Tung-Han Yang

High Density Unaggregated Au Nanoparticles on ZnO Nanorod Arrays Function as Efficient and Recyclable Photocatalysts for Environmental Purification

Photodegradation of organic pollutants in aqueous solution is a promising method for environmental purification. Photocatalysts capable of promoting this reaction are often composed of noble metal nanoparticles deposited on a semiconductor. Unfortunately, the separation of these semiconductor-metal nanopowders from the treated water is very difficult and energy consumptive, so their usefulness in practical applications is limited. Here, a precisely controlled synthesis of a large-scale and highly efficient photocatalyst composed of monolayered Au nanoparticles (AuNPs) chemically bound to vertically aligned ZnO nanorod arrays (ZNA) through a bifunctional surface molecular linker is demonstrated. Thioctic acid with sufficient steric stabilization is used as a molecular linker. High density unaggregated AuNPs bonding on entire surfaces of ZNA are successfully prepared on a conductive film/substrate, allowing easy recovery and reuse of the photocatalysts. Surprisingly, the ZNA-AuNPs heterostructures exhibit a photodegradation rate 8.1 times higher than that recorded for the bare ZNA under UV irradiation. High density AuNPs, dispersed perfectly on the ZNA surfaces, significantly improve the separation of the photogenerated electron-hole pairs, enlarge the reaction space, and consequently enhance the photocatalytic property for degradation of chemical pollutants. Photoelectron, photoluminescence and photoconductive measurements confirm the discussion on the charge carrier separation and photocatalytic experimental data. The demonstrated higher photodegradation rates demonstrated indicate that the ZNA-AuNPs heterostructures are candidates for the next-generation photocatalysts, replacing the conventional slurry photocatalysts.

Promising electron field emitters composed of conducting perovskite LaNiO3 shells on ZnO nanorod arrays

We report a semiconductor–perovskite composite system with promising field emission properties. The composite system was fabricated by sputtering perovskite LaNiO3 (LNO) shells on one dimensional (1D) well-aligned hydrothermally produced ZnO nanorod arrays (ZNAs). The ZNA–LNO core–shell hetero-structures were demonstrated to be much more efficient field emitters than ZNAs. Since the work function of LNO (4.5 eV) is lower than that of ZnO (5.3 eV), a shallow well is formed in thermal equilibrium in the ZNA–LNO heterojunction. When an electric field is applied, the produced well is of much benefit for the flow of electrons from the GZO seed layers through the ZNA to the LNO shells. Consequently, the emission of electrons into vacuum by tunneling is easily realized due to the low work function of the LNO coatings. Our 1D semiconductor–perovskite composite system provides a prospect for the development of practical field emission electron sources.

Facet‐Dependent Photocatalytic Activity and Facet‐Selective Etching of Silver(I) Oxide Crystals with Controlled Morphology

The shape of Ag2O crystals that evolve from edge and corner‐truncated cubes into rhombicuboctahedrons, then to hexapods can be conducted precisely by simply controlling the amount of AgNO3, NH4NO3 and NaOH precursors. The edge and corner‐truncated cube crystals possess the highest photocatalytic activity, followed by the rhombicuboctahedrons, then the hexapods. The photocatalytic activity of the Ag2O crystals depends greatly on the type of the exposed facets. The {1 0 0} facets exhibit the highest photocatalytic activity in methyl orange solution under full‐spectrum light irradiation, followed by the {1 1 0} facets, then the {1 1 1} facets. The {1 0 0} facets are also demonstrated to show intense susceptibility toward etching by NH3.

Prominent electric properties of BiFeO3 shells sputtered on ZnO-nanorod cores with LaNiO3 buffer layers

In this work, template-assisted methods were adopted to grow BiFeO3 (BFO)-nanorod arrays on substrates. Well-aligned ZnO-nanorod arrays (ZNAs) grown hydrothermally were chosen as positive templates. It was found that perovskite BFO could not be radio frequency (RF)-magnetron sputtered directly on a ZNA at elevated temperatures. Only amorphous BFO was obtained. However, polycrystalline BFO shells could be fabricated by RF-magnetron sputtering on ZNA templates by the introduction of LaNiO3 (LNO) buffer layers. The LNO buffer layer deposited on the ZNA by RF-magnetron sputtering was demonstrated to improve the adhesion and crystallization of the sequentially sputtered BFO shells. The electrical properties were evaluated by conductive atomic force microscopy and piezoresponse force microscopy. Bulk-limited Poole-Frenkel emission dominates the conduction of BFO shells at positive bias, while barrier-limited Schottky emission accounts for the conduction at negative bias due to the interface between the Pt/Ir-coated tip and the BFO. The piezoelectric coefficient (d33) was estimated to be ∼32.93 pm V(-1) and a polarization of 133 μC cm(-2) was derived. These values are higher than those reported previously for BFO films.

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.