Preparation of porous manganese oxide nanomaterials by one-pot synthetic sol–gel method

For the first time, the simple epoxide addition, sol–gel method has been employed to successfully prepare porous, high surface area manganese (II) aerogel nanomaterials. These uniform materials can then undergo calcination at relatively low temperature to selectively yield the mixed-valent Mn₃O₄ complex illustrating both an ease of preparation and synthesis versatility.     

The synthesis and characterization of zinc ferrite aerogels prepared by epoxide addition

Over the past decade sol–gel methods have become increasingly popular alternatives to the solid state synthesis of metal oxides. In many cases sol–gel synthesis is preferred due to desirable physical properties such as high surface area, high porosity, and small crystallite size. Monolithic zinc ferrite aerogels were produced by the epoxide addition sol–gel method. It was observed that addition of propylene oxide to 2-propanol solution of either the hydrated metal nitrate salts or the hydrated metal chloride salts resulted in the formation of stable red–brown gels. Aerogels were characterized using powder X-ray diffraction, high resolution scanning electron microscopy, transmission electron microscopy, and nitrogen adsorption/desorption analysis. The metal salt used in the synthesis was found to significantly influence the properties of the aerogel. All aerogels synthesized exhibited low densities and high surface areas (>340 m²/g). Annealing of the aerogel at relatively low temperatures (below 450 °C) yielded a highly crystalline porous material which is composed of nanometer sized particles.     

Homoleptic tris(methoxydimethylsilyl)silanides of the alkaline earth metals: first zwitterionic silanides with two naked silyl anions

The first zwitterionic alkaline earth metal silanides featuring two naked silyl anions were synthesized and a combined structural and computational study on these zwitterions revealed a correlation between the energy of the HOMO and the degree of negative charge of the naked silyl anions.     

Monitoring the formation of self-assembled monolayers of alkanedithiols using a micromechanical cantilever sensor

Using a micromechanical cantilever device, the surface stress induced during the growth of alkanedithiol (HS(CH2)nSH) monolayers on gold in solution is continuously monitored and reported. Adsorption of alkanedithiols of varying chain lengths is observed and compared to each other, as well as to the adsorption of hydroxyalkanethiols (HS(CH2)nOH) and alkanethiols (HS(CH2)nCH3). The results have revealed a significant change in surface stress on the basis of the chain length of the alkanedithiol. The long-chain (n > 10) alkanedithiol adsorption imposes a tensile stress on the gold-coated surface of the cantilever rather than the compressive stress exhibited by both alkanethiols and short-chain dithiols. Our results suggest a phenomenon in which the two thiols of the alkanedithiol adsorb onto the gold surface forming a loop inducing a tensile stress on the cantilever for long chain lengths. This study shows that micromechanical cantilever sensors can be very valuable tools in the exploration and characterization of self-assembled monolayers.     

Controlling the morphology of a zinc ferrite-based aerogel by choice of solvent

Zinc ferrite-based aerogels were prepared by the epoxide addition method. The effects of changing the reaction solvent were investigated. The porosity of the resultant materials was investigated by gas adsorption techniques while the microstructure of the aerogels was investigated by scanning electron microscopy and transmission electron microscopy. The solvent in which the gels were formed was found to have a profound impact on the surface morphology of the aerogels and the size of the nanoparticles therein. The aerogels were further analyzed by thermal gravimetric analysis and powder X-ray diffraction. After annealing at 350 °C, the porous material is found to maintain its nanocrystalline properties.     

High surface area alumina-supported nickel (II) oxide aerogels using epoxide addition method

Nickel (II) oxide aerogels with an amorphous alumina support were synthesized by the expoxide addition method. The monoliths were obtained by adding propylene oxide to an alcoholic solution of hydrated metal nitrate salts. The wet gels were dried by supercritical extraction to produce porous monolithic aerogels. The as-synthesized aerogels were amorphous containing aluminum and nickel hydroxides. Annealing of the as-synthesized aerogels at 400 °C yields crystalline nickel oxide materials which retain the high surface areas (>160 m²/g) and porosities of the original aerogels. The resultant aerogel materials were characterized using powder X-ray diffraction, thermo-gravimetric analysis, scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray analysis, and nitrogen adsorption/desorption analysis.     

Thermodynamic analysis of pure and impurity doped pentaerythritol tetranitrate crystals grown at room temperature

Pentaerythritol tetranitrate (PETN) powders are used to initiate other explosives. During long-term storage, changes in powder properties can cause changes in the initiation performance. Changes in the morphology and surface area of aging powders are observed due to sublimation and growth of PETN crystals through coarsening mechanisms, (e.g. Ostwald ripening, sintering, etc.). In order to alleviate the sublimation of PETN crystals under service conditions, stabilization methods such as thermal cycling and doping with certain impurities during or after the crystallization of PETN have been proposed. In this report we present our work on the effect of impurities on the morphology and activation energy of the PETN crystals. The pure and impurity doped crystals of PETN were grown from supersaturated acetone solution by solvent evaporation technique at room temperature. The difference in the morphology of the impurity-doped PETN crystal compared to pure crystal was examined by optical microscopy. The changes in the activation energies and the evaporation rates are determined by thermogravimetry (TG). Our activation energies of evaporation agree with earlier reported enthalpies of vaporization. The morphology and activation energy of PETN crystals doped with Ca, Na, and Fe cations are similar to that for pure PETN crystal, whereas the Zn-ion-doped PETN crystals have different morphology and decreased activation energy.     

Gold modified cadmium sulfide aerogels

Monolithic aerogels composed of cadmium sulfide nanoparticles partially modified with metallic gold (CdS-Au) are reported. The semiconductor–metal nanoparticles are synthesized using an inverse micelle media of Bis-(2-ethylhexyl)sulfosuccinate sodium salt (AOT) in heptane, followed by capping with 4-fluorothiophenol and precipitation with triethylamine. The nanoparticles are then dispersed in acetone and gel formation is achieved using nanoparticle condensation strategy. The resultant CdS-Au aerogel materials are mesoporous, with an interconnected network of semiconductor–metal nanoparticles. A detailed microstructure analysis of the semiconductor–metal aerogels via transmission electron microscopy indicates that the final gold concentration significantly impacts the semiconductor–metal aerogel morphology and porosity.     

Controllable thermal degradation of 2,4,6-trinitrotoluene (TNT) by absorption and confinement into mixed metal sponges

In this work, we report the absorption and confinement of 2,4,6-trinitrotoluene (TNT) in porous metals (Ag, Ag/Al, and Ag/Cu), and the effect of the physical properties of the metal on the calorimetric properties of TNT using thermogravimetric analysis and differential scanning calorimetry. The surface area and pore size distribution of the confiners were calculated to determine their effect on both the onset temperature and the rate at which TNT volatilizes. Confinement of TNT into the mixed metal sponges was confirmed by scanning electron microscopy. Overall, this study provides an insight into the fundamental factors influencing the properties of energetic materials under confinement that could potentially allow for more controlled and reliable degradation techniques depending on the characteristics of the porous material.