Molar Ratio Of Precursors Research Articles

Shape effects of CdS photocatalysts on hydrogen production

Granular and lamellar structured cadmium sulfide (CdS) with the shapes of branches, cauliflower and nanorods, were synthesized via a hydrothermal process. During the synthesis, ethylenediamine (EN) was used as a template and deionized water (DIW) as a coordination agent. Experimental results show that the morphology of CdS nanoparticles was controlled by EN concentration, CdS precursor concentration and molar ratio of Cd(NO3)2·4H2O to thiourea (NH2CSNH2). It was found that the key shape-controlling step is the formation of CdS nuclei via the decomposition of the cadmium-ethylenediamine complex. Various shapes of CdS nanoparticles were obtained based on the concentrations of EN in water. CdS particles synthesized in pure water show granular and lamellar shapes with a mixture of hexagonal and cubic crystal structures. When EN concentration was increased to 30%, branched morphology of CdS particles was observed. Further increasing EN concentration to 70% CdS catalyst particles resulted in a cauliflower-like shape. Finally, CdS nanorod particles with a hexagonal structure were developed when synthesized in a pure EN solution. Although EN concentration plays an important role in the shapes of CdS particles, experimental observation showed that the diameter and aspect ratio of as prepared CdS nanorods were determined by concentrations of CdS precursors. In the course of photocatalytic hydrogen production, nearly 2577 μmol H2 was produced over 0.05 g CdS nanorods in 4.0 h. The rate of hydrogen evolution over the CdS nanorods based photocatalyst was approximately 42.6 times higher than that over granular and agglomerated lamellar CdS.

Colloidal Synthesis of InSb Nanocrystals with Controlled Polymorphism Using Indium and Antimony Amides

We report a new synthetic pathway for growing monodisperse colloidal indium antimonide nanocrystals. We propose that highly reactive element-nitrogen bonded precursors, such as In and Sb amides, may provide required nucleation and growth kinetics for the formation of uniform colloidal nanocrystals of InSb. Size-dependent absorption and emission spectra of InSb nanocrystals in the near-infrared region of 1500–2000 nm point to semiconductor behavior with quantum confinement. Furthermore, we demonstrate zinc blende/wurzite polymorphism and polytypism of InSb nanocrystals, conveniently controlled by the In/Sb molar ratio of precursors. This amide-based synthesis route may open new opportunities for designing near- and mid-IR active III–V semiconductor nanostructures.

A novel hybrid sol–gel method for the synthesis of highly porous silica employing hyperbranched poly(ethyleneimine) as a reactive template

A novel hybrid sol–gel templating route employing hyperbranched polymers for the production of nanostructured silica with tailored porosity and high specific surface area values is proposed based on the use of hyperbranched poly(ethyleneimine) both as a reactive template and as a macromolecular “porogen”. The procedure developed involves dissolution of hyperbranched poly(ethyleneimine), PEI, of two different molecular weights (5,000 and 25,000), in N,N-dimethylformamide or chloroform serving as solvents of different polarity and addition of 3-(triethoxysilyl)propyl isocyanate as a silica precursor which is also reactive towards PEI’s amino groups. The obtained triethoxysilyl functionalized macromolecules after hydrolysis and subsequent polycondensation reactions lead to the formation of a novel silica network architecture. By firing this hybrid material a silica powder of nanoporous structure and advanced textural properties is obtained. Synthetic reactions are monitored by FTIR spectroscopy, while the silica network formed after firing is characterized by TGA, low and wide-angle XRD, TEM and N2 adsorption techniques. The influence of several parameters, i.e., molecular weight of PEI, PEI/silica precursor molar ratio and solvent polarity on silica’s porosity is studied. Depending on the synthesis conditions, this novel templating route proved effective for the successful imprinting of mesoporous cavities into silica structure. In this way, nanostructures with tailor-made properties were obtained exhibiting specific surface area values varying from ∼600 to 1100m2/g and pore diameters up to around 5nm.

Influence of Ligand–Precursor Molar Ratio on the Size Evolution of Modifiable Iron Oxide Nanoparticles

During the synthesis of nanoparticles via thermal decomposition of iron precursors, the capping ligand–precursor ratio influences the resulting size of the iron oxide nanoparticles. As the molar ratio of aliphatic amines to iron precursor is increased, the average diameter of the synthesized iron oxide nanoparticles decreases. This trend is opposite to previously reported results. We investigated this phenomenon by independently varying the ligand chain length, the ligand–precursor molar ratio, and the degree of saturation of the aliphatic chain. Nuclear magnetic resonance spectra of the precursor illustrated the presence of a primary amine peak before heating and the peak absence after heating, potentially indicating that the primary amine acts as reducing agent to promote the decomposition of the iron precursor. We hypothesize that the amine groups play a dominant role in the nucleation of the particles, while the chain length and degree of aliphatic saturation have only a minor effect on particle size....

Synthesis of Well-Distributed SnO2-Sn-Ag3Sn Nanoparticles in Carbon Nanofibers Using Co-Electrospinning

Well-distributed <TEX>$SnO_2$</TEX>-Sn-<TEX>$Ag_3Sn$</TEX> nanoparticles embedded in carbon nanofibers were fabricated using a co-electrospinning method, which is set up with two coaxial capillaries. Their formation mechanisms were successfully demonstrated. The structural, morphological, and chemical compositional properties were investigated by field-emission scanning electron spectroscopy (FESEM), bright-field transmission electron microscopy (TEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). In particular, to obtain well-distributed <TEX>$SnO_2$</TEX> and Sn and <TEX>$Ag_3Sn$</TEX> nanoparticles in carbon nanofibers, the relative molar ratios of the Ag precursor to the Sn precursor including 7 wt% polyacrylonitrile (PAN) were controlled at 0.1, 0.2, and 0.3. The FESEM, bright-field TEM, XRD, and XPS results show that the nanoparticles consisting of <TEX>$SnO_2$</TEX>-Sn-<TEX>$Ag_3Sn$</TEX> phases were in the range of ~4 nm-6 nm for sample A, ~5 nm-15 nm for sample B, ~9 nm-22 nm for sample C. In particular, for sample A, the nanoparticles were uniformly grown in the carbon nanofibers. Furthermore, when the amount of the Ag precursor and the Sn precursor was increased, the inorganic nanofibers consisting of the <TEX>$SnO_2$</TEX>-Sn-<TEX>$Ag_3Sn$</TEX> nanoparticles were formed due to the decreased amount of the carbon nanofibers. Thus, well-distributed nanoparticles embedded in the carbon nanofibers were successfully synthesized at the optimum molar ratio (0.1) of the Ag precursor to the Sn precursor after calcination of <TEX>$800^{\circ}C$</TEX>.

Wet cation exchange route to semiconductor alloys: the case study of Mg&lt;SUB align="right"&gt;xZn&lt;SUB align="right"&gt;1-xO

We developed a novel cation exchange method to prepare the alloyed semiconductors. A series of self–assembled magnesium doped zinc oxide (MgxZn1–xO) particles were synthesised by varying the molar ratios of Mg precursor Mg5(CO3)4(OH)2•4H2O to Zn precursor ZnAc2•4H2O from 1:1 to 3:1 at different cation exchange time. Powder X–ray Diffraction (XRD) indicates that the samples are a mixture of hexagonal and cubic phases. The UV–visible (UV–vis) absorption spectra show that the band gap of MgxZn1–xO particles can be readily tuned by optimising the cation exchange time and the molar ratio of precursors. The morphology of MgxZn1–xO particles was observed by Scanning Electron Microscopy (SEM).

Facile preparation of a variety of bimetallic dendrites with high catalytic activity by two simultaneous replacement reactions

Herein, two simultaneous replacement reactions were explored to prepare a variety of bimetallic dendrites (AgCu, AgPd, AuPd, CuAu, CuPt and CuPd) in one step, using commercial Mg powder as a sacrificial metal to reduce the bimetallic precursors in aqueous solution. We demonstrate in detail how the morphologies and compositions of the bimetallic dendrites are affected by factors such as the potential difference between the metal redox couples, molar ratios of precursors, ligands, reaction times and total precursor concentrations, taking dendritic AgCu as an example. In addition, monometallic Ag and Cu dendrites were also prepared for comparison. The application of these prepared dendrites as high performance catalysts for the reduction of 4-nitrophenol in aqueous solution at room temperature was further explored. The order of activity CuPd > CuPt > CuAu > Cu > Ag1Cu1 > Ag3Cu1 > AuPd > Ag1Cu3 > AgPd > Ag was established for the prepared dendrites based on normalized kinetic parameters according to our proposed formula.

Surface polarity induced three-dimensional wurtzite ZnS/ZnSxSe1−x nano-heterostructures with integrating emission property

By controlling the reaction conditions and molar ratio of precursors carefully, three-dimensional ZnS/ZnS0.3Se0.7 nano-heterostructures were synthesized via a simple two-step magnetic force assistant growth technique. Scanning electron microscopy, X-ray powder diffraction, energy dispersive X-ray spectroscopy and transmission electron microscopy were used to characterize and analyze the morphology, phase structure, crystallinity and composition of the as-prepared nano-heterostructures. Remarkably, the epitaxial ZnS nanoribbon is single crystalline and preserves the structure and orientation of the matrix ZnSxSe1−x nanobelt with an epitaxial relationship of (0001)ZnS//(0001)ZnS0.3Se0.7 and (100)ZnS//(100)ZnS0.3Se0.7. A polar-surface induced growth process for the three-dimensional nano-heterostructures is proposed according to the experimental results and crystallography relationship. This approach can offer a prevailing way to fabricate more complex three-dimensional nanostructures with built-in heterojunctions. Room temperature PL spectra were used to investigate the emission property of the as-prepared samples. The PL spectra of ZnSe and ZnSxSe1−x nanobelts show strong near bandgap emission, demonstrating a high crystal quality of these as-synthesized nanobelts. The PL spectrum of three-dimensional ZnS/ZnS0.3Se0.7 nano-heterostructures shows the near bandgap emission of ZnS and ZnS0.3Se0.7 simultaneously, demonstrating the incorporating function. These three-dimensional nano-heterostructures with unique structure and morphology can be used to investigate the incorporating function and find extensive applications in nanophotonics.

Surface controlled synthesis of MFe2O4(M = Mn, Fe, Co, Ni and Zn) nanoparticles and their magnetic characteristics

Engineered magnetic nanoparticles, MFe2O4 (where M = Mn, Fe, Co, Ni and Zn), of mean size 2–16 nm (standard deviation σ ≤ 15%) with controlled magnetic properties have been synthesized through a solventless thermolysis technique. In this ‘energy-efficient’ facile approach, a long-chain amine is utilized as the solvent, reducing and surface-functionalizing agent. The particle sizes between 2–9 nm are tuned by simple manipulation of the amine to precursor molar ratio while the larger sizes (12–16 nm) are attained by seed-mediated growth. The synthesized nanoparticles are magnetic and show cubic-spinel structure as characterized by HRTEM, SAED, XRD and Raman spectroscopy. The spin–orbit coupling, which induces larger magnetocrystalline anisotropy energy, leads to an increase of the blocking temperature in an order of Zn, Ni, Mn, Fe and Co. Additionally the saturation magnetization (magnetization at 2 T) of nanoparticle decreases in an order as per the periodic arrangement i.e. Mn > Fe > Co > Ni > Zn. This trend is better understood in terms of a cationic distribution of varying magnetic moments in these spinel oxides. For all the ferrites, the magnetization saturates to the bulk value at sizes ≥12 nm, indicating strict control over the dead layer thickness. The effect of surface coordination on the magnetic properties of the ferrite nanoparticles is analyzed. In contrast to trioctylphosphine oxide (TOPO) and oleic acid (OA) functionalized nanoparticles the saturation magnetization of amine protected nanoparticles is higher, which suggests a strong coupling of amine molecules to cations at the particle interface.

Investigation on one-pot hydrothermal synthesis, structural and optical properties of ZnS quantum dots

The advantage of hydrothermal synthesis of semiconductor quantum dots (QDs) over the control of particles size, morphology and stability is reported here. In a typical synthesis procedure, the zinc and sulfur precursor molar ratio of 1:3 was used in an aqueous solution at 150 °C. The cubic phase of ZnS with average particles size of 5 nm was confirmed and estimated from the X-ray diffraction (XRD) analysis. The composition and purity of the sample were analyzed from (energy dispersive-ray analysis) EDAX and (X-ray photoelectron spectroscopy analysis) XPS spectra. The absorption spectrum shows the large shift in the absorption band over 90 nm due to the quantum confinement of carriers. The emission spectrum of quantum dots carry more evidence on the presence of shallow trap, deep trap in the band gap of the material responsible for weak emission in the spectral region of 450–500 nm. High resolution transmission electron microscope and scanning electron microscope studies reveal the structural and morphological features of ZnS with slightly distorted spherical morphology. We found that the coordinating ability of solvent strongly influences the reaction process and morphology of the products.

Effect of the thermal treatment conditions on the formation of zinc ferrite nanocomposite, ZnFe2O4, by sol–gel method

Zinc ferrite nanocomposite was synthesized via thermal decomposition of zinc acetate and iron nitrate at three different temperatures (350, 450, and 550 °C). The influence of the thermal decomposition of precursors on the formation zinc ferrites was studied by differential thermal gravimetry and thermogravimetry (TG). The TG curve shows two steps for the thermal decomposition with mass loss of 17.3 % at 78 °C and 63.3 % at 315 °C. The prepared zinc ferrites nanocomposite was characterized by X-ray diffraction and scanning electron microscopy. The X-ray diffractograms of ZnFe2O4 shows that a crystalline phase, spinel system is formed. SEM micrograph of the zinc ferrite nanocomposite indicates the formation of uniformly spherical 48-nm nanograins. The properties of the zinc ferrite phase were strongly dependent on their calcinations temperature and molar ratio of precursors.

STRUCTURE OF LATTICE STRAIN AND EFFECT OF SOL CONCENTRATION ON THE CHARACTERIZATION OF TIO-2CUO-SIO2 NANOPARTICLES

We report on the synthesis, morphology, chemically and structurally of TiO2-CuO-SiO2 nanostructure with different precursors molar ratio and calcined temperatures. In the present work, ternary reactive powders in the TiO2-CuO-SiO2 systems have been obtained using the sol-gel method, by the simultaneous gelation of all cations. The compounds and other elements change in special chemical and physical qualities in this nano oxide. Powders and coatings have been characterized by XRD, SEM, EDX and FTIR. X-ray diffraction showed the formation of nano crystalline CuO (Tenorite) and anatase phases. The average crystallite size was calculated by using X-ray diffraction analysis. The activation energy (E) of nanoparticles formation during thermal treatment were calculated. The lattice strain evaluated by Williamson-Hall's equation. SEM revealed that nanoaggregation structure formed by increasing the calcined temperature and grains like to make a spherical shape. EDX spectroscopy confirmed the composition of the ternary powders and coating, which are formed during the gelation process. FTIR spectra showed that Si-O-Ti, Ti-O, Cu-O, Ti-O-Ti, Ti-OH and Si-O-Si bonds are formed and indicated that titanium is in four-fold coordination with oxygen in the SiO 4. The effects of chemical compositions and the strong process on the surface topography and the crystallization of anatase and CuO (Tenorite) were studied. With increasing the molar ratio (content of CuO) in as-prepared state, the formation of rod region was more prominent than agglomerate region.

Porous TiO2 microspheres with tunable properties for photocatalytic air purification

The synthesis of highly-crystalline porous TiO2 microspheres is reported using ultrasonic spray pyrolysis (USP) in the presence of colloidal silica as a template. We have exploited the interactions between hot SiO2 template particles surface and TiO2 precursor that occur during reaction inside the droplets, to control the physical and chemical properties of the resulting particles. Varying the SiO2 to titanium precursor molar ratio and the colloidal silica dimension, we obtained porous titania microspheres with tunable morphology, porosity, BET surface area, crystallite size, band-gap, and phase composition. In this regard, we have also observed the preferential formation of anatase vs. rutile with increasing initial surface area of the silica template. The porous TiO2 microspheres were tested in the photocatalytic degradation of nitrogen oxides (NOx) in the gas phase. USP prepared nanostructured titania samples were found to have significantly superior specific activity per surface area compared to a commercial reference sample (P25 by Evonik-Degussa).

Tailored Jeffamine Molecular Tools for Ordering Mesoporous Silica

Herein, we report the formation of organized mesoporous silica materials prepared from a novel nonionic gemini surfactant, myristoyl-end-capped Jeffamine, synthesized from a polyoxyalkyleneamine (ED900). The behavior of the modified Jeffamine in water was first investigated. A direct micellar phase (L(1)) and a hexagonal (H(1)) liquid crystal were found. The structure of the micelles was investigated from the SAXS and the analysis by generalized indirect Fourier transformation, which show that the particles are globular of core-shell type. The myristoyl chains, located at the ends of the amphiphile molecule, are assembled to form the core of the micelles and, as a consequence, the molecules are folded over on themselves. Mesoporous materials were then synthesized from the self-assembly mechanism. The recovered materials were characterized by SAXS measurements, nitrogen adsorption-desorption analysis, and transmission and scanning electron microscopy. The results clearly evidence that by modifying the synthesis parameters, such as the surfactant/silica precursor molar ratio and the hydrothermal conditions, one can control the size and the nanostructuring of the resulting material. It was observed that, the lower the temperature of the hydrothermal treatment, the better the mesopore ordering.

49.3: Synthesis of High Quality CdSe Quantum Dots with Tunable Size

AbstractA cheaper, greener approach for the synthesis of highly monodisperse and tunable size CdSe semiconductor quantum dots was developed by thermolysis of a mixed solution of CdO and Se in non‐coordinating solvent 1‐octadecene at 240°C. Systematic vary of the precursor molar ratios allowed the particle size (from 2.5 nm to 5.5 nm) to be tuned and the size distribution (full width at half maximum of photoluminescence spectra from 26 nm to 37 nm) to be controlled. The results revealed that initial Cd:Se molar ratios play an important role in controlling both the size and size distribution of the as‐prepared CdSe quantum dots. Moreover, the obtained CdSe quantum dots are all of zinc blende phase. The possible reason was discussed. The reaction has been conducted in relatively low temperature at 210°C in the absence of expensive organic phosphine ligands, such as trioctylphoshine and trioctylphoshine oxide. This approach has great value for both the laboratory research and industrial application in term of “green chemical principles”.

Lanthanum-Doped Titania Film Coated on Light Leakage Fiber Photo-Degradation Methyl Orange

Lanthanum-doped anatase TiO2 coatings, which are composed of assemble crystalline of 50 nm diameter particles, when the percentage of dopant is 0.5 wt%, have been successfully fabricated by sol–gel dip-coating process on light leakage silica fiber (LSF) which length is 15cm and diameter is 125μm. This was achieved by adjustment of the lanthanum-doped sol–gel parameters such as molar ratio of precursors in lanthanum-doped TiO2-sols, the ratio of titanium tetrabutoxide to polyvinyl alcohol, dip-coating velocity, drying duration in air, thermal treatment and number of cyclical time of the process. Titania nano crystals were prepared at ambient temperature in a liquid media using titanium tetrabutoxide as precursor, and the crystallization of amorphous precursor was preceded by peptizing with acid and then refluxing for a periodic time in homothermal water-bath. The photocatalytic properties of the La-TiO2 films had been testified by the photo degradation of methyl orange. The lanthanum-doped anatase TiO2 thin films were characterized by XRD and TEM. The products show much improved photocatalytic activity that will be useful in the design of a novel antibacterial, deodorant and antipollution photo reactor.

Wettability study of surface modified silica aerogels with different silylating agents

In wettability study, surface free energy interactions are of crucial importance for silica aerogels in which absorption of organic liquids and transportation of chemicals carried out for chemical and biotechnological applications. In present study, we have used Lifshitz–van der Waals/acid–base approach for calculation of surface free energy of aerogel sample. We have investigated that the surface free energy values of aerogels are 45.95, 51.42 and 45.69 mJ/m2 by modifying their surfaces using 7 % chlorotrimethylsilane (TMCS), dimethyldichlorosilane (DMDCS) and hexamethyldisilazane (HMDZ) silylating reagents with solvent, respectively. The alcogels were prepared by two step acid–base catalyzed process where the molar ratio of precursors tetraethoxysilane:methanol:oxalic acid:NH4OH:NH4F was kept at optimal value of 1:16.5:0.71:0.58:0.60:0.98, respectively. To modify gel surfaces, TMCS, DMDCS and HMDZ concentration have been varied from 5 to 12 % and such alcogels were dried at ambient pressure. The aerogels have been characterized by fourier transform infrared spectroscopy, scanning electron microscopy, thermo-gravimetric and differential thermal analysis and Wetting properties of silica aerogel surfaces was studied by contact angle measurements. The surface chemical composition of DMDCS modified silica aerogels was studied by using X-ray photoelectron spectroscopy. As there is not any direct method, we have used Lifshitz–van der Waals/acid–base approach which gives, polar and non-polar components of aerogels surface free energy.

Structural and optical properties of CdS thin films prepared by chemical bath deposition at different ammonia concentration and S/Cd molar ratios

CdS thin films were prepared by chemical bath deposition technique using the precursors of SC(NH2)2, CdCl2, NH4Cl, NH3·H2O and deionized water. The obtained thin films were characterized by scanning electron microscopy, X-ray diffraction, energy dispersive spectrometer, UV–VIS specrophotometry and photoluminescence spectroscopy. The morphology, structural and optical properties of CdS thin films were investigated as a function of ammonia concentration and S/Cd molar ratios in precursors. The results reveal that morphology of CdS films change from flake like into spherical particle like, crystal structure from wurtzite structure to zinc blende structure, S/Cd atom ratios in CdS thin films increase and optical band gap E g decrease with increasing ammonia concentration in precursors. The room temperature photoluminescence spectrum of CdS thin films shows a strong peak at about 500 nm and a weak peak at about 675 nm.

Synthesis of nano-sized lithium cobalt oxide via a sol–gel method

In this study, nano-structured LiCoO2 thin film were synthesized by coupling a sol–gel process with a spin-coating method using polyacrylic acid (PAA) as chelating agent. The optimized conditions for obtaining a better gel formulation and subsequent homogenous dense film were investigated by varying the calcination temperature, the molar mass of PAA, and the precursor's molar ratios of PAA, lithium, and cobalt ions. The gel films on the silicon substrate surfaces were deposited by multi-step spin-coating process for either increasing the density of the gel film or adjusting the quantity of PAA in the film. The gel film was calcined by an optimized two-step heating procedure in order to obtain regular nano-structured LiCoO2 materials. Both atomic force microscopy (AFM) and scanning electron microscopy (SEM) were utilized to analyze the crystalline and the morphology of the films, respectively.

Rapid solid state synthesis by spark plasma sintering and magnetic properties of LaMnO3 perovskite manganite

LaMnO3 oxide was successfully synthesized from La(OH)3 and Mn2O3 precursors (molar ratio La/Mn=0.6) using the spark plasma sintering technique (SPS). The in-situ reaction proceeds in a few minutes at 900°C under 50MPa with the very high heating rate of 100°C/min. LaMnO3 powder was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and magnetic measurements. The Rietveld refinement of the X-ray powder diffraction shows that LaMnO3 sample crystallizes in a perovskite structure O′-type orthorhombic symmetry with Pbnm space group. Our sample undergoes an A-type antiferromagnetic order with Néel temperature equal to 138K. The magnetic susceptibility shows the Curie–Weiss behavior between 170 and 320K with the effective magnetic moment μeff=4.78μB/f.u and the Curie constant θP=−20K (antiferromagentic sign).