| 1. |
- Hudson, Thomas J., et al.
(författare)
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International network of cancer genome projects
- 2010
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 464:7291, s. 993-998
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Tidskriftsartikel (refereegranskat)abstract
- The International Cancer Genome Consortium (ICGC) was launched to coordinate large-scale cancer genome studies in tumours from 50 different cancer types and/or subtypes that are of clinical and societal importance across the globe. Systematic studies of more than 25,000 cancer genomes at the genomic, epigenomic and transcriptomic levels will reveal the repertoire of oncogenic mutations, uncover traces of the mutagenic influences, define clinically relevant subtypes for prognosis and therapeutic management, and enable the development of new cancer therapies.
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| 2. |
- Li, Zongbao, et al.
(författare)
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Upconversion Luminescence of Graphene Oxide through Hybrid Waveguide
- 2018
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Ingår i: The Journal of Physical Chemistry C. - : AMER CHEMICAL SOC. - 1932-7447 .- 1932-7455. ; 122:29, s. 16866-16871
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Tidskriftsartikel (refereegranskat)abstract
- Phonon-assisted upconversion is a promising way to generate short-wavelength emissions under excitation of long wavelength based on unique anti-Stokes luminescence properties. Graphene oxide nanosheets (GONs) exhibit excellent optical properties owing to quantum confinement and edge effects, which have driven research into fundamental principles and potential applications. Here, we experimentally demonstrate upconversion emission by exciting an easily fabricated GON hybrid waveguide (GHVV) with enhanced photothermal effects. The results reveal different origins of short-wavelength range and long-wavelength range in the upconversion spectra, whereas the emissive surface defects of GONs and GHW structure play significant roles in the behavior of photoluminescence. Introducing other upconversion materials to promote emission efficiency, the hybrid waveguide system might readily provide the possibility for the construction of upconversion fiber lasers and remote control of the upconversion luminescence.
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| 3. |
- Baber, Ashleigh E., et al.
(författare)
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Stabilization of Catalytically Active Cu plus Surface Sites on TitaniumCopper Mixed-Oxide Films**
- 2014
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Ingår i: Angewandte Chemie International Edition. - : Gesellschaft Deutscher Chemiker. - 1433-7851 .- 1521-3773. ; 53:21, s. 5336-5340
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Tidskriftsartikel (refereegranskat)abstract
- The oxidation of CO is the archetypal heterogeneous catalytic reaction and plays a central role in the advancement of fundamental studies, the control of automobile emissions, and industrial oxidation reactions. Copper-based catalysts were the first catalysts that were reported to enable the oxidation of CO at room temperature, but a lack of stability at the elevated reaction temperatures that are used in automobile catalytic converters, in particular the loss of the most reactive Cu+ cations, leads to their deactivation. Using a combined experimental and theoretical approach, it is shown how the incorporation of titanium cations in a Cu2O film leads to the formation of a stable mixed-metal oxide with a Cu+ terminated surface that is highly active for CO oxidation.
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| 4. |
- Dobryden, Illia, et al.
(författare)
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An atomic force microscopy study of the interaction between magnetite particles: The effect of Ca2+ ions and pH
- 2013
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Ingår i: Powder Technology. - : Elsevier BV. - 0032-5910 .- 1873-328X. ; 233, s. 116-122
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Tidskriftsartikel (refereegranskat)abstract
- Force interactions between a microsize (m-s) magnetite probe and thin layers of synthesized magnetite particles as well as microsize (m-s) magnetite particles from magnetite concentrate were investigated using atomic force microscopy (AFM). Of special interest was the influence of Ca2 + ions and pH on the interaction between the probe and the two different magnetite particle surfaces. The probe and the magnetite surfaces were immersed in aqueous Ca2 + solutions (100, 10, and 1 mM) at various pH values (4, 6, and 10). The colloidal probe technique and a self-made computer program for automatic evaluation of adhesion forces were used. The analysis revealed an increase in adhesion force with increased calcium concentration at pH 6 for both the systems investigated. However, the adhesion behavior between the probe and the m-s and n-s magnetite particle surfaces is different at pH 10. The possible appearance of calcium carbonate precipitated onto the magnetite surfaces as well as the possible influence of already adsorbed silicate on magnetite particles from the concentrate is discussed. In addition to Ca, Cl and Na atoms, added to the working solutions, and the Fe and O detected signals, the SEM-EDS analysis also detected Si atoms on the surface of the m-s particles.
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| 5. |
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| 6. |
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| 7. |
- Holmgren, Allan, et al.
(författare)
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A polarized Fourier transform infrared spectrometry attenuated total reflection study of bentonite settled onto magnetite
- 2008
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 112:42, s. 16609-16615
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Tidskriftsartikel (refereegranskat)abstract
- Sodium bentonite in aqueous suspension was allowed to settle onto a layer of magnetite, and the orientation of the bentonite platelets was monitored using the Fourier transform infrared spectrometry-attenuated total reflection technique. This study is the first reported use of polarized IR to study the in situ settling of delaminated bentonite platelets onto a thin layer of magnetite nanoparticles. The experiment was performed at a pH value (pH 5.6) close to the point of zero charge for the edge surfaces of the bentonite platelets in order to possibly enhance the probability for the (001) surface of bentonite to adhere to the positively charged magnetite particles. The order parameter (S) of the platelets was calculated both for the dry film and the film formed during water evaporation. These results were compared with the orientation of bentonite platelets on the internal reflection element (ZnSe) without magnetite particles, a system where the three layer model is valid. During settling of the bentonite, the tilt angle of the normal to the (001) surface of the platelets decreases and reaches a minimum value for the dry film. When the film is still covered by a layer of water, the tilt angles indicate the film to be at least partly built up of so-called card-house structures, implying that the edge surfaces of the platelets are at least partly adhering to the basal (001) surfaces.
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| 8. |
- Lei, Xiuchuan, et al.
(författare)
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Quantitative Comparison of the Recrystallization Kinetics of Two Industrially Processed 5xxx Aluminum Alloys
- 2022
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Ingår i: Metallurgical and Materials Transactions. A. - : Springer. - 1073-5623 .- 1543-1940. ; 53:2
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Tidskriftsartikel (refereegranskat)abstract
- Abstract: The annealing kinetics of cold-rolled AA5182 and AA5657 aluminum alloy sheets have been investigated and compared. The microstructures of a series of partially recrystallized samples are characterized by electron back scattered diffraction and key stereological parameters including volume fraction recrystallized, interfacial areas and contiguity are determined. The overall recrystallization kinetics as well as the nucleation and growth rates are thereby quantified. The results reveal that the nuclei develop in clusters. This matches well with the observation of a low kinetics exponent n = 2 in AA5182. Much more surprising is that n is 2.8 in AA5657, even though the nucleation is clustered. Also, it is higher than almost all recrystallization kinetics investigations which generally find values significantly below 3. Effects of nucleation rate, spatial distribution of nuclei and growth rate are discussed and used in a quantitative analysis of recrystallization kinetics in the two alloys. Graphic Abstract: [Figure not available: see fulltext.] © 2021, The Minerals, Metals & Materials Society and ASM International.
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| 9. |
- Li, Zongbao, et al.
(författare)
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High throughput trapping and arrangement of biological cells using self-assembled optical tweezer
- 2018
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Ingår i: Optics Express. - : OPTICAL SOC AMER. - 1094-4087. ; 26:26, s. 34665-34674
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Tidskriftsartikel (refereegranskat)abstract
- Lately, a fiber-based optical tweezer that traps and arranges the micro/nanoparticles is crucial in practical applications, because such a device can trap the biological samples and drive them to the designated position in a microfluidic system or vessel without harming them. Here, we report a new type of fiber optical tweezer, which can trap and arrange erythrocytes. It is prepared by coating graphene on the cross section of a microfiber. Our results demonstrate that thermal-gradient-induced natural convection flow and thermophoresis can trap the erythrocytes under low incident power, and the optical scattering force can arrange them precisely under higher incident power. The proposed optical tweezer has high flexibility, easy fabrication, and high integration with lab-on-a-chip, and shows considerable potential for application in various fields, such as biophysics, biochemistry, and life sciences.
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| 10. |
- Potapova, Elisaveta, et al.
(författare)
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Interfacial properties of natural magnetite particles compared with their synthetic analogue
- 2012
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Ingår i: Minerals Engineering. - : Elsevier BV. - 0892-6875 .- 1872-9444. ; 36-38:S1, s. 187-194
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Tidskriftsartikel (refereegranskat)abstract
- Understanding of the interactions between iron oxides and flotation reagents is important both for flotation and agglomeration of iron ore. Model systems comprising synthetic iron oxides and pure chemical reagents are commonly applied in experimental work in order to obtain high quality data and to ease the interpretation of the empirical data. Whether the results obtained using model systems are valid for iron ore minerals and commercial reagents is a question seldom addressed in the literature. It is shown in this work that previously reported results obtained from a model system, concerning adsorption of a carboxylate surfactant and sodium metasilicate onto synthetic magnetite nanoparticles, as obtained by in situ ATR-FTIR spectroscopy and contact angle measurements, are applicable to adsorption of flotation reagents on magnetite concentrate. Additionally, the problem of restoring magnetite wetting after flotation is addressed since good wetting of a magnetite concentrate is required to produce iron ore pellets by wet agglomeration. The results from the present work indicate that the wettability of both synthetic magnetite coated with surfactant and magnetite concentrate after flotation can be improved by adsorbing a hydrophilizing agent such as silicate or polyacrylate.
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| 11. |
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| 12. |
- Potapova, Elisaveta, et al.
(författare)
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The effect of calcium ions, sodium silicate and surfactant on charge and wettability of magnetite
- 2011
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Ingår i: Colloids and Surfaces A. - : Elsevier BV. - 0927-7757 .- 1873-4359. ; 386:1-3, s. 79-86
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Tidskriftsartikel (refereegranskat)abstract
- Anionic carboxylate surfactants and sodium silicate are used in the reverse flotation of iron ore to separate magnetite from apatite. In this work, consecutive adsorption of sodium silicate and an anionic surfactant on synthetic magnetite modified with calcium ions was studied in the pH range 7.5–9.5 using in situ ATR-FTIR spectroscopy. The effect of these chemicals on the zeta-potential and wetting properties of magnetite was also investigated. While adsorption of silicate increased with increasing pH, subsequent surfactant adsorption went through a maximum at pH 8.5. Surfactant adsorption in the presence of calcium ions was not affected by the amount of silicate adsorbed on magnetite. Calcium ions were found to render the magnetite surface positive in the pH range 3–10 and could reduce the dispersing effect of silicate in flotation of apatite from magnetite. While treatment with calcium chloride and sodium silicate made magnetite more hydrophilic, subsequent adsorption of the anionic surfactant increased the water contact angle on the magnetite surface from about 10° to 40–50°. Although the latter values are not high enough to make magnetite float, the hydrophobic areas on the magnetite surface could result in the incorporation of air bubbles inside the iron ore pellets produced by wet agglomeration, lowering the pellet strength.
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| 13. |
- Roonasi, Payman, et al.
(författare)
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Competition between sodium oleate and sodium silicate for a silicate/oleate modified magnetite surface studied by in-situ ATR-FTIR Spectroscopy
- 2010
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Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 0021-9797 .- 1095-7103. ; 343:2, s. 546-552
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Tidskriftsartikel (refereegranskat)abstract
- Attenuated Total Reflection (ATR) IR spectroscopy was utilized to monitor adsorption of sodium oleate and sodium silicate onto synthetic magnetite at pH=8.5, both individually and in a competitive manner. Oleate was adsorbed within a concentration range of 0.01 mM-0.5 mM. It was observed that adsorption of oleate increased linearly with increasing concentration of oleate in solution up to a concentration of 0.1 mM. The infrared spectrum of oleate showed a broad single band at 1535 cm-1 assigned to the asymmetric stretching vibration of carboxylate, implying chemisorption of oleate to the magnetite surface. The kinetics of oleate adsorption followed a pseudo first-order reaction with an apparent rate constant of k1= 0.030 ± 0.002 min-1. Competitve adsorption of silicate and oleate was performed either by adding silicate solution to a magnetite film initially equilibrated with 0.1 mM oleate or adding oleate solution to magnetite treated with silicate solutions in the concentration range 0.1 mM - 5mM. It was shown that silicate, within reasonable time, had only minor effect on the amount of oleate already adsorbed on magnetite. On the other hand, oleate did not efficiently compete with silicate if the latter substance was already adsorbed on the iron oxide.
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| 14. |
- Xia, Lixin, et al.
(författare)
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Selective reduction of nitroaromatic compounds on silver nanoparticles by visible light
- 2012
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Ingår i: Journal of Raman Spectroscopy. - : Wiley. - 1097-4555 .- 0377-0486. ; 43:8, s. 1024-1028
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Tidskriftsartikel (refereegranskat)abstract
- For the first time, we report experimentally and theoretically that nitroaromatic compounds, 2,4-dinitrobenzenethiol and 4-chloro-2-nitrobenzenethiol, on silver sols can be selectively reduced to 2-amino-4-nitrobenzenethiol and 2-amino-4-chlorobenzenethiol simply by irradiating with a visible light in ambient conditions, and the selective photoreduction is a very facile process. The results of quantum chemical calculations are in good agreement with our experimental data. Copyright (c) 2012 John Wiley & Sons, Ltd.
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| 15. |
- Yang, Qinli, et al.
(författare)
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A generic framework to analyse the spatiotemporal variations of water quality data on a catchment scale
- 2019
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Ingår i: Environmental Modelling and Software. - : Elsevier BV. - 1364-8152. ; 122
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Tidskriftsartikel (refereegranskat)abstract
- Most spatiotemporal studies treat spatial and temporal analysis separately. However, spatial and temporal changes occur simultaneously and are correlated. In this study, we propose a generic framework to simultaneously analyse the spatial and temporal variations of water quality on a catchment scale. Specifically, we analyse the heterogeneity of temporal evolution of water quality data among different sampling sites, and the heterogeneity of spatial distribution of water quality data over different sampling times, respectively, by integrating the techniques of normalized mutual information, dynamic time wrapping and cluster analysis. To bring deep insight into the spatiotemporal variations, inter-change and intra-change are further defined and distinguished, respectively. Taking the Fuxi River catchment as a case study, results indicate that the proposed framework is intuitive and efficient. Beyond this, the generic framework can be expanded for other catchments and various environmental data.
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| 16. |
- Yang, Xiaofang, et al.
(författare)
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A study of sodium silicate in aqueous solution and sorbed by synthetic magnetite using in situ ATR-FTIR spectroscopy
- 2008
-
Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 0021-9797 .- 1095-7103. ; 328:1, s. 41-47
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Tidskriftsartikel (refereegranskat)abstract
- The sorption of sodium silicate by synthetic magnetite (Fe3O4) at different pH conditions (pH 7-11) and initial silicate concentrations (1×10-3 and 10 x 10-3 mol L-1) was studied using in situ attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy. The analysis of infrared spectra of sodium silicate in solution as well as adsorbed on magnetite nano-particles clearly showed the evolution of different silicate species depending on pH and silica concentration. The silicate concentration studied (10 x 10-3 mol L-1 ) contained polymeric or condensed silicate species at lower pH as well as monomers at high pH, as evident from infrared spectra. Condensation of monomers resulted in an increased intensity of absorptions in the high frequency part (>1050 cm-1) of the spectral region, which contains information about both silicate in solution and sorbed silicate viz. 1300 cm-1-850 cm-1. In the pH range studied, infrared spectra of sorbed silicate and sorbed silicate during desorption both indicated the presence of different types of surface complexes at the magnetite surface. The sorption mechanism proposed is in accordance with a ligand exchange reaction where both monodentate and bidentate complexes could exist at low surface loading level, the relative proportion of the complexes being due to both pH and concentration in solution. Oligomerization occurred on the magnetite surface at higher surface loading.
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| 17. |
- Yang, Xiaofang, et al.
(författare)
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Application of ATR-FTIR spectroscopy in the study of adsorption on environmental micro-interfaces
- 2010
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Ingår i: Huaxue jinzhan. - 1005-281X. ; 22:6, s. 1185-1194
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Tidskriftsartikel (refereegranskat)abstract
- Interfacial adsorption process is the initial step or key step for most of environmental micro-interface reactions. The online study of environmental micro-interfacial adsorption by in situ research methods provides direct information about interface reactions and reliable evidence for the detection of reaction mechanisms which are of great importance to understand the rule of transformation and distribution of pollutants in the environment. Because of its unique sampling principle, convenient sample pre-treatment and wide applicability, attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR) is becoming a powerful tool for investigating the interface reactions. Based on a brief introduction of the working principle of ATR-FTIR, the application of this technique in the investigation of adsorption on environmental interfaces, especially mineral-water interfaces, is summarized. Furthermore, the perspective of this method is discussed as well.
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| 18. |
- Yang, Xiaofang, et al.
(författare)
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Effect of phosphate on heterogeneous Fenton oxidation of catechol by nano-Fe3O4 : Inhibitor or stabilizer?
- 2016
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Ingår i: Journal of Environmental Sciences(China). - : Elsevier BV. - 1001-0742 .- 1878-7320. ; 39, s. 69-76
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Tidskriftsartikel (refereegranskat)abstract
- The effect of phosphate on adsorption and oxidation of catechol, 1,2-dihydroxybenzene, in a heterogeneous Fenton system was investigated. In situ attenuated total reflectance infrared spectroscopy (ATR-FTIR) was used to monitor the surface speciation at the nano-Fe3O4 catalyst surface. The presence of phosphate decreased the removal rate of catechol and the abatement of dissolved organic compounds, as well as the decomposition of H2O2. This effect of phosphate was mainly due to its strong reaction with surface sites on the iron oxide catalyst. At neutral and acid pH, phosphate could displace the adsorbed catechol from the surface of catalyst and also could compete for surface sites with H2O2. In situ IR spectra indicated the formation of iron phosphate precipitation at the catalyst surface. The iron phosphate surface species may affect the amount of iron atoms taking part in the catalytic decomposition of H2O2 and formation of hydroxyl radicals, and inhibit the catalytic ability of Fe3O4 catalyst. Therefore, phosphate ions worked as stabilizer and inhibitor in a heterogeneous Fenton reaction at the same time, in effect leading to an increase in oxidation efficiency in this study. However, before use of phosphate as pH buffer or H2O2 stabilizer in a heterogeneous Fenton system, the possible inhibitory effect of phosphate on the actual removal of organic pollutants should be fully considered.
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| 19. |
- Yang, Xiaofang
(författare)
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Interaction of magnetite with soluble silicates and bentonite : implications for wet agglomeration of magnetite concentrate
- 2011
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Iron ore green pellets are produced by agglomeration of moist magnetite concentrates. The quality of green pellets is essential for the transportability and metallurgical benefits of the final product. The agglomeration behavior of magnetite concentrate particles is strongly influenced by its surface properties which are affected by the interactions with flotation reagents (i.e. water glass and collector) and species in process water. However, the mechanisms of these interactions and the influence on the following agglomeration process are still not completely understood. The present work has been focused on the interaction of magnetite with water glass (sodium silicate) and bentonite clay (silicate mineral) aiming for better fundamental knowledge of the magnetite surface properties in order to improve the agglomeration behavior of the magnetite concentrate. Water glass is used as a dispersing or depressing agent in flotation of magnetite. The former function is to improve the separation of mineral particles in the pulp, while the latter function is to protect the magnetite surfaces from attachment of the collector which is known to cause problems in the subsequent agglomeration process. Sodium activated bentonite clay is commonly used as an external binder in iron ore agglomeration owing to its swelling properties. The particle interaction between magnetite and bentonite platelets, which is expected to be affected by the surface properties of magnetite, is of importance for the wet and dry strength of the pellets. Sorption mechanisms of sodium silicate onto the magnetite surface at the molecular scale were studied at various pH and silicate concentrations using in-situ ATR-FTIR spectroscopy. Silicate concentration, pH, and conditioning time are the most important factors for silicate sorption and speciation at the surface of magnetite. A maximum sorption was observed in the pH range 8.5 - 9.5. Oligomeric or polymeric silicate species are formed and dominate at high surface loading of silicate. These oligomeric or polymerized species have stronger affinity for the magnetite as compared to monomeric species, resulting in a slower and less extent of desorption and implying a higher depressing efficiency in flotation. Sodium silicate makes the magnetite surface more negatively charged, while adsorbed calcium ions on the surface compensate this negative surface charge. Calcium ions promote the oligomerization of silicate on the surface of magnetite at high pH (pH > 10) possibly due to the increased local silicate concentration by additional sorption of silicate on adsorbed calcium at the surface. The competitive sorption between sodium silicate and collector (sodium oleate) for the magnetite surface was studied using the in situ ATR-FTIR technique. It was confirmed that oleate could still be adsorbed onto a sodium silicate modified magnetite surface but the amount of adsorbed oleate decreased with increasing concentration of silicate (0.1 - 5 mmol•L-1). This depression effect became much more significant when the concentration of sodium silicate was higher than 0.4 mmol•L-1 above which more dimers or oligomeric silicate species were formed at the magnetite surface. However, when the magnetite surface was pre-treated firstly with sodium oleate, the addition of sodium silicate only slightly reduced the adsorption of oleate. Meanwhile, the sorption of silicate anions was depressed and resulted in a lower degree of oligomerization or polymerization at high silicate dosage. Sessile drop method and Wilhelmy method were used to measure the water contact angle of synthesized magnetite, and Washburn method was used for contact angle measurements of magnetite concentrate. The synthesized magnetite has lower contact angle compared to mineral particles. Nevertheless, similar tendency of changes in wettability upon interaction with calcium, sodium silicate and collector was observed for synthesized magnetite and magnetite concentrate. Sorption of calcium and silicate increased the wettability of the surface, while adsorption of collector made the surface more hydrophobic. Further exposure of the collector modified magnetite surface to sodium silicate could restore the surface wettability. Therefore, an interesting implication for magnetite flotation and agglomeration is that the decreased hydrophilicity of magnetite by attachment of collector could be improved by further chemical conditioning with sodium silicate (water glass). The interaction of bentonite with magnetite was investigated by means of settling of bentonite platelets onto a layer of magnetite nano-particles. The magnetite layer was deposited on a horizontal ZnSe crystal to be able to examine the orientation of the platelets by polarized ATR-FTIR. The measured dichroic ratio of the bentonite platelets decreased with time in wet film and approached a minimum value in the dry bentonite film regardless of the pH of the bentonite suspension. This tendency is in good agreement with the results observed for settling on bare crystal, indicating a more ordered structure of platelets upon evaporation of water. The bentonite platelets in dry film were evidently tending to orient with their basal plane surfaces to the magnetite layer, whilst wet films adopted a much more disordered structure. Similarly, a rather disordered wet bentonite film was formed on the calcium and sodium silicate modified magnetite layer. These bentonite platelets became more ordered when the wet film was dried.
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| 20. |
- Yang, Xiaofang
(författare)
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Interactions between iron oxides and silicates
- 2008
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The main objective of this Licentiate thesis was to acquire a better understanding of the mechanisms involved in the sorption of dissolved silicate from aqueous solutions onto iron oxide surfaces by using Attenuated Total Reflection Fourier Transform Infrared (ATR-FTIR) spectroscopy and subsequently to develop a method to monitor the orientation of bentonite platelets settling onto the bare iron oxide using polarized ATR-FTIR technique. The infrared spectra show that the silicate concentration and pH both determine the species of sorbed silicate on the iron oxide surfaces. In the last part of this thesis, the orientation of bentonite platelets on a ZnSe ATR crystal as well as on a layer of magnetite particles deposited on the crystal was analyzed with polarized horizontal ATR-FTIR Spectroscopy.The iron oxide layer contributed to an increased order of the settled bentonite platelets.
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| 21. |
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| 22. |
- Yang, Xiaofang, et al.
(författare)
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Kinetics of silicate sorption on magnetite and maghemite : an in-situ ATR-FTIR study
- 2009
-
Ingår i: Colloids and Surfaces A. - : Elsevier BV. - 0927-7757 .- 1873-4359. ; 343:1-3, s. 24-29
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Tidskriftsartikel (refereegranskat)abstract
- Attenuated Total Reflection Fourier Transform Infrared (ATR-FTIR) spectroscopy was used to monitor the in situ sorption of sodium metasilicate from aqueous solution onto synthesized magnetite and maghemite particles in the pH range 10.8-7.0 using silicate concentrations between 0.1 mM and 5 mM. The spectral data showed that both pH and silicate concentration had great influence on the interfacial reaction between soluble silicate and the iron oxide surfaces, regarding the amount adsorbed per unit mass of iron oxide and the surface species formed. A pH dependent sorption of silicate on iron oxides was observed, implying that a maximum sorption took place in the pH range of 9.5 - 7.0. All experiments showed a fast initial increase in the absorption intensity followed by a slower sorption stage which was strongly dependent on the concentration of silicate in solution and the pH value. The amount of sorption onto magnetite was 3 to 5 times larger than onto maghemite, but there was no significant difference in the line shape of corresponding absorption bands. At pH 8.5 and low concentration (≤ 0.1 mM), the silicate monomers dominate in solution and on the iron oxide surface also monomeric species were dominating as evident from the infrared band at 950 cm-1. However, at higher concentration (0.4-5.0 mM), the dominating absorption band at about 1000 cm-1 shifted to higher frequency during the sorption indicating that oligomeric surface silicate species were formed on the iron oxide surface. Desorption of silicate from the surface of the iron oxides was easier to accomplish at low silicate concentration, whilst the highest concentration showed a comparatively low relative amount of desorbed silicate, suggesting that polymerized species had a stronger affinity for the iron oxide surface as compared to monomeric species.
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| 23. |
- Yang, Xiaofang, et al.
(författare)
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Surface acid-base properties and hydration/dehydration mechanisms of aluminum (hydr)oxides
- 2007
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Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 0021-9797 .- 1095-7103. ; 308:2, s. 395-404
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, surface physiochemical properties of three typical aluminas, γ-Al(OH)3, γ-Al2O3, and α-Al2O3, were investigated by means of XRD, SEM, TEM, BET surface area, TG/DTA, and potentiometric titration techniques. Based on the titration data, surface protonation and deprotonation constants were determined using the constant capacitance model (CCM). The emphasis of this research was laid on the comparison of the crystal structure, surface hydration/dehydration and acid-base properties of these three typical alumina minerals. The calculation results revealed that the surface acidity of the aluminas is in the order of α-Al2O3>γ-Al(OH)3>γ-Al2O3 after being hydrated for 1 h. The correlation between the hydration/dehydration mechanisms of alumina and its acid/base properties is discussed.
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