Surfactant-free Synthesis Research Articles

Surfactant-free electrochemical synthesis of metallic nanoparticles via stochastic collisions of aqueous nanodroplet reactors

Stochastic collisions of aqueous nanodroplets (AnDs) on a microelectrode were observed in situ by electrochemistry. Reduction of Cu2+ ions enclosed in the reacting AnDs resulted in surfactant-free synthesis of copper nanoparticles on the electrode surface. The particle size distribution was reasonably controllable by the modulation of electrode voltage. The versatility of the synthetic method was established by its application in synthesizing nanoparticles of silver and cobalt oxyhydroxide.

Surfactant-free one-pot synthesis of CeO2, TiO2 and Ti@Ce oxide nanoparticles for the ultrafast removal of Cr(vi) from aqueous media.

Cerium oxide (CeO2), titanium oxide (TiO2) and titanium oxide impregnated with cerium oxide (Ti@Ce oxide) nanoparticles were synthesized using a simple one-pot surfactant-free method. The synthesized adsorbents were tested against the removal of Cr(vi) from aqueous medium. Comprehensive characterization methods like BET, XRD, SEM, EDAX, HR-TEM, SAED, HR-XPS and FT-IR were performed at different stages of the adsorption process and synthesis. A N2-BET study revealed the large surface area (268 m2 g-1) and pore size (6.8 nm) of CeO2 nanoparticles, which decreased after impregnation of titania. An XRD study demonstrated the phase transformation of TiO2 from the anatase phase to the rutile phase after the impregnation with CeO2 by lowering the phase transformation temperature from >550 °C to 400 °C. Ti0.3@Ce0.7 oxide nanoparticles showed 81% removal of Cr(vi) within 2.5 min of initiating the adsorption process while more than 92% removal of Cr(vi) was achieved within 10 min of adsorption. A HR-XPS study indicated the dual oxidation states of ceria and titania metals, which helped to convert the more toxic Cr(vi) ions to less toxic Cr(iii) ions during the adsorption process. The adsorption pattern depicted the monolayer behavior of Cr(vi) obeying the Redlich-Peterson isotherm and followed pseudo second-order kinetics. An intraparticle diffusion model disclosed the surface and pore resistance diffusion of Cr(vi) on the surface of adsorbents.

Surfactant-free synthesis of Cu2O yolk-shell cubes decorated with Pt nanoparticles for enhanced H2O2 detection.

Pt decorated yolk-shell Cu2O cubes are obtained using a surfactant-free and multiple-step method. Porous yolk-shell cubic structures, together with synergistic effects between Pt and Cu2O, endow the yolk-shell Pt-Cu2O based nonenzymatic H2O2 sensors with enhanced sensing performance.

Size effect studies in catalysis: a simple surfactant-free synthesis of sub 3nm Pd nanocatalysts supported on carbon.

Supported Pd nanoparticles are prepared under ambient conditions via a surfactant-free synthesis. Pd(NO3)2 is reduced in the presence of a carbon support in alkaline methanol to obtain sub 3 nm nanoparticles. The preparation method is relevant to the study of size effects in catalytic reactions like ethanol electro-oxidation.

Facile surfactant-free synthesis of polybenzoxazine-based polymer and nitrogen-doped carbon nanospheres

Facile surfactant-free synthesis of monodisperse polymer and nitrogen-doped carbon nanospheres with controllable sizes less than 200 nm based on the benzoxazine chemistry.

A Surfactant-Free Synthesis Technique of Coral-Like Zno Hierarchical Structures for Photocatalytic Degradation of Resorcinol under UV Irradiation

Hierarchical coral-like ZnO structures were successfully prepared by a surfactant-free wet chemical method. Various characterization tests were carried out to analyze the as-prepared ZnO samples. The coral-like ZnO was used to degrade resorcinol at three different solution pH values (pH 5.0, pH 8.0 and pH 11.0). It was observed that the resorcinol adsorption onto the ZnO was strongly dependent on the electrical charge properties of both photocatalyst and resorcinol. Photocatalytic degradation of resorcinol reached the highest at pH 11.0 due to high concentration of hydroxyl ions for hydroxyl radicals generation.

Extreme downsizing in the surfactant-free synthesis of spin-crossover nanoparticles in a microfluidic flow-focusing junction.

A new surfactant-free, flow-focusing droplet microfluidic approach was developed as an important alternative to existing synthesis techniques for the preparation of spin crossover nanoparticles. It enables great control of the mixing of the reactants, and produces crystals of [Fe(pyrazine)(Pt(CN)4)] with an unexpected 20-fold downsizing compared to classical bulk synthesis.

Surfactant-free synthesis of high surface area silica nanoparticles derived from rice husks by employing the Taguchi approach

High surface area biogenic silica nanoparticles extracted from rice husks (RH) were synthesized through a surfactant-free process by employing a design optimization of the Taguchi approach. This approach is a systematic and efficient method to design factorial experiments with a minimum number of experiments. Here, the amount of rice husk ash, pH and aging time were adopted as design parameters to determine the particle size and structural properties including porosity and surface area in the synthetic process. The average particle size of silica nanoparticles ranging 24–87nm and surface area to ∼740.77m2/g could be tuned in the factorial optimization, where the degree of parameters that influence the structural properties were investigated, combined with surface characterizations. The surface area, pore volume and pore size of the samples were analyzed by adsorption–desorption characteristics of N2 gas. An amount of silica contents was analyzed by X-ray fluorescence for each step of RH treatment. Scanning electron microscopy and transmission electron microscopy were utilized to show the morphology and primary particle size of the silica nanoparticle. The analysis showed that the optimized experimental parameters calculated based on “signal” to “noise” ratio derived from Taguchi approach shortened the number of experimental variations with a noticeable improvement of surface area, whose individual effects are elucidated. This synthetic technology of biogenic nano silica with high surface area based on the Taguchi approach has potential for efficient time savings and quality control strategies to optimize the synthetic process.

Surfactant-free synthesis, photocatalytic and electrochemical property study of Co3O4 nanoparticles

A facile surfactant-free route for size-control preparation of Co3O4 nanoparticles in aqueous solution was reported. The feeding ratio of OH− to Co2+ influences the conversion of Co2+ to Co3O4 crystals, and affects the crystallinity of the final Co3O4 products. The size of Co3O4 nanoparticles can be controlled to be 15, 18, 27 and 30nm by simply regulating the concentration of NaOH solution through a β-Co(OH)2→Co3O4 process. A linear relationship between Co3O4 size and NaOH concentration was found. The photocatalytic property for rhodamine B (RhB) degradation and electrochemical property for supercapacitor of the Co3O4 nanoparticles are size dependent. Co3O4 nanoparticles in the size of 15nm showed the highest photocatalytic efficiency of 70% in pH 3 under visible-light irradiation for 3h, and behaved the highest specific capacitance of 177Fg−1.

Enhanced photovoltaic performance of dye sensitized solar cell using SnO2 nanoflowers

The study highlighted enhanced performance of SnO2 based DSSC using photoanode with nanostructured morphology. The simple organic surfactant free hydrothermal synthesis method was used for preparation of SnO2 nanoflowers for dye sensitized solar cell (DSSC) application. The hydrothermal reaction time was varied to obtain different SnO2 nanostructures. The hydrothermal reaction time showed considerable effect on optical and structural properties of the prepared samples. The results indicated that the prepared samples were pure rutile SnO2. The band gap of prepared samples was greater than bulk SnO2 and varied from 3.64 to 3.81 eV with increase in hydrothermal reaction time. With increase in reaction time from 4 to 24 h, the microstructure of SnO2 changed from agglomerated nanoparticles to nanopetals and finally to self-assembled nanoflowers. Flower-like SnO2 nanostructures showed size around 300–700 nm, and composed of large numbers of 3 dimensional petals connected with each other forming 3D nanoflowers by self-assembly. Consequently, the DSSC with flower-like SnO2 nanostructures exhibited good photovoltaic performance with Voc, Jsc and η about 0.43 V, 4.36 mA/cm2 and 1.11%, respectively.

Surfactant-free synthesis of m-BiVO4 nanoribbons and enhanced visible-light photocatalytic properties

Monoclinic Bismuth vanadate (m-BiVO4) is a promising material for photocatalytic degradation of organic moieties. Uniform m-BiVO4 nanoribbons were synthesized by facile solvothermal route without using the surfactant and characterized by X-ray diffraction, scanning electron microscopy and UV–vis diffuse reflectance spectra technique. The obtained m-BiVO4 nanoribbons possess well defined 1-D architectures with homogenous morphology and surface area of 22.4m2/g. The prepared photocatalyst showed efficient photocatalytic activities up to 97% in 30min against the degradation of methylene blue (MB) under visible-light irradiation. The prepared photocatalyst is recyclable and showed a very small change in activity after three consecutive cycles. This higher activity can be attributed to higher surface area and crystallinity, which signify the promising commercial application of m-BiVO4 nanoribbons as highly novel and highly efficient photocatalyst for the degradation of organic pollutants.

Facile synthesis of 2D silver nanocrystals by a gas–solution interface technique

The templateless and surfactant-free facile synthesis of 2D silver nanocrystals was carried out for the first time by a gas–solution interface technique using an aqueous solution of AgOAc and gaseous N2H4 as reactants.

Surfactant-Free Vapor-Phase Synthesis of Single-Crystalline Gold Nanoplates for Optimally Bioactive Surfaces

We report the surfactant-free vapor-phase synthesis of atomically flat and ultraclean gold nanoplates. These gold nanoplates can offer optimally functional surfaces through the immobilization of molecules without unspecific adsorption and defect, which could be quite valuable for diverse applications including biomedical sensing, plasmonics, molecular electronics, electrochemistry, etc. The ultraflat, ultraclean, and single-crystalline nanostructures, including gold nanoparticles (NPs), gold nanowires (NWs), gold nanobelts, and gold nanoplates, are stereoepitaxially grown on a substrate with a specific orientation. Moreover, the nanostructures can be selectively synthesized by experimental conditions and locations of the substrate. The geometry and orientation of the nanostructures show strong correlations, suggesting a growth process of seed NPs → NWs → nanobelts → nanoplates. This synthetic process can be explained by the mechanism in which the height-to-width ratio of gold nanostructures is determined ...

Surfactant-free microwave hydrothermal synthesis of SnO2 nanosheets as an anode material for lithium battery applications

SnO2 nanosheets were synthesized using microwave hydrothermal method without using a surfactant and organic solvents. Formation of pure nanocrystalline rutile phase of SnO2 sample was confirmed by X-ray diffraction (XRD) results and the average crystallite size of SnO2 sample calculated using Scherrer's formula and XRD data is found to be 6nm. HR-TEM, SAED and EDX results showed the formation of agglomerated nanosize sheets like morphology with high porous structured SnO2 powder. Further, the formation of high porous structured SnO2 powder was confirmed from BET surface area results (59.28m2g−1). The electrochemical performance of the lithium-ion battery made up of SnO2 nanosheets, as an anode, was tested through the cyclic voltammetry and galvanostatic charge-discharge measurements. The galvanostatic charge-discharge results of the lithium-ion battery showed good discharge capacity of 257.8mAhg−1 after 50 cycles at a current density of 100mAg−1. The improved electrochemical properties may be due to the formation of a unique nanosize sheets type morphology with high porous structured SnO2 powder. High porous structured nanosize sheets type morphology of SnO2 can help to reduce the diffusion length and sustain the volume changes during the charging-discharging process.Hence, high porous structured nanosize sheets morphology of SnO2 prepared using the microwave hydrothermal method without using a surfactant and organic solvents can be a better anode material for lithium ion battery applications.

Adjuvant-Loaded Spiky Gold Nanoparticles for Activation of Innate Immune Cells.

Gold nanoparticles are versatile carriers for delivery of biomacromolecules. Here, we have developed spiky gold nanoparticles (SGNPs) that can efficiently deliver immunostimulatory agents. Our goal was to develop a platform technology for co-delivery of multiple adjuvant molecules for synergistic stimulation and maturation of innate immune cells. SGNPs were synthesized by a seed-mediated, surfactant-free synthesis method and incorporated with polyinosinic-polycytidylic acid (pIC) and DNA oligonucleotide containing unmethylated CpG motif (CpG) by an electrostatic layer-by-layer approach. Adjuvant-loaded SGNP nano-complexes were examined for their biophysical and biochemical properties and studied for immune activation using bone marrow-derived dendritic cells (BMDCs). We have synthesized SGNPs with branched nano-spikes layered with pIC and/or CpG. Adjuvant-loaded SGNP nano-complexes promoted cellular uptake of the adjuvants. Importantly, we achieved spatio-temporal control over co-delivery of pIC and CpG via SGNPs, which produced synergistic enhancement in cytokine release (IL-6, TNF-α) and upregulation of co-stimulatory markers (CD40, CD80, CD86) in BMDCs, compared with pIC, CpG, or their admixtures. SGNPs serve as a versatile delivery platform that allows flexible and on-demand cargo fabrication for strong activation of innate immune cells.

Rhodium–Tin Binary Nanoparticle—A Strategy to Develop an Alternative Electrocatalyst for Oxygen Reduction

A Rh–Sn nanoparticle is achieved by combinatorial approaches for application as an active and stable electrocatalyst in the oxygen reduction reaction. Both metallic Rh and metallic Sn exhibit activities too low to be utilized for electrocatalytic reduction of oxygen. However, a clean and active Rh surface can be activated by incorporation of Sn into a Rh nanoparticle through the combined effects of lateral repulsion, bifunctional mechanism, and electronic modification. The corrosion-resistant property of Rh contributes to the construction of a stable catalyst that can be used under harsh fuel cell conditions. Based on both theoretical and experimental research, Rh–Sn nanoparticle designs with inexpensive materials can be a potential alternative catalyst in terms of the economic feasibility of commercialization and its facile and simple surfactant-free microwave-assisted synthesis.

Surfactant-free synthesis of ellipsoidal and spherical shaped TiO2 nanoparticles and their comparative photocatalytic studies

The work presents surfactant-free synthesis of ellipsoidal and spherical TiO2 nanoparticles (NPs) and their photocatalytic activities are compared with commercially available cubic shaped titania. The ellipsoidal TiO2 NPs having average length of ∼21nm and width ∼10nm were synthesized via a facile solvothermal method. The spherical TiO2 NPs were prepared by the solvent evaporation method having average diameter of ∼8nm. We effectively control the shape and size of TiO2 NPs under mild reaction conditions without using any surfactant. XRD patterns show diffraction peak at 25.3° corresponding to (101) crystalline plane, which confirmed the anatase phase of TiO2 NPs. BET surface area of the ellipsoidal and spherical TiO2 NPs are 2.22 and 1.85 times higher than cubic TiO2, respectively. Kubelka–Munk plots demonstrate significant decrease in the band gap of ellipsoidal (3.0eV) and spherical (3.17eV) NPs as compared to cubic shaped TiO2 (3.24eV). The photocatalytic activities of these materials investigated by decolorization/removal of rhodamine-6G (R6G) and methylene blue (MB) under UV–visible light irradiation. In first 15min of photo-degradation experiments, the results indicated 98, 86 and 71% decolorization and 90, 80 and 60% total organic carbon (TOC) removal of R6G by ellipsoidal, spherical, and cubic shaped TiO2 NPs, respectively. Similar findings were obtained for the photo-degradation of MB solution. This confirms the superior photocatalytic characteristics of the ellipsoidal NPs among the reported TiO2 shapes.

Ag+ reduction and silver nanoparticle synthesis at the plasma–liquid interface by an RF driven atmospheric pressure plasma jet: Mechanisms and the effect of surfactant

The involvement of plasma produced species in the reduction of silver ions at the plasma–liquid interface is investigated using a well-characterized radio-frequency driven atmospheric pressure plasma jet. The absolute gas phase H density was measured using two photon absorption laser induced fluorescence in the free jet. Broadband absorption and transmission electron microscopy were used to study the synthesis of silver nanoparticles (AgNPs). It is shown that fructose, an often used surfactant/stabilizer for AgNP synthesis, also acts as a reducing agent after plasma exposure. Nonetheless, surfactant free AgNP synthesis is observed. Several experimental findings indicate that H plays an important role in the reduction of silver ions for the plasma conditions in this study. Vacuum ultraviolet photons generated by the plasma are able to reduce silver ions in the presence of fructose. Adding H2 to the argon feed gas leads to the production of a large amount of AgNPs having a particle size distribution with a maximum at a diameter of 2–3 nm, which is not observed for argon plasmas. This finding is consistent with a smaller concentration of reducing species at the plasma–liquid interface for Ar with the H2 admixture plasma. The smaller flux of reactive species to the liquid is in this case due to a less strong interaction of the plasma with the liquid. The formation of the nanoparticles was observed even at a distance of 6–7 mm below the tip of the plasma plume, conditions not favoring the injection of electrons.

Surfactant-Free Synthesis of Carbon-Supported Palladium Nanoparticles and Size-Dependent Hydrogen Production from Formic Acid-Formate Solution.

Steerable hydrogen generation from the hydrogen storage chemical formic acid via heterogeneous catalysis has attracted considerable interest given the safety and efficiency concerns in handling H2. Herein, a series of carbon-supported capping-agent-free Pd nanoparticles (NPs) with mean sizes tunable from 2.0 to 5.2 nm are developed due to the demand for more efficient dehydrogenation from a formic acid-formate solution of pH 3.5 at room temperature. The trick for the facile size-controlled synthesis of Pd/C catalysts is the selective addition of Na2CO3, NH3·H2O, or NaOH to a Pd(II) solution to attain initial pH values of 7-9.5. For comparison, cuboctahedron modeling and electrochemical COads stripping methods are applied to evaluate active surface Pd sites for turnover frequency (TOF) calculation. Both mass activity and specific activity (TOF) of hydrogen production are not only time-dependent but also Pd-size-dependent. An initial H2 production rate of 246 L·h-1·gPd-1 is achieved on 2.0 nm Pd/C at 303 K, together with a TOF of 1815 h-1 on the basis of cuboctahedron modeling of surface-active Pd sites. The initial TOF exhibits a significant rise from 3.5 down to 2.8 nm and then levels off below 2.8 nm and even shows a maxima at ca. 2.2 nm using the electrochemical surface area for calculation. The volcano-shaped dependence of TOF on Pd NP size may be better attributed to the changing ratios of terrace sites to defect sites on Pd NPs.

Textured SnSe micro-sheets: One-pot facile synthesis and comprehensive understanding on the growth mechanism

Preferential aligned SnSe micro-sheets were successfully synthesized via a surfactant-free hydrothermal synthesis route. The Lotgering factor F and the intensity ratio of (400) to (111) for SnSe Micro-sheets prepared by the optimized process is 0.64, 9.85, respectively, which verify the obvious textured characteristic of micro-sheets. The micro-sheets with uniform composition are polycrystallines with an orthorhombic crystal structure, show the preferential aligned morphology assembled by a great deal of nano-particles according to observation and analysis from the electron diffraction pattern, the lattice fringe, the Energy-dispersive spectroscopy and the transmission electron microscopy (TEM) images. Through deep observation from high-resolution transmission electron microscopy, an arc pattern verifies the textured characteristic of the SnSe sheet. The preferential aligned growth mechanism can be understood by researching effect of reaction temperature, alkali concentration on phase, preferred orientation and morphology. A proper temperature can control textured degree via adjusting effective diffusion, rotation of nano-crystal and fluid movement. Increasing alkali concentration enhances the surface adsorption stability of chalcogenides, and decreases new nucleation site in the (011) face, and helps the dis-matched nano-crystal re-dissolute, which results in formation of square-like textured micro-sheets. A proposed growth mechanism of textured SnSe micro-sheets with two growth models (the lateral growth model and the vertical growth model) is provided, and the two growth models control textured characteristic of micro-sheets, which can be adjusted by change of reaction temperature and alkali concentration.