The temporal course of the photooxidation of sulforhodamine-B (SRB) in aqueous media illuminated by visible wavelengths in the presence of TiO2 has been examined to determine the nature of the intermediate species produced and to explore the operative reaction pathway(s). Two pathways are described to account for the differences in the final photooxidation products whose nature depends on the different modes of adsorption of the dye on the metal-oxide mediator. In the SRB/TiO2 system, when SRB is adsorbed on the positively charged TiO2 particle surface through a sulfonate group cleavage of the SRB chromophore structure predominates and N-de-ethylation occurs only to a slight extent with the major photooxidation products being diethylamine and carbon dioxide. In the presence of the anionic dodecylbenzenesulfonate surfactant DBS, when SRB is near the negatively charged DBS/TiO2 interface through the positive diethylamine group N-de-ethylation occurs preferentially before destruction of the structure with the major products being acetaldehyde and carbon dioxide.
The electronic structure and the highest occupied molecular orbitals (HOMO)/the lowest unoccupied molecular orbitals (LUMO) alignment at the molecular semiconductor heterointerface of nanostructured TiO 2 /ZnPcGly dye sensitizer were characterized by X-ray and ultraviolet photoemission spectroscopy (XPS and UPS). The HOMO level of the dye ZnPcGly was determined to be located at 1.62 eV below the Fermi edge, and the corresponding LUMO level was estimated to be 0.10 eV above the conduction band of TiO 2 based on the HOMO/LUMO gap (1.82 eV) of ZnPcGly determined by optical absorption measurements. This energy level matching between the orbitals of the dye and the bands of TiO 2 can enable efficient electron transfer from photoexcited ZnPcGly to TiO 2 , which is very important in photoinduced charge-transfer reactions and for applications in dye-sensitized solar cells.
The electrolysis of aqueous solutions produces solutions that are supersaturated in oxygen and hydrogen gas. This results in the formation of gas bubbles, including nanobubbles ∼100 nm in size that are stable for ∼24 h. These aqueous solutions containing bubbles have been evaluated for cleaning efficacy in the removal of model contaminants bovine serum albumin and lysozyme from surfaces and in the prevention of the fouling of surfaces by these same proteins. Hydrophilic and hydrophobic surfaces were investigated. It is shown that nanobubbles can prevent the fouling of surfaces and that they can also clean already fouled surfaces. It is also argued that in practical applications where cleaning is carried out rapidly using a high degree of mechanical agitation the role of cleaning agents is not primarily in assisting the removal of soil but in suspending the soil that is removed by mechanical action and preventing it from redepositing onto surfaces. This may also be the primary mode of action of nanobubbles during cleaning.
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