Muhammad Yahaya

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.

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.

Solution-Processed Ga-Doped ZnO Nanorod Arrays as Electron Acceptors in Organic Solar Cells

This paper reports the utilization of ZnO nanorod arrays (NRAs) doped with various concentrations of Ga (0, 0.5, 1, 2, and 3 at %) as electron acceptors in organic solar cells. The donor, poly(3-hexylthiophene) (P3HT), was spin coated onto Ga-doped ZnO NRAs that were grown on fluorine-doped tin oxide (FTO) substrates, followed by the deposition of a Ag electrode by a magnetron sputtering method. Adjusting the Ga precursor concentration allowed for the control of the structural and optical properties of ZnO NRAs. The short circuit current density increased with increasing Ga concentration from 0 to 1 at %, mainly because of improved exciton dissociation and increased charge extraction. Meanwhile, the reduced charge recombination and lower hole leakage current led to an increase in the open circuit voltage with Ga concentrations up to 1 at %. The device with the optimum Ga concentration of 1 at % exhibited power conversion efficiency nearly three times higher compared to the device without Ga doping. This finding suggests that the incorporation of Ga can be a simple and effective approach to improve the photovoltaic performance of organic solar cells.

Controlled Defects of Fluorine-incorporated ZnO Nanorods for Photovoltaic Enhancement

Anion passivation effect on metal-oxide nano-architecture offers a highly controllable platform for improving charge selectivity and extraction, with direct relevance to their implementation in hybrid solar cells. In current work, we demonstrated the incorporation of fluorine (F) as an anion dopant to address the defect-rich nature of ZnO nanorods (ZNR) and improve the feasibility of its role as electron acceptor. The detailed morphology evolution and defect engineering on ZNR were studied as a function of F-doping concentration (x). Specifically, the rod-shaped arrays of ZnO were transformed into taper-shaped arrays at high x. A hypsochromic shift was observed in optical energy band gap due to the Burstein-Moss effect. A substantial suppression on intrinsic defects in ZnO lattice directly epitomized the novel role of fluorine as an oxygen defect quencher. The results show that 10-FZNR/P3HT device exhibited two-fold higher power conversion efficiency than the pristine ZNR/P3HT device, primarily due to the reduced Schottky defects and charge transfer barrier. Essentially, the reported findings yielded insights on the functions of fluorine on (i) surface –OH passivation, (ii) oxygen vacancies (Vo) occupation and (iii) lattice oxygen substitution, thereby enhancing the photo-physical processes, carrier mobility and concentration of FZNR based device.

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.

Enhancement of ZnO nanorod arrays-based inverted type hybrid organic solar cell using spin-coated Eosin-Y

This paper reports the effect of Eosin-Y coating concentration on the performance of inverted type hybrid organic solar cell based on ZnO nanorod arrays and poly(3-hexylthiophene-2,5-diyl) (P3HT). The Eosin-Y solution with concentrations of 0.05, 0.2, 2.0 and 5.0 mM was spin-coated onto the ZnO nanorod arrays grown on the fluorine-doped tin oxide glass substrate. The P3HT film was then spin-coated onto Eosin-Y-coated ZnO nanorod arrays, followed by deposition of silver (Ag) as anode using magnetron sputtering technique. The short circuit current density increased with the Eosin-Y coating concentration up to 0.2 mM, after which it started to decrease, mainly due to the aggregation of Eosin-Y which reduced the charge extraction from P3HT to ZnO. Meanwhile, the open circuit voltage increased with the Eosin-Y coating concentration, indicating reduced back charge recombination of electron on the ZnO and hole on the P3HT, as well as reduced leakage current through the direct contact between the ZnO nanorods and the Ag metal contact. The power conversion efficiency of the device with the optimum coating concentration was approximately eight times higher than that without Eosin-Y modification.