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Chemisorption of Copper on Hydroxy-Aluminum-Hectorite: An Electron Spin Resonance Study

Published online by Cambridge University Press:  02 April 2024

J. B. Harsh ,
H. E. Doner  and
M. B. McBride
J. B. Harsh
Affiliation:
Department of Plant and Soil Biology, University of California, Berkeley, California 94720
H. E. Doner
Affiliation:
Department of Plant and Soil Biology, University of California, Berkeley, California 94720
M. B. McBride
Affiliation:
Department of Agronomy, Cornell University, Ithaca, New York 14853
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Abstract

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Copper adsorption on a hydroxy-aluminum-hectorite complex (OH-Al-hectorite) at pH 4.5, 5.7, 7.4, and 7.8 was examined by means of electron spin resonance. The spectra of these samples were compared to those of Cu2+-hectorite and various aluminum hydrous oxides. Copper on the OH-Al-hectorite in aqueous gels occurred as mobile Cu(H20)62+ and chemisorbed to discrete sites of the OH-Al interlayer. As pH was increased, the ratio of chemisorbed to mobile Cu2+ increased. At pHs above 7 the solubility product of Cu(OH)2 was exceeded, but chemisorbed Cu2+ remained as the dominant species. These results contrast with the precipitation of Cu observed on microcry stalline gibbsite above pH 5 and indicate that the interlayer OH-A1 retained more Cu2+ on discrete sites. The greater adsorption capacity probably resulted in part from a higher specific surface area. Electron spin resonance spectra of Cu2+ in air-dried films of the OH-Al-hectorite at pH 4.5 and 7.4 showed Cu2+ in square planar symmetry, oriented with the z-axis perpendicular to the OH-Al-hectorite a-b plane. At the higher pH, the spectrum resembled that of Cu(OH)42- on alumina, suggesting a ligand exchange mechanism for Cu2+ adsorption on the complex.

Резюме

Резюме

Адсорбция меди комплексом гидрокси-алюминий-гекторит (ОН-Аl-гекторит) при рН рав¬ным 4,5, 7,4, и 7,8 исследовалась при помощи електронного спинового резонанса. Спектры этих образцов сравнивались со спектрами Сu2+-гекторита и различных водных окисей алюминия. Медь на ОН-Аl-гекторите в водных гелях залегала в виде Си(Н2O)62+ и хемисорбировалась на дискретных местах слоя ОН-Аl. При увеличении рН, отношение хемисорбированных ионов к подвижным ионом Сu2+ также увеличивалось. При значениях рН выше 7, величина произведения растворимости Си(ОН)2 превышалась, но хемисорбированный Сu2+ оставался главным видом. Эти результаты сопоставлялись с осаждением Си, наблюдаемому на микрокристаллическом гиббсите при рН выше 5, и указывали на то, что слой ОН-Аl удерживал большое количество Сu2+ на дискретных местах. Большая адсорб¬ционная способность была, вероятно, частично результатом большой удельной площади поверхности. Спектры электронного спинового резонанса Сu2+ в осушенных на воздухе фильмах ОН-Аl-гекторита при рН равных 4,5 и 7,4 указывали на квадратную плоскую симметрию Сu2+ с осей 2 по направлению нормальному к плоскости a-b ОН-Аl-гекторита. При высших рН, спектр был похожий на Си(ОН)42− на глиноземе, указывая на лигандовый механизм обмена для адсорбции Cu2+ комплексом. [E.G.]

Resümee

Resümee

Die Kupferadsorption an einen Hydroxy-Al-Hektoritkomplex (OH-Al-Hektorit) wurde bei pH 4,5, 5,7, 7,4, und 7,8 mittels Elektronenspinresonanz untersucht. Die Spektren dieser Proben wurden mit denen von Cu2+-Hektorit und verschiedenen wasserhaltigen Al-Oxiden verglichen. Das Kupfer trat an dem OH-Al-Hektorit in wässrigen Gelen als mobiles Cu(H20)62+ auf und chemisorbierte an bestimmten Plätzen der OH-Al-Zwischenschicht. Wenn der pH zunahm, dann nahm das Verhältnis des chemisor-bierten zum mobilen Cu2+ zu. Bei pH-Werten über 7 wurde das Löslichkeitsprodukt von Cu(OH)2 überschritten, doch das chemisorbierte Cu2+ überwog weiterhin. Diese Ergebnisse stehen im Gegensatz mit der Ausfällung von Cu, die an mikrokristallinem Gibbsit über pH 5 beobachtet wurde, und deuten darauf hin, daß die OH-Al-Zwischenschicht mehr Cu2+ an bestimmten Stellen zurückhielt. Die größere Adsorptionskapazität resultierte wahrscheinlich zum Teil aus einer größeren spezifischen Oberfläche. Elektronenspinresonanzspektren von Cu2+ in Luft-getrockneten Schichten von OH-Al-Hektorit bei pH 4,5 und 7,5 zeigten, daß Cu2+ in einer quadratischen planaren Symmetrie auftritt und mit der z-Achse senkrecht zu der a-b-Ebene des OH-Al-Hektorit orientiert ist. Bei höheren pH-Werten ähnelt das Spektrum dem von Cu(OH)42~ an Aluminiumoxid, was auf einen Ligandenaustauschmechanismus für die Cu2+-Adsorption an den Komplex hindeutet. [U.W.]

Résumé

Résumé

On a examiné au moyen de la résonnance à spin d’électrons l'adsorption de cuivre sur un complexe hectorite-hydroxy-aluminium (OH-Al-hectorite) aux pH 4,5, 5,7, 7,4, et 7,8. Les spectres de ces échantillons ont été comparés à ceux de l'hectorite Cu2+ et d'oxides aluminium hydres variés. Le cuivre sur l'hectorite OH-A1 dans des gels aqueux se trouve sous forme de Cu(H20)62+ mobile et a chémisorbé à des sites discrets de l'intercouche OH-A1. Au fur et à mesure de l'augmentation du pH, la proportion de Cu2+ chémisorbé a augmenté par rapport au Cu2+ mobile. Aux pH au dessus de 7, le produit de solubilité de Cu(OH)2 a été excédé, mais Cu2+ chémisorbé est resté l'espèce dominante. Ces résultats contrastent avec la précipitation de Cu observé sur la gibbsite microcristalline au dessus du pH 5, et indiquent que l'intercouche OH-A1 a retenu plus de Cu2+ sur des sites discrets. La capacité d'adsorption plus grande était en partie le résultat d'une aire de surface spécifique plus élevée. Les spectres de spin à résonnance d’électrons de Cu2+ dans des films d'hectorite OH-A1 sechés à l'air aux pH 4,5 et 7,4 a montre Cu2+ en symmétrie plane carrée, orienté avec l'axe-z perpendiculaire au plan a-b de l'hectorite OH-A1. Au pH plus élevé, le spectre ressemblait à celui de Cu(OH)42_ sur l'alumine, suggérant un mécanisme d’échange de ligand pour l'adsorption de Cu2+ sur le complexe. [D.J.]

Keywords

AdsorptionAluminumCopperElectron spin resonanceHectoriteHydroxy-aluminum complex
Type
Research Article
Information
Clays and Clay Minerals , Volume 32 , Issue 5 , October 1984 , pp. 407 - 413
Copyright
Copyright © 1984, The Clay Minerals Society

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