Craig A. Grimes

Synthesis and deposition of ultrafine Pt nanoparticles within high aspect ratio TiO2 nanotube arrays: application to the photocatalytic reduction of carbon dioxide

Using a rapid microwave-assisted solvothermal approach ultrafine Pt nanoparticles are synthesized and deposited in situ within high aspect ratio nanotube arrays. Adjusting the initial concentration of metal ion precursor inside the nanotube support controls the resulting Pt nanoparticle sizes. The Pt-nanoparticle/TiO2 nanotube composite is shown to greatly promote the photocatalytic conversion of carbon dioxide and water vapor into methane, a behavior attributed to the homogeneous distribution of metal co-catalyst nanoparticles over the TiO2 nanotube array surface providing a large number of active reduction sites. The novelty and flexibility of the technique, described herein, could prove useful for the deposition of metal, metal alloy, or metal oxide nanoparticles within a variety of nanotubular or nanoporous material systems with the resulting nanocomposites useful in catalysis, photocatalysis, photovoltaic, and photoelectrochemical applications.

Fabrication of coaxial TiO2/Sb2S3 nanowire hybrids for efficient nanostructured organic–inorganic thin film photovoltaics

We report on low-cost, all solution fabrication of efficient air-stable nanostructured thin film photovoltaics comprised of n-type Sb(2)S(3) chemically deposited onto TiO(2) nanowire array films, forming coaxial Sb(2)S(3)/TiO(2) nanowire hybrids vertically oriented from the SnO(2):F coated glass substrate, which are then intercalated with poly(3-hexylthiophene) (P3HT) for hole transport and enhanced light absorption.

A novel method for the preparation of a photocorrosion stable core/shell CdTe/CdS quantum dot TiO2 nanotube array photoelectrode demonstrating an AM 1.5G photoconversion efficiency of 6.12%

Type-II core/shell CdTe/CdS quantum dots (QDs) are assembled onto TiO2 nanotube array (NTA) films using a bi-functional linker molecule with the help of a hydrothermal method coupled with successive ionic layer adsorption and reaction process. Spatial separation of the electron and hole wave functions within the core/shell heterostructured nanocrystals appears to result in an extended charge separation state, resulting in a significant increase in photocurrent and excellent device stability. When only CdS or CdTe QDs are used as the sensitizer, the largest photocurrent densities are 1.31 mA cm−2 and 1.23 mA cm−2, respectively. For the core/shell CdTe/CdS QDs sensitized TiO2 NTA photoelectrodes the photocurrent density increases to ≈9.17 mA cm−2, dramatically larger than the values obtained with only one sensitizer. The core/shell CdTe/CdS QDs sensitized TiO2 NTA photoelectrodes provide a remarkable photoelectrochemical cell efficiency of 6.12%. To the best of our knowledge this photoconversion efficiency is the highest in the field of QD-sensitized photoelectrodes. A corresponding hydrogen evolution rate as high as 1560 μmol h−1 W−1 was achieved.

Titania nanoporous/tubular structures via electrochemical anodization of titanium: effect of electrolyte conductivity and anodization voltage on structural order and porosity

The formation mechanisms of self-organized anodic titania nanotube arrays have been widely studied with an aim towards enabling precise control of nanotube array morphology and properties, thereby allowing control of fabrication parameters for optimal performance of the resulting films in their given application. Building upon recent work [S. Yoriya and C. A. Grimes, J. Mater. Chem., 2011, 21, 102–108], we elucidate the self-ordering and porosity of nanoporous and nanotubular anodic titania films as a function of anodization conditions.

A CdS/ZnSe/TiO2 nanotube array and its visible light photocatalytic activities.

A novel CdS/ZnSe/TiO2 nanotube array (NTA) photoelectrode was prepared by deposition of ZnSe nanoparticles (NPs) using pulse electrodeposition technique onto a TiO2 NTA. By successive ion layer adsorption and reaction (SILAR), CdS quantum dots (QDs) deposit onto a ZnSe/TiO2 NTA photoelectrode. The as-prepared CdS/ZnSe/TiO2 NTA photoelectrode performance is significantly improved, which not only greatly extends spatial separation of charges, but also enhance the utilization efficiency of visible-light. This system exhibits excellent charges transport property. The maximum photocurrent density of an 8.25mAcm(-2) was observed in the CdS/ZnSe/TiO2 NTA photoelectrode, which is 37.5, 15.86 and 1.56 times higher than bare TiO2 NTA, ZnSe/TiO2 NTA, and CdS/TiO2NTA photoelectrodes, respectively. The photocatalytic activity of CdS/ZnSe/TiO2 NTA is tested by the degradation of methyl orange (MO) in distilled water under solar light irradiation of 100mW/cm(2). Within about 120min of irradiation, 90.05% MO are removed.

Towards efficient visible-light active photocatalysts: CdS/Au sensitized TiO2 nanotube arrays.

A visible-light active photocatalyst, CdS/Au/TiO2 nanotube array (NTA) photoelectrode, was prepared by electrodeposition of Au nanoparticles onto TiO2 NTA with subsequent deposition of visible-light absorbable 2.4eV band-gap CdS quantum dots using successive ion layer adsorption and reaction (SILAR). The Au nanoparticles here act as electron sinks facilitating charge carrier separation. Under AM1.5G illumination a photoconversion efficiency of 4.06% was achieved for the CdS/Au/TiO2 NTA photoelectrode, suggesting the promise of the material architecture for achieving high-performance cost-effective materials.

CdS/ZnIn2S4/TiO2 3D-heterostructures and their photoelectrochemical properties

We describe the synthesis and application of a three-dimensional (3D) CdS quantum dot/ZnIn2S4 nanosheet/TiO2 nanotube array (CdS/ZnIn2S4/TiO2) heterostructured material architecture. TiO2 nanotube arrays (TiO2 NTAs) are used as the synthetic template, subsequently sensitized using hydrothermal and successive ion layer adsorption and reaction (SILAR) techniques. The described synthesis approach offers a powerful technique in the design of 3D heterostructure systems. Under AM1.5G illumination, the 3D CdS/ZnIn2S4/TiO2 samples generate a photocurrent of approximately 4.3 mA cm−2, with a photoconversion efficiency of 2%. Samples are tested for their ability to photocatalytically degrade target agents; it is noteworthy that after 90 min illumination 100% of 2,4-dichlorophenoxyacetic acid (2,4-D) is removed.