L. L. Koh

Investigations into the Engineering of Inorganic/Organic Solids: Hydrothermal Synthesis and Structure Characterization of One-Dimensional Molybdenum Oxide Polymers

Two one-dimensional intercalating molybdenum oxide polymers have been synthesized using different structure-directing units under specific hydrothermal conditions. MoO-0 (NaNH4Mo3O10) was synthesized using tetramethylammonium hydroxide, and MoO-1(C6H18N2Mo4O13) was synthesized using 1,6-hexanediamine. The two crystal structures have been determined by the single-crystal X-ray diffraction method. Both consist of bundles of parallel molybdenum oxide chains interspersed with metals or organic cations which play the role of intercalating agent in the host structure. The Mo has a 6+ valence state and distorted octahedral coordination. Mo-0 has orthorhombic symmetry (Pnma, No. 62) with a = 8.407(2) A, b = 7.603(2) A, and c = 14.350(3) A. MoO-1 has triclinic symmetry (P1, No. 2) with a = 8.267(2) A, b = 8.986(2) A, c = 12.714(3) A, α = 87.58(3)°, β = 76.48(3)°, γ = 67.97(3)°. The study suggests that the structures and properties of intercalation-type molybdenum oxide polymers can be engineered by incorporating ...

Synthesis and Polymerization of Surface-Active Sodium Acrylamidoundecanoate

Abstract The polymerizable surfactant sodium 11-acrylamidoundecanoate (Na 11-AAU) was synthesized from acryloyl chloride and 11-aminounde-canoic acid. It had a low critical micelle concentration (CMC) of 4.3 × 10−4 mol/L. Polymerization of Na 11-AAU initiated by K2S2O8 was very fast in aqueous solution, with an activation energy of only 63.2 kJ/mol. The polymerization followed first-order kinetics with respect to Na 11-AAU and one-half order with respect to K2S2O8. The MW of poly(Na 11-AAU) was very high (1–2 million) but the MWD was rather narrow ( M w / M n = 1.45). Polymerization of Na 11-AAU in the micellar state may be responsible for the phenomena observed.

Microemulsion systems with monobutyl ether of ethylene glycol or diethylene glycol as cosurfactant

Abstract Microemulsions with two water soluble glycol derivatives as cosurfactant and sodium dodecyl sulfate or cetyltrimethylammonium bromide were investigated. Maximization of solubilization of toluene and water was achieved for both systems at low concentration of surfactant. But with one exception, the same effect was not observed for all the heptane containing microemulsions. The results did not seem to show the complementary function between the nitrogen containing surfactant CTAB and the glycol cosurfactants nor the solubility of the cosurfactant in water is a decisive factor for high solubilization of water and toluene.

Soil lead and other metal levels in industrial, residential and nature reserve areas in Singapore

The use of pressure feedback microwave digestion technique has permitted rapid and efficient digestion of soil and sediment samples. The evaluation of different acid mixtures to digest soil samples were studied by mixed-level orthogonal array design. The selected acid mixture of HCl-HNO3-HF was employed in the survey of Pb, Zn, Cu, Cr and Mn in soil samples. Surface soil samples were collected from industrial, residential and nature reserve areas in Singapore. The five metal concentrations were determined by flame atomic absorption spectrometry and graphite furnace atomic absorption spectrometry. The lead and other metal contents in NBS SRM 1645, NIES CRM No. 2 and NRCC BCSS-1 sediment standard references were determined concurrently with the survey samples. Five measured metal loading on the surface soils was in the order: industrial area > residential area > nature reserve area. The trace metal concentrations in surface soil from areas of heavy traffic are higher than those from residential areas. The main sources of trace metal pollution are vehicular exhaust and industrial activities.

Temperature effects on the leaching of lead from unplasticized poly(vinyl chloride) pipes

Abstract The leaching of lead from unplasticized poly(vinyl chloride) pipes under different temperatures and by different extractants was studied. The extractants used were tap water, sodium hydrogen carbonate and disodium hydrogen phosphate solutions. The results show that for tap water and sodium hydrogen carbonate extractants, increasing the temperature generally increases the leaching rate of lead. The reverse was observed for the phosphate extractant. The study also shows that the extrusion temperature of the pipes affects the leaching rate of lead by water. Less lead is leached from pipes extruded at higher temperature.

Factors Affecting the Leaching of Lead from UPVC Pipes

This paper summarizes the results of a series of studies on the various factors that affect the leaching of lead from unplasticized poly(vinyl chloride) (UPVC) pipes. Factors that were studied include temperature, pH and extractants. Results showed that, for a given UPVC pipe, the rate of leaching of lead depended primarily on temperature and the nature of extractants. While the rate of leaching of lead was quite low with distilled water, it was very much enhanced by the presence of low concentration of anions such as Cl-, HPOinf4sup2-HCOinf3sup-, NOinf3sup-, SOinf4sup2-and EDTA. EDTA, being a strong complexing agent, was most effective. Rates of leaching were found to be higher at elevated temperature except in the cases of HPOinf4sup2-and EDTA. Effect of pH was not pronounced. The temperature at which the UPVC pipes were extruded was found to affect the rate of leaching of lead. Pipes extruded at 190°C were found to have lower rate of leaching than those extruded at 180°C and 170°C. Analysis of the pipes by Scanning Electron Microscopy showed that the distribution of lead in the pipes extruded at 190°C was more uniform than those extruded at 170°C.

Micellar polymerization of surfactants

SummaryMicelle-forming sodium 6-acrylamidocaproate (Na 6-AAC) and sodium 11-(N-methyl acrylamido)undecanoate (Na 11-MAAU) were synthesized and polymerized in aqueous solutions. The polymerization was very rapid and it followed first-order kinetics with respect to the monomer and one-half order to K2S2O8. The activation energy for the polymerization of Na 11-MAAU (62.3 kJ/mol) was much lower than that for Na 6-AAC (98.1 kJ/mol). The ¯Mw. for the former was around one million and it was only one-third of that for the latter. Their MWD (¯Mw/¯Mn ∼- 1.5) are relatively narrow. The relationships between intrinsic viscosity [η]o and ¯Mw for these polysurfactants have also been established.

Micellar Polymerization of Sodium 11-(N-Ethylacrylamido)Undecanoate: Kinetics and Solution Properties

Abstract Polymerizations of micelle-forming sodium 11-(N-ethylacryl-amido) undecanoate (Na 11-EAAU) in water were carried out at different concentrations of the anionic monomer and potassium per-sulfate from 50 to 60°C. the polymerization kinetics was close to half order with respect to the initiator and first order to the monomer. with the low activation energy of only 45.7 kJ/mol, polymerization of Na 11-EAAU in the micellar aggregates proceeded very rapidly. High molecular weights (∼106) poly(Na 11-EAAU) could easily be obtained. the results suggest that the organized structures of the micellar monomers in aqueous solution are responsible for fast polymerization and high MW. the effect of NaCl and aging on the solutuion behavior of poly(Na 11-EAAU) have also been studied.

Micellization and adsorption of a polymerizable surfactant: Sodium 11-(N-methyl acrylamido) undecanoate

Abstract Micellization of sodium 11-(N-methyl acrylamido) undecanoate is favored both energetically and entropically. It exhibited a relatively large area per surfactant molecule at the saturated monolayer adsorption at the air-water interface (σmm), and its limiting area per surfactant molecule (σ0) is large as well. This implies that the polymerizable surfactant molecule may highly bend at the air-water interfacial adsorption.

New insights into the study of indiumphosphate molecular sieves

A new microporous indiumphosphate InPO4-2, In2P2O8(OH)(H2O)(NH4)·H2O (the second member of the series) is obtained by the hydrothermal synthesis (473 K, 11 days, autogenous pressure) from a mixture of 1.0In2O3: 1.0P2O5: 1.2HF: 2.0Piperidine: 160H2O. It is monoclinic, space group P21/n with a=10.043(2), b=9.136(2), c=9.136(2), c=10.325(2), β=102.60(3)o, V=924.6(5) 3 and Z=2. The three-dimensional framework is built up from two basic building units, tetramer where two InO5(OH) and InO4(OH)(H2O) octahedra are joint by sharing both corners and edges, and PO4 tetrahedra which serve as bridges linking InO6 octahedra. An unusual linkage between two InO6 octahedra via shared-edge and (μ4-OH) are found in InPO4-2 where the oxygen is shared by three InO6 octahedra. The structure contains 8-ring zig-zag channels along b-axis. NH4+ and H2O are situated within the main channels. The crystallization and structural features of InPO4-2 exhibit certain similarity to that of InPO4-1 and contrast strongly to those of M(III)X(v)O4-type molecular sieves. It suggests the unusual hydrothermal chemistry of the microporous indiumphosphate.