Nonaqueous Route Research Articles

The Role of Zn Ions in the Structural, Surface, and Gas-Sensing Properties of SnO2:Zn Nanocrystals Synthesized via a Microwave-Assisted Route.

Although semiconducting metal oxide (SMOx) nanoparticles (NPs) have attracted attention as sensing materials, the methodologies available to synthesize them with desirable properties are quite limited and/or often require relatively high energy consumption. Thus, we report herein the processing of Zn-doped SnO2 NPs via a microwave-assisted nonaqueous route at a relatively low temperature (160 °C) and with a short treatment time (20 min). In addition, the effects of adding Zn in the structural, electronic, and gas-sensing properties of SnO2 NPs were investigated. X-ray diffraction and high-resolution transmission electron microscopy analyses revealed the single-phase of rutile SnO2, with an average crystal size of 7 nm. X-ray absorption near edge spectroscopy measurements revealed the homogenous incorporation of Zn ions into the SnO2 network. Gas sensing tests showed that Zn-doped SnO2 NPs were highly sensitive to sub-ppm levels of NO2 gas at 150 °C, with good recovery and stability even under ambient moisture. We observed an increase in the response of the Zn-doped sample of up to 100 times compared to the pristine one. This enhancement in the gas-sensing performance was linked to the Zn ions that provided more surface oxygen defects acting as active sites for the NO2 adsorption on the sensing material.

Fabrication of TiO2/Fe2O3/g-C3N4 ternary photocatalyst via a low-temperature calcination and solvothermal route and its visible light assisted photocatalytic properties

This study reported the fabrication of TiO2/Fe2O3/g-C3N4 ternary Z-scheme photocatalyst via low-temperature calcination followed by a nonaqueous route with tunable particle size and strong interfacial contact. The subsequent Fe2O3/g-C3N4 and TiO2/Fe2O3/g-C3N4 were investigated in terms of structure, morphology, optical properties, and surface chemical composition analysis via transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), energy dispersive x-ray spectroscopy (EDX), UV–visible spectroscopy, and photoluminescence spectroscopy (PL). The crystalline nature of the samples was investigated by X-ray diffraction (XRD) and HRTEM. Under visible light, the photocatalytic capabilities of as-fabricated TiO2/Fe2O3/g-C3N4 were examined by degrading Rhodamine B (RhB), and an enhancement in photocatalytic efficacy was found. TiO2 works as a primary photosensitizer, providing extra photoinduced electrons, while Fe2O3 acts as a “bridge” for electron transport from the TiO2 moiety to the g-C3N4 thereby establishing an indirect charge transport pathway based on the Z-scheme. Radical scavenging tests were conducted to further explore the cause of increased activity and degradation mechanisms. The proposed technique might be a viable option for the removal of rhodamine b compounds and remedying freshwater reservoirs.

Structural, optical and frequency dependent dielectric studies of nanoscale Na0.5Bi0.5TiO3 processed via non-aqueous route

The present work reports on structural, optical, and dielectric properties of nanoscale Na0.5Bi0.5TiO3 (NBT) derived through a non-aqueous, solid-state cum sintering route. Whereas transmission electron microscopy (TEM) has revealed the formation of nearly spherical particles, x-ray diffraction (XRD) analyses suggest particles crystallize into rhombohedral crystal structure. The band gap of NBT is of direct type, as predicted through first principle calculations. The optical band gaps are also determined from the UV–visible absorption spectra, which showed a declining trend with increase in sintering temperature. The Urbach energy, which accounts for the transitional events between the extended and localized states and featuring long tailing in the absorption spectra is found to be smaller than the Tauc gap by several orders. Moreover, a broad-luminescence response as acquired on Photoluminescence spectroscopy, is discussed in the light of quantum confinement effect, near band-edge features, defect states, and self-trapped excitons. Furthermore, dielectric studies have been carried out in the frequency range, 100 Hz-5 MHz, in which one could observe a decreasing trend of capacitance with increasing frequency. However, the real part of the impedance experiences a slow declining trend initially and abrupt fall eventually beyond 1 MHz thereby suggesting a rise in conductivity at higher frequencies as a greater number of carriers are now able to follow the frequency imposed. At the same time, the single semi-circular peak of the Cole-Cole plot suggests a simple equivalent circuit of the device comprising parallel resistance (grain boundary resistance, Rp) and capacitance (grain boundary capacitance, Cp) network in series with a resistance Rs due to the grain.

A quantitative analysis of dicalcium silicate synthesized via different sol-gel methods

In this paper, the synthesis of dicalcium silicate (C2S) via sol-gel (acid-catalyzed) process including aqueous route, non-aqueous route, and the Pechini method is reported. The composition of C2S (α, β, and γ) polymorphs, by-products, and amorphous content is established by employing QXRD (quantitative X-ray diffraction) studies. The attention has been focused to comprehend assay-amorphous relationships of C2S yield. The intermediate dried gels have been investigated via thermal analysis to monitor changes in the gel structures and precursors at low temperatures. The synthetic parameters including calcination time and temperature, Ca/Si molar ratio and mode of cooling have been optimized to get pure β-C2S with low amorphous content. The dependency of β → γ C2S polymorphic transformation on mean crystallite size (Dcryst) is studied. Overall, the Pechini method exhibits the most promising results for the purity and tuning of β-C2S polymorph. Moreover, the non-aqueous and aqueous routes require calcining the dried gel at a temperature higher than 1200 ℃ due to the presence of CaO precursors as CaCO3. The theoretical calculations of amorphous content have revealed that the change in the stoichiometry from 2.0 to 1.7 Ca/Si ratio is not a viable solution to improve the C2S product yield.

Removal of Remazol Red RR from Aqueous Solution by Glass Supported Films of Synthesized ZnO Nanoparticles.

The nanoparticles of ZnO (n-ZnO) have been synthesized by a sol-gel method and characterized by UV-visible and FTIR spectroscopy, scanning electron microscopy (SEM), energy dispersive X-Ray spectrometry (EDX) and powder X-ray diffractometry (XRD). Precursor of n-ZnO particles were prepared via a non-aqueous route, which was calcined at 500oC. These particles were then deposited on a glass substrate for adsorption and photodegradation of a typical textile dye, Remazol Red R (RRR). Especially, the high surface to volume ratio of nanoparticles has appealed much attention to use these particles both as an adsorbent and a photocatalyst. A comparative study was carried out between n-ZnO and a commercially available ZnO (c-ZnO) to investigate the removal efficiency of RRR from its aqueous solution under different conditions. The removal efficiency has been optimized by varying several operating variables and the highest performance has been obtained with 0.115 g/slide of ZnO and 0.5 × 10-4 M aqueous solution of RRR under sunlight irradiation. It is important to note that the use of the films of ZnO in the presence of solar light makes it suitable for recycling and causes no secondary environmental pollution.

Nickel(0) catalyzed oxidation of organosilanes to disiloxanes by air as an oxidant

We report here an efficient non-aqueous route to symmetrical disiloxanes from their corresponding organosilanes using Ni(COD)2 with 3,4,7,8-tetramethyl-1,10-phenanthroline in air. Our methodology is very simple and high yielding. The reaction mechanism is also proposed.

A facile nonaqueous route for preparing mixed-phase TiO2 with high activity in photocatalytic hydrogen generation

A facile and simple method was developed to prepare amorphous titanium oxalate from nonaqueous reaction of tetrabutyl titanate and oxalic acid in ethanol at room temperature. This complex was converted to mixed-phase TiO2 (anatase/rutile) by calcinations. The mixed-phase TiO2 obtained at the optimum calcination temperature (600 °C) consisting of 67 wt% anatase and 33 wt% rutile exhibited superior photocatalytic hydrogen production activity (1026 μmol h−1) with high stability, which can be ascribed to the phase-junctions (anatase/rutile) and high crystalline.

A simple non-aqueous route to nano-perovskite mixed oxides with improved catalytic properties

Highly crystalline LaBxO3 (B=Co, Mn) perovskites are produced through a simple non-aqueous benzyl alcohol (BA) route. Textural properties of BA-derived materials were compared to those obtained for solids of comparable composition, prepared by classical citric acid complexation method. Oxygen mobility in synthesized materials was evaluated by oxygen isotopic (18O) exchange (OIE). Perovskites obtained with the BA route shows much larger specific surface area, smaller crystallite size and superior oxygen mobility. Such improvement in properties is in favor of low temperature catalytic oxidation, as evaluated by CO oxidation.

Monodisperse ZnFe2O4 nanospheres synthesized by a nonaqueous route for a highly slective low-ppm-level toluene gas sensor

Monodisperse ZnFe2O4 nanospheres were succesuffully synthesized via a nonaqueous route in benzyl alcohol at low temperaure of 200°C. It was found that the ZnFe2O4 is 7–16nm in diameter with a large surface area of 87.40m2/g. The gas sensor based on ZnFe2O4 nanospheres shows a high pontential for detecting low-ppm-level toluene, exhibiting a good linearity ranging from 1 to 100ppm with a high response (100ppm:9.98) and excellent selectivity.

Role of reduced precursor and solvolytic reagent molar ratio on preparation and properties of ionogel

In the present study, ionogels have been synthesized by immobilizing IL (1-ethyl-3-methylimidazolium tetrafluoroborate) in silica gel matrices using non-aqueous route. In this process, tetraethyl orho-silane (TEOS) as a precursor to silicon dioxide and formic acid as a solvolytic gelating reagent in reduced molar ratio 1:4 were used. We find that reduced molar concentration of formic acid results the formation of ionogels having less number of closed pores (totally isolated from their neighbours), larger density and stable monolithic form. TEM and SEM measurements are used to visualize the morphology of sample and closed pores present in the sample. N2-sorption measurement is used to measure the pore parameters of the silica matrices which shows the mesoporous structure. DSC and TGA results show the change in phase transition temperature and thermal stability of IL upon confinement in silica matrices. Moreover, ionic conductivity of bulk and confined IL is measured using impedance spectroscopy and it has been found that it increases with increasing the temperature as well as concentration of IL in ionogels. Apart from these characterization techniques, ionogels have been characterized using FTIR and fluorescence spectroscopy which exhibit the change in vibrational frequencies and fluorescence behaviour of confined IL.

Low cost room temperature curable alumina ink for printed electronic applications

A low cost, room temperature curable alumina ink has been prepared by non-aqueous route. The ink is printed on flexible biaxially-oriented polyethylene terephthalate (BoPET) substrate as well as on photographic paper. The dielectric constant of the printed alumina on BoPET film is found to be 3.29 and 3.26 at 5 and 15 GHz respectively with a dielectric loss of the order of 10–3. The printed alumina layer (without substrate) has a dielectric constant of 4.54 and loss tangent 0.010 at 15 GHz. The temperature coefficient of dielectric constant for alumina ink with BoPET substrate and alumina ink with photographic paper are 60 and 66 ppm/°C respectively. The variation of dielectric constant and loss tangent with the thickness of the printed layer is also investigated. The results indicate that the alumina dielectric ink can be used as a potential candidate for future printed electronic applications.

Nanocomposites by the use of simultaneous twin polymerization: tin alloys in a carbon/silica matrix

Twin polymerization is used as a novel nonaqueous route to synthesize composites composed of nanoparticular tin alloys in a porous carbon/silica matrix.

Nonaqueous synthesis of Ag-functionalized In2O3/ZnO nanocomposites for highly sensitive formaldehyde sensor

In this work, Ag-functionalized In2O3/ZnO (IZO) nanocomposites with various contents were successfully fabricated by a nonaqueous route. The ZnO and In2O3 showed separated phases and different sizes deriving from the faster growth of ZnO than In2O3 using benzyl alcohol as the oxygen supplying agent. To demonstrate the usage of such Ag-functionalized IZO, the gas sensors have been fabricated and investigated for formaldehyde (HCHO) detection. The results reveal that the as-synthesized 3wt% Ag-functionalized IZO samples exhibit high response of about 842.9 towards 2000ppm HCHO at operating temperature of 300°C. All sensors show rapid response and recovery. The highly sensing properties are attributed to the synergistic effects arising from the presence of these multiple functional materials, i.e. the special structure of IZO nanocomposites, the formation of the heterojunctions, the influence of Ag nanoparticles, and the mutual doping effect.

Non-aqueous colloidal processing route for fabrication of highly dispersed aramid nanofibers attached with Ag nanoparticles and their stability in epoxy matrixes

Abstract In order to achieve the one-dimensional alignment of Ag nanoparticles (NPs) in epoxy resins, a simple technique to attach Ag NPs on aramid nanofibers (ANFs) and then to disperse the prepared Ag NP/ANF composites in epoxy resins and their processing solvents has been established. To facilitate the attachment of Ag NPs on ANFs and the stabilization of the Ag NP/ANF composites, the surface of the Ag NPs was modified with polyethyleneimine (PEI) and an anionic surfactant that branches into alkyl- and polyethylene glycol-based chains, which improved the stability of the NPs in various solvents and polymers. The prepared Ag NPs were then dispersed into ethanol or toluene and mixed with an ANF suspension prepared in dimethyl sulfoxide (DMSO) with the assistance of ultrasonication. The effect that the solvents and the Ag NPs/ANFs ratio, during the mixing procedure, had on the morphology and stability of the prepared Ag NP/ANF composites was investigated. It was found that Ag NPs could attach on ANFs without forming strong aggregates, when ethanol was chosen as the solvent. An increase in the average diameter of the Ag NPs attached on the ANFs was observed as the relative number of Ag NPs increased; this could be due to the dissolution and reduction of Ag + during the ultrasonication treatment, assisted by the PEI layer on the Ag NPs. The prepared Ag NP/ANFs were found to be dispersible in epoxy/toluene mixtures and epoxy resins, and their long-term stability (>3 days) was ensured when the suspension viscosity was controlled at >1.7 Pa s.

Facile preparation of TiO2–polyvinyl alcohol hybrid nanoparticles with improved visible light photocatalytic activity

Hybrid inorganic/organic core/shell nanoparticles were prepared through a two step synthesis procedure. In the first step, pure anatase TiO2 nanoparticles were synthesized though a rapid microwave assisted non-aqueous route. Then, the obtained titania nanoparticles were coated with polyvinyl alcohol (PVA) using a simple solution method followed by relatively low temperature treatment.The PVA-coated titania nanoparticles samples were prepared at different TiO2–PVA weight ratio and they were characterized using X-Ray diffraction, transmission electron microscopy, infrared spectroscopy and Brunauer–Emmett–Teller (BET) analysis.Photocatalytic performance was also evaluated for all samples and the results indicated that TiO2:PVA weight ratio was a key factor to obtain an improvement of the photocatalytic activity with respect to bare TiO2 nanoparticles, since PVA concentration influenced the surface area and the aggregation of nanoparticles and the thickness of the coating layer. This inexpensive system provides a simple, quick and effective approach which allows to obtain core/shell hybrid nanostructures.

ZnO/Ag heterostructured nanoassemblies: Wet-chemical preparation and improved visible-light photocatalytic performance

We reported a simple and convenient approach for the synthesis of high-yield ZnO/Ag nanocomposites by applying one-pot nonaqueous route. The products were characterized by X-ray diffraction, transmission electron microscopy, UV–vis spectroscopy and photoluminescence spectroscopy. The results showed that the products consisted of metallic Ag and ZnO components; Ag nanoparticles were attached to the ZnO nanorod cores; ZnO/Ag hybrid nanoarchitectures displayed tunable optical properties. Moreover, these ZnO/Ag heterostructured nanoassemblies possessed enhanced visible-light photocatalytic activity based on the unique ZnO–Ag interphase boundaries and synergetic effect between neighboring Ag nanoparticles and ZnO nanorods.

Polymorphic phase transition among the titania crystal structures using a solution-based approach: from precursor chemistry to nucleation process.

Nanocrystalline titania are a robust candidate for various functional applications owing to its non-toxicity, cheap availability, ease of preparation and exceptional photochemical as well as thermal stability. The uniqueness in each lattice structure of titania leads to multifaceted physico-chemical and opto-electronic properties, which yield different functionalities and thus influence their performances in various green energy applications. The high temperature treatment for crystallizing titania triggers inevitable particle growth and the destruction of delicate nanostructural features. Thus, the preparation of crystalline titania with tunable phase/particle size/morphology at low to moderate temperatures using a solution-based approach has paved the way for further exciting areas of research. In this focused review, titania synthesis from hydrothermal/solvothermal method, conventional sol-gel method and sol-gel-assisted method via ultrasonication, photoillumination and ILs, thermolysis and microemulsion routes are discussed. These wet chemical methods have broader visibility, since multiple reaction parameters, such as precursor chemistry, surfactants, chelating agents, solvents, mineralizer, pH of the solution, aging time, reaction temperature/time, inorganic electrolytes, can be easily manipulated to tune the final physical structure. This review sheds light on the stabilization/phase transformation pathways of titania polymorphs like anatase, rutile, brookite and TiO2(B) under a variety of reaction conditions. The driving force for crystallization arising from complex species in solution coupled with pH of the solution and ion species facilitating the orientation of octahedral resulting in a crystalline phase are reviewed in detail. In addition to titanium halide/alkoxide, the nucleation of titania from other precursors like peroxo and layered titanates are also discussed. The non-aqueous route and ball milling-induced titania transformation is briefly outlined; moreover, the lacunae in understanding the concepts and future prospects in this exciting field are suggested.

Hierarchical porous BiOI architectures: Facile microwave nonaqueous synthesis, characterization and application in the removal of Congo red from aqueous solution

Three-dimensional (3D) hierarchical porous architectures have become promising candidates for adsorption-based environmental remediation in recent years. However, such type of adsorbents often suffers from the complicated production and undesirable regeneration, limiting their practical environmental application greatly. In this contribution, a novel adsorbent based on hierarchical porous bismuth oxyiodide (BiOI) architectures combining the highly effective adsorption and green photocatalytic regeneration were designed and fabricated by a facile and rapid microwave nonaqueous route. The resultant samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), nitrogen adsorption–desorption measurements, and UV–vis diffuse reflectance spectroscopy (DRS). The BiOI architectures displayed remarkable performance towards removal of Congo red (CR) from aqueous solution, showing a maximum adsorption capacity reached up to 216.8mgg−1. The kinetics and equilibrium of adsorption process were found to follow the pseudo-second-order kinetic and Freundlich isotherm models, respectively. More importantly, the BiOI architectures were not only easy to separate from the reaction system because of the hierarchical structure and large sizes, but also attractive to photocatalytic regeneration due to their intrinsically prominent photoresponse in visible light region. By means of providing the facile preparation, high adsorption efficiency, easy solid–liquid separation, and economical photocatalytic regeneration, the synthesized BiOI architectures established an outstanding example for the design of multifunctionalized adsorbent with high performance for environmental remediation.

A Facile Non-Aqueous Approach for the Synthesis of Cu Nanowires

A non-aqueous synthetic route has been developed for the preparation of uniform Cu nanowires with length up to tens of micrometers. Unlike commonly used one-pot synthesis approach that usually involve a fast reduction of metal precursors in the presence of reducing agents, a continuous-injection approach has been to utilized to control the speed of reaction and the concentration of Cu nuclei. In this approach, copper (II) chloride dihydrate and nickel (II) acetylacetone which are dissolved in oleylamine solutions have been injected into octadecene by a syringe-pump. The as-prepared samples have been characterized by transmission electron microscopy, scanning electron microscopy and energy-dispersive X-ray spectroscopy. The results show that the products are pure Cu nanowires which have preferred <110> growth directions. The formation mechanism and major influencing factors on the synthesis of Cu nanowires have been discussed.

Tailoring Two Polymorphs of LiFePO4 by Efficient Microwave-Assisted Synthesis: A Combined Experimental and Theoretical Study

LiFePO4 typically crystallizes in the olivine-type phase (denoted as α-phase hereafter). When high pressure (65 kbar) and elevated temperature (900 °C) are applied, the α-LiFePO4 transforms into a high-pressure phase (denoted as β-phase hereafter). Here, we report a facile approach to directly tailor the two polymorphs of LiFePO4 in a controlled way under mild conditions. Employing a microwave-assisted nonaqueous route, highly crystalline LiFePO4 with either α- or β-phase can be efficiently synthesized within 3 min, by simply tuning the ratio of the solvents, benzyl alcohol, and 2-pyrrolidinone. The resulting β-LiFePO4 particles exhibit a hierarchical self-assembled bow-tie-like microstructure, whereas the α-phase consists of nanoplates. In addition, the β-phase irreversibly transforms into the α-phase upon heat treatment without alteration of the morphology. After carbon-coating, α-LiFePO4 and phase-transformed β-LiFePO4, that is, α-LiFePO4 with the hierarchical morphology of the β-phase, exhibit excellent electrochemical performance, whereas pristine β-LiFePO4 displays unfavorable properties. Density functional total energy calculations are performed to get the relative energies and lattice stability of the two phases. A qualitative understanding of the poor electrochemical performance of the β-phase can be deduced from the molecular dynamics of the mobile Li ions in both structures.