Citric acid is a widely used surface-modifying ligand for growth and processing of a variety of nanoparticles; however, the inability to easily prepare derivatives of this molecule has restricted the development of versatile chemistries for nanoparticle surface functionalization. Here, we report the design and synthesis of a citric acid derivative bearing an alkyne group and demonstrate that this molecule provides the ability to achieve stable, multidentate carboxylate binding to metal oxide nanoparticles, while also enabling subsequent multistep chemistry via the Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC) reaction. The broad utility of this strategy for the modular functionalization of metal oxide surfaces was demonstrated by its application in the CuAAC modification of ZnO, Fe(2)O(3), TiO(2), and WO(3) nanoparticles.

Metal oxides play a key role in many emerging applications in renewable energy, such as dye-sensitized solar cells and photocatalysts. Because the separation of charge can often be facilitated at junctions between different materials, there is great interest in the formation of heterojunctions between metal oxides. Here, we demonstrate use of the copper-catalyzed azide-alkyne cycloaddition reaction, widely referred to as "click" chemistry, to chemically assemble photoactive heterojunctions between metal oxide nanoparticles, using WO(3) and TiO(2) as a model system. X-ray photoelectron spectroscopy and Fourier-transform infrared spectroscopy verify the nature and selectivity of the chemical linkages, while scanning electron microscopy reveals that the TiO(2) nanoparticles form a high-density, conformal coating on the larger WO(3) nanoparticles. Time-resolved surface photoresponse measurements show that the resulting dyadic structures support photoactivated charge transfer, while measurements of the photocatalytic degradation of methylene blue show that chemical grafting of TiO(2) nanoparticles to WO(3) increases the photocatalytic activity compared with the bare WO(3) film.

SnO 2 is a promising material for photovoltaic and photocatalytic applications because it exhibits high electron mobility, its conduction band lies at a convenient energy to act as an electron acceptor, and it can be easily grown in a variety of different nanostructures including nanoparticles, nanorods, and nanosheets. However, strategies for surface functionalization of SnO 2 are much less well developed than alternative oxides. Here, we demonstrate the growth and subsequent chemical functionalization of SnO 2 nanorods to enable the chemically directed assembly of SnO 2 nanorod-TiO 2 nanoparticle heterojunctions, and we characterize the charge-transfer properties using time-resolved surface photovoltage measurements. Vertically aligned SnO 2 nanorods were grown via a high-pressure chemical synthesis method. The SnO 2 nanorods were square in cross-section, exposing sidewalls consisting of {110}-type crystal planes. Functionalization via photochemical grafting with butenol yielded nanorods terminated with a high density of -OH groups that were converted to azide groups. The azide groups were linked with alkyne-modified TiO 2 nanoparticles via the Cu(I)-catalyzed Azide-Alkyne Cycloaddition (CuAAC) reaction, a form of ''click'' chemistry, thereby covalently grafting the TiO 2 nanoparticles to the SnO 2 nanorods. Time-resolved surface photovoltage measurements of the resulting adducts showed that the covalent bonding of TiO 2 nanoparticles to the SnO 2 nanorods enhances the interfacial charge transfer compared to the unmodified SnO 2 nanorods, leading to an increased accumulation of holes at the surface.

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Observing that the field of executive assessment has not significantly evolved during the past two generations, the authors draw the following conclusions. Old fashioned pencil and paper tests continue to provide generalized labels without giving meaningful answers about what is being measured. The almost universal employment of interviews in conjunction with these tests has permitted assessors to apply intuitive metalinguistic strategies to the assessments. It is this intuitive analysis of linguistic behavior which gives executive assessment its validity as a predictor of future success. The authors suggest that conscious, intentional linguistic approaches to assessment will enhance its effectiveness and advance the integration of the fields of psychology and behavioral linguistics.