Reduction of Graphene Oxide Thin Films by Cobaltocene and Decamethylcobaltocene

Reduced graphene oxide (RGO) films have been prepared by immersion of graphene oxide (GO) films at room temperature in nonaqueous solutions containing simple, outer-sphere metallocene reductants. Specifically, solutions of cobaltocene, cobaltocene and trifluoroacetic acid (TFA), and decamethylcobaltocene each showed activity for the rapid reduction of GO films cast on a wide variety of substrates. Each reactant increased the conductivity of the films by several orders of magnitude, with RGO films prepared with either decamethylcobaltocene or cobaltocene and TFA possessing the highest conductivities (∼10⁴ S m^–1). X-ray photoelectron spectroscopy suggested that while all three reagents lowered the content of carbon–oxygen functionalities, solutions of cobaltocene and TFA were the most effective at reducing the material to sp² carbon. Separately, Raman spectra and atomic force micrographs indicated that RGO films prepared with decamethylcobaltocene consisted of the largest graphitic domains and lowest macroscopic roughness. Cumulatively, the data suggest that the outer-sphere reductants can affect the conversion to RGO but the reactivity and mechanism depend on the standard potential of the reductant and the availability of protons. This work both demonstrates a new way to prepare high-quality RGO films on a wide range of substrate materials without annealing and motivates future work to elucidate the chemistry of RGO synthesis through the tunability of outer-sphere reductants such as metallocenes

<i>D</i>. <i>pulex</i> survival with vitamin D₃.

<p><i>D</i>. <i>pulex</i> (N = 12) exposed to acute UV-A in the presence of vitamin D₃. Blue line = 0 mg D₃; Black line = 5 mg D₃; Red line = 10 mg D₃. No reproduction was observed in any individuals during the experimental period. Error = standard error of the mean across 3 trials.</p

UV-Stressed <i>Daphnia pulex</i> Increase Fitness through Uptake of Vitamin D₃

<div><p>Ultraviolet radiation is known to be highly variable in aquatic ecosystems. It has been suggested that UV-exposed organisms may demonstrate enough phenotypic plasticity to maintain the relative fitness of natural populations. Our long-term objective is to determine the potential photoprotective effect of vitamin D₃ on <i>Daphnia pulex</i> exposed to acute or chronic UV radiation. Herein we report our initial findings in this endeavor. <i>D</i>. <i>pulex</i> survival and reproduction (fitness) was monitored for 5 d as a proof of concept study. Significantly higher fitness was observed in the <i>D</i>. <i>pulex</i> with D₃ than those without (most extreme effects observed were 0% survival in the absence of D₃ and 100% with 10 ppm D₃). Vitamin D₃ was isolated from the culture media, the algal food (<i>Pseudokirchneriella</i>), and the <i>D</i>. <i>pulex</i> and quantified using high performance liquid chromatography (HPLC). Vitamin D₃ was fluorescently labeled using a phenothiazinium dye and added to cultures of <i>D</i>. <i>pulex</i>. Images demonstrating the uptake of D₃ into the tissues and carapace of the <i>D</i>. <i>pulex</i> were acquired. Our initial findings suggest a positive role for D₃ in ecosystems as both UV-stressed algae and <i>Daphnia</i> sequester D₃, and <i>D</i>. <i>pulex</i> demonstrate increased fitness in the presence of D₃.</p></div

D. pulex.

<p><i>D</i>. <i>pulex</i> were exposed to ethylene blue for 15 min, rinsed thoroughly, and imaged using a Maximum Intensity Projection Z Plane Stack (10x, Leica SP5 Scanning Laser Confocal Microscope). The intensity image presented here was used as proof of concept during the characterization of ethylene blue.</p

D. pulex.

<p><i>D</i>. <i>pulex</i> were exposed to ethylene blue for 15 min, rinsed thoroughly, and imaged using a Maximum Intensity Projection Z Plane Stack (10x, Leica SP5 Scanning Laser Confocal Microscope). The intensity image presented here was used as proof of concept during the characterization of ethylene blue.</p

Synthetic route for the preparation of fluorescently labeled vitamin D₃.

<p>The carbodiimidazole (CDI) coupling of vitamin D₃ and the fluorescent dye linker.</p

Tracking vitamin D₃ in <i>D</i>. <i>pulex</i>.

<p>(A) A live <i>D</i>. <i>pulex</i> was placed in a 1:10 solution of ethylene blue, with no vitamin D₃ (“control”) and images were captured 30 min post exposure (10x, Leica SP5 Scanning Laser Confocal Microscope). Note the presence of the dye in the gut tract (red stain). (B). Live <i>D</i>. <i>pulex</i> were placed in a 1:10 solution of ethylene blue linked vitamin D₃, rinsed thoroughly, and images were captured 120 min post exposure (10x). Image was compiled from a 90-min time lapse to capture sequestration of vitamin D₃ (red) into the tissues of the <i>D</i>. <i>pulex</i> from the intestine. The high intensity red “dots” in the image are concentrated dye on the outside of the carapace that was not removed during the rinsing stages. The yellow circle indicates a region where D₃ sequestration was detected.</p