Iodide-Switched Deposition for the Synthesis of Segmented Pd-Au-Pd Nanorods: Crystal Facet Matters.

Segmented metallic nanorods with well-defined shapes and controllable components play an important role on the systematic investigation of their shape-dependent catalytic, electric, and plasmonic properties of metal nanostructures. Unfortunately, the shape and composition of segmented nanorods are difficult to be precisely controlled via colloidal methods. Here, we reported the growth of Pd-Au-Pd bimetallic heterostructures by using Au 5-fold twinned bipyramids (BPs) as seeds, with KI as a structure-directing reagent. Through a series of control experiments we revealed that two parameters were identified as critical factors for the growth of segmented Pd-Au-Pd nanorods. First, 5-fold twinned Au BPs with low-index end facets and high-index side facets function as a unique template for directed growth. Second, iodide can switch the deposition of Pd on the Au BPs. A high concentration of iodide is believed to block the high-index facets of the Au BPs and lower the reaction kinetics to promote the selective growth of two Pd segments on the Au BPs. As a result, uniformed segmented Pd-Au-Pd nanorods were obtained. The segmented nanorods exhibit intense extinction in the near-IR range and could be a potential candidate for plasmon-based biological applications such as thermal therapy.

Dodecahedral gold nanocrystals: the missing Platonic shape.

Platonic noble metal nanocrystals (NCs) have attracted considerate attention due to their symmetry, aesthetic beauty, and potential applications in catalysis, plasmonics, sensing, and spectroscopy. Although Platonic noble metal NCs with tetrahedral, cubic, octahedral, and icosahedral geometries have been chemically synthesized, the growth of Platonic dodecahedral noble metal NCs remains elusive. Here we propose a crystal structure of Platonic dodecahedral noble metal NCs and show that via a tailored seed-mediated synthetic approach, Platonic dodecahedral Au NCs can be grown from icosahedral multiply twinned Au seeds. By systematically tuning the ratio between {111} and {110} facets grown on the icosahedral Au seeds, NCs with icosahedral, icosidodecahedral, and dodecahedral shapes can be obtained. These shapes represent a family of Au NCs with icosahedral (Ih) symmetry.

Growth of Au@Ag core-shell pentatwinned nanorods: tuning the end facets.

Au@Ag core-shell nanorods with tunable end facets are obtained by coating Au bipyramids (BPs) with Ag. The resultant nanorods exhibit a pentatwinned crystal structure with tips terminated with either {110} or {111} facets. The control over the end facets is achieved by varying the capping agents and tuning the reduction rate of Ag. Specifically, when Ag is reduced slowly, Au@Ag nanorods with flat {110} end facets are formed with cetyltrimethylammonium bromide (CTAB) as the capping agent. If CTAB is replaced with cetyltrimethylammonium chloride (CTAC), Au@Ag nanorods with tips terminated with {111} facets are obtained. However, at a high Ag reduction rate, dumbbell-shaped Au@Ag nanorods are formed, with either CTAB or CTAC as the capping agent. The morphological evolution of the nanorods in each case is closely followed and a growth mechanism is proposed.

Multicausal analysis on water deterioration processes present in a drinking water treatment system.

The fluctuation of water turbidity has been studied during summer in the settling tanks of a drinking water treatment plant. Results from the multiple cause-effect model indicated that five main pathways interactively influenced thequalityof tank water. During rain, turbidity levels increased mainly as a result of decreasing pH and anaerobic reactions (partial effect = 68%). Increasing water temperature combined with dissolved oxygen concentration (partial effect = 64%) was the key parameterforcontrolling decreases in water turbidity during nighttime periods after a rainy day. The dominant factor influencing increases in turbidity during sunny daytime periods was algal blooms (partial effect = 86%). However, short-circuiting waves (partial effect = 77%) was the main cause for increased nighttime water turbidity after a sunny day. The trade offbetween regulatory pathways was responsible for environmental changes, and the outcome was determined by the comparative strengths of each pathway.

Hierarchically structured MnO2 nanowires supported on hollow Ni dendrites for high-performance supercapacitors.

We report a hierarchical Ni@MnO2 structure consisting of MnO2 nanowires supported on hollow Ni dendrites for high-performance supercapacitors. The Ni@MnO2 structure, which was prepared via a facile electrodeposition method, is highly porous and appears like a forest of pine trees grown vertically on a substrate. At a MnO2 mass loading of 0.35 mg cm(-2), the Ni@MnO2 electrode demonstrated a specific capacitance of 1125 F g(-1) that is close to the theoretical value. In addition, a remarkable high-rate performance (766 F g(-1) at a discharge current density of 100 A g(-1)) was achieved. Electrochemical tests in a two-electrode configuration for the Ni@MnO2 structure with a high MnO2 loading of 3.6 mg cm(-2) showed a low equivalent series resistance (ESR) of 1 Ω and a high specific power of 72 kW kg(-1). This superior performance can be attributed to the highly porous and hierarchical structure of Ni@MnO2 that favors rapid diffusion of an electrolyte, highly conductive pathway for electron transport, and efficient material utilization.

A novel amperometric biosensor based on single walled carbon nanotubes with acetylcholine esterase for the detection of carbaryl pesticide in water.

Amperometric biosensor is fabricated for the detection of carbaryl based on single walled carbon nanotubes (SWCNTs) and acetylcholine esterase (AchE). The dispersion of SWCNTs in positively charged polyelectrolyte, poly(diallyldimethylammonium chloride) (PDDA), possibly takes place due to weak supramolecular interaction between them, which then binds electrostatically to the negatively charged AchE at pH 7.4 using layer-by-layer (LbL) self-assembly technique. The optical intensity of UV/vis spectra increased with the number of layers, indicating the build up of a multilayer coating on the electrode. The activity of acetylcholine esterase on modified electrode of 3mm in diameter was found to be 0.2U. The biosensor showed good sensitivity and stability towards the monitoring of carbaryl pesticides in water with the detection limit of 10(-12)gL(-1) and recovery of 99.8 ± 2.7% to 10(-10)gL(-1). This protocol can be used for the immobilization of other enzymes to fabricate a range of biosensors.