Smaller Average Particle Size Research Articles

Synthesis and structural characteristics of Co1-xCuxFe2O4 magnetic ferrite nanoparticles using hydrothermal technique

In this work, copper substituted cobalt ferrite nanoparticles withchemical formula Co1-xCuxFe2O4 (x=0, 0.3, and 0.7), has beensynthesized via hydrothermal preparation method. The structure ofthe prepared materials was characterized by X-ray diffraction (XRD).The (XRD) patterns showed single phase spinel ferrite structure.Average crystallite size (D), lattice constant (a), and crystal density(dx) have been calculated from the most intense peak (311).Comparative standardization also performed using smaller averageparticle size (D) on the XRD patterns of as-prepared ferrite samplesin order to select most convenient hydrothermal synthesis conditionsto get ferrite materials with smallest average particle size.

Selection of Polyanions as Complexation Agent in the Formation of Nanochitosan by Polyelectrolyte Complex Method

The aqueous dispersion of nanochitosan was prepared by polyelectrolyte complex (PEC) method with various mixing ratios of chitosan and polyanions, i.e., chitosan-glucomannan, chitosan-hyaluronic acid, and chitosan-Arabic gum. The formation of nanochitosan was carried out by adding the polyanion solution dropwise into the acid solution of chitosan. The study aimed to determine the best polyanion among the variations tested in this study, concerning the targeted particle size and the stability of the dispersion over time. Particle size distribution was observed by Particle Size Analyzer (PSA). The result indicated that Arabic gum gave the smallest average particle size, i.e. 192.5 nm, at a chitosan/polyanion mass ratio of 3:1 and pH value of 4.

Synthesis and Characterization of Titanium Dioxide Nanoparticles for Application in Enhanced Oil Recovery

In this study, titanium dioxide nanoparticles were synthesized for possible application in enhanced oil recovery. Sol-gel method was employed with titanium (IV) isopropoxide as the precursor. The prepared materials were characterized using Powder X-Ray Diffraction (XRD), Field Emission Scanning Electron Microscopy (FESEM), High-Resolution Transmission electron microscopy (HRTEM) and Brunauer–Emmet–Teller (BET) techniques. Reaction parameter such as calcination temperature was varied during the preparation to obtain the uniform TiO2 nanoparticles with the smallest particle size and high surface area. The results of study revealed that 400 °C is the optimum calcination temperature in preparing TiO2 nanoparticles producing the smallest crystallite and particle sizes. XRD results indicated that the nanoparticles have formed anatase phase at 400 °C and achieved low crystallite size of 7.27 nm with the smallest average particle size of 19.53 nm through FESEM and HRTEM observations. BET analysis had achieved the highest surface area 103.64 m2/g.

Study on the Shear Band of Sand with Various Particle Characteristics Using PIV Analysis

The phenomenon of ground undergoing large plastic deformation, leading to collapse, occurs due to the localization of unstable deformation. The investigation of shear band is important in order to understand the destructive phenomenon. Therefore, a series of experiments were conducted on sands with different particle characteristics so that behaviour of the shear band of sand under plane strain compression could be investigated. Specifically, Toyoura sand and two kinds of coral sand, hereafter referred to as coral sand A (with smaller average particle size) and coral sand B (with larger average particle size) were used. The shear band was evaluated using PIV (Partial Image Velocimetry) analysis. As a result, it became clear that the relationship between shear inclination angle and internal friction angle does not hold for the two kinds of coral sand because the shear inclination angle is low. The ratio of the average value of the shear band width to the average grain size at the peak was 10 to 20 times, 7 to 10 times, and 5 to 8 times in the order of Toyoura sand, coral sand A, and coral sand B. The sample standard deviation was 0.1 to 0.9 mm, 0.9 to 1.6 mm, and 1.4 to 1.9 mm.

Investigation of electrophysical properties of nanomodified fireproof EVA polymer compositions

The object of research is the electrophysical properties of fireproof composite materials of ethylene with vinyl acetate, which include filler-flame retardants and modifiers. One of the biggest problems is the change in the electrophysical properties of fireproof composite materials, depending on the chemical properties and dispersion of fillers, fire retardants and modifiers. In order to solve this problem, the dependence of electric strength, specific volume electrical resistance, permittivity and tangent of dielectric loss angle on the number of modifiers and properties of ingredients of polymer compositions is investigated. A copolymer of ethylene with vinyl acetate is used as well as methods for determining the electrical strength, electrical bulk resistance, dielectric loss tangent, permittivity. The results show that the dielectric strength significantly increases to 32-35 kV/mm in the case of use as fillers-flame retardants of aluminum oxide trihydrate with a smaller average particle diameter of the EVA-1-based polymer matrix and modifier 1. When using the EVA-2-based polymer matrix, high rates (41 kV/mm) obtained for compositions with hydromagnesite and modifier 2. The specific volume electrical resistance varies little for modified polymer compositions using magnesium oxide dihydrate with a smaller average particle size and modifier 2, as well as for the EVA-1 and EVA-2 polymer matrices. After exposure to moisture, the specific volume electrical resistance has a maximum value of 1.2∙10 13 Ohm ∙ cm for the EVA-1-based polymer composition, a flame retardant – aluminum oxide trihydrate and modifier 1. The permittivity and dielectric loss tangent have the best performance for EVA-1-based polymer compositions, hydromagnesite and modifier 2 ( e=3.3; tg =6∙10 -3 ). This makes it possible to increase the electrical properties of fireproof compositions for the manufacture of insulation and cable sheaths compared with similar known materials, this reduces material consumption by reducing thickness and makes it possible to increase the economic efficiency of production of fire-resistant cables.

Characterizations of Ag Nanoparticles Prepared by Different Reducing Agents

Pure Ag nanoparticles were successfully prepared by using KBH4 , ascorbic acid, and holly leaf extract as reducing agents. The prepared Ag nanoparticles were characterized by various techniques to understand their chemical and physical properties. All the Ag nanoparticles showed granular particle morphology with a nano-scale size of 16.1- 29.2 nm and three visible photoluminescence peaks. By comparison, KBH4 showed sufficient high reducing ability and so resulted in a rapid formation of Ag nanoparticles, largest average particle size, and highest crystallinity. In contrary, holly leaf extract leads to the slowest formation of Ag nanoparticles, smallest average particle size, and lowest crystallinity. The Ag nanoparticles prepared with the KBH4 and holly leaf extract showed the highest and lowest photocatalytic activities, respectively. The crystallinity plays a more important role in photocatalytic activity rather than average particle size. Moreover, some hydroxyls existed on the surface of the Ag nanoparticles exists, indicating a good surface hydrophilicity. Small amounts of the impurities coming from the reducing agent residues acting as a capping layer were found on the surface of the Ag nanoparticles.

Eco-friendly synthesis and characterizations of single-wall carbon nanotubes/Ag nanopaticle hybrids for environmental decontamination

Single-wall carbon nanotubes (CNTs) functionalized by various molecules and semiconductors have provided a unique class of tunable chemistries for a variety of application. This work functionalized the CNTs with Ag nanoparticles that were in situ synthesized by using holly leaf extract as a reduction agent to achieve a photocatalyst with high photocatalytic activity. The hybrids were characterized by various techniques to understand their chemical and physical properties. The Ag nanoparticles were successfully formed and well coupled on the CNTs surface. The holly leaf extract with low reduction ability leads to a slow formation of Ag nanoparticles and so small average particle size. The formed Ag nanoparticles showed granular particle morphology with a nano-scale size of ∼7–20.3 nm. Lower Ag+ concentration in the precursor solution for the hybrid with lower Ag content leads to smaller average particle size. The two photoluminescence peaks weakened with increasing Ag content, originating from the increase in average particle size. Moreover, hydroxyls existed on the surface of the hybrids exists, indicating a good surface hydrophilicity. Ag showed a efficient sensitization, making the hybrids exhibited a better photocatalytic activity than pure CNTs. Appropriate low Ag content of 5 wt% resulted in the highest activity. The Ag sensitization also enhanced the reductive photocatalysis of CNTs, resulting in further degradation of phenyl in the intermediates.

Preparation of an activated carbon from hazelnut shells and its hybrids with magnetic NiFe2O4 nanoparticles

A low cost activated carbon was prepared from hazelnut shells by chemical activation with sodium hydroxide at 600 °C in a N2 atmosphere and then combined with magnetic NiFe2O4 nanoparticles by hydrothermal and co-precipitation methods. Samples were characterized by FESEM, TEM, XRD, FT-IR, nitrogen adsorption and magnetic measurements. Results indicated that the NiFe2O4 nanoparticles synthesized by the hydrothermal method had a higher saturation magnetization and smaller average particle size than those produced by the co-precipitation method. The specific surface area and total pore volume of the activated carbon decreased from 314 to 288 m2/g and 0.3639 to 0.3338 cm3/g, respectively by forming a hybrid with the magnetic NiFe2O4 nanoparticles synthesized by the hydrothermal method. NiFe2O4 nanoparticles were mainly distributed on the surface, although a few were inside the pores of the activated carbon. Their sizes were the same as those of the original ones. The saturation magnetization of the hybrids was lower than those of the original NiFe2O4 nanoparticles due to the existence of the activated carbon. They showed superparamagnetic behavior at room temperature and were easily separated from solutions by an external magnet.

Efficient hydrogen evolution catalytic activity of graphene/metallic MoS2 nanosheet heterostructures synthesized by a one-step hydrothermal process

Metallic (1T)-transition metal dichalcogenides is of excellent optical and electrical properties and so especially suitable for various applications including hydrogen evolution catalysis, electronics, and photoelectrons. To date, achieving 1T-MoS2 nanosheets with a simple chemical process still is a challenge. Here we report a hydrothermal synthesis of the 1T-MoS2 nanosheets by incorporating reduced graphene oxide (RGO) or using citric acid/slow successive heating. A small amount of RGO induced the formation of pure 1T-MoS2 nanosheets. Citric acid/slow successive heating induced the formation of 1T-MoS2 nanosheets with a small amount of 2HMoS2. Citric acid/slow successive heating also resulted in smaller average particle size in the present of RGO. Synthesized 1T-MoS2 nanosheets and RGO/1T-MoS2 nanosheet hybrids showed remarkably enhanced conduction and wettability compared with their semiconductor (2H)-nanostructures. Thus, dramatically enhanced hydrogen evolution catalytic activity and stability compared with the 2H-nanostructures were observed. RGO/1T-MoS2 nanosheet hybrids synthesized by incorporating graphene oxide and using citric acid/slow successive heating exhibited greatest photocatalytic activity (71.2 mmol./g·h) and electrocatalytic activity (onset potential of −15 mV vs. reversible hydrogen electrode and Tafel slopes of 43 mV/decade). These facile processes might also be significant for the synthesis and application of other 1T-transition metal dichalcogenides nanosheets and their hybrids with RGO.

Hydrocracking of vacuum gas oil over NiMo/zeolite-Al2O3: Influence of zeolite properties

Hydrocracking of vacuum gas oil has been studied over NiMo/zeolite-Al2O3 catalysts. Three different zeolites have been used for catalysts preparation: zeolites Beta (BEA) and Y (FAU) having small crystal size and zeolite Y modified by recrystallization (RFAU). HRTEM, low-temperature N2 adsorption, FTIR of adsorbed CO and TPD-NH3 showed that zeolites had different crystal sizes, mesopore volume, strength and concentration of acid sites. Sulfide active component particles have been revealed to be similar in all catalysts by HRTEM and XPS. NiMo/BEA catalyst having zeolite with the smallest average particle size and the highest concentration of Brønsted acid sites (BAS) demonstrated the highest hydrocracking activity. Selectivity to middle distillates decreased in the following order: NiMo/FAU > NiMo/RFAU > NiMo/BEA. This effect is accounted for by optimal zeolite acidity and improved availability of the acid sites for bulky molecules of the heavy feedstock.

Effect of Reducing Agent on Preparation and Electroactivity of MnO₂/Graphene Composite Electrode for Capacitors.

Supercapacitor electrodes materials with improved electrochemical properties were prepared by synthesizing manganese dioxide (MnO2) in an aqueous solution of graphene having a wide specific surface area and high electrical conductivity. MnO2/graphene composites were synthesized by reducing potassium permanganate with three kinds of reducing agent (ethanol, ethylene glycol, DMF). TEM-image confirmed that the MnO2/graphene composite which was reduced by ethanol had a small average particle size. Electrochemical properties were characterized by cyclic voltammetry (CV) and galvanostatic charge-discharge test in 1 M Na2SO4 aqueous electrolyte solution. The MnO2/graphene composite reduced by ethanol showed higher specific capacitance than the MnO2/graphene composite reduced by ethylene glycol or DMF. It was concluded that the manganese dioxide reduced by ethanol having a small average particle size, resulting in a large specific surface area and low impedance characteristics.

Gambogic Acid-Loaded Polymeric Micelles for Improved Therapeutic Effect in Breast Cancer.

Gambogic acid (GA) possesses good anti-tumor efficacy in preclinical studies, however, its poor hydrophilicity, short blood circulation time and side effect limited its clinical application. In this work, monomethyl poly(ethylene glycol)-poly(ε-caprolactone) (MPEG-PCL) copolymer was synthesized and used to encapsulate GA by a facile one-step solid dispersion and form nano-sized micelles (GA micelles). The GA micelles exhibited small average particle size (29±2 nm), high encapsulation efficiency (92.1±0.3%), and long drug release time-in vitro. Compared to free GA, GA micelles showed superior aqueous dispersity, better tumor cellular uptake, enhanced cytotoxicity and apoptosis induction effect against MCF-7 cells. Furthermore, in vivo studies demonstrated that GA micelles have better antitumor effect in the MCF-7 subcutaneous xenograft tumor model. Histopathological analysis of Ki-67 and TUNEL staining further proved that GA micelles could significantly suppress proliferation as well as increase the apoptosis of tumor cells. These results suggested that GA micelles could potentially improve therapeutic outcomes for breast cancer therapy.

Effects of drying methods on quality of fermented plant extract powder

ABSTRACTFermented plant extract (FPE) is a kind of plant functional food fermented by various microorganisms to make a beverage or other physical forms. To provide technical support for the industrial production of fermented plant extract powder, the quality characteristics of fermented plant extract powder prepared by hot air-drying, spray drying, vacuum microwave drying, and freeze-drying are compared for an FPE product. The effects of maltodextrin, soluble starch, and β-cyclodextrin as a drying agent on drying effect were studied. Results show that spray-dried FPE powder has the highest bulk density, the smallest average particle size, while the FPE powder produced by freeze-drying has the best color and flavor, the highest content of key components including total sugar, soluble protein, vitamin C, total polyphenol content, and highest antioxidant capacity.

Pilot-scale formation of whey protein aggregates determine the stability of heat-treated whey protein solutions—Effect of pH and protein concentration

Denaturation and consequent aggregation in whey protein solutions is critical to product functionality during processing. Solutions of whey protein isolate (WPI) prepared at 1, 4, 8, and 12% (wt/wt) and pH 6.2, 6.7, or 7.2 were subjected to heat treatment (85°C × 30 s) using a pilot-scale heat exchanger. The effects of heat treatment on whey protein denaturation and aggregation were determined by chromatography, particle size, turbidity, and rheological analyses. The influence of pH and WPI concentration during heat treatment on the thermal stability of the resulting dispersions was also investigated. Whey protein isolate solutions heated at pH 6.2 were more extensively denatured, had a greater proportion of insoluble aggregates, higher particle size and turbidity, and were significantly less heat-stable than equivalent samples prepared at pH 6.7 and 7.2. The effects of WPI concentration on denaturation/aggregation behavior were more apparent at higher pH where the stabilizing effects of charge repulsion became increasingly influential. Solutions containing 12% (wt/wt) WPI had significantly higher apparent viscosities, at each pH, compared with lower protein concentrations, with solutions prepared at pH 6.2 forming a gel. Smaller average particle size and a higher proportion of soluble aggregates in WPI solutions, pre-heated at pH 6.7 and 7.2, resulted in improved thermal stability on subsequent heating. Higher pH during secondary heating also increased thermal stability. This study offers insight into the interactive effects of pH and whey protein concentration during pilot-scale processing and demonstrates how protein functionality can be controlled through manipulation of these factors.

Interaction of soybean protein isolate and phosphatidylcholine in nanoemulsions: A fluorescence analysis

Two types of nanoemulsions were prepared using ultrasound (US) treatment and high pressure homogenization (HPH) with optimized conditions. The effect of US and HPH on the structure and the interaction between soybean protein isolate (SPI) and phosphatidylcholine (PC) were studied using fluorescence spectrum. Results showed that these two preparation methods were capable of producing stable nanoemulsions. The nanoemulsions prepared using HPH had smaller average particle size, higher surface charge, lower turbidity and greater emulsifying yield than US, but the specific energy required for the HPH (4.0 kJ/g) was nearly 1.5 times higher than that of US (2.7 kJ/g). Fluorescence data showed that the fluorescence quenching of SPI with PC was the result of the formation of SPI-PC complex. According to the Stern–Volmer equation, the association constant (KA) of the SPI-PC interaction using HPH was higher than US at three different temperatures. The positive enthalpy and entropy changes suggested that hydrophobic interactions were the dominant binding force in stabilizing the complex. The distance r for binding between HPH treated PC and SPI was lower suggesting that the binding was stronger. These comparative results showed that the HPH-nanoemulsions were more stable than US-nanoemulsions, which was proposed to be due to HPH promoting the exposure of more hydrophobic residues on the surface of SPI, which would permit more PC to interact with SPI. But US is a relatively more energy-efficient method as compared to HPH and may better meet industrial needs.

Synthesis and Utilization of Low Dispersity Acrylic Macromonomer as Dispersant for Nonaqueous Dispersion Polymerization

The effect of dispersity on the stabilization performance of poly(butyl methacrylate) (P(BMA)) ω-unsaturated macromonomer used as a reactive dispersant in nonaqueous acrylic dispersion (NAD) polymerization is investigated for the first time. Macromonomer with low dispersity (1.3) is synthesized in a one-pot process by the addition of bis(difluoroboryldiphenylglyoximato)cobalt(II) (CoPheBF) as a catalytic chain transfer (CCT) agent to P(BMA) chains mediated by atom transfer radical polymerization (ATRP); addition of the CoPheBF at a BMA monomer conversion of ∼80% leads to good control of chain length and dispersity while achieving a high fraction of terminal double bond (TDB) functionality. The lower dispersity P(BMA) macromonomer provides better stabilization to NAD systems per dispersant chain compared to material of the same number-average molecular weight (∼6000 Da) and TDB functionalization (∼70–75%) but higher dispersity (1.8), as characterized by the smaller average particle sizes and the higher wei...

The promotional role of Nd on Mn/TiO2 catalyst for the low-temperature NH3‑SCR of NOx

A series of rare-earth metal doped 30% Mn-3% RE/TiO2 (RE = Ce, Sm, Nd, Er, Y) catalysts were prepared by adopting two step incipient wetness impregnation method and investigated for the low-temperature SCR of NOx with NH3. It was found that 3% of rare earth elements (Nd, Er, Y) was added to 30% Mn/TiO2 catalyst even could increase the catalytic performance at the low temperature, in addition to usual used Ce and Sm. And the promoting effect of Nd was among the most significant. Then the 30%Mn-3%Nd/TiO2 catalyst was synthesized by another two methods, Coprecipitation and Sol-gel, for a comparative study. Various techniques were applied to characterize the catalysts. The catalysts prepared by Coprecipitation and Sol-gel method exhibited higher surface area and smaller average particle size in comparison with catalyst prepared by impregnation with TiO2 support. The addition of Nd made surface area and dispersion of MnOx species increase. It also led both the content of amorphous MnO2 and the content of crystalline Mn2O3 to decrease, but the proportion of MnOx species with low oxidation state increased. H2-TPR results showed that the low temperature reduction peak of MnOx was shifted to much lower temperatures with the doping of Nd, which improved the redox property of the catalysts. The all characteristics shown above could well explain the promotional role of Nd doping in the 30%Mn-3%Nd/TiO2 catalyst, that improved the low temperature SCR catalytic activity.

The Promoting Effect of Ce on the Performance of Au/CexZr1−xO2 for γ-Valerolactone Production from Biomass-Based Levulinic Acid and Formic Acid

The production of γ-valerolactone (GVL) directly from biomass-based levulinic acid (LA) and formic acid (FA) without extra hydrogen source is attractive but challenging, due to the requirement of a highly active and stable catalyst. In present work, Au/CexZr1−xO2 with various Ce/Zr ratios were prepared as the catalyst for GVL production from LA with the equivalent molar FA, and characterized by XRD, Raman-spectra, BET, NH3-TPD, TEM and XPS. It was found that the doped Ce in Au/CexZr1−xO2 catalyst could improve the reduction of Au3+ to metallic Au0, and also promoted the dispersion of Au0, yielding uniform Au0 nanoparticles with a small average particle size of about 2.4 nm, thus enhancing both the decomposition of FA to CO-free H2 and the hydrogenation of LA. Meanwhile, a certain amount of doped Ce (x ≤ 0.4) could facilitate the formation of tetragonal phase (the most desired structure on LA conversion to GVL), and increase the amount of weak and medium-strength acidic sites of catalyst, thereby promoting the dehydration reaction of the intermediate derived from LA hydrogenation. Au/Ce0.4Zr0.6O2 catalyst exhibited the best catalytic activity, achieving 90.8% of LA conversion and 83.5% of GVL yield (TON = 2047.8), with good recyclability, and the activity showed no obvious change after 5 runs.

High-performance and stable La0.8Sr0.2Fe0.9Nb0.1O3-δanode for direct carbon solid oxide fuel cells fueled by activated carbon and corn straw derived carbon

The novel perovskite La0.8Sr0.2Fe0.9Nb0.1O3-δ (LSFNb) anode for direct carbon-solid oxide fuel cells (DC-SOFCs) is evaluated using activated carbon and corn straw carbon as fuels. Activated carbon possesses less ratio of disorder carbon, smaller average particle size and much higher specific surface area, as well as porous structure with micropores and mesopores compared with corn straw carbon. Electrolyte-supported DC-SOFCs with LSFNb anode demonstrate excellent performance with peak power densities of 302.8 mW cm−2 and 218.5 mW cm−2, respectively, when operated with activated carbon and corn straw carbon at 850 °C. Polarization resistances of LSFNb anode indicate that performance of DC-SOFCs is largely determined by the reverse Boudouard reaction, which is related to specific surface area of fuels. Cells fueled by corn straw carbon exhibit more stable output, higher released electric quantity and higher fuel utilization rate than that using activated carbon. Despite more disorder carbon and better thermal reactivity of corn straw carbon, higher initial output performance is obtained with activated carbon, proving that specific surface area of fuels, particle size and porosity have a considerable influence on the reverse Boudouard reaction and cell performance. These results indicate that LSFNb is a promising perovskite anode material for DC-SOFC.

Low-Temperature CO Oxidation: Effect of the Second Metal on Activated Carbon Supported Pd Catalysts

Activated carbon (AC) supported monometallic Pd and bimetallic Pd-M (M = Co, Ni, and Cu) catalysts were prepared by impregnation-reduction method and investigated for carbon monoxide (CO) oxidation. X-ray diffraction (XRD) and transmission electron microscopy (TEM) revealed highly disperse Pd-M nanoparticles (~ 3–5 nm) on the AC support. The addition of the second transition metal in Pd/AC resulted in an increase in the specific surface area and smaller average particle size. CO oxidation experiments were carried out in a vertical fixed-bed quartz reactor at gas hourly space velocity (GHSV) of 30,000 h− 1 under atmospheric pressure. The catalytic order is as follows: Pd–Cu/AC > Pd–Ni/AC > Pd–Co/AC > Pd/AC. The T50 (50% CO conversion) value of Pd–Cu/AC and Pd/AC catalysts are 30 and 70 °C. BET, XRD and TEM analysis of the used Pd-M/AC and Pd/AC catalysts were performed in order to find any change in the specific surface area, structure, morphology, and average particle size of the catalysts after CO oxidation. The results showed that the bimetallic Pd-M/AC catalysts had better catalytic activity and stability than the monometallic Pd/AC catalyst. Pd–Cu/AC showed excellent time-on-stream stability of 50 h. The apparent activation energy of the Pd–Cu/AC is found to be 69.32 kJ mol− 1. Thus, bimetallic Pd-M/AC catalysts have a potential for practical CO oxidation reaction.