Le regole del gioco: Primo incontro con l'ingegneria strategica

Cu particles decorated carbon composite microspheres (CCMs) with a unique sesame ball structure have been prepared by combining the mass-producible spray drying technique with calcinations. The conventional cuprammonium cellulose complex solution obtained by dissolving cellulose in a cuprammonia solution has been applied as raw materials for the preparation of Cu­(NH₃)₄²⁺/cellulose complex microspheres via a spray drying process. The resulted Cu­(NH₃)₄²⁺/cellulose complex microspheres are then transformed into the Cu particles homogeneously decorated porous carbon spheres <i>in situ</i> by calcinations at 450 or 550 °C. The coordination effect between the Cu­(NH₃)₄²⁺ species and the hydroxyl groups of the cellulose macromolecules has been exploited for directing the dispersion of the Cu particles in the resultant composite CCMs. The antimicrobial effects of the CCMs are evaluated by determining the minimum growth inhibitory concentrations using Staphylococcus aureus and Escherichia coli as representatives, respectively. The CCMs show high efficiency catalytic properties to the conversion of 4-nitrophenol to 4-aminophenol using NaBH₄ as a reductant in a mild condition. The recyclability and stability of the CCM catalysts have also been studied

Facile Synthesis of ZnFe₂O₄ Nanoparticles with Tunable Magnetic and Sensing Properties

Nanoparticles (NPs) and colloidal nanocrystal clusters (CNCs) of ZnFe₂O₄ were synthesized by using a solvothermal method in a controlled manner through simply adjusting the solvents. When a glycerol/water mixture was used as the solvent, ZnFe₂O₄ NPs were obtained. However, using ethylene glycol solvent yielded well-dispersed ZnFe₂O₄ CNCs. X-ray diffraction (XRD) and transmission electron microscopy (TEM) data confirmed that the ZnFe₂O₄ NPs were a single crystalline phase with tunable sizes ranging from 12 to 20 nm, while the ZnFe₂O₄ CNCs of submicrometer size consisted of single-crystalline nanosheets. Magnetic measurement results showed that the ZnFe₂O₄ NPs were ferromagnetic with a very small hysteresis loop at room temperature. However, CNCs displayed a superparamagnetic behavior due to preferred orientations of the nanosheets. Electrochemical sensing properties showed that both the size of the NPs and the structure of the CNCs had a great influence on their electrochemical properties in the reduction of H₂O₂. Based on the experimental results, the formation mechanisms of both the ZnFe₂O₄ CNCs and NPs as well as their structure–property relationship were discussed

Structural Regulation of PdCu₂ Nanoparticles and Their Electrocatalytic Performance for Ethanol Oxidation

Two types of PdCu₂ nanoparticles were prepared through one-pot synthesis and a two-step reducing process, named as PdCu₂-1 and PdCu₂-2, respectively. The morphology and structure of as-prepared samples were investigated by transmission electron microscopy, high-resolution transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and inductively coupled plasma-optical emission spectrometry. Results showed that more Pd atoms were buried in the inside of PdCu₂-1, whereas more available Pd sites were distributed on the surface of PdCu₂-2. The electrochemical measurements indicated that both PdCu₂-1 and PdCu₂-2 nanoparticles showed a higher electrocatalytic activity than that for pure Pd nanoparticles. In particular, PdCu₂-2 predictably exhibited a better stability and durability as well as a lower onset potential and a higher catalytic current density than that of PdCu₂-1 toward ethanol oxidation in alkaline media. On the basis of these studies, the formation mechanisms of both the PdCu₂ catalysts and the relationship between their structure and properties were discussed in this paper

Spray-Drying-Induced Assembly of Skeleton-Structured SnO₂/Graphene Composite Spheres as Superior Anode Materials for High-Performance Lithium-Ion Batteries

Three-dimensional skeleton-structured assemblies of graphene sheets decorated with SnO₂ nanocrystals are fabricated via a facile and large-scalable spray-drying-induced assembly process with commercial graphene oxide and SnO₂ sol as precursors. The influences of different parameters on the morphology, composition, structure, and electrochemical performances of the skeleton-structured SnO₂/graphene composite spheres are studied by XRD, TGA, SEM, TEM, Raman spectroscopy, and N₂ adsorption–desorption techniques. Electrochemical properties of the composite spheres as the anode electrode for lithium-ion batteries are evaluated. After 120 cycles under a current density of 100 mA g^–1, the skeleton-structured SnO₂/graphene spheres still display a specific discharge capacity of 1140 mAh g^–1. It is roughly 9.5 times larger than that of bare SnO₂ clusters. It could still retain a stable specific capacity of 775 mAh g^–1 after 50 cycles under a high current density of 2000 mA g^–1, exhibiting extraordinary rate ability. The superconductivity of the graphene skeleton provides the pathway for electron transportation. The large pore volume deduced from the skeleton structure of the SnO₂/graphene composite spheres increases the penetration of electrolyte and the diffusion of lithium ions and also significantly enhances the structural integrity by acting as a mechanical buffer

Carrageenan Asissted Synthesis of Palladium Nanoflowers and Their Electrocatalytic Activity toward Ethanol

Palladium (Pd) nanoflowers with tunable thorns were prepared by a facile and rapid route with the assistance of carrageenan. The superior nature of well-dispersed Pd nanoflowers has been disclosed by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy measurements. The growth of thorns of Pd nanostructures was first stimulated with the continuous introduction of l-ascorbic acid in the synthesis system and then reached a maximum length of about 132 nm, followed by a slight decrease in concentration. Electrochemical data showed that Pd nanoflowers with the longest thorns exhibited the highest catalytic current density of 1160 mA/mg, optimized tolerance to the poisoning, and the lowest onset potential while others showed a better cycle stability with a catalytic activity maintenance of above 96% after 300 cycles. It is suggested that the structure of thin thorns of Pd nanoflowers should be easier to damage than thick thorns during the electrocatalysis of ethanol. The relationship between Pd nanoflowers and properties as well as the key factors to form the nanoflower structure were discussed based on the experimental data

Formic Acid-Assisted Synthesis of Palladium Nanocrystals and Their Electrocatalytic Properties

Palladium (Pd) nanocrystals have been synthesized by using formic acid as the reducing agent at room temperature. When the concentration of formic acid was increased continuously, the size of Pd nanocrystals first decreased to a minimum and then increased slightly again. The products have been investigated by a series of techniques, including X-ray diffraction, high-resolution transmission electron microscopy (HRTEM), UV–vis absorption, and electrochemical measurements. The formation of Pd nanocrystals is proposed to be closely related to the dynamical imbalance of the growth and dissolution rate of Pd nanocrystals associated with the adsorption of formate ions onto the surface of the intermediates. It is found that small Pd nanocrystals showed blue-shifted adsorption peaks compared with large ones. Pd nanocrystals with the smallest size display the highest electrocatalytic activity for the electrooxidation of formic acid and ethanol on the basis of cyclic voltammetry and chronoamperometric data. It is suggested that both the electrochemical active surface area and the small size effect are the key roles in determining the electrocatalytic performances of Pd nanocrystals. A “dissolution–deposition–aggregation” process is proposed to explain the variation of the electrocatalytic activity during the electrocatalysis according to the HRTEM characterization