W. L. Tan

Modified natural rubber induced aqueous to toluene phase transfer of gold and platinum colloids

Citrate-stabilized gold and platinum particles were prepared in aqueous phase and transferred to toluene phase by employing 2-propanol as the transfer agent. It was found that the modified natural rubber (ENR) induced the phase transfer and assisted the dispersion of the citrate-free metal particles into the organic phase. The amounts of gold and platinum transferred are 93.4% and 86.1%, respectively. This phase transfer technique produced organosols of smaller particle sizes and narrower size distribution with self-assembly arrangements when compared to those prepared via the previous in situ preparations. The respective average particle size and standard deviation of gold before and after phase transfer were 6.3 ± 1.7 nm and 7.2 ± 1.3 nm, while for platinum they were 4.0 ± 0.7 nm and 4.2 ± 0.8 nm. The slight increase in the average sizes and overall size distributions in both metals after transfer was attributed to multiparticle aggregation in the organic phase.

Surface Characteristics and Catalytic Activity of Copper Deposited Porous Silicon Powder

Porous structured silicon or porous silicon (PS) powder was prepared by chemical etching of silicon powder in an etchant solution of HF: HNO3: H2O (1:3:5 v/v). An immersion time of 4 min was sufficient for depositing Cu metal from an aqueous solution of CuSO4 in the presence of HF. Scanning electron microscopy (SEM) analysis revealed that the Cu particles aggregated upon an increase in metal content from 3.3 wt% to 9.8 wt%. H2-temperature programmed reduction (H2-TPR) profiles reveal that re-oxidation of the Cu particles occurs after deposition. Furthermore, the profiles denote the existence of various sizes of Cu metal on the PS. The Cu-PS powders show excellent catalytic reduction on the p-nitrophenol regardless of the Cu loadings.

Effect of anion of lithium salt on the property of lithium salt-epoxidized natural rubber polymer electrolytes

Lithium salt, LiX (where X = BF4−, I−, CF3SO3−, COOCF3− or ClO4−), was incorporated into epoxidized natural rubber (ENR). Thin films of LiX-ENR polymer electrolytes (PEs) were obtained via solvent casting method. These electrolytes were characterized using SEM/X-mapping, FTIR, differential scanning calorimeter, thermogravimetry analysis, and impedance spectroscopy. The trend in thermal stability and ionic conductivity of LiX-ENR PEs follow LiBF4 > > LiCF3SO3 ~ LiCOOCF3 > LiI > > LiClO4. The LiClO4 hardly dissociates and formed LiClO4 aggregates within the polymer matrix that resulted in a PE with low thermal stability and low ionic conductivity. The LiCF3SO3, LiCOOCF3, and LiI, however, exert moderate interactions with the ENR, and their respective PEs exhibit moderate ionic conductivity and thermal property. The occurrence of epoxide ring opening and complexation or cross-linking reactions in and between the ENR chains that involve BF4− ions have produced a LiBF4-ENR PE with superior thermal property and ionic conductivity as compared to other PEs studied in this work.

Electrical and thermal behavior of copper-epoxy nanocomposites prepared via aqueous to organic phase transfer technique

The preparation, electrical, and thermal behaviors of copper-epoxy nanocomposites are described. Cetyltrimethylammonium bromide - (CTAB-) stabilized copper (Cu) particles were synthesized via phase transfer technique. Isopropanol (IPA), sodium borohydride (NaBH4), and toluene solution of diglycidyl ether of bisphenol A (DGEBA) were used as transferring, reducing agent, and the organic phase, respectively. The UV-Vis absorbance spectra of all the sols prepared indicate that the presence of Cu particles with the particles transfer efficiency is ≥97%. The amount, size, and size distribution of particles in the organosol were dependent on the content of organic solute in the organosol. The composites were obtained upon drying the organosols and these were then subjected to further studies on the curing, thermal, and electrical characteristic. The presence of Cu fillers does not significantly affect the completeness of the composite curing process and only slightly reduce the thermal stability of the composites that is >300°C. The highest conductivity value of the composites obtained is 3.06 × 10-2 S cm-1.

Enhanced removal efficiency of methyl red via the modification of halloysite nanotubes by copper oxide

ABSTRACT Halloysite nanotubes (HNTs) were modified with CuO to form CuO-HNT composites. Results revealed that the CuO particles deposited on the HNT have higher specific surface area (SBET) and pore volume compared to unmodified HNT. Application of the composites for the removal of methyl red (MR) dye was investigated. The composites have better removal efficiency than HNT. The data fitted the Freundlich adsorption isotherms. Kinetics of adsorption favored the pseudo-second-order model. Removal efficiency was faster and higher in alkaline conditions. Reusability experiments show that the low-cost composites were effective up to seven cycles. GRAPHICAL ABSTRACT

Rapid Degradation of Methyl Orange by Ag Doped Zeolite X in the Presence of Borohydride

Abstract A series of Ag nanoparticles impregnated on zeolite X (Ag-ZX) containing various amounts of Ag (in wt%) were prepared via impregnation method. The pristine zeolite X and Ag-ZX catalysts were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), N2 adsorption desorption analyses and atomic absorption spectroscopy (AAS). The prepared catalysts were employed for the decolourization of methyl orange (MO) in the presence of potassium borohydride (KBH4). Various parameters such as the amount of Ag impregnated, MO concentration, KBH4: MO mole ratios, pH and catalyst reusability were investigated. It was found that the best decolourization efficiency was obtained when 0.06 g of Ag-ZX (6.7) catalyst was employed using a KBH4: MO mole ratio of 731: 1 at pH 5. The degradation process obeyed pseudo first-order kinetics.

Natural Composite Membranes for Water Remediation: Toward a Sustainable Tomorrow

Natural composites as green membranes have shown great potential in water remediation. These membranes combine merits from both natural polymer and inorganic or organic additives. Natural polymers are biodegradable, non-toxic and offer flexibility for design purposes. Incorporation of additives can enhance the mechanical and thermal properties or impart antibacterial and catalytic properties to the composite. This chapter provides an overview of the different types of natural polymer composite membranes and their functions. It also highlights the recent development of cellulose, chitosan, and natural rubber composite-based membranes in water treatment technologies between 2010 and 2015.

Metal Chloride Induced Formation of Porous Polyhydroxybutyrate (PHB) Films: Morphology, Thermal Properties and Crystallinity

Polyhydroxybutyrate (PHB) films with highly porous structures were synthesized using a one phase system comprising of metal chloride/methanol/PHB/chloroform (MCl2/CH3OH/PHB/CHCl3). SEM analyses confirmed that the MCl2 (where M = Cu2+ or Ni2+) induced porous structures with pore sizes ranging from 0.3 - 2.0 μm. The average pore size increased with the increasing MCl2 content. There existed weak physical interactions between the PHB chains and MCl2 as revealed by FTIR and NMR spectroscopies. The residue of MCl2 in the porous PHB film does not exert significant influence on the thermal stability of PHB. Nevertheless, the crystallinity of the prepared film is enhanced, as MCl2 acts as the nucleation sites to promote the growth of spherullites.

Hydrogenation of Liquid Styrene by Alumina Supported Nickel Catalysts: Comparison between Classical and Non-Classical Methods

Almina supported Ni catalysts (Ni/Al2O3) with different Ni weight percentages (wt%) were prepared via classical and non-classical methods. All samples were prepared via impregnation technique. The samples prepared via non-classical methods were reduced using KBH4 as the reducing agent. The catalysts were tested for the hydrogenation of styrene in liquid phase. Optimum activation conditions for the hydrogenation reaction were found to be 633 K for 2 hours. Comparison of the catalytic reactivity for all catalysts at these activation conditions showed that catalysts prepared via classical methods exhibited better activity. Furthermore the 7.6wt% Ni-Al2O3/C showed enhanced activity when compared to the 5.9wt% and 13.8wt% Ni-Al2O3/C catalyst. This phenomenon is mainly attributed to the type of Ni active sites available on the catalyst. The surface properties of the catalysts investigated via H2- temperature programmed reduction (H2-TPR), H2-chemisorption and H2-temperature programmed desorption (H2-TPD) confirm this.

Synthesis and properties of nanosized silver catalyst supported on chitosan-silica nanocomposites

This work described the immobilization of noble metal nanoparticles on silica microspheres mediated by chitosan. The dual support system is comprised of organicinorganic materials prepared via core-shell method. Chitosan/silica nanocomposites were successfully synthesized with different chitosan concentrations in order to get the optimized shell thickness. When high concentration of chitosan was employed, it was found that the shell completely coats the silica. The silver nanoparticles were then immobilized on the shell of the support through a sol-gel method. Various quantities of silver were studied in order to get the maximum loading thereby it is related to coating thickness. The catalyst was then tested by employing hydrogenation of cyclohexene in methanol as a model reaction.