatured sour milk and its multifunctional applications in the fluorometric determination of gold ions, in vitro bioimaging and fluorescent polymer film

In the present study, the multifunctional applications of food waste derived carbon quantum dots (CQD) have been demonstrated. The results obtained from the absorption and fluorescence spectroscopic analysis affirmed the superior photophysical property of the prepared CQD. X-ray diffraction (XRD), Fourier transformed infra-red spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS) studies further confirmed the crystallographic phase and surface functional groups present in the CQD. The ultrafine size of the CQD is established from the high-resolution transmission electron microscope (HR-TEM) micrographs with the grain size of 2−4 nm. The excellent fluorescence property of the CQD is utilised to detect trace levels of Au3+ ions by simply mixing aqueous dispersion of CQD with ascorbic acid (AA). The sensing mechanism is based on the reduction of Au3+ to gold nanoparticles (AuNPs) by AA and the subsequent AuNPs induced fluorescence quenching of CQD by synergistic static quenching and inner filter effect. The CQD/AA probe could selectively detect Au3+ ion as low as 0.95 μM. The cytotoxicity of the CQD toward U-251 MG glioblastoma cell revealed that the CQD did not possess any significant cytotoxicity. The application of CQD in bioimaging of cells is ascertained by fluorescence microscopic analysis. Furthermore, fluorescent polymer films were prepared by incorporating CQD within the polymer matrix (poly-vinyl-alcohol).

Intensified photocatalytic degradation of 2, 4–dicholorophenoxyacetic acid using size-controlled silver nanoparticles: Effect of pre-synthesis extraction

In this study, ultrafine silver (Ag) nanoparticles were synthesised in Orthosiphon stamineus (OS) extract via facile electrochemical method. Different pre–synthesis extraction methods, namely ultrasonic assisted extraction hydro–distillation (UAE–HD) and classical aqueous extraction (AE) were used and compared. UAE–HD attained the highest total phenolic compounds at 8563.90 mg/kg. The Ag nanoparticles prepared via pre–synthesis extraction of UAE–HD (AgUAE-HD) and classical AE (AgAE) gave ultrafine sizes of 2 nm and 15 nm, respectively. It was suggested from the characterisation results that the phenolic compounds present in the OS extract had a significant role in the capping and stabilisation of Ag nanoparticles. Moreover, it was also demonstrated that the size of the Ag nanoparticles could simply be altered by varying the amount of total phenolic content (TPC) using different pre–synthesis extraction methods prior to the synthesis of Ag. Next, the photocatalytic activity of the Ag nanoparticles was tested towards the degradation of 2, 4–dicholorophenoxyacetic acid (2,4–D) herbicide. The synthesised Ag nanoparticles also showed outstanding photocatalytic activity with maximum degradation efficiency of up to 99.78% at pH 3, 0.01 g L−1 of catalyst dosage and 10 mg L−1 of 2, 4-D concentration. High amount of TPC contributed to the low energy band–gap (Eg) of AgUAE-HD catalyst and significantly inhibited the electron-hole recombination as well as enhanced the photocatalytic activity. The figures of merit based on electric energy consumption (EEO) indicate that less energy was consumed during the degradation of 2,4–D in the presence of AgUAE-HD compared with other catalysts. Therefore, it could be concluded that AgUAE-HD is a promising material for high photocatalytic degradation efficiency of 2,4–D under optimal condition.

Layered double hydroxides supported atomically precise Aun nanoclusters for air oxidation of benzyl alcohol: Effects of size and active site structure

The effects of size and active site structure on catalytic activity were deeply investigated in air oxidation of benzyl alcohol over a series of Ni3Al-LDH (layered double hydroxides)-supported Aun nanocluster (NC) catalysts Aun/LDH (n = 25, 38, ~127), obtained by modified electrostatic adsorption of atomically precise Au25Capt18, Au38Capt24 and Au~127-Capt (Capt: captopril) NCs followed proper calcination. Detailed characterizations show that the Au25/LDH, Au38/LDH and Au~127/LDH possess ultrafine Au NCs size of 1.2 ± 0.2, 1.4 ± 0.3 and 1.8 ± 0.5 nm, respectively, which are majorly dispersed on the edge sites of the small-sized LDH nanosheets (20–40 nm). All the catalysts exhibit excellent catalytic activities in air oxidation of benzyl alcohol without external base associated with the remarkable size- and active site structure-dependence. The catalyst Au38/LDH shows the highest activity with TOF of 1884 h−1, which can be attributable to the ultrafine bi-icosahedron structure Au38 NCs and the strongest Au38 NCs – Ni-OH (LDH) synergistic effect facilitating the activation of α-CH bond of benzyl alcohol over more negatively charged Au sites upon XPS, CO-DRIFTs and kinetic isotope studies. The findings of the size- and active site structure-dependence of supported Aun cluster catalysts in the oxidation of benzyl alcohol provide important guiding principles for the rational design of supported Aun cluster catalysts.

Experimental study on the formation of ultrafine particulate matters (PMs) during pulverized coal (PC) char combustion in O2/N2 and O2/CO2 atmospheres

Under the force of increasingly strict emission standard of particulate matters (PMs) and serious haze in China, further understanding of the formation of ultrafine PMs during coal combustion is crucial. In this work, the formation characteristics of ultrafine PMs during pulverized coal (PC) char combustion in O2/N2 and O2/CO2 atmospheres were investigated through a high-temperature drop tube furnace (DTF) with a two-stage dilution sampling system and a 14-stage electrical low pressure impactor (ELPI+). Results showed that in both number-based and mass-based particle size distribution (PSD) the peaks of ultrafine PMs located nearby 0.2 μm under all experimental atmospheres including O221%/N279%, O221%/CO279%, O227%/CO273% and O233%/CO267% (O21N79, O21C79, O27C73 and O33C67). And the peak values increased with the increase of O2 concentration in O2/CO2 atmospheres because of the high char combustion temperature at elevated O2 level. However, the mass and number concentration of ultrafine PMs in O2/CO2 atmospheres reduced significantly compared with these in O2/N2 atmosphere. When O21N79 atmosphere switched to O21C79, O27C73, O33C67 atmosphere, the mass concentration of ultrafine PMs reduced by 80.90%, 76.58% and 14.31%, and the number concentration reduced by 74.16%, 63.17% and 10.50%, respectively. Furthermore, the total mass of the ultrafine PMs was determined by the mass of the ultrafine PMs with larger particle size, whereas the total number of ultrafine PMs was determined by the number of the ultrafine PMs with smaller particle size. In this work, the ultrafine PMs with the aerodynamic size smaller than 0.3 μm were collected on the 1st to 7th impactor surfaces of the ELPI+. Among the ultrafine PMs, the particles on the 7th impactor (PMs with the superior limit of ultrafine PMs size) accounted for more than 94.8% of the total ultrafine PMs by mass, but less than 2.3% of the total ultrafine PMs by number; The particles deposited on the 1st impactor (PMs with the detectable minimum size of ultrafine PMs) accounted for more than 79.6% of the total ultrafine PMs by number, but less than 0.4% of the total ultrafine PMs by mass. In addition, PM0.1 which accounted for 96% of the total number of the ultrafine PMs was analyzed for chemical composition by Inductively Coupled Plasma Mass Spectrometer (ICP-MS). Results showed that the prominent components of PM0.1 were Ca, Na, and Si in both O2/N2 and O2/CO2 atmospheres. However, compared with O2/N2 atmosphere, Na, Si, Al, and Fe were more enriched in PM0.1 in O2/CO2 atmospheres.

Generalized Domino-Driven Synthesis of Hollow Hybrid Carbon Spheres with Ultrafine Metal Nitrides/Oxides

<h2>Summary</h2> Hollow hybrid spheres have been the focus of substantial efforts in areas of energy storage/conversion, especially those with carbon shells. However, current synthesis methods require complicated multistep procedures and show inadequate capability to anchor ultrafine particles with compositional complexity and controllable content, thus far restricting the potentials. Here, we report the preparation of hollow hybrid carbon spheres with encapsulated ultrafine metal nitrides/oxides by one-pot domino-driven synthesis, which involves micelle-interfacial copolymerization for shell formation and spontaneous copolymerization-induced oxometallate condensation inside micelles for encapsulation, followed by controlled pyrolysis. The synthetic platform shows remarkable generality and adjustability, enabling full access to multifarious particles with ultrafine size and tunable content. The reduced dimension of the vanadium nitride nanocluster encapsulated in a hollow carbon cavity facilitates surface-dominated potassium storage with superior capacity and high rate performance. The versatile synthesis and manipulation will expand the scope of hollow hybrid material for widespread applications.

Supersonic antigravity aerodynamic atomization dusting nozzle based on the Laval nozzle and probe jet

To improve the trapping efficiency of respiratory dust by aerodynamic atomization and to maintain the health and safety of workers, a numerical simulation (droplet fragmentation and particle tracking in a high Mach number flow) and an aerodynamic atomization experiment were adopted on the basis of the existing supersonic aerodynamic atomization nozzles that utilize the Laval nozzle as the core. A new type of this kind of nozzle based on a probe structure was designed and optimized. Both the simulation and experimental results have shown that the probe injection method is more suitable for the progress of supersonic aerodynamic atomization. The new nozzle inherits the characteristics of fast droplet speed, conservation of water and pressure, long-range and slow attenuation. The atomization performance of the new nozzle is better than that of traditional nozzles at the same power, and the new nozzle has a larger atomization angle, smaller atomization granularity, lower noise and a more stable atomization output. For the first time, the process of breaking particles by using supersonic gas in the field of dust removal is truly realized. When the pressure is more than 0.1 MPa, antigravity water absorption can be realized. The dust removal rate can be approximately twice as high as that of the traditional ultrasonic atomization method. Compared with the traditional ultrasonic atomization method (84.75%), the dust isolation efficiency can reach 94.07%. The droplets of ultra-fine size with high-speed produced by the new nozzle will have a strong trapping effect on respiratory dust and will save more energy by the vacuum force siphon than currently used nozzles (the amount of gas saved by the same efficiency is 40% and the amount of water saved is 45%).

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.

Achieving Superior Electrocatalytic Performance by Surface Copper Vacancy Defects during Electrochemical Etching Process.

Vacancy defects of catalysts have been extensively studied and proven to be beneficial to various electrocatalytic reactions. Herein, an ultra-stable three-dimensional PtCu nanowire network (NNW) with ultrafine size, self-supporting rigid structure, and Cu vacancy defects has been developed. The vacancy defect-rich PtCu NNW exhibits an outstanding performance for the oxygen reduction reaction (ORR), with a mass activity 14.1 times higher than for the commercial Pt/C catalyst (20 %.wt, JM), which is currently the best performance. The mass activity of the PtCu NNW for methanol oxidation reaction (MOR) is 17.8 times higher than for the commercial Pt/C catalyst. Density-functional theory (DFT) calculations indicate that the introduction of Cu vacancies enhances the adsorption capacity of Pt atoms to the HO* intermediate and simultaneously weakens the adsorption for the O* intermediate. This work presents a facile strategy to assemble efficient electrocatalysts with abundant vacancy defects, at the same time, provides an insight into the ORR mechanism in acidic solution.

Achieving Superior Electrocatalytic Performance by Surface Copper Vacancy Defects during Electrochemical Etching Process

AbstractVacancy defects of catalysts have been extensively studied and proven to be beneficial to various electrocatalytic reactions. Herein, an ultra‐stable three‐dimensional PtCu nanowire network (NNW) with ultrafine size, self‐supporting rigid structure, and Cu vacancy defects has been developed. The vacancy defect‐rich PtCu NNW exhibits an outstanding performance for the oxygen reduction reaction (ORR), with a mass activity 14.1 times higher than for the commercial Pt/C catalyst (20 %.wt, JM), which is currently the best performance. The mass activity of the PtCu NNW for methanol oxidation reaction (MOR) is 17.8 times higher than for the commercial Pt/C catalyst. Density‐functional theory (DFT) calculations indicate that the introduction of Cu vacancies enhances the adsorption capacity of Pt atoms to the HO* intermediate and simultaneously weakens the adsorption for the O* intermediate. This work presents a facile strategy to assemble efficient electrocatalysts with abundant vacancy defects, at the same time, provides an insight into the ORR mechanism in acidic solution.

The stability of TiO2/POE nanolubricant for automotive air-conditioning system of hybrid electric vehicles

Nanolubricant are containing nanoparticles that are mixed with the base lubricant. Nanoparticle consists of ultra-fine size of particles from 1 to 100 nm. It was widely used as additional material to enhance properties of lubricant. The thermo-physical properties of the nanolubricant enhanced and thus able to improve the performance of vapour compression refrigeration system (VCRS) and automotive air-conditioning (AAC) system. The stability condition is one of the priority in formulation of nanolubricant for new application in AAC system of hybrid electric vehicles (HEV). The main objective of this study is to investigate the stability of TiO2 nanoparticles dispersed in Polyol-Ester (POE) lubricant. The TiO2/POE nanolubricant was prepared at volume concentration of 0.01 to 0.1% using the two-step method without any surfactant. The stability investigations were conducted by using visual sedimentation observation, micrograph observation, UV-Vis Spectrophotometer measurement and zeta potential measurement. The findings by visual sedimentation observation showed the best stability condition for more than 14 days at 0.01% and 0.03% volume concentration. Meanwhile the optimum sonication time is observed at 5 hours by visual and supported by UV-Vis evaluation. Further, the concentration ratio from UV-Vis evaluation was recorded above 95% for 5 hours sonication time and more than 30 days observation. Finally, the Zeta potential for the present nanolubricant was measured with 81.1 mV and obtained within the range of very good stability condition. Hence, this can confirm a good stability condition for the present TiO2/POE nanolubricant. Further investigation is required for the properties evaluation and performance of the nanolubricant in AAC system of HEV.

Possible morphological similarities between lunar dust particles and interplanetary dust particles collected from earth's atmosphere

This paper shows morphological similarity between aggregates separated from the lunar regolith ultra-fine size fraction and interplanetary dust particles (IDPs) collected in Earth’s stratosphere. It also demonstrates morphological difference between mentioned above and cometary particles from comet Wild 2 collected in the “Stardust” project. Given the number of lunar meteorites found on Earth, the Moon’s proximity to Earth, and its large surface area subject to high energy meteoroid impacts, makes it highly likely that all size spectrum of material ejected from lunar surface may have been grazed by Earth.

Experimental evaluation of the in-the-field capabilities of total-reflection X-ray fluorescence analysis to trace fine and ultrafine aerosol particles in populated areas

European countries have made progress in reducing particulate air pollution in recent decades being concerned about their heath and climate effect. In addition to determining particulate number size distributions, it is crucial to have a methodology to determine size distribution of elemental concentrations down to the ultrafine size fraction. The present study shows capabilities for combination of May-type cascade impactor sampling and laboratory total-reflection X-ray fluorescence analysis on ambient aerosol samples taken in urban areas of Budapest (Hungary) and Cassino (Italy). In addition, results for a sample collected in Budapest during the fireworks provided for the Hungarian National Day are discussed.The combined novel method is suitable for determining size distributions for major and trace elemental concentrations form ultrafine to coarse particles (70 nm up to 10 μm) in seven size fractions. Moreover, short sampling times (1–4 h) are sufficient for reaching detection limits in the range of 100 pg/m3 for transition metals. The size and time resolution were found to be optimal for identifying pollution episodes with elevated elemental concentrations. The in-the-field analytical applicability of the proposed method for major and trace elements is demonstrated by comparison to elemental size distributions resulted from destructive analytical techniques.

Synthesis, Microstructures and Mechanical Behaviour of Cr0.21Fe0.20Al0.41Cu0.18 and Cr0.14Fe0.13Al0.26Cu0.11Si0.25Zn0.11 Nanocrystallite Entropy Alloys Prepared by Mechanical Alloying and Hot-Pressing

Four component Cr0.21Fe0.20Al0.41Cu0.18 medium entropy alloy (Quaternary, 4C-MEA) and six component Cr0.14Fe0.13Al0.26Cu0.11Si0.25Zn0.11 high entropy alloy (sexinary, 6C-HEA) were designed and developed in non-equiatomic ratio to attain improved mechanical properties. These 4C-MEA, and 6C-HEA were synthesized via mechanical alloying (MA), and consolidated by hot pressing (HPing) at 723 K. For comparison, the same atomic ratio of four and six components of coarse grain alloys (4C-CGA and 6C-CGA) were also manufactured by conventional blending method. Nanocrystallite size powders of 27 ± 5.20 nm and 38 ± 3.7 nm were achieved for 4C-MEA and 6C-HEA respectively after 20 h MA. The phase evolutions, structural properties, and powder surface morphologies were characterized using X-ray diffraction and several electron microscopes. The 4C-MEA has possessed more quantity of body centred cubic (BCC) and less amount of face centred cubic (FCC) phases due to the more solid dissolution of 4 components. However, 6C-HEA exhibited more quantity of FCC and a small amount of BCC phases due to the incorporation of more FCC components compared to 4C-MEA and less solid dissolution due to more atomic radius difference among the mixing elements (atomic radius of Cr = 166 pm, Fe = 156 pm, Al = 118 pm, Cu = 145 pm, Si = 111 pm and Zn = 142 pm). The HPed samples produced ultra-fine crystallite size of 177 nm and 499 nm for 4C-MEA and 6C-HEA respectively. Further, 4C-MEA and 6C-HEA exhibited the ultimate compressive strength (UCS) of 365 MPa and 456 MPa respectively due to dissolution and lattice distortion of mixing elements. Also, 6C-HEA possessed Vickers hardness strength of around 1.97 GPa which was 2 times higher than 4C-MEA. The theoretical background of various strengthening mechanisms, various physicochemical, thermodynamic parameters, and four core effects behind the improved properties in entropy alloys was discussed and reported. The dislocation strengthening and solid solution strengthening were the major factors in exhibiting more UCS in 4C-MEA and 6C-HEA than 4C-CGA and 6C-CGA.

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.

Synthesis and spectroscopic study of highly fluorescent carbon dots derived from orange juice with Stilbene 420 dye

Highly-fluorescent Carbon Quantum Dots (CQDs) are synthesized in simple step by hydrothermal carbonization method of natural precursor such as orange juice as a carbon source. Hydrothermal method for synthesized CQDs requires simple and inexpensive equipment and raw materials, thus this method are now common synthesis method. The prepared CQDs have ultrafine size up to few nanometers and several features such as high solubility in water, low toxicity, high biocompatibility, photo-bleaching resistant, Chemical inertness and ease of functionalization which qualifies it for use in many applications such as bio-imaging, photo-labeling and photo-catalysis.&#x0D; This research demonstrates the method of prepared highly fluorescence CQDs and also briefly introduce the most commonly used techniques for characterizing CQDs and the results obtained and studying their optical properties by adding Stilbene 420 dye in a method that changes the input power of used laser and prove that the output power intensity depends on the input power.

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.

Investigating size-segregated sources of elemental composition of particulate matter in the South China Sea during the 2011 &amp;lt;i&amp;gt;Vasco&amp;lt;/i&amp;gt; cruise

Abstract. The South China Sea (SCS) is a receptor of numerous natural and anthropogenic aerosol species from throughout greater Asia. A combination of several developing countries, archipelagic and peninsular terrain, a strong Asian monsoon climate, and a host of multi-scale meteorological phenomena make the SCS one of the most complex aerosol–meteorological systems in the world. However, aside from the well-known biomass burning emissions from Indonesia and Borneo, the current understanding of aerosol sources is limited, especially in remote marine environments. In September 2011, a 2-week research cruise was conducted near Palawan, Philippines, to sample the remote SCS environment. Size-segregated aerosol data were collected using a Davis Rotating Uniform size-cut Monitor (DRUM) sampler and analyzed for concentrations of 28 elements measured via X-ray fluorescence (XRF). Positive matrix factorization (PMF) was performed separately on the coarse, fine, and ultrafine size ranges to determine possible sources and their contributions to the total elemental particulate matter mass. The PMF analysis resolved six sources across the three size ranges: biomass burning, oil combustion, soil dust, a crustal–marine mixed source, sea spray, and fly ash. Additionally, size distribution plots, time series plots, back trajectories and satellite data were used in interpreting factors. The multi-technique source apportionment revealed the presence of biogenic sources such as soil dust, sea spray, and a crustal–marine mixed source. Anthropogenic sources were also identified: biomass burning, oil combustion, and fly ash. Mass size distributions showed elevated aerosol concentrations towards the end of the sampling period, which coincided with a shift of air mass back trajectories to southern Kalimantan. Covariance between coarse-mode soil dust and fine-mode biomass burning aerosols were observed. Agreement between the PMF and the linear regression analyses indicates that the PMF solution is robust. While biomass burning is indeed a key source of aerosol, this study shows the presence of other important sources in the SCS. Identifying these sources is not only key for characterizing the chemical profile of the SCS but, by improving our picture of aerosol sources in the region, also a step forward in developing our understanding of aerosol–meteorology feedbacks in this complex environment.

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.