Anisotropic noble-metal structures are attracting increasing attention because of interesting size- and shape-dependent properties and have emerging applications in the fields of optics and catalysis. However, it remains a significant challenge to overcome chemical contributions and acquire molecular insight into the relationship between Raman enhancement and photocatalytic activity. This study gives visualized experimental evidence of the anisotropic spatial distribution of Raman signals and photocatalytic activity at the level of single nanometer-thin Au microtriangles and microhexagons. Theoretical simulations indicate an anisotropic spatial distribution and sharpness-dependent strength of the electric-field enhancement. Analysis by using statistical surface-enhanced Raman scattering (SERS) supports this view, that is, Raman enhancement is on the order of corner>edge>face for a single microplate, but SERS measurements at different depths of focus also imply a concentration-dependent feature of SERS signals, especially at the corners and edges. Similarly, the SERS signals of product molecules in plasmonic photocatalysis also exhibit asymmetrical strengths at different corners of the same microplate. However, by examining the variations in the relative intensities of the SERS peaks, the difference in the photocatalytic activities at the corners, edges, and faces has been successfully calculated and is highly consistent with electric-field simulations, thus indicating that an increased number of molecules adsorbed at specific sites does not necessarily lead to a higher conversion ratio in noble-metal photocatalysis. Our strategy weakens the assumed impact of plasmonic local heating and, to a certain extent, excludes the influence of concentration effects and chemical contributions in noble-metal photocatalysis, thus clearly profiling plasmon-related characteristics. This study also promises a new research direction to understand the enhancement mechanism of SERS-active structures.

Surface-enhanced resonance Raman scattering (SERRS) is not realized for most molecules of interest. Here, we developed a new SERRS platform for the fast and sensitive detection of 2,4,6-trinitrotoluene (TNT), a molecule with low Raman cross section. A cationic surfactant, cetylpyridinium chloride (CPC) was modified on the surface of silver sols (CP-capped Ag). CPC not only acts as the surface-seeking species to trap sulfite-sulfonated TNT, but also undergoes complexation with it, resulting in the presence of two charge-transfer bands at 467 and 530 nm, respectively. This chromophore absorbs the visible light that matches with the incident laser and plasmon resonance of Ag sols by the use of a 532.06 nm laser, and offered large resonance Raman enhancement. This SERRS platform evidenced a fast and accurate detection of TNT with a detection limit of 5×10⁻¹¹ M under a low laser power (200 μW) and a short integration time (3 s). The CP-capped Ag also provides remarkable sensitivity and reliable repeatability. This study provides a facile and reliable method for TNT detection and a viable idea for the SERS detection of various non-resonant molecules.

A novel method to prepare TiO₂-coated Ag nanowire arrays for use as multifunctional surface enhanced Raman scattering (SERS) active substrates is introduced. Such an array is made by the synthesis of an Ag nanowire array utilizing an anodic aluminum oxide (AAO) template, followed by coating of the Ag wires with a layer of titania that is several nanometers thick. Employing these TiO₂-coated Ag nanowire substrates in the detection of organic contaminants allows high SERS enhancement to be achieved. Moreover, owing to the high photocatalytic activity of titania, the substrate can degrade target molecules into small inorganic molecules under UV irradiation, and in this manner the arrays are able to self-clean. The unique properties of this integrated substrate enable it to exhibit its feasibility as an analytical tool for the assessment of environmental pollution and thus to assist in the detection and disposal of contaminants.

A multifunctional Au-coated TiO₂ nanotube array is made via synthesis of a TiO₂ nanotube array through a ZnO template, followed by deposition of Au particles onto the TiO₂ surface using photocatalytic deposition and a hydrothermal method, respectively. Such arrays exhibit superior detection sensitivity with high reproducibility and stability. In addition, due to possessing stable catalytic properties, the arrays can clean themselves by photocatalytic degradation of target molecules adsorbed to the substrate under irradiation with UV light into inorganic small molecules using surface-enhanced Raman spectroscopy (SERS) detection, so that recycling can be achieved. Finally, by detection of Rhodamine 6G (R6G) dye, herbicide 4-chlorophenol (4-CP), persistent organic pollutant (POP) dichlorophenoxyacetic acid (2,4-D), and organophosphate pesticide methyl-parathion (MP), the unique recyclable properties indicate a new route in eliminating the single-use problem of traditional SERS substrates and show promising applications for detecting other organic pollutants.

ZnS microspheres have been synthesized in large scale by a hydrothermal route. The influence of reaction time on the phase constitution is studied. The evolution process from cubic phase to hexagonal phase is showed with prolonging reaction time. It is observed that the luminescence intensity of the same sample decreases dramatically with increasing the temperature. At the same time, the Luminescence intensity of ZnS particles increases with prolonging the reaction time. The luminescence intensity of the particles is affected by the reaction time and temperature. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

PbS microspheres have been synthesized in large scale by a hydrothermal route, in which tungstosilicate acid (TSA) is used. The obtained PbS microspheres have been characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), Scanning electron microscopy (SEM) and X-ray photoemission spectroscopy (XPS). Experiments show that Tungstosilicate acid plays an important role for the control of the morphology of PbS microstructures. An evolution process is described based on experimental facts. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)