Sheela Chandren

Structure and properties of oil palm-based nanocellulose reinforced chitosan nanocomposite for efficient synthesis of butyl butyrate

In this study, nanocellulose (NC) was successfully extracted from oil palm frond leaves (OPFL) using a combination of bleaching, alkaline treatment and acid hydrolysis. X-ray diffractogram revealed the extracted NC was crystalline with a crystallinity index of 70.2%. This indicates its suitability as nano-fillers for preparing the chitosan/nanocellulose (CS-NC) supports to immobilize Candida rugosa lipase (CRL) to produce the CRL/CS-NC biocatalysts. FTIR, FESEM and TGA characterizations of the CRL/CS-NC confirm the CRLs were successfully conjugated to the CS-NC supports. The air-dried CS-NC supports gave satisfactory immobilization of the CRLs (5.2mg/g) with the resultant CRL/CS-NCs catalysed conversions of ≥80% of butyl butyrate within 6h. Time course reaction profile revealed that 76.3% butyl butyrate conversion was achieved at 4h immobilization time using 3mg/mL of CRL/CS-NCs. NMR analyses on the purified butyl butyrate confirmed that the ester was successfully synthesized.

Textile/Al2O3–TiO2 nanocomposite as an antimicrobial and radical scavenger wound dressing

Improving the antimicrobial activity and radical scavenging ability of a textile-based nanocomposite (textile/TiO2, textile/Al2O3/TiO2, textile/Al2O3 and textile/Al2O3–TiO2 bimetal oxide nanocomposite) is the key issue in developing a good and flexible wound dressing. In this work, flexible textile attached with Al2O3–TiO2 nanoparticles was prepared by dipping the textile in a suspension containing Al2O3–TiO2 nanoparticles (150 mmol l−1). The mean radical scavenging ability for textile/TiO2, textile/Al2O3/TiO2, textile/Al2O3 and textile/Al2O3–TiO2 bimetal oxide nanocomposites as measured by liquid ultraviolet visible spectroscopy (UV-Vis) coupled with dependence formula was 0.2%, 35.5%, 35.0% and 38.2%, respectively. Based on the X-ray diffraction (XRD) patterns, the preface reactive oxygen species (ROS) scavenging ability shown by the textile/Al2O3–TiO2 bimetal oxide nanocomposite is most probably caused by the crystal structure concluding in a corundum-like structure, with Al3+ ions filling the octahedral sites in the lattice. Increased antimicrobial activity measured by optical density at 600 nm recorded for textile/Al2O3–TiO2 bimetal oxide nanocomposites showed better interaction between Al2O3 and TiO2 nanoparticles. This good interaction is expected to lead to better antimicrobial and radical scavenging ability as shown by the E. coli and human skin fibroblast (HSF) cytotoxicity tests, respectively.

Friedel-crafts alkylation of resorcinol over mesoporous alumina loaded with sulfuric acid

Mesoporous alumina which contains only Lewis acidity was synthesized by sol-gel method and was then impregnated with sulfuric acid to generate Brönsted acidity. The catalyst was used in Friedel-Crafts alkylation of resorcinol with methyl tert-butyl ether to produce 4-tert-butylresorcinol and 4,6-di-tert-butylresor- cinol as the major and minor products respectively. It was demonstrated that Lewis and Brönsted acidities play a synergetic role in this reaction.

Characterization, optimization and stability studies on Candida rugosa lipase supported on nanocellulose reinforced chitosan prepared from oil palm biomass

The contribution of chitosan/nanocellulose (CS-NC) to the enzymatic activity of Candida rugosa lipase covalently bound on the surface of CS-NC (CRL/CS-NC) was investigated. Cellulosic material from oil palm frond leaves (OPFL) were bleached, alkaline treated and acid hydrolyzed to obtain the purified NC and used as nano-fillers in CS. XRD, Raman spectroscopy and optical fluorescence microscopic analyses revealed existence of strong hydrogen bonds between CS and the NC nanofillers. The CRLs were successfully conjugated to the surface of the CS-NC supports via imine bonds that occurred through a Schiffs based mechanism. Process parameters for the immobilization of CRL were assessed for factors temperature, concentration of glutaraldehyde and pH, to afford the highest enzyme activity to achieve maximum conversion of butyl butyrate within 3h of incubation. Conversion as high as 88% was reached under an optimized condition of 25°C, 0.3% glutaraldehyde concentration and buffer at pH7. Thermal stability of CRL/CS-NCs was 1.5-fold greater than that of free CRL, with biocatalysts reusability for up to 8 successive esterification cycles. This research provides a promising approach for expanding the use of NC from OPFL for enhancing enzyme activity in favour of an alternative eco-friendly means to synthesize butyl butyrate.

Titania-Loaded Coal Char as Catalyst in Oxidation of Styrene with Aqueous Hydrogen Peroxide

Abstract Titania-loaded coal char catalyst was successfully prepared. The preparation steps involved pyrolysis of low rank coal at different temperatures and durations, sulfonation, impregnation of titanium(IV) isopropoxide, and then heating at 110 °C. It is found that the coal chars’ surfaces were rough after sulfonation and impregnation, while large pore volume, high surface area and carbon composition were observed at low pyrolysis temperature for short duration. These properties contributed to high selectivity towards benzaldehyde (> 90 %) at 600 °C (0.5–2 h)) in styrene oxidation using aqueous hydrogen peroxide as the oxidant.

Extraction of nanosilica from oil palm leaves and its application as support for lipase immobilization

The study reports the preparation of a composite consisting of magnetite coated with nanosilica extracted from oil palm leaves (OPL) ash as nanosupports for immobilization of Candida rugosa lipase (CRL) and its application for the synthesis of butyl butyrate. Results of immobilization parameters showed that ∼ 80% of CRL (84.5 mg) initially offered was immobilized onto the surface of the nanosupports to yield a maximum protein loading and specific activity of 67.5 ± 0.72 mg/g and 320.8 ± 0.42 U/g of support, respectively. Surface topography, morphology as well as information on surface composition obtained by Raman spectroscopy, atomic force microscopy, field emission scanning electron microscopy and transmission electron microscopy showed that CRL was successfully immobilized onto the nanosupports, affirming its biocompatibility. Under optimal conditions (3.5 mg/mL protein loading, at 45 ℃, 3 h and molar ratio 2:1 (1-butanol:n-butyric acid) the CRL/Gl-A-SiO2-MNPs gave a maximum yield of 94 ± 0.24% butyl butyrate as compared to 84 ± 0.32% in the lyophilized CRL. CRL/Gl-A-SiO2-MNPs showed an extended operational stability, retaining 50% of its initial activity after 17 consecutive esterification cycles. The results indicated that OPL derived nanosilica coated on magnetite can potentially be employed as carrier for lipase immobilization in replacement of the non-renewable conventionalsilica sources.

One-Dimensional-Like Titania/4′-Pentyl-4-Biphenylcarbonitrile Composite Synthesized Under Magnetic Field and its Structure–Photocatalytic Activity Relationship

The demonstration of the structure–properties relationship of shape-dependent photocatalysts remains a challenge today. Herein, one-dimensional (1-D)-like titania (TiO2), as a model photocatalyst, has been synthesized under a strong magnetic field in the presence of a magnetically responsive liquid crystal as the structure-aligning agent to demonstrate the relationship between a well-aligned structure and its photocatalytic properties. The importance of the 1-D-like TiO2 and its relationship with the electronic structures that affect the electron–hole recombination and the photocatalytic activity need to be clarified. The synthesis of 1-D-like TiO2 with liquid crystal as the structure-aligning agent was carried out using the sol–gel method under a magnetic field (0.3 T). The mixture of liquid crystal, 4′-pentyl-4-biphenylcarbonitrile (5CB), tetra-n-butyl orthotitanate (TBOT), 2-propanol, and water, was subjected to slow hydrolysis under a magnetic field. The TiO2–5CB took a well-aligned whiskerlike shape when the reaction mixture was placed under the magnetic field, while irregularly shaped TiO2–5CB particles were formed when no magnetic field was applied. It shows that the strong interaction between 5CB and TBOT during the hydrolysis process under a magnetic field controls the shape of titania. The intensity of the emission peaks in the photoluminescence spectrum of 1-D-like TiO2–5CB was lowered compared with the TiO2–5CB synthesized without the magnetic field, suggesting the occurrence of electron transfer from 5CB to the 1-D-like TiO2–5CB during ultraviolet irradiation. Apart from that, direct current electrical conductivity and Hall effect studies showed that the 1-D-like TiO2 composite enhanced electron mobility. Thus, the recombination of electrons and holes was delayed due to the increase in electron mobility; hence, the photocatalytic activity of the 1-D-like TiO2 composite in the oxidation of styrene in the presence of aqueous hydrogen peroxide under UV irradiation was enhanced. This suggests that the 1-D-like shape of TiO2 composite plays an important role in its photocatalytic activity.

Hollow Core–Shell Titania Photocatalysts for Selective Organic Synthesis

Titania, as one of the most widely used material for heterogeneous semiconductor photocatalysts, shows exceptional characteristics such as high chemical stability, nontoxicity, low cost, and capacity to induce various kinds of chemical reactions. A common drawback, however, is its lack of selectivity. This problem has been addressed through the synthesis of hollow core–shell particles, which consisted of commercially available titania particles incorporated into a hollow silica shell, via a multistep process comprising carbon and silica coatings followed by calcination to remove the carbon layer. The silica shell was found to be porous, water-swollen, and not directly connected to the titania particles. In the photocatalytic redox-combined synthesis of pipecolinic acid (l-PCA) from l-lysine to obtain optically active PCA, the hollow core–shell particles showed improved stereoselectivity, maintaining the l-lysine conversion. The PCA selectivity was also almost unchanged from those observed in a bare titania particle system. It is deduced that the acidic microenvironment of the titania core induced by the silica shell effectively controlled the position of oxidation by positive holes as the first step of the redox-combined process, leading to the improved stereoselectivity.

Hydrophobic effect of silica functionalized with silylated Ti-salicylaldimine complex on limonene oxidation by aqueous hydrogen peroxide

AbstractThis research work describes the effect of hydrophobicity in inducing the diffusion of alkene substrates to the catalytic active sites. The aim of this research is to improve the catalytic activity by tailoring the degree of hydrophobicity of the catalyst. Silica functionalized with solid non-silylated Ti-salicylaldimine complex was prepared at room temperature by mixing imine ligand and Ti(IV) sulphate solution. The amorphous, solid complex formed was further silylated with octadecyltrimethoxysilane (OTMS) to induce hydrophobicity. The composition of the resulting silica functionalized with silylated Ti-salicylaldimine complex was varied with Ti:OTMS molar ratio in the range of 1:1/4 to 1:4 at room temperature. The successful attachment of alkylsilyl groups to silica functionalized with Ti-salicylaldimine complex was proven by the FTIR and 29Si solid state NMR spectra. The FTIR spectra showed increasing peak area for sp 3 C-H stretching mode (ca. 2919 cm−1 and 2850 cm−1) and decreasing peak area for Si-OH band with increasing amount of OTMS. TGA showed less water content with higher amount of alkylsilyl groups in the catalyst. This is in agreement with the lower kinetic rate of water adsorption capacity for the hydrophobic catalysts prepared. It was observed that the hydrophobic, silica functionalized with silylated Ti-salicylaldimine complex exhibited higher substrate conversion and reusability compared to the non-silylated catalyst. Graphical AbstractSilica functionalization with silylated Ti-salicylaldimine complex was varied with octadecyltrimethoxysilane (OTMS) concentration to induce hydrophobicity. It was found that the higher degree of hydrophobicity has decreased the water content. Hence, the catalytic activity and TON for Ti increased. It showed that the surface property is important in the design of catalysts.

Synthesis of titania with different shapes

Titania (TiO₂) has been an important renewable material that is able to convert solar energy into chemical energy in recent years. Therefore, the main focus of this paper centers around different strategies and precursors to prepare TiO₂ with various shapes, e.g. perforated hollow TiO₂, anatase hollow TiO₂ spheres, well-aligned TiO₂ and rambutan-like TiO₂/liquid crystal composite, so as to utilize these materials in an environmental-benign way.