Sheng-Hsin Huang

Fabrication of Ag-loaded multi-walled TiO2 nanotube arrays and their photocatalytic activity

TiO2 multi-walled nanotube arrays (MWNTAs) were synthesized by atomic layer deposition (ALD) using anodic aluminum oxide (AAO) as the template. TiO2 and Al2O3 layers were alternately deposited into the AAO pores by ALD. The tube thickness and the gap span were controlled by the ALD cycle numbers of TiO2 and Al2O3, respectively. A MWNT composed of two or three concentric tubes with different diameters was formed after removal of Al2O3. Silver nanoparticles were then deposited on both inner and outer surfaces of the tubes by photochemical reduction. Degradation of methylene blue was carried out to evaluate the photocatalytic activity of bare and silver-loaded TiO2 MWNTAs. It was found that the amount of TiO2, the reaction surface area, the crystalline phase, and silver modification were the factors to determine the photocatalytic activity. The triple-walled MWNTAs showed the best performance, and Ag loading further enhanced the activity.

Toward highly efficient photocatalysis: a flow-through Pt@TiO2@AAO membrane nanoreactor prepared by atomic layer deposition

A Pt@TiO2@AAO membrane nanoreactor was fabricated by atomic layer deposition. The photodegradation test of methylene blue demonstrated that the nanoreactor shows efficient photocatalysis performance. It exhibited ~28% photodegradation of methylene blue after ten flow-through cycles, corresponding to about 2.7 × 10(-2) s of contact time of methylene blue with Pt@TiO2 nanotubes.

Preparation and Characterization of Molecularly Homogeneous Silica–Titania Film by Sol–Gel Process with Different Synthetic Strategies

Three silica-titania thin films with various degrees of molecular homogeneity were synthesized by the sol-gel process with the same precursor formula but different reaction paths. The dried films prepared by a single spin-coating process have a thickness of 500-700 nm and displayed no cracks or pin holes. The transmittances and refractive indices of the samples are >97.8% in the range of 350-1800 nm and 1.62-1.65 at 500 nm, respectively. The in-plane and out-of-plane chemical homogeneities of the films were analyzed by X-ray photoelectron spectroscopy and Auger electron spectroscopy, respectively. For the film with the highest degree of homogeneity, the deviations of O, Si, and Ti atomic contents in both in-plane and out-of-plane directions are less than 1.5%, indicating that the film is highly molecularly homogeneous. It also possesses the highest transparency and the lowest refractive index among the three samples.

Direct formation of anatase TiO2 nanoparticles on carbon nanotubes by atomic layer deposition and their photocatalytic properties.

TiO2 with different morphology was deposited on acid-treated multi-walled carbon nanotubes (CNTs) by atomic layer deposition at 100 °C-300 °C to form a TiO2@CNT structure. The TiO2 fabricated at 100 °C was an amorphous film, but became crystalline anatase nanoparticles when fabricated at 200 °C and 300 °C. The saturation growth rates of TiO2 nanoparticles at 300 °C were about 1.5 and 0.4 Å/cycle for substrate-enhanced growth and linear growth processes, respectively. It was found that the rate constants for methylene blue degradation by the TiO2@CNT structure formed at 300 °C were more suitable to fit with second-order reaction. The size of 9 nm exhibited the best degradation efficiency, because of the high specific area and appropriate diffusion length for the electrons and holes.

Extremely high efficient nanoreactor with Au@ZnO catalyst for photocatalysis

We fabricated a photocatalytic Au@ZnO@PC (polycarbonate) nanoreactor composed of monolayered Au nanoparticles chemisorbed on conformal ZnO nanochannel arrays within the PC membrane. A commercial PC membrane was used as the template for deposition of a ZnO shell into the pores by atomic layer deposition (ALD). Thioctic acid (TA) with sufficient steric stabilization was used as a molecular linker for functionalization of Au nanoparticles in a diameter of 10 nm. High coverage of Au nanoparticles anchored on the inner wall of ZnO nanochannels greatly improved the photocatalytic activity for degradation of Rhodamine B. The membrane nanoreactor achieved 63% degradation of Rhodamine B within only 26.88 ms of effective reaction time owing to its superior mass transfer efficiency based on Damköhler number analysis. Mass transfer limitation can be eliminated in the present study due to extremely large surface-to-volume ratio of the membrane nanoreactor.

Synthesis of Pt@TiO2@CNTs Hierarchical Structure Catalyst by Atomic Layer Deposition and Their Photocatalytic and Photoelectrochemical Activity

Pt@TiO2@CNTs hierarchical structures were prepared by first functionalizing carbon nanotubes (CNTs) with nitric acid at 140 °C. Coating of TiO2 particles on the CNTs at 300 °C was then conducted by atomic layer deposition (ALD). After the TiO2@CNTs structure was fabricated, Pt particles were deposited on the TiO2 surface as co-catalyst by plasma-enhanced ALD. The saturated deposition rates of TiO2 on a-CNTs were 1.5 Å/cycle and 0.4 Å/cycle for substrate-enhanced process and linear process, respectively. The saturated deposition rate of Pt on TiO2 was 0.39 Å/cycle. The photocatalytic activities of Pt@TiO2@CNTs hierarchical structures were higher than those without Pt co-catalyst. The particle size of Pt on TiO2@CNTs was a key factor to determine the efficiency of methylene blue (MB) degradation. The Pt@TiO2@CNTs of 2.41 ± 0.27 nm exhibited the best efficiency of MB degradation.