Large-area preparation of high-quality and uniform three-dimensional graphene networks through thermal degradation of graphene oxide-nitrocellulose composites.

We demonstrate a simple method to prepare high-quality and uniform three-dimensional (3D) graphene networks through thermal degradation of graphene oxide (GO)-nitrocellulose composites over a large area. The nitrocellulose simultaneously acts as a support and aids in the reduction of GO by exothermic decomposition. The graphene networks have tunable porous morphology where the pore size can be controlled by adjusting the concentration of GO in the composite. This new technique is a very simple method to obtain 3D graphene networks and has the potential to produce 3D graphene-modified substrates for use in energy storage and conversion applications, in supporting frameworks of catalyst, and in sensors. In this report, the prepared 3D graphene networks were directly used as the electrodes of supercapacitors without using a binding agent and/or conducting additive with a high specific capacitance of 162.5 F g(-1) at 0.5 A g(-1) current density.

Preparation-morphology-performance relationships in cobalt aerogels as supercapacitors.

The ability to direct the morphology of cobalt sol-gel materials by using the simple synthetic parameters in epoxide-driven polycondensations has been dramatically demonstrated, and the influence of such morphological differences upon the supercapacity of the materials has been explored. Precursor salt, epoxide, and solvent all influence the speed of the sol-gel transition and the size and shape of the features observed in the as-prepared materials, thereby leading to highly varied microstructures including spheres, sponge-like networks, and plate assemblies of varied size. These morphological features of the as-prepared cobalt aerogels were observed for the first time by high resolution scanning electron microscopy (HRSEM). The as-prepared aerogel materials were identified by powder X-ray diffraction and thermogravimetry as weakly crystalline or amorphous cobalt basic salts with the general formula Co(OH)(2-n)X(n) where X = Cl or NO3 according to the precursor salt used in the synthesis. For all samples, the morphology was preserved through mild calcining to afford spinel phase Co3O4 in a variety of microstructures. Wide-ranging specific surface areas were determined for the as-prepared and calcined phases by physisorption analysis in agreement with the morphologies observed by HRSEM. The Co3O4 aerogels were evaluated for their supercapacitive performance by cyclic voltammetry. The various specimens exhibit capacitances ranging from 110 to 550 F g(-1) depending upon the attributes of the particular aerogel material, and the best specimen was found to have good cycle stability. These results highlight the epoxide-driven sol-gel condensation as a versatile preparative route that provides wide scope in materials' properties and enables the analysis of structure-performance relationships in metal oxide materials.

Formation of three-dimensional ordered hierarchically porous metal oxides via a hybridized epoxide assisted/colloidal crystal templating approach.

Three-dimensionally ordered hierarchically porous alumina, iron(III) oxide, yttria, and nickel oxide have been prepared through the hybridization of colloidal crystal-templating and a modified sol-gel method. Simply, highly ordered arrays of poly(methyl methacrylate) (PMMA) were infiltrated with a precursor solution of metal salt and epoxide. Calcination after solidification of the material removed the polymer template while forming the inverse replicas, simultaneously. These hierarchical structures possessing macropore windows and mesopore walls were characterized by powder X-ray diffraction (PXRD), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and N2 adsorption/desorption techniques to probe the structural integrity. It was revealed by PXRD that the prepared 3D frameworks were single-phase polycrystalline structures with grain sizes between 5 and 27 nm. The thermal stability as studied by TGA illustrates expected weight losses and full decomposition of the PMMA template. SEM reveals the bimodal, hierarchical macroporous frameworks with well-defined macropore windows and mesoporous walls. Gas sorption measurements of the ordered materials display surface areas as high as 93 m(2) g(-1), and average mesopore diameter up to 33 nm. Due to the versatility of this method, we expect these materials will be ideal candidates for applications in catalysis, adsorption, and separations. Furthermore, the implementation of this technology for production of three-dimensionally ordered macroporous materials can improve the cost and efficiency of metal oxide frameworks (MOFs) due to its high versatility and amenability to numerous systems.

Metal-organic frameworks (MOFs) as safer, structurally reinforced energetics.

Second-generation cobalt and zinc coordination architectures were obtained through efforts to stabilize extremely sensitive and energetic transition-metal hydrazine perchlorate ionic polymers. Partial ligand substitution by the tridentate hydrazinecarboxylate anion afforded polymeric 2D-sheet structures never before observed for energetic materials. Carefully balanced reaction conditions allowed the retention of the noncoordinating perchlorate anion in the presence of a strongly chelating hydrazinecarboxylate ligand. High-quality X-ray single-crystal structure determination revealed that the metal coordination preferences lead to different structural motifs and energetic properties, despite the nearly isoformulaic nature of the two compounds. Energetic tests indicate highly decreased sensitivity and DFT calculations suggest a high explosive performance for these remarkable structures.

Solvent-tuned hierarchical porosity in nitrocellulose aerogels.

We describe the simple preparation of nitrocellulose gels and high surface area (300 + m(2) g(-1)) aerogels and their hierarchical pore structures. The solvent in which the gels form greatly influences the pore geometry and size distribution of the gels in both the macro- and mesopore domains.

Ionic polymers as a new structural motif for high-energy-density materials.

Energetic materials have been used for nearly two centuries in military affairs and to cut labor costs and expedite laborious processes in mining, tunneling, construction, demolition, and agriculture, making a tremendous contribution to the world economy. Yet there has been little advancement in the development of altogether new energetic motifs despite long-standing research efforts to develop superior materials. We report the discovery of new energetic compounds of exceptionally high energy content and novel polymeric structure which avoid the use of lead and mercury salts common in conventional primary explosives. Laboratory tests indicate the remarkable performance of these Ni- and Co-based energetic materials, while DFT calculations indicate that these are possibly the most powerful metal-based energetic materials known to date, with heats of detonation comparable with those of the most powerful organic-based high explosives currently in use.

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.

PLGA microparticles encapsulating prostaglandin E1-hydroxypropyl-ß-cyclodextrin (PGE1-HPßCD) complex for the treatment of pulmonary arterial hypertension (PAH).

PURPOSE: To test the efficacy and viability of poly (lactic-co-glycolic acid) (PLGA) microspheres encapsulating an inclusion complex of prostaglandin E(1) (PGE(1)) and 2-hydroxypropyl-ß-cyclodextrin (HPßCD) for pulmonary delivery of PGE(1) for treatment of pulmonary arterial hypertension (PAH), a disease of pulmonary circulation. METHODS: PLGA-based microparticulate formulations of PGE(1)-HPßCD inclusion complex or plain PGE(1) were prepared by a double-emulsion solvent evaporation method. HPßCD was used as a complexing agent to increase the aqueous solubility of PGE(1), act as a porosigen to produce large porous particles, and promote absorption of PGE(1). Particles were characterized for micromeritic properties, in vivo absorption, metabolic degradation, and acute safety. RESULTS: Incorporation of HPßCD in the microparticles resulted in development of large particles with internal pores, which, despite large mean diameters, had aerodynamic diameters in the inhalable range of 1 to 5 µm. HPßCD incorporation also resulted in a significant increase in the amount of drug released in vitro in simulated interstitial lung fluid, showing a desirable burst release profile required for immediate hemodynamic effects. Compared to plain PLGA microparticles, entrapment efficiency was decreased upon complexation with HPßCD. In vivo absorption profile indicated prolonged availability of PGE(1) in circulation following pulmonary administration of the optimized microparticulate formulations, with an extended half-life of almost 4 hours. Metabolic degradation and acute toxicity studies suggested that microparticulate formulations were stable under physiological conditions and safe for the lungs and respiratory epithelium. CONCLUSIONS: This study demonstrates the feasibility of PGE(1)-HPßCD complex encapsulated in PLGA microparticles as a potential delivery system for controlled release of inhaled PGE(1).

A supramolecular approach to zwitterionic alkaline metal silanides and formation of heterobimetallic silanides.

Incorporating pendant polydonor groups is key to the synthesis and isolation of a series of novel and truly zwitterionic alkaline metal silanides of formula {Si[SiMe(2)O(CH(2))(n)OMe](3)}M (n = 2, 3; M = Li, Na, K) that can easily be converted into heterobimetallic silanides.

Monolithic aerogels of silver modified cadmium sulfide colloids.

Monolithic mesoporous aerogels comprising cadmium sulfide nanoparticles partially coated with metallic silver (CdS-Ag) are synthesized, and it is determined that the concentration of silver has a significant impact on the resultant CdS-Ag aerogel morphology and porosity.

Synthesis of cobalt oxide aerogels and nanocomposite systems containing single-walled carbon nanotubes.

The synthesis and characterization of porous nanostructured cobalt oxide (Co3O4) aerogels using epoxide addition method is described. Cobalt-containing monoliths were obtained by sol-gel processing of an alcoholic cobalt chloride solution with propylene oxide as the gelation agent. The alcogels were dried by supercritical CO2 fluid extraction to obtain the highly porous amorphous cobalt (II) aerogels. To enhance and control the structural properties of the aerogels, single-walled carbon nanotubes (SWCNT) were incorporated into the cobalt (II) aerogel network to form a homogenous composite material. The resulting materials were characterized using powder X-ray diffraction and nitrogen adsorption/desorption analysis. The detailed microstructure of aerogel networks was investigated using scanning and transmission electron microscopy, which showed significant structural changes induced by the incorporation of SWCNT to the cobalt aerogel. Annealing of the aerogel materials at 600 degrees C yields a highly crystalline well-faceted Co3O4 network.

Nondestructive experimental determination of bimaterial rectangular cantilever spring constants in water.

In order to address the issue of spring constant calibration in viscous fluids such as water, a new method is presented that allows for the experimental calibration of bimaterial cantilever spring constants. This method is based on modeling rectangular cantilever beam bending as a function of changing temperature. The temperature change is accomplished by heating water as it flows around the cantilever beams in an enclosed compartment. The optical static method of detection is used to measure the deflection of cantilever at the free end. Experimentally determined results are compared to Sader's method and to the Thermotune method most commonly used in cantilever calibrations. Results indicate that the new bimaterial thermal expansion method is accurate within 15%-20% of the actual cantilever spring constant, which is comparable to other nondestructive calibration techniques.

A simple method for the removal of thiols on gold surfaces using an NH4OH-H2O2-H2O solution.

The removal behavior of self-assembled monolayers (SAMs) of thiol molecules on a gold substrate by an NH(4)OH-H(2)O(2)-H(2)O solution was studied using attenuated total reflectance infrared spectroscopy (ATR-IR) and atomic force microscopy (AFM). Furthermore, the impact of the concentration of NH(4)OH and H(2)O(2) in the solution and reaction temperature on the SAM removal rate and efficiency was explored. The SAM removal rate and efficiency were significantly influenced by the concentration of NH(4)OH rather than H(2)O(2). The solution containing the 2 : 1 molar ratio of NH(4)OH : H(2)O(2) among three different solutions showed the highest removal rate and efficiency in the removal of 11-mercapto-1-undecanol. The increase in the reaction temperature resulted in the enhancement on the SAM removal rate, but it led to the fast delamination of the gold layer. These results may be useful in the regeneration of sensor surfaces relying on gold/thiol chemistry.

Luminescence Decay Dynamics and Trace Biomaterials Detection Potential of Surface-Functionalized Nanoparticles.

We have studied the luminescence decay and trace biomaterials detection potential of two surface-functionalized nanoparticles, poly(ethylene glycol) bis(carboxymethyl) ether-coated LaF(3):Ce,Tb (~20 nm) and thioglycolic acid-coated ZnS/Mn (~5 nm). Upon UV excitation, these nanoparticles emitted fluorescence peaking at 540 and 597 nm, respectively, in solution. Fluorescence imaging revealed that these nanoparticles targeted the trace biomaterials from fingerprints that were deposited on various nonporous solid substrates. Highly ordered, microscopic sweat pores within the friction ridges of the fingerprints were labeled with good spatial resolutions by the nanoparticles on aluminum and polymethylpentene substrates, but not on glass or quartz. In solution, these nanoparticles exhibited multicomponent fluorescence decays of resolved lifetimes ranging from nano-to microseconds and of average lifetimes of ~24 and 130 micros for the coated LaF(3):Ce,Tb and ZnS:Mn, respectively. The long microsecond-decay components are associated with the emitters at or near the nanocrystal core surface that are sensitive to the size, surface-functionalization, and solvent exposure of the nanoparticles. When the nanoparticles were bound to the surface of a solid substrate and in the dried state, a decrease in the microsecond decay lifetimes was observed, indicative of a change in the coating environment of the nanocrystal surface upon binding and solvent removal. The average decay lifetimes for the surface-bound ZnS:Mn in the dried state were ~60, 30, and 11 micros on quartz, aluminum, and polymethylpentene, respectively. These values were still 2 orders of magnitude longer than the typical fluorescence decay background of most substrates (e.g., ~0.36 micros for polymethylpentene) in trace forensic evidence detections. We conclude that coated ZnS: Mn nanoparticles hold great promise as a nontoxic labeling agent for ultrasensitive, time-gated, trace evidence detections in nanoforensic applications.

Exploration of the use of novel SiO2 nanocomposites doped with fluorescent Eu3+/sensitizer complex for latent fingerprint detection.

Silicon dioxide-based nanocomposites have shown great potential in novel chemical and biological sensor development due to their large loading capacity and high surface area to volume ratio for trapping molecular complexes of various sizes. However, their potential applications in forensic science, latent fingerprint detection in particular, were still unclear. In this study, we have succeeded in trapping the highly fluorescent and photo-stable Eu3+ metal ions/sensitizer complex in silicon dioxide-based nanocomposites, doped xerogels, using the sol-gel method. We have tested the spectroscopic properties of Eu3+ in several combinations of rare earth sensitizers and different derivatives of silicon dioxide nanoporous templates. Our results indicated that the use of 1,10-phenanthroline (OP) sensitizer in tetraethoxysilane (TEOS) template provides the best fluorescently doped xerogels applicable for latent fingerprint detections on various forensic relevant materials, including metal foil, glass, plastic, colored paper, and a green tree leaf. The fabrication procedure, UV/vis and fluorescence characterizations, and fingerprint labeling results of these new Eu3+/OP/TEOS nanocomposites are presented in this exploratory study.

Effect of surface conjugation chemistry on the sensitivity of microcantilever sensors.

Microcantilever sensors are an offshoot of atomic force microscopy and are useful tools for effectively detecting a target biomolecule. The recognition of the target molecule on the biosensor is based on the physical bending of the microcantilever, which is driven by a specific molecular interaction between the target molecule and the sensor surface. In this study, to enhance the sensitivity of the microcantilever sensor, the sensor surface was modified through a surface conjugation method using self-assembled monolayers (SAMs) and heterobifunctional cross-linkers. After the surface modification of the microcantilever sensor, the sensitivity for L-cysteine was recorded. The detection of L-cysteine was influenced by the active site and the molecular size of the cross-linked compound attached onto the surface of the microcantilever.

Static deflection measurements of cantilever arrays reveal polymer film expansion and contraction.

An optical static method of detection is used to interpret surface stress induced bending related to cantilevers coated on one side with poly(vinyl alcohol), poly(vinyl butyral-co-vinyl alcohol-co-vinyl acetate), and poly(vinyl chloride-co-vinyl acetate-co-2-hydroxypropyl acrylate), or respectively, PVA, PVB, and PVC, and exposed to various solvent vapors. Results indicate that the adsorption and surface interactions of the different solvent vapors that cause polymer swelling and shrinking lead to rearrangements, which have been shown to change the elastic properties of the polymer film, and subsequently, the spring constant of the polymer coated cantilever. Static deflection measurements allow the direction of cantilever bending to be determined, which adds a new dimension of usefulness for surface functionalized cantilevers as transducers in the development of novel microelectromechanical systems (MEMS).

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.