Seed-Mediated Growth of Silver Nanocubes in Aqueous Solution with Tunable Size and Their Conversion to Au Nanocages with Efficient Photothermal Property.

Two seed-mediated approaches for the growth of silver nanocubes in aqueous solution have been developed. Addition of a silver-seed solution to a mixture of cetyltrimethylammonium chloride (CTAC), silver trifluoroacetate, and ascorbic acid and heating the solution at 60 °C for 1.5 h produces uniform Ag nanocubes with tunable sizes from 23 to 60 nm by simply adjusting the volume of silver-seed solution introduced. Alternatively, the silver-seed solution can be injected into a mixture of cetyltrimethylammonium bromide (CTAB), silver nitrate, copper sulfate, and ascorbic acid and heated to 80 °C for 2 h to generate 46 nm silver nanocubes. Plate-like Ag nanocrystals exposing {111} surfaces can be synthesized by reducing Ag(NH3 )2 (+) with ascorbic acid in a CTAC solution. Relatively large Ag nanocubes were converted to cuboctahedral Au/Ag and Au nanocages and nanoframes with empty {111} faces through a galvanic replacement reaction. The nanocages showed a progressive plasmonic band red-shift with increasing Au content. The nanocages exhibited high and stable photothermal efficiency with solution temperatures quickly reaching beyond 100 °C when irradiated with an 808 nm laser for large heat and water vapor generation.

Direct Synthesis of Palladium Nanocrystals in Aqueous Solution with Systematic Shape Evolution.

Palladium octahedra, truncated octahedra, cuboctahedra, truncated cubes, and nanocubes with sizes of tens of nanometers have been synthesized in an aqueous mixture of H2PdCl4 solution, cetyltrimethylammonium chloride (CTAC) surfactant, KBr solution, dilute KI solution, and ascorbic acid solution at 35 °C for 30 min. By tuning the amount of dilute KBr solution introduced, particle shape control can be achieved. Adjusting the volumes of the Pd precursor and KBr solutions added, smaller and larger Pd nanocrystals were obtained with excellent shape control. Extensive structural and optical characterization of these nanocrystals has been performed. Two absorption bands in the ultraviolet region can be discerned for these Pd nanocrystals. Concave Pd cubes can also be prepared. Pd cubes were found to grow at a faster rate than that for the formation of octahedra. The concentrations of KBr and KI in the solution are so low that spectral shifts were not detected upon their addition to the solution. The Pd nanocrystals can readily be used for various applications after simple removal of surfactant.

Aqueous phase synthesis of Au-Ag core-shell nanocrystals with tunable shapes and their optical and catalytic properties.

In this study, rhombic dodecahedral gold nanocrystals were used as cores for the generation of Au-Ag core-shell nanocrystals with cubic, truncated cubic, cuboctahedral, truncated octahedral, and octahedral structures. Gold nanocrystals were added to an aqueous mixture of cetyltrimethylammonium chloride (CTAC) surfactant, AgNO3, ascorbic acid, and NaOH to form the core-shell nanocrystals. The nanocrystals are highly uniform in size and shape, and can readily self-assemble into ordered packing structures on substrates. Results from observation of solution color changes and variation in the reaction temperature suggest octahedra are produced at a higher growth rate, while slower growth favors cube formation. The major localized surface plasmon resonance (LSPR) band positions for these nanocrystals are red-shifted compared to those for pristine silver particles with similar dimensions due to the LSPR effect from the gold cores. By increasing the concentrations of reagents, Au-Ag core-shell cubes and octahedra with tunable sizes were obtained. Au-Ag cubes with body diagonals of 130, 144, and 161 nm and octahedra with body diagonals of 113, 126, and 143 nm have been prepared, allowing the investigation of size effect on their optical properties. Au-Ag octahedra with thinner Ag shells (12-16.5 nm) exhibit a blue-shifted major LSPR band relative to the LSPR band at 538 nm for the gold cores. For Au-Ag octahedra and cubes with thicker shells (22.5-37 nm), the major LSPR band is progressively red-shifted from that of the gold cores with increasing shell thickness and particle size. The Au-Ag octahedra show higher catalytic activity than cubes toward reduction of 2-amino-5-nitrophenol by NaBH4 at 30 °C, but both particle shapes display significantly enhanced catalytic efficiency at 40 °C.

Microwave-assisted headspace solid-phase microextraction for the rapid determination of organophosphate esters in aqueous samples by gas chromatography-mass spectrometry.

The rapid and solvent-free determination of organophosphate esters (OPEs) in aqueous samples via one-step microwave-assisted headspace solid-phase microextraction (MA-HS-SPME) followed by gas chromatography-mass spectrometry (GC-MS) analysis is described. Tri-n-butyl phosphate (TnBP) and tris-(2-ethylhexyl) phosphate (TEHP) were selected as model compounds for the method of development and validation. The effects of various extraction parameters for the quantitative extraction of these analytes by MA-HS-SPME were systematically investigated and optimized. The analytes, in a 20 mL water sample (in a 40 mL sample bottle containing 2g of NaCl, pH 3.0), were efficiently extracted by a polydimethylsiloxane-divinylbenzene (PDMS-DVB) fiber placed in the headspace when the system was microwave irradiated at 140 W for 5 min. The limits of quantification (LOQs) for TnBP and TEHP were 0.5 and 4 ng/L, respectively. Using the standard addition method, MA-HS-SPME coupled with GC-MS was utilized to determine selected OPEs in surface water and wastewater treatment plants (WWTP) influent/effluent samples. Preliminary results show that TnBP was commonly detected OPEs in these aqueous samples, the correlation coefficients (r(2)) of the standard addition curves were greater than 0.9822, indicating that the developed method appears to be a good alternative technique for analyzing OPEs in aqueous samples.