Nanostructured metal oxides as adsorbents and photocatalysts

This research underlines the extensive application of nanostructured metal oxides in environmental systems such as hazardous waste remediation and water purification. This study tries to forge a new understanding of the complexity of adsorption and photocatalysis in the process of water treatment. Sodium niobate doped with a different amount of tantalum, was prepared via a hydrothermal reaction and was observed to be able to adsorb highly hazardous bivalent radioactive isotopes such as Sr2+ and Ra2+ions. This study facilitates the preparation of Nb-based adsorbents for efficiently removing toxic radioactive ions from contaminated water and also identifies the importance of understanding the influence of heterovalent substitution in microporous frameworks. Clay adsorbents were prepared via a two-step method to remove anionic and non-ionic herbicides from water. Firstly, layered beidellite clay was treated with acid in a hydrothermal process; secondly, common silane coupling agents, 3-chloro-propyl trimethoxysilane or triethoxy silane, were grafted onto the acid treated samples to prepare the adsorption materials. In order to isolate the effect of the clay surface, we compared the adsorption property of clay adsorbents with ƒ×-Al2O3 nanofibres grafted with the same functional groups. Thin alumina (£^-Al2O3) nanofibres were modified by the grafting of two organosilane agents 3-chloropropyltriethoxysilane and octyl triethoxysilane onto the surface, for the adsorptive removal of alachlor and imazaquin herbicides from water. The formation of organic groups during the functionalisation process established super hydrophobic sites along the surfaces and those non-polar regions of the surfaces were able to make close contact with the organic pollutants. A new structure of anatase crystals linked to clay fragments was synthesised by the reaction of TiOSO4 with laponite clay for the degradation of pesticides. Based on the Ti/clay ratio, these new catalysts showed a high degradation rate when compared with P25. Moreover, immobilized TiO2 on laponite clay fragments could be readily separated out from a slurry system after the photocatalytic reaction. Using a series of partial phase transition methods, an effective catalyst with fibril morphology was prepared for the degradation of different types of phenols and trace amount of herbicides from water. Both H-titanate and TiO2-(B) fibres coated with anatase nanocrystal were studied. When compared with a laponite clay photocatalyst, it was found that anatase dotted TiO2-(B) fibres prepared by a 45 h hydrothermal treatment followed by calcination were not only superior in performance in photocatalysis but could also be readily separated from a slurry system after photocatalytic reactions. This study has laid the foundation for the development of the ability to fabricate highly efficient nanostructured solids for the removal of radioactive ions and organic pollutants from contaminated water. These results now seem set to contribute to the development of advanced water purification devices in the future. These modified nanostructured materials with unusual properties have broadened their application range beyond their traditional use as adsorbents, to also encompass the storage of nuclear waste after concentrating from contaminated water.

Proton-transfer compounds of isnipecotamide with the aromatic dicarboxylic acids 4-nitrophthalic, 4,5-dichlorophthalic, 5-nitroisophthalic and terephthalic acid

The structures of the 1:1 proton-transfer compounds of isonipecotamide (4-piperidinecarboxamide) with 4-nitrophthalic acid, 4-carbamoylpiperidinium 2-carboxy-4-nitrobenzoate, C6H13N2O8+ C8H4O6- (I), 4,5-dichlorophthalic acid, 4-carbamoylpiperidinium 2-carboxy-4,5-dichlorobenzoate, C6H13N2O8+ C8H3Cl2O4- (II) and 5-nitroisophthalic acid, 4-carbamoylpiperidinium 3-carboxy-5-nitrobenzoate, C6H13N2O8+ C8H4O6- (III) as well as the 2:1 compound with terephthalic acid, bis(4-carbamoylpiperidinium)benzene-1,2-dicarboxylate dihydrate, 2(C6H13N2O8+) C8H4O42- . 2H2O (IV)have been determined at 200 K. All salts form hydrogen-bonded structures, one-dimensional in (II) and three-dimensional in (I), (III) and (IV). In (I) and (III) the centrosymmetric R2/2(8) cyclic amide-amide association is found while in (IV) several different types of water-bridged cyclic associations are present [graph sets R2/4(8), R3/4(10), R4/4(12), R3/3(18) and R4/6(22)]. The one-dimensional structure of (I), features the common 'planar' hydrogen 4,5-dichlorophthalate anion together with enlarged cyclic R3/3(13) and R3/4(17) associations. With the structures of (I) and (III) the presence of head-to-tail hydrogen phthalate chain substructures is found. In (IV) head-to-tail primary cation-anion associations are extended longitudinally into chains through the water-bridged cation associations and laterally by piperidinium N-H...O(carboxyl) and water O-H...O(carboxyl) hydrogen bonds. The structures reported here further demonstrate the utility of the isonipecotamide cation as a synthon for the generation of stable hydrogen-bonded structures. An additional example of cation--anion association with this cation is also shown in the asymmetric three-centre piperidinium N-H...O,O'(carboxyl) interaction in the first-reported structure of a 2:1 isonipecotamide-carboxylate salt.

High-pressure Raman spectroscopic and other structural studies of hydrotalcites containing intercalated dicarboxylic acid anions

The results of pressure-tuning Raman spectroscopic, X-ray powder diffraction and solid-state 13C-NMR studies of selected dicarboxylate anions intercalated in a Mg-Al layered double hydroxide (talcite) lattice are reported. The pressure dependences of the vibrational modes are linear for pressures up to 4.6 GPa indicating that no phase transitions occur. The interlayer spacings show that the oxalate, malonate and succinate dianions are oriented perpendicular to the layers, but the glutarate and adipate are tilted. The solid-state 13C-NMR spectra of these materials show full chemical shift anisotropy and, therefore, the anions are not mobile at room temperature.

Photocatalytic hydrogen production with iron oxide under solar irradiation

As solar hydrogen is a sustainable and environmental friendly energy carrier, it is considered to take the place of fossil fuels in the near future. Solar hydrogen can be generated by splitting of water under solar light illumination. In this study, the use of nanostructured hematite thin-film electrodes in photocatalytic water splitting was investigated. Hematite (á-Fe2O3) has a narrow band-gap of 2.2 eV, which is able to utilise approximately 40% of solar radiation. However, poor photoelectrochemical performance is observed for hematite due to low electrical conductivity and a high rate of electron-hole recombination. An extensive review of useful measures taken to overcoming the disadvantages of hematite so as to enhance its performance was presented including thin-film structure, nanostructuring, doping, etc. Since semiconductoring materials which exhibit an inverse opal structure are expected to have a high surface-volume ratio, unique optical characteristics and a shorter distance for photogenerated holes to travel to the electrode/electrolyte interface, inverse opals of hematite thin films deposited on FTO glass substrate were successfully prepared by doctor blading using PMMA as a template. However, due to the poor adhesion of the films, an acidic medium (i.e., 2 M HCl) was employed to significantly enhance the adhesion of the films, which completely destroyed the inverse opal structure. Therefore, undoped, Ti and Zn-doped hematite thin films deposied on FTO glass substrate without an inverse opal structure were prepared by doctor blading and spray pyrolysis and characterised using SEM, EDX, XRD, TGA, UV-Vis spectroscopy and photoelectrochemical measurements. Regarding the doped hematite thin films prepared by doctor blading, the photoelectrochemical activity of the hematite photoelectrodes was improved by incorporation of Ti, most likely owing to the increased electrical conductivity of the films, the stabilisation of oxygen vacancies by Ti4+ ions and the increased electric field of the space charge layer. A highest photoresponse was recorded in case of 2.5 at.% Ti which seemed to be an optimal concentration. The effect of doping content, thickness, and calcination temperature on the performance of the Ti-doped photoelectrodes was investigated. Also, the photoactivity of the 2.5 at.% Ti-doped samples was examined in two different types of electrochemical cells. Zn doping did not enhance the photoactivity of the hematite thin films though Zn seemed to enhance the hole transport due to the slow hole mobility of hematite which could not be overcome by the enhancement. The poor performance was also obtained for the Ti-doped samples prepared by spray pyrolysis, which appeared to be a result of introduction of impurities from the metallic parts of the spray gun in an acidic medium. Further characterisation of the thin-film electrodes is required to explain the mechanism by which enhanced performance was obtained for Ti-doped electrodes (doctor blading) and poor photoactivity for Zn and Ti-doped samples which were synthesised by doctor blading and spray pyrolysis, respectively. Ti-doped hematite thin films will be synthesised in another way, such as dip coating so as to maintain an inverse opal structure as well as well adhesion. Also, a comparative study of the films will be carried out.

Oral intake and serum levels of ascorbic acid in continuous ambulatory peritoneal dialysis patients

Oral intake of ascorbic acid is essential for optimum health in human beings. Continuous ambulatory peritoneal dialysis (CAPD) patients have an increased need for ascorbic acid, because of increased loss through dialysate, reduced intake owing to nausea and loss of appetite, and increased oxidative stress. However, optimum intake is still controversial. We studied 50 clinically stable patients to determine the relationship between oral ascorbic acid intake and serum ascorbic acid (SAA) level. Total oral intake ranged from 28 mg daily to 412 mg daily. Only one patient had an oral intake of ascorbic acid below 60 mg per day. The SAA levels ranged from 1 mg/L to 36.17 mg/L. Although a strong correlation existed between intake and SAA (p < 0.001, R2 = 0.47), the variation in SAA at any given intake level was wide. Of the studied patients, 62% had an SAA < 8.7 mg/L, 40% had an SAA < 5.1 mg/L (below the level in a healthy population), and 12% had a level below 2 mg/L (scorbutic). None of the patients demonstrated clinical manifestations of scurvy. Our results show that, in CAPD patients, ascorbic acid deficiency can be reliably detected only with SAA measurements, and oral intake may influence SAA level. To maintain ascorbic acid in the normal range for healthy adults, daily oral intake needs to be increased above the U.S. recommended dietary allowance to 80-140 mg.