Carbon nanotube (CNT) carpet growth behavior is systematically investigated on a pristine and ion beam-bombarded family of basic catalyst substrates: MgAl 2 O 4 (100), MgAl 2 O 4 (110), MgAl 2 O 4 (111), and MgO (100). Interrelationships between physicochemical properties of catalyst substrates (composition, phase, basicity, and surface structure) and CNT carpet growth efficiency (catalyst lifetime and CNT growth rate) for a conventional feedstock (C 2 H 4 ) and an industrial waste (a gaseous product mixture from Fischer−Tropsch synthesis, FTS-GP) as a feedstock are established. Growth on MgAl 2 O 4 spinel substrates shows ion beam bombardment is effective in transforming "inactive" basic catalyst substrates to "active" substrates that support CNT carpet growth. For "active" catalyst substrates (MgO and ion beamdamaged MgAl 2 O 4 ), growth efficiency of a supported catalyst exhibits high sensitivity to the type of feedstock. FTS-GP outperforms C 2 H 4 as a feedstock in terms of growth efficiency and the ability of a supported catalyst to promote CNT carpet growth. Superior growth efficiency and CNT quality associated with FTS-GP is attributed to the unique composition of the feedstock that consists of a mixture of hydrocarbons (saturated and unsaturated), nitrogen, and unreacted synthesis gas.

Biological thiols are antioxidants essential for the prevention of disease. For example, low levels of the tripeptide glutathione are associated with heart disease, cancer, and dementia. Mn2+-doped wide bandgap semiconductor nanocrystals exhibit luminescence and magnetic properties that make them attractive for bimodal imaging. We found that these nanocrystals and silica-encapsulated nanoparticle derivatives exhibit enhanced luminescence in the presence of thiols in both organic solvent and aqueous solution. The key to using these nanocrystals as sensors is control over their surfaces. The addition of a ZnS barrier layer or shell produces more stable nanocrystals that are isolated from their surroundings, and luminescence enhancement is only observed with thinner, intermediate shells. Tunability is demonstrated with dodecanethiol and sensitivities decrease with thin, medium, and thick shells. Turn-on nanoprobe luminescence is also generated by several biological thiols, including glutathione, N-acetylcysteine, cysteine, and dithiothreitol. Nanoparticles prepared with different ZnS shell thicknesses demonstrated varying sensitivity to glutathione, which allows for the tuning of particle sensitivity without optimization. The small photoluminescence response to control amino acids and salts indicates selectivity for thiols. Preliminary magnetic measurements highlight the challenge of optimizing sensors for different imaging modalities. In this work, we assess the prospects of using these nanoparticles as luminescent turn-on thiol sensors and for MRI.