Modified Synthesis Method Research Articles

Electronic structure study of dual-doped II-VI semiconductor quantum dots towards single-source white light emission.

Single-source white light emitting colloidal semiconductor quantum dots (QDs) is one of the most exciting and promising high-quality solid-state light sources to meet the current global demand for sustainable resources. While most of the previous methods involve dual (green-red) emissive nanostructures coated on blue LEDs to achieve white light, this work describes a single-source white light emitter of robust and superior quality using dual-doping. A modified synthesis method for intense white light emitting Cu, Mn dual-doped ZnSe QDs is engineered such that the extent of doping and concentration of ligands can alter their electronic structures. This is then customized to obtain various types of white light emissions ranging from warm white to cool white. Further, the composition-driven change in the electronic structure of the host QDs is exploited to achieve emission tunability over the entire visible range.

Magnetic properties and morphology of ultra-small iron oxide nanoparticles

Maghemite nanoparticles prepared with the modified synthesis method published by Sun et al. 2004 and followed by filtering to extract a sample of the smallest nanoparticle size were investigated. The 2-5 nm nanoparticles of monocrystalline and multi-twinned morphology without surface shells were observed. Superparamagnetic behavior was detected above the temperature of 40 K. An exchange bias loop shift of ~ 2 mT at 3 K after cooling with an external field of 3 T suggested a low influence of the surface spin disorder effect. Mössbauer spectroscopy confirmed the two phases with different blocking temperatures, the maghemite phase as well as a second one likely originating from the disordered surface component.

Tailoring the Growth of Nanosized α-Zirconium Phosphate.

Nanosized α-zirconium phosphate (α-ZrP), unlike microcrystalline α-ZrP, takes less time to prepare and is synthesized directly in organic solvents. During the synthesis of nanosized α-ZrP, the heating step is critical because during which the particle growth/aggregation is ongoing. In order to explore more details of this step, extra water molecules were intentionally introduced to the ethanol gel of nanosized α-ZrP so that the evaporation of the solvent was slowed. To heat the gels at 65 °C for different periods (1-6 days), one could control with ease the synthesized α-ZrP in size, from 63 to 155 nm, and in morphology, from amorphous to highly crystalline. Furthermore, the heating step also affects the intercalated solvent and the dangling propionate groups on the edge of the nanosized α-ZrP, which could be deduced from the intercalation/exfoliation behavior of the nanocrystals. This modified synthesis method of nanosized α-ZrP offers an alternate means to tune the size and morphology of the nanosized α-ZrP for broad applications.

Tuning the properties of ZnxS1-x nanoparticles by controlling reaction conditions

In this work, a modified synthesis method was deployed to obtain nanocrystalline zinc sulfide from zinc acetate. By utilizing the hydrothermal and sol gel method, the influence of: reaction time, solvent and temperature control were used to tune the properties of zinc sulfide. Our results showed that ZnS(B) (which was obtained by sol gel in water + hydrothermal) typified formation of increased sulfur vacancies while an increase in reaction time resulted in decreased sulfur vacancies. The introduction of chemical defects in ZnS(A) (which was obtained by sol gel in methanol + KOH) resulted in lower crystallite size. We observed that crystallinity improved with increased reaction time and utilization of water as solvent improved the crystallinity of the material as confirmed in ZnS(C) and ZnS(B). Furthermore, our result showed that reaction time influenced dislocation density of the material to a greater extent than type of solvent used. The crystallite size estimated by Scherer formula was in the range 1.35 nm – 18.64 nm while the band gap energy of the ZnS samples were calculated in the range 3.8 eV- 4.6 eV. Utilizing these novel syntheses methods can stimulate new directions in synthesizing ZnS crystals with options of choosing appropriate method for specific applications depending on properties to be traded off.

A new mechanism for pore enlargement in mesoporous materials and its application on biodiesel production

ABSTRACT In the conventional method of synthesis by using cyclohexylamine (CA) as template produces in the pore range of 0–3 nm. To enlarge the pore size which is suitable for biodiesel synthesis, the modified synthesis method is adopted by using CA as a template. In this novel method, pore size is enlarged to 7 nm. Cyclohexylamine was applied as a template for AlPO4 and AlSiO4 molecular sieves synthesis. In AlSiO4 synthesis, tetraethyl orthosilicate hydrolyzed to produce ethyl carbocation which is used for ethylation of CA in the presence of aluminum chloride. This ethylated CA size is large enough to produce a large pore size (7 nm). In AlPO4 two types of pore are produced with a pore size of 3 and 7 nm. The 3 nm are created by CA and 7 nm by the binding of CA with phosphoric acid. The synthesized materials are analyzed by physicochemical characterization. AlPO4 has a neutral framework, but the synthesized AlPO4 has acidity which is evidence for the CA binding with phosphoric acid. The synthesis of a promising catalyst (AlPO4-7 and AlSiO4-7) with an enlarged pore that can be effectively applied for the production of biodiesel from waste cooking oil (WCO) at room temperature. The acidity of the synthesized AlPO4 and AlSiO4 are 0.168 and 0.548 mmol/g. These catalysts are active at room temperature due to higher acidity. So the reaction takes place faster and it will reduce the reaction time. It is observed that AlSiO4 produces 90% biodiesel and AlPO4 produces 72% biodiesel with a shorter reaction time. This result reveals that 7 nm pores are suitable for biodiesel production. The diethyl ether selectivity of AlPO4 and AlSiO4 is 24% and 4%, respectively. This is due to the 3 nm pore size created by CA in AlPO4 and it favors diethyl ether synthesis.

Preparation of Al(OH)3-based layered structural material by shear alignment from aqueous dispersion of colloidal gibbsite platelets

Development of the technological and industrial capabilities to obtain hexagonal gibbsite nanoplatelets with a regularly well-defined configuration is an ongoing consideration that has not yet covered a required level of feasible architecture. Here we present a convenient method to synthesize the colloidal gibbsite particles based on a simple hydrothermal process from aluminum alkoxides in weak acid media. These colloids are near-regularly shaped and fairly monodisperse hexagons with an average diameter of 185 nm and a thickness of ~5.3 nm. The aqueous dispersion of gibbsite platelets can be shear-aligned to form highly ordered, continuous films on a substrate by an industrially adaptable method for producing large-area membranes. Overall, the modified synthesis method exhibits an excellent potential for scalable-up production with high quality in various practical applications. The aligned films also have outstanding properties due to the self-assemblies and interfacial physical interactions between adjacent gibbsite platelets and the possibility of industrial fabrication from those layered structural materials. Moreover, we prepare this shear-aligned membrane by the in-plane shearing method to introduce the great promise of disk-like-derived gibbsite as new gas-barrier material or surface-protective materials.

Facile synthesis of CuBTC and its graphene oxide composites as efficient adsorbents for CO2 capture

Abstract Easily regenerable adsorbents are highly desirable for CO2 capture. In this regard, a modified synthesis method for preparing CuBTC and its graphene oxide (CuBTC@GO) composites as adsorbents is developed using a mixed solvent strategy at 323 K for the first time. The addition of N, N-Dimethylformamide was vital for the crystallization of CuBTC at low temperature by accelerating the nucleation. The newly synthesized CuBTC showed much higher surface area and total pore volume, compared with CuBTC synthesized by conventional method. As a result, the as-synthesized CuBTC showed a CO2 adsorption capacity of 8.02 mmol/g at 273 K, 1 bar, which was 17–90% higher than the reported CO2 capacity of CuBTC prepared by conventional method. The fabrication of CuBTC@GO composites enhanced the CO2 adsorption capacity mainly through the improved porosity and dispersion force. Compared with CuBTC, an improved CO2/N2 selectivity for CuBTC@1%GO was obtained from the binary breakthrough experiments, which is beneficial to practical gas separations. The partition coefficient of CuBTC and CuBTC@GO composite were evaluated at different breakthrough levels, e.g., 5%, 10% and 100%, with an inlet CO2 partial pressure of 0.15 bar. CuBTC@1%GO displayed higher partition coefficient values than CuBTC at all three breakthrough levels. The cyclic adsorption experiments for regenerability evaluation showed that the CO2 adsorption reversibility for CuBTC@1%GO composite could maintain above 90%, while that of CuBTC dropped to less than 74% after five adsorption-desorption cycles. The CuBTC@GO composite would be a promising CO2 capture adsorbent with both high CO2 adsorption capacity and remarkable regeneration performance.

Preparation of DMMTAV and DMDTAV Using DMAV for Environmental Applications: Synthesis, Purification, and Confirmation.

Dimethylated thioarsenicals such as dimethylmonothioarsinic acid (DMMTAV) and dimethyldithioarsinic acid (DMDTAV), which are produced by the metabolic pathway of dimethylarsinic acid (DMAV) thiolation, have been recently found in the environment as well as human organs. DMMTAV and DMDTAV can be quantified to determine the ecological effects of dimethylated thioarsenicals and their stability in environmental media. The synthesis method for these compounds is unstandardized, making replicating previous studies challenging. Furthermore, there is a lack of information about storage techniques, including storage of compounds without species transformation. Moreover, because only limited information about synthesis methods is available, there may be experimental difficulties in synthesizing standard chemicals and performing quantitative analysis. The protocol presented herein provides a practically modified synthesis method for the dimethylated thioarsenicals, DMMTAV and DMDTAV, and will help in the quantification of species separation analysis using high performance liquid chromatography in conjunction with inductively coupled plasma mass spectrometry (HPLC-ICP-MS). The experimental steps of this procedure were modified by focusing on the preparation of chemical reagents, filtration methods, and storage.

Carbon-Supported Pt Hollow Nanospheres as a Highly Efficient Electrocatalyst for the Oxygen Reduction Reaction

In this study, carbon black Vulcan XC-72R (VC)-supported Pt hollow nanospheres (HNSs) were prepared through a simple synthesis strategy using VC-supported Co nanoparticles (NPs) as the template combined with the replacement of Co by PtCl6 2− ions. The new modified synthesis method results in improved Pt distribution and performance compared to the previously reported conventional synthesis method. The as-developed Pt(20 wt%)HNS/VC catalyst has a homogenous Pt HNS particle size of ca. 18 nm and a uniform particle distribution on the VC support. Furthermore, the Pt HNSs are found to be composed of discrete Pt NPs with a crystallite size of ca. 2–3 nm. Due to the unique nanostructure and alloying with Co of the Pt HNS, the Pt(20 wt%)HNS/VC outperforms significantly a state-of-the-art Pt(20 wt%)NP/VC for the oxygen reduction reaction.

Enhanced NH3-SCR activity of Sb-V/CeO2–TiO2 catalyst at low temperatures by synthesis modification

In this work, the synthesis of Sb-V/CeO2–TiO2 catalyst was modified by controlling pH with the addition of monoethanolamine solution. All the catalysts were systematically investigated for NO x reduction with NH3 at different reaction conditions and then characterized by XRD, BET-surface area, X-ray photoelectron spectroscopy, NO-TPD, NH3-TPD, and H2-TPR. This modified synthesis method for the Sb-V/CeO2–TiO2 catalyst exhibited noticeably higher NO x reduction activity at low temperatures (<250 °C). H2-TPR revealed an increase of reducible species for the modified catalyst at basic pH, followed by neutral pH and acidic pH, respectively. High activity of the catalyst synthesized at basic pH was persistent for NO x reduction with time that was confirmed by the time on stream durability test under SO2 and water. The Ce 3d XPS spectra of spent catalyst synthesized at basic pH explains the gradual decrease in activity due to the decrease of Ce4+ to Ce3+ ratio by the formation of sulfates.

Size Effect of Chevrel MgxMo6S8 as Cathode Material for Magnesium Rechargeable Batteries

Submicrosized chevrel Mo6S8 powder is synthesized using mechanical milling of the starting materials and the powder yield is increased by using modified synthesis method. The effect of particle size is investigated using various electrochemical techniques. The submicrosized chevrel shows enhanced discharge capacity compared with that of microsized chevrel, and voltage profile indicates that the low capacity arising from Mg trapping at the Mg‐1 site is improved for submicrosized chevrel. Mg trapping is also verified by ex situ X‐ray diffraction measurement and the results are in good agreement with the electrochemical profile. Open‐circuit voltage measurements and AC‐impedance spectroscopy are used to identify the kinetics of Mg2+ insertion. The improved electrochemical properties obtained with the submicrosized chevrel are attributed to the smaller particles that provide shorter diffusion lengths for Mg2+ ions.

Astatine-211 labeling: a study towards automatic production of astatinated antibodies

Targeted alpha therapy is especially interesting for therapy of microscopic cancer tumors due to short path length and high linear energy transfer of the alpha particles. One of the most promising nuclides for targeted alpha therapy is At-211. To facilitate larger clinical studies using At-211, the current manual synthesis of radiolabeled antibodies would benefit from being transferred into an automated method. In this work, successful modifications of the manual synthesis have been performed in order to adapt it to automation. The automatic synthesis has also been tested using the modified synthesis method.

TiO2 Nanorods for Lithium-Ion Anodes

This work deals with TiO2 based anode material for lithium-ion secondary batteries. The aims of this study is to synthetize and characterize TiO2 - nanorod based active anode material using up scalable process with just slightly modified synthesis method commonly used for production of this type material. Low temperature treatment of raw samples was made and structural and electrochemical properties in correlation with treatment temperature were investigated. Using of these substances as promising li-ion anode materials was successfully tested by charge-discharge cycling and structural characterization by XRD and SEM was made.

Facile synthesis of concentrated gold nanoparticles with low size-distribution in water: temperature and pH controls

The citrate reduction method for the synthesis of gold nanoparticles (GNPs) has known advantages but usually provides the products with low nanoparticle concentration and limits its application. Herein, we report a facile method to synthesize GNPs from concentrated chloroauric acid (2.5 mM) via adding sodium hydroxide and controlling the temperature. It was found that adding a proper amount of sodium hydroxide can produce uniform concentrated GNPs with low size distribution; otherwise, the largely distributed nanoparticles or instable colloids were obtained. The low reaction temperature is helpful to control the nanoparticle formation rate, and uniform GNPs can be obtained in presence of optimized NaOH concentrations. The pH values of the obtained uniform GNPs were found to be very near to neutral, and the pH influence on the particle size distribution may reveal the different formation mechanism of GNPs at high or low pH condition. Moreover, this modified synthesis method can save more than 90% energy in the heating step. Such environmental-friendly synthesis method for gold nanoparticles may have a great potential in large-scale manufacturing for commercial and industrial demand.

A modified synthesis method of manganese perovskite La 0.67Ca 0.33MnO 3 by high energy ball milling and post heat treatment

A modified synthesis method of La 0.67Ca 0.33MnO 3 by high energy ball milling and post sintering is reported. The characteristics of samples from this modified method are also studied. The new synthesis method has some advantages including reducing the synthesis procedure into two simple steps, shortening the sintering time, and obtaining similar properties compared with conventional synthesis method. High energy ball milling was employed for 10 h to refine the starting materials into a sub-micron particle size (for comparison, samples milled for 30 and 50 h were also synthesized); during the process, ethanol was added as a milling medium for avoiding amorphization or crystallization, as well as suspending the starting powders for more profound milling. Finally, the as-milled powder was sintered in air to crystallize. The samples show metal-to-insulator transitions at around 260 K, with grain size from 200 nm to 8 μm, and exhibit large magnetoresistance up to 21% at a magnetic field of 3000 Oe near the transition temperature. The possible mechanism is discussed.

Outstanding problems posed by nonpolymeric particulates in the synthesis of a well-structured geopolymeric material

In the conventional geopolymer synthesis of ternary reactants system of silicate anions [Na 2O·2SiO 2], metakaolin [Al 2O 3·2SiO 2] and aqueous alkali [Na 2O], the SiO 2/Al 2O 3 molar ratio can only be varied from ∼2 to 8. For geopolymerisation to occur, the minimum mole percentage of metakaolin reactant is about 25% and the maximum mole percentage of Na 2O content is about 30%. As the reduction of metakaolin and increase of alkali content is limited, the total conversion of metakaolin into polymeric material is uncertain. The identification of the presence or absence of metakaolin in the cured geopolymer product is not possible in this synthesis of a ternary reactant system even by 29Si NMR, as the signal due to metakaolin is indistinguishable from a broad 29Si NMR peak consisting of many resonance lines of polymer network of cross-linked Si/Al tetrahedra. With our modified synthesis method employing colloidal SiO 2 as an additional component, the metakaolin content is decreased while keeping an optimum amount of Na 2O, thereby increasing the compositional SiO 2/Al 2O 3 molar ratio. In this case, the signals related to Al-substituted SiO 4 tetrahedra are reduced, indicating the reduction of Al-substituted SiO 4 tetrahedra in the polymer network, resulting in better-resolved 29Si NMR lines. The 29Si NMR signal related to metakaolin is then distinguishable in the spectra of cured products by observing a series of samples with 11, 7, 5 and 3 mol% of metakaolin reactant. 29Si NMR signal related to metakaolin was only absent in the spectra of cured product when metakaolin reactant content is ≤5 mol%; that is, the compositional SiO 2/Al 2O 3 molar ratio is ≥20.

Growth and luminescence mechanisms of Ba 2ErCl 7: a new laser up-conversion crystal

A modified synthesis method for the preparation of Ba 2ErCl 7, a new laser up-conversion material using Er 2O 3, BaCl 2·2H 2O and NH 4Cl, is reported for the first time. Single crystals 5–8 mm in diameter and 10–20 mm in length were grown by both the Czochralski and Bridgman methods. The transmittance spectra for a Ba 2ErCl 7 single crystal was first measured using a HITACHI U-3500 spectrophotometer. There were three intense absorption peaks 4 I 9/2, 4 I 11/2 and 4 I 13/2 in the infrared range which can be excited by 803 and 980 nm and 1.5 μm laser diode (LD), respectively. The cut-off wavelength of the crystal was 230 nm. Intense green luminescence was observed when the crystals were pumped by an 803 nm LD. Up-conversion mechanisms are discussed.