| 1. |
- Holmgren, Allan, et al.
(författare)
-
A polarized Fourier transform infrared spectrometry attenuated total reflection study of bentonite settled onto magnetite
- 2008
-
Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 112:42, s. 16609-16615
-
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.
|
|
| 2. |
- Yang, Xiaofang, et al.
(författare)
-
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
-
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.
|
|
| 3. |
- Yang, Xiaofang
(författare)
-
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.
|
|
| 4. |
|
|
| 5. |
- Yang, Xiaofang, et al.
(författare)
-
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
-
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.
|
|
| 6. |
- Yang, Xiaofang, et al.
(författare)
-
Surface acid-base properties and hydration/dehydration mechanisms of aluminum (hydr)oxides
- 2007
-
Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 0021-9797 .- 1095-7103. ; 308:2, s. 395-404
-
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.
|
|
