Jiang, Shuang | Search NASA

DOE OSTI2017

Facile synthesis of TiO{sub 2} hierarchical tubes with enhanced photocatalytic activity

Graphical abstract: Hierarchical micro/nanostructured tubular TiO{sub 2} were prepared by impregnation-calcination method with FCT (the fluff of the chinar tree) as biological template and titanium tetrachloride as precursor. The resultant TiO{sub 2} samples possess curly tubular structure and the exterior outline of the samples look like fried dough twist. Moreover, the wall of the tube is assembled with spherical-likely nanoparticles. During the bio-inspired synthetic process, the FCT plays important roles as template and inducer for assembling the tubular micro/nanostructure. Furthermore, the resultant TiO{sub 2} exhibits favorable photocatalytic activity and good stability for degrading methyl orange under UV light irradiation. - Highlights: • The fluff of chinar tree was employed as template and inducer for preparing hierarchical micro/nanostructured tubular TiO{sub 2}. • The wall of the micro/nanostructured tubular TiO{sub 2} is assembled with spherical-likely nanoparticles. • The resultant TiO{sub 2} exhibits favorable photocatalytic activity and good recyclability. - Abstract: Hierarchical micro/nanostructured tubular TiO{sub 2} were prepared by impregnation-calcination method with FCT (the fluff of the chinar tree) as biological template and titanium tetrachloride as precursor. The resultant samples possess curly tubular structure and the exterior outline of the samples look like fried dough twist. Moreover, the wall of the tube is assembled with spherical-likely nanoparticles. Apparently in the process of preparation, the FCT played pivotal roles as substrate and inducer for assembling the curly tubular structure of micro/nanostructured TiO{sub 2}. Furthermore, the micro/nanostructured TiO{sub 2} have abundant pore structures and large surface area, which are beneficial to the improvement of photocatalytic activity. Under UV light irradiation, the as-prepared TiO{sub 2} exhibits nearly 100% photocatalytic decolorization rate in 30 min and 90% TOC (total organic carbon) degradation rate in 60 min for dye methyl orange (MO).

36 MATERIALS SCIENCE↗

DOE OSTI2016

Chiral Graphene Quantum Dots

Chiral nanostructures from metals and semiconductors attract wide interest as components for polarization-enabled optoelectronic devices. Similarly to other fields of nanotechnology, graphene-based materials can greatly enrich physical and chemical phenomena associated with optical and electronic properties of chiral nanostructures and facilitate their applications in biology as well as other areas. Here, we report that covalent attachment of l/d-cysteine moieties to the edges of graphene quantum dots (GQDs) leads to their helical buckling due to chiral interactions at the “crowded” edges. Circular dichroism (CD) spectra of the GQDs revealed bands at ca. 210–220 and 250–265 nm that changed their signs for different chirality of the cysteine edge ligands. The high-energy chiroptical peaks at 210–220 nm correspond to the hybridized molecular orbitals involving the chiral center of amino acids and atoms of graphene edges. Diverse experimental and modeling data, including density functional theory calculations of CD spectra with probabilistic distribution of GQD isomers, indicate that the band at 250–265 nm originates from the three-dimensional twisting of the graphene sheet and can be attributed to the chiral excitonic transitions. The positive and negative low-energy CD bands correspond to the left and right helicity of GQDs, respectively. Exposure of liver HepG2 cells to l/d-GQDs reveals their general biocompatibility and a noticeable difference in the toxicity of the stereoisomers. Molecular dynamics simulations demonstrated that d-GQDs have a stronger tendency to accumulate within the cellular membrane than l-GQDs. Finally, emergence of nanoscale chirality in GQDs decorated with biomolecules is expected to be a general stereochemical phenomenon for flexible sheets of nanomaterials.

36 MATERIALS SCIENCE↗