Muhamad Mat Salleh

Enriching the selectivity of metalloporphyrins chemical sensors by means of optical technique

Abstract In the electronic nose, the sensing elements must demonstrate high selectivity feature toward various kinds of gases. This paper reports the use of the optical technique to enrich the selectivity of four metallo-octaethyl porphyrins (with the metal atoms of Mn, Fe, Co and Ru) Langmuir–Blodgett (LB) films toward four vapor samples; 2-propanol, ethanol, acetone and cyclohexane. The optical system was developed using these materials as sensing elements and four LED’s of different colors; red, yellow, green and blue, as light sources. The sensing sensitivity was based on the change on the light intensity at the peak wavelength of light sources after being reflected by the films. The sensitivity of the films was observed to depend on the wavelength of the light source used and the metal atom at the center of the metalloporphyrins molecules. Each thin film produced four response signals or 16 signals for the whole system for a particular vapor. These 16 signals constituted the pattern of the “signature” of a vapor. The signature of each vapor was found to be different from each other. This work indicated that the amount of the sensing elements used to create a high selectivity gas sensor system may be reduced.

Controlled growth of silicon nanowires synthesized via solid-liquid-solid mechanism

The growth of silicon nanowires using solid—liquid—solid method is described. In this method, silicon substrates coated with a thin layer of gold were heat treated in nitrogen ambient. Gold particles started to diffuse into the silicon substrate and Au—Si alloy formed at the interface. The alloy would have molten to form liquid droplets on the substrate when temperature increases above their eutectic point, and more Si atoms diffused into these alloy droplets when heating continues. Rapid cooling of the droplet surface due to nitrogen flow into the chamber would eventually lead to the phase separation of silicon atoms from the surface of the alloy, created the nucleation and thus the growth of silicon nanowires. Controlled growth of the nanowire could be achieved by annealing the sample at 1000 ˚C with nitrogen flow rate set to around 1.5 l/min. The synthesized nanowires with diameter varied from 30 to 70 nm, were straight and grew along the N2 flow. Larger amount and longer nanowires were grown when longer period of heating was applied. Nanowires with lengths more than several hundreds of micrometers were achieved by annealing the sample for 4 h.

ZnO nanocubes with (1 0 1) basal plane photocatalyst prepared via a low-frequency ultrasonic assisted hydrolysis process

The crystallographic plane of the ZnO nanocrystals photocatalyst is considered as a key parameter for an effective photocatalysis, photoelectrochemical reaction and photosensitivity. In this paper, we report a simple method for the synthesis of a new (101) high-energy plane bounded ZnO nanocubes photocatalyst directly on the FTO surface, using a seed-mediated ultrasonic assisted hydrolysis process. In the typical procedure, high-density nanocubes and quasi-nanocubes can be grown on the substrate surface from a solution containing equimolar (0.04 M) zinc nitrate hydrate and hexamine. ZnO nanocubes, with average edge-length of ca. 50 nm, can be obtained on the surface in as quickly as 10 min. The heterogeneous photocatalytic property of the sample has been examined in the photodegradation of methyl orange (MO) by UV light irradiation. It was found that the ZnO nanocubes exhibit excellent catalytic and photocatalytic properties and demonstrate the photodegradation efficiency as high as 5.7 percent/μg mW. This is 200 times higher than those reported results using a relatively low-powered polychromatic UV light source (4 mW). The mechanism of ZnO nanocube formation using the present approach is discussed. The new-synthesized ZnO nanocubes with a unique (101) basal plane also find potential application in photoelectrochemical devices and sensing.

Optical sensing of capsicum aroma using four porphyrins derivatives thin films

Abstract The Langmuir–Blodgett thin films of n -tetraphenyl porphine iron (III) chloride, n -tetraphenyl porphine manganese (III) chloride, n -tetrakis (4-methoxyphenyl) porphine cobalt (II) and n -octaethyl porphine cobalt (II) mixed with arachidic acid were used as sensing elements for optical detection of capsicum (chili) aroma. The sensing sensitivity of aroma was based on changes of optical absorption of the films taken at four wavelengths i.e. 646, 615, 601 and 585 nm. The responses of the films upon aroma exposure were fast and recoverable. The patterns of the absorption changes were able to distinguish three capsicum samples; dried capsicum annum, fresh capsicum annum and capsicum minimum.

Optical properties of MoO3 thin films for electrochromic windows

Molybdenum oxide thin films have been used in microbatteries and other ionic devices. This paper reports the preparation of MoO3 by electron beam evaporation technique. The films were deposited onto glass substrates at temperatures in the range of 100–250°C. The films were characterized by studying their structure, electrical and optical properties. The films formed at 100°C are amorphous with conductivity of about 2.5×10−5 Ω−1 cm−1. The absorption spectrum of MoO3 doped with LiO2 varies with dopant which suggests that MoO3 is suitable for electrochromic films.The effect of deposition temperature on the optical and electrical properties of the films are discussed.

Efficient heterogeneous catalytic hydrogenation of acetone to isopropanol on semihollow and porous palladium nanocatalyst.

Highly efficient and remarkable selective acetone conversion to isopropanol has been achieved via a heterogeneous catalytic hydrogenation of acetone by NaBH4 in the presence of semihollow palladium nanoparticles (PdNPs) grown on ITO substrate. PdNPs with high surface defect grown on an indium tin oxide (ITO) surface were prepared via a simple immersion of the substrate into a solution containing K2PdCl6, sodium dodecyl sulphate (SDS), and formic acid for 2 h at room temperature. The sample showed remarkably high heterogeneous catalytic efficiency by producing 99.8% of isopropanol within 6 min using only 0.28 μg of PdNPs on the ITO surface. The present system exhibits heterogenenous catalytic hydrogenation efficiency 1 × 10(6) time higher than using the conventional Raney Ni system.

Ag–ZnO Nanoreactor Grown on FTO Substrate Exhibiting High Heterogeneous Photocatalytic Efficiency

This Research Article reports an unusually high efficiency heterogeneous photodegradation of methyl orange (MO) in the presence of Ag nanoparticle-loaded ZnO quasi-nanotube or nanoreactor (A-ZNRs) nanocatalyst grown on FTO substrate. In typical process, photodegradation efficiency of as high as 21.6% per μg per Watts of used catalyst and UV power can be normally obtained within only a 60-min reaction time from this system, which is 10(3) order higher than the reported results. This is equivalent to the turnover frequency of 360 mol mol(-1) h(-1). High-density hexagonal A-ZNRs catalysts were grown directly on FTO substrate via a seed-mediated microwave-assisted hydrolysis growth process utilizing Ag nanoparticle of approximately 3 nm in size as nanoseed and mixture aqueous solution of Zn(NO3)·6H2O, hexamethylenetetramine (HMT), and AgNO3 as the growth solution. A-ZNRs adopts hexagonal cross-section morphology with the inner surface of the reactor characterized by a rough and rugged structure. Transmission electron microscopy imaging shows the Ag nanoparticle grows interstitially in the ZnO nanoreactor structure. The high photocatalytic property of the A-ZNRs is associated with the highly active of inner sides surface of A-ZNRs and the oxidizing effect of Ag nanoparticle. The growth mechanism as well as the mechanism of the enhanced-photocatalytic performance of the A-ZNRs will be discussed.

Detection of Formaldehyde in Water: A Shape-Effect on the Plasmonic Sensing Properties of the Gold Nanoparticles

The effect of morphology on the plasmonic sensing of the presence of formaldehyde in water by gold nanostructures has been investigated. The gold nanostructures with two different morphologies, namely spherical and rod, were prepared using a seed-mediated method. In typical results, it was found that the plasmonic properties of gold nanostructures were very sensitive to the presence of formaldehyde in their surrounding medium by showing the change in both the plasmonic peaks position and the intensity. Spherical nanoparticles (GNS), for example, indicated an increase in the sensitivity when the size was increased from 25 to 35 nm and dramatically decreased when the size was further increased. An m value, the ratio between plasmonic peak shift and refractive index change, as high as 36.5 nm/RIU (refractive index unit) was obtained so far. An expanded sensing mode to FD was obtained when gold nanostructures with nanorods morphology (GNR) were used because of the presence of two plasmonic modes for response probing. However, in the present study, effective plasmonic peak shift was not observed due to the intense plasmonic coupling of closely packed nanorod structures on the surface. Nevertheless, the present results at least provide a potential strategy for response enhancement via shape-effects. High performance plasmonic sensors could be obtained if controlled arrays of nanorods can be prepared on the surface.

A simple route to vertical array of quasi-1D ZnO nanofilms on FTO surfaces: 1D-crystal growth of nanoseeds under ammonia-assisted hydrolysis process.

AbstractA simple method for the synthesis of ZnO nanofilms composed of vertical array of quasi-1D ZnO nanostructures (quasi-NRs) on the surface was demonstrated via a 1D crystal growth of the attached nanoseeds under a rapid hydrolysis process of zinc salts in the presence of ammonia at room temperature. In a typical procedure, by simply controlling the concentration of zinc acetate and ammonia in the reaction, a high density of vertically oriented nanorod-like morphology could be successfully obtained in a relatively short growth period (approximately 4 to 5 min) and at a room-temperature process. The average diameter and the length of the nanostructures are approximately 30 and 110 nm, respectively. The as-prepared quasi-NRs products were pure ZnO phase in nature without the presence of any zinc complexes as confirmed by the XRD characterisation. Room-temperature optical absorption spectroscopy exhibits the presence of two separate excitonic characters inferring that the as-prepared ZnO quasi-NRs are high-crystallinity properties in nature. The mechanism of growth for the ZnO quasi-NRs will be proposed. Due to their simplicity, the method should become a potential alternative for a rapid and cost-effective preparation of high-quality ZnO quasi-NRs nanofilms for use in photovoltaic or photocatalytics applications. PACS: 81.07.Bc; 81.16.-c; 81.07.Gf.

Characterization of multilayer graphene prepared from short-time processed graphite oxide flake

Multilayer graphene has been prepared by thermal reduction of graphene oxide film. The graphite oxide flake was first synthesized by using modified Hummers method with a relatively small amount of oxidizing agent and short-time processing at ambient temperature. The graphite oxide flake was dispersed in deionized water and deposited on quartz substrates to form graphene oxide film. The red shift of absorption peak and decrease of interlayer distance as interpreted from the X-ray diffraction spectrum indicate the formation of multilayer graphene. The resultant multilayer graphene has been successfully used as counter electrode in FTO/ZnO nanorods/electrolyte/multilayer graphene dye sensitized solar cell.