Electron Interactions in Carbon Nanomaterials

The following research reflects two areas of interest in carbon nanomaterials: (1) enzymatic oxidation and (2) photocatalytic applications.\ud Horseradish peroxidase (HRP) is known to catalyze oxidation of carbon nanomaterials. Here, we closely examine the kinetics of enzymatic oxidation of carbon nanotubes (CNTs) using HRP. We show that CNTs oxidized by harsh acid treatment become shorter, more defective, and lose their specific absorption bands and fluorescent signals. After treatment with HRP and H2O2, these oxidized CNTs show a decrease in average CNT length, a decrease in defective area, and return of characteristic absorption bands and fluorescence. We observed that CNTs chemically oxidized using weaker oxidation treatment were shortened, slightly more defective than before acid treatment, did not lose their characteristic absorption bands, but did lose fluorescence. After treatment with HRP and H2O2 there was a decrease in length, a decrease in defective area, no observed change in absorption spectra bands and fluorescent signal did not return. H2O2 treated oxidized CNTs, showed similar results to HRP treated samples but did not recover their fluorescent signals.\ud TiO2 is a popular photocatalyst due to its small band gap, low cost, and low toxicity. Limitations in photocatalysis using TiO2 are due to electron – hole recombination following electron excitation from the valence band to conduction band. Efforts to retard electron – hole recombination involve doping TiO2 with metals, which have electron trapping sites on their surfaces. Carbon nanomaterials show promise as TiO2 dopants due to their large surface area,electron storage capacity, and interaction with metal oxide surface groups. Here, we demonstrate synthesis of TiO2 – carbon nanomaterials using sol – gel techniques and that electron transfer is possible under UV irradiation. Comparing synthesized TiO2-SWNTs and commercially available anatase TiO2 nanoparticles, we find no significant improvement in photocatalytic oxidation of dye. Furthermore, TiO2 – SWNTs do not photoreduce CO2. P25 TiO2 nanoparticles oxidize dye in these studies, and have demonstrated the ability to reduce CO2 in published works. Lack of homogeneity in the TiO2 crystalline structure may be responsible for these differences. We show prolonged UV expose may degrade TiO2 – GO photocatalysts, possibly through ROS generation