Aqueous Chemical Synthesis Research Articles

Aqueous Chemical Synthesis of Nanosized ZnGa2O4 Using Mild Reaction Conditions: Effect of pH on the Structural, Morphological, Textural, Electronic, and Photocatalytic Properties

The effect of pH on the structural, textural, morphological, and electronic properties of ZnGa2O4 nanoparticles obtained by coprecipitation using mild reaction conditions (25 °C; 30 min) was studied. The pH ranges in which coprecipitation reactions occurred and the chemical species associated with the reaction mechanism were identified. It was determined that the samples synthesized at pH values between 6 and 10 consisted of Zn-Ga oxide blends, with spinel ZnGa2O4 being the majority phase. Conversely, the material prepared at pH 12 was constituted by Zn-Ga layered double hydroxide phase along with wurtzite ZnO traces. The synthesis pH determined the reaction product yield, which decreased from 51 to 21% when the reaction medium turned from softly acidic (pH 6) to strongly alkaline conditions (pH 12). The bandgap energies of the synthesized materials were estimated to be in the range of 4.71–4.90 eV. A coprecipitation-dissolution-crystallization mechanism was proposed from the precipitation curve, with specific mononuclear and polynuclear species being involved in the formation of the different precipitates. Phenol was employed as a probe molecule to evaluate the photocatalytic performance of the synthesized samples. Among the samples, the one prepared at pH 6 showed the largest photodegradation efficiency (~98%), which was superior to commercial TiO2-Degussa P25 (~88%) under the same process conditions, which can be attributed to both its high specific surface area (140 m2 g−1) and the formation of a Zn2xGa2−2xO3+x/ZnGa2O4 heterojunction.

In situ characterisation for studying nucleation and growth of nanostructured materials and thin films during liquid-based synthesis

Knowledge about the nucleation, growth, and formation mechanisms during materials synthesis using sol-gel and solution-based methods is important to design a material with desired properties. We used aqueous chemical synthesis as an environmentally friendly and highly flexible route to tailored and reproducible synthesis of oxide nanomaterials and thin films. For studies of hydrothermal synthesis an in situ cell using synchrotron X-ray diffraction was used to investigate the formation mechanisms of SrxBa1-xNb2O6 piezoelectrics. Aqueous chemical solution deposition of phase pure oriented piezoelectric thin films demands strong control of processing parameters. An in situ cell for synchrotron X-ray diffraction studies of the annealing and crystallisation steps during aqueous chemical solution deposition was used to understand the nucleation and crystallisation of Ba0.85Ca0.15Zr0.1Ti0.9O3 (BCZT). We discuss how the knowledge about nucleation and growth obtained by in situ characterisation can be used to design the optimal procedure for fabrication of oxide materials with desired properties.Graphical abstract

Composite Li-ion battery cathodes formed via integration of carbon nanotubes or graphene nanoplatelets into chemical preintercalation synthesis of bilayered vanadium oxides

Bilayered vanadium oxides are attractive cathode materials for rechargeable batteries. The expanded interlayer space and versatile chemistries of these oxides yield high specific capacities. However, capacity retention and rate performance are limited due to structural instability and low electronic conductivity of these materials. Assembling the oxides with one- and two-dimensional carbon nanoparticles may produce highly efficient heterointerfaces that would enhance electrochemical charge storage properties. Here, we synthesize for the first time bilayered vanadium oxide composites with carbon nanotubes (CNTs) and graphene nanoplatelets (GNPs). The nanostructured carbons were initially functionalized by flash oxidation in air to create polar groups on the carbon surface, producing fCNTs and fGNPs, and improve compatibility with an aqueous chemical preintercalation synthesis route. Lithium preintercalated bilayered vanadium oxide, LVO (LVO = δ-LixV2O5·nH2O), was selected as a redox active oxide component to facilitate Li+ ion diffusion through the interlayer region of δ-V2O5. A one-step process was developed to synthesize LVO/fCNT and LVO/fGNP composites by an in situ low temperature sol-gel method. We observed marked improvements in capacity retention and rate performance in the nanocomposites as compared to the pristine oxide, which were attributed to both improved electron transport and heterointerface stabilization effect enabled by integration with fCNTs and fGNPs. This work illustrates the ability to enhance material functionality through the in situ synthesis of nanocomposites with controllable heterointerface.

Aqueous chemical synthesis of iron oxides magnetic nanoparticles of different morphology and mesostructure

Magnetic nanoparticles of magnetite structure were obtained by the aqueous chemical synthesis, namely: using the chemical co-precipitation from the 1:2 M ratio mix of the iron chlorides (II, III) water solution with the ammonia used as precipitation agent as well as with oleic acid. Obtained nanopowders were studied using the X-Ray diffraction, infrared spectroscopy, scanning and transmission electron microscopy, low-temperature nitrogen absorption, and small-angle X-Ray scattering methods in order to determine the influence of synthesis techniques (homogenization procedure, separation methods – decantation, vacuum filtration, rotary evaporation, or magnetic separation), on the phase composition, size, morphology and magnetic parameters of the nanoparticles. It was demonstrated that the value of the specific surface area of nanoparticles with the average size of 10–20 nm is relatively high (75–132 m2/g) and their shape is lamellar or rod-shaped as well as cylindrical (round). The technique of separating nanoparticles from the mother liquor had a dominant effect on the morphology of nanoparticles. Dynamic and Electrophoretic Light Scattering methods showed that homogenization procedure, separation methods and especially surface modification with oleic acid affect the size and surface charge of the nanopowders.

The Structure and Properties of TiO2 Nanopowders for Use in Agricultural Technologies

TiO2 nanopowder has been prepared with aqueous chemical synthesis for use in agriculture. A commercial nanopowder was taken for comparison. A comprehensive study of the phase composition, morphology, and structure of both nanopowders was carried out using methods of X-ray phase analysis, Raman spectroscopy, scanning electron microscopy, ultra-small-angle and small-angle neutron scattering, and low-temperature nitrogen adsorption. A comparison of the photocatalytic activity of these powders was carried out. Aqueous suspensions of these powders were used for the pre-sowing treatment of white cabbage seeds. A positive effect of suspensions of both titanium dioxide powders at a concentration of 0.3 g/l on the germination and biometric characteristics of plant seedlings of cabbage seedlings was revealed. As a tendency, we can note the more beneficial effect of the synthesized powder, which has a high specific surface area and porosity, is weakly crystallized in the anatase phase, and has a three-level fractal structure. No direct effect of photocatalytic activity on the germination and growth characteristics of plant seedlings was found.

Optical properties from photoelectron energy-loss spectroscopy of low-temperature aqueous chemically synthesized ZnO nanorods grown on Si

The optical properties of zinc oxide (ZnO) nanorods (NRs) synthesized by the low-temperature aqueous chemical method on top of silicon (Si) substrate have been investigated by means of photoelectron energy loss spectroscopy (PEELS). The ZnO NRs were obtained by the low temperature aqueous chemical synthesis on top of Si substrate. The measured valence band, the dynamical dielectric functions and optical absorption of the material show a reasonable agreement when the trending and shape of the theoretical calculations are considered. A first-principle calculation based on density functional theory (DFT) was performed using the partially self-consistent GW approximation (scGW0) and compared to the experimental results. The application of these two techniques brings a new analysis of the electronic properties of this material. The experimental results regarding the density of states (DOS) obtained for the valence band using x-ray photoelectron spectroscopy (XPS) was found to be consistent with the theoretical calculated value. Due to this consistency, the same wavefunctions was then employed to calculate the dielectric function of the ZnO NRs. The experimentally extracted dielectric function was also consistent with the calculated values.

Aqueous Chemical Synthesis and Consolidation of Size-Controlled Bi2Te3 Nanoparticles for Low-Cost and High-Performance Thermoelectric Materials

Bi2Te3 nanoparticles (NPs) were synthesized with controlled mean diameters of 58 nm, 82 nm, and 100 nm using an aqueous chemical reduction, in which ascorbic acid was used instead of the commonly employed toxic reducing agent. In general, organic capping agents remained on the Bi2Te3 NP surfaces, which prevented the sintering of Bi2Te3 NPs and affected their thermoelectric properties. Not only the capping agent, but also water from the synthesis process, remained on the Bi2Te3 NPs even after their consolidation by spark plasma sintering. Consequently, evaporation of the water led to the collapse of sintered Bi2Te3 NPs when heated above 100°C. After the complete removal of the surface impurities and water, the sintered Bi2Te3 NPs became stable. To achieve enhanced thermoelectric properties, a high relative density of ∼ 96% was achieved in the sintered Bi2Te3 NPs without large grain growth by optimizing the sintering temperature and holding time. Subsequently, their thermoelectric properties showed that zT of the sintered Bi2Te3 NPs 100 nm in size is higher (0.41 at 390 K) than those of smaller sizes (58 nm and 82 nm). Finally, the effect of grain size, particle size and density on their thermoelectric properties is discussed.

Cadmium chalcogenide derived fluorescent quanta-sensor for melamine detection

The present work reports the detection of melamine (artificial protein) in milk using mercapto-propionic acid capped cadmium selenide (m-CdSe) quantum dots (QDs) as fluorescent labels, denoted as quanta-sensor. The m-CdSe QDs were prepared using aqueous chemical synthesis method and were characterized to get insight about their structural and functional properties. The formation of m-CdSe QDs was confirmed by using Transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). The optical properties (absorption and emission) of m-CdSe QDs were studied as a function of cadmium salt concentration, selenide salt concentration and pH. The effect of incubation time with melamine on fluorescence of QDs was also studied in order to check the stability of quanta-sensor. The linearity range of this quanta-sensor was found to be 0.01 nM to 60 μM, with LOD of 0.013 nM. The quanta-sensor exhibited good reproducibility, selectivity and acted as a potential probe for detection of melamine in milk samples.

On the growth mechanism of ZnO nano structure via aqueous chemical synthesis

Because of multi-functional properties with high specific surface area, ZnO nano architectures are finding immense utilities in variegated applications viz., sensing, diagnostics, etc. To investigate the concept behind the long and vertical growth of the ZnO nano structures, understanding of surface energy, molecular interaction, their reactions at certain physical environment such as temperature and pressure, etc., is utmost important. The high aspect hexagonal crystal growth inside aqueous chemical solution is rarely explained by researchers. This crystal growth mechanism involves variety of variables such as solute concentrations, seed orientation, reaction rate, other impurities, etc. Based on the experimental observation herein, a theoretical modeling for ZnO crystal vertical growth is proposed and its epitaxial growth rate along with side length and with function of time is investigated.

An effective low-temperature solution synthesis of Co-doped [0001]-oriented ZnO nanorods

We demonstrate an efficient possibility to synthesize vertically aligned pure zinc oxide (ZnO) and Co-doped ZnO nanorods (NRs) using the low-temperature aqueous chemical synthesis (90 °C). Two different mixing methods of the synthesis solutions were investigated for the Co-doped samples. The synthesized samples were compared to pure ZnO NRs regarding the Co incorporation and crystal quality. Electron paramagnetic resonance (EPR) measurements confirmed the substitution of Co2+ inside the ZnO NRs, giving a highly anisotropic magnetic Co2+ signal. The substitution of Zn2+ by Co2+ was observed to be combined with a drastic reduction in the core-defect (CD) signal (g ∼ 1.956) which is seen in pure ZnO NRs. As revealed by the cathodoluminescence (CL), the incorporation of Co causes a slight red-shift of the UV peak position combined with an enhancement in the intensity of the defect-related yellow-orange emission compared to pure ZnO NRs. Furthermore, the EPR and the CL measurements allow a possible model of the defect configuration in the samples. It is proposed that the as-synthesized pure ZnO NRs likely contain Zn interstitial (Zni+) as CDs and oxygen vacancy (VO) or oxygen interstitial (Oi) as surface defects. As a result, Co was found to likely occupy the Zni+, leading to the observed CDs reduction and hence enhancing the crystal quality. These results open the possibility of synthesis of highly crystalline quality ZnO NRs-based diluted magnetic semiconductors using the low-temperature aqueous chemical method.

Low temperature simple aqueous phase chemical synthesis and characterization of ZnO thin films

Zinc oxide (ZnO) nanorods were successfully deposited on the glass and fluorine doped tin oxide coated glass substrate in an aqueous alkaline medium using zinc acetate, ethylene diamine, hexamethylene tetraamine and ethanol by simple chemical reflux method at low temperature. An Optical, structural, morphological compositional and photoelectrochemical (PEC) properties of ZnO thin films were investigated. Optical absorption study of the sample shows band gap value 3.24 eV. The X-ray diffraction (XRD) pattern indicates that the deposited material is nanocrystalline and nanorods formation takes place along (002) plane having hexagonal wurtzite crystal structure. The scanning electron microscopy (SEM) images demonstrate existence of hexagonal nanorods with average50nm lengths and 10 nm diamete.The X-ray photoelectron spectroscopy (XPS) study confirms well composed thin film formation. The PEC study revel that material exhibit photo conversion efficiency 1.84% for solar cell application.

Seed layer synthesis effect on the concentration of interface defects and emission spectra of ZnO nanorods/p‐GaN light‐emitting diode

As the low‐temperature aqueous chemical synthesis (LT‐ACS), holds great promises for the synthesis of one‐dimensional (1D) ZnO nanostructure‐based light‐emitting diodes (LEDs) and hence require parameter tuning for optimal performance. N‐ZnO nanorods (NRs)/p‐GaN heterojunction LEDs have been synthesized by the LT‐ACS using ZnO nanoparticle (NPs) seed layers prepared with different precursor solutions. The effect of these seed layers on the interface defect properties and emission intensity of the as‐synthesized n‐Zn/p‐GaN heterojunction LEDs has been demonstrated by spatially resolved cathodoluminescence (CL) and electroluminescence (EL) measurements, respectively. A significant reduction of the interface defects in the n‐ZnO NRs/p‐GaN heterostructure synthesized from a seed layer prepared from zinc acetate (ZnAc) with a mixture of potassium hydroxide (KOH) and hexamethylenetetramine (HMTA) (donated as ZKH seed) compared with those prepared from ZnAc and KOH (donated as ZK seed) is observed as revealed by spatially resolved CL. Consequently, the LEDs based on n‐ZnO NRs/p‐GaN prepared from ZKH seed show an improvement in the yellow emission (∼578 nm) compared to that based on the ZK seed as deduced from the electroluminescence measurements. The improvement in the yellow EL emission on the ZKH LED probably attributed to the low presence of the non‐radiative defect as deduced by light‐output current (L–I) characteristics analysis.

Influence of ZnO seed layer precursor molar ratio on the density of interface defects in low temperature aqueous chemically synthesized ZnO nanorods/GaN light-emitting diodes

Low temperature aqueous chemical synthesis (LT-ACS) of zinc oxide (ZnO) nanorods (NRs) has been attracting considerable research interest due to its great potential in the development of light-emitting diodes (LEDs). The influence of the molar ratio of the zinc acetate (ZnAc): KOH as a ZnO seed layer precursor on the density of interface defects and hence the presence of non-radiative recombination centers in LT-ACS of ZnO NRs/GaN LEDs has been systematically investigated. The material quality of the as-prepared seed layer as quantitatively deduced by the X-ray photoelectron spectroscopy is found to be influenced by the molar ratio. It is revealed by spatially resolved cathodoluminescence that the seed layer molar ratio plays a significant role in the formation and the density of defects at the n-ZnO NRs/p-GaN heterostructure interface. Consequently, LED devices processed using ZnO NRs synthesized with molar ratio of 1:5 M exhibit stronger yellow emission (∼575 nm) compared to those based on 1:1 and 1:3 M ratios as measured by the electroluminescence. Furthermore, seed layer molar ratio shows a quantitative dependence of the non-radiative defect densities as deduced from light-output current characteristics analysis. These results have implications on the development of high-efficiency ZnO-based LEDs and may also be helpful in understanding the effects of the ZnO seed layer on defect-related non-radiative recombination.

ZnO nanoflowers-based photoanodes: aqueous chemical synthesis, microstructure and optical properties

AbstractWe have developed an efficient, low temperature, synthetic route for ZnO nanoflowers (NFs) as photoanode material. This alternative route yields small flowerlike nanostructures, built from densely self-assembled tip-ended rod structures. The obtained ZnO NFs possess a large bandgap of 3.27 - 3.39 eV, enabling the generation of an average open current voltage of 0.56 V. Additionally, they show a high internal light harvesting of 14.6•10-7A-mol-1. The growth mechanism and self-assembly of ZnO NFs were studied in detail by joint spectroscopic-TEM investigations. It is shown that the ZnO crystallite size increases with increasing annealing temperatures and that the stress and the improved crystallinity are induced by annealing and reduce the lattice strain and the dislocation density. The bandgaps of ZnO are affected by the lattice strain revealing an optimal region of lattice strain to gain high bandgap energies. The properties of the synthesized ZnO NFs are compared with other morphologies, i.e. ZnO spherical aggregates (SPs) and ZnO nanorods (NRs), and are tested as electrode materials in dye-sensitized solar cells.

Effect of precursor solutions stirring on deep level defects concentration and spatial distribution in low temperature aqueous chemical synthesis of zinc oxide nanorods

Hexagonal c-axis oriented zinc oxide (ZnO) nanorods (NRs) with 120-300 nm diameters are synthesized via the low temperature aqueous chemical route at 80 °C on silver-coated glass substrates. The influence of varying the precursor solutions stirring durations on the concentration and spatial distributions of deep level defects in ZnO NRs is investigated. Room temperature micro-photoluminesnce (μ-PL) spectra were collected for all samples. Cathodoluminescence (CL) spectra of the as-synthesized NRs reveal a significant change in the intensity ratio of the near band edge emission (NBE) to the deep-level emission (DLE) peaks with increasing stirring durations. This is attributed to the variation in the concentration of the oxygen-deficiency with increasing stirring durations as suggested from the X-ray photoelectron spectroscopy analysis. Spatially resolved CL spectra taken along individual NRs revealed that stirring the precursor solutions for relatively short duration (1-3 h), which likely induced high super saturation under thermodynamic equilibrium during the synthesis process, is observed to favor the formation of point defects moving towards the tip of the NRs. In contrary, stirring for longer duration (5-15 h) will induce low super saturation favoring the formation of point defects located at the bottom of the NRs. These findings demonstrate that it is possible to control the concentration and spatial distribution of deep level defects in ZnO NRs by varying the stirring durations of the precursor solutions.

Local Controlled Release of Polyphenol Conjugated with Gelatin Facilitates Bone Formation.

Catechins are extensively used in health care treatments. Nevertheless, there is scarce information about the feasibility of local administration with polyphenols for bone regeneration therapy, possibly due to lack of effective delivery systems. Here we demonstrated that the epigallocatechin-3-gallate-conjugated gelatin (EGCG/Gel) prepared by an aqueous chemical synthesis using 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-morpholinium chloride (DMT-MM) gradually disintegrated with time and facilitated bone formation in a critical size defect of a mouse calvaria. Conjugation of EGCG with the Gel generated cross-linking between the two molecules, thereby leading to a retardation of the degradation of the EGCG/Gel and to a delayed release of EGCG. The prepared EGCG/Gels represented significant osteogenic capability compared with that of the uncross-linked Gel and the cross-linked Gel with uncombined-EGCG. In vitro experiments disclosed that the EGCG/Gel induced osteoblastogenesis of a mouse mesenchymal stem cell line (D1 cells) within 14 days. Using fluorescently-labeled EGCG/Gel, we found that the fraction of EGCG/Gel adsorbed onto the cell membrane of the D1 cells possibly via a Gel-cell interaction. The interaction might confer the long-term effects of EGCG on the cells, resulting in a potent osteogenic capability of the EGCG/Gel in vivo. These results should provide insight into local controlled release of polyphenols for bone therapy.

Habit-modifying additives and their morphological consequences on photoluminescence and glucose sensing properties of ZnO nanostructures, grown via aqueous chemical synthesis

Generally, the anisotropic shape of inorganic nano-crystal can be influenced by one or more of different parameters i.e. kinetic energy barrier, temperature, time, and the nature of the capping molecules. Here, different surfactants acting as capping molecules were used to assist the aqueous chemical growth of zinc oxide (ZnO) nanostructures on Au coated glass substrates. The morphology, crystal quality and the photoluminescence (PL) properties of the ZnO nanostructures were investigated. The PL properties of the prepared ZnO nanostructures at room temperature showed a dominant UV luminescence peak, while the “green–yellow” emissions were essentially suppressed. Moreover, the ZnO nanostructures were investigated for the development of a glucose biosensor. An adsorbed molecule has direct contribution on the glucose oxidase/ZnO/Au sensing properties. We show that the performance of a ZnO-based biosensor can be improved by tailoring the properties of the ZnO–biomolecule interface through engineering of the morphology, effective surface area, and adsorption capability.

Efficient room temperature aqueous Sb2S3 synthesis for inorganic-organic sensitized solar cells with 5.1% efficiencies.

Sb2S3 sensitized solar cells are a promising alternative to devices employing organic dyes. The manufacture of Sb2S3 absorber layers is however slow and cumbersome. Here, we report the modified aqueous chemical bath synthesis of Sb2S3 absorber layers for sensitized solar cells. Our method is based on the hydrolysis of SbCl3 to complex antimony ions decelerating the reaction at ambient conditions, in contrast to the usual low temperature deposition protocol. This simplified deposition route allows the manufacture of sensitized mesoporous-TiO2 solar cells with power conversion efficiencies up to η = 5.1%. Photothermal deflection spectroscopy shows that the sub-bandgap trap-state density is lower in Sb2S3 films deposited with this method, compared to standard deposition protocols.

Aqueous chemical route synthesis and the effect of calcination temperature on the structural and optical properties of ZnO nanoparticles

This article reports the controlled size of ZnO nanoparticles synthesized via simple aqueous chemical route without the involvement of any capping agent. The effect of different calcination temperatures on the size of the ZnO nanoparticles was investigated. X-ray diffraction (XRD) results indicated that all the samples have crystalline wurtzite phase, and peak broadening analysis was used to evaluate the average crystallite size and lattice strain using Scherrer's equation and Williamson–Hall (W–H) method. Morphology and elemental compositions were investigated using atomic force microscopy (AFM) and scanning electron microscopy (SEM) with energy-dispersive X-ray (EDX) spectroscopy. The average crystallite size of ZnO nanoparticles estimated from Scherrer's formula and W–H analysis was found to increase with the increase in calcination temperature. These results were in good agreement with AFM results. Optical properties were investigated using UV–vis spectroscopy in diffused reflectance (DR) mode, with a sharp increase in reflectivity at 375nm and the material has a strong reflective characteristic after 420nm at 500°C calcination temperature. Furthermore, photoluminescence spectroscopic results revealed intensive ultraviolet (UV) emission with reduced defect concentrations and a slight shifting in band gap energies with increased calcination temperature from 200°C to 500°C. This study suggests that the as-prepared ZnO nanoparticles with bandgap tunability might be utilized as window layer in optoelectronic devices.

Gd2Zr2O7 and Nd2Zr2O7 pyrochlore prepared by aqueous chemical synthesis

Abstract Pyrochlore structured Gd2Zr2O7 and Nd2Zr2O7 are produced via complex precipitation processing. A suite of characterization techniques, including FTIR, Raman, X-ray and electron diffraction, TEM, SEM as well as nitrogen sorption are employed to investigate the structural and grain size evolution of the synthesized and calcined powder. Results show that Gd2Zr2O7 with the pyrochlore structure are produced after calcination at 1400 °C for 12 h while Nd2Zr2O7 has already formed the pyrochlore structure at 1200 °C. This method allows the formation of dense materials at relatively low temperature, with bulk densities over 92% of the theoretical values achieved after sintering at 1400 °C for 50 h. This unique aqueous synthetic method provides a simple pathway to produce pyrochlore lanthanide zirconate without using either organic solvent and/or mechanical milling procedures, making the synthesis protocol an attractive potential scale-up production of highly refractory ceramics.