Surfactant-mediated Synthesis Research Articles

Using Ex Situ and In Situ HERFD-XANES to Reveal the Superior Oxidation and Reduction Cycling of Ceria Nanocubes Dispersed in Silica Aerogel.

The oxygen storage capacity of ceria-based catalytic materials is influenced by their size, morphology, and surface structure, which can be tuned using surfactant-mediated synthesis. In particular, the cuboidal morphology exposes the most reactive surfaces; however, when the capping agent is removed, the nanocubes can agglomerate and limit the available reactive surface. Here, we study ceria nanocubes, lanthanum-doped ceria nanocubes, and ceria nanocubes embedded inside a highly porous silica aerogel by high-energy resolution fluorescence detection-X-ray absorption near edge spectroscopy at the Ce L3 edge. In situ measurements showed an increased reversibility of redox cycles in ceria nanocubes when embedded in the aerogel, demonstrating enhanced reactivity due to the retention of reactive surfaces. These aerogel nanocomposites show greater improvement in the redox capacity and increased thermal stability of this catalytic material compared to the surfactant-capped nanocubes. Ex situ measurements were also performed to study the effect of lanthanum doping on the cerium oxidation state in the nanocubes, indicating a higher proportion of Ce4+ compared to that of the undoped ceria nanocubes.

Surfactant-mediated synthesis of monodisperse Poly(benzyl methacrylate)-based copolymer microspheres

Polymeric microspheres (MSs) have broad applications. Poly(benzyl methacrylate) (PBzMA) have various important applications, such as optical materials, electrochromatography, and photoresists. However, previous studies on PBzMA were on fabricating bulk polymers or nano-sized (<500 nm) spheres. In this study, by introducing a cationic surfactant, cetyltrimethylammonium bromide (CTAB), into the processing, we were the first to successfully synthesize PBzMA-based (pristine and co-polymer) highly monodisperse microspheres. In the synthesis, poly(vinyl pyrrolidone) (PVP) is used as the stabilizer to prevent particle aggregation, and cetyltrimethylammonium bromide (CTAB) is used to assist dispersion polymerization. The sizes of PBzMA-based MSs can be tuned between 1.0 and 10.0 µm with a high monodispersity by controlling the CTAB and monomer concentrations. The morphology, molecular structure, molecular weight distribution, thermal stability, and glass transition behavior of the MS samples are determined. Particularly, the glass transition temperature can be tuned continuously and smoothly between 59 °C–120 °C by adjusting the monomer ratio in the synthesis of the copolymer MSs. This study provides insights into a controlled synthesis of size- and property-tunable polymeric and copolymer MSs for broad applications.

Thermally stable surfactant-free ceria nanocubes in silica aerogel

Surfactant-mediated chemical routes allow one to synthesize highly engineered shape- and size-controlled nanocrystals. However, the occurrence of capping agents on the surface of the nanocrystals is undesirable for selected applications. Here, a novel approach to the production of shape-controlled nanocrystals which exhibit high thermal stability is demonstrated. Ceria nanocubes obtained by surfactant-mediated synthesis are embedded inside a highly porous silica aerogel and thermally treated to remove the capping agent. Powder X-ray Diffraction and Scanning Transmission Electron Microscopy show the homogeneous dispersion of the nanocubes within the aerogel matrix. Remarkably, both the size and the shape of the ceria nanocubes are retained not only throughout the aerogel syntheses but also upon thermal treatments up to 900 °C, while avoiding their agglomeration. The reactivity of ceria is measured by in situ High-Energy Resolution Fluorescence Detected - X-ray Absorption Near Edge Spectroscopy at the Ce L3 edge, and shows the reversibility of redox cycles of ceria nanocubes when they are embedded in the aerogel. This demonstrates that the enhanced reactivity due to their prominent {100} crystal facets is preserved. In contrast, unsupported ceria nanocubes begin to agglomerate as soon as the capping agent decomposes, leading to a degradation of their reactivity already at 275 °C.

Photocatalytic Degradation of Organic Pollutants over MFe2O4 (M\u2009=\u2009Co, Ni, Cu, Zn) Nanoparticles at Neutral pH

In this study, we report a surfactant-mediated synthesis of ferrites (MFe2O4: M = Co, Ni, Cu, Zn) using the co-precipitation-oxidation method. The band gap calculated from UV-Visible diffuse reflectance spectra were found in the range of 1.11–1.81 eV. These ferrite nanocatalysts were studied for the photocatalytic degradation of multiple organic dyes in a 32 W UV-C/H2O2 system. All the four ferrites showed an excellent dye degradation rate in the range of 2.065–2.417 min−1 at neutral pH. In the optimized condition, NiF was found to degrade 89%, 92%, 93%, and 78% of methylene blue, methyl orange, bromo green, and methyl red, respectively within 1 min of UV-irradiation. A 40% TOC removal was recorded after 5 min of degradation reaction, which increased to 60% after 50 min. Mechanism elucidated by scavenger studies and fluorescence spectroscopy revealed that •OH and holes were the primary reactive radicals responsible for the degradation process. Ferrite photocatalysts showed an insignificant performance loss in seven consecutive cycles. The photocatalyst was found efficient in the presence of a high concentration of salts. Thus, it was concluded that these photocatalysts are highly suitable for the remediation of dye-contaminated wastewater.

Synthesis of coral-like α-Fe2O3 nanoparticles for dye degradation at neutral pH

This study reported a surfactant-mediated synthesis of coral-like α-Fe2O3 nanoparticles (FONP) via a simple co-precipitation-oxidation route. The synthesized FONP photocatalyst had a hexagonal morphology, as observed in the transmission electron micrographs. A surface area of 15 m2 g−1 was calculated from the N2 adsorption-desorption isotherm. The photocatalyst showed strong absorbance in the entire UV–Visible range with a low bandgap energy of 1.91 eV as estimated using the Tauc plot. The photocatalytic activity of FONP was evaluated by degrading several organic dyes at neutral pH. In the optimized experimental conditions, the FONP photocatalyst showed fast degradation of Methylene blue (95%), Methyl orange (94%), Bromo green (94%), and Methyl red (76%) within 5 min in 32 W UV/H2O2 system. The reusability study showed a 10% loss in the degradation efficiency after five cycles. A possible photo-Fenton degradation mechanism was deduced based on scavenger studies.

Surfactant-mediated synthesis of polyhydroxybutyrate (PHB) nanoparticles for sustained drug delivery.

In this study, polyhydroxybutyrate (PHB) nanoparticles were synthesised following nanoprecipitation method having different solvents and surfactant (Tween 80) concentrations. In this study, PHB nanoparticles were encapsulated with curcumin and subjected for sustained curcumin delivery. Both the curcumin loaded and unloaded PHB nanoparticles were characterised using FTIR, SEM, and AFM. Sizes of the particles were found to be between 60 and 300 nm. The drug encapsulation efficiency and in vitro drug release of the nanoparticles were analysed. Antibacterial activity and anticancer activity were also evaluated. The LC50 values of most of the nanoparticles were found to be between 10 and 20 µg/100 µl, anticancer activity of curcumin loaded PHB nanoparticles were further confirmed by AO/PI staining and mitochondrial depolarisation assay.

Mixed Surfactant-Mediated Synthesis of Hierarchical PANI Nanorods for an Enzymatic Glucose Biosensor

The hierarchical nanoscale structure plays a crucial role in achieving excellent property, which can successfully be used in preparing tailor-made materials for sensing applications. These hierarch...

New 2,3-diphenylquinoxaline containing organic D-A-π-A dyes with nickel oxide photocathode prepared by surfactant-mediated synthesis for high performance p-type dye-sensitized solar cells

Dye-sensitized solar cells (DSSCs) are one of the most promising organic photovoltaics. The optimized efficiency of a tandem cell combined with both n- and p-type DSSCs was theoretically predicted to be 43%. The bottleneck for reaching the optimized performance is limited by the p-type half-cell, particularly the lacking of an appropriate semiconducting material as the photocathode. In this regard, we report the surfactant-mediated synthesis of nickel oxide nanomaterial using a chemical co-precipitation method. The new material was fully characterized by XRD, SEM, XPS, EDS, and BET. The BET result indicates the nickel oxide nanoparticles synthesized with surfactant attain higher surface area than the conventional one. In addition, the new organic dyes with electron-deficient diphenylquinoxaline incorporated within the molecular structure were prepared for p-type dye-sensitized solar cells with the newly prepared NiO as the photocathode. The new organic dyes consist of carboxylic acid as the anchoring group, triphenylamine as the electron donor, 2,3-diphenylquinoxaline as the auxiliary acceptor moiety, 2-methylenemalononitrile as electron acceptor, connected with thiophene, 3,4-ethylenedioxythiophene, and 2,2′-bithiophene as the π-spacer. Sensitizers with mono-anchoring group (EH166, EH122, and EH174) performed better than their corresponding double-anchoring sensitizers (EH162, EH126, and EH170). Among these, dye EH174 exhibited the best conversion efficiency up to 0.207% with a short-circuit photocurrent density of 4.84 mAcm−2, an open-circuit photovoltage of 137 mV, and a fill factor of 0.312. The current results indicate that the combination of electron-deficient quinoxaline motif with suitable π-linker in a D-A-π-A molecular structure is a promising design of p-type sensitizers for NiO-based p-DSSCs.

Surfactant-mediated synthesis of single-crystalline Bi3O4Br nanorings with enhanced photocatalytic activity

We present a surfactant-mediated approach to the production of single-crystal Bi3O4Br nanorings via a simple solvothermal method.

DC Electrical Conductivity Retention, Optical Properties and Ammonia Sensing Analysis of Naturally Degraded CSA-Doped Graphene/polyaniline Composite Nanofibers Prepared with CTAB

In this paper, we report surfactant-mediated synthesis of camphor sulfonic acid (CSA)-doped polyaniline/graphene (PANI/GN) composite nanofibers as an electrical conductor and excellent ammonia sensor. The synthesis was mediated by cetyltrimethylammonium bromide as surfactant. The as-synthesized composite nanofibers were characterized by Raman spectroscopy, scanning electron microscopy, tunneling electron microscopy, x-ray diffraction, diffused reflectance spectroscopy and differential scanning calorimetry. The electrical conductivity of the CSA-doped PANI/GN composite nanofibers was found to be remarkably enhanced as compared to the CSA-doped PANI. The boost in electronic conductivity could be attributed to an improved electronic interaction between CSA-doped PANI backbone and GN present in the composite system. The naturally degraded CSA-doped PANI/GN composite nanofibers showed a decrease in electrical conductivity but worked as a good ammonia sensor in open atmospheric conditions.

Surfactant-mediated synthesis of ZnCo2O4 powders as a high-performance anode material for Li-ion batteries

The synthesis as well as the electrochemical properties study of highly crystalline ZnCo2O4 powders is presented. ZnCo2O4 powders with a particle diameter of 15–35 nm have been successfully prepared with the surfactant-mediated method. The thorough structural characterization including X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) were employed to examine the morphology and the microstructure of the final product. The as-synthesized powders were used as anode materials for lithium-ion battery, whose charge–discharge properties, cyclic voltammetry, and cycle performance were examined and revealed very good properties. Galvanostatic cycling of ZnCo2O4 powders in the voltage range 0.005–3.0 V versus Li at 60 mA g−1 maintained charge and discharge capacities of 1,308 and 1,336 mAh g−1 after 40 cycles when cycled at 25 °C, respectively.

Ultrathin 2D Coordination Polymer Nanosheets by Surfactant-Mediated Synthesis

Low-dimensional nanostructures offer a host of intriguing properties which are distinct from those of the bulk material, owing to size-confinement effects and amplified surface areas. Here, we report on the scalable, bottom-up synthesis of ultrathin coordination polymer nanosheets via surfactant-mediated synthesis and subsequent exfoliation. Layers of a two-dimensional (2D) zinc coordination polymer are self-assembled in the interlamellar space of a reverse microemulsion mesophase into stacks of nanosheets interleaved with cethyltrimethylammonium bromide (CTAB) at regular intervals, thus giving rise to a lamellar hybrid mesostructure with a lattice period of ~8 nm and an underlying highly crystalline substructure. The basic structural motif is composed of 2D acetato-benzimidazolato-zinc layers of tetrahedrally coordinated zinc joined together by anionic acetate and benzimidazolate ligands. The hierarchical structure was studied by PXRD, TEM, EDX, EELS, AFM, and solid-state NMR spectroscopy, revealing a high level of order on both the atomic and mesoscale, suggesting fairly strong interactions along the organic-inorganic hybrid interface. Exfoliation of the hybrid material in organic solvents such as THF and chloroform yields sheet- and belt-like nanostructures with lateral sizes between 10's and 100's of nanometers and a height of about 10 nm measured by AFM, which precisely maps the basal spacing of the lamellar mesostructure; further exfoliation results in nanobelts with minimum sizes around 4 nm. Finally, the sheetlike nanostructures behave as morphological chameleons, transforming into highly regular multiwalled coordination polymer nanotubes upon treatment with organic solvents.

Surfactant‐Concentration‐Dependent Shape Evolution of Au–Pd Alloy Nanocrystals from Rhombic Dodecahedron to Trisoctahedron and Hexoctahedron

The surface structure-controlled synthesis of noble metal nanocrystals (NCs) bounded by high-index facets has become a hot research topic due to their potential to significantly improve catalytic performance. This study reports the preparation of monodisperse Au-Pd alloy NCs with systematic shape evolution from rhombic dodecahedral (RD) to trisoctahedral (TOH), and hexoctahedral (HOH) structures by varying the concentration of surfactant in the surfactant-mediated synthesis. The as-prepared three kinds of alloy NCs possess almost the same size and composition as each other. It is suggested that the surfactant containing long-chain octadecyltrimethyl ammonium (OTA(+)) ions plays a key role in the formation of high index facets, and the crystal growth kinetics may also have an effect on the formation of different nanocrystal morphologies. In addition, the catalytic activities of these NCs are evaluated by structure-sensitive reactions, including ethanol electro-oxidation and the catalytic reduction of 4-nitrophenol (4-NPh). These three types of Au-Pd alloy NCs exhibit different catalytic selectivities towards these two reactions. The catalytic activities toward electro-oxidation of ethanol are in the order of HOH > RD > TOH, which follows the order of their corresponding surface energies. However, the activities toward catalytic reduction of 4-NPh are in the order of RD > TOH > HOH, which should be related to the local structure of the surfaces.

Chemical control of the characteristics of Mo-doped carbon xerogels by surfactant-mediated synthesis

Carbon xerogels doped with Mo were prepared by a sol–gel modified method for the resorcinol (R) – formaldehyde (F) polymerization (RF-gels). The use of surfactants (S) yields composites (RFS-gels), the S molecules are incorporated to the gel structure generating different metal anchoring sites. The interaction of molybdate ions (MoO42-) with RF and RFS-gels was analysed. The MoO42- adsorption is favoured by the attractive interactions with the RFS-gel containing a cationic surfactant, and by the presence of oxygenated chemical groups introduced by the non-ionic surfactant. The smallest Mo-loading was obtained in RFS-gels containing anionic surfactant as a consequence of repulsive interactions. The adsorbed Mo-species influence on the curing of the polymeric gels, inducing a larger shrinkage and a lower microporosity of the carbon xerogels. The dispersion and chemical nature of Mo particles depend also on the Mo-gel interactions. Stronger attractive interactions avoid sintering in some extent and favour the reduction of the molybdate with formation of a mixture of α-Mo2C and MoO3, while MoO3 particles were only found in RF-Mo or anionic RFS-Mo carbon xerogels. Only propene was obtained as product of the isopropanol decomposition showing the acid character of these catalysts. The catalytic activity is correlated to the proportion of Mo2C formed in each sample.

Nonionic Brij Surfactant-Mediated Synthesis of Raspberry-Like Gold Nanoparticles with High Surface Area

We report a rapid, simple, single-step, and high-yielding solution-phase synthesis of raspberry-like gold nanoparticles (Au RLNPs) with rich edges and high surface areas. Au RLNPs were synthesized through the reduction of HAuCl4 simply mediated by nonionic Brij surfactant in basic conditions without any other reducing agents or organic molecules. The synthesized nanoparticles possessed high surface areas and were stable in basic or neutral conditions, which are potentially useful structural factors for the applications. The unique, highly red-shifted surface plasmon resonances (SPRs) of Au RLNPS originate from their rough, raspberry-like surfaces. The sizes of Au RLNPs were controllable by varying the amounts of NaOH and HAuCl4. However, there are very few reported facile syntheses of size-controlled multi-branched gold nanoparticles simply mediated by surfactant without any other reducing agents or organic molecules.

Controlled Synthesis of Monodisperse CeO2 Nanoplates Developed from Assembled Nanoparticles

Surfactant-mediated synthesis of monodisperse CeO2 nanoplates (15 nm × 50 nm, 2 nm thick) was conducted by the thermal decomposition of cerium acetate in 1-octadecene. X-ray diffraction patterns indicated selective (200) plane growth of fluorite cubic CeO2 in the CeO2 nanoplates, and transmission electron microscopy revealed that most of the side surfaces exhibited {200} lattice fringes. Smaller amounts of surfactants resulted in larger nanoplates composed of assemblies of small CeO2 nanoparticles (NPs). The formation of this polycrystalline structure of assembled NPs is preferable to induce stability by decreasing the surface energy and positive charge of the NPs. The bandgap energy of CeO2 nanoplates for direct transitions was larger than that for polyhedral CeO2 NPs.

Adsorption of Cu2+ on Amine-Functionalized Mesoporous Silica Brackets

A directly amine-functionalized mesoporous silica (AMS) was prepared via an anionic surfactant-mediated synthesis method and used as adsorbents for deep removal of Cu2+ ions from aqueous solution at room temperature. The synthesized AMS had been characterized by X-ray diffraction, nitrogen physisorption measurement, and thermogravimetric analysis. The amine groups prefer to position to the surface of AMS material due to the S−N+ ∼ I− mechanism. Copper adsorption process had been studied from both kinetic and equilibrium points of view for AMS material. Experiments proved that the aqueous Cu2+ adsorption rates were fast and adsorption capacity was about 53.3 mg/g.

Selective synthesis, characterization, and photoluminescence study of YPO 4:Eu 3+ nanorods and nanoparticles

Two different morphological varieties of YPO 4:Eu 3+ (nanorods and nanoparticles) have been synthesized by convenient template-assisted routes. A surfactant-mediated synthesis route generated the nanorods, while a complex based precursor solution method led to the formation of the nanoparticles. The nanorods have an average diameter of ∼33 nm and an average length of ∼290 nm, whereas the spherical nanoparticles show an average diameter of ∼34 nm. Upon photoluminescence study of the as-prepared samples, the chromaticity of the dopant ion was found to be sensitive to the host morphology as well as the preparative strategy adopted for sample fabrication.

CO 2 adsorption using amine-functionalized mesoporous silica prepared via anionic surfactant-mediated synthesis

A series of directly amine-functionalized mesoporous silicas was prepared via an anionic surfactant-mediated synthesis method and applied to CO 2 adsorption at room temperature. The structurally robust amine functionality in the material accompanied by preferential positioning of amine groups normal to the surface of a silica support due to the S −N + ∼ I − mechanism proved to be beneficial for CO 2 adsorption. Rather than surface area or pore volume, amine content of the mesoporous material was found to be the governing factor to achieve high CO 2 adsorption capacity. Covalently bonded amine species in the mesoporous silica were robust enough to maintain steady adsorption performance during 10 repetitions of the adsorption–desorption cycle.

Surfactant-Mediated Synthesis of a Novel Nanoporous Carbon−Silica Composite

A novel nanoporous carbon−silica composite with medium hydrophilicity is synthesized by a series of methods consisting of preexpansion of the interlayer of graphite oxide (GO) by surfactant intercalation, the intercalation of tetraethoxylsilane (TEOS) and its hydrolysis in the interlayer, followed by post carbonization to form a robust bridged/pillared network. High-resolution N2 adsorption results show that carbonization at 823 K gives a composite having the highest specific surface area of more than 1000 m2/g with both microporosity and mesoporosity. Varieties of analytical results using DRIFT, NMR, XPS, and RAMAN spectra indicate that this composite contains small graphene sheets in its structure and its silicon components are silica particles with +4 valence. Morphology observation, thermal desorption, and other properties suggest the important roles of dispersion of GO in aqueous solution, preexpansion of GO interlayer, interlayer hydrolysis of TEOS molecules, and the carbonization condition in the formation mechanism of this nanoporous composite.