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Preparation of mesoporous alumina and in situ ATR-FTIR investigation of phosphate at the alumina-water interface
2008 (English)Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
Abstract [en]

The aim of this study was to synthesize aluminum oxide with high surface area and then investigate phosphate adsorption on the aluminum oxide surface. The method we used to probe phosphate surface complexes at aluminum oxide phase was in situ Attenuated Total Reflection Fourier Transform Infrared (FTIR) spectroscopy, which is very sensitive to the coordination environment and protonation state of phosphate complexes, and therefore a useful tool for characterizing phosphate surface species at the molecular scale. Mesoporous alumina material had been synthesized using PEG as structure directing reagent and dodecylamine as co-template. XRD, SEM, N2 adsorption/desorption technique and zeta potential charge measurement were used to characterize the general properties of the synthesized material. The results showed that the aluminum oxide material is £f-Al2O3 with a high surface area viz. 329 m2g-1. The deposited alumina on the crystal surface was a film assembled with small alumina particles about 20-30 nm and the thickness of the film was around 3-4 ƒÝm. The zeta potential was affected by electrolyte concentration and the adsorbed phosphate on the surface of the alumina film could significantly influence the charge as well as the PZC value and make PZC to occur at pH values less than that without phosphate. Phosphate adsorption on alumina surface was investigated by in situ ATR- FTIR spectroscopy. Spectroscopic studies on these systems have shown that phosphate forms inner-sphere complexes at the solid¡Vliquid interface. In higher pH value (9.0) only one complex exist in the water-alumina interface, however, a mixture of different phosphate complexes formed at lower pH value (4.05 and 4.96). The adsorption isotherms and kinetics at acid and base environment were also studied. The results show that the amount of phosphate adsorbed on aluminum oxide increased with increasing concentration but the increase gradually became smaller at higher concentrations. The adsorption data were evaluated with the Langmuir and Freundlich isotherm models. It was indicated that the adsorption data fits the Langmuir isotherm better than the Freundlich isotherm at lower [PO4] concentration, however, it fits the Freundlich isotherm better than the Langmuir isotherm at higher [PO4] concentration both at pH 9.0 and 4.15. Adsorption kinetics show that both adsorption at 9.0 and 4.96 have similar characteristics except at 5ƒÝM, with a fast adsorption between t = 0 and 10 min, and a slower adsorption at longer times. Finally, seven possible molecular symmetries are proposed for this Al-P complex with C2v or lower symmetry.

Place, publisher, year, edition, pages
Keyword [en]
Physics Chemistry Maths, Mesoporous alumina, Adsorption, Phosphate, In-situ ATR-FTIR
Keyword [sv]
Fysik, Kemi, Matematik
URN: urn:nbn:se:ltu:diva-48823ISRN: LTU-PB-EX--08/047--SELocal ID: 63f7146b-209f-4588-bd5d-fc3d379adfedOAI: diva2:1022167
Subject / course
Student thesis, at least 30 credits
Educational program
Chemical Engineering, master's level
Validerat; 20101217 (root)Available from: 2016-10-04 Created: 2016-10-04Bibliographically approved

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