Structure-directing Reagent Research Articles

Template-free synthesis of g-C3N4 microprisms for significant enhancement of photocatalytic H2 evolution under visible light

Graphitic carbon nitride (C3N4) hexagonal microprisms were synthesized via a self-assembly route using (NH4)2CO3 as a structure-directing reagent. It shows that the extraordinary hierarchical structure is favorable to improving the photocatalytic activity of C3N4 toward water splitting under visible light irradiation (λ>420nm). The photocatalytic H2-evolution rate on the microprisms is 185 µmol/h, 16.8 times higher than that over bulk C3N4. The enhanced photocatalytic performance of the as-prepared microprisms mainly originates from the characteristic micro-nanostructure, possessing enlarged surface area for efficient charge separation.

Designed multimetallic Pd nanosponges with enhanced electrocatalytic activity for ethylene glycol and glycerol oxidation

We report an effective synthesis of surfactant-free multimetallic Pd nanosponges with tunable compositions using EDTA as the structure-directing reagent and NaBH4 as the reducing reagent.

Green synthesis of nickel species in situ modified hollow microsphere TiO2 with enhanced photocatalytic activity

A green template-free solvothermal approach was developed to synthesize hollow microsphere TiO2-modified in situ with nickel species (Ni2+/Ni3+). Oxalic acid played a pivotal role in the formation of hollow architecture, acting as chelating agent, structure-directing reagent, and acidity-modulation reagent, while isopropyl alcohol ensured the formation of spherical structure. The microstructure and composition of the products were characterized with various techniques, and the results showed that the products exhibited not only highly crystallized anatase phase, large specific surface areas, and the mesoporous shell and hollow architecture, but also the coexistence of Ni2+/Ni3+. The unique structure and composition of the photocatalysts resulted in improved UV and visible photocatalytic activity for degradation of Rhodamine-B and 2,4-dichlorophenol.

Facile Synthesis of Element-Substituted Hydroxyapatite Whiskers Using α-Tricalcium Phosphate as Precursors

In the absence of any surfactants, organic solvents or structure-directing reagents, the cation- and anion-substituted HAp whiskers, and cation-/anion-co-substituted HAp whiskers with controllable substitution amounts were successfully synthesized via hydrothermal treatment of the same precursor of α-TCP in an aqueous solution containing the objective substituted elements. Through regulating the initial ion concentrations of the aqueous solutions, the element substitution level could be well facilely tailored. The cytocompatibility of the products was confirmed by Cell Counting Kit-8 (CCK-8) assay using the osteoblast cell line MC3T3-E1. This study provided a facile strategy for the synthesis of element-substituted HAp materials.

Improving the specific capacitance of Ni(OH)2-based supercapacitors by tailoring its porous structures and particle size

Ni(OH)2 samples were synthesized by hydrothermal process, accompanied with poly(acrylamide) (PAM) or cetyltrimethylammonium bromide (CTMAB) as structure-directing reagents. Under the effects of PAM and CTMAB, both of the Ni(OH)2 samples show wider pore size distribution, especially more mesopores. Besides, Ni(OH)2-PAM presents fluffy wadding, and Ni(OH)2-CTMAB looks like pompon sphere. The Ni(OH)2-PAM and Ni(OH)2-CTMAB based electrodes have a specific capacitance of 1200 and 757Fg−1, respectively at the discharge current density of 1Ag−1, much higher than that of Ni(OH)2 with no structure-directing reagent (only 113Fg−1). Therefore, appropriate structure-directing reagents are necessary to improve the electrochemical performance of electrode materials.

Synthesis and mechanical characterization of mechanically strong, polyurea-crosslinked, ordered mesoporous silica aerogels

Mechanically strong polymer-crosslinked templated silica aerogel (CTSA) monoliths with ordered tubular mesopores were synthesized through an acid-catalyzed, surfactant-templated sol–gel process followed by covalent crosslinking of the elementary building blocks with polyurea. Specifically, a structure-directing reagent (triblock copolymer, Pluronic P123) was used in combination with variable amounts of a micelle-swelling reagent (1,3,5-trimethylbenzene) to regulate the size, shape, morphology of the elementary building blocks, as well as the pore size distribution of acid-catalyzed silica. The structure was subsequently treated with variable concentrations of a diisocyanate that reacts with surface –OH groups as well as residual gelation water adsorbed on the surface of silica. The developing polymer (polyurea) adheres to the walls of the mesoporous tubes and leaves macropores open. Rather than using a typical supercritical fluid (typically from CO2) drying protocol, the polymer-crosslinked materials of this study are strong enough to withstand stresses imposed by evaporating solvents and were dried from pentane under ambient pressure. The morphostructural properties of CTSAs were characterized before and after compression testing using a battery of methods including SEM, TEM and small-angle X-ray scattering. Mechanical properties were investigated using quasi-static compression tests, tensile, high-strain-rate dynamic tests as well as shear creep measurements. In addition, dynamic mechanical analysis as well as heat transfer tests was conducted. The Young’s modulus was found to be about 800 MPa while the specific energy absorption was as high as 123 J/g, making this material a prime candidate for ballistic protection. Mechanically strong polymer-crosslinked templated silica aerogel (CTSA) monoliths with ordered tubular mesopores were synthesized through an acid-catalyzed, surfactant-templated sol–gel process followed by covalent crosslinking of the elementary building blocks with polyurea, leaving macropores open. Using pentane under ambient pressure drying protocol, the CTSAs are strong enough to withstand stresses imposed by evaporating solvents. The mechanical and morphostructural properties of CTSAs were characterized using SEM, TEM and small-angle X-ray scattering (SAXS). The Young’s modulus was found to be about 800 MPa while the specific energy absorption was as high as 123 J/g, making this material a prime candidate for energy absorption under impact. TEM/SEM images and SAXS of X-MP4-T045-11/94 templated aerogel. (a) TEM images before compression; (b) TEM images after 85 % compressive strain; (c) SAXS data at different strain. (d) SEM images before compression; (e) SEM images after 23 % strain; (f) SEM images after 83 % strain. Insets of (e) and (f) are the compressive stress-strain curves.

Spectroscopic Investigation of Surface-Dependent Acid–Base Property of Ceria Nanoshapes

In addition to their well-known redox character, the acid–base property is another interesting aspect of ceria-based catalysts. Herein, the effect of surface structure on the acid–base property of ceria was studied in detail by utilizing ceria nanocrystals with different morphologies (cubes, octahedra, and rods) that exhibit crystallographically well-defined surface facets. The nature, type, strength, and amount of acid and base sites on these ceria nanoshapes were investigated via in situ IR spectroscopy combined with various probe molecules. Pyridine adsorption shows the presence of Lewis acid sites (Ce cations) on the ceria nanoshapes. These Lewis acid sites are relatively weak and similar in strength among the three nanoshapes according to the probing by both pyridine and acetonitrile. Two types of basic sites, hydroxyl groups and surface lattice oxygen are present on the ceria nanoshapes, as probed by CO2 adsorption. CO2 and chloroform adsorption indicate that the strength and amount of the Lewis base sites are shape dependent: rods > cubes > octahedra. The weak and strong surface dependence of the acid and base sites, respectively, are a result of interplay between the surface structure dependent coordination unsaturation status of the Ce cations and O anions and the amount of defect sites on the three ceria nanoshapes. Furthermore, it was found that the nature of the acid–base sites of ceria can be impacted by impurities, such as Na and P residues that result from their use as structure-directing reagent in the hydrothermal synthesis of the ceria nanocrystals. This observation calls for precaution in interpreting the catalytic behavior of nanoshaped ceria where trace impurities may be present.

CuS–Bi2S3 hierarchical architectures: controlled synthesis and enhanced visible-light photocatalytic performance for dye degradation

Novel CuS–Bi2S3 heterojunctions were fabricated by a one-step solvothermal method using glycol as solvent and l-lysine as structure-directing reagent. The composites showed enhanced photocatalytic activity towards dye degradation under visible light.

Flowerlike Bi2S3microspheres: facile synthesis and application in the catalytic reduction of 4-nitroaniline

Flowerlike Bi2S3 microspheres have been successfully synthesized via a facile wet chemical route in air at 110 °C for 10 min, employing bismuth nitrate and thiourea in a molar ratio of 1 : 2 as the starting reactants, ethylene glycol as the reaction medium and polyvinylpyrrolidone (PVP) as the structure-directing reagent. Electron microscopy observations showed that the as-obtained product looked like an Asteraceae plant called Echinops Sphaerocephalus Linn in nature. The N2 sorption–desorption experiments showed that the Brunauer–Emmett–Teller (BET) area of the flowerlike microspheres was 32.4 m2 g−1. Some factors influencing the formation of flowerlike Bi2S3 microspheres were investigated, including the reaction temperature, and the sort and amount of the surfactant. The experiments showed that the Bi2S3 micro/nanostructures prepared in the present work could be used as new-type catalysts for the reduction of some aromatic nitro compounds, such as 4-nitroaniline, 2-nitrophenol and 4-nitrophenol. It was found that the as-obtained flowerlike Bi2S3 microspheres contributed to the best catalytic activity.

Nanocrystal–Organic Hybrid Antifungal Agent: High Level Oriented Assembly of Zinc Hydroxide Carbonate Nanocrystals in Chitosan

A novel high level oriented assembly of zinc hydroxide carbonate nanocrystals in chitosan was fabricated via a hydrothermal process. Hydrated chitosan acts as a template supporting and structure-directing reagents for the formation and assembly of zinc hydroxide carbonate nanocrystals. Zinc hydroxide carbonate nanocrystals were heterogeneously nucleated at the interface of hydrated chitosan crystallization regions through hydrogen bonding, lattice geometrical matching, and stereochemical matching interactions with ordered chitosan chains. The products obtained at different reaction stages were characterized with SEM, TEM, XRD, XPS, and TGA. The antifungal activity assays of CZHC, zinc hydroxide carbonate, chitosan, chitosan simply blended with zinc hydroxide carbonate (1:1), and nano zinc oxide were investigated. The study exhibited that the CZHC nanocrystals showed an antifungal activity against Cotton Verticillium, Rhizopus, and Mucorales and showed a better antifungal activity than other test samples a...

One-step synthesis and gas sensing properties of hierarchical SnO2 materials

Hierarchical tin oxide(SnO2) architectures were synthesized with a facile hydrothermal method. In the hydrothermal synthesis, sodium dodecyl benzene sulfonate(SDBS) surfactant plays an important role as structure-directing reagent. The synthesized samples were characterized by powder X-ray diffraction(XRD), field emission scanning electron microscopy(FESEM), transmission electron microscopy(TEM) and high-resolution transmission electron microscopy(HRTEM). The results clearly reveal that the hierarchical architectures of SnO2 were composed of aggregated nanosheets with a thickness of about 100 nm. A possible mechanism for the formation of the SnO2 hierarchical architectures was proposed. In addition, the gas sensing properties of the as-prepared products were investigated and it was found that the sensor based on the special SnO2 hierarchical architectures exhibited a high response and good selectivity to NO2 at the optimal working temperature of 160 °C.

One-step fabrication of hollow aluminosilicate microspheres with a composite zeolite/glass crystalline shell

One-step procedure to fabricate hollow aluminosilicate microspheres with a composite NaA(NaX)/glass/mullite composite shell was demonstrated by the direct conversion of low-silica cenospheres (Si/Al=1.8) separated from coal fly ash. The reported method does not involve seeding and structure-directing reagents. Composition of cenospheres and the stirring of reactants at the optimal synthesis temperature (T=80°C) and alkaline molarity (2.5M NaOH) are parameters affected the formation of a monozeolitic phase (NaA or NaX). The influence of the silica–alumina composition of cenospheres on the type of zeolite phase formation is only revealed under stirring conditions. In the case of the low-silica cenospheres, NaA (LTA) zeolite crystallizes as a dominant phase (43wt.%) (Si/Al=1.8) under stirring of reactants, while the static conditions favor formation of the NaX (FAU) zeolite phase (45wt.%).

Hydrothermal synthesis and tunable luminescence of persimmon-like sodium lanthanum tungstate:Tb3+, Eu3+ hierarchical microarchitectures

Persimmon-like NaLa(WO4)2 microarchitectures were prepared via hydrothermal process with using trisodium citrate (Na3Cit) as chelated reagent and characterized by X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM), photoluminescence (PL), and fluorescent dynamics. The influences of Na3Cit concentration, organic additivities, and reaction time on the morphologies of NaLa(WO4)2 phosphor were studied. The results revealed that Na3Cit species had double functions of strong ligand and structure-directing reagent that could efficiently control the formation of persimmon-like NaLa(WO4)2 microarchitectures. The possible mechanism for the growth of persimmon-like NaLa(WO4)2 microarchitectures was attributed to the Ostwald ripening mechanism. The energy transfer from Tb3+ to Eu3+ in the persimmon-like NaLa(WO4)2 phosphors was observed. The energy transfer efficiencies and emission colors can be tuned by changing the concentration of Eu3+. Finally, it was deduced that the electric dipole–dipole interaction (D–D) is the main mechanism for energy transfer between Tb3+ and Eu3+ in the persimmon-like NaLa(WO4)2 phosphor.

Controlled synthesis and electrochemical properties of vanadium oxides with different nanostructures

Vanadium oxides (V3O7·H2O and VO2) with different morphologies have been selectively synthesized by a facile hydrothermal approach using glucose as the reducing and structure-directing reagent. The as-obtained V3O7·H2O nanobelts have a length up to several tens of micrometers, width of about 60–150 nm and thickness of about 5–10 nm, while the as-prepared VO 2 (B) nanobelts have a length of about 1·0–2·7 μm, width, 80–140 nm and thickness, 2–8 nm. It was found that the quantity of glucose, the reaction temperature and the reaction time had significant influence on the compositions and morphologies of final products. Vanadium oxides with different morphologies were easily synthesized by controlling the concentration of glucose. The formation mechanism was also briefly discussed, indicating that glucose played different roles in synthesizing various vanadium oxides. The phase transition from VO2(B) to VO2(M) were investigated and the phase transition temperature of the VO2(M) appeared at around 68 °C. Furthermore, the electrochemical properties of V3O7·H2O nanobelts, VO2(B) nanobelts and VO2(B) nanosheets were investigated and they exhibited a high initial discharge capacity of 296, 247 and 227 mAh/g, respectively.

Synthesis and luminescence properties of Y2O3:Eu with flower-like microstructure

Europium-doped yttrium hydroxide (Y(OH)3:Eu) with flower-like microstructure has been successfully prepared via a facile hydrothermal process, using potassium sodium tartrate (C4H4O6KNa) as a structure-directing reagent. Europium-doped yttrium oxide (Y2O3:Eu) with similar morphology is prepared by calcining the as-prepared Y(OH)3:Eu at 700°C for 4h. Influencing factors such as the concentration of potassium sodium tartrate, the amount of sodium hydroxide, and the temperature used for hydrothermal synthesis are systematically investigated. Possible formation mechanism for the flower-like microstructure is proposed on the basis of time-dependent experiment. Y2O3:Eu samples show a strong red emission corresponding to the 5D0-7F2 transition of Eu3+ ions under excitation. Emission intensity varies between samples with different morphologies. The optimum Eu3+ doping concentration is also explored. This work sheds some light on the design and preparation of novel microstructures.

Synthesis of Length-Controlled Polyvalent Silver Nanowire–DNA Conjugates for Sensitive and Selective Detection of DNA Targets

We have developed a facile method to rapidly synthesize the monodisperse silver nanowire-DNA conjugates with a constant diameter and systematically controllable lengths in the range of 0.5-2.5 μm. The synthesis of silver nanowires takes advantage of poly(sodium 4-styrenesulfonate) as a structure-directing reagent and is performed under very mild conditions such as room temperature and aqueous media. The nanowires are densely conjugated with DNA sequences enough to exhibit the cooperative properties for the sensitive and selective detection of DNA targets. The limit of detection is 50 pM.

Controlled structural evolution of large silver nanoparticles and their DNA-Mediated bimetallic reversible assemblies

We have synthesized the monodisperse large silver nanoparticles with a variety of controlled shapes and sizes using poly (sodium 4-styrene sulfonate) as a structure-directing reagent. We have demonstrated that the molecular weight (70K, 200K and 1000K) and concentration of the polymer can effectively and systematically control the silver nanoparticle structures that are strongly associated with the unique optical properties based upon their surface nanostructures. The crystalline structures of the particles have been further analyzed by diffraction methods. Importantly, the silver nanoparticles can be functionalized with DNA for reversible assembly formation with complementary DNA-gold nanoparticle conjugates, demonstrating that these novel structures can be utilized as smart probes and functional platforms for diagnostic and therapeutic applications. The reversibility of the bimetallic assembly is confirmed by the thermal denaturation.

Adsorption Behavior of Environmental Hormone Bisphenol A onto Mesoporous Silicon Dioxide

Mesoporous silicon dioxide (meso-SiO2) was prepared using cetyltrimethylammonium bromide as the structure-directing reagent and tetraethyl orthosicate as the silicon source. The influence of pH value on the adsorption behavior of bisphenol A (BPA) was investigated. The adsorption capacity of BPA onto meso-SiO2 increases slightly with pH value from 2 to 6, and then gradually decreases as further improving pH value. The effect of temperature was also studied, and the adsorption capacity of BPA gradually declines with increasing temperature. The adsorption kinetics and thermodynamics of BPA were examined. It is found that the adsorption of BPA onto meso-SiO2 is in good agreement with Langmuir adsorption model. The rate constant of adsorption is 5.17 × 10 �3 g mg �1 min �1 , and the maximum adsorption capacity is as high as 353.4 mg g �1 at 20 o C.

Preparation and Electrochemical Properties of VO2(B) Nanobelts

VO2(B) nanobelts have been successfully prepared in V2O5 and water mixed suspension assisted by polyvinyl alcohol (PVA) via a mild hydrothermal approach. The as-obtained VO2 nanobelts are several hundred nanometers to several micrometers long, typically 100-300 nm wide and about 20-30 nm thick. It was found that PVA could not only act as the reducing reagent but also as the structure-directing reagent. Besides, the PVA-assisted solid-solution-solid (SSS) transformation mechanism was proposed to illuminate the possible formation mechanism of VO2(B) nanobelts. Furthermore, the electrochemical properties of VO2(B) nanobelts were studied and they exhibited a high initial discharge capacity of 268 mAh/g, indicating that VO2(B) nanoblets are promising electrode materials in lithium battery.

Synthesis and photochemical performance of morphology-controlled CdS photocatalysts for hydrogen evolution under visible light

Novel CdS nanomaterials were synthesized by a simple “one-pot” hydrothermal biomolecule-assisted method using glutathione (GSH) as the sulfur source and structure-directing reagent. Various morphologies of CdS photocatalysts, such as solid nanospheres (s-CdS), hollow nanospheres (h-CdS) and nanorods (r-CdS), were obtained by controlling only the hydrothermal temperatures. The X-ray diffraction patterns confirmed that all of the samples were typical hexagonal wurtzite CdS. It was found that the absorption edge of s-CdS was at 465 nm with a greater blue shift compared to that of h-CdS and r-CdS. The photocatalytic activity of s-CdS was superior to that of h-CdS and r-CdS under visible light. Photoluminescence measurements revealed their different photogenerated electron/hole recombination ability, which was in accordance with the order of s-CdS < h-CdS < r-CdS. The excellent photocatalytic activity of s-CdS was ascribed to the small sizes of sub-nanocrystallites, which make it easy for photoinduced electrons and holes on the solid sphere to migrate to the surface and react with water and the sacrificial agent quickly. It was crucial to control the temperature for preparing CdS photocatalysts via hydrothermal methods. The formation mechanism of different morphology might be due to complexation, S–C bond rupture, spherical aggregation and Ostwald ripening processes.