Kheng Soo Tay

Ozonation of parabens in aqueous solution: Kinetics and mechanism of degradation

This study investigated the reaction kinetics and degradation mechanism of parabens (methylparaben, ethylparaben, propylparaben and butylparaben) during ozonation. Experiments were performed at pH 2, 6 and 12 to determine the rate constants for the reaction of protonated, undissociated and dissociated paraben with ozone. The rate constants for the reaction of ozone with dissociated parabens (3.3 × 10(9)-4.2 × 10(9)M(-1)s(-1)) were found to be 10(4) times higher than the undissociated parabens (2.5 × 10(5)-4.4 × 10(5)M(-1)s(-1)) and 10(7) times higher than with the protonated parabens (1.02 × 10(2)-1.38 × 10(2)M(-1)s(-1)). The second-order rate constants for the reaction between parabens with hydroxyl radicals were found to vary from 6.8 × 10(9) to 9.2 × 10(9)M(-1)s(-1). Characterization of degradation by-products (DBPs) formed during the ozonation of each selected parabens has been carried out using GCMS after silylation. Twenty DBPs formed during ozonation of selected parabens have been identified. Hydroxylation has been found to be the major reaction for the formation of the identified DBPs. Through the hydroxylation reaction, a variety of hydroxylated parabens was formed.

Degradation of DEET by ozonation in aqueous solution.

This study was undertaken in order to understand the factors affecting the degradation of an insect repellent, N,N-diethyl-m-toluamide (DEET) by ozonation. Kinetic studies on DEET degradation were carried out under different operating conditions, such as varied ozone doses, pH values of solution, initial concentrations of DEET, and solution temperatures. The degradation of DEET by ozonation follows the pseudo-first-order kinetic model. The rate of DEET degradation increased exponentially with temperature in the range studied (20-50 degrees C) and in proportion with the dosage of ozone applied. The ozonation of DEET under different pH conditions in the presence of phosphate buffer occurred in two stages. During the first stage, the rate constant, k(obs), increased with increasing pH, whereas in the second stage, the rate constant, k(obs2), increased from pH 2.3 up to 9.9, however, it decreased when the pH value exceeded 9.9. In the case where buffers were not employed, the k(obs) were found to increase exponentially with pH from 2.5 to 9.2 and the ozonation was observed to occur in one stage. The rate of degradation decreased exponentially with the initial concentration of DEET. GC/MS analysis of the by-products from DEET degradation were identified to be N,N-diethyl-formamide, N,N-diethyl-4-methylpent-2-enamide, 4-methylhex-2-enedioic acid, N-ethyl-m-toluamide, N,N-diethyl-o-toluamide, N-acetyl-N-ethyl-m-toluamide, N-acetyl-N-ethyl-m-toluamide 2-(diethylamino)-1-m-tolylethanone and 2-(diethylcarbamoyl)-4-methylhex-2-enedioic acid. These by-products resulted from ozonation of the aliphatic chain as well as the aromatic ring of DEET during the degradation process.

Ozonation of ofloxacin in water: By-products, degradation pathway and ecotoxicity assessment

Application of ozonation in water treatment involves complex oxidation pathways that could lead to the formation of various by-products, some of which may be harmful to living organisms. In this work, ozonation by-products of ofloxacin (OFX), a frequently detected pharmaceutical pollutant in the environment, were identified and their ecotoxicity was estimated using the Ecological Structure Activity Relationships (ECOSAR) computer program. In order to examine the role of ozone (O3) and hydroxyl radicals (∙OH) in the degradation of ofloxacin, ozonation was performed at pH2, 7 and 12. In this study, 12 new structures have been proposed for the ozonation by-products detected during the ozonation of ofloxacin. According to the identified ozonation by-products, O3 and ∙OH were found to react with ofloxacin during ozonation. The reaction between ofloxacin and O3 proceeded via hydroxylation and breakdown of heterocyclic ring with unsaturated double-bond. The reaction between ofloxacin and ·OH generated various by-products derived from the breakdown of heterocyclic ring. Ecotoxicity assessment indicated that ozonation of OFX could yield by-products of greater toxicity compared with parent compounds.

Magnetic nanoparticle assisted dispersive liquid–liquid microextraction for the determination of 4-n-nonylphenol in water

A fast extraction technique involving dispersive liquid–liquid microextraction (DLLME) coupled with magnetic nanoparticle-based dispersive solid-phase microextraction (D-μ-SPE) was developed. For preliminary study, this method was applied for the extraction of 4-n-nonylphenol (4-NP) in water. In this method, n-octyl-triethoxysilane surface-modified magnetic iron oxide nanoparticles (C8MNPs) were first synthesized. The DLLME was performed by injecting 1 mL of methanol (disperser) containing 10 μL of 1-octanol (extraction solvent) into 15 mL of water sample. To this solution, C8MNPs were immediately added for the retrieval of the extraction solvent and of the extracted 4-NP by sonication. Subsequently, a magnet was held next to the vial to attract and isolate the C8MNPs. Then, the water sample was decanted, the nanoparticles were freeze-dried, and the 4-NP was extracted from nanoparticles by sonication with methanol. The detection of 4-NP was performed using a HPLC coupled with a fluorescence detector. Under optimal extraction conditions, a low method of detection limit (13.9 ng L−1), good linearity (R2 = 0.9958), and repeatability (1.7–2.2%) were achieved during 4-NP extraction. This method was also successfully used to analyze the real water samples such as drinking water and secondary wastewater. Generally, this sample preparation method offered an alternative to the conventional DLLME, because, in this method, centrifugation is not required and the retrieval of the extraction solvent is based on the adsorption process by magnetic nanoparticles (MNPs). Also, this two-step method improved the versatility of DLLME because the selection of the extraction solvent was no longer limited to the high density solvents. Because MNPs can be surface-modified for the extraction of different organic solvents, this method could have great prospects in the future.

Ozonation of metoprolol in aqueous solution: ozonation by-products and mechanisms of degradation

This study investigated the degradation pathway of metoprolol, a widely used β-blocker, in the ozonation via the identification of generated ozonation by-products (OPs). Structure elucidation of OPs was performed using HPLC coupled with quadrupole time-of-flight high-resolution mass spectrometry. Seven OPs were identified, and four of these have not been reported elsewhere. Identified OPs of metoprolol included aromatic ring breakdown by-products; aliphatic chain degraded by-products and aromatic ring mono-, di-, and tetrahydroxylated derivatives. Based on the detected OPs, metoprolol could be degraded through aromatic ring opening reaction via reaction with ozone (O3) and degradation of aliphatic chain and aromatic ring via reaction with hydroxyl radical (•OH).

Synthesis, characterization, and theoretical study of an acrylamide-based magnetic molecularly imprinted polymer for the recognition of sulfonamide drugs

Abstract In this work, a magnetic molecularly imprinted polymer (MION-MIP) was prepared for the recognition and extraction of sulfadiazine (SDZ). The acrylamide-based MIP was imprinted directly onto the surface of 3-(trimethoxysilyl)propyl methacrylate-modified magnetic iron oxide nanoparticles. The synthesized MION-MIP with a diameter about 100 nm possesses fast adsorption kinetics and high adsorption capacity. The results also indicated that a higher maximum adsorption capacity (775 μg g-1) was achieved by the synthesized MION-MIP. The Langmuir adsorption isotherm model was found to describe well the equilibrium adsorption data. The results from the competitive binding experiment showed that MION-MIP was not only selective toward SDZ but the adsorption of sulfamerazine was also dramatically high. SDZ and sulfamerazine have an almost similar substructure where these two compounds were only differentiated by one methyl group. To explain this result, a computational study was carried out. From a different level of calculation with semiempirical (PM3), Hartree-Fock (HF), and density functional theory (DFT) calculation, SDZ and sulfamerazine showed similar interaction energy and interaction mechanism with the acrylamide monomer. Therefore, both SDZ and sulfamerazine could have the same binding property with the MION-MIP.

Chromatographic and Spectroscopic Studies on β-Cyclodextrin Functionalized Ionic Liquid as Chiral Stationary Phase: Enantioseparation of Flavonoids

In this study, β-cyclodextrin functionalized ionic liquid was prepared by adding 1-benzylimidazole onto 6-monotosyl-6-deoxy-β-cyclodextrin (β-CDOTs) to obtain β-CD-BIMOTs. β-CD-BIMOTs were then bonded onto the modified silica to produce chiral stationary phases (β-CD-BIMOTs-CSP). The performance of β-CD-BIMOTs-CSP was evaluated by observing the enantioseparation of flavonoids. The performance of β-CD-BIMOTs stationary phase was also compared with native β-CD stationary phase. For the selected flavonoids, flavanone and hesperetin obtained a high resolution factor in reverse phase mode. Meanwhile, naringenin and eriodictyol attained partial enantioseparation in polar organic mode. In order to understand the mechanism of separation, the interaction of selected flavonoids and β-CD-BIMOTs was studied using spectroscopic methods (1H NMR, NOESY and UV–Vis spectrophotometry). The enantioseparated flavanone and hesperetin were found to form an inclusion complex with β-CD-BIMOTs. However, naringenin and eriodictyol were not enantioseparated due to the formation of hydrogen bonding at exterior torus of β-CD-BIMOTs.

Characterization and sources of extractable organic matter from sediment cores of an urban lake (Tasik Perdana), Kuala Lumpur, Malaysia

AbstractThe extractable organic matter of sediment samples from six sampling sites in Lake Perdana, Kuala Lumpur, was analyzed to characterize the source inputs. The analysis of aliphatic homologous series indicated that terrestrial higher plant waxes can be assigned as the major sources of the identified aliphatic components in the lake sediments. The presence of an unresolved complex mixture of branched and cyclic compounds and a series of hopanes ranging from C27 to C35 reflected the contamination by petroleum residues from urban vehicular emissions brought in by runoff and fallout. The steroids present included stenols and stanols and showed an input of organic matter from higher plants. The detected pentacyclic triterpenoids comprised oleanane, ursane, lupane and friedelane skeletons including unsaturated oxygenated, mono-, di- and triaromatic counterparts. They are recognized as biomarkers for angiosperms. The presence of des-A-triterpenoids and their aromatized derivatives as the major diagenetic products of triterpenoids reflected the degradation of natural organic matter in the sediments occurring under mainly anoxic conditions. In addition, the presence of tetrahymanol and ββ-bishomohopan-32-ol indicated a minor algal/plankton and bacterial input to the sediments.

β-Cyclodextrin functionalized ionic liquid as chiral stationary phase of high performance liquid chromatography for enantioseparation of β-blockers

Two covalently bonded β-Cyclodextrin (β-CD) based CSPs were prepared by immobilizing the native β-CD and mono-6-deoxy-6-(3-benzylimidazolium tosylate)-β-CD (β-CD-BIMOTs) onto modified silica gel. β-CD-BIMOTs is a β-CD based CSP with ionic liquid (3-benzylimidazolium tosylate) substituent. The enantioseparation capability of the synthesized CSPs was examined using 4 racemic mixtures of β-blockers (propranolol, metoprolol, pindolol and atenolol). The results indicated that β-CD-BIMOTs based CSP afforded more favorable enantioseparations than native β-CD based CSP. In order to study the mechanism of enantioseparation, inclusion complexes β-CD-BIMOTs and β-blockers were prepared and these inclusion complexes were characterized by using 1H NMR and NOESY. In addition, the separation conditions such as pH and composition of mobile phase were varied to study the role of β-CD and ionic liquid in enantioseparation. In general, it can be concluded that the complete enantioseparation of propranolol and metoprolol is achieved through the formation of inclusion complex with β-CD-BIMOTs and the formation π-π interaction with the ionic liquid moiety of β-CD-BIMOTs. The result also showed the poor enantioseparation of pindolol and atenolol on the β-CD-BIMOTs based CSP due to the strong interaction at the exterior torus of β-CD-BIMOTs.

Removal of organic matter from stabilized landfill leachate using Coagulation-Flocculation-Fenton coupled with activated charcoal adsorption:

The treatment of stabilized landfill leachate (SLL) by conventional biological treatment is often inefficient due to the presence of bio-recalcitrant substances. In this study, the feasibility of coagulation-flocculation coupled with the Fenton reaction in the treatment of SLL was evaluated. The efficiency of the selected treatment methods was evaluated through total organic carbon (TOC) removal from SLL. With ferric chloride as the coagulant, coagulation-flocculation was found to achieve the highest TOC removal of 71% at pH 6. Then, the pretreated SLL was subjected to the Fenton reaction. Nearly 50% of TOC removal was achieved when the reaction was carried out at pH 3, H2O2:Fe2+ ratio of 20:1, H2O2 dosage of 240 mM and 1 h of reaction time. By coupling the coagulation-flocculation with the Fenton reaction, the removal of TOC, COD (chemical oxygen demand) and turbidity of SLL were 85%, 84% and 100%, respectively. The ecotoxicity study performed using zebrafish revealed that 96 h LC50 for raw SLL was 1.40% (v/v). After coagulation-flocculation, the LC50 of the pretreated SLL was increased to 25.44%. However, after the Fenton reaction, the LC50 of the treated SLL was found to decrease to 10.96% due to the presence of H2O2 residue. In this study, H2O2 residue was removed using powdered activated charcoal. This method increased the LC50 of treated effluent to 34.48% and the removal of TOC and COD was further increased to 90%. This finding demonstrated that the combination of the selected treatment methods can be an efficient treatment method for SLL.