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Surface smoothing of metallic glasses by swift heavy ion irradiation
(Elsevier Ltd., 1999) Narayan, Himanshu; Agrawal, H. M.; Kushwaha, R. P. S.; Kanjilal, D.; Sharma, S. K.
Self supporting samples of Metglass 2204 (Ti50Be40Zr10) and substrate bound samples of Metglass 2705M (Co69B12Si12Fe4Mo2Ni1) have been irradiated with 260 MeV 107Ag and 130 MeV 28Si ions, respectively at liquid nitrogen temperature. The surfaces have been examined by Scanning Electron Microscopy prior to and after irradiation. It is found that the surfaces have been smoothened after irradiation in both cases. The heights of the ÔhillsÕ have been decreased and the ÔvalleysÕ have been ®lled, without any detectable mass loss. The observed surface smoothing has been explained on the basis of shear ¯ow mechanism within the framework of the viscoelastic model. Ó 1999 Elsevier Science B.V. All rights reserved.
An SEM and STM investigation of surface smoothing in 130 MeV Si-irradiated metglass MG2705M
(IOP Publishing Ltd, 1999) Narayan, Himanshu; Samanta, S. B.; Agrawal, H. M.; Kushwaha, R. P. S.; Kanjilal, D.; Sharma, S. K.; Narlikar, A. V.
Metglass MG2705M foils of about 17 m thickness were irradiated at 90 K by 130 MeV 28Si ions, up to a fluence of 1:154 1016 ions cm−2. The surface modifications induced by irradiation have been examined by scanning electron microscopy (SEM) and scanning tunnelling microscopy (STM). It has been observed that smoothing of the sample surface is evident in both SEM and STM micrographs. The SEM pictures show a decrease in the heights of the ‘hills’ and filling up of the ‘valleys’ on micrometre length scales. The STM pictures, on the other hand, show smoothing of scratchlike surface disorders at nanometre length scales. However, the electronic energy loss Se, of 5:75 keV nm−1, does not lead to detectable track diameters, in agreement with the existing results. The observations have been attributed to a large electronic energy deposition due to high fluence, and a subsequent local shear relaxation of the near surface atoms. The theory of shear flow mechanism has been extended further to explain the results.
Afm, stm and sts studies of grain boundaries And ion-beam induced defects in MGB2
(Nova Science Publishers, 2001-06) Narayan, Himanshu; Narlikar, A. V.; Herrmann, P. S. P.; Samanta, S. B.; Gupta, Anurag; Kanjilal, D.; Muranaka, T.; Akimitsu, J.; Vijayaraghavan, R.
Er1−yCayBa2Cu3−x(Fe, Zn)xO7−δ superconductors: a study of microstructure and resistive transitions in a dc magnetic field
(IOP Publishing Ltd, 2001-10-15) Chaudhuri, Sukalpa; Gupta, Anurag; Ganesan, V.; Das, I.; Kumar, Anil; Zaleski, A. J; Narayan, Himanshu; Narlikar, A. V.
We report an investigation of structure by x-ray diffraction, microstructure by atomic force microscopy (AFM) and broadening of resistive transitions in high dc magnetic fields (0–20 kOe) in Er1−yCayBa2Cu3−x(Fe, Zn)xO7−δ (y = 0.1, 0.2; and 0 x 0.20) ceramic superconductors. The XRD shows that the presence of Ca does not alter the known effect of Fe/Zn substitution on the structure of the pure (y = 0) system. Substitution of both Fe and Zn leads to a decrease in the grain size and micro-hardness. Interesting results were obtained on the influence of various dopants on the broadening of resistive transitions in dc magnetic fields, in general: (1) an increase in Ca content suppresses it; (2) Zn substitution has no effect; and (3) Fe substitution enhances it. We show that these results can be interpreted in terms of a thermally activated flux motion (TAFM), and the effect of various dopants on the properties like pinning barrier and anisotropy.
SEM, STM/STS and heavy ion irradiation studies on magnesium diboride superconductor
(Elsevier Ltd., 2002) Narayan, Himanshu; Samanta, S. B.; Gupta, Anurag; Narlikar, A. V.; Kishore, R.; Sood, K. N.; Kanjilal, D.; Muranaka, T.; Akimitsu, J.
We have presented here the results of SEM and STM/STS investigations carried out on MgB2 superconductor. The SEM pictures show porous surface and well-linked granular structure in which bigger grains (few micrometer size) seem to be agglomeration of smaller, nearly hexagonal grains (size nearly 100 nm). Hexagonal structure of Mg and B layers have been directly observed in atomically resolved STM images. The lattice constants have been determined to be aMg ¼ 3:1 AA, aB ¼ 1:7 AA and c ¼ 3:5 AA. Grain boundaries (GB) of width ranging from 50 to 200 AA have been observed. Absence of weak link effects despite wide GBs has been attributed to the metallic nature of the amorphous region of the GB interior as inferred from STS analysis. Irradiation with 200 MeV 107Ag ions gives tracks of about 65 AA in the bulk of the sample. This is expected to give higher value of critical current density owing to the flux pinning mechanism, which is related to possibility of wide practical application of this material.
A possible correlation between suppression of superconductivity, magnetic ordering and normal state resistivity parameters in the Yb1−xprxba2cu3o7−_ system
(World Scienti fic Publishing Company, 2002) Gupta, Anurag; Narayan, Himanshu; Lisboa-Filho, P. N.; Cardoso, C. A.; Moreira, Fernando M. Araujo; De Lima, O. F.; Narlikar, A. V.
Polycrystalline samples of the Pr doped Yb1−xPrxBa2Cu3O7− (i.e. Yb(Pr)-123) system for 0 x 1 have been investigated for resistivity and magnetization M as a function of temperature in normal and superconducting states. The gradual decrease in superconducting critical temperature Tc(x) is found to be correlated with the xdependent ratio of resistivity slope (d =dT )cc (corresponding to the linear (T) region) and residual resistivity 0. In particular, the observed di erence of critical Pr concentration where superconductivity is destroyed (xc) in Yb(Pr)-123 (xc 0:65) and Y(Pr)-123 (xc 0:55) matches with the di erence in the value of Pr concentration where the ratio (d =dT )cc= 0 tends to go to zero in them. The M(T) data of the Yb(Pr)-123 samples show magnetic ordering for x > xc at characteristic temperatures, Tn, that increase with x. Interestingly, the Yb(Pr)-123 sample with Pr content (x = 0:6) near xc reveals several anomalous features like transition from metallic to semiconducting-like (T), an excessive broadening of the diamagnetic transition and weakening of the M(T) signal related to antiferromagnetic ordering of Pr ions. These observations can be consistently interpreted by assuming the presence of dynamically fluctuating striped phase in these systems.
Grain boundaries as weak links: The case of MgB2 with reference to YNi2B2C
(The American Physical Society, 2002-02-20) Samanta, S. B.; Narayan, Himanshu; Gupta, Anurag; Narlikar, A. V.; Muranaka, T.; Akimitsu, J.
The grain boundaries ~GB’s! in the intermetallic superconductor MgB2 , interestingly, do not show suppression of supercurrent density. This unexpected behavior has been investigated by a scanning tunneling microscopy/spectroscopy technique at atomic resolution. The GB in MgB2 is seen as an amorphous region extending from ;50 to 200 Å and has a metallic character. This observation supports proximity coupling between the grains, which explains why supercurrent density does not degrade in this material. The results for another intermetallic superconductor YNi2B2C having GB’s ~average width ;30 Å! that are quasi-insulating in nature have also been presented and compared with the former.
A detailed investigation of surface modification in metallic glasses subjected to 130 MeV 28Si ion irradiation
(2002-05) Narayan, Himanshu; Samanta, S. B.; Agrawal, H. M.; Kushwaha, R. P. S.; Gupta, Anurag; Sharma, S. K.; Narlikar, A.V.; Kanjilal, D.
Surface modification induced in four metallic glasses by4.64 MeV/u 28Si ion irradiation has been investigated in detail using optical microscopy, SEM and STM. Results obtained in two separate runs have been presented here. The effects of ion fluence (/) and tilt angle (h) on surface modification have been studied both qualitativelyand quantitatively. It has been found that for Se values smaller than that for track formation, swift heavyion irradiation leads to smoothing of the irradiated surfaces. The smoothing is evident from decreasing mean roughness Rq and reduction in height of the hills and filling up of the valleys in the SEM and STM pictures. The observations have been explained on the basis of the theoryof shear flow within the framework of the viscoelastic model.
Study of magnetization and pinning mechanisms in MgB2 thin film superconductors: effect of heavy ion irradiation
(IOP Publishing Ltd, 2003) Narayan, Himanshu; Gupta, Anurag; Astill, D.; Kanjilal, D.; Ferdeghini, C.; Paranthaman, M.; Narlikar, A. V.
We report magnetization studies on MgB2 superconducting thin films in a temperature range 4.2–40 K and magnetic field range 0–6 T. Thin films prepared by both pulsed laser deposition (PLD) and electron beam evaporation (EBE) methods were investigated. In addition, both films were studied before and after heavy ion irradiation by 200 MeV Ag ions with a dose of 1011 ions cm−2. Variation of sweep rates during the measurement of the magnetization loop reveals the presence of flux creep in both films. The PLD film, after irradiation, shows a severe degradation of Tc, critical current densities (Jc) in low fields and irreversibility line (B∗(T )). In contrast, the EBE film shows a slight enhancement in Tc, and nearly no change in Jc(B) and the position of irreversibility line after irradiation. For both pristine films, the obtained volume pinning forces Fp versus reduced field b = B/B∗ shows a good scaling for T 10 K, which matches well with the theoretical curve based on the flux line shear (FLS) pinning model. These and other results can be interpreted in terms of grain boundaries in MgB2 films acting as FLS channels.
Study of microstructural changes in MgB2 thin film superconductors irradiated with 200 MeV 107Ag ions
(IOP Publishing Ltd, 2004-06-18) Narayan, Himanshu; Gupta, Anurag; Narlikar, A. V.; Sood, K. N.; Kishore, R.
MgB2 superconductor thin films, prepared by pulsed laser deposition (PLD) and electron beam evaporation (EBE), have been investigated by scanning electron microscopy (SEM) before and after 200 MeV 107Ag ion irradiation. The severe degradation of superconducting properties in irradiated PLD film and the absence of the same in EBE film correlates with the observed changes in their microstructures. The micrographs of the PLD film show an overall smoothing, flow pattern and reduction in size of the bigger agglomerates after irradiation. On the other hand, the microstructure of the EBE film does not show any significant change after irradiation. The flow pattern observed in the PLD film can be understood on the basis of the viscoelastic model for irradiation induced shear flow in amorphous solids. The observed degradation of the PLD film may thus be attributed primarily to its disordered nature under irradiation, whereas the radiation hardness of the EBE film may be due to its higher crystallinity.
Phase formation and superconductivity of fe-tube encapsulated and vacuum-annealed MgB2
(World Scienti fic Publishing Company, 2006) Singh, K. P.; Awana, V. P. S.; Shahabuddin, M. D.; Husain, M.; Saxena, R. B.; Nigam, Rashmi; Ansari, M. A.; Gupta, Anurag; Narayan, Himanshu; Halder, S. K.; Kishan, H.
We report optimization of the synthesis parameters viz. heating temperature (TH), and hold time (thold) for vacuum-annealed (10􀀀5 Torr) and LN2 (liquid nitrogen) quenched MgB2 compound. These are single-phase compounds crystallizing in the hexagonal struc- ture (space group P6=mmm) at room temperature. Our XRD results indicated that for phase-pure MgB2, the TH for 10􀀀5 Torr annealed and LN2-quenched samples is 750 C. The right stoichiometry i.e., MgB2 of the compound corresponding to 10􀀀5 Torr and TH of 750 C is found for the hold time (thold) of 2.30 hours. With varying thold from 1{4 hours at xed TH (750 C) and vacuum (10􀀀5 Torr), the c-lattice parameter decreases rst and later increases with thold (hours) before a near saturation, while the a-lattice parameter rst increases and later decreases beyond a thold of 2.30 hours. The c=a ratio versus thold plot showed an inverted bell-shaped curve, touching the lowest value of 1.141, which is the reported value for perfect stoichiometry of MgB2. The optimized stoichi- metric MgB2 compound exhibited superconductivity at 39.2 K with a transition width of 0.6 K. In conclusion, the synthesis parameters for phase pure stoichimetric vacuum- annealed MgB2 compound are optimized and are compared with widely-reported Ta tube encapsulated samples.
Application of solution state NMR to structural problems in chemistry
(Durham University, 2006-09) Khoabane, Ntai Martin; Dr. Sanderson, John; Dr. Grayson, Elizabeth; Dr. Natrajan, Louise; Mr. McKeag, Ian; Mrs. Heffernan, Catherine
First and foremost I would like to thank the Lord almighty for the life he has given me. My stay and study at Durham University was funded and supported by Canon Collins Trust to whom I am very thankful. I would also like to pass my gratitude to the National University of Lesotho for releasing me on staff development leave, my dependants’ allowance, and funding my travel both ways. I would like to thank my supervisory team: Dr. Alan M. Kenwright for his supervision and training and demonstrated kindness and patience. He motivated and encouradme during this period. I am also grateful to him for coming up with original ideas of a project on which I worked. Dr. John Sanderson cannot be forgotten for his co-supervisory role. I am also grateful to Dr. Elizabeth Grayson for the supervision in chemistry and for the protection and deprotection of the mannoside compounds. Dr. Louise Natrajan, I thank you for the lanthanide complexes I worked on. I would also like to thank Mr. Ian McKeag and Mrs Catherine Heffernan who contributed a lot to my training in solution state NMR. Other groups of people who contributed to my training need to be mentioned: all my lectures in the taught modules, the mass spectrometry facility and all the Chemistry Department staff. Last but not least my family members. Most importantly my wife and son who suffered the loneliness of my being thousands of miles away from them without complaint. Nuclear Magnetic Resonance (NMR) spectroscopy is a robust, non invasive technique applicable in structure determination as well as in the study of dynamic behaviour of chemical compounds. This thesis is in two sections, the first dealing mainly with a structure determination application of NMR and the second dealing mainly with a study of dynamic behaviour. Section 1 NMR characterisation of carbohydrates has proved challenging because of the limited chemical shift ranges of both the proton and carbon signals. The broad signals due to the labile hydroxyl protons cause further complications by overlapping proton signals from the ring. Protecting group chemistry is vital in the preparation and manipulation of synthetic carbohydrates and can potentially help with the assignment of the (otherwise extremely complicated) NMR spectra of carbohydrates. However, the widely used benzyl protecting group can make the spectrum more difficult to interpret because the benzyl CH2 proton signals often come in the same region of the spectrum as the anomeric protons, usually used as reporter groups of carbohydrates and the benzyl CH2 carbon signals come in the same region as the carbohydrate ring carbons. This section reports the invetsigation and application of a family of alternative protecting groups, namely various fluorobenzyl groups, which have not been used in carbohydrate chemistry before. With pentafluorobenzyl, the proton chemical shift dispersion is improved, and the CH2 and carbohydrate ring carbon signals are shifted to lower frequency, considerably simplifying the task of assigning the carbon spectrum, facilitating the interpretation of all 1H-13C correlation experiments (HSQC, HMQC, HMBC). Section 2 Cyclen complexes of lanthanide (III) ions have found use in magnetic resonance imaging (MRI), luminescence imaging and assay studies. In particular, europium (III) complexes have potential in anlytical, forensic, and biomedical applications based on their impressive emissive properties. However, the emissive properties are modulated by the thermodynamic stability and kinetic inertness of the complexes. For biomedical applications, chelation is necessary to avoid europium toxicity that may be triggerd by accidental dissociation of the complex and release of the metal in vivo. A new cyclen europium(III) complex with pyridyl pendant ligands instead of the usual acetate groups has been synthesised by a group at Manchester University. The pyridyl ligands confer higher emmisive intensities to the complex, to enable applicability of the complex in time gated measurements. The chemical structure determination of the compound was accomplished by 1H, 13C, COSY, HMQC / HSQC and EXSY NMR experiments. Selective inversion experiments data were evaluated using the CIFIT simulation program, and showed that in aqueous solutions from -0.2º C to 107.6º C the dominant dynamic process is flipping of the pendant (pyridyl) arms, and isomerism is biased towards the twisted square antiprism (TSAP).
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, Himanshu
Polyaniline (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.
Swift heavy ion irradiation of MgB2 thin films: a comparison between gold and silver ion irradiations
(2007) Narayan, Himanshu; Agrawal, H. M.; Kushwaha, R. P. S.; Kishan, H.; Bhatt, Ravindra K.
The effect of 200 MeV Au ion irradiation on the temperature and field dependence of the critical current density, Jc, of MgB2 thin films on sapphire substrates is reported. The results have been presented in comparison with those obtained after 200 MeV Ag ion irradiation of a similar film. After irradiation, the critical temperature Tc decreased for all samples except for the one with a higher dose of gold ions, where it increased marginally. This observation was also confirmed from measurements of magnetization as a function of temperature with a constant applied field of 10−2 T. The critical current density, Jc, was estimated from the widths of magnetization loops using Bean’s critical state model. It has been found that Jc increases after irradiation, the enhancement being more pronounced for the Au ion irradiation. The higher enhancement of Jc by Au ion irradiation may be attributed to higher flux-pinning efficiency of the irradiated samples. It has been concluded that, although the flux-line shear (FLS) model satisfactorily explains the silver ion irradiation induced enhancement of Jc, some other mechanisms also seem to play a role in the Jc enhancement by gold ion irradiation.
Control of Penicillium digitatum on Citrus Fruit Using Two Plant Extracts and Study of Their Mode of Action
(Springer, 2007-05-07) Mekbib, Sissay Bekele; Regnier, Thierry J. C.; Korsten, Lise
Extracts from two plants from Ethiopia, Withania somnifera and Acacia seyal, were evaluated for their potential as natural biopesticides and to study their mode of action. Methanolic extracts of these plants were tested in vivo on citrus fruit for their efficacy to control Penicillium digitatum when applied on wounded or unwounded fruit surfaces. Relative to the control, 70% and 75% of wound – inoculated fruit did not develop decay symptoms for up to 21 days of storage at 25◦C and >85% r.h. An increase in cell wall-bound phenolics was evident in wounded fruit treated with plant extracts and inoculated with a spore suspension of P. digitatum. Scanning electron microscopy revealed deposition of crystalline plant material sticking to the pathogen and around the wound site. The application of the plant extracts increased the epiphytic background total microbial population but decreased diversity. KEY WORDS: Citrus fruit; postharvest diseases; natural compounds; plant phenolics; host resistance.
Hopping photoconductivity and the effectiveness of phonon detection in GaAs:Zn bolometers
(Elsevier Ltd., 2008-03-03) Taele, B. M.; Narayan, Himanshu; Mukaro, R.
We have studied the effect of white light on hopping conduction and the effectiveness of non-equilibrium phonon detection in Zndoped GaAs bolometers over the temperature range 1.35 K 6 T 6 2.15 K. The temperature dependence of the low electric field resistance indicates that the mechanism of conduction is due to variable range hopping. Using a heat-pulse technique we show that the sensitivity of a GaAs:Zn bolometer with an acceptor concentration, na = 4.2 1017 cm 3 is significantly enhanced in the presence of suitably applied irradiation, despite the value of its temperature coefficient of resistance, aðTÞ ¼ ð1=RÞðoR=oT Þ, actually being decreased by light. It is proposed that the effect of light is to populate excited states of the acceptors, which have larger wave functions and hence show enhanced hopping.
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.
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.
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, Madhavi
The 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.
Evaluation of Ethiopian plant extracts, Acacia seyal and Withania somnifera, to control green mould and ensure quality maintenance of citrus (Citrus sinensis L.)
(EDP Sciences, 2009) Mekbib, Sissay Bekele; Regnier; Thierry, J. C.; Korsten, Lise; Sivakumar, Dharini
Green mould, Penicillium digitatum (Pers.: Fr.) Sacc., causes economically important postharvest disease in citrus. Materials and methods. Ethiopian plant extracts of Acacia seyal (Del. Var. Seyal) and Withania somnifera (L.) Dual were used to test the control of green mould in wound-inoculated fruit, stored for 21 d at 7 °C and at > 85% RH. The chemical compositions of the two extracts were determined using high-performance chromatography. Thereafter, freshly harvested (naturally infected) fruit were subjected to different postharvest treatments and stored for 50 d to investigate the effects of the two plant extracts on fruit quality parameters. Treatments included (pre-wax + leaf extracts), (wax + leaf extracts incorporated into wax, Citrosol A®), (leaf extract alone), (fruit washed in chlorinated water at 5.25%), (untreated fruit) and (commercially treated fruit). Results. Extracts of A. seyal and W. somnifera reduced the incidence of green mould by 56.1% and 50%, respectively, in wound-inoculated fruit. A. seyal extract contained a high concentration of gallic acid (60.3 mg·mL–1) whilst W. somnifera contained low concentrations of caffeic acid (8.7 mg·mL–1), salicylic acid (6.3 mg·mL–1) and 3,4 dihydroxy benzoic acid (3.8 mg·mL–1). Green mould was absent in naturally infected fruit subjected to (pre-wax + leaf extracts), (wax mixed with leaf extracts) and (leaf extracts) treatments. (Pre-wax + leaf extracts) and (wax mixed with leaf extract) treatments significantly reduced weight loss; retained firmness and colour; and they maintained eating qualities and a maturity index (SSC/TA) similar to commercial treatment. Conclusion. Both extracts of A. seyal and W. somnifera showed potential to be used as an alternative in combined applications with wax application under low temperature storage to replace synthetic fungicides, to ultimately control green mould and retain overall fruit quality.

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