Narrow Diameter Distribution Research Articles

Large-Scale Preparation of Carboxylated Cellulose Nanocrystals and Their Application for Stabilizing Pickering Emulsions.

Cellulose nanocrystals (CNCs) with varied unique properties have been widely used in emulsions, nanocomposites, and membranes. However, conventional CNCs for industrial use were usually prepared through acid hydrolysis or heat-controlled methods with sulfuric acid. This most commonly used acid method generally suffers from low yields, poor thermal stability, and potential environmental pollution. Herein, we developed a high-efficiency and large-scale preparation strategy to produce carboxylated cellulose nanocrystals (Car-CNCs) via carboxymethylation-enhanced ammonium persulfate (APS) oxidation. After carboxymethylation, the wood fibers could form unique "balloon-like" structures with abundant exposed hydroxy groups, which facilitated exfoliating fibril bundles into individual nanocrystals during the APS oxidation process. The production process under controlled temperature, time period, and APS concentrations was optimized and the resultant Car-CNCs exhibited a typical structure with narrow diameter distributions. In particular, the final Car-CNCs exhibited excellent thermal stability (≈346.6 °C) and reached a maximum yield of 60.6%, superior to that of sulfated cellulose nanocrystals (Sul-CNCs) prepared by conventional acid hydrolysis. More importantly, compared to the common APS oxidation, our two-step collaborative process shortened the oxidation time from more than 16 h to only 30 min. Therefore, our high-efficiency method may pave the way for the up-scaled production of carboxylated nanocrystals. More importantly, Car-CNCs show potential for stabilizing Pickering emulsions that can withstand changeable environments, including heating, storage, and centrifugation, which is better than the conventional Sul-CNC-based emulsions.

Growth of high-density single-wall carbon nanotubes with a uniform structure using a CoRu catalyst

The inefficient production of structurally uniform single-wall carbon nanotubes (SWCNTs) is an obstacle to their practical use in high-performance electronic devices. We have synthesized SWCNTs with a narrow diameter distribution (1.35 ± 0.25 nm) using a CoRu catalyst. Monodispersed nanoparticles with a narrow size distribution (2.4 ± 0.6 nm) and different compositions were prepared and used as catalysts for SWCNT growth. A furnace with an 80 cm-long uniform temperature zone (±10 °C) was designed and used to study the effect of catalyst composition on the growth of SWCNTs under the same conditions. By optimizing the composition of the bimetallic CoRu catalyst, SWCNTs with a uniform structure were efficiently synthesized. In addition, the effect of the growth conditions of temperature and carbon feed rate was investigated, and it was found that with an increase in yield, the structural uniformity of SWCNTs usually became worse. Both catalysts with elements in the suitable proportions and appropriate growth conditions are critical to achieving the high-efficiency structure-controlled growth of SWCNTs.

The improvement of yield and thermal stability of single-walled carbon nanotubes fabricated by Gd-assisted FCCVD

In this work, single-walled carbon nanotubes (SWNTs) were synthesized by a scalable floating catalyst chemical vapor deposition (FCCVD) method, in which Gd was used as growth promotor to improve the yield and quality of SWNTs. Based on the characterization results of electron microscope, thermogravimetric analysis and Raman spectroscopy, the application of Gd leads to a great increase in the production of large-diameter SWNTs with a narrow diameter distribution and an enhanced thermal stability. The newly developed FCCVD technique makes it possible to produce large-diameter SWNTs at a low cost, and the generated structurally homogenous SWNTs are suitable for their applications in the fields of electronic systems and electromagnetic shielding, etc.

Comparison of Physical Properties and Degradation of Polylactic Acid and Polypropylene Facemask Layer

The current 3-ply facemasks are produced mostly using polypropylene (PP) as the main plastic layer that is a non-biodegradable polymer. The objective of this study was to fabricate a polylactic acid (PLA) layer, a biodegradable polymer, using the electrospinning process. Comparison on the degradation trend of PLA layer and PP layer obtained from commercial 3-ply face mask (CFM) layer in seawater, river water, soil, and compost environment for a total of 60 days was observed. Results showed that the electrospinning method can produce PLA layers with similar thickness with current CFM layer, narrow distribution of fiber diameter, and slightly dense surface morphology comparable to the CFM. Synthesized PLA fiber layer shows 68.6%, 39.8%, and 415.7% improvement in tensile strength, Young’s modulus, and elongation at break, respectively, compared to CFM samples. Meanwhile, for the degradation study, PLA samples show more significant changes on its morphology corresponding to the degradation process that occurred on its fibers in the seawater, river water, and soil environment, whereas for the weight change study, only the soil environment shows significant changes after 45 days. In contrast, CFM samples did not show any significant changes corresponding to degradation activity.

High thermal conductivity, good electrical insulation, and excellent flexibility of FGN/PVA films based on a large sheet and narrow diameter distribution of fluorographene

Electronic components urgently need high thermal conductivity materials with good mechanical and insulation properties. Monolayer fluorographene nanosheets (FGN) were obtained by a mild exfoliation method using the low-cost and small sheets fluorographene. FGN/polyvinyl alcohol (PVA) composite films prepared by FGN (1.5–2.5 μm) had higher in-plain thermal conductive (21.6 W/(m·K)) and tensile strength (23.7 MPa) than these with small sheet and/or ungraded FGN. The ductility of FGN with large sheets made it a horizontally directional arrangement during filtration, and then the thin and uniform sheets were packed tightly and orderly along the vertical direction of the films structure. PVA connected adjacent FGN in the horizontal direction of the composite films by a hydrogen bond, and penetrates into the middle of the lamella, effectively reducing the high heat resistance from air gap and providing a continuous transmission of phonons in a horizontal direction. At the same time, the thermal conductivity and electrical insulation of the FGN/PVA composite films were increased due to the hydrogen bond and PVA penetrates. It provides an effective way to obtain low-cost films with high thermal conductivity, excellent flexibility, and good electrical insulation.

Coprecipitation Synthesis of Large-Pore-Volume γ-Alumina Nanofibers by Two Serial Membrane Dispersion Microreactors with a Circulating Continuous Phase

A coprecipitation method was developed for the synthesis of fibrous γ-alumina using serial membrane dispersion microreactors with a circulating continuous phase and high concentrations of NaAlO2 and Al2(SO4)3 as reactants. Owing to the ultra-high mixing intensity and reduction of supersaturation due to the large circular phase ratio, a large pore volume and specific surface area and an extremely narrow pore diameter distribution were realized using the high-concentration and high-viscosity precipitation system. The influence of the phase ratio, dispersion order of reactants, Al2(SO4)3 residence time, and the precipitation reaction pH and time were investigated, and the nanofiber formation mechanism was explored employing theoretical calculations. By controlling the Al2(SO4)3 residence time of 3 s, phase ratio of 16, and pH of 8.0, γ-Al2O3 nanofibers with a pore volume of 1.36 cm3/g, a specific surface area of 376 m2/g, and a length/diameter ratio in the range of 30–54 were obtained without any organic reagents. This study provides an economical and readily scalable method for the synthesis of fibrous γ-Al2O3 with excellent pore properties and a large specific surface area, which can potentially be applied as an excellent catalyst support for diesel and bio-oil hydrogenation.

Honey and propolis for wound healing

Background: Wound healing has global healthcare concept where fighting infection, rapid cure, correct epithelization with minimal scar formation and feasible potent wound dressing management is targeted through recent researches with natural products. There is a renaissance in apitherapy wound dressing especially those related to honey and propolis. The review acted with the activity of these api-products on wound healing as antimicrobial, immunomodulator, antioxidant and anti-inflammatory agents referring to some mechanism of action. Recent api-products nanofabrication wound dressings have advantages of easy applicable potent with different api-products activities and short treatment regimen especially those polymeric networks. Moreover, maintaining wound moisture suitable for fast re-epithelialization. Rather than, small diameter, high porosity, narrow diameter distribution, gas permeation.

Characteristic comparison of lignocellulose nanofibrils from wheat straw having different mechanical pretreatments

AbstractWheat straw (WS) was considered the most abundant agricultural residue in China. Therefore, it was meaningful to explore the effective utilization of WS. Thus far, WS has been considered a potential raw material to produce lignocellulose nanofibrils (LCNFs) with the rapid development of nanotechnology. Unfortunately, the existing methods of LCNFs preparation directly from WS still faced some hurdles. Herein, screw extrusion and ball milling considered the common mechanical pretreatments were employed to directly prepare LCNFs from WS. The different impacts of screw extrusion and ball milling pretreatments on the properties of LCNFs were revealed by systematically comparing physicochemical analyses. The results showed that the crystalline and chemical structure of samples was little affected by the mechanical pretreatment. However, the mechanical pretreatment caused a change in the morphology, yield, and chemical composition of LCNFs. LCNFs prepared by screw extrusion with a high yield of 73% had the narrowest diameter distribution (0 ~ 80 nm), the most cellulose content (51.1%), and the maximum crystallinity degree (44.7%). LCNF samples all exhibited good thermal stability. This work could not only offer theoretical guidance on the preparation of LCNFs by mechanical pretreatments but also expand the high‐value application of WS in polymer composites.

Preparation of isolated semiconducting single-wall carbon nanotubes by oxygen-assisted floating catalyst chemical vapor deposition

Semiconducting single-wall carbon nanotubes (s-SWCNTs) are promising for use in flexible electronics as a channel material. However, it remains a big challenge to directly grow high purity, high-quality s-SWCNTs in large scale. Here we report the synthesis of isolated s-SWCNTs by an oxygen-assisted floating catalyst chemical vapor deposition method. By controlling the density of nucleated SWCNTs, isolated or small-bundled, rather than large-bundled SWCNTs were generated in a floating state, so that the oxygen introduced could more efficiently selectively etch the metallic-SWCNTs formed. In addition, it was found that the oxygen also functions in limiting the size of Fe catalyst nanoparticles in a narrow range of 5–8 nm. As a result, isolated s-SWCNTs with a narrow diameter distribution were synthesized. The content of s-SWCNTs reached ∼96%, and the percentage of isolated tubes was estimated to be ∼83%. Thin-film transistors (TFTs) constructed using the s-SWCNT film showed high on/off ratios ranging from 2.1 × 104 to 1.2 × 106, verifying the effective enrichment of s-SWCNTs.

Formation of disaggregated polymer microspheres by a novel method combining pulsed voltage electrospray and wet phase inversion techniques

Polymer microspheres with controlled sizes have attracted interest due to their potential use in medical field. Therefore it is of great importance to be able to produce a large number of disaggregated microspheres with a narrow diameter distribution. This work describes the successful elaboration of the method combining electrospray and wet phase inversion for the manufacturing of such polymer microspheres with mean diameters of 2 – 15 µm. Their recovery and drying are easy and they can be directly applied afterwards. The method is universal enough to produce microspheres from various polymers (polycaprolactone, polyethersulfone) and different solvents (dimethylformamide, N-methylpyrrolidone). It was noticed on the basis of microscopic images and using the nitrogen adsorption–desorption method that the specific surface of the microspheres differs depending on the polymer and solvent used. The work introduces additional parameters resulting from the use of pulsed voltage in the electrospray (pulse frequency f and duration τ) which results in better process control. As an example of the use of microspheres as drug carriers, they were loaded with rhodamine and its release was tested. Such microspheres could be dispersed in polymer solution and used in extrusion-based techniques (electrospinning, 3D printing) to form novel complex drug delivery systems.

Facile preparation of lignin-containing cellulose nanofibrils from sugarcane bagasse by mild soda-oxygen pulping

Lignin-containing cellulose nanofibrils (LCNFs) with tunable lignin contents from sugarcane bagasse were directly prepared by low-temperature soda‑oxygen pulping combined with simple mechanical treatment. The residual lignin structure, morphology and physical dimensions of LCNFs, and properties of the relevant cellulose nanopapers (CNPs) were investigated. In situ 2D Heteronuclear Single Quantum Coherence (HSQC) NMR spectra showed β–O–4 linkages, ferulate, and para-coumarate were well preserved in the LCNFs. Compared with the cellulose nanofibrils (CNFs), LCNFs displayed a more uniform size and narrow diameter distribution. The corresponding CNPs exhibited outstanding mechanical properties (tensile strength reached 152.9 MPa), and excellent combined optical properties both in the UV blocking and visible light transparency. Moreover, the water contact angles (50.0–80.2°) of LCNFs were much higher than that of CNFs (21.7°). Direct preparation of LCNFs under mild condition would unlock the full potential of cellulosic materials and provide enhanced opportunities for cellulose to fabricate multi-functional and high-value materials.

Selective extraction of synthetic cathinones new psychoactive substances from wastewater, urine and cocktail using dummy molecularly imprinted polymers

Dummy molecularly imprinted polymers (DMIPs) for selective extraction of five common synthetic cathinones (SCs) were prepared by bulk polymerization. DMIPs materials possessed narrow diameter distribution (30–60 µm) and large specific surface area (329.6 m2 g-1). Imprinting factors for cathinone, methcathinone, mephedrone, methylone and ethylone were 1.11–1.82. DMIPs could also quickly adsorb SCs from aqueous solutions within 5 min. Therefore, the materials were used as solid-phase extraction (SPE) sorbents to selectively extract five SCs in complex samples. An accurate and sensitive analytical method based on DMIPs-SPE combined with HPLC-MS/MS was established. Under optimal conditions, the established method showed low limits of detection (0.002–0.1 ng mL-1), satisfactory recoveries (84.1–97.7%) and good repeatability (relative standard deviation (RSD) below 9%). The method was successfully verified using wastewater, urine and cocktail samples. Recoveries of SCs at three spiking levels were in the range of 75.1–98.6%, with RSD values below 7.0%. Compared with commercial sorbents, DMIPs showed better clean-up ability with matrix effect values of −24.1%–8.3% for all SCs in wastewater, urine and cocktail samples. Therefore, the developed DMIPs-SPE-HPLC-MS/MS strategy could be used as a specific and cost-effective method for sensitive determination of SCs in complex samples.

Size effect of PdC nanoparticles synthesized by S-containing silane coupling agents on semi-hydrogenation of acetylene

S-containing silane coupling agents (SCA) with various structures were chosen as regulators to synthesize PdC nanoparticles in different sizes for semi-hydrogenation of acetylene. Characterization and catalytic performance demonstrate that the catalytic property of PdC is deeply influenced by particle size. PdC particles prepared by employing SCA containing sulfhydryl has a smaller size and narrow diameter distribution. They exhibited better inhibition on ethane formation than those by containing thioether bond. Catalysts with larger PdC particles have lower selectivity to C4 and green oil. Reaction paths on typical (111) surface of PdC nanoparticles with different dimensions were investigated by DFT calculations. It reveals that within a certain particle size range (∼2.6 nm), surfaces of smaller PdC particles have weaker adsorption strength of ethylene. As particle size exceeds 2.6 nm, the adsorption strength no longer increases. C4 and green oil are more likely to be generated when PdC particles are around 2 nm, and the size smaller or larger than 2 nm will weaken the tendency of C4 and green oil formation.

Thermal-assisted synthesis of gold nanoparticles using aqueous extract of Helicteres isora L. fruit: Characterization and antioxidant activity

A quick and one-pot method for the green synthesis of gold nanoparticles (AuNPs) using small amounts of aqueous extract of Helicteres isora L. fruit has been developed. The results showed that by increasing the reaction temperature from ambient to 95 °C, the time required to synthesize AuNPs was reduced significantly. The SEM image clearly showed the formation of spherical AuNPs with narrow diameter distributions in the range of 6–25 nm. AuNPs exhibited excellent free radical scavenging activity (IC50 = 4.98 ± 0.03 µg mL−1) in a short time due to their large surface area.

Thermal and mechanical characterization of complex electrospun systems based on polycaprolactone and gelatin

Nowadays, continuous development of soft-electronics and wearable devices opens to the development needs of stretchable and flexible materials able to interface with the human body. In this scenario, biopolymers are particularly intriguing materials given their biocompatibility and biodegradability. For the application in this specific field the material requires several properties such as biological and mechanical performance and thermal stability. In this study, membranes able to fulfill some of these requirements are described. The electrospun membranes, composed of a blend of polycaprolactone (PCL) and gelatin (GN), have been produced in various configurations. The results show how blend or coaxial systems have different effects on both the interactions between the polymers and their thermal and mechanical properties. An important result of the chosen experimental conditions is the narrow dimensional distribution of the nanofiber diameters constituting the electrospun membranes. Thermal and mechanical tests evidenced that, by properly choosing the material composition and the method of the electrospinning process, membranes capable of withstanding high strain values before the failure can be obtained. In particular, optimizing the electrospinning process and using a blend PCL/GN with a mass ratio of 80/20, it is possible to increase the thermal stability up to 310 °C and confer to the sample the ability to reach a percentage of strain up to 350%.

Improved hybrid-shelled perfluorocarbon microdroplets as ultrasound- and laser-activated phase-change platform

HypothesisWe propose significant improvements to perfluorocarbon microdroplets, conferring them colloidal stability, chemical versatility, and size control. Decafluoropentane cores are stabilized by biocompatible interfaces – either a monolayer of the cationic surfactant dimethyldioctadecylammonium bromide (DDAB) or a double shell obtained by adding crosslinked dextran methacrylate as further coating – and functionalised with gold nanoparticles. We hypothesize that this formulation enables dual, acoustic (ADV) and optical (ODV) vaporisation of microdroplets into microbubbles, yielding a versatile “phase-change” theranostic platform. ExperimentsMicrodroplets synthesis is optimized by high-speed homogenization methodology. Functionalisation with gold nanoparticles is achieved by electrostatic decoration. The colloidal suspension is characterised by the concerted use of dynamic light scattering, electrophoresis, and confocal microscopy, to assess microdroplets’ stability. Additional structural details are provided by small-angle X-ray scattering. We analysed the ultrasound- and laser-stimulated transition into microbubbles and characterised their response to ultrasound by acoustic spectroscopy. FindingsHybrid-shelled microdroplets were produced at high density, with narrow diameter distribution (~1 µm). The highly charged surface and the long hydrocarbon tails of DDAB protruding within the core provide high stability. The elastomeric dextran layer at the water interface allows obtaining stable cavitating microbubbles by ADV exhibiting interesting viscoelastic features. The presence of gold nanoparticles unlocks the opto-thermal microdroplet vaporisation.

Laser switching characteristics of enriched (7,5) single-walled carbon nanotubes at 640 nm

Single-walled carbon nanotubes (SWCNTs) with a narrow diameter or chirality distribution have great potential in promoting carbon nanophotonics and nanoelectronics. In this paper, SWCNTs with dominant (7,5) species, which are fabricated by chemical vapor deposition method from a magnesia-supported Co catalyst, are applied for the nonlinear optical measurements. The SWCNTs exhibit efficient saturable absorption properties at a wavelength of 640 nm in terms of a modulation depth of 27.7% and a saturable intensity of 5.7 GW/cm2. Such a 640 nm absorption is correlated with the S22 absorbance bands of the semiconducting SWCNTs. Consequently, by employing the SWCNTs as a saturable absorber (SA), stable Q-switched pulses with the shortest pulse width of 200 ns and maximum pulse repetition rate of 238 kHz are achieved at 640 nm. Our findings indicate that subnanometer semiconducting SWCNT could act as an excellent optical switcher device at 640 nm, which may help to explore potential applications in visible nonlinear optics.

Development of highly photoluminescent electrospun nanofibers for dual-mode secure authentication

The photochromic phenomenon has been recently used as a fascinating technology in the development of highly efficient anti-counterfeiting materials with dual-mode security encoding of concurrent photochromism and fluorescence emission. Herein, we successfully developed lanthanide-doped aluminate nanoparticles (LAN)/polystyrene (PS) electrospun nanofibers as novel secure authentication films. Different ratios of lanthanide-doped aluminate nanoparticles were mixed with polystyrene-based copolymer solutions in N,N -dimethylformamide (DMF) and subjected to electrospinning to afford photochromic and fluorescent nanofibers. The generated electrospun nanofibers demonstrated a narrow diameter distribution, a smooth surface and well-defined morphological properties. The produced smart nanofibers were applied onto cellulose paper sheets to demonstrate a dual-mode secure strategy with a simple and rapid authentication. LAN was prepared in the nano-scale for better dispersion in PS, which guarantee the formation of transparent films. LAN was studied by transmission electron microscope (TEM) and X-ray diffraction (XRD). LAN displayed diameters of 5–12 nm. On the other hand, the fibrous diameters of LAN-PS samples were studied by scanning electron microscopy (SEM) to indicate diameters of 200–300 nm. The induced security marking was invisible (363 nm) under visible daylight turning into visible green (520 nm) color under ultraviolet irradiation demonstrating a bathochromic shift. Both excitation and emission displayed high intensities. The security marking was fully reversible under ultraviolet/visible irradiation cycles without fatigue. Those advantageous properties could be attributed to the high surface area of the chromogenic nanofibrous films to result in high absorption of light leading to strong optical dual-mode photo-responsiveness. The generated LAN-PS hybrid films showed improved hydrophobic properties with increasing LAN. The nanofibers showed transparency, stretchability and flexibility. The present strategy can be reported as an efficient technology to develop many anti-counterfeiting products toward a better market with social and economic values to avoid fake products.

Kinetics-Controlled Growth of Metallic Single-Wall Carbon Nanotubes from CoRex Nanoparticles.

The controlled growth of metallic single-wall carbon nanotubes (m-SWCNTs) is very important for the fabrication of high-performance interconnecting wires, transparent conductive electrodes, light and conductive fibers, etc. However, it has been extremely difficult to synthesize m-SWCNTs due to their lower abundance and higher chemical reactivity than semiconducting SWCNTs (s-SWCNTs). Here, we report the kinetically controlled growth of m-SWCNTs by manipulating their binding energy with the catalyst and promoting their growth rate. We prepared CoRe4 nanoparticles with a hexagonal close-packed structure and an average size of ∼2.3 nm, which have a lower binding energy with m-SWCNTs than with s-SWCNTs. The selective growth of m-SWCNTs from the CoRe4 catalyst was achieved by using a low concentration of carbon source feed at a relative low temperature of 760 °C. The m-SWCNTs had a narrow diameter distribution of 1.1 ± 0.3 nm, and their content was over 80%.

Testing of photocatalytic potential of silver nanoparticles produced through nonthermal plasma reduction reaction and stabilized with saccharides

In this study, silver nanoparticles (AgNPs) were produced through an atmospheric pressure plasma reduction reaction and tested for photodegradation of methyl blue (MB) under sunlight exposure. The argon plasma born reactive species were used to reduce silver ions to AgNPs in the solution. Glucose, fructose and sucrose were also added in the solution to stabilize the growth process. The glucose stabilized reaction produced the smallest nanoparticles of 12 nm, while sucrose stabilized reaction produced relatively larger nanoparticles (14 nm). The nanoparticles exhibited rough morphology and narrow diameter distribution regardless of stabilizer type. The narrow diameter distribution and small band gap helped activating majority of nanoparticles at a single wavelength of light spectrum. The band gap energy of AgNPs varied from 2.22 eV to 2.41 eV, depending on the saccharide type. The photoluminescence spectroscopy of AgNPs produced emission peaks at 413 nm, 415 nm, and 418 nm. The photocatalytic potential of AgNP samples was checked by degrading MB dye under sunlight. The degradation reaction reached a saturation level of 98% after 60 min of light exposure.