Hydrothermal growth and gas sensing property of flower-shaped SnS2 nanostructures

Unusual 3D flower-shaped SnS2 nanostructures have been synthesized using a mild hydrothermal treatment in the presence of octyl-phenol-ethoxylate ( Triton X-100) at 160 degrees C. The nanostructures have an average size of 1 mu m, and consist of interconnected nanosheets with thicknesses of about 40 nm. Based on time-dependent experimental results, we ascribe the oriented attachment mechanism to the growth of the SnS2 nanostructures. The nonionic surfactant Triton X-100 plays a key role in the formation of the flower-like morphology. Room temperature gas-sensing measurements show that the 3D SnS2 nanostructures could serve as sensor materials for the detection of NH3 molecules.

Purified phenolics from hydrothermal treatments of biomass: ability to protect sunflower bulk oil and model food emulsions from oxidation

The phenolic fractions released during hydrothermal treatment of selected feedstocks (corn cobs, eucalypt wood chips, almond shells, chestnut burs, and white grape pomace) were selectively recovered by extraction with ethyl acetate and washed with ethanol/water solutions. The crude extracts were purified by a relatively simple adsorption technique using a commercial polymeric, nonionic resin. Utilization of 96% ethanol as eluting agent resulted in 47.0-72.6% phenolic desorption, yielding refined products containing 49-60% w/w phenolics (corresponding to 30-58% enrichment with respect to the crude extracts). The refined extracts produced from grape pomace and from chestnut burs were suitable for protecting bulk oil and oil-in-water and water-in-oil emulsions. A synergistic action with bovine serum albumin in the emulsions was observed.

Vanadium Pentoxide Nanostructures: An Effective Control of Morphology and Crystal Structure in Hydrothermal Conditions

A systematic study was made of the synthesis of V(2)O(5)center dot nH(2)O nanostructures, whose morphologies, crystal structure, and amount of water molecules between the layered structures were regulated by strictly controlling the hydrothermal treatment variables. The synthesis involved a direct hydrothermal reaction between V(2)O(5) and H(2)O(2), without the addition of organic surfactant or inorganic ions. The experimental results indicate that high purity nanostructures can be obtained using this simple and clean synthetic route. Oil the basis of a study of hydrothermal treatment variables such as reaction temperature and time, X-ray diffraction (XRD) and scanning transmission electron microscopy (STEM) revealed that it was possible to obtain nanoribbons of the V(2)O(5)center dot nH(2)O monoclinic phase and nanowires or nanorods of the V(2)O(5)center dot nH(2)O orthorhombic phase. Thermal gravimetric analysis (TGA) shows also that the water content in the Structure call be controlled at appropriate hydrothermal conditions. Concerning the oxidation state of the vanadium atoms of as-obtained samples, a mixed-valence state composed of V(4+) and V(5+) was observed ill the V(2)O(5)center dot nH(2)O monoclinic phase, while the valence of the vanadium atoms was preferentially 5+ in the V(2)O(5)center dot nH(2)O orthorhombic phase. The X-ray absorption near-edge structure (XANES) results also indicated that the local structure of vanadium possessed a higher degree of symmetry in the V(2)O(5)center dot nH(2)O monoclinic phase.

Nanohydroxyapatite coating on a titanium–niobium alloy by a hydrothermal process

A novel one-step hydrothermal coating process was used to produce nanohydroxyapatite (nano-HA) coating on a titanium–niobium (TiNb) alloy substrate in a newly designed solution containing calcium and phosphate ions. The morphology of the coating was studied using scanning electron microscopy. The phase identification of the coating was carried out using X-ray diffraction, attenuated total reflectance Fourier transform infrared spectroscopy and transmission electron microscopy. The reaction between the surface of TiNb alloy and the solution during the hydrothermal process was studied by Xray photoelectron spectroscopy. Results show that the coating formed on the surface of TiNb alloy was composed of nano-HA particles. During the hydrothermal process, TiO₂ and Nb₂O₅ formed on the TiNb alloy surface and hydrated to Ti(OH)4 and Nb(OH)₅, respectively. Calcium phosphate nucleated and grew into a layer of nano-HA particles on the surface of TiNb alloy under the hydrothermal conditions. The crystallinity of the nano-HA coating was improved with the increase in hydrothermal treatment temperature and time duration. Nano-HA coating with good crystallinity was produced on the TiNb alloy via the hydrothermal process at a temperature of 200 ºC for 12 h.

Growth kinetics of tin oxide nanocrystals in colloidal suspensions under hydrothermal conditions

Colloidal suspensions of tin oxide nanocrystals were synthesized at room temperature by the hydrolysis reaction of tin chloride (II), in an ethanolic solution. The coarsening kinetics of such nanocrystals was studied by submitting the as-prepared suspensions to hydrothermal treatments at temperatures of 100, 150 and 200 degrees C for periods between 60 and 12,000 min. Transmission electron microscopy (TEM) was used to characterize the samples (i.e. distribution of nanocrystal size, average particle radius and morphology). The results show that the usual Ostwald ripening coarsening mechanism does not fit well the experimental data, which is an indicative that this process is not significant for SnO2 nanocrystals, in the studied experimental conditions. The morphology evolution of the nanocrystals upon hydrothermal treatment indicates that growth by oriented attachment (OA) should be significant. A kinetic model that describes OA growth is successfully applied to fit the data. (c) 2006 Elsevier B.V. All rights reserved.

Stable colloidal suspensions of nanostructured zirconium oxide synthesized by hydrothermal process

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Behavior of Peruvian carrot (Arracacia xanthorrhiza) and cassava (Manihot esculenta) starches subjected to heat-moisture treatment

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Titanate nanotubes produced from microwave-assisted hydrothermal synthesis: Photocatalytic and structural properties

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Facile synthesis and characterization of ZrO2 nanoparticles prepared by the AOP/hydrothermal route

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Hydrothermal Synthesis of Layered Double Hydroxides (LDHs) from Mixed MgO and Al2O3: LDH Formation Mechanism

The formation of MgA1 layered double hydroxide (LDH) from physically mixed MgO and Al2O3 oxides upon hydrothermal treatment has been extensively investigated, and a formation mechanism has been proposed. We observed that the formation of LDH from the oxide mixture occurs upon heating at 110 degreesC. In general, LDH is the major component while the minor phases are mainly determined by the initial pH of the oxide suspension as well as the MgO/Al2O3 ratio. The neutrality in the initial suspension results in a minor Mg(OH)(2) as the impure phase, while the alkalinity in the suspension keeps some MgO unreacted throughout the whole hydrothermal treatment. We suggest that MgO and Al2O3 be hydrated into Mg(OH)(2) and Al(OH)(3), respectively, in the initial stage for all samples. We further Suggest that in the neutral condition Mg(OH)2 be quickly dissociated to Mg2+ and OH- which then deposit on the surface of Al(OH)(3)/Al2O3 to form a M-Al pre-LDH material. Al(OH)(4)(-), ionized from Al(OH)(3) in the basic solution, deposits on the surface of Mg(OH)(2)/MgO to result in a similar MgAl pre-LDH material. Such a pre-LDH material is then well crystallized upon continuous heating via the diffusion of metal ions in the solid lattice. Such a dissociation-deposition-diffusion mechanism via two pathways has been supported by the phase composition, morphological features of crystallites, and [Mg]/[Al] ratios on the crystallite surface. and presumably applied to the general formation of LDHs with various synthetic methods. Such as coprecipitation, homogeneous preparation, and reconstruction.

Hydrothermal carbonization of lignocellulosic biomass: Effect of process conditions on hydrochar properties

Although hydrothermal carbonization of biomass components is known to be mainly governed by reaction temperature, consistent reports on the effect and statistical significance of process conditions on hydrochar properties are still lacking. The objective of this research was to determine the importance and significance of reaction temperature, retention time and solid load on the properties of hydrochar produced from an industrial lignocellulosic sludge residue. According to the results, reaction temperature and retention time had a statistically significant effect on hydrochar ash content, solid yield, carbon content, O/C-ratio, energy densification and energy yield as reactor solid load was statistically insignificant for all acquired models within the design range. Although statistically significant, the effect of retention time was 3–7 times lower than that of reaction temperature. Predicted dry ash-free solid yields of attained hydrochar decreased to approximately 40% due to the dissolution of biomass components at higher reaction temperatures, as respective oxygen contents were comparable to subbituminous coal. Significant increases in the carbon contents of hydrochar led to predicted energy densification ratios of 1–1.5 with respective energy yields of 60–100%. Estimated theoretical energy requirements of carbonization were dependent on the literature method used and mainly controlled by reaction temperature and reactor solid load. The attained results enable future prediction of hydrochar properties from this feedstock and help to understand the effect of process conditions on hydrothermal treatment of lignocellulosic biomass.

Synthesis and characterization of boehmite nanofibers

Boehmite nanofibers of high quality were synthesized through a wet-gel conversion process without the use of a surfactant. The long nanofibers of boehmite with clear-cut edges were obtained by steaming the wet-gel precipitate at 170 ºC for 2 days under a pH 5. Hydrothermal treatment of the boehmite gels enabled self-assembly through directed crystal growth. Detailed characterization using X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Infrared Emission Spectroscopy (IES) and Raman Spectroscopy is presented.

Transition of chromium oxyhydroxide nanomaterials to chromium oxide : a hot stage Raman spectroscopic study

The transition of disc-like chromium hydroxide nanomaterials to chromium oxide nanomaterials has been studied by hot stage Raman spectroscopy. The structure and morphology of α-CrO(OH) synthesised using hydrothermal treatment was confirmed by X-ray diffraction and transmission electron microscopy. The Raman spectrum of α-CrO(OH) is characterised by two intense bands at 823 and 630 cm-1 attributed to ν1 CrIII-O symmetric stretching mode, bands at 1179 cm-1 attributed to CrIII-OH δ deformation modes. No bands are observed above 3000 cm-1. The absence of characteristic OH vibrational bands may be due to short hydrogen bonds in the α-CrO(OH) structure. Upon thermal treatment of α-CrO(OH), new Raman bands are observed at 599, 542, 513, 396, 344 and 304 cm-1, which are attributed to Cr2O3. This hot-stage Raman study shows that the transition of α-CrO(OH) to Cr2O3 occurs before 350 °C.

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.