Newaz Mohammed Bahadur

Fast and facile synthesis of silica coated silver nanoparticles by microwave irradiation.

A novel, fast and facile microwave technique has been developed for preparing monodispersed silica coated silver (Ag@SiO(2)) nanoparticles. Without using any other surface coupling agents such as 3-aminopropyltrimethoxysilane (APS) or polymer such as polyvinyl pyrrolidone (PVP), Ag@SiO(2) nanoparticles could be easily prepared by microwave irradiation of a mixture of colloidal silver nanoparticles, tetraethoxysilane (TEOS) and catalyst for only 2 min. The thickness of silica shell could be conveniently controlled in the range of few nanometers (nm) to 80 nm by changing the concentration of TEOS. Transmission electron microscopy (TEM) and UV-visible spectroscopy were employed to characterize the morphology and optical properties of the prepared Ag@SiO(2) nanoparticles, respectively. The prepared Ag@SiO(2) nanoparticles exhibited a change in surface plasmon absorption depending on the silica thickness. Compared to the conventional techniques based on Stöber method, which need 4-24 h for silica coating of Ag nanoparticles, this new technique is capable of synthesizing monodispersed, uniform and single core containing Ag@SiO(2) nanoparticles within very short reaction time. In addition, straightforward surface functionalization of the prepared Ag@SiO(2) nanoparticles with desired functional groups was performed to make the particles useful for many applications. The components of surface functionalized nanoparticles were examined by Fourier transform infrared (FT-IR) spectroscopy, zeta potential measurements and X-ray photoelectron spectroscopy (XPS).

Synthesis and characterization of ZnO-TiO2 nanocomposites and their application as photocatalysts

Nanocomposite ZnO-TiO2 powders of varying ZnO/TiO2 molar ratios have been prepared from their salt/compound by heating at 600°C and 900°C and characterized using scanning electron microscope and X-ray diffraction techniques. The nanosized powders can decolorize/degrade brilliant golden yellow (BGY), an azo dye extensively used in textile industries, in water under solar irradiation. The effects of various parameters such as photocatalyst loading, molar ratio of ZnO/TiO2, pH of the solution, initial dye concentration, and irradiation time on the photodecolorization have been investigated. ZnO-TiO2 nanocomposite (6 g/L) in the molar ratio of 1:1 or 3:1, prepared at 900°C, can efficiently decolorize about 98% of 20 mg/L BGY at pH of about 7 by 2-h illumination in sunlight. The initial dye decolorization follows pseudo-first-order kinetics. Finally, trial experiments were done using real textile wastewater to find out the effectiveness of the photocatalysts to a more complex system.

Sonochemical synthesis, photocatalytic activity and optical properties of silica coated ZnO nanoparticles

In this paper, we report the synthesis of silica coated ZnO nanoparticles by ultrasound irradiation of a mixture of dispersion of ZnO, tetraethoxysilane (TEOS), and ammonia in an ethanol-water solution medium. The silica coating layer formed at the initial TEOS/ZnO loading of 0.8 for 60 min ultrasonic irradiation was uniform and extended up to 3 nm from the ZnO surface as revealed from HR-TEM images. Silica coated ZnO nanoparticles demonstrated a significant inhibition of photocatalytic activity against photodegradation of methylene blue dye in aqueous solution. The effects of silica coating on the UV blocking property of ZnO nanoparticles were also studied.

Preparation of aminosilane–alginate hybrid microcapsules and their use for enzyme encapsulation

Organic–inorganic hybrid microcapsules (AP-capsules) were fabricated by sequential preparation of calcium alginate microcapsules (Alg-capsules), followed by the addition of the Alg-capsules to an aqueous solution of 3-aminopropyltriethoxysilane (APTES) in mild conditions without the use of any catalyst. Results showed that the shell thickness of AP-capsules was found to vary with time during the APTES incorporation onto the Alg-capsules, suggesting that the shell thickness was dependent on the amount of CaCl2 contained initially in the core solution as well as on the reaction time. A model enzyme, formate dehydrogenase (FDH), was successfully encapsulated in AP-capsules, and maximum efficiency of encapsulation was found with the capsule size of 1 mm diameter. The AP-capsules were reused efficiently for 10 cycles without loss of FDH activity. The approach developed in this study could evolve as a generic platform of enzyme immobilization for biotechnology applications using core–shell microcapsule technology.

Microcapsule with a heterogeneous catalyst for the methanolysis of rapeseed oil.

This study has demonstrated that microcapsules can be used as a microreactor for the transesterification of rapeseed oil with calcium oxide (CaO) base catalyst. CaO-loaded microcapsules were prepared by coextrusion technique, and the transesterification reaction was carried out by adding methanol into the prepared microcapsules and oil in a batch-type reactor. Results showed that the microcapsules system could promote the transesterification and hinder the dissolution of the catalyst, in contrast to a biodiesel production with CaO particles. The optimal conditions for methanol to oil molar ratio, catalyst content in the microcapsules and reaction temperature were found to be 8:1, 20 wt.%, and 65 °C, respectively. The results of reusability tests showed that CaO-loaded microcapsules could be successfully reused for three times without loss of the catalytic activity. It was concluded from these results that microcapsules have the potential to improve the performance of solid base catalyst for biodiesel production.