ABSTRACT
Nanostructured ZnO has been widely investigated as a gas sensing material. Antimony is an important dopant for ZnO that catalyses its surface reactivity and thus strengthens its gas sensing capability. However, there are not enough studies on the gas sensing of antimony-doped ZnO single wires. We fabricated and characterized ZnO/ZnO:Sb core-shell micro-wires and demonstrated that individual wires are sensitive to oxygen gas flow. Temperature and light illumination strongly affect the oxygen gas sensitivity and stability of these individual wires. It was found that these micro- and nano-wire oxygen sensors at 200°C give the highest response to oxygen, yet a vanishingly small effect of light and temperature variations. The underlying physics and the interplay between these effects are discussed in terms of surface-adsorbed oxygen, oxygen vacancies and hydrogen doping.
ABSTRACT
A series of monobenzoporphyrins (WH1-WH4) bearing different conjugated spacer groups were designed and synthesized as sensitizers for dye-sensitized solar cells. Although a phenyl spacer only has a minimal impact on the absorption bands of the monobenzoporphyrin, an ethynylphenyl (WH3) or a vinyl (WH4) spacer redshifts and broadens the absorption bands of the dyes to result in much enhanced light-harvesting ability. Dye-sensitized solar cells based on these monobenzoporphyrin dyes displayed remarkable differences in power conversion efficiencies (PCEs). The monobenzoporphyrin bearing no spacer (WH1) resulted in a PCE of only 0.5 %; in contrast, the monobenzoporphyrin bearing vinyl spacers (WH4) achieved a PCE of 5.2 %. The high efficiency of the WH4 cell is attributed to the higher light-harvesting ability, the lesser extent of aggregation on the TiO2 surface, and the more favorable electron-density distributions of the HOMO and LUMO for electron injection and collection. This work demonstrates the exceptional tunability of benzoporphyrins as sensitizers for dye-sensitized solar cells.
Subject(s)
Coloring Agents/chemistry , Electric Power Supplies , Porphyrins/chemistry , Solar Energy , Models, Molecular , Molecular Conformation , Optical Phenomena , Surface Properties , Titanium/chemistryABSTRACT
Developing coatings on implant surface as drug carriers can reduce organ toxicity and effectively deliver drug locally to the target compared with the oral approach. Titanium dioxide (TiO2) nanotube has great potential for this application for widely used Ti implants because of its high surface area, ability to promote bone growth, and biocompatibility. However, there are two issues needed to be solved before further advancing TiO2 nanotubes technology as drug carriers: uncontrolled drug release and poor mechanical properties. In this study, a drug carrier using a composite of biodegradable polymer/TiO2 nanotubes is engineered. Ibuprofen is selected as a concept drug because it is a commonly used anti-inflammatory, fever, and pain-reducing drug. In addition, ibuprofen has a very short plasma half-life of only 1-3 h. A simple characterization method is developed to investigate the infiltration of polymer into TiO2 nanotubes. Good infiltration was observed of polymer into TiO2 nanotubes. The synthesized drug carrier demonstrated much better sustained drug release profiles for ibuprofen of 5 days (low-molecular-weight polymer) and 9 days (high-molecular-weight polymer) compared with 30 min of pure TiO2 nanotubes. The drug carrier also exhibited much improved mechanical strength and flexibility compared with pure TiO2 nanotubes.
Subject(s)
Anti-Inflammatory Agents, Non-Steroidal/administration & dosage , Delayed-Action Preparations/chemistry , Ibuprofen/administration & dosage , Lactic Acid/chemistry , Nanotubes/chemistry , Polyglycolic Acid/chemistry , Titanium/chemistry , Nanotubes/ultrastructure , Polylactic Acid-Polyglycolic Acid Copolymer , Prostheses and Implants , Tensile StrengthABSTRACT
New opp-dibenzoporphyrins were prepared in a concise method that was based on a Pd(0)-catalyzed cascade reaction. These porphyrins, which contained carboxylic-acid linker groups on benzene rings that were fused to the porphyrin at their ß,ß'-positions, were examined as sensitizers for dye-sensitized solar cells for the first time. Whereas all of the porphyrins showed solar-energy-to-electricity conversion, an opp-dibenzoporphyrin with conjugated carboxylic-acid linkers displayed the highest conversion efficiency and an exceptionally high J(sc) value. Cyclic voltammetry of these porphyrins suggested that the fusion of two aromatic benzene rings onto the periphery of the porphyrin lowered the HOMO-LUMO energy gap; the incorporation of a conjugated carboxylic-acid linker group decreased the HOMO-LUMO gap even further. These CV data are consistent with DFT calculations for these porphyrins and agree well with the UV/Vis absorption- and fluorescence spectra of these porphyrins.
