Shape-dependent Catalytic Activity Research Articles

Enzyme-free fluorescent DNA detection based on nucleic acid-templated click reaction via controllable synthesis of Cu2O as heterogeneous nanocatalyst

In the field of nucleic acid amplification assays, developing enzyme-free, easy-to-use, and highly sensitive amplification approaches remains a challenge. In this work, we synthesized a heterogeneous Cu2O nanocatalyst (hnCu2O) with different particle sizes and shapes, which was used for developing enzyme- and label-free nucleic acid amplification methods based on the nucleic acid-templated azide–alkyne cycloaddition (AAC) reaction catalyzed by hnCu2O. The hnCu2O exhibited size- and shape-dependent catalytic activity, with smaller sizes and spherical-like shapes exhibiting superior activity. Spherical-like hnCu2O (61 ± 8 nm) not only achieved a ligation yield of up to 84.2 ± 3.9 % in 3 min but also exhibited faster kinetics in the nucleic acid-templated hnCu2O-catalyzed AAC reaction, with a high reaction rate of 0.65 min−1 and a half-life of 1.07 ± 0.09 min. Based on this result, we developed nucleic acid-templated click ligation linear amplification reaction (NA-CLLAR) and nucleic acid-templated click ligation exponential amplification reaction (NA-CLEAR) approach. By combining the recognition (complementary to the target sequence) and signal output (split G-quadruplex sequence) elements into a DNA probe, the NA-CLLAR and NA-CLEAR fluorescence assays achieved highly specific detection of target nucleic acids, with a detection limit of 2.8 aM based on G-quadruplex-enhanced fluorescence. This work is a valuable reference and will inspire researchers to design enzyme-free nucleic acid signal amplification strategies by developing different types of Cu(I) catalysts with improved catalytic activity.

MnO2 shape dependent catalytic activity in vapour phase benzyl alcohol (BnOH) oxidation in presence of air

Understanding the relationship between the structure and the activity of the catalyst relies on the shape–controlled synthesis of nanostructures is crucial importance. The vapor phase oxidation of benzyl alcohol (BnOH) process over morphologically designed shape–selective manganese oxide nanorods (MnO2NR) and nanospheres (MnO2NS) catalysts are studied. The key catalytic properties are determined and demonstrated by various characterisation techniques such as P–XRD, BET, H2–TPR, O2–TPD, and Raman analysis. In addition, EDX and STEM–HRTEM microscopic analysis were carried out in better understanding the surface morphology, shape, and structure of the nanocatalysts. The prepared nanoporous MnO2NS catalyst enabled to generate more crystal defects, high surface area, strong reducing capacity, enhanced oxygen vacancies (Ov), and increased reactive surface oxygen species compared to nanorod shaped–MnO2NR catalyst. Significantly the rate of benzaldehyde (BnZA) formation in BnOH oxidation reaction over MnO2NS catalyst is ∼ 1.55 times higher than that of MnO2NR. Over MnO2NS creation of abundant O vacancies considerably improved the capacity of oxygen activation and redox ability.Thus, as a result, there are more active oxygen species which are mobile and reactive in accelerating the BnOH oxidation process.

Morphological effect of ceria-supported platinum catalyst on low-temperature ethylene oxidation

Three types of Pt/CeO2 catalysts with different support morphologies (rod (CeO2-R), cube (CeO2-C), and octahedron (CeO2-O) were synthesized especially for catalytically oxidizing C2H4 at low temperatures. The as-prepared catalysts exhibited strong shape-dependent catalytic activity in the order of Pt/CeO2-O > Pt/CeO2-C > Pt/CeO2-R. Such unique performance is mainly attributed to the different steps of C2H4 oxidation associated with the variation of oxygen species activated by Pt/CeO2 catalysts. Among the three catalysts, Pt/CeO2-O had the least issue with the accumulation of intermediate species and consequently performed the highest low-temperature C2H4 catalytic oxidation activity. Moreover, the negative impact of water condensation on the catalyst can be readily eliminated by refreshing the catalyst with N2 purging. Overall, this work led to a novel catalytic system for efficient low-temperature ethylene oxidation and a better understanding of the catalytic mechanism, thus benefiting the preservation of fruits and vegetables as one of the applications.

Shape-Dependent Catalytic Activity of Gold and Bimetallic Nanoparticles in the Reduction of Methylene Blue by Sodium Borohydride

In this study the catalytic activity of different gold and bimetallic nanoparticle solutions towards the reduction of methylene blue by sodium borohydride as a model reaction is investigated. By utilizing differently shaped gold nanoparticles, i.e., spheres, cubes, prisms and rods as well as bimetallic gold–palladium and gold–platinum core-shell nanorods, we evaluate the effect of the catalyst surface area as available gold surface area, the shape of the nanoparticles and the impact of added secondary metals in case of bimetallic nanorods. We track the reaction by UV/Vis measurements in the range of 190–850 nm every 60 s. It is assumed that the gold nanoparticles do not only act as a unit transferring electrons from sodium borohydride towards methylene blue but can promote the electron transfer upon plasmonic excitation. By testing different particle shapes, we could indeed demonstrate an effect of the particle shape by excluding the impact of surface area and/or surface ligands. All nanoparticle solutions showed a higher methylene blue turnover than their reference, whereby gold nanoprisms exhibited 100% turnover as no further methylene blue absorption peak was detected. The reaction rate constant k was also determined and revealed overall quicker reactions when gold or bimetallic nanoparticles were added as a catalyst, and again these were highest for nanoprisms. Furthermore, when comparing gold and bimetallic nanorods, it could be shown that through the addition of the catalytically active second metal platinum or palladium, the dye turnover was accelerated and degradation rate constants were higher compared to those of pure gold nanorods. The results explore the catalytic activity of nanoparticles, and assist in exploring further catalytic applications.

Shape Effect of Zinc Nanostructures on Electrochemical CO2 Reduction

To mitigate CO2 emissions and enable the conversion of CO2 to carbon-neutral fuels, the research on electrochemical reduction of CO2 (CO2RR) is gaining momentum. As an earth-abundant material, Zn is a promising electrocatalyst for highly active and selective reduction for the reduction of CO2 to CO. However, the shape effect of the Zn-based electrocatalysts on CO2RR has not been well understood. Herein, we synthesized hexagonal Zn nanoplates and systematically explored its shape-dependent catalytic activity for CO2RR, so as to achieve a better understanding of the relationship between the morphology and the catalytic activity of non-noble metal catalysts. Compared with the similarly-sized Zn nanoparticles, the H-Zn-NPs exhibit remarkably enhanced current density, together with an improved CO Faradaic efficiency of over 85% in a wide potential window. Theoretical results reveal that the unique hexagonal Zn nanostructure offers an increased number of catalytically active sites which are active for CO2RR to CO.

Highly Selective Electroreduction of CO2 to CO over Zinc Nanostructures

To mitigate CO2 emissions and enable the conversion of CO2 to carbon-neutral fuels, the research on electrochemical reduction of CO2 (CO2RR) is gaining momentum and so is the search for an earth-abundant electrocatalysts to achieve high catalytic activity and desirable selectivity for the target fuel. Herein, we synthesized hexagonal Zn nanoplates (H-Zn-NPs) and systematically explored its shape-dependent catalytic activity for CO2RR, so as to achieve a better understanding of the relationship between the morphology and the catalytic activity of non-noble metal catalysts. The prepared H-Zn-NPs are found to efficiently promote CO2RR toward CO production with improved catalytic activity, good stability and remarkably high CO selectivity of over 85% in a broad potential range. Theoretical results reveal that the unique hexagonal Zn nanostructure offers an increased number of catalytically active sites which are active for CO2RR to CO. The H-Zn-NPs undoubtedly hold a great potential as an alternative to noble metal for highly selective CO2RR to CO.

Facet-Dependent Reactivity of Fe2O3/CeO2 Nanocomposites: Effect of Ceria Morphology on CO Oxidation

Ceria has been widely studied either as catalyst itself or support of various active phases in many catalytic reactions, due to its unique redox and surface properties in conjunction to its lower cost, compared to noble metal-based catalytic systems. The rational design of catalytic materials, through appropriate tailoring of the particles’ shape and size, in order to acquire highly efficient nanocatalysts, is of major significance. Iron is considered to be one of the cheapest transition metals while its interaction with ceria support and their shape-dependent catalytic activity has not been fully investigated. In this work, we report on ceria nanostructures morphological effects (cubes, polyhedra, rods) on the textural, structural, surface, redox properties and, consequently, on the CO oxidation performance of the iron-ceria mixed oxides (Fe2O3/CeO2). A full characterization study involving N2 adsorption at –196 °C, X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS), temperature programmed reduction (TPR), and X-ray photoelectron spectroscopy (XPS) was performed. The results clearly revealed the key role of support morphology on the physicochemical properties and the catalytic behavior of the iron-ceria binary system, with the rod-shaped sample exhibiting the highest catalytic performance, both in terms of conversion and specific activity, due to its improved reducibility and oxygen mobility, along with its abundance in Fe2+ species.

Shape dependent catalytic activity of unsupported gold nanostructures for the fast reduction of 4-nitroaniline

A one step seed mediated strategy is adopted here for synthesizing spherical, dog bone and rod shaped gold nanoparticles. Usually noble metals decorated by supporting materials are used for chemical catalysis. Here, a variety of unsupported gold nanoparticles (spherical, dog bone and rod shaped) originating from the same growth procedure are used for the catalytic reduction of para-nitroaniline (4-NA). The product obtained, para-phenylenediamine, is an important material, especially in the field of dye industry. The reaction kinetic values were analyzed based on to the Langmuir–Hinshelwood (LH) mechanism. A comparison of the rate constants obtained for gold nanoparticles of different shapes with almost similar volume pointy that gold nanorods are superior to that of spherical and dog bone like nanoparticles. The turnover frequency obtained here is high compared to other reported results and is found to be sensitive to the shape of the nanoparticles.

Shape-controlled synthesis of Ni nanocrystalsviaa wet-chemistry strategy and their shape-dependent catalytic activity

We have synthesized Ni nanocrystals with different shapesviaa facile wet-chemistry strategy, and investigated their shape-dependent performances.

Novel synthesis and shape-dependent catalytic performance of Cu–Mn oxides for CO oxidation

Transition metal oxides with large specific surface area are attractive for high-activity catalysts, and hierarchical structures of transition metal oxides with porous feature possess the structural advantage in the transfer of gaseous reactant and product. In this work, porous Cu–Mn oxides with high surface area were successfully obtained through low-temperature coprecipitation method in alcohol/water solvent and then post-annealing. The addition of alcohol showed great influences on the shape and catalytic performances for CO oxidation. Dumbbell-like Cu–Mn oxide particles with splitting ends displayed high catalytic activity and a complete conversion of CO was achieved at 45°C, suggesting a shape-dependent catalytic activity. The oxidative activity was attributed to a combination of factors including specific surface area, active surface oxygen species and Mn(IV) cations. The results may supply a new thought to design high-performance Cu–Mn oxide catalysts.

Shape-dependent catalytic activity of CuO nanostructures

Ligand-regulated growth of various morphologies of copper oxide (CuO) nanostructures has been achieved through an aqueous-based chemical precipitation route where the Cu2+ ions were stabilized through complexation with different organic acids (viz. acetic/citric/tartaric acid). The rod-, spherical-, star-, and flower-shaped morphologies of the CuO nanostructures, obtained in the presence of the different carboxylic acids, have been characterized using XRD, FTIR, HRTEM, DLS, and zeta potential measurements, while their specific surface areas and the associated band gap energies have been compared. The catalytic performance of the different CuO nanostructures has been affirmed by monitoring the reduction of 4-nitrophenol by NaBH4 in real time using UV–visible absorption spectroscopy. The star-shaped morphologies of CuO have been found to show maximum catalytic activity toward the reduction of 4-nitrophenol in the presence of NaBH4, which can be correlated to their higher specific surface area and positive surface charge and to the presence of a high indexed facet.

Biorecovery of gold as nanoparticles and its catalytic activities for p-nitrophenol degradation.

Recovery of gold from aqueous solution using simple and economical methodologies is highly desirable. In this work, recovery of gold as gold nanoparticles (AuNPs) by Shewanella haliotis with sodium lactate as electron donor was explored. The results showed that the process was affected by the concentration of biomass, sodium lactate, and initial gold ions as well as pH value. Specifically, the presence of sodium lactate determines the formation of nanoparticles, biomass, and AuCl4 (-) concentration mainly affected the size and dispersity of the products, reaction pH greatly affected the recovery efficiency, and morphology of the products in the recovery process. Under appropriate conditions (5.25g/L biomass, 40mM sodium lactate, 0.5mM AuCl4 (-), and pH of 5), the recovery efficiency was almost 99%, and the recovered AuNPs were mainly spherical with size range of 10-30nm (~85%). Meanwhile, Fourier transforms infrared spectroscopy and X-ray photoelectron spectroscopy demonstrated that carboxyl and amine groups might play an important role in the process. In addition, the catalytic activity of the AuNPs recovered under various conditions was testified by analyzing the reduction rate of p-nitrophenol by borohydride. The biorecovered AuNPs exhibited interesting size and shape-dependent catalytic activity, of which the spherical particle with smaller size showed the highest catalytic reduction activity with rate constant of 0.665min(-1).

Cuboctahedral vs. octahedral platinum nanoclusters: insights into the shape-dependent catalytic activity for fuel cell applications

The shape of a catalyst plays an important role in any catalytic reaction.

Shape-dependent catalytic activity of Fe3O4 nanostructures under the influence of an external magnetic field for multicomponent reactions in aqueous media

Fe3O4 nanostructures were synthesized under external magnetic field, shown shape-dependent catalytic activity for the synthesis of imidazole derivatives in water.

Shape-dependent catalytic activity of oxygen reduction reaction (ORR) on silver nanodecahedra and nanocubes

The structure effects on the oxygen reduction reaction (ORR) are studied on similar sized silver nanodecahedra and nanocubes which are enclosed by (111) and (100) facets, respectively. The results show that the oxygen reduction proceeds one-step “direct” four-electron reduction on silver nanodecahedra, while two-step processes on silver nanocubes. The simulations results suggest that the different ORR catalytic activity can be interpretated by the adsorption competition between oxygen and hydroxyl on different silver facets. We demonstrate that the surface facet of silver nanocrystals is a decisive parameter to designing catalysts for ORR and other electrocatalytic reaction.

Shape dependent catalytic activity of nanoflowers and nanospheres of Pd4S generated via one pot synthesis and grafted on graphene oxide for Suzuki coupling.

Nanoflowers and nanospheres of Pd4S have been prepared for the first time from a single source precursor complex, [PdCl2(PhS-CH2CH2CH2-NH2)] (), by its one pot thermolysis at 195 °C. In oleylamine, flower shaped nanoparticles of Pd4S were formed but in an oleic acid (OA) and octadecene (ODE) mixture (1 : 1) the product was nanospheres of Pd4S (size in the range ∼23-38 nm and 15-28 nm, respectively). These nanoparticles (NPs) were grafted on graphene oxide (GO) at room temperature to prepare nanocomposites, GO-Pd4S. HRTEM, powder X-ray diffraction (PXRD) and TEM-EDX have been used to authenticate the nanoparticles and their composites. XPS of Pd4S NPs indicates the oxidation states of Pd and S are both zero with a Pd : S ratio ∼4.1 : 0.9. For the catalysis of Suzuki-Miyaura coupling reactions the nanoparticles individually and in the form of composites with GO were explored. The flower shaped NPs are superior than the spherical ones for this catalysis in aqueous ethanol and the catalytic efficiency increases on grafting the nanoflowers/spheres onto GO. The conversion was ∼99% (in 5 h; at 80 °C) for the composite of graphene oxide (GO) with the Pd4S nanoflowers (Pd: 0.2 mol%). The catalytic efficiency follows the order GO-Pd4S-nanoflowers > GO-Pd4S-nanospheres > Pd4S nanoflowers > Pd4S nanospheres. The recyclability of the GO-Pd4S nanoflower catalyst was examined for the coupling reaction and conversion was found to be ∼46% in the fourth run even after increasing the reaction time to 12 h. To understand whether the catalytic process with the GO-Pd4S nanoflowers was homogeneous or heterogeneous mercury poisoning, triphenylphosphine and three phase tests were carried out. They suggest that active Pd leached from GO-Pd4S nanoflowers does the catalysis significantly in a homogeneous fashion. Overall the catalysis appears to be a cocktail of homogeneous and some heterogeneous nature.

Shape-dependent catalytic activity of palladium nanoparticles for the direct synthesis of hydrogen peroxide from hydrogen and oxygen

In this study, single-crystal Pd nanocubes and nanooctahedrons were prepared by the colloidal method and their catalytic activities were compared in direct hydrogen peroxide synthesis. Using sodium tetrachloropalladate (II) as the Pd precursor, l-ascorbic acid (or formaldehyde) as the reducing agent, potassium bromide as the capping agent, and polyvinylpyrrolidone as the stabilizer, Pd nanocubes were obtained in a uniform size (9nm). Pd octahedrons (23nm in edge length) were synthesized via seed-mediated growth of the Pd nanocube, where the morphology of the cube was altered to that of a cuboctahedron, truncated octahedron, and octahedron, in series. The cubes and octahedrons were enclosed by {100} and {111} facets, respectively. In activity tests, the Pd octahedron presented higher hydrogen peroxide selectivity and productivity than the Pd cube. It is therefore suggested that the Pd {111} facet is more active than the Pd {100} facet in direct hydrogen peroxide synthesis.

Synthesis of a morphology controllable Fe3O4nanoparticle/hydrogel magnetic nanocomposite inspired by magnetotactic bacteria and its application in H2O2detection

Owing to the shape-dependent catalytic activity of Fe3O4 nanoparticles, controlling their morphology is of great significance. In this work, we propose a simple, nontoxic, water-based strategy for the fabrication of magnetic nanoparticle/hydrogel nanocomposites in which highly crystalline Fe3O4 nanooctahedra can be fabricated in situ within a negatively charged hydrogel matrix. The morphology of the Fe3O4 nanocrystals can be easily tuned by adjusting the crosslinking concentration of the hydrogel. Furthermore, the catalytic activities of the magnetic nanocomposites were studied, and the magnetic nanocomposite loaded with Fe3O4 nanooctahedra exhibited excellent catalytic activity and provided a sensitive response toward H2O2 detection. This scalable approach for the fabrication of magnetic nanocomposites, loaded with morphology controllable Fe3O4 nanoparticles, potentially promotes their applications in biotechnology and environmental chemistry.

Synthesis, characterization and catalytic activity of gold nanoparticles biosynthesized with Rhizopus oryzae protein extract

A simple one-pot green chemical method for the biosynthesis of gold nanoparticles (AuNPs) by reducing chloroauric acid (HAuCl4) with protein extract of Rhizopus oryzae to produce novel gold nano-bio-conjugates (AuNBC) is described. AuNBCs, having sizes ranging from 5 to 65 nm, were synthesized by altering the HAuCl4–protein extract ratio. The conjugates were characterized by spectroscopic, electron microscopic, light scattering and electrophoretic mobility measurements. It was found that the aqueous AuNBC suspensions exhibited excellent stability over a wide range of ionic strength, pH and temperature. The effect of pH and ionic strength indicated that stabilization is due to electrostatic repulsion arising from the negative charge of the conjugate proteins. The AuNBCs were stable at temperatures lower than the denaturation temperature of the fungal proteins. The catalytic activity of the as-synthesized AuNBCs was quantified by analysing the reduction of p-nitrophenol by borohydride. The conjugates exhibited interesting size and shape dependent catalytic activity, which was stronger than that observed for AuNPs prepared by conventional chemical methods. The catalytic activity was found to be sensitive to both the surface-area-to-volume ratio and the thickness of the protein coating on the NP.

Shape-dependent catalytic activity of palladium nanocrystals for the oxidation of carbon monoxide

It is of great interest to study the shape effect on the catalytic activity of metal nanocrystals, which exposed different crystallographic facets upon adopting various shapes. The investigations on shape-dependent catalysis of supported metal nanocrystals need to be conducted over nanocrystals with well-defined shapes and cleaned surface. The palladium nanocrystals with cubic, octahedral, and spherical morphologies were synthesized and well dispersed onto the inert silica support after removing the capping agents, which were used as the heterogeneous catalysts for carbon monoxide (CO) oxidation. It was found that the crystal facets of Pd nanoparticles played an essential role in determining the catalytic oxidation properties. As a result, the octahedral and spherical nanoparticles that predominantly exposed the Pd {111} crystal facets exhibited significantly better catalytic activity than the palladium nanocubes that possessed the Pd {100} crystal facets as the basal plane for the CO catalytic oxidation. It was inferred that the appropriate adsorption strength of CO molecules on Pd {111} planes was beneficial to the enhancement of the catalytic activity.