Siew Ling Lee

Removal of hazardous heavy metals from aqueous environment by low-cost adsorption materials

The rapid growth of the human population and industrialization in the world has indirectly increased environmental problems such as water, air and land pollution. Amongst all, heavy metals can be considered as the most problematic pollutants. Numerous efforts have been attempted to minimize the impact of heavy metals. This chapter discusses the recent developments and technical applicability of different treatment methods for heavy metal removal. The adsorption process using various low-cost materials as the potential alternative for heavy metal removal is being highlighted and summarized.

Synthesis of new schiff base ester liquid crystals with a benzothiazole core

A series of new calamitic liquid crystals, 6-methoxy-2-(4-alkanoyloxybenzylidenamino)benzothiazoles, comprising a benzothiazole core, terminal methoxy group and a Schiff base linkage were synthesised and characterised. This series comprises 12 members wherein members differ by the length of the alkanoyloxy chain (C n-1H2n-1COO-, where n = 2–8, 10, 12, 14, 16, 18). Their mesomorphic properties were studied by using differential scanning calorimetry, optical polarising microscopy and powder X-ray diffraction techniques. The short chain derivatives (n = 2 and 3) were non-mesogenic compounds, while an enantiotropic nematic phase was present throughout the remaining members of the series. The smectic C phase emerged from the decanoyloxy derivative onwards.

Equilibrium studies for Basic blue 3 adsorption onto durian peel (Durio zibethinus Murray)

Abstract A waste material with practically no cost, durian peel (DP) was studied for its ability to remove Basic blue 3 (BB3) from aqueous solutions. Batch kinetic studies were carried out to study the adsorption characteristics under various experimental conditions. The optimum pH for the dye removal occurred in the pH range of 3–10. Adsorption was found to be concentration dependent. The kinetics of dye adsorption fitted a pseudo-second order rate expression. Both Langmuir and Freundlich models appeared to provide reasonable fittings for the adsorption data of BB3 on DP. Application of Langmuir isotherm indicated that under the experimental condition of room temperature (25 ± 2°C) with natural pH of the dye solution and shaken at 150 rpm, the maximum adsorption capacity of DP for BB3 was 49.50 mg g−1. The percentage uptake of BB3 increased with the increase in temperature. Adsorption of BB3 was found to be endothermic and various thermodynamic parameters were evaluated using van’t Hoff plot.

Mesogenic Schiff base esters with benzothiazole core: synthesis and phase transition studies

A series of new rod-shaped mesomorphic compounds, 6-ethoxy-2-(4-alkanoyloxybenzylidenamino)benzothiazoles, consisting of a 2,6-disubstituted benzothiazole core and a Schiff base central linkage, were synthesized and their structures were ascertained via elemental analysis and spectroscopic techniques. Their mesomorphic properties were studied using differential scanning calorimetry (DSC), polarized optical microscopy (POM) and X-ray diffraction (XRD) analysis. All compounds showed enantiotropic mesomorphism. Whilst the lower members of the series, hexanoyloxy and octanoyloxy derivatives exhibited nematic phase, the higher members (decanoyloxy, dodecanoyloxy, tetradecanoyloxy, hexadecanoyloxy and octadecanoyloxy derivatives) exhibited nematic and smectic C phases.

Mesoporous carbon nitride for adsorption and fluorescence sensor of N-nitrosopyrrolidine

A metal-free mesoporous carbon nitride (MCN) was investigated for the first time as an adsorbent for N-nitrosopyrrolidine (NPYR), which is one of the nitrosamine pollutants. Under the same condition, the adsorption capability of the MCN was found to be higher than that of the MCM-41. Since the adsorption isotherm was consistent with Langmuir and Freundlich model equations, it was suggested that the adsorption of NPYR molecules on the MCN occurred in the form of mono-molecular layer on the heterogeneous surface sites. It was proposed that MCN with suitable adsorption sites was beneficial for the adsorption of NPYR. The evidence on the interaction between the NPYR molecules and the MCN was supported by fluorescence spectroscopy. Two excitation wavelengths owing to the terminal N-C and N=C groups were used to monitor the interactions between the emission sites of the MCN and the NPYR molecules. It was confirmed that the intensity of the emission sites was quenched almost linearly with the concentration of NPYR. This result obviously suggested that the MCN would be applicable as a fluorescence sensor for detection of the NPYR molecules. From the Stern-Volmer plot, the quenching rate constant of terminal N-C groups was determined to be ca. two times higher than that of the N=C groups on MCN, suggesting that the terminal N-C groups on MCN would be the favoured sites interacted with the NPYR. Since initial concentration can be easily recovered, the interactions of NPYR on MCN were weak and might only involve electrostatic interactions.

Novel Nanostructured Photocatalyst of Vanadium‐Doped Silica‐Titania Aerogel

An excellent UV and visible irradiation response of vanadium‐doped silica‐titania photocatalysts has been successfully prepared. The designed photocatalyst possesses high surface areas of 610 m2/g. Its outstanding photocatalytic activity is attributed to the presence of tetrahedrally coordinated vanadia species in forms of Ti–O–V bonding. Besides, the incorporation of V extends the light adsorption edge of V‐doped silica titania aerogels and resulting in reduced band gap energy.

Synthesis and Mesomorphic Properties of 6-Methoxy- and 6-Ethoxy-2-(2-Hydroxy-4-Alkanoyloxybenzylidenamino)Benzothiazoles

Two new series of Schiff base thermotropic liquid crystals, 6-methoxy-2-(2-hydroxy-4-alkanoyloxybenzylidenamino)benzothiazoles and 6-ethoxy-2-(2-hydroxy-4-alkanoyloxybenzylidenamino)benzothiazoles, comprising different terminal groups, a methoxyl and ethoxyl group, respectively, were synthesized. Structural elucidation was carried out using elemental analysis and spectroscopic techniques such as Fourier transform infrared (FTIR), 1H and 13C nuclear magnetic resources (NMR), and mass spectrometry. The mesomorphic properties and thermal stabilities of the title compounds were studied by using differential scanning calorimetry, optical polarizing microscopy, and thermogravimetric analysis. No liquid-crystal phases were observed for the short-chain members (n = 2 and 3) in both series, and the remaining members all exhibited nematic phase with Schlieren or marble-like textures. Effects of the lateral hydroxyl group, terminal group, and the length of the terminal alkanoyloxy chain on the mesomorphic properties are discussed. Structure-property relationships were established upon comparison with other structurally related compounds.

Synthesis and phase transition behaviours of new non-symmetric liquid crystal dimers

A new series of non-symmetric liquid crystal dimers N-(4-(n-(4-(benzothiazol-2-yl)phenoxy)alkyloxy)-4-nitro-benzylideneimine) containing benzothiazole and benzylideneaniline as the mesogenic core units connected by a flexible alkyl spacer, -(CH2)n-, with n ranging from 2 to 6, 8, 10 and 12 have been prepared. Their molecular structures were proposed via spectroscopic techniques. Mesomorphic properties were studied using differential scanning calorimetry and polarising optical microscopy. The results showed that the clearing temperatures decreased upon lengthening of the alkyl spacers. Whilst even member with the shortest alkyl spacer (n = 2) exhibited nematic phase, the rest of even members (n = 4, 6, 8, 10 and 12) possessed smectic and nematic properties. Nematic phase range gradually decreased from n = 2 to n = 12. Odd members are belonged to non-mesogenic compounds except for n = 5 which exhibited monotropic (metastable) nematic phase.

Cheap Materials to Clean Heavy Metal Polluted Waters

The rapid growth of the human population and industrialization in the world has increased the environmental problems such as water, air and land pollution. Heavy metals can be considered as one of the most problematic pollutants. This chapter reviews developments and technical applicability of treatments methods for the removal of heavy metals. We focus on the use of low-cost materials to remove heavy metals. Isotherm equilibrium models and kinetics are discussed. Designing adsorption columns under continuous flow conditions are evaluated.

Synthesis and Characterization of Acid Modified Silica-Titania Aerogel as Oxidative-Acidic Bifunctional Catalyst

Acid tr eatment using H2SO4, HCl and H3PO4 has been carried ou t in an attempt to improve catalytic performance of silica-titania aerogel. X-ray diffraction results s howed the amorphous structure of the aerogels remained after the acid impregnation and calcinations steps. Hammert analysis revealed these acid modified silica-titania aerogels were superacids with pKa < -14.52. Different Ti species was observed in the samples upon the acid treatment. As compared to silica-titania aerogel, Lewis acidity increased remarkably in HCl treated sample without formation of any Bronsted acid site. Meanwhile, H2SO4 and H3PO4 treate d samples possessed both Lewis and Bronsted acid sites. The catalytic performance of these samples was evaluated through a consecutive transformation of 1-octene to 1,2-octanediol through the formation of 1,2-epoxyoctane using aqueous hydrogen peroxide as oxidant.