The development of electrically conductive and high surface area carbon is important for the improvement of supercapacitor energy densities. Yttrium hydroxide microspindles were prepared and shown to catalyze carbon growth. The carbon exhibited a high surface area of 932 m2/g and high conductivity of 2.2 × 105 S/m. The carbon/yttrium oxide interface was probed using XPS, Raman spectroscopy, infrared spectroscopy, and solid-state fluorescence. Supercapacitor cells were assembled using the yttrium-catalyzed carbon and EMI-TFSI ionic liquid as the electrolyte. The symmetric supercapacitor cell had a specific capacitance of 137.2 F/g, energy density of 57.4 Wh/kg, and power density of 1724.3 W/kg, at 1 A/g.
Biphenyl wrinkled mesoporous silica nanoparticles with controlled particle size and high surface area were evaluated for the storage and delivery of doxorubicin. The average particle size and surface area were ~70 nm and ~1100 m2/g. The doxorubicin loading efficiency was 38.2 ± 1.5 (w/w)% and the release was pH dependent. The breast cancer cell line, MCF-7 (Michigan Cancer Foundation-7) was used for the in vitro drug release study. The cytotoxicity of doxorubicin-loaded nanoparticles was significantly higher than free doxorubicin. Fluorescence images showed biphenyl wrinkled mesoporous silica (BPWS) uptake by the MCF-7 cells. The biphenyl bridged wrinkled silica nanoparticles appear promising for hydrophobic drug loading and delivery.
The biological response of multi-walled carbon nanotubes (MWNTs) is related to their physicochemical properties and a thorough MWNT characterization should accompany an assessment of their biological activity, including their potential toxicity. Beyond characterizing the physicochemical properties of MWNTs from different sources or manufacturers, it is also important to characterize different production lots of the same MWNT product from the same vendor (i.e., lot-to-lot batch consistency). Herein, we present a comprehensive physicochemical characterization of two lots of commercial pristine MWNTs (pMWNTs) and carboxylated MWNTs (cMWNTs) used to study the response of mammalian macrophages to MWNTs. There were many similarities between the physicochemical properties of the two lots of cMWNTs and neither significantly diminished the 24-h proliferation of RAW 264.7 macrophages up to the highest concentration tested (200 μg cMWNTs/mL). Conversely, several physicochemical properties of the two lots of pMWNTs were different; notably, the newer lot of pMWNTs displayed less oxidative stability, a higher defect density, and a smaller amount of surface oxygen species relative to the original lot. Furthermore, a 72-h half maximal inhibitory concentration (IC-50) of ~90 µg pMWNTs/mL was determined for RAW 264.7 cells with the new lot of pMWNTs. These results demonstrate that subtle physicochemical differences can lead to significantly dissimilar cellular responses, and that production-lot consistency must be considered when assessing the toxicity of MWNTs.
The development of inexpensive and environmentally friendly graphene-like carbon is critical for its integration into industrial products. This work highlights the production of graphene-like carbon structures from calcium hydroxide. The chemical vapor deposition conditions to grow graphitic carbon on a calcium hydroxide catalyst are reported. Acetylene, steam, and calcium hydroxide are used to grow a crumpled carbon morphology. The crumpled carbon resulted in a high surface area of 1276 m 2 /g and high electrical conductivity (>10 5 S/m). Additionally, the significance and origin of the C 1s X-ray photoelectron spectroscopy (XPS) π−π* plasmon loss peak as it is related to high electrical conductivity is reported. A unique mechanism for the catalytic process involving calcium acetylide is proposed. Several deposition times, steam concentration, and catalyst morphology were tested to synthesize a variety of carbon morphologies from calcium-based materials. Crumpled carbon, hollow nanospheres, bamboo-like carbon nanotubes, multi-walled carbon nanotubes, and graphene fiber morphologies were all formed using calcium-based catalysts. Multiple reaction conditions, a scaled reaction (300 g), and catalyst recyclability were investigated. Calcium-based materials were then used as catalysts for the growth of other graphene-like carbons.
To overcome electronic transport issues of layered titanates in sodium-ion batteries, we have designed and synthesized composites of lepidocrocite titanates with reduced graphene oxide through a solution-based self-assembly approach. The parent lepidocrocite titanate (K 0.8 [Ti 1.73 Li 0.27 ]O 4 ) was exfoliated by a softchemical approach and mechanical shaking. Exfoliated layered titania sheets (LTO) were then combined with reduced graphene oxide (rGO) layers to assemble into composites through flocculation. Countercations (i.e., Mg 2+ ) were used for the selfassembly of negatively charged titania and rGO nanosheets via flocculation. The carbon content in the composites was tuned from 1 to 17% by changing the ratio of titania and rGO sheets in the mixed colloidal suspensions. Electrodes were processed with as-prepared LTO−rGO composites without any carbon additives and tested in sodium half-cell configurations. Mg + -coagulated LTO−rGO composite electrodes deliver higher capacities than electrodes prepared with coagulated titania sheets and 10% acetylene black in sodium half-cells and display good capacity retention after 50 cycles. Electrochemical impedance spectroscopy results indicate lower charge transfer resistance for LTO−14.5%rGO composites than that of coagulated titania sheets with 10% acetylene black. A power law analysis of cells containing the composites indicate a hybrid mechanism consisting of both surface and diffusional processes. A comparison with a similar system, that of dopaminederived LTO-C heterostructures, reveal significant differences. While capacities showed a strong dependence on carbon content for the dopamine-derived materials, this was not true for the LTO−rGO composites. Instead, the highest capacity was obtained for the 14.5% rGO sample, with a lower value obtained for the 17% rGO sample. A greater proportion of the redox processes were surface rather than diffusional in nature for the LTO−rGO composites as well.
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