Browsing by Author "Alemu, Hailemichael"
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Item Fast and complete degradation of Congo red under visible light with Er3+ and Nd3+ ions doped TiO2 nanocomposites(PAGEPress, 2012) Narayan, Himanshu; Alemu, Hailemichael; Alotsi, Ntjamang Daniel; Macheli, Lebohang; Thakurdesai, Madhavi; Jaybhaye, Sandesh; Singh, ArvindWe report fast and complete destruction of the dye Congo red (CR) under visible light in the presence of Nd3+ and Er3+ doped TiO2 nanocomposites (NCs). TiO2 NCs with general composition TiO2[R2O3]x, {x=0.1, 0.2; R≡ Nd, Er} and particle size 12-16 nm were synthesized through co-precipitation/hydrolysis (CPH). A set of similar composites was also prepared through solid state reaction (SSR) route, which produced 31- 47 nm particles. After characterization, visible light photocatalytic activity of all the samples was recorded for the degradation of CR. NCs with molar concentration x=0.2 of both doping types produced close to 100% degradation in 180 min. The apparent rate constant (kobs) was found to be 2.91×10–2 min–1 and 2.36×10–2 min–1, for these Nd3+ and Er3+ doped NCs, respectively. The other NCs with x=0.1, also showed significant degradation of CR, but the samples prepared through SSR performed worse. The excellent degradation obtained with the NCs may be attributed to their small particle size. Moreover, the doping of Nd3+ and Er3+ ions further supported the photocatalysis through formation of intermediate energy levels within the band gap of TiO2. These new levels not only acted as electron traps for efficient suppression of the undesired e–/h+ recombination, but also facilitated to a certain extent the absorption of visible irradiation.Item Fly ash composites with polyaniline: Synthesis, characterization and conductivity measurements(Nova Science Publishers, 2009) Narayan, Himanshu; Alemu, Hailemichael; Somerset, Vernon S.; Iwuoha, Emmanuel I.; Hernández, Monica L.; Hernández, July A.; Montaño, Angela M.; Henao, José A.In the past few decades, Fly Ash (FA) has rapidly emerged as one of the most costeffective and environment friendly resources rather than just being a waste material. A number of novel applications have been identified and are being exploited as well. The pozzolanic properties of FA make it a suitable candidate for cement replacement, as well as for the production of ceramics and glasses to be used as construction material. It can be utilized in the construction of embankments and structural fill; waste stabilization and solidification; mine reclamation; road sub-base; aggregate and mineral filler in asphalt concrete; soil amendment of soft soil and to increase bioavailability of nutrients in the soils, as well as adsorbent for heavy toxic metals. Other applications include production of roofing tiles, paints, metal casting, and as filler in wood and plastic products. Alkali rich FA can be used to neutralize the waste water from Acid Mine Drainage (AMD). Most of the current applications of FA, however, are primarily based on its microstructure and chemical composition only. Other physical and chemical properties of FA, and of the materials based on it, could possibly be utilized in other practical applications also. With this idea, we report in this chapter about the synthesis and characterization of a composite made of FA together with a very common conducting polymer: Polyaniline (PANI). The polyaniline/fly ash (PANI/FA) composites with various concentrations (20, 40 and 50 %wt) of fly ash were synthesized by the process of in-situ polymerization, by aging the starting materials (aniline and FA) before oxidative polymerization, and also by including poly-(styrene sulphonic acid) (PSSA). It was found that the process of aging assisted the composites to self-organize as nanotubes (crosssectional diameters of 50-110 nm), and that involving PSSA, produced nanorods and nanofibres (diameters of 100-500 nm, length up to 10 μm). Powder X-ray diffraction (XRD), scanning electron microscopy (SEM), UV-vis spectroscopy, Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) were used to characterize the samples. Further, electrochemical analysis was performed and the dc-conductivity of the samples was measured as a function of temperature in the range 80-290 K. An expected decrease of conductivity was observed with addition of FA into PANI. The temperature dependence of the dc-conductivity for pure PANI and FA/PANI composites has been explained on the basis of the quasi one-dimensional variable range hopping (quasi-1D VRH) model. Excellent agreement was found between the experimental data and the theory.Item Role of particle size in visible light photocatalysis of Congo Red using TiO2⋅[ZnFe2O4]x nanocomposites(Springer-Verlag, 2009) Narayan, Himanshu; Alemu, Hailemichael; Macheli, Lebohang; Sekota, 'Mantoa; Thakurdesai, Madhavi; Gundu Rao, T. K.TiO2⋅[ZnFe2O4]x (x = 0⋅0–0⋅5) nanocomposites (NCs) with an average particle size of 72⋅4 nm were synthesized by the method of co-precipitation/hydrolysis (CPH). For the comparison of particle-size dependent effects, a set of polycrystalline samples with similar compositions was also prepared by solid state reaction (SSR) route. Average particle size for SSR prepared samples was about 3⋅0 μm. All the samples were characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), particle size analyzer, Raman spectroscopy and Fourier transform infra-red (FTIR) spectroscopy. Their visible light photocatalytic activity was tested for the degradation of Congo Red dye. Maximum photodegradation was observed for the NC with x = 0⋅1 synthesized by CPH (particle size, 71 nm). Similar composition prepared by SSR method (particle size, 6⋅19 μm) showed lower photoactivity in comparison even with that observed for pure TiO2 (particle size, 4⋅03 μm). It was, therefore, concluded that enhanced photodegradation is directly related to the reduced particle size of the composites, which implies that photosensitization is the process primarily involved. Although, doping of TiO2 with ZnFe2O4 does extend the cut-off wavelength towards visible parts of the spectrum, its contribution in the enhancement is not as significant as that due to the photosensitization.Item Synthesis and characterization of Y3+-doped TiO2 nanocomposites for photocatalytic applications(IOP Publishing Ltd, 2009) Macheli, Lebohang; Narayan, Himanshu; Alemu, Hailemichael; Gundu Rao, T. K.; Thakurdesai, MadhaviThe TiO2·[Y2O3]x (x = 0.1–0.4) nanocomposites (NCs) with an average particle size of 74 nm were prepared by the method of chemical co-precipitation followed by hydrolysis (CPH). Their visible light photocatalytic activity was investigated for the degradation of congo red (CR) dye. All NCs showed improved degradation as compared to the polycrystalline samples of similar compositions prepared by the solid-state reaction (SSR) route (average particle size of a few micrometers), as well as to the pure TiO2. The better photocatalytic activity of the NCs was attributed to their smaller particle size. Another comparison of the results with those obtained with Zn2+/Fe3+ ions co-doped TiO2 NCs, under similar experimental conditions, revealed that in the Y3+-doped NCs, particle size might not be the only factor responsible for the improved photocatalytic properties. It was concluded that the Y3+ ion-mediated suppression of the unwanted e−/h+ recombination could be the possible factor leading to additional enhancement.Item Synthesis, characterization and conductivity measurements of polyaniline and polyaniline/fly-ash composites(WILEY-VCH Verlag GmbH & Co., 2006-10-24) Iwuoha, Emmanuel I.; Alemu, Hailemichael; Narayan, HimanshuPolyaniline (PANI) and polyaniline/fly ash (PANI/FA) composites with various concentrations of fly ash (20%, 40% and 50%) were synthesized by the process of in-situ polymerization. The samples were characterized by powder X-ray diffraction, thermogravimetric analysis, infrared spectroscopy, and scanning electron microscopy. Moreover, the dc conductivity of the samples was measured as a function of temperature in the range 80–290 K and it was found that the addition of FA decreases the conductivity. The temperature dependence of the dc conductivity for PANI and FA/PANI composites has been explained on the basis of the quasi one-dimensional variable hopping model. A very good agreement was found between the experimental data and the theory.