A study of the ordered adsorption of metal ions on the surface of cellulose microfibrils

Abstract

Following observations already made on copper impregnated wood, a detailed study is made of the adsorption by a variety of celluloses of a number of cations from salt solutions. The uptake/concentration curve follows a Langmuir adsorption isotherm so that a surface phenomenon is certainly involved. The uptake is accompanied by a fall in pH of the solution, so that cations appear to be exchanged for hydrogen ions, and is initially rapid.The resultant metal-cellulose complex gives characteristic electron diffraction diagrams of which two types only have been found (together with “hybrids” between them). These diagrams are identically the same whatever the source of the cellulose and for any metallic cation. They can be interpreted on the basis of two-dimensional arrays of copper ions whose parameters are: I: p = 6.15 A, q = 7.05 A, Ø = 90°; II: p = 7.32 Å, q = 5.68 A Ø = 87°–90° (variable). It is concluded that the copper is adsorbed as a monolayer on the outer surface of the microfibrils and this is taken to imply order in the disposition of the chain-molecules at this surface. The parameters bear no relation to the accepted parameters of the (three-dimensional) unit cell of cellulose and suggest further, therefore, that the order at the surface is in some way different from that inside the microfibrils.The impact of the above findings on methods of determining the -COOH content of cellulose is briefly discussed.