Sonication induced redox reactions of the Ojén (Andalucía, Spain) vermiculite

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• 作者：Juan Poyato ; Jos&#xe9 ; Luis P&#xe9 ; rez-Rodr&#xed ; guez ; Veró ; nica Ram&#xed ; rez-Valle ; Anton Lerf ; Friedrich E. Wagner
• 关键词：Vermiculite ; Sonication ; Redox reactions ; Mö ; ssbauer spectroscopy
• 刊名：Ultrasonics Sonochemistry
• 出版年：2009
• 出版时间：April 2009
• 年：2009
• 卷：16
• 期：4
• 页码：570-576
• 全文大小：677 K

文摘

Sonication in a 1:1 mixture (volume ratio) of water and concentrated H₂O₂ (30 % ) is a soft method for particle size reduction of phyllosilicate minerals like vermiculites. Repeated sonication causes a particle size reduction to about 70 nm for the Santa Olalla and to 45 nm for the Ojén-vermiculite. In this context the question arises whether the strong oxidising effect of the hydrogen peroxide affects the oxidation state of the iron in the vermiculites. Therefore, the Fe³⁺/Fe_total ratio before and after sonication was determined by means of Mössbauer spectroscopy. Whereas this ratio was found to remain almost constant in the Santa Olalla vermiculite, it increased from 0.79 to 0.85 in case of the Ojén sample. In the latter case, the oxidation is accompanied by a decrease of the layer charge.

Surprisingly, sonication in pure water leads to a decrease of the Fe³⁺/Fe_total ratio in the case of the Ojén-vermiculite, i.e., to an increase of the Fe²⁺ fraction to roughly twice the value before sonication. Again the Fe³⁺/Fe_total ratio of the Santa Olalla vermiculite remains unchanged. The surface area S_BET of the reduced Ojén-vermiculite amounts to 50 m²/g, which is close to the value obtained in the presence of hydrogen peroxide. The results presented should be taken as a warning that particle size reduction by sonication may be accompanied by a change of the redox state and the layer charge of the material.