Louisa J. Hope-Weeks

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.

Aerosolized PLA and PLGA nanoparticles enhance humoral, mucosal and cytokine responses to hepatitis B vaccine.

Porous poly(L-lactic acid) (PLA) and poly(lactic-co-glycolic acid) (PLGA) nanoparticles were tested for pulmonary delivery of hepatitis B vaccine. In particular, the effects of particle size and hydrophobicity on mucosal and cell-mediated immune responses were investigated. Three formulations of PLA and PLGA nanoparticles containing a fixed amount of hepatitis B surface antigen (HBsAg) were prepared by a double-emulsion-solvent-evaporation method and characterized for surface morphology, charge, size, density and in vitro release. The immune responses were studied by measuring secretory IgA levels in mucosal fluids and quantitating cytokine levels in rat spleen homogenates. Particle uptake was studied in rat alveolar macrophages. Scanning electron microscopy revealed particles with smooth surfaces. Zeta potential measurements indicated that the particles carried negative surface charges. The antigen was continuously released for 42 days in phosphate buffer. Hydrophobic particles >500 nm elicited a more robust increase in secretary IgA, interleukin-2 and interferon-γ levels compared to hydrophilic particles <500 nm. Large hydrophobic particles were more efficiently internalized by rat alveolar macrophages compared to smaller hydrophilic particles. Calu-3 cell viability studies indicate that the viability of cells is not affected by nanoparticulate formulations. This study demonstrates that inhalable nanoparticles of HBsAg produce an enhancement of immune responses.

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.

Thermoelectric properties of porous multi-walled carbon nanotube/polyaniline core/shell nanocomposites

Porous polyaniline (PANI)-coated multi-walled carbon nanotube (MWNT) core/shell nanohybrids were fabricated through in situ polymerization and subsequently assembled into macroscopic composites. N(2) adsorption/desorption analysis indicated that the volume of nanopores increased significantly, which could make a significant contribution to phonon scattering. Thermal annealing was also carried out to improve the Seebeck coefficient of the as-produced nanocomposites. The optimal sample showed electrical conductivity of 14.1 S cm(-1), a Seebeck coefficient of 79.8 μV K(-1) and thermal conductivity of 0.27 W mK(-1), resulting in a highest figure of merit (ZT) of 0.01 at a very low loading of MWNTs (<1 wt%). These results will provide a potential direction to enhance thermoelectric performance of organic materials and also facilitate the application of organic materials in thermal energy harvesting or cooling.

Copper(II) aerogels via 1, 2-epoxide gelation

We report a simple one-step synthesis to prepare a porous high surface area copper(II) aerogel; calcination of the aerogel at relatively low temperatures induced a phase change which resulted in the formation of a mesoporous copper(II) oxide material.

Synthesis and photoluminescence properties of hierarchical architectures of YBO3:Eu3+

We present a general hydrothermal method without any organic solvent or surfactant for the synthesis of YBO3:Eu3+ nano- and micro-structures. The samples were of excellent quality with uniform, well dispersed, self-assembled and self-purified YBO3:Eu3+. Single crystal nanoflakes gathered together to evolve into a hierarchical architecture with eight different types of three dimensional morphologies. Strong photoluminescence spectra were obtained at 592, 611 and 627 nm at excitations wavelengths 254 and 363 nm. The emission spectra are associated with the transitions from the excited 5D0 level to the 7FJ (J = 1, 2, 3, 4) levels of Eu3+ activators. YBO3:Eu3+ prepared using ethanol solvent exhibited the highest chromaticity values yet reported.

Effect of titanium dioxide nanomaterials and ultraviolet light coexposure on African clawed frogs (Xenopus laevis)

Titanium dioxide nanomaterials (nano-TiO(2) ) exhibit stronger photochemical oxidation/reduction capacity compared with their bulk counterparts, but the effectiveness of nano-TiO(2) interaction with ultraviolet (UV) light strongly depends on particle size. In this study, the dependence of nano-TiO(2) toxicity on particle size and interaction with UV light were investigated. Toxicity tests with Xenopus laevis included eight concentrations of nano-TiO(2) in the presence of either white light or UVA (315-400 nm). We quantified viability and growth of Xenopus laevis. Results showed that, regardless of UV light exposure, increasing TiO(2) concentration decreased X. laevis survival (p < 0.05). Coexposure to 5-nm TiO(2) and UVA caused near-significant decreases in X. laevis survival (p = 0.08). Coexposure to 10-nm TiO(2) and UVA significantly decreased X. laevis survival (p = 0.005). However, coexposure to 32-nm TiO(2) and UVA had no statistical effect on X. laevis survival (p = 0.8). For all three particle sizes, whether alone or with UV light, the nano-TiO(2) concentrations significantly affected growth of tadpoles as determined by total body length, snout-vent length, and developmental stage. High-concentration TiO(2) solutions suppressed tadpole body length and delayed developmental stages. Further research to explore reasons for the growth and mortality in tadpoles is still underway in our laboratory. Given the widespread application of nano-TiO(2) , our results may be useful in the management of nano-TiO(2) released from industrial, municipal, and nonpoint sources.

Tailoring cobalt doped zinc oxide nanocrystals with high capacitance activity: factors affecting structure and surface morphology

Highly crystalline zinc cobaltite (ZnCo2O4) nanocrystals were successfully synthesized through an epoxide driven, sol–gel method using Zn(NO3)·6H2O and CoCl2·6H2O as precursors. The crystal phase, morphology, specific surface areas, porosity, and capacitance activity of the prepared materials were characterized by powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), gas sorption techniques, and cyclic voltammetry, respectively. Results reveal that the synthesized nanocrystals are ∼4 nm in diameter. Electron microscopy studies illustrate significant changes brought on by varying the solvent and epoxide. Gas sorption analyses detail high specific surface areas (>200 m2 g−1) and porosities of the as prepared and annealed samples. Cyclic voltammetry experiments show that these zinc cobaltite nanocrystals have exceptional capacitance (∼700 Fg−1) and excellent cycle durability making them an excellent electrode material for supercapacitors.

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.

Aerogel nanocomposites of ZnO–SnO2 as efficient photocatalysts for the degradation of rhodamine B

For the first time, aerogel nanocomposites containing ZnO and SnO2 were successfully prepared through a facile, sol–gel method without the use of a template or supporting matrix. These nanoparticles exhibit high potential for application as a photocatalyst for wastewater remediation.