King Lun Yeung

Palladium-silver composite membranes by electroless plating technique

Abstract The exact conditions for deposition of pure palladium and pure silver membranes as well as simultaneous, co-deposition of palladium and silver have been identified for a hydrazine-based plating bath containing both palladium and silver precursors. The electroless plating kinetics have been determined for co-deposition of palladium and silver from the mixed plating bath. A mathematical model has been developed to predict the film thickness, plating rate and composition profile as a function of plating parameters (i.e., reactant concentrations and time). The evolution of the microstructure and composition of the film during electroless plating has also been investigated. A hydrogen permeation study has demonstrated that the Pd–Ag alloy membrane has superior performance compared to a pure palladium membrane of similar thickness. In addition, the formation of a single-phase alloy results in substantial enhancement in the hydrogen permeation rate.

Palladium composite membranes by electroless plating technique: Relationships between plating kinetics, film microstructure and membrane performance

Thin supported palladium membranes were prepared using electroless plating technique. The intrinsic plating kinetics were determined for hydrazine-based palladium plating baths. Mathematical models were developed to predict film thickness and plating rate as a function of plating parameters (i.e., reactant concentrations, temperature and time). Analyses of film surface microstructure indicate that grain structure is dependent on both plating chemistry and plating rate. The evolution of film morphology during electroless plating was also investigated. Hydrogen permeation study demonstrated that film structure has a significant influence on the permeation performance of the palladium membrane.

The influence of surface properties on the photocatalytic activity of nanostructured TiO2

Nanostructured TiO2 with 11- (P11) and 5-nm (P5) crystal sizes were prepared by a modified sol–gel method. Controlled crystallization and a pretreatment process were employed to obtain TiO2 with different surface roughness and degree of hydroxylation, while maintaining an identical crystal (i.e., 11 or 5 nm) and aggregate (i.e., 100 nm) sizes, phase structure (i.e., anatase), and crystallinity (i.e., X-ray diffraction peak intensity). Using the photooxidation of airborne trichloroethylene as a probe reaction, we were able to identify that the hydroxyl groups on low-coordinated titanium atoms are responsible for the generation of dichloroethylene and dichloroacetaldehyde by-products. Their presence usually means lower TCE conversion and in some cases leads to catalyst deactivation.

Effects of electroless plating chemistry on the synthesis of palladium membranes

Abstract The effects of plating chemistry on palladium deposition, plating efficiency and membrane microstructure have been studied for two palladium electroless plating solutions, hydrazine-based and hypophosphite-based plating baths. The electroless plating kinetics of palladium onto seeded supports have been determined for hypophosphite-based plating bath, and a simple kinetic model has been developed. The model provides an accurate prediction of deposition rate and film thickness as a function of plating parameters. Most importantly, the experimental results demonstrated that plating chemistry plays a vital role on both plating performance and film microstructure.

Precious metal recovery by selective adsorption using biosorbents.

Silk sericin and chitosan biosorbents are low cost and highly efficient biosorbents derived from waste biomass. Both biosorbents displayed good capacity and excellent selectivity for gold adsorption. Silk sericin and chitosan adsorbed respectively 1 and 3.3mmolg(-1) of gold and have K(d) values of 450 and 34,000, respectively. Experimental evidence showed that gold adsorbed on the amide groups of the silk sericin, while gold and copper adsorbed on the amino groups of chitosan via charge-interactions and complexation. Binary (Au-Cu), five (Au-Co-Ni-Cu-Zn) and six (Au-Pd-Co-Ni-Cu-Zn) component separations consistently showed that silk sericin has better selectivity (Sel(Au)>2.4) than chitosan. It is possible to recover gold at 99.5% purity by silk sericin and 90% if the solution contained palladium.

Performance of alumina, zeolite, palladium, Pd–Ag alloy membranes for hydrogen separation from Towngas mixture

Abstract The hydrogen permeation and separation properties of alumina, zeolite (ZSM-5), palladium and Pd–Ag alloy membranes were measured and compared. Hydrogen separation from a commercial Towngas mixture (49% H 2 , 28.5% CH 4 , 19.5% CO 2 and 3% CO) was conducted. The commercial alumina membrane displayed excellent hydrogen permeation rate but was unable to separate hydrogen from the Towngas. Supported ZSM-5 membrane prepared by ex situ method was able to produce a product stream containing 60% H 2 from Towngas, whereas, high purity hydrogen was generated using thin palladium and Pd–Ag alloy membranes prepared by electroless plating technique. Some of the constituent gases in Towngas mixture inhibit hydrogen flux through the palladium membrane, but the addition of silver serves to ameliorate the situation.

Incorporating zeolites in microchemical systems

Abstract Using a new fabrication method based on microelectronic fabrication and zeolite thin film technologies, MFI-type zeolites with engineered structures were incorporated as catalyst, membrane and structural material within the design architecture of a microreactor, membrane microseparator and microeletrochemical cell. Complex microchannel geometry and network (

Performance of a membrane-catalyst for photocatalytic oxidation of volatile organic compounds

The performance of a hybrid Sil-1/nanostructured anatase TiO2 membrane-catalyst and a catalytic titanium silicalite-1 (TS-1) membrane was evaluated for gas-phase photocatalytic oxidation (PCO) of trichloroethylene. The membrane-catalyst outperformed the catalytic plate coated with a similar amount of nanostructured TiO2 catalyst. However, the activity of the catalytic TS-membrane for PCO is low due to the insufficient number of active titanium sites in the TS-1 zeolite.

Curcumin-conjugated magnetic nanoparticles for detecting amyloid plaques in Alzheimer's disease mice using magnetic resonance imaging (MRI).

Diagnosis of Alzheimers disease (AD) can be performed with the assistance of amyloid imaging. The current method relies on positron emission tomography (PET), which is expensive and exposes people to radiation, undesirable features for a population screening method. Magnetic resonance imaging (MRI) is cheaper and is not radioactive. Our approach uses magnetic nanoparticles (MNPs) made of superparamagnetic iron oxide (SPIO) conjugated with curcumin, a natural compound that specifically binds to amyloid plaques. Coating of curcumin-conjugated MNPs with polyethylene glycol-polylactic acid block copolymer and polyvinylpyrrolidone by antisolvent precipitation in a multi-inlet vortex mixer produces stable and biocompatible curcumin magnetic nanoparticles (Cur-MNPs) with mean diameter <100 nm. These nanoparticles were visualized by transmission electron microscopy and atomic force microscopy, and their structure and chemistry were further characterized by X-ray diffraction, thermogravimetric analysis, X-ray photoelectron spectroscopy, time-of-flight secondary ion mass spectrometry, and Fourier transform infrared spectroscopy. Cur-MNPs exhibited no cytotoxicity in either Madin-Darby canine kidney (MDCK) or differentiated human neuroblastoma cells (SH-SY5Y). The Papp of Cur-MNPs was 1.03 × 10(-6) cm/s in an in vitro blood-brain barrier (BBB) model. Amyloid plaques could be visualized in ex vivo T2*-weighted magnetic resonance imaging (MRI) of Tg2576 mouse brains after injection of Cur-MNPs, and no plaques could be found in non-transgenic mice. Immunohistochemical examination of the mouse brains revealed that Cur-MNPs were co-localized with amyloid plaques. Thus, Cur-MNPs have the potential for non-invasive diagnosis of AD using MRI.

Preparation of supported Sil-1, TS-1 and VS-1 membranes - Effects of Ti and V metal ions on the membrane synthesis and permeation properties

Abstract The incorporation of titanium and vanadium metal ions into the structural framework of MFI zeolite imparts the material with catalytic properties. These zeolites are good candidates for catalytic membranes. The Sil-1, TS-1 and VS-1 membranes were grown on pre-seeded porous stainless steel support using hydrothermal synthesis method. The effects of silica and metal (i.e. Ti and V) contents, template concentration and temperature on the zeolite membrane growth and morphology were investigated. The addition of Ti and V metal ions inhibits the zeolite growth and, thus, restricting the amount of metals (i.e. Ti and V) that can be effectively incorporated into the membrane without compromising its separation performance. Optimum Si and TPAOH concentrations were identified for the synthesis of well-intergrown zeolite membranes. An increase in the synthesis temperature can result in a change in film crystallographic orientation and the appearance of imperfections in the form of imbedded zeolite crystals. Single gas permeation experiments were conducted for noble gases (He and Ar), inorganic gases (H2, N2, SF6) and hydrocarbons (methane, n-C4, i-C4) to determine the separation performance of these membranes. The results indicate that the gas transport through Sil-1 and VS-1 membranes is predominantly through the zeolite pores and that the presence of vanadium in VS-1 has significant influence on the permeance of adsorbed gases (e.g. hydrocarbons). Laminar flow is important for the TS-1 membrane that exhibited microscopic cracks.