Development of Carriers with Controlled Concentration of Charged Surface Groups in Aqueous Solutions.
Development of Carriers with Controlled Concentration of Charged Surface Groups in Aqueous Solutions.
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水溶液中带电表面基团浓度受控的载体的开发。
DOI：
10.1002/chin.198645035
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发表时间：
1986
期刊：
影响因子：
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通讯作者：
A. Lycourghiotis
中科院分区：
文献类型：
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作者：
L. Vordonis;P. Koutsoukos;A. Lycourghiotis
通过在γ-Al 2 O3中掺入不同量的Li+和F-离子制备了两个系列的载体，并在较宽的pH范围内用电位法测定了零电荷点（ZPC）、表面酸性常数以及带电表面基团、Al OH 2+和Al O-的浓度。发现每g γ-Al 2 O3中加入0.621mmol Li+，可使ZPC由5.30变为9.80.相应地，负物种（Al OH 2+）的吸附位的浓度增加，而表面酸性常数降低，并且抑制了Al O−位的形成。锂含量的进一步增加导致在pH低于8.0时Al OH+ 2基团的浓度显著增加。由于锂掺杂所引起的影响与先前研究的钠改性后观察到的影响的比较表明，在钠引起催化失活的情况下，可以使用锂代替钠。然而，与钠相比，更大量的锂是必要的，以便在给定pH下实现Al OH 2+基团浓度的相同增加。已被用来解释在本研究中观察到的Li+的影响，通过钠掺杂的氧化铝的机制类似。关于F−离子的掺杂，观察到用0.125 mmol F−/g γ-Al 2 O 3修饰γ-Al 2 O 3使ZPC从5.30降低到3.40。因此，F−掺杂可以用来扩大pH范围，在较低的pH值下，正物质可以通过吸附沉积在γ-Al 2 O 3上。此外，这种改性带来的正性物种，铝O-的吸附位点的浓度增加，以及在表面酸度常数的值。当pH值高于3.40时，F−离子浓度的进一步增加会引起Al O−基团浓度的显著增加，尽管它不会进一步影响ZPC和表面酸度常数的值。
Two series of carriers were prepared by doping γ-Al 2 O 3 with various amounts of Li+ and F− ions and the point of zero charge (ZPC), the surface acidity constants as well as the concentration of the charged surface groups, Al OH 2+ and Al O− were determined potentiometrically over a wide pH range. It was found that 0.621 mmol Li+ per g of γ-Al 2 O 3 were sufficient to cause a shift of the ZPC from 5.30 to 9.80. Accordingly, the concentration of adsorption sites for negative species (Al OH 2+) was increased, while the surface acidity constants decreased and the formation of Al O− sites was inhibited. Further increase in the lithium content causes a marked increase in the concentration of the Al OH+ 2 groups at pH lower than 8.0. Comparison of the effects caused due to the lithium doping with those observed after sodium modification studied previously, showed that lithium can be used instead of sodium in the cases where the latter causes catalytic deactivation. However, larger amounts of lithium, as compared with that of sodium, are necessary in order for the same increase in the concentration of the Al OH 2+ groups at a given pH to be achieved. A mechanism similar to that adopted for the sodium-doped alumina has been used to explain the Li+ effects observed in the present study. Concerning the doping by F− ions it was observed that modification of γ-Al 2 O 3 with 0.125 mmol F− per g of γ-Al 2 O 3 decreases the ZPC from 5.30 to 3.40. F− doping thus can be used to extend the pH range, where positive species could be deposited on γ-Al 2 O 3 by adsorption, at lower pH values. Moreover, this modification brings about an increase in the concentration of the adsorption sites for positive species, Al O−, as well as in the values of the surface acidity constants. Additional increase in the concentration of the F− ions provokes a considerable increase in the concentration of the Al O− groups at pH higher than 3.40 though it does not further affect the values of ZPC and surface acidity constants.